Air vaporizer
Content
LNG VAPORIZATION STUDY
OREGON LNG IMPORT TERMINAL
~ Feasibility Study ~
Prepared for ~
Prepared by ~
H | H —C— H | H
LNG
LNG
H H C H H
CH·IV International
Houston Office 1221 McKinney, Suite 3325 Houston, TX 77010 713-964-6775
Baltimore Office 1341A Ashton Road Hanover, MD 21076 410-691-9640
CH·IV International Document: TR-07902-000-002
Client Review Draft December 5, 2007
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TABLE OF CONTENTS 1 2 INTRODUCTION BACKGROUND
2.1 Vaporizer System Overview 2.1.1 Vaporization System Requirements 2.1.3 Impact of Constraints and Assumptions on System Selection
4 4
5 5 7
2.1.2 Constraints and Assumptions Considered in Vaporization System Selection 5
3
AMBIENT AIR VAPORIZATION
3.1 Direct Ambient Air Vaporizers (AAVs) 3.1.1 Direct Natural Draft Ambient Air Vaporizers 3.1.2 Direct Forced Draft Ambient Air Vaporizers 3.2 Indirect Ambient Air Vaporizers 3.2.1 Ambient Air Heat Exchanger with Heat Transfer Fluid (AAV-HTF) 3.2.2 Smart Air ® Vaporizer 3.2.3 Other Indirect Ambient Air Heating Systems 3.2.4 Limitations on Use of Indirect Ambient Air Systems 3.3 EFFLUENTS DISCUSSION 3.4 IMPORT TERMINAL COMPATIBILITY
9
9 11 13 15 15 20 21 21 22 22
4
SUPPLEMENTARY HEATING
4.1 Submerged Combustion Vaporizers (SCVs) 4.1.1 Performance 4.1.2 Emissions and Effluents 4.1.3 Physical Characteristics
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25 26 26 27
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4.1.4 Capital and Operating Costs 4.2 Gas Fired Heater with Heat Transfer Fluid (GFH–HTF) 4.2.1 Performance 4.2.2 Emissions and Effluents 4.2.3 Physical Characteristics 4.2.4 Capital and Operating Costs 4.3 IMPORT TERMINAL COMPATIBILITY 28 28 29 29 30 30 30
5
CONCLUSIONS AND RECOMMENDATIONS
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LIST OF FIGURES Figure 3.1.1 – Schematic of Direct Ambient Air Vaporizer.......................................................10 Figure 3.1.1.1 – Direct Natural Draft Ambient Air Vaporizer in Operation ..............................11 Figure 3.1.2.1 – Direct Forced Draft Ambient Air Vaporizers without Shrouds .......................13 Figure 3.1.2.2 – Direct Forced Draft Ambient Air Vaporizers with Shrouds.............................14 Figure 3.2.1.3.1 – Dahej LNG Terminal.....................................................................................18 Figure 3.2.1.3.2 – Air Towers Under Construction at Freeport LNG Terminal.........................19 Figure 3.2.1.3 – STVs Under Construction at Freeport LNG Terminal .....................................19 Figure 4.1.1 Submerged Combustion Vaporizer .......................................................................25 Figure 4.1.3.1 – SCV Installation, 1.0 bscfd capacity ................................................................27 Figure 4.2.1 – Schematic of GFH–HTF Vaporization System...................................................29
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1 INTRODUCTION
The LNG Development Company, LLC, and the Oregon Pipeline Company, LLC (collectively, Oregon LNG) proposes to construct and operate a liquefied natural gas (LNG) import terminal (Import Terminal) on the East Bank Skipanon Peninsula (ESP) near the confluence of the Skipanon and Columbia Rivers in Warrenton, Clatsop County, Oregon. The proposed Oregon LNG Terminal and Oregon Pipeline (collectively, the Project) consists of construction of a slip and berth for offloading LNG carriers (LNGCs), facilities to receive and regasify LNG for transport to the United States (U.S.) natural gas transmission grid, and approximately 120 miles of 36-inch-outside-diameter (OD) natural gas pipeline (Pipeline), which in turn will interconnect with other natural gas pipelines, including the interstate natural gas transmission system of Williams Northwest Pipeline (Williams) at the Molalla Gate Station. To minimize environmental concerns and maximize operating efficiency, the project design basis requires that primary vaporization of LNG at the Import Terminal be achieved from the heat available in ambient air. For seasonal conditions when ambient heat is unable to meet design requirements, a fired heating system will supplement the ambient system. The selection of a suitable vaporization system (a combination of ambient and fired heating) for the Oregon LNG Import Terminal is therefore of principal importance. The selected system will directly influence the capital cost, operational cost and environmental impact of the Import Terminal. Additionally, the selection will also affect the regulatory requirements, availability, operability and the general public perception of the Import Terminal. The objective of this report is to select a suitable vaporization system for the Import Terminal based on evaluation of various available vaporization systems. The selection is based on the requirement to use heat available from ambient air to the extent possible, and to determine the optimum method for providing supplementary heating at times when the heat available from ambient air is insufficient to meet the sendout requirements. Different ambient air vaporizers and supplemental (fired) heating systems are evaluated and compared based on mechanical performance, capital and operating costs, emissions and effluent discharge. Although no environmental modeling has been performed in the preparation of this study, consideration has been given to emission and effluent discharge data provided by equipment vendors in selecting the vaporization system.
2
BACKGROUND
Oregon LNG holds a long term sub-lease for approximately 96 acres of land located on the East Skipanon Peninsula near the confluence of the Skipanon and Columbia Rivers in Warrenton, Clatsop County, Oregon. The company proposes to build an LNG Import Terminal on this parcel of land.
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The Import Terminal will provide a natural gas baseload sendout capacity of 1.0 billion standard cubic feet per day (bscfd) and a peak sendout capacity of up to 1.5 bscfd. LNG supplied to the Import Terminal via LNG carriers will be stored at -260°F in three 160,000 cubic meter above ground, full containment storage tanks. LNG vaporized into natural gas will be transferred from the Import Terminal at 40°F via an approximately 117 mile long sendout pipeline. 2.1 Vaporizer System Overview The Import Terminal will use available heat from the ambient air for LNG vaporization to the maximum extent possible, augmented, when necessary, with a supplementary (fired) heat system to achieve the sendout temperature of 40°F. Selection of a vaporization system therefore requires consideration of (1) the optimum method for extracting heat from the ambient air, and (2) a compatible and efficient system for providing the supplementary heat. 2.1.1 Vaporization System Requirements The system requirements and constraints are summarized below. These requirements are obtained from the Import Terminal Design Basis (document 07902-TS-000-002) and are as follows: Import terminal location: Baseload sendout: Peak sendout: Gas sendout temperature: Primary vaporization heat source: 2.1.2 Pacific Northwest 1.0 bscfd Up to 1.5 bscfd 40°F Ambient Air
Constraints and Assumptions Considered in Vaporization System Selection When considering the use of ambient air heat for vaporization of LNG under the design requirements listed above, there are several key constraints that must be considered. These constraints are described below. • Ambient environmental conditions. Obviously, climate conditions are a major factor in considering use of ambient air as a heat source for LNG vaporization. The air temperature and relative humidity in particular have a major impact on the performance of the ambient air vaporizers, and
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other factors such as solar radiation and wind can also impact performance (more so for natural draft vaporizers). The table below shows the annual average temperatures in Warrenton, Oregon between 2001 and 2005 (as measured at the nearby Astoria Clatsop County Airport, COOP ID # 350328). The data represents five years of average temperatures. As shown in the table, the average annual temperature is 51.5°F, and the average relative humidity is high. The temperatures vary seasonally, with a winter temperature typically in the 30-40°F range and a summer temperature typically in the 60-70°F range. The lowest temperature recorded in this time period was 25°F; review of other weather data for the region revealed an extreme low of 6°F over the past 30 years.
Table 2.1.2.1 Average Ambient Conditions in Warrenton Oregon Year Average Temp (°F) Average Humidity (%) 2001 2002 2003 2004 2005 Average
50.8
51.0
52.2
51.8
51.5
51.5
84.0
81.2
82.1
85
82.9
83
•
Ambient air vaporizer approach temperature limitations. For heat exchangers which operate by transferring heat between opposing flows of hot and cold fluids, there are practical limitations in how closely the heated fluid temperature can approach the temperature of the fluid providing the heat. The difference between the inlet temperature of the fluid providing the heat, and the outlet temperature of the fluid being heated, is called the approach temperature. The achievable approach temperature for a heat exchanger is a function of parameters such as the available heat exchanger surface area, resistances in heat transfer between the two fluids, and fluid flow rates. For this study, vendors were contacted to determine the achievable approach temperatures for ambient air LNG vaporizers. Approach temperatures typically vary from 20 to 40°F, and
worsen with running time due to heat transfer resistance resulting from accumulation of ice on the vaporizer surfaces.
•
Lack of available, local waste heat source. Currently there is no local source of waste heat available for use for supplementary heating for this Import Terminal. If a waste heat source (such as a power plant condenser
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or other industrial heat source) becomes available, the need for burning fuel gas for supplementary heating could be reduced. However, this report will assume that all supplementary heating will be provided by on-site, fired heating equipment with no credit taken for waste heat sources. • Emissions and effluents. Of primary importance in selecting a suitable vaporization system for this Import Terminal is the minimization of environmental emissions and effluents. Ambient air vaporizers generate no emissions; and they only generate ice and condensed water (possibly with some entrained particulate matter) as effluents. However, fired heating systems do generate emissions and effluents which generally require treatment systems. The choice of supplementary heating system will therefore consider the emissions and effluents associated with each option. Baseload and peak sendout. The vaporization system is designed to sendout a baseload 1.0 bscfd and a peak of up to 1.5 bscfd. The peak output can be provided with all spare equipment operating. The baseload case must be provided with reliability, such that no credit can be taken for standby equipment. Accordingly, the supplemental heating system will be designed with spare equipment to ensure that in conjunction with the ambient air vaporization system it can reliably provide sendout of 1.0 bscfd at 40°F. To achieve peak sendout of 1.5 bscfd, the spare equipment in the supplementary heating system can be credited.
•
2.1.3
Impact of Constraints and Assumptions on System Selection As pointed out in the previous section: • • The design basis sendout temperature is 40°F; The approach temperature for ambient air vaporizers varies considerably depending on physical parameters and vaporizer run times, and is on the order of 20 to 40°F; The annual average ambient temperature is slightly over 50°F, and there are periods during the year when the temperatures are lower.
•
To produce sendout gas at 40°F with an approach temperature on the order of 2040°F, the ambient temperatures would have to be no lower than 60°F and possibly as high as 80°F. Since the weather data show that at many times during the year the ambient temperature is below this level, the gas exiting the ambient air
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vaporizers will require supplemental heating to achieve the design basis sendout temperature of 40°F . Consequently, the supplemental heating system will be required to raise the gas temperature exiting the ambient air system to the sendout temperature. For the purposes of this evaluation, the ambient air system will be assumed to be able to produce gas at 0°F, and the supplemental system will be designed to raise the gas temperature to the sendout design basis temperature of 40°F. The basis for selection of 0°F for the ambient air system is as follows: • It is assumed that the design and quantity of ambient air vaporizers will be such that the average approach temperature will ensure exit gas temperature of at least 0°F at times when the ambient air temperatures are at the year round average (51.5°F) or higher. This requirement will be included in the specifications provided to the vendor. At times when the temperature is lower than the year round average, the absolute content of water vapor in the ambient air will be relatively lower than on hotter days. Accordingly, the vaporizers will accumulate frost and ice at a slower rate, which will reduce the approach temperature. So, it is appropriate to assume that the vaporization system should be able to achieve 0°F under these conditions. If the provided ambient air vaporization system is unable to heat gas to at least 0°F due to accumulation of ice on the heat exchanger surfaces, terminal operators can take action to remove the ice mechanically or by other means. It is assumed that the terminal design and operating procedures will account for this potential.
•
•
It is recognized that under extreme cold conditions, it may not be possible to achieve 0°F gas exit temperature from the ambient air system. These events are expected to be very rare. To ensure the baseload sendout can meet these conditions, the supplementary heating system will include design margin. Table 2.1.3.1 summarizes the proposed vaporization system design parameters for the Import Terminal.
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Table 2.1.3.1 Ambient Air Vaporizer and Supplementary Heater System Design Parameters Average Ambient Temperature Assumed Temperature at Outlet of Ambient Air Vaporizers (°F) Heat Provided From Ambient Air Temperature at Outlet of Supplemental Vaporizers (°F) Minimum Heat Required from Supplemental System
Sendout Capacity (bscfd)
(°F) 51.5
(MMBtu/hr) 751
(MMBtu/hr) 133
1.5
0
40
Having established that ambient air vaporizers in tandem with supplementary heating systems are required for the Import Terminal, attention will now be focused on the various ambient and supplementary fired systems – specifically, the modes of operation, capital and operating costs and the emissions and effluents associated with each.
3
AMBIENT AIR VAPORIZATION
Ambient air vaporization systems draw heat from the surrounding ambient air to vaporize LNG. There are two primary methods of vaporization using heat from the ambient air: by direct or indirect heat transfer into the LNG. 3.1 Direct Ambient Air Vaporizers (AAVs) Direct AAVs transfer heat from the ambient air directly into the LNG through a heat exchanger heat transfer surface. In typical Direct AAVs, the cryogenic liquid is passed through a manifold that divides the flow into a number of vaporizer units where a series of smaller flows are directed through individual heat transfer tubes. Each tube has aluminum fins for increased heat exchange area and is in direct contact with the ambient air. Figure 3.1.1 shows a schematic of a typical Direct AAV.
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Warm Ambient Air
Natural Draft or Fan Assisted
Cold Liquid LNG Cool Ambient Air
Natural Gas
Figure 3.1.1 – Schematic of Direct Ambient Air Vaporizer
One disadvantage to the use of Direct AAVs is lack of experience with these units in high volume vaporization of LNG. However, Direct AAVs have been used in liquid nitrogen service (a fluid colder than LNG) for over fifty years. While Direct AAVs are in operation, frost and/or ice will build up on the units due to the proximity of the LNG to the ambient air. The longer a unit runs, the more frost and/or ice builds, which gradually reduces the performance of the unit. Hence, Direct AAV units need to be periodically shut down and de-iced. De-icing becomes difficult when the ambient air temperature drops below freezing. In this case, the system must be provided with another source of heat for de-icing, such as electric heaters or water spray. At the proposed site, weather data shows that the temperature rarely drops below freezing and then only for short periods of time. Fortunately, during cold periods the available moisture in the air is relatively low, minimizing the rate of ice buildup at these times. Experience from current users and vendors (e.g., Thermax and Cryoquip Inc.) of Direct AAVs has shown that during periods of extended cold weather, longer operating durations can be achieved by running all the units simultaneously at a reduced rate while gradually increasing the supplementary heat as frost continues to form on the vaporizer. The design of the system will account for having adequate vaporization capacity and availability year-
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round taking into consideration downtime of a subset of the unit population for deicing. It should be noted that although Direct AAVs can only heat gas up to a temperature approaching the ambient temperature, the units can provide a high percentage of the total heat load for vaporizing LNG. Per one vendor contacted, a Direct AAV operating at arctic conditions of -80°F could provide over 50% of the total heat duty needed to vaporize LNG. There are two types of Direct AAVs – Natural Draft AAVs and Forced Draft AAVs. 3.1.1 Direct Natural Draft Ambient Air Vaporizers Direct Natural Draft AAVs rely on wind and natural convective currents to move air over the tubes and fins of the vaporizer unit. As warm air contacts the tubes containing LNG, the air cools and becomes dense, causing it to flow downwards to the bottom of the vaporizer unit. This causes warm ambient air from the surroundings to be drawn through the top of the unit. Figure 3.1.1.1 illustrates a Direct Natural Draft AAV in operation.
Figure 3.1.1.1 – Direct Natural Draft Ambient Air Vaporizer in Operation
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3.1.1.1 Performance The outlet gas temperature of a Direct AAV is dependent not only on ambient conditions but on other factors such as run time and amount of units in operation. Consider a single AAV unit; at the onset of operation the temperature of the outlet stream is nearly the same as the ambient temperature. As the run time increases, the unit begins to frost and/or ice up, thus reducing the amount of heat being transferred to the LNG. A significant amount of heat transfer is still achieved, but the temperature of the outlet stream reduces as time passes and ice accumulates. As more units come into operation, more surface area becomes available for heat transfer. Per a vendor contracted for this study, it is estimated that 12 basic trains (13 units/train) plus 6 duty cycle extra trains (that is, idle vaporizers that are out of service undergoing de-icing while others operate) would be required to vaporize 1.5 bscfd of LNG. 3.1.1.2 Emissions and Effluents Cooling of the moist ambient air results in condensation of a large amount of water vapor from the atmosphere. Some of this condensed water collects as frost and/or ice on the tubes of each unit. Typically, the ice from the surface of each unit melts and drains to a collection basin during the de-icing cycle. This water is expected to have minor or no contamination and may be treated prior to disposal or used within the Import Terminal. Another issue resulting from the cooling of the ambient air is the formation of water vapor as “fog”, which can create a visible cloud close to the Import Terminal. 3.1.1.3 Physical Characteristics Per one vendor contacted for this study, typical Natural Draft AAVs that would be used for this import terminal consist of vertical tube bundles 42-ft in length with a plot area of 12-ft by 12-ft each. The vaporizers are elevated above grade to prevent recirculation of cold dense air from the bottom of the unit back to the inlet at the top of the unit. The total footprint of these vaporizers is therefore 320ft x 230-ft, or 73,600 ft2, assuming a 6-ft clearance between the estimated 236 units (18 trains, with 13 units/train) required for operation and duty cycle. Each unit weighs approximately 52,000 lbs when dry and can withstand ice loading up to an additional 60,000 lbs. 3.1.1.4 Capital and Operating Costs Capital costs for the Natural Draft AAV arrangement for an LNG sendout capacity of 1.5 bscfd have been estimated by Cryoquip Inc. to be $58 million (vaporizers only). Operating costs on the other hand would be low. The power input for these units is zero. There are no moving parts in the vaporizers and they
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are, for practical purposes, maintenance free. The only costs involved in operation would be those required to handle the effluents from the vaporizers.
3.1.2
Direct Forced Draft Ambient Air Vaporizers
In Direct Forced Draft AAVs, airflow into the unit is controlled by fans installed on top of the vaporizer. Each unit can be equipped with shrouds on each side to direct airflow through the vaporizer. Direct forced draft vaporizers are approximately 1.7 times more effective than Natural Draft AAVs i.e., they move 1.7 times more air across the tubes of the unit. Figures 3.1.2.1 and 3.1.2.2 show two types of Direct Forced Draft Ambient Air vaporizers.
Figure 3.1.2.1 – Direct Forced Draft Ambient Air Vaporizers without Shrouds
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Figure 3.1.2.2 – Direct Forced Draft Ambient Air Vaporizers with Shrouds 3.1.2.1 Performance Since the airflow through the forced draft units is higher than for natural draft units, fewer forced draft units will be required to achieve the same duty. Per one vendor contacted for this study, it is estimated that 10 basic trains (10 units/train) plus 5 duty cycle extra trains would be required for the vaporization of 1.5 bscfd. 3.1.2.2 Emissions and Effluents Emissions and effluents for forced draft units are similar to the natural draft units as described in 3.1.1.2, except that with Forced Draft AAVs the formation of fog is diminished by the forced airflow (from the fans on top of each unit) around the tubes. There is also more ice formed in Forced Draft units because the increased air flow over the tubes increases the rate of water condensation and consequently the rate of ice formation. The shrouds around the tube bundles impede the amount of radiant heat reaching the ice forming on the tubes, which can increase the ice buildup rate.
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3.1.2.3 Physical Characteristics Physical requirements are similar to the Natural Draft AAVs arrangement, except that fewer forced draft units are needed. Assuming 150 units and 6-ft spacing between each unit and each train, the total land area needed for all the vaporizers is estimated at 170-ft x 260-ft or 44,200 ft2. The weights of these units are comparable to the natural draft units, with a small addition due to the weight of the shrouds and fans. 3.1.2.4 Capital and Operating Costs The total capital costs for Forced Ambient Air vaporizers has been estimated at $56 million (vaporizers only) by Cryoquip Inc. Operating costs for Forced Draft AAVs would be higher than natural draft AAVs due to the electric power needed for the fans; each unit requires power to the fans on the order of 60 HP (about 45 kW). With 15 trains in constant operation (units in the de-icing cycle would also have the fans on) the power requirement would be on the order of 9,000 HP or 6.7 mW.
3.2
Indirect Ambient Air Vaporizers Indirect vaporizers operate by transferring heat from ambient air to an intermediate fluid which in turn transfers heat to LNG through a separate heat exchanger. The different arrangements of Indirect Ambient Air Vaporizers are described below.
3.2.1
Ambient Air Heat Exchanger with Heat Transfer Fluid (AAV-HTF) This type of vaporization system consists of Shell and Tube Heat Exchangers, Fin-fan Air Heaters or Reverse Cooling Towers and a Heat Transfer Fluid loop. Fin-Fan Air Heaters are used to transfer heat from ambient air into the HTF, which is then sent to the LNG shell and tube vaporizer. The cooled HTF flows into a surge tank and is then pumped back to the Air Heaters. Schematics of the different vaporization processes are shown below in Figures 3.2.1.1 and 3.2.1.2.
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WARM HTF
AIR HEATERS
LNG
Pipeline Gas
SHELL AND TUBE VAPORIZER
COLD HTF
HTF SURGE TANK
HTF PUMP
Figure 3.2.1.1 – Schematic of AAV-HTF System Using Air Heat Exchangers
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Figure 3.2.1.2 – Schematic of AAV-HTF System Using Reverse Cooling Tower
Although the main heat source for this vaporization arrangement is the heat contained in the warm ambient air, supplemental heating is also required to maintain capacity and delivery temperature when the ambient air temperature drops below a nominal value. The vaporization system using fin-fan heat exchangers shown in Figure 3.2.1.1 is in operation at the Dahej LNG terminal in India and is being installed at the Lake Charles LNG terminal in Louisiana. The vaporization system using Reverse Cooling Towers shown in Figure 3.2.1.2 is being used at the Freeport LNG project.
3.2.1.1 Performance Typical indirect air heating systems in operation in the hot areas like India and the Gulf of Mexico area are capable of delivering about 90% of the annual heat load. In more temperate climatic regions like Oregon, that capability is reduced to between 55-60%. This availability is also applicable to Fin Fan Air Heat exchangers. These vaporization systems also have a significant electrical load.
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3.2.1.2 Emissions and Effluents Water produced from condensation of water vapor from the surrounding air must be continuously discharged and safely discarded. For Reverse Cooling Tower systems, the circulating water stream is likely to require chemical treatment and the blowdown needs to be appropriately handled. 3.2.1.3 Physical Characteristics The AAV-HTF system presents a significant demand on its supporting infrastructure. A Google Earth® satellite photo of the Dahej terminal is shown in Figure 3.2.1.3.1. The components shown on the right side of the photo outline the air heat exchanger arrangements for the vaporization of 1.0 bscfd, which is the baseload case for the Oregon LNG Import Terminal. Figures 3.2.1.3.2 and 3.2.1.3.3 illustrate Air Towers and Shell and Tube Vaporizers (STVs, used for supplemental heating when the heat available from ambient air is insufficient) under construction at the Freeport LNG terminal. The heating towers require a large plot area.
Figure 3.2.1.3.1 – Dahej LNG Terminal
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Figure 3.2.1.3.2 – Air Towers Under Construction at Freeport LNG Terminal
Figure 3.2.1.3 – STVs Under Construction at Freeport LNG Terminal TR-07902-000-002 Page 19 of 32 December 5, 2007
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3.2.1.4 Capital and Operating Costs Shell and tube heat exchangers rated for high sendout pressures (over 1000 psi) and capacities (approximately 100 to 150 mmscfd) are estimated at roughly $500,000 a unit. The Oregon LNG Import Terminal would require at least 10 of these units for a maximum sendout capacity of 1.5 bscfd. Also, as stated earlier, Reverse Cooling Towers are large structures and would require significant capital investment for construction and operation. Power consumption costs due to ancillary equipment such as fans and pumps should also be taken into account, making this vaporization system cost intensive.
3.2.2
Smart Air ® Vaporizer The Smart Air® vaporization system is similar to the AAV-HTF system discussed in section 3.2.1, except that the system uses Potassium Formate (KF) as the heat transfer fluid. The system consists of Air Heaters, a Surge Tank, Pumps, and Shell and Tube LNG vaporizers. The Air Heaters transfer heat from the warm ambient air into cool KF fluid from the Shell and Tube LNG Vaporizer. The warmed KF fluid is then sent to the Surge Tank. KF fluid is pumped from the Surge Tank back to the Shell and Tube vaporizers where it provides heat to the LNG, is cooled, and then sent back to the Air Heaters. The Air Heaters used in the Smart Air® vaporization system are proprietary to Mustang Engineering. Each Air Heater contains layers of finned tubes and has fans forcing the ambient air from the surroundings to flow through the top of the unit downwards, over the tube bundle. The Air Heaters are elevated above grade to prevent recirculation of cold dense air from the bottom of the unit to the fan inlet. As with other ambient air vaporization systems, supplementary heat will be required when design ambient conditions cannot be met.
3.2.2.1 Performance Promoters of the Smart Air® Vaporization system claim the system would be able to provide 65% of the annual heat duty for the Oregon area. As this vaporization system is yet to be installed in a region of similar climate as Oregon, this claim remains unconfirmed. Smart Air® vaporization systems also have significant electric power demands for the ancillary equipment including fans for air heaters and pumps. A system rated for 1.5 bscfd would require about 9000 HP.
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3.2.2.2 Emissions and Effluents Cold, condensed water from the atmosphere continuously forms on the surface of the tubes containing cold KF fluid. The water falls off the tubes exiting from the bottom of the air heater with the flow of cooled air. The water can be collected in a basin below the air heaters and utilized in the plant, treated and used for potable water or discarded. The condensed water is clean, freshwater and does not require significant treatment and can be discarded easily. Estimated waste water flow rate for a system rated at 1.5 bcsfd is 1000 gpm. 3.2.2.3 Physical Characteristics For a sendout capacity of 1.0 bscfd, the LNG Smart Air® vaporization system would require a total surface area of 27,240 ft2. The vaporization system at Oregon will be sized for a total capacity of 1.5 bscfd; hence it is reasonable to assume that the acreage needed would be approximately 40,860 ft2. Each threefan Air Heater unit measures 14ft wide, 60ft long and 40ft high. 3.2.2.4 Capital and Operating Costs The total cost for a Smart Air® Vaporization system with a 1.5 bscfd capacity is estimated to be $80 million. Extra costs will also be incurred due to treatment and handling of wastewater produced by the Air Heaters and electrical power consumption from the fans for the heaters.
3.2.3
Other Indirect Ambient Air Heating Systems Other Ambient Air vaporization systems exist but are not discussed here because they either cannot be incorporated into the Oregon LNG Import Terminal design or they are not proven technologies. An example of such a vaporization system is the Heat Integrated Ambient Air Vaporization (HIAAV). HIAAV systems involve the use of Waste Heat recovery units installed in combination with gas turbines which the Oregon LNG Import Terminal design does not include.
3.2.4
Limitations on Use of Indirect Ambient Air Systems Per discussions with vendors, indirect systems work best when air temperatures are above 70°F; when the ambient air temperature drops below that value, the heat available from the ambient air is insufficient and supplemental heat must be added to the HTF. When the air temperatures drop below about 50°F, heat transfer from the ambient air is ineffective and essentially all vaporization heat must be provided from supplement heat sources. Note that the year-round average temperature at the terminal site is on the order of 50°F, so these indirect methods
would need to be backed up by supplemental systems operating at 100% of the required
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duty for vaporization for much of the year. That is, if an Indirect Ambient Air Vaporization were to be used at this terminal, two different, full capacity vaporization systems would need to be installed.
3.3
EFFLUENTS DISCUSSION One of the advantages of using ambient air vaporizers is that they do not produce any emissions. However all ambient air vaporization methods create effluents that need to be properly handled. In Direct Ambient Air Vaporizers, frost and/or ice builds up on the tube bundles of each unit as a result of the freezing of condensed water from the ambient air that forms on the tubes. During the de-icing cycle all the ice falls off the unit and has to be properly discarded. Indirect Ambient Air Vaporizations systems also generate condensed water as effluent. However, since air does not come in direct contact with a heat transfer surfaces containing cryogenic fluid, there is little or no ice formation. For each type of vaporizer, the rate of amount of water formation (as ice or condensate) can be as high as 1000 gpm (liquid water equivalent) for a 1.5 bscfd terminal. The terminal design needs to address treatment of this effluent.
3.4
IMPORT TERMINAL COMPATIBILITY Table3.4.1 shows a comparison of the ambient air vaporization systems discussed in Section 3 of this report.
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Table 3.4.1 –Comparison of Air Vaporization Systems
Direct Ambient Air Vaporization Natural Draft Forced Draft
Indirect Ambient Air Vaporization*1 AAV-HTF (Air Heat Exchangers) AAV-HTF (Reverse Cooling Towers)
Smart Air®
Ambient Temperature Operating Range Estimated Capital Cost Land Usage Power Usage for AAVs Effluents
Provides large fraction of total heat duty at all expected ambient temperatures
Provides large fraction of total heat duty during hot ambient conditions; Provides little or no heat duty at times when temperatures drop below 50°F $98 million 167,000 ft2 High (fans and pumps) Water $100 million 100,000 ft2 Moderate (pumps) Water $95 million 40,860 ft2 High (fans and pumps) Water
$152 million 73,600 ft2 None
$147 million 44,200 ft2 High (fans)
Water and ice Water and ice In summary:
• During much of the year the ambient air temperature at the site is on the order of
50°F or lower. Under these conditions, indirect systems provide little or no heat. Accordingly, for these systems, a 100% capacity supplemental system would be required in order to achieve sendout during cold periods. This would increase the capital cost and land area needed for the Import Terminal, and increase the yearly emissions from the terminal. For these reasons, indirect systems are considered inappropriate for this facility.
• Direct AAVs would provide much of the heat duty but require supplemental heat
during cold periods.
• Of the two types of direct AAVs, fewer forced draft AAVs are needed than natural
draft AAVs; thus, significant land area can be saved if forced draft AAVs are used. However, natural draft AAVs do not require electric power whereas forced draft AAVs use electrically powered fans.
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Therefore, the Direct Forced Draft Ambient Air vaporization system will be the most suitable option for the Oregon LNG Import Terminal. It is estimated that 10 basic trains (10 units per train) plus 5 duty cycle extras can provide the entire heat load expected from the Direct Forced Draft AAVs for the peak sendout capacity of 1.5 bscfd. On occasions when the ambient conditions cannot provide sufficient heat, supplemental heat would be provided, as discussed in the next section.
4
SUPPLEMENTARY HEATING
When the ambient temperature is not warm enough to raise the temperature of the vaporized LNG to 40°F, supplement heating must be provided to reach this design basis sendout temperature. Figure 4.1 illustrates how the supplemental heating system would be integrated with the Ambient Air Vaporization system at the Oregon LNG Import Terminal. The minimum amount of heat needed from the supplemental system has been determined section 2.1.3 to be 133 MMBtu/hr. To be conservative, the supplemental vaporization system will be sized for 180 MMBtu/hr which provides 35% extra capacity.
VAPORIZED LNG @ <40°F
Natural Gas @ 40°F Sendout Station
VAPORIZED LNG @ >40°F Supplemental Gas Fired Vaporizer
COLD LNG FROM TANK
Ambient Air Vaporizer
Figure 4.1 – Overall Schematic of Vaporization System
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As illustrated above, cold LNG from the storage tanks is pumped to the AAVs which vaporize the LNG. If the AAVs do not provide sufficient heat to raise the temperature to 40°F, a side stream of the gas exiting the ambient air vaporizers is sent through the supplemental heating system and warmed to a temperature greater than 40°F. The warm stream is blended with the cooler, vaporized LNG from the AAVs and sent to the metering station at 40°F. Gas fired heating systems are proven and effective methods of providing heat for vaporizing LNG. They can also operate largely unaffected by surrounding climatic conditions. However, these systems consume fuel and generate emissions. Two gas fired heating system options were considered for Oregon LNG and are described below: 4.1 Submerged Combustion Vaporizers (SCVs) SCVs are designed to use fuel gas or low pressure boiloff gas from the terminal. High pressure LNG flows through a stainless steel tube bundle that is submerged in a water bath heated with exhaust gases generated from a combustion burner. The water transfers the heat from the combustion process to the LNG. The SCV alternative offers simplicity and has become the vaporization choice for many new and existing U.S. regasification terminals. Figure 4.1.1 is a schematic for the SCV process.
Figure 4.1.1 Submerged Combustion Vaporizer
The hot exhaust gases from this combustion are sparged into the water bath and create a relatively low temperature (typically in the range of 50° to 60° F) thermally stable
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heat source for the vaporization coils. The vaporized LNG exits the coils at pipeline pressure and design basis temperature for downstream transmission. 4.1.1 Performance
SCVs have very high thermal efficiencies (above 95%) because the combustion products are bubbled directly into the water bath hence all the available heat is transferred directly to the water. This includes the latent heat of condensation of water vapor in the exhaust gas which also condenses in the water bath. Gas outlet temperatures for SCVs range from 35°F to 60°F. Since the water bath is at high thermal capacity, stable operation is generally achievable, even for sudden start-ups, shutdowns or deviations in load. Electric power is also required to run the combustion air blower and the water circulation pumps. 4.1.2 Emissions and Effluents Due to the combustion process NOx, CO and other emissions are produced when the SCVs are in operation. Table 4.1.2.1 contains the emissions from a typical SCV unit.
Table 4.1.2.1 – Emissions from a Typical SCV Unit (rated at 94.2 MMBtu/hr)
Pollutant NOx CO VOC
Emissions (pounds per million Btu @ 3% O2) <0.0345 <0.025 <0.003
Particulate Matter (PM 10) is also emitted at a rate of 0.0015 lb/MMBtu. Reducing these emissions (especially the NOx) will require the use of a selective catalytic reactor (SCR). SCRs are expensive and do not operate efficiently with SCVs. SCR catalysts can be “poisoned” or “fouled” during SCV operation due to contact with potassium or sodium salts used in pH neutralization of the water bath. Optimum temperatures for an SCR reaction range from 650-750°C and may go as high as 1000°C depending on what catalyst is used. SCVs cannot generate exhaust gas at these temperatures and hence SCV exhaust cannot be treated via SCRs without costly re-heating of the exhaust gas.
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During SCV operation the water in the bath becomes acidic as it absorbs combustion products. The pH of the water bath is monitored and controlled by introducing alkaline chemicals such as caustic soda or sodium carbonate. It is important to maintain a relatively neutral pH level (between 6 and 7) in the water bath. During the combustion process, waste water is also produced and must be treated before disposal. For a single SCV unit rated for approximately 94 MMBtu/hr (which is about 50% of the maximum supplemental heat needed) there is a water overflow rate of about 15.5gpm. Hence it is expected that an SCV system installed at the import terminal would produce about 30 gpm of waste water. 4.1.3 Physical Characteristics An SCV unit with a vaporization capacity ranging from 150-200 mmscfd (typical size of a unit) will have a minimum footprint of 408 ft2. Stack heights can vary based on owner requirements. The layout of SCVs can be seen in Figure 4.1.3.1.
Figure 4.1.3.1 – SCV Installation, 1.0 bscfd capacity
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4.1.4 Capital and Operating Costs SCV units usually have a vaporization capacity range of 150-200 mmscfd. Each unit costs approximately $2 million. Two units would be needed for the supplemental heat system at Oregon LNG. Hence a total capital cost (vaporizers only) of $4 million would be required. This amount takes into account the cost of ancillary equipment such as the air blower, circulation pump, fuel gas heater, controls and associated piping. This cost does not include an SCR unit. The greatest disadvantage of purchasing SCVs is the operating costs. Current technology is such that fuel consumption is in the range of 1.3% to 1.5% of throughput. It is important to note that for the Oregon terminal throughput does not refer to the full sendout capacity of the terminal, as the supplemental system is only designed to heat the gas exiting the ambient air vaporizers, which has already been heated. Instead, it refers to the equivalent amount of LNG (at -260°F) that is vaporized by 180MMBtu/hr, i.e., approximately 300 mmscfd. The annual power consumption costs for the air blowers must also be considered due to the motor size and required excess air. The estimated annual operating costs for two SCV units running at their maximum output (i.e., a total of 180 MMbtu/hr) is $6 million. 4.2 Gas Fired Heater with Heat Transfer Fluid (GFH–HTF) The GFH–HTF vaporization systems involve the use of gas fired heaters as the primary source of heat to vaporize LNG. Heat is supplied to shell and tube LNG vaporizers through a closed circuit with a heat transfer fluid, usually a mixture of water and ethylene glycol (WEG), as the heat transfer fluid. A schematic of the system is shown in Figure 4.2.1. Gas fired heaters heat the HTF which is then sent directly to the LNG vaporizer. The cooled HTF is collected in a surge tank and pumped back to the Gas Fired heaters. A system very similar to that shown is used on multiple vaporizer systems at the Distrigas LNG Terminal in Everett, MA.
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Figure 4.2.1 – Schematic of GFH–HTF Vaporization System
4.2.1
Performance The fired heaters used in this vaporization system are capable of heating WEG to temperatures up to 200°F. Based on the proposed operation of the vaporization system at the Oregon LNG Import Terminal, the capability of heating up a side stream of the vaporized LNG to temperatures much greater than 40°F is necessary. The GFH–HTF system has this capability. Gas fired heaters used in this system burn approximately 1.8% - 2.2% of throughput1 and have efficiencies of approximately 83%. The system will also have a significant electrical load from heater forced draft fans, HTF pumps and other ancillary equipment.
4.2.2
Emissions and Effluents Typical air emissions data for the burner associated with a Gas Fired Heater with a heat duty of 60 MMBtu/hr are presented in Table 4.2.2.1.
1 Note that the throughput in this case has been defined in section 4.1.4
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Table 4.2.2.1 – Air Emissions from Gas Fired Heater
Pollutant NOx CO VOC
Emissions (pounds per million Btu @ 3% O2) <0.013 <0.025 <0.003
It should be noted that Gas Fired Heaters are very compatible with SCRs due to the high temperature of the exhaust. Hence, SCRs work very efficiently when installed on Gas Fired Heaters and are capable of significantly reducing NOx and CO emissions rates. 4.2.3 Physical Characteristics The GFH–HTF system presents a minimal vaporizer footprint with the HTF pumps and heaters located nearby typically in a “boiler house.” Footprints for Gas Fired Heaters vary according to the size of the heaters. Next to the SCV, the STV-GF requires the least land area due to minimal system components. Vertical shell and tube heat exchangers used in this application have an approximate outer diameter of about 42 inches. Multiple exchangers will be needed for the supplementary heating system. 4.2.4 Capital and Operating Costs Shell and tube heat exchangers used in this system are estimated to cost $500,000 a unit. The Oregon LNG Import Terminal will require at least three heat exchangers. Gas fired heaters rated at 60 MMBtu/hr with an SCR and associated ancillary equipment i.e., surge tank, pumps etc. can cost up to $1 million per unit. Estimated total capital costs for this system is $4.5 million. Operating costs will comprise mainly of power and fuel consumption charges for the unit. Power consumption from the system would be mostly from horsepower requirements for the heater forced draft fans pumps. 4.3 IMPORT TERMINAL COMPATIBILITY SCVs are not considered acceptable for supplemental heating for this terminal since they are not effective at heating gas to high temperatures (which is needed for
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blending purposes). In addition, the emissions from SCVs cannot be controlled using normal SCR technology. Gas fired heaters with a heat transfer fluid loop and shell and tube heat exchangers offer a more flexible and efficient option. The heaters and heat exchangers can be used to raise the natural gas temperatures to high values to aid in blending to reach the 40°F sendout temperature. The number and capacity of Gas Fired Heaters can be optimized to allow large turn down ratios. Gas fired heaters also work very well with SCRs to reduce emissions rates. Shell and tube heat exchangers are versatile, simple and widely used components, and can be easily customized to meet various operations requirements.
5
CONCLUSIONS AND RECOMMENDATIONS
LNG vaporization at the Oregon LNG Import Terminal will occur in two stages: (1) an ambient air vaporization system will provide much of the heat needed for vaporization, and (2) a supplemental heating system will provide the remaining heat needed when ambient conditions are not sufficient to reach the design sendout temperature. At Oregon, the year-round temperature is such that indirect ambient air vaporization systems will not be effective during much of the year. Use of indirect systems would therefore require installation of 100% capacity backup fired heating systems. This would result in large capital costs and generation of more annual emissions than a system using direct AAVs. Accordingly, direct AAVs are deemed to be the most appropriate method for extracting heat from the ambient air at this terminal. Of the two types of direct AAVs, forced draft AAVs are recommended over natural draft AAVs at this time due to the reduced capital costs and land area. One disadvantage to using Forced Draft AAVs is its lack of a proven track record in high volume LNG vaporization service. However, AAVs have been effectively used for years to vaporize liquid nitrogen which is a cryogenic fluid colder than LNG. Of the two options considered for the supplementary heating system, the Gas Fired Heaters with Heat Transfer Fluid (GFH-HTF) system is considered a better choice than Submerged Combustion Vaporizers (SCV). The GTF-HTF works well with a Selective Catalytic Reduction system (SCR) hence its emissions rates can be efficiently and significantly reduced, unlike SCV units. Also SCVs are not efficient at delivering natural gas at the high temperatures needed for downstream blending with cold gas for achieving the design sendout temperature, thus ruling out their use for supplementary heating at this terminal.
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In summary, CH·IV recommends that Oregon LNG use Direct Forced Draft Ambient Air Vaporizers for its primary vaporization system and a GFH-HTF as a supplemental heating system. This combination presents the most effective option for LNG vaporization at the Import Terminal.
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~ Feasibility Study ~
Prepared for ~
Prepared by ~
H | H —C— H | H
LNG
LNG
H H C H H
CH·IV International
Houston Office 1221 McKinney, Suite 3325 Houston, TX 77010 713-964-6775
Baltimore Office 1341A Ashton Road Hanover, MD 21076 410-691-9640
CH·IV International Document: TR-07902-000-002
Client Review Draft December 5, 2007
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TABLE OF CONTENTS 1 2 INTRODUCTION BACKGROUND
2.1 Vaporizer System Overview 2.1.1 Vaporization System Requirements 2.1.3 Impact of Constraints and Assumptions on System Selection
4 4
5 5 7
2.1.2 Constraints and Assumptions Considered in Vaporization System Selection 5
3
AMBIENT AIR VAPORIZATION
3.1 Direct Ambient Air Vaporizers (AAVs) 3.1.1 Direct Natural Draft Ambient Air Vaporizers 3.1.2 Direct Forced Draft Ambient Air Vaporizers 3.2 Indirect Ambient Air Vaporizers 3.2.1 Ambient Air Heat Exchanger with Heat Transfer Fluid (AAV-HTF) 3.2.2 Smart Air ® Vaporizer 3.2.3 Other Indirect Ambient Air Heating Systems 3.2.4 Limitations on Use of Indirect Ambient Air Systems 3.3 EFFLUENTS DISCUSSION 3.4 IMPORT TERMINAL COMPATIBILITY
9
9 11 13 15 15 20 21 21 22 22
4
SUPPLEMENTARY HEATING
4.1 Submerged Combustion Vaporizers (SCVs) 4.1.1 Performance 4.1.2 Emissions and Effluents 4.1.3 Physical Characteristics
24
25 26 26 27
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4.1.4 Capital and Operating Costs 4.2 Gas Fired Heater with Heat Transfer Fluid (GFH–HTF) 4.2.1 Performance 4.2.2 Emissions and Effluents 4.2.3 Physical Characteristics 4.2.4 Capital and Operating Costs 4.3 IMPORT TERMINAL COMPATIBILITY 28 28 29 29 30 30 30
5
CONCLUSIONS AND RECOMMENDATIONS
31
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LIST OF FIGURES Figure 3.1.1 – Schematic of Direct Ambient Air Vaporizer.......................................................10 Figure 3.1.1.1 – Direct Natural Draft Ambient Air Vaporizer in Operation ..............................11 Figure 3.1.2.1 – Direct Forced Draft Ambient Air Vaporizers without Shrouds .......................13 Figure 3.1.2.2 – Direct Forced Draft Ambient Air Vaporizers with Shrouds.............................14 Figure 3.2.1.3.1 – Dahej LNG Terminal.....................................................................................18 Figure 3.2.1.3.2 – Air Towers Under Construction at Freeport LNG Terminal.........................19 Figure 3.2.1.3 – STVs Under Construction at Freeport LNG Terminal .....................................19 Figure 4.1.1 Submerged Combustion Vaporizer .......................................................................25 Figure 4.1.3.1 – SCV Installation, 1.0 bscfd capacity ................................................................27 Figure 4.2.1 – Schematic of GFH–HTF Vaporization System...................................................29
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1 INTRODUCTION
The LNG Development Company, LLC, and the Oregon Pipeline Company, LLC (collectively, Oregon LNG) proposes to construct and operate a liquefied natural gas (LNG) import terminal (Import Terminal) on the East Bank Skipanon Peninsula (ESP) near the confluence of the Skipanon and Columbia Rivers in Warrenton, Clatsop County, Oregon. The proposed Oregon LNG Terminal and Oregon Pipeline (collectively, the Project) consists of construction of a slip and berth for offloading LNG carriers (LNGCs), facilities to receive and regasify LNG for transport to the United States (U.S.) natural gas transmission grid, and approximately 120 miles of 36-inch-outside-diameter (OD) natural gas pipeline (Pipeline), which in turn will interconnect with other natural gas pipelines, including the interstate natural gas transmission system of Williams Northwest Pipeline (Williams) at the Molalla Gate Station. To minimize environmental concerns and maximize operating efficiency, the project design basis requires that primary vaporization of LNG at the Import Terminal be achieved from the heat available in ambient air. For seasonal conditions when ambient heat is unable to meet design requirements, a fired heating system will supplement the ambient system. The selection of a suitable vaporization system (a combination of ambient and fired heating) for the Oregon LNG Import Terminal is therefore of principal importance. The selected system will directly influence the capital cost, operational cost and environmental impact of the Import Terminal. Additionally, the selection will also affect the regulatory requirements, availability, operability and the general public perception of the Import Terminal. The objective of this report is to select a suitable vaporization system for the Import Terminal based on evaluation of various available vaporization systems. The selection is based on the requirement to use heat available from ambient air to the extent possible, and to determine the optimum method for providing supplementary heating at times when the heat available from ambient air is insufficient to meet the sendout requirements. Different ambient air vaporizers and supplemental (fired) heating systems are evaluated and compared based on mechanical performance, capital and operating costs, emissions and effluent discharge. Although no environmental modeling has been performed in the preparation of this study, consideration has been given to emission and effluent discharge data provided by equipment vendors in selecting the vaporization system.
2
BACKGROUND
Oregon LNG holds a long term sub-lease for approximately 96 acres of land located on the East Skipanon Peninsula near the confluence of the Skipanon and Columbia Rivers in Warrenton, Clatsop County, Oregon. The company proposes to build an LNG Import Terminal on this parcel of land.
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The Import Terminal will provide a natural gas baseload sendout capacity of 1.0 billion standard cubic feet per day (bscfd) and a peak sendout capacity of up to 1.5 bscfd. LNG supplied to the Import Terminal via LNG carriers will be stored at -260°F in three 160,000 cubic meter above ground, full containment storage tanks. LNG vaporized into natural gas will be transferred from the Import Terminal at 40°F via an approximately 117 mile long sendout pipeline. 2.1 Vaporizer System Overview The Import Terminal will use available heat from the ambient air for LNG vaporization to the maximum extent possible, augmented, when necessary, with a supplementary (fired) heat system to achieve the sendout temperature of 40°F. Selection of a vaporization system therefore requires consideration of (1) the optimum method for extracting heat from the ambient air, and (2) a compatible and efficient system for providing the supplementary heat. 2.1.1 Vaporization System Requirements The system requirements and constraints are summarized below. These requirements are obtained from the Import Terminal Design Basis (document 07902-TS-000-002) and are as follows: Import terminal location: Baseload sendout: Peak sendout: Gas sendout temperature: Primary vaporization heat source: 2.1.2 Pacific Northwest 1.0 bscfd Up to 1.5 bscfd 40°F Ambient Air
Constraints and Assumptions Considered in Vaporization System Selection When considering the use of ambient air heat for vaporization of LNG under the design requirements listed above, there are several key constraints that must be considered. These constraints are described below. • Ambient environmental conditions. Obviously, climate conditions are a major factor in considering use of ambient air as a heat source for LNG vaporization. The air temperature and relative humidity in particular have a major impact on the performance of the ambient air vaporizers, and
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other factors such as solar radiation and wind can also impact performance (more so for natural draft vaporizers). The table below shows the annual average temperatures in Warrenton, Oregon between 2001 and 2005 (as measured at the nearby Astoria Clatsop County Airport, COOP ID # 350328). The data represents five years of average temperatures. As shown in the table, the average annual temperature is 51.5°F, and the average relative humidity is high. The temperatures vary seasonally, with a winter temperature typically in the 30-40°F range and a summer temperature typically in the 60-70°F range. The lowest temperature recorded in this time period was 25°F; review of other weather data for the region revealed an extreme low of 6°F over the past 30 years.
Table 2.1.2.1 Average Ambient Conditions in Warrenton Oregon Year Average Temp (°F) Average Humidity (%) 2001 2002 2003 2004 2005 Average
50.8
51.0
52.2
51.8
51.5
51.5
84.0
81.2
82.1
85
82.9
83
•
Ambient air vaporizer approach temperature limitations. For heat exchangers which operate by transferring heat between opposing flows of hot and cold fluids, there are practical limitations in how closely the heated fluid temperature can approach the temperature of the fluid providing the heat. The difference between the inlet temperature of the fluid providing the heat, and the outlet temperature of the fluid being heated, is called the approach temperature. The achievable approach temperature for a heat exchanger is a function of parameters such as the available heat exchanger surface area, resistances in heat transfer between the two fluids, and fluid flow rates. For this study, vendors were contacted to determine the achievable approach temperatures for ambient air LNG vaporizers. Approach temperatures typically vary from 20 to 40°F, and
worsen with running time due to heat transfer resistance resulting from accumulation of ice on the vaporizer surfaces.
•
Lack of available, local waste heat source. Currently there is no local source of waste heat available for use for supplementary heating for this Import Terminal. If a waste heat source (such as a power plant condenser
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or other industrial heat source) becomes available, the need for burning fuel gas for supplementary heating could be reduced. However, this report will assume that all supplementary heating will be provided by on-site, fired heating equipment with no credit taken for waste heat sources. • Emissions and effluents. Of primary importance in selecting a suitable vaporization system for this Import Terminal is the minimization of environmental emissions and effluents. Ambient air vaporizers generate no emissions; and they only generate ice and condensed water (possibly with some entrained particulate matter) as effluents. However, fired heating systems do generate emissions and effluents which generally require treatment systems. The choice of supplementary heating system will therefore consider the emissions and effluents associated with each option. Baseload and peak sendout. The vaporization system is designed to sendout a baseload 1.0 bscfd and a peak of up to 1.5 bscfd. The peak output can be provided with all spare equipment operating. The baseload case must be provided with reliability, such that no credit can be taken for standby equipment. Accordingly, the supplemental heating system will be designed with spare equipment to ensure that in conjunction with the ambient air vaporization system it can reliably provide sendout of 1.0 bscfd at 40°F. To achieve peak sendout of 1.5 bscfd, the spare equipment in the supplementary heating system can be credited.
•
2.1.3
Impact of Constraints and Assumptions on System Selection As pointed out in the previous section: • • The design basis sendout temperature is 40°F; The approach temperature for ambient air vaporizers varies considerably depending on physical parameters and vaporizer run times, and is on the order of 20 to 40°F; The annual average ambient temperature is slightly over 50°F, and there are periods during the year when the temperatures are lower.
•
To produce sendout gas at 40°F with an approach temperature on the order of 2040°F, the ambient temperatures would have to be no lower than 60°F and possibly as high as 80°F. Since the weather data show that at many times during the year the ambient temperature is below this level, the gas exiting the ambient air
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vaporizers will require supplemental heating to achieve the design basis sendout temperature of 40°F . Consequently, the supplemental heating system will be required to raise the gas temperature exiting the ambient air system to the sendout temperature. For the purposes of this evaluation, the ambient air system will be assumed to be able to produce gas at 0°F, and the supplemental system will be designed to raise the gas temperature to the sendout design basis temperature of 40°F. The basis for selection of 0°F for the ambient air system is as follows: • It is assumed that the design and quantity of ambient air vaporizers will be such that the average approach temperature will ensure exit gas temperature of at least 0°F at times when the ambient air temperatures are at the year round average (51.5°F) or higher. This requirement will be included in the specifications provided to the vendor. At times when the temperature is lower than the year round average, the absolute content of water vapor in the ambient air will be relatively lower than on hotter days. Accordingly, the vaporizers will accumulate frost and ice at a slower rate, which will reduce the approach temperature. So, it is appropriate to assume that the vaporization system should be able to achieve 0°F under these conditions. If the provided ambient air vaporization system is unable to heat gas to at least 0°F due to accumulation of ice on the heat exchanger surfaces, terminal operators can take action to remove the ice mechanically or by other means. It is assumed that the terminal design and operating procedures will account for this potential.
•
•
It is recognized that under extreme cold conditions, it may not be possible to achieve 0°F gas exit temperature from the ambient air system. These events are expected to be very rare. To ensure the baseload sendout can meet these conditions, the supplementary heating system will include design margin. Table 2.1.3.1 summarizes the proposed vaporization system design parameters for the Import Terminal.
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Table 2.1.3.1 Ambient Air Vaporizer and Supplementary Heater System Design Parameters Average Ambient Temperature Assumed Temperature at Outlet of Ambient Air Vaporizers (°F) Heat Provided From Ambient Air Temperature at Outlet of Supplemental Vaporizers (°F) Minimum Heat Required from Supplemental System
Sendout Capacity (bscfd)
(°F) 51.5
(MMBtu/hr) 751
(MMBtu/hr) 133
1.5
0
40
Having established that ambient air vaporizers in tandem with supplementary heating systems are required for the Import Terminal, attention will now be focused on the various ambient and supplementary fired systems – specifically, the modes of operation, capital and operating costs and the emissions and effluents associated with each.
3
AMBIENT AIR VAPORIZATION
Ambient air vaporization systems draw heat from the surrounding ambient air to vaporize LNG. There are two primary methods of vaporization using heat from the ambient air: by direct or indirect heat transfer into the LNG. 3.1 Direct Ambient Air Vaporizers (AAVs) Direct AAVs transfer heat from the ambient air directly into the LNG through a heat exchanger heat transfer surface. In typical Direct AAVs, the cryogenic liquid is passed through a manifold that divides the flow into a number of vaporizer units where a series of smaller flows are directed through individual heat transfer tubes. Each tube has aluminum fins for increased heat exchange area and is in direct contact with the ambient air. Figure 3.1.1 shows a schematic of a typical Direct AAV.
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Warm Ambient Air
Natural Draft or Fan Assisted
Cold Liquid LNG Cool Ambient Air
Natural Gas
Figure 3.1.1 – Schematic of Direct Ambient Air Vaporizer
One disadvantage to the use of Direct AAVs is lack of experience with these units in high volume vaporization of LNG. However, Direct AAVs have been used in liquid nitrogen service (a fluid colder than LNG) for over fifty years. While Direct AAVs are in operation, frost and/or ice will build up on the units due to the proximity of the LNG to the ambient air. The longer a unit runs, the more frost and/or ice builds, which gradually reduces the performance of the unit. Hence, Direct AAV units need to be periodically shut down and de-iced. De-icing becomes difficult when the ambient air temperature drops below freezing. In this case, the system must be provided with another source of heat for de-icing, such as electric heaters or water spray. At the proposed site, weather data shows that the temperature rarely drops below freezing and then only for short periods of time. Fortunately, during cold periods the available moisture in the air is relatively low, minimizing the rate of ice buildup at these times. Experience from current users and vendors (e.g., Thermax and Cryoquip Inc.) of Direct AAVs has shown that during periods of extended cold weather, longer operating durations can be achieved by running all the units simultaneously at a reduced rate while gradually increasing the supplementary heat as frost continues to form on the vaporizer. The design of the system will account for having adequate vaporization capacity and availability year-
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round taking into consideration downtime of a subset of the unit population for deicing. It should be noted that although Direct AAVs can only heat gas up to a temperature approaching the ambient temperature, the units can provide a high percentage of the total heat load for vaporizing LNG. Per one vendor contacted, a Direct AAV operating at arctic conditions of -80°F could provide over 50% of the total heat duty needed to vaporize LNG. There are two types of Direct AAVs – Natural Draft AAVs and Forced Draft AAVs. 3.1.1 Direct Natural Draft Ambient Air Vaporizers Direct Natural Draft AAVs rely on wind and natural convective currents to move air over the tubes and fins of the vaporizer unit. As warm air contacts the tubes containing LNG, the air cools and becomes dense, causing it to flow downwards to the bottom of the vaporizer unit. This causes warm ambient air from the surroundings to be drawn through the top of the unit. Figure 3.1.1.1 illustrates a Direct Natural Draft AAV in operation.
Figure 3.1.1.1 – Direct Natural Draft Ambient Air Vaporizer in Operation
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3.1.1.1 Performance The outlet gas temperature of a Direct AAV is dependent not only on ambient conditions but on other factors such as run time and amount of units in operation. Consider a single AAV unit; at the onset of operation the temperature of the outlet stream is nearly the same as the ambient temperature. As the run time increases, the unit begins to frost and/or ice up, thus reducing the amount of heat being transferred to the LNG. A significant amount of heat transfer is still achieved, but the temperature of the outlet stream reduces as time passes and ice accumulates. As more units come into operation, more surface area becomes available for heat transfer. Per a vendor contracted for this study, it is estimated that 12 basic trains (13 units/train) plus 6 duty cycle extra trains (that is, idle vaporizers that are out of service undergoing de-icing while others operate) would be required to vaporize 1.5 bscfd of LNG. 3.1.1.2 Emissions and Effluents Cooling of the moist ambient air results in condensation of a large amount of water vapor from the atmosphere. Some of this condensed water collects as frost and/or ice on the tubes of each unit. Typically, the ice from the surface of each unit melts and drains to a collection basin during the de-icing cycle. This water is expected to have minor or no contamination and may be treated prior to disposal or used within the Import Terminal. Another issue resulting from the cooling of the ambient air is the formation of water vapor as “fog”, which can create a visible cloud close to the Import Terminal. 3.1.1.3 Physical Characteristics Per one vendor contacted for this study, typical Natural Draft AAVs that would be used for this import terminal consist of vertical tube bundles 42-ft in length with a plot area of 12-ft by 12-ft each. The vaporizers are elevated above grade to prevent recirculation of cold dense air from the bottom of the unit back to the inlet at the top of the unit. The total footprint of these vaporizers is therefore 320ft x 230-ft, or 73,600 ft2, assuming a 6-ft clearance between the estimated 236 units (18 trains, with 13 units/train) required for operation and duty cycle. Each unit weighs approximately 52,000 lbs when dry and can withstand ice loading up to an additional 60,000 lbs. 3.1.1.4 Capital and Operating Costs Capital costs for the Natural Draft AAV arrangement for an LNG sendout capacity of 1.5 bscfd have been estimated by Cryoquip Inc. to be $58 million (vaporizers only). Operating costs on the other hand would be low. The power input for these units is zero. There are no moving parts in the vaporizers and they
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are, for practical purposes, maintenance free. The only costs involved in operation would be those required to handle the effluents from the vaporizers.
3.1.2
Direct Forced Draft Ambient Air Vaporizers
In Direct Forced Draft AAVs, airflow into the unit is controlled by fans installed on top of the vaporizer. Each unit can be equipped with shrouds on each side to direct airflow through the vaporizer. Direct forced draft vaporizers are approximately 1.7 times more effective than Natural Draft AAVs i.e., they move 1.7 times more air across the tubes of the unit. Figures 3.1.2.1 and 3.1.2.2 show two types of Direct Forced Draft Ambient Air vaporizers.
Figure 3.1.2.1 – Direct Forced Draft Ambient Air Vaporizers without Shrouds
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Figure 3.1.2.2 – Direct Forced Draft Ambient Air Vaporizers with Shrouds 3.1.2.1 Performance Since the airflow through the forced draft units is higher than for natural draft units, fewer forced draft units will be required to achieve the same duty. Per one vendor contacted for this study, it is estimated that 10 basic trains (10 units/train) plus 5 duty cycle extra trains would be required for the vaporization of 1.5 bscfd. 3.1.2.2 Emissions and Effluents Emissions and effluents for forced draft units are similar to the natural draft units as described in 3.1.1.2, except that with Forced Draft AAVs the formation of fog is diminished by the forced airflow (from the fans on top of each unit) around the tubes. There is also more ice formed in Forced Draft units because the increased air flow over the tubes increases the rate of water condensation and consequently the rate of ice formation. The shrouds around the tube bundles impede the amount of radiant heat reaching the ice forming on the tubes, which can increase the ice buildup rate.
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3.1.2.3 Physical Characteristics Physical requirements are similar to the Natural Draft AAVs arrangement, except that fewer forced draft units are needed. Assuming 150 units and 6-ft spacing between each unit and each train, the total land area needed for all the vaporizers is estimated at 170-ft x 260-ft or 44,200 ft2. The weights of these units are comparable to the natural draft units, with a small addition due to the weight of the shrouds and fans. 3.1.2.4 Capital and Operating Costs The total capital costs for Forced Ambient Air vaporizers has been estimated at $56 million (vaporizers only) by Cryoquip Inc. Operating costs for Forced Draft AAVs would be higher than natural draft AAVs due to the electric power needed for the fans; each unit requires power to the fans on the order of 60 HP (about 45 kW). With 15 trains in constant operation (units in the de-icing cycle would also have the fans on) the power requirement would be on the order of 9,000 HP or 6.7 mW.
3.2
Indirect Ambient Air Vaporizers Indirect vaporizers operate by transferring heat from ambient air to an intermediate fluid which in turn transfers heat to LNG through a separate heat exchanger. The different arrangements of Indirect Ambient Air Vaporizers are described below.
3.2.1
Ambient Air Heat Exchanger with Heat Transfer Fluid (AAV-HTF) This type of vaporization system consists of Shell and Tube Heat Exchangers, Fin-fan Air Heaters or Reverse Cooling Towers and a Heat Transfer Fluid loop. Fin-Fan Air Heaters are used to transfer heat from ambient air into the HTF, which is then sent to the LNG shell and tube vaporizer. The cooled HTF flows into a surge tank and is then pumped back to the Air Heaters. Schematics of the different vaporization processes are shown below in Figures 3.2.1.1 and 3.2.1.2.
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WARM HTF
AIR HEATERS
LNG
Pipeline Gas
SHELL AND TUBE VAPORIZER
COLD HTF
HTF SURGE TANK
HTF PUMP
Figure 3.2.1.1 – Schematic of AAV-HTF System Using Air Heat Exchangers
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Figure 3.2.1.2 – Schematic of AAV-HTF System Using Reverse Cooling Tower
Although the main heat source for this vaporization arrangement is the heat contained in the warm ambient air, supplemental heating is also required to maintain capacity and delivery temperature when the ambient air temperature drops below a nominal value. The vaporization system using fin-fan heat exchangers shown in Figure 3.2.1.1 is in operation at the Dahej LNG terminal in India and is being installed at the Lake Charles LNG terminal in Louisiana. The vaporization system using Reverse Cooling Towers shown in Figure 3.2.1.2 is being used at the Freeport LNG project.
3.2.1.1 Performance Typical indirect air heating systems in operation in the hot areas like India and the Gulf of Mexico area are capable of delivering about 90% of the annual heat load. In more temperate climatic regions like Oregon, that capability is reduced to between 55-60%. This availability is also applicable to Fin Fan Air Heat exchangers. These vaporization systems also have a significant electrical load.
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3.2.1.2 Emissions and Effluents Water produced from condensation of water vapor from the surrounding air must be continuously discharged and safely discarded. For Reverse Cooling Tower systems, the circulating water stream is likely to require chemical treatment and the blowdown needs to be appropriately handled. 3.2.1.3 Physical Characteristics The AAV-HTF system presents a significant demand on its supporting infrastructure. A Google Earth® satellite photo of the Dahej terminal is shown in Figure 3.2.1.3.1. The components shown on the right side of the photo outline the air heat exchanger arrangements for the vaporization of 1.0 bscfd, which is the baseload case for the Oregon LNG Import Terminal. Figures 3.2.1.3.2 and 3.2.1.3.3 illustrate Air Towers and Shell and Tube Vaporizers (STVs, used for supplemental heating when the heat available from ambient air is insufficient) under construction at the Freeport LNG terminal. The heating towers require a large plot area.
Figure 3.2.1.3.1 – Dahej LNG Terminal
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Figure 3.2.1.3.2 – Air Towers Under Construction at Freeport LNG Terminal
Figure 3.2.1.3 – STVs Under Construction at Freeport LNG Terminal TR-07902-000-002 Page 19 of 32 December 5, 2007
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3.2.1.4 Capital and Operating Costs Shell and tube heat exchangers rated for high sendout pressures (over 1000 psi) and capacities (approximately 100 to 150 mmscfd) are estimated at roughly $500,000 a unit. The Oregon LNG Import Terminal would require at least 10 of these units for a maximum sendout capacity of 1.5 bscfd. Also, as stated earlier, Reverse Cooling Towers are large structures and would require significant capital investment for construction and operation. Power consumption costs due to ancillary equipment such as fans and pumps should also be taken into account, making this vaporization system cost intensive.
3.2.2
Smart Air ® Vaporizer The Smart Air® vaporization system is similar to the AAV-HTF system discussed in section 3.2.1, except that the system uses Potassium Formate (KF) as the heat transfer fluid. The system consists of Air Heaters, a Surge Tank, Pumps, and Shell and Tube LNG vaporizers. The Air Heaters transfer heat from the warm ambient air into cool KF fluid from the Shell and Tube LNG Vaporizer. The warmed KF fluid is then sent to the Surge Tank. KF fluid is pumped from the Surge Tank back to the Shell and Tube vaporizers where it provides heat to the LNG, is cooled, and then sent back to the Air Heaters. The Air Heaters used in the Smart Air® vaporization system are proprietary to Mustang Engineering. Each Air Heater contains layers of finned tubes and has fans forcing the ambient air from the surroundings to flow through the top of the unit downwards, over the tube bundle. The Air Heaters are elevated above grade to prevent recirculation of cold dense air from the bottom of the unit to the fan inlet. As with other ambient air vaporization systems, supplementary heat will be required when design ambient conditions cannot be met.
3.2.2.1 Performance Promoters of the Smart Air® Vaporization system claim the system would be able to provide 65% of the annual heat duty for the Oregon area. As this vaporization system is yet to be installed in a region of similar climate as Oregon, this claim remains unconfirmed. Smart Air® vaporization systems also have significant electric power demands for the ancillary equipment including fans for air heaters and pumps. A system rated for 1.5 bscfd would require about 9000 HP.
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3.2.2.2 Emissions and Effluents Cold, condensed water from the atmosphere continuously forms on the surface of the tubes containing cold KF fluid. The water falls off the tubes exiting from the bottom of the air heater with the flow of cooled air. The water can be collected in a basin below the air heaters and utilized in the plant, treated and used for potable water or discarded. The condensed water is clean, freshwater and does not require significant treatment and can be discarded easily. Estimated waste water flow rate for a system rated at 1.5 bcsfd is 1000 gpm. 3.2.2.3 Physical Characteristics For a sendout capacity of 1.0 bscfd, the LNG Smart Air® vaporization system would require a total surface area of 27,240 ft2. The vaporization system at Oregon will be sized for a total capacity of 1.5 bscfd; hence it is reasonable to assume that the acreage needed would be approximately 40,860 ft2. Each threefan Air Heater unit measures 14ft wide, 60ft long and 40ft high. 3.2.2.4 Capital and Operating Costs The total cost for a Smart Air® Vaporization system with a 1.5 bscfd capacity is estimated to be $80 million. Extra costs will also be incurred due to treatment and handling of wastewater produced by the Air Heaters and electrical power consumption from the fans for the heaters.
3.2.3
Other Indirect Ambient Air Heating Systems Other Ambient Air vaporization systems exist but are not discussed here because they either cannot be incorporated into the Oregon LNG Import Terminal design or they are not proven technologies. An example of such a vaporization system is the Heat Integrated Ambient Air Vaporization (HIAAV). HIAAV systems involve the use of Waste Heat recovery units installed in combination with gas turbines which the Oregon LNG Import Terminal design does not include.
3.2.4
Limitations on Use of Indirect Ambient Air Systems Per discussions with vendors, indirect systems work best when air temperatures are above 70°F; when the ambient air temperature drops below that value, the heat available from the ambient air is insufficient and supplemental heat must be added to the HTF. When the air temperatures drop below about 50°F, heat transfer from the ambient air is ineffective and essentially all vaporization heat must be provided from supplement heat sources. Note that the year-round average temperature at the terminal site is on the order of 50°F, so these indirect methods
would need to be backed up by supplemental systems operating at 100% of the required
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duty for vaporization for much of the year. That is, if an Indirect Ambient Air Vaporization were to be used at this terminal, two different, full capacity vaporization systems would need to be installed.
3.3
EFFLUENTS DISCUSSION One of the advantages of using ambient air vaporizers is that they do not produce any emissions. However all ambient air vaporization methods create effluents that need to be properly handled. In Direct Ambient Air Vaporizers, frost and/or ice builds up on the tube bundles of each unit as a result of the freezing of condensed water from the ambient air that forms on the tubes. During the de-icing cycle all the ice falls off the unit and has to be properly discarded. Indirect Ambient Air Vaporizations systems also generate condensed water as effluent. However, since air does not come in direct contact with a heat transfer surfaces containing cryogenic fluid, there is little or no ice formation. For each type of vaporizer, the rate of amount of water formation (as ice or condensate) can be as high as 1000 gpm (liquid water equivalent) for a 1.5 bscfd terminal. The terminal design needs to address treatment of this effluent.
3.4
IMPORT TERMINAL COMPATIBILITY Table3.4.1 shows a comparison of the ambient air vaporization systems discussed in Section 3 of this report.
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Table 3.4.1 –Comparison of Air Vaporization Systems
Direct Ambient Air Vaporization Natural Draft Forced Draft
Indirect Ambient Air Vaporization*1 AAV-HTF (Air Heat Exchangers) AAV-HTF (Reverse Cooling Towers)
Smart Air®
Ambient Temperature Operating Range Estimated Capital Cost Land Usage Power Usage for AAVs Effluents
Provides large fraction of total heat duty at all expected ambient temperatures
Provides large fraction of total heat duty during hot ambient conditions; Provides little or no heat duty at times when temperatures drop below 50°F $98 million 167,000 ft2 High (fans and pumps) Water $100 million 100,000 ft2 Moderate (pumps) Water $95 million 40,860 ft2 High (fans and pumps) Water
$152 million 73,600 ft2 None
$147 million 44,200 ft2 High (fans)
Water and ice Water and ice In summary:
• During much of the year the ambient air temperature at the site is on the order of
50°F or lower. Under these conditions, indirect systems provide little or no heat. Accordingly, for these systems, a 100% capacity supplemental system would be required in order to achieve sendout during cold periods. This would increase the capital cost and land area needed for the Import Terminal, and increase the yearly emissions from the terminal. For these reasons, indirect systems are considered inappropriate for this facility.
• Direct AAVs would provide much of the heat duty but require supplemental heat
during cold periods.
• Of the two types of direct AAVs, fewer forced draft AAVs are needed than natural
draft AAVs; thus, significant land area can be saved if forced draft AAVs are used. However, natural draft AAVs do not require electric power whereas forced draft AAVs use electrically powered fans.
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Therefore, the Direct Forced Draft Ambient Air vaporization system will be the most suitable option for the Oregon LNG Import Terminal. It is estimated that 10 basic trains (10 units per train) plus 5 duty cycle extras can provide the entire heat load expected from the Direct Forced Draft AAVs for the peak sendout capacity of 1.5 bscfd. On occasions when the ambient conditions cannot provide sufficient heat, supplemental heat would be provided, as discussed in the next section.
4
SUPPLEMENTARY HEATING
When the ambient temperature is not warm enough to raise the temperature of the vaporized LNG to 40°F, supplement heating must be provided to reach this design basis sendout temperature. Figure 4.1 illustrates how the supplemental heating system would be integrated with the Ambient Air Vaporization system at the Oregon LNG Import Terminal. The minimum amount of heat needed from the supplemental system has been determined section 2.1.3 to be 133 MMBtu/hr. To be conservative, the supplemental vaporization system will be sized for 180 MMBtu/hr which provides 35% extra capacity.
VAPORIZED LNG @ <40°F
Natural Gas @ 40°F Sendout Station
VAPORIZED LNG @ >40°F Supplemental Gas Fired Vaporizer
COLD LNG FROM TANK
Ambient Air Vaporizer
Figure 4.1 – Overall Schematic of Vaporization System
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As illustrated above, cold LNG from the storage tanks is pumped to the AAVs which vaporize the LNG. If the AAVs do not provide sufficient heat to raise the temperature to 40°F, a side stream of the gas exiting the ambient air vaporizers is sent through the supplemental heating system and warmed to a temperature greater than 40°F. The warm stream is blended with the cooler, vaporized LNG from the AAVs and sent to the metering station at 40°F. Gas fired heating systems are proven and effective methods of providing heat for vaporizing LNG. They can also operate largely unaffected by surrounding climatic conditions. However, these systems consume fuel and generate emissions. Two gas fired heating system options were considered for Oregon LNG and are described below: 4.1 Submerged Combustion Vaporizers (SCVs) SCVs are designed to use fuel gas or low pressure boiloff gas from the terminal. High pressure LNG flows through a stainless steel tube bundle that is submerged in a water bath heated with exhaust gases generated from a combustion burner. The water transfers the heat from the combustion process to the LNG. The SCV alternative offers simplicity and has become the vaporization choice for many new and existing U.S. regasification terminals. Figure 4.1.1 is a schematic for the SCV process.
Figure 4.1.1 Submerged Combustion Vaporizer
The hot exhaust gases from this combustion are sparged into the water bath and create a relatively low temperature (typically in the range of 50° to 60° F) thermally stable
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heat source for the vaporization coils. The vaporized LNG exits the coils at pipeline pressure and design basis temperature for downstream transmission. 4.1.1 Performance
SCVs have very high thermal efficiencies (above 95%) because the combustion products are bubbled directly into the water bath hence all the available heat is transferred directly to the water. This includes the latent heat of condensation of water vapor in the exhaust gas which also condenses in the water bath. Gas outlet temperatures for SCVs range from 35°F to 60°F. Since the water bath is at high thermal capacity, stable operation is generally achievable, even for sudden start-ups, shutdowns or deviations in load. Electric power is also required to run the combustion air blower and the water circulation pumps. 4.1.2 Emissions and Effluents Due to the combustion process NOx, CO and other emissions are produced when the SCVs are in operation. Table 4.1.2.1 contains the emissions from a typical SCV unit.
Table 4.1.2.1 – Emissions from a Typical SCV Unit (rated at 94.2 MMBtu/hr)
Pollutant NOx CO VOC
Emissions (pounds per million Btu @ 3% O2) <0.0345 <0.025 <0.003
Particulate Matter (PM 10) is also emitted at a rate of 0.0015 lb/MMBtu. Reducing these emissions (especially the NOx) will require the use of a selective catalytic reactor (SCR). SCRs are expensive and do not operate efficiently with SCVs. SCR catalysts can be “poisoned” or “fouled” during SCV operation due to contact with potassium or sodium salts used in pH neutralization of the water bath. Optimum temperatures for an SCR reaction range from 650-750°C and may go as high as 1000°C depending on what catalyst is used. SCVs cannot generate exhaust gas at these temperatures and hence SCV exhaust cannot be treated via SCRs without costly re-heating of the exhaust gas.
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During SCV operation the water in the bath becomes acidic as it absorbs combustion products. The pH of the water bath is monitored and controlled by introducing alkaline chemicals such as caustic soda or sodium carbonate. It is important to maintain a relatively neutral pH level (between 6 and 7) in the water bath. During the combustion process, waste water is also produced and must be treated before disposal. For a single SCV unit rated for approximately 94 MMBtu/hr (which is about 50% of the maximum supplemental heat needed) there is a water overflow rate of about 15.5gpm. Hence it is expected that an SCV system installed at the import terminal would produce about 30 gpm of waste water. 4.1.3 Physical Characteristics An SCV unit with a vaporization capacity ranging from 150-200 mmscfd (typical size of a unit) will have a minimum footprint of 408 ft2. Stack heights can vary based on owner requirements. The layout of SCVs can be seen in Figure 4.1.3.1.
Figure 4.1.3.1 – SCV Installation, 1.0 bscfd capacity
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4.1.4 Capital and Operating Costs SCV units usually have a vaporization capacity range of 150-200 mmscfd. Each unit costs approximately $2 million. Two units would be needed for the supplemental heat system at Oregon LNG. Hence a total capital cost (vaporizers only) of $4 million would be required. This amount takes into account the cost of ancillary equipment such as the air blower, circulation pump, fuel gas heater, controls and associated piping. This cost does not include an SCR unit. The greatest disadvantage of purchasing SCVs is the operating costs. Current technology is such that fuel consumption is in the range of 1.3% to 1.5% of throughput. It is important to note that for the Oregon terminal throughput does not refer to the full sendout capacity of the terminal, as the supplemental system is only designed to heat the gas exiting the ambient air vaporizers, which has already been heated. Instead, it refers to the equivalent amount of LNG (at -260°F) that is vaporized by 180MMBtu/hr, i.e., approximately 300 mmscfd. The annual power consumption costs for the air blowers must also be considered due to the motor size and required excess air. The estimated annual operating costs for two SCV units running at their maximum output (i.e., a total of 180 MMbtu/hr) is $6 million. 4.2 Gas Fired Heater with Heat Transfer Fluid (GFH–HTF) The GFH–HTF vaporization systems involve the use of gas fired heaters as the primary source of heat to vaporize LNG. Heat is supplied to shell and tube LNG vaporizers through a closed circuit with a heat transfer fluid, usually a mixture of water and ethylene glycol (WEG), as the heat transfer fluid. A schematic of the system is shown in Figure 4.2.1. Gas fired heaters heat the HTF which is then sent directly to the LNG vaporizer. The cooled HTF is collected in a surge tank and pumped back to the Gas Fired heaters. A system very similar to that shown is used on multiple vaporizer systems at the Distrigas LNG Terminal in Everett, MA.
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OREGON LNG IMPORT TERMINAL LNG VAPORIZATION STUDY
Figure 4.2.1 – Schematic of GFH–HTF Vaporization System
4.2.1
Performance The fired heaters used in this vaporization system are capable of heating WEG to temperatures up to 200°F. Based on the proposed operation of the vaporization system at the Oregon LNG Import Terminal, the capability of heating up a side stream of the vaporized LNG to temperatures much greater than 40°F is necessary. The GFH–HTF system has this capability. Gas fired heaters used in this system burn approximately 1.8% - 2.2% of throughput1 and have efficiencies of approximately 83%. The system will also have a significant electrical load from heater forced draft fans, HTF pumps and other ancillary equipment.
4.2.2
Emissions and Effluents Typical air emissions data for the burner associated with a Gas Fired Heater with a heat duty of 60 MMBtu/hr are presented in Table 4.2.2.1.
1 Note that the throughput in this case has been defined in section 4.1.4
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OREGON LNG IMPORT TERMINAL LNG VAPORIZATION STUDY
Table 4.2.2.1 – Air Emissions from Gas Fired Heater
Pollutant NOx CO VOC
Emissions (pounds per million Btu @ 3% O2) <0.013 <0.025 <0.003
It should be noted that Gas Fired Heaters are very compatible with SCRs due to the high temperature of the exhaust. Hence, SCRs work very efficiently when installed on Gas Fired Heaters and are capable of significantly reducing NOx and CO emissions rates. 4.2.3 Physical Characteristics The GFH–HTF system presents a minimal vaporizer footprint with the HTF pumps and heaters located nearby typically in a “boiler house.” Footprints for Gas Fired Heaters vary according to the size of the heaters. Next to the SCV, the STV-GF requires the least land area due to minimal system components. Vertical shell and tube heat exchangers used in this application have an approximate outer diameter of about 42 inches. Multiple exchangers will be needed for the supplementary heating system. 4.2.4 Capital and Operating Costs Shell and tube heat exchangers used in this system are estimated to cost $500,000 a unit. The Oregon LNG Import Terminal will require at least three heat exchangers. Gas fired heaters rated at 60 MMBtu/hr with an SCR and associated ancillary equipment i.e., surge tank, pumps etc. can cost up to $1 million per unit. Estimated total capital costs for this system is $4.5 million. Operating costs will comprise mainly of power and fuel consumption charges for the unit. Power consumption from the system would be mostly from horsepower requirements for the heater forced draft fans pumps. 4.3 IMPORT TERMINAL COMPATIBILITY SCVs are not considered acceptable for supplemental heating for this terminal since they are not effective at heating gas to high temperatures (which is needed for
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OREGON LNG IMPORT TERMINAL LNG VAPORIZATION STUDY
blending purposes). In addition, the emissions from SCVs cannot be controlled using normal SCR technology. Gas fired heaters with a heat transfer fluid loop and shell and tube heat exchangers offer a more flexible and efficient option. The heaters and heat exchangers can be used to raise the natural gas temperatures to high values to aid in blending to reach the 40°F sendout temperature. The number and capacity of Gas Fired Heaters can be optimized to allow large turn down ratios. Gas fired heaters also work very well with SCRs to reduce emissions rates. Shell and tube heat exchangers are versatile, simple and widely used components, and can be easily customized to meet various operations requirements.
5
CONCLUSIONS AND RECOMMENDATIONS
LNG vaporization at the Oregon LNG Import Terminal will occur in two stages: (1) an ambient air vaporization system will provide much of the heat needed for vaporization, and (2) a supplemental heating system will provide the remaining heat needed when ambient conditions are not sufficient to reach the design sendout temperature. At Oregon, the year-round temperature is such that indirect ambient air vaporization systems will not be effective during much of the year. Use of indirect systems would therefore require installation of 100% capacity backup fired heating systems. This would result in large capital costs and generation of more annual emissions than a system using direct AAVs. Accordingly, direct AAVs are deemed to be the most appropriate method for extracting heat from the ambient air at this terminal. Of the two types of direct AAVs, forced draft AAVs are recommended over natural draft AAVs at this time due to the reduced capital costs and land area. One disadvantage to using Forced Draft AAVs is its lack of a proven track record in high volume LNG vaporization service. However, AAVs have been effectively used for years to vaporize liquid nitrogen which is a cryogenic fluid colder than LNG. Of the two options considered for the supplementary heating system, the Gas Fired Heaters with Heat Transfer Fluid (GFH-HTF) system is considered a better choice than Submerged Combustion Vaporizers (SCV). The GTF-HTF works well with a Selective Catalytic Reduction system (SCR) hence its emissions rates can be efficiently and significantly reduced, unlike SCV units. Also SCVs are not efficient at delivering natural gas at the high temperatures needed for downstream blending with cold gas for achieving the design sendout temperature, thus ruling out their use for supplementary heating at this terminal.
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OREGON LNG IMPORT TERMINAL LNG VAPORIZATION STUDY
In summary, CH·IV recommends that Oregon LNG use Direct Forced Draft Ambient Air Vaporizers for its primary vaporization system and a GFH-HTF as a supplemental heating system. This combination presents the most effective option for LNG vaporization at the Import Terminal.
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