Section 4.1 Slaked Lime
Content
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
TABLE OF CONTENTS
1. I N T R O D U C T I O N .............................................................................................................................2 1.1 O V E R V I E W ......................................................................................................................2 1.2 S A F E T Y H A Z A R D S A N D P R O C E D U R E S ............................................................................3 2. S Y S T E M D E S C R I P T I O N ................................................................................................................4 2.1 L I M E S I L O .....................................................................................................................4 2.1.1 Lime Silo Controls...........................................................................................5 2.1.2 Measurement and conveying system...........................................................6 2.2 L I M E S L A K E R S ...............................................................................................................7 2.2.1 Slaker and Grit Separation System Controls..........................................7 3. O P E R A T I N G P R O C E D U R E S ..........................................................................................................8 3.1 F I L L I N G T H E L I M E S I L O .................................................................................................8 3.1.1 Ordering Deliveries of Lime.........................................................................8 3.1.2 Manual Operation of Lime Silo...................................................................8 3.2 L I M E F E E D E R H O P P E R R E F I L L S E Q U E N C E ...................................................................9 3.2.1 Automatic Lime Hopper Refill.....................................................................9 3.2.2 Manual Lime Hopper Refill........................................................................10 3.3 L I M E S L A K E R S T A R T S E Q U E N C E ................................................................................10 3.3.1 Automatic Lime Slaker Start Sequence...................................................10 3.3.2 Manual Lime Slaker Start Sequence........................................................12 3.4 L I M E S L A K E R S T A N D B Y S H U T D O W N S E Q U E N C E .......................................................13 3.4.1 Automatic Lime Slaker Standby Shutdown Sequence........................13 3.4.2 Manual Lime Slaker Shutdown Sequence...............................................14 3.5 L I M E S L A K E R E X T E N D E D S H U T D O W N S E Q U E N C E ...................................................14 3.5.1 Automatic Extended Shutdown Sequence..............................................14 3.5.2 Manual : Flush Sequence............................................................................14 3.6 R E C O R D K E E P I N G ........................................................................................................14 4. P R O C E D U R E F O R P E R F O R M I N G M A I N T E N A N C E O N T H E L I M E S L A K I N G S Y S T E M ...........15 4.1 S A F E T Y .........................................................................................................................15 4.2 M A I N T E N A N C E .............................................................................................................15 4.2.1 Bin Filters.........................................................................................................15
Section 4.1 – Slaked Lime
1 PAGE 1
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
1. I NTR ODUC TION
1.1 O V E R V I E W The Lime Slaking Package for the Britannia Mine AMD Water Treatment Plant is designed to provide bulk storage of quicklime (CaO) and the equipment necessary for slaking the lime to produce lime slurry. Quicklime is supplied to site in selfunloading bulk trucks which is then pneumatically conveyed into the silo with the blower mounted on the bulk truck. A silo vent filter is supplied to prevent lime dust from escaping into the atmosphere. From the silo, a rotary valve feeds quicklime into one of two volumetric feeder hoppers by way of a diverter valve. A bin activator and aeration pads in the silo operate while the silo is discharging to promote the flow of the lime from the silo. Quicklime is metered from the volumetric feeder into screw conveyors which transport the quicklime into the lime slakers. In the lime slakers, quicklime is mixed with water in order to slake the quicklime to produce hydrated lime (CaOH2). The water to lime ratio is controlled based on the thickness or consistency of the lime paste as determined by the power draw on the mixing motor. Reacted lime paste overflows the mixing chamber with the aid of spray jets into the grit separator. The slurry is further diluted at the grit separator. Heavy, oversized particles fall to the bottom of the separator and are removed with an inclined auger for disposal. Light particles overflow from the separator and flow into the lime storage tank. A venturi-type dust & vapour arrestor is located in the slaking chamber to remove dust and vapour from the vented air stream. An exhaust fan runs at all times to assist with venting of the slaker and to maintain a slight negative pressure in the slaker.
Section 4.1 – Slaked Lime
2 PAGE 2
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
1.2 S A F E T Y
HAZARDS AND
PRO CEDURES
Quick Lime Oxide) CaO:
(Calcium Solid White or grey lumps or powder, odorless. Odorless 2,850 Celcius 2,570 Deg. Celsius N/A 1.6 – 2.8 gr/cc (water = 1.00) N/A (Air=1.0) Reactive with water to produce Ca(OH) 2 with large amounts of heat. by 0% 12.4 at 25 o C.
Physical State: Appearance and Odor: Odor Threshold: Boiling Point: Melting/Freezing Point: Vapor Pressure: Specific Gravity: Vapor Density: Solubility: Percent Volume pH: Volatile
Calcium oxide is corrosive and reacts with water to produce heat and is highly alkaline in solution. . Warning: Calcium Oxide is an extremely dangerous chemical. Refer to the MSDS binder for the Material Safety Data Sheet. Extreme care should be taken when dealing with Quicklime. This substance is harmful if inhaled or if it comes in contact with skin. It is classified as mild to moderately corrosive. Skin and eye contact should be avoided as irritation will occur. Contact lenses should not be worn when working with lime products Inhalation can cause coughing sneezing or breathing problems. Material in contact with wet skin could cause sever irritation and/or burning. When working with lime precautions should be taken to protect skin and eyes from dust and to avoid inhalation. When working in the Lime Silo Building or the Lime Slaking Building, gloves, overalls, safety goggles and dust masks should be worn at all times. In the event that the material comes into contact with skin or eyes it should be washed off immediately.
Section 4.1 – Slaked Lime
3 PAGE 3
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
2. S YS TEM D ESC RIPTION
The Lime Slaking System is manufactured by Stanco Projects Ltd. The Lime Slaking System consists of the following pieces of equipment • Lime Storage Silo • Silo • Rotary Feed Valve • Feeder Hoppers • Screw Conveyors • Lime Slakers • Mixers driven by Slaker Motor • Grit removal auger
2.1 L I M E S I L O • The Silo is contained within a sealed building and is fitted with a vent filter to prevent lime dust from escaping to atmosphere. (Capacity: 53.6m 3 . 75,000kg. H: 12.2m, D: 4.7m). Full details are shown on P& ID Drawing P-006. • A Rotary Valve (RV-501) at the base of the lime silo controls the forward feed of lime into one of two volumetric Feed Hoppers (Rated capacity: 5.8m 3 /hour). The Feed Hoppers (FE-502/503) are operated in rotation and deliver the lime to the Screw Conveyors (SC-504/505) which then convey the lime to the Lime Slakers. The rated capacity of the Feed Hoppers is 450kg/hour, while the rated capacity of the Screw conveyors is >450kg/hour. The screw conveyors operate at a fixed rate.
Section 4.1 – Slaked Lime
4 PAGE 4
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
Figure 4.1.1-Lime Silo
2.1.1 L I M E S I L O C O N T R O L S • The lime storage silo has a lime fill control panel, which monitors the level of the lime inside the silo. The measurement comprises of a continuous level sensor/transmitter (LIT-500) and a high level probe switch. The PLC/HMI shall log and display on screen the continuous level and silo high level, low level, and high-high alarms. The silo has a ventilation filter, which filters the exhaust air. Plant instrument air is used to purge the air filter periodically for automatic cleaning of the filter.
•
Section 4.1 – Slaked Lime
5 PAGE 5
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
•
The lime discharge is facilitated by a bin activator. The bin activator may be operated in hand or auto control. In auto mode, the bin activator is energized whenever material is required, and is controlled by the local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet. The lime discharges through a rotary valve. The rotary valve may be operated in hand or auto controlled. In auto mode, the rotary valve is energized whenever material is required, and is controlled by the local PLC. Motor run status and overload alarm are monitored by the local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet. From the rotary valve, lime is directed to one of the two hoppers by a diverter valve. The diverter valve is pneumatically actuated by a solenoid. The solenoid has a three position switch, namely, position 1, position 2, and automatic. In auto mode, the valve is open to the position where the material is required, signaled by a low level switch in each hopper. The PLC/HMI shall log and display on screen the status and alarm via Ethernet.
•
•
Figure 4.1.2 - Lime Slaker Control Panel 2.1.2 M E A S U R E M E N T •
AND CONVEYING SYSTEM
Two feeder hoppers each with high level and low switch work with the diverter valve, rotary valve, and bin actuator to automatically maintain a constant supply of material in the hoppers to the volumetric feeders. The feeder hopper also has an air-operated vibrator controlled by a solenoid valve. The vibrator is automatically switched ON-Off depending on the operation of the feeder
Section 4.1 – Slaked Lime
6 PAGE 6
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
Each volumetric feeder is driven by a dc variable speed drive. The local PLC controls the dc drive to adjust the volume of the material discharge to the downstream screw conveyor. The dc drive has a H-O-A switch to select the mode of operation. A speed feed back is connected to the local PLC. In hand mode, the speed is adjusted at the local panel. In auto mode, the speed is controlled by the local PLC based on the setpoint and the start-stop sequence of operation. The speed of the feeder drive is displayed on the local control panel. The PLC/HMI shall log and display on screen the status and alarm via Ethernet.
2.2 L I M E S L A K E R S • • • • There are 2 No. Lime Slakers which are operated in rotation (SKR-504/505). The Slakers contain paddles which rotate and mix the lime and water to form slaked lime which is then pumped forward to the Lime Slurry Tank (TK-512). The slaking system also consists of a grit removal system which uses an auger driven by the grit removal motor to remove solids from the system. The rated capacity of the Lime Slaker is 450kg/hr. The lime slaker system also contains a slaker exhaust fan, slaking water control valve, cut-off spray solenoids, dust arrestor solenoids and grit spray solenoids. The slaker exhaust fan runs at all times. 2.2.1 S L A K E R GRI T SEPARATIO N SYSTEM CONTRO LS
AND
• Two screw conveyors deliver the measured quantity of lime to the two slakers.
Each screw conveyor has a H-O-A switch to select the mode of operation. In auto mode, the screw conveyor is start-stop by the local PLC. Motor run status and overload alarm are monitored by the local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet. signal to a motorized valve. The quantity depends on the start-stop sequence as well as the consistency of the slurry. Consistency of the slurry is measured by the load current of the slaker’s main drive. Low water pressure is also monitored by the local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet. control cabinet. The motor has a H-O-A switch to select the mode of operation. In auto mode, the motor is start-stop by the local PLC. The motor load current is measured by a watt transducer and is fed to the local PLC. The local PLC adjust the amount of water added to maintain consistency by monitoring the main drive motor load current. Motor run status and overload alarm are monitored by the local PLC. Motor stalling is also monitored by the 7 PAGE 7
• Water addition is controlled by the local PLC automatically by an analog
• The slaker main drive motor is controlled by a magnetic starter in the local
Section 4.1 – Slaked Lime
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet.
• The grit separator further dilutes the lime slurry and sort out the heavy
oversized particles. Motor run status and overload alarm are monitored by the local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet. run status and overload alarm are monitored by the local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet.
• Each slaker has an exhaust fan to remove the dust and excess moisture. Motor
3. O PER ATING P ROCEDUR ES
3.1 F I L L I N G
THE LI ME SILO OF
3.1.1 O R D E R I N G D E L I V E R I E S
LIME
• When the quantity of lime in Silo reaches 45 tonnes additional lime should be ordered. When the level indicator in the Silo indicates that the level of lime has reached between 4.3m and 5m in depth (depends on build density of the lime) a delivery of lime should be ordered. For lime with a bulk density of 1,000 kg/m 3 the re-order height is 5m, for lime with a bulk density of 1,400kg/m 3 the re-order height is 4.3m. The SCADA System should be programmed to deliver an order message when the level in the silo reaches this pre-set level. • The level of lime in the silo is measured using a continuous level sensor/transmitter (LIT-500) and a high level probe switch. The PLC/HMI logs and displays on the screen the continuous level and the silo high level, low level and high-high level alarms. 3.1.2 M A N U A L O P E R A T I O N LIME SILO
OF
1. Position the bulk truck in the correct position to minimize bends in the connecting flexible hoses. 2. Connect the hose from the silo to the truck discharge outlet. Ensure that the silo fill panel power switch is in the ON position. 3. 4. Place the silo vent filter switch in the ON position. Commence unloading of bulk truck.
5. When the truck is empty or if the high level alarm is triggered, shut down the blower truck immediately.
Section 4.1 – Slaked Lime
8 PAGE 8
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
6.
Disconnect hose from silo fill line and reposition dust cap. Solenoids will continue to cycle for an
7. Turn off silo dust filter. additional 10 minutes.
3.2 L I M E
FEEDER
HO PPE R REFI LL SEQUENCE
3.2.1 A U T O M A T I C L I M E H O P P E R R E F I L L Actions Required 1. 2. Step 1: Ensure the Power Switch on the Control Panel in the Lime Slaking Building is set to On. Step 2: On the Control Panel in the Lime Slaking Building switch both Lime Feeders to Automatic. Once the Lime Feeders have been set to Automatic they will be controlled by the PLC and will run automatically. Step 2 : Switch the Diverter Valve to Automatic. Step 3: Set the Rotary Valve to Automatic and ensure it is also switched to the ‘Forward’ setting. Step 4: Ensure the Bin Activator is Set to Automatic. The system will be set on the PLC to either activate Lime Slaker 1 or 2 first. This can be changed by the Operator periodically to ensure equal wear on both lines. If Lime Slaker 1 receives a Feed Rate signal from the level probes in the Slaked Lime Holding Tank it will automatically start Lime Feeder 1 and Screw Conveyor 1.
3. 4. 5. 6.
Description of Automatic Cycle • The forward feed of lime to the Volumetric Feeder Hoppers is controlled by the Rotary Feed Valve at the base of the Lime Silo. Each of the Feeder Hoppers is equipped with a high level and low level switch to control the refill process. All feed equipment upstream reacts to these signals to deliver lime to the feeder hoppers. Lime is transferred from the silo to volumetric feeder (FE-502/503) hoppers prior to delivery to the slakers to ensure accurate feeding of product into the slakers. Each of the feeder hoppers is equipped with a high and low level switch to control the refill process. All feed equipment upstream reacts to these signals to deliver lime to the feeder hoppers. Upon detection of a low level in a feeder hopper, the PLC will check to see if the feed train in question has been enabled on the Human Machine Interface (HMI). If that train has been enabled, the PLC will initiate a refill 9 PAGE 9
•
•
Section 4.1 – Slaked Lime
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
cycle for that hopper. The PLC will first check and switch the diverter valve position as necessary to direct product to the hopper needing product. If the other feeder hopper is currently being filled however, the PLC will wait for the completion of that refill cycle prior to starting the cycle for the second hopper. • Once the diverter valve has been moved to select the appropriate train the rotary valve (RV-501) will start to meter product from the lime silo. The bin activator is interlocked with the running of the rotary valve to promote flow of lime out of the silo. While the rotary valve is running, the aeration pads solenoid valve will operate on a timed cycle to inject pulses of air into the lime to fluidize the product and promote flow. The timer setpoints for the aeration cycle are adjustable on the lime system HMI. The default time settings are 2 seconds ON and 30 seconds OFF. When the high level in the feeder hopper has been reached, the rotary valve, bin activator and aeration pads will shut down.
•
3.2.2 M A N U A L L I M E H O P P E R R E F I L L Actions Required 1. 2. 3. 4. 5. 6. 7. Step 1: Switch on the Control Power on the Control Panel in the Lime Slaking Building. Step 2: Check the level of Lime in each of the Hoppers. If a Hopper requires more lime then it can be manually refilled as follows. Step 3: Switch the Diverter Valve to either Lime Feeder Hopper 1 or 2 as required. Step 4: Switch the Bin Activator to the Hand setting. Step 5. Switch the Rotary Valve to the Hand setting and ensure it is set to the Forward Position. Step 6: When the Lime Feed Hopper is full switch the Rotary Valve to Off. Switch the Bin Activator to Off.
3.3 L I M E S L A K E R S T A R T S E Q U E N C E 3.3.1 A U T O M A T I C L I M E S L A K E R S T A R T S E Q U E N C E
Section 4.1 – Slaked Lime
10 P A G E 10
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
Actions Required 1. Set Both Lime Slakers to Automatic. 2. The HDS Plant PLC will send a start/stop signal to the lime slaking equipment whenever lime slurry is needed in the lime slurry tank. The start/stop signal will be derived from a continuous level transmitter in the lime slurry tank. 3. The start signal will activate either Lime Slaker 1 or 2 as set on the system by the Operator. Which of Lime the Slakers is activated is set in the system and can be changed by the Operator periodically to ensure equal wear on both lines. 4. The PLC will also activate the Volumetric Feeder and Screw Conveyors in the lime delivery system. 5. If lime slurry is needed in the Lime Slurry Tank while one of the Lime Slakers is in operation, the PLC will activate and alarm. At this point Operator intervention will be required to start the second lime slaker. The Forward Feed Set Points will need to be adjusted by the operator at this stage to balance the rate of lime slurry production between the slakers. The Lime Slakers have a turndown ratio of 1:5 and so can be cut back to a forward feed rate of 90kg/hour if required. If the rate of lime slurry throughput exceeds 450kg/hour and is say, 550 kg/hour, then the Forward Feed Rate for each slaker should be set to 225kg/hour to ensure both produce an equal quantity of slurry. The components operate in sequence as follows: • • • Open slaking water control valve to 90%. Start slaker mixing motor (SKR-506/507). The slaker will continue running for 2 minutes to finish filling the slaking chamber with water. NB: Prior to starting the system, it must be ensured that the slaking chamber is full of water up to the level of the mixing shafts. Open the cut-off spray solenoid, dust & vapour arrestor solenoid and grit spray solenoid. Start grit remover motor. At this point the slaking water control valve will be placed into the control of the Programmable Logic Controller (PLC) to achieve the desired consistency of lime paste in the Lime Slaker. Start screw conveyor (SC-504/505). After 30 seconds, start volumetric feeder (FE-502/503).
• • •
• •
Section 4.1 – Slaked Lime
11 P A G E 11
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
• The volumetric feeder (FE-502/503) will operate initially at 60% speed for 10 minutes regardless of the Slaking Rate Setpoint to get the slaking reaction started quickly. • The Volumetric Feeder will have been calibrated during start-up and commissioning so that when the operator inputs a desired feed rate in kg/hour, the controller will convert this to the corresponding motor speed automatically. The forward feed rate of lime or the Slaking Rate Setpoint from the Volumetric Feeder to the Lime Slaker can be set separately for each Lime Slaker. This will not need to be input when the plant is operating on the Automatic Mode. • During the initial feeding phase, the slaking water control valve will be open 10% to ensure minimum water flow requirements to the slaker shaft seals. As the mixture in the slaking chamber begins to thicken, the valve will open more to control the paste thickness at the setpoint. • After the 10 minute start phase, the feeder feedrate will change to the setpoint as entered by the operator, or dictated by the plant SCADA. The slaker will continue to operate in this mode until high level is reached in the lime slurry tank (TK-512) or if instructed to stop by the operator.
3.3.2 M A N U A L L I M E S L A K E R S T A R T S E Q U E N C E Actions Required 1. Ensure that the Lime Feeder Hopper for the Lime Slaker you intend to use is full of lime. If the Lime Feeder Hopper requires lime, follow the procedure set out in Section 3.2.2. 2. Switch the Lime Slaker you wish to use (1 / 2) to Hand. 3. Open the Slaking Water Control Valve to 90% open. 4. The mixing chamber MUST be full of water before starting the Mixing Motor. 5. Start the Slaker Mixing Motor. 6. Allow the Slaking Chamber to fill with water. 7. Open the cut-off spray solenoid, dust and vapor arrestor solenoid and grit spray solenoid. 8. Set the Grit Remover Motor to Hand. 9. Set the corresponding Screw Conveyor (1 / 2) to Hand.
Section 4.1 – Slaked Lime
12 P A G E 12
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
10. Wait until the Screw Conveyor has been operational for 30 seconds and then switch the Volumetric Feeder to Hand. In the Hand Mode the rate of forward feed of the Volumetric Feeder can be adjusted by a local panel. The forward feed rate should be adjusted to 60% of the maximum for the 10 minutes to get the slaking reaction started quickly. 11. During the initial feeding phase the slaking water control valve should be open to 10% to ensure minimum water flow requirements to the slaker shaft seals. As the mixture in the slaking chamber begins to thicken, the water control valve should be opened to control the paste thickness. The desired thickness should be determined by a visual inspection of the consistency of the material in the lime slaker. The slaked lime should have a consistency of between and 15 and 20% solids.
3.4 L I M E S L A K E R S T A N D B Y S H U T D O W N S E Q U E N C E 3.4.1 A U T O M A T I C L I M E S L A K E R S T A N D B Y S H U T D O W N S E Q U E N C E The system occurs: • • • goes into standby shutdown sequence when any or the following high level in the lime slurry tank, low water pressure alarm, by operator instruction (STOP key is pressed).
The sequence has the following steps: • • The lime volumetric feeder (FE-502/503) is stopped. After a 2 minute delay, the screw conveyor (SC-504/505) is stopped.
• The slaking water control valve PID control will continue operating to maintain the paste at the thickness setpoint. • After a preset time (Default = 150 seconds), the cut-off spray, dust and vapour arrestor, and grit spray solenoids will close and the grit remover motor will stop. • The slaker will continue to operate in this manner for a preset time (Default = 30 minutes) with the slaker water control valve continuing to control the paste thickness and the slaker mixer motor running. • If the slaker is instructed to start, or if the slurry tank high level alarm or low water pressure alarm clears during this time, the feed system will start immediately at the setpoint, bypassing the normal startup procedure of the slaker.
Section 4.1 – Slaked Lime
13 P A G E 13
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
3.4.2 M A N U A L L I M E S L A K E R S H U T D O W N S E Q U E N C E Actions Required 1. 2. Switch the Lime Volumetric Feeder (FE-502/503) to Off. Wait 2 minutes and Switch the Screw Conveyor to Off.
3. Monitor and adjust the water control valve to ensure the desired consistency of paste is achieved. 4. After 3 minutes, shut off the cut-off spray, dust and vapor arrestor and grit spray solenoids and the grit removal motor. 5. The Slaker should then be allowed to operate with the slaker water valve open until the desired consistency of lime paste is achieved. If more lime slurry is required at this stage, the feed system can be started up at the Feed Rate Set Point without the need to go through the Manual Lime Slaker Start-up sequence.
3.5 L I M E S L A K E R E X T E N D E D S H U T D O W N S E Q U E N C E 3.5.1 A U T O M A T I C E X T E N D E D S H U T D O W N S E Q U E N C E When the time set on the standby shutdown timer described above has been exceeded, the slaker will go into the extended shutdown sequence as follows: • Open cut-off spray, dust & vapour arrestor and grit spray solenoid valves. • • Start grit remover motor. Open slaking water control valve to 90% open.
• The slaking chamber will now be flushed with water for 10 minutes to clean the chamber of lime paste. After this time, all motors are stopped and all valves are closed. The slaker is now shut down. 3.5.2 M A N U A L : F L U S H S E Q U E N C E • Whether the FLUSH key is pressed during the Start sequence or Standby Shutdown sequence, the controller will immediately enable the Extended Shutdown sequence. 3.6 R E C O R D K E E P I N G Records of all deliveries of lime to site will be maintained. The quantity of lime used will be recorded based on the level used from the silo. A weekly
Section 4.1 – Slaked Lime
14 P A G E 14
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
visual inspection of the level in the lime silo will also be carried out and recorded.
4. P ROCEDUR E F OR P ER FOR MING M AI NTENANC E
4.1 S A F E T Y
ON TH E
L I M E S LAKI NG S YS TEM
Observe the following safety precautions before carrying out maintenance on the Lime Slaking System. PPE when changing the bin filters should include: • Coveralls • Gloves • Dust Mask • Eye Protection In the event of contact with skin or eyes wash off immediately. Good housekeeping is an important part of maintaining a safe and trouble free environment for the bulk chemical system. After servicing equipment, clean spilled chemical off the operating floor and equipment surface. In general, dry chemical is better to be vacuumed rather than washed down.
4.2 M A I N T E N A N C E Maintenance procedures will be reviewed with equipment manufacturer's representatives during commissioning, to finalise preventative main procedures and predictive parameters. Following commissioning in September 2005, the complete maintenance requirements and procedures will be fully documented and the Operations and Maintenance Manual updated accordingly. The following are some key maintenance items associated with the system: 4.2.1 B I N F I L T E R S Regular inspections of the bin filters should be carried out once every 2 months. The bin filters are automatically cleaned by air bursts back through the cartridge. Refer to Section 9.1 or the Stanco Operation and Maintenance Manual for complete details.
Section 4.1 – Slaked Lime
15 P A G E 15
EPCOR Water Services August 2005
TABLE OF CONTENTS
1. I N T R O D U C T I O N .............................................................................................................................2 1.1 O V E R V I E W ......................................................................................................................2 1.2 S A F E T Y H A Z A R D S A N D P R O C E D U R E S ............................................................................3 2. S Y S T E M D E S C R I P T I O N ................................................................................................................4 2.1 L I M E S I L O .....................................................................................................................4 2.1.1 Lime Silo Controls...........................................................................................5 2.1.2 Measurement and conveying system...........................................................6 2.2 L I M E S L A K E R S ...............................................................................................................7 2.2.1 Slaker and Grit Separation System Controls..........................................7 3. O P E R A T I N G P R O C E D U R E S ..........................................................................................................8 3.1 F I L L I N G T H E L I M E S I L O .................................................................................................8 3.1.1 Ordering Deliveries of Lime.........................................................................8 3.1.2 Manual Operation of Lime Silo...................................................................8 3.2 L I M E F E E D E R H O P P E R R E F I L L S E Q U E N C E ...................................................................9 3.2.1 Automatic Lime Hopper Refill.....................................................................9 3.2.2 Manual Lime Hopper Refill........................................................................10 3.3 L I M E S L A K E R S T A R T S E Q U E N C E ................................................................................10 3.3.1 Automatic Lime Slaker Start Sequence...................................................10 3.3.2 Manual Lime Slaker Start Sequence........................................................12 3.4 L I M E S L A K E R S T A N D B Y S H U T D O W N S E Q U E N C E .......................................................13 3.4.1 Automatic Lime Slaker Standby Shutdown Sequence........................13 3.4.2 Manual Lime Slaker Shutdown Sequence...............................................14 3.5 L I M E S L A K E R E X T E N D E D S H U T D O W N S E Q U E N C E ...................................................14 3.5.1 Automatic Extended Shutdown Sequence..............................................14 3.5.2 Manual : Flush Sequence............................................................................14 3.6 R E C O R D K E E P I N G ........................................................................................................14 4. P R O C E D U R E F O R P E R F O R M I N G M A I N T E N A N C E O N T H E L I M E S L A K I N G S Y S T E M ...........15 4.1 S A F E T Y .........................................................................................................................15 4.2 M A I N T E N A N C E .............................................................................................................15 4.2.1 Bin Filters.........................................................................................................15
Section 4.1 – Slaked Lime
1 PAGE 1
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
1. I NTR ODUC TION
1.1 O V E R V I E W The Lime Slaking Package for the Britannia Mine AMD Water Treatment Plant is designed to provide bulk storage of quicklime (CaO) and the equipment necessary for slaking the lime to produce lime slurry. Quicklime is supplied to site in selfunloading bulk trucks which is then pneumatically conveyed into the silo with the blower mounted on the bulk truck. A silo vent filter is supplied to prevent lime dust from escaping into the atmosphere. From the silo, a rotary valve feeds quicklime into one of two volumetric feeder hoppers by way of a diverter valve. A bin activator and aeration pads in the silo operate while the silo is discharging to promote the flow of the lime from the silo. Quicklime is metered from the volumetric feeder into screw conveyors which transport the quicklime into the lime slakers. In the lime slakers, quicklime is mixed with water in order to slake the quicklime to produce hydrated lime (CaOH2). The water to lime ratio is controlled based on the thickness or consistency of the lime paste as determined by the power draw on the mixing motor. Reacted lime paste overflows the mixing chamber with the aid of spray jets into the grit separator. The slurry is further diluted at the grit separator. Heavy, oversized particles fall to the bottom of the separator and are removed with an inclined auger for disposal. Light particles overflow from the separator and flow into the lime storage tank. A venturi-type dust & vapour arrestor is located in the slaking chamber to remove dust and vapour from the vented air stream. An exhaust fan runs at all times to assist with venting of the slaker and to maintain a slight negative pressure in the slaker.
Section 4.1 – Slaked Lime
2 PAGE 2
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
1.2 S A F E T Y
HAZARDS AND
PRO CEDURES
Quick Lime Oxide) CaO:
(Calcium Solid White or grey lumps or powder, odorless. Odorless 2,850 Celcius 2,570 Deg. Celsius N/A 1.6 – 2.8 gr/cc (water = 1.00) N/A (Air=1.0) Reactive with water to produce Ca(OH) 2 with large amounts of heat. by 0% 12.4 at 25 o C.
Physical State: Appearance and Odor: Odor Threshold: Boiling Point: Melting/Freezing Point: Vapor Pressure: Specific Gravity: Vapor Density: Solubility: Percent Volume pH: Volatile
Calcium oxide is corrosive and reacts with water to produce heat and is highly alkaline in solution. . Warning: Calcium Oxide is an extremely dangerous chemical. Refer to the MSDS binder for the Material Safety Data Sheet. Extreme care should be taken when dealing with Quicklime. This substance is harmful if inhaled or if it comes in contact with skin. It is classified as mild to moderately corrosive. Skin and eye contact should be avoided as irritation will occur. Contact lenses should not be worn when working with lime products Inhalation can cause coughing sneezing or breathing problems. Material in contact with wet skin could cause sever irritation and/or burning. When working with lime precautions should be taken to protect skin and eyes from dust and to avoid inhalation. When working in the Lime Silo Building or the Lime Slaking Building, gloves, overalls, safety goggles and dust masks should be worn at all times. In the event that the material comes into contact with skin or eyes it should be washed off immediately.
Section 4.1 – Slaked Lime
3 PAGE 3
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
2. S YS TEM D ESC RIPTION
The Lime Slaking System is manufactured by Stanco Projects Ltd. The Lime Slaking System consists of the following pieces of equipment • Lime Storage Silo • Silo • Rotary Feed Valve • Feeder Hoppers • Screw Conveyors • Lime Slakers • Mixers driven by Slaker Motor • Grit removal auger
2.1 L I M E S I L O • The Silo is contained within a sealed building and is fitted with a vent filter to prevent lime dust from escaping to atmosphere. (Capacity: 53.6m 3 . 75,000kg. H: 12.2m, D: 4.7m). Full details are shown on P& ID Drawing P-006. • A Rotary Valve (RV-501) at the base of the lime silo controls the forward feed of lime into one of two volumetric Feed Hoppers (Rated capacity: 5.8m 3 /hour). The Feed Hoppers (FE-502/503) are operated in rotation and deliver the lime to the Screw Conveyors (SC-504/505) which then convey the lime to the Lime Slakers. The rated capacity of the Feed Hoppers is 450kg/hour, while the rated capacity of the Screw conveyors is >450kg/hour. The screw conveyors operate at a fixed rate.
Section 4.1 – Slaked Lime
4 PAGE 4
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
Figure 4.1.1-Lime Silo
2.1.1 L I M E S I L O C O N T R O L S • The lime storage silo has a lime fill control panel, which monitors the level of the lime inside the silo. The measurement comprises of a continuous level sensor/transmitter (LIT-500) and a high level probe switch. The PLC/HMI shall log and display on screen the continuous level and silo high level, low level, and high-high alarms. The silo has a ventilation filter, which filters the exhaust air. Plant instrument air is used to purge the air filter periodically for automatic cleaning of the filter.
•
Section 4.1 – Slaked Lime
5 PAGE 5
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
•
The lime discharge is facilitated by a bin activator. The bin activator may be operated in hand or auto control. In auto mode, the bin activator is energized whenever material is required, and is controlled by the local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet. The lime discharges through a rotary valve. The rotary valve may be operated in hand or auto controlled. In auto mode, the rotary valve is energized whenever material is required, and is controlled by the local PLC. Motor run status and overload alarm are monitored by the local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet. From the rotary valve, lime is directed to one of the two hoppers by a diverter valve. The diverter valve is pneumatically actuated by a solenoid. The solenoid has a three position switch, namely, position 1, position 2, and automatic. In auto mode, the valve is open to the position where the material is required, signaled by a low level switch in each hopper. The PLC/HMI shall log and display on screen the status and alarm via Ethernet.
•
•
Figure 4.1.2 - Lime Slaker Control Panel 2.1.2 M E A S U R E M E N T •
AND CONVEYING SYSTEM
Two feeder hoppers each with high level and low switch work with the diverter valve, rotary valve, and bin actuator to automatically maintain a constant supply of material in the hoppers to the volumetric feeders. The feeder hopper also has an air-operated vibrator controlled by a solenoid valve. The vibrator is automatically switched ON-Off depending on the operation of the feeder
Section 4.1 – Slaked Lime
6 PAGE 6
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
Each volumetric feeder is driven by a dc variable speed drive. The local PLC controls the dc drive to adjust the volume of the material discharge to the downstream screw conveyor. The dc drive has a H-O-A switch to select the mode of operation. A speed feed back is connected to the local PLC. In hand mode, the speed is adjusted at the local panel. In auto mode, the speed is controlled by the local PLC based on the setpoint and the start-stop sequence of operation. The speed of the feeder drive is displayed on the local control panel. The PLC/HMI shall log and display on screen the status and alarm via Ethernet.
2.2 L I M E S L A K E R S • • • • There are 2 No. Lime Slakers which are operated in rotation (SKR-504/505). The Slakers contain paddles which rotate and mix the lime and water to form slaked lime which is then pumped forward to the Lime Slurry Tank (TK-512). The slaking system also consists of a grit removal system which uses an auger driven by the grit removal motor to remove solids from the system. The rated capacity of the Lime Slaker is 450kg/hr. The lime slaker system also contains a slaker exhaust fan, slaking water control valve, cut-off spray solenoids, dust arrestor solenoids and grit spray solenoids. The slaker exhaust fan runs at all times. 2.2.1 S L A K E R GRI T SEPARATIO N SYSTEM CONTRO LS
AND
• Two screw conveyors deliver the measured quantity of lime to the two slakers.
Each screw conveyor has a H-O-A switch to select the mode of operation. In auto mode, the screw conveyor is start-stop by the local PLC. Motor run status and overload alarm are monitored by the local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet. signal to a motorized valve. The quantity depends on the start-stop sequence as well as the consistency of the slurry. Consistency of the slurry is measured by the load current of the slaker’s main drive. Low water pressure is also monitored by the local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet. control cabinet. The motor has a H-O-A switch to select the mode of operation. In auto mode, the motor is start-stop by the local PLC. The motor load current is measured by a watt transducer and is fed to the local PLC. The local PLC adjust the amount of water added to maintain consistency by monitoring the main drive motor load current. Motor run status and overload alarm are monitored by the local PLC. Motor stalling is also monitored by the 7 PAGE 7
• Water addition is controlled by the local PLC automatically by an analog
• The slaker main drive motor is controlled by a magnetic starter in the local
Section 4.1 – Slaked Lime
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet.
• The grit separator further dilutes the lime slurry and sort out the heavy
oversized particles. Motor run status and overload alarm are monitored by the local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet. run status and overload alarm are monitored by the local PLC. The PLC/HMI shall log and display on screen the status and alarm via Ethernet.
• Each slaker has an exhaust fan to remove the dust and excess moisture. Motor
3. O PER ATING P ROCEDUR ES
3.1 F I L L I N G
THE LI ME SILO OF
3.1.1 O R D E R I N G D E L I V E R I E S
LIME
• When the quantity of lime in Silo reaches 45 tonnes additional lime should be ordered. When the level indicator in the Silo indicates that the level of lime has reached between 4.3m and 5m in depth (depends on build density of the lime) a delivery of lime should be ordered. For lime with a bulk density of 1,000 kg/m 3 the re-order height is 5m, for lime with a bulk density of 1,400kg/m 3 the re-order height is 4.3m. The SCADA System should be programmed to deliver an order message when the level in the silo reaches this pre-set level. • The level of lime in the silo is measured using a continuous level sensor/transmitter (LIT-500) and a high level probe switch. The PLC/HMI logs and displays on the screen the continuous level and the silo high level, low level and high-high level alarms. 3.1.2 M A N U A L O P E R A T I O N LIME SILO
OF
1. Position the bulk truck in the correct position to minimize bends in the connecting flexible hoses. 2. Connect the hose from the silo to the truck discharge outlet. Ensure that the silo fill panel power switch is in the ON position. 3. 4. Place the silo vent filter switch in the ON position. Commence unloading of bulk truck.
5. When the truck is empty or if the high level alarm is triggered, shut down the blower truck immediately.
Section 4.1 – Slaked Lime
8 PAGE 8
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
6.
Disconnect hose from silo fill line and reposition dust cap. Solenoids will continue to cycle for an
7. Turn off silo dust filter. additional 10 minutes.
3.2 L I M E
FEEDER
HO PPE R REFI LL SEQUENCE
3.2.1 A U T O M A T I C L I M E H O P P E R R E F I L L Actions Required 1. 2. Step 1: Ensure the Power Switch on the Control Panel in the Lime Slaking Building is set to On. Step 2: On the Control Panel in the Lime Slaking Building switch both Lime Feeders to Automatic. Once the Lime Feeders have been set to Automatic they will be controlled by the PLC and will run automatically. Step 2 : Switch the Diverter Valve to Automatic. Step 3: Set the Rotary Valve to Automatic and ensure it is also switched to the ‘Forward’ setting. Step 4: Ensure the Bin Activator is Set to Automatic. The system will be set on the PLC to either activate Lime Slaker 1 or 2 first. This can be changed by the Operator periodically to ensure equal wear on both lines. If Lime Slaker 1 receives a Feed Rate signal from the level probes in the Slaked Lime Holding Tank it will automatically start Lime Feeder 1 and Screw Conveyor 1.
3. 4. 5. 6.
Description of Automatic Cycle • The forward feed of lime to the Volumetric Feeder Hoppers is controlled by the Rotary Feed Valve at the base of the Lime Silo. Each of the Feeder Hoppers is equipped with a high level and low level switch to control the refill process. All feed equipment upstream reacts to these signals to deliver lime to the feeder hoppers. Lime is transferred from the silo to volumetric feeder (FE-502/503) hoppers prior to delivery to the slakers to ensure accurate feeding of product into the slakers. Each of the feeder hoppers is equipped with a high and low level switch to control the refill process. All feed equipment upstream reacts to these signals to deliver lime to the feeder hoppers. Upon detection of a low level in a feeder hopper, the PLC will check to see if the feed train in question has been enabled on the Human Machine Interface (HMI). If that train has been enabled, the PLC will initiate a refill 9 PAGE 9
•
•
Section 4.1 – Slaked Lime
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
cycle for that hopper. The PLC will first check and switch the diverter valve position as necessary to direct product to the hopper needing product. If the other feeder hopper is currently being filled however, the PLC will wait for the completion of that refill cycle prior to starting the cycle for the second hopper. • Once the diverter valve has been moved to select the appropriate train the rotary valve (RV-501) will start to meter product from the lime silo. The bin activator is interlocked with the running of the rotary valve to promote flow of lime out of the silo. While the rotary valve is running, the aeration pads solenoid valve will operate on a timed cycle to inject pulses of air into the lime to fluidize the product and promote flow. The timer setpoints for the aeration cycle are adjustable on the lime system HMI. The default time settings are 2 seconds ON and 30 seconds OFF. When the high level in the feeder hopper has been reached, the rotary valve, bin activator and aeration pads will shut down.
•
3.2.2 M A N U A L L I M E H O P P E R R E F I L L Actions Required 1. 2. 3. 4. 5. 6. 7. Step 1: Switch on the Control Power on the Control Panel in the Lime Slaking Building. Step 2: Check the level of Lime in each of the Hoppers. If a Hopper requires more lime then it can be manually refilled as follows. Step 3: Switch the Diverter Valve to either Lime Feeder Hopper 1 or 2 as required. Step 4: Switch the Bin Activator to the Hand setting. Step 5. Switch the Rotary Valve to the Hand setting and ensure it is set to the Forward Position. Step 6: When the Lime Feed Hopper is full switch the Rotary Valve to Off. Switch the Bin Activator to Off.
3.3 L I M E S L A K E R S T A R T S E Q U E N C E 3.3.1 A U T O M A T I C L I M E S L A K E R S T A R T S E Q U E N C E
Section 4.1 – Slaked Lime
10 P A G E 10
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
Actions Required 1. Set Both Lime Slakers to Automatic. 2. The HDS Plant PLC will send a start/stop signal to the lime slaking equipment whenever lime slurry is needed in the lime slurry tank. The start/stop signal will be derived from a continuous level transmitter in the lime slurry tank. 3. The start signal will activate either Lime Slaker 1 or 2 as set on the system by the Operator. Which of Lime the Slakers is activated is set in the system and can be changed by the Operator periodically to ensure equal wear on both lines. 4. The PLC will also activate the Volumetric Feeder and Screw Conveyors in the lime delivery system. 5. If lime slurry is needed in the Lime Slurry Tank while one of the Lime Slakers is in operation, the PLC will activate and alarm. At this point Operator intervention will be required to start the second lime slaker. The Forward Feed Set Points will need to be adjusted by the operator at this stage to balance the rate of lime slurry production between the slakers. The Lime Slakers have a turndown ratio of 1:5 and so can be cut back to a forward feed rate of 90kg/hour if required. If the rate of lime slurry throughput exceeds 450kg/hour and is say, 550 kg/hour, then the Forward Feed Rate for each slaker should be set to 225kg/hour to ensure both produce an equal quantity of slurry. The components operate in sequence as follows: • • • Open slaking water control valve to 90%. Start slaker mixing motor (SKR-506/507). The slaker will continue running for 2 minutes to finish filling the slaking chamber with water. NB: Prior to starting the system, it must be ensured that the slaking chamber is full of water up to the level of the mixing shafts. Open the cut-off spray solenoid, dust & vapour arrestor solenoid and grit spray solenoid. Start grit remover motor. At this point the slaking water control valve will be placed into the control of the Programmable Logic Controller (PLC) to achieve the desired consistency of lime paste in the Lime Slaker. Start screw conveyor (SC-504/505). After 30 seconds, start volumetric feeder (FE-502/503).
• • •
• •
Section 4.1 – Slaked Lime
11 P A G E 11
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
• The volumetric feeder (FE-502/503) will operate initially at 60% speed for 10 minutes regardless of the Slaking Rate Setpoint to get the slaking reaction started quickly. • The Volumetric Feeder will have been calibrated during start-up and commissioning so that when the operator inputs a desired feed rate in kg/hour, the controller will convert this to the corresponding motor speed automatically. The forward feed rate of lime or the Slaking Rate Setpoint from the Volumetric Feeder to the Lime Slaker can be set separately for each Lime Slaker. This will not need to be input when the plant is operating on the Automatic Mode. • During the initial feeding phase, the slaking water control valve will be open 10% to ensure minimum water flow requirements to the slaker shaft seals. As the mixture in the slaking chamber begins to thicken, the valve will open more to control the paste thickness at the setpoint. • After the 10 minute start phase, the feeder feedrate will change to the setpoint as entered by the operator, or dictated by the plant SCADA. The slaker will continue to operate in this mode until high level is reached in the lime slurry tank (TK-512) or if instructed to stop by the operator.
3.3.2 M A N U A L L I M E S L A K E R S T A R T S E Q U E N C E Actions Required 1. Ensure that the Lime Feeder Hopper for the Lime Slaker you intend to use is full of lime. If the Lime Feeder Hopper requires lime, follow the procedure set out in Section 3.2.2. 2. Switch the Lime Slaker you wish to use (1 / 2) to Hand. 3. Open the Slaking Water Control Valve to 90% open. 4. The mixing chamber MUST be full of water before starting the Mixing Motor. 5. Start the Slaker Mixing Motor. 6. Allow the Slaking Chamber to fill with water. 7. Open the cut-off spray solenoid, dust and vapor arrestor solenoid and grit spray solenoid. 8. Set the Grit Remover Motor to Hand. 9. Set the corresponding Screw Conveyor (1 / 2) to Hand.
Section 4.1 – Slaked Lime
12 P A G E 12
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
10. Wait until the Screw Conveyor has been operational for 30 seconds and then switch the Volumetric Feeder to Hand. In the Hand Mode the rate of forward feed of the Volumetric Feeder can be adjusted by a local panel. The forward feed rate should be adjusted to 60% of the maximum for the 10 minutes to get the slaking reaction started quickly. 11. During the initial feeding phase the slaking water control valve should be open to 10% to ensure minimum water flow requirements to the slaker shaft seals. As the mixture in the slaking chamber begins to thicken, the water control valve should be opened to control the paste thickness. The desired thickness should be determined by a visual inspection of the consistency of the material in the lime slaker. The slaked lime should have a consistency of between and 15 and 20% solids.
3.4 L I M E S L A K E R S T A N D B Y S H U T D O W N S E Q U E N C E 3.4.1 A U T O M A T I C L I M E S L A K E R S T A N D B Y S H U T D O W N S E Q U E N C E The system occurs: • • • goes into standby shutdown sequence when any or the following high level in the lime slurry tank, low water pressure alarm, by operator instruction (STOP key is pressed).
The sequence has the following steps: • • The lime volumetric feeder (FE-502/503) is stopped. After a 2 minute delay, the screw conveyor (SC-504/505) is stopped.
• The slaking water control valve PID control will continue operating to maintain the paste at the thickness setpoint. • After a preset time (Default = 150 seconds), the cut-off spray, dust and vapour arrestor, and grit spray solenoids will close and the grit remover motor will stop. • The slaker will continue to operate in this manner for a preset time (Default = 30 minutes) with the slaker water control valve continuing to control the paste thickness and the slaker mixer motor running. • If the slaker is instructed to start, or if the slurry tank high level alarm or low water pressure alarm clears during this time, the feed system will start immediately at the setpoint, bypassing the normal startup procedure of the slaker.
Section 4.1 – Slaked Lime
13 P A G E 13
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
3.4.2 M A N U A L L I M E S L A K E R S H U T D O W N S E Q U E N C E Actions Required 1. 2. Switch the Lime Volumetric Feeder (FE-502/503) to Off. Wait 2 minutes and Switch the Screw Conveyor to Off.
3. Monitor and adjust the water control valve to ensure the desired consistency of paste is achieved. 4. After 3 minutes, shut off the cut-off spray, dust and vapor arrestor and grit spray solenoids and the grit removal motor. 5. The Slaker should then be allowed to operate with the slaker water valve open until the desired consistency of lime paste is achieved. If more lime slurry is required at this stage, the feed system can be started up at the Feed Rate Set Point without the need to go through the Manual Lime Slaker Start-up sequence.
3.5 L I M E S L A K E R E X T E N D E D S H U T D O W N S E Q U E N C E 3.5.1 A U T O M A T I C E X T E N D E D S H U T D O W N S E Q U E N C E When the time set on the standby shutdown timer described above has been exceeded, the slaker will go into the extended shutdown sequence as follows: • Open cut-off spray, dust & vapour arrestor and grit spray solenoid valves. • • Start grit remover motor. Open slaking water control valve to 90% open.
• The slaking chamber will now be flushed with water for 10 minutes to clean the chamber of lime paste. After this time, all motors are stopped and all valves are closed. The slaker is now shut down. 3.5.2 M A N U A L : F L U S H S E Q U E N C E • Whether the FLUSH key is pressed during the Start sequence or Standby Shutdown sequence, the controller will immediately enable the Extended Shutdown sequence. 3.6 R E C O R D K E E P I N G Records of all deliveries of lime to site will be maintained. The quantity of lime used will be recorded based on the level used from the silo. A weekly
Section 4.1 – Slaked Lime
14 P A G E 14
BRITANNIA TREATMENT PLANT - OPERATIONS MANUAL Section 4.1 – Slaked Lime
EPCOR Water Services August 2005
visual inspection of the level in the lime silo will also be carried out and recorded.
4. P ROCEDUR E F OR P ER FOR MING M AI NTENANC E
4.1 S A F E T Y
ON TH E
L I M E S LAKI NG S YS TEM
Observe the following safety precautions before carrying out maintenance on the Lime Slaking System. PPE when changing the bin filters should include: • Coveralls • Gloves • Dust Mask • Eye Protection In the event of contact with skin or eyes wash off immediately. Good housekeeping is an important part of maintaining a safe and trouble free environment for the bulk chemical system. After servicing equipment, clean spilled chemical off the operating floor and equipment surface. In general, dry chemical is better to be vacuumed rather than washed down.
4.2 M A I N T E N A N C E Maintenance procedures will be reviewed with equipment manufacturer's representatives during commissioning, to finalise preventative main procedures and predictive parameters. Following commissioning in September 2005, the complete maintenance requirements and procedures will be fully documented and the Operations and Maintenance Manual updated accordingly. The following are some key maintenance items associated with the system: 4.2.1 B I N F I L T E R S Regular inspections of the bin filters should be carried out once every 2 months. The bin filters are automatically cleaned by air bursts back through the cartridge. Refer to Section 9.1 or the Stanco Operation and Maintenance Manual for complete details.
Section 4.1 – Slaked Lime
15 P A G E 15
