Checking Mill Air Flow

Published on March 2017 | Categories: Documents | Downloads: 36 | Comments: 0 | Views: 156
of x
Download PDF   Embed   Report

Comments

Content

How to check the air flow through the mill
Grinding
PR-GRI P06-05 V1

1/3

Introduction
Proper mill ventilation is essential to ensure the removal of : fine particles all along the mill heat produced by grinding humidity from water spray and feed material Proper mill ventilation also helps reduce kWh/t and prevent quality problems of finished product caused by excessive gypsum dehydration.

Gas velocity
The gas velocity in a finish ball mill should be: Above the ball charge Closed circuit Open circuit 1.4 – 2.2 m/s Empty mill 1 – 1.5 m/s

30 – 40 % less than in closed circuit

The gas velocity in a raw mill can be higher because of drying requirement. False air entering the mill system and pressure loss in the mill (plugged slots) has to be minimised as it decreases the amount of air going through the mill. Check fan against the performance curve. Maximum trunnion velocity 25m/s

Safety aspects
Follow safety guidelines and wear appropriate Personal Protective Equipment

Prerequisites Equipment & material:
Portable oxygen analyser – in case of false air detection based on oxygen difference. Anemometer, Pitot tube – in case of direct air flow measurement Thermocouple In this procedure you may find references to other documents (tools, other “How to” procedures, etc) which are available in their respective domain of the Web Cement Portal (e.g. Grinding, Pyroprocessing, etc).

How to check the air flow through the mill
Grinding
PR-GRI P06-05 V1

2/3

Action Steps 1.
Identify airflow changes
Carry out listed checks to identify airflow change (decrease) through the mill and its source. Make sure your measuring equipment used for indicating airflow change is calibrated properly: flow rate measurement, pressure and temperature measurement

2.

Checks to do when the mill is running
Measure airflow at the mill inlet (beware of rotating parts), after the mill outlet box and after the filter if possible. Use anemometer at the mill inlet and pitot tube for measurements in ducts. Compare measured values and calculate amount of false air in each section. Follow flow rate measurement – if installed. Note that this value will not give you the airflow through the mill when false air is sucked in the system. Follow pressure value after the mill. Lower suction/under pressure can mean: clogged equipment (e.g. filter), bad functioning of flaps false air entering the mill system. Checking the fan against the performance curve is also recommended. False air can be calculated from the oxygen content in case of heated mills (measure the increase of oxygen content between two points. How to measure the false air (Pyroprocessing)

3.

Checks to do when the mill is stopped
Check the cleanliness of the partition slots and of the ventilation opening. If necessary, clean to reduce the pressure loss inside the mill. Clean possible build-ups in the mill outlet duct. After a crash stop, check the material temperature at the mill outlet (inside). Compare it with the temperature of the ground product (outside) and the mill filter. You can use this difference to estimate the amount of false air entering the system via the mill outlet box and filter section

4.

Take corrective actions
Once you have identified the reasons for the decreased airflow in the mill, take corrective actions such as: Cleaning equipment if needed Sealing equipment in case of false air detection (around 30% false air is expected for a finish mill), Checking fan if needed. Potential entry points of false air are :

How to check the air flow through the mill
Grinding
PR-GRI P06-05 V1

3/3

Action Steps
Holes in ducts, Feeding points, Flaps, expansion joints, Connections, Filters, Mill outlet Trunnions, Inefficient pneumatic locks between mill ventilation and material transport system, etc.

Sponsor Documents

Or use your account on DocShare.tips

Hide

Forgot your password?

Or register your new account on DocShare.tips

Hide

Lost your password? Please enter your email address. You will receive a link to create a new password.

Back to log-in

Close