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MILL performance.ppt

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DavinderMakhija1

This document discusses factors that affect mill performance in coal power plants. Key factors include input coal quality parameters like calorific value, volatile matter, moisture content, hardness, and silica/quartz content. Other important factors are the condition of grinding elements and operating parameters such as mill outlet temperature, primary air flow, mill differential pressure, and mill current. Maintaining these factors within design limits optimizes mill loading capacity and improves combustion stability and efficiency.

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MILL PERFORMANCE OPTIMISATION ROLE OF OPERATION
PERFORMANCE INDICATORS: Mill performance is said to be good when it takes the design / tested load and delivers the product at the designated fineness values with minimum current consumption and reject rate.
FACTORS AFFECTING PERFORMANCE: Mill performance depends on a variety of factors other than proper maintenance which are listed below: • Input coal quality. • Grinding elements life. • Operating parameters.
1.0 INPUT COAL QUALITY: 1.1 Calorific Value: Calorific value directly indicates the quality of coal and hence, the amount of coal to be fired. In most of the stations the calorific value of coal is less than the design value, which in turn causes an increased loading on the mills. In some cases, deterioration in coal quality leads to increased number of mills run for full load. While operating, care should be taken to load the mills evenly to the extent possible for improved combustion and mill performance. Mill loading should be kept within the prescribed minimum and maximum limits.
1.2 Volatile Matter: Volatile Matter in coal is a factor, which aids combustion and gives combustion stability. Higher the VM, the coal will burn better and burn nearer to the burner. VM varies from about 12% to 23% in the coals used at our stations. Low VM coal requires a better PF fineness compared to high VM coal. This aspect is to be kept in mind while loading the mill and fineness readings are to be taken and monitored more frequently. When fineness cannot be increased beyond a limit due to various reasons like mill design, coal flow rate etc. other parameters like total air flow, PA flow, secondary air distribution, etc. should be optimized for better combustion stability.
1.3 Moisture Content: Mill should be able to remove total surface moisture and up to half of the inherent moisture from the design range of coal. With increased moisture content, the mill output reduces. Tube mills are more sensitive to moisture compared to vertical spindle mills (see curve). Efforts should be made to minimize the external moisture by coordinating with CHP. Mill loading should be adjusted so as to maintain the mill temp. within operating limits. Sometimes more number of mills may have to be run for achieving this. SCAPH can be charged to improve the APH outlet temp. Mill outlet temp. should not be allowed to drop below 60ºC.
EFFECT OF MOISTURE ON MILL CAPACITY (BOWL MILL) 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 0 2 4 6 8 10 12 14 16 18 20 22 MOISTURE IN COAL (%) MILL CAPACITY FACTOR
EFFECT OF MOISTURE ON MILL CAPACITY (TUBE MILL) 0 0.2 0.4 0.6 0.8 1 1.2 0 5 10 15 20 25 MOISTURE IN COAL (%) CAPACITY FACTOR
1.4 Hardness: Mill loading capacity and PF fineness deteriorate when harder coals (with low HGI) are used (see curve). If the mill is properly designed taking into consideration the realistic HGI of coal, limitations in mill output due to a change in Hardness can be avoided. Normally mills are designed to handle harder coal and will give an increased output with softer coals. Though this is an uncontrollable factor, monitoring the hardness will help in understanding the behaviour of the mill.
GRINDABILITY INDEX VS MILL OUTPUT 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 30 40 50 60 70 80 90 100 GRINDABILITY INDEX (HGI) MILL OUTPUT X 100%
1.5 Silica / Quartz Content: Inherent or external silica / quartz content reduces the grindability of coal and increases the wear on mill parts. Hardness of coal is 0.5 to 2.5 MHO whereas hardness of quartz is as high as 7 MHO. As the abrasiveness of coal is increased, the bull ring segments and rolls of vertical spindle bowl mills wear preferentially in zones of high local coal bed pressure. This leads to increased clearances in these areas thereby reducing grinding efficiency. Increased abrasiveness reduces the grinding element life (see curve). Apart from this, sand particles settle at the bottom of the mill and form a bed. This will increase the mill DP, current and reject rate. Whenever the DP crosses a prescribed limit, the mill should be purged by cutting of coal and air supply to take out the sand accumulation. Coal pipes also can be purged with air to prevent deposition of sand / coal.
EFFECT OF QUARTZ IN COAL ON MILL WEAR 0 0.2 0.4 0.6 0.8 1 1.2 4 5 6 7 8 9 10 11 12 QUARTZ, % ABRASION DEPTH, MM/1000 TONS OF COAL
Whenever more stones are observed in coal, CHP should be informed for taking corrective action like increasing the efficiency of stone picking or taking up the matter with the mines. Operating the mills with higher spring compression or an increased air fuel ratio will grind the sand particles and send it to the furnace. But this should be avoided it will cause increased wear in coal pipes, burners and pressure parts. Moreover, the silica / quartz will get deposited in the furnace walls. This will considerably reduce heat transfer and are very difficult to remove.
1.6 Foreign Material: Increased amount of foreign material in coal causes feeder / mill breakdowns and frequent reject passage choking. If abnormal sound or reject passage choking is noticed, the mill should be stopped at the earliest to reduce the extent of damage. Prolonged operation of the mill with a blocked reject passage will increase the damage and downtime. Choking of reject passage with stones can lead to clinkering in the scrapper box. Coal Handling Plant should be regularly appraised about the presence of foreign material / stones in coal. Proper operation of MD / MS, crusher screens and proper sizing of bunker grills should be always ensured.
1.7 Size of Input Coal: Size of input coal is a factor, which determines the mill loading capacity. The size should be maintained nearer to the design values in co-ordination with CHP. Sieve analysis is of the crushed coal should be done at regular intervals to ensure that the size of coal is within limits.
2.0 Grinding Elements Life: The wear life / condition of grinding elements will have a considerable effect on the performance of the mill. Each station will have an average grinding element life for a type of mill, depending on coal quality, mill setting, operating conditions etc. During this life time the loading capacity gradually reduces and the current consumption gradually increases. Mill PM requirements also increase as the wear increases. This phenomenon is more predominant in bowl mills. If the mill is loaded beyond its capacity w.r.t. its wear life, the performance will suffer. Operating personnel should be aware of the life and wear pattern of each mill and load the mill accordingly.
Classifier setting of the mill should be adjusted to different positions during its life cycle. Initially when the grinding elements are new, the losses across the mill are minimum and primary classification will be less. This necessitates a lower classifier opening for proper product fineness. When the grinding elements grow older the mill DP will increase and primary classification improves. During this time classifier vanes can be opened gradually which will improve the loading at the same fineness. For tube mills, performance level can be maintained by adding fresh charge of balls at regular intervals.
3.0 Operating Parameters: 3.1 Mill Outlet Temp.: For good pulveriser and combustion performance, the temperature of the coal air mixture leaving the mill should be maintained as high as possible within the safe temperature limit of the particular coal. A temperature of 85 to 90ºC is acceptable for coals with normal VM. An outlet temp. below 60ºC may not dry the coal sufficiently. Operating the mill with lower than allowable temp. will cause coal pipe choking also due to the presence of moisture, as the air may reach its dew point.
3.2 PA Flow: Primary Air Flow should be low enough to avoid ignition instability and high enough to avoid settling and drifting in the coal pipes or excessive spillage of coal from the pulveriser through the tramp iron spout. To avoid blockage of fuel pipes, a minimum average transport velocity of 20 m / s should be maintained. The normal operating velocity will be between 24 m / s and 27 m/s. Increase in the ‘mill to furnace DP’ measurement (if provided) will indicate coal pipe choking. In some stations coal pipe temp. or drop in temp across the coal pipe is monitored for early detection of coal pipe choking. Running the mill with choked coal pipe / pipes is not advisable.
A higher PA flow also affects the PF fineness by reducing primary classification as it lifts the coarser particles. This factor can be confirmed by taking PF fineness at different PA flows and plotting a curve. To meet the above requirements, PA flow has to be varied w.r.to coal flow as per the ‘Coal Vs PA flow’ curve. On medium speed vertical spindle mills the ratio is approximately 1:1.7 to 1:2.2 and on tube mills its about 1:1.2 to 1:1.5.
3.3 Mill DP: Mill DP is an indication of the losses inside the mill. It increases with a higher mill loading or with other factors like wear of grinding elements, accumulation of coal or sand inside the mill, choking of throat area, blockage of classifier cone etc. In case of Tube mills, mill DP indicates the amount of coal inside the mill. If the DP is allowed to cross the design values, mill performance will deteriorate. The reason for a high DP should be investigated and corrective actions like mill purging, PM jobs etc. should be taken.
3.4 Mill Current: Mill current is an indication of the mill loading and the condition of the mill. Different types of mills have different power consumption per ton of coal ground. Mill power consumption increases with loading as well with mill wear, particularly in vertical spindle mills. Care should be taken not to exceed the allowable maximum current limit. Maximum economy of milling plant power is obtained by operating the optimum number of mills at their maximum output rather than operating more number of mills at part load. Where partial mill loading is necessary to meet a reduced boiler output, it is good practice to load each mill to the same degree.
3.5 PF Fineness: Mill output and fineness are interdependent and an increase in output can be obtained only at the expense of a deterioration in fineness, assuming that power input to the mill remain same. This practice is not recommended unless the coarser pulverised fuel provides satisfactory combustion (see curve). To take preventive actions, fineness readings should be taken as frequently as possible and should be monitored by Operation and Maintenance staff. PF sample collection and analysis should be done as per the standard procedure and the readings should be validated in a Rosin-Rammler chart. If the readings are not in line with the chart, the sampling procedure, air flow or the mill internals should be checked.
MILL LOADING VS MILL FINENESS CURVE FOR AN XRP 1003 MILL 68.3 63.3 58 56 58 60 62 64 66 68 70 40 50 60 70 MILL LOAD T/HR MILL FINENESS (-200), %
MILL OUTPUT VS MILL FINENESS CURVE FOR AN XRP 1003 MILL 0.6 1.3 3.5 0 0.5 1 1.5 2 2.5 3 3.5 4 40 50 60 70 MILL OUTPUT, TPH FINENESS (+50), %
SIEVE DISTRIBUTION CHART 60 70 80 90 100 0 50 100 150 200 250 US STANDARD SIEVE FINENESS, % PASSING THRU
Factors affecting PF Fineness: a) Overloading of the mill. b) Improper setting of spring tension, classifier vanes etc. c) Excessively worn out grinding elements d) Damage to mill internals. e) Higher PA flow. f) Improper sampling procedure – non-usage of aspirating fittings. g) Improper sample analysis. Whenever a deterioration in fineness is noticed corrective action should be taken at the earliest, so that the effect on combustion, boiler efficiency, coal pipe choking etc. are minimized.
MONITORING: The effect of the various factors mentioned above underscores the need for monitoring the operating parameters regularly for taking corrective actions in time. Useful feedback regarding quality of coal like wetness, foreign material / stones and the damage caused by them, input coal size etc should be given to CHP for taking corrective action. Similarly, mill-operating parameters should be monitored regularly by maintenance staff also. It will give an insight into the mill performance and provide input for scheduling mill maintenance. The operating parameters should be co-related with other mill parameters at least once in a week and corrective action should be taken for deviations.
CONCLUSION By proper understanding of the factors affecting mill performance and by proper monitoring of those factors, one should be able to predict the mill performance in normal cases. Mill operating parameters can be adjusted within the allowable ranges to suite the changing characteristics of coal. Mill maintenance personnel should also monitor the mill parameters, which will give an insight into the healthiness of the mill and will help in planning the maintenance.
MILL OPERATING PARAMETERS UNIT: DATE: Unit load, MW: Total Coal Flow, tph: Total Air flow, tph: PA header pressure, mmwc: Seal air header pressure, mmwc: SL NO. PARAMETER MILL A B C D E F 01 Coal Flow, tph 02 Mill current, A 03 PA flow, tph 04 Mill DP, mmwc 05 Mill to furnace DP, mmwc 06 Mill outlet temp. º C 07 Inlet PA temp. º C 08 HAD position, % 09 CAD position, % 10 Mill fineness, %: +50 - 200 11 Date of PM jobs (last) 12 Date of grinding elements replacement (last) 13 Coal quality (as on: -------): GCV, kcal / kg: HGI: Moisture, %: VM, %: 14 Unburnt carbon content (as on: --------): Bottom ash, %: Fly ash, %:
MILL PERFORMANCE MONITORING SHEET UNIT: DATE: Unit load, MW: Total Coal Flow, tph: Total Air flow, tph: PA header pressure, mmwc: Seal air header pressure, mmwc: SL NO. PARAMETER MILL A B C D E F 01 Coal Flow, tph 02 Mill current, A 03 PA flow, tph 04 Mill DP, mmwc 05 Mill to furnace DP, mmwc 06 Mill outlet temp. º C 07 Mill fineness, %: +50 - 200 08 Classifier position 09 Date of PM jobs (last) 10 Date of grinding elements replacement (last) 11 Running hours since last GE replacement 12 Grinding elements make: BRS: Rolls: 13 Roll wear, mm 14 Ring – roll gap, mm 15 Spring Compression, psi 16 Venturi height, inches 17 Throat gap, mm 18 Mill Rejects, %: CV:
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MILL performance.ppt

  • 2. PERFORMANCE INDICATORS: Mill performance is said to be good when it takes the design / tested load and delivers the product at the designated fineness values with minimum current consumption and reject rate.
  • 3. FACTORS AFFECTING PERFORMANCE: Mill performance depends on a variety of factors other than proper maintenance which are listed below: • Input coal quality. • Grinding elements life. • Operating parameters.
  • 4. 1.0 INPUT COAL QUALITY: 1.1 Calorific Value: Calorific value directly indicates the quality of coal and hence, the amount of coal to be fired. In most of the stations the calorific value of coal is less than the design value, which in turn causes an increased loading on the mills. In some cases, deterioration in coal quality leads to increased number of mills run for full load. While operating, care should be taken to load the mills evenly to the extent possible for improved combustion and mill performance. Mill loading should be kept within the prescribed minimum and maximum limits.
  • 5. 1.2 Volatile Matter: Volatile Matter in coal is a factor, which aids combustion and gives combustion stability. Higher the VM, the coal will burn better and burn nearer to the burner. VM varies from about 12% to 23% in the coals used at our stations. Low VM coal requires a better PF fineness compared to high VM coal. This aspect is to be kept in mind while loading the mill and fineness readings are to be taken and monitored more frequently. When fineness cannot be increased beyond a limit due to various reasons like mill design, coal flow rate etc. other parameters like total air flow, PA flow, secondary air distribution, etc. should be optimized for better combustion stability.
  • 6. 1.3 Moisture Content: Mill should be able to remove total surface moisture and up to half of the inherent moisture from the design range of coal. With increased moisture content, the mill output reduces. Tube mills are more sensitive to moisture compared to vertical spindle mills (see curve). Efforts should be made to minimize the external moisture by coordinating with CHP. Mill loading should be adjusted so as to maintain the mill temp. within operating limits. Sometimes more number of mills may have to be run for achieving this. SCAPH can be charged to improve the APH outlet temp. Mill outlet temp. should not be allowed to drop below 60ºC.
  • 7. EFFECT OF MOISTURE ON MILL CAPACITY (BOWL MILL) 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 0 2 4 6 8 10 12 14 16 18 20 22 MOISTURE IN COAL (%) MILL CAPACITY FACTOR
  • 8. EFFECT OF MOISTURE ON MILL CAPACITY (TUBE MILL) 0 0.2 0.4 0.6 0.8 1 1.2 0 5 10 15 20 25 MOISTURE IN COAL (%) CAPACITY FACTOR
  • 9. 1.4 Hardness: Mill loading capacity and PF fineness deteriorate when harder coals (with low HGI) are used (see curve). If the mill is properly designed taking into consideration the realistic HGI of coal, limitations in mill output due to a change in Hardness can be avoided. Normally mills are designed to handle harder coal and will give an increased output with softer coals. Though this is an uncontrollable factor, monitoring the hardness will help in understanding the behaviour of the mill.
  • 10. GRINDABILITY INDEX VS MILL OUTPUT 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 30 40 50 60 70 80 90 100 GRINDABILITY INDEX (HGI) MILL OUTPUT X 100%
  • 11. 1.5 Silica / Quartz Content: Inherent or external silica / quartz content reduces the grindability of coal and increases the wear on mill parts. Hardness of coal is 0.5 to 2.5 MHO whereas hardness of quartz is as high as 7 MHO. As the abrasiveness of coal is increased, the bull ring segments and rolls of vertical spindle bowl mills wear preferentially in zones of high local coal bed pressure. This leads to increased clearances in these areas thereby reducing grinding efficiency. Increased abrasiveness reduces the grinding element life (see curve). Apart from this, sand particles settle at the bottom of the mill and form a bed. This will increase the mill DP, current and reject rate. Whenever the DP crosses a prescribed limit, the mill should be purged by cutting of coal and air supply to take out the sand accumulation. Coal pipes also can be purged with air to prevent deposition of sand / coal.
  • 12. EFFECT OF QUARTZ IN COAL ON MILL WEAR 0 0.2 0.4 0.6 0.8 1 1.2 4 5 6 7 8 9 10 11 12 QUARTZ, % ABRASION DEPTH, MM/1000 TONS OF COAL
  • 13. Whenever more stones are observed in coal, CHP should be informed for taking corrective action like increasing the efficiency of stone picking or taking up the matter with the mines. Operating the mills with higher spring compression or an increased air fuel ratio will grind the sand particles and send it to the furnace. But this should be avoided it will cause increased wear in coal pipes, burners and pressure parts. Moreover, the silica / quartz will get deposited in the furnace walls. This will considerably reduce heat transfer and are very difficult to remove.
  • 14. 1.6 Foreign Material: Increased amount of foreign material in coal causes feeder / mill breakdowns and frequent reject passage choking. If abnormal sound or reject passage choking is noticed, the mill should be stopped at the earliest to reduce the extent of damage. Prolonged operation of the mill with a blocked reject passage will increase the damage and downtime. Choking of reject passage with stones can lead to clinkering in the scrapper box. Coal Handling Plant should be regularly appraised about the presence of foreign material / stones in coal. Proper operation of MD / MS, crusher screens and proper sizing of bunker grills should be always ensured.
  • 15. 1.7 Size of Input Coal: Size of input coal is a factor, which determines the mill loading capacity. The size should be maintained nearer to the design values in co-ordination with CHP. Sieve analysis is of the crushed coal should be done at regular intervals to ensure that the size of coal is within limits.
  • 16. 2.0 Grinding Elements Life: The wear life / condition of grinding elements will have a considerable effect on the performance of the mill. Each station will have an average grinding element life for a type of mill, depending on coal quality, mill setting, operating conditions etc. During this life time the loading capacity gradually reduces and the current consumption gradually increases. Mill PM requirements also increase as the wear increases. This phenomenon is more predominant in bowl mills. If the mill is loaded beyond its capacity w.r.t. its wear life, the performance will suffer. Operating personnel should be aware of the life and wear pattern of each mill and load the mill accordingly.
  • 17. Classifier setting of the mill should be adjusted to different positions during its life cycle. Initially when the grinding elements are new, the losses across the mill are minimum and primary classification will be less. This necessitates a lower classifier opening for proper product fineness. When the grinding elements grow older the mill DP will increase and primary classification improves. During this time classifier vanes can be opened gradually which will improve the loading at the same fineness. For tube mills, performance level can be maintained by adding fresh charge of balls at regular intervals.
  • 18. 3.0 Operating Parameters: 3.1 Mill Outlet Temp.: For good pulveriser and combustion performance, the temperature of the coal air mixture leaving the mill should be maintained as high as possible within the safe temperature limit of the particular coal. A temperature of 85 to 90ºC is acceptable for coals with normal VM. An outlet temp. below 60ºC may not dry the coal sufficiently. Operating the mill with lower than allowable temp. will cause coal pipe choking also due to the presence of moisture, as the air may reach its dew point.
  • 19. 3.2 PA Flow: Primary Air Flow should be low enough to avoid ignition instability and high enough to avoid settling and drifting in the coal pipes or excessive spillage of coal from the pulveriser through the tramp iron spout. To avoid blockage of fuel pipes, a minimum average transport velocity of 20 m / s should be maintained. The normal operating velocity will be between 24 m / s and 27 m/s. Increase in the ‘mill to furnace DP’ measurement (if provided) will indicate coal pipe choking. In some stations coal pipe temp. or drop in temp across the coal pipe is monitored for early detection of coal pipe choking. Running the mill with choked coal pipe / pipes is not advisable.
  • 20. A higher PA flow also affects the PF fineness by reducing primary classification as it lifts the coarser particles. This factor can be confirmed by taking PF fineness at different PA flows and plotting a curve. To meet the above requirements, PA flow has to be varied w.r.to coal flow as per the ‘Coal Vs PA flow’ curve. On medium speed vertical spindle mills the ratio is approximately 1:1.7 to 1:2.2 and on tube mills its about 1:1.2 to 1:1.5.
  • 21. 3.3 Mill DP: Mill DP is an indication of the losses inside the mill. It increases with a higher mill loading or with other factors like wear of grinding elements, accumulation of coal or sand inside the mill, choking of throat area, blockage of classifier cone etc. In case of Tube mills, mill DP indicates the amount of coal inside the mill. If the DP is allowed to cross the design values, mill performance will deteriorate. The reason for a high DP should be investigated and corrective actions like mill purging, PM jobs etc. should be taken.
  • 22. 3.4 Mill Current: Mill current is an indication of the mill loading and the condition of the mill. Different types of mills have different power consumption per ton of coal ground. Mill power consumption increases with loading as well with mill wear, particularly in vertical spindle mills. Care should be taken not to exceed the allowable maximum current limit. Maximum economy of milling plant power is obtained by operating the optimum number of mills at their maximum output rather than operating more number of mills at part load. Where partial mill loading is necessary to meet a reduced boiler output, it is good practice to load each mill to the same degree.
  • 23. 3.5 PF Fineness: Mill output and fineness are interdependent and an increase in output can be obtained only at the expense of a deterioration in fineness, assuming that power input to the mill remain same. This practice is not recommended unless the coarser pulverised fuel provides satisfactory combustion (see curve). To take preventive actions, fineness readings should be taken as frequently as possible and should be monitored by Operation and Maintenance staff. PF sample collection and analysis should be done as per the standard procedure and the readings should be validated in a Rosin-Rammler chart. If the readings are not in line with the chart, the sampling procedure, air flow or the mill internals should be checked.
  • 24. MILL LOADING VS MILL FINENESS CURVE FOR AN XRP 1003 MILL 68.3 63.3 58 56 58 60 62 64 66 68 70 40 50 60 70 MILL LOAD T/HR MILL FINENESS (-200), %
  • 25. MILL OUTPUT VS MILL FINENESS CURVE FOR AN XRP 1003 MILL 0.6 1.3 3.5 0 0.5 1 1.5 2 2.5 3 3.5 4 40 50 60 70 MILL OUTPUT, TPH FINENESS (+50), %
  • 26. SIEVE DISTRIBUTION CHART 60 70 80 90 100 0 50 100 150 200 250 US STANDARD SIEVE FINENESS, % PASSING THRU
  • 27. Factors affecting PF Fineness: a) Overloading of the mill. b) Improper setting of spring tension, classifier vanes etc. c) Excessively worn out grinding elements d) Damage to mill internals. e) Higher PA flow. f) Improper sampling procedure – non-usage of aspirating fittings. g) Improper sample analysis. Whenever a deterioration in fineness is noticed corrective action should be taken at the earliest, so that the effect on combustion, boiler efficiency, coal pipe choking etc. are minimized.
  • 28. MONITORING: The effect of the various factors mentioned above underscores the need for monitoring the operating parameters regularly for taking corrective actions in time. Useful feedback regarding quality of coal like wetness, foreign material / stones and the damage caused by them, input coal size etc should be given to CHP for taking corrective action. Similarly, mill-operating parameters should be monitored regularly by maintenance staff also. It will give an insight into the mill performance and provide input for scheduling mill maintenance. The operating parameters should be co-related with other mill parameters at least once in a week and corrective action should be taken for deviations.
  • 29. CONCLUSION By proper understanding of the factors affecting mill performance and by proper monitoring of those factors, one should be able to predict the mill performance in normal cases. Mill operating parameters can be adjusted within the allowable ranges to suite the changing characteristics of coal. Mill maintenance personnel should also monitor the mill parameters, which will give an insight into the healthiness of the mill and will help in planning the maintenance.
  • 30. MILL OPERATING PARAMETERS UNIT: DATE: Unit load, MW: Total Coal Flow, tph: Total Air flow, tph: PA header pressure, mmwc: Seal air header pressure, mmwc: SL NO. PARAMETER MILL A B C D E F 01 Coal Flow, tph 02 Mill current, A 03 PA flow, tph 04 Mill DP, mmwc 05 Mill to furnace DP, mmwc 06 Mill outlet temp. º C 07 Inlet PA temp. º C 08 HAD position, % 09 CAD position, % 10 Mill fineness, %: +50 - 200 11 Date of PM jobs (last) 12 Date of grinding elements replacement (last) 13 Coal quality (as on: -------): GCV, kcal / kg: HGI: Moisture, %: VM, %: 14 Unburnt carbon content (as on: --------): Bottom ash, %: Fly ash, %:
  • 31. MILL PERFORMANCE MONITORING SHEET UNIT: DATE: Unit load, MW: Total Coal Flow, tph: Total Air flow, tph: PA header pressure, mmwc: Seal air header pressure, mmwc: SL NO. PARAMETER MILL A B C D E F 01 Coal Flow, tph 02 Mill current, A 03 PA flow, tph 04 Mill DP, mmwc 05 Mill to furnace DP, mmwc 06 Mill outlet temp. º C 07 Mill fineness, %: +50 - 200 08 Classifier position 09 Date of PM jobs (last) 10 Date of grinding elements replacement (last) 11 Running hours since last GE replacement 12 Grinding elements make: BRS: Rolls: 13 Roll wear, mm 14 Ring – roll gap, mm 15 Spring Compression, psi 16 Venturi height, inches 17 Throat gap, mm 18 Mill Rejects, %: CV: