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10 Difficult Problems about Raw Grinding with Vertical Roller Mill Systems and their solutions

First : High vibrations

Potential causes:
Too many fines in mill feed
Material bed on grinding table not stable

Proposed solutions:
Increase feed size
Adjust crushers
Maybe eliminate a crusher

Expected results:
Less vibrations
Less fine fractions in mill feed
Lower crushing costs (energy, wear, maintenance)

Estimated costs:
Minimal

Implementation time:
Short-term

High amount of false air

Potential causes:
Defects on external seals

Proposed solutions:
Improve maintenance

Expected results:
Improved drying of mill product
Reduced specific power consumption (fans)

Estimated costs:
Minimal

Implementation time:
Short-term

Dynamic seal not working effectively

Potential causes:
Seal space too big
Possible damages on seal

Proposed solutions:
Improve maintenance (check status of seal more frequently)
Repair damages

Expected results:
Less coarse mill product
Reduced specific power consumption

Estimated costs:
Minimal

Implementation time:
Short-term

Mill exit temperature too low

Potential causes:
False air
Damper positions

Proposed solutions:
Reduce damper between conditioning tower and filter
Reduce damper of re-circulation air flow

Expected results:
Less humidity in mill product
Lower temperature in filter

Estimated costs:
Minimal

Implementation time:
Short-term

Roller pressure too low

Potential causes:
High vibrations
Pressure adjustment does not follow wear

Proposed solutions:
Train mill operators
Adjust pressure periodically

Expected results:
Increased feed rate and higher production
Reduced specific power consumption

Estimated costs:
Minimal

Implementation time:
Short-term

Air speed variations in mill

Potential causes:
Cone design
Inclination of nozzles

Proposed solutions:
Redesign cone
Adjust inclination of nozzles (35° to 60°)

Expected results:
More uniform speed increase
Less material falling through nozzle ring
Reduced specific power consumption

Estimated costs:
Minimal

Implementation time:Mid-term

Material distribution on grinding table not optimal

Potential causes:
Feed chute too short

Proposed solutions:
Prolong feed chute

Expected results:
More stable material bed
Less vibrations

Estimated costs:
Minimal

Implementation time:Mid-term

Grinding tools with high wear

Potential causes:
Recommendation of equipment supplier

Proposed solutions:
Investigate alternative (better) grinding tools

Expected results:
Prolonged lifetime of grinding tools
Reduced specific grinding costs

Estimated costs:
Medium

Implementation time:Mid-term

Manual operation

Potential causes:
Original installation not improved

Proposed solutions:
Investigate possible automation

Expected results:
More stable operation
Reduced specific costs of milling

Estimated costs:
High

Implementation time:Long-term

Material falling through nozzle ring

Potential causes:
Original installation not improved

Proposed solutions:
Install external material circulation

Expected results:
Less cleaning necessary
Environmental aspects improved

Estimated costs:
High

Implementation time:Long-term