Mill Optimisation

Influence on Mill Performance on Combustion and Boiler Performance

Milling performance is critical in controlling the combustion process in the boiler.

Coal pf fineness influences:

• ignition delay;  
• combustion efficiency;
• particle erosion;
• loss on ignition (and hence coal costs);
• value of ash and ability to dispose / sell;
• emission levels;
• boiler slagging and fouling;
• potential damage to superheater tubes from combustion delay.

• Mill maintenance costs are one of the highest maintenance costs in a coal fired power station;
• Testing allows a change to 'condition based' maintenance (from set mill operating hours) which in HRL's experience can increase time between minor / major mill overhauls by up to 10%;
• Optimising milling performance can reduce coal consumption and therefore costs;
• Testing can help detect mill performance issues early and can help direct / target maintenance activity.

The EUcoalsizer fits into the broader mill performance service offer to assist in optimising mill performance.

• Measurement of pf flow per burner duct microwave technology;
• Coal flow balancing (e.g. by adjustment of values on PF pipes);
• Check / calibration of coal flow obtained from volumetric or gravimetric coal feeder to mill and check on mill capacity limits (and assessment of reason for limits);
• Mill power consumption (per unit of coal throughput) including as a check on classifier recirculation rates;
• CFD modelling of milling system to solve flow related issues;
• Adjustment of classier vane setting or redesign to adjust pf fineness;
• Mill condition and inspection;
• Measurement of pressure drop across mill / classifier;
• Mill performance as a function of load / coal throughput;
• Measurement of PA flow / auxiliary air / mill seal air flowrate;
• Comparison of measurements against station instruments;
• 'Clean' (no coal flow) testing to measure air flow distribution to burners;
• Assessment of individual mill performance and recommendations for maintenance, physical modifications, or operational changes;
• Measurement of mill inlet / outlet temperature, and check on temperature stability;
• Testing of mill performance following major overhaul to demonstrate performance gain and to help optimise future overhaul scope of work;
• Assessment of materials, failure analysis, requirement for repair or replacement.

• Measures (in real time) pf particle size distribution (PSD), coal and air flow;
• Provides spatially resolved (2D) readings;
• Allows real time coal : air flow tuning and adjustment of coal feeders / mill control settings;
• Requires larger 3" ports to be installed.

• Cost of testing is dramatically reduced.  Testing is conducted by a single operator;
• The cost competitiveness allows regular e.g. quarterly or bi-annual testing of all mills;
• This in turn facilitates moving to a 'condition based' maintenance program and hence a reduction in mill maintenance cost, as well as prioritising mill maintenance to optimise combustion performance;
• Allows milling performance to be characterised following a change in coal supply (or evaluation of suitability of a particular coal supply);
• Allows real-time assessment of changes to mill operation and settings on pf size and hence adoption
•  of a mill operation optimisation program;
• Optimising mill performance can result in reduction in coal consumption, carbon in ash and allows full benefit to be obtained from combustion tuning.