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Mill Optimisation

Importance of Milling

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;

Need for Testing

  • 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.

Broader HRL Mill Performance Capability

The EUcoalsizer fits into HRL's 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.

Introducing the EUcoalsizer

EUcoalsizer Features

  • 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.

Benefits of EUcoalsizer

  • 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.


Meet the expert


Over 6 years' experience in providing technical and engineering support for industrial and utility boilers. This includes a specialization in combustion optimisation of large power station boilers through onsite measurements and the tuning of combustion control systems. Read more


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