Calorific value basis 6000 kcalkg NCV minimum 5850 NCV Hardgrove Grindability

Calorific value basis 6000 kcalkg ncv minimum 5850

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Calorific value: basis 6000 kcal/kg NCV, minimum 5850 NCV Hardgrove Grindability Index: typical, and not to be used for determining whether or not a shipment complies with the Specification Fusibility of ash (DT) [ash fusion temperature - initial deformation]
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Commercial testing for coal quality and behaviour during combustion continues at power plants as part of daily operations, but results are rarely published. Public research continues but more in the field of understanding the effects of cofiring biomass or waste with coal. Research into the combustion behaviour of coal and fly ash from blending different coals is still published by some groups but the findings are usually for either small-scale furnaces or associated with technologies such as gasification or oxyfuel based environments. These papers are therefore atypical of the current operating fleet of power stations worldwide. Nevertheless, work has been done since the 1990s when various studies examined the effects of changes in ash deposition, corrosion, moisture, and stack emissions during a period when blending and switching coal was becoming increasingly necessary. The IEA CCC studied the effects of switching to cheaper coals in power stations (Carpenter, 1998) in a literature study on large-scale operating plants. Much of the study by Carpenter (1998) focused on switching to low rank coals such as lignite, which is an unusual measure for most power station operators. However, much of the analysis also discussed the issues of switching from a 100% bituminous coal to a blend of, or complete switch to, subbituminous coals in the USA in the 1990s. It is relevant to look at the experiences in the 1990s during a time when power stations in the USA were being subjected to stricter regulations on SO 2 emissions, forcing some utilities to consider blending lower sulphur coals. This section draws on the experience of power stations in the USA that tested subbituminous coals from the PRB of Montana and Wyoming. Although some generalisations can be made about the behaviour of introducing new coals, each unique combination of coal and unit design is individually evaluated to confirm the acceptability of the coal and performance of the station. Even if a blended coal product closely resembles the design coal specification, the blend may not burn in the same way. Blending or switching to imported coals of a lower rank, notably subbituminous coals, is more complex than just heating values and moisture, although they are fundamental to the impact assessment on boiler and power station performance. This section of the report examines just a few aspects of introducing new coals that must be considered by power station operators and fuel procurement officers, these include: ash deposition, moisture content, chlorine related corrosion, and sulphur emissions.
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