Technical Market Support » Thermal Coal
The review has considered the available information on coal blends from two points of view -firstly, coal properties and their additivity and secondly, the performance of blends in pulverised fuel (pf) firing. The review has concluded that the level of understanding on properties is incomplete, and knowledge of performance is very poor for a number of plant performance issues.
The review has highlighted several research topics for which research is needed.
Tests on the following coal properties require further research. These properties are not additive, in that the blend property is not the weighted average of the properties of the individual coals, and they also provide a poor basis for predicting blend performance:
- Hardgrove grindability index
- Crucible swelling number
- Ash fusibility temperatures
- Coal flow properties
- Volatile matter
- Crossing point temperature
The following areas are appropriate for future research effort, as properties are not readily related to plant performance and they also have a major impact on plant operations:
| Summary of the plant performance issues recommended for further research |
| Coal property | Plant aspect | Plant performance issues |
| moisture, particle size, mineralcomposition | Coal handling | Flow properties of blends |
| nitrogen, ash fusibility | Boiler | NOx control causing increased carbon in ash and ash deposition |
| trace elements | Boiler | Trace elements: changes in deportment with Blends |
| ash fusibility | Boiler | Deposition and ash character in blends |
| sulphur | Particulate removal | Precipitation of ash from blends |
| nitrogen | NOx control | Prediction of NOx from blends |
| all | Entire plant | Model for the changing performance of a boilerwith blended coals |
This report summarises the understanding of blends and their impact on pf plants identified to date and elaborates on the key areas recommended above for future research on blends.