Technical Market Support » Thermal Coal
For about twenty years the pilot-scale combustion test facility run by ACIRL at Riverview Queensland has provided a service to the coal industry, whereby the performance of coals in pulverised-fuel fired power plant is simulated. This service enables coal producers and users to evaluate new coal resources; compare blending and beneficiation options; and investigate plant modifications or operating tactics.
Though there is still a healthy demand for these services, it has become apparent that there are important plant performance issues today that were not considered when the plant was designed and built. Most of these are environmental issues. Consequently ACARP commissioned this review with the following objectives:
- To define and prioritise options to upgrade the plant to provide new services,
- To develop design concepts for these options,
- Hence, to provide facilities to perform testing and research for the coal industry.
Based on the recommendations from this review, the industry will be made aware of the potential for initiating testing and research in these areas. This review does not imply any guarantee of funding either by ACIRL or the outside bodies to cover the upgrades.
Based on a review of the issues, the following upgrade options were identified:
Low NOx Combustion
Modern power plants are fitted with burner systems designed to produce low emissions of oxides of nitrogen (NOx), and hence it is relevant to develop the capability to determine the effectiveness of low-NOx combustion for test coals. Low-NOx combustion has side-effects on other performance parameters that are presently measured or that may be proposed, notably burnout efficiency and ash deposition, but potentially several other parameters as well. The need to model combustion conditions correctly when measuring these parameters accentuates the need for low-NOx combustion to be fitted.
A conceptual design has been developed to provide the Boiler Simulation Furnace with air-staging which is a measure in wide use. It is considered to be undesirable to irreversibly change the existing burner because of the need for some continuity of the coal performance database and so that it will still be possible to simulate older plant. Therefore the staged air would be injected through external ports to be added to the furnace.
Modifications to the furnace would involve the addition of ducting, injection ports and facilities to measure and control the staged air. The principal challenge would be the aerodynamic design of the ports, not the hardware. Consequently some Computational Fluid Dynamic modelling may be undertaken to assist with the configuration.
Oxy-Fuel Combustion
Oxy-Fuel Combustion is a technology proposed for coal-fired power plants to allow for efficient large-scale capture of CO2 from the exhaust gas so that it may be sequestered.
Oxy-Fuel Combustion simplifies capture by increasing the concentration of CO2 in the boiler off-gases. The combustion air normally supplied to the burners is replaced by a mixture of oxygen and recycled flue gas. By this means the CO2 concentration in the off-gas is increased from about 15% to about 95% (not counting water vapour).
Oxy-Fuel Combustion has been shown to be feasible in a number of pilot-scale facilities outside Australia and retrofits of full-scale plant have been proposed in Australia and elsewhere. There are many issues relating to the effects that the modified combustion conditions could have on processes such as particle burn-out, heat transfer, fly ash and deposit formation, and pollutant formation. These are also coal-related issues and hence we need to test a range of coal qualities to demonstrate the feasibility of the process.
The conceptual design includes storage and reticulation facilities for oxygen and CO2, ducting, fans and compressors, an extensive system of flow controllers and safety interlocks. The level of process control required will be much greater than the existing, hence it is envisaged that a separate Process Logic Controller will need to be acquired and integrated with the existing recently upgraded System Control and Data Acquisition system.
The design does not include an oxygen-production plant or CO2 capture equipment.