Gas cleaning for advanced coal-based power generation, IEACR/53

Author(s): Kelly Thambimuthu

Ref: IEACR/53
ISBN: 92-9029-211-3
Published Date: 01/03/1993
No. of Tables: 37
No. of Figures: 100
No. of Pages: 163

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The development of several high efficiency advanced power generation technologies based on the pressurised gasification or combustion of coal is shown to depend on the availability of gas cleaning processes suitable for use under arduous process conditions. Gas cleaning for removal of particulate, acid gases and trace elements is necessary to minimise environmental emissions and to afford greater protection of gas turbines or fuel cells. Newly emerging environmental standards regulating hazardous pollutants, the disposal of solid and liquid effluents, and greenhouse gas emissions impose further requirements on the development of these gas cleaning processes. In the gasification based cycles, the low temperature or cold cleaning of a pressurised fuel gas may be undertaken using well proven technologies currently employed in the process industries. These are based on wet scrubbers which remove particulates, tars, condensed organics, trace elements and aqueous soluble reduced nitrogen and halogen gases to a high product purity. Acid gas separation processes are then used for the removal of sulphurous gases. The removal of CO2 may also be undertaken during acid gas treatment. However, additional water gas shift reactors are required to convert all of the CO to CO2. These cold cleaning processes are shown to result in a relatively high efficiency penalty on the gasification power generation cycles. High temperature and pressure or hot cleaning processes rely on mainly separate and disparate unit operations for the removal of particulates, sulphurous gases, nitrogenous gases, minor and trace elements. A common feature in the development of particle separation devices is shown to depend on the availability of tertiary, fine particulate filters that can perform reliably without significant degradation of engineering materials and components. The separation of sulphurous gases is accomplished by using gas-solid adsorption processes which require the development of regenerable sorbents or improved operating conditions that minimise the formation of solid residues in a power plant. A mix of technologies based on combustion modifications and catalytic decomposition processes is required for NOx control. The unusually high N2O emissions from AFBC and PFBC units require special measures to mitigate these emissions. With limited opportunities for the removal of trace elements by condensation, the separation of corrosive alkalis and acid halogen gases requires special unit operations. For the balance of the trace elements, an assessment is made of the extent of their, mainly coincidental, separation in other pollutant control systems. It is concluded that current developments in some of the gas cleaning technologies will not unduly impede the commercial development of a first generation of initially lower efficiency, IGCC, PFBC and hybrid topping cycle power plants. However, further progress is necessary in order to realise the full potential of the higher efficiency cycles.

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