Crushed Coal Gasification Combustion in a Cyclone Slagging Combustor

Abstract

This paper describes the experimental results of crushed coal firing two-stage combustion with the primary stage of cycolone slagging combustion. Combustion experiments were carried out under various air equivalence ratios in primary combustion, in several experiment series with different coal type, coal feed rate and coal in-jection azimuth. The emphasis was directed toward the carbon conversion, ash retention and NOx formation in the primary stage combustion (partial gasification combustion).
The optimum condition of primary combustion air equivalence ratio that gives the best carbon conversion efficiency depends upon coal type (stoichiomeric air volume), coal feed rate and coal injection azimuth. This suggests that in crushed coal cyclone slagging combustion the hydrodynamic mixing process between coal jet and swirling air flow (secondary air flow) plays a dominant role in determining the gasification combustion performance. In every experiment series, the best results of 95% both for carbon conversion and ash retention efficency were achieved. The measured product gas composition in the primary combustion shows good agreement with equilibirum calculation, suggesting that the gas phase reaction in the cyclone slagging combustion proceeds to attain chemical equilibrium. NOx emission of 100-150ppm (in flue gas, O₂ 6% base) was achieved under the condition of primary air equivalence ratio less than 0.8. The obtained results of NOx emission control represent the availability of the crushed coal burning two-stage combusion with the primary stage of cyclone slagging combustion to meet satisfactorily the NOx emission regulation.