Effect of high pressure carbonization on the strength and structure of cokes from low rank bituminous coals

Abstract

Commercial gasification processes are usually operated at high pressure for economic considerations. However, there is very little information available on the influence of pressure on the carbonization of coal under conditions relevant to high pressure fixed bed gasifiers. This investigation involved high pressure carbonization studies (0.5–8 MPa) simulating the conditions found in the British Gas-Lurgi gasifier. Two low rank bituminous coals typical of likely gasifier feedstocks were used in the study. The physical properties of the resultant cokes, such as porosity, tensile strength and abrasion resistance, were measured and several interrelationships between the coke structural parameters, mechanical properties and experimental conditions have been established. In general, for the two low rank coals studied the main effect of pressure is to initially enhance macropore development during carbonization at slow heating rates resulting in highly macroporous cokes, which consequently have relatively low tensile strength and low resistance to abrasive forces compared with metallurgical cokes. The results are discussed in terms of the relationships between coal thermoplasticity, coke structural characteristics and mechanical properties.