Characterization of ash melting behaviour at high temperatures under conditions simulating combustible solid waste gasification

Abstract

To achieve high-temperature gasification-melting of combustible solid waste, ash melting behaviour under conditions simulating high-temperature gasification were studied. Raw ash (RA) and gasified ash (GA) were prepared respectively by waste ashing and fluidized bed gasification. Results of microstructure and composition of the two-ash indicated that GA showed a more porous structure and higher content of alkali and alkali earth metals among metallic elements. Higher temperature promoted GA melting and could reach a complete flowing state at about 1250°C. The order of melting rate of GA under different atmospheres was reducing condition > inert condition > oxidizing condition, which might be related to different existing forms of iron during melting and different flux content with atmosphere. Compared to RA, GA showed lower melting activity at the same condition due to the existence of an unconverted carbon and hollow structure. The melting temperature for sufficient melting and separation of GA should be at least 1250°C in this work.

Evolution of pyrolysis and gasification as waste to energy tools for low carbon economy

“…In high‐temperature gasification, referred to as the gasification and melting approaches, in addition to the reformation of the organic part, significant changes occur in the mineral fraction of the feedstock. Contrary to the statements of some authors that reducing the atmosphere reduces the melting temperature of ash, Niu et al's study (Niu et al, 2018) has demonstrated that under gasification conditions, a temperature over 1250°C was needed for total ash melting and separation.…”

Experimental and computational study on the effect of ash deposition on fluid dynamic behavior in a bubbling fluidized bed gasifier

“…Bartels et al have investigated the mechanism of agglomeration and concluded the fact that agglomeration takes place due to the adhesiveness of bed material caused by alkali compounds present in the biomass (Bartels et al, 2008). Pietsch (Pietsch, 2008) defined agglomeration as the formation of larger entities from particulate solid by sticking particles together by short range physical forces between the particles themselves, or through substances that adhere chemically or physically to the solid surface and form a material bridge between the particles. Visser and Tardos (Visser et al, 2008;Tardos et al, 1995) found two different routes for the initiation of bed agglomeration: melt-induced agglomeration and coating-induced agglomeration.…”

“…Usually, high temperature is more favorable for carbon conversion because it produces less amount of tar. However, it brings other technological issues like ash melting and bed agglomeration (Niu et al, 2018).The alkali metals present in the biomass ash, will together with sulphur and chlorine in biomass fuels contribute to the bed agglomeration in fluidized bed reactors.…”