To optimize operational parameters of fluidized-bed lignite gasification technology. Experiments have been conducted with Huolinhe (HLH) and Xiaolongtan (XLT) lignite ashes to investigate the mineral transformation behaviors under reducing atmosphere by X-ray diffraction (XRD). The results show that the initial melted parts are primarily result from wustite interacted other minerals under reducing atmosphere. Wustite can react with aluminosilicate minerals to form some low-melting eutectic compounds, and lead to its initial melting temperature 200 °C below the deformation temperature. Mullite is formed at 1000 °C or so, and its content increases and then decreases with the temperature increase, and reaches maximum at 1200 °C. Gehlenite and anorthite come from the reaction between calcium oxide and mullite. Owing to the generation of some gases during mineral transformation under weak reducing atmosphere, many holes are formed on the surface of molten ash.

Experiments have been conducted with Huolinhe lignite low temperature ashes (HLH-LTA) to investigate the mineral behaviors under gasification atmosphere (H2/CO2=1:1, volume ratio) with the temperature increase by SEM and XRD. The results show that the contents of SO3 and alkali metal oxide (e.g. K2O, Na2O) are higher in the HLH-LTA than that in laboratory HLH ashes. The formation of some low-melting ferrous eutectic compounds causes the initial melting temperature of HLH-LTA is lower about 300 °C than its deformation temperature. The formation of slag during HLH fluidized-bed gasification is the results of the interaction among minerals and phase changes with the temperature increases under reducing atmosphere.

To investigate fusibility characteristics of slag from Jincheng Anthracite (JC) pressurized ash agglomerate fluidized bed (AFB) gasification of Jincheng Anthracite (JC), the slag samples were examined by an ash fusion temperature (AFT) analyzer, scanning electron microscope (SEM), and X-ray diffraction (XRD). The results show that the AFTs of three kinds of slag are lower than that of JC greatly, and the AFTs of three kinds of slag decrease from the slag formed that on the central tube (SC) to distribution plate (SD) to inner face (SI), as a result of the increase of total base content and the differences in their mineral compositions accordingly. Not all slag during AFB gasification are composed of molten mineral matters. This can be explained that the phenomena that the slag formation during fluidized-bed gasification when the operating temperature is below the AFTs of coal.

The sintering temperature of coal ashes plays a great important role in the design and operation of fluidized-bed gasifier. The sintering temperatures (Ts) of Huolinhe lignite (HLH) ashes under different atmospheres and pressures were tested by self-made pressure-difference measuring system. The results show that the Ts under reducing atmosphere (H2, CO or the mixture of 50% CO and H2,volume ratio) are lower than those of under oxidizing atmosphere (O2, CO2, N2). The Ts of HLH ashes decrease with the pressure increase, it changes slightly under low pressure, and decrease clearly under 0.7~1.0 MPa, after that, decrease slightly again with the pressure increase further.

Fusion characteristics of ash residues from Xiaolongtan lignite pressurized fluidized-bed gasification were investigated with ash fusion point detector and sintering temperature analyzer. The results show that the sintering temperature (Ts) and ash fusion temperature (AFT) of three ashes residues decrease from gangue ashes to agglomerate to slag, which result from the differences of mineral type and content in three ash residues, and the decrease of the total basic constituents increases the AFT. The formations of three ash residues during gasification are the interactions among mineral matter and their transformations under high temperature.