Study On Gasification Characteristics And Physicochemical Properties Of Coal Chars Derived From Hydropyrolysis

To produce hydrogen by the steam gasification of the chars resulting from coal hydropyrolysis (Hydro-char), the gasification reactivities and physicochemical properties of various Hydro-chars have been investigated in this thesis, by comparing with the coal chars obtained by the pyrolysis under an inert gas atmosphere (Non-hydro-char). The main contents include three aspects as follows.First, the carbon dioxide and steam gasification experiments were carried out both on a thermogravimetic analyzer (TGA) and on a fixed-bed gasifier using the Hydro-chars and Non-hydro-chars derived from YX and ZD coals. The hydro-chars examined in this part of work were produced by hydropyrolysis using a laboratory pressurized fixed-bed reactor. The hydro-chars were more reactive than the Non-hydro-chars of a close carbon conversion for both coals. Increasing hydrogen pressure firstly enhanced the reactivities of chars, but lately showed a downtrend. The expansion of holding time were adverse to the reactivities of chars. Elevating gasification temperature increased the concentrations of H2 and CO2 but lowered that of CO in the gaseous product. The gas compositions gradually reached the thermodynamic equilibrium as the temperature increased up to 1050℃.Second, the experiments were conducted to steam-gasify the hydro-chars generated by the hydropyrolysis of FG and YN coals in a pilot-scale entrained-bed reactor. XRF, SEM, BET, TG and XRD were applied to examine the physicochemical properties of hydro-chars in comparison with those of Non-hydro-chars. Hydro-chars contained more alkali metals, higher porosities, and more active sites than Non-hydro-chars derived, but the former chars had a smaller BET area and a larger degree of graphitization. Overall, the gasification reactivities of Hydro-chars were better than Non-hydro-chars.Third, a calculation was conducted to estimate the gas yields and gas compositions by the water-slurry gasification of FG and YN in terms of the mass and energy balance with some simplified assumptions. The concentrations of effective gas and the gasification efficiency were obtained under different oxygen-char ratios. The estimation indicated that increasing the oxygen-char mass ratio from 0.80 to 0.92 increased the concentrations of effective gas and decreased the gasification efficiency.