Coal Gasification Using the ZnO/Zn Redox System

Abstract

A two-step thermochemical process is proposed for converting coal to high-quality synthesis gas. In the first, high temperature, endothermic step, coal is reacted with zinc oxide to form metallic zinc and an H2−CO gas mixture. In the second, low temperature, exothermic step, zinc is used for splitting water and producing hydrogen and zinc oxide. The hydrogen is employed to enrich and adjust the synthesis gas mixture obtained in the first step, while the zinc oxide is recycled to the first step. Experimental studies have shown a more effective chemical conversion obtained via the proposed two-step scheme as compared to that obtained via the conventional single-step direct steam gasification. CO formation was more favorable with the coal−ZnO redox reaction than with the coal−H2O reaction in the 1173−1373 K temperature range. This highly endothermic reaction could be conducted using concentrated solar radiation as the energy source of high-temperature process heat, allowing for a combined utilization of coal and solar energy, and consequently for a significant reduction of the CO2 emissions derived from the combustion of coal.

Behavior of Chars from Bursa Mustafa Kemal Paşa Alpagut and Balıkesir Dursunbey Çakirca Lignite (Turkey) during Non-catalytic and Catalytic Gasification

“…The results show that reactivities of non-catalytic gasification of chars are lower than those of catalytic gasification. Catalysts can improve the kinetics and chemical conversion and reduce the operating temperature requirements (Tsuji et al, 1996). The presence of sodium carbonate accelerates the gasification and ignition processes and leads to the more reactive chars than chars which contain no sodium carbonate.…”

Hydrogen Production Technologies From Solar Thermal Energy

“…The first step corresponds to the solar carbothermal reduction of metal oxides using carbonaceous materials such as coal, coke or NG as reducing agents [28][29][30][31][32][33]:…”

“…Using NG as a reducing agent combines in a single process the reduction of metal oxides with the NG reforming in the absence of catalysts for the co-production of metals and syngas with an H 2 /CO mole ratio of two, which is especially suitable for synthesizing methanol. Ni, Zn) for either methane reforming or coal gasification was investigated [30][31][32][33]. Concerning the combined ZnO reduction and CH 4 reforming process, Zn yields approaching 90% were reported at 930-1330°C in a 5 kW volumetric gas-particle vortex-flow solar reactor based on the direct irradiation of ZnOCCH 4 [29].…”

Catalytic Gasification of Coal Using Eutectic Salt Mixtures

“…The temperature programmed desorption (TPD) spectra and x -ray diffraction (XRD) also clarified that the active species is highly dispersed iron metal and the deactivated species are sintered iron and highly oxidized iron. Tsujiet et al [26] studied the coal gasification by using the ZnO/Zn redox system. A more effective chemical conversion was obtained via a proposed two-step scheme as compared to that obtained via the conventional singlestep direct steam gasification.…”