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Pulverized Japanese bituminous coal (Taiheiyo coal) samples with diameter ranges of 38−75 μm and 180−250 μm were gasified with high-pressure steam in the presence of Ca-based CO2 sorbents. The experiments were carried out at 873 and 973 K and at holding times ranging from 0 to 120 min using a laboratory-scale fixed-bed reactor, and the solid−solid reaction between the Ca-based sorbents and the coal-included minerals during the steam gasification was investigated. Local scanning electron microscopy−energy-dispersive X-ray analysis of the solid residues obtained under different conditions showed that some constituents of the coal-included minerals, such as Si and Al, were contained in the sorbent particles. The solid−solid interaction between the Ca-based sorbents and coal-included minerals became significant at the higher temperature and at longer holding periods. This interaction will locally decrease the CO2 sorption ability of the sorbents. However, when a holding time of less than 10 min was employed, ...

Deactivation of Ca-based sorbents by coal-derived minerals during multicycle CO2 sorption reactions at elevated temperature and pressure was investigated using a laboratory-scale horizontal-tube re...

Pulverized Taiheiyo coal (Japanese subbituminous coal) was gasified with steam in the presence of CO2 sorbent (Ca(OH)2) under relatively high pressure (approximately 20 MPa; subcritical condition) using a tubing-bomb microreactor (TB reactor). The transient characteristics in the conversion of coal and the formation of gaseous products during the gasification were investigated. During initial heating period, 40–50 wt.% of the coal initially loaded was rapidly converted to gas or tar. In the presence of Ca(OH)2, the yield of gaseous products was apparently increased owing to the catalytic effects of Ca(OH)2 on coal gasification. No CO2 was observed in the produced gas at any soaking time in the gasification with Ca(OH)2, suggesting that CO2 sorption by Ca(OH)2 took place effectively under high-pressure conditions. A rigid agglomeration of char and CO2 sorbent was observed at relatively high temperature, which is attributed to the formation of melts of the CO2 sorbent.

In an effort to develop a novel hydrogen production process in which coal is gasified with high-pressure steam in the presence of CO2 sorbents, the fundamental CO2 sorption characteristics of Ca-based sorbents during repetitive carbonation−calcination reactions at different pressures were investigated using a conventional TG/DTA analyzer and a laboratory-scale horizontal-tube reactor. The results revealed that, as a result of sintering and crystal growth, Ca-based sorbents were significantly deactivated by high-temperature calcination treatment. As a consequence, the CO2 uptake capacity of the sorbents decreased with cycle number under both atmospheric and pressurized conditions. An intermediate hydration treatment was found to enhance the reactivity and durability of the sorbents for multicycle CO2 sorption. Because of the presence of eutectics in the CaO−Ca(OH)2−CaCO3 ternary system, the formation of sorbent melts was observed in repetitive calcination−hydration−carbonation reactions at elevated pressur...