Yasuaki Ueki

本研究ではNi-YSZのアノード極を持つSOFCにタール模擬物質を混合した燃料ガスを供給し，SOFCの劣化挙動を調査した。バイオマスガス化研究において典型的なタール構成物質とされているトルエンを3.1％水蒸気含有水素に添加した。発電特性を考察するため，トルエン添加濃度を0 mg/Nm³から1900 mg/Nm³まで変化させて定電流モードにて約30 時間の発電実験を実施した。また，開放端でのインピーダンス測定を行うことによりSOFC内部抵抗を評価した。トルエン無添加実験ではSOFCは良好な状態及び安定した発電が持続したのに対して，200 mA/cm²の電流を印加すると380 mg/ Nm³の低濃度トルエン添加においても電圧の降下が見られた。さらにトルエン濃度が高くなると電圧降下も大きくなる傾向があった。トルエン濃度1900 mg/Nm³の場合には，電圧降下が深刻する一方でアノード極表面に炭素析出した様子も確認できた。ただし，アノード極構造に重篤なダメージがない限り，発電性能は部分的に回復した。

Integrated coal gasification combined cycle systems are expected to raise the power generation efficiency of coal-fired power plants. In Japan, coal gasifiers are required to treat various kinds of coal imported from many countries because almost all of the coal is imported from abroad. In an entrained-bed coal gasifier, the slag-tapping hole must be heated adequately to discharge the molten slag. Thus, a heating technique has been developed to heat the hole from below, without using any auxiliary fuels. The technique is to burn the syngas, which descends through the hole at high temperature, by supplying oxygen from a pair of nozzles facing each other installed just below the hole. In this study, a design procedure to heat the hole by those nozzles was developed through thermal and flow simulations and actual gasification tests in a 150 t/d entrained-bed coal gasifier of pilot scale.

The effective utilization of sub-bituminous coals should be extended as an energy source for power generation because of their low cost and long minable years. However, sub-bituminous coal may undergo spontaneous combustion owing to high reactivity with oxygen in low-temperature air compared with bituminous coal. Therefore, the objective of this study is to elucidate the low-temperature oxidation behaviors of sub-bituminous coal. In particular, transition from oxygen chemisorption to low-temperature oxidation of sub-bituminous coal has been experimentally examined in detail. Isothermal gravimetric analyses are conducted for several bituminous and sub-bituminous coal samples at temperatures varying between 356 K and 476 K in oxygen-enriched air. The chemical compositions of emission gas are continuously monitored under low-temperature oxidation conditions. The changes in the chemical structure of the coals are analyzed using Fourier transform infrared (FTIR) spectrometry. The experimental results show that the mass of all tested coals, including those of bituminous and sub-bituminous coals, increases at temperatures below 426 K as a result of oxygen chemisorption. At 476 K, the mass of sub-bituminous coal increases slightly with low H₂ and CO₂ emissions at the beginning and subsequently decreases with high CO and CO₂ emissions. This mass change indicates that the transition from oxygen chemisorption to low-temperature oxidation occurs during this period. In addition, the FTIR spectra of sub-bituminous coals show the existence of carbonyl groups even in raw coal samples. These carbonyl groups are considered to contribute to the formation of CO₂ and H₂ from the beginning of reactions, triggering the transition from oxygen chemisorption to low-temperature oxidation.