Inhibition and elimination of carbon deposition in dry gas desulfurization process under oxy-fuel IGCC derived coal gas environment

• Dry gas desulfurization is essential in oxy-fuel IGCC power generation plant.
• The dry gas sulfur removal process is operated by repeating three steps cyclically.
• Carbon deposition is prevented if the exhaust is recirculated to the process.
• Carbon deposition effect is limited while exhaust is not available in the plant.
• Regeneration eliminates the amount of deposited carbon to sufficiently low level.

Oxy-fuel IGCC is a concept of new coal fueled power generation with CO2 capture capability without large penalty on thermal efficiency. It is estimated that thermal efficiency will attain 44% at lower heating value, LHV along with 99% CO2 capture capability. An imperative issue to be solved to realize this concept is to reconcile pre-combustion sulfur removal and retaining the inorganic gas composition of the coal derived gas. Although introduction of dry gas sulfur removal is desired to protect gas turbine from corrosion and to preserve the gas composition, the sulfur removal sorbent containing zinc ferrite installed in the process may suffer from the severe side reaction of carbon deposition. Although it was found that mixing the coal gas with the circulating exhaust in the plant would effectively prevent the carbon deposition in the process, exhaust will not be available until gas turbine comes into normal operation after the plant start-up.The amount of deposited carbon was evaluated and its behavior was examined during the reduction and succeeding regeneration steps performed under expected starting up condition of the plant, which is severe condition for carbon deposition. While carbon deposition occurs during reduction step under start-up conditions, the deposit can be released as carbon dioxide during succeeding regeneration step of scheduled duration. The deposited carbon totalling 0.8 wt% as maximum can be eliminated by regeneration to sufficiently low level below 0.03 wt% for the range of expected operating conditions. The carbon deposition may not affect the desulfurization performance of the zinc ferrite sorbent for the expected condition range at plant start-up. It was confirmed that the carbon deposition and elimination from the sorbent would be adequate measure for operating the dry gas purification process in the oxy-fuel IGCC power generation plant.