Integrated Hot and Cold Synthesis Gas Clean-Up

摘要

It is generally accepted that gasification of coal is the most promising route for clean utilization of coal for differentapplications. The gasification process converts coal and other feedstocks into synthetic raw gas suitable for differentutilization areas such as production of electricity, value-added chemicals and liquid fuels. However, coal-derivedsynthesis gas contains harmful contaminants which need to be removed. The sulfur removal is a must prior toutilization of the gasification products either as a fuel for gas turbines, gas engines or fuel cells or as a synthesis gasfor Fischer-Tropsch syntesis, ammonia or methanol productions. Hydrogen sulfide and other sulfur compounds cancause corrosion in pipelines thus limit the plant lifetime. Hydrogen sulfide is also a well-known catalyst poison. Forthese reasons, it is necessary to reduce the H_2S concentration around one ppmv level.A semi-pilot scale bubbling bed gasification system equipped with hot and cold synthesis gas (syngas) clean-up unitshas been installed at Energy Institute of TUBITAK MAM. This system has been used for coal derived syngas cleanuppurposes. A pilot scale pressurized bubbling fluidized bed gasification system is also current being developed byTUBITAK MAM. By using a combination of various techniques, we have already been able to we reduced the H_2Scontent of syngas below 1 ppmv level. The ongoing research efforts will be described in this paper with a particularfocus on sulfur compounds removal.High temperature desulfurization performance of dolomite for coal derived syngas was investigated in this study.The results indicated that dolomite can be active in sulfur removal at the temperatures higher than 750°C. However,due to the thermodynamic equilibrium conditions, H_2S clean-up was limited to around 150-200 ppmv in presence ofwater vapor. The presence of water vapor in the dolomite bed seemed to inhibit sulfidation reactions. On the otherhand, the presence of CO_2 in the gas stream did not have a suppressing effect on sulfidation reactions, whereas, ittended to depress the calcination of CaCO_3 to CaO.