Removal of Sulfur from Gasified Coal At or Above 800 °C
EPA Phase I SBIR Contract EP-D-07-027
Coal contains substantial sulfur that, if not captured when burned, can significantly impact human health, which is why SOx emissions are highly regulated. Eltron is developing a novel, proprietary approach for removing sulfur from gasified coal products at gasification temperatures. The approach is based on using sulfide ion conducting metal sulfides. At high temperatures, and under a sulfur partial pressure gradient, the sulfur contained in the feedstream will be selectively separated out. The use of a separation membrane will allow for true hot gas cleanup of sulfur from gasified coal. This will allow the concentration and low-cost capture of the sulfur.
While there are several metal oxides that exhibit oxygen ion conductivity (such as yttria-stabilized zirconia or doped ceria), there are very few materials that exhibit sulfide ion conductivity. However, there is a class of novel, mixed metal sulfides that exhibit sulfide ion conductivity. Ion conductivity is a thermally activated process, ideally suiting these materials to high temperature applications. Like stabilized zirconia and doped ceria, this class of metal sulfides is characterized as solid electrolytes, meaning they are pure ion conductors with little, if any, electronic conductivity. For example, when used as sensors or as solid oxide fuel cell membranes, the solid electrolyte is in contact with electrodes, connecting it to an external circuit for electron transfer. When used as a separation membrane, however, the process can be simplified – if the external circuit is eliminated. This is done by short-circuiting the ion conducting membrane by providing an electronic pathway. The electronic pathway can be built into the membrane by mixing the solid electrolyte with an electronically conducting phase, forming a two-phase composite. Eltron has used this strategy successfully with oxygen separation, and it will be used in this technology for sulfur separation.
Eltron has extensive experience in the area of ion selective ceramic membranes. Eltron has granted license to Air Products allowing them to use our proprietary materials in their ITM Syngas and ITM Oxygen processes. Eltron has a state-of-the-art ceramics processing facility.
We soon will have demonstrated the feasibility of using sulfide ion conducting membranes for hot gas desulfurization. In subsequent research and development, we will move the technology out of the lab and construct a demonstration-scale unit that can be tied to an existing coal gasifier to demonstrate performance in an industrial setting and at an appropriate scale.