Development of reusable mercury sorbents for an oxy-fuel IGCC power generation system

Abstract

Gaseous elemental mercury (Hg0) removal tests, using copper-based sorbents (CBS) developed in-house, were performed in a laboratory scale fixed-bed reactor. The aim was to find potential candidate sorbents to use in a dry syngas purification process plant. The dry purification process is under development for oxy-fuel integrated gasification combined cycle (IGCC) power generation with an efficient carbon dioxide separation function. The performance of CBS was evaluated as a function of two major characteristics. First, Hg0 removal performance of the CBS is improved by pre-sulfidation. Second, Hg0 removal performance of the spent CBS is recovered through moderate heating under diluted O2 conditions. A honeycomb type sorbent was prepared by impregnating raw material of the CBS onto the honeycomb-shaped support. Since copper sulfide will effectively capture Hg0 in a reducing gas atmosphere, the CBS honeycomb was initially pre-sulfurized by H2S diluted with N2 at 120 °C in a fixed-bed reactor until complete breakthrough of H2S. The simulated syngas from the oxy-fuel IGCC was fed into the reactor with conditions set at 140 °C and 0.98 MPa, where the Hg0 in the syngas was reduced to below 1.0 µg/m3N by the CBS honeycomb. The spent CBS honeycomb was regenerated by introducing 1 vol-% of O2 diluted with N2 at 280 °C. The sequential operation of pre-sulfidation, mercury removal, and regeneration steps was performed cyclically three times, during which the CBS honeycomb maintained a satisfying Hg0 removal performance. These results revealed that the A-CBS honeycomb is a potential candidate for the dry mercury removal process in the Oxy-fuel IGCC power generation plant.