Study of Calcium-Based Sorbents for High-Temperature H2S Removal. 3. Comparison of Calcium-Based Sorbents for Coal Gas Desulfurization

Abstract

H2S sorption by 18-35 mesh particles (average mass radius of 0.40 mm) of three different calcium-based sorbents (limestone, CaC03; dolomitic limestone, dolomite, MgC03-CaC03) was tested under simulated coal gas in a differential tube reactor.Two fundamentally different behaviors were observed. Above the calcination temperature of CaC03, complete conversion of CaC03 to C a s can be achieved with all three sorbents; the reaction rate increases as the magnesium-to-calcium ratio increases in the sorbent and the reaction rate is controlled by the diffusion of H2S through the Cas product layer and by the kinetics of the calcination of CaC03 to CaO. However, below the calcination temperature of CaC03 (about 900 "C under 1 bar of C o d , less than 20% of the CaC03 in limestone can be converted to C a s compared t o 100% in dolomite. For the dolomitic limestone, all the calcium atoms associated with the dolomite regions can be converted to C a s whereas only 20% of those associated with the limestone regions can be converted. Above 710 "C, the sulfidation rate of dolomite and dolomitic limestone is controlled by the diffusion of H2S through the product layer. Below 710 "C, the kinetics of calcination of MgC03 as well as the rate of the chemical reaction between CaC03 and H2S become the limiting steps in the overall reaction kinetics.

Design of Entrained-Flow and Moving-, Packed-, and Fluidized-Bed Sorption Systems: Grain-Model Kinetics for Hot Coal-Gas Desulfurization with Limestone

“…It has been established by Fenouil and Lynn (1995) that lime (CaO), or limestone (CaCO 3 ) under specific conditions, can be a suitable high-temperature sorbent for H 2 S in coal gas through the following reactions:…”

“…We will make use of the physical and kinetic data obtained by Fenouil and Lynn (1995) as well as those from Borgwardt et al (1984) to estimate the desulfurization performances of these calcium-based sorbents. Most of our attention will be focused on reaction (1a), since even millimeter-sized particles of CaO can be completely and rapidly converted to CaS.…”

Regenerative Copper–Alumina H2S Sorbent for Hot Gas Cleaning through Chemical Swing Adsorption

“…Candidate sulfur sorbents have been evaluated for several decades, and the selected materials are often oxides made from alkaline earth (calcium, strontium, and barium) or transition metals (vanadium, manganese, iron, cobalt, nickel, copper, and zinc) or combinations of several of these elements. − Both unsupported and supported sorbents have been studied, and supported sorbents tend to perform better because of larger surface area and chemical and mechanical stability. RTI International has developed and patented a state of the art permanent H 2 S trap (RTI-3) based on ZnO supported by alumina .…”

Hot Gas Clean‐Up with Dolomites: Effect of Gas Composition on Sulfur Removal Activity

“…Unreactive MgO in the matrix hinders sintering of CaO and CaS, and facilitates gas diffusion within the solid. Consequently, dolomite has a higher H 2 S removal efficiency than limestone . However, due to thermodynamic constraints, the H 2 S removal efficiencies of calcium containing sorbents are about 90 % under typical coal gasification conditions, resulting in residual H 2 S levels of 100 ppmv (0.1 dm 3 /m 3 ) or greater.…”

“…Consequently, dolomite has a higher H 2 S removal efficiency than limestone. [1,4,[10][11][12] However, due to thermodynamic constraints, the H 2 S removal efficiencies of calcium containing sorbents are about 90 % under typical coal gasification conditions, resulting in residual H 2 S levels of 100 ppmv (0.1 dm 3 /m 3 ) or greater. Therefore, these sorbents are mostly preferred for bulk H 2 S removal and an additional downstream guard bed of proper sorbent is needed for further sulfur polishing.…”