Configurations and methods for effluent gas treatment

#The field of the invention is treatment of effluent gases, and especially removal of sulfur dioxide from oxygen-containing gases.

#Currently known processes for sulfur dioxide from oxygen-containing gases typically employ caustic processes (e.g., Amerex, Belco, Croll-Reynolds, Envirochem, Turbosonic), or non-caustic processes (e.g., Cansolv, ClausMaster, CrystaTech). While the capital investment for a caustic process is generally low, operating and disposal costs may be prohibitively expensive. On the other hand, all or almost all of the currently known non-caustic processes are more capital intensive and are frequently not commercially proven.

#For example, sulfur dioxide is removed in some of the known configurations using a caustic process in which gaseous sulfur compounds are converted into soluble sulfite/sulfate compounds. Typical examples of such configurations are shown in U.S. Pat. Nos. 3,719,742 to Terrana et al. and 3,790,660 to Earl et al. However, most of such configurations have a relatively high stripping steam requirement and are therefore economically less attractive. Other known caustic processes are described, for example, in U.S. Pat. No. 3,920,794 to La Mantia et al. Here, NaOH and Na2CO3 scrubbing solutions remove SO2 from gas streams. After the adsorption or scrubbing step, an oxidation step is performed to convert sulfites to sulfates by addition of catalytically effective metals (e.g., Fe, Cu, Co, Mn, and/or Ni). While such oxidation is relatively simple and effective, salts need to be added, and a secondary oxidation step may be required, especially where the level of sulfites in the scrubbing solution after adsorption of SO2 is relatively high.

#FIG. 1 is an exemplary configuration of a desulfuration plant in which the second catalytic reactor is operated as a Claus reactor.

#FIG. 2 is an exemplary configuration of a desulfuration plant in which the second catalytic reactor is operated as a Claus reactor, in which inert gas is removed via an absorber, and in which recycle gas is concentrated via an absorber/regenerator.

#FIG. 3 is an exemplary configuration of a desulfuration plant in which the second catalytic reactor is operated as a catalytic direct reduction reactor.

#The inventors have discovered that sulfur dioxide can be effectively removed from oxygen-containing acid gases in a plant configuration in which the oxygen is first catalytically removed (i.e., consumed in a catalyzed reaction) using hydrogen sulfide, and in which sulfur is produced from one portion of the oxygen-depleted acid gas, and hydrogen sulfide is formed from another portion of the oxygen-depleted acid gas (which is preferably used as a recycle stream in the oxygen removal reaction).

#Viewed from another perspective, elemental sulfur is catalytically produced in a Claus reaction from sulfur dioxide of the acid gas using a hydrogen sulfide recycle stream while at the same time removing oxygen. The so formed elemental sulfur is then removed in a sulfur condenser, and a first portion of the remaining sulfur dioxide is catalytically reduced to hydrogen sulfide (e.g., using hydrogen or carbon monoxide) to form the hydrogen sulfide recycle stream. A second portion of the remaining sulfur dioxide is catalytically converted to hydrogen sulfide, which may be reacted to additional elemental sulfur in a Claus reaction or direct reduction reaction.

#Therefore, the inventors generally contemplate a plant that includes a first catalytic reactor that receives a hydrogen sulfide recycle stream and an oxygen-containing acid gas comprising sulfur dioxide, wherein the first catalytic reactor is configured to catalytically consume the oxygen using the hydrogen sulfide recycle stream to thereby form an oxygen depleted hydrogen sulfide/sulfur dioxide enriched stream. A second catalytic reactor is fluidly coupled to the first catalytic reactor and configured to produce elemental sulfur from a first portion of the oxygen depleted hydrogen sulfide/sulfur dioxide enriched stream, while a third catalytic reactor is fluidly coupled to the first and optionally second catalytic reactor and configured to produce the hydrogen sulfide recycle stream from a second portion of the oxygen depleted hydrogen sulfide/sulfur dioxide enriched stream. The term “oxygen depleted” as used herein refers to an oxygen content of less than 2 vol %, more typically less than 1 vol %, and most typically less than 0.01 vol %.