Recovery of Sulfur from Flue Gases Using a Copper Oxide Absorbent

Abstract

The body of information presented in this paper is directed to those individuals concerned with development of methods to remove SO₂ from stack gases. The manuscript describes a dry, solid absorbent prepared by impregnating copper salts into a 1/16-inch alumina catalyst support. A preliminary process design and economic evaluation for power plant utilization are included. Previous pilot-scale and economic studies of an SO₂ removal process using a mixed metal oxide, alkalized alumina, identified major disadvantages of the absorbent. They were rapid degradation of the solid, excessive consumption of reducing gas, and high temperature difference between absorption and regeneration steps. Thermodynamic calculations and commercial availability of a strong alumina catalyst support suggested that the disadvantages would be minimized for an absorbent prepared by impregnation of copper salts into the support. A number of such absorbents were prepared and their properties determined experimentally. Absorption of SO₂ from flue gas occurs readily at 300°C or above and is most rapid when the support contains 4 to 6 wt % copper. While thermal regeneration is ineffective, reductive regeneration can be accomplished using H₂ or CH₄. Use of CH₄ is preferred since both gas consumption and residual sulfur level are lower. Physical and chemical properties remain stable after many cycles of absorption and regeneration. If the process is designed to be incorporated in a typical power plant, SO₂ is removed at 300°C in a fluid bed, where the solids are contained for 1 hour. The absorbent is then heated, and regeneration is accomplished at 425°C with CH₄ in a gravitating-bed reactor. The SO₂ evolved during regeneration is converted to concentrated sulfuric acid. The cost before byproduct credit is 1.62 mills per kilowatt-hour of power produced. If the power plant is modified so that absorption can be carried out at 425°C, costs may be significantly reduced.