(181b) An On-Site Process for Producing High Reactivity Calcium-Based Sorbents for Acid Gas Removal From Combustion Flue Gases

Based on a US Energy Information Administration 2009 report, approximately 45% of electricity in the U.S is generated from coal-fired power plants. Thus, controlling the emissions of gaseous pollutants, such as acid gases, mercury, and other air toxics in flue gas is an important concern. Sorbents are widely used to remove some of these pollutants by injection into the flue gas. Calcium-based sorbents such as limestone, lime, and hydrated lime have been most commonly used in the removal of acid gases, such as SO2 and SO3, as well as metal compounds such as selenium and arsenic. However, the process by which hydrated lime or lime, in particular, is produced is energy intensive, making these sorbents relatively expensive.

EPRI and University of Illinois at Urbana-Champaign have developed a patented technology, sorbent activation process (SAP), for on-site production of various sorbents that can be directly injected into coal combustion flue gas to capture gaseous and vapor-phase pollutants. A bench-scale SAP was used to obtain process engineering and scale-up data and a prototype unit was recently demonstrated at two utility sites for producing low-cost activated carbon (AC) to remove vapor-phase mercury from power plant flue gas. The properties and mercury removal performance of ACs prepared in the SAP were comparable to those of the commercial ACs. The SAP concept is currently being tested for producing high reactivity calcium-based sorbents to remove acid gases from combustion gases. In this paper a description of the SAP and a summary of recent data related to the properties and reactivity of calcium-based sorbents prepared in the bench-scale SAP unit will be presented. The advantages of the SAP unit over conventional processes for sorbent production in terms of energy efficiency and cost savings will also be discussed.