Development and pilot plant evaluation of silica-enhanced lime sorbents for dry flue gas desulfurization

Abstract

EPA’s efforts to develop low cost, retrofitable flue gas cleaning technology include the development of highly reactive sorbents. Recent work addressing lime enhancement and testing at the bench-scale followed by evaluation of the more promising sorbents in a pilot plant are discussed here.The conversion of Ca(OH)2with SO2increased several-fold compared with Ca(OH)2alone when Ca(OH)2was slurrled with fly ash first and later exposed to SO2in a laboratory packed bed reactor. Ca(OH)2enhancement increased with the increased fly ash amount. Dlatomaceous earths were very effective reactivity promoters of lime-based sorbents. Differential scanning calorimetry of the promoted sorbents revealed the formation of a new phase (calcium silicate hydrates) after hydration, which may be the basis for the observed Improved SO2capture.Fly ash/lime and diatomaceous earth/lime sorbents were tested in a 100 m3h pilot facility incorporating a gas humidifier, a sorbent duct injection system, and a baghouse. The inlet SO2concentration range was 1000-2500 ppm. With once-through dry sorbent injection into the humidified flue gas [approach to saturation 10–20°C (18–36°F) in the baghouse], the total SO2removal ranged from 50 to 90 percent for a stoichiometric ratio of 1 to 2. Recycling the collected solids resulted in a total lime utilization exceeding 80–90 percent. Increased lime utilization was also investigated by the use of additives. © 1988 Taylor & Francis Group, LLC.