Low‐temperature carbon‐based process for flue‐gas cleanup

Abstract

AbstractA low‐temperature process employing activated carbon‐based catalysts and operating downstream of the electrostatic precipitator (ESP) is being developed jointly by Research Triangle Institute (RTI) and the University of Waterloo (Waterloo). The RTI‐Waterloo process is capable of removing more than 95% SO2 and 75% NOx from coal combustion flue gas. The flue gas leaving the ESP is first cooled to approximately 100°C. The SO2 is then catalytically oxidized to SO3 which is removed as medium‐strength sulfuric acid in a series of periodically flushed trickle‐bed reactors containing an activated carbon‐based catalyst. The SO2‐free gas is then reheated to approximately 150°C and NH3 is injected into the gas stream. It is then passed over a fixed bed of a different promoted activated carbon‐based catalyst to reduce the NOx to N2 and H2O. The clean flue gas is then vented to the stack. The feasibility of the process has been demonstrated in laboratory‐scale experiments using simulated flue gas. Catalysts have been identified which gave the required performance for SO2 and NOx removal with less than 25 ppm NH3 slip. Potential for producing greater than 10N H2SO4 by periodically flushing the SO2 removal reactor was also demonstrated. Cost for the RTI‐Waterloo process was competitive with conventional selective catalytic reduction (SCR)‐flue gas desulfurization (FGD) process and other emerging combined SO2/NOx removal processes.