SORBENT AND AMMONIA INJECTION AT ECONOMIZER TEMPERATURES UPSTREAM OF A HIGH-TEMPERATURE BAGHOUSE

The current technology of choice—world–wide—for post–combustion NOx control is selective catalytic reduction (SCR) with ammonia. The application of SCR to coal–fired units has proven to be somewhat more difficult than its application to natural gas and oil–fired units due to SO2 poisoning of the catalyst, catalytic oxidation of SO2 to SO3, and erosion and fouling of the catalyst by fly ash [1]. These problems could be potentially diminished if SO2 and particulate removal systems were placed upstream of the SCR reactor. However, this is not easily accomplished since SCR systems operate best in the temperature range of 600°F–800°F (315°C–425°C). Several SCR installations in Europe employ conventional flue gas desulfurization (FGD) and particulate control upstream of flue gas reheat and SCR. However, the flue gas reheat typically imposes a 1%–2% energy penalty [2]. Several recent technical developments now offer a technology whereby these limitations of SCR for coal applications can be alleviated. These technical developments are in the areas of high temperature filtration, improved SCR catalysts, and advances in sorbent injection. These advances have been incorporated into a patented process known as the SOxNOxRox Box™ (SNRB) process. Briefly, this process consists of a “hot” baghouse employing woven ceramic fabric bags, a zeolite SCR catalyst incorporated into the baghouse, and the injection of either calcium–or sodium–based sorbent upstream of the baghouse (see Figure 1). This paper deals with the status and development of the SNRB process, including some results from recently completed pilot–plant tests performed under a contract with the Ohio Coal Development Office (OCDO). Copyright © 1990 American Institute of Chemical Engineers