United States Environmental Protection Agency Air and Energy Engineering Research Laboratory Research Triangle Park, NC 27711 Research and Development EPA/600/SR-93/188 December 1993 EPA Project Summary Evaluation of Simultaneous SO2/NOX Control Technology Kevin R. Bruce and Walter F. Hansen The Clean Air Act Amendments of 1990 (CAAA) have led to accelerated research into novel sulfur dioxide (SO2) and nitrogen oxide (NO) control tech- nologies for coal-fired industrial boil- ers. One of these technologies com- bines sorbent injection and selective non-catalytic reduction for simultaneous SO2/NOx removal. The work presented herein concentrated on characterizing three process operational parameters of this technology: injection tempera- ture, sorbent type, and reductant/pol- lutant stoichiometric ratio. A slurry com- posed of a urea-based solution (NOxOUT A or NOxOUT A+) and various calcium-(Ca-) based sorbents was in- jected at a range of temperatures and reactant/pollutant stoichiometries in a natural-gas-fired, pilot-scale reactor with doped pollutants.. Up to 80% reduction of SO2 and NOx at reactant/pollutant stoichiometric ratios of 2 and 1.5, re- spectively, was achieved. SO2 emission reductions from slurry injection were enhanced moderately when compared with dry sorbent injection methods, pos- sibly caused by sorbent fracturing to smaller, more reactive particles. Emis- sions from ammonia (NH3) slip (unreacted nitrogen-based reducing agent) and nitrous oxide (N2O) forma- tion were reduced in comparison with other published results, while similar NOx reductions were obtained. In- creased carbon monoxide (CO) emis- sions, caused by the decomposition of urea, were moderate. Emissions of CO, NH3, and NO for the enhanced urea solution (NoxOUT A+) were substan- tially less than the levels observed dur- ing urea (NOXOUT A) injection. The in- jection of the urea-based solution en- hanced SO removal, probably because of the formation of (NH^CAfSOJ, H2O. The results of this pilot-scale study have shown high reduction of both SO, and NO. This Project Summary was developed by EPA's Air and Energy Engineering Research Laboratory, Research Tri- angle Park, NC, to announce key find- ings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at back). Introduction The project work reported here was ini- tiated through a Cooperative Research and Development Agreement (CRADA) be- tween EPA and Nalco Fuel Tech, a com- mercial licensor of a urea-based reducing agent injection technology for NOx reduc- tion. Experimental testing of Nalco Fuel Tech's urea-based NOxOUT A and NOXOUT A+ reducing agents for NOx con- trol, in combination with Ca-based sorbent injection for SO2 control, was conducted from June to November 1991. Testing was performed at EPA's Environmental Re- search Center in Research Triangle Park, NC, in a pollutant-doped, natural-gas-fired 50,000 Btu/h (15 kW) furnace. The project scope of work included test- ing furnace sorbent injection of several Ca-based sorbents to remove SO2 from flue gas. The tested sorbents came from a single source of commercially prepared slaked lime [Ca(OH) ], limestone (CaCO3), and quicklime (CaO). A comparison of Printed on Recycled Paper ------- SO2 removal efficiency was made between dry and slurry injection. The effect of CaCO3 sorbent particle size was also stud- ied. Slurry sorbent injection was found to be superior to dry injection for SO2 removal. Dry injection of Ca(OH)2 achieved a maxi- mum of 60% SO removal (at a Ca/S ratio = 2), while the Ca(OH)2 slurry removed 72%. Removal efficiency with Ca(OH) was superior to that with CaCO3 in both dry (43%) and slurry (58%) testing. CaO was tested in slurry form by slaking to form Ca(OH)2 slurry, and compared to the com- mercially prepared Ca(OH)2. The slaked CaO proved identical in its SO2 removal performance to the commercially prepared Ca(OH)2. Both NOXOUT A and NO OUT A+ achieved maximum NOx removal when in- jected at a temperature of about 1,100 °C. Almost no difference in the two reducing agents existed at the optimum tempera- ture; approximately 80% NOx removal was observed for both reducing agents. At tem- peratures higher than the optimum, NOx removal efficiency dropped quickly. At about 1,170°C, the reducing agents be- gan producing NOx, caused probably by high temperature oxidation of the NH3 pro- duced by urea decomposition. At tempera- tures lower than the optimum, NOx re- moval efficiency gradually decreased!! Varying the molar ratb of reducing agent (urea) to baseline NOx, or N/NOx|( showed that increasing N/NO^ to a value of near 2 produced significant improvement in NOx removal. Further N/NOx| increases had little or no effect on removal efficiency. The work mentioned above also en- tailed characterizing NH3, N2O, and CO emissions produced by injecting the re- ducing agent over a range of tempera- tures and N/NOxl. Each reducing agent produced maximum NH3 slip (unreacted nitrogen-based reducing agent) at the lower injection temperatures; around 821 °C, the amount of slip was about 140 ppm for both NOXOUT A and NOXOUT A+. As injection temperature increased, NH3 slip for the NOXOUT A decreased quickly, while slip from NOXOUT A+ dropped off almost completely at around 875 °C. At 900-1,000 °C, slip generated by NOxOUT A gradually decreased to a level of about 60 ppm. Throughout this temperature re- K. Bruce and W. Hansen are with Acurex Environmental Corp., Research Triangle Park, NC 27709. Brian K. Gullett is the EPA Project Officer (see below). The complete report, entitled "Evaluation of Simultaneous SO2/NOx Control Tech- nology," (Order No. PB94-114741/AS; Cost: $27.00; subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Air and Energy Engineering Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 gime, NOXOUT A+ produced negligible NH3 slip (<10 ppm). CO emissions produced by NOxOUT A rose gradually from about 20 ppm at 800 °C to a maximum of 25 ppm at 1,100 °C. NOXOUT A+ produced low CO at 800-1,000 °C (<10 ppm), with a maxi- mum of 50 ppm around 1,100 °C. NO production by NOxOUT A was neg- ligible at lower injection temperatures (ap- proximately 25 ppm), but increased with injection temperature to a maximum of 200 ppm at approximately 1,150 °C, about 42% of the NOx reduced. NOXOUT A+ produced only moderate levelsx of N2O (typically <40 ppm, less than 20% of the NOx reduced) over the entire temperature range. A maximum of about 30 ppm was observed at around 1,150 °C. Aqueous ammonia solution was injected to ensure that these results would be re- producible on other facilities. Available data for NOx removal using aqueous ammonia injection showed comparable results to others' work. These data validated improve- ments shown by this work with both NOXOUT solutions and suggested the ap- plicability of these results to other facilities. 'U.S. Government Printing Office: 1994 — 550-067/60136 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati, OH 45268 Official Business Penalty for Private Use $300 BULK RATE POSTAGE & FEES PAID EPA PERMIT No. G-35 EPA/600/SR-93/188 ------- |