OCR Text |
Show ( - LNB and SCR are in the commercial state of development. In-furnace urea injection is being demonstrated in the United State and Europe on coal and oil fired units/2, 3, 4/. The results of these demonstrations indicate high NOx removal is achieved when an aqueous solution of urea is injected into the boiler at temperatures ranging between 950 - 1150°C. A maj or research program is underway at Ontario Hydro's Combustion Research Facility (CRF), aimed at optimizing the parameters affecting NOx capture and utilization by additive injection and to minimize any detrimental effect on the electrostatic precipitator (ESP). The slip gases are being analyzed for HCN, NH3 and N20. The study is in support of the planned full scale demonstration of the technology at Lakeview TGS. The schematic of the process is shown in Figure 1. An aqueous solution of nitrogen based sorbent (urea, ammonia or ammonium carbonate) is sprayed into the combustion gas via a high pressure twin fluid atomizer at a temperature ranging between 975 to 1250°C. This technique assures good mixing and distribution of the reagent with the gas stream. As the solution is sprayed into the furnace, the water is flash evaporated, the reagents dissociate into amine radical (NH2) and react with the NOx to form nitrogen (N2). The chemistry of NOx reduction by urea and other nitrogen based additives is complex and not fully understood. The overall reaction describing NOx removal by urea is given below: The most important variables affecting NOx reduction by urea are: • Type of atomizer which determine droplet size, reagent penetration, mixing and distribution with the flue gas; • Injection location (temperature and residence time); • Additive addition rate; • Additive concentration; and • Flue gas NOx concentration. The process variables under conditions simulating full scale operation were optimized for maximum NOx capture and utilization using: a medium S US bituminous coal and a high S coal from Nova Scotia. EXPERIMENTAL COMBUSTION RESEARCH FACILITY The study was conducted at Ontario Hydro's Combustion Research Facility (CRF), designed for a maximum coal feed rate of about 20 kg/h US bituminous coal at a firing rate of 640 MJjh (Figure 2). The furnace is a refractory-lined |