OCR Text |
Show the development of S0X in the combustion process. The amount of fuel bound sulfur can be controlled to reduce the emissions of S0X. However, SO2 is stable at flame temperature and cannot be controlled in the combustion process. SO3, on the other hand, is stable at ambient temperature and can be controlled in the combustion process by the use of chemicals and by limiting the amount of excess oxygen used in the combustion of the fuel. As chemical treatment requires a substantial initial investment for equipment, plus an ongoing operating expense, and as there is also some concern that the chemicals might contribute to the solids burden, it was determined that the best possible control over SO3 in combustion was by reducing the base emission through low oxygen combustion. The problem is that SO3 is a hygroscopic substance and will react with moisture to form sulfuric acid, causing corrosion in the cooler sections of the process heater, outlet ducting, and air preheater. Furthermore, sulfuric acid, being a condensate rather than a gas, will form when the relative humidity is far below saturation. This, of course, also causes an acid plume that, when combined with particulate, creates acid fallout or acid smut, all of which are regulated under existing environmental codes. Figure 15 outlines SO3 versus O2 data points collected during operational tests. Reducing the amount of excess oxygen dramatically reduces SO3 emissions. Although the tests were performed using 3.02% sulfur fuel oil, sufficient data has been previously collected which indicate emissions reductions 12-36 |