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Q: I have an incineration system in which we incinerate liquid waste & Aq. We use a spray quencher with 5-1,000 ppm tds water and have venturi scrubber. We are suffering by high emissions of spm App 400-500 ppm. During a study, we found 20,000-100,000 tds in the recirculation tank (RCT) and in the stack condensate, we have nearly the same tds. How do we reduce spms from the stack if it is due to tds carrying by flue gas?
A: My friend Tom McGowan recommended that they institute a blowdown on the recirculation tank to keep the water at under 5% total solids, both suspended and dissolved, and that they check their demister (if they don't have one they need one) for holes and short circuiting, and that they may want to institute a small continuous was on the demister (if it is a mesh screen - which is the best one to use in his opinion) to insure that solids buildup and fouling do not occur. I can attest to the fact that a mesh type demister is better than a chevron type, but a good bit depends upon the size and efficiencies of the design. Without more information we cannot provide much more assistance. Tom McGowan runs TMTS Associates in Atlanta, and has been a contributor to Perry's CHE Handbook.
If I understand the shorthand in the message, it sounds like the recirculation tank is accumulating solids which need to be reduced by some form of chemical treatment or precipitation. I assume the spm is small particulate matter which I believe could be caused by the high solids in the recirculation tank. At the indicated levels, he is running 1-2% in the recirc tank, and at those levels, it does not take much to flash off solids into the gas. I'd analyze the tds (complete water analysis including hardness, pH alkalinity, metals and other cations and anions. It sounds like the water may be very easily treated by chemical precipitation on a recirculation stream to keep the total dissolved solids (tds) down to a few thousand ppm maximum. This will be a bit of a trial and error solution. The other possiblity is to arrange a bleed feed to the recirc tank to lower the solids. Even a relatively small bleed should do the job nicely.
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