Cross-effects and total gas clean-up system lay-out Gas clean-up for power plants and waste incinerators Effect of emission control on emissions and emission control for other species see: www.hut.fi/~rzevenho rzevenho/gasbook
HELSINKI UNIVERSITY OF TECHNOLOGY Pulverised coal combustion and gas clean-up
Power plants and engines Hot fi cold or furnace fi stack Gas firing low NOx burners, flue gas recycling, water injection, SNCR, SCR Oil firing low NOx burners, flue gas recycling, water injection, SNCR, SCR, wet or dry FGD Pulverised coal / lignite / peat firing Pulverised coal / lignite / peat firing low NOx methods, furnace sorbent injection SNCR, hot-side ESP, SCR, dry sorbent injection, cold-side ESP, baghouse filter.
Fluidised bed furnaces and clean coal technology Hot fi cold or furnace fi stack AFBC (bubbling and circulating), PFBC (bubbling) Low NOx methods, in situ sulphur capture with calcium based sorbents, high temperature cyclone, SNCR, expansion turbine (PFBC), SCR, low temperature filter or ESP IGCC for coal or biomass Before gas turbine: in situ sulphur capture with calcium based sorbents and tar cracking, hot gas filter and alkali removal, halogen removal, COS H 2 S, H 2 S removal, NH 3 removal
An MSW incineration process line (Germany) Furnace and boiler Temperature (C) Flue gas clean-up Temperature (C) 1 Primary combustion chamber 260-800 4 Electrostatic precipitator 180-300 2 Secondary combustion chamber 800-1200 5 HCl scrubber (ph ~ 1) 60-70 3 Heat recovery boiler 600-800 6 SO2 scrubber (ph ~ 6) 60-70 7 Re-heater 350-400 8 SCR DeNOx 300-400 9 Active coke bed 100-150
Waste incinerators and cement plants Hot fi cold or furnace fi stack Waste incineration: : cold-side ESP or filter, dry sorbent injection + filter, acid wet scrubber for HCl,, wet scrubber for SO 2, SCR for NOx,, activated carbon bed(s) for VOCs/PAHs PAHs,, dioxins/furans and trace elements Cement plant Usually only ESP or baghouse filters
Sulphur species emission control : effects on other pollutants ] Low-sulphur fly ash problematic for ESP ] Dry scrubbing by calcium sorbent injection removes also HCl,, HF, HBr and also some trace elements ] SO 2 in flue gases reduces dioxins/furans formation ] In situ calcium-based sorbents in FBC reduce NO emissions but may increase N 2 O emissions ] For FB biomass gasifiers, in situ dolomite for sulphur capture may lower tar levels ] Low SO 2 concentrations in SCR for DeNOx give less problems of NH 4 HSO 4 / (NH 4 ) 2 SO 4
Nitrogen species emission control : effect on other pollutants ] SCR for DeNOx may give an NH 3 slip ] SCR catalyst catalyses SO 2 fi SO 3, Hg fi Hg 2+ ] SNCR with urea may give N 2 O emissions ] Deposits of NH 4 HSO 4 / (NH 4 ) 2 SO 4 after SCR if sulphur concentrations are too high ] NO is used in CRT catalyst/filter for diesel exhaust soot ] NOx plays an important role in ground-level ozone formation ] Low NOx methods may increase CO and carbon-in-ash ] Dioxin/furan concentrations are reduced by SCR
Particulate emission control : effect on other pollutants ] Hot-side ESPs protect SCR catalysts for DeNOx ] Fly ash may adsorb trace elements and alkali ] Fly ash in wet FGD scrubbers may cause deposit formation or low quality FGD gypsum ] A cyclone before an ESP or filter may save costs ] Filters used with sorbent duct injection give particulate and gaseous species control
VOCs and PAHs emission control : effect on other pollutants ] VOC emissions control reduces ground-level ozone formation ] VOCs and PAHs may compete with trace elements (mercury!) for adsorption on activated carbon ] PAHs may foul or poison, i.e. deactivate SCR or VOC oxidation catalysts ] VOCs and PAHs play a role in dioxin/furan formation
Halogens and dioxins/furans emission control : effect on other pollutants ] HCl and CL 2 control may reduce dioxin/furan formation ] HF may lead to AlF x deposit formation in wet FGD ] HCl,, HF, HBr will affect the ph and thereby the performance of wet FGD ] Chlorine influences volatile trace metals (mercury!) and alkali levels ] Chlorine and other halogens hinder CO burnout ] HF attacks silicates, for example in filter bags
Trace elements and alkali emission control : effect other pollutants ] Activated carbons adsorb many other gaseous species ] Trace metals such as Cr and Mn may bind mercury, Hg ] Nickel is an active tar cracking catalyst ] Vanadium (V 2 O 5 ) catalyses SO 2 fi SO catalyst SO 3, and is SCR ] Na 2 S 4 for mercury trapping may give an H 2 S slip ] Some metallic trace element reduce soot formation