Canadian Biomass • September/October 2011 • Page 15

MAXIMUM ENERGY GAIN FROM FLUE GASES With the patented ERCS process (Energy Recovery & Cleaning Systems) for treating ﬂ ue gases from biomass-ﬁ red combustion plants, results like these are possible: • 50% of the boiler thermal output can be recovered • 30% fuel savings can be realized • 20% reduction in investment costs for the heating plant can be achieved. The costs for the integration of new ERCS systems or for retroﬁ tting ERCS systems to existing plants are amortized within two years. Scheuch Inc. 2351 Huron Street, Unit 1 London, Ontario, N5V 0A8, Canada Phone: 519 951-7700 I Fax: 519 951-7711 ofﬁ [email protected] www.scheuch.ca and infeed speeds from a central control room, regulating the fuel flow. Originally a circulating fluidized bed boiler, the furnace was converted to a bubbling bed to reduce erosion from sand circulation and improve biomass combus-tion, says Stock. “They both have a sand bed in the furnace, which is basically your mass of heat. In the circulating style, the sand is actually blown up to the top of the boiler, collected in hoppers, and reinject-ed into the furnace,” he explains. In the bubbling bed, the sand stays in the fur-nace, and air is bubbled upwards through it. “It’s a lot more efficient and there’s a lot less maintenance cost to it,” adds Stock. The sand bed operates at 1750°F (954°C), essentially gasifying the biomass. Rocks, impurities, and slag, which are heavier than sand, fall below the air nozzles at the bottom of the bubbling bed. Periodically, one of three outlets at the bottom of the furnace opens, dropping these items and some of the sand onto a vibrating screen. The sand falls through and is returned to the boiler, whereas the impurities pass to a chute that takes them to a disposal pile outside the boiler room. Wood ash is mixed with a small amount of water to prevent it from becoming air-borne and then drops onto an ash pile. The furnace heats a boiler, generating steam, which turns a Turbodyne turbine, creating the power, explains Stock. The system is virtually closed, with the steam condensed and returned to the boiler as water. The power is sold to TransAlta, a power generator and wholesale electricity marketer headquartered in Calgary, and then to Alberta customers. Byproducts “All the ash that we generate basically goes to local farmers,” says Stock. They usually apply it in the fall or early spring to increase soil pH. Dapp may or may not charge a loading fee, and providing it to local grow-ers keeps it out of the landfill, notes Stock. Emissions are controlled by a Clyde Bergemann electrostatic precipitator that Stock says was totally rebuilt in fall 2009. “We have an online emissions monitor-ing control system, which is reportable to Alberta Environment monthly. It’s a regu-lation in Alberta that you have an online monitoring control system, and every-thing is recorded as either one-hour aver-ages or six-minute averages, depending on which particular parameter they require,” he explains. If emissions exceed the limits for any reason, the plant must take correc-tive action and report to Alberta Environ-ment within 24 hours, notes Stock. A side benefit to burning landfill-di-verted wood is that the Alberta provincial government has a carbon credit system in place that rewards this re-use. It involves keeping track of how much wood is di-verted from landfill, as well as third-party verification and auditing of the records. Stock says the goal is to burn mainly land-fill-diverted wood, both for the carbon credits and because it is dryer than the hog fuel that comes from forestry residue. “This past year [2010], we burned approximately 40% landfill-diverted wood,” he notes. • To read about the Biofuels Division that supplies construction and demolition biomass to Dapp Power, see Landfill Diversion in the March/April 2011 is-sue of Canadian Biomass (http://www. canadianbiomassmagazine.ca/index. php?option=com_content&task=view &id=2395&Itemid=132). Canadian BIOMASS 15