When installation is completed in 2009, the CHP system will supply 60 percent of the plant’s steam and almost all its electricity. Carbon emissions from fossil fuels will be cut by 87 percent.
The brewery, owned by Heineken after its acquisition of Scottish & Newcastle’s British business, is part of a growing number of European food and beverage companies discovering the power of waste. Rising energy and waste disposal costs combined with pressure to cut carbon emissions and divert wastes from landfills is spurring firms to implement new technologies converting wastes into renewable energy. But efforts are still in the early stages.
The food industry is a major consumer of energy and contributor to greenhouse gas emissions. In the U.K., for example, the industry accounts for 14 percent of energy consumed by businesses and emits 7 million tons of carbon. The sector’s waste accounts for 10 percent of the U.K.’s industrial and commercial waste stream.
While the industry is not among the most energy intensive, certain sectors are significant energy users with coincidental heat and power loads and large waste streams. For these
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users, CHP fueled by biomass or biogas, is emerging as a practical solution.
CHP, also known as cogeneration, provides a highly efficient means of generating thermal energy and electricity from a variety of fuel sources in a single process. “With CHP you can get 85 percent of useable energy out of the fuel,” says Tauno Kuitunen, Wärtsilä Biopower’s general manager for sales. Helsinki-based Wärtsilä is installing the biomass boiler at the Royal Brewery. Conventional generation or separate heat-and-power systems result in overall efficiency less than 50 percent.
Breweries are good candidates for CHP. The process satisfies an important criterion for CHP, a significant demand for heat that is predictable and stable, Kuitunen explains. Steam is required during several steps in the brewing process, such as boiling the wort, fermentation and pasteurizing the final product, and for cleaning equipment. Electricity is used for refrigeration, compressed air generation and pumping.
The Royal Brewery CHP plant will produce 7.4 megawatts (MW) of thermal power and 3.1 MW of electricity, fueled by a mixture of spent grain left over from the brewing process and clean wood waste. Wood is required due to insufficient quantities of spent grain.
Before the spent grain is fed to the boiler, the moisture content is reduced from 80 percent to 60 percent, Kuitunen explains. “That is good enough for our combustion system.”
The boiler, a Wärtsilä Biopower 5, contains a conical, rotating grate. Fuel is fed from underneath to the center of the grate. As the grate rotates, the fuel migrates down the cone to the combustion zone on the outer rim. Because the fuel is fed from the middle, it is completely dried by the heat radiating from the lining of the boiler and flames in the chamber before it is combusted on the outer rim, Kuitunen explains. “The system is very flexible and able to accommodate moisture variations in the feedstock.”
Food processing giant Tate & Lyle PLC is installing a biomass-fired CHP system at its east London sugar refinery. Wheat husks, a byproduct of flour production, will fuel a $41.4 million, 65-MW biomass boiler. Using biomass will slash energy consumption from fossil fuels by 70 percent, with a corresponding 70 percent reduction in carbon emissions. Steam produced by the boiler will generate electricity and satisfy the refinery’s process heat requirements. Excess power produced by the system will be sold to the National Grid.
Once the boiler is at full capacity the carbon footprint for Tate & Lyle’s sugarcane, from field to factory gate, will drop from an already low 0.43 tons of carbon per ton of sugar to 0.32 tons, says Steven Hermiston, the company’s sales and marketing director.
Biogas-Powered CHP
For food and beverage companies producing moist or liquid waste, anaerobic digestion (AD) offers a good solution for generating renewable fuel for CHP systems. AD employs microbes in an oxygen-free environment to break down organic waste into biogas. The biogas, composed of methane and carbon dioxide, feeds a reciprocating engine, microturbine or boiler to generate electricity and process heat.
McCain Foods in Whittlesey, U.K., constructed an 828,000-square-foot covered anaerobic lagoon to process wastewater from the U.K.’s largest french fry factory. Wastewater containing potato starch generated during processing is piped to the lagoon and produces more than 400-standard-cubic-feet per minute of biogas. The firm may add other potato wastes, such as peels and nubbins, to increase biogas production.
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