Feeding it Back

The U.K.'s food industry is discovering the economic benefits of using combined-heat-and-power systems fueled by biomass or biogas. New technologies to convert wastes to renewable energy are gaining in popularity due to the high cost of energy and waste disposal, pressure to reduce carbon emissions and divert waste from landfills.
By Diane Greer
At the Royal Brewery in Manchester, U.K., green beer is not just for St. Patrick's Day. Soon all the beer produced by the plant will be "green," thanks to a new energy efficient combined-heat-and-power system (CHP) fueled by wastes from the brewing process.

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
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.

Initially, the biogas fueled a boiler to produce steam but an engineering study determined that more value could be derived from the biogas by producing electricity, explains Carmine Fontana, vice president of gas processing for Ontario, Canada-based Eco-Tec. The biogas now feeds a General Electric Jenbacher reciprocating engine that produces more than 1 MW of electricity, satisfying 10 percent of the plant's electrical requirements. Heat generated by the engine warms the lagoon.

Before biogas is fed to the engine, it must be purified to remove hydrogen sulfide. Within an engine, hydrogen sulfide and water vapor from the moist biogas react to form sulfuric acid, Fontana explains. The acid causes corrosion and other engine problems. Eco-Tec is installing a biogas purification system, which removes 99 percent of the contaminants by using a catalyst to chemically breakdown the hydrogen sulfide into sulfur, Fontana says.

Austria-based Agrana, one of Central Europe's leading sugar and starch producers, recently installed a $10.5 million AD system at its sugar refinery in Kaposvár, Hungary. The digester processes spent beet pulp and beet syrup to produce almost 3.9 million cubic feet of biogas a day.

The biogas feeds the plant's boiler to produce steam, which drives a turbine generating electricity and is used for process heat. The biogas replaces 60 percent of the plant's energy requirements and cuts carbon emissions by 10,000 tons.

In the past, the company sold spent beet pulp to nearby cattle farms. Over time the farms transitioned from raising cattle to growing cereal crops. Agrana was faced with the decision to install a drier so the pulp could be dried for shipment outside the area or a biogas plant, explains Johann Marihart, Agrana's chief executive officer. At the same time natural gas prices in Hungary, among the highest in Europe, were rising and the Hungarian state was offering a tax credit for firms investing in renewable energy. "The decision was quite easy," Marihart says.

Agrana is optimizing the system to increase biogas production and replace 80 percent of its natural gas usage. Marihart is also considering installing systems at its potato starch factory in Hungary and sugar plant in the Czech Republic. "The more energy prices increase the more the energy content of the pulp product is interesting for use as an energy source and not as a feed source," Marihart explains.

Third-Party Solutions
Converting wastes into renewable energy is still in its early stages in the food and beverage industry. "The regulatory and economic drivers are fairly new or have just come together over the past few years, explains Ian Coate, director with London-based Insource Energy. "Many food and beverage companies need to move up the learning curve to understand the technologies, engineering and financing to set up waste-to-energy plants," Coate says. "It is not part of their core business."

The U.K.-based Carbon Trust created Insource to spur development of the commercial waste-to-energy market. The firm provides on-site solutions to firms wishing to outsource their waste-to-energy processes. "Our view is that it's sensible to outsource to an external partner the design, development, building, financing and operation of waste-to-energy systems," Coate says.

Initially, Insource is focusing on six sectors in the food and drink industry that are well-suited for waste-to-energy systems: distilling, brewing and soft drinks, red meat, dairy products, fruit and vegetables, frozen and chilled foods. "We are looking for high volumes of consistent types of wastes, which work best with the technologies available," Coate says.

The company is currently working with five major U.K. food and beverage companies. "In many cases, AD and CHP are the most appropriate technologies," Coate says. However, the company can deploy a wide range of technologies since no single technology can treat all wastes.

Some companies may be reluctant to colocate an AD plant with their food processing operation or may generate insufficient waste to run their own waste-to-energy plant. For these firms, the National Industrial Symbiosis Programme offers a different approach to divert wastes from landfills, and to promote waste-to-energy projects.

"The amount of waste that is going to a landfill or is receiving a low added value is huge," explains Peter Laybourn, NISP program director. "We bring companies together from different sectors to explore the possibility of mutual advantage." NISP has developed a database identifying opportunities for firms to partner to solve waste problems. For each member the database contains the quantities and types of waste materials being sent to landfills and where the waste is produced.

Using the database, NISP can map the location of companies with organic wastes near existing AD plants. "Where we see a density of production, we also encourage new AD capacity to come into the market," Laybourn adds. "What a program like this can do is aggregate feedstock across a region, filling in information gaps to make some of these projects viable."

Recently NISP started working with Severn Trent Water, the U.K.'s largest independent water company, to divert industrial food waste from landfills to STW's AD plants across the U.K. "There is a big move in the U.K. for companies to build new AD plants to process food wastes," says James Woodcock, NSIP practitioner. "Being familiar with STW and the water industry in general, I thought there are a lot of these plants in existence already treating sewage mixed with industrial waste."

STW utilizes AD to treat more than 700,000 gallons of wastewater and sewage a day. Biogas produced by the digesters fuels CHP units generating 154,000 MW hours of electricity, representing 17 percent of STW's electrical requirements. Thermal energy is used in the treatment process.

Adding industrial organic wastes to STW's AD systems will increase biogas production and renewable energy generation, improving the sustainability of the treatment process. Industrial food waste producers will benefit by cutting waste disposal costs by as much as two-thirds over landfill costs, Woodcock says.

"This is not an environmental program," Laybourn says. "It is a business opportunity program, but because we are dealing with resources such as waste, carbon and water, invariably if we solve the commercial problem we also help the environment."

Diane Greer is a New York-based writer and researcher specializing in renewable energy, clean technologies and sustainable business.