Cogeneration Power Plants
The first example of a cogeneration biomass power plant comes from Germany because its concept and design won awards for its efficiency and best management practices. The German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety presented this power plant at the United Nations Global Summit for Sustainable Development at Johannesburg, South Africa in 2002; and at the United Nations Global Summit on Climate Change at Bonn, Germany in 2005.
Biomass Cogeneration Plant at Pfaffenhofen,
Bavaria / Germany
- power, heat and chill based on wood chips -
In Pfaffenhofen, Bavaria / Germany, a district community of about 24,000 residents, a biomass cogeneration plant, generating electric power, heat and cooling, started operation in July of 2001 with an output of 27 MWth and 7.5 MVAel. Existing community facilities are connected to it through a district heat supply system. Steam, heat and cooling are delivered to a hospital, a school, a food producing company and additional companies.
The location of the biomass cogeneration plant easily allows the delivery of energy to connected customers. The plant supplies steam to a producer of baby-food at a temperature of 180 °C / 356 °F through a special conduction pipe. A community district heating system provides heat for more than 150 customers on two levels of temperature (130 °C / 266 °F and 85 °C / 176 °F) via special pipelines. A low-temperature grid for neighboring customers (up to 40 °C / 104 °F) has also been installed. Moreover, absorption chillers provide cooling for air conditioning and for low-temperature applications, like a hospital and a local brewery.
Due to the fact that demand for heat is rather constant during the year, the degree of effectiveness of the cogeneration plant is very high. Wood chips are burned in a special biomass boiler on a water-cooled vibration grate. The maximum heating power is 26.7 MW. Its capacity was calculated by means of comprehensive demand-related designing. In addition, there are two backup steam boilers with 10.5 respectively 21 MW heating power for supporting the biomass-furnace during high loads and to ensure safe heat delivery. The main fuel for the backup system is natural gas. In total up to 120 GWh heat are sold every year. With a capacity of about 7.5 MW electrical power, the steam turbine supplies an amount of more than 42 GWh electricity per year into the electric grid.
The calculated fuel demand is a total of about 80,000 tons per year: 30 % natural wood and bark; 70 % wood waste from sawmills. The continuous demand of 250 t per day requires efficient logistics for harvesting, processing and transport of woody biomass. Forest owners can supply wood ranging from complete stems to wood chips. All species of trees are suitable for wood chip production. Container trucks will transport the fuel to the cogeneration plant. This guaranties a flexible and efficient supply with minimal traffic.
The Federal Government of Germany is committed to reduce carbon dioxide emissions by 25 % by 2005 in relation to Germany's 1990 figures. With the start of the plant’s operation, we reached this target for the city of Pfaffenhofen already in 2001. The cogeneration plant in Pfaffenhofen offers both energy efficiency and labor policy advantages: We had a particular positive employment effect for 200 persons during the construction phase and we created permanent jobs for 25 persons for the plant and in wood procurement after its completion.
Technical Data Generating Heat and Electricity with Wood Fuel
• Water-cooled vibration grate for biomass with a heating power of 26.7 MW; steam parameters: temperature 450 °C, pressure 6 MPa (60 bar)
• Two backup steam boilers with a capacity of 10.5 respectively 21 MW heating power for supporting biomass-furnace during high loads and to ensure safe heat delivery. Main fuel: natural gas.
• Steam turbine: 7.5 MVA; expected amount of electricity per year: 42 GWh.
• Wood-fuel: total consumption 80,000 tons/ delivered from an area with a radius of 25 miles (40 km) ….
- 30 % natural wood and bark*
- 70 % wood waste of sawmills*
* These numbers depend on the available fuel wood.
• Special steam conducting pipe to a producer of baby-food (HIPP company):
length 950 m; Steam parameters: temperature 180 °C, pressure 12.5 Mpa
• District heating for more than 150 customers between 15 and 3,500 kW:
- High-temperature net; length 8.5 miles (13.5 km) at a max. temperature: 130 °C
- Medium-temperature net; length 2.5 miles (4.0 km) at a max. temperature: 85 °C
- Low-temperature net for neighboring customers (still under construction)
- One Li-Br absorption chiller (8/13 °C) for a hospital; cooling capacity: 300 kW
- One Li-Br absorption chiller (6/14 °C) for the basic demand of cold in two business buildings; cooling capacity: 700 kW.
- One NH3-absorption chiller (-6/14 °C) in combination with an electric piston compressor chiller (2 x 125 kW) for high loads and for low temperature applications of a brewery during night and for air-conditioning of several business buildings via district-cooling during day time: cooling capacity: 650 kW.
Costs, Savings, Realization
• Total costs of cogeneration plant, fuel logistics, steam- and district-heat delivery as well as connecting customers, absorption chillers with district-cooling: approx. € 41.4 million (contributed by the Bavarian Ministry of Agriculture and Forestry and the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety)
• Savings of natural gas and oil by using a renewable fuel: 24 million liters (about 6,550 million gallons) per year. Savings of carbon dioxide: approx. 65,000 tons CO2 per year.
• Planning and construction: Kraftanlagen Anlagenbau, München, Germany
• Conception and realization: eta Energieberatung, Pfaffenhofen, Germany
Update: The first energy delivery contracts were in effect for 10 years and came due for renewal. All customers chose to renew their contracts. Since operation started 10 years ago, the pipeline system was expanded to allow new customers to be connected. The power plant continues to work efficiently and is economically very productive in the profits it produces.
Note: The above concept and executive summary is the property of eta Energy Consulting, Pfaffenhofen, Germany. It is used here with permission by the designers.
Absorption Chilling illustrated and explained
The following image shows the components of an absortion chiller.
Image courtesy of eta-Energyberatung, Pfaffenhofen, Germany
Image courtesy of eta-Energyberatung, Pfaffenhofen, Germany
From Wikipedia .....
An absorption refrigerator is a refrigerator that uses a heat source (e.g., solar, kerosene-fueled flame) to provide the energy needed to drive the cooling system. Absorption refrigerators are a popular alternative to regular compressor refrigerators where electricity is unreliable, costly, or unavailable, where noise from the compressor is problematic, or where surplus heat is available (e.g., from turbine exhausts or industrial processes, or from solar plants).
Absorption cooling was invented by the French scientist Ferdinand Carré in 1858. The original design used water and sulfuric acid.
In 1922 Baltzar von Platen and Carl Munters, while they were still students at the Royal Institute of Technology in Stockholm, Sweden, enhanced the principle with a 3 fluids configuration. This "Platen-Munters" design can operate without a pump.
Commercial production began in 1923 by the newly formed company AB Arctic, which was bought by Electrolux in 1925. In the 60s the absorption refrigeration saw a renaissance due to the substantial demand for refrigerators for caravans. AB Electrolux established a subsidiary in the U.S, named Dometic Sales Corporation. The company marketed refrigerators for caravans under the Dometic brand. In 2001 Electrolux sold most of its Leisure Products line to the venture-capital company EQT. The Dometic Group was created.
In 1926 Albert Einstein and his former student Leó Szilárd proposed an alternative design known as Einstein refrigerator.
In 2007, Adam Grosser presented his research of a new, very small, "intermittent absorption" refrigeration system for use in third world countries at the TED Conference. The refrigerator is a small unit placed over a campfire, that can later be used to cool 3 gallons of water to just above freezing for 24 hours in a 30 degree Celsius environment.
The absorption cooling cycle can be described in three phases:
- Evaporation: A liquid refrigerant evaporates in a low partial pressure environment, thus extracting heat from its surroundings – the refrigerator.
- Absorption: The gaseous refrigerant is absorbed – dissolved into another liquid - reducing its partial pressure in the evaporator and allowing more liquid to evaporate.
- Regeneration: The refrigerant-laden liquid is heated, causing the refrigerant to evaporate out. It is then condensed through a heat exchanger to replenish the supply of liquid refrigerant in the evaporator.