GEOTHERMAL COGENERATION

Transcription

1 GEOTHERMAL COGENERATION GENERAL PRESENTATION Context Deep geothermal energy has high potential. How the geothermal resource under the surface of the earth can be efficiently used depends on the temperature and flow rate (in case of geothermal water) of the geothermal resource. For the use of geothermal energy a distinction is made between electricity generation and direct use in a geothermal power plant. Electricity production is dominated by high-enthalpy resources. With special technologies like ORC or Kalina-Cycle the low and medium temperature resources can also be used for electricity production. Direct application for heating is far more efficient than electricity generation and has less demanding temperature requirements. Heat may either come directly as direct use from the geothermal resources over a geothermal heat plant or from co-generation with a geothermal electrical plant. Co-generation means the use of the geothermal resource for multi-purposes in order to increase the efficiency of the geothermal energy exploitation. State of the art Geothermal cogeneration also named as combined heat and power (CHP) means the simultaneous generation of more than one useful form of geothermal energy. In a geothermal cogeneration system the geothermal resource is decoupled for simultaneously using it for electricity-production, heating purposes and direct uses like greenhouses or spas. For direct uses the supplied utilities have to be very close to the plant. The cascading use of energy from high-to low-temperature makes cogeneration more efficient than separate geothermal systems for electricity and heat production. From the viewpoint of optimization of efficiencies combined heat and power (CHP) is optimal. The geothermal plants for electricity generation can work on several technologies: Flash steam plants use hot pressurised water with temperature of above 180 C. The hot water is pumped under great pressure to the surface. When it reaches the surface the pressure decreases to the stage it vaporises. This leads to a two-phase water-steam mixture and a vapour lift process. The steam drives a turbo-alternator for electricity production. Dry steam plants use hydrothermal fluids that are primarily steam and emerge at the earths surface. The steam goes directly to a turbine, which drives a generator that produces electricity. Binary plants extract energy from geothermal fluids of about 75 to 180 C. Hot geothermal fluid and a binary fluid with a much lower boiling point than the geothermal water pass through a heat exchanger. Heat from the geothermal fluid causes the binary fluid to flash to vapour. The vapour drives the turbines. Attached to the electricity generation plant a heating system is attached. Part of the geothermal resource is decoupled to the heating plant/system and direct use applications. The different temperatures needed for the direct uses are shown in the following graphic. 1 / 6

2 Currently cogeneration is trending towards increased efficiencies in order to optimize the power generation of CHP plants. Moderate-temperature water between 75 and 180 C is by far the most common geothermal resource. This will lead to the fact that especially in a steadily increasing geothermal technology environment the share of binary cycle plants will increase. The steady improvement of Enhanced Geothermal Systems (EGS) technology is expected to significantly widen the spectrum of geothermal CHP. Geothermal solution Geothermal CHP plants offer the opportunity to combine electricity generation with direct heat applications. The utilization for direct heat applications can be accomplished using the thermal energy available in a waste brine and rejected heat in a condenser to heat fresh water, which can then be distributed to a variety of end users. The technical feasibility and design of such co-generation power plants depend on a number of factors, including the reservoir temperature of the geothermal fluid, the type of flash system used in the power plant, the distance to end users and the types of applications. The principal technical advantage of geothermal cogeneration systems is their ability to improve the efficiency of geothermal energy use in the production of electrical and thermal energy what improves the economics of the entire system. Many CHP plants, especially those using a low-temperature resource, started as district heating project. The electric power plant was later added, and became economical, as the well and pumping systems were already in place. Nowadays the CHP is in most cases more profitable and efficient than separate geothermal solutions for electricity generation and direct use. 2 / 6

3 Compared to conventional power plants on electricity production and district heating, the technical advantages of cogeneration out of geothermal energy lead to significant environmental advantages. The increase in efficiency and non-use of fuel use by the geothermal cogeneration system, compared to separate processes for thermal and electrical energy production, lead to large reductions in environmental emissions. Geothermal cogeneration is not the end of the process. The by-product heat at moderate temperatures ( C) can also be used in absorption chillers for cooling. This offers the possibility of a polygeneration plant, producing electricity, heat and cold. Cogeneration is a proven technology. Polygeneration is the next step. FOCUSING ON THE GEOTHERMAL SOLUTION Current status of the solution Scientific Project (only on paper or under preparation) Demonstration project Scientific Pilot Industrial Pilot Industrial stage Other? Comments Geothermal cogeneration plants are already in use in several European countries. Advantages (1, 2, 3, 4 Comments or 5) * Environmental 5 Reduction of greenhouse gases and pollutants emissions. The closed loop of a geothermal cogeneration unit leads to almost no emission. Economical 4 Increasing the profitability by dual use of geothermal energy Social Scientifically 4 The possibility of the use of the geothermal water of different temperature is not yet finally explored. Advantages against other applications Cogeneration technology provides greater conversion efficiencies than traditional generation methods as it cascades the geothermal heat for different applications and though increases the use and exploitation of the geothermal resource. A geothermal co-generation plant compared to separate processes for geothermal heat and electricity production increases the profitability of the system. Reduction of greenhouse gases compared to conventional power plants on electricity production and district heating 3 / 6

4 Focusing on Economic Feasibility - Estimated costs Make cost estimation on the costs (low, medium, high) for one average solution. - Impact on profitability Highlight the impact on the profitability of a geothermal project: compare the use of the innovative technology to the initial situation. (This question is difficult, quasi impossible for pilot projects ) EXAMPLES/CASE STUDIES Let us just mention a few examples for CHP-Plants: Altheim Bad Blumau Unterhaching Landau Svartsengi Nesjavellir Hellisheidi Neustadt-Glewe The CHP-Plant in Neustadt-Glewe will be more detailed described in a short case study. Location Germany, Mecklenburg Western Pommerania, Neustadt-Glewe Technical characteristics of the operation - Type of exploitation Hot (geothermal) water is used to produce energy, both electricity and heat. - Production The geothermal heat plant has a capacity of 7,0 MW th and produces 16,000 MWh / a, of which up to 98% is provided through geothermal heat. The 2003 opened geothermal power plant has an installed capacity of 230 kw (0.2 MWe). It produces MWh / a. - Pilot project? The power plant of Neustadt-Glewe can be seen as a pilot project for Germany in several ways. It was the first project on geothermal electricity production in Germany. As it was combined with an already existing geothermal heat plant it was also the first cogeneration plant in Germany. Besides the geothermal power plant Neustadt-Glewe was based on the ORC technology for geothermal electricity production using the lowest temperature geothermal resource worldwide. The thermal water temperature 4 / 6

5 of 98 C made it the world's "coldest" geothermal power plant for three years until in August 2006 a power plant in Alaska (Cheena Hot Springs) started that required temperatures of 77 C. - Specifications The development well is down in m depth that explored hot thermal water with a temperature of almost 100 C (max C) and a flow rate of m³/h. The reinjection well is down 1.5 km ahead from the development well. - Impact on market The geothermal heat plant supplies a total number of residential units and 23 small commercial customers with district heating. Besides it provides process heat for a leather factory in Neustadt-Glewe. The geothermal power plant supplies 500 households with electricity. The heat supply has priority. In summer the power plant runs in full power and stands still in winter at frost degrees. This improves the overall optimal efficiency of the system. - Financial aspects The geothermal power plant of Neustadt-Glewe was funded for the heat plant by the Federal Ministry of Education and Research and the Land Mecklenburg Western Pommerania. The construction of the power plant was funded by the Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU). SOURCES AND CONTACTS Information on geothermal cogeneration Brochure_Geothermal_E_CHP.pdf Information on CHP projects CHP-Plant in Altheim CHP-Plant in Bad Blumau Geothermie Unterhaching Landau Combined Heat and Power (CHP) Geothermal Power Plant 5 / 6

6 Svartsengi Combined Heat and Power (CHP) Geothermal Power Plant Nesjavellir (CHP) Geothermal Power Plant Hellisheidi (CHP) Geothermal Power Plant CHP-Plant in Neustadt-Glewe 6 / 6