Cogeneration

Combined heat and power (CHP ) or combined heat and power (CHP ) is the simultaneous production of mechanical energy that is converted directly into electricity in the rule, and useful heat for heating (district heating or district heating ) or for production processes ( process heat) in a thermal power plant. It is thus the extraction of useful heat especially in electricity generation from fuels. In most cases, provide cogeneration power plants heat for heating public and private buildings ready, or provide them as an industrial power plant operations with process heat (eg in the chemical industry). The release of unused waste heat to the environment is thereby largely avoided. Are becoming increasingly important smaller CHP plants for the supply of individual residential areas, or individual multi - family houses, and even so-called combined heat and power (CHP).

Advantage of cogeneration is the reduced fuel demand for electricity and heat supply, whereby the pollutant emissions will be greatly reduced. The promotion by the Combined Heat and Power Act ( CHP ) and the Renewable Energy Sources Act ( EEG) to accelerate the expansion.

• 3.1 Promotion in Germany 3.1.1 CHP Act
• 3.1.2 Renewable Energies Act (EEG )
• 3.1.3 Tax benefits

Introduction

The spectrum of electrical and thermal output of CHP plants ranges from a few kilowatts to several hundred megawatts. Increasingly Since about 2000 there are about large washing machine, so-called mini - and micro combined heat and power systems for use in single-family homes, apartment buildings, smaller commercial buildings and hotels on the market. 2009, a project was launched by VW and bright spot in the 100,000 small CHP units are to be installed with a total capacity of around 2 gigawatts. These, therefore, are more suitable for multi-family and commercial units. The 700 MW of electrical power is currently the largest cogeneration plant in Europe is in England. So today are CHP solutions available for the full range of the heat demand.

The typical thermal power stations, which cover a large part of the electricity demand in Germany, exclusively produce electricity with the released heat from a fuel. If, in addition, the waste heat is used, eg for process heat or in a district heating network fed, called these CHP plants; they have a higher utilization rate. During achieve pure power-generating equipment efficiencies between 33% ( older plants ) and 58.4 % (gas -steam combined cycle power plants ), it comes in cogeneration plants at efficiencies of 80 % and higher. In cogeneration and thermal energy [ kWhth ] is so far available in addition to the electrical energy [ kWh el ]. In the operated with steam as the working substance public thermal power plants - these are usually condensing extraction systems - this increase in utilization has been coupled with a reduction in electricity production ( lower electrical efficiency). The steam must be obtained before the last turbine stage so that its temperature is sufficiently high for heating. In contrast, the residual heat is discharged through the condenser and the cooling tower to the environment from power plants without combined heat and power.

Compared to the most recent technologies of separate production of electricity and heat cogeneration plants achieve depending on the supply situation for primary energy savings of about 10 % to about 30%. The fact that the savings may not be even higher in the section, is related to that of the real power and heat demand strong and different fluctuations, especially in residential areas with only a low heat demand in summer, which can not be compensated by heat storage over longer periods.

The unrealized total in Germany high savings potential has prompted the legislature to promote cogeneration in order to overcome market barriers that exist through the central supply structures over 100 years grown. On the part of the major energy suppliers, there are obvious reasons reservations about the promotion of cogeneration, which is supported by arguments of individual experts.

The picture on the right shows the left part makes the principle of withdrawal. The after medium-pressure part (MD ) of the turbine, before the low-pressure part (LP ) branched off steam flows into the heating condenser ( HK), where it liquefies, releasing heat to the district heating circuit ( temperature level around 100 ° C). From there the condensate is fed into the feed water circuit. The remaining vapor is working in the low- pressure part, and then the capacitor (Co ) at about 25 ° C liquefies (depending on the ambient condition ) and the condensate pump (LD) to the ( here not shown ) is supplied to the feed water container. The right-hand side shows the corresponding idealized Ts diagram (see Rankine process ) for an operating state, in which half of the steam for heating purposes is used. The whole red area corresponding to the used heat, the upper surface of the hatched portion of the power loss in the low pressure stage.

Technology

In the power -heat coupling a portion of the resulting vapor is extracted in a power plant for heating purposes. Thus, although the efficiency of the power generation decreases ( electrical energy ); the overall efficiency but increases to 90 %. When used in carbon dioxide (CO2) in the costs arising from the combustion gases ( for example in greenhouses farms ) could even be an overall efficiency above 90 % to be possible. Here, the CO2 for photosynthesis of the exhaust gases would be supplied to the greenhouse, but would have to be prepared by a catalyst in advance.

Fuels

The principle of CHP can be used with any fuel and any power source with a temperature range from about 210 ° C. In consideration besides fossil fuels such as coal, lignite, natural gas and fuel oil, renewable energy sources such as biogas, sewage gas, landfill gas, vegetable oil, wood, pellets, bioethanol, solar thermal and geothermal, as well as municipal waste come ( incineration and landfill gas ) as well as nuclear energy. The Greifswald nuclear power plant (also called nuclear power plant Lubmin ) fed by 1990 the district heating network of Greifswald.

Interpretation

A distinction is made between current and heat -guided design of cogeneration plants, depending on the priority that is attributed to one of the two forms of energy. Current controlled systems optimize power yield, heat-controlled systems the heat output. The highest efficiency is achieved with heat- guided interpretation, because there the lowest energy losses. From an economic perspective, however, the current-controlled mode of operation is often more attractive because per kWh of electricity significantly higher yields than per kilowatt hour of heat. The heat storage can be accomplished by use of a district heating reservoir. The heat produced is used as hot water, the so-called district heating, or water vapor over insulated pipes for heating buildings, for industrial purposes ( process heat) or in food production (eg aquaculture). The use of large heat storage in the cogeneration process (always simultaneous ) production of heat and electricity can be decoupled in time again, as the heat can be cached. Thus, a cogeneration plant operated flow out and still ensure the provision of heat of a heat-controlled operation. In times of high power and low heat demand, the system can be operated in full load and load the excess heat in the memory. In times of low power and yet high heat demand, the CHP plant can be operated at part load, the residual heat can be provided temporarily by the heat storage.

Since the connection of CHP plants and large heat storing results in a high flexibility and ensures efficient use of fuel, the federal government has taken with the promotion of heat storage with the last amendment to the Combined Heat and Power Act in the promotion.

Variants

An increasingly popular method are so-called combined heat and power (CHP). These are small to medium-sized CHP plants based on combustion engines or gas turbines. While in these systems, the heat supply to a particular object or the surrounding area (such as a residential " block " ) is limited, the larger -scale CHP plants are used for district heating supply or generation of process heat in industry. In large plants for district heating line losses are on the one hand much higher than in cogeneration plants, thereby increasing the efficiency of energy use decreases. On the other hand, increases with increasing power of the systems the power to heat ratio ( ie the ratio of electricity to heat production) and thus the Exergieausbeute, which in turn increases efficiency.

CHP systems can be, among others:

• Fuel cell systems
• Steam turbine,
• Gas and steam turbines ( CCGT),
• Gas turbine,
• Combustion engines or

Of combined heat, cooling and power ( CHCP ) is when the plant can also produce cold. The useful heat of the process is used to drive an absorption chiller. Despite the significantly higher investment compared to a compression chiller, the trigeneration plant can be operated economically, because the run times are increased by the use of heat for air conditioning in summer.

Support measures

Promotion in Germany

In Germany, the CHP generally by the Combined Heat and Power Act ( CHP ) is encouraged. Plants using renewable energy in CHP use (eg biogas CHP with district heating networks ), can optionally also under the Renewable Energy Sources Act ( EEG) be remunerated.

CHP Act

The Act for the maintenance, modernization and expansion of combined heat and power ( cogeneration of heat and power law ( CHP ) ) the preservation, modernization and expansion of cogeneration will be promoted in the Federal Republic of Germany, the fossil energies are operated. For modernized plants that have been taken by the end of 2005 back in service by 2010, a bonus is paid on the injected current from an average of approximately 1.65 cents per kilowatt hour. By modernizing the old efficiency CHP plants was considerably increased. Without modernization preserve existing CHP plants reduced effect, which is to prevent the early decommissioning of plants. The operators of very small CHP plants with a capacity up to 50 kW receive an additional 5.41 cents on each generated by the CHP plant kilowatt hour of electricity for 10 years. It is immaterial whether the electricity consumed itself or is fed. Small CHP plants up to 2 MW of electrical power received by 2010 an additional fee. This 2002 was 2.56 cents / kWh for the entry into force of the law and was lowered to 2010 to 1.94 cents / kWh. By increasing the use of cogeneration plants a further reduction of carbon dioxide emissions is to be achieved. The CHP Act entered into force on 1 April 2002. On 1 June 2008, a significant expansion of promotion was decided in an amendment to the CHP Act. The law stipulates that by 2020 a quarter of the power supply is managed by combined heat and power.

Critics argue that funding was too low and the conditions required to be high to help the CHP to a breakthrough.

The amended Combined Heat and Power Act of October 25, 2008 entered into force on 1 January 2009. Another category justify CHP facilities that begin continuous operation between January 1, 2009 and December 31, 2016, the claim to the CHP surcharge. Additionally, it will also get operators to CHP surcharge that provide electricity for internal power supply and not feed into the general supply networks.

Renewable Energies Act (EEG )

With the force since 2009 amendment to the Renewable Energy Sources Act is ( EEG 2009, § 27, paragraph 4) the use of waste heat from electricity generation from biomass (such as biogas plants and biomass cogeneration plants ) by a CHP bonus of 3 cents / kWh cogenerated electricity (EEG 2004: 2 cents / kWh) stimulated. This bonus will be deducted from the basic pay under the EEG and is payable by the operator of the upstream grid. The bonus eligible amount of power ( CHP electricity ) is calculated as the product of useful heat ( actually used waste heat) and the current ratio of the system ( electrical power / Nutzwärmestrom, here is - different from above - meant by useful heat the theoretically usable portion; through the plant equipment such as generator and heat exchangers is given the power to heat ratio of a system. ). A high electrical efficiency and the intensive use of waste heat therefore increase the proportion of eligible bonus amount of electricity. Various conditions must for payment of the CHP bonus met ( Annex 3 of the EEG 2009).

In addition, another so-called technology bonus is ( innovation bonus ) of up to 2 cents / kWh for the use of certain cogeneration technologies (fuel cells, gas turbines, steam engines, Organic Rankine systems, multi-fuel plants, especially Kalina -cycle plants, or Stirling engines ) paid ( Appendix 1 of the EEG 2009). These supplements and bonuses are allocated indirectly to all end users.

Tax breaks

For the fuels natural gas, fuel oil and liquefied petroleum gas until April 1, 2012, when used in CHP plants with an annual utilization rate of at least 70 percent, the energy tax, formerly " mineral oil " fully reimbursed. Due to a short-term application by the German authorities at the EU Commission, the processing of applications for energy tax relief in 2012 was temporarily suspended. By amending legislation, the complete relief is only received in arrears on April 1, 2012 when the system was not yet fully depreciated for tax purposes in addition to the minimum efficiency of 70 percent and is highly efficient in the sense of Directive 2004/8/EC of the European Parliament. For electricity from CHP systems up to 2 MW of electrical power consumed by the plant operator in the " spatial context ", also no electricity tax (2.05 cents / kWh) must be paid.

Promotion in Switzerland

In Switzerland, the combined heat and power in biomass, waste water treatment and waste incineration plants is indirectly supported by the federal government.