Mature technologies are now available for the combined production of electricity and heat (cogeneration). They can use fossil or nuclear energy carriers, as well as biomass .In a proper comparison (serving the same energy needs through both alternatives), cogeneration uses 15-20% less energy, and contributes an equivalent amount of emission reductions, compared to the production of electricity and heat in separate facilities, i.e. a thermal power plant and a modern boiler this concept is taught in best mechanical diploma engineering college in pune . In this case, the comparison needs to be based on the same fuel. When cogeneration is combined with a fuel switch – from coal to gas, the impact of switching fuel is more important than the impact of cogeneration, due to the favorable characteristics of gas compared to coal.
The advantage of cogeneration also decreases with higher efficiency of future power plants .Cogeneration is above all meaningful for applications where there is a large and continuous(not just seasonal) demand for heat close to the cogeneration facility. If there is no demand for heat from a cogeneration facility, its efficiency for the production of electricity will be lower than for optimized thermal power stations. Larger cogeneration facilities have in general lower production costs than smaller units. But on the other hand, transport of heat to users takes longer and is more expensive .Cogeneration provides 6% of heat in Germany. Each year, about 55 TWh2 is produced.
Cogeneration means the combined production of electricity and heat in an energy conversion facility. Technically, it means that part of the heat (steam or hot air)energy for the production of electricity in steam or gas turbines, or residual heat from combustion engine or fuel cell is used for room heating or as process heat in industry or commerce .Basically the cogeneration principle could be used in any generation facility .It makes only sense though, when there is demand of heat .The heat demand should be large ,and continues over long part of the year.
A broad range of mature technologies is available for cogeneration. They can use all energy carriers, from biomass or hydrogen in small facilities, such as mini-CHP units and fuel cells, to coal and nuclear energy in facilities of any desired size.
The advantage of the combined production of heat and power
Meaningful applications can be found primarily where electricity production can be combined with a long-term stable and constant heat production, that is competitive in the heat market. Such production also contributes to the demand for electricity, which varies as well throughout the year, but to a lower extent than heat. Applications for cogeneration vary according to heat demand, the temperature of the heat required, and its variation over time .Two typical application domains for cogeneration have emerged: the combined heat & power (CHP) plant in industry, and the heat and power sector in the electricity supply(’municipal heat and power supply’). The latter produces mainly low-temperature heat for heating and hot water supply in buildings. In addition, block heat and power plants with ratings of a few kW to a few MW are becoming relatively important
More promising are the conditions for the development of cogeneration in industry. The reducing heat demand in this sector is compensated by 2 factors: by the higher technical potential of cogeneration compared to the heat demand in industry, related to higher fuel prices, and by the high utilization related to a heat demand all year round. Higher CHP coefficients provide an additional driving force.
A lot is expected from decentralized cogeneration in smaller facilities, such as block heat and power plants, and fuel cells, for use in industry as well as small applications (households ,commerce, public facilities). The advantage here is the elimination, or strong reduction of costs for heat transport, as well as avoided costs for using the grid. Disadvantages are the significantly higher investment costs, as well as fuel, operating and maintenance costs, and the lower efficiency for electricity production in relatively small units.
The technical possibility exists to fully cover the demand for low temperature heat ( up to 100 degrees) by cogeneration. The extent to which this theoretical potential can be exploited depends on whether the combined production of heat and electricity, compared to separate production, results in economic, energy or ecological advantages.
Large cogeneration plants in the range of a few 100 Megawatt (MW) using coal or natural gas are capable to produce electricity at lower costs, despite their higher investment costs, if they can lower their fuel costs through realising their energy efficiency advantage. This advantage needs to be weighed against the cost of heat transport, which has a strong impact in the case of district heating. This applies particularly for the construction of new district heating networks. In large areas, this can lead to high start-up losses, due to protracted development of new connections. These effects can reduce, or even eliminate the economic advantage of lower heat production cost.
Prof. Pragati Ambekar
Pimpri Chinchwad Polytechnic