part 1: overview of cogeneration and its status in asia - Fire

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State of art review of cogeneration 13 CHAPTER 2: STATE OF ART REVIEW OF COGENERATION 2.1 Technological Advances in Cogeneration Cogeneration plants benefit from many of the energy efficiency improvements that are brought about in utility power generation because the same basic technology is employed in both cases. However, cogeneration being more attractive for small-scale decentralized applications, significant technological progress has been made in the development of modular and packaged cogeneration systems of lower capacities. Moreover, as such systems are being adopted in industrial zones and city centres, the stringent laws and regulations put in place for protecting the local environment has obliged the cogeneration technology providers to innovate incessantly. The greater availability of natural gas in many parts of the world has helped in the maturing of gas turbine technology. In addition, the possibility of using alternative fuels such as wood, agro-industrial residues, biogas, etc., for powering small-scale cogeneration systems has led to further technological progresses by taking the specific characteristics of the fuels into consideration. This section briefly describes some of the developments in this domain. 2.2 Reciprocating Engines Reciprocating engines are mostly employed in low and medium power cogeneration units. The lower and upper limits of engine sizes are often a function of the fuel in use; these can range from 50 kW to 10 MW for natural gas, from 50 kW to 50 MW for diesel, and 2.5 MW to 50 MW for heavy fuel oil. One of the major advantages of reciprocating engines is their higher electrical efficiency as compared to other prime movers. The two main types of internal combustion engines employed in cogeneration systems are diesel engines and Otto engines. The characteristic feature of the Otto engine is that an electric spark from a spark plug ignites a mixture of fuel and air, and this is thus known widely as a spark-ignition engine. In power generation applications, the Otto engine may be either a gasoline engine or a diesel engine converted to have spark-ignition operation. Gasoline engines have the ratings ranging from 20 kW to 1.5 MW. The spark-ignition engines converted from diesel engines and running on natural gas are available in ratings from 5 kW to 4 MW. The Otto engines operate at speeds between 750-3,000 rpm and have the electrical efficiencies of 25-35 per cent. These engines can run on different fuels such as gasoline, natural gas, producer gas, and digester gas. As opposed to Otto engines, fuel is injected into the diesel engine cylinders in which it mixes with air and is ignited by the heat generated when the pistons compress the fuel/air mixture, and this engine is often known as a compression-ignition engine. Diesel engines can generally be classified into two main categories, i.e. two-stroke and four-stroke engines. The two-stroke engine is also known as a low-speed engine, and is characterized by ignition taking place once every revolution, and by the engine running at a speed below 200 rpm and delivering an output of 1-50 MW at a high electrical efficiency of 45-53 per cent. In a fourstrike engine, ignition takes place during every other revolution, and this engine can be divided into two categories. Medium speed engines are those running at speeds between 400 and 1,000 rpm and can be designed for ratings between 0.5 and 20 MW with electrical efficiencies of 35-48 per cent. High-speed engines are those operating at speeds between 1,000 and 2,000 rpm and with ratings between a few kW and about 2 MW with electrical efficiencies of 35-40 per cent.
14 Part I: Overview of cogeneration and its status in Asia Diesel engines can run on a variety of fuels such as diesel, heavy fuel oil, light fuel oil, LPG, natural gas, producer gas, digester gas, etc. The diesel engines that are converted to gas engines are also known as dual-fuel engines. In their operation, the main fuel is gas, which is ignited by a small quantity of pilot oil, usually diesel oil. The pilot oil is used to make sure that the gas in the cylinder will ignite. The gas/oil ratio is normally controlled so that the proportion of pilot oil at full engine power will be around 5 per cent of the fuel quantity supplied. Diesel engines running in gas engine mode can be classified in another way into two groups: lowpressure dual-fuel engines and high-pressure dual-fuel engines. Typical heat balance diagram of a gas engine is shown in Figure 2.1. About 25 per cent of the heat recovered from the engine cooling system (cooling water, oil cooler and inlet air cooler) is low grade at a temperature of about 95°C. Considering the same power output, the amount of heat recoverable at high temperature is lower than that for the gas turbine. That is why cogeneration with reciprocating engine is more commonly used for producing hot water/hot air or low pressure steam. However, medium pressure steam can be generated by employing supplementary firing since exhaust gases from gas engines have an O2 content of about 15 per cent. 1.5% Generator losses 100 % Mechanical Thermal 38% 62% 36.5% 25.0% 24.5% Electrical Thermal 36.5% 49.5% Overall efficiency 86% Engine Cooling System Exhaust gas Figure 2.1 Typical heat balance of a gas engine 5% Radiation losses 7.5% Exhaust gas losses In the operation of low-pressure dual-fuel engines, gas at low pressure, i.e. 3-5 bar, is mixed with the engine combustion air during the induction cycle. The gas/combustion air mixture is compressed in the cylinder and is ignited at the top dead centre by a small amount (approximately 5 per cent) of diesel oil being injected into the cylinder and ignited in the usual manner. Low-pressure dual-fuel engines have relatively low ratings and efficiencies. The system is sensitive to variations in gas quality. Gas is compressed outside the engine in a separate compressor in a high-pressure dualfuel engine up to 250 bar and is injected into the cylinder with a minor amount of pilot oil when the piston is in the vicinity of the top dead centre. High-pressure dual-fuel engines have
Page 1: PART 1: OVERVIEW OF COGENERATION AN
Page 4 and 5: 4 Part I: Overview of cogeneration
Page 14 and 15: State of art review of cogeneration
Page 36 and 37: Policy framework for promoting coge
Page 46 and 47: Cogeneration in Asia today 49 1.1 I
Page 48 and 49: Cogeneration in Asia today 51 4,000
Page 50 and 51: Cogeneration in Asia today 53 1.3 T
Page 52 and 53: Cogeneration in Asia today 55 1.3.3
Page 58 and 59: Cogeneration in Asia today 61 1.7 R
Page 60 and 61: Cogeneration in Asia today 63 Every
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Cogeneration in Asia today 65 Cogen
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68 Part II: Cogeneration experience
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Cogeneration experiences around the
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PART 3: SUMMARY OF COUNTRY STUDIES
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98 Part3: Summary of country studie
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100 Part3: Summary of country studi
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Sample case study in a pulp and pap
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Summary of country study - Banglade
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Summary of country study - Viet Nam
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