Technology & Engineering
Cogeneration
Cogeneration, also known as combined heat and power (CHP), is a process where a single fuel source is used to generate both electricity and useful heat. This efficient method reduces energy waste by utilizing the heat that is typically lost in conventional power generation. Cogeneration systems are commonly used in industrial and commercial settings to improve energy efficiency and reduce environmental impact.
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10 Key excerpts on "Cogeneration"
- Asif Syed(Author)
- 2012(Publication Date)
- Wiley(Publisher)
CHAPTER 11
Cogeneration
Cogeneration IS ALSO REFERRED TO AS COMBINED HEAT AND power generation (CHP). Cogeneration is the process of simultaneously generating two forms of energy: electrical power and heat. In standard power generation, electrical energy is used, but heat is wasted by exhausting it through the stack. Cogeneration recovers the heat energy that would have been lost and puts it to use. The heat energy can be used in several ways, including space heating in winter, absorption cooling or air conditioning in summer, and domestic hot water use year-round. Another unique feature of Cogeneration is that it is localized, or located at the point of use of energy. Cogeneration produces electrical power and heat at the consumer’s site, avoiding the purchase of electricity from a utility company. Electrical generation with fossil fuel is normally done via gas boilers, which burn to produce heat; the heat produces steam to drive the turbines, which in turn power the generators, producing electricity. Another form of electrical power generation with fossil fuels uses direct-fired equipment such as gas turbines and internal combustion engines. Fossil fuel is burned directly in the engine or turbine, which powers the generators, producing electricity. In both turbines and internal combustion engines, heat energy is converted into electrical energy. The process of conversion of heat energy to electrical energy is only 30 to 40 percent efficient; 60 to 70 percent of the heat is released to the atmosphere via a flue stack or cooling tower. Of all the energy produced in the United States, 63.9 percent is lost in the conversion process;1 or, two-thirds of the fuel used to generate power is lost as heat.Figure 11-1 Conventional power plant efficiency.Asif SyedThe location of the plant where power is generated is important, if the waste heat has to be captured and used. Most large industrial power plants are located far from population centers or industrial centers, in areas where waste heat cannot be put to use. The locations of power plants are generally determined by the availability and transportation of fuel. In some instances, power plants located near population centers and industrial centers do capture and use the waste heat. In New York City, waste heat from a power plant is used to generate high-pressure steam, which is distributed via a piping network to buildings in Manhattan. This steam is used for heating and cooling the buildings: In winter, steam is used for heating, after its pressure is adjusted in pressure-reducing valves; it can generate hot water or be used directly in radiators. In summer, high-pressure steam is used in steam turbine–driven chillers or absorption chillers. In the Middle East, cities such as Dubai, Kuwait, and Jeddah use the waste heat from power plants to produce desalinated water. However, in most power plants in the United States and in other parts of the world, waste heat is not recovered. The average site-to-source energy ratio is 3.6—that is, about 3.6 units of fossil fuel energy are consumed for every 1 unit of electrical energy delivered to the site or building.
eBook - ePubThe Brilliance of Bioenergy
In Business and In Practice
- Ralph E H Sims(Author)
- 2013(Publication Date)
- Routledge(Publisher)
Chapter 8 Cogeneration of combined heat and powerWhen biomass (or coal, oil or natural gas for that matter) is used as a fuel in a conversion plant to generate electricity, some heat is always produced. This relates to the laws of energy (thermodynamics), as covered in Chapter 1 , and is unavoidable. However, if this heat can be usefully used and not ‘wasted’, as it normally is in traditional thermal power generation plants, then the overall system efficiency will be greatly improved. To be classed as ‘Cogeneration’ the by-product heat must be put to good use in some way, normally as process heat in a nearby processing plant (Figure 8.1 ). Producing steam that only drives a condensing turbine (where the waste steam is condensed and the heat rejected into the environment) is not Cogeneration.In Europe Cogeneration is also known as CHP or combined heat and power . ‘Power’ is normally assumed to be the generation of electricity, but it can also be used to describe work by a rotating shaft to drive a pump, compressor or other mechanical process machine.So a definition of Cogeneration is:The generation of two energy products from a single fuel, usually being a combination of useful heat and electricity .Figure 8.1 Cogeneration is the production of both electricity and useful heatLarge and small Cogeneration applications provide heat (usually in the form of steam) and electricity for use in activities such as mineral processing or the manufacture of pulp and paper, petrochemicals, food and textiles, as well as in hospitals, hotels, office complexes, commercial buildings and swimming pools. A range of fuels can be used for Cogeneration including biomass in the form of rice husks, straw and methane from landfill sites and biogas plants. A key growth area for Cogeneration around the world is the increasing utilization of such biomass waste products.Many successful examples of bioenergy Cogeneration plants exist in Scandinavia, North America, Australasia and elsewhere. The global trend towards privatization of the power industry has created business opportunities for the owners of biomass material to set up new business ventures by becoming independent power producers (IPP). This is normally best achieved by the resource owner’s partnering with a utility company and a third-party joint venture investor rather than trying suddenly to gain expertise in a totally new business area. A sugar company best knows how to produce sugar, not how to produce and market power! Sugar companies owning bagasse, farmers owning chicken litter, forestry companies owning wood residues and city councils owning MSW are all able to utilize their resource for generating heat and power, not only for use on-site but also for export to the grid or to neighbouring industry or dwellings.
eBook - PDFEnergy Audit of Building Systems
An Engineering Approach, Second Edition
- Moncef Krarti(Author)
- 2016(Publication Date)
- CRC Press(Publisher)
13 -1 13.1 Introduction Cogeneration and combined heat and power (CHP) are terms used interchangeably to denote the simul-taneous generation of power (electricity) and usable thermal energy (heat) in a single integrated system. A CHP plant derives its efficiency, and hence lower costs, by recovering and utilizing the heat produced as a by-product of the electricity generation process that would normally be wasted in the environment. The overall fuel efficiency of typical CHP installations can be in the range of 70–90 percent, compared with 35–50 percent for conventional electricity generation. Overall, CHP achieves a 35 percent reduc-tion in primary energy usage compared with remote power stations and heat-only boilers. Moreover, CHP also avoids transmission and distribution losses because it supplies electricity generally close to the generation site. Although the CHP concept is not new, it has only recently been applied to a wide range of com-mercial buildings. Indeed, until the 1980s, Cogeneration systems were used only in large industrial or institutional facilities with high electricity demand (typically over 1,000 kW). After the energy crisis of 1973 during which fuel and electricity prices increased significantly (by a factor of five), in 1978 the U.S. government passed the National Energy Act (NEA) which includes the Public Regulatory Policies Act (PURPA). The PURPA regulations have forced utilities to purchase electricity and to provide supple-mentary or back-up power to any qualified Cogeneration facilities. The Energy Policy Act of 1992 has increased the appeal of Cogeneration systems even more by opening up transmission line access and retail wheeling. The term wheeling refers to the process by which utilities can buy or sell electricity to or from other utilities in order to meet peak demands or shed excess generation.
eBook - ePub- Paul Breeze(Author)
- 2005(Publication Date)
- Newnes(Publisher)
5Combined heat and power
Publisher Summary
This chapter explains the concept of combined heat and power (CHP), various CHP technologies, and the related environmental considerations. Low-grade heat can be used to produce hot water or for space heating while higher-grade heat will generate steam, which can be exploited by some industrial processes. In this way, the waste heat from power generation can replace the heat or steam produced from a high-grade energy source such as gas, oil, or even electricity. Systems that utilize waste heat in this way are called CHP systems. Such systems can operate with an energy efficiency of up to 90%. This represents a major saving in fuel cost and in environmental degradation. Yet, while the benefits are widely recognized, the implementation of CHP remains low. Most types of power generation technology are capable of being integrated into a CHP system; however, there are obvious exceptions such as hydropower, wind power, and solar photovoltaic. Fuel cells are probably one of the best CHP sources while conventional technologies such as steam turbines, gas turbines, and piston engine plants can all be easily adapted. The primary environmental impact associated with a CHP plant will be a function of the technology employed in the plant. Atmospheric emissions will vary, depending on whether the plant employs a diesel engine, a gas turbine, a steam turbine with a biomass boiler, or a nuclear reactor as the energy conversion system.The production of electricity from fossil, biomass or nuclear fuels is an inefficient process. While some modern plants can achieve nearly 60% energy conversion efficiency, most operate closer to 30% and smaller or older units may reach only 20%. The USA, which has a typical mix of fossil-fuel-based combustion plants, achieves an average power plant efficiency of 33%. Other countries would probably struggle to reach even this level of efficiency.
eBook - PDFDistributed Generation
The Power Paradigm for the New Millennium
- Anne-Marie Borbely, Jan F. Kreider, Anne-Marie Borbely, Jan F. Kreider(Authors)
- 2001(Publication Date)
- CRC Press(Publisher)
292 References ............................................................................................. 294 Power generation systems create large amounts of heat in the process of con-verting fuel into electricity. For the average utility-sized power plant, more than two-thirds of the energy content of the input fuel is converted to heat. Conventional power plants discard this waste heat, and by the time electric-ity reaches the average American outlet, only 30% of the energy remains. Dis-tributed generation (DG), due to its load-appropriate size and siting, enables the economic recovery of this heat. An end user can generate both thermal and electrical energy in a single combined heat and power (CHP) system located at or near its facility. CHP systems can deliver energy with efficiencies exceeding 90% (Casten, 1998). CHP systems have been used by energy intensive industries (e.g., pulp and paper, petroleum) to meet their steam and power needs for more than 100 years. They can be deployed in a wide variety of sizes and configurations for industrial, commercial, and institutional users. CHP strategies can even be used with utility-sized generation, usually in conjunction with a district energy system (Spurr, 1999). CHP systems can also involve nonelectric or shaft power, or the electricity can be used only internally.* In the U.S., how-ever, most CHP applications have been Cogeneration (medium-sized CHP for electricity and steam).** This chapter discusses only CHP applications that generate electricity using DG prime movers. 10.1 CHP Definition and Overview Combined heat and power (CHP) systems capture the heat energy from elec-tric generation for a wide variety of thermal needs, including hot water, steam, and process heating or cooling. Figure 10.1 gives an example of the efficiency difference between separate and combined heat and power. A typ-ical U.S. CHP system converts 80 out of 100 units of input fuel to useful energy — 30 to electricity and 50 to heat.
No longer available |Learn more- Albert Thumann, D. Paul Mehta(Authors)
- 2020(Publication Date)
- River Publishers(Publisher)
9 Cogeneration: Theory and Practice Because of its enormous potential, it is important to understand and apply Cogeneration theory. In the overall context of energy manage-ment theory, Cogeneration is just another form of the conservation process. However, because of its potential for practical application to new or exist-ing systems, it has carved a niche that may be second to no other conser-vation technology. This chapter is dedicated to development of a sound basis of current theory and practice of Cogeneration technology. It is the blend of theory and practice, or praxis of Cogeneration, that will form the basis of the most work-able conservation technology currently available. DEFINITION OF “Cogeneration” Cogeneration is the sequential production of thermal and electric en-ergy from a single fuel source. In the Cogeneration process, heat is recovered that would normally be lost in the production of one form of energy. That heat is then used to generate the second form of energy. For example, take a situation in which an engine drives a generator that produces electricity: with Cogeneration, heat would be recovered from the engine exhaust and/ or coolant, and that heat would be used to produce, say, hot water. Making use of waste heat is what differentiates Cogeneration facili-ties from central station electric power generation. The overall fuel utiliza-tion ef fciency of Cogeneration plants is typically 70-80% versus 35-40% for utility power plants. This means that in Cogeneration systems, rather than using energy in the fuel for a single function, as typically occurs, the available energy is cascaded through at least two useful cycles. 253 254 Handbook of Energy Engineering To put it in simpler terms: Cogeneration is a very ef fcient method of making use of all the available energy expended during any process generating electricity (or shaft horsepower) and then utilizing the waste heat.
eBook - PDF- Lijun Wang(Author)
- 2014(Publication Date)
- CRC Press(Publisher)
417 21 Combined Heat and Power Generation from Biomass Hao Liu and Rabah Boukhanouf 21.1 INTRODUCTION The process of fuel energy conversion to mechanical energy is governed by well-understood laws of thermodynamics. These impose severe limitations on the thermal performance of heat-to-mechanical conversion devices, or heat engines, which depends greatly on the available heat source and the heat sink temperatures. Often, this means that huge quantities of low-temperature heat energy are rejected from industrial-scale power plants such as coal-fired steam power plants. Even in modern combined cycle power plants where the heat source temperature can be as high as 1300°C, the maximum electrical efficiencies are only about 50%. Hence, the impossibility of converting all fuel energy into useful work has led many energy consumers both large and small scale to adopt energy-efficient techniques such as combined heat and power (CHP) to reduce energy consumption and alleviate the environmental impact of burning fossil fuels. CONTENTS 21.1 Introduction .......................................................................................................................... 417 21.2 CHP Technologies ................................................................................................................ 418 21.2.1 CHP Performance Characterization ......................................................................... 419 21.2.2 Prime Mover Selection ............................................................................................. 420 21.2.2.1 Steam Turbines .......................................................................................... 420 21.2.2.2 Gas Turbines .............................................................................................. 423 21.2.2.3 Microgas Turbines .....................................................................................
eBook - ePub- Farshid Zabihian(Author)
- 2021(Publication Date)
- CRC Press(Publisher)
Figure 10.7 ). The thermal efficiency (but not the electrical efficiency) of these plants is much higher than that of individual systems. Their efficiency can be determined by the following equation:FIGURE 10.7 Schematic of a typical extraction Cogeneration plant.(10.15)η Cogen=+W ˙ElecQ ˙CogenQ ˙Inwhereη Cogenis the overall efficiency (the thermal and electrical efficiencies combined) of the Cogeneration plant,is the generated electrical power in the plant (W),W ˙Elecis the time rate of the generated thermal energy in the plant (W), andQ ˙Cogenis the time rate of the input thermal energy (from fuel combustion) of the plant (W). The thermal energy generated in these plants can be used to provide either steam or hot water for industrial applications, such as food processing and paper manufacturing, or thermal energy for building heating systems. Small- and medium-size Cogeneration plants have gained remarkable popularity in the past few decades to provide superheated or saturated steam for indusial processes or to provide heat (and of course electricity) for space heating in large complexes, such as airports or university campuses.Q ˙InTechnically speaking, Cogeneration plants can be based on gas turbine power plants, steam power plants, internal combustion engines, or fuel cells. The main design objective of these plants can be different from that of typical power plants. In some applications, the main objective is to provide thermal energy (typically steam) at desired conditions at all times rather than to maximize electricity generation and its efficiency. The design of these units can be challenging since the electrical and thermal loads may not coincide. For this reason, there is a wide variety of configurations depending on the requirements of a specific application.1 Recently, the idea of trigeneration or combined cooling, heat, and power (CCHP) are also being investigated.These plants can be topping cycles or bottoming cycles. In topping cycles, electricity is generated first and then the remaining thermal energy is recovered from the plant exhaust flow for the thermal load. In these plants the thermal needs can be provided by the outlet flow of a steam turbine (known as back-pressure CHP plants, below), can be extracted from the stages of a steam turbine (referred to as extraction CHP plants, below), or can be recovered from the flue gas from the combustion process of a power generation unit. The former two types are based on steam power plants while the latter is used in gas turbines or internal combustion engines.
eBook - ePub- Paul Breeze(Author)
- 2014(Publication Date)
- Newnes(Publisher)
Chapter 6Combined Heat and Power
Abstract
All combustion power plants operate inefficiently, with much of the fuel energy going to waste as heat. This heat can be exploited in a variety of ways, raising the overall efficiency of the power plant. Heat is used for district heating in some US and European cities but this has not proved widely popular. Some industries can also make use of steam for their processes. Wood and paper processing factories will often have their own power plant that supplies both heat and electricity. Combined heat and power plants are most effective when both electricity and heat are supplied to the same customers. Many types of power generation plant can be used for combined heat and power but coal-fired boilers, gas turbines and piston engine-based systems are the most common. Fuel cells can also be exploited. Sizing a combined heat and power plant correctly is the key to economic viability.Keywords combined heat and power CHP Cogeneration district heating process heat steam generation gas turbine micro-turbine fuel cellThe production of electricity from coal, oil, gas, and biomass is an inefficient process. While some modern combustion plants can achieve 60% energy conversion efficiency, most operate closer to 30%, and smaller or older units may reach only 20%. The United States, which has a typical developed-world mix of fossil fuel–based combustion plants, achieves an average power plant efficiency of 33%, a level that has barely shifted for the past 30 years. Other countries would probably struggle to reach even this level of efficiency.Put another way, between 40% and more than 80% of all the energy released during combustion in power plants is wasted. The wasted energy emerges as heat that is dumped in one way or another. Sometimes it ends up in cooling water that has passed through a power plant and then returned to a river or the sea, but most often it is dissipated into the atmosphere through some form of air–heat exchanger. This heat can be considered a form of pollution.
eBook - ePub- Dimitris Al. Katsaprakakis(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
In such types of applications, the electricity production efficiency ranges between 5%–15%. It is underlined, yet, that electricity production constitutes an additional product, based on the achieved heat recovery, which otherwise would have been disposed in the ambient. Consequently, even with this considerably low efficiency, electricity production can be feasible in such types of Cogeneration systems.
There are two basic types of CHP configurations with gas turbines, the open and closed type CHP systems. The consumed fuel is usually natural gas, liquefied petroleum gas (LPG), or diesel oil.5.3.2 Gas Turbine Cogeneration Systems5.3.2.1 Cogeneration Systems with Open-Cycle Gas TurbinesOpen-cycle gas turbines are the conventional gas turbines presented in Chapter 2 . Air is suctioned from the ambient, compressed, and led to the combustion chamber. The produced hot gases after the ignition of fuel and the combustion of the fuel-air mixture are expanded, releasing power which is captured in the form of mechanical work by the turbine. The remaining hot gases are eventually disposed in the atmosphere with a temperature that can range from 300° C to 600° C.The disposed heat exploitation from an open-cycle gas turbine in a Cogeneration system can be approached with two alternative ways:- With its direct uses in thermal processes (district heating, industrial thermal processes, etc.).
- By supplying it to heat recovery units, named heat recovery boilers or simply gas boilers. High enthalpy steam is then produced in these gas boilers, appropriate for various production processes, like thermal processes, or also to drive a steam turbine for additional electricity production. This last implementation is the classic case of a combined cycle for electricity production, presented thoroughly in Chapter 2 .
In the above mentioned systems, there is the possibility to increase the hot gases’ specific enthalpy, and, subsequently, the delivered thermal energy, due to their high oxygen content. This is achieved by inserting a combustion chamber between the gas turbine and the heat recovery boiler, where, with the consumption of additional fuel, the capturing process of the contained oxygen is integrated, creating improved combustion conditions and increasing the system’s overall efficiency (Figure 5.8
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