Combined Heat and Power (CHP)

Combined Heat and Power (CHP)

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nAbstract

nCombined Heat and Power are useful system which facilitates efficient utilization of energy source. They have the capacity to produce both the heat and electrical energy simultaneously. CHP are used in industries, and other buildings to provide thermal and electrical energy. Cogenerations have numerous advantages as compared to traditional facilities because of their efficiency, reliability and environmental benefits. In terms of environmental advantages, they play a major role in reducing emissions of greenhouses gases such as SO2 and CO2. They also have the capacity to produce large amount of energy in a given energy input which means that they have high efficiency as compared to traditional systems. Therefore, they can be used as back-up facilities to supply electric energy in case of power outages. There are various factors that a firm should consider prior to installation of CHP. These include size of the systems, gas and electric tariffs and prices of electricity. Therefore, it is critical to pay close attention to all factors that may limit the efficiency of the systems.

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nIntroduction

nCombined heat and power is an engine that produces both heat and electricity simultaneously which can also be referred to as cogeneration. Heat generated in these engines can be utilized to produce cooling. Research indicated that Combined Heat and Power are very beneficial in the current world in terms of environmental, cost, reliability and efficiency (Yan, Chou and Wei 2015). Moreover, these engines have the capacity to produce large amounts of electricity which have critical role in improvement of environmental and economic potential of a given nation. CHP engines have high rate of efficiency because they generate electricity and heat from one source of fuel (Saha, Chakraborty and Ng 2011). CHP excerpt more beneficial energy from single source of fuel as compared to traditional power systems which generate electricity and heat separately. CHP systems run at an efficiency of 80 per cent relative to standard power plant which works at an efficiency of 45 per cent (Oliveira Júnior 2013). In this regard, these systems have the capacity to reduce carbon emission and cost of energy.

nCogeneration vs. Traditional System, Source (Saha, Chakraborty and Ng 2011)

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nApplication of CHP

nThe global reserves for natural gas, coal and oil are diminishing hence inefficient machines are not sustainable. In addition, these fuels cause global warming which are the leading causes of climatic change. However, nearly 90 percent of the global energies use these forms of energy (Sundmacher 2012). A traditional power system is normally inefficient to produce electricity. Thermal power systems have no capacity to change all the thermal energy into electrical energy. In this respect, a large amount of heat is lost in the majority of heat systems. However, CHP are neutral in terms of production of energy because it can use both fossil and renewable fuels (Yan, Chou and Wei 2015). Most importantly, the CHP system is able to utilize the surplus heat, which is wasteful in a traditional power plant. Consequently, these system uses lower amount of fuel to generate equal energy levels as traditional thermal powers

nThe CHP are constructed in a manner that allows steam turbines to utilize lower pressures of steam after going through various stages in the turbine. Similarly, they are constructed to utilize the back pressures. The CHP viability particularly in minor installations of CHO is dependent on a proper operations base load. The efficiency of the CHP increases when heat can be applied near it (Anon 2011). On the contrary, its efficiency decreases in case the heat has to be conveyed for longer distances. Consequently, it needs severely insulated tubes that are inefficient and expensive. However, transfer of electricity requires a wire which is relatively cheaper and can be transported over a long distance. An automobile engine can operates as a CHP especially in winter because the waste energy in form of heat can be utilized to warm the vehicle in the interior parts (Sundmacher 2012). Thermally enhanced oil recovery systems usually generate large amount of electricity.

nCHP Steam Turbines, Source (Sundmacher 2012)

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nThere are different plants that apply the combined heat and power systems such as in bottoming and topping cycle. Topping cycle systems normally use steam turbines to generate electricity. Condensation process then occur which enables utilization of exhausted steam to produce heat at lower temperature (Saha, Chakraborty and Ng 2011). The process of condensation, therefore, can be applied in desalination of water and district heating. On the contrary, bottoming cycle system generates heat at higher temperature especially in manufacturing processes in industries. Additionally, electrical plant is supplied through recovery boiler of waste heat (Yan, Chou and Wei 2015). Bottoming cycle system is only applied in case the manufacturing process needs very large amount of heat especially in furnaces used in metal and glass manufacturing (Khartchenko and Kharchenko 2013). Therefore, bottoming process systems are not commonly used

nLarge system of Combined Heat and Power generates electricity and heating water for a certain town or for industrial area. Some CHP uses natural gas to turn turbines utilizing the waste energy. Moreover, some CHP utilize an interchanging gas engine that is more efficient as compared to gas turbine (Pilatowsky Figueroa 2011). It also uses natural gas as the fuel. CHP gas engines are designed as completely packaged systems that can be connected within an external or plant room area. It uses simple networks to the heating systems, electrical distribution and gas source. CHP can also use alternating diesel engine or gas engine based on the type of biofuel available. In this case, it is beneficial to use biofuel because it minimizes consumption of hydrocarbon fuel (Saha, Chakraborty and Ng 2011). Therefore, it decreases the emissions of carbon in the environment. CHP also uses steam turbines in the heating mechanisms. Furthermore, the combined heat and power is able to use nuclear power where turbines with extractions are connected to the heating system.

nSmaller CHPs can apply either Stirling engine or reciprocating engine. The radiator or exhaust removes heat. Smaller systems are commonly used because it is less expensive to operate smaller diesel or gas engines. In some instance, municipal and industrial solid waste or biomass is used to run the combined heat and power (Umeda 2012). Similarly, waste gas such as sewage gas, coal mine gas, landfill gas and animal waste gas can be utilized as fuel.

nMicro Combined Heat and Power

nMicro CHP are usually referred to as Distributed Energy Resource or micro cogeneration. They are usually used in small and medium size business as well as in houses. In addition, they normally generate power less than 5000 Watts. The power generated in the Micro CHP is used to operate business activities and in homes. In some instance, some businesses can sell excess power into the main power grid (Oliveira Júnior 2013). More significantly, they play a major role in provision of electric backup especially in homes and buildings using photovoltaic system. Studies have confirmed that a hybrid system using both photovoltaic system and micro CHP has many benefits in terms of decrease in the waste energy particularly in heating and electrical appliances. Furthermore, it can be applied to supply the waste energy to an absorption chiller (Yan, Chou and Wei 2015). Therefore, modifications on the micro CHP can be used as cooling system in homes and businesses. The capacity of these systems to minimize emissions is higher relative to traditional systems of cooling, heating and power.

nIndustrial Combined Heat and Power

nChemical plants, refineries, paper and pulp mills use cogeneration systems. In this processes, high degrees of heat are required especially in drying tasks. Industrial cogenerations are flexible, valuable and losses low amount of heat although small amount of power is lost (Umeda 2012). More importantly, they improve sustainability because they significantly decrease the carbon footprint relative to purchasing electricity from the national grid or on-site fuel burning or producing steam (Yan, Chou and Wei 2015). Industrial CHP system usually runs at a decreased level of pressure as compared to utility pressures. Higher pressure costs are also higher for utilities compared to industrial CHP (Kolanowski 2011). Therefore, it is expensive to operate utilities due to high costs of operation in terms of pressure required and power.

nCombined Heat and Power plants are also applied in the generators for heat recovery steam which are used to produce steam after water heating. They use either reciprocating engines or gas turbines through gases at intense heat (Anon 2011). Steam produced is used to move turbines or in other processes that need high temperatures.

nEconomic and practical factors that influence CHP viability

nThe viability Combined Heat and Power (CHP) is determined by economic factors, environmental benefits, reliability, and efficiency factors.

nEconomic factors

nCombined Heat and Power systems have a variety of benefits with regard to decline in the cost of energy. CHP appliances have a high efficiency level hence hey consume less amount of energy which ultimately minimizes the cost of energy. Economic benefits are realized from CHP system users because the cost of electricity is minimized (Umeda 2012). The users of CHP systems need to compare the CHP technology cost in terms of maintenance, operation, fuel and installation on one hand and electricity prices on the other hand. Using CHP systems is a meaningful investment if the cost of electricity is reduced significantly relative to investment (Saha, Chakraborty and Ng 2011). Furthermore, CHP system produces heat which is less costly as compared to other appliances providing thermal energy.

nThere are also indirect benefits associated with minimum cost of energy. For instance, CHP devices offer many advantages because it decreases cost of offset capital and enhancement of reliability. Traditional thermal and power energy appliances need frequent update or replacement of chillers and boilers (Oliveira Júnior 2013). Therefore, installation of CHP appliances eliminates installation capital incur in needless chillers and boilers.

nSince Combined Heat and Power appliances have higher reliability, they have several economic advantages. In this case, it is beneficial to use CHP devices particularly as power backup systems because they enable users to use their own electricity in case the electricity prices are unsustainable (Sundmacher 2012). Furthermore, CHP devices offers economic benefits because they eliminate losses from distribution and transmission since they are usually situated nearby as opposed to traditional energy generation which losses huge amount of power through distribution and transmission processes (Knopf 2012).

nEfficiency advantages

nAs compared to traditional thermal and electricity generation system, Combined Heat and Power systems uses lower amounts of fuels to generate a certain output of energy. Therefore, these systems provide a wide range of advantages in terms of production of electricity and heat (Umeda 2012). Most of the power systems using fossil fuels waste approximately 67 per cent of the total produced energy through heat energy. Combined Heat and Power system has the capacity to increase operating and production capacity to a minimum of 75 per cent or maximum of 88 per cent (Yan, Chou and Wei 2015). The total operating and production efficiency of traditional thermal and power system is less than 33 percent which means they consume more fuels to generate a given electrical and thermal energy output (Sundmacher 2012). CHP applications are also associated with substantial improvement of quality of environment and reliability of power.

nThrough recovery of waste energy, CHP engines normally accomplish efficiencies of total system of between 60 and 80% in the process of generating heat and electricity. Moreover, some engines have the ability to accomplish 90 per cent efficiency (Knopf 2012). The type of technology applied determines the level of efficiency in the CHP design system. For instance, CHP made of steam turbine has 80 percent efficiency while micro turbines have an efficiency of between 60 and 70 per cent (Anon, 2011). Others like reciprocating engine, combustion turbine and fuel cell have efficiencies of 75 percent, 65 percent and 55 per cent respectively (Saha, Chakraborty and Ng 2011).

nEnvironmental factors

nA variety of environmental benefits are associated to Combined Heat and Power systems as compared to on-site production of thermal and electrical energy production. A study by Kolanowski (2011) suggested that improvement of efficiency on CHP play a critical role in enhancing environmental benefits. Low amounts of fuels are needed to operate CHP engines to generate the same level of thermal and electrical energy as compared to traditional power systems (Kolanowski 2011). More importantly, Combined Heat and power systems have the capacity to generate fewer pollutants in the air which reduces cases of global warming. In addition, they decrease the emissions of greenhouse gas such as carbon (IV) oxide. Combined Heat and Power systems are also important because they minimize air pollutants such as sulphur dioxide and nitrogen oxide (Yan, Chou and Wei 2015). The consumption of water is also minimized because the systems have efficiency steam turbines.

nA study conducted by Khartchenko and Kharchenko (2013) indicated that Combined Heat and Power systems contribute to 85 GW of power in the United States. In this case, they contribute to 9 per cent of the power in the national grid. The report proposed that by 2030, the United States will be using approximately 20 per cent of its power through the CHP (Khartchenko and Kharchenko 2013). Other reports have noted that there is growing level of power generation via the Combined Heat and Power system. Fortunately, use of power produced via the CHP helps to reduce 848 MMT of carbon dioxide in the environment (Dinçer and Zamfirescu 2011).

nUsing CHP helps to minimize consumption of energy which means that approximately 50 per cent of the total energy that is used in the United States currently can be reduced. Furthermore, various investments related to CHP would open new investments worth billions of capital (Anon 2011). Consequently, the amount of carbon monoxide would be reduced by more than 50 per cent of the current emissions. More significantly, reports by Beith (2011) estimated that using CHP system is likely to reduce approximately 60 per cent of the expected carbon monoxide emissions between 2015 and 2030 (Beith 2011). Therefore, the report suggests that CHP is efficient in reduction of CO, CO2 and SO2 in the environment (Umeda 2012). Consequently, policies should be formulated to ensure that greenhouse gases are minimized.

nEnvironmental benefits in CHP vs. Traditional System Source (Beith 2011)

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nReliability of Power

nCombined Heat and Power engines have enhanced reliability of power which also associated to improved economic advantages. A cogeneration system can be situated strategically at the right place. Therefore, the system does not depend on power from the main grid (Sundmacher 2012). Moreover, it is self-reliant because it less likely that it will lose power. Cogeneration engines offer thermal and electric energy to an area continuously. In this regard, it enable industries, homes and hospitals to develop their own sources of thermal and power needs especially when the cost of electricity is relatively high (Anon 2015). In this respect, people should use the Combined Heat and Power when the costs of fuels are low and the prices of electricity are high. Furthermore, cogeneration is reliable in provision of back-up power hence users can use them as an alternative to installation of more generators (Umeda 2012). They are very useful especially in case of power outages.

nFactors that influence the choice of CHP plant

nMany firms have adapted Combined Heat and Power plant aiming to reduce total cost of energy and improve the efficiency of their systems (Kolanowski 2011). However, there are certain factors that they consider when choosing the cogeneration plant that they can install.

nUse of both electricity and heat

nTypically, firms need to consider whether the CHP plant is only a source of generation of electricity. Based on the design of cogeneration, nearly 30 per cent of energy input is actually produced as electricity. Therefore, 70 per cent of output is generated as waste thermal energy. If the industry does not have to use the waste thermal energy, it will be released into the atmosphere (Yan, Chou and Wei 2015). Consequently, the efficiency of the CHP will be reduced. Additionally, the economics of operating the system will not be sustainable. Utilization of water thermal energy involves hot water or steam for use process or just providing hot water or heat to control the CHP space. According to Anon (2011) the CHP systems heat loads are effective when they are needed throughout the year instead of loads required during certain seasons. For instance, during hot seasons, the CHP applications can supply heat utilized to run absorption chillers (Anon 2011).

nThe industry management should therefore, select a CHP application that utilizes more of the heat energy. Utilization of large amounts of the waste thermal energy improves the efficiency of cogeneration (Sundmacher 2012). More economic benefits can be achieved when the efficiency of cogeneration is high. In some industries, they do not use the exhaust heat which reduces the efficiency of the CHP system (Saha, Chakraborty and Ng 2011). Therefore, thermal efficiency should be used when choosing a cogeneration system because it can help to save financial resources that can be used in other processes.

nPrices of energy

nEnergy prices are factors industry need to consider when choosing the cogeneration system. It is advisable to select the CHP when the prices of fuel and natural gas are low and the prices of electricity are high (Dinçer and Zamfirescu 2011). When the utility electricity is lower or when the government supply at reduced prices, it is not right to use the cogeneration because it may not cut it further. This is particular applicable if the government does not reduce the cost of fuel and natural gas (Yan, Chou and Wei 2015). In addition, firm’s management must consider expected prices of energy in the future.

nIn this case, when the CHP system has only economic benefits with a very thin line of energy prices, the project may not be economical if the prices of energy are lower. A firm should also select a CHP if it has a wide range of fuel sources at cheaper price (Anon 2015). For instance, biomass, furniture and wood processing systems utilize the CHP since there is a variety of wood waste which they can utilize as fuel in the CHP system.

nSize of CHP system

nPrior to installation of CHP system it is essential to consider its appropriate size. Therefore, the choice of cogeneration should be guided by the right prices. For instance, when a firm has a very large CHP, it may affect it overall efficiency because it will be producing too much heat that is wasted into the atmosphere (Sundmacher 2012). Moreover, the system will not operate at its full capacity which also minimizes its efficiency. A large CHP would also produce large amount of electricity which forces the firm to sell it to the main grid. In most cases, the firm would sell the excess electricity at lower prices as compared to what they would have purchased it from the utility (Umeda 2012). More importantly, the firm would require large capital costs which affect the viability of the project. In this regard, the firm should have correct information on the heat and electricity requirement in order to choose a project that meets their needs.

nChange of Gas and electric tariffs rates

nWhen choosing a CHP system, it is critical to know the effects of cogeneration on the gas and electric rates. For instance, installation of CHP may change the rate of electricity from the utility firm because the consumption of electricity will reduce (Anon 2011). Most of the utility companies offer a different tariff to companies using an on-site production. In cases the CHP system uses natural gas; the consumption of gas will considerably increase (Yan, Chou and Wei 2015). Ultimately, the firm will be required to adapt higher tariff based on the level of natural gas intake. Therefore, when choosing a CHP system it is necessary to consider the economies of changing tariff rates. Moreover, installation of CHP requires interrelating with the main power supply (utility company) (Saha, Chakraborty and Ng 2011). However, this process is long and costly hence it is necessary to talk with the utility company prior to installation of cogeneration.

nOverall system economics

nThe combined heat and power systems are usually economical when both thermal and electric outputs are utilized in the industry. Research has revealed that the prices of electricity from electrical utilities may be lower as compared to cost of installation and running cogeneration systems (Beith 2011). In addition, an industry saves more when the cogeneration facilities are operating continuously and effectively. Therefore, the size of cogeneration plant must be dependent on minimum heat and electricity needs of the industry to facilitate continuous operation (Sundmacher 2012). This helps to utilize the thermal and electrical energy efficiently.

nPractical example

nA cogeneration plant has waste thermal production of 60 per cent with 40 per cent electrical efficiency in the process of manufacturing. The maximum electrical output energy is 500 kW while maximum thermal output is 300 kW for an industrial plant, determine the appropriate size of CHP that can economically utilize all the thermal and electrical energy (Sundmacher 2012).

nThe cogeneration facility can be designed as demonstrated below. Fuel input is Qf, waste heat is Qw, electrical output is E and beneficial heat is Qu.

nElectric efficiency Effe = (Sundmacher 2012) and

nThe efficiency of heat exchanger Effhx =

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nMerging efficiency associations and balances of energy provides a Qu equation with regards to Effhx, Effe and E: (Yan, Chou and Wei 2015)

nQu = E (1)

nBased on diagrams on loads profiles, the maximum electrical energy needed constantly is 500 kW. Therefore, using Equation I, the operating thermal energy, Qu, from a cogeneration is:

nQu = 500

nQu = 450 kW

nAccording to the calculation, at an electrical power output of 500 kW, the beneficial heat output would be 450 kW. Nonetheless, on constant basis, the industry can only utilize 30 kW of heat power. Therefore, beneficial power of 300 kW is the constraint. Using equation 1, at the beneficial constraint thermal power of 300 kW will produce:

nE = 300

nTherefore, E = 333 kW

nTherefore, the biggest cogeneration system where thermal and electrical power can be utilized is Emax = 333kW and Qumax = 300 kW.

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nConclusion

nCombined Heat and Power (CHP) are very important systems especially in utilization of energy. They provide many environmental advantages because they reduce emissions of greenhouse gases such as SO2 and CO2 (Pilatowsky Figueroa 2011). In addition, they have high rate of efficiency in terms of utilization of energy. Cogeneration plants have a higher rate of reliability because their electrical efficiency is higher as compared to other traditional system (Anon 2011). Therefore, this means that they can produce more electrical and thermal energy as compared to traditional systems. They can be applied in industries, homes and buildings. CHP are best suited to provide electricity when the rates from the utility are higher (Beith 2011). Moreover, a company intending to install a cogeneration system should consider the size, changes of tariffs rates and cost of fuel. They are also expensive to purchase and operate hence the firm management should pay attention to its economies of scale.

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nReferences

nAnon, 2011. Better policies to support eco-innovation. Paris: OECD.

nAnon, 2011. Conversion of Coal-Fired Power Plants to Cogeneration and Combined-Cycle. London: Springer London.

nAnon, 2011. Urbanism in the Age of Climate Change. Washington, DC: Island Press/Center for Resource Economics.

nAnon, 2015. Sustainable Future Energy Technology and Supply Chains. Cham: Springer International Publishing.

nBeith, R., 2011. Small and micro combined heat and power (CHP) systems. Oxford: Woodhead Publishing.

nDinçer, I. and Zamfirescu, C., 2011. Sustainable energy systems and applications. New York: Springer.

nKhartchenko, N. and Kharchenko, V., 2013. Advanced Energy Systems, Second Edition. Hoboken: CRC Press.

nKnopf, F., 2012. Modeling, analysis, and optimization of process and energy systems. Hoboken, N.J.: Wiley.

nKolanowski, B., 2011. Small-scale cogeneration handbook. Lilburn, GA: Fairmont Press.

nOliveira Júnior, S., 2013. Exergy: Production, Cost and Renewability. London: Springer.

nPilatowsky Figueroa, I., 2011. Cogeneration fuel cell-sorption air conditioning systems. London: Springer.

nSaha, B., Chakraborty, A. and Ng, K., 2011. Innovative materials for processes in energy systems. London: Springer.

nSundmacher, K., 2012. Fuel cell engineering. Amsterdam: Elsevier/Academic Press.

nUmeda, Y., 2012. Design for innovative value towards a sustainable society. Dordrecht: Springer.

nYan, J., Chou, S. and Wei, Y., 2015. Handbook of clean energy systems. Chichester, West Sussex: Wiley.