E-mail address: kds97dee gmail. Use the link below to share a full-text version of this article with your friends and colleagues. Learn more. The classical DEA model is analyzed to identify the efficient ones from the whole gamut of plants run by various organizations of the central government, state government, and private sector. Slack analysis is carried out to explore the specific areas that need to be focused on, in quantitative terms, for the overall efficiency improvement.
On the basis of the insights provided by the outcome of the analysis, both qualitative and quantitative measures are proposed for improvement of the plant performances. The result of this analysis may assist the management of the power plants to introspect and review their systems and processes for optimal use of resources. The methodology adopted in the present work can also be employed for deeper understanding of power plants in other parts of India as well as in other countries.
Volume 21 , Issue 6. The full text of this article hosted at iucr. If you do not receive an email within 10 minutes, your email address may not be registered, and you may need to create a new Wiley Online Library account. If the address matches an existing account you will receive an email with instructions to retrieve your username. Vinod Kumar Yadav E-mail address: v7k7y7 yahoo. Obtained results indicated that the effects had the highest irreversibilities in the desalination system. It should be noted that effective waste utilization and a high efficiency ORC require a working fluid with a high critical temperature.
Noctane is a conventional organic working fluid for employing in ORC plants since it provides the needed critical high temperature K. Pine sawdust is considered as the most typical waste wood product in wood industry since pine trees are a common plant species in the whole world. Performing wood processing on pine wood results sawdust. Pine sawdust due to its large waste production is typically employed as a biomass. Hence, this type of biomass is considered in this investigation. Moreover, inlet temperatures of pump and turbine are given. In addition, other parameters which play role in the output of modeling such as ambient conditions including temperature and pressure and heat transfer coefficients of utilized components are represented.
Moreover, working under constant pressure is assumed for all equipment except pumps, valves, and ORC turbine. In addition, complete combustion is assumed for the biomass burner. Q i represents the supplied total heat rate of the biomass burner: M w indicates the moisture content of the used fuel.
HHV f is defined as the higher heating value and similarly to LHV definition, Dulong and Perit presented an equation for its calculation as follows : The heating cogeneration efficiency is expressed as: Here, Q h indicates the heating power and the heating cogeneration is represented by subscript cog, h. The heating power is: The subscripts hp,1 and hp,2 indicate the inlet and outlet of the heating process section respectively. The cooling cogeneration efficiency is expressed as: Here, the cooling cogeneration and the produced cooling energy through the chilling process in the evaporator are represented via subscripts cog, c, and ev respectively.
The evaporator cooling load is calculated as: Here, h ev,1 and h ev,2 indicate the inlet and outlet specific enthalpy of the cooling evaporator respectively. Hence, its modeling is discussed in detail here. In addition, u is the biomass moisture content factor in the chemical reaction and can be calculated as: M w refers to the biomass moisture content. The biomass molar flow rate of the biomass calculated as: M CHO represents the biomass molecular weight. The enthalpy balance between the inlet and outlet of the biomass burner should be written in order to obtain the burner flame temperature.
The enthalpy balance is written as: In this balance, is not known. Therefore, it can be obtained by employing the following equation: Similar to state 3, the total enthalpy at state 4 can be calculated as: The evaporator pinch point temperature is stated as : Exergy destruction plays a significant role in exergy analysis.
It is demonstrated the lost potential work that is wasted as a result of irreversibility. Here, T, ex , and Ex d indicate temperature, exergy per mass flow rate, and exergy destruction rate respectively. The subscript j indicates the property value at state j and the subscript 0 is the ambient property value. The inlet and outlet of the defined control volume is shown by subscripts i and e respectively.
The total exergy rate is stated as: Here, enthalpy per unit mass, entropy per unit mass, velocity, elevation, and gravity are represented by h , s , V , z , and g respectively. In this study, it is assumed that there is no change in the velocity and elevation during the process. Thus, their related terms in physical exergy calculation are neglected. For an ideal gas, the chemical exergy of species j is calculated as Ref. The variables x indicates the molar concentration and R is the universal gas constant.
The net electrical exergy efficiency is expressed as: Ex f is defined as the fuel biomass chemical exergy and obtained as: The cooling cogeneration exergy efficiency is calculated as: The exergy efficiency of the heating cogeneration is expressed as: Cogeneration and trigeneration systems are considered as one of the most important parts of energy system in different countries.
Additionally, these systems are one of the most sustainable energies based on energy conservation and environmental aspects. Efficiency analysis plays an important role for designing process of cogeneration based district energy system. Various working conditions were considered in this study. Results showed that exergy destruction was not influenced by number of stages, capacity of desalination system, top turbine temperature, and temperature of cooling water.
Both exergy destruction, including avoidable and unavoidable, in a cogeneration unit can be simply approximated. In addition, exergy destruction of the system was calculated. Results showed that for all the steam inlet conditions in cogeneration power plants utilized in sugar industries, higher pressure and temperature of steam generation led to obtaining lower exergy losses and exergetic efficiency enhancement. In this study, results showed that the boiler was the main reason for inefficiency of the plant.
Both energy and exergy efficiencies have been applied to assess performance of a combustion gas turbine cogeneration system with reheat. Energy and exergy analyses have been performed on the other systems ie combined heating, cooling and power generation in order to evaluate their performance. The utilization of hybrid systems, which use both biomass and solar energy, has been developed in recent years.
Various analysis including energy, exergy and economic were applied in cogeneration and trigeneration hybrid system. The optimal performances were compared under the same conditions for different cogeneration systems. Results indicated that exergy efficiency of sCO2 cycle enhanced by approximately Furthermore, based on the results, the highest exergy efficiency and the minimum cost of product unit for the cycle were achieved in the case of utilizing isobutane and RC as the ORC operating fluid respectively.
The ORC had low working pressure and cost because of its simplicity. In the reviewed papers, several analyses have been conducted including exergy, energy, economic, and exergoeconomic analyses. In order to get better insight, these studies are represented as well. Based on the summaries of the studies, which are represented in the above table, in the most of the cases, the highest exergy destruction occurs in boiler and combustion chamber.
It can be attributed combustion process, which has high exergy destruction, and heat transfer in high temperature difference. In addition, it can be concluded that using exergy analysis results in better insight into the plant defects and its potential to achieve higher efficiencies and more favorable performance compared with energy analysis. Integrating power plants with other systems such as fuel cells or desalination units will lead to enhancement in both energy and exergy efficiencies since it prevents heat losses. The performance of power plants integrated with other systems depend on several factors such as working condition, efficiency of each component and etc.
In order to enhance the efficiencies, it is necessary to figure out the components which have inappropriate performance and improve their efficiency. Moreover, finding the optimal working condition is another approach to achieve higher efficiencies. In this paper, various studies conducted on thermal power plants have been reviewed and derived key results are presented.
The highest level of energy losses occurred in the condenser and boiler respectively. In addition, it can be concluded that the cost of exergy destruction in the boiler and turbine is more than the other parts. In a CCPP, the maximum amount of exergy destruction has been taken place in combustion chamber based on obtained results from exergy analysis. This issue is because of the material that cannot sustain very high pressures and temperatures in the plant.
The efficiency of power plants can be enhanced by applying novel methods such as working under supercritical conditions. This magnitude of saving can be derived by operating the power plant with increased efficiency demands through concentrated efforts of the research community in this realm.
In fact, this matter is possible only if the metallurgical scientists significantly progress the development of new material that can withstand higher temperatures and pressures. Volume 7 , Issue 1. The full text of this article hosted at iucr. If you do not receive an email within 10 minutes, your email address may not be registered, and you may need to create a new Wiley Online Library account. If the address matches an existing account you will receive an email with instructions to retrieve your username.
Mohammad H. Ahmadi Corresponding Author E-mail address: mohammadhosein. Tingzhen Ming Corresponding Author E-mail address: tzming whut. Josua P. Tools Request permission Export citation Add to favorites Track citation. Share Give access Share full text access. Share full text access. Please review our Terms and Conditions of Use and check box below to share full-text version of article. Abstract Surging in energy demand makes it necessary to improve performance of plant equipment and optimize operation of thermal power plants.
Figure 1 Open in figure viewer PowerPoint. Figure 2 Open in figure viewer PowerPoint. The schematic design of a gas turbine power plant Air compressor Air preheater Combustion chamber CC Gas turbine Figure 4 Open in figure viewer PowerPoint. Schematic of gas turbine trigeneration system Figure 5 Open in figure viewer PowerPoint. Figure 6 Open in figure viewer PowerPoint. Schematic of proposed combined cycle Figure 7 Open in figure viewer PowerPoint. Exergy flow in the power plant Figure 8 Open in figure viewer PowerPoint. Schematic of a combined cycle power plant with an auxiliary fired heater Air compressor Air is delivered to the compressor at ambient pressure 1 bar and temperature T 1.
Combustion chamber CC The variation of air mass flow rate, lower heating value of the fuel LHV , and the efficiency of the combustor should be specified to calculate the combustion chamber's outlet properties: Duct burner The auxiliary burner system is provided to burn the remained fuel in order to raise up the exhaust gas temperature that is transmitted through the HRSG.
Cost anlaysis In order to have an estimation on the cost of exergy destruction in each part of the investigated plant, the cost balances for each part is considered and solved in the first step. Structure of CCPP Figure 10 Open in figure viewer PowerPoint. The feeding biomass chemical combustion equation with air and also regarding the assumed complete combustion is: Energy losses are not significant due to its low quantity based on exergy analysis.
The highest amount of exergy destruction occurred in boiler. Exergy destruction cost in boiler and turbine were more than the other parts of the system. Malfunction analysis was presented in this study.
Life cycle assessment (LCA) of solar thermal tower power plants
Results depicts that the highest amount of energy losses occurred in condenser. In addition, the highest amount of irreversibilities occurred in boiler. It was necessary for improving equipment thermal performance to decrease endogenous exergy destruction. Then, external system structure must be optimized to reduce exergy destruction. Based on thermodynamic approach, fuel saving mode was better which was attributed to the greater net power output of solar and efficiency of net power generation.
The mode of fuel saving was more feasible using solar energy more efficiently. Unit cost for the turbine power plant was obtained and equal to 3. Reducing the inlet temperature which leads to both consuming lower power in compressor and having less amount of exergy destruction.
Monitoring fuel air ratio in the combustion chamber. Total cost rate and exergy efficiency are considered as objective functions. In Pareto solution, the middle point was considered as the optimal solution, which had the minimum total cost rate 1. All performance characteristics diminish by increasing of pressure ratios at lower values of equivalence ratios, but they increase by surging in pressure ratios at higher equivalence ratios. The highest amount of exergy destruction occurred in gasification process.
Heat recovery steam generator had the second level in term of exergy destruction. Following results have been derived: The highest amount of exergy losses was caused by mixing in the combustor The highest amount of exergy waste occurred in the heat recovery steam generator. The highest amount of exergy losses were because of inefficiencies in the power section. The unit plant has a turbine to convert to convert thermal energy of steam into mechanical shaft rotation. The turbine has three pressure stages high pressure, intermediate pressure and low pressure. In all three stages, there are stream extractors to facilitate regenerative heating of feed water heater.
Three low-pressure heaters LPH , one deaerator and two highpressure heaters HPH use bled steam for regenerative feed heating. A condenser is used in the power plant to condense low pressure steam into water. The condenser is water-cooled type and it has been built for seawater operation. There is a minor loss of water in the plant process. Therefore, makeup water for the boiler feed is added into the condenser hot-well after passing through a deaerating system.
It has been found that the requirement for makeup water in the boiler is very low compared to the total requirement. The condensate passes through a series of heat exchangers - LPHs, deaerator and HPHs which take heat from the regenerative bled stream as mentioned earlier. The highest capacity of the power plant is MW of electrical power.
This is the maximum capacity rating MCR of the power plant. The capacities of all individual process components were configured with appropriate data to produce the rated power. A detailed description of the configuration of all individual process components is provided while describing the model flow sheets in the subsequent section.
Institute of Engineering Thermodynamics - Thermal Power Plant Components
Process model development In this research, the power plant was represented by two separate flow sheets. The detailed descriptions of these two model flow sheets are provided in the next sections. Power generation model The flow sheet for the power generation cycle is presented in Figure 3.
It shows the steam cycle of the power plant. This cycle is known as the Rankine cycle  including reheating and regeneration. The boiler in the power plant has feed water heater, superheater and reheater. The boiler feed water heater and super heater are included in the boiler model while the reheater is represented as a separate heater denoted as reheating as shown in Figure 3. The whole turbine is modelled using 7 unit turbine models as shown in the figure. This was done to simultaneously facilitate the use of the inbuilt SysCAD turbine model and steam extraction. The steam leaving the low-pressure turbine was connected with a condenser, which is described using a shell and tube type heat exchanger in SysCAD.
The condenser is supplied with cooling water to perform steam condensation. The pressure of the steam at this stage is very low. The bled steam extracted from the turbine is recycled in to the condenser. The makeup water required in the process is added after the condenser. The condensate pump is located after the condenser, and it boosts the pressure of the condensate high enough to prevent boiling in the low-pressure feedwater heaters. The condensate mixes with the makeup water before entering the condensate pump. There are three low-pressure heaters connected with the extracted steams from different turbine stages as shown in Figure 3.
The feed water is gradually heated, taking heat from steam with increasing temperature and pressure at each stage. In a low-pressure heater, heat exchange occurs in two stages. At first, the steam condenses to its saturation temperature at steam pressure and then occurs sensible heat exchange.
All the three heaters were developed based on the same principle. The main purpose of a deaerator is to remove dissolved gases including oxygen from the feed water. Some heat exchange occurs in the deaerator. In this model, the deaerator is treated as a heat exchanging device where steam and feed water exchange heat through direct contact.
The tank model built in SysCAD was used to represent the deaerator. The feed water, after heating in the deaerator, is pumped through the feed water pump. The high pressure feed water is heated through two more high-pressure heaters. The steam for the high pressure heaters is extracted from the high pressure turbine exhaust, and from an inter-stage bleed on the intermediate pressure turbine. Each of the high-pressure heaters is developed using two SysCAD heat exchange models as described earlier for the low-pressure heaters. The operations of all the individual components used in the model flow sheet are described in detail in the subsequent discussion.
The discussion includes data used to configure each component for the modelling. Boiler and reheating The boiler model in SysCAD calculated energy required by the boiler based on the boiler feed water, the required drum pressure and the superheated steam conditions. It is a very simple model, which does not take into account the type of fuel used or the type of economiser. It heats the high pressure feed water stream to saturation temperature and then to the super heated condition as specified.
A portion of saturated water is blown down from the boiler to discharge impurities and maintain water purity. In this turbine stage, part of the steam energy is converted to mechanical shaft rotation and the pressure and temperature of the steam drops based on turbine configuration and supplied data discussed later. A portion of the steam is taken out to regeneration before it goes to reheating. The reheating model is a simple heater for sensible heating and no phase change occurs. The simple heater only calculates the heat required for reheating.
Steam turbine The built-in steam turbine model in SysCAD transforms steam energy into electrical power. In a flow sheet, it needs to be connected with one single steam input and one single stream output. The inlet conditions of the steam, such as temperature, pressure, mass flow and quality of steam need to be defined. Using steam inlet data and specified turbine efficien cy, SysCAD calculates turbine output power and the condition of the outlet stream.
The reheater heats up the steam to a high temperature to improve the quality of steam. A portion of the steam is extracted before the reheater and fed to a high-pressure heater named HP6. In Figure 3, the reheated steam enters the intermediate-pressure turbine. This stage was modelled using two turbine unit models. It should be noted here that the SysCAD turbine model ignored changes of potential and kinetic energy since the changes are negligible.
The turbine efficiency, mechanical efficiency, outlet pressure and steam bleed of the turbine in different stages are configured with data supplied by the plant and provided in Table 1. Condenser The condenser was represented by a shell and tube heat exchanger, and it transfers energy from one stream to another.
The primary use of this model is to transfer latent heat by steam condensation. The model performed the following calculations as defined in SysCAD. For the heat transfer to the individual stream. In this model, the vapour entering the condenser first comes to the saturation temperature In this model, the vapour entering the condenser first comes to the saturation temperature and then condensed.
Nocooling furtherof cooling of occurs. No further the liquid Theoccurs. Each of the heaters uses two models to The low pressure and high-pressure heaters were developed primarily using the shell and tube achieve its desired functionality. The first one was used to condense steam into saturated heat exchanger model as described earlier.
Each of the heaters uses two models to achieve its water and the second exchanger was used to cool the saturated water to a temperature desired functionality. The first one was used to condense steam into saturated water and the below the saturation temperature through sensible cooling. In SysCAD, a heat exchanger second exchanger was used to cool the saturated water to a temperature below the saturation model has only one desired functionality. If one heat exchange model performs temperature through sensible cooling. In SysCAD, a heat exchanger model has only one condensation of steam from some temperature above the saturation temperature, it cannot 3.
Low pressure and high pressure heaters desired functionality. If one heat exchange model performs condensation of steam from some temperature above the saturation temperature, it cannot perform any further cooling to the stream. Therefore, the second heat exchanger was used to achieve the desired functionality as. Deaerator The fundamental purpose of a deaerator in power generation is to remove oxygen and dissolved gases from boiler feed water.
This helps prevent corrosion of metallic components from forming oxides or other chemical compounds. However, in the power generation model the deaerator was treated as a direct contact heat transfer component in order to describe it for the desired purpose of this study. In the deaerator, steam comes in direct contact with liquid water and therefore heat transfer occurs. A tank model in SysCAD is a multipurpose model.
There are sub-models available with a tank model such as reaction, environmental heat exchange, vapour liquid equilibrium, heat exchange, make-up, evaporation, and thermal split.
It was used here for defining the deaerator. This tank model was configured to achieve vapour liquid equilibrium only. The other submodels were not used. The size of the deaerator tank was kept at 10 m3 and all the streams were brought to the lowest pressure through a built-in flashing mechanism. Pumps There are two pump models used in the power generation model.
One is a condensate pump and the other is a feed water pump. The pump model boosts pressure of liquid to a specified pressure.
In order to configure a pump in SysCAD it needs to be connected with an incoming stream and an output stream. It was assumed that the process is adiabatic and there were negligible changes of potential and kinetic energy, and they were therefore ignored. The two pump models were configured with their required pressure boost data as provided in Table 2. There is a large amount of information on the stream displayed in the pipe model. It also allows some userdefined calculations using data found on the pipe.
The pipe model can take pipe friction loss. However, in this project the loss in the pipe was considered to be insignif icant and was therefore ignored. In the pipe model, at different points of the power generation model code was applied to perform an exergy flow calculation. The details of exergy calculation are discussed later in section 4. Controls and calculation of power generation model There are two general controllers and two PIDs used to control the model to perform its set objectives. Codes were also used to calculate the net power output and the feed water require ments.
The net power output was calculated by deducting power used in the pumps from the generated power in the turbine. Boiler combustion model The boiler combustion model was developed to supply the desired amount of heat to the boiler. The model flow sheet is presented in Figure 5. As shown in the figure, the main components of this model are a boiler combustion, a water heater economiser , a superheater, a reheater and an air preheater. The combustion model was developed using a tank model, three heaters by simple heaters and the air preheater by a heat exchanger model built in SysCAD.
Boiler combustion The combustion model used a tank model built in SysCAD to perform the transformation of chemical energy to heat energy. A reaction sub-model was configured to perform that transformation. The chemical composition of the fuel was supplied by the plant and defined in the feed of the combustor named FUEL. The reactions and their extent were defined in a reaction editor of the tank model. The chemistry of combustion is complex and depends on many different factors.
It was assumed that there is sufficient air supplied to complete the combustion of coal in air. Nevertheless, the stoichiometric chemical equations used here were placed in a logical order based on the chemical affinity of the components. The power plant uses thermal coal supplied from nearby coal mines. The gross calorific value GCV of the coal at dry ash free daf conditions is Data on the composition of the coal was supplied by the power plant and is presented in Table 3.
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As mentioned earlier, chemical reactions were performed in reaction editor in SysCAD. In the reaction editor reaction, extent and sequence is provided. The combustion reaction for this modelling purpose is provided in Table 4. Combustion Reaction. An environmental heat exchange is configured to allow for some heat lost to the environment from the combustor. Water heater economiser , superheater and reheater These three components were modelled using the simple heater model built in SysCAD. The simple heater does not consider heating media or heater size.
It only provides an estimation of heater duty required at stream outlet temperature or stream outlet temperature for specific heater duty. It can also be configured to specify heater duty irrespective of temperature. In this model, the heaters were configured to supply a specific amount of heat through heater duty calculated in the boiler and reheater in the power generation model by a so-called duty method in SysCAD. Only the duty of such heating was calculated for these heaters. Air preheater The air preheater in this flowsheet was built using the heat exchanger model described previously.
Control and calculation in combustion model In this model, three control elements were used. The two PIDs for fuel and air regulate the required fuel and excess air to achieve a set point. The fuel requirement of the combustion was set dependent on the energy requirements in boiler and reheating in power generation model. This has increased the functionality of the model to produce any set amount of power output.
Make Carnot Batteries with Molten Salt Thermal Energy Storage in ex-Coal Plants
Similar to the power generation model, in pipes at different points of the boiler combustion model, code was applied to perform the exergy calculation using the Model Procedure MP of SysCAD. Energy analysis and efficiency improvement Energy analysis of a process is very important for identifying where energy is lost. It is performed through a process energy balance. This essentially considers all energy inputs in and outputs out of the system.
When the system is balanced, the sum of all energy inputs equals the sum of all energy outputs. In a power generation plant, the objective is to convert the maximum possible energy input into useful work. According to the second law of thermodynamics, due to thermodynamic irreversibility not all energy input is converted in to useful work. Traditionally, the energy analysis of a process is performed through energy balance based on the first law of thermodynamics. It focuses on the conservation of energy.
The shortcoming of this analysis is that it does not take into account properties of the system environment, or degradation of energy quality through dissipative processes . In other words, it does not take account of the irreversibility of the system. Moreover, the first law analysis often gives a. Getting an accurate estimate warrants a higher order analysis based on the second law of thermodynam ics, as this enables us to identify the major sources of loss and shows avenues for performance improvement .
This essentially refers to exergy analysis that characterises the work potential of a system with reference to the environment. Energy balance calculation The energy balance was performed for the whole power generation process. As it was assumed that the energy lost in pipes is negligible, the loss of energy in process components represents the loss of energy of the whole process.
The analysis was, therefore, performed to balance energy flow against all process components such as the boiler, turbine, and heat exchangers. This calculation provided information about where and how much energy is lost. The process model developed in SysCAD performs mass and energy balances considering all the input and output streams and heat and work into and out of each component.
The equations used for these balances are provided in Equations 5, 6 and 7.
In order to obtain a balance of energy flow against different components of the power plant Figure 6 is used. The points in these figures were chosen very carefully so that they could describe the inflow and outflow of energy carried by streams to and from each component. The work inflows and outflows were observed from the SysCAD process energy balance and were used in balance calculations where they applied.
Legends 1. High pressure boiler feed water before entering boiler 2. Boiler superheated steam 3. HP Turbine exhaust steam 4. Reheated stream 5. IP Turbine exhaust stream 6. LP Turbine exhaust stream 7. The energy flows at the mentioned points were obtained directly from the SysCAD process balance at each mentioned point and exported to Microsoft Excel. It is important to note here that as potential and kinetic energy of the stream was ignored, SysCAD calculated the energy flow of the stream using Equation 7.
The work in and out of the components, particularly in different stages of turbine and pumps, were found in the SysCAD process balance. Therefore, the balance of energy flow was calculated observing all energy into and out of each component in the form of either heat or work. The details of energy balance calculations were performed in Microsoft Excel across various process equipment using equations provided in Table 5.
Here, E represents energy flow in kW. The subscripts used in the energy balance represent point numbers in Figure 6. E with subscript l represents energy lost and the corresponding process is mentioned in the subscript within the bracket. W represents work and the corre sponding process component is mentioned in the subscript within the bracket. Exergy balance calculation Exergy can be defined as work potential, meaning the maximum theoretical work that can be obtained from a system when its state is brought to the reference or dead state under standard atmospheric conditions.
Exergy analysis helps in identifying the process of irreversibility leading to losses in useful work potential and thus pinpointing the areas where improvement can be sought. Rosen  identified various exergy studies conducted by different researchers and found the significance of application for process energy analysis whether it is small or large but partic ularly more important for energy intensive ones e. From this point of view, exergy analysis for power plants can be useful for identifying the areas where thermal efficiency can be improved. It does so by providing deep insights into the causes of irreversibility.
The exergy is thermodynamically synonymous to availability of maximum theoretical work that can be done with reference to the environment. The terms with the subscript r are the properties of the exergy reference environment. The generalised equation above can be simplified or specified based on a process. The kinetic and potential energies are small in relation to the other terms, and therefore they can be ignored. The exergy flow was calculated at different points before and after the process components in different streams. The exergy of a stream was treated for both physical and chemical exergy.
The physical exergy accounts for the maximum amount of reversible work that can be achieved when the stream of a substance is brought from its actual state to the environmental state. According to Amrollahi et. This equation was applied for all liquid streams in the power plant. The reference environment mentioned earlier was considered as temperature At this temperature and pressure, the enthalpy and entropy were obtained for water.
Using Equation 9 exergy flow at different points of the power plant steam cycle was 10 9. Equation 10 was applied to the different gas streams such as the air stream entering combustion and the flue gas following combustion. Therefore, it enters the boiler combustor with only the chemical exergy with it. The chemical exergy flow of the fuel was calculated through Equation Standard Molar Exergy at C and 1 atm was found in the appendix of Moran and Shapiro  and used in Equation 12 to calculate exergy flow with fuel.
The values of molar exergy of important chemical species in standard conditions are presented in Table 5. The reference temperature is slightly higher than this temperature. At this small temperature difference, the change of molar exergy is negligible and therefore ignored. Once the exergy flows of all input and output streams were calculated, and the work inputs or outputs were obtained from different components, the destruction of exergy could be calculated by using Equation 13 after calculating all exergy inputs and outputs for a unit operation.
The simulation of the whole process model produces process a mass and energy balance. The simulation performed the balance at steady state using the configuration inputs provided to each component described in section 3. There is a wide range of thermo-physical data available in addition to process mass and energy balances. Using those data the exergy flow calculation was performed at the different points.
The balance of exergy flow against different components of the power plant was per formed individually for each component observing exergy flows into and out of the component. Equation 13 is used to calculate an exergy balance which is similar to energy balance calculation described earlier. The same points in the power plant were used to observe the exergy flow of the streams as in the energy balance calculation. Similar to the energy flow calculation, the work inflow and outflow were obtained from the SysCAD process energy balance and were used in exergy balance calculations where they ap plied.
The details of the exergy balance calculations of the power plant are presented in Table 7.
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As was the case for the energy balance calculation, the results of the exergy balance were exported to Microsoft Excel where, using equations described in Table 7, the exergy balance for all individual components was performed. In Table 7, the notation A represents exergy flow rate in kW. The subscript number in this table represents the point number in Figure 6.
A with subscript d represents exergy destruction in the corresponding process mentioned within the bracket. W represents work and the corre sponding process component is mentioned in a subscript within the bracket. Result and discussion As mentioned earlier, exergy analysis is performed to assess the loss of useful work potential; that is, the exergy destruction. The result of the exergy balance performed in the power plant is presented in Figure 7. In this figure, the exergy destruction is shown in percentages for different components of the power plant. The reason behind choosing percentage of total exergy destruction in different components is that these figures can easily be used to locate where the maximum exergy is destroyed.
In other words, they can help direct the focus of the improvement by considering the components where most of the exergy is destroyed. The reason why this amount of exergy is destroyed is also important for identifying how best to reclaim the lost energy back in the process. Figure 7. Figure 7 shows the result of this exergy destruction analysis. It is important to note that the boiler includes both reheating of steam after expansion in the high pressure turbine and preheating of air coming into the combustor. The results of exergy analysis are markedly different from the results of the energy balance, which shows most of the energy being lost in the condenser.
It shows that there are very significant differences between exergy destruction and energy lost for different process components. Figure 2. In other words, it indicates that the waste heat in the condenser does not have much potential to be utilised as a source of work and to improve the efficiency the power plant. On the other hand, further investigation of the exergy lost in the Figure 1. In an attempt to improve the efficiency of the power plant, the exergy analysis was revisited. It is found that the largest exergy destruction in the process occurs in the boiler.
Therefore, it Fluegas Blowdown is considered first for a detailed investigation. They are 1 the boilers internal heat transfer mecha nism from the combustor to the heating medium, which determines the boilers internal efficiency, 2 the heat loss in the departing flue gas stream and 3 the loss in the blowdown stream of the boiler. The contribution of the three losses of exergy flow in the boiler is presented in Figure 9. The simulation at steady state MW electrical power output showed that the flue gas after air preheating is leaving with an exergy flow of kW which constitutes about.
The blowdown stream of the boiler is another source of boiler exergy destruction.
It carries about kW exergy flow. The boilers internal heat transfer Figure 2. The exergy loses from flue gas and blowdown stream could be easily reutilised in the process Figure 3. However, the greatest single amount of exergy is destroyed in the boilers internal heat transfer arrangement. If the exergy lost through the boiler could be utilised in the system, this would improve the efficiency of the power plant very significantly. The chemical reactions occur in the boiler at a temperature of oC and produce huge amounts of exergy.
However, due to the limitations of the material used in the boiler, it is not capable of transferring the full amount of useable heat energy or exergy to the boiler feed water which is heated to only oC. In modern power plants, this limitation has received much attention with the invention of new materials for heat transfer used in boilers.
However, the power plant used as the subject of this study was an aging plant. The improvements needed to address such a big loss would require huge physical changes of the boiler system and may need further detailed investigation in terms of both technical and economic viability. The exergy lost in the turbine is investigated by looking at the losses at different stages of the turbine. The exergy lost in all three turbine stages is found to be due to the turbines internal performance. This can be better described as converting thermal energy to mechanical energy and then to electrical power.
The turbine system used in the plant is highly compact and specially designed for the process. Therefore, the task of reducing exergy destruction or improving the efficiency of the turbine system is very specialised in terms of its internal system. Similar to the boiler system improvement, it also needs further detailed investigation to assess the technical and economic feasibility of such changes.
It is noted that there are opportunities to improve energy efficiency of power plants by improving the performance of the boilers and the turbine system. The current trends towards ultra-supercritical power plant cycles are consistent with this aim. Conclusions In this study, exergy analysis of the power plant identifies areas where most of the useful energy is lost and discusses potential of the lost energy for improvement of the plant energy efficiency.
It shows that the boiler of a subcritical power generation plant is the major source of useful energy lost. Only negligible amounts of useful waste energy can be recovered through implementing some heat recovery system. In order to achieve significant improvement of energy efficiency the boiler and turbine systems need to be altered, which require further techno-economic study.
Author details R. Ltd, Editor. Metz, P. Bosch, R. Dave, L. Meyer eds , Editor. K, et al. Energy Conversion and Management, Exergy analysis of a thermal power plant with measured boiler and turbine losses. Applied Thermal Engineering, Thermodynamic irreversibilities and exergy balance in combustion processes. Progress in Energy and Combustion Science, Can exergy help us understand and address environmental concerns?
Exergy, An International Journal, Fundamentals of Engineering Thermodynamics. CO2 capture pilot test at a pressurized coal fired CHP plant. Energy Procedia, Analysis of retrofitting coal-fired power plants with carbon dioxide capture.