Environmental thermoeconomic performance analysis of gas turbine combined cycle under off‐design conditions

Although the gas turbine combined cycle (GTCC) system has better environmental performance, it still emits pollution gases such as CO2 and NOx. It is reasonable and necessary to add the environmental cost to the power production cost of the GTCC system. Based on the structure theory of thermoeconomics, through the reasonable pricing of pollutants (considering the environmental costs of CO2 and NOx emission), the system environmental thermoeconomic cost (ETC) model is developed in this study, which achieves absolute internalization of environmental costs. Taking GTCC with different gas turbine (GT) operation strategies as the research object, the influences of different operation strategies and environmental conditions on the GTCC system ETC are studied. The results of this study show that it is beneficial to maintain higher turbine inlet temperatures (T3) and turbine outlet temperatures (T4), thus ensuring better GTCC environmental thermoeconomic performance, and GTCC with the operation strategy (using inlet guide vane (IGV) control to maintain T3 at the design value and then to keep T4 at its maximum value (IGVT3‐650‐F) has the lowest ETC, which are 0.09429 $/kW·h at 75% gas turbine load rate (GTLR) and 0.10079 $/kW·h at 50% GTLR, respectively; reducing the emission of pollutants can reduce the unit ETC; for the combustion chamber, as the pollutant generation component of GTCC unit, it is most affected by the environmental damage cost; reducing the inlet air temperature can improve the system environmental thermoeconomic performance.


| INTRODUCTION
Energy is the material basis for human survival and an indispensable basic condition for social development. China's primary energy consumption is heavily dependent on coal. In recent years, with the emergence of environmental protection problems and strict environmental pollutants discharge standards, the disadvantages of coal-fired power generation are increasingly prominent. [1][2][3] Therefore, as clean fossil energy, natural gas has attracted more and more attention, and the proportion of natural gas power generation in China's electric power industry has gradually increased.
During the operation of the gas turbine combined cycle (GTCC) unit, due to frequent participation in the peak load regulation of the power grid, the GTCC system often operates in off-design conditions. However, with the decrease in the gas turbine load rate (GTLR), its thermal efficiency is reduced accordingly. 4,5 Therefore, the research on GTCC system performances under the full operation conditions (design/off-design condition) and energy-saving control strategy of GTCC systems have been paid more and more attention in recent years. 5 Researchers have conducted numerous studies on GTCC part-load performance improvement from the perspective of load regulation strategy optimization based on existing load regulation methods. 5,6 Variable inlet guide vane (VIGV) control and fuel-only control are two main methods of partial load power management for heavy-duty gas turbine (GT). The air mass flow entering the cycle can be controlled by the compressor inlet guide vane (IGV) angle. One of two practical principles is to be followed for unit load management via VIGV: keeping turbine inlet temperature (TIT, T 3 ) or turbine exhaust temperature (TET, T 4 ) constant at the design value. 4 For the Class F gas turbines, about 20% load reduction can be achieved when the constant TIT principle is employed, while the power load of the units can vary within 40-100% when the constant TET principle is used. The constant TIT principle has higher efficiency than the other one because of the higher initial parameters, however, it results in an increase in TET as the load decreases due to the decreasing expansion ratio. 7,8 Normally, below the minimum load of the TIT principle, the TET principle or fuel-only control is employed. The strategy of fuel-only control is to vary the fuel mass flow and not involve air mass flow regulation, which is normally working when IGV has been fixed. 8 Therefore, when different operation strategies are applied for GT, the variation laws of thermodynamic parameters and system performance will be different under variable load conditions. 9 The research results of Kim 10 showed that IGV regulation mode had a beneficial effect on the GTCC performance of uniaxial configuration. The thermodynamic performances of combined cycle units under different GT regulation modes were compared and analyzed, and the result showed that IGV regulation was favorable for the performance improvement of the combined cycle system. 11,12 Huang et al. 13 studied the effects of both the IGV regulation strategy and the conventional TIT regulation strategy on the combined cooling, heating, and power (CCHP) system performance. The results showed that the IGV regulation strategy could reinforce the part-load performance of the CCHP system.
The thermodynamic analysis only considers the unit thermodynamic performance parameters such as power, efficiency, and heat consumption rate, but does not consider the cost factors such as investment cost, fuel cost, and operation and maintenance cost, so it cannot comprehensively evaluate the production performance of the unit and its components. [11][12][13][14] How evaluating the comprehensive performance of the GTCC system, including the economic performance, has become a research hotspot.
Thermoeconomics with a combination of thermodynamics and economics is applied in cost accounting and performance optimization of the GTCC system. [15][16][17] After continuous efforts and exploration, Valero et al. proposed the structure theory of thermoeconomics (STOT) as the calculation standard of thermoeconomics in 1999, which provided a general mathematical form for thermoeconomic calculation. 18 In terms of cost analysis, STOT has been applied to many types of energy systems. 19,20 Valero et al. analyzed traditional coal-fired power generation systems and GT power plants several times during the process of establishing the STOT. 19 Li et al. established a thermoeconomic cost model based on enthalpy and negentropy (H&S) theory. 20 Yang. 21 analyzed the exergy and exergoeconomic cost of the CCHP system based on the thermoeconomics structural theory. The results showed that the STOT could provide reasonable and accurate results for multiproduct energy systems. Carlo et al. 22 studied the influence of turbine parameters on the thermoeconomic performance of CCHP. The results showed that the system power generation cost can be reduced by optimizing the design parameters of the steam turbine (ST).
With the increasingly serious environmental pollution problems, environmental factors have been considered in the field of thermoeconomics. Frangopoulos 23 first put forward the analysis method of thermoeconomics considering environmental impact-"environmental economics," and introduced the establishment of optimization objective function and solution method of environmental economics. Villafana et al. 24 established an environmental thermoeconomic optimization model for the supercritical CO 2 cycle system with a simple cycle and introduced the environmental impact into the model in the form of environmental damage cost. Abbaspour et al. 25 established a thermoeconomic environment evaluation optimization model for the cogeneration system.
With the development of load regulation methods, load operation modes will be more diversified. 5 When the GT adopts different operating modes, the variation laws of the system thermodynamic performance will be different under off-design conditions. It is necessary to reveal the influence of the main control factors in the operation mode on the GTCC environmental thermoeconomic cost (ETC). Only by mastering the performance variation laws of the GTCC system influenced by load operation modes and finding out the key parameters affecting the ETC, can we improve the system's environmental thermoeconomic performance and reduce the system power generation cost. Moreover, the change in air temperature (AT) can have an impact on the system operation, causing it to inevitably deviate from the design condition. 26 Calculating the ETC of the GTCC system at different ATs is essential to improve the GTCC thermoeconomic performance, but the research on the thermoeconomic performance of GTCC system under different ATs is not sufficient, and most of them focus on the thermodynamic performance without considering environmental factors. The research results can provide theoretical guidance for the practical application of the system under different environmental conditions. For the calculation of the system ETC, due to the complex production relationships among different components, this study rationalizes the environmental costs into the cost balance equations of the components that produce pollutants so that each component of the system has its corresponding environmental cost and to achieve absolute internalization of environmental costs. Only in this way, the real economic performance of the GTCC system can be revealed.
The aim of thermoeconomics environmental evaluation is to add environmental factors on the basis of thermoeconomics cost analysis. The impact of the GTCC system on the environment mainly comes from the pollutants (CO 2 and NOx) in the flue gas produced by burning natural gas. In this study, based on the analysis of energy cost and nonenergy cost of each piece of equipment in the system, and through reasonable pricing of pollutants, the environmental damage model is used to calculate the system environmental cost, which realizes the absolute internalization of external environmental cost. On this basis, taking GTCC with different GT operation modes as the research object, the effects of the main control factors on the ETC are studied. Moreover, sensitivity analysis is performed to investigate the effects of the main variables and AT on the ETC of the system.

| System description
In this study, the model of the GTCC system is established by using the Ebsilon. The combustion chamber (CC) is simplified without considering the switching of combustion mode. The GT adopts the simplified model of stage-by-stage turbine cooling, and the whole GT is divided into three stages. The flowchart of the GTCC system (including the blade cooling model) is shown in Figure 1.
wThe design parameters of the GTCC system 27,28 are shown in Table 1. The design/off-design operation condition model of the reference GTCC unit is described in detail in, 9 so the calculation method of off-design characteristics of GTCC components will not be repeated in this study. To verify the accuracy of the model, the GTCC system is simulated in this study, and the simulation results are compared with the unit design data. The comparison of calculation results is shown in Table 2. The results show that the relative errors between the simulation value and the design value of the main parameters of the GTCC system are less than 3%, which indicates that the model can accurately reflect the operation characteristics of the GTCC system.

| GT off-design operation strategy
The off-design operation modes of GTCC subsystems are affected by many restrictive conditions, for example, the outlet temperature of the gas turbine is not overheated; the stable operation of both the compressor and gas turbine and enough safety margin distance between the compressor operating line and the surge boundary should be ensured. Since this study focuses on the influence of different GT operation strategies on the system ETC, the following four GT operation strategies are mainly adopted.
IGV T3-F: T 3 is kept constant from 100% to 82% of the gas turbine's full load by regulating the IGV angle and fuel flow, the IGV angle keeps unchangeable, and the gas turbine load rate changes from 82% to 19% by only regulating the fuel flow.
IGV T4-F: T 4 is kept constant from 100% to 38% of the gas turbine's full load by regulating both the IGV angle and fuel flow, the IGV angle keeps unchangeable, and the gas turbine load rate changes from 38% to 22% by only regulating the fuel flow.
IGV T3-650-F: T 3 is kept constant from 100% to 82% of the gas turbine full load by regulating both the IGV angle and fuel flow, then T 4 is kept 650°C constant when the gas turbine load rate changes from 82% to 41% by regulating both the IGV angle and fuel flow, and at last IGV angle is kept unchangeable and the gas turbine load rate changes from 41% to 22% by only regulating the fuel flow.
IGV T4 gradual rise-F: T 4 gradually rises to 650°C from 100% to 43% of the gas turbine full load by regulating both the IGV angle and fuel flow, and at last IGV angle is kept unchangeable and the gas turbine load rate changes from 41% to 22% by only regulating the fuel flow.
GT performance parameters affected by the operation strategy are listed as the theoretical support for the subsequent study of the GTCC environmental thermoeconomic performance. The variation trends of GT performance parameters with the GTLR are shown in  Assuming that the HRSG inlet flue gas temperature is T 4 , the heat dissipation loss of the pipeline is ignored.

| Environmental thermoeconomic modeling
Compared with the thermoeconomic cost model, the main difference between the ETC model and the thermoeconomic cost model is that environmental factors are considered. The impact of GTCC on the environment mainly comes from pollutants (CO 2 , NOx) produced in the process of natural gas combustion in the CC. If pollutants are directly discharged into the atmosphere, it will produce a greenhouse effect and other hazards. Generally speaking, there is only a qualitative understanding of environmental hazards, but no concept of quantitative evaluation. How to effectively evaluate the harm degree of environmental impact, internalize the externalities and correctly reflect the real economic performance of the GTCC power The GT performance parameters versus GTLR. (A) AC pressure ratio, (B) GT inlet temperature (T 3 ), and (C) GT exhaust temperature (T 4 ). GTLR, gas turbine load rate; GT, gas turbine. generation process is the key problem to be solved by environmental thermoeconomics. 29 Environmental impact costs are external because although these costs are real, they are not taken into account by the producer of environmental pollution when making decisions, and they are generally not paid for. An effective means of eliminating externalities is to internalize the external costs, that is, to incorporate the external costs of environmental damage into the price market and add them to the cost of the product. The production sector or the consumer should bear this cost.
The process of using thermoeconomic methods to internalize environmental costs is to calculate the environmental costs of components that emit pollutants and the environmental costs of other components that have a production interaction with these components. 24 In Figure 3, for the CC component, it is necessary to add the environmental damage cost of the pollutant to its cost balance equation. The cost balance equation is only for the components that produce pollutants. The costs of other components will also change accordingly.
As shown in Figure 3, FS i represents the fuel negentropy, FB i represents the fuel exergy, Pi represents the product, PO i represents the pollutant, and Z i represents cash investment. For this component (CC), the following cost balance equation can be listed: where, c PO,i is the unit cost of pollutants.

| Physical and production structure diagram
In thermoeconomic analysis of the GTCC system, the system's physical structure diagram needs to be drawn first. According to the research purpose, the required solution accuracy, and the function of each component, the components in the system are combined or decomposed, that is, the appropriate "integration degree" is selected to establish a more reasonable "physical structure diagram." When dividing the physical structure of the same system, the lower the integration degree is, the more subsystems the system will be divided into, the more complex the calculation process will be, and accordingly, the more accurate the performance evaluation of equipment will be. The selection of "integration degree" should be determined according to the research purpose. In this study, a lower energy integration degree is selected and appropriately simplified. The system's physical structure diagram is shown in Figure 4A.
According to the production relationships among various components and the definition of "fuel-product," the production structure diagram considering environmental cost can be obtained as shown in Figure 4B. There exist pollutants (CO 2 and NOx) emissions in the production process of component CC, which is represented by PO 2 . In Figure 4B, "fuel" flows into the component, and "product" flows out of the component. The terms PB and FB represent the product exergy and fuel exergy (including exergy flow and workflow) of each component, respectively. The terms PS and FS represent the product negentropy and fuel negentropy of each component, respectively. The condenser in the system is a typical dissipative component. Its "fuel" is the exergy drop of the working fluid passing through the condenser, but its "product" cannot be quantified by the exergy, because its production purpose is to make the wet steam after doing work return to the state of the initial condensate in the cycle. Therefore, the "product" of the condenser is usually expressed by "negative entropy (FS)," that is, the entropy of the working fluid in the condenser is reduced, and the FS is proportionally distributed to the equipment involved in the combined cycle system. The diamond-shaped component represents the collection component, and the circular component represents the branch component. In the collection and branch components, the negative entropy of the entrance and exit remains conserved.
A productive structure diagram can clearly describe the distribution and flow of "fuel" and "product" in the system, and more intuitively describe the production characteristics of the components themselves and the interactive relationship with other components. It can reflect the production connection of each component in the system, and it is also easier to build the corresponding thermoeconomic model based on this interactive production relationship. In Figure 4, due to the complex production relationships among different components, a reasonable inclusion of environmental costs in the cost balance equation of the component that generates pollutants (CC) will increase the cost of other component products accordingly, and each component bears the corresponding environmental cost, and each flow in the system has its corresponding environmental cost, achieving absolute internalization of environmental costs.

| Nonenergy cost
The ETC includes not only the energy cost but also the nonenergy cost that is composed of the investment, operation, and maintenance costs of components. For the investment cost of each component in the system, a costing function is usually used to complete the estimation.
This study adopts the cost functions proposed in Zhang and colleagues. [30][31][32] In the ETC calculation, it is necessary to convert the equipment investment into the investment cost per unit time. The nonenergy cost calculation equations of each component used in this study have been described in detail in the published article. 27 Using the equation in the literature, the nonenergy cost of each piece of equipment in the system can be obtained, as shown in Table 3.

| Exergy efficiency
The ratio of the exergy loss of a component to the total fuel exergy is defined as the exergy loss coefficient of a component.
Total exergy loss coefficient can be obtained as follows: The relation between the exergy efficiency (η) and the total exergy loss coefficient is expressed as follows:

| ETC equations
In the pricing process of environmental external cost, the cost of environmental damage is based on the damage value caused by pollution activities. 33 Under the environmental damage model, the c PO,i in Equation (1) corresponds to the environmental damage cost of each pollutant. The estimation of environmental damage cost involves many factors, which is a difficult, time-consuming, and expensive research. This study adopts the estimate method of discharge of pollutants in reference. 34 The environmental damage cost data of pollutants are mainly referred to in the literature. 33 In this study, only the environmental damage costs of both CO 2 and NOx are considered. 35,36 The environmental damage costs of NOx and CO 2 are 1.0159 and 0.0175 $/kg, respectively. 33 For the component CC, the ETC balance equation is listed as Equation (1). For other components, the cost balance equations are listed according to Equations (5)- (6). Because there are interactions and constraints among the components in the system, changes in the CC ETC will cause changes in the ETC of other components. Table 4 shows the ETC equations of each component. The ETC equations of each component are solved jointly to obtain the unit product ETC of each component. The price of natural gas is 9.065 $/GJ (0.349 $/m 3 ) (2020, China). 37 The ETC of the productive component can be obtained as follows: The ETC of the dissipative component can be obtained as follows: where c ENV,i is the environmental part cost, $/kWh; c NON-E,i is the nonenergy part cost, $/kWh; c ENG,i is the energy part cost, $/kWh.

| Performance evaluation index
To reveal the importance of including the environmental cost in the system performance evaluation and product pricing process, a new performance evaluation index (environmental coefficient f i ) is proposed in this study and shown below. The f i is the ratio of thermoeconomic cost (without considering environmental factors) to the ETC. The f i reflects the relationship between c system and where c system is the system ETC, $/kWh; c ′ system is the system thermoeconomic cost, $/kWh.

| Result of exergy analysis
Four typical load conditions are considered in this study. The AT is 15°C, the pressure is 1 bar, the relative humidity is 60%, and the air-specific exergy is set as zero. Table 5 shows the exergy efficiencies under different GTLRs. With the decrease of the GTLR, the system exergy efficiency decreases. And the difference in thermodynamic performance between operation strategy I and the other operation strategy tends to increase gradually. At 75% GTLR, the exergy efficiency of the operation strategy Ⅲ is the highest, which is 58.11%. At 50% GTLR, the exergy efficiency of the operation strategy Ⅲ is the highest, which is 53.68%. By changing the GT operation strategy, the trend of decreasing the system exergy efficiency can be slowed down. It can be seen that T 3 is decisive for the GTCC performance. The IGV operation strategy is beneficial to maintain higher T 3 and T 4 , thus ensuring better GTCC thermodynamic performance. Operation strategy Ⅲ is the GT operation strategy with the highest system exergy efficiency under all working conditions.

| Results of ETC analysis
The results of the ETC calculations for the GTCC system are presented as follows: Figure 5 shows the ETC of each component under different GTLRs, which includes the drawing of partial enlargement for the system ETC under different GT operation strategies. Under different GT operation strategies, the variation laws of the ETC of different components are basically consistent. As shown in Figure 5, with the decrease of the GTLR, the ETC of each component increases. The system ETC decreases as the GTLR increases. At 75% GTLR, the system ETC of the operation strategy Ⅱ is the highest, and that of operation strategy Ⅲ is the lowest. At 50% GTLR, the system ETC of the operation strategy Ⅰ is the highest, and that of the operation strategy Ⅲ is the lowest. This is because each component deviates from the design operating point with the decrease of GTLR, resulting in the reduction of energy efficiency. And the T 3 plays a decisive role in the thermodynamic performance of the GTCC system. Operation strategy Ⅲ in the GTLR operation strategy is beneficial to maintain higher T 3 and T 4 , so as to ensure higher GTCC output power. The larger the system's annual power generation capacity is, the less the environmental cost allocated to the unit electrical energy is, so the lower the unit ETC is. It can be seen from Figure 5 that the operation strategy of keeping T 3 as high as possible via variable IGV control shows an obvious advantage in the system ETC. Under four GT operation strategies, the system ETC of GTCC with the operation strategy Ⅲ is the lowest. Therefore, it is beneficial to maintain higher T 3 and T 4 , thus ensuring better GTCC environmental thermoeconomic performance.
The system ETC calculated above considers the environmental impact on the basis of the thermoeconomic cost. To reflect the importance of incorporating environmental costs into the system performance evaluation and product pricing process, the ratio of the c ′ system to the c system is calculated in this study. The f i reflects the impact of the environmental cost on the system generation cost after considering environmental factors. When f i is smaller, the system is more influenced by environmental factors and vice versa. Figure 6 shows the f i of each component (100% GTLR). For the system, the economic loss caused by pollutant emissions to the environment in power generation costs cannot be ignored. It can be seen from Figure 6 that the f i of the CC is smaller. This is due to the CC as the sewage component of the GTCC unit, and located in the front end of the GTCC unit, so the CC is more influenced by environmental factors. For the CC, pollutant emissions can be reduced by optimizing the burner construction. The components with higher values of f i are ST. Therefore, the ST is less influenced by environmental factors.
From Equation (7) that the ETC is composed of the following three parts: c ENV,i , c NON-E,i and c ENG,i . To obtain the detailed reasons for the increase of ETC, this study analyzes the detailed compositions of the ETC. GTCC systems with the 100-50% GTLRs are selected to analyze the detailed compositions of the cost. Figure 7  component of the GTCC unit, because the CC is located in the front end of GTCC unit, the proportion of its environmental cost part is greater than that of the nonenergy part. Therefore, reducing the emission of pollutants can reduce its ETC. The ST has a relatively higher nonenergy part, and the main reason is that these equipment investment costs are relatively large. Therefore, for the ST, reducing investment costs can also reduce its ETC. Figure 8 shows the environmental cost in the system ETC under different GTLRs. As can be seen from Figure 8, at 75% GTLR, the environmental cost of operation strategy II is the highest, and that of operation strategy Ⅲ is the lowest. At 50% GTLR, the environmental cost of the operation strategy Ⅰ is the highest, and that of the operation strategy Ⅲ is the lowest. This is because the T 3 values of different GT operation strategies are different, and the combustion conditions of natural gas in the CC are also different. When T 3 is higher, the T 4 is higher and the system exergy efficiency is higher. The system output power is higher the pollutant emissions from the system are smaller, thus the proportion of the environmental cost is smaller. So the environmental cost changes with the change of the GT operation strategy. Changing the GT operation strategy can reduce the system pollutant emissions. Operation strategy Ⅲ is beneficial to maintain higher T 3 and T 4 , thus reducing pollutant emissions.

| Sensitivity analysis
The ETC includes the energy part, nonenergy part, and environment part. Energy cost is affected by the fuel price, that is, natural gas price (NGP). The nonenergy part is affected by investment, operation, and other costs. The environment part is affected by the environmental damage cost of CO 2 . Therefore, this study also analyzes the impact of the above factors on the ETC of each component. Figure 9 shows the ETC change rate of each component. It can be seen from Figure 9 that when the growth rates of both the NGP and the investment cost are the same, the impact of NGP growth on the ETCs of most components is greater than that of the investment cost. It can be seen from the figure that components sensitive to NGPs are not sensitive to changes in investment costs. For the CC, it is greatly affected by the NGP. The ST, especially the HPT, is the least sensitive to the NGP, so the HPT is also the most sensitive component to the investment cost. Reducing the investment cost of ST can effectively reduce its ETC. It can be seen from Figure 9C, the effects of growth rates of both the CO 2 environmental damage cost and NGP on the ETC have the same variation trend. For every 10% increase in the change rate of the CO 2 environmental damage cost, the system ETC increases by approximately 0.95%. The CC is greatly affected by the CO 2 environmental damage cost. This is because CC is the pollutant-generating component. Reducing the pollutant emissions of the CC can effectively reduce its ETC.

| The system ETC under different ATs
The GT power station has the advantages of high thermal efficiency, good environmental performance, quick start and stop, flexible operation, and so on. However, its performance parameters are obviously affected by AT. [38][39][40][41] The change of AT will affect the air density, which in turn affects the air compressor (AC) inlet flow rate, and this will have a significant impact on the GT output power and operational performance. With the reduction of the AT, to guarantee the safe operation of the GT, this study applies the IGVT3-650-F operation strategy and analyzes the impacts of different ATs (−10°C to 30°C) on the ETC of each component. The AT range is selected according to the literature. 42,43 The selected AT range is common in the literature. 42,43 In this study, the law of the GTCC system environmental thermoeconomic performance influenced by the AT is mainly revealed. Therefore, the influence of extreme temperature on the GTCC system's environmental thermoeconomic performance is not considered in this study. Figure 10 shows the system ETC versus the AT. In Figure 10A, with the increase of the AT, the system ETC increases. When the AT is −10°C, the system ETC is the lowest, which is 0.0913 $/kWh. When the AT is 30°C, the system ETC is the highest, which is 0.0933 $/kWh. For every 10°C increase in temperature, the system ETC increases by approximately 0.54%. Figure 10B shows the system environmental cost in the system ETC for different ATs. With the increase of the AT, the environmental cost in the system ETC increases. For every 10°C increase in temperature, the system environmental cost increases by approximately 0.46%. This is because when the inlet temperature increases, the air density becomes less, and the air mass flow rate entering the AC and GT becomes less, thus reducing the GTCC unit power generation capacity. As a result, the pollutant emissions from the system are large and the environmental cost is higher. This shows that choosing a lower inlet AT can increase system power generation, improve system exergy efficiency and reduce the environmental cost, which is an effective way to improve system environmental thermoeconomic performance.

| CONCLUSION
This study aims at improving the GTCC system thermoeconomic performances under off-design conditions, based on the GTCC system environmental thermoeconomic model, and explores methods to improve offdesign condition environmental thermoeconomic performance from the perspective of operating strategies and environmental conditions. From the results of this study, the main conclusions are as follows: (i) The system ETC calculation model reasonably adds the environmental damage cost into the cost balance equation of the components that produce pollutants. Due to the complex production relationship between components, a reasonable inclusion of environmental costs in the cost balance equation