Study on the Coupling E ﬀ ect of a Solar-Coal Unit Thermodynamic System with Carbon Capture

: Based on the structural theory of thermo-economics, a 600 MW unit was taken as an example. An integration system which uses fuel gas heat and solar energy as a heat source for post-combustion carbon capture was proposed. The physical structure sketch and productive structure sketch were drawn and a thermo-economics model and cost model based on the deﬁnition of fuel-product were established. The production relation between units was analyzed, and the composition and distribution of the exergy cost and thermo-economic cost of each unit were studied. Additionally, the inﬂuence of the fuel price and equipment investment cost of the thermo-economic cost for each product was studied. The results showed that the main factors a ﬀ ecting the unit cost are the fuel exergy cost, component exergy e ﬃ ciency, and irreversible exergy cost of each unit, and the main factors a ﬀ ecting the thermo-economics cost are the speciﬁc irreversible exergy cost and investment exergy cost. The main factors a ﬀ ecting the thermal economics of solar energy collectors and low-pressure economizers are the invested exergy cost, negentropy exergy cost, and irreversible exergy cost of each unit.


Introduction
Climatic change resulting from greenhouse gases has become the most serious air pollution problem facing humanity at present [1]. The flue gas emissions from coal-fired power plants represent the largest CO 2 emission contributor, and the trend will continue in the foreseeable future [2]. Considering this, CO 2 capture and storage (CCS), resource utilization of CO 2 , and renewable energy, as three measures that appeared successively, remain the Gordian techniques for rapidly and effectively reducing CO 2 emissions. According to the prediction of the Global CCS Institute in 2018 [3], a 14% cumulative CO 2 emissions reduction must be achieved in order to reach the Paris target by 2060 [4].
The widespread use of renewable energy is deemed an effective way of reducing CO 2 emissions. As renewable energy, solar energy has a wide range of applications at home and abroad in many fields [5]. However, carbon capture is deemed the most immediate way of decreasing CO 2 emissions. Post-combustion CO 2 capture (PCC), oxygen-enriched combustion, and chemical looping combustion are prospective technologies which can be applied to active coal-fired power plants [6]. However, the

Pollutant Emission Reduction Method of a Solar Auxiliary Coal-Fired Unit
The parabolic trough solar collector is one of the solar collectors with a medium temperature. All of the solar thermal generation systems operated commercially in America and Europe apply this technology. Currently, many research institutes are trying to find a way to combine this technology with fossil fuel power plants. When water is used as a medium which is heated by the direct steam generation (DSG) solar trough collector integrated with the coal-fired unit, there is not only energy Energies 2020, 13, 4779 3 of 14 transfer, but also the exchange of substances between the two systems. When the flue gas waste heat and the DSG solar collector provide the heat source for the post-combustion carbon capture system, and the unit steam extraction provides the heat source for the liquid ammonia evaporator in the denitration system, the matching of the material flow and energy flow needs to be considered; that is, a certain amount of water is drawn from a certain part of the thermal system to be heated by the flue gas waste heat system and the solar heat collection system, which provides a heat source for the carbon capture system.
In this paper, the N600-24.2/566/566-type generator set is taken as the research object, according to the calculated acid dew point temperature, the low-pressure economizer is used to heat the No. 3 low-pressure heater (3DJ) to draw the working fluid [17][18][19], and the solar heat is then collected by the DSG parabolic trough collector [20]. Furthermore, condensed water is heated to the conditions required for regeneration of the amine-based catalyst and then introduced into the reboiler as a heat source for regeneration of the desorbent solution in the carbon dioxide capture system, using its latent heat of vaporization to provide the reboiler solvent regeneration requirements. At the same time, steam extraction of the unit is used to provide a heat source for the liquid ammonia evaporator in the denitration system. In view of the unbalanced solar radiation, in order to ensure that the solar-assisted coal-fired system can produce a balanced amount of heat required for desorbent regeneration, heat storage needs to be installed in the system. Considering the parameter matching, the water returned after heating the reboiler is introduced into the inlet of the No. 5 heater. The integration scheme is shown in Figure 1.
Energies 2020, 13, x FOR PEER REVIEW 3 of 14 gas waste heat and the DSG solar collector provide the heat source for the post-combustion carbon capture system, and the unit steam extraction provides the heat source for the liquid ammonia evaporator in the denitration system, the matching of the material flow and energy flow needs to be considered; that is, a certain amount of water is drawn from a certain part of the thermal system to be heated by the flue gas waste heat system and the solar heat collection system, which provides a heat source for the carbon capture system. In this paper, the N600-24.2/566/566-type generator set is taken as the research object, according to the calculated acid dew point temperature, the low-pressure economizer is used to heat the No. 3 low-pressure heater (3DJ) to draw the working fluid [17][18][19], and the solar heat is then collected by the DSG parabolic trough collector [20]. Furthermore, condensed water is heated to the conditions required for regeneration of the amine-based catalyst and then introduced into the reboiler as a heat source for regeneration of the desorbent solution in the carbon dioxide capture system, using its latent heat of vaporization to provide the reboiler solvent regeneration requirements. At the same time, steam extraction of the unit is used to provide a heat source for the liquid ammonia evaporator in the denitration system. In view of the unbalanced solar radiation, in order to ensure that the solar-assisted coal-fired system can produce a balanced amount of heat required for desorbent regeneration, heat storage needs to be installed in the system. Considering the parameter matching, the water returned after heating the reboiler is introduced into the inlet of the No. 5 heater. The integration scheme is shown in Figure 1.

The Model of Structural Theory for the Integration System
In general, the "fuel-product" is used to define the input and output of components in thermo-economics. The input and output of the integration system are analyzed according to the

The Model of Structural Theory for the Integration System
In general, the "fuel-product" is used to define the input and output of components in thermo-economics. The input and output of the integration system are analyzed according to Energies 2020, 13, 4779 4 of 14 the physical structure, including the physical structure and production structure. Among them, the physical structure reflects the physical association between equipment components, and the production structure reflects the production relationship of the system. In order to clarify the input and output of each component, it is necessary to divide the physical structure of the thermal system and determine the "fuel" and "product" of each component [19,20].

Physical Structure
According to the function of each device, the integrated system is divided into the physical structure shown in Figure 2. According to the arrangement of the steam extraction ports, the steam turbines are divided as follows: The regulating stage serves as a component, and the remaining steam extraction ports and steam extraction ports form a component. The steam leakage and shaft seal systems are grouped into the corresponding steam turbine stage group; each device of the regenerative system is used as a component; the shaft seal heater and the adjacent low-pressure heater are combined into a component; the boiler is divided into a superheater component (13) and a reheater component (17); and the steam turbine (25), condensate pump (28), solar collector field (5), carbon dioxide capture system (6), denitration system (26), and low-pressure economizer system (4) are considered to be components, respectively.
Energies 2020, 13, x FOR PEER REVIEW 4 of 14 physical structure, including the physical structure and production structure. Among them, the physical structure reflects the physical association between equipment components, and the production structure reflects the production relationship of the system. In order to clarify the input and output of each component, it is necessary to divide the physical structure of the thermal system and determine the "fuel" and "product" of each component [19,20].

Physical Structure
According to the function of each device, the integrated system is divided into the physical structure shown in Figure 2. According to the arrangement of the steam extraction ports, the steam turbines are divided as follows: The regulating stage serves as a component, and the remaining steam extraction ports and steam extraction ports form a component. The steam leakage and shaft seal systems are grouped into the corresponding steam turbine stage group; each device of the regenerative system is used as a component; the shaft seal heater and the adjacent low-pressure heater are combined into a component; the boiler is divided into a superheater component (13) and a reheater component (17); and the steam turbine (25), condensate pump (28), solar collector field (5), carbon dioxide capture system (6), denitration system (26), and low-pressure economizer system (4) are considered to be components, respectively.

Production Structure
In this study, the "fuel-product" is used to define the production purpose of each piece of equipment. The product (P) is the purpose of the component which is quantified by exergy and the fuel (FB) is the exergy consumption. According to the function of the production equipment in the overall situation, the actual flow of the input and output of each piece of equipment is decomposed or combined to obtain multiple fuel flows and product flows. In this way, the physical structure diagram of the actual system can be converted into a production structure diagram represented by the "fuel-product", as shown in Figure 3. In Figure 3, rectangles represent physical components, diamonds represent influx components, and circles represent branch components. The arrows F, P,

Production Structure
In this study, the "fuel-product" is used to define the production purpose of each piece of equipment. The product (P) is the purpose of the component which is quantified by exergy and the fuel (FB) is the exergy consumption. According to the function of the production equipment in the overall situation, the actual flow of the input and output of each piece of equipment is decomposed or combined to obtain multiple fuel flows and product flows. In this way, the physical structure diagram of the actual system can be converted into a production structure diagram represented by the "fuel-product", as shown in Figure 3. In Figure 3, rectangles represent physical components, diamonds Energies 2020, 13, 4779 5 of 14 represent influx components, and circles represent branch components. The arrows F, P, and N of every physical component represent the fuel consumption, the product, and the negentropy consumption, respectively. In the influx or branch components, the inlet and outlet of the exergy or negentropy remain balanced.
Energies 2020, 13, x FOR PEER REVIEW 5 of 14 and N of every physical component represent the fuel consumption, the product, and the negentropy consumption, respectively. In the influx or branch components, the inlet and outlet of the exergy or negentropy remain balanced.  Figure 3. Productive structure of the integration system.
The production structure diagram is a graphical representation of the production relationship of the integrated system, which intuitively reflects the production relationship in the power plant. The product P of each component is collected by the influx component J, and then redistributed to other components through the branch component B. When the investment cost of equipment (external resources) is taken into account, it can be directly input into the corresponding component, and the mathematical Equation (1) of the thermo-economics model can be obtained according to the production structure diagram.
where Bi is the inlet flow of each component, xi is the internal parameter set of the component, Bj is the output stream of the component, m is the number of components in the production structure, and Gi () is the function between Bi and Bj and xi of the i component. Every input and output flow in the production system is always represented by exergy, negentropy, cash, enthalpy, or entropy. The internal parameter set xl is usually represented by pressure, temperature, efficiency, and so on. Setting up a model based on thermo-economics usually requires the thermo-economics model to be defined with a linear equation. When the characteristic equation is a homogeneous first-order equation on subset Bj, according to Euler theorem, Equation (1) can be represented as where n is the number of input flows and kij is the technical product coefficient, which represents the proportion of product consumed from component i when the unit product is produced by component j. The n × n dimensional matrix <KP> composed of kij is the unit exergy consumption matrix, which reflects the distribution of the fuel and product in the structure. The production structure diagram is a graphical representation of the production relationship of the integrated system, which intuitively reflects the production relationship in the power plant. The product P of each component is collected by the influx component J, and then redistributed to other components through the branch component B. When the investment cost of equipment (external resources) is taken into account, it can be directly input into the corresponding component, and the mathematical Equation (1) of the thermo-economics model can be obtained according to the production structure diagram.
where B i is the inlet flow of each component, x i is the internal parameter set of the component, B j is the output stream of the component, m is the number of components in the production structure, and G i () is the function between B i and B j and x i of the i component. Every input and output flow in the production system is always represented by exergy, negentropy, cash, enthalpy, or entropy. The internal parameter set x l is usually represented by pressure, temperature, efficiency, and so on. Setting up a model based on thermo-economics usually requires the thermo-economics model to be defined with a linear equation. When the characteristic equation is a homogeneous first-order equation on subset B j , according to Euler theorem, Equation (1) can be represented as where n is the number of input flows and k ij is the technical product coefficient, which represents the proportion of product consumed from component i when the unit product is produced by component j. The n × n dimensional matrix <KP> composed of k ij is the unit exergy consumption matrix, which reflects the distribution of the fuel and product in the structure.

Characteristic Equation
Generally, three types of characteristic models are included in the thermo-economics model: Characteristic equations for production and dissipation components, structural equations for aggregate and branch components, and cost calculation equations. The sum of k ij , which is the technical production coefficient of a component, is the unit exergy consumption of this component, and can be calculated by Equation (3).
where P is the product, kw; F is the fuel, kw; and i and j represent the i-th component and the j-th component, respectively.
The characteristic equation of the production and dissipative component is calculated by Equation (4), which reflects the relationship between production functions P i and the fuel F i of the i-th component with unit exergy efficiency (k i ).
The structural equation is composed of the aggregate component Equation (5) and the branch component Equation (6).
where r ij represents the efficiency and p j is the product of the j-th aggregated component.
where F j represents the fuel of the j-th branch assembly.

Exergy Cost Equation
The exergy cost is defined as the amount of exergy required to generate exergy flow in the system. The unit cost refers to the amount of energy consumed per unit of stream produced, and its dimension is the ratio of exergy to exergy, which is denoted as k*. The unit exergy cost includes the exergy cost of unit product k * p , exergy cost of unit fuel k * FB , and unit negentropy exergy cost k * FS . Figure 4 shows the structural diagram of an energy system.

Characteristic Equation
Generally, three types of characteristic models are included in the thermo-economics model: Characteristic equations for production and dissipation components, structural equations for aggregate and branch components, and cost calculation equations. The sum of kij, which is the technical production coefficient of a component, is the unit exergy consumption of this component, and can be calculated by Equation (3).
where P is the product, kw; F is the fuel, kw; and i and j represent the i-th component and the j-th component, respectively.
The characteristic equation of the production and dissipative component is calculated by Equation (4), which reflects the relationship between production functions Pi and the fuel Fi of the i-th component with unit exergy efficiency (ki).
The structural equation is composed of the aggregate component Equation (5) where rij represents the efficiency and pj is the product of the j-th aggregated component.
where Fj represents the fuel of the j-th branch assembly.

Exergy Cost Equation
The exergy cost is defined as the amount of exergy required to generate exergy flow in the system. The unit cost refers to the amount of energy consumed per unit of stream produced, and its dimension is the ratio of exergy to exergy, which is denoted as k*. The unit exergy cost includes the exergy cost of unit product * , exergy cost of unit fuel * , and unit negentropy exergy cost * . Figure 4 shows the structural diagram of an energy system. In Figure 4, FBm is the fuel input of a system, kW; FSs is the negentropy input of a system, kW; Z is the non-energy cost input of a system; and FBm, FSs, Z, and P represent the fuel input of the system, the negentropy, the non-energy input, and the product, respectively. The exergy cost equation of the above system is calculated by Equation (7), and the unit exergy cost equation is calculated by Equation (8). In Figure 4, FB m is the fuel input of a system, kW; FS s is the negentropy input of a system, kW; Z is the non-energy cost input of a system; and FB m , FS s , Z, and P represent the fuel input of the system, the Energies 2020, 13, 4779 7 of 14 negentropy, the non-energy input, and the product, respectively. The exergy cost equation of the above system is calculated by Equation (7), and the unit exergy cost equation is calculated by Equation (8).
There are multiple exergy flows transferring between systems or components. Therefore, the calculation equation of the unit product exergy cost is k * P,i = k 0,i + n j=1 k ji · k * P,j i = 1, 2, . . . , n.
The cost equation expresses the investment cost of the system as a thermodynamic variable and a functional form of the component product. The unit thermo-economics cost cp of the product belongs to the economic dimension, and its calculation method is Equation (10).
In Equation (10), U is a 29 × 29-dimension unit diagonal matrix, <KP> t is the 29 × 29 dimension transpose matrix of the unit exergy cost, c e is the product vector (10 −6 ¥/kJ) of the unit price c Fuel and k 0.i , c Fuel is equal to the ratio of the coal-fired price to coal-fired calorific value, and k 0.i represents the unit exergy cost of the components by directly obtaining fuel from the environment. kZ is the vector of cost capital (¥/kJ), which reflects the external investment and other costs needed by the components. Therefore, Equation (10) can be further divided as follows:

The Results and Discussion
By applying the structural theory of thermo-economics in the integration system, the formation and distribution of the generation cost can be analyzed in the carbon capture system of a power plant, and the internal reasons of the generation cost increase can be revealed. Table 1 shows the unit cost of each component (product cost, negative entropy cost, fuel cost, etc.) of the solar-assisted coal-fired unit pollutant emission reduction thermal system under turbine heat acceptance (THA) conditions. The condenser is a dissipation device and is used to reduce the increase of entropy produced by the irreversibility in the thermodynamic cycle, so the work substance can return to the initial state of the thermodynamic cycles. The reduction of entropy means the production of negentropy. Some scholars [21][22][23][24] regard negentropy as the product of the condenser. In thermal economics, it means that the fuel consumption allocates the fuel resources consumed by the waste heat discharge of the condenser to each piece of equipment according to the irreversible degree of each piece of equipment, as the additional fuel consumed by each piece of equipment due to the irreversible entropy increase. In the integrated system, since the functions of the reboiler and the evaporator are similar to the condenser, the negative entropy generated by it will be distributed as a product to each piece of production equipment in the production system. Therefore, in the entire system, except for the condenser, reboiler, evaporator, and generator, all equipment consumes negative entropy. Here, C ar , H ar , O ar , N ar , and S ar represent carbon, hydrogen, oxygen, nitrogen, and sulfur in the fuel, as received (%).
The system in Figure 1 was studied and the composition of the coal is shown in Table 1. In addition, the chemical exergy of the coal was 24,209.82 kJ/kg [25], and the radiation exergy model of solar thermal power generation was calculated [26,27]. The expression applies in the case of fully concentrated solar radiation and blackbody absorbers. If solar collectors consider a small concentration ratio and their absorbers are not blackbody, but selective, exergy factors refer to other literature [28].
According to the equation of the exergy cost, the unit product exergy cost is composed of the fuel exergy cost, irreversibility exergy cost, and negentropy exergy cost. It can be seen from Table 2 that the product exergy cost, negative entropy cost, and fuel exergy cost in the integrated system are higher than those in the original system. This is due to the low efficiency of the solar heat collecting field and the increased consumption of the integrated system.
There is a different unit fuel exergy cost k * FB in the irreversibility produced by different equipment in the original system and integration system. When the product is determined, the k * FB equals the irreversible unit exergy cost. The unit product exergy cost and unit fuel exergy cost have a decreasing trend along the direction of the thermodynamic cycle. Specifically, for the feedwater heater system components, k* P gradually decreases from the low-pressure heater to the high-pressure heater, reaching a minimum value at 1 GJ. The original system and the integrated system are 2.178 and 2.631 kw/kw, respectively. For the steam turbine stage group, the exergy costs of the high-pressure cylinder adjustment stage group HP1 and the low-pressure cylinder final stage group LP5 are larger than other stage groups. The main reason for this is that the HP1 has a larger steam loss, and the LP5 wet steam loss is greater. The unit cost k*P of the generator (GEN) in the integrated system is relatively high, equaling 2.764 kw/kw, mainly due to the higher unit cost of fuel. The unit product exergy cost of superheater assembly (B-SH) and reheater assembly(RH) is much higher than their unit fuel exergy cost, because of the irreversible loss in the boiler.
The unit product exergy cost of the low-pressure economizer is the highest (5.795 kw/kw). The reason for this is that the exergy loss of the low-pressure economizer is high and the exergy efficiency is low. The unit product exergy cost of solar collector field (SF) is 4.538 kw/kw. This is mainly because of the high exergy loss and the low exergy efficiency. The exergy efficiency of the solar collector field is low, and it consumes so much solar exergy to heat the condensate water that the unit exergy costs of most of the components in the integration system are higher than those of the original system. The reason for the increasing exergy cost of No. 4 low-pressure heater (4DJ), B-SH, RH, Small steam turbine(BFPT), reboiler (RB) and denitration system (SG) is mainly the high specific irreversible exergy cost and high specific negentropy cost. Moreover, the increase of the exergy cost caused by specific negentropy is much lower than that caused by specific irreversibility. The specific irreversible exergy cost of 4DJ is the highest among all heaters. This is mainly because of the increase of internal exergy loss caused by heat exchange at a low temperature. The fuel exergy cost of SF and LPE is 0, which is due to the zero consumption of fossil fuel. The increase in cost due to the negative entropy of condenser (CND), GEN, RB, and SG is zero, mainly because CND is a condenser component, and GEN, RB, and SG are similar condenser components, which do not consume negative entropy. Furthermore, the reason for the higher cost of other component products is the higher cost of fuel consumed. The unit exergy cost reflects the structure of the energy cost. However, it cannot precisely reflect the effect of the energy price, equipment investment, and other non-energy costs. In order to precisely reflect the unit thermo-economic cost, the elements, including the impact of the energy price, equipment investment, and other non-energy costs, must be considered. It can be seen from Equation (11) that the thermo-economic cost of the system is composed of the fuel unit thermo-economic cost, unit thermo-economic cost caused by irreversibility, unit thermo-economic cost caused by the consumption of negentropy, and investment thermo-economic cost. Table 3 reflects the thermo-economic cost and its distribution law of the original system and integration system, without considering the investment cost. It can be seen from Table 3 that the unit product thermo-economic cost of the components in the integration system is lower than that in the original system. The reason for this is that the exergy cost consumption of the solar collector field in the integration system is 0, which reduces the energy cost. The unit product thermo-economic cost of the low-pressure economizer and solar collector field equals their negentropy thermo-economic cost, without considering the investment cost. When the investment cost is considered, the thermo-economic cost of the system is composed of the unit fuel exergy cost, the thermo-economic cost caused by irreversibility, and the thermo-economic cost caused by the consumption of negentropy. The installation and acquisition cost is included in the investment cost and the construction cost of other equipment is not considered [19,[29][30][31]. When the radiant intensity is 800 W/m 2 , the solar collector field can be calculated according to its area. The composition of the unit thermo-economic cost and its distribution law in the original system and the integration system considering the investment cost are shown in Table 4.
It can be seen from Table 4 that the product thermo-economic cost of the components in the integration system is higher than that in the original system. The reason for this is that the investment costs of the solar collector field, CO 2 removal system, low-pressure economizer, and denitration system increase the cost. It can also be seen from Table 4 that the cost increase caused by the irreversible ratio of components such as 4DJ, B-SH, RH, LPE, SF, RB, and SG accounts for the largest proportion of the unit thermo-economics cost, because these components display relatively big irreversible losses. The unit product thermo-economic cost of the low-pressure economizer and solar collector field is composed of the thermo-economic cost caused by irreversibility and the consumption of negentropy. Their fuel exergy cost is 0. The large irreversible loss and large negative entropy consumption of the low-pressure economizer and heat collector field are mainly caused by the low efficiency of the heat collector field. The unit product thermal economic cost caused by the investment cost of the liquid ammonia evaporator in the denitration system is very high, mainly because the investment cost of the denitration system is large and the product negative entropy is small. Solar radiation is changing at any time, so in the integrated system of the carbon dioxide emission reduction of solar-assisted coal-fired power generation, there are many optional solar radiation design intensities. Different radiation intensities not only affect the thermal economy of the unit, but also have a certain impact on the technical economy. As a result, the efficiency of the collector will change, and the heat released by the solar collector will also change. When the radiant intensity changes, the storage device or the 5 section extraction steam will be used as the heat source of the carbon emission reduction system and will provide the heat needed by the regeneration of the desorbent. The efficiency and area of the solar collector field can be calculated according to the radiation intensity. When the energy produced by the solar collector is certain and the radiant intensity is changing, the relationship between the efficiency and area is as shown in Figure 5. It can be seen from Figure 5 that the efficiency of solar collectors has an increasing trend with an increasing radiation intensity. The area of the solar collector field is closely related to the heat release and the efficiency. When the heat release is certain, the area of the collector field decreases with the increase of the radiation intensity. For the radiation distribution of a certain area, if a high radiation intensity is selected, the area of the solar collector field can be reduced, but if the solar radiation intensity in this area is always lower than the design value, the collector is in a low-load operating state, which reduces the thermal efficiency. If the actual radiation intensity is greater than this design value, the collector field will be operated under the rated working conditions. According to the designed heat storage device, the excess heat generated can be saved by the heat storage device. When the radiation intensity is zero, and the heat storage device has no stored heat, the standby steam source is activated to provide regenerative heat. reduces the thermal efficiency. If the actual radiation intensity is greater than this design value, the collector field will be operated under the rated working conditions. According to the designed heat storage device, the excess heat generated can be saved by the heat storage device. When the radiation intensity is zero, and the heat storage device has no stored heat, the standby steam source is activated to provide regenerative heat.  The increase in energy consumption and investment costs raises the cost of generating electricity for the pollutant emission reduction system of solar-assisted coal-fired units, and it also highlights the economic obstacles to the reduction of pollutant emissions of solar-powered coal-fired units. However, if taxes are imposed on CO 2 emissions and the CO 2 product is sold, the integrated system is expected to break through economic obstacles and achieve massive CO 2 emission reductions. Considering the environmental impact, CO 2 removal is necessary and beneficial. Therefore, the integrated system is not only environmentally friendly, but also has high economic competitiveness.

Conclusions
In this present paper, an integrated system combining fuel gas and solar-aided CO 2 desorption with a 600 MW coal-fired power plant is proposed and studied. The information provided by the conventional thermodynamic methods to evaluate the production performance of the system and devices has proved to be insufficient, and only considers the thermal performance evaluation of the system, while neglecting the cost factors. In this paper, the cost analysis method based on the structural theory of thermo-economics is applied to the integrated system. The thermo-economic model and the exergy cost model for the integrated system based on the fuel-product concept have been defined to quantify the productive interaction between different devices. The physical structure sketch and the productive structure sketch were drawn and a thermo-economic model and a cost model based on the definition of the fuel-product were established. The production relation between units was analyzed, and the composition and distribution of the exergy cost and thermo-economic cost of each unit were studied. The influence of the fuel price and equipment investment cost of the thermo-economic cost for each product was studied. According to the presented results, several conclusions can be drawn, as follows: (1) The insufficiency of the traditional thermodynamics analysis is compensated for by the structural theory of thermo-economics. The information of the cost structure and energy transformation of the relevant equipment can be analyzed based on this theory; (2) The unit exergy cost and its distribution law in every component in the integration system and the original system are calculated based on the structural theory. The high exergy cost of the components in the integration system is mainly due to the increase of the irreversible exergy cost.
The unit exergy cost of the component is impacted by the exergy efficiency and fuel exergy cost of the component. The unit exergy cost can be reduced by increasing the exergy efficiency of the boiler and solar collector field;