Exergy and economic analyses of CCP system using full capacity of steam production and waste heat recovery in Kurdistan petrochemical complex

The objective of this study is to analyze a combined cooling and power system from both exergy and economic perspectives, taking into account low-, medium-, and high-pressure steams. The system configuration consists of various components, namely the boiler, tank, turbine, generator, unit referred to as 180, absorption chiller, and separator. The high- and medium-pressure steams are utilized to generate power in the chiller turbine. Additionally, the low-pressure steam, which is discharged from the turbines and recycled from different sections of the system, is used to provide heat for the absorption chillers and cool the water used in the production line, thereby reducing the capacity requirements of the wet cooling towers. Among the available options, the turbine with a cost of 300 €/kW proves to be the most suitable choice for the proposed system. The results indicate that increasing the generator temperature from 65 °C to 90 °C leads to an increase in the coefficient of performance (COP) from 0.67 to 0.77. Moreover, the COP, power production, turbine efficiency, and total exergy efficiency of the proposed system are determined as 0.73, 5000 kW, 16,876 kW, 35.98%, and 57%, respectively. Ultimately, by implementing the proposed system, the product's production has been enhanced by 7% while generating an additional 16 MW of power, which represents a significant capacity for the Kurdistan Petrochemical Complex. Exergy and economic analyses are performed on a CCP to utilize the waste heat recovery of Kurdistan Petrochemical Complex. Five parameters, including total exergy efficiency, power production, COP, and turbine efficiency are calculated. Results showed that by using the proposed CCP, both products’ production and electricity power of KPC are enhanced. Exergy and economic analyses are performed on a CCP to utilize the waste heat recovery of Kurdistan Petrochemical Complex. Five parameters, including total exergy efficiency, power production, COP, and turbine efficiency are calculated. Results showed that by using the proposed CCP, both products’ production and electricity power of KPC are enhanced.


Introduction
The petrochemical industry plays a crucial role in the global manufacturing of various everyday items used by humans worldwide.It primarily involves the refining and cracking of crude oil to produce a wide range of chemical products derived from petroleum [1].These petrochemicals find extensive applications in diverse sectors such as agriculture, food, pharmaceuticals, and technology.However, it is important to acknowledge that the petrochemical industry also carries significant environmental implications, contributing to air, water, and soil pollution, posing potential risks to living organisms [2][3][4].
Trigeneration systems, also known as combined cooling and power (CCP) systems, consist of two main subsystems: a power subsystem and a cooling subsystem.These systems offer numerous advantages, including reduced fuel and energy costs, lower electricity consumption, significant reductions in greenhouse gas emissions, absence of harmful chemical pollutants, and efficient production of electricity and heat [5][6][7].Xia et al. [8] conducted a thermo-economic analysis of a CCP system focused on engine waste heat recovery.They investigated the impact of key parameters on the system's thermodynamic performance and performed optimization using a genetic algorithm (GA).Cao et al. [9] studied the performance of a Kalina-based CCP integrated with a low-grade heat source and examined the effects of various parameters.They used a GA to optimize the system's performance and concluded that increasing the expander's inlet pressure leads to higher exergy efficiency.Furthermore, they found that the proposed system outperforms a standalone power generation system in terms of exergy efficiency.Rostamzadeh et al. [10] conducted energy and exergy analyses of a novel CCP system.They introduced the concept of a power sub-cycle to modify the proposed system and explored different environmentally-friendly working fluids for the cycles.Their findings indicated that increasing the generator pressure and the mass ratio of the ejector result in higher exergy efficiency.Ghaebi et al. [11] performed thermoeconomic and thermodynamic analyses of a novel CCP system integrated with ejector refrigeration and the Kalina cycle.They utilized a genetic algorithm to optimize the system and determined that the optimum exergy and thermal efficiencies were 16.69% and 20.4%, respectively.Their study also revealed that the ejector and condenser were the components with the highest exergy destruction.
Several studies have focused on evaluating the economic performance of systems by considering equipment expenditure [12][13][14][15].However, it is important to note that efficient thermodynamic performance does not necessarily guarantee good economic performance.Therefore, the exergoeconomic method, which combines exergy and cost analyses, is necessary.This method provides designers with information that traditional energy and economic analyses cannot offer, enabling the design of cost-efficient energy systems.Zhao et al. [16] investigated a geothermal-driven CCP system and conducted a parametric study to optimize the system.Their findings revealed that the optimal exergoeconomic design does not always yield the best thermodynamic performance.They also identified the vapor generators, steam turbine, and flashing device as the components with the highest exergy destruction.Tian et al. [7] performed an exergoeconomic optimization for a CCP system integrated with a novel doubleflash geothermal system.They incorporated two boosters to increase the cooling load, resulting in 47.8% and 38.9% higher cooling load and electricity compared to previous systems.Furthermore, they determined that the condenser caused the maximum exergy destruction (2570 kW).Zhou et al. [17] examined a combined cooling, desalination, and power system from energy, exergy, and exergoeconomic perspectives.They analyzed critical parameters influencing system efficiency and found that increasing the condenser pressure led to decreased unit costs of products but reduced exergy efficiency.Zandi et al. [18] conducted energy, exergy, exergoeconomic, and exergoenvironmental analyses of a refrigeration cycle (RC) and a CCP system using CO 2 and N2O as working fluids.The analyses demonstrated that the system using CO 2 achieved an exergy efficiency of 30.7% and a coefficient of performance (COP) of 2.82.Additionally, they determined the total product cost to be 1.44 $/h and the product environmental impacts to be 149.01mpts/h.
The literature review indicates that the implementation of a CCP system can result in significant improvements in cooling load and electricity production.However, there is a lack of studies addressing the utilization of CCP systems to enhance efficiency and reduce environmental impacts specifically in the context of a petrochemical complex.Therefore, the objective of this study is to utilize a CCP system in the Kurdistan petrochemical complex in Iran to increase productivity and reduce costs.In this study, the low-, moderate-, and high-pressure steams generated as byproducts from various components within the petrochemical complex are harnessed simultaneously to generate electricity and provide cooling.This is achieved by incorporating an absorption chiller and a steam turbine to capture the high-pressure steam from the boiler and the moderate-pressure steam in the turbine.The remaining of the research is organized as follows: Description of problem and proposed CCP is provided in Sect. 2. Governing equations for each component of the system are given in Sect.3.Then, the validation and results obtained from the analysis are discussed in Sect. 4. Finally, the conclusion is presented in Sect. 5.

Problem description
The Kurdistan Petrochemical Company (KPC) is located in Sanandaj city, Iran and has the capacity to export over 155,000 tons of polyethylene, valued at more than $192.6 million.Sanandaj is situated in the western part of Iran, with geographical coordinates of 35° 18′ 53.82′′ N and 6° 59′ 55.79′′ E. Within the KPC, there are two direct flame boilers.One of the boilers operates at approximately 30% of its capacity and produces 11 tons per hour of steam.This boiler is responsible for supplying steam to various processes, including the reactor, HVAC components, tank heating, and heat exchangers.It also provides steam to the unit referred to as "180".The other boiler, known as the backup boiler, generates around 3 tons of steam per hour.The steam produced by this boiler is mostly unused and released into the atmosphere.Its main purpose is to supply steam during specific situations such as start-up and tripping.Figure 1 illustrates a schematic of the primary cycle utilized in the KPC.Natural gas with a heat value of 43,000 kJ/kg is used as the fuel for this system.The steam generated in the complex is divided into three categories: high-pressure steam at 42 bar and 420 °C, medium-pressure steam exiting the reactor at 8.5 bar and 185 °C, and low-pressure steam at 5 bar and 170 °C.The nominal efficiency of the boiler is 93%, and its fuel consumption is approximately 2.5 tons per hour.The boilers are always in operation; however, their utilization is postponed to the specific conditions of the process, which will reduce their useful life.However, this capacity can be used to generate electricity, cooling, and heating optimally.
The description of the schematic shown in Fig. 1 is as follows: (i) Steam discharges to the environment.This steam flow is generated due to the reservation of one of the boilers, which can be recovered.The amount of wasted heat is 1792 kW.(ii) Steam dispatches to the heat exchanger, the heat production, and ventilation sections for temperature stabilization.(iii) The low-pressure steam is used to supply heat for the heating system.(iv) The medium-pressure steam produced in the reactor is practically not used.This steam can be used as auxiliary steam of the turbine for power generation.The amount of heat energy wasted in this part is 9326 kW.(v) The low-pressure steam is used in regenerative heat exchangers and cooling and heating systems.The amount of energy wasted in this section is 13,167 kW.Currently, a significant amount of thermal energy, totaling 24,285 kW, is being wasted as water vapor in Sects. 1, 4 and 5.However, with the implementation of appropriate measures, this wasted heat can be recovered.Figure 2 illustrates a schematic of the proposed combined cooling and power (CCP) cycle, which aims to utilize the wasted heat to simultaneously generate cooling and electrical power.The proposed model is divided into three main parts: (i) utilizing the boilers at their nominal conditions and operating at maximum load to generate electricity; (ii) utilizing the moderate-pressure steam from unit 180 as auxiliary steam, which is fed into the turbine (iii) utilizing the low-pressure steam from unit 180 in the absorption chillers to provide the required cooling load.
The design includes a single-effect absorption chiller and steam turbine cycle, which is depicted in Fig. 3.The high-pressure and medium-pressure steams enter the turbine at points 1 and 2, respectively.The low-pressure steam exits the turbine at point 3.The steam then enters the generator at point 4 and exits at point 5.The fluid leaving the generator at point 5 enters the pump at point 6, where the pressure of the weak solution is increased to match the pressure of the heat exchanger at point 7.The weak solution then enters the generator at point 8. Exiting the generator at point 9, the fluid exchanges heat in the heat exchanger.There are three flows entering the absorber: one from the cooling tower at point 15, another from the heat exchanger at point 10, and the third from the refrigerant vapor at point 14.The refrigerant vapor and the strong solution enter the condenser, where the heat is dissipated.The condenser has two outlets: one entering the cooling tower at point 17 and the other entering the expansion valve at point 12.The evaporator receives three inlets: one from the expansion valve at point 13, another from the refrigerant pump at point 18, and the third from the chilled water.The refrigerant vapor exits the evaporator and enters the absorber at point 14, while the chilled water exits the evaporator at point 19.In this design, the outlet pressure of the turbine is set at 0.1 bar since the primary objective is to generate electricity through the turbine.A schematic of the single-effect absorption chiller and steam turbine cycle is shown in Fig. 3.The high-pressure and medium pressure steams enter the turbine (1 & 2), then the low-pressure steam exits the turbine (3).The outlet pressure enters the generator (4), and exits the generator at point 5.The fluid enters pump at point 6 where the weak solution pressure is increased by the pump and reached the pressure of the heat exchanger (7).Then the weak solution entering the generator at point 8.The fluid exists the generator at point 9, then exchange its heat in the heat exchanger.Three flows enter the absorber from cooling tower (15), heat exchanger (10) and refrigerant vapor (14).Then, the refrigerant vapor (11) and strong solution (16) entering the condenser where its heat is dissipated.There are two outlets from the condenser, one enters the cooling tower (17), and the other enters the expansion valve (12).There are three inlets entering the evaporator which are from expansion valve (13), refrigerant pump (18) and chilled water.Then the refrigerant vapor exits the evaporator to enter the absorber (14), and the chilled water exists the evaporator at point 19.

Mass, energy and exergy equations
In the following, the equations of mass balance, energy balance, exergy, exergy rate, and exergy efficiency are given separately for the turbine and each component of the single-effect lithium bromide absorption chiller.

• Turbine
The mass balance is given as follows [19,20]: Energy balance for turbine is defined by Eq. ( 2) [21,22]: where ẆST is the total power of the turbine, ẆST,MP is the power of medium-pressure steam turbine and ẆST,HP is the power of high-pressure steam turbine.The thermal efficiency of the turbine can be calculated via Eq.( 3) [23].
Fig. 3 The cycle of single-effect absorption chiller and the steam turbine Mass balance equation for the generator is as follows [23].
The energy balance is expressed by [24], where X denotes the mass fraction of the lithium bromide solution.Since there is only water vapor at point 11 and the concentration of the lithium bromide solution is zero, hence X 11 = 0.
The energy balance in the generator is given as below [25]: Equation ( 12) can be used for defining the exergy balance [26,27].
The specific exergy and the exergy rate of the various points are obtained from Eqs. ( 8) and ( 9) [27].
Equations ( 8) and ( 9) can be used for all points of the cycle shown in Fig. 3.It should be noted that the values of h 0 and S 0 are equal at all points outside the cycle of lithium bro- mide solution, which are obtained in terms of T 0 = 25 °C and P 0 = 1bar .However, these values at points 6-10 at which the lithium bromide solution flows are calculated in terms of T 0 = 25 • C, and the concentration of lithium bromide lotion is calculated at point i , i.e., x i ( T 0 must be in terms of Kelvin).
The following equations can be used to calculate the enthalpy and entropy at different points of the single-effect absorption chillers cycle shown in Fig. 3, points 6-10 [28].
where the temperature used in the enthalpy equation, i.e., Eq. ( 15), should be defined in Kelvin, while in Eq. ( 16), the temperature is defined in Celsius degrees.The constants used in the above equations are as below [29].
where T i (K ) and X i denote the temperature and concentra- tion of the lithium bromide lotion at point i, respectively.It is while that these two parameters for water and steam at T i and P i are defined as follows.

• Condenser
The mass balance in the condenser is given as below [30,31].Also, the energy balance is given as below [31].( 11) The specific exergy, exergy rate, and exergy balance in the condenser points 11, 12, 16, and 17, can be calculated by using Eqs.( 7), (8), and (9).Since there is superheat steam at the condenser inlet and saturated water at the condenser outlet (no lithium bromide solution), the enthalpy and entropy values at the desired points are obtained by Eqs. ( 12) and ( 13).

• Evaporator
The mass balance in condenser is given as below [32].Also, the energy balance is given as below [32].
where Qeva is the heat transfer rate in the evaporator.The specific exergy, exergy rate and exergy balance in the evaporator can be calculated by using Eqs.( 7), (8), and (9).Besides, the enthalpy and entropy in the evaporator are obtained by Eqs. ( 12) and ( 13).

• Absorber
The mass balance in the condenser is given as below [33].
Since there is only water vapor at point 11 and concentration of the lithium bromide solution is zero, hence X 14 = 0.
Also, the energy balance is given as below [34].
where Qabs is the heat transfer rate in the absorber.The specific exergy, exergy rate, and exergy balance in the evaporator can be calculated by using Eqs.( 7), (8), and (9).Besides, since there is lithium bromide solution at points 6 and 10, the enthalpy and entropy at these points are obtained by Eqs. ( 10)- (13).The enthalpy and entropy can be obtained for the remaining points using Eqs.( 14) and (15).

• Pump
The mass energy balance in the pump is expressed as below.
The energy balance in the pump is defined as below [35].
The specific exergy, exergy rate, and exergy balance at points at which no lithium bromide solution flows are calculated using Eqs.( 7)-( 9).Besides, since there is lithium bromide solution at the inlet and outlet of the pump, i.e., points 6 and 7, the enthalpy and entropy at these points are obtained using Eqs.( 10)-( 13).

• Heat exchanger
The mass balance in the heat exchanger is expressed as follows [36].
The equations defining the energy balance in the heat exchanger used in the proposed cycle is as below [37].
The relations for calculating specific exergy, exergy rate, exergy balance, enthalpy, and entropy at different points of the heat exchanger are the same as those of the pump.

• Boiler
The mass balance in the boiler is expressed as follows [37].
where ṁNG , ṁAir and ṁw,in denote the natural gas, air, and water mass entering the boiler, and ṁs,out is the steam mass exits the boiler.
The energy balance in the boiler is expressed as below [38].
The relations for calculating specific exergy, exergy rate, exergy balance, enthalpy, and entropy at different heat exchanger points are the same as those of the pump.
The exergy efficiency and exergy rate equations for different components of the proposed cycle are given in Table 1.

System efficiency
The overall efficiency of the system can be calculated as below [39].
where LHV NG denotes the heat value of the natural gas in kj/kg.The heat value of the natural gas fed to the KPC is 43,000 kJ/kg.Besides, n b is the number of boilers ( n b = 2), S P is the steam content which is equal to 54 66 , and F P is the consumed fuel which is equal to 2432 3600 .The net outlet power of the turbine is denoted by ẆST,net (kW) which is cal- culated by Eq. ( 28).The refrigeration energy rate needed for enhancing the power generation, Qeva (kW), is calcu- lated by Eq. ( 29).
where ẆST,MP , and Ẇsolutionpump represent the power obtained by the low-pressure and high-pressure steams, respectively.Besides, the power required for running the refrigerant pump is denoted by ẆRefrigerantpump .Since the power needed for running solution and refrigerant pumps is negligible compared to the turbine's power, so they can be neglected.

Economic analysis
Economic is an inseparable part of engineering designs.So, the economic estimation for building and developing a petrochemical complex is of great importance.The significant economic factors include electricity price, total cost investment (TCI), return on interest (ROI), fuel consumption cost, and components' price.In this study, three parameters, among all are considered for the economic analysis, including TCI ( Z C ), fuel consumption cost ( Z f ) and repair & mainte- nance costs ( Z OM ).
The following equation is used to convert the abovementioned costs unit to cost per kilowatt-hour of produced electricity [29,30]: As stated earlier, the costs can be categorized into two main groups fixed costs (initial investment) and lateral costs (fuel, repair, and maintenance costs).In general, these costs can be expressed as below [31,32].(28) ẆST,net = ẆST,HP + ẆST,MP − Ẇsolutionpump + ẆRefrigerantpump where CRF is the cost recovery factor, and TCI is total cost investment.The parameter denotes the repair and maintenance factor which is defined based on the powerplant type; if there is no comprehensive information, the value of 1.06 can be used [29].Besides, Ẇ and H represent the net produced power and the total annual performance hours of the powerplant, respectively.Usually, the average value of 8000 h is considered for H parameter [24].
In the present research, TCI includes the costs for purchasing turbines and chillers, which is calculated as below.
Given the power range needed for the steam cycle (nearly 16 MW), the average total cost per kilowatt hour of turbine building is nearly € 330 [33].The cooling towers of the chillers can be of dry, wet, or hybrid type [40].The following relation is used to calculate the CRF [36,37].
where n is the lifetime of the complex which is considered 20 years.Besides, i is the gain rate which is considered 0.12 [38].
The fuel cost per kilowatt hour is expressed as below.
where C f denote the consumed fuel cost in C kJ and HR PP is the heat rate of the complex in kJ kWh .The fuel cost and heat rate can be calculated using Eqs.(37) and (38).
where C fm is the price of a cubic meter of natural gas in C m 3 , and LHV Gas is the heat value of the natural gas which is equal to 43,000 kJ/kg.Besides, is the net thermal efficiency of the cycle.
The total cost per kilowatt of electricity generation is calculated as below. (31) The return of the investment period is defined as below.
where A t is total annual profit of the petrochemical com- plex, which is calculated as following.
where Z pr is the profit obtained from a 7% increase in prod- uct sales, and Z power is the profit obtained from additional power sales.

Results and discussions
Table 2 shows the temperature, pressure, mass flow rate, lithium bromide solution concentration, and fluid status at all points in the desired cycle.

Validation
In this section, the results obtained in the present research are compared with those of other published articles to validate the results.Firstly, a comparison is made between the results of the present study and those of Omar and Micallef [38].In their work, authors have investigated the effect of inlet generator temperatures on the coefficient of performance (COP).They used the lithium bromide solution as the working fluid.The data comparison of both works is shown in Fig. 4. It can be seen that for both plots, with increasing the generator temperature, the COP increases.It is while that Omar and Micallef [38] reported higher values for COP than in the present study.However, the maximum difference between the results is less than 3%, indicating a good agreement between the results.The second validation part is dedicated to the LiBr mass concentration in terms of generator temperature (see Fig. 5).It can be seen from both plots that by increasing the generator temperature, the LiBr mass concentration steadily increases.The maximum difference between the results is less than 4%, which again indicates the excellent agreement between the results.

Exergy analysis results
Table 3 presents the findings pertaining to exergy production rate, exergy flow rate, exergy destruction rate, and ( 39) A t = Z pr + Z power exergy efficiency for various components.The results indicate that the boiler and turbine exhibit the highest exergy production rates, measuring 22,490 kW and 15,564 kW, respectively.In contrast, the pump demonstrates the lowest exergy production rate, at 16.5 kW.When considering the flow rate, the boiler exhibits the highest value at 46,767 kW, while the pump demonstrates the lowest value at 16.5 kW.The last column of the table, which signifies exergy efficiency, reveals that the pump and turbine exhibit the highest efficiencies, with values of 94.2% and 83.93%, respectively.These findings provide scientific validation regarding the exergy characteristics of each component and emphasize the varying levels of efficiency and exergy production within the system.Results are supported by the results reported in [41,42] In this section, we have examined two cases.The first case involves solely utilizing medium-pressure steam (MPS) from the boilers.Figure 6 illustrates the turbine's  Fig. 5 The LiBr mass concentration in terms of generator temperature obtained by the present study and Omar and Micallef [38] power output as a function of pressure for both cases, with and without MPS.It is evident from the results that, in the presence of MPS, the turbine's power exhibits a consistent decrease as pressure increases.Specifically, increasing the pressure from 0.1 to 0.2 bar leads to a reduction in turbine power from 13,695 to 12,620 kW, indicating a decrease of approximately 8.5%.By harnessing the potential of MPS, a significant increase in turbine power is achieved.
For instance, at a constant pressure of 0.14 bar, the turbine's power is 14,930 kW when MPS is utilized, while it is 13,260 kW when MPS is not employed.This observation indicates that harnessing the MPS results in an approximate enhancement of 12% in turbine power.Furthermore, it is noteworthy that the maximum turbine power of 15,075 kW is attained in the case where MPS is utilized.These findings provide a scientific basis for understanding the impact of utilizing medium-pressure steam on turbine performance.The results demonstrate the potential benefits of incorporating MPS into the system, highlighting its role in enhancing turbine power output.Figure 7 presents the turbine power as a function of the turbine's isentropic efficiency for both cases, with and without utilizing the medium-pressure steam wasted from unit 180.It is noteworthy that an increase in the turbine's isentropic efficiency leads to an increase in its power for both cases.The black dotted line in the graph represents the turbine's power at an isentropic efficiency of 83%.In this case, the turbine power is 1379 kW when utilizing MPS and 1581 kW when not utilizing MPS.These results indicate that by incorporating the wasted MPS from unit 180, the turbine's isentropic efficiency is improved by approximately 13%.The exergy efficiency rates of different components within the system are shown in Fig. 8. Notably, the pump, turbine,  evaporator, and heat exchanger exhibit the highest exergy efficiencies, respectively.Conversely, the generator demonstrates the lowest exergy efficiency among the components analyzed.Al-Tahaineh et al. [43] and Lake et al. [44]reported similar findings that validated our results.

Economic analysis
In this section, the results of the economic analysis using the EES software are presented.The cost of energy resources is a significant factor in the economic analysis.Table 4 provides the price of the energy resources used in the KPC in Euros.Figure 9 illustrates the relationship between the annual benefit and payback period, both in terms of the cost of power.An interesting finding from the graph is that as the cost of power increases, the two factors exhibit opposite trends.Specifically, the payback period increases, while the annual benefit decreases.In this figure, the dotted black line representing a cost of power of 0.0056 €/kWh.At this cost, the annual saving is 2.02 ×10 6 €, and the payback period is 3.5 years.However, as the cost of power increases, a trade-off point is reached at a cost of power of 0.006 €/kWh.At this point, the payback period extends to 3.6 years, while the annual benefit decreases to 1.96 ×10 6 €.These findings dem- onstrate the interplay between the cost of power, payback period, and annual benefit.As the cost of power rises, the payback period becomes longer, indicating a longer timeframe for recovering the initial investment.Simultaneously, the annual benefit decreases, signifying a reduction in the financial returns obtained annually.This analysis provides a scientific basis for understanding the economic implications and considerations associated with the system's cost of power.It highlights the need for careful evaluation and optimization to strike a balance between the payback period and annual benefit, taking into account the specific cost of power in question.The finginds of this section are supported by the results reported by Jafari et al. [45] and Ebrahimi and Moradpoor [41].
The cost of water is another crucial parameter that significantly impacts both the payback period and annual benefit.Water is primarily utilized in refrigeration and power generation processes within the system.As shown in Table 4, the cost of water ranges from 0.037 to 0.057 €/m 3 .Figure 10 depicts the variations of annual benefit and payback period in relation to the cost of water.Similar to Fig. 9, there exists an inverse relationship between the trends of annual benefit and payback period concerning the cost of water.At a certain point, a trade-off occurs between the two factors.For instance, let's consider the trade-off point indicated in the graph.It corresponds to a payback period of approximately four years and an annual benefit of nearly 1.787 million €.At this specific cost of water, the system strikes a balance between the duration required to recover the initial investment (payback period) and the annual financial returns obtained (annual benefit).Our findings are in good agreement by the findings in [46].
Figure 11 compares the water consumption of wet and hybrid chillers, and its implications on the cost of water.The graph reveals that the water consumption and cost of water for the wet chiller are nearly twice that of the hybrid chiller.Since the cost of water significantly impacts Fig. 9 The annual benefit and payback period in terms of cost of power Fig. 10 The annual benefit and payback period in terms of cost of water the economic costs in the system, it becomes crucial to incorporate a hybrid chiller in the design.The lower water consumption of hybrid chillers compared to wet chillers suggests that the cost of water has a relatively low impact on the annual benefit in the Knowledge Production Company (KPC).This observation aligns with previous research works [35,41].Furthermore, when analyzing the data point represented by the dotted line in the graph, where the cost of water remains constant at 0.046 €/m3, the annual benefit for the hybrid chiller is 1.787 million €, while it is 1.791 million € for the wet chiller.This indicates that the hybrid chiller outperforms the wet chiller in terms of both economic and environmental aspects [35].These findings highlight the importance of selecting the appropriate chiller type, considering the water consumption and cost of water, to optimize both economic and environmental performance in the KPC.By opting for a hybrid chiller with lower water consumption, the system can achieve enhanced economic benefits and contribute to a more sustainable operation.
The impact of fuel cost on the annual benefit and payback period is investigated in Fig. 12.Similar to previous analyses, a reverse trend is observed between the two dependent factors, namely annual benefit and payback period, and the independent factor, fuel cost.The graph demonstrates that as fuel cost increases, the annual benefit decreases and the payback period increases, which are both undesirable outcomes.The trade-off point is represented by the dotted line, corresponding to a fuel cost of 0.012 €/m 3 .At this specific point, the system achieves a balance between the annual benefit and payback period.The annual benefit is measured at 1.787 million €, while the payback period stands at 4.064 years.These findings emphasize the significance of considering fuel cost when evaluating the economic performance of the system.Higher fuel costs result in reduced annual benefits and longer payback periods, which can impact the financial viability of the project.Therefore, it is crucial to carefully assess and optimize fuel costs to achieve the desired balance between annual benefits and payback period, ultimately ensuring the economic sustainability of the system.The similar results are reported in [46].
Figure 13 illustrates the impact of turbine cost on the annual benefit and payback period.It is evident from the graph that as the turbine cost increases, the annual benefit decreases and the payback period increases.This relationship is observed consistently throughout the data.For example, at a turbine cost of 330 €/kW, the corresponding annual benefit is 1.738 million €, and the payback period is approximately 4.7 years.As the turbine cost decreases, the annual benefit increases, and the payback period decreases (similar findings are reported in [41,45]).The trade-off point is identified at a turbine cost of 305 €/kW, where the annual benefit is 1.78 million € and the payback period is 4.1 years.If the primary objective is to maximize Fig. 11 Comparison of water consumption in wet and hybrid chillers Fig. 12 The annual benefit and payment period in terms of fuel cost Fig. 13 The annual benefit and payment period in terms of turbine cost the annual benefit, regardless of the payback period, the optimal turbine cost would be 2450 €/kW.Choosing this option would lead to the highest annual benefit, although the payback period would likely be longer.These findings emphasize the importance of carefully evaluating the turbine cost in relation to the desired annual benefit and payback period.Optimizing the turbine cost can significantly impact the economic performance of the system and ensure the best possible financial outcome.
Figure 14 presents a comparison of the overall thermal efficiency variations between the cases with and without MPS, in terms of turbine isentropic efficiency.The utilization of MPS results in higher overall thermal efficiency compared to the case without MPS.For instance, at a turbine isentropic efficiency of 0.83, the overall thermal efficiencies for the cases without MPS and with MPS are 0.392 and 0.44, respectively.Notably, the overall thermal efficiency for the case with MPS is approximately 11% higher than that without MPS.This highlights the positive impact of utilizing MPS on the overall efficiency of the system.Figure 15 explores the effect of product cost on the annual benefit and payback period.In contrast to the previous plots, an increase in product cost leads to a decrease in the payback period and an increase in the annual benefit.However, it is crucial to strike a balance as excessively high product costs may negatively impact marketing and income.Thus, a trade-off needs to be carefully considered.For instance, at a product cost of 250 €/ hr, the system achieves an annual benefit of 1.73 million € and a payback period of 4.3 years.The minimum payback period (3.3 years) and maximum annual benefit (2.2 million €) occur at a product cost of 300 €/hr.These findings emphasize the importance of analyzing the impact of product cost on the annual benefit and payback period.While increasing product cost can enhance the financial performance of the system, there is a need to find the optimal balance to ensure both economic viability and market competitiveness [41].
Table 5 presents the performance indicators of the proposed system in the KPC, including the COP, refrigeration load, power production, turbine's thermal efficiency, and total exergy efficiency.One notable observation is that the proposed CCP system effectively contributes to the system's operation.It adds a refrigeration load of 5000 kW, providing the necessary cooling capacity for various processes within the KPC.Additionally, the system generates a power output of 16,876 kW, which is a significant contribution to meeting the power demand of the KPC.By utilizing the wasted heat and optimizing fuel consumption, the system successfully reduces its environmental impact.This is achieved through the power production of 16,876 kW, which partially meets the power needs of the KPC.This approach helps minimize fuel consumption and decreases the reliance on conventional power generation methods, resulting in environmental benefits and improved sustainability.Furthermore, the turbine's thermal efficiency and the total exergy efficiency of the proposed system play vital roles in maximizing energy utilization and minimizing energy losses.These efficiencies contribute to the overall performance of the system and further enhance its environmental and economic benefits.The total exergy efficiency is 57% which is supported by the results reported in [42,47].

Conclusion
In the present study, a CCP system was proposed to utilize the low-, medium-, and high-preíssure steam to simultaneously produce power and cooling for the Kurdistan Petrochemical Company (KPC).To this end, the low-pressure steam at the outlet of turbines and those recovered from other parts of the KPC are used to supply the power needed for absorption chillers' turbine and cooling the water used for lowering the capacity of the wet cooling towers.Exergy and energy analyses were performed on the proposed system to determine its feasibility.It should be noted that the proposed method is successfully installed and used in the KPC.The significant results of the present study are highlighted as follows: • By increasing the generator temperature from 65 to 90 °C, the COP increases from 0.67 to 0.77.• The LiBr mass concentrations is increased from 0.55 to 0.67 as the generator temperature is increased from 65 to 90 °C.• Maximum exergy production rate corresponds to the boiler (22,490 kW) and turbine (15,564 kW), respectively.
• By increasing the pressure from 0.1 to 0.2 bar, the turbine's power decreased from 13,695 kW to 12,620 kW, respectively, indicating a reduction of nearly 8.5%.• The maximum exergy efficiency is related to the pump, turbine, evaporator, and heat exchanger, respectively.• By increasing the cost of power, the annual benefit decreases while the payback period increases.The trade-off occurs at a cost of power of 0.006 €/kWh, where the payback period and annual benefits are 3.6 years and 1.96 million €, respectively.• The water consumption (and the paid cost for consumed water) of a hybrid chiller is significantly lower than the wet chiller.For example, at the cost of water of 0.46 €/m 3 , the annual benefit of hybrid and wet chillers are 1.787 million € and 1.791 million €, respectively.
• The trade-off point for the cost of fuel is 0.012 €/m 3 , at which the payback period and annual benefit are 4.064 years and 1.787 million €, respectively.• Turbine cost greatly affects the payback period, so by increasing the turbine cost from 250 to 350 €/kW, the payback period increases from 3.2 years to 5.2 years.So, the turbine with a cost of 300 €/kW was selected for the proposed system.
• Increasing product costs will increase annual benefits and decrease the payback period, which both are desired.However, increasing the product cost negatively affects the market and their sales.So, the optimum product cost was found to be 240 €/hr.• The COP, power production, turbine efficiency, and total exergy efficiency of the proposed system are 0.73, 5000 kW, 16,876 kW, 35.98%, and 0.57, respectively.• Utilization of MPS significantly increases the overall thermal efficiency by nearly 20% compared to the case without MPS.
Since the purpose of this article was to use the full capacity of steam and waste heat production in the Kurdistan Petrochemical Complex, there were many limitations in the selection of CCP due to the country's special conditions in the selection of equipment (especially the turbine) and the amount of the budget.The use of the new CCP and the optimization of the system using new methods have been left as future works.

Fig. 1
Fig. 1 Schematic of the KPC system

Fig. 2
Fig. 2 Schematic of proposed system

Fig. 4
Fig.4COP in terms of generator temperature obtained by present study and Omar and Micallef[38]

Fig. 6 Fig. 7 Fig. 8
Fig. 6 Turbine power in terms of pressure for the case without MPS and with MPS

Fig. 14 Fig. 15
Fig.14 Overall thermal efficiency in terms of turbine isentropic efficiency for the cases with and without MPS

Table 2
Thermodynamic parameters at different cycle's points

Table 3
Enthalpy, entropy and specific exergy of the cycle Component ⋅ E P (kW) ⋅ E F (kW) ⋅ E D (kW) EX (%)

Table 4
Energy resources cost in Euros

Table 5
Energy resources cost in Euros