Dynamic 6E analysis of a novel power and freshwater production based on integration of combined cycle power plant-MED-TVC-RO-STC-ORC systems

Abstract

In this study, a novel power and potable aqua creation system has been proposed based on a combination of the gas cycle, steam cycle, multieffect desalination (MED), reverse osmosis (RO) desalination units, organic Rankine cycle (ORC), and the solar thermal collector (STC). In this regard, the Energy, Exergy, Exergoeconomic, Exergoenvironmental, Emergoeconomice, and EmergoEnvironment (6E) assessments and further dynamic analysis are executed on the novel suggested system. Dynamic analysis helps us to understand the system performance at different times. The validation has been performed based on THERMOFLEX simulation and base references with high accuracy. The results show that the proposed system produces 60 and 73.61 kg/s of freshwaters, respectively. The gas cycle generates 25 MW of power standing alone, and adding ORC as the bottom cycle can generate 4.89 MW extra power using the excess energy of the gas cycle, which elevates the system's thermal efficiency from 36.51 to 43.27%. Using a thermal vapor compressor (TVC) in the MED unit reduces the demand for motive steam from 12.59 to 5.38 kg/s, increasing this unit's performance ratio (PR) from 4.76 to 11.15. Integrating the system with the STC improves the system's thermal efficiency from 42.82 to 43.27 percent.

Keywords

desalination organic Rankine cycle solar thermal collector 6E analysis dynamic analysis

Introduction

Today, with the ever-increasing growth of the world's population and the increase in energy needs, power generation and fresh water have been proposed as two critical factors for meeting human needs. At present, the fossil energy sources that are mostly exploited are facing environmental problems and non-renewability. Also, lack of potable aqua is considered a serious menace for many regions of the world due to climate change and destruction of water resources.¹

Accordingly, the use of concurrent energy and potable aqua creation systems is one of the efficient solutions to improve this situation.² The use of new technologies increases production efficiency in simultaneous production systems. Altmann et al.³ investigated a system of the concurrent output of energy and freshwater with the approach of using different water desalination technologies. The results of this study show that purification technologies with multistage evaporation and multieffect evaporation have higher efficiency in conditions of energy and exergy. In another research conducted by Ghorbani et al.,⁴ a system of concurrent production of power and potable aqua using renewable energies was evaluated for energy and exergy. The hybrid system of simultaneous generation has been developed with the assistance of MATLAB application. The outcomes indicate that the net power generation and exergy yield of the whole system are equal to 2580 MW and 53% respectively. In another investigation conducted by Pietrasanta et al.,⁵ an optimal cogeneration system consisting of gas power generation systems, absorption cooling, and thermal desalination is presented. The outcomes show that the production of power, fresh water, and cooling is equal to 40 MW, 100 kg/s and, 2 MW respectively. Development and appraisal of a new proposed system to create crude helium, natural gas, and methanol were performed by Ghorbani and Amidpour.⁶ They found that the primary sources of exergy destruction are heat exchangers and reactors by 56.2% and 13.8% of whole exergy demolition of the system. The use of simultaneous production systems can help improve the production of various products and increase efficiency.

Jabari et al.⁷ evaluated a cogeneration system for power and potable aqua. The presented system has subsystems of gas power generation, steam Rankine cycle and thermal desalination. The outcomes of the energy appraisal of the unified system show that the creation of potable aqua and electric power is equal to 3 L and 6 MW, respectively. Jabari et al.⁸ performed a technofinancial investigation of a concurrent production of power, potable aqua and cooling system with biofuel for the city of Ahvaz. The production of cooling in this system is done by electric chillers. The techno-economic results show that the use of biofuel has reduced the expense of electricity generation in the integrated system by 50%. In another investigation performed by Jabari et al.,⁹ a simultaneous power generation and cooling system has been thermodynamically examined. The outcomes indicate that the use of gas turbine (GT) exhaust gases has increased energy efficiency. Khoshgoftar Manesh et al.¹⁰ investigated a combined cycle power plant (CCPP) system integrated with multieffect distillation (MED) and reverse osmosis (RO) desalination technologies. They used advanced and conventional exergy-based analyses. The results revealed a decrease of 5% in exergy efficiency but production of 27 kg/s freshwaters after integrating the CCPP with the water salinity removal units. The use of new technologies in simultaneous production can lead to an increase in product production performance in various integrated systems.

Solar energy is one of the sustainable and endless sources of energy that benefits from the light and heat of the sun.¹¹ Solar energy is used directly or indirectly.¹² In direct utilization applications, sunlight reaches solar converters like solar panels and converts into electrical energy.¹³ In indirect utilization, sunlight converts into heat through systems like solar heat or solar thermal and is used in processes like steam production or space heating.¹³ Cogeneration systems can integrate with solar energy. Ghorbani et al.¹⁴ proposed and examined a multi-generation system driven by solar energy. The exergy evaluation outcomes performed on the proposed system show that the primary sources of exergy demolition are heat exchangers, splitters, drums, and valves. The comparison of two types of cooling systems utilized in a solar power plant was performed by Blanco-Marigorta et al.¹⁵ They use Gate Cycle software to simulate the system. The outcomes indicate that the efficiency of the system can be enhanced, and the mentioned comparison can be performed using exergy analysis. Vazini et al.¹⁶ presented a system of simultaneous production of power and fresh water with the approach of using solar energy. Dynamic exergy analysis is being done to accurately identify the negative effects of the equipment used in the system. The outcomes show that the environmental effects and expense rates of the provided system are decreasing. The use of solar systems in simultaneous production systems will reduce the expenses and ecological consequences of the product.

Desalination devices and technologies are used to purify saltwater or seawater into potable water.¹⁷ In the water desalination process, salts, solids, and other pollutants in the water are removed to obtain usable and drinkable water.¹⁷ In simultaneous production systems, the use of water purification technologies increases product production efficiency. Mokhtari et al.¹⁸ integrated a GT technology with MED and RO systems. The proposed scheme shows the capability to meet the power and freshwater requirements of Bashagard City. Khoshgoftar Manesh et al.¹⁹ evaluated the integration of a power plant with MED and MSF desalination technologies from exergy and economic points of view. The results show a reduction of 0.1% and 9.2% in exergy destruction costs by combining the system with MED and MSF, respectively. Onishi et al.²⁰ proposed and optimized an innovative system for a zero-emission desalination unit integrated with renewable energy sources. They show that the proposed scheme saves costs and diminishes environmental impacts. Blanco-Marigorta et al.²¹ conducted the exergy analysis on a desalination unit that exists in Spain. They compared the exergetic parameters for the diverse elements of the system. They show that the exergetic efficiency parameter has the capability to be used as a tool to enhance the achievement of the entire system. Water purification technologies in simultaneous production systems can help to increase the sustainability of product production and improve the drinking water supply.

Energy, exergy, economic, and environmental (4E) evaluations of cogeneration systems are a scientific and formal approach to evaluating the efficiency and sustainability of these systems.²² In these evaluations, different criteria are used to analyze the performance of simultaneous production systems.²² Accordingly, the investigation of a multigeneration system from energy and exergy points of view was performed by Moghimi et al.²³ The outcomes suggest the ability of the system to produce 86 kg/s distillate, 30 MW power, 2 MW cooling, and 1.1 MW heating. Onishi et al.²⁴ presented and optimized a new model for networks of heat exchangers from economic and environmental points of view. They find that the single objective optimization processes reduce the heat transfer area by 79% and the capital costs by 32%. Shahidian et al.²⁵ studied an innovative procedure for the combination of hot oil and combined heat and power systems via Pinch technology and mathematical modeling. The outcomes of using this proposed procedure for a case study determine that the total earnings of the traditional plan procedure are 341 k$/year while the proposed methodology obtains earnings of 445 k$/year, a 30% increase. Table 1 shows an overview of the articles used in the introduction. Various evaluations done on simultaneous production systems can give a comprehensive view of comparing and summarizing different simultaneous production systems.

Table 1.

Review and compare the articles used in the introduction.

Reference	Year	Evaluations	Products	Main results
²⁰	2017	Energy	Heat	The presented system has been optimized economically and environmentally.
²⁰	2017	Pinch	Heat
²¹	2017	Energy	Freshwater	Exergy analysis helps to improve the performance of water desalination units.
²¹	2017	Exergy	Freshwater
²⁴	2017	Economic	Heat	Optimizing the thermal level of the heat exchanger network reduced economic costs and environmental effects.
		Ecological
		Optimization
⁹	2018	Energy	Power	Increase energy efficiency.
⁹	2018	Energy	Cooling	Increase energy efficiency.
²⁵	2019	Economic	Hot oil	The proposed method has caused a 30% increase in investment costs.
		Pinch	Power
		Pinch	Heat
³	2019	Energy	Power	High energy and exergy efficiency multi-stage evaporation technology.
³	2019	Exergy	Freshwater
⁸	2019	Energy	Power	Reducing the price of electricity production.
		Economic	Freshwater
		Economic	Cooling
²⁶	2020	Energy	Power	Fresh water production is equal to 27 kg/s.
²⁶	2020	Exergy	Freshwater	Fresh water production is equal to 27 kg/s.
⁴	2020	Energy	Power	Net power generation is 2580 MW.
		Exergy	Power
		Exergy	Freshwater
		Dynamic	Freshwater
¹⁴	2020	Energy	Power	Hydrogen production is equal to 2030 kg/h.
		Exergy	Cooling	The production cooling rate is estimated at 1.8 MW.
		Exergy	Hydrogen	The power output is approximately equal to 4.5 MW.
¹⁶	2020	Energy	Power	Fuel consumption has decreased.
		Exergy	Power
		Economic	Heat (solar)
		Dynamic	Heat (solar)
¹⁹	2020	Energy	Power	The rate of exergy destruction cost has decreased.
		Exergy	Power
		Exergy	Freshwater
		Economic	Freshwater
²²	2021	Energy	Power	Fresh water production is equal to 86 kg/s.
		Exergy	Freshwater	The production cooling rate is estimated at 2 MW.
			Freshwater	The power output is approximately equal to 30 MW.
			Cooling	The power output is approximately equal to 30 MW.
			Heating	The heat produced is equal to 1.1 MW.
⁶	2021	Energy	Crude helium	The main cause of exergy destruction was heat exchangers and reactors.
		Exergy	Methane
		Exergy	Methanol
⁵	2022	Energy	Power	Fresh water production is equal to 100 kg/s.
			Freshwater	The production cooling rate is estimated at 2 MW.
			Cooling	The power output is approximately equal to 40 MW.
⁷	2022	Energy	Power	Fresh water production is equal to 3 L.
⁷	2022	Energy	Freshwater	Net power generation is 6 MW.

The study proposes an innovative layout that combines various technologies, including the gas cycle, steam cycle, multieffect and RO desalination technologies, ORC, and solar thermal field, to generate power and distillate. The novel recommended system is subjected to 6E analyses and dynamic analysis, providing different insights into the system. Overall, the study introduces a new layout for power and distillate generation, analyzes it from multiple perspectives, and discusses its implications.

System description

In this study, an innovative scheme for producing power and distillate has been proposed. The schematic diagram of the presented system has been shown in Figure 1. As demonstrated in Figure 1, this novel system includes a gas cycle, steam unit, organic Rankine cycle (ORC), thermal solar system, MED unit, and RO unit. The gas cycle power generation unit works as the prime mover of the entire plant. This unit includes an air compressor (AC), a combustion chamber (CC), a GT, and a regenerator. The excess heat removal from the GT transfers to the thermal desalination unit by the heat recovery steam generator (HRSG) in the steam unit. The flue gas exited from HRSG provides the feed energy of the ORC in the ORC heat exchanger (ORC HEX). Also, another heat stream is injected into ORC from the solar thermal system in the solar heat exchanger (Solar HEX). In the desalination unit, two different desalination systems are working; thermal (MED-thermal vapor compressor [TVC]) and mechanical (RO) types. In the MED-TVC section, using the motive steam provided by HRSG, freshwater is produced from the seawater supply. In this unit, seawater enters the condenser of the component at seawater conditions. The seawater supply is considered the required cooling water of the condenser and makes a part of the steam produced in the last effect of MED transformed into a liquid form.

Figure 1.

Schematic of the proposed combined cycle power plant integrated with the MED-TVC and RO desalination units, solar system, and organic Rankine cycle. MED-TVC: multieffect desalination-thermal vapor compressor; RO: reverse osmosis.

After a bit of warming, the seawater is divided into two parts. One part goes toward the effects of the MED as the feed stream. And the other part provides the feed stream of the RO unit. The feed of MED is sprayed on the pipes of the effects which have the warmer steam inside. By receiving the heat, a part of the feed stream evaporates. The rest of the feed stream leaves the effect as the brine stream of that effect. Another part of the steam generated in the last effects does not enter the condenser of MED but returns to TVC to be entrained and utilized as the motive steam of the first effect. Using TVC in a MED unit, on account of using one part of steam produced inside the unit, leads to less motive steam demand from HRSG, thereby more efficiency of the desalination unit. The cooling water discharge's temperature is higher than that of the seawater supply, and their salinity is the same. To enhance the yield of RO and its produced freshwater, the cooling water discharge stream extracted from MED could be utilized as the feed stream of an RO desalination unit. The feed water of RO passes through the pretreatment section to remove its suspended and big particles. After that, the feed saline water is pressurized by the RO pump and passes through the membrane unit. In this process, freshwater is produced, and brine is extracted from another outlet of the component.

In fact, the motive required force of RO is raising the mechanical pressure to overcome the osmotic type. In a solar thermal system, the heat transfer fluid (HTF), which is Therminol-vp1, receives the solar energy engrossed by the solar thermal collector (STC). The STCs used in this study are parabolic trough collector type. The HTF is heated to STC outlet temperature and transfers its energy to ORC in the Solar HEX. In ORC, organic fluid isobutene is heated in two stages and with two different heat sources; solar energy in the Solar HEX and flue gas heat in the ORC HEX. Then, the heated organic fluid enters the ORC turbine (ORCT) and produces power in this unit. Regenerator 2 acts in ORC to achieve two aims; cooling the outlet stream of ORCT and preheating the inlet stream of the ORC HEX. After the cooling process is performed in Regenerator 2, the ORC condenser provides the remaining required cooling to make the stream ready to be compressed in the ORC pump (ORCP).

The assumptions used in this research are given below:

Ambient temperature and pressure are equal to 25 °C and 101.30 kPa respectively.

Isentropic efficiency is considered for rotating equipment.

Heat loss in the CC is considered.

Table 2 indicates the technical data for the proposed CCPP integrated with MED-TVC and RO desalination units, solar system, and ORC. This table consists of input data for thermodynamic simulation performed on the system.

Table 2.

The scientific information for the suggested combined cycle power plant integrated with MED-TVC and RO. desalination units, solar system, and organic Rankine cycle.

Unit	Parameter	Symbol	Unit	Value
Gas Cycle	The compression ratio of AC	$r_{p, A C}$	$-$	8.00
	The isentropic efficiency of AC	$η_{A C}$	%	87.00
	The isentropic efficiency of GT	$η_{G T}$	%	90.00
	The inlet temperature of GT	$T I T$	$^{\circ} C$	1200.00
	The net power output of the gas cycle	${\dot{W}}_{n e t, g c}$	kW	25,000
	The thermal efficiency of CC	$η_{C C}$	%	98.00
	Specific heat of air at constant pressure	$c_{p, a i r}$	kJ/kg.K	1.004
	Specific heat of flue gas at constant pressure	$c_{p, f g}$	kJ/kg.K	1.17
	The ratio of specific heats for air	$γ_{a i r}$	$-$	1.40
	The ratio of specific heats for flue gas	$γ_{f g}$	$-$	1.33
	Effectiveness of Regenerator 1	$ε_{R e g 1}$	$%$	85.00
	The lower heating value of fuel	$L H V_{f u e l}$	kJ/kg	50,000
MED-TVC	The number of the effects of MED	$n_{e f f e c t s}$	$-$	5
	The distillate flow rate for MED	${\dot{m}}_{d, M E D}$	kg/s	60.00
	Motive steam temperature	$T_{m s}$	$^{\circ} C$	60.25
	Sea water salinity	$x_{s w}$	g/kg	36.00
	The terminal temperature difference of MED	$T T D_{M E D}$	$^{\circ} C$	2.00
	The recovery ratio of MED	$R R_{M E D}$	$-$	0.44
	The temperature of the last effect of MED	$T_{e, n}$	$^{\circ} C$	45.00
	Seawater temperature rise in the condenser of MED	$Δ T_{c o n d, M E D}$	$^{\circ} C$	10.00
	Superheat degree of super heater	$T_{s u p, S H}$	$^{\circ} C$	5.03
ORC	Condenser pressure of ORC	$P_{c o n d, O R C}$	kPa	404.20
	The cooling water temperature rise of the ORC condenser	$Δ T_{c o n d, O R C}$	°C	3.00
	ORC's high-pressure level	$P_{h p, O R C}$	kPa	1600.00
	ORC pump isentropic efficiency	$η_{O R C P}$	%	85.00
	Isentropic efficiency of ORC turbine	$η_{O R C T}$	%	85.00
	Effectiveness of Reg2	$ε_{R e g 2}$	%	80.00
	Effectiveness of ORC HEX	$ε_{O R C H X}$	%	80.00
RO	Feed pressure of RO	$P_{F e e d, R O}$	kPa	5000
	Isentropic efficiency of RO pump	$η_{R O P}$	%	85.00
	The salinity of distillate in MED and RO	$x_{d}$	g/kg	0.00
STC	The outlet temperature of STC	$T_{S T C, o u t}$	°C	300.00
	Effectiveness of SHX	$ε_{S H X}$	%	80.00
	Apparent sun temperature	$T_{s u n}$	K	5778
	Oil pump discharge pressure	$P_{O I L P}$	kPa	2500
	Isentropic efficiency of the oil pump	$η_{O I L P}$	%	80.00

STC: solar thermal collector; RO: reverse osmosis; ORC: organic Rankine cycle; MED-TVC: multieffect desalination-thermal vapor compressor; AC: air compressor; GT: gas turbine; CC: combustion chamber.

Methodology

In this section, the equations used in each evaluation have been reviewed. The 6E assessment conducted for the integrated system has many details, each of which is discussed in a separate section.

Thermodynamic analysis

Thermodynamic evaluation is the first step in evaluating integrated equipment in a cogeneration system. One of the most important outputs of this evaluation is energy efficiency. The relationship shows how to calculate the energy efficiency of the integrated system.

η_{e n e r g y} = \frac{({\dot{W}}_{G T} + {\dot{W}}_{O R C T}) - ({\dot{W}}_{A C} + {\dot{W}}_{O R C P u m p} + {\dot{W}}_{O i l P u m p})}{{\dot{m}}_{f u e l} \times L H V_{M e t h a n e} + {\dot{Q}}_{S o l a r}}

(1)

The equations required for modeling the energy of ORC equipment and the solar cycle are collected in Table 3.

Table 3.

The equations, inputs, and outputs of the organic Rankine cycle's components.

Equipment	Thermodynamic equations needed for equipment modeling	Inputs	Outputs
ORCT	$P_{27} = P_{O R C C}$ $s_{27 s} = s_{26} h_{27 s} = h_{(P_{27}, s_{27 s})}$ $h_{27} = h_{26} - η_{O R C T} \times (h_{26} - h_{27 s})$ $T_{27} = T_{(P_{27}, h_{27})}$ ${\dot{W}}_{O R C T} = {\dot{m}}_{O R C} \times (h_{26} - h_{27})$ Reference: ^{27, 28}	$P_{26}$ $T_{26} P_{O R C C}$ ${\dot{m}}_{O R C}$ $η_{O R C T}$	${\dot{W}}_{O R C T} h_{27}$ $T_{27}$
Regenerator2	$P_{28} = P_{27} - Δ P_{R e g_{2}, h o t}$ $P_{24} = P_{23} - Δ P_{R e g_{2}, c o l d}$ $ε_{R e g_{2}} = \frac{h_{24} - h_{23}}{h_{27} - h_{23}}$ ${\dot{Q}}_{R e g_{2}} = {\dot{m}}_{O R C} \times (h_{27} - h_{28})$ Reference: ^27,28	$T_{27}$ $P_{27} T_{23}$ $P_{23} ε_{R e g_{2}}$ ${\dot{m}}_{O R C}$ $Δ P_{R e g_{2}, h o t}$ $Δ P_{R e g_{2}, c o l d}$	$T_{28} T_{24}$ ${\dot{Q}}_{R e g_{2}}$
ORC condenser	$T_{30} = T_{29} + C W T R_{O R C C} P_{22} = P_{28}$ $P_{30} = P_{29} - Δ P_{O R C C, c w} {\dot{m}}_{O R C} \times (h_{28} - h_{22}) = {\dot{m}}_{c w} \times (h_{29} - h_{30})$ ${\dot{Q}}_{O R C C} = {\dot{m}}_{O R C} \times (h_{28} - h_{22})$ Reference: ^{27, 28}	$T_{28}$ $P_{28} T_{29}$ $P_{29} {\dot{m}}_{O R C}$ $Δ P_{O R C C, c w}$ $C W T R_{O R C C}$	$T_{30}$ $P_{30} T_{22}$ $P_{22} {\dot{Q}}_{ORCC}$
ORC pump	$s_{23 s} = s_{22} P_{23} = P_{O R C, h p} h_{23 s} = h_{(P_{23}, s_{23 s})}$ $h_{23} = \frac{h_{23 s} - h_{22}}{η_{O R C P}} + h_{22}$ ${\dot{W}}_{O R C P} = {\dot{m}}_{O R C} (h_{23} - h_{22})$ Reference: ^{27, 28}	$P_{22}$ $T_{22} P_{23}$ ${\dot{m}}_{O R C}$ $η_{O R C P}$	${\dot{W}}_{O R C P} h_{23}$ $T_{23}$
ORC HEX	$P_{25} = P_{24} - Δ P_{O R C H E X, C o l d}$ $P_{11} = P_{10} - Δ P_{O R C H E X, H o t} ε_{O R C H E X} = \frac{T_{25} - T_{24}}{T_{10} - T_{24}}$ ${\dot{m}}_{O R C} \times (h_{24} - h_{25}) = {\dot{m}}_{f g} \times (h_{11} - h_{10})$ ${\dot{Q}}_{O R C H E X} = {\dot{m}}_{O R C} \times (h_{25} - h_{24})$ Reference: ^27,28	$T_{24}$ $P_{24}$ $T_{10}$ $P_{10}$ $Δ P_{O R C H E X, C o l d}$ $Δ P_{O R C H E X H o t}$ $ε_{O R C H E X}$	$T_{25} {\dot{m}}_{O R C}$ ${\dot{Q}}_{O R C H E X}$
Solar HEX	${\dot{m}}_{O R C} \times (h_{25} - h_{26}) = {\dot{m}}_{S T C} \times (h_{32} - h_{31}) P_{26} = P_{25} - Δ P_{S H X, O R C}$ $P_{32} = P_{31} - Δ P_{S H X, S T C} ε_{S H X} = \frac{T_{32} - T_{31}}{T_{31} - T_{25}} {\dot{Q}}_{S H X} = {\dot{m}}_{O R C} \times (h_{26} - h_{25})$ Reference: ^29–31	$P_{31}$ $T_{31} P_{25}$ $T_{25} ε_{S H X}$ $Δ P_{S H X, O R C}$ $Δ P_{S H X, S T C}$ ${\dot{m}}_{O R C}$	${\dot{Q}}_{S H X} T_{26}$ $P_{26} T_{32}$ $P_{32}$
Oil pump	$s_{33 s} = s_{32} P_{33} = P_{O I L P} h_{33 s} = h_{(P_{33}, s_{33 s})}$ $h_{33} = \frac{h_{33 s} - h_{32}}{η_{O I L P}} + h_{32} {\dot{W}}_{O I L P} = {\dot{m}}_{S T C} \times (h_{33} - h_{32})$ Reference: ^29–31	$P_{32}$ $T_{32} P_{33}$ ${\dot{m}}_{S T C} η_{O I L P}$	${\dot{W}}_{O I L P} h_{33}$ $T_{33}$
STC	${\dot{Q}}_{S T C} = {\dot{m}}_{S T C} \times (h_{31} - h_{33})$ $h_{Therminol, V P 1} = 3.172 \times 10^{- 7} \times T^{3} + 10.99 \times 10^{- 4} \times T^{2} + 1.571 \times T - 23.85$ $η_{S T C} = 0.75 - 4.5 \times 10^{- 5} (T_{31} - T_{0}) - 0.039 (\frac{T_{31} - T_{0}}{G}) - 0.0003 {(\frac{T_{31} - T_{0}}{G})}^{2}$ $η_{S T C} = \frac{{\dot{Q}}_{S T C} \times 1000}{A_{S T C} \times G}$ $S F = \frac{{\dot{Q}}_{S H X}}{{\dot{Q}}_{S H X} + {\dot{Q}}_{O R C H E X}}$ Reference: ^29–31	$P_{33}$ $T_{33} T_{31} G$ $T_{0} Δ P_{S T C}$	${\dot{Q}}_{S T C} h_{31}$ $P_{31} η_{S T C}$ $A_{S T C}$

STC: solar thermal collector; ORC: organic Rankine cycle; ORCT: ORC turbine.

Exergy analysis

The second law of thermodynamics can evaluate the quality of energy. In the previous part, where the thermodynamic and energy evaluation of the system was examined, it was determined, for example, how much power the GT equipment produces. To check the quality of electricity production in this equipment, the second law of thermodynamics should be used. The material streams’ specific physical and chemical exergy and the chemical exergy of fuel could be calculated using the following equations.³²

e x^{P H} = (h - h_{0}) - T_{0} (s - s_{0})

(2)

e x^{C H} = \sum x_{k} e {\bar{x}}_{k}^{C H} + \bar{R} T_{0} \sum x_{k} \ln (x_{k})

(3)

The material streams’ total specific exergy could be calculated using the equation below^27,32:

e x_{i} = e x_{i}^{C H} + e x_{i}^{P H}

(4)

Equation (5) shows the exergy destruction rate and equation (6) indicates the exergetic efficiency of the system.^27,32

\dot{E} x_{D, k} = \dot{E} x_{F, k} - \dot{E} x_{P, k}

(5)

ψ_{T o t a l} = \frac{(\dot{E} x_{P_{G T}} + \dot{E} x_{P_{O R C T}}) - (\dot{E} x_{F_{A C}} + \dot{E} x_{F_{O R C P u m p}} + \dot{E} x_{F_{O i l P u m p}})}{\dot{E} x_{4}}

(6)

Exergoeconomic analysis

In this part of the manuscript, the concepts and calculations of the exergoeconomic analysis have been gathered. In order to conduct this analysis on the system, it is needed to obtain the costs of the equipment for being purchased (PEC).^27,32–38 The equipment's cost due to exergy destruction could be obtained by the following equation.³²

{\dot{C}}_{D, k} = c_{F, k} . \dot{E} x_{D, k}

(7)

Equation (8) shows the exergoeconomic factor for the equipment.

f_{k} = \frac{{\dot{Z}}_{k}}{{\dot{Z}}_{k} + c_{f, k} {\dot{E}}_{D, k}}

(8)

Equation (9) shows the components’ relative cost difference:

r_{k} = \frac{c_{P, k} - c_{F, k}}{c_{F, k}}

(9)

Exergoenvironmental analysis

In this analysis, three steps need to be followed: (1) conducting the exergy analysis. (2) Calculating the equipment's ecological impacts due to their manufacturing, operation, and depletion. (3) Calculating the streams’ environmental impacts by using the exergoenvironmental balances. In order to calculate the environmental impacts of each equipment's, the SimaPro 7.0 software was used, which works based on the life cycle assessment concepts and the Eco-Indicator-99. The equipment's environmental impact rate due to exergy destruction could be determined by the following equation.³⁰

{\dot{B}}_{D, k} = b_{F, k} . \dot{E} x_{D, k}

(10)

The equipment's environmental impacts could be determined as follows³⁰:

y_{k} = w_{k} \times b m_{k}

(11)

where

y_{k}

is the equipment's environmental impacts in

p t s

w_{k}

is the equipment's weight in tons and

b m_{k}

is the equipment's environmental impacts per unit of mass in

p t s / t o n

. The values for

b m_{k}

are based on Eco-indicator-99 and the equipment's composition^30,39 and the amounts of weights could be obtained using the weight functions.^16,30

Emergy analysis

In this analysis, all financial and ecological elements for the streams and equipment are converted into a standardized unit known as “sej” or solar emergy joules, following a scientific approach. Different materials and types of energy have specific values for the emergy transformity factor. These values can be obtained through various sources, including the research conducted by Aghbashlo and Rosen in 2018.⁴⁰ In order to convert emergy values based on energy into emergy values based on exergy, a conversion factor called β is employed. The value of β can be determined using the equation provided by Aghbashlo and Rosen in their study conducted in 2018.⁴⁰

β = 1 + \frac{1}{3} {(\frac{T_{0}}{T_{s}})}^{4} - \frac{4}{3} (\frac{T_{0}}{T_{s}})

(12)

In this equation,

T_{0}

is the ambient temperature and,

T_{s}

is the surface of the sun's temperature. The value acquired for

β

is about 0.93.⁴⁰

Emergoeconomic analysis

To acquire the precise monetary emergy of the streams, one can derive and utilize the monetary emergy balance for each component according to the methodology proposed by Aghbashlo and Rosen.⁴⁰

\sum (m_{i n} \dot{E} x_{i n})_{k} - \sum (m_{o u t} \dot{E} x_{o u t})_{k} + {\dot{U}}_{k} = 0

(13)

Emergoenvironmental analysis

To acquire the specific ecological emergy of the streams, one can derive and employ the ecological emergy balance for each component according to the methodology presented by Aghbashlo and Rosen⁴⁰ in their study.

\sum (n_{i n} \dot{E} x_{i n})_{k} - \sum (n_{o u t} \dot{E} x_{o u t})_{k} + {\dot{V}}_{k} = 0

(14)

Dynamic analysis

Dynamic analysis has been performed on the system to study the system's behavior in the different ambient conditions through the year and a day. In this analysis, the environmental data gathered in Vazini Modabber and Khoshgoftar Manesh¹⁶ has been utilized for Iran's southern coasts. The developed code, including all mentioned analyses, has been run 8760 times proportional to each hour of the year. This analysis reveals the system's weak points through a year with various ambient conditions, so practical and improving suggestions can be presented to cover those weaknesses. The ordinary and static analyses are not able to provide such a viewpoint.

Computer-based analysis

To conduct 6E analyses, a set of computational models has been employed. Within this developed code, the thermodynamic properties of gaseous streams are determined using data extracted from the JANAF tables.⁴¹ Meanwhile, the thermodynamic properties of steam and water streams are obtained from the IAPWS tables.⁴²

Furthermore, dynamic analysis has been performed on the system to study the system's behavior in the different ambient conditions through the year and a day. In this analysis, the environmental data gathered in Vazini Modabber and Khoshgoftar Manesh¹⁶ has been utilized for Iran's southern coasts. The developed code, including all mentioned analyses, has been run 8760 times proportional to each hour of a year. The ordinary and static analyses are not able to provide such a viewpoint. Figure 2 illustrates the computational algorithm for conducting the 6E dynamic analysis on the system.

Figure 2.

The computational algorithm for performing the 6E dynamic analysis.

The presented system has the ability to produce power and fresh water at the same time. In this system, the gas cycle has been used to generate power, and in order to reduce the environmental effects and increase the product production efficiency, thermal recovery from the exhaust gas of the gas cycle turbine has been done. Accordingly, the energy efficiency and exergy of the whole system have elevated compared to the single-product mode. It can also be said that the use of freshwater production system has caused the stability of product production in this system and more coverage for the needs of the target community. The integrated system can create water and electric power together, however, when the GT goes out of the circuit, it causes the system to fail completely because the most important limitation that this system faces is the supply the heat from the flue gas is the output of the GT, and when this flow is interrupted, the other sub-systems of the system are removed from the production circuit.

With the advancement of technology, the possibility of using methods based on renewable energy for the simultaneous production of electricity and fresh water has increased. Among the technologies that can be effective in this field are solar cells, wind turbines, water turbines, and hybrid power plant systems. In line with the simultaneous production of electricity and fresh water, efforts have been made toward the optimal use of water resources. This includes the use of advanced water purification technologies, the use of rainwater collection and storage technologies, and changing the water consumption pattern.

Results and discussion

Thermodynamic analysis

Table 4 shows the validation performed for different subsystems of the simultaneous production system. In the validation related to the MED desalination unit, it can be seen that the validation accuracy of this unit is suitable with the selected reference, but the two parameters performance ratio and motive steam mass flow rate contain more errors than other parameters, which it can be related to the difference of thermodynamic calculations in the reference and its related code.

Table 4.

Validation for integrated subsystems in coproduction system.

Unit	Parameters	Units	Value (Ref.)	Present study	Difference (%)
ORC	The net power output of the cycle	kW	582.5	584.79	3.93
	Mass flow rate of working fluid	kg/s	5	5.06	1.20
	Thermal efficiency of the entire cycle	%	20.71	21.27	2.70
	Working fluid	Isobutane
	Reference	⁴³
RO	The pressure of feed saline water	bar	50.0	50.0	0.00
	The salinity of feed saline water	%	3.00	3.00	0.00
	The recovery ratio	-	0.51	0.5008	1.80
	Reference	⁴⁴
MED	Number of the effects	-	8.00	8.00	0.00
	Product mass flow rate	kg/s	6.36	6.36	0.00
	Salinity of feed	g/kg	35.00	35.00	0.00
	The performance ratio	-	5.422	5.810	6.71
	Specific heat transfer area	m²s/kg	292.94	297.50	1.56
	Motive steam mass flow rate	kg/s	1.174	1.096	6.64
	Feed mass flow rate	kg/s	12.7315	12.7300	0.01
	Seawater supply mass flow rate	kg/s	45.84	46.11	0.59
	Brine mass flow rate	kg/s	6.3657	6.3660	0.01
	Cooling water discharge mass flow rate	kg/s	33.1097	33.3800	0.81
	Reference	³¹
GT	Gas turbine power production	MW	71.03	70.85	0.25
	Power consumption of the compressor	MW	40.06	41.72	4.14
	Reference	⁴⁵

ORC: organic Rankine cycle; MED: multieffect desalination-thermal vapor compressor; GT: gas turbine; RO: reverse osmosis.

Table 5 shows the validation of the equipment integrated into the system with valid authorities. Based on this table, the error rate of modeled equipment has been evaluated and investigated in MATLAB and Thermoflex software.

Table 5.

Comparison of the error percentage of consumption and production of simulated equipment in MATLAB and thermoflex software with main references.

Component	Ref.	MATLAB (%)	Thermoflex (%)
Gas turbine	⁴⁶	0.65	0.32
	⁴⁷	0.89	0.38
	⁴⁸	0.31	0.25
Compressor	⁴⁶	0.58	0.29
	⁴⁷	0.65	0.41
	⁴⁸	0.21	0.16
Economiser	⁴⁹	0.25	0.17
Economiser	⁵⁰	0.28	0.18
Evaporator	⁴⁹	0.25	0.17
Evaporator	⁵⁰	0.28	0.18
Superheater	⁴⁹	0.29	0.19
	⁵⁰	0.28	0.17

The results of thermodynamic modeling for all streams are presented in Table 6, which was obtained through MATLAB. These results are then compared with the simulation conducted using Thermoflex software. The findings indicate that thermodynamic modeling accurately represents various components within the system, demonstrating the acceptability of the modeling approach.

Table 6.

Validation of thermodynamic results for all streams of the system (overall plant).

	$\dot{m} (k g / s)$			$T (^{\circ} C)$			P (bar)
No.	Code	Thermoflow	Error (%)	Code	Thermoflow	Error (%)	Code	Thermoflow	Error (%)
1	80.72	80.73	0.01	25.00	25.00	0.00	1.013	1.013	0.00
2	80.72	80.73	0.01	303.08	308.60	1.79	8.104	8.086	0.22
3	80.72	80.73	0.01	644.75	620.20	3.96	7.704	7.701	0.04
4	1.37	1.31	4.53	25.00	25.00	0.00	1.013	20.000	0.00
5	82.09	82.04	0.06	1200.00	1200.00	0.00	7.319	7.334	0.21
6	82.09	82.04	0.06	705.05	704.50	0.08	1.113	1.066	4.41
7	82.09	82.04	0.06	416.75	414.30	0.59	1.063	1.015	4.73
8	82.09	82.04	0.06	415.84	413.80	0.49	1.038	1.015	2.27
9	82.09	82.04	0.06	304.31	299.60	1.57	1.038	1.014	2.37
10	82.09	82.04	0.06	264.98	255.00	3.91	1.013	1.013	0.00
11	82.09	82.04	0.06	120.00	120.10	0.08	1.013	1.013	0.00
12	5.38	5.49	1.98	60.25	59.14	1.88	20.000	20.000	0.00
13	5.38	5.49	1.98	212.38	212.40	0.01	20.000	20.000	0.00
14	5.38	5.49	1.98	212.38	212.40	0.01	20.000	20.000	0.00
15	5.38	5.49	1.98	217.42	217.40	0.01	20.000	20.000	0.00
16	60.00	60.00	0.00	44.39	43.44	2.18	4.500	4.500	0.00
17	281.93	292.00	3.45	35.00	35.00	0.00	20.000	20.000	0.00
18	76.08	78.05	2.52	45.00	44.01	2.25	1.013	1.014	0.10
19	145.85	149.60	2.51	45.00	45.00	0.00	1.013	1.014	0.10
20	72.23	73.47	1.68	46.44	46.50	0.12	1.013	1.014	0.10
21	73.61	76.13	3.31	45.00	45.00	0.00	1.013	1.014	0.10
22	60.54	58.69	3.14	25.95	26.94	3.66	4.042	4.040	0.05
23	60.54	58.69	3.14	27.46	28.29	2.92	16.000	16.000	0.00
24	60.54	58.69	3.14	163.34	158.68	2.94	16.000	16.000	0.00
25	60.54	58.69	3.14	244.65	244.60	0.02	16.000	16.000	0.00
26	60.54	58.69	3.14	250.70	250.00	0.28	16.000	16.000	0.00
27	60.54	58.69	3.14	214.61	213.90	0.33	4.042	4.040	0.05
28	60.54	58.69	3.14	29.95	31.06	3.56	4.042	4.040	0.05
29	724.83	716.05	1.23	25.00	25.00	0.00	1.013	1.040	2.60
30	724.83	716.05	1.23	28.00	28.00	0.00	1.013	1.040	2.60
31	10.00	10.00	0.00	300.00	300.00	0.00	17.000	17.010	0.06
32	10.00	10.00	0.00	255.72	265.90	3.83	12.000	11.980	0.17
33	10.00	10.00	0.00	256.72	266.11	3.53	25.000	25.000	0.00

Exergy analysis

The exergy analysis results for the equipment are presented in Table 7. The data from Table 7 highlights that the CC, GT, AC, GT package, desalination units, and HRSG exhibit the highest levels of exergy destruction. On the other hand, the condenser, desalination units, HRSG, and STC demonstrate the lowest exergy efficiency values. These findings suggest that these specific components are operating inefficiently and require improvements to enhance their performance.

Table 7.

The result of exergy assessment.

Component	$\dot{E} x_{D} (k W)$	$ψ (%)$	$\dot{E} x_{F} (k W)$	$\dot{E} x_{P} (k W)$
AC	1265.26	94.39	22536.23	21270.96
CC	22213.69	80.03	111220.50	89006.81
GT	7412.25	86.51	54948.48	47536.23
Regenerator1	692.19	96.41	19284.23	18592.04
Regenerator2	231.97	96.17	6053.00	5821.03
ORCT	530.12	90.21	5416.18	4886.05
ORC condenser	99.29	31.39	144.73	45.44
ORC HEX	160.27	96.52	4609.29	4449.02
ORC pump	130.63	50.34	263.02	132.40
Economiser	935.76	49.94	1869.39	933.63
Evaporator	1712.92	69.60	5634.63	3921.71
Superheater	186.82	14.86	219.43	32.61
MED-TVC	4677.76	16.24	5584.47	906.71
RO	544.12	55.07	1210.93	666.81
STC	613.79	51.70	1270.83	657.04
Solar HEX	243.38	63.69	670.36	426.98
Oil pump	6.45	67.35	19.77	13.32

STC: solar thermal collector; RO: reverse osmosis; ORC: organic Rankine cycle; MED-TVC: multieffect desalination-thermal vapor compressor; AC: air compressor; GT: gas turbine; CC: combustion chamber; ORCT: ORC turbine.

Exergoeconomic analysis

The findings of the analysis conducted on the system components are consolidated in Table 8. This table provides information on various parameters, including the cost rate, cost rate due to exergy destruction, exergoeconomic factor, and relative cost difference of the equipment. The exergoeconomic factor is determined by the combined effect of the cost rate and the cost rate due to the exergy destruction of each component. A minimal exergoeconomic factor indicates a significant portion of the cost rate is attributed to exergy destruction. Therefore, it is advisable to improve the thermodynamic efficiency of the component to reduce exergy destruction and associated costs.

Table 8.

The results of exergoeconomic and exergoenvironmental analyses for the components of the system.

Component	$\dot{Z} ($ / h)$	${\dot{C}}_{D} ($ h)$	$f (%)$	$r (%)$	$\dot{Y} (m p t s / h)$	${\dot{B}}_{D} (p t s / h)$	$f_{b} (%)$	$r_{b} (%)$
AC	19.32	56.47	25.50	7.98	29.18	24.68	0.12	5.96
CC	1.83	685.15	0.27	25.02	158.06	299.77	0.05	24.97
GT	2.55	285.83	0.88	15.73	367.45	125.01	0.29	15.64
Regenerator1	0.34	26.69	1.24	3.77	547.67	11.67	4.48	3.90
Regenerator2	5.59	9.09	63.17	10.02	614.05	3.48	14.99	4.34
ORCT	7.48	20.77	77.48	48.19	67.67	7.96	0.84	10.94
ORC condenser	1.16	3.89	23.01	283.86	113.92	1.49	7.10	235.24
ORC HEX	0.39	6.18	5.93	3.57	300.71	2.70	10.01	3.73
ORC pump	0.19	7.58	2.48	101.17	1.08	2.18	0.05	98.71
Economiser	1.83	36.08	4.83	105.31	1.91	15.78	0.01	100.24
Evaporator	3.49	66.05	5.01	45.98	12.66	28.89	0.04	43.70
Superheater	0.64	7.20	8.20	623.97	4.18	3.15	0.13	573.57
MED-TVC	17.47	254.47	6.42	723.41	27861.63	109.12	71.86	2405.39
RO	27.06	16.89	83.43	861.21	18015.74	7.38	70.94	490.92
STC	6.72	0.00	100.00	∞	4.59	0.00	100.00	∞
Solar HEX	1.08	2.77	27.95	79.11	50.61	0.14	26.32	77.36
Oil pump	0.04	0.29	11.06	54.50	0.09	0.13	0.07	48.50

Based on the results presented in Table 8, it is recommended to enhance the performance of the gas cycle, HRSG unit Regenerator1, and condenser. These components exhibit inefficiencies that contribute significantly to the system's total costs, as indicated by the interpretation of the exergoeconomic factor. The exergoeconomic factor of the STC is 100%, primarily because its feed exergy is derived from cost-free solar irradiation. While a substantial amount of exergy destruction occurs in this component, it does not incur additional adverse costs. Therefore, optimizing the gas cycle, HRSG unit Regenerator1, and condenser can lead to cost reductions associated with inefficiencies while the exergy destruction in the STC does not contribute to additional costs due to its unique feed source.

Exergoenvironmental analysis

Similar to the principles of exergoeconomic analysis, the concept of exergoenvironmental analysis involves evaluating the environmental impacts of system components. The exergoenvironmental factor is determined by the environmental impact rate and the environmental impact rate due to the exergy destruction of each component. A minimal exergoenvironmental factor indicates a significant portion of the environmental impacts is attributed to exergy destruction. To mitigate these impacts, it is recommended to improve the thermodynamic efficiency of the component, thereby reducing exergy destruction and its associated environmental impacts. Table 8 showcases the results of the exergoenvironmental analysis for the system's components. The table presents information on various parameters, including the environmental impact rate, environmental impact rate due to exergy destruction, exergoenvironmental factor, and relative environmental impact difference of the equipment. By assessing these results, one can identify components with higher environmental impacts and focus on improving their thermodynamic efficiency to decrease both exergy destruction and environmental impacts.

The environmental impact rate of the components quantifies the negative environmental effects caused by the equipment over a given period. The exergoenvironmental factor combines the environmental impact rate of each component and the environmental impact rate attributed to exergy destruction. A minimal exergoenvironmental factor suggests that a significant portion of the environmental impact rate is due to exergy destruction. Therefore, enhancing the thermodynamic efficiency of the component is recommended to reduce exergy destruction and its associated environmental impacts. Based on the evaluation of Table 8, it is advisable to improve the performance of the gas cycle, ORC turbine, and HRSG unit to mitigate their inefficiencies’ environmental impacts. These components have a significant influence on the system's overall environmental impacts, as indicated by the interpretation of the exergoenvironmental factor. The exergoenvironmental factor of the STC is 100% because its feed exergy is derived from environmentally benign solar irradiation, resulting in no associated environmental impacts. Therefore, although the STC experiences a substantial amount of exergy destruction, it does not contribute to any subsequent adverse environmental impacts. This observation highlights the significance of the exergoenvironmental factor and the environmental impacts resulting from exergy destruction. It emphasizes the importance of prioritizing improvements in the inefficiencies of components with higher exergoenvironmental factors and environmental impacts due to exergy destruction. For further details regarding the stream-related parameters of the exergy-based analyses, please refer to Table A1.

Emergy analysis

The results of the monetary and ecological emergy analyses for the different parts of the system have been shown in Table 9. These results include the monetary and the ecological emergy rate, the emergy rate due to exergy destruction, the emergoeconomic factor, the emergoenvironmental factor, and the relative emergy difference of the equipment.

Table 9.

The outcomes of the monetary and ecological emergy analysis for the components of the system.

Component	$\dot{U} (10^{12} s e j / h)$	${\dot{M}}_{D} (10^{12} s e j / h)$	$f_{m} (%)$	$r_{m} (%)$	$\dot{V} (10^{12} s e j / h)$	${\dot{N}}_{D} (10^{12} s e j / h)$	$f_{n} (%)$	$r_{n} (%)$
AC	19.184	56.056	25.50	7.98	1.791	350.392	0.51	5.98
CC	1.816	680.171	0.27	25.02	8.929	4250.395	0.21	25.01
GT	2.530	283.753	0.88	15.73	20.891	1772.974	1.16	15.78
Regenerator1	0.333	26.498	1.24	3.77	73.860	165.569	30.85	5.38
Regenerator2	15.476	9.023	63.17	10.02	82.811	54.550	60.29	9.29
ORCT	7.962	20.621	77.48	48.19	3.846	124.665	2.99	11.18
ORC Condenser	1.154	3.862	23.01	283.86	15.363	23.350	39.68	362.33
ORC HEX	0.387	6.135	5.93	3.57	40.555	38.336	51.41	6.92
ORC pump	0.191	7.530	2.48	101.17	0.024	34.155	0.07	98.73
Economiser	1.817	35.822	4.83	105.31	0.257	223.829	0.11	100.34
Evaporator	3.461	65.573	5.01	45.98	1.707	409.722	0.41	43.86
Superheater	0.639	7.152	8.20	623.97	0.237	44.686	0.53	575.86
MED-TVC	17.338	252.618	6.42	723.41	3757.669	1563.715	96.00	16943.33
RO	84.446	16.767	83.43	861.21	2429.613	108.896	95.71	3325.78
STC	6.667	0.000	100.00	∞	0.735	0.000	100.00	∞
Solar HEX	1.067	2.751	27.95	79.11	6.825	2.255	75.16	229.49
Oil pump	0.036	0.286	11.06	54.50	0.002	1.787	0.11	48.52

The monetary emergy rate and ecological emergy rate of each component determine the negative monetary and ecological emergy caused by that component over time. The emergoeconomic and emergoenvironmental factors establish the relationship between the cost rate and cost due to exergy destruction, as well as the connection between the environmental impact rate and environmental impacts of exergy destruction. To effectively address the emergy-related issues, it is recommended to enhance the performance of the CC, GT, and HRSG unit. This improvement will lead to a reduction in the monetary and ecological emergy resulting from their inefficiencies, which significantly affects the total emergy rate of the system. This observation underscores the importance of emergoeconomic and emergoenvironmental factors, as well as the monetary and ecological emergy caused by exergy destruction in the components. It emphasizes the need to prioritize the improvement of equipment with higher emergoeconomic and emergoenvironmental factors and greater monetary and ecological emergy caused by exergy destruction. For detailed information regarding the monetary and ecological emergy parameters related to the streams, please refer to Table A2.

Table 10 shows the results of the evaluations used for the integrated system. Based on this table, the net power generation rate of the system is estimated to be 29.62 MW. Also, the total exergy destruction of all the integrated equipment in the system is equal to 41.66 MW. In the economic evaluation made for the system, the total cost rate of the system is estimated to be 0.94 $/s.

Table 10.

The general results of the evaluations for the integrated system of simultaneous production of power and fresh water.

Assessment	Parameter	Unit	Value
Energy	Total power generation	MW	29.62
	The amount of purified water	kg/s	133.61
	Thermal efficiency	%	43.27
Exergy	Total exergy destruction	MW	41.66
Exergy	Exergy efficiency	%	40.99
Economic	Total cost rate	$/s	0.94
	Cost of power produced by the system	$/MWh	46.73
	Cost of power produced by gas cycle	$/MWh	44.63
	Cost of power produced by ORC	$/MWh	58.06
	The cost of producing purified water by desalination units	$/m³	0.84
Environmental	Environmental impact of power produced by gas cycle	pts/MWh	19.50
	Environmental impact of power produced by ORC	pts/MWh	16.65
	Environmental impact of power produced by system	pts/MWh	19.06
	The rate of environmental effects caused by the production of purified water	mpts/m³	885.76
Monetary emergy	Monetary emergy of power produced by gas cycle	sej/kWh	4.43 $\times 10^{10}$
	Monetary emergy of power produced by ORC	sej/kWh	5.76 $\times 10^{10}$
	Monetary emergy of power produced by system	sej/kWh	4.64 $\times 10^{10}$
	Monetary emergy of water produced by the system	sej/m³	83.69 $\times 10^{10}$
Ecological emergy	Ecological emergy of power produced by gas cycle	sej/kWh	27.69 $\times 10^{10}$
	Ecological emergy of power produced by ORC	sej/kWh	26.15 $\times 10^{10}$
	Ecological emergy of power produced by the system	sej/kWh	27.45 $\times 10^{10}$
	Ecological emergy of water produced by the system	sej/m³	86.85 $\times 10^{10}$

ORC: organic Rankine cycle.

Dynamic analysis

The dynamic analysis is performed on the system to study the system's behavior in different ambient conditions throughout the year and a day. The ordinary and static analyses are not able to provide such a viewpoint. Figure 3(a) presents the distribution of solar fraction over a day (Jun 21st), and Figure 3(b) shows the distribution of this parameter over a year on average for each month. According to Figure 3, the distribution of solar fraction is primarily a function of solar irradiation over time.

Figure 3.

Distribution of solar fraction.

As indicated in Figure 3(b), the solar fraction is larger in the summer season than in other seasons. One of the reasons for this increase is due to the increase in the solar time period in the summer season and the absorption of more solar radiation in this season. Figure 4(a) presents the distribution of the total thermal efficiency of the system over a day (Jun 21st), and Figure 4(b) shows the distribution of this parameter over a year in average form for each month.

Figure 4.

Distribution of the system's total thermal efficiency.

As shown in Figure 4(b), the total thermal efficiency did not change much during the different months of the year. This is due to the low role of the solar system in the integrated system of power and freshwater production. This is the task of the solar system in this heat supply system required by the ORC cycle. In fact, this system is responsible for providing the temperature of the fluid entering the organic turbine. This is because two opposite factors act simultaneously; one leads to an increase in the system's total thermal efficiency, and another one makes it decrease. In warm times of a day and a year, higher ambient temperature increases fuel consumption and drives the total thermal efficiency of the system to reduce. On the other hand, in warm times of a day and a year, on account of higher solar irradiation, the solar fraction is increased; consequently, enhancing the feed energy of ORC, and thereby total thermal efficiency of the system will result.

Figure 5(a) presents the distribution of fuel mass flow rate over a day (Jun 21st), and Figure 5(b) shows the distribution of this parameter over a year in average form for each month.

Figure 5.

Distribution of the mass flow rate of fuel.

According to Figure 6, the net power generated by the system is enhanced in warm times of a day and a year. In these times, on account of higher solar irradiation, the solar fraction is increased. Figure 7(a) presents the distribution of the performance ratio of MED-TVC desalination unit over a day (Jun 21st), and Figure 7(b) shows the distribution of this parameter over a year in average form for each month.

Figure 6.

Distribution of the net power produced by the system.

Figure 7.

Distribution of performance ratio of MED-TVC desalination unit. MED-TVC: multieffect desalination-thermal vapor compressor.

According to Figure 7, the performance ratio of the multieffect desalination unit is increased in warm times of a day and a year. This is because increasing ambient temperature makes the feed stream of MED-TVC warmer. Hence, less amount of steam is demanded to evaporate the feed to generate distillate. On account of lowering the steam demand rate in MED-TVC, the performance ratio of this unit increases.

According to Figure 8, the mass flow rate of total distillate is increased in warm times of a day and a year. This is because increasing ambient temperature makes the cooling water discharge of MED-TVC warmer. Since the cooling water discharge of MED-TVC is the feed stream of the RO desalination unit, the temperature of the feed stream is enhanced, which leads to producing more distillate in RO. Figure 9(a) presents the distribution of total exergy destruction of the system over a day (Jun 21st), and Figure 9(b) shows the distribution of this parameter over a year in average form for each month.

Figure 8.

Distribution of the mass flow rate of total distillate.

Figure 9.

Distribution of total exergy destruction of the plant.

According to Figure 9, the total exergy destruction rate of the site is increased in warm times of a day and a year. In warm weather, the AC demands more inlet power. Figure 10(a) presents the distribution of total monetary emergy of power produced by the system over a day (Jun 21st), and Figure 10(b) shows the distribution of this parameter over a year in average form for each month.

Figure 10.

Distribution of total monetary emergy of power produced by the system.

Figure 11(a) presents the distribution of total monetary emergy of freshwater produced by the system over a day (Jun 21st), and Figure 11(b) shows the distribution of this parameter over a year in average form for each month.

Figure 11.

Distribution of total monetary emergy of freshwater produced by the system.

Figure 12(a) presents the distribution of total ecological emergy of power produced by the system over a day (Jun 21st), and Figure 12(b) shows the distribution of this parameter over a year in average form for each month.

Figure 12.

Distribution of total ecological emergy of power produced by the system.

According to Figures 10 and 12, for the power generated by the system, it is observed that the monetary and ecological emergy are increased in warm times of a day and a year. This is primarily because of the increasing fuel consumption rate, which affects cost, environmental impacts, and the emergy of power produced by the gas cycle. Figure 13(a) presents the distribution of total ecological emergy of freshwater produced by the system over a day (Jun 21st), and Figure 13(b) shows the distribution of this parameter over a year in average form for each month.

Figure 13.

Distribution of total ecological emergy of freshwater produced by the system.

According to Figures 11 and 13, for the freshwater generated by the system, it is observed that the cost, environmental impacts, and monetary and ecological emergy diminish in warm times of a day and a year. This is because of the decreasing motive steam demand of desalination unit. This stream is the primary fuel of the desalination unit; so, reducing its mass flow rate will lead to a decrease in costs, environmental impacts, and emergy of distillate produced by the system.

Sensitivity analysis

In this section, the results of the sensitivity analysis for the integrated system have been investigated. Ambient temperature is considered one of the main decision variables. As the ambient temperature changes in different seasons of the year, the desired outputs of the system, that is electric power and fresh water, change. Therefore, the evaluation of this decision variable is important for the system. The ّFigure 14 shows the change in energy and exergy efficiency of the whole system with the change of ambient temperature from 20 °C to 30 °C.

According to this figure, energy and exergy efficiencies decreased with the increase in ambient temperature. Because the temperature of the air entering the AC increases, this factor causes the AC to use more energy to compress the air, and as a result, the net power of the entire system decreases. In the Figure 15 the changes in two other important parameters of the system have been examined. In the graph below, the total cost rate and the total environmental impact rate changed with the change in environmental temperature.

According to this figure, with the increase of the ambient temperature, the two objective functions introduced increased. Because the increase in ambient temperature increases the costs of repairs and maintenance and service of equipment due to frequent breakdowns. Also, the environmental effects are due to the increase in the temperature of the exhaust gases from the system.

Conclusion

In this study, an innovative hybrid solar-driven multigeneration system has been proposed and evaluated with 6E analysis. The evaluation of the system's energy has revealed several reasons for the observed increases and decreases. Initially, the gas cycle alone was able to produce 25 MW of power. However, by incorporating an ORC to recover heat from the GT's exhaust flue gas, the net power generation of the system increased to 29.89 MW. This improvement can be attributed to the additional energy extraction from the exhaust gases. The integration of ORC also resulted in a notable enhancement in the thermal efficiency of the integrated system, which rose from 36.51% to 43.27%. This increase can be attributed to the utilization of waste heat, which would have otherwise been lost, to generate additional power.

Furthermore, the integration of water desalination units with the power generation system resulted in the production of 133.61 kg/s of fresh water by the MED unit. This accounts for approximately 45% of the total freshwater output. The utilization of a TVC within the MED unit played a significant role in achieving this higher production rate. By reducing the demand for drive steam from 12.59 to 5.38 kg/s, the TVC increased the efficiency ratio of the unit from 4.76 to 11.15. As a result, the MED-TVC system operates more efficiently compared to the MED unit alone. Moreover, the integration of solar systems into the overall system contributed to a 1.1% increase in the system's thermal efficiency. The exergy efficiency of the whole integrated system has been evaluated and its value is estimated to be 40.99%.

Regarding the economic and environmental evaluations carried out on the integrated system, we can refer to the rate of total costs and the rate of total environmental effects. Based on this, the estimated total cost rate is equal to 0.94 $/s. Also, the environmental impact rate of all the equipment integrated into the system is equal to 0.47 pts/s.

These areas could be explored to further enhance the performance and address the limitations of the integrated system. In future work, optimizing the gas cycle to improve its efficiency and power output can be considered. Also, investigating optimal ORC system designs, exploring suitable working fluids, and enhancing heat transfer mechanisms to maximize energy recovery from the exhaust flue gas can be investigated.

Figure 14.

Sensitivity analysis performed for energy efficiency and exergy efficiency of cogeneration system.

Figure 15.

Sensitivity analysis performed for total cost rate and total ecological impact rate of cogeneration system.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

ORCID iDs

Mohammad Hassan Khoshgoftar manesh

Gholamreza Salehi

Mahdi Movasaghi Gilani is PhD student of Energy Systems Engineering, in Islamic Azad university, North Tehran Branch. His interest is power generation and energy management.

Dr. Masoud Torabi Azad is Professor of Marine Physics at Islamic Azad University-North Tehran Branch (IAUNT), Iran since 1999. He worked as the Science Consultant of Iranian Environment Organization, Department of Marine Environment from 1993 to 1999. He has published around 60 peer reviewed papers in journals and about 40 papers in conference proceedings. Some of these papers have been focused on application of Air- Sea interaction and remote sensing techniques in Iranian marginal seas. He has worked as a reviewer for more than 8 international journals indexed by ISC. His main research topics include Renewable Energy & Satellite Oceanography, Numerical Modeling of Large Scale & Mesoscale Processes between Sea and Air.

Mohammad Hassan Khoshgoftar manesh is an Associate Professor at the University of Qom, Faculty of Technology and Engineering, Department of Mechanical Engineering, Division of Thermal Sciences and Energy Systems. He is also the Head of Energy, Environmental, and Biological Research Lab (EEBRlab). His research interests include polygeneration, renewable energy, energy systems, energy conversion systems, and machine learning.

Kamran Lary received his PhD degree in 2004. He was the Dean of the Faculty of Marine Science and Technology, Islamic Azad University, North Tehran Branch, Tehran, Iran. Currently, he is an associate professor. His research interests are marine renewable energy, coastal engineering, and marine geodesy.

Gholamreza Salehi is associated professor of mechanical engineering in central Tehran branch of Islamic Azad university, his interest is energy modeling and optimization, energy recovery.

Acronym	Parameter	Unit	Acronym	Parameter	Unit
A	Area	$m^{2}$	w	Weight	$t o n s$
AC	Air compressor	$-$	x	Molar fraction	$-$
B	Brine	$-$	X	Salinity	$g / k g$
b	Ecological effect per exergy unit	$p t s / k J$	y	Components’ environmental impact	$p t s$
$\dot{B}$	Ecological effect rate of the streams	$p t s / s$	$\dot{Y}$	Components’ environmental impact rate	$p t s / s$
$b m$	Ecological effect per mass unit	$p t s / k g$	$\dot{Z}$	Components’ cost rate	$$ / s$
c	Expense per exergy unit	$$ / k J$
CC	Combustion chamber	-	Greek letters
$\dot{C}$	Expense rate of the streams	$$ / s$	$β$	Transformity	$-$
Cond	Condenser	$-$	γ	The proportion of the specific heats	$-$
CRF	Capital recovery factor	$-$	Δ	Difference	$-$
$c_{p}$	Specific heat at constant pressure	$k J / k g K$	$ψ$	Exergetic efficiency	$%$
D	Distillate	$-$	η	Efficiency	$%$
EC	Economizer	$-$	φ	Maintenance factor	$-$
$\dot{E}$	Energy rate	$k W$	ρ	Density	$k g / m^{3}$
ex	Specific exergy	$k J / k g$	$ε$	Effectiveness	$%$
$\dot{E} x$	Exergy rate	$k W$
f	Exergoeconomic factor	$%$	Subscript
F	Feed	$-$	0	Ambient condition
$f_{b}$	Exergoenvironmental factor	$%$	fg	Flue gas
$f_{m}$	Emergoeconomic factor	$%$	c	Condenser
$f_{n}$	Emergoenvironmental factor	$%$	cwd	Cooling water Discharge
GOR	Gained output ratio	$-$	D	Destruction
GT	Gas turbine	$-$	e	Effect
h	Enthalpy	$k J / k g$	F	Fuel
HEX	Heat exchanger	$-$	fb	Flash box
HRSG	Heat recovery steam generator	$-$	fh	Feed heater
HTF	Heat transfer fluid	$-$	fw	Feed water
LHV	Lower heating value	$k J / k g$	gc	Gas cycle
m	Streams monetary emergy per exergy unit	$s e j / k J$	hp	High pressure
$\dot{m}$	Mass flow rate	$k g / s$	i	Counter of streams
$\dot{M}$	Streams monetary emergy rate	$s e j / s$	k	Counter of components
MED	Multieffect desalination	$-$	ms	motive steam
MW	Molecular weight	$k g / k m o l$	ORCC	ORC condenser
n	Streams ecological emergy per exergy unit	$s e j / k J$	P	Product
N	Yearly functioning hours of the system	$h$	s	Steam
$\dot{N}$	Streams ecological emergy rate	$s e j / s$	sat	Saturated
$n_e f f e c t s$	Number of effects	$-$	sr	Steam returned
$n y$	Functioning years of the system	$y e a r s$	sub	Subcooled
ORC	Organic Rankine cycle	$-$	sup	Superheated
P	Pressure	$k P a$	sw	Seawater
PEC	Purchase equipment cost
PR	Performance ratio	$-$	Superscripts
PTC	Parabolic trough collector	$-$	*	Restricted dead state
$\dot{Q}$	Heat duty	$k W$	0	Global dead state
r	Relative expense variation	$%$	CH	Chemical
$r_{b}$	Relative ecological effect variation	$%$	PH	Physical
$r_{m}$	Relative monetary emergy difference	$%$
$r_{n}$	Relative ecological emergy variation	$%$
$\bar{R}$	Universal gas constant	$k J / k g K$
$r_{p}$	Pressure ratio	$-$
RR	Recovery ratio	$-$
s	Entropy	$k J / k g K$
SA	Specific area	$m^{2} . s / k g$
$s e j$	Solar energy joule	$-$
STC	Solar thermal collector	$-$
T	Temperature	$^{\circ} C$
TIT	Turbine inlet temperature	$^{\circ} C$
TVC	Thermal vapor compressor	$-$
U	Overall heat transfer coefficient	$k W / m^{2} K$
$\dot{U}$	Components monetary emergy rate	$s e j / s$
$\dot{V}$	Components ecological emergy rate	$s e j / s$
$\dot{W}$	Work	$k W$

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