Simulation Analysis of Novel Integrated LNG Regasification-Organic Rankine Cycle and Anti-Sublimation Process to Generate Clean Energy

Abstract

Recently, the depletion of fossil fuel reserves and the harmful environmental effects caused by burning fossil fuels have signified the supreme importance of utilizing sustainable energy reserves such as geothermal and solar energies. The advancement of the Organic Rankine Cycle as a clean energy generation path by researchers has gained momentous demand for its commercialization. The sole Organic Rankine Cycle can produce a large amount of energy in contrast to other power production cycles. To make this clean energy recovery sustainable, liquefied natural gas cold energy can be utilized through regasification to integrate the Organic Rankine Cycle with the anti-sublimation carbon dioxide capture process, merging the biogas setup. Liquefied natural gas cold energy recovery has paramount importance with aspects of energy economy and environment preservation. Liquefied natural gas regasification in shell and tube heat exchangers poses a minimal freezing risk and is high duty. Anti-sublimation of biogas is an energy-intensive process. It can be materialized from liquefied natural gas cold energy implementation through the Organic Rankine Cycle by maintaining cryogenic temperatures there. In this situation, greenhouse gas emissions can be minimized. The simulation analysis is performed based on thermodynamic and techno-economic assessments of the poly-generation energy systems. It is proved to be useful in conducting by regulating different working fluids. The optimum electric power generated is 2492 MW. While the optimum net present value, energy efficiency, and exergy efficiency of this proposed energy system are 19.5, 57.13%, and 76.20%, respectively. The governmental authorities and environmental protection can benefit from this scientific research work to create an environmentally friendly atmosphere and energy for contemporary society.

1. Introduction

Energy sources play an important part in the smooth progress of an emerging industrial economy, which helps keep production costs low to compete in international markets. As a result, a good economy provides resources to improve healthcare, education, water supply, and sanitation for the citizens [1]. Industrial growth, economic progress, and a good living environment are directly related to a cheap and clean energy supply. Therefore, sustainable clean energy sources are always in demand, and lots of work is being done in research [2]. It is noted in the British Petroleum statistical energy review of world energy (2019) that world energy demand will increase from 580.5 TJ in 2019 to 775 TJ in 2060 [3]. Economic growth and population increase are the major causes of this rise in global energy demand [4]. In energy production networks, the energy gap between supply and demand is large because of off-peak and on-peak times [5]. Therefore, there is a need to develop efficient clean energy generation technologies to meet global energy demands.

Fossil fuels (coal, oil, and natural gas) have been the primary energy source until now. These fuels generate greenhouse gases, which consist of carbon dioxide, carbon monoxide, nitrogen oxide, and sulfur oxide [6]. These emissions increased by up to 1.2% annually between 2009 and 2018 [7]. According to the 20-20-20 directive, the European Union (EU) has decided to decrease CO₂ emissions up to 20% by 2020, as per1990 emissions [8]. The International Maritime Organization (IMO) has also initiated a greenhouse gas strategy to decrease these contaminants up to 50% by 2050 [9]. Therefore, it is high time to develop such technologies that can restrict CO₂ emissions.

The transformation of low grade heat energy into electric power is the major property of Organic Rankine cycle (ORC) [10]. The investigation of this power cycle efficiencies and the turbine has paramount importance for identification of their electricity production performance. It is also crucial to select environmentally affable organic working fluids those have compatibility with ORC facility [11]. Japan was the first country to utilize and recover LNG cold energy with ORC at Senboku terminal in 1979. There were used Propane (C₃H₈) as working fluid and hot sea water as thermal resource in evaporator. There was total electric energy generation was 1.45 MW [12]. ORC has emerged as suitable option to exploit LNG cold energy to produce electricity [13]. The LNG cold energy has capability to improve the power cycle efficiency and minimize greenhouse gases emissions [14]. Computational studies show that the Genetic algorithm (GA) has ability to increase the electricity production from ORC [15].

The world economy is considerably dependent on fossil fuels at present. These energy sources produce huge quantities of environmental contaminants. Considering these serious environmental challenges, it has become necessary to utilize clean energy fuels to control contaminant emissions [16]. Natural gas (NG) is a clean fuel because of its chemical composition, and it is quickly becoming a primary power source with the benefit of clean and effective combustion and multiple usages in vehicles, energy generation plants, industrial purposes, and as a kitchen gas [17]. The worldwide NG demand increased up to 3.67 trillion cubic meters (TCM) in 2017. Their consumption is expected to grow around 4.9 TCM till 2040 [18]. Liquefied natural gas (LNG) has cold energy around (830 to 860 kJ/kg) [19]. Therefore, efforts must be made to develop technologies for utilizing LNG’s cold energy potential. This cold energy has the potential to run the cryogenic processes. Furthermore, this source can produce clean energy and curtails environmental pollutants such as CO₂.

A substantial quantity of energy is consumed in LNG production from NG. Regasification is the process by which LNG is changed back into its gaseous phase [20]. The LNG regasification has strong potential for energy regeneration [21]. The majority of LNG regasification terminals are functioning without any energy regeneration technique. This recovered energy can be used to increase power generation efficiency [22] and to run cryogenic processes [23]. The world’s scientists are well aware of this beneficial proposal. They are working to develop different integrated energy systems integrated with LNG regasification facilities.

Cryogenic CO₂ capture has not been extensively investigated like amine absorption or oxy-combustion. It is because of the reason that it is analyzed as an energy-intensive technique, although it produces liquid CO₂ [24]. The prominent cryogenic technologies that can be employed to capture CO₂ are cryogenic distillation, external cooling loop cryogenic carbon capture (CCCECL), anti-sublimation (ANSU) CO₂ capture, the CryoCell cryogenic process, and the Stirling cooler system (SCS) [25]. These options are not considered as energy-efficient or cost-effective processes.

Moreover, the carbon capture and storage (CCS) technique is quite promising and one of the quickest solutions to confront environmental change [26]. Many programs are underway globally for developing an effective and minimal energy consumption CCS technique [27]. The specific techniques that are employed for capturing CO₂ are solvent absorption, membrane separation, adsorption, and low temperature separation [28]. The main cryogenic or low-temperature separation methods are liquefaction and ANSU separation. These methods can be employed by recycling dissipated cold energy. According to the CO₂ phase diagram, it is evident that liquefaction needs high pressure, up to 15,000 kPa. In the ANSU technique, CO₂ is converted directly from a gaseous state at a pressure lower than its triple point (for ANSU pressure at −78 °C, this is 100 kPa). Because of such impactful benefits, including lower pressure systems for plant safety and relatively minimal energy consumption, cryogenic ANSU CO₂ capture has an edge over other techniques [29].

Cryogenics is a new approach in comparison to different biogas purification technologies. It comprises the purification of gases relative to their condensation or sublimation temperatures. The selection of CO₂ separating techniques among ANSU or distillation depends on the desired phase (solid or liquid) [30]. Cryogenic distillation needs high pressure and cryogenic temperatures [31]. It consumes a high amount of energy in the steps of compression and chilling. It also needs a multi-stage compression system, which negatively affects cost optimization [32]. The main components of biogas are methane (CH₄) and CO₂. To acquire a good purity of CH₄ as a substitute for NG, CO₂ and other impurities (N₂, H₂S, and O₂) are required to be separated from biogas [33]. In the ANSU CO₂ capture process [34], CO₂ is separated from biogas via solidification at the heat exchanger surface (a categorically fabricated cold box) and removed subsequently through the surface in a liquid or vapor state with better product quality [34]. Biomethane can be liquified (also called LBM) at a substantially lower price through the ANSU process in comparison to the cryogenic distillation process [32].

In this research study, a novel integrated energy system of LNG regasification—ORC— and an anti-sublimation process uniting a biogas system is proposed. This system produces electrical energy from LNG integration at ORC. The ANSU CO₂ low-temperature capture is highly energy consuming and costly process. According to studies, it is now established that using LNG cold energy for the ANSU process appreciably improves the thermodynamic and technoeconomic feasibility of the process, i.e.,; (energy and exergy efficiencies). The environmental regulation bodies, government authorities, energy development boards, industrialists, and other related fields may benefit from this poly-generation (tertiary) system. In the coming years, focusing on economic optimization of the process (product cost) is the key to materializing this proposed energy system on a commercial basis.

This paper is compiled in such a manner that initially the benefits and importance of clean energy recovery and the sustainability of cold energy recovery techniques are discussed in (Section 1 and Section 2). Section 3 delineates the methodology to optimize this system. It also devised a model to utilize clean energy sources such as ORC. In Section 4, the obtained results of thermodynamic and techno-economic assessments are elaborated. And finally, conclusions along with future directions are delineated in Section 5.

2. Literature Review

Regasification terminals are now the center of attention for exploiting the potential of LNG’s cold energy. In regasification the of LNG, the temperature gradient is from −161 °C to ambient temperature. This cold energy has an estimated worldwide potential of producing 100 billion kWh and its market value is around 10 billion USD and increasing. Japan is taking measures to exploit this cold energy potential by producing electric power [12]. LNG cold energy can be efficaciously utilized in an ORC condenser, which is a clean geothermal source [35]. In this power production cycle, careful manipulation of organic working fluids/refrigerants is required to generate power [36]. Studies have shown that ORC is an efficient power generation technology. It is due to the fact that the maximum energy efficiency of an ORC configuration is around 67%. While, the Stirling, Brayton, and Kalina power cycles energy efficiencies are 37.2%, 51.2%, and 13.45%, respectively [37]. GA has the key potential for optimizing the ORC for better results [38]. Hereafter, clean electricity can be obtained using this geothermal source [39]. In addition, LNG cold energy can run industrial cryogenic processes [40], similar to ANSU.

For many decades, various investigations have been performed to discuss the CCS techniques from the perspective of elaborating their process parameters. As a result, environmental problems are on the rise due to growing energy demands and the burning of fossil fuels [41]. In this context, Yurata et al. purified the hydrogen (H₂) by separating CO₂ using the ANSU process in 2019. The total energy consumption for the removal of one kg CO₂ was 8.19–11 (MJ/kg) [42]. In 2020, Gatti et al. mentioned the technical and economic capability of CO₂ capture processes. The result shows that the ANSU process can separate CO₂ from flue gas of natural gas fired plant, and its total equipment cost is 159 million [43]. In 2021, Cann et al. conducted an experimental study using the CO₂ anti-sublimation mechanism in CCS. There was a comparison made between ceramic and steel bed materials to enhance CO₂ removal [44]. In 2022, Ababneh et al. investigation also purified flue gas, limiting 0.3% CO₂ in clean gas, using a combination of anti-sublimation and a solid–vapor separation unit [45]. In 2022, Naquash et al. worked on CO₂ removal from liquefied hydrogen using ANSU. This system has a total acquisition cost, energy consumption, and exergy efficiency of up to 52.8 million$/y, 9.62 kWh/kg, and 31.5%, respectively [46].

In the present energy scenario of the world, it is high time to propose an effective and economically viable multi-dimensional energy system that purifies raw gases and provides a clean energy recovery system. Considering the abovementioned literature, some significant configurations are proposed to make clean electrical energy.

Contributions of This Paper

This simulation research work is making these contributions to the current scientific literature:

• The present research work shows unique thermodynamic and economic comparisons among 14 configurations of LNG regasification and electricity production with a capacity of around 200 million tons per year. This study’s goal is to increase system efficiency and CO₂ separation through the utilization of LNG cryogenic cold energy. The analyzed solutions could assist the national electric grid as an additional power source, meet power requirements in carrier ships at ports, provide electricity to port industries areas, provide electric power to railways, supply power to naval strategic bases at ports, and provide electric supply to medical and education centers of developing areas in the vicinity. It also supports the policy of minimal environmental impact, supports cold-ironing, and the decrease of the environmental impact of maritime transports. This low-cost ANSU purification system can be useful for the world’s largest biogas plant in Vaasa, central Finland.
• In the current scientific literature, modes of power output and its economic analysis are discussed. The present work demonstrated both first and second law efficiency and techno-economic values.
• The avent-grade regasification system parameters are described, and a smart differentiation is presented on the basis of working fluid selection for proposed energy system configurations.

3. Conceptual Framework

The objective of the present investigation is to propose and recognize productive configurations to formulate clean energy via LNG regasification and also to purify the biogas. It can relieve the environmental, energy, and economic burdens and will have a positive contribution to the current energy scenario of any power deficient country. At first, there are reported configurations which can make valuable electric power and remove CO₂ using LNG’s cold energy. Afterwards, a description of the adopted methodology is presented. These proposed configurations are distinguished by thermodynamic and technoeconomic assessments.

3.1. Hypothesis

In this work, a novel integrated LNG regasification-ORC-ANSU energy system is demonstrated in Figure 1. It consists of installations to produce electric power and separate CO₂ from biogas. In this cryogenic process activity, this energy system has the following properties:

• Hot sea water is used as a thermal resource at the ORC evaporator.
• Working fluid manipulation in combined and single mode to increase net turbine power.
• The LNG pump pressure is higher than the present studies, which is 35,000 kPa.

3.2. Methodology

The major assumptions and explanations of the mathematical models devised to make the present energy system are described in

Table 1. Detail of the fixed parameters used for simulation of LNG regasification process-ORC-ANSU energy system.

Fixed Parameters	Values
Turbine polytropic efficiency (%)	80
Pump adiabatic efficiency (%)	80
Ambient temperature (°C)	22
Water temperature as hot medium in ORC evaporator (°C)	31
Minimum approach temperature in heat exchangers (°C)	9
Pressure drop of heat exchangers (kPa)	10
Thermodynamic fluid property package	Peng-Robinson
Inlet LNG pressure (kPa)	120
Inlet LNG temperature (°C)	Saturated (−159.5 °C)
Inlet LNG mass flow rate (kg/h)	2.278 × 107
Liquefied Natural gas composition: pure CH4 (%)	100
Regasified NG pressure at outlet (kPa)	3090
Regasified NG temperature at outlet (°C)	−20
Total equipment cost	16.4 million USD

. The LNG integrated ORC energy system is described in Figure 2. Additionally, the particulars of the optimization procedure and the adopted optimization technique (algorithm) are discussed ahead.

3.2.1. Model of the System

The thermodynamic modeling of all the configurations were performed in Aspen-Hysis V11 [47]. The fixed parameters of the numerical simulation are reported in Table 1.

Uniform (steady state) function;

Constant values of adiabatic and polytropic efficiencies at mechanical devices;

Constant pressure gradient at heat devices;

Total adiabatic thermal devices;

LNG constituent: pure CH₄;

Biogas fraction: CH₄: 0.65 and CO₂: 0.35.

3.2.2. Optimization Algorithm

In this work, the GA is used for turbine optimization in this energy network [48]. This optimization can be upgraded by recognizing the categorization process through an applied algorithm [49]. Current market trends suggest reducing the operating costs of the process [50]. Therefore, performance monitoring has a vital role where variables require adjustment [51]. The industrial progress from electronic stages in these systems is outdated in comparison to the mechanical components, which produces complications in their different applications [52]. Therefore, machinery performance assessment is an engineering problem that needs to be studied intensively [53].

The GA has the property to acquire natural selection and genetic theory by uniting a survival rule of most-suitable relative to biological evolution through random details transfer [54]. To efficiently secure the optimum value of the objective function, GA executes these steps: firstly, GA employs an initial population in which individuals are irregularly produced. After that, the objective function (turbine power) is calculated. A segment of the population is chosen, and the methods of crossover, reproduction, and mutation are constantly applied until the optimized population has converged. Figure 3 demonstrates the process optimization using the GA optimizer.

Table 2. Operating values of the GA.

Operating Parameter	Value
Population size	200
Number of generation/iterations	400
Cross over fraction	0.8
Migration fraction	0.1
Stall generation	50
Function tolerance	1 × 10−6

reports the operating parameters of GA used in the present system optimization.

The GA is coded in the MATLAB R2021a environment. MATLAB R2021a is interfaced with or coupled with Aspen Hysys V11 to complete the optimization step. The total number of iterations was 400 for all 14 poly-generation (tertiary) configurations.

3.3. System Modeling and Analysis

The parameters and variables which are employed for this poly-generation system analysis are described there.

3.3.1. Thermodynamic Analysis

Energy efficiency of the novel integrated LNG regasification-ORC-ANSU energy system to be estimated from the first law of thermodynamics mentioned in [55].

$$\mathrm{Energy}\mathrm{Efficiency}\left(\%\right)=\frac{W_{out}-Q_{in}}{Q_{in}}\times 100$$

(1)

Whereas work output = W_out and energy input = Q_in.

Exergy analysis describes how much input exergy is taken by the system [56]. Exergy destruction demonstrates the inadequacy of the system analytically. The main objective of the exergy analysis is to choose the location and amount of irreversible entropy production in various components of a process as well as the parameters affecting its generation. Besides the assessment of the efficiency of various parts of a system, feasible solutions for improving the system efficiency are also determined in exergy analysis [57]. In particular, exergy is characterized as the maximum content of work that can be performed by the system when it reaches a standard or dead state. Dead state is indicated as 25 °C and 101.325 kPa [58]. Exergy efficiency was counted using the second law of thermodynamics as reported in [59].

$$\mathrm{Exergy}\mathrm{Efficiency}\left(\%\right)=\frac{E_{el,net}}{W_{lng}\times S_{e,lng}-W_{NG}\times S_{e,ng}}\times 100.$$

(2)

Whereas

E_el,net = Total energy by turbines and recovery system

W_lng = Mass of LNG entering into system

S_e,lng = Total exergy of LNG

S_e,ng = Total exergy of regasified natural gas

3.3.2. Economic Analysis

In the ORC energy system, the heat exchanger’s economic value (price) is equivalent to 80–90% of the entire system price. This is due to the fact that this heat transfer equipment covers a major part of the ORC system, their correct work measurement displays a paramount part in upgrading the total value of this ORC based energy system. In the present investigation, the ORC system consists of a turbine, pump, and heat transfer equipment (condenser and evaporator). The cost assessment is established on the total investment cost, which comprises the equipment price of every item in the system. The bare module price, C_BM for an individual item is the product of the item price Cp and the module price element Fbm [60].

For heat transfer equipment,

$${\mathrm{C}}_{\mathrm{BM}}={\mathrm{C}}_{\mathrm{P}}+{\mathrm{F}}_{\mathrm{bm}}={\mathrm{C}}_{\mathrm{P}}\times \left({\mathrm{B}}_1+{\mathrm{B}}_2\times {\mathrm{F}}_{\mathrm{m}}\times {\mathrm{F}}_{\mathrm{P}}\right)$$

(3)

$$\log {\mathrm{C}}_{\mathrm{P}}={\mathrm{K}}_1+{\mathrm{K}}_2\mathrm{logA}+{\mathrm{K}}_3{\mathrm{logA}}^2$$

(4)

$$\log {\mathrm{F}}_{\mathrm{P}}={\mathrm{C}}_1+{\mathrm{C}}_2\mathrm{logP}+{\mathrm{C}}_3{\mathrm{logA}}^2$$

(5)

B₁ and B₂ represent the constants established with respect to the heat exchanger category, Fm shows the material factor, and F_P represents the pressure factor. The A and P denote the area and pressure of the item simultaneously. These economics analysis parameter values are delineated in

Table 3. Detailed description of the economic assessment parameters.

Equipment	B1	B2	Fm	K1	K2	K3	C1	C2	C3
Pump	1.89	1.35	1.6	4.3247	−0.3030	0.1634	0.0388	−0.1127	0.08183
Heat Exchanger	1.63	1.66	1.4	4.3247	−0.3030	0.1634	0.0388	−0.1127	0.08183
Turbine	0	1	3.4	2.7051	1.4398	−0.1776	0	0	0
Compressor	1.79	1.28	1.49	3.821	0.051	0.16	−0.3789	0.3940	0.0811

.

For turbine,

$${\mathrm{C}}_{BM}=C_P+F_{bm}=C_P\times \left(B_1+B_2\times F_m\times F_P\right)$$

(6)

$$\log C_P=K_1+{\mathrm{K}}_2\log W_{exp}+{\mathrm{K}}_3\log W_{exp}{}^2$$

(7)

Whereas W_exp shows the electric power obtained from turbine.

For the pump,

$${\mathrm{C}}_{BM}=C_P+F_{bm}=C_P\times \left(B_1+B_2\times F_m\times F_P\right)$$

(8)

$$\log C_P=K_1+{\mathrm{K}}_2{\mathrm{logW}}_{pump}+{\mathrm{K}}_3{\mathrm{logW}}_{pump}{}^2$$

(9)

Whereas W_pump power needed to derive the pump.

For the compressor,

$${\mathrm{C}}_{BM}=C_P+F_{bm}=C_P\times \left(B_1+B_2\times F_m\times F_P\right)$$

(10)

$$\log C_P=K_1+{\mathrm{K}}_2{\mathrm{logW}}_{comp}+{\mathrm{K}}_3{\mathrm{logW}}_{comp}{}^2$$

(11)

$$\log F_P=C_1+{\mathrm{C}}_2\mathrm{logP}+{\mathrm{C}}_3{\mathrm{logP}}^2$$

(12)

Whereas W_comp power needed to derive the compressor.

The total investment value of this system can be counted from Equation (13).

$${\mathrm{C}}_{\mathrm{tot}}={\left({\mathrm{C}}_{\mathrm{BM},\mathrm{hx}}+{\mathrm{C}}_{\mathrm{BM},\exp }+C_{BM,comp}+{\mathrm{C}}_{\mathrm{BM},\mathrm{pump}}\right)}_{2001}\times \frac{{\mathrm{CEPCI}}_{2018}}{{\mathrm{CEPCI}}_{2001}}$$

(13)

CEPCI shows the chemical engineering plant cost index. The real investment prices for 2018 can be counted from the price value for 2001 shown by CEPCI. The CEPCIs values for 2001 and 2018 are 397 and 648.7, simultaneously as reported in [61].

3.3.3. Techno-Economic Assessment

The techno-economic value of this reported energy system is demonstrated by the net present value (NPV) in Equation (14).

$$\mathrm{NPV}=-{\mathrm{C}}_{\mathrm{tot}}+{\sum }_{\mathrm{t}=1}^{\mathrm{n}}\left(\frac{\mathrm{TF}}{{\left(1+\mathrm{i}\right)}^{\mathrm{t}}}\right)$$

(14)

Whereas C_tot shows the total capital investment, TF the total cash flow in year n, i the interest rate set as 5%, and n the lifetime = 20 years.

3.4. Results Validation

In this section, results validation is carried out by analyzing the obtained results with past investigations of each model to confirm that the simulation results are correct. Upon novel integration with this energy network, their model results validation is executed by considering each sub system. The results in Ref. [59] were taken into consideration to validate the ORC and LNG-NG loops. The optimizing parameters are LNG pump inlet pressure and working fluids inlet (pressure, flow rate, and temperature) at the turbine. The ORC validation is performed by regulating working fluids.

The comparison results are in fine consensus, and relative errors are in allowed domain. The small discrepancies come out due to the fact that Ref. [59] employed Refprop’s equation of state (EoS) as a fluid property package and particle swarm optimization (PSO). On the other side, there are exploited Peng Robinson fluid property package and GA in the current study. While the preceding studies of LNG regasification-ORC energy systems did not show the robust manipulation of organic working fluids and LNG pump inlet pressure to generate efficient clean energy. For the ANSU process validation, the results in Ref. [32] were considered.

4. Results and Discussion

In this section, the simulation results of power generation, energy efficiency, exergy efficiency, and NPV are presented.

4.1. Power Generation

In Figure 4, the obtained power is (MW) up to 2492, 1741, 1670, 1192, 1042, 940.7, and 837.7 by regulating seven working fluids in single mode at this energy system. Figure 5 shows the obtained power output (MW) up to 1687, 1382, 1202, 1124, 1091, 899.4, and 704.3 for manipulating seven working fluids in multiple modes. From this study, cyclohexane emerges as the most suitable working fluid to generate clean electric energy around 2492 MW, which slightly surpasses pentane, which secures power around 1741 MW.

Table 4. Detail of Configuration I operating values using cyclohexane as the working fluid.

Thermodynamic Point	Temperature [°C]	Pressure (kPa)	Mass Flow Rate [kg/h]	Fluid
1	−159.5	120	2.278 × 107	LNG
2	−159.5	120	2.278 × 107	LNG
3	−157.8	3500	2.278 × 107	LNG
4	65	1995	1.04 × 105	Cyclohexane
5	64.7	3490	1.04 × 105	Cyclohexane
6	22	15	7.206 × 106	H2O
7	31	4.425	7.206 × 106	H2O
8	336.8	3000	1.04 × 107	Cyclohexane
9	80	2000	1.04 × 107	Cyclohexane
10	−60	3490	2.278 × 107	LNG
11	40	55	1.292 × 104	Biogas
12	89	50	1.292 × 104	Biogas
13	348.5	500	1.292 × 104	Biogas
14	300	50	1.292 × 104	Biogas
15	718.5	1000	1.292 × 104	Biogas
16	700	1000	1.292 × 104	Biogas
17	744	1300	1.292 × 104	Biogas
18	650	1300	1.292 × 104	Biogas
19	876.8	5000	1.292 × 104	Biogas
20	−56	60	1.292 × 104	Biogas
21	10	60	1.292 × 104	Biogas
22	557	5000	1.292 × 104	Biogas
23	−51	4990	1.292 × 104	Biogas
24	14.32	4990	7702	CO2
25	−91	4990	5214	CH4
26	−20	3090	2.278 × 107	NG

,

Table 5. Detail of Configuration II operating values using carbon dioxide as the working fluid.

Thermodynamic Point	Temperature [°C]	Pressure (kPa)	Mass Flow Rate [kg/h]	Fluid
1	−159.5	120	2.278 × 107	LNG
2	−159.5	120	2.278 × 107	LNG
3	−157.8	3500	2.278 × 107	LNG
4	−30	40.78	9.242 × 106	Carbon dioxide
5	−28.91	30,000	9.242 × 106	Carbon dioxide
6	22	15	7.206 × 106	H2O
7	31	4.425	7.206 × 106	H2O
8	470	30,000	9.242 × 106	Carbon dioxide
9	40	76	9.242 × 106	Carbon dioxide
10	−60	3490	2.278 × 107	LNG
11	40	55	1.292 × 104	Biogas
12	89	50	1.292 × 104	Biogas
13	348.5	500	1.292 × 104	Biogas
14	300	50	1.292 × 104	Biogas
15	718.5	1000	1.292 × 104	Biogas
16	700	1000	1.292 × 104	Biogas
17	744	1300	1.292 × 104	Biogas
18	650	1300	1.292 × 104	Biogas
19	876.8	5000	1.292 × 104	Biogas
20	−56	60	1.292 × 104	Biogas
21	10	60	1.292 × 104	Biogas
22	557	5000	1.292 × 104	Biogas
23	−51	4990	1.292 × 104	Biogas
24	14.32	4990	7702	CO2
25	−91	4990	5214	CH4
26	−20	3090	2.278 × 107	NG

and

Table 6. Detail of Configuration III operating values using butane as the working fluid.

Thermodynamic Point	Temperature [°C]	Pressure (kPa)	Mass Flow Rate [kg/h]	Fluid
1	−159.5	120	2.278 × 107	LNG
2	−159.5	120	2.278 × 107	LNG
3	−157.8	3500	2.278 × 107	LNG
4	−40	100	1.236 × 105	Butane
5	64.7	3000	1.236 × 105	Butane
6	22	15	7.206 × 106	H2O
7	31	4.425	7.206 × 106	H2O
8	460	3000	1.236 × 105	Butane
9	80	1.094 × 10−5	1.236 × 105	Butane
10	−60	3490	2.278 × 107	LNG
11	40	55	1.292 × 104	Biogas
12	89	50	1.292 × 104	Biogas
13	348.5	500	1.292 × 104	Biogas
14	300	50	1.292 × 104	Biogas
15	718.5	1000	1.292 × 104	Biogas
16	700	1000	1.292 × 104	Biogas
17	744	1300	1.292 × 104	Biogas
18	650	1300	1.292 × 104	Biogas
19	876.8	5000	1.292 × 104	Biogas
20	−56	60	1.292 × 104	Biogas
21	10	60	1.292 × 104	Biogas
22	557	5000	1.292 × 104	Biogas
23	−51	4990	1.292 × 104	Biogas
24	14.32	4990	7702	CO2
25	−91	4990	5214	CH4
26	−20	3090	2.278 × 107	NG

report the operating values of configurations I, II, and III deploying cyclohexane carbon dioxide and butane as the working fluids in the ORC energy system. The electric production by turbine was maximized after each iteration using GA. The selection process consists of initialization, fitness evaluation, subset of solution, reproduction, replacement, and termination. The obtained results demonstrate that the clean electric energy generated from turbines is based on the working fluid thermodynamic properties [62].

4.2. Energy Efficiency

The obtained energy efficiencies of the novel integrated energy system are demonstrated in Figure 6 and Figure 7. Using cyclohexane, butane, pentane, ethylene, propane, ethane, and CO₂ in a single mode of the ORC, the obtained energy efficiencies (%) are around 57.13, 50.34, 11.59, 9.10, 40.24, 20.09, 11.59 and 26.52 respectively. On the other side, the obtained energy efficiencies (%) of working fluids CO₂-fluoroform-CF₄ (WFn-I), CO₂-propane (WFn-II), ethylene-propene-ref-113 (WFn-III), CO₂-benzene (WFn-IV), ethane-ref112a-112FC2 (WFn-V), propane-fluoroform-propene (WFn-VI) and CO₂-cyclohexane-benzene (WFn-VII) in multiple modes are found as 30.01, 25.55, 11, 7.33, 2.56, 1.54, and 0.59 simultaneously.

4.3. Exergy Efficiency

The obtained exergy efficiencies of this energy network are mentioned in Figure 8 and Figure 9. The obtained exergy efficiencies (%) are up to 76.20, 74.30, 64, 34.67, 37, 63.89, and 40.10 by manipulating the working fluids cyclohexane, butane, pentane, ethylene, ethane, propane, and CO₂ in a single mode of the ORC. The multiple modes of working fluids or refrigerants CO₂-fluoroform-CF₄ (WFn-I), CO₂-propane (WFn-II), ethylene-ref112a-refrig-113 (WFn-III), CO₂-benzene (WFn-IV), ethane-ref112a-112FC2 (WFn-V), propane-fluoroform-propene (WFn-VI) and CO₂-cyclohexane-benzene (WFn-VII) manipulation of the ORC can produce exergy efficiencies (%) around 36.51, 44.21, 64.53, 39.50, 37.67, 55.69, and 31.34 simultaneously.

4.4. Economic Assessments

The calculated total equipment cost of this proposed energy network is around 16.4 million USD. The NPV of cyclohexane configuration I is 19.5. It is obtained by calculating the total equipment cost and cash flow values up to 16.4 million USD, and 4.34 × 10³ million USD, respectively. Figure 10 and Figure 11 show the NPV values of 14 configurations having different cash flows.

Table 7. Results comparison of the present study and reference work.

Analysis	Present Study	Reference Work
Energy efficiency (%)	57.13	36.5
Exergy efficiency (%)	76.20	49
NPV	19.5	17.5

reports the comparison between results of the present study and similar work.

5. Conclusions and Future Directions

It is proven from this investigation that this novel integrated energy system has energy efficiency up to 57.13 %. It is due to the careful manipulation of organic working fluids in the ORC turbine. It is confirmed that the ORC energy system is identical to a steam engine. Now, it has materialized as a real clean energy generation system with technological advancement. Its major features are good flexibility and conversion efficiency at cryogenic conditions. There is a need to enhance its economic viability through the latest integration techniques, various manufacturing processes and materials, more novel development in optimization techniques, and low-cost, environmentally affable working fluids in the near future.

It is verified that the manipulation of a single working fluid of the ORC can generate a large amount of power, up to 2492 MW, in comparison to working fluids of multiple modes. It is because of this reason that its thermodynamic characteristics i.e., (i)—Critical temperature, (ii)—Boiling temperature, (iii)—Specific heat, (iv)—Latent heat of evaporation, (v)—Heat transfer coefficient, (vi)—Enthalpy drop, (vii)—Thermal stability, (viii)—Viscosity, (ix)—Specific volume, do not coincide with each other. It is also evident from the obtained results that the 2nd law of thermodynamics efficiency is higher than the 1st law of thermodynamic efficiency for identical energy systems.

This research work discloses a business case that is not shown in previous scientific studies showing consumption of LNG cold energy to generate clean electric energy and running ANSU CO₂ capture process. It devises LNG regasification capacity 200 million tons annually at a seaport vicinity. It positively portrays to generate clean electric energy and minimizing an environmental contaminant (CO₂) from novel integrated bio-gas setup via LNG cold energy.

The heat transfer devices that are linked to the presented novel integrated energy system are classified as condenser/regenerator, evaporator, and preheater. It is now evident that shell and tube heat exchangers show better results. For practical implications, there is also a recommendation to deploy shell and tube heat exchanger as condenser and evaporator in a practical ORC facility. It is due to its features of optimum heat transfer, minimum LNG freezing risk, on-shore/off-shore operation modes, and maintenance. This investigation makes a call to consume seaport area hot water in the ORC evaporator with the effects of its facile handling and no cost in summer.

The biogas has a large CO₂ content of around 35%, and there is a large energy requirement for its cryogenic capture. It can be resolved by this proposed novel integrated clean energy system utilizing LNG cold energy. In this situation, environmental regulatory bodies, government authorities, industrialists, and academics can take advantage of the obtained thermodynamic and techno-economic assessments of this innovative integrated energy network.