Simulation and Economic Investigation of CO₂ Separation from Gas Turbine Exhaust Gas by Molten Carbonate Fuel Cell with Exhaust Gas Recirculation and Selective Exhaust Gas Recirculation

Abstract

The paper presents a simulation investigation of using a molten carbonate fuel cell (MCFC) combined with exhaust gas recirculation (EGR) or selective exhaust gas recirculation (SEGR) to reduce CO₂ emission from the gas turbine in order to cope with climate change problem. EGR or SEGR can be used to concentrate the low-concentration CO₂ in gas turbine exhausts. The CO₂ concentration is then raised further by adding gas turbine exhaust to the MCFC’s cathode. The suggested gas–steam combined cycle system paired with MCFC and CO₂ collection without EGR is contrasted with two novel gas–steam combined cycle systems integrated with MCFC, EGR, or SEGR with CO₂ capture (the reference system). The thermal efficiency of the gas–steam combined cycle systems’ integrated MCFC, EGR and SEGR with CO₂ collection is 56.08%, which is 1.3% higher than the reference system. The cost of CO₂ avoided in the new system with SEGR will be equal to that of the system with the MEA technique for CO₂ capture if the MCFC cost is reduced to 904.4 USD/m².

1. Introduction

Reducing CO₂ emissions is a significant way to solve the problem of global warming, as CO₂ is the main component of greenhouse gases [1]. The establishment of low-carbon cities is promoted in China to keep CO₂ emissions under control [2]. In the past 30 years, nearly 40% of CO₂ in China has been released by fossil fuel power plants [3]. Therefore, it is necessary to lower China’s fossil fuel power plants’ CO₂ emissions. Gas turbines (GT) are employed more frequently than conventional coal-fired power plants because of their dependability, flexibility and comparatively low CO₂ emissions [4]. Because the gas turbine uses around 2.5 times as much air as is required for full combustion, the CO₂ content in the exhaust stream is quite low (about 3–4 percent points), necessitating a further expensive CO₂ extraction process [5].

Due to its unique properties, the molten carbonate fuel cell (MCFC) may be utilized to remove CO₂ from the gas turbine exhaust. Gas turbine exhaust gas’s CO₂ and O₂ combine to form carbonate ions when it is injected into the MCFC’s cathode. The MCFC’s molten electrolyte is then used to carry the carbonate ions from the cathode to the anode. At the anode of MCFC, the carbonate ions react with H₂, then H₂O and CO₂ are generated. Once the anode exhaust gas is burned in the afterburner with pure O₂ acting as the oxidizer, all that is left are CO₂ and H₂O. Pure CO₂ gas can be achieved after being dehydrated. Stefano Campanari et al. [6] investigated the performance of MCFC as a CO₂ separator integrated into natural gas combined cycles. According to the findings, with a CO₂ recovery rate of around 71%, the specific energy consumption for CO₂ avoidance was less than 0.5 MJ/kgCO₂. A gas–steam combined cycle (GSCC) system that incorporates CO₂ capture was investigated by Duan et al. [7]. The system efficiency was around 54.96% when the CO₂ avoidance rate was 85%. Nonetheless, it has been established that the MCFC efficiency is sensitive to the gas turbine exhaust gas’s $c_{{\mathrm{CO}}_2}$ content [8]. Wang et al. [9] introduced the comparison among different fuel cells for carbon capture. The results showed that MCFC-based configurations could gain better performance than the solid oxide fuel cell (SOFC) based configurations.

Gas turbine exhaust gas recirculation (EGR) is a popular technique for increasing the cycle’s $c_{{\mathrm{CO}}_2}$ while lowering the energy required for the carbon capture process [10]. The EGR process is as follows: a part of the exhaust gas is returned to the air compressor (AC) after the heat recovery steam generator releases it (HRSG). Air mass flow into the AC is reduced to maintain a constant total mass flow of the working medium, which raises the CO₂ concentration in the cycle. The application of EGR also reduces the emissions of nitrogen oxide because both the oxygen and nitrogen concentrations are decreased in the cycle [11]. The effects of EGR on full load and partial load operation performances of GTs were studied by Joe Hachem et al. [4]. By using four distinct techniques, Hailong Li et al. [10] assessed the impact of raising the CO₂ content in the exhaust gas of GT-based power plants. According to the research, the combined cycle with EGR had the highest electrical efficiency and could change the CO₂ molar fraction over the widest range, from 3.8 mol% to at least 10 mol%. In order to explore strategies for increasing efficiency, Pan et al. [12] assessed the effectiveness and effects of a post-combustion CO₂ capture (PCC) on the natural gas combined cycle (NGCC). The findings demonstrated that when the EGR ratio grew, the stripper’s energy consumption fell because EGR reduced the mass flow rate of exhaust gas and increased $c_{{\mathrm{CO}}_2}$, which reduced the stripper’s need for steam in a PCC. The upper bound of EGR ratio was 33% due to the restriction of the minimum oxygen concentration. The impact of a carbon capture procedure on the NGCC was investigated by Woo-Sung Lee et al. [13]. As a consequence, 533 MW of net electricity was produced using an NGCC with a 90% CO₂ recovery rate. The total cost of CO₂ collection was around 46.5 USD/ton. Carapellucci et al. [14] investigated the functioning of NGCC integrated with MCFC using EGR without CO₂ capture and with CO₂ capture. The results showed that the addition of an MCFC fed by GT exhaust gases markedly increases the rated plant capacity.

The term “selective exhaust gas recirculation” (SEGR) refers to a different method of recycling CO₂ from gas turbine exhaust gas with membranes to increase the $c_{{\mathrm{CO}}_2}$ in the cycle. Zhao et al. [15] used multi-stage membrane systems to capture CO₂ from coal-fired power plants. The results showed that CO₂ purity of 95 mol% and 90% CO₂ capture rate could be achieved with the SEGR method. Merkel et al. [16] used membranes to capture CO₂ in the post-combustion power plant. The results showed that processes using a vacuum at the permeate side required less energy than processes using the compression of the feed gas. The CO₂ generated by the integrated gasification combined cycle (IGCC) power plants was captured by Merkel et al. [17] using the H₂-selective and CO₂-selective membranes. The results showed that, compared to cold absorption, 60% of the capital cost and 50% of the energy consumption could be reduced. The impact of the sweep gas on the membrane area and the degree of CO₂ separation was studied by Franz J et al. [18]. The findings demonstrated that for a 600 MW reference power plant, the technological approach utilizing sweep gas allowed for an efficiency reduction of 3.8 percentage points with a 70% CO₂ capture. The membrane techniques were employed by Richard et al. [5] to remove CO₂ from the gas turbine combined cycle power plants. The results revealed that the SEGR method made CO₂ capture easier, and the lowest capture cost occurred with CO₂ capture rates of 60–70%. Herraiz L et al. [19] used SEGR and amine-based chemical absorption technology to capture CO₂ of the natural gas-fired combined cycle plants. The results showed that the SEGR increased $c_{{\mathrm{CO}}_2}$ in gas turbine flue gas to 13–14 vol%. Gatti M et al. [20] presented the preliminary technical and economic assessment of four alternative technologies (including MCFC and CO₂ permeable membranes) suitable for post-combustion CO₂ capture from NGCC exhaust gases. The results showed that MCFC seemed to outperform the baseline from both performance and cost; CO₂ permeable membranes are affected by the large area and high capital costs.

According to the previous description, both the EGR and SEGR can enrich CO₂ with almost no energy input. The SEGR is driven by the difference in CO₂ partial pressure between air and flue gas while employing the air stream as the sweep gas. Compressors or vacuum pumps are not needed. To move the gas streams through the membrane unit, fans or blowers are the sole energy consumption sources. However, the enrichment of $c_{{\mathrm{CO}}_2}$ of flue gas by EGR or SEGR is limited, only 15–20 vol% [5]. With the combination of the EGR or SEGR with MCFC, the $c_{{\mathrm{CO}}_2}$ of flue gas will further increase, which encourages CO₂ collection while using less energy. There is no research on the combination of SEGR with MCFC currently.

On the base of the above research, two GSCC systems integrated with MCFC, EGR or SEGR and CO₂ capture are proposed in this paper. In the first system, EGR increases the $c_{{\mathrm{CO}}_2}$ of the GT exhaust gas; in the second system, SEGR and EGR increase the $c_{{\mathrm{CO}}_2}$ of the GT exhaust gas. The thermal and economic performances of different systems are analyzed and compared. On the thermal efficiency and financial performance of the new systems, the impacts of the EGR/SEGR ratio and the CO₂ collection rate are investigated.

2. Description of System

2.1. The GSCC System Coupled with MCFC and CO₂ Capture without EGR (Reference System)

The GSCC system paired with MCFC and CO₂ collection without EGR was chosen as the reference system, and the flowchart is shown in Figure 1. After being compressed in compressor 1, the fuel (2) is fed into the combustor. After being compressed in compressor 2, the air is split into two parts. One part (4) is fed into the combustor; the other part (6) is fed into the GT as the cooling air. The combustion chamber outlet’s flue gas expands in the GT to generate electricity, and the exhaust gas from the GT is subsequently supplied into the MCFC cathode. In order to avoid the issue of carbon deposition, a portion of the anode exhaust gas (15) goes into the pre-reformer. This converts the fuel into H₂ and CO. H₂ interacts with the carbonate ions brought in from the cathode in the anode to create H₂O and CO₂. The cathode output gas (9), which has high-temperature and low-$c_{{\mathrm{CO}}_2}$ following the electrochemical process, is released into the environment after releasing heat in the heat recovery steam generator (HRSG) (10). The air separation unit’s pure O₂ (19) is used to burn the remaining anode exhaust gas (16) in the afterburner (ASU). The HRSG is then supplied with the afterburner’s output gas (20) to release heat. Ultimately, the liquid CO₂ is created by condensing and compressing the cooled afterburner exhaust gas (21), which is composed exclusively of H₂O and CO₂ (25).

2.2. The GSCC System Integrated with MCFC and CO₂ Capture with EGR (Case 1)

Figure 2 shows the simplified flowchart of the GSCC system that is integrated with MCFC and CO₂ capture using EGR. The exhaust gas from a GT is split into two pieces. After being heated in the HRSG to a temperature of 923.15 K, one part (9) is injected into the MCFC cathode. The other part (12) is fed into the condenser to remove H₂O (15) after cooling down in the HRSG and Cooler 1 to the temperature of 353.15 K. After being compressed in compressor 3, 40% of the water-removed exhaust gas (18) is supplied into the gas turbine as the cooling gas (19) to keep the O₂ concentration ($c_{{\mathrm{O}}_2}$) in the combustor over 15 mol%. Air 1 is fed into the combustor chamber after being mixed with the rest exhaust gas (17) and compressed in compressor 2.

2.3. The GSCC System Integrated MCFC, EGR and SEGR with CO₂ Capture (Case 2)

Figure 3 shows a simplified flowchart of the GSCC system integrated MCFC, EGR and SEGR with CO₂ capture. After releasing heat in HRSG, a part of the gas turbine exhaust gas (13) is cooled down in cooler 1 to the temperature of 303.15 K. In contrast to the flowchart for Case 1, 40% of the water-removed exhaust gas (21) is supplied into splitter 3, and 60% of the exhaust gas (18) is vented into the selective CO₂ transfer system. Then part of the exhaust gas (23) goes into the gas turbine as the cooling gas (24) after being compressed in compressor 3. Air 1 (3) goes into the selective CO₂ transfer system as the sweep gas. The air that contains CO₂ that has passed through the membranes is then combined with some of the exhaust gas (22), which is then compressed in compressor 2.

3. System Modeling

The Aspen Plus software was used to build the system models.

Table 1. Main simulation parameters of new systems.

Components	Parameters	Value
	Ambient conditions [7]	298.15 K, 1.01 atm
	Compositions of air [7]	N2 79%, O2 21%
	Generator efficiency [7]	99%
Gas turbine	Fuel composition	CH4 100%
	Lower heating value (LHV) (kJ/kg) [7]	50,030
	Mass flow of GT fuel (kg/s)	15
	Ratio of pressure	16
	Inlet temperature of turbine (K)	1561
Membranes	CO2 permeance (gpu) [17]	1000
	CO2/N2 selectivity (-) [17]	50
HRSG	Steam pressure of LP/MP/HP (MPa) [7]	0.39/3.6/17.6
	Mechanical efficiency of turbine [7]	99%
	Isentropic efficiency of LP/MP/HP [7]	92%/91%/90%
Air separation unit	Operating pressure of AC (MPa) [22]	0.6
	AC isentropic efficiency [22]	86%
CO2 compression	Compression stage number [7]	3
	Outlet pressure (atm) [7]	80
	Outlet temperature (K) [7]	303.15

shows the parameters of the new systems, while

Table 2. Parameters of MCFC.

Parameters		Value
Fuel		CH4 100%
Fuel mass flow (kg/s)		3.75
Fuel after the pre-reformer (mass fraction)		H2 1.51% CO2 85.7% H2O 12.79%
Fuel mass flow after the pre-reformer (kg/s)		102.7
H2 LHV (kJ/kg) [23]		121,000
Current density (A/m2) [7]		1500
Area (m2)		102,245
Steam-to-carbon ratio [7]		3.5
Fuel utilization rate		0.85
Operation temperature (K) [22]		923.15
${\eta }_{\mathrm{DC}-\mathrm{AC}}$ [22]		95%
Thickness (mm) [24]	Anode	0.6
	Cathode	0.6
	Electrolyte	1
Standard exchange current (A/m2) [24]	Anode	50
	Cathode	2
Active surface area (m2/m3) [24]	Anode	2.7 × 105
	Cathode	3.0 × 105
Electrical conductivity (S/m−1) [24]	Anode	100
	Cathode	100
	Electrolyte	138.6
Effective diffusivity (m2/s) [24]	Anode	3.97 × 10−6
	Cathode	1.89 × 10−6

lists the parameters of the MCFC. Some assumptions are as follows [21]:

• Steady-state conditions;
• The MCFC is thermally insulated, and there is no entropy flow to the outside environment;
• The permeability of the membranes is constant, and no coupling effect is taken into account;
• The system’s interactions with potential or kinetic energy are disregarded;
• The assumption is that all gases are perfect incompressible gases.

Pure CH₄ is given to the MCFC anode as the electrochemical reaction fuel to ensure that the exhaust gas from the afterburner includes only CO₂ and H₂O. The MCFC is simulated with a Fortran code. The main reaction equations are as follows:

Reforming reaction [7]:

$${\mathrm{CH}}_4+{\mathrm{H}}_2\mathrm{O}\to \mathrm{CO}+3{\mathrm{H}}_2,$$

(1)

$$\mathrm{CO}+{\mathrm{H}}_2\mathrm{O}\to {\mathrm{CO}}_2+{\mathrm{H}}_2,$$

(2)

Cathode reaction [7]:

$$0.5{\mathrm{O}}_2+{\mathrm{CO}}_2+2{\mathrm{e}}^{-}\to {\mathrm{CO}}_3^{2-},$$

(3)

Anode reaction [7]:

$${\mathrm{H}}_2+{\mathrm{CO}}_3^{2-}\to {\mathrm{H}}_2\mathrm{O}+{\mathrm{CO}}_2+2{\mathrm{e}}^{-},$$

(4)

The ideal reversible voltage, $E_{\mathrm{Nerst}}$ (V), can be calculated as follows [24]:

$$E_{\mathrm{Nerst}}=\frac{\Delta G}{nF}+\frac{RT}{nF}ln\left[\frac{p_{{\mathrm{H}}_2}{\left(p_{{\mathrm{O}}_2}\right)}^{0.5}{P}_{{\mathrm{CO}}_2,\mathrm{ca}}}{P_{{\mathrm{H}}_2\mathrm{O}}{P}_{{\mathrm{CO}}_2,\mathrm{an}}}\right],$$

(5)

$$\Delta G=\mathrm{242,000}-45.8T,$$

(6)

where $\Delta G$ represents the Gibbs free energy (kJ/kg), n indicates the number of electrons that the H₂ molecule emitted, and $p_i$ is the species i’s partial pressure (MPa).

The activation loss can be calculated as follows [24,25]:

$${\eta }_{\mathrm{act}}={\eta }_{\mathrm{act},\mathrm{an}}+{\eta }_{\mathrm{act},\mathrm{ca}},$$

(7)

$${\eta }_{\mathrm{act},\mathrm{an}}=\frac{RT}{\mathsf{\alpha }nF}ln\frac{j{p}_{{\mathrm{H}}_2}}{j_{0,\mathrm{an}}{p}_{{\mathrm{H}}_2,\mathrm{TPB}}},$$

(8)

$${\eta }_{\mathrm{act},\mathrm{ca}}=\frac{RT}{\mathsf{\alpha }nF}ln\frac{j{\left(p_{{\mathrm{O}}_2}\right)}^{0.5}{p}_{{\mathrm{CO}}_2,\mathrm{ca}}}{j_{0,\mathrm{ca}}{\left(p_{{\mathrm{O}}_2,\mathrm{TPB}}\right)}^{0.5}{p}_{{\mathrm{CO}}_2,\mathrm{ca},\mathrm{TPB}}},$$

(9)

$$j_{0,\mathrm{an}}=j_{0,\mathrm{an}}^0{\left(p_{{\mathrm{H}}_2}^{}\right)}^{0.25}{\left(p_{{\mathrm{H}}_2\mathrm{O}}^{}\right)}^{0.25}{\left(p_{{\mathrm{CO}}_2,\mathrm{an}}^{}\right)}^{0.25},$$

(10)

$$j_{0,\mathrm{ca}}=j_{0,\mathrm{ca}}^0{\left(p_{{\mathrm{O}}_2}^{}\right)}^{0.375}{\left(p_{{\mathrm{CO}}_2,\mathrm{ca}}^{}\right)}^{-1.25},$$

(11)

where ${\eta }_{\mathrm{act}}$ represents the activation voltage loss (V), j represents the current density (A/m²), $j_0$ is the exchange current density (A/m²), and $j_0^0$ is the standard exchange current density (A/m²).

The ohmic loss can be calculated as follows [26]:

$${\eta }_{\mathrm{ohm}}=j{R}_{\mathrm{ohm}},$$

(12)

$$R_{\mathrm{ohm}}=\frac{{\tau }_{\mathrm{an}}}{{\sigma }_{\mathrm{an}}}+\frac{{\tau }_{\mathrm{elec}}}{{\sigma }_{\mathrm{elec}}}+\frac{{\tau }_{\mathrm{ca}}}{{\sigma }_{\mathrm{ca}}},$$

(13)

where ${\eta }_{\mathrm{ohm}}$ is the ohmic voltage loss (V), $R_{\mathrm{ohm}}$ is the ohmic polarization cell resistance ($\mathsf{\Omega }·{\mathrm{m}}^2$), $\tau$ is the thickness (mm), and $\sigma$ is the electrical conductivity (S/m⁻¹).

The gas transport model in porous media is used in Equations (17)–(21), where it is used to compute the partial pressures of gas at the three-phase boundaries ($p_{\mathrm{i},\mathrm{TPB}}$). The concentration loss can be calculated as follows [26]:

$${\eta }_{\mathrm{conc}}={\eta }_{\mathrm{conc},\mathrm{an}}+{\eta }_{\mathrm{conc},\mathrm{ca}},$$

(14)

$${\eta }_{\mathrm{conc},\mathrm{an}}=\frac{RT}{2F}ln\left(\frac{p_{{\mathrm{H}}_2}{p}_{{\mathrm{H}}_2\mathrm{O},\mathrm{TPB}}{p}_{{\mathrm{CO}}_{2,}\mathrm{an},\mathrm{TPB}}}{p_{{\mathrm{H}}_2,\mathrm{TPB}}{p}_{{\mathrm{H}}_2\mathrm{O}}{p}_{{\mathrm{CO}}_{2,}\mathrm{an}}}\right),$$

(15)

$${\eta }_{\mathrm{conc},\mathrm{ca}}=\frac{RT}{2F}ln\left(\frac{p_{{\mathrm{CO}}_2,\mathrm{ca}}{\left(p_{{\mathrm{O}}_2}\right)}^{0.5}}{p_{{\mathrm{CO}}_2,\mathrm{ca},\mathrm{TPB}}{\left(p_{{\mathrm{O}}_2,\mathrm{TPB}}\right)}^{0.5}}\right),$$

(16)

$$p_{{\mathrm{H}}_2,\mathrm{TPB}}=p_{{\mathrm{H}}_2}-\frac{RT{\tau }_{\mathrm{an}}}{2F{D}_{\mathrm{eff},\mathrm{an}}}j,$$

(17)

$$p_{{\mathrm{H}}_2\mathrm{O},\mathrm{TPB}}=p_{{\mathrm{H}}_2\mathrm{O}}+\frac{RT{\tau }_{\mathrm{an}}}{2F{D}_{\mathrm{eff},\mathrm{an}}}j,$$

(18)

$$p_{{\mathrm{CO}}_{2,}\mathrm{an},\mathrm{TPB}}=p_{{\mathrm{CO}}_{2,}\mathrm{an}}+\frac{RT{\tau }_{\mathrm{an}}}{2F{D}_{\mathrm{eff},\mathrm{an}}}j,$$

(19)

$$p_{{\mathrm{O}}_2,\mathrm{TPB}}=p_{{\mathrm{O}}_2}-\frac{RT{\tau }_{\mathrm{ca}}}{4F{D}_{\mathrm{eff},\mathrm{ca}}}j,$$

(20)

$$p_{{\mathrm{CO}}_2,\mathrm{ca},\mathrm{TPB}}=p_{{\mathrm{CO}}_2,\mathrm{ca}}-\frac{RT{\tau }_{\mathrm{ca}}}{2F{D}_{\mathrm{eff},\mathrm{ca}}}j,$$

(21)

where ${\eta }_{\mathrm{conc}}$ is the concentration voltage loss (V), $p_{i,\mathrm{TPB}}$ represents the partial pressure of the species i at the three-phase boundary (MPa), and $D_{\mathrm{eff}}$ is the effective diffusivity (m²/s).

The actual MCFC voltage can be calculated as follows:

$$V_{\mathrm{cell}}=E_{\mathrm{Nerst}}-{\eta }_{\mathrm{act}}-{\eta }_{\mathrm{ohm}}-{\eta }_{\mathrm{conc}},$$

(22)

where $V_{\mathrm{cell}}$ is the cell voltage (V).

These are the formulas for calculating the MCFC power output, $W_{\mathrm{MCFC}}$ (W):

$$W_{\mathrm{MCFC}}=A_{\mathrm{c}}j{V}_{\mathrm{cell}},$$

(23)

where $A_{\mathrm{c}}$ represents the cell active area (m²).

The net power output can be calculated as follows:

$$W_{\mathrm{MCFC},\mathrm{net}}={\eta }_{\mathrm{DC}-\mathrm{AC}}{W}_{\mathrm{MCFC}},$$

(24)

where the efficiency of converting direct current into the alternative current is known as ${\eta }_{\mathrm{DC}-\mathrm{AC}}$.

The following formula may be used to calculate the MCFC’s thermal efficiency, ${\eta }_{\mathrm{MCFC}}$:

$${\eta }_{\mathrm{MCFC}}=\frac{W_{\mathrm{MCFC},\mathrm{net}}}{\dot{m_{\mathrm{fuel} \mathrm{after} \mathrm{pre}-\mathrm{reformer}}{\theta }_{H_2}}LH{V}_{H_2}},$$

(25)

where $\dot{m_{\mathrm{fuel} \mathrm{after} \mathrm{pre}-\mathrm{reformer}}}$ represents the fuel mass flow after the pre-reformer (kg/s), ${\theta }_{H_2}$ represents the H₂ mass fraction of the fuel mass flow after the pre-reformer, and $LH{V}_{H_2}$ represents the low heat value of H₂ (kJ/kg).

The selective CO₂ transfer system is set as counter-current. The selective CO₂ transfer system is simulated with the Aspen Custom Modeler. These are the formulas for calculating a species i’s gas permeance [18]:

$$d\dot{n_i}=dA·Q_i\left(p_{i,f}-p_{i,p}\right),$$

(26)

where $Q_i$ is the permeability of the species i (kmol/(m²s·MPa)), $d\dot{n_i}$ represents the gas permeance of species i for a segment of area (kmol/s), A represents the area (m²), $p_{i,f}$ represents the partial pressure of the species i at the feed side (MPa), and $p_{i,p}$ represents the partial pressure of species i at the permeate side (MPa).

The fuel utilization rate of MCFC can be calculated as follows:

$$U_{\mathrm{fuel}}=1-\frac{m_{\mathrm{fuel},\mathrm{outlet}}}{m_{\mathrm{fuel},\mathrm{inlet}}},$$

(27)

The CO₂ utilization rate of MCFC can be calculated as follows:

$$U_{{\mathrm{CO}}_2}=1-\frac{m_{{\mathrm{CO}}_2,\mathrm{outlet}}}{m_{{\mathrm{CO}}_2,\mathrm{inlet}}},$$

(28)

The overall CO₂ capture rate can be calculated as follows:

$$OCCR=\frac{m_{{\mathrm{CO}}_2,\mathrm{capture}}}{m_{{\mathrm{CO}}_2,\mathrm{emissions}}},$$

(29)

The overall system thermal efficiency can be calculated as follows:

$$\eta =\frac{W_{\mathrm{total},\mathrm{net}}}{\dot{m_{\mathrm{fuel} \mathrm{after} \mathrm{pre}-\mathrm{reformer}}{\theta }_{{\mathrm{H}}_2}}LH{V}_{{\mathrm{H}}_2}+\dot{m_{\mathrm{GT}}}LHV},$$

(30)

4. Model Validation

4.1. The Reference System Model Validation with Literature

In reference [7], the study used a GSCC system with integrated MCFC for CO₂ collection. The findings indicated that the system’s total efficiency was 54.96% at 85% CO₂ collection and 85% fuel utilization rate. In this paper, the overall efficiency of the reference system is 54.78% with the same MCFC operating parameters.

4.2. The Selective CO₂ Transfer System Validation with Experiment Data

In reference [27], a post-combustion CO₂ collection experiment was run in counter-current air sweep mode for mixed gas permeation. Investigations were conducted on the impacts of pressure ratio, sweep gas ratio and temperature. The results showed that the CO₂ permeance was 1000 (gpu) and the CO₂/N₂ selectivity was 50, which made the selective CO₂ transfer system model in this paper validated.

4.3. The MCFC Model Validation with Experiment

An MCFC planar unit cell with a porous Ni/Cr alloyed anode and a porous NiO cathode was tested to check the model reliability, as shown in Figure 4. A 62 % Li₂CO₃ and a 38 % K₂CO₃ combination made up the electrolyte. LiAlO₂ is the electrolyte matrix. The experimental facility was made up of measuring, heating and gas flow control equipment, as well as an MCFC unit cell. In an atmosphere, the cell operates at 650 °C. The current density and cell voltage are set and measured by the electrochemical workstation. Figure 5 shows the simulation voltage and the real voltage operating at various $c_{{\mathrm{CO}}_2}$ during the experiment. The error indicator RMSE is calculated in Equation (31) [28], which value is 0.014V in this paper. It is obvious that the modeling results and the experimental findings correspond perfectly.

$$RMSE\left(x\right)=\sqrt{\frac{1}{N}{{\displaystyle \sum }}_{i=1}^N{\left(I_i^{experimental}-I_i^{estimated}\right)}^2},$$

(31)

5. Results and Discussion

5.1. Analysis of Case 1

To determine Case 1’s performance traits, a case ($U_{\mathrm{fuel}}$ = 0.85 and $U_{{\mathrm{CO}}_2}$ = 0.85) was thoroughly examined. In Figure 2, the streamlined flowchart for Case 1 is shown. The EGR percentage for Splitter 1 is 0.5, which means that 50% of the GT exhaust gas goes into the MCFC’s cathode. In splitter 2, 40 vol% of the water-removed exhaust gas goes into compressor 3 to maintain the $c_{{\mathrm{O}}_2}$ at the combustor 15 mol% [5].

Table 3. Detailed stream data of Case 1.

	Temperature	Pressure	Mole Flow	Mole Fraction (-)
	(K)	(MPa)	(kmol/s)	CH4	CO	H2	CO2	N2	O2	H2O
1	298.15	0.102	0.935	1	-	-	-	-	-	-
2	551.52	1.621	0.935	1	-	-	-	-	-	-
3	298.15	0.102	12.5	-	-	-	-	0.79	0.21	-
4	300.73	0.102	19.44	-	-	-	0.029	0.813	0.158	-
5	693.32	1.621	19.44	-	-	-	0.029	0.813	0.158	-
6	1727.3	1.621	20.37	-	-	-	0.073	0.776	0.059	0.092
7	888.11	0.102	25	-	-	-	0.075	0.79	0.06	0.075
8	888.11	0.102	12.5	-	-	-	0.075	0.79	0.06	0.075
9	923.15	0.102	12.5	-	-	-	0.075	0.79	0.06	0.075
10	923.15	0.102	11.31	-	-	-	0.012	0.873	0.032	0.083
11	380.15	0.102	11.31	-	-	-	0.012	0.873	0.032	0.083
12	888.11	0.102	12.5	-	-	-	0.075	0.79	0.06	0.075
13	380.15	0.102	12.5	-	-	-	0.075	0.79	0.06	0.075
14	303.15	0.102	12.5	-	-	-	0.075	0.79	0.06	0.075
15	303.15	0.102	0.935	-	-	-	-	-	-	1
16	303.15	0.102	11.57	-	-	-	0.081	0.854	0.065	-
17	303.15	0.102	6.94	-	-	-	0.081	0.854	0.065	-
18	303.15	0.102	4.626	-	-	-	0.081	0.854	0.065	-
19	791.03	1.621	4.626	-	-	-	0.081	0.854	0.065	-
20	298.15	0.102	0.234	1	-	-	-	-	-	-
21	875.83	0.102	3.341	0.07	0.047	0.04	0.593	-	-	0.25
22	772.18	0.102	3.498	0.044	0.06	0.114	0.572	-	-	0.21
23	923.15	0.102	3.107	-	0.05	0.044	0.637	-	-	0.269
24	923.15	0.102	4.603	-	0.05	0.044	0.637	-	-	0.269
25	923.15	0.102	1.496	-	0.05	0.044	0.637	-	-	0.269
26	298.15	0.102	0.355	-	-	-	-	0.79	0.21	-
27	305.15	0.105	0.241	-	-	-	-	0.99	0.01	-
28	305.15	0.105	0.072	-	-	-	-	-	1	-
29	1385.89	0.102	1.498	-	-	-	0.687	-	-	0.313
30	380.15	0.102	1.498	-	-	-	0.687	-	-	0.313
31	303.15	0.102	1.498	-	-	-	0.687	-	-	0.313
32	303.15	0.102	0.468	-	-	-	-	-	-	1
33	303.15	0.102	1.031	-	-	-	1	-	-	-
34	303.15	8.106	1.031	-	-	-	1	-	-	-

lists the specific information for Case 1’s primary streams. A total of 88.16% of the CO₂ was captured overall in Case 1, with a system thermal efficiency of 54.71%.

The MCFC’s CO₂ consumption rate is held constant at 0.85 to assess the effect of the EGR rate on system performance. The mass flow of air 1 into the mixer was decreased when the EGR rate was raised from 0 to 0.5 to keep the turbine inlet temperature constant, as illustrated in Figure 6. The GT exhaust gas’s CO₂ content goes from 0.038 to 0.075 when the air mass flow into the combustor is decreased. The amount of CO₂ injected into the MCFC cathode and the amount of fuel fed into the MCFC are both maintained constant when the EGR rate is changed. Therefore, the OCCR of the system is not affected by the change in the EGR rate, which is kept constant at 0.8816.

Both the current density of the MCFC and the CO₂ mass flow of the gas turbine exhaust are maintained constants to study how the system performance depends on the MCFC’s rate of CO₂ usage. In order to vary the CO₂ utilization rate of MCFC from 0.45 to 0.95, the area of MCFC was increased from 54,118 m² to 126,293 m². Figure 7 shows that when the EGR rate is kept at 0.5, and the CO₂ utilization rate of MCFC is varied from 0.45 to 0.95, the overall CO₂ capture rate of the system is increased from 0.516 to 0.973. The $c_{{\mathrm{CO}}_2}$ of gas turbine exhaust gas is not influenced by the $U_{{\mathrm{CO}}_2}$ of MCFC.

In line with the increase in $c_{{\mathrm{CO}}_2}$ of GT exhaust gas, the cell voltage of MCFC increases with the growth in EGR rate while the current density is held constant. As shown in Figure 8, when the power of MCFC rises with the increase in the cell voltage and the intake fuel mass flow of MCFC is kept constant, with a rise in EGR rate, the system’s thermal efficiency rises. The power output of the system will be raised along with the MCFC intake fuel as the CO₂ utilization rate rises, resulting in an increase in the total intake of fuels. The system’s thermal efficiency will drop, as shown in Figure 8, since the $U_{{\mathrm{CO}}_2}$ has a greater influence on the system’s input fuels than it does on its output power.

5.2. Analysis of Case 2

To determine the performance traits of Case 2, a case ($U_{\mathrm{fuel}}$ = 0.9 and $U_{{\mathrm{CO}}_2}$ = 0.85) was thoroughly examined. The simplified flowchart of Case 2 is displayed in Figure 3. Forty percent of the exhaust gas from the GT is directed into the MCFC’s cathode when splitter 1’s EGR percentage is 0.6. In splitter 2, 70 vol% of the exhaust gas goes into the selective CO₂ transfer system, where 94.4% of the CO₂ in the exhaust gas is transferred to the sweep air. To keep the $c_{{\mathrm{O}}_2}$ at the combustor over 15 mol %, splitter 3 feeds 40 volume % of the exhaust gas into compressor 3.

Table 4. Data on the streams from Case 2 in detail.

	Temperature	Pressure	Mole Flow	Mole Fraction (-)
	(K)	(MPa)	(kmol/s)	CH4	CO	H2	CO2	N2	O2	H2O
1	298.15	0.102	0.935	1	-	-	-	-	-	-
2	551.52	1.621	0.935	1	-	-	-	-	-	-
3	298.15	0.102	17.99	-	-	-	-	0.79	0.21	-
4	298.15	0.102	18.83	-	-	-	0.046	0.757	0.197	-
5	298.94	0.102	21.19	-	-	-	0.053	0.76	0.187	-
6	694.36	1.621	21.19	-	-	-	0.053	0.76	0.187	-
7	1614.6	1.621	22.12	-	-	-	0.093	0.728	0.094	0.085
8	894.24	0.102	23.7	-	-	-	0.093	0.733	0.095	0.079
9	894.24	0.102	9.478	-	-	-	0.093	0.733	0.095	0.079
10	923.15	0.102	9.478	-	-	-	0.093	0.733	0.095	0.079
11	923.15	0.102	8.286	-	-	-	0.011	0.838	0.061	0.09
12	380.15	0.102	8.286	-	-	-	0.011	0.838	0.061	0.09
13	894.24	0.102	14.22	-	-	-	0.093	0.733	0.095	0.079
14	380.15	0.102	14.22	-	-	-	0.093	0.733	0.095	0.079
15	303.15	0.102	14.22	-	-	-	0.093	0.733	0.095	0.079
16	303.15	0.102	1.122	-	-	-	-	-	-	1
17	303.15	0.102	13.1	-	-	-	0.101	0.796	0.103	-
18	303.15	0.102	9.167	-	-	-	0.101	0.796	0.103	-
19	313.15	0.11	9.167	-	-	-	0.101	0.796	0.103	-
20	313.15	0.11	8.32	-	-	-	0.006	0.873	0.121	-
21	303.15	0.102	3.929	-	-	-	0.101	0.796	0.103	-
22	303.15	0.102	2.357	-	-	-	0.101	0.796	0.103	-
23	303.15	0.102	1.571	-	-	-	0.101	0.796	0.103	-
24	784.18	1.621	1.571	-	-	-	0.101	0.796	0.103	-
25	298.15	0.102	0.234	1	-	-	-	-	-	-
26	875.83	0.102	3.341	0.07	0.047	0.041	0.593	-	-	0.249
27	772.18	0.102	3.498	0.044	0.06	0.114	0.574	-	-	0.208
28	923.15	0.102	4.603	-	0.05	0.044	0.637	-	-	0.269
29	923.15	0.102	3.107	-	0.05	0.044	0.637	-	-	0.269
30	923.15	0.102	1.496	-	0.05	0.044	0.637	-	-	0.269
31	298.15	0.102	0.355	-	-	-	-	0.79	0.21	-
32	305.15	0.105	0.241	-	-	-	-	0.995	0.005	-
33	305.15	0.105	0.072	-	-	-	-	-	1	-
34	1385.78	0.102	1.498	-	-	-	0.687	-	-	0.313
35	380.15	0.102	1.498	-	-	-	0.687	-	-	0.313
36	303.15	0.102	1.498	-	-	-	0.687	-	-	0.313
37	303.15	0.102	0.468	-	-	-	-	-	-	1
38	303.15	0.102	1.031	-	-	-	1	-	-	-
39	303.15	8.106	1.031	-	-	-	1	-	-	-

lists the specific information for Case 2’s primary streams. The entire CO₂ collection rate is 88.16%, while the new system’s thermal efficiency, in this case, is 56.38%.

In order to investigate the effect of the EGR rate (splitter 1, as shown in Figure 3) on the system performance, the SEGR rate (splitter 2, as shown in Figure 3) is kept at 0.7, and the CO₂ utilization rate of MCFC is kept at 0.85. When the EGR rate is raised from 0.4 to 0.7 to keep a consistent turbine inlet temperature, the mass flow of air 1 as the sweep gas decreases, which lowers the gas turbine’s $c_{{\mathrm{O}}_2}$, as shown in Figure 9. With the reduction in the mass flow of air into the combustor, the $c_{{\mathrm{CO}}_2}$ of GT exhaust increases, as shown in Figure 9. The selective CO₂ transfer rate is increased by raising the area of the membrane. Naturally, as shown in Figure 9, when the EGR is maintained constant, and the selective CO₂ transfer rate is raised, the $c_{{\mathrm{CO}}_2}$ of gas turbine exhaust gas rises and the $c_{{\mathrm{O}}_2}$ falls.

The mass flow of CO₂ supplied into the MCFC cathode is decreased when the EGR rate is increased. Both the cell area and the fuel mass flow of MCFC are decreased to maintain a steady rate of CO₂ and fuel usage. Therefore, both the mass flow rates of the CO₂ collected and the system’s overall CO₂ output drop. However, as the effect of the EGR rate rise on the captured CO₂ is greater than the total system CO₂ emission, the overall CO₂ capture rate of the system is reduced, as shown in Figure 10. When the EGR rate is changed, the system’s thermal efficiency is mainly influenced by the MCFC output power, which is determined by the MCFC cell voltage. When the EGR rate is increased from 0.4 to 0.6, the cell voltage is determined by the $c_{{\mathrm{CO}}_2}$, because the $c_{{\mathrm{CO}}_2}$ is obviously smaller than the $c_{{\mathrm{O}}_2}$. As a result, when the EGR rate is increased from 0.4 to 0.6, the thermal efficiency of the system rises with an increase in $c_{{\mathrm{CO}}_2}$, and the slope decreases as the $c_{{\mathrm{O}}_2}$ decreases with the increase in the EGR rate. When the EGR rate is maintained constant and the selective CO₂ transfer rate is increased, the system thermal efficiency increases with a rise in $c_{{\mathrm{CO}}_2}$, as shown in Figure 10. When the EGR rate is increased from 0.6 to 0.7, the cell voltage is determined by the $c_{{\mathrm{O}}_2}$, because the $c_{{\mathrm{O}}_2}$ is obviously smaller than the $c_{{\mathrm{CO}}_2}$. The system’s thermal efficiency, therefore, reduces with the decrease in $c_{{\mathrm{O}}_2}$ when the EGR rate is raised from 0.6 to 0.7; similarly, when the EGR rate is held constant at 0.7, and the selective CO₂ transfer rate is raised, the system thermal efficiency reduces with the decrease in $c_{{\mathrm{O}}_2}$, as illustrated in Figure 10.

In order to investigate the effect of the SEGR rate (splitter 2, as shown in Figure 3) on the system performance, the EGR rate (splitter 1 in Figure 3) is kept at 0.6, and the CO₂ utilization rate of MCFC is kept at 0.85. In order to maintain the turbine inlet temperature constant, the SEGR rate is changed from 0.4 to 0.7, which raises the mass flow of air 1 as the sweep gas and raises the gas turbine’s $c_{{\mathrm{O}}_2}$, as illustrated in Figure 11. With the rise of the mass flow of the air into the combustor, the $c_{{\mathrm{CO}}_2}$ of GT exhaust gas decreases slightly, as shown in Figure 11. The selective CO₂ transfer rate is increased by raising the area of the membrane. Obviously, when the EGR is maintained constant, and the selective CO₂ transfer rate is raised, the $c_{{\mathrm{CO}}_2}$ of gas turbine exhaust gas rises and the $c_{{\mathrm{O}}_2}$ decreases, as shown in Figure 11.

As was indicated before, as the SEGR rate is raised, the mass flow of CO₂ fed to the MCFC cathode decreases, which lowers the system’s overall CO₂ capture rate. When the SEGR rate is changed, the system’s thermal efficiency is mainly influenced by the MCFC output power, which is determined by the MCFC cell voltage. When the SEGR rate is increased from 0.4 to 0.7, the cell voltage is determined by the $c_{{\mathrm{O}}_2}$, as the $c_{{\mathrm{CO}}_2}$ is not influenced significantly. Therefore, the system’s thermal efficiency rises with the increase in $c_{{\mathrm{O}}_2}$ when the SEGR rate is increased from 0.4 to 0.7. Because the $c_{{\mathrm{O}}_2}$ is plainly less than the $c_{{\mathrm{CO}}_2}$, as shown in Figure 12, the system’s thermal efficiency decreases with the drop of $c_{{\mathrm{O}}_2}$ when the SEGR rate is maintained at 0.4 or 0.5, and the selective CO₂ transfer rate is raised. Because the $c_{{\mathrm{CO}}_2}$ is visibly less than the $c_{{\mathrm{O}}_2}$ when the SEGR rate is held constant at 0.7 and the selective CO₂ transfer rate is raised, as illustrated in Figure 12, the system thermal efficiency increases as the $c_{{\mathrm{CO}}_2}$ rises.

5.3. Comparison of Different Systems

The MCFC size, current density and OCCR were held constant to compare the overall system thermal efficiencies of the new systems (Case 1 and Case 2) to the reference system. The operating conditions and results are listed in

Table 5. Operating conditions and thermal efficiency of the investigated systems.

	The Reference System	Case 1	Case 2
EGR rate (splitter 1 in Figure 2 or Figure 3)	-	0.5	0.6
SEGR rate (splitter 2 in Figure 3)	-	-	0.7
MCFC CO2 utilization rate	0.85	0.85	0.9
Selective CO2 transfer rate	-	-	0.944
Overall CO2 capture rate (%)	88.16	88.16	88.16
$c_{{\mathrm{CO}}_2}$ of GT exhaust (%mol)	3.84	7.48	9.32
Cell voltage of MCFC (V)	0.59	0.66	0.72
Cell current density (A/m2)	1500	1500	1500
Cell area (m2)	102,245	102,245	102,245
CO2 purity (%)	99.8	99.8	99.8
Overall system thermal efficiency (%)	54.78	55.64	56.08

. In order to ensure the operation of MCFC, there must be enough O₂ mass flow in the GT exhaust gas that fed into the MCFC cathode, which makes that the recirculation rate of the EGR system is not over 0.5 and that of the SEGR system is not over 0.7. With the same total CO₂ capture rate of 88.16%, Table 5 demonstrates that Cases 1 and 2 have thermal efficiencies that are 1.81% and 2.89% greater than the reference system, respectively. In reference [14], NGCC integrated with MCFC using turbine exhaust gas recirculation is studied. With 60% of exhaust gas at the turbine outlet put back into the air at the compressor inlet, the $c_{{\mathrm{CO}}_2}$ at the MCFC cathode input is raised to 5.71% mol, which can validate the correctness of the results obtained in this paper. It can also be seen that, compared with the recirculation of the turbine exhaust gas in reference [14], the recirculation of the MCFC cathode exhaust gas in this paper raises the $c_{{\mathrm{CO}}_2}$ at the MCFC cathode inlet higher.

6. Economic and Environment Performance Evaluation

This section compares the environmental and economic performances of new systems to those of the reference system. The cost of energy (COE) and the cost of CO₂ avoided (CCA) are the main economic factors considered when comparing different CO₂ collection techniques. The COE is calculated with the IEA methodology [29,30], which sets the net present value (NPV) of the power plant to zero. This can be achieved by varying the per kWh price until the revenues balance all the expenses over the whole lifetime of the power plant. The CCA, USD/${\mathrm{ton}}_{{\mathrm{CO}}_2}$, is described as follows:

$$\mathrm{CCA}=\frac{1000(CO{E}_{{\mathrm{CO}}_2,\mathrm{CAP}}-CO{E}_{\mathrm{REF}})}{EC{O}_{2\mathrm{REF}}-EC{O}_{2{\mathrm{CO}}_2,\mathrm{CAP}}},$$

(32)

Table 6. Staple assumptions for COE evaluation.

Parameters	Value
Discount rate (%) [7]	8
Lifespan (Year) [7]	25
Working hours of the first year (h) [7]	5750
Rest of lifetime operating hours (h) [7]	7500
Membrane replacement cost (USD/m2) [5]	15
Membrane life (Year) [32]	4
$\mathrm{Costs} \mathrm{of} \mathrm{fuel} (\mathrm{USD}/{\mathrm{GJ}}_{\mathrm{LHV}}$) [33]	7.085

displays a few significant presumptions for the COE evaluation.

Table 7. Assessment of economic performance of different systems. (MCFC specific cost = 1891 USD/m²).

Parameters	GSCC System without CO2 Capture [7]	The Reference System	Case 1	Case 2
Power (MW)
GT output	285.85	285.85	275.01	277.12
ST output	133.94	156.48	165.92	161.68
MCFC output	-	90.5	101.5	110.49
CO2 compressor consumption	-	17.76	17.76	17.76
ASU consumption	-	2.24	2.24	2.24
Blower consumption	-	-	-	2.73
Net power	419.79	512.83	522.43	526.56
Overall thermal efficiency (%)	55.94	54.78	55.64	56.08
Economic parameters
Plant component TEC (M$)
GT	62.15	62.15	62.15	62.15
ST	25.26	28.52	29.85	29.64
MCFC	-	193.41	193.41	193.41
HRSG	27.93	40.73	41.26	39.3
Membrane	-	-	-	18.47
Heat rejection	30.19	45.86	46.62	44.48
BOP	0.23	16.12	16.53	17.55
ASU	-	5.82	5.82	5.82
CO2 compressor	-	16.78	16.78	16.78
TEC (M$)	145.76	409.39	412.42	427.6
EPC (M$)	279.16	812.82	828.62	850.22
TPC (M$)	321.04	934.74	952.91	977.75
IDC (M$)	22.47	65.43	66.7	68.44
TPI (M$)	343.51	1000.18	1007.31	1046.2
Specific total plant cost (USD/kW)	764.76	1822.71	1802	1856.86
COE components (USD/MWh)
Capital	11.43	27.32	27.21	27.77
Fixed O&M	4.64	5.13	5.09	5.25
Consumables	0.71	6.19	6.07	6.48
Fuel	44.08	46.56	45.08	44.20
COE (USD/MWh)	60.86	85.2	83.45	83.7
CO2-specific emission (g/kWh)	352.38	44.74	43.30	42.19
$\mathrm{Cost} \mathrm{of} {\mathrm{CO}}_2 \mathrm{avoided} (\mathrm{USD}/{\mathrm{ton}}_{{\mathrm{CO}}_2})$	-	79.12	73.08	73.63

presents the comparing findings. The price per square foot for MCFC is fixed at 1891 USD/m² [31].

The COE values of the new systems are substantially higher when compared to those of other systems, as shown in Table 7. Compared with the CCA of the traditional mono-ethanol ammine (MEA) method for CO₂ capture [34], the CCA values for the new systems in this paper are higher. Due to the high expense of MCFC, this viewpoint is short-term. The cost of MCFC will decrease as MCFC technology develops [35].

According to Figure 13, the cost of CO₂ avoided by the system with CO₂ capture by MCFC will be equal to the CCA of the GSCC system with CO₂ capture by the MEA technique if the MCFC cost is reduced from the present 1891 USD/m² to 707.6 USD/m². The cost of CO₂ saved in Case 2 will be equal to the CCA of the system with the MEA technique for CO₂ capture if the MCFC cost is reduced from the present 1891 USD/m² to 904.4 USD/m² [33]. Figure 14 demonstrates that the COE for the system with MCFC-based CO₂ capture will be equal to that of the system using the MEA technique for CO₂ capture when the MCFC cost is reduced from the present 1891 USD/m² to 705.7 USD/m². When the MCFC cost is reduced from the current 1891 USD/m² to 897.6 USD/m², the COE for the system with MCFC and SEGR for CO₂ collection will be equivalent to that of the system with the MEA method for CO₂ capture [33]. As a result, the cost of the MCFC-specific equipment strongly influences whether the new system’s COE or CCA will drop.

7. Conclusions

This study proposes new CO₂ recovery integrated gas turbine, MCFC, EGR and SEGR systems. Compared to the GSCC system coupled with MCFC and CO₂ collection without EGR, the new technologies are more effective (the reference system). The thermal efficiency of the GSCC system combined with MCFC and CO₂ collection with EGR is 55.64% when the OCCR is 88.16%, and it is 56.08% when the system is also integrated with EGR and SEGR. The thermal efficiencies of new systems are higher compared with the reference system. The thermal efficiency of the new GSCC system integrated with MCFC and CO₂ capture with EGR is 0.3% lower than that of the original GSCC system without CO₂ capture, and the thermal efficiency of the new GSCC system integrated with MCFC and CO₂ capture with EGR and SEGR is 0.14% higher than that of the original GSCC system without CO₂ capture.

• For case 1, when the EGR is raised from 0 to 0.5, the $c_{{\mathrm{CO}}_2}$ of the GT exhaust is increased from 3.84% to 7.48%, and the system thermal efficiency is increased; when the $U_{{\mathrm{CO}}_2}$ of MCFC is raised from 0.45 to 0.95, the overall CO₂ capture rate of the system is increased from 51.6% to 97.3%;
• For case 2, when the EGR is raised and SEGR is kept constant, the overall capture rate is reduced, and the system thermal efficiency is firstly raised and then reduced. When the EGR is maintained constant and SEGR is raised, the overall capture rate is reduced, and the system thermal efficiency is raised;

Due to the high cost of MCFC at the moment, the new system does not offer obvious advantages in terms of technical or economic performance. The benefit of the MCFC-based CO₂ capture system and upcoming technological advancements will assist in improving its economic performance.