Economic Evaluation of Carbon Capture and Utilization Applying the Technology of Mineral Carbonation at Coal-Fired Power Plant

Based on the operating data of a 40 tCO2/day (2 megawatt (MW)) class carbon capture and utilization (CCU) pilot plant, the scaled-up 400 tCO2/day (20 MW) class CCU plant at 500 MW power plant was economically analyzed by applying the levelized cost of energy analysis (LCOE) and CO2 avoided cost. This study shows that the LCOE and CO2 avoided cost for 400 tCO2/day class CCU plant of mineral carbonation technology were 26 USD/MWh and 64 USD/tCO2, representing low LCOE and CO2 avoided cost, compared to other carbon capture and storage CCS and CCU plants. Based on the results of this study, the LCOE and CO2 avoided cost may become lower by the economy of scale, even if the CO2 treatment capacity of the CCU plant could be extended as much as for similar businesses. Therefore, the CCU technology by mineral carbonation has an economic advantage in energy penalty, power plant construction, and operating cost over other CCS and CCU with other technology.


Introduction
Carbon dioxide (CO 2 ) emissions in the atmosphere from anthropogenic activities continue to grow worldwide [1][2][3], as CO 2 emissions in the period 2010 to 2014 grew about 31.9 to 35.5 GtCO 2 per year, an average rate of 2.75% per year [4], escalating global warming. Various studies have been made to mitigate carbon emission to hold average global warming below 2 • C above pre-industrial levels [5,6]. Carbon capture and storage (CCS) and carbon capture and utilization (CCU) are evaluated by the International Energy Agency (IEA) and U.S. Energy Information Administration (EIA) as two of the most cost-effective methods for climate change mitigation among various technologies [7]. CCS permanently captures and stores CO 2 to reduce greenhouse gas from coal-fired power plants or cement manufacturing facilities [8]. CCU involves chemical reaction, converting CO 2 into valuable chemical compounds [9].
CCU by mineral carbonation technology, also called CO 2 mineralization, is a less explored method of sequestering CO 2 compared to other CCS methods, such as geological sequestration [10][11][12], ocean disposal [13][14][15], and biological fixation [16][17][18]. Mineral carbonation involves the chemical conversion of CO 2 to solid inorganic carbonates permanently fixing carbon with a negligible risk of return to the atmosphere without having a great impact on the surrounding environment and ecosystems [19,20].
As CCS and CCU are relatively recent technologies, their effectiveness still needs to be analyzed. Large-scale CCS projects were mostly based on enhanced oil recovery, whereby CO 2 is used to obtain the last remains of an oil field by injection of gaseous, liquid, or supercritical CO 2 into subsurface reservoirs inducing the geological storage of CO 2 in porous rocks, which was proved to be effective for cutting the CO 2 emission but still remains to be studied for their cost-effectiveness compared to others technologies [21][22][23]. Also, IEA has published a research report, "cost and performance of carbon dioxide capture from power generation, IEA, 2011," comparing the economic feasibility of CCS-applied technologies (post-combustion, pre-combustion, oxy-combustion) between the levelized cost of energy analysis (LCOE) and CO 2 avoided cost [24]. The economic evaluation of CCS has been made on the assessment method of the expectation of the energy penalty for applying CCS technology [25], comparing LCOE and CO 2 avoided cost for applied CCS technology (supercritical, ultra-supercritical, integrated gasification combined cycle (IGCC), oxy-combustion, natural gas combined cycle (NGCC)) at power generation on economic aspects [26].
On the other hand, the economic evaluation of CCU focused on sales profit from selling CO 2 compounds produced from applying CCU technology or on the life cycle assessment (LCA) [27]. One analyzed a manufacturing technology of high-valued compounds, sodium bicarbonate (NaHCO 3 ), through carbon dioxide carbonization, and the result of the internal rate of return for 20 years was 67.2% [28]. Techno-economic assessment of CO 2 utilization was studied by applying LCA of the Canadian emerald energy from a waste facility [29]. LCA conducted for a comprehensive analysis of the climate change mitigation potential of CCU, in applying fields such as fertilizer process [30], CO 2 -based polymers used as raw materials for plastics [31], chemical industry [32], and electrocatalytic conversion of CO 2 into commercially-valued products, including carbon monoxide, methane, and methanol [33][34][35].
Most CCS economic evaluation of power generation uses LCOE and CO 2 avoided cost, with the CCS technology by applying the energy penalty when constructing the power generation plant [36,37]. As mentioned previously, CCU economic evaluation focuses on the sales revenue of the resulting CO 2 compounds from the technology [29,38,39]. LCOE represents the average revenue per unit of electricity generated that would be required to recover the costs of building and operating a generating plant during an assumed financial life and duty cycle, CO 2 captured cost is calculated by comparing a capture plant to any reference plant, and CO 2 avoid cost is derived from the equalization of the net present values of costs of the power plant with and without CCUS technology [40].
Based on the operating data and input cost of a 40 tCO 2 /day (2 megawatt (MW)) class CCU pilot plant at a coal-fired power plant, the scaled-up 400 tCO 2 /day (20 MW) class CCU plant at 500 MW coal-fired power plant was economically analyzed by applying the LCOE and CO 2 avoided cost, considering the energy penalty. Moreover, the CCU technology in this study, utilizing the resulting compounds as construction ingredients, has insufficient economic evaluation and comparative studies according to applied technology on the economic evaluation results [19,41]. Here, we have calculated the LCOE and CO 2 avoided cost for mineral carbonation, resulting in 26 USD/MWh and 64 USD/tCO 2 each, and conducted comparative studies with other CCS and CCU technologies, which were higher cost for each factor.
To remind, this paper is structured as follows: Section 2 introduces the methods and technology of applied examination, with the detailed explanation of the components and the process; Section 3 gives detailed information on the experiment results with the analysis of LCOE and CO 2 avoided cost; Section 4 shows the comparison of the economic analysis between the applied technology in this study and other CCU technologies, and also include sensitivity analysis; Section 5 addresses the conclusion on the applied CCU technology.
The following subjects were considered to increase the accuracy of this research, and a comparative analysis was conducted between the resulting economic outcomes and other CCS or CCU references.

1.
Considering the energy penalties resulting from the CCU plant at a 500 MW coal-fired power plant.

2.
Application of the actual operational data of a 40 tCO 2 /day (2 MW) class pilot plant installed at a 500 MW coal-fired power plant. For the 400 tCO 2 /day (20 MW class) CCU plant installed at a 500 MW coal-fired power plant that manages the economic evaluation, apply the estimated price of equipment based on the actual preliminary design.

5.
By applying the levelized cost of energy analysis (LCOE), compare the "CO 2 avoided cost" and "CO 2 captured cost" in similar businesses.

Applied Technology
Mineral carbonation process can effectively utilize the industrial CO 2 emissions to form various products and carbonate precipitates, as it is a thermodynamically favorable reaction. The mineral carbonation using alkaline solid wastes has merits of low feedstock cost and availability near the source of CO 2 [27]. The utilization process for this study, CCU of mineral carbonation technology, produces construction ingredients from converting the CO 2 -captured compounds to CaCO 3 through the direct reaction of CO 2 in the flue gas at the coal-fired power plant.
This technology operates a 40 tCO 2 /day (2 MW) class CCU pilot plant at a coal-fired power plant in Korea from November 2017. Inserted partial flue gas, emitted from the power plant duct into the CCU plant, produce CO 2 -captured compounds (CaCO 3 ), and unreacted CO 2 returns to the power plant duct to maintain the CO 2 concentration below 1% in the atmosphere. The applied technology and main equipment configuration are as follows ( Figure 1, Table 1): Sustainability 2020, 12, x 3 of 15 2. Application of the actual operational data of a 40 tCO2/day (2 MW) class pilot plant installed at a 500 MW coal-fired power plant. 3. Application of the actual operational data of the captured CO2 amount collected through a 40 tCO2/day (2 MW) class continuous-capture-process. 4. For the 400 tCO2/day (20 MW class) CCU plant installed at a 500 MW coal-fired power plant that manages the economic evaluation, apply the estimated price of equipment based on the actual preliminary design. 5. By applying the levelized cost of energy analysis (LCOE), compare the "CO2 avoided cost" and "CO2 captured cost" in similar businesses.

Applied Technology
Mineral carbonation process can effectively utilize the industrial CO2 emissions to form various products and carbonate precipitates, as it is a thermodynamically favorable reaction. The mineral carbonation using alkaline solid wastes has merits of low feedstock cost and availability near the source of CO2 [27]. The utilization process for this study, CCU of mineral carbonation technology, produces construction ingredients from converting the CO2-captured compounds to CaCO3 through the direct reaction of CO2 in the flue gas at the coal-fired power plant.
This technology operates a 40 tCO2/day (2 MW) class CCU pilot plant at a coal-fired power plant in Korea from November 2017. Inserted partial flue gas, emitted from the power plant duct into the CCU plant, produce CO2-captured compounds (CaCO3), and unreacted CO2 returns to the power plant duct to maintain the CO2 concentration below 1% in the atmosphere. The applied technology and main equipment configuration are as follows ( Figure 1, Table 1):    After storing mineral powder and slag powder, provide a quantitative influx into the reaction agent dissolved tank, and dissolve it for (30-40) min. → Mix (30-40) min for all of the CaO to react → Transport steam and dust generated from the reaction agent reacting process to the desorption liquid storage tank (no wastewater generation).

CO 2 removal process system
The first removal of CO 2 through reacting agent and gas-liquid contact in the first reaction tower. → Discharge after removing residual CO 2 with the reacting agent in the secondary reaction tower. → Supplement from the secondary reaction tower by the CO 2 -captured transfer pump of the first reaction tower when the chemical agents in the first reaction tower reach below pH 8.5, while reacting with CO 2 in the emission gas. Real-time monitoring and analysis of CO 2 concentration by CO 2 analyzer installed before and after the reaction tower duct. Real-time monitoring and control from the main computer by measuring the temperature, flow rate, flux, and flow pressure.
Captured CO 2 treatment system Some of the generated CO 2 -captured compounds are used as the ingredient of construction materials (bricks, cements block, and so forth) after the dehydrating process in a dehydrator. The remaining undehydrated CO 2 -captured compounds are used as reagent, such as a desulfurization agent. → Effluent from the dehydration process is used as the full chemical reagent manufacturing water, and the deficiency is supplemented with water. → The dehydrated cake is placed in a ton bag for a certain time, and then taken out.

Applied Scale and Process
The applicable field scale for this study, a 400 tCO 2 /day class CCU plant, can be designed by knowing the actual amount of reduced CO 2 from the operating 40 tCO 2 /day class CCU pilot plant, and modifying the operational problems from the pilot plant. Based on this scaled-up field scale plant, the economic evaluation was conducted for a 400 tCO 2 /day class CCU plant. The scaled-up preliminary design of the 400 tCO 2 /day class CCU plant is as follows (Table 2, Figure 2): Preliminary design of machinery, such as ingredients and chemical reagent supply facility, CO 2 removal reacting facility, CO 2 -captured treatment facility, and other process facilities.

Electric measurement and control field
Preliminary design of electric measurement and control field, such as motor control center (MCC) module, electric panel, and process measuring instrument. Therefore, the applied facility and process of this study are as follows (Table 3): Precipitate the CO2-captured in settling tank, supernatant overflows into the supernatant treating tank, and reuse it as process liquid. The residual sediment is sent to the sediment storage pit, and then stacked on the drying bed by excavator. After the sediments are dried, they are taken out to supply the required site. Rain water and domestic wastewater treatment plan Connected treatment of rain water through rain water pipeline into the manufacturing plant rainwater pipeline. Therefore, the applied facility and process of this study are as follows (Table 3):  Rain water and domestic wastewater treatment plan Connected treatment of rain water through rain water pipeline into the manufacturing plant rainwater pipeline. Connected treatment of domestic wastewater through wastewater pipeline into the manufacturing plant wastewater pipeline.
Emission gas capture method Portion of emission gas is captured from the emission gas transfer duct generated during the carbon fuel combustion process.

Cost Calculation of a 500 MW Coal-Fired Power Plant
To conduct the economic evaluation by demonstration plant of the 400 tCO 2 /day class CCU plant, an economic evaluation of a 500 MW coal-fired power plant was first conducted ( Table 4). The applying assumptions are based on the applied data of IEA economic evaluation, and the information provided by the actual domestic power generation companies. The additional capex for installing the 400 tCO 2 /day class CCU plant at the 500 MW coal-fired power plant is based on the 2018 price level, which was also applied for the preliminary design of the 400 tCO 2 /day class CCU plant. The information on additional construction costs is as follows ( Table 5): The additional opex for installing the 400 tCO 2 /day class CCU plant at the 500 MW coal-fired power plant is based on the 2018 electric and water cost, which was also applied for the preliminary design of the 400 tCO 2 /day class CCU plant. The information on additional operating costs is as follows ( Table 6):  Energy penalty caused by the installation of a CCU facility • Increase in the construction cost according to the increased facility capacity by the energy penalty First, to calculate the energy penalty by the installation of a CCU plant, the actual measured electric power consumption of the 40 tCO 2 /day class CCU pilot plant was applied. The electric power consumption per hour of the 40 tCO 2 /day class CCU pilot plant was 0.8 MW. Accordingly, the power consumption for the 400 tCO 2 /day class CCU plant was analyzed to consume 4 MW power by applying the "6-10 power rule." Approximate costs can be obtained if the cost of a similar item of different size or capacity is known. The "6-10 power rule," also called 0.6 rule or six tenth rule, is used for scale-up of the capacity-cost when analyzing the plant economics. This rule has its origins in the relationship between the increase in equipment cost (C) and the increase in capacity (V) given by C 1 /C 2 = (V 1 /V 2 ) α , where α denotes the scale coefficient. The value of α = 0.6 refers to equipment such as tanks and pipes which give significant economies of scale [42]. The electric power consumption for the basic design of the 400 tCO 2 /day class CCU plant was 3.1 MW. The "6-10 power rule" was applied to the relationship between the capacity and the electric power consumption at the 400 tCO 2 /day class CCU plant and the electric power consumption for the basic design. In this regard, the cost analysis was conducted by applying 4 MW, a conservative energy penalty.
Therefore, to secure the sufficient capacity of 500 MW coal-fired power plants, it should be designed as 504 MW in consideration of the energy penalty, which is calculated to be (504 − 500)/504 × 100 = 0.8%.
Additional cost is incurred, as the installation of a 504 MW coal-fired power plant increases the power generation capacity owing to the energy penalty. The additional cost was recalculated according to the "6-10 power rule," which is used for scale-up of the capacity-cost in economic evaluation.

Cost Calculation of the 500 MW Coal-Fired Power Plant Including 400 tCO 2 /day Class CCU Plant
The cost of the 500 MW coal-fired power plant including 400 tCO 2 /day class CCU plant is presented in Table 7 [43]. Further detailed data can be found in Table S1.

CO 2 Captured Efficiency and Utilization Rate
The captured efficiency was calculated based on the actual data of a currently running 40 tCO 2 /day class CCU pilot plant. The utilization rate was calculated through this captured efficiency. The following data is measured data at the site of the 40 tCO 2 /day class CCU pilot plant, and the continuously measured data for more than 20 h in normal operation was applied. The measured data utilized the real-time continuously measured on-site data of flow rate, and CO 2 concentration in the inlet and outlet. The following is the monitoring results from the real-time measuring instrument along the time sequence for every hour from 05/29 14:00 to 05/30 12:00 (Figures 3 and 4).

CO2 Captured Efficiency and Utilization Rate
The captured efficiency was calculated based on the actual data of a currently running 40 tCO2/day class CCU pilot plant. The utilization rate was calculated through this captured efficiency. The following data is measured data at the site of the 40 tCO2/day class CCU pilot plant, and the continuously measured data for more than 20 h in normal operation was applied. The measured data utilized the real-time continuously measured on-site data of flow rate, and CO2 concentration in the inlet and outlet. The following is the monitoring results from the real-time measuring instrument along the time sequence for every hour from 05/29 14:00 to 05/30 12:00 (Figures 3 and 4).   To calculate the utilization rate of the CCU plant, it is necessary to convert the power generating capacity of the 400 tCO2/day class CCU plant. Accordingly, by applying the actual data from a domestic coal-fired power plant, the capacity of the CCU plant was converted based on the captured CO2 amount that could be treated based on the amount of greenhouse gas emissions at the 500 MW coal-fired power plant. A domestic coal-fired power plant emits 6800 tCO2 per 1 MW. Moreover, a 400 tCO2/day class CCU plant captures CO2 of 20 MW power generation capacity. The captured To calculate the utilization rate of the CCU plant, it is necessary to convert the power generating capacity of the 400 tCO 2 /day class CCU plant. Accordingly, by applying the actual data from a domestic coal-fired power plant, the capacity of the CCU plant was converted based on the captured CO 2 amount that could be treated based on the amount of greenhouse gas emissions at the 500 MW coal-fired power plant. A domestic coal-fired power plant emits 6800 tCO 2 per 1 MW. Moreover, a 400 tCO 2 /day class CCU plant captures CO 2 of 20 MW power generation capacity. The captured efficiency was 85.71% and the utilization rate was 4% for a 400 tCO 2 /day class CCU plant among the 500 MW coal-fired power plant emitted CO 2 . As a result, the captured CO 2 utilization rate by a CCU plant was calculated to be 3.43%.

Calculation of the CO 2 Avoided Cost
The "CO 2 avoided" was calculated using the analyzed data from Section 3.4.1. The CO 2 avoided is the amount of avoided (reduced) CO 2 by operating the CCU plant. The following are the CO 2 avoided value (Table 8): As calculated in the above table, the CO 2 avoided was calculated to be 90,304 tCO 2 /year compared to the former coal-fired power plant by the introduction of a 20 MW CCU plant, which can process 400 tCO 2 /day (Table 9):

Comparative Analysis with Other Studies
To sum up, the economic analysis results show that when CO 2 content is 3.43% of captured and utilization, the captured and recovery emission is 117,504 tCO 2 /year, LCOE as 26 USD/MWh, and CO 2 avoided cost as 64 USD/tCO 2 . Table 10 compares the economic analysis of this study and other CCS or CCU technology. Different CCS technologies at coal-fired power plants such as IGCC + CCS, NGCC + CCS, PC supercritical, etc., which can capture and utilize 90% of CO 2 , as compared to have higher LCOE and CO 2 avoided cost, considering the cost for the processes like CO 2 compression, refinement, transport, and storage. Among CCU technologies in Table 10, the Coal-fired power plant (500 MW, 2010, recovery by dry sorbent), Coal-fired power plant (2010, US), and Aluminum production (2013, Norway) were calculated to have smaller LCOE and CO 2 avoided cost than the studied mineral carbonation because they only included the refinement and compression process of CO 2 and did not consider the CO 2 utilization cost. By comparing with a similar study, Coal powered (UK, 600 MW, mineral carbonation), our study resulted to be more economic. Additionally, for precise comparison, they should be compared with the same capacity and CO 2 captured efficiency. However, this study shows the economic analysis results of a 20 MW CCU facility, handling 400 tCO 2 /day based on the operating CCU plant. Therefore, the reliability lowering assumption, such as capacity expansion, and capture amount increase, was not included.

Sensitivity Analysis
The sensitivity of LCOE and CO 2 avoided cost, which were results from the economic analysis, was analyzed as the initial conditions changed ( Figure 5). The sensitivity of LCOE was analyzed according to the alternation of capital expenditure (CAPEX) and operating expenditure (OPEX) cost and the sensitivity of CO 2 avoided cost was analyzed according to the change in CO 2 captured and utilization rate, and energy penalty (Figure 5a). Figure 5b illustrates when CAPEX was altered ±10%, LCOE was ±6.55% altered, and the ±10% OPEX alternation resulted in ± 5.65% alternation of LCOE. ±10% change of energy penalty and CO 2 captured and utilization rate resulted ±0.71% and −9.09~11.11% alternation of CO 2 avoided cost each. LCOE was most affected by the CAPEX and the OPEX also effected the LCOE as it is linked with CAPEX. CO 2 captured and utilization rate affected the CO 2 avoided cost the most, showing greater sensitivity than by the effect of energy penalty alternation.

Conclusions
Using LCOE and CO2 avoided cost, the economic assessment was conducted for the mineral carbonation CCU technology at the coal-fired thermal power plant, which produces CaCO3 through direct reaction with CaO without refinement or compression process for CO2 in the flue gas. In order to increase the accuracy and reliability of this analysis, based on the actual operating data of the 40 tCO2/day class CCU pilot plant, the scaled-up 400 tCO2/day CCU plant factors were used. Furthermore, the additionally generated power capacity from the CCU facility energy penalty was also considered for the economic analysis including coal-fired power plant construction and operating cost. The utilization rate for the CO2 capture of the CCU plant in this study is 3.43%, which represents a lower capacity of CCU compared to similar businesses and the CO2 avoided cost for the 400 tCO2/day class CCU plant applying mineral carbonation technology was 64 USD/tCO2, representing low avoided cost, compared to similar scaled CCS and other CCU plant. However, according to the sensitivity analysis, LCOE was greatly affected by CAPEX, showing 6.55% variation, and CO2 captured and utilization rate was the biggest effect to cause variation to the CO2 avoided cost. Based on this study, the CO2 avoided cost may become lower by the economy of scale, even if the CO2 treatment capacity of the CCU plant could be extended as much as similar businesses. This suggests that CCU technology by mineral carbonation has an economic advantage in energy penalty, power plant construction, and operating cost over other CCS and CCU with other technology.
Also, this economic analysis is based on the actual operation data of CCU plant and has a relatively small CCU plant capacity compared to other studies. Therefore, there is a limitation that CO2 captured and utilization rate is low. However, with further research, we plan to conduct economic analysis on actual large scaled CCU plant and plan to contribute to commercialization of CCU technology.
Supplementary Materials: The following are available online at www.mdpi.com/xxx/s1, Table S1: Economic evaluation of the 500 MW coal-fired power plant installed 400 tCO2/day class CCU plant. The sensitivity analysis represented that the CO 2 avoided cost of the mineral carbonation technology in this study, was greatly affected by the CO 2 captured and utilization rate; however, owing to the low energy penalty of this study, the energy penalty had little impact.

Conclusions
Using LCOE and CO 2 avoided cost, the economic assessment was conducted for the mineral carbonation CCU technology at the coal-fired thermal power plant, which produces CaCO 3 through direct reaction with CaO without refinement or compression process for CO 2 in the flue gas. In order to increase the accuracy and reliability of this analysis, based on the actual operating data of the 40 tCO 2 /day class CCU pilot plant, the scaled-up 400 tCO 2 /day CCU plant factors were used. Furthermore, the additionally generated power capacity from the CCU facility energy penalty was also considered for the economic analysis including coal-fired power plant construction and operating cost. The utilization rate for the CO 2 capture of the CCU plant in this study is 3.43%, which represents a lower capacity of CCU compared to similar businesses and the CO 2 avoided cost for the 400 tCO 2 /day class CCU plant applying mineral carbonation technology was 64 USD/tCO 2 , representing low avoided cost, compared to similar scaled CCS and other CCU plant. However, according to the sensitivity analysis, LCOE was greatly affected by CAPEX, showing 6.55% variation, and CO 2 captured and utilization rate was the biggest effect to cause variation to the CO 2 avoided cost. Based on this study, the CO 2 avoided cost may become lower by the economy of scale, even if the CO 2 treatment capacity of the CCU plant could be extended as much as similar businesses. This suggests that CCU technology by mineral carbonation has an economic advantage in energy penalty, power plant construction, and operating cost over other CCS and CCU with other technology.
Also, this economic analysis is based on the actual operation data of CCU plant and has a relatively small CCU plant capacity compared to other studies. Therefore, there is a limitation that CO2 captured and utilization rate is low. However, with further research, we plan to conduct economic analysis on actual large scaled CCU plant and plan to contribute to commercialization of CCU technology.