CO2 Compression Research Articles

Modeling of the Production of Lipid Microparticles Using PGSS® Technique.

Solid lipid microparticles (SLMPs) are attractive carriers as delivery systems as they are stable, easy to manufacture and can provide controlled release of bioactive agents and increase their efficacy and/or safety. Particles from Gas-Saturated Solutions (PGSS®) technique is a solvent-free technology to produce SLMPs, which involves the use of supercritical CO2 (scCO2) at mild pressures and temperatures for the melting of lipids and atomization into particles. The determination of the key processing variables is crucial in PGSS® technique to obtain reliable and reproducible microparticles, therefore the modelling of SLMPs production process and variables control are of great interest to obtain quality therapeutic systems. In this work, the melting point depression of a commercial lipid (glyceryl monostearate, GMS) under compressed CO2 was studied using view cell experiments. Based on an unconstrained D-optimal design for three variables (nozzle diameter, temperature and pressure), SLMPs were produced using the PGSS® technique. The yield of production was registered and the particles characterized in terms of particle size distribution. Variable modeling was carried out using artificial neural networks and fuzzy logic integrated into neurofuzzy software. Modeling results highlight the main effect of temperature to tune the mean diameter SLMPs, whereas the pressure-nozzle diameter interaction is the main responsible in the SLMPs size distribution and in the PGSS® production yield.

Evaluation of supercritical CO2 compressor off-design performance prediction methods

A supercritical CO2 (S–CO2) Brayton cycle has a compact and simple layout, which suggests the possibility to serve as a small scale distributed power conversion system. Off-design behaviors of each component determine the system off-design performance in the S–CO2 power cycle. Among components, compressor performances have the largest impact on the system off-design analysis since it operates nearest to the critical point of CO2. In the system analysis, the off-design performance of a compressor is usually pre-calculated for the fixed inlet conditions. The performance map is then converted for the off-design performances prediction using corrected mass flow rate and corrected rpm. Similitude models are used for the conversion. Several similitude models have been developed mostly for air conditions previously, but the applicability of these models to S–CO2 still needs to be tested. In this paper, to evaluate the existing models for the S–CO2 conditions, experimentally validated 1D mean-line code is used to generate wide range of S–CO2 compressor data set. As a result of the evaluation, Pham model showed the most accurate enthalpy rise prediction resulting in the best pressure rise prediction, and the efficiency prediction could be modified with density correction to improve the off-design performance prediction.

Conceptual design and performance analysis of a novelCHPsystem integrated with solid oxide fuel cell and supercriticalCO2partial preheating cycle

The paper proposes a novel combined heating and power (CHP) system integrated with solid oxide fuel cell (SOFC) and supercritical CO2 (SCO2) partial preheating cycle to improve the energy utilization rate by employing the SCO2 cycle to recover the waste heat from the SOFC. The SCO2 partial preheating cycle can not only improve the net output power but also preheat the air supplied to the SOFC for enhancing the system efficiency. Sensitivity analysis is implemented to study the influences of six key parameters (ie, fuel flow rate, excess air ratio, fuel utilization factor, CO2 turbine inlet temperature, CO2 compressor pressure ratio, and CO2 split ratio) on the proposed system in terms of thermodynamic behaviors. And then the optimal operating conditions for the different objectives are determined by parametric optimization. The results indicate that the optimal overall electrical efficiency and CHP efficiency of the proposed system are 72.84% and 83.83% respectively, while the exergy efficiency can achieve 70.84%. Furthermore, the best trade-off result is obtained with the energy output of 434.71 kW and the exergy efficiency of 64.28%. Finally, the investigation demonstrates the fuel flow rate is the most sensitive parameter which should be determined with the comprehensive consideration of the efficiency and energy output, and the lower excess air ratio and higher CO2 turbine inlet temperature are preferred for power generation.

Thermodynamic and techno-economic assessment of pure and zeotropic fluid ORCs for waste heat recovery in a biomass IGCC plant

The present study includes a thermodynamic and techno-economic assessment of Organic Rankine Cycle (ORC) for waste heat recovery (WHR) from three types of waste heat sources in biomass-fuelled integrated gasification combined cycle (BIGCC) plants equipped with carbon capture and storage (CCS). These include (1) the air separation unit (ASU) air compression intercoolers, (2) the CCS CO2 compression intercoolers and (3) syngas cooler at the water gas shift reactor outlet. The use of ORCs operating with pure working fluids and zeotropic mixtures is investigated. In each scenario, the optimal cycles that maximize plant efficiency improvement are determined and are subsequently economically evaluated. Among the three, the syngas cooling integration scenario leads to the highest plant efficiency improvement (2.81%) and best economic performance, showing a levelized cost of electricity (LCOE) and discounted payback period (DPP) of 35.42–35.67 €/MWhe and 5.7–5.8 years. Meanwhile, if all three heat sources are utilized, an efficiency improvement of 4.61% is achieved, while the corresponding LCOE and DPP are about 49.76–51.08 €/MWhe and 9.3–9.7 years. In all scenarios, the best thermodynamic and economic results are obtained by ORCs operating with mixtures. Despite their thermodynamic superiority, however, zeotropic ORCs have a relatively small economic advantage over pure fluid cycles.

Controlling the Fluid Induced Instability of a Supercritical CO2 Compressor Supported by Magnetic Bearing

Since sCO₂ (Supercritical Carbon Dioxide) turbomachinery are generally small and operate at high rotational speed, the bearings remain a significant challenge to the design of the turbomachinery for the sCO₂ power cycles. However, a fluid induced instability similar to the oil whirl may occur even with the magnetic bearing under high pressure and high speed conditions of the sCO₂ turbomachinery. This paper presents experimental investigation on the instability of a sCO₂ compressor supported by the magnetic bearing. First, we introduce the sCO₂ compressor supported by the magnetic bearing. The procedure to guarantee the rotordynamic performance of the sCO₂ compressor supported by the magnetic bearing is provided. Then, the effects of the working condition such as the pressure and rotating speed on the fluid induced instability are investigated experimentally. Finally, a strategy to resolve the fluid-induced instability with conventional PID control is proposed and experimentally verified.

Hydrogenation of polyethylene terephthalate to environmentally friendly polyester over Vulcan XC-72 carbon supported Rh-Pt bimetallic catalyst

This study demonstrates the direct hydrogenation of polyethylene terephthalate (PET) dissolved in 1,1,1,3,3,3-hexafluro-2-propanol to environmentally friendly polyester polyethylene-1,4-cyclohexanedicarboxylate (PECHD) using a Vulcan XC-72 supported Rh-Pt bimetallic catalyst synthesized via a polyol method. The hydrogenation of PET was promoted by RhOx species present on the catalyst support surface which was generated using the polyol synthesis method. As compared to the monometallic Rh catalyst, the Rh-Pt bimetallic catalyst was found to be superior for hydrogenation of PET. This superiority was attributed to the strong aromatic ring adsorption ability of Rh working in synergy with an increased H2 spillover by Pt. At a H2 pressure of 6.89 MPa and 50 °C for 60 min, complete hydrogenation of PET to PECHD was achieved over the Rh-Pt bimetallic catalyst possessing theoretical Rh and Pt metal loadings of 2.5 wt% each. PECHD was found to be recovered to a very high extent using the compressed CO2 anti-solvent technique after hydrogenation of PET.

Fused deposition modeling of hierarchical porous polyetherimide assisted by an in-situ CO2 foaming technology

This work provides a novel approach to manufacture hierarchical porous parts via an in-situ foaming fused deposition modeling (FDM) method. The cell nucleation, growth, and stabilization occurred as the CO2-saturated polyetherimide (PEI) filament was heated, and the layer-by-layer deposition of porous strands was controlled by a planned path. The microporous structure with cell size of 2–30 μm and cell density of 1010−11 cells/cm3 was generated inside and on the surface of the porous PEI strand, and the macroporous structure with size of about 1–50 mm was constructed within the porous PEI honeycombs and cylinder. The compressed CO2 exhibited extremely slow diffusivity in PEI filaments, and the stable CO2 content ensured that the hierarchical porous PEI part could be 3D printed with high accuracy for a long time.

Analysis of a hybrid transcritical CO2 vapor compression and vapor ejector refrigeration system

The paper presents analysis of a hybrid transcritical CO2 (T-CO2) refrigeration cycle coupled with a heat-driven vapor ejector refrigeration cycle. The heat generated by compression of CO2 in the transcritical vapor compression refrigeration system (VCRS) is utilized to drive the secondary vapor ejector refrigeration system (VERS). The performance of the hybrid system is evaluated by maintaining identical evaporator temperatures for both T-CO2 VCRS and VERS. Cooling capacity and COP of the VERS is influenced by heat recovered from T-CO2 system, thus, limiting the choice of working fluids for the VERS. Analytical model based on conservation of mass, momentum and energy, incorporating real gas behavior is used for arriving at an optimum ejector geometry used in the VERS. Amongst the five fluids analyzed, R32 is found to be most suitable for the VERS used in the hybrid system. R32 provides the highest coefficient of performance (COP) and cooling capacity by recovering maximum heat from the generator, while, other fluids yield nearly identical performance. The proposed hybrid system using R32 provides significant improvement in system performance ranging from 10 to 50% in cooling capacity over the baseline T-CO2 system for the range of evaporating temperatures from −2.5 °C to 12.5 °C.

Experiments on vapour-liquid equilibrium of CO2-ionic liquid under flow conditions and influence on its refrigeration cycle

CO2 is a potential alternative refrigerant because of its excellent thermodynamic properties and environmental friendliness, but its high operating pressure in the refrigeration cycle limits its wide application. To reduce the operational high pressure of the conventional CO2 compression refrigeration system, a novel CO2 compression-absorption refrigeration system with ionic liquid (IL) as absorbent was proposed. The IL [emim][Tf2N] was selected and combined with CO2 as a working pair. Experimental investigations on the dynamic vapour-liquid equilibrium of CO2-[emim][Tf2N] under flow conditions and the influence on its refrigeration cycle were conducted. The effects of solution pump frequency, CO2 inlet temperature and pressure, and system pressure ratio on the key parameters such as depressurization amplitude, absorption completion and desorber temperature were investigated. Within the working conditions of this study, the system operational high pressure could be reduced by 29% at most, and the absorption completion of CO2-IL mixture at the absorber outlet could reach about 70%. It was found that both CO2 inlet pressure and temperature had important effects on the key parameters, and a larger pressure ratio could obtain larger depressurization amplitude and absorption completion and lower desorption temperature. These provide a reference for further optimizing system design and improving system performance.

Optimization of energy requirements for CO2 post-combustion capture process through advanced thermal integration

The energy optimization modeling work described here was performed to determine efficiency improvements that could be achieved for existing coal-fired power plants to retrofit a partial CO2 capture from the post-combustion flue gas for carbon sequestration through thermal integration. The work presented includes optimization of the mono-ethanol amine (MEA)-based post-combustion CO2 capture to reduce energy requirements that could be achieved at existing power plants by thermal integration of the steam turbine cycle, boiler, CO2 compression train and post-combustion CO2 capture process to offset efficiency and capacity losses that would be incurred by retrofit or implementation of post-combustion CO2 capture. Partial CO2 capture, involving treatment of less than 100% of the flue gas leaving the plant and modular design of the CO2 scrubbing system, was also investigated. Thermal integration of the steam turbine cycle with boiler and CO2 compression train improved cycle and plant performance and offset, in part, the negative effects of post-combustion CO2 capture. The best-analyzed integration options improved gross power output by 5% and net unit efficiency by 1.57%, relative to the conventional MEA process. Operating with 40% CO2 capture increased gross power output by 11.6–14% (depending on the MEA thermal integration option), relative to the conventional MEA integration and 90% CO2 capture. The improvement in net unit performance is larger compared to the improvement in turbine cycle performance because of the CO2 compression work, which is also reduced by partial CO2 capture.

Measurement and modeling of nitrogen oxides absorption in a pressurized reactor relevant to CO2 compression and purification process

The removal of nitrogen oxides under a high pressure has been widely accepted as an effective method for the treatment of oxy-fuel combustion flue gas. The high pressure promotes the oxidation of NO to NO2, subsequently removed by water to form nitric acid. However, both the measurement and modeling of nitrogen oxides absorption shows uncertainties. To quantify the nitrogen mass balance, gas-phase NO/NO2 and HNO2 were measured online, whereas liquid-phase HNO2 and HNO3 were analyzed offline. Nitrogen mass balance was achieved with a relative error within ±8%. To improve modeling accuracy, a novel multiparameter optimization method was proposed. Mass transfer coefficients of NO2/NO, rate constant of NO oxidation, surface area, and volume of liquid were optimized. The absorption of NO2 into a liquid was dominated by gas-phase mass transfer with the mass transfer coefficient decreasing from 1.77 × 10―4 mol m−2 s-1 Kpa-1 to 1.26 × 10―4 mol m−2 s-1 Kpa-1 with the increase of reactor pressure from 5 bar to 20 bar. The pressure dependent rate constant for NO oxidation agreed with gas-phase NO oxidation experimental measurement. It first decreased with the reactor pressure from 5 bar to 15 bar followed by an increase from 15 bar to 20 bar. The surface area of liquid decreased while the liquid volume increased with the rising reactor pressure indicating that liquid droplets were formed by gas bubbling and attached onto the inner surface of the reactor. This study resolved the uncertainties in measurement and modeling of the nitrogen oxides absorption process.

Integration of solar thermal energy to improve NGCC with CO2 capture plant performance

A large percentage of CO2 emissions are due to the combustion of fossil fuels for electricity generation. While a transition away from coal towards natural gas will reduce CO2 emissions, an even greater reduction in CO2 emissions can be achieved by retrofitting natural gas combined cycle (NGCC) plants with post-combustion CO2 capture (PCC) systems. A typical NGCC plant equipped with PCC was modeled in Aspen Plus and validated against similar models generated by the National Energy Technology Laboratory (NETL), and then adjusted to match the conditions of a plant located at Poza Rica, Mexico. After validation of the NGCC plant model with PCC, heat integration options were considered where heat from the flue gas cooler, CO2 dryer, and CO2 compressor intercoolers was used for heating of feedwater or low pressure (LP) steam in the steam cycle. The model was further modified to include solar-assisted carbon capture (SACC), to offset the detrimental impact of the PCC system on plant operations. The use of parabolic trough solar thermal collectors for heating of the stripper reboiler in the PCC system was considered in the Aspen Plus modeling. It was found that by using solar thermal energy for PCC reboiler heating, the LP steam extraction used to supply heat to the carbon capture reboiler element could be reduced in flow rate or eliminated depending on the quantity of solar thermal energy available. Modeling showed that if 100 % of the reboiler duty could be supplied via solar thermal energy, net plant power would increase significantly relative to the case without solar thermal collectors. The availability of the solar resource was also predicted for the target location in Mexico using the System Advisor Model (SAM) developed by the National Renewable Energy Laboratory (NREL). By coupling the modeling results from SAM with those produced by Aspen Plus, annual plant energy production for an NGCC plant with PCC and using solar thermal energy for reboiler heating was found. A final case was modeled in both Aspen and SAM, where solar thermal energy was used for LP steam heating. While this case has marginally better performance than the case where solar thermal heat was applied to the reboiler, the added complexity of this system outweighs the slight increase in net annual power generation. This modeling effort demonstrated that solar thermal heating of the stripper reboiler in an NGCC plant with PCC could meaningfully offset the detrimental impact of carbon capture on plant efficiency and power generation loss, offering an attractive renewable energy option to NGCC carbon mitigation.

Measurement and modeling of nitrogen oxides absorption in a pressurized reactor relevant to CO2 compression and purification process

The removal of nitrogen oxides under a high pressure has been widely accepted as an effective method for the treatment of oxy-fuel combustion flue gas. The high pressure promotes the oxidation of NO to NO2, subsequently removed by water to form nitric acid. However, both the measurement and modeling of nitrogen oxides absorption shows uncertainties. To quantify the nitrogen mass balance, gas-phase NO/NO2 and HNO2 were measured online, whereas liquid-phase HNO2 and HNO3 were analyzed offline. Nitrogen mass balance was achieved with a relative error within ±8%. To improve modeling accuracy, a novel multiparameter optimization method was proposed. Mass transfer coefficients of NO2/NO, rate constant of NO oxidation, surface area, and volume of liquid were optimized. The absorption of NO2 into a liquid was dominated by gas-phase mass transfer with the mass transfer coefficient decreasing from 1.77 × 10−4 mol m−2 s−1 Kpa−1 to 1.26 × 10−4 mol m−2 s−1 Kpa−1 with the increase of reactor pressure from 5 bar to 20 bar. The pressure dependent rate constant for NO oxidation agreed with gas-phase NO oxidation experimental measurement. It first decreased with the reactor pressure from 5 bar to 15 bar followed by an increase from 15 bar to 20 bar. The surface area of liquid decreased while the liquid volume increased with the rising reactor pressure indicating that liquid droplets were formed by gas bubbling and attached onto the inner surface of the reactor. This study resolved the uncertainties in measurement and modeling of the nitrogen oxides absorption process.

Evaluation of CO2 production for enhanced oil recovery from four power plants

Abstract Four coal-based power plants were evaluated with respect to their capacity to produce CO2 for Enhanced Oil Recovery (EOR). The plant characteristics were evaluated using energy and exergoeconomic criteria and a robust coal gasification/combustion mathematical model that can predict temperature, converted fraction and particle size distribution for solids have been used for a high pressure fluidized bed. Other models based on Python, Aspen Hysys and Microsoft Excel have been used too. Integrating carbon sequestration reduces the global energy and exergy efficiencies of all power plants (up to 10%). However, the Integrated Gasification Combined Cycle (IGCC) is a promising technology utilizing coal for generating electrical energy and direct compression of CO2 (11–20 MPa). Similarly, integrating gasification with Solid Oxide Fuel Cells (SOFC), allows for the pre-combustion capture of CO2, with the advantage of lower initial investment costs. The oxy-fuel combustion (OXY) plant offers high energy and exergy efficiencies, but the exergoeconomic cost of CO2 is increased by 31 USD/t as compared to IGCC. The conventional thermoelectric (CT) plant exhibit disadvantages due to their simple power cycle and the elevated initial investment costs. This suggests that coal-gasification based plants are the best alternatives for CO2 production for EOR and co-generated electrical power.

Geoelectrical characterisation of CO2\u2013water systems in porous media: application to carbon sequestration

Carbon sequestration is a promising method for the reduction of carbon dioxide (CO2) emissions as it permits the storage of compressed CO2 in the subsurface. The carbon sequestration sites must be monitored to detect potential leaks; one possible method involves the monitoring of geoelectrical properties such as electrical conductivity (σb) and dielectric constant (εb). This investigation focuses on using a time domain reflectometry (TDR) sensor to determine the influence of different factors on the measurements of the electrical conductivity (σb) and dielectric constant (εb) of a porous rock reservoir in relation to the soil water saturation (Sw). The factors investigated were presence of surfactant, salt concentration, pH and rock type which are unique to a given storage site. A number of dynamic two-phase flow experiments were performed using gaseous CO2. It was found that salt concentration, rock type and presence of a surfactant had a notable effect on the σb–Sw and εb–Sw relationships. Higher salt concentrations were found to give higher values for σb and εb for given Sw values. Limestone was found to result in the highest values of both σb and εb for any given Sw, followed by silica and basalt samples. The presence of a surfactant resulted in higher values for σb at higher Sw values and lower values for σb at lower Sw values compared to the case when no surfactant was present. Surfactant presence also resulted in lower values for εb at given Sw values. Initial pH values (with silica sand) were found to have no significant effect on the σb–Sw and εb–Sw relationships. The measurements of σb and εb indicate that the use of TDR presents a viable monitoring option. Furthermore, statistical analysis using non-linear regression was carried out on the experimental results and the model shows a good reliability in the prediction of the monitoring process in geological carbon sequestration.

Optimization and comparison of the two promising oxy-combustion cycles NET Power cycle and Graz Cycle

Carbon capture and storage (CCS) is considered an effective measure to reduce the anthropogenic CO2 emissions. Oxy-combustion with a theoretical capture rate of 100% is a very promising CCS technology. In order to show the potential of oxy-combustion two highly-efficient power cycles, the NET Power cycle and the Graz Cycle, are thus thermodynamically optimized and compared at full load for firing with natural gas.The simulation of both cycles is carried out using the thermodynamic simulation software IPSEpro. Particular attention is paid to provide the same boundary conditions and assumptions for both processes to ensure a correct comparison. As a starting point a base case for each cycle is simulated based on the literature data. Both power cycles are then optimized by varying the main cycle parameters using a genetic algorithm. The optimized processes show a slightly higher net efficiency considering oxygen supply and CO2 compression for the Graz Cycle with 53.5% compared to 52.7% for the NET Power cycle. Moreover, the main differences of both cycles are discussed and the impact of assumptions of component losses and efficiencies as well as the minimum cycle temperature on both cycles is discussed.

Life cycle energy, emissions and cost evaluation of CO2 air source heat pump system to replace traditional heating methods for residential heating in China: System configurations

Heat pump is an efficient method to substitute traditional boilers for cleaner space heating. A new configuration of CO2 heat pump system integrated with vapor injection and dedicated mechanical subcooling (VIDMS) is proposed, and compared with five configurations of CO2 heat pump system and three traditional heating methods. The life cycle model of energy consumption, pollutant emissions, and economic performance is developed. Assessment is conducted by taking seven typical cities located in different climate regions of China as scenarios. Coefficient of performance (COP) of VIDMS system is superior to other transcritical CO2 systems, and the COP is enhanced more notably in the case of severe cold or cold regions. The COP reaches up to 2.13 at the low ambient temperature of −20 °C, 36.51% higher than the baseline (BASE) CO2 system. The primary energy consumption (PEC) of the other five CO2 systems and coal-fired boiler (CFB) can decrease by 4.15–18.26% and 19.27%, respectively, when VIDMS is adopted. Moreover, the PEC reduction is more prominent when used in severe cold region. Life cycle climate performance (LCCP) decreases significantly by employing VIDMS compared with other transcritical CO2 systems and traditional heating methods. CO2 emissions can be reduced by 13.81–23.20% and 16.56–34.31% in contrast to BASE and CFB, respectively. Furthermore, the gaseous (NOx and SO2) and particulate matter (PM2.5 and PM10) emissions also decrease. Life cycle cost (LCC) by using VIDMS is much lower than the other transcritical CO2 systems. The payback period is reduced from 5.58 to 3.55 years if the price of electricity and CO2 compressor are both reduced by 20%. The new proposed VIDMS is a more promising CO2 heat pump solution to replace traditional heating methods.

Techno-Economic Assessment of a Combined Heat and Power Plant Integrated with Carbon Dioxide Removal Technology: A Case Study for Central Poland

The objective of this study is to assess the techno-economic potential of the proposed novel energy system, which allows for negative emissions of carbon dioxide (CO2). The analyzed system comprises four main subsystems: a biomass-fired combined heat and power plant integrated with a CO2 capture and compression unit, a CO2 transport pipeline, a CO2-enhanced geothermal system, and a supercritical CO2 Brayton power cycle. For the purpose of the comprehensive techno-economic assessment, the results for the reference biomass-fired combined heat and power plant without CO2 capture are also presented. Based on the proposed framework for energy and economic assessment, the energy efficiencies, the specific primary energy consumption of CO2 avoidance, the cost of CO2 avoidance, and negative CO2 emissions are evaluated based on the results of process simulations. In addition, an overview of the relevant elements of the whole system is provided, taking into account technological progress and technology readiness levels. The specific primary energy consumption per unit of CO2 avoided in the analyzed system is equal to 2.17 MJLHV/kg CO2 for biomass only (and 6.22 MJLHV/kg CO2 when geothermal energy is included) and 3.41 MJLHV/kg CO2 excluding the CO2 utilization in the enhanced geothermal system. Regarding the economic performance of the analyzed system, the levelized cost of electricity and heat are almost two times higher than those of the reference system (239.0 to 127.5 EUR/MWh and 9.4 to 5.0 EUR/GJ), which leads to negative values of the Net Present Value in all analyzed scenarios. The CO2 avoided cost and CO2 negative cost in the business as usual economic scenario are equal to 63.0 and 48.2 EUR/t CO2, respectively, and drop to 27.3 and 20 EUR/t CO2 in the technological development scenario. The analysis proves the economic feasibility of the proposed CO2 utilization and storage option in the enhanced geothermal system integrated with the sCO2 cycle when the cost of CO2 transport and storage is above 10 EUR/t CO2 (at a transport distance of 50 km). The technology readiness level of the proposed technology was assessed as TRL4 (technological development), mainly due to the early stage of the CO2-enhanced geothermal systems development.

Parametric Process Design and Economic Analysis of Post-Combustion CO2 Capture and Compression for Coal- and Natural Gas-Fired Power Plants

For the envisaged large number of commercial-scale carbon capture and storage (CCS) projects that are to be implemented in the near future, a number of issues still need to be resolved, the most prominent being the large capital and operational costs incurred for the CO2 capture and compression process. An economic assessment of the capture and compression system based on optimal design data is important for CCS deployment. In this paper, the parametric process design approach is used to optimally design coal and natural gas monoethanolamine (MEA)-based post-combustion CO2 absorption–desorption capture (PCC) and compression plants that can be integrated into large-scale 550 MW coal-fired and 555 MW natural gas combined cycle (NGCC) power plants, respectively, for capturing CO2 from their flue gases. The study then comparatively assesses the energy performance and economic viabilities of both plants to ascertain their operational feasibilities and relative costs. The parametric processes are presented and discussed. The results indicate that, at 90% CO2 capture efficiency, for the coal PCC plant, with 13.5 mol.% CO2 in the inlet flue gas, at an optimum liquid/gas ratio of 2.87 kg/kg and CO2 lean loading of 0.2082 mol CO2/mol MEA, the CO2 avoidance cost is about $72/tCO2, and, for the NGCC PCC plant, with 4.04 mol.% CO2 in the inlet flue gas, at an optimum liquid/gas ratio of 0.98 kg/kg and CO2 lean loading of 0.2307 mol CO2/mol MEA, the CO2 avoidance cost is about $94/tCO2.

Cost Analysis of Direct Air Capture and Sequestration Coupled to Low-Carbon Thermal Energy in the United States.

Negative emissions technologies will play an important role in preventing 2 °C warming by 2100. The next decade is critical for technological innovation and deployment to meet mid-century carbon removal goals of 10-20 GtCO2/yr. Direct air capture (DAC) is positioned to play a critical role in carbon removal, yet remains under paced in deployment efforts, mainly because of high costs. This study outlines a roadmap for DAC cost reductions through the exploitation of low-temperature heat, recent U.S. policy drivers, and logical, regional end-use opportunities in the United States. Specifically, two scenarios are identified that allow for the production of compressed high-purity CO2 for costs ≤$300/tCO2, net delivered with an opportunity to scale to 19 MtCO2/yr. These scenarios use thermal energy from geothermal and nuclear power plants to produce steam and transport the purified CO2 via trucks to the nearest opportunity for direct use or subsurface permanent storage. Although some utilization pathways result in the re-emission of CO2 and cannot be considered true carbon removal, they would provide economic incentive to deploying DAC plants at scale by mid-century. In addition, the federal tax credit 45Q was applied for qualifying facilities (i.e., producing ≥100 ktCO2/yr).