Post-combustion Capture System Research Articles

Optimizing lean and rich Vapor compression with solar Assistance for post-combustion carbon capture in natural gas-fired power plant

The integration of post-combustion capture (PCC) CO2 technologies with power plants and high-emission industrial processes has become imperative for reducing carbon emissions and mitigating environmental impacts. This study focuses on addressing the significant energy consumption associated with PCC and explores the potential of using solar thermal energy to optimize configurations, thereby enhancing sustainability and reducing dependency on conventional power sources. Simulate various configurations under steady-state conditions using Aspen HYSYS V11 and Aspen Economic Evaluation software. The results indicate a substantial reduction in energy consumption to 2.1 GJ/ton CO2 after the initial optimization steps. The key innovations involve the integration of Lean Vapor Compression (LVC), Solvent Split Flow (SSF), Rich Solvent Recycle (RSR), and Rich Vapor Compression (RVC). Further optimization was conducted by integrating a reboiler with parabolic trough collectors (PTC), to reduce energy penalties. The LVC + RVC + RSR + SSF + PTC configuration results reveal a notable improvement in exergoeconomic factors, ranging from 3.13% to 7.8%, highlighting the economic feasibility of the optimized configurations. Simultaneously, the energy penalty decreased by 11.1%, signifying enhanced sustainability in the proposed PCC system. This study contributes to the gap in research by demonstrating the efficacy of solar thermal energy in optimizing PCC configurations, providing a pathway towards more sustainable and energy-efficient solutions for carbon capture in high-emission industrial sectors. The findings offer insights for researchers, engineers, and policymakers aiming to address the pressing issue of carbon emissions from industrial processes.

A hydrate-based post-combustion capture system integrated with cold energy: Thermodynamic analysis, process modeling and energy optimization

Carbon capture is a crucial part of global warming mitigation. Carbon capture via clathrate hydrate is an attractive approach due to its high capture capacity, high carbon dioxide purity, water-based benign process, ease of recycling, and robustness to contaminants. In this work, we propose a two-stage hydrate-based carbon dioxide separation system integrated with cold energy for carbon capture from flue gases. A thermodynamic cycle consisting of two sub-cycles was constructed to simulate the process. Operating conditions were optimized within the range of 274.15–282.15 K and 0.1–28.04 MPa, resulting in the lowest electricity consumption of 2.22 MJ/kg CO2 with 95.24 mol% CO2 purity and 65.97 % CO2 recovery. A higher CO2 recovery rate can be achieved by recycling the residual gas of Sub-cycle 2. Gas compression to the high operating pressure (16.01 MPa) is the major contributor to electricity consumption. By incorporating 100 % expansion work recovery from the high-pressure gases, the electricity consumption can be reduced to 0.43 MJ/kg CO2 (i.e., 0.119 kWh/kg CO2). A more realistic scenario assuming 80 % compression/pumping efficiency and 90 % expansion work recovery gives an electricity consumption of 1.16 MJ/kg CO2 (i.e., 0.322 kWh/kg CO2), representing an energy penalty of 33.1 % for a coal-fired power plant. Future direction for further improvement could be a paradigm shift to hydrate process with thermodynamic promoters, which can potentially reduce the operation pressure by over 90 % and thus cut down the energy consumption dramatically. This work established a framework to simulate the hydrate-based carbon capture process, evaluated its minimum energy consumption and examined how operating conditions affect the separation performance. The results could offer valuable guidelines for the design and optimization of real hydrate-based carbon capture systems.

Techno-economic comparison of optimized natural gas combined cycle power plants with CO2 capture

Natural gas combined cycle (NGCC) power plants account for a large share of the global energy market. Although many alternative layouts of NGCC plants have already been addressed in the scientific literature, there are still relevant gaps of knowledge in comparative techno-economic performances of the previously proposed alternatives. This article presents a comprehensive comparative study of 19 alternative NGCC power plants with pre-combustion, post-combustion or oxy-fuel combustion CO2 capture processes involving different choices of CO2 absorbents and organic Rankine cycles for energy savings. The purpose of this study is to shed light on comparative techno-economic performances of power plants with different CO2 capture strategies and various organic Rankine cycle configurations. First, performance of each alternative was optimized from a technical (equivalent work) standpoint. Then, the economic performance of each optimized alternative was evaluated. Based on the results within the sample of NGCC plants, using activated methyldiethanolamine could lead to better technical and economic performances than monoethanolamine in pre- and post-combustion capture systems. Moreover, the efficacy of organic Rankine cycles for enhancing the technical and economic performance of NGCC plants with CO2 capture was shown, with a reduction of up to 1.39 years in the payback period for various process configurations.

Optimization and energy assessment of technological process for CO2 capture system of natural gas and coal combustion

Flue gas stream generated from combusted natural gas, petroleum, and coal in power plants contains enormous CO2 with detrimental effects on the environment. CO2 capture systems must be integrated into these power plants to prevent emissions of CO2 into the open atmosphere. This work uses rate-based process modelling and a parametric design approach to optimally design large-scale amine-based PCC and compression systems that can be integrated into real 550 MW coal-fired and 555MW NGCC fired power plants. A comparative analysis of energy and economy is also conducted. Based on monoethanolamine (MEA), the process parameters of the post-combustion capture and compression system for CO2 were used as the study baseline. Different amines and alternative flow scheme optimization of the post-combustion capture with compression models are developed for coal and natural gas combined cycle (NGCC) cases and their energy consumption performances compared. Also, the operating and capital costs of the CO2 Capture and Storage (CCS) plant are determined for the overall process of economic evaluation concerning technical and economic performance parameters. The results show that rich solvent cooled recycle (RSR) and lean vapour compression (LVC) process modification under the integration case of CO2 capture and compressed Coal, energy savings of 20.4%, 41.8% and 34.8% for MEA, piperazine activated methyldiethanolamine solution (MDEA+PZ) and piperazine activated monoethanolamine (MEA+PZ) respectively, is possible when compared with the basic situation of MEA. RSR+LVC process modification under the integration case of CO2 capture and compressed NGCC, energy savings of 18.9%, 35.4% and 34.4% for MEA, MDEA+PZ and MEA+PZ, respectively, is possible when compared with the basic situation of MEA. Economic performance: the total annual operating costs of MDEA+PZ, RSR+LVC technological process optimized for the coal case was reduced by approximately 30% compared with the basic situation of MEA, while that for the NGCC case was reduced by 19%. The cost of CO2 avoided for the coal used MDEA+PZ into RSR+LVC technological process optimized capture is decreased by 13% compared with coal captured in MEA basic situation. For the NGCC cases, the cost of CO2 avoided for the NGCC of MDEA+PZ, RSR+LVC process optimized capture is decreased by 7% compared with NGCC with MEA basic case capture.

Experimental Investigation on Carbon Dioxide Reduction by Using Post Combustion Carbon Capture System in a Spark-Ignition Engine

Global warming is a serious environmental concern that affects humans, wildlife, and ecosystems. Carbon dioxide reduction is the need of the hour as it a major constituent of global warming. The quantum of carbon dioxide released in the exhaust depends on the number of carbon atoms present in the fuel used. The present study investigates the reduction of engine out carbon dioxide emission. For carbon dioxide reduction post combustion capture sys- tem is used. In post combustion capture system carbon dioxide is absorbed by using absorption catalyst. In this capture system, carbon dioxide is absorbed after the combustion. Among various absorption catalyst, monoethanolamine (MEA) is used, as it can react more quickly with carbon dioxide than other absorbents. Monoethanolamine is continuously injected in the exhaust mani- fold. Empty chamber is added in the exhaust manifold for increasing the resi- dent time of the reaction of amine with carbon dioxide. MEA reacts with carbon dioxide forms ammonium carbamate. Carbamate is approved by the Environ- mental Protection Agency as an inert ingredient, used for insect and rodent control in areas where agricultural products are stored.

Energy assessments of onboard CO2 capture from ship engines by MEA-based post combustion capture system with flue gas heat integration

An early phase feasibility study was carried out for offshore CO2 capture from ship engines of a CO2 transport ship. A flexible in-house process simulator was applied in the assessments. Parametric studies of the overall onboard process were enabled by a fast data-driven capture plant model derived from supervised machine learning by PLS regression of a large dataset of rigorous simulations. The results show, based on the given models and assumptions, that the thermal energy coming from the ship engine exhaust gas is not sufficient alone to cover the thermal energy demand of an absorption-based CO2 capture unit operating above 50% capture rate using 30 wt% MEA (mono-ethanolamine) as solvent. The thermal energy demand can be met using a fuel afterburner as heat source. The added fuel consumption is estimated to increase the fuel consumption by 6–9% when operating with liquefied natural gas (LNG) as fuel source, while an increase of 8–12% is expected with diesel as fuel source. The effect of absorber height on energy consumption at a given CO2 capture rate is limited, especially for lower capture rates, and may be an important degree of freedom for optimizing the CAPEX/OPEX trade-offs. Use of state-of-the art solvents with lower specific energy consumptions will shift the results towards higher capture rates before a fuel afterburner is required to meet the thermal energy demands.

The energy demand and environmental impacts of oxy-fuel combustion vs. post-combustion capture in China

Oxy-fuel combustion is one of the clean coal combustion technologies for CO2 capture. However, post-combustion capture is studied as a challenged technology against oxy-fuel combustion. This paper presented the life cycle assessment (LCA) of these two CO2 capture technologies used in the 300 MW coal fired power plant. The purpose was to identify and quantify the energy demand and the environmental impacts of oxy-fuel combustion throughout its whole life cycle and compared the results with post-combustion capture by an amine (MEA) absorbent. The results showed an increase in cumulative energy demand in oxy-fuel combustion compared with post-combustion capture. Total life cycle energy consumption of oxy-fuel combustion system was more 0.065 MJ than post-combustion capture system. However, oxy-fuel combustion can reduce 0.00047 mPET2000 of global warming, 0.04084 mPET2000 of acidification, 0.04486 mPET2000 of eutrophication, 0.001 mPET2000 of photochemical ozone formation and 0.35082 mPET2000 of slag and ashes compared with post-combustion capture. The total environmental impact loading (EIL) of oxy-fuel combustion to produce 1 kWh of electric energy was 9.06382 mPET2000, which was less than that of post-combustion capture (9.50181 mPET2000), indicating that the oxy-fuel combustion can play a relatively important role in reducing environmental impacts.

Selective Exhaust Gas Recycling in Gas Turbines with CO2 capture: A comprehensive technology assessment

Modern gas turbines operate with large amounts of excess air for cooling and dilution of the combustion gases, in order to maintain gas turbine blade integrity. Selective recycling of CO2 into the gas turbine compressor inlet, also referred as Selective Exhaust Gas Recirculation (SEGR), can reduce the large volumetric flow rate through a CO2 capture system caused by the gas turbine excess air requirements, by 70 - 77%. It also increases CO2 concentrations to 14-18 vol% from 3-4% vol, increasing the driving force for post-combustion capture systems. This paper provides a comprehensive assessment of the concept and presents research outcomes from the UK-funded SELECT project, including power plant and process modelling, techno-economic assessments, pilot-scale gas turbine experimental work and experimental combustion tests on a representative combustor. Using an integrated model of turbomachinery, power cycles and a generic post-combustion CO2 capture technology with a 30%wt MEA solvent, we show that a reduction of up to 50% of the absorber of the capture plant – the most capital intensive part of the process – can be achieved. The compressor and gas turbine operate without any significant deviation from their design point, and a marginal increase of 0.5% point in the net electrical efficiency can be achieved. Pilot-scale testing - conducted at the Pilot Scale Advanced Capture Technologies (PACT) facilities at the University of Sheffield - show that CO2 injection at the compressor inlet of a 100 kW micro gas turbine (mGT) connected to a 1 tonne per day CO2 capture plant reduces net electrical efficiency by 1-2 %point. This is caused by lower flame temperatures, and, unlike in larger gas turbines, the control system of the micro gas turbine. Combustion tests at Cardiff University’s Gas Turbine Research Centre (GTRC) in a pilot-scale high-pressure generic premixed swirl burner, representative of modern dry-low emissions (DLR) gas turbine burners, show the effect of CO2 as diluent on the operational premixed CH4/air flame stability, chemical kinetics and measured exhaust gas composition. CO2 acts as a combustor inhibitor, causing downstream migration of the premixed flame zone, leading to eventual blow-off, instability and extinction, requiring a change in the operation equivalence ratio. The effect of adding CO2 leads to a reduction in the adiabatic flame temperature due to thermal quenching, which results in higher CO emissions and smaller thermal NOx emissions. Increasing pressure has a significant reducing effect on CO emissions, yet it results in higher NOx production, which may require mitigation if this trend is found to continue towards pressures approaching that of the F-class gas turbine. Finally, a conceptual design assessment of a regenerative adsorption wheel with structured adsorbents is proposed for the selective recycling of CO2 in combined cycle gas turbine (CCGT) power plants. It has the advantage of a relatively small pressure drop to reduce the derating of the gas turbine compared to selective CO2 membrane systems. An equilibrium model of a rotary adsorber with commercially available activated carbon adsorbents shows that four rotary wheels of 24 m diameter and 2 m length would be required in an 820MW CCGT plant. A reduction of 50% in the mass of adsorbent would be possible with an adsorbent with a higher capacity, such as Zeolite X13, with upstream dehydration of the flue gases.

The mutual benefits of renewables and carbon capture: Achieved by an artificial intelligent scheduling strategy

Renewable power and carbon capture are key technologies to transfer the power industry into low carbon generation. Renewables have been developed fast, however, the intermittent nature has imposed higher requirement for the flexibility of the power grid. Retrofitting carbon capture technologies to existing fossil-fuel fired power plants is an important solution to avoid the “lock-in” of emissions, but the high operating costs hinders their large scale application. The coexistence of renewable power and carbon capture opens up a new avenue that the deployment of carbon capture can provide additional flexibility for better accommodation of renewable power while excess renewables can be used to reduce the operating costs of carbon capture. To this end, this paper proposes an artificial intelligence based optimal scheduling strategy for the power plant-carbon capture system in the context of renewable power penetration to show that the mutual benefits between carbon capture and renewable power can be achieved when the carbon capture process is made fully adjustable. An artificial intelligent deep belief neural network is used to reflect the complex interactions between carbon, heat and electricity within the power plant carbon capture system. Multiple operating goals are considered in the scheduling such as minimizing the operating costs, renewable power curtailment and carbon emission, and the particle swarm heuristic optimization is employed to find the optimal solution. The impacts of carbon capture constraint mode, carbon emission penalty coefficient, carbon dioxide production constraints and renewable power installed capacity are investigated to provide broader insight on the potential benefit of carbon capture in future low-carbon energy system. A case study using real world data of weather condition and load demand shows that renewable power curtailment can be reduced by 51% with the integration of post-combustion capture systems and 35% of total carbon emission are captured by the use of excess renewable power through optimal scheduling. This paper points out a new way of using artificial intelligent technologies to coordinate the couplings between carbon and electricity for efficient and environmentally friendly operation of future low-carbon energy system.

Transient CO2 capture for open-cycle gas turbines in future energy systems

In complex electricity systems with a varied generation mix, the security of supply is important, and the quick-response nature of gas turbines is invaluable in providing system flexibility. Accompanied with post-combustion capture (PCC) of CO2, gas turbines can support the transition to a future low-carbon electricity system. This study presents the development and validation of a dynamic rate-based model of the benchmark CO2 absorption process, using 30 wt% monoethanolamine (MEA). The model is scaled up from pilot-scale to match the flue gas output from a modern small-scale gas turbine operating in open-cycle configuration. Simulations of various flexible operating scenarios shows the rapid transitioning between full and partial load is beneficial in delivering higher time-averaged CO2 capture rates, compared to the Baseload scenario where the PCC system is operated at full load for 5 h. Maintaining a constant liquid/gas (L/G) ratio results in 90.01% CO2 capture; however, this increases the energy demand due to constant reboiler steam flowrate. To compensate, the steam flowrate is also ramped, resulting in a small decrease in reboiler duty compared to the Baseload scenario. Importantly, no negative energy or capture rate related issues to highly-transient PCC operation are found.

U.S. DOE/NETL large pilot-scale testing of advanced carbon capture technologies

The mission of the United States (U.S.) Department of Energy/National Energy Technology Laboratory (DOE/NETL) Carbon Capture Program is to develop the next generation of advanced CO2 capture concepts for the power-generation sector. The Carbon Capture Program employs a down-selection process that graduates technologies from a large portfolio of laboratory/bench-scale projects to a smaller set of small-scale pilot projects and eventually to an even smaller group of large-scale pilot projects. At every scale, computer simulation plays a significant role in guiding experimental efforts and accelerating the overall pace of technology development. This down-selection process serves to de-risk industrial investment, given that there is insufficient information generated at the laboratory/bench scale to confidently predict eventual commercial success.The Carbon Capture Program is currently engaged in efforts to advance the next generation of capture technologies to large pilot scale. Three capture technologies have been awarded Phase I projects in a competition to build large-scale pilots for advanced energy and post combustion capture systems. In addition, six capture technologies are working toward large-scale pilot testing at Technology Center Mongstad in Norway. Advances along three innovation pathways—materials, processes, and equipment—have been critical in preparing these technologies for large pilot-scale testing.This paper describes the approach that is being followed by the Carbon Capture Program to advance the technologies and provides brief descriptions of the technical innovations that have prepared individual technologies for large pilot-scale testing.

Investigation of novel Pistacia khinjuk biodiesel in DI diesel engine with post combustion capture system

The exploration of new renewable based alternative fuel to the conventional fossil fuel research gains more attention due to increase in cost and environmental effect. The present study focused on obtaining new alternative fuel from non-edible oil namely Pistacia khinjuk seed oil using transesterification process. The fatty acid composition of neat biodiesel was evaluated using Gas Chromatography Mass Spectrometry method. Pistacia khinjuk methyl ester (PKME) was blended with diesel and investigated in the diesel engine. Diesel showed better performance characteristics than PKME blends due to its low calorific value and density. At all loads, PKME blends exhibited lower engine exhaust emissions than diesel. On the other hand, increasing trend of brake specific oxides of nitrogen (BSNO) was noticed with PKME blends. In order to minimize the emission without compromising performance parameters, Post-combustion Capture System (PCS) was installed in tail pipe. At all loads, diesel and PKME blends were individually investigated with PCS. Due to presence of selective catalytic reduction in PCS unit, B20 sample showed lower BSNO emission than diesel and other blends. Higher in-cylinder pressure and heat release rate were observed with PKME blends. In addition, B20 showed better engine characteristics than other blends proximate to mineral diesel.

Application of ITM to improve the efficiency of SOFC/GTCC triple combined cycle with carbon capture

Carbon capture and storage processes are being researched to reduce carbon dioxide emissions from power plants. This paper proposes a new system that applies an ion transport membrane (ITM) to a triple combined cycle, which includes the gas turbine combined cycle and a solid oxide fuel cell. Two systems which differ in the method of utilization of the fluid that is separated by the ion transport membrane were compared. Then, the better system was determined, and its performance characteristics were analyzed in detail. The operating temperature of the fuel cell and the pressure ratio of the compressor were varied within the operating conditions of the ITM as the main design variables. The performance of the proposed system was compared with that of a post-combustion system and other oxy-fuel combustion capture systems. The proposed system had 1.70% and 4.0%p higher power and efficiency than the post-combustion capture system, respectively. Furthermore, the purity of the carbon dioxide captured from the proposed system was 97.4%, which is 9.1%p higher than that of the semi-closed cycle oxy-fuel combustion system, while the efficiency was 7.8%p higher.

A sequential approach for the economic evaluation of new CO2 capture technologies for power plants

This paper describes a simplified method to estimate the cost of CO2 avoided for a power plant with a novel CO2 capture system based on only a limited number of fundamental input parameters used to establish basic mass and energy flows for the plant. The cost calculation method follows a sequential approach, estimating first the cost and efficiency penalty impacts of those elements of the plant that are standard and well characterized. We then define the cost gap allowed for the novel elements to break even against a benchmark plant. This method allows one to estimate: (i) the maximum cost reduction potential that a novel CO2 capture technology can achieve with respect to a benchmark technology, and (ii) target breakeven costs for technology developers in the form of combinations of CAPEX and OPEX for a novel capture technology needed to make the technology competitive with the benchmark system. Case studies are presented applying the proposed method to post-combustion and oxy-combustion capture systems, showing that: (i) a clear relationship exists between the breakeven costs and the efficiency penalty caused by the CO2 capture process, mainly because of its effect on the specific capital cost ($/kWe) of the conventional power plant components; and (ii) the minimum cost of CO2 avoided is closely related to the capture system efficiency penalty. For the case study assumptions, avoidance costs vary from ∼20 $/tCO2 to ∼60 $/tCO2 for efficiency penalties ranging from 2.7% pts to 11% pts, respectively.

Reducing the water usage of post-combustion capture systems: The role of water condensation/evaporation in rotary regenerative gas/gas heat exchangers

Water usage is expected to greatly increase when CO2 capture is added to thermal power plants. A major contribution is the reduction of flue gases temperatures from 100 to 150 °C to 30–50 °C. The majority of studies to date propose the use of direct contact cooling, combining a cold water loop with water cooling. This article expands on a previous study of the same authors (Herraiz et al., 2015) proposing dry air-cooled options with rotary regenerative gas/gas heat exchangers, relying on ambient air as the cooling fluid, to eliminate the use of process and cooling water prior to the carbon capture system. It proposes, for the first time, a new stand-alone model of a bi-sector air/gas rotary heat exchanger, which includes the contribution to heat transfer of condensation/evaporation when flue gases are cooled below the dew point. It shows that water condensation from the flue gases in one sector of the heat exchanger, enhances the total heat transfer rate, due to the diffusion of water through the non-condensable gases boundary layer. In order to maintain the cooling capacity of these rotary regenerative heat exchangers, initially designed to operate without condensation, this article shows that they should be designed with surface properties, gas velocities and heat transfer channel geometries with the aim of allowing water condensate to remain on the metal elements surface, and then evaporate into the air stream when the metal elements have rotated to the air side. The model also predicts the location of water condensation, so that enamelled elements can be incorporated to the cold-end tiers of metal elements and mitigate any possible long-term corrosion problems.

Mitigation of carbon footprints through a blend of biofuels and oxygenates, combined with post-combustion capture system in a single cylinder CI engine

Abstract Mitigation of carbon footprints in compression ignition (CI) engines can be achieved using biofuels (carbon neutral and carbon dioxide (CO2) sequestration effects), with oxygenates and effective post-combustion capture systems. The present study focuses on the net reduction of CO2 emissions through the combination of karanja oil methyl ester (KOME), orange oil (ORG), oxygenates blended fuel and zeolite-based post-combustion capture system (ZPCS) in a single cylinder CI engine. KOME emitted higher CO2 emissions as compared to the diesel. Blending equal volume of ORG with KOME reduced CO2 emissions further by 27% compared to KOME but still higher compared to diesel by 11%, at 100% load condition. Four oxygenates, namely methanol (M), ethanol (E), n-butanol (B) and n-pentanol (P) were blended 20% by volume with the KOME-ORG. KOME-ORG + M20 emitted minimum CO2 compared to other oxygenate blends due to stoichiometric carbon balance, about 38% less compared to KOME nearly reaching diesel emission characteristics at 100% load. Additionally ZCPS was placed in the exhaust line and tested with all oxygenate blends with KOME-ORG, methanol blend led to 65% reduction in CO2 emissions compared to KOME and 53% reduction compared to diesel, at 100% load.

Effect of electrochemical conversion of biofuels using ionization system on CO2 emission mitigation in CI engine along with post-combustion system

Global warming caused by greenhouse gas emission is a major threat in recent times. Carbon dioxide (CO2) is a major source of greenhouse gas emission from CI engine. The present study aims to investigate the effect of pre-combustion, oxygenate and post-combustion system with biofuel blends in single cylinder CI engine on CO2 emission. All the experiments were conducted in a single cylinder CI engine with 5.2 kW rated power at 1500 rpm at 50% and 100% load. Diesel is replaced with Karanja oil methyl ester (KOME) and both are taken as baseline data. Low carbon biofuel namely orange oil (ORG) was blended on an equal volume basis with KOME and tested. Zeolite based post-combustion capture system (ZPCS) and fuel ionization filter (FIF) as pre-combustion capture system was tested along with 20% methanol (M) blend with KOME-ORG. FIF electrochemically ionizes the fuel molecules and aids in quick dispersion of the ions for improved combustion. Hydrocarbon based biofuels are converted to carbon, hydrogen and oxygen ions, where hydrogen takes part in combustion and oxygen enhances the combustion process. At 100% load, CO2 emission for KOME-ORG + M20 + FIF + ZPCS is 68% less compared to KOME. The combination also reduces NO and smoke by 48% and 51% compared to KOME at 100% load. The combined effect of FIF, ZPCS and methanol aided in the simultaneous reduction of NO, smoke and CO2 emission.

Design, process simulation and construction of a 100 kW pilot-scale CO2 membrane rig: Improving in situ CO2 capture using selective exhaust gas recirculation (S-EGR)

Carbon capture and storage (CCS) from natural gas-fired systems is an emerging field and many of the concepts and underlying scientific principles are still being developed. Preliminary studies suggest this approach can boost the CO2 content in the feed gas up to 3 times compared to the ‘no recycle’ case (CO2 concentration increased to 18% vs. 6%), with a consequent reduction in flow to the post-combustion capture unit by a factor of three compared to conventional, non-S-EGR. For this project, Cranfield University developed a pilot-scale 100 kW CO2 membrane rig facility in order to investigate simultaneously EGR and S-EGR technologies, the latter being achieved by using a CO2 sweep air polymeric membrane. A bench-scale membrane rig has also been developed to investigate the permeability and selectivity of different polymeric membranes to CO2. Currently a small-scale polydimethylsiloxane (PDMS) membrane module is also being investigated to study its selectivity/permeability. The tests include exploring the performance improvement of the PDMS membrane using different operating conditions with a view to developing scale-up procedures for the membrane unit for the actual 100 kW pilot-scale rig.Process simulations were performed using Aspen Plus software to predict the behaviour of the pilot-scale rig using a model developed based on empirical parameters (i.e., mass transfer coefficient of CO2 through the membrane and permeance), measured in the bench-scale membrane test unit. The results show that CO2 concentrations of up to 14.9% (comparable to CO2 level in coal combustion) can be achieved with 60% EGR, with a 90% CO2 removal efficiency of the membrane units. However, the results generated with the membrane model in which specific permeance values to PDMS were applied, predicted concentrations of CO2 in flue gases up to 9.8% (v/v) for a selective recycle of 60%. The study shows that the S-EGR technique is an effective method that can provide similar conditions to that of a coal-fired power plant for the post-combustion capture system operating on natural gas-fired units, but also highlights the fact that more research is required to find more suitable materials for membranes that optimise the CO2 removal efficiencies from the flue gas.

Considerations in the Development of Flexible CCS Networks

This paper discusses considerations for the design of flexibly operated Carbon Capture and Storage (CCS) pipeline networks and is based on the findings of the Flexible CCS Network Development project (FleCCSnet), funded as part of the UK CCS Research Centre. The project considered the impact of flexibility across the whole CCS chain, as well as studying the interfaces between each element of the system; e.g. at the entry to the pipeline system from the capture plant and at the exit from the pipeline to the storage site. The factors identified are intended to allow CCS network designers to determine the degree of flexibility in the system; allowing them to react effectively to short, medium and long term variations in the flow of CO2 from capture plants and the constraints imposed on the system by CO2 injection and storage.The work of the project is reviewed in this paper which explores the flexibility of power plants operating with post combustion capture systems; quantifies the available time to store (line pack) CO2 in the pipeline as a function of pipeline size, the inlet mass flow rate and operating pressure; and explores the influence that uncertainty in injection and storage parameters have on the design of the pipeline. In addition, parameters influencing short and longer term network designs are discussed in terms of varying flow rates. Two practitioner workshops [1,2] contributed to the direction of the project. The first workshop identified and confirmed key questions to be considered in order to understand the most likely impacts of variability in both the CO2 sources and CO2 sinks on CO2 transport system design and operation. The second workshop focused on transient issues in the pipeline and storage site.Although the case studies in the work are UK based, this work is applicable to other situations where large and small sources of CO2 are expected to be feeding into a CCS transportation system. The work is expected to inform a broad range of stakeholders and allow network designers to anticipate potential problems associated with the operation of a CCS network. For an effective design of CCS infrastructure, all of the factors that will have a substantial impact on CO2 flow will have to be analysed at an early stage to prevent possible bottle necks in the whole chain.

CCS on Offshore Oil and Gas Installation - Design of Post-Combustion Capture System and Steam Cycle

Most of the released CO2 on offshore oil and gas installation originates from the gas turbines that power the installations. For certain offshore installations, CO2 capture and storage (CCS) could be an alternative to decrease the CO2 emissions. When opting for a chemical absorption CO2 capture system, a heat source for the stripper reboiler is needed. Since most offshore installations are powered by simple cycle GTs, there is typically no steam available that could be used for stripper reboiler heat. A compact steam bottoming cycle could, in addition to providing the reboiler steam, partly or fully provide power from a steam turbine generator to the equipment in the CCS system, including CO2 compressors, pumps, and flue gas booster fan. Three different steam cycle configurations were designed, modeled, and simulated. The design of the post-combustion CO2 capture system is also presented but the main focus in the paper is on the steam cycle design. In addition to the energy and mass balance results, a weight assessment of the major equipment was done with the objective to come up with a simplified weight relationship for changes in the oil and gas installation size in terms of changes in total mass flow from the gas turbines. A steam cycle with a back-pressure steam turbine was ultimately selected. The back-pressure option was able to provide all necessary steam and power (with some margin) to the CO2 capture and compression system.