This paper provides an insight on state-of-the-art, limits and potentials of pressure swing adsorption (PSA) as CO2 capture technology into power plants. To get a complete picture both post- and ...pre-combustion cases are considered. The expertise developed with modeling and simulation of PSA processes in power plants stressed the need of a holistic approach to the analysis. The different domains which determine the viability of the technology are taken into account, together with their mutual influence. Accordingly, adsorbent materials characteristics, process configurations and integration strategies are investigated and discussed, in order to provide a general evaluation. In post-combustion applications, PSA has been widely assessed with regard to adsorbent materials and processes. The integration into power plant does not entail significant issues, with a good potential for retrofitting old plants. An excessively large footprint of the separation unit has been reported, which seems to question the feasibility of PSA. In pre-combustion applications, prospects for improving adsorbent materials and processes are noticed. Good potential for PSA is envisaged whit hot gas separation processes, especially with sorption-enhanced processes. Furthermore, the complexity of the arrangements in pre-combustion cases may open room for interesting alternative system configurations, like power and H2 coproduction layouts.
In this paper, a gas-fired combined cycle power plant subjected to a pre-combustion CO2 capture method has been analysed under different design conditions and different heat integration options. The ...power plant configuration includes the chemical looping reforming (CLR) of natural gas (NG), water gas shift (WGS) process, CO2 capture and compression, and a hydrogen fuelled combined cycle to produce power. The process is denoted as a CLR-CC process. One of the main parameters that affects the performance of the process is the pressure for the CLR. The process is analysed at different design pressures for the CLR, i.e., 5, 10, 15, 18, 25 and 30 bar. It is observed that the net electrical efficiency increases with an increase in the design pressure in the CLR. Secondly, the type of steam generated from the cooling of process streams also effects the net electrical efficiency of the process. Out of the five different cases including the base case presented in this study, it is observed that the net electrical efficiency of CLR-CCs can be improved to 46.5% (lower heating value of NG basis) by producing high-pressure steam through heat recovery from the pre-combustion process streams and sending it to the Heat Recovery Steam Generator in the power plant.
This paper presents a multi-loop control strategy for a SOFC/GT hybrid system. A detailed dynamic model of the system is presented and its part-load performance is studied. The control objectives are ...discussed, with the main issue being a fairly constant fuel cell temperature under all conditions. Based on the system configuration and part-load performance, input and output variables of the control system are detected. Control cycles are introduced and their design is discussed. The responses of the resulting system on load changes, external disturbances as well as malfunction and degradation incidents are investigated. The system is stable under all incidents. An error in fuel flow measurement or assumed fuel quality provokes a steady-state fuel cell temperature offset. For a degraded system, it may be advisable to readjust the control system to the new characteristics.
•Pressure Swing Adsorption (PSA) is evaluated as a CO2 separation technique.•The layout of coal-fired power plants operating with PSA is defined and modeled.•Process simulations of coal-fired power ...plants are proposed.•PSA shows to be outperformed by absorption in a post-combustion scenario.•PSA attains performance close to absorption in a pre-combustion scenario.
The paper provides with a first assessment on the suitability of Pressure Swing Adsorption (PSA) as a valid option for Carbon Capture and Storage (CCS) in coal-fired power plants. A full-plant analysis of an Advanced SuperCritical (ASC) pulverized coal plant and of an Integrated Gasification Combined Cycle (IGCC) plant, operating with a PSA unit, is presented. The systems selected aim to represent the most diffused options for coal-based power generation, respectively in a post- and pre-combustion application of CO2 separation. The definition of the PSA process is tailored for the two different scenarios considered, starting from the adsorbent selected (zeolite 5A and activated carbon, respectively for post- and pre-combustion). The objective is to investigate the competitiveness of PSA with respect to the benchmark technology for CCS, namely absorption. In order to consider the different aspects measuring the effectiveness of a CO2 separation technique, the performance of the power plants is evaluated in terms of CO2 separation performance, energy efficiency and footprint of the technology. The post-combustion scenario analysis shows that PSA can be competitive with regard to the separation and the energy performance. PSA is able to match the CO2 separation requirements, and the relative energy penalty is slightly lower than that resulting from amine-absorption. Despite that, the footprint of the PSA unit demonstrates to be way larger than that related to absorption and unlikely acceptable. PSA in the pre-combustion scenario returns more encouraging results, approaching the outcomes achieved with absorption both in terms of CO2 separation performance and plant energy efficiency. The footprint, even though significantly larger than with absorption, appears to be reasonable for actual implementation.
The temperature profile generated by a thermo-electro-chemical model was used to calculate the thermal stress distribution in a tubular solid oxide fuel cell (SOFC). The solid heat balances were ...calculated separately for each layer of the MEA (membrane electrode assembly) in order to detect the radial thermal gradients more precisely. It appeared that the electrolyte undergoes high tensile stresses at the ends of the cell in limited areas and that the anode is submitted to moderate tensile stresses. A simplified version of the widely used Weibull analysis was used to calculate the global probability of survival for the assessment of the risks related to both operating points and load changes. The cell at room temperature was considered and revealed as critical. As a general trend, the computed probabilities of survival were too low for the typical requirements for a commercial product. A sensitivity analysis showed a strong influence of the thermal expansion mismatch between the layers of the MEA on the probability of survival. The lack of knowledge on mechanical material properties as well as uncertainties about the phenomena occurring in the cell revealed itself as a limiting parameter for the simulation of thermal stresses.
The coproduction of power and ultrapure H2 within an Integrated Gasification Combined Cycle (IGCC) plant implementing CO2 capture offers advantages in terms of flexible operation while retaining good ...efficiency. The common design includes an absorption unit for removing CO2 from a high pressure syngas followed by a Pressure Swing Adsorption (PSA) unit for purifying a part of the resulting H2-rich gas stream. A drawback of this design consists in the necessity for compression of the PSA tail gas in order to recover the energy available in the residual H2 content. This paper presents two novel configurations for power and H2 coproduction with CO2 capture, entirely based on PSA technology. The first relies on two PSA trains in series (Two-train PSA), while the other is able to carry out CO2 separation and H2 purification within a single PSA train (One-train PSA). The two systems were defined and simulated through a composite model of the whole plant. The process simulation results showed that both the configurations proposed are able to shift between the two energy products without compromising the performance of the plant. The load of the plant could be decreased by increasing the ultrapure H2 throughput, while maintaining a constant feed of coal to the gasifier. The Two-train PSA configuration achieved higher performance in terms of energy efficiency and H2 purity. The One-train PSA configuration returned slightly lower but still good performance, while its design includes a single separation stage instead of two. Additionally, both configurations enable the avoidance of PSA tail gas compression giving an advantage against the absorption-based design. A comparative analysis with results taken from the literature seems to confirm this assertion.
•Process simulations of an IGCC plant coproducing power and ultrapure H2 with CO2 capture.•Two novel PSA-based plant configurations are modeled and simulated.•PSA for both H2 purification and CO2 capture entails process integration opportunities.•Both configurations are able to shift between the two energy products retaining good efficiency.•A flexible power-to-hydrogen output enables to follow the fluctuations in power demand.
In this paper, two concepts of CO2 removal in CC are compared from the performance point of view. The first concept has been proposed in the framework of the European Joule II programme and is based ...on a semi-closed gas turbine cycle using CO2 as the working fluid and a combustion with pure oxygen generated in an air separation unit. This is a zero emission system as the excess CO2 produced in the combustion process is totally captured without the need of costly and energy consuming devices. The second concept calls for a partial recirculation of the flue gas at the exit of the heat recovery boiler of a CC. The remaining flow is sent to a CO2 scrubber. Ninety percent of the CO2 is removed in an absorber/stripper device. The two systems are compared to a state-of-the-art CC when the most advanced technology is used, namely a 9FA type gas turbine and a three pressure level and heat recovery boiler. Our results show also that the CO2 semi-closed CC cycle performances are not very dependent on the configuration of the heat recovery boiler and that the recirculated gas CC performances are only slightly sensitive to the recirculation ratio. A high value of this latter mainly gives a significant reduction of the size and hence of the cost of the CO2 scrubber. From the performance point of view, the results show that the system efficiency with partial recirculation and a CO2 scrubber is always higher by 2–3% points than the CO2-based CC efficiency in comparable conditions.
•Analyses on the performances of PSA for pre-combustion CO2 capture.•Process simulations of an IGCC integrating a PSA unit.•Several process configurations and operating conditions are tested and ...analyzed.•The influence of advancements in the adsorbent material is evaluated.•An overview on the actual status of pre-combustion PSA and of its potentials is presented.
The main goal of this paper is to provide a comprehensive overview on the performance of an integrated gasification combined cycle (IGCC) implementing CO2 capture through a pressure swing adsorption (PSA) process. The methodology for integrating a PSA process into the IGCC plant is first defined and then a full-plant model is developed. A reference case is outlined both for the PSA-based plant and for an absorption-based plant. Physical absorption is considered the benchmark technology for the application investigated. The full-plant model allowed an assessment of the potentials of PSA in this framework. The plant performance obtained was evaluated mainly in terms of energy penalty and CO2 capture efficiency. Several process configurations and operating conditions were tested. The results of these simulations demonstrated the influence of the PSA process on the overall performance and the possibility to shape it according to specific requirements. A sensitivity analysis on the adsorbent material was also carried out, aiming to establish the possible performance enhancements connected to advancements in the material. Improving the properties of the adsorbent demonstrated to have a strong impact not only on the CO2 separation process but also on the performance of the entire plant. However, nor modifications in the process or in the material were able to fully close the gap with absorption. In this sense a synergetic approach for addressing further performance enhancements is outlined, based on the close collaboration between process engineering and material science.
The performance of different working fluids to recover low-temperature heat source is studied. A simple Rankine cycle with subcritical configuration is considered. This work is to screen working ...fluids based on power production capability and component (heat exchanger and turbine) size requirements. Working fluids considered are R134a, R123, R227ea, R245fa, R290, and n-pentane. Energy balance is carried out to predict operating conditions of the process. Outputs of energy balance are used as input for exergy analysis and components (heat exchanger and turbine) design. The heat exchanger is divided into small intervals so that logarithmic mean temperature difference (LMTD) method is applicable. R227ea gives highest power for heat source temperature range of 80–160
°C and R245fa produces the highest in the range of 160–200
°C. There is optimal pressure where the heat exchanger surface area is minimum. This optimal pressure changes with heat source temperature and working fluid used. The least heat exchanger area required at constant power rating is found when the working fluid is n-pentane. At lower heat source temperature (80
°C), the maximum power output and minimum heat exchanger surface area for different working fluids is comparable.
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