Search

The coproduction of power and ultrapure H 2 within an Integrated Gasification Combined Cycle (IGCC) plant implementing CO 2 capture offers advantages in terms of flexible operation while retaining good efficiency. The common design includes an absorption unit for removing CO 2 from a high pressure syngas followed by a Pressure Swing Adsorption (PSA) unit for purifying a part of the resulting H 2 -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 H 2 content. This paper presents two novel configurations for power and H 2 coproduction with CO 2 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 CO 2 separation and H 2 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 H 2 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 H 2 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. [ABSTRACT FROM AUTHOR]

Dynamic operation of a multi-train Sorption Enhanced Water Gas Shift (SEWGS) system, based on a Pressure Swing Adsorption (PSA) process, is investigated by a detailed dynamic modeling and simulation. The multi-train SEWGS system, which consists of eight reactors in each train, operating in parallel, treats the feed syngas being produced continuously in a gasifier of an Integrated Gasification Combined Cycle (IGCC). Syngas is converted to a H 2 -rich product and a separate CO 2 -rich stream is also produced. The SEWGS system is designed for pre-combustion CO 2 capture in the IGCC power plant. Therefore dynamic characteristic of the system at different loads of feed syngas is interesting for investigation of the performance of IGCC power plant at different Gas Turbine (GT) load levels. Simulation results reveal performance of the system in terms of components breakthrough curves and steam consumption of the system with a CO 2 recovery rate of 95% and 99% purity of the recovered CO 2 . The H 2 -rich product purity achieved is around 81%. It is found that changing the rinse and purge steam amount affects the CO 2 purity and recovery rate. However, the H 2 -rich product purity remains almost unchanged. Simulation results at different loads of feed syngas shows that to maintain the CO 2 recovery and purity of the design case as the target performance, in addition to changing the rinse and purge steam loads, duration of the feed step and thus the cycle time should be varied as well. The H 2 -rich stream flow rate is found to undergo a periodic fluctuation of around ±33%, which should be minimized due to the GT requirements. It is tried to reduce the fluctuations by scheduling operation of the trains with time lags. Operation of the SEWGS system under two different scheduled operation scheme is investigated. H 2 -rich stream flow rate fluctuations are decreased from ∼±33% in the basic operation scheme to ∼±14% and ∼±11% in the first and second scheme. However, compared to the basic scheme, the H 2 -rich stream overall production rate drops around 5.5% and 6.2% on average, respectively. [ABSTRACT FROM AUTHOR]

Abstract: A new approach to improve the performance of supercritical carbon dioxide Rankine cycle which uses low temperature heat source is presented. The mechanical pump in conventional supercritical carbon dioxide Rankine cycle is replaced by thermal driven pump. The concept of thermal driven pump is to increase the pressure of a fluid in a closed container by supplying heat. A low grade heat source is used to increase the pressure of the fluid instead of a mechanical pump, this increase the net power output and avoid the need for mechanical pump which requires regular maintenance and operational cost. The thermal driven pump considered is a shell and tube heat exchanger where the working fluid is contained in the tube, a tube diameter of 5mm is chosen to reduce the heating time. The net power output of the Rankine cycle with thermal driven pump is compared to that of Rankine cycle with mechanical pump and it is observed that the net power output is higher when low grade thermal energy is used to pressurize the working fluid. The thermal driven pump consumes additional heat at low temperature (60°C) to pressurize the working fluid. [Copyright &y& Elsevier]

This article illustrates aspects of heat recovery Steam generator (HRSG) design when employing process integration in an integrated reforming combined cycle (IRCC) with precombustion CO2 capture. Specifically, the contribution of this paper is to show how heat integration in a precombustion CO2 capture plant impacts the selection of HRSG design. The purpose of such a plant is to generate power with very low CO2 emissions, typically below 100 g CO2/net kWh electricity. This should be compared with a state-of-the-art natural gas combined cycle (NGCC) plant with CO2 emissions around 380 g CO2/net kWh electricity. The design of the HRSG for the JRCC process was far from standard because of the significant amount of steam production from the heat generated by the autothermal reforming process. This externally generated steam was transferred to the HRSG superheaters and used in a steam turbine. For an NGCC plant, a triple- pressure reheat steam cycle would yield the highest net plant efficiency. However~ when generating a significant amount of high-pressure steam external to the HRSG, the picture changed. The complexity of selecting an HRSG design increased when also considering that steam can be superheated and low-pressure and intermediate-pressure steam can be generated in the process heat exchangers. For the concepts studied, it was also of im- portance to maintain a high net plant efficiency when operating on natural gas. There- fore, the selection of HRSG design had to be a compromise between NGCC and IRCC operating modes. [DOT: 10.1115/1.4001822] [ABSTRACT FROM AUTHOR]

Three concepts for capturing CO2 from natural gas-fired combined gas/steam turbine power plants are evaluated and compared in this paper: (A) separation of CO2 from exhaust gas coming from a standard gas turbine power plant, using chemical absorption by amine solutions. (B) Gas turbine combined cycle (CC) using a semi-closed gas turbine with near to stoichiometric combustion using oxygen from an air separation unit as an oxidizing agent. This produces CO2 and water vapour as the combustion products. The gas turbine working fluid is mainly CO2. (C) Decarbonization, which comprises an autothermal reforming reactor with air-blown catalytic partial oxidation of gas natural gas, a water-shift reaction and a high-pressure CO2 capture process. The hydrogen-rich reformed fuel gas is combusted in a gas turbine CC, which is integrated (air, steam and heat) with the decarbonization process. A novel method is presented that compares power plant concepts including CO2. Instead of using extensive thermodynamic calculations for these concepts, reaction equations for the conservation of molecular species together with specific energy consumption numbers for the different process sections are used to characterize the concepts with respect to fuel-to-electricity conversion efficiency. With a combined gas/steam turbine power plant giving 58% total fuel-to-electricity conversion efficiencies (no CO2 capture), calculations for the concepts with CO2 capture including CO2 compression gave: (A) 49.6%; (B) 47.2%; and (C) 45.3%. The mechanisms leading to a reduced efficiency for concepts A–C are discussed and quantified and compared to combined gas/steam turbine with no capture of CO2. [Copyright &y& Elsevier]

The focus of this study is to carry out techno-economic analysis of a pre-combustion capture method in Natural Gas based power plants with a novel reactor concept, Gas Switching Reforming (GSR). This reactor concept enables auto thermal natural gas reforming with integrated CO 2 capture. The process analysed integrates GSR, Water Gas Shift (WGS), and Pressure Swing Adsorption (PSA) into a Natural Gas based combined cycle power plant. The overall process is defined as GSR-CC. Sensitivity studies have been carried out to understand the performance of the GSR-CC process by changing the oxygen carrier utilization and Steam/Carbon ratio in GSR. The net electrical efficiency of the GSR-CC lies between 45.1% and 46.2% and the levelised cost of electricity lies between 124.4 and 128.1 $/MWh (at European natural gas prices) for the parameter space assumed in this study. By eliminating the WGS step from the process, the net electrical efficiency improves to 47.4% and the levelised cost of electricity reduces to 120.7 $/MWh. Significant scope exists for further efficiency improvements and cost reductions from the GSR-CC system. In addition, the GSR-CC process achieves high CO 2 avoidance rates (>95%) and offers the possibility to produce pure H 2 during times of low electricity demands. [ABSTRACT FROM AUTHOR]

This paper discusses the limitations and prospects of using equilibrium-based column models for the dynamic simulation of post-combustion CO 2 capture processes. Based on their features, one of three available commercial process simulators was chosen for this study. A pilot plant configuration adopted from literature was modeled and simulated using this simulator. Simulation results were compared with plant data and with results using standard rate-based models as available in literature. Temperature profiles in columns and overall mass and energy balances were found to be similar to plant data; however, CO 2 capture-rate, reboiler-duty, and rich-loading using the model were overestimated. A method of reduced stage efficiencies in the absorber was used, which improved performance prediction further with a maximum deviation of 5%. Further, this dynamic model was used to analyze the process subjected to variation in flue gas flow-rate with a similar trend of futuristic power plants by controlling either liquid to gas ratio or CO 2 capture-rate. Controlling liquid to gas ratio provided more control over the reboiler-duty while controlling the capture-rate focused on maintaining a certain capture ratio. The advantages and disadvantages of both methods are discussed and based on that, the controlling capture ratio was found suitable for using while power plant works flexibly with stringent emission regulations. [ABSTRACT FROM AUTHOR]

Post-combustion CO 2 capture (PCC) plant for a typical 600 MW natural gas fueled thermal power plant was designed as a trade-off between operability and mitigation of the efficiency penalty. Two modified PCC plant configurations with low efficiency penalty were selected. The methodology for designing PCC plants was adapted by incorporating design constraints based on operability and the construction of absorbers. This was applied in sizing the equipment of the plants. Two configurations of absorbers were analyzed based on flue gas flow rate at full-load condition and at time-average of an assumed load variation of a power plant operating flexibly. It was found that the absorber designed at time-average load provided a reduction of approximately 4% in the purchased cost of absorbers. The performance of the designed plants under power plant load variation, flow maldistribution and variable capture ratio was analyzed using off-design condition simulations. The absorber designed at full-load condition was found to lead to lower reboiler duty in order to maintain a similar capture rate to that of the other absorber during part-load operation. Dynamic simulations of the plants with the existing control structure were performed under similar power plant load variations to confirm their operability, and suggestions for selecting one of them were presented. [ABSTRACT FROM AUTHOR]

Offshore oil and gas installations are mostly powered by simple cycle gas turbines. To increase the efficiency, a steam bottoming cycle could be added to the gas turbine. One of the keys to the implementation of combined cycles on offshore oil and gas installations is for the steam cycle to have a low weight-to-power ratio. In this work, a detailed combined cycle model and numerical optimization tools were used to develop designs with minimum weight-to-power ratio. Within the work, single-objective optimization was first used to determine the solution with minimum weight-to-power ratio, then multi-objective optimization was applied to identify the Pareto frontier of solutions with maximum power and minimum weight. The optimized solution had process variables leading to a lower weight of the heat recovery steam generator while allowing for a larger steam turbine and condenser to achieve a higher steam cycle power output than the reference cycle. For the multi-objective optimization, the designs on the Pareto front with a weight-to-power ratio lower than in the reference cycle showed a high heat recovery steam generator gas-side pressure drop and a low condenser pressure. [ABSTRACT FROM AUTHOR]

Abstract: Many industrial processes are based on two reactions: a primary one related to the achievement of the main process objective and a secondary one which is necessary to continuously run the process. Those reactions can be performed continuously by means of two interconnected fluidized beds. The proposed design consists of two interconnected circulating fluidized beds (CFB). Both reactors can be operated in fast fluidization regime improving the particles' gas contact and reducing the reactor's system volume. The two CFBs are interconnected by means of pneumatically controlled divided loop-seals and a bottom extraction/lift. The divided loop-seals can re-circulate back to the reactor of origin part of the entrained solids; this implies that the amount of exchanged solids can be controlled and uncoupled from the amount of entrained solids. The bottom extraction/lift compensates the lower entrainment capability of the reactor with less fluidizing gas availability. An intense hydrodynamic test campaign has been performed with a full scale cold flow model. The design has proven to be reliable offering a stable operational window. Some interesting dependencies of the entrained solids flux have been found: from the cyclone pressure drop and the superficial gas velocity. The divided loop-seal allowed a stable internal recirculation of the entrained solids, up to 50%, without affecting the reactors' hydrodynamics. Such system could work effectively by controlling the pressures in correspondence of the points where the loop-seals return legs merge with the reactors. In this way gas backflows and particle losses through the cyclones are avoided. A safe operational procedure of the pneumatically controlled double loop CFB has been defined by means of a combined usage of the two key components: the bottom extraction/lift and the pneumatically controlled divided loop-seals. Design improvements were also identified. [Copyright &y& Elsevier]

Abstract: One option for pre-combustion CO2 capture in power plants is the integrated reforming combined cycle (IRCC). IRCCs have previously been studied from multiple viewpoints: thermo-economic analysis, process optimization, environmental impact, and plant flexibility. This paper is focused on the design of the heat recovery steam cycle (HRSC), including the heat recovery steam generator (HRSG), and aims to define the optimal steam cycle configurations for plant efficiency and dual-fuel flexibility. A recently developed optimization algorithm was successfully applied to obtain a set of flexible and efficient designs for IRCCs. Results showed that the preferred designs consisted of a dual-pressure level HRSG with reheat and limited supplementary firing in duct burners, high-pressure evaporators and economizers in the syngas coolers, limited high-pressure level (140–154bar), and feedwater preheating. The most attractive optimized dual-pressure designs showed improvements of approximately 0.5% points in the net plant efficiency compared to the non-optimized base case. The resulting net plant efficiency was about 45.8% with a net power output of around 425MW for the best cases. [Copyright &y& Elsevier]

Abstract: A systematic approach to quantify uncertainties in an integrated reforming combined cycle (IRCC) process model employing CO2 capture is presented. IRCC involves reforming of natural gas into a hydrogen-rich fuel which is then used as gas turbine fuel. Included in an IRCC plant is also a steam bottoming cycle. The analysis treats uncertain parameters as random variables whose probability distributions are estimated from limited existing information using entropy maximization. Uncertainties of model parameters were propagated through the process model using the deterministic equivalent modeling method as a computationally efficient alternative to Monte Carlo simulations. The method also quantifies the effect of each parameter on the total uncertainty of model outputs. The IRCC process model was evaluated in terms of four performance metrics: (1) net plant power output, (2) net plant efficiency, (3) CO2 capture rate, and (4) CO2 emitted per kWh of generated electricity. Simulation results showed that there was considerable uncertainty in the predicted net power output whereas the other three variables were less affected by input uncertainties. The IRCC plant was predicted to have a median net plant efficiency of 43.4% with a standard deviation of 0.5%, representing a loss of approximately 13%-points compared to a natural gas combined cycle plant without CO2 capture. Results also indicated that the probability of meeting the requirement of at least 85% CO2 capture rate for the plant was approximately 95%. Parameters with the largest impact on uncertainties of power output and efficiency predictions proved to be gas turbine inlet temperature, and compressor and turbine efficiencies. For the CO2 emissions, the equipment pressure drop and the steam-to-carbon ratio proved important. Therefore, the focus of future work should be to reduce uncertainties in these parameters in order to improve the confidence of the IRCC model. [Copyright &y& Elsevier]

Abstract: In the first part of this paper we present a detailed model of an oxygen mixed conducting membrane (OMCM) monolith for air separation. In addition to the oxygen separation, the OMCM operates as a heat exchanger at elevated temperature and pressure. The model is based on energy and species conservation balances. It is shown that the oxygen permeation through perovskite-related materials is strongly dependent on the oxygen partial pressure difference across the membrane and on the temperature of the solid wall. The numerical results obtained from steady state as well as transient simulations agree well with the available data. In the second part, linear model reduction is applied to the OMCM model. The method for model reduction used here, balanced residualisation, reduces states while preserving steady-state behaviour. The comparison of two reduced-order models (19 states and 5 states, respectively) with the full-order model (>2000 states), reveals good agreement for frequencies lower than 1Hz. The reduced models simulate faster, and can be used for controllability analysis and control design. [Copyright &y& Elsevier]

Life-cycle assessment is an established tool for industrial ecology. An analysis of the energy use in the chemical and other energy-intensive industries is still under discussion in this field. We argue that the concept of exergy can play a role in industrial ecology, using a recent Norwegian power production policy question as illustration. The question is whether to build a standard natural gas- or a hydrogen-fired gas-turbine combined-cycle power plant to meet increased needs for electricity in Norway. Several indicators are relevant for this discussion, and we calculate three based on exergy calculations, as proposed in the literature. The indicators are exergy renewability, exergy efficiency, and environmental compatibility. We show how these indicators can be used to evaluate paths for sustainable power production in two gas-fired combined-cycle power plants. We found that the two plants in question were equivalent, as judged by their exergy renewability and their environmental compatibility, but not by their exergy efficiency. This indicator favored the standard power plant, possibly in combination with carbon dioxide (CO2) sequestration in a depleted gas reservoir. The analysis suggested that the present situation for power production in gas-fired combined-cycle power plants is such that one may have to choose in general between power production with a high exergy efficiency, but low renewability indicator, or the opposite, low exergy efficiency and high renewability indicator. The general importance of exergy analysis was demonstrated by this example. It enables communication between different professional groups. The technological details, understood by the engineers, can be transposed to meaningful aggregated indicators for decision makers. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents part-load evaluation of a natural gas-fired chemical looping combustion (CLC) combined cycle with CO2 capture. The novel combined cycle employs an air-based gas turbine, a CO2-turbine and a steam turbine cycle. In this combined cycle, the CLC reactors replace combustion chamber of the gas turbine. The proposed combined cycle has a net plant efficiency of about 52.2% at full-load, including CO2 compression to 200bar. The part-load evaluation shows that reducing the load down to 60% results in an efficiency drop of 2.6%-points. However, the plant shows better relative part-load efficiency compared to conventional combined cycles. The pressure in CLC-reduction and -oxidation reactors is balanced by airflow control, using a compressor equipped with variable guide vanes. A combination of control strategies is discussed for plant start-up and shutdown and for part-load when airflow reduction is not practically possible with current generation of compressors. The results show that the combined cycle has a promising efficiency even at part-load; however, it requires an advanced control strategy. [Copyright &y& Elsevier]

Abstract: Nine different concepts for natural gas fired power plants with CO2 capture have been investigated, and a comparison is made based on net plant efficiency and emission of CO2. The cycles are one post-combustion, six oxy-fuel and two pre-combustion capture concepts. A 400MW combined cycle plant is applied as a reference case. A common basis for the comparison of all concepts is defined and employed in heat- and mass-balance simulations of the various concepts. As gas turbine cooling impacts the net plant efficiency at high turbine inlet temperatures, a simplified turbine cooling model has been applied in the simulations. It is found that the concepts, in which novel technology (the hydrogen membrane separation reformer—-MSR-H2, the advanzed zero emission power plant—AZEP, the solid oxide fuel cell combined with a gas turbine— and the chemical looping combustion—CLC concepts) is employed, exhibit the best performance with respect to both efficiency and in most cases also CO2 capture (capture rates close to 100%). Post-combustion capture and pre-combustion capture with auto-thermal reforming, which are based on more mature technology, show a lower efficiency and a capture rate of typically 90%. The concept exhibits the best cycle performance and even better than a standard CC plant, however, any realization of a SOFC-GT 400MW plant has a very distant future perspective. In order to conduct a complete assessment of these diverse concepts, other criteria for comparison such as e.g. technology level and costs should also be considered. This is not, however, included in the present work. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

The current work shall prove the feasibility and show methods to safely operate a simple SOFC/GT hybrid system under part-load and load change. Dynamic and steady state studies on a detailed model of a SOFC/GT hybrid system have been performed. A design point is selected. Steady-state part-load behavior is shown by means of performance maps. An operation line with fairly constant temperatures in the upper part-load regime and an almost constant efficiency down to approximately 25% part-load is proposed and the dynamic behavior of the system on rapid load changes is investigated. Strategies for the dynamic controlling of power by manipulating fuel flow are shown that might enable the system to adapt to a new setpoint power quite quickly. [ABSTRACT FROM AUTHOR]

A concept for natural-gas (NG) fired power plants with CO2 capture was investigated using exergy analysis. NG was reformed in an auto-thermal reformer (ATR), and the CO2 was separated before the hydrogen-rich fuel was used in a conventional combined-cycle (CC) process. The main purpose of the study was to investigate the integration of the reforming process and the combined cycle. A corresponding conventional CC power plant with no CO2 capture was simulated for comparison. A base case with CO2 capture was specified with turbine-inlet temperature (TIT) of 1250 °C and an air-compressor outlet pressure of 15.6 bar. In this case, the net electric-power production was 48.9% of the lower heating value (LHV) of the NG or 46.9% of its chemical exergy. The captured and compressed CO2 (200 bar) represented 3.1% of the NG chemical exergy, while the NG, due to its pressure (50 bar), had a physical exergy equal to 1.0% of its chemical exergy. The effects of the changed NG composition and environmental temperature were investigated. Higher pressure in the gas turbine and reformer increased the combustion in the ATR and reduced the overall efficiency. Supplementary firing (SF) was investigated as an alternative means of heating the ATR. This also reduced the efficiency. Heating the feeds of the ATR with its product stream was shown to reduce the irreversibility and improve the efficiency of the plant. Both this, and the effect of increased TIT to 1450 °C were investigated. Combining both measures, the net electric-power production was increased to 53.3% of the NG LHV or 51.1% of the NG chemical exergy. On the other hand, both increased TIT and the ATR product-feed heat exchange reduced the conversion of hydrocarbons to CO2. [Copyright &y& Elsevier]

A survey is made of high-temperature membranes and several possible applications of membrane reactors for integration in power generation cycles with CO2 capture. Current performance and limitations of relevant inorganic membranes are presented and discussed. Integrated H2, O2 or CO2 membrane separation is analysed and it is concluded that development of power plant concepts including membrane technology is not yet fully explored. Significant design optimisation would be required in order to identify efficient, feasible and environmentally sound technical solutions. In addition, further development and validation of performance of membranes in real applications are needed. [Copyright &y& Elsevier]

Abstract: SINTEF Energy Research and the Norwegian University of Science and Technology – NTNU have proposed a 150kWth reactor system design aiming at further development of chemical looping processes. It consists of a double loop circulating fluidized bed, meant to be used as a platform to study atmospheric chemical looping combustion configurations, as well as other possible chemical looping processes e.g. gas turbine combustion and reforming. The hydrodynamic viability of the design needs to be tested by means of a cold flow model, operated without chemical reactions. An evaluation of the state of the art within cold flow model testing was done. It led to the choice of building a full scale (i.e. 1:1) cold model of the 150kWth hot rig design, in order to reduce wall-effects which have considerably larger influence at smaller reactor diameters than on larger ones. The cold flow model was extensively tested and experimental results are presented. The aimed design condition, mirroring a chemical looping combustion process adapted to steam generation, was achieved successfully and in a stable way. The performance of the reactor system was further tested in off-design conditions to define operational guidelines for the hot operation. In addition, attempts were done to resemble other chemical looping processes, getting some understanding of how the reactor system may perform and consequently providing solid hydrodynamic bases to improve the design for those applications. In all cases, stable operational sets were found in order to satisfy the cold flow model hydrodynamic requirements consistently with the actual high temperature processes. [Copyright &y& Elsevier]

gas turbine power plant for CO capture, based on oxygen-permeable membranes with mixed ionic-electronic conductivity, was analysed with respect to long-term stability by means of numerical simulation. Due to the attractive transport and physicochemical properties of mixed-conducting LaNiO, this nickelate was selected as a prototype membrane material for this application. Experiments showed very slow degradation of LaNiO membranes at oxygen chemical potentials close to atmospheric conditions, which are associated with kinetic demixing and other microstructure-related factors. Interaction with CO in the intermediate temperature range also leads to lower oxygen permeation, whilst increasing oxygen pressure may cause partial phase decomposition and microstructural changes, thus again limiting the range of possible operation conditions. The relevant operational constraints were included in a detailed membrane-based gas turbine power plant model. The membrane performance degradation with time was approximated by a linear function with average rate of 3.3% per 1,000 operation hours. Furthermore, performance deterioration of the gas turbine compressor and turbine were also considered. Simulations revealed that the power plant is substantially affected by degradation of the ceramic membranes and turbomachinery components. The already rather small operating window was further narrowed when compared with a conventional gas turbine power plant. Two different designs of the membrane-based power plant were analysed: (1) with and (2) without additional combustors (afterburners) between the membrane reactor and the gas turbine. Afterburners increase thermal efficiency as well as power output, but also lead to non-negligible CO emissions. In order to have a frame of comparison, results for a conventional gas turbine power plant with degradation of turbomachinery components are also presented. Simulations representing changes in ambient temperature and fuel composition as well as failure incidents were executed to analyse the susceptibility of the gas turbine power plant to external and internal changes. [ABSTRACT FROM AUTHOR]

Abstract: In this article, a dynamic, lumped model of a solid oxide fuel cell (SOFC) is described, as a step towards developing control relevant models for a SOFC combined with a gas turbine (GT) in an autonomous power system. The model is evaluated against a distributed dynamic tubular SOFC model. The simulation results confirm that the simple model is able to capture the important dynamics of the SOFC and hence it is concluded that the simple model can be used for control and operability studies of the hybrid system. Several such lumped models can be aggregated to approximate the distributed nature of important variables of the SOFC. Further, models of all other components of a SOFC-GT-based autonomous power system are developed and a control structure for the total system is developed. The controller provides satisfactory performance for load changes at the cost of efficiency. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

Abstract: The paper describes two 2D steady-state models for solid oxide fuel cells (SOFC) with planar and tubular geometries fuelled by methane. Following a description of the basic geometries and general premises the approaches, assumptions and simplifications for the calculation of ohmic resistance, convective, conductive and radiative heat transfer are given. The modeling approach of the chemical reactions and molar and thermal balances are depicted in detail with the intention to allow for reproduction of the models. The required boundary conditions and input parameters of the models are also discussed. Relying on models, a bottoming GT cycle is introduced and specified and a base case for operation defined. The influence of pressure ratio, air inlet temperature, air flow rate and anode gas recycling are investigated in a parameter study. For both designs air flow rate and pressure ratio are the most important parameters considering the system performance, but for the tubular system these parameters have less impact than for the planar design. Based on the parameter study, a near-optimum case is defined specifically for both systems and the conditions in the fuel cells are investigated. The cycle balance is different in both systems, as the tubular fuel cell requires a lower air inlet temperature. Both fuel cell systems achieve above 65% electric efficiency. [Copyright &y& Elsevier]