Supercritical Coal-fired Power Plant Research Articles

Operational flexibility options in power plants with integrated post-combustion capture

Flexibility in power plants with amine based carbon dioxide (CO2) capture is widely recognised as a way of improving power plant revenues. Despite the prior art, its value as a way to improve power plant revenues is still unclear. Most studies are based on simplifying assumptions about the capabilities of power plants to operate at part load and to regenerate additional solvent after interim storage of solvent. This work addresses this gap by examining the operational flexibility of supercritical coal power plants with amine based CO2 capture, using a rigorous fully integrated model. The part-load performance with capture and with additional solvent regeneration, of two coal-fired supercritical power plant configurations designed for base load operation with capture, and with the ability to fully bypass capture, is reported. With advanced integration options configuration, including boiler sliding pressure control, uncontrolled steam extraction with a floating crossover pressure, constant stripper pressure operation and compressor inlet guide vanes, a significant reduction of the electricity output penalty at part load is observed. For instance at 50% fuel input and 90% capture, the electricity output penalty reduces from 458kWh/tCO2 (with conventional integration options) to 345kWh/tCO2 (with advanced integration options), compared to a reduction from 361kWh/tCO2 to 342kWh/tCO2 at 100% fuel input and 90% capture. However, advanced integration options allow for additional solvent regeneration to a lower magnitude than conventional integration options. The latter can maintain CO2 flow export within 10% of maximum flow across 30–78% of MCR (maximum continuous rating). For this configuration, one hour of interim solvent storage at 100% MCR is evaluated to be optimally regenerated in 4h at 55% MCR, and 3h at 30% MCR, providing rigorously validated useful guidelines for the increasing number of techno-economic studies on power plant flexibility, and CO2 flow profiles for further studies on integrated CO2 networks.

Modelling and comparison of calcium looping and chemical solvent scrubbing retrofits for CO2 capture from coal-fired power plant

Carbon capture and storage (CCS) is expected to provide a cost-effective means of CO2 emission reduction from the power sector. Amine scrubbing, which is the closest CCS technology to the market, is a suitable option for coal-fired power plants in retrofit scenarios. However, the energy requirement for solvent regeneration in chemical absorption CO2 capture processes causes a substantial reduction in the power plant efficiency and power output. Therefore, novel technologies with lower efficiency penalties need to be developed. One promising option is calcium looping (CaL) which is based on the reversible carbonation/calcination reaction of calcium-based sorbent that takes place at high temperature. For the purpose of this study, the CaL process was model was developed and then linked to a high-fidelity model of a reference 580MWel supercritical coal-fired power plant. A secondary steam cycle was also modelled for recovery of high-grade heat from the CaL process. The results of the process analysis revealed that the efficiency penalty imposed in the CaL plant retrofit scenario was 6.7–7.9% points. Such performance compares favourably to the monoethanolamine and chilled ammonia scrubbing retrofit scenarios, which have efficiency penalties of 9.5% and 9.0%, respectively. Moreover, the retrofit of the CaL process was found to be less complex, and would result in two times higher net power output compared to the chemical solvent scrubbing scenarios. This is an important advantage of the CaL plant over the more mature CO2 capture technologies, especially for the power plant operators who are looking to increase the system capacity to meet the increasing electricity demand and, at the same time, to reduce the CO2 emissions.

An analysis of the investment risk related to the integration of a supercritical coal-fired combined heat and power plant with an absorption installation for CO2 separation

For two variants of a supercritical coal-fired combined heat and power plant a thermodynamic, economic and risk analyses were carried out. The first variant consists of a unit working without realization of CO2 capture process. The second one is the unit integrated with a chemical absorption CO2 capture installation. In this variant the heat required for the desorption process is supplied with steam extracted from the steam turbine. The developed model of the CHP plant allowed to obtain main operation characteristics for annual change of load. For the two analyzed variants the characteristics of the amount of produced electricity (gross and net), generated heat and consumed chemical energy of fuel, as a function of the cogeneration unit operation time per year, were determined. In the next stage of calculations these characteristics were required to carry out the economic and risk analysis. Economic performances were evaluated in terms of the break-even price of electricity. The performed analysis proves that both investment projects will achieve the same economic effect, i.e. 85.26€/MWh, if the price of emissions allowances reaches the value of 47.88€/MgCO2. In this case, the potentially better variant of the system may be indicated based on the result of the risk analysis. In order to perform the risk analysis the main technical and economic risk factors concerning implementation of this technology were identified. The risk analysis was conducted with the use of Monte Carlo method. Based on the determined cumulative probability curves of obtaining specified values of the break-even price of electricity, it was possible to obtain values for defined in the paper indices of the investment risk assessment. The results of risk analysis are presented and discussed in the paper.

Dynamic model for controller design of condensate throttling systems

Improving the load adjustment rate of coal-fired power plants in China is very important because of grid load fluctuations and the construction of new large-scale power plants connected to the country׳s power grid. In this paper, a new application of condensate throttling system for rapid load adjustment is proposed on the basis of the characteristics of turbine-stored energy. To ensure effective and safe operation of the condensate throttling system, a non-linear control model is derived through reasonable simplifications of fundamental physical laws, and the model parameters are identified using experimental data from a 660MW supercritical coal-fired power plant. The model outputs are compared with actual measured data for different unit loads. Results show that the established model׳s responses strongly correlate with the actual unit׳s responses and can be used for controller design.

Study on heat integration of supercritical coal-fired power plant with post-combustion CO2 capture process through process simulation

Coal-fired power plant (CFPP) is one of the main sources of anthropogenic CO₂ emissions. Capturing CO₂ from CFPP by post-combustion process plays an important role to mitigate CO₂ emissions. However, a significant thermal efficiency drop was observed when integrating CFPP with post-combustion carbon capture (PCC) process due to the steam extraction for capture solvent regeneration. Thus research efforts are required to decrease this energy penalty. In this study, a steady state model for 600 MWe supercritical CFPP was developed as a reference case with a low heating value (LHV) based efficiency of 41.6%. A steady state model for MEA-based PCC process was also developed and scaled up to match the capacity of the CFPP. CO₂ compression process was simulated to give an accurate prediction of its electricity consumption and cooling requirement. Different integration cases were set up according to different positions of steam extraction from the CFPP. The results show that the efficiency penalty is 12.29% and 14.9% when steam was extracted at 3.64 bar and at 9.1 bar respectively. Obvious improvements were achieved by utilizing waste heat from CO₂ capture and compression process, taking part of low pressure cylinders out of service, and adding an auxiliary turbine to decompress the extracted steam. The efficiency penalty of the best case decreases to 9.75%. This study indicates that comprehensive heat integrations can significantly improve the overall energy efficiency when the CFPP is integrated with PCC and compression process.

Efficiency improvements for the coal-fired power plant retrofit with CO 2 capture plant using chilled ammonia process

Abstract Development of clean coal technologies for power generation is crucial in meeting the European Union 2050 target to reduce greenhouse gas emissions. CO2 capture technology using chemical solvents currently has the highest potential to decarbonise coal-based power generation. Substitution of amine solvent with NH3 has been proposed as a viable option to reduce the efficiency penalty. In this study, the scenario of a supercritical coal-fired power plant retrofitted with a chilled ammonia process capture plant and CO2 compression unit was modelled in a common simulation environment. To fully assess the integration impact on power plant performance, the pressure loss due to steam extraction has been taken into account by using the Stodola ellipse law. Analysis of a basic integration scenario revealed that the efficiency penalty fell between 10.4% and 10.9% points depending on the stripper pressure. The quality of extracted steam became insufficient to meet the reboiler heat requirement above a stripper pressure of 21.8 bar, and the lowest efficiency penalty was obtained when reboiler condensate was returned to the deaerator in the power plant. In evaluating measures to improve integration, the efficiency penalty was reduced to 8.7–8.8% points through the integration of a single-stage or two-stage auxiliary steam turbine, respectively, and a back-pressure turbine. Nevertheless, the analysis has indicated that the net impact on power plant performance is similar to that of an amine-based post-combustion CO2 capture plant.

Parametric Optimization for Power De-Rate Reduction in the Integrated Coal-Fired Power Plant with Carbon Capture and Storage

Carbon capture and storage (CCS) has attracted worldwide attention as a near-term technology to decelerate global warming. Postcombustion CO2 capture utilizes existing coal-fired power plants, and aqueous monoethanolamine (MEA) scrubbing is the most common capture technology. However, the heat and energy requirements of solvent regeneration and CO2 liquefaction cause a 30% decrease in net power output. This power de-rate is a major obstacle to implementing CCS. In this study, simulation-based parametric optimization was performed to minimize the power de-rate. Postcombustion CO2 capture with aqueous MEA scrubbing (85%, 90%, and 95% removals) and CO2 liquefaction integrated with a 550 MWe supercritical coal-fired power plant was simulated. The liquid to gas ratio and stripper operating pressure of the CO2 capture process were the manipulated variables with steam extracted from the intermediate pressure–low pressure crossover pipe and the first low pressure turbine as possible heat sources. The power de-rate was reduced to 17.7% when operating at optimum conditions.

Generalized Predictive Control for superheated steam temperature regulation in a supercritical coal-fired power plant

The design and implementation of a Generalized Predictive Control (GPC) strategy for the superheated steam temperature regulation in a supercritical (SC) coal-fired power plant is presented. A Controlled Auto-Regressive MovingAverage (CARMA) model of the plant is derived from using the experimental data to approximately predict the plant's future behavior. This model is required by the GPC algorithm to calculate the future control inputs. A new GPC controller is designed and its performance is tested through extensive simulation studies. Compared with the performance of the plant using a conventional PID controller, the steam temperature controlled by the GPC controller is found to be more stable. The stable steam temperature leads to more efficient plant operation and energy saving, as demonstrated by the simulation results. Plant performance improvement is also tested while the plant experiences the load demand changes and disturbances resulting from the malfunctioning of coal mills.

Steady state simulation and exergy analysis of supercritical coal-fired power plant with CO2 capture

Integrating a power plant with CO2 capture incurs serious efficiency and energy penalty due to use of energy for solvent regeneration in the capture process. Reducing the exergy destruction and losses associated with the power plant systems can improve the rational efficiency of the system and thereby reducing energy penalties. This paper presents steady state simulation and exergy analysis of supercritical coal-fired power plant (SCPP) integrated with post-combustion CO2 capture (PCC). The simulation was validated by comparing the results with a greenfield design case study based on a 550MWe SCPP unit. The analyses show that the once-through boiler exhibits the highest exergy destruction but also has a limited influence on fuel-saving potentials of the system. The turbine subsystems show lower exergy destruction compared to the boiler subsystem but more significance in fuel-saving potentials of the system. Four cases of the integrated SCPP-CO2 capture configuration was considered for reducing thermodynamic irreversibilities in the system by reducing the driving forces responsible for the CO2 capture process: conventional process, absorber intercooling (AIC), split-flow (SF), and a combination of absorber intercooling and split-flow (AIC+SF). The AIC+SF configuration shows the most significant reduction in exergy destruction when compared to the SCPP system with conventional CO2 capture. This study shows that improvement in turbine performance design and the driving forces responsible for CO2 capture (without compromising cost) can help improve the rational efficiency of the integrated system.

Rate-based model development, validation and analysis of chilled ammonia process as an alternative CO2 capture technology for coal-fired power plants

Due to recent concerns about climate change, which has been triggered by greenhouse gas emissions, the European Union has recommended the decarbonisation of the power sector by 2050 in order to meet its emission reduction target. As a large share of the power generation is currently based on fossil fuels, mainly coal, with this trend expected to continue, clean coal technologies need to be developed. Carbon capture and storage using chemical solvents has been identified to be the most suitable option for coal-fired power plants. The technology which is closest to market commercialisation uses amines, such as monoethanolamine, as a solvent. However, high degradation rates due to impurities present in the flue gas and a considerable heat requirement for solvent regeneration make the application of alternative solvents necessary. In this study, a rate-based aqueous ammonia process model was developed, validated and then modified to a chilled ammonia process model. The model was then scaled up to process flue gas from a 580MWel supercritical coal-fired power plant. A sensitivity study revealed that the lowest parasitic load occurs for the lean solvent characterised by 12.5%wt NH3 concentration and 0.29 loading, with the stripper operated between 12.5 and 17.5bar. The equivalent work requirement for a CAP plant operated at such conditions was found to be up to 15.7% lower than the reference amine scrubbing plant.

The multi-period optimisation of an amine-based CO2 capture process integrated with a super-critical coal-fired power station for flexible operation

In this work, we present a model of a super-critical coal-fired power plant integrated with an amine-based CO2 capture process. We use this model to solve a multi-period dynamic optimisation problem aimed at decoupling the operation of the power plant from the efficiency penalty imposed by the CO2 capture plant, thus providing the power plant sufficient flexibility to exploit price variation within an electricity market. We evaluate four distinct scenarios: load following, solvent storage, exhaust gas by-pass and time-varying solvent regeneration. The objective is to maximise the decarbonised power plant's short run marginal cost profitability. It is found that while the solvent storage option provides a marginal improvement of 4% in comparison to the load following scenario, the exhaust gas bypass scenario results in a profit reduction of 17% whereas the time-varying solvent regeneration option increases the profitability of the power plant by 16% in comparison to the reference scenario.

Analysis of thermodynamics of two-fuel power unit integrated with a carbon dioxide separation plant

Abstract The article presents the results of thermodynamic analysis of the supercritical coal-fired power plant with gross electrical output of 900 MW and a pulverized coal boiler. This unit is integrated with the absorption-based CO2 separation installation. The heat required for carrying out the desorption process, is supplied by the system with the gas turbine. Analyses were performed for two variants of the system. In the first case, in addition to the gas turbine there is an evaporator powered by exhaust gases from the gas turbine expander. The second expanded variant assumes the application of gas turbine combined cycle with heat recovery steam generator and backpressure steam turbine. The way of determining the efficiency of electricity generation and other defined indicators to assess the energy performance of the test block was showed. The size of the gas turbine system was chosen because of the need for heat for the desorption unit, taking the value of the heat demand 4 MJ/kg CO2. The analysis results obtained for the both variants of the installation with integrated CO2 separation plant were compared with the results of the analysis of the block where the separation is not conducted.

Efficiency improvement strategies for the feedwater heaters network designing in supercritical coal-fired power plants

Coal will continue playing a major role in worldwide electricity generation during next years. This trend will augment CO2 emission to the atmosphere. Improving power plant efficiency could alleviate the negative effect of coal consumption on CO2 emissions. Main efforts have been focused on supercritical boiler technology (once-through units) and materials development (austenitic steels) with the aim of accomplishing high steam parameters that allow this efficiency enhancement. However, improvement in supercritical steam parameters should be followed by an exhaustive review of the steam cycle design. This paper shows a strategy for the optimization of the feedwater heaters network and the flue gas heat recovery system design. Starting with the lay-out of a supercritical steam cycle using the best available technology, this paper analyses not only the steam cycle itself, but also its integration with the boiler cold-end. By means of thermodynamic optimization it is possible to propose new feedwater heat exchanger network configurations and reducing steam consumption from turbine bleeds, achieving optimum power plant efficiency. Simulations have been carried out using Aspen Plus software and optimization procedure is based on a sequential quadratic programming method that maximized overall plant efficiency taking turbine bleeds pressure as independent variables. Results show a feasible improvement of the overall plant efficiency of 0.7 points in comparison with state-of-the-art reference plant. This increase implies a direct reduction of CO2 emissions of about 1.3% compared with the best plant currently available. Moreover, an economic analysis confirms the feasibility of the proposals analysed and shows important additional yearly incomes.

Dynamic Modeling and Evaluation of an Industrial-Scale CO2 Capture Plant Using Monoethanolamine Absorption Processes

This paper presents a step-by-step method to scale-up an MEA (monoethanolamine) absorption plant for CO2 capture from a 750 MW supercritical coal-fired power plant. This CO2 capture plant consists of three absorbers (each 11.8 m in diameter and with 34 m of height) and two strippers (each 10.4 m in diameter with 16 m of height); the plant has been designed to achieve 87% CO2 recovery at 95% CO2 purity. A dynamic mechanistic model of a commercial-scale CO2 capture plant with a control scheme was developed in gPROMS and evaluated under several scenarios. The analysis revealed that this plant is able to reject various disturbances and switch between different operating points displaying prompt responses in the key controlled variables. Also, this study highlights that poor wetting in strippers can be avoided if the CO2 capture removal set point is scheduled based on the periodic operation of the power plant.

Heat integration and exergy analysis for a supercritical high-ash coal-fired power plant integrated with a post-combustion carbon capture process

The International Energy Agency (IEA) has recommended eliminating at least 80% of the CO2 emission from the power sector by 2050 as a response to climate change. Meeting this target is expected to be challenging since a lion’s share of the power generation is based upon coal combustion. A cost effective strategy to decarbonise the power sector would require carbon capture and storage, largely through a post-combustion capture (PCC). In this study, a model of the supercritical coal-fired power plant (CFPP) fed with a high-ash coal was developed and validated, a validated model of a PCC pilot plant using monoethanolamine (MEA) solvent is scaled-up to meet the CFPP capacity, a CO2 compression unit model was developed to fully assess the energy penalty, and the three models were integrated for a 90% capture level. This required determination of the PCC steam requirement and identification of the optimal condensate return location. The performance of the integrated models was compared with the reference CFPP model (with a net efficiency of 39.1%), and the energy penalty was estimated to cause a 25% fall in the CFPP power output. Then, energy saving opportunities were investigated through the heat exchanger network (HEN) analysis. Several HEN designs were analysed, revealing that heat can be recovered from the flue gas leaving the CFPP, and used to heat up boiler feedwater to enhance the plant efficiency. Such a configuration resulted in reduction of energy penalty by 4.15%, improving the performance of the integrated plant. Finally, it is inferred from the exergy analysis that further energy savings can be achieved by reducing the exergy destruction in the PCC.

Parametric optimization of supercritical coal-fired power plants by MINLP and differential evolution

The design trade-offs between thermodynamics and economics of energy conversion systems can be more effective by combining a superstructure and mixed-integer non-linear programming (MINLP) techniques. The front of decision space showing the optimal sets of economic behavior and system efficiency with different corresponding optimal system structures and process variables can provide additional and useful information on cost-effective design of thermal systems. In this paper, this idea was successfully applied to supercritical coal-fired power plants to investigate the economically-optimal designs at each efficiency level. The superstructure involving up to ten feedwater preheaters, up to two reheatings and a secondary turbine with steam extractions (ET) was built. An improved differential evolution algorithm was used to simultaneously solve the parametric and structural optimization problem. The differences among the fronts of various types of plants, the front changes with plant efficiency and the effects of introducing an ET were discussed in detail. For a single reheating unit, a decrease of 2% in cost of electricity can be achieved. The optimal pressure ratios of reheatings are 0.15–0.25 (for single reheating), 0.2–0.3 and 0.15–0.3 (for double reheatings).

Exergy Evaluation of a 600MWe Supercritical Coal-fired Power Plant Considering Pollution Emissions

In the present work, a pulverized coal-fired power plant is studied, to explore the exergy destruction and the pollutant emissions characteristics of the plant, a system simulation calculation model is carried out. The system modules contain boiler, turbine, and corresponding auxiliary equipments, as well as flue gas desulphurization (FGD) unit. Thermodynamic analysis show details of exergy consumption distribution of different components, the results also demonstrate that SO2 volume concentration of flue gas in FGD unit outlet is relevant with the plant output work and the sulfur fraction of coal, and the latter factor performed the main role to emission concentration.

Dynamic Modelling and Controllability Studies of a Commercial-scale MEA Absorption Processes for CO2 Capture from Coal-fired Power Plants

Abstract This paper presents a mechanistic dynamic model of an industrial-scale carbon dioxide (CO 2 ) capture plant using Monoethanolamine (MEA) as an absorbent. In order to remove 87% of CO 2 from the flue gas stream generated from a 750 MW supercritical coal-fired power plant and produce a CO 2 concentration of 95% in the CO 2 product stream, a post-combustion CO 2 capture plant with three absorbers and two strippers are needed,. A decentralized control structure composed of 11 proportional- integral (PI) controllers was proposed to maintain the dynamic operability of this commercial-scale CO 2 capture plant. The evaluation of the plant's performance in closed-loop were conducted using multiple scenarios, i.e., the loss of CO 2 recovery (%CC) control loop during variation of flue gas flow rate, a positive ramp change in the flue gas flow rate under a maximum withdrawal constraint on the reboilers’ heat duty, and the disturbance in the flue gas composition resulting from the variation in coal composition and air flow rate. The controllability analysis performed on the proposed industrial-scale MEA absorption plant using the control system designed in this study shows that the plant is able to recover fast from most of the disturbances considered in the analysis. The insight provided from the present study can then be used to address the integration of the present CO 2 capture plant to a coal-based power plant and evaluate the dynamic feasibility of this integration under various scenarios.

Conceptual study of a high efficiency coal-fired power plant with CO2 capture using a supercritical CO2 Brayton cycle

A concept of coal-fired power plant built around a supercritical CO2 Brayton power cycle and 90% post-combustion CO2 capture have been designed. The power cycle has been adapted to the coal-fired boiler thermal output, this boiler has been roughly designed in order to assess the power cycle pressure drop and its cost, an adapted CO2 capture process has been designed and finally the overall heat integration of the power plant has been proposed. Due to the high complexity of such as plant, this paper does not intend to provide definitive evaluation of the concept but to explore its potential.A coal power plant with CO2 power cycle without carbon capture could achieve a net efficiency of 50% (LHV) with a maximal temperature and pressure of 620 °C and 300 bar, these performances has to be validated but the first results on pilot plant are encouraging. The CO2 capture process use monoethanolamine as solvent and is equipped with vapor recompression systems in order to reduce the heat needed from the CO2 cycle. It achieves around 2.2 GJ/tCO2 of specific boiler duty with 145 kWh/tCO2 of electrical auxiliary consumption including compression to 110 bar. The energetic evaluation of the overall power plant carried out highlights the promising potential of CO2 supercritical cycle. A net power plant efficiency of 41.3% (LHV), with carbon capture and CO2 compression to 110 bar, seem to be achievable with available or close-to-available equipment.A technical-economic evaluation of the designed power plant has been performed. It shows a levelized cost of electricity reduction of 15%, and a cost of avoided CO2 reduction of 45%, without transport and storage, compared to a reference supercritical coal-fired power plant equipped with standard carbon capture process.

Numerical thermodynamic optimization of supercritical coal fired power plant with support of IPSEpro software

Abstract The paper presents a thermodynamic optimization of supercritical coal fired power plant. The aim of the study was to optimize part of the thermal cycle consisted of high-pressure turbine and two chosen highpressure feed water heaters. Calculations were carried out using IPSEpro software combined with MATLAB, where thermal efficiency and gross power generation efficiency were chosen as objective functions. It was shown that the optimization with newly developed framework is sufficiently precise and its main advantage is the reduction of computation time on comparison to the classical method. The calculations have shown the tendency of the increase in efficiency, with the rise of a number of function variables.