Solar-aided Coal-fired Power Generation System Research Articles

Exergy Analysis of Off-Design Performance in Solar-Aided Power Generation Systems: Evaluating the Rationality of Using Part-load Operation Solution of Coal-Fired Plants

Solar aided coal-fired power generation (SAPG) technology has been proven to be an effective way of renewable energy utilization. However, the efficiency of coal-fired units declines at partial loads, and solar inputs may further force the system to deviate from its design condition. In particular, part-load operation solutions for coal-fired units (PLOS) are conventionally applied to the SAPG system, a practice whose appropriateness has not yet been thoroughly evaluated. This paper, therefore, selects a 330 MW SAPG plant as a case study to conduct an exhaustive exergy analysis under off-design conditions. The findings indicate that the governing stage of the steam turbine and the slip-pressure operation are the main contributors to the efficiency degradation at partial loads. In addition, solar input resulted in significant changes in key operating parameters, such as exhaust flow rate and the pressure of each turbine stage. Merely adopting the PLOS for SAPG systems results in a marked increase in standard coal consumption by 0.99, 2.82, and 3.63 g/kWh at 50%, 40%, and 30% load, respectively. However, the introduction of solar energy presents the potential to operate the unit more efficiently, particularly when valve point conditions are optimally adjusted. For instance, upon input of 28 MW solar thermal power, the #3 valve point condition shifted from a load of 321 MW to 330 MW, achieving a reduction in standard coal consumption by 0.96 g/kWh, compared to the design condition of the original coal-fired unit. This study underscores the irrationality of directly applying PLOS from coal-fired units to SAPG system without tailored adjustments for solar integration.

A study on a novel solar contribution evaluation method for the solar-aided coal-fired power generation system

Solar-aided coal-fired power generation (SACPG) technology is an effective method of solar energy utilization. It could balance the demand of carbon dioxide emission reduction and renewable energy efficient power generation and promote carbon peaking and carbon neutralization. Accurate analysis of the share of solar energy in the unit output power could benefit the selection of the best integration scheme and exploitation of solar energy for further research. A novel solar contribution evaluation method of an SACPG system is put forward. The exergy is taken as the evaluation benchmark, and the method can be applied in an SACPG system with multiple integration positions with solar energy. The solar energy input from different positions in the system is analyzed separately. The solar energy input positions and the impact of solar exergy destruction on the solar energy contribution are considered. The proposed method also analyzes the flow direction and destruction of each solar exergy in different parts of the SACPG system and expresses the solar contribution in the electricity generated by each stage steam turbine in the form of a theoretical formula. Ultimately, the solar exergy contribution in the whole SACPG system is calculated by accumulating each result. Furthermore, the new method is applied to a tower solar-aided coal-fired power generation (TSACPG) system with thermal energy storage (TES) for comparative analysis. Compared with other solar contribution evaluation methods, the comprehensiveness and accuracy of the novel method are analyzed. Meanwhile, the exergy destruction distributions of the TSACPG system are revealed. The method can also be further used to excavate the application potential of solar energy in coal-fired units and provide theoretical support for highly efficient utilization of solar energy.

Life cycle assessment of coal-fired solar-assisted carbon capture power generation system integrated with organic Rankine cycle

Pollutant emissions from coal-fired power plants are an important cause of increasingly severe environmental issues, hence realizing clean utilization of energy in such power plants is the key to address environmental problems. Considering a coal-fired power plant (CPGS) as a benchmark, two technical scenarios are proposed: (1) a coal-fired CCS power generation system (CPGS-CCS); and (2) a solar-aided coal-fired power generation system integrating organic Rankine cycle (ORC) and CCS (SCPGS-ORC-CCS). The energy balance and overall performance of three scenarios are investigated with EBSILON, and based on SimaPro 9.0.0.48 software, the life cycle assessment (LCA) of three scenarios is conducted by the ReCiPe Midpoint (H) V1.13 method. The impact of the integrated auxiliary equipment on the environmental categories in the life cycle is examined, and that of key factors on the performance and environment is explored by a sensitivity analysis. The results show that the climate change potential (CCP) is the highest share, and the ozone depletion potential (ODP) is the smallest share among the impact scores of all selected categories of functional units. The integration of CCS, ORC and solar systems results in the following scores of impact categories except for CCP: SCPGS-ORS-CCS > CPGS-CCS > CPGS. Among the three scenarios, CPGS presents the highest CCP score. The coal mining-transportation stage presents the largest contribution to the human toxicity potential (HTP) score, while the operation stage contributes the most to the scores of other impact categories. Sensitivity analysis shows that for SCPGS-ORC-CCS, increasing the service life of equipment, solar radiation intensity and heat ratio can reduce the environmental impact scores. The LCA indicates that CPGS-CCS is a preferred strategy to realize clean energy production. However, comprehensively considering the thermo-economic performance and environmental impact, by selecting appropriate raw materials for auxiliary equipment and sites with sufficient solar radiation intensity, and increasing the life cycle of systems, SCPGS-ORS-CCS is likely to be a more promising strategy in the energy conservation, emission reduction and clean production.

Off-Design Dynamic Performance Analysis of a Solar Aided Coal-Fired Power Plant

Coal consumption and CO2 emissions are the major concerns of the 21st century. Solar aided (coal-fired) power generation (SAPG) is paid more and more attention globally, due to the lesser coal rate and initial cost than the original coal-fired power plant and CSP technology respectively. In this paper, the off-design dynamic performance simulation model of a solar aided coal-fired power plant is established. A 330 MW subcritical coal-fired power plant is taken as a case study. On a typical day, three various collector area solar fields are integrated into the coal-fired power plant. By introducing the solar heat, the variations of system performances are analyzed at design load, 75% load, and 50% load. Analyzed parameters with the change of DNI include the thermal oil mass flow rate, the mass flow rate of feed water heated by the solar energy, steam extraction mass flow rate, coal consumption, and the plant thermal efficiency. The research results show that, as DNI increases over a day, the coal saving rate will also increase, the maximum coal saving rate reaches up to 5%, and plant thermal efficiency reaches 40%. It is analyzed that the SAPG system gives the best performance at a lower load and a large aperture area.

Thermoeconomic evaluation of double-reheat coal-fired power units with carbon capture and storage and waste heat recovery using organic Rankine cycle

Coal-fired power generation units using carbon capture and storage (CCS) can reduce CO2 emissions significantly whereas CCS consumes large amounts of renewable energy, leading to an efficiency penalty. To decrease the steam extraction and promote energy utilization efficiency, this study employs organic Rankine cycle (ORC) to recover the waste heat of reboiler condensate and utilizes the waste heat in CO2 compressed processes to provide energy for carbon capture system. Three technical scenarios are proposed: (1) Coal-fired carbon capture power generation system: the medium-pressure cylinder exhaust is throttled by an auxiliary turbine and exchanges heat with H6 heater to provide energy for a reboiler; (2) Coal-fired carbon capture power generation system using ORC to recover the residual heat of reboiler condensate; (3) Solar-aided coal-fired power generation system using ORC and CCS: waste heat in CO2 compression processes is supplied for a reboiler and ORC recovers the residual heat of reboiler condensate. The energy balance and overall performance of different scenarios are investigated with EBSILON, and the parameter sensitivity of scenario III is conducted. Results reveal that all scenarios improve the thermal performance of the system, and the thermo-economics of scenario III is the best at the heat ratio of 0.4.

Analysis of CO2 Abatement Cost of Solar Energy Integration in a Solar-Aided Coal-Fired Power Generation System in China

Utilization of renewable energy, improvement of power generation efficiency, and reduction of fossil fuel consumption are important strategies for the Chinese power industry in response to climate change and environment challenges. Solar thermal energy can be integrated into a conventional coal-fired power unit to build a solar-aided coal-fired power generation (SACPG) system. Because solar heat can be used more efficiently in a SACPG system, the solar-coal hybrid power system can reduce coal consumption and CO2 emissions. The performance and costs of a SACPG system are affected by the respective characteristics of its coal-fired system and solar thermal power system, their coupling effects, the solar energy resource, the costs of the solar power system, and other economic factors of coal price and carbon price. According to the characteristics of energy saving and CO2 emission reductions of a SACPG system, a general methodology of CO2 abatement cost for the hybrid system is proposed to assess the solar thermal energy integration reasonably and comprehensively. The critical factors for carbon abatement cost are also analyzed. Taking a SACPG system of 600 MW in Jinan, Shandong and in Hohhot, Inner Mongolia in China as an example, the methodology is further illustrated. The results show that the efficiency of solar heat-to-electricity should be high and it is 0.391 in the scheme of SIH1 in Hohhot, and that the designed direct normal irradiation (DNI) should be greater than 800 W/m2 in order to make full use of solar energy resources. It is indicated that the abatement cost of a SACPG system depends significantly both on the cost of solar power system and its relevant costs, and also on the fuel price or the carbon prices, and that the carbon abatement cost can be greatly reduced as the coal prices or CO2 price increase. The methodology of carbon abatement cost can provide support for the comprehensive assessment of a SACPG system for its design and optimal performance.

Full-day dynamic characteristics analysis of a solar aided coal-fired power plant in fuel saving mode

Solar aided (coal-fired) power generation (SAPG) technology has been rapidly developed over the last few years for its fewer coal consumption rate than the original coal-fired power plant and the lower initial investment than the solar alone thermal power generation. However, due to the frequent variation of meteorological conditions, the operation behaviors of the SAPG plant are ever-changing. In this paper, according to the transient models of SAPG plant, the continuous operation behaviors of a 330 MW SAPG system in a full day are studied. The coupling and decoupling times of the solar field are optimized, and variations of oil and feed water parameters in the solar field during the coupling and decoupling processes are discussed. Besides, some dynamic thermal performances of the SAPG system are studied under the control strategy of maintaining the solar field outlet heat transfer fluid (HTF) temperature constant when the direct normal irradiance (DNI) varies. The research results indicate that during a whole day, the main operating parameters of the SAPG system can operate within the safety ranges, and the system power generation almost keeps 330 MW constant, both the solar output power and the carbon dioxide emission reductions are 207.7 MWh and 186.7t/day, respectively.

Allocating Output Electricity in a Solar-Aided Coal-Fired Power Generation System and Assessing Its CO2 Emission Reductions in China

Coal-fired power generation in China is facing huge challenges due to its high share in the total electricity generation and its environmental problems. A solar-aided coal-fired power generation (SACPG) system, based on the integration of solar thermal energy into a conventional coal-fired power system, is an effective way to utilize solar energy and reduce coal consumption. The reasonable allocation of output electricity to solar energy and coal in a SACPG system and the evaluation of its CO2 emission reductions can help to acquire subsidies or financial support granted to renewable electricity and CO2 emission reductions. A methodology is proposed from the view of the technical characteristics of a SACPG system and the government regulation. The coal-to-electricity efficiency of the baseline unit or the coal-fired power system in a SACPG system is the key factor in the methodology, and it can be calculated on the basis of the norm of energy consumption of coal-fired power units in China. Then, the allocation of the output electricity to solar energy and coal can be calculated, and so can the CO2 emission reductions by the solar-coal hybrid system. Taking a 600 MW SACPG system as an example, the methodology is further illustrated. The methodology can guarantee that the calculation of output electricity allocation in a SACPG system and the calculation of its CO2 emission reductions are accurate, conservative and transparent for its subsidies or financial support.

Dynamic characteristics of a solar‐aided coal‐fired power generation system under direct normal irradiance (DNI) feedforward control

AbstractA solar‐aided coal‐fired power generation (SAPG) system is a new type of power generation system in the field of solar thermal power generation. However, the instability of solar radiation will cause fluctuations in steam temperature, which is unfavorable for the operation of boilers and steam turbines. Based on a 600 MW subcritical coal‐fired power generation unit, TRNSYS software is applied to establish a transient simulation model of SAPG in this paper. A dynamic feedforward control system for steam temperature is set up. Some essential parameters, such as the fuel consumption rate, solar‐heated steam extraction rate, water spraying flow rate, and flue gas damper opening, are under the control of direct normal irradiance (DNI). Then, the dynamic characteristics of SAPG are analyzed using typical weather data. The simulation results show that under the fuel‐saving mode, when solar irradiation changes, the SAPG system achieves a coal reduction of 4.9% by using the steam temperature control system with DNI feedforward control, and the main steam temperature fluctuation is less than 5°C with the reheat steam temperature reduced within a reasonable range. The power generation fluctuation is less than 10 MW, and the solar‐to‐electricity efficiency reaches 22.5%. Some parameters on both the flue gas side and the water/steam side in the utility boiler are simulated to demonstrate the effectiveness of DNI control.

Proposal of solar-aided coal-fired power generation system with direct steam generation and active composite sun-tracking

A novel solar-aided coal-fired power generation system (SCPGS) with direct-steam-generation (DSG) solar field and active composite (AC), i.e. active off-focus plus double-axis, sun-tracking strategy is proposed, where the DSG technology is to reduce the cost and the AC sun-tracking strategy is to improve the performance. It is found that the aperture area of DSG solar field could be saved by 12.18% compared to the HTF solar field. The AC sun-tracking strategy is experimentally verified by stabilizing the heat gain (relative deviation < 2%) under DNI fluctuation (relative variation = 35%). The proposed AC-DSG SCPGS is comprehensively evaluated in references of north-south single-axis (1A) DSG, double-axis (2A) DSG and AC heat-transfer-fluid (HTF) SCPGSs. For performance, the annual solar-to-electrical efficiency of AC-DSG SCPGS is 44.33% higher than that of 1A-DSG SCPGS. For environmental impacts, the saved amounts of CO2, NOx and SO2 emissions of AC-DSG SCPGS are 38.11% more than those of 1A-DSG SCPGS. For economics, the levelized cost of electricity (LCOE) of AC-DSG SCPGS is 44.56% lower than that of AC-HTF SCPGS. Eventually, the proposed AC-DSG SCPGS comprehensively stands out of all the reference systems. The present work evidentially provides a potential way for the smart and low-cost SCPGS in future.

Study on the general system integration optimization method of the solar aided coal-fired power generation system

Solar aided coal-fired power generation (SAPG) has been attracted more and more attentions in recent years. However, its integration and optimization is a rather challenging work. Most of the studies are based on the researches of one or several certain schemes, and no general system integration optimization method (GIOM) considering all possibilities has been proposed. In this paper, a general system integration optimization model is developed, which is configured with 8 virtual molten salt heat exchangers (FHms) and used to simulate any scheme of different integration locations and heat distributions. A SAPG system based on Solar Two plant and a 600 MWe supercritical coal-fired plant is studied. The results show that at the relatively higher heliostat field power (HFP) work conditions, the heat energy should be injected into the highest pressure feedwater heater (FHs) as a priority. While at the relatively lower HFP and higher turbine power work conditions, the heat should be distributed to the two highest pressure FHs in a certain proportion instead of fully distributed to the highest pressure FHs. The performances of both the receiver and the power block are improved. The solar-electric conversion efficiency of SAPG system is obviously higher than that of Solar Two.

Simulated performance analysis of a solar aided power generation plant in fuel saving operation mode

Solar aided (coal-fired) power generation (SAPG) system has been proved to be an efficient way to utilize the solar energy for power generation. Due to the instability of the solar radiation, a SAPG system generally operates under transient working conditions. In this paper, performance simulation sub-models of main components in a SAPG plant are established based on the lumped parameter assumption. A 330 MW SAPG power plant as a case study is simulated. The variations of the performances, main parameters of the plant with the solar field heat output and the dynamic responses under a typical day are analyzed. The results show that when the heat output of the solar field changes from 0 kJ/h to 2.13 × 108 kJ/h, the coal saving rate will increase to 6.4%, and the solar power generation share (the proportion of the power from the solar energy to the total power from the SAPG plant) will increase to 7.74%. During the analysis process, in order to optimize the solar field, the concept of the solar field equivalent efficiency (SFEE) is proposed and the optimal velocity of heat transfer fluid (HTF) in absorber tube is obtained.

Comprehensive evaluation for different modes of solar-aided coal-fired power generation system under common framework regarding both coal-savability and efficiency-promotability

Solar-aided coal-fired power generation system (SCPGS) is a promising medium-term solution to reduce CO2 and PM2.5 emissions from numerous coal-fired power plants in China, yet lacking of unified theoretical guidance. In the present work, firstly, various specific integration schemes are reasonably generalized and unified by theoretical modelling. Secondly, the “superposition effect” has been revealed that the overall coal-savability of SCPGS is determined by not only the direct benefit due to local integration of solar energy but also the global effect of the integration on the system components in a superposition way. Meanwhile, the “promotion effect” has been revealed that the promotability of SCPGS on solar thermal exergy is primarily dependent on the higher-temperature Rankine cycle but sensitive to the energy level coupling between the solar thermal energy and the working fluid. Thirdly, the comprehensive evaluation factor (f), which serves as the common evaluation index between different SCPGSs considering both the coal-savability and efficiency-promotability, is proposed. Finally, with the help of the comprehensive evaluation factor, examples of application are given as demonstration for the comprehensive evaluations between 12 individual cases of SCPGS within a common framework. The present work is expected to fundamentally guide the future research and application of SCPGS.

Impact of power station capacities and sizes of solar field on the performance of solar aided power generation

Solar aided (coal-fired) power generation (SAPG) which is an efficient way to integrate solar thermal energy into normal coal fired power generation can reduce standard coal consumption rate (SCCR) for the coal fired power station and enhance solar-to-electricity efficiency (SEE) compared with solar alone thermal power generation. A SAPG model has been developed to study the energy and economic benefits of the SAPG system with different capacities, in this study. The benefits are analyzed and discussed based on 5 criteria i.e. SEE, solar power generation (SPG), saved SCCR, annual SEE and levelized cost of energy (LCOE). The results show that the SAPG benefits are linked with the capacity of coal power plant and the collector areas installed. The results of a case study show a general trend that SEE, SPG and saved SCCR all peaked at designed aperture areas of solar field, but LCOE and annual SEE are optimum at a larger than designed collector areas. The results also show the saved SCCR is greater in smaller plants while the annual SEE is higher in larger plants. Therefore, for different solar field aperture area and capacity of units, optimization integrated scenario is different based on different criteria.

Annual economic performance of a solar-aided 600 MW coal-fired power generation system under different tracking modes, aperture areas, and storage capacities

The solar-aided coal-fired power generation (SACPG) system is proven to be an effective way to use solar energy. In this work, a 600MW SACPG system using solar parabolic trough technology is simulated based on hourly meteorological data. Solar field is used to preheat feedwater to replace high-pressure extraction steam of the original coal-fired unit.Based on annual and off-design performance, the main parameters of the SACPG system, such as thermal energy storage (TES) hours, solar multiple (SM) and ratio of row spacing to aperture width (S/W ratio) are optimized from the thermodynamic and economic viewpoints. Besides, a sensitive economic analysis is performed when the cost of a specific component changes.The thermodynamic and sensitive economic analysis reveals the S/W ratio should be determined depending on land cost and tracking mode to balance between annual solar-to-electricity efficiency (SEE) and lower levelized cost of electricity (LCOE). Besides, although a TES system could annual SEE of SACPG system, its optimized capacity should be determined by the cost of the solar field and the TES system. Therefore, a balance point is proposed in the end to determine on what condition it is economical to set a TES system.

Analysis of a solar-aided coal-fired power generation system based on thermo-economic structural theory

Solar-aided coal-fired power generation system is the integration of solar energy and conventional coal-fired power system. The first stage extraction from turbines was replaced by solar energy to heat feedwater, so that the replaced high pressure steam can continue to work in Rankine cycle. Thermo-economic structural theory was applied to perform a comparative study between the fuel-saving mode and power-boosting mode of SAPG (solar aided power generation) system. The physical and productive structures of systems were built to describe the interactions of all components in the system. Then thermo-economic costs of each component were calculated on the basis of exergy analysis. The results showed that compared to coal-fired power generation system, coal consumption rate is decreased by 15.04 g/kWh in fuel-saving mode. The power output is 57.2 MW higher in power-boosting mode. The unit thermo-economic cost of electricity is increased by 16.9–21.6% due to the large investment of solar collector field. Although the cost of solar energy is considered free, the thermo-economic cost of solar energy was found to be very high because of this large investment. Analysis of the condenser suggested that the exergy cost of condenser is all of irreversibility and thermo-economic cost of condenser is made up of irreversibility and investment.

Annual performance of a solar aided coal-fired power generation system (SACPG) with various solar field areas and thermal energy storage capacity

Integrating solar energy into a conventional fossil-fuel fired power plant through solar-aided coal-fired power generation (SACPG) mechanism has been proven to be an efficient way to use solar energy for power generation purposes. However, due to the rather intermittency of solar radiation, SACPG systems always work under off-design conditions. In this paper, hourly based annual performances of a SACPG system was simulated and analyzed with various solar field sizes and thermal energy storage (TES) capacity under different (plant) load conditions in a 330MW power plant case study. The results indicate that, TES system could stabilize the solar thermal output and improve the stability of the SACPG system at different loads. And it could also improve solar contribution in the power generation and annual peak solar-to-electricity efficiency. Through case study, the minimum levelized energy of costs and corresponding aperture area in this case are $0.0629/kWh, 1.413×105m2 for 100% load, $0.0654/kWh, 9.42×104m2 for 75% load, and $0.0730/kWh and 5.89×104m2 for 50% load, respectively. And the corresponding optimized TES hour with different loads is found to be 0.5h. The values are relatively lower than the reference trough plant.

Improved Optimization Study of Integration Strategies in Solar Aided Coal-Fired Power Generation System

Solar aided coal-fired power generation system (SACFPGS) combines solar energy and traditional coal-fired units in a particular way. This study mainly improves the solar thermal storage system. Genetic algorithm is used to optimize the SACFPGS. The best integration approach of the system, the collector area, and the corresponding thermal storage capacity to replace each high-pressure extraction are obtained when the amount of coal saving in unit solar investment per hour is at its largest. System performance before and after the improvement is compared. Results show that the improvement of the thermal storage system effectively increases the economic benefit of the integrated system.

Optimization study of integration strategies in solar aided coal-fired power generation system

Parabolic trough solar-aided coal-fired power generation system has been developed to achieve efficient use of solar energy resources by coupling conventional coal-fired power plant with solar energy. However, there are no appropriate evaluation criteria about the thermal and economic performance of the system presently. This paper proposes the evaluation standard of the solar aided coal-fired power plant, and then based on this standard an optimization of this system is applied by the genetic algorithm model. According to the optimization research of this system, a series of parameters such as the solar collector area; the way of the coupling the power plant; whether storage is needed and the relevant storage capacity are obtained.

Research on solar aided coal-fired power generation system and performance analysis

Integrating solar power utilization systems with coal-fired power units, the solar aided coal-fired power generation (SACPG) shows a significant prospect for the large-scale utilization of solar energy and energy saving of thermal power units. The methods and mechanism of system integration were studied. The parabolic trough solar collectors were used to collect solar energy and the integration scheme of SACPG system was determined considering the matching of working fluid flows and energy flows. The thermodynamic characteristics of solar thermal power generation and their effects on the performance of thermal power units were studied, and based on this the integration and optimization model of system structure and parameters were built up. The integration rules and coupling mechanism of SACPG systems were summarized in accordance with simulation results. The economic analysis of this SACPG system showed that the solar LEC of a typical SACPG system, considering CO2 avoidance, is 0.098 $/kW·h, lower than that of SEGS, 0.14 $/kW·h.