Gas-steam Combined Cycle Research Articles

Study of an integrated gas turbine -Molten carbonate fuel cell-organic Rankine cycle system with CO2 recovery

A huge amount of energy is consumed by recovering CO2 in the gas turbine (GT) exhaust gas with the traditional method because of the low CO2 concentration. A new system integrated with gas turbine, MCFC and ORC with CO2 capture is proposed in this article. CO2 in the gas turbine exhaust gas is concentrated by the MCFC electrochemical reaction. Compared with traditional CO2 capture methods, it effectively decreases the energy consumption of CO2 capture. The mid-temperature exhaust gas heat is recovered by two stages organic Rankine cycle systems. The influences of the major parameters on the new system performance are deeply studied. Also, the thermal and economic performances of the new system are compared with those of the reference system without CO2 capture and with CO2 capture based on the traditional mono-ethanol ammine (MEA) method. The results show that, when the CO2 capture rate is 0.85, the thermal efficiency of the new system is 62.34%, 3 percentage points higher than that of the gas steam combined cycle system without CO2 capture; and the exergy efficiency is 60.08%, 2.47 percentage points higher than that of the gas steam combined cycle system without CO2 capture. Its economic performance will be improved with the reduction of the MCFC cost in the future.

Thermodynamic analysis of two novel very high temperature gas-cooled reactor-based hydrogen-electricity cogeneration systems using sulfur-iodine cycle and gas-steam combined cycle

In this paper, two novel system layouts are proposed to improve the thermodynamic performance of the conventional very high temperature gas-cooled reactor (VHTR)-based hydrogen-electricity cogeneration system using sulfur-iodine (S–I) cycle and gas-steam combined cycle (GSCC). The heat and electricity consumption data of the S–I cycle are obtained from our previous Aspen Plus simulation results, and the thermodynamic model of the entire hydrogen-electricity cogeneration system is established using energy and exergy analysis methods. The performance of the system under benchmark conditions is analyzed, and the effects of several key operating parameters on system performance are investigated. The results show that with these two new system layouts, the thermal efficiency and exergy efficiency of the conventional system are improved by 8.56%–10.27% and 9.01%–10.82%, respectively. The largest exergy loss of the system occurs in the VHTR, and the exergy efficiency of the S–I cycle is very low, only about 50.8%. Therefore, when the hydrogen production load is large, it is very important to optimize the process flow and operating parameters of the S–I cycle. Besides this, it is found that the S–I cycle-based nuclear hydrogen production efficiencies are lower than the GSCC-based nuclear power generation efficiencies.

Thermodynamic simulation and economic analysis of combined cycle with inlet air cooling and fuel pre-heating: Performance enhancement and emission reduction

Gas-steam combined cycle power plant (CCPP) performance suffers from sensitivity to ambient condition, higher fuel consumption rate and greenhouse gas emission. Several solutions were adapted to resolve one or two problems with expense of other. In this study, a hybrid process for compressor inlet air cooling (CIAC) and fuel pre-heating (FPH) is proposed to enhance the CCPP performance with simultaneous reduction in fuel consumption and emission. Three simulation cases have been presented for CCPP design and off-design mode of operation at a site-specific condition. The result shows that, compared to conventional cases the influence of CIAC and FPH leads to capacity increment of 10.7% to 12.7 % with load variation from 40% to 100%. The associated overall efficiency enhancement is 2.2 – 0.58% when ambient air temperature Ta cooled from 35 °C to 15 °C operating at site condition Ta = 35 °C, RH = 65%. The sensitivity analysis is performed based on monthly mean weather data. The rate of fuel consumption and CO2 emitted are considered per unit of power generated. The CO2 emitted is maximum at low Ta in the range of 26 – 28 °C and lower RH. The CCPP at its full-load, for an operating period of 24 h the fuel consumption will reduce approximately to 12226 kg and this will lead to saving in operating cost of 4307 dollars per day.

Cumulative solar exergy allocation in heat and electricity cogeneration systems

Heat and electricity cogeneration is effective to improve energy efficiency but with no a unified allocation method. Both the emergy and cumulative exergy methods could evaluate the resources consumption, with the issues caused by total inheritance principle and inequivalence of primary exergy, respectively. This paper takes solar exergy as the basis for cumulative exergy, proposing a concept of cumulative solar exergy (CSE), which provides a new insight for allocation problems and sustainability evaluation. The CSE allocation is performed by taking the CSE transformities (TrCSE) in the stand-alone heat and electricity generation systems (alternative systems) as baselines. The CSE method is applied in the biomass and coal gasification cogeneration systems, with back pressure steam turbine (BPT), extraction condensing steam turbine (ECT) and gas-steam combined cycle (GSC) taken as power generation facilities. The results show that the TrCSE of biomass-based systems are lower than those of the coal-based systems. The resource utilization efficiencies can be improved by cogeneration according to the TrCSE of cogeneration and alternative systems. The allocation results of CSE and exergy methods are in the range of energy and enthalpy drop methods. The electricity coefficients of the CSE method are higher than those of the exergy method.

Performance evaluation of a novel CCHP system integrated with MCFC, ISCC and LiBr refrigeration system

This paper proposes a novel combined cooling, heating, and power (CCHP) system integrated with molten carbonate fuel cell (MCFC), integrated solar gas-steam combined cycle (ISCC), and double-effect absorption lithium bromide refrigeration (DEALBR) system. According to the principle of energy cascade utilization, part of the high-temperature waste gas discharged by MCFC is led to the heat recovery steam generator (HRSG) for further waste heat utilization, and the other part of the high-temperature waste gas is led to the MCFC cathode to produce CO32−, and solar energy is used to replace part of the heating load of a high-pressure economizer in HRSG. Aspen Plus software is used for modeling, and the effects of key factors on the system performances are analyzed and evaluated by using the exergy analysis method. The results show that the new CCHP system can produce 494.1 MW of electric power, 7557.09 kW of cooling load and 57,956.25 kW of heating load. Both the exergy efficiency and the energy efficiency of the new system are 61.69% and 61.64%, respectively. Comparing the research results of new system with similar systems, it is found that the new CCHP system has better ability to do work, lower CO2 emission, and can meet the cooling load, heating load and electric power requirements of the user side at the same time.

Exergy estimate of a novel hybrid solar-gas power and organic Rankine cycle-based hydrogen-production system

This study proposes a novel hybrid solar-gas power and hydrogen-production system, which is comprised by the solar tower thermal system, gas-steam turbine combined cycle and organic Rankine cycle-based hydrogen-production system. Based on the Ebsilon code, the operation processes of the hybrid system are simulated. The results show that the output power and electric efficiency of the hybrid system are 103.9 MW and 41.3%, and the daily hydrogen output is 62.2 kg. The operation simulation results of the hybrid system reveal that the gas-steam combined cycle and solar island can both achieve stable operations, and the power generation section and hydrogen-production device can both work effectively, which means the hybrid system is technically feasible. The exergy estimate results of the hybrid system show that the combustion chamber and solar receiver have the two largest exergy destructions, which are 56.5 MW and 45.3 MW. That means the performances of the two components can be further improved. For the hydrogen-production system, the exergy destructions of the proton exchange membrane electrolyzer, turbine, condenser and evaporator of the organic Rankine cycle are 0.156 MW, 0.111 MW, 2.338 MW and 1.891 MW, and the corresponding exergy efficiencies are 51.2%, 92.6%, 80.7% and 79.5%, respectively.

Thermodynamic performance study on gas-steam cogeneration systems with different configurations based on condensed waste heat utilization

In view of the limited application of the traditional water-cooled GSPP (gas-steam combined cycle power plant) in water-deficient areas, an air-cooled GSPP is proposed based on AHP (absorption heat pump) to achieve conservation of energy and water in this paper. The thermodynamic performance is comprehensively compared with three other configurations from both the energy and exergy analysis perspectives. Four cogeneration systems are considered: traditional water-cooled GDES (GSPP with direct extraction steam for heating), water-cooled GAS (GSPP with AHP system), air-cooled GDES and air-cooled GAS. Compared with water-cooled GDES, net output power, energy and exergy efficiencies increase by 17,815 kW, 1.43% and 1.53% in air-cooled GAS with 384,382 kW heating capacity. The results demonstrate that the performance of an air-cooled GAS can surpass that of a traditional water-cooled GDES, which shows that the energy-saving effect of waste heat recovery can compensate for the performance reduction caused by air cooling modification. Therefore, the traditional water-cooled GDES can be modified into an air-cooled GAS to implement dual purposes of saving energy and water in water-starved regions. The water-cooled GAS achieves the best performance and should be selected in water-rich areas. This research can provide theoretical support for different energy- and water-saving modification needs.

Thermal-economy optimization for single/dual/triple-pressure HRSG of gas-steam combined cycle by multi-objective genetic algorithm

This investigation proposed the RBF-NSGA-Ⅱ optimization algorithm and explored the thermal economy of different bottom combined cycles under 16 design parameters. The maximum efficiency, minimum exergy loss and minimum unit investment of different gas–water system combined cycles under various design factors were compared with traditional optimization, NSGA-Ⅱ optimization and RBF-NSGA-Ⅱ optimization. The results indicated that the combined cycle efficiency optimized by NSGA-Ⅱ and RBF-NSGA-Ⅱ increased by 25.2%, the exergy loss was reduced by 32%, and the specific investment was reduced by 38% compared with the traditional optimization. This investigation showed that the convergence speed of the newly proposed RBF-NSGA-Ⅱ optimization algorithm is increased by three times compared to the NSGA-Ⅱ optimization algorithm. Furthermore, through single-parameter sensitivity analysis, the relationship between compressor outlet pressure, gas turbine inlet temperature, pinch point temperature difference, approach point temperature difference, waste heat boiler pressure and combined cycle efficiency, exergy loss, and specific investment costs were investigated. The paper provided a new way for combined cycle design and guided the operation of combined cycle power plants.

Review of Research on System Thermal Inertia Modelling and Optimal Scheduling from the Perspective of Flexible Resources

The thermal inertia of the existing heating system is often considered an adverse factor, which will affect the operation of the system. However, under the perspective of resource flexibility, the thermal inertia of the system can effectively increase the flexibility of the system operation, significantly reduce the energy consumption and enhance the ability of energy supply and demand balance, and enhance the new energy integration, such as the wind power. Based on the flexible resources, it focuses on the study of the thermal inertia of the “network side” heating pipe network of the system and the optimal scheduling of the heating system. Combined with the thermal inertia of the pipe network, the operation characteristics of the power/heat output of the gas-steam combined cycle unit were analysed theoretically. On this basis, the optimal scheduling model of the system was established. Taking the energy supply system of an industrial park as an example, the model was verified to achieve a more stable power output effect of the unit.

Performance analysis of a solar based waste to energy multigeneration system

In this study, a solar-powered waste-to-energy multigeneration system is designed to produce various useful outputs, such as hydrogen, ethanol, heating, cooling and power generation, for a sustainable community is developed and analyzed in addition a comprehensive performance assessment. In this regard, thermodynamic analyses using both energy and exergy approaches are conducted to study and examine the effects of system and operation parameters, such as steam feed rate and gasification temperature on the system performance and investigate possible improvements in the amounts of ethanol and hydrogen produced. The present system utilizes the solar tower as a renewable energy source to produce energy and steam. This steam and animal manure are used as a gasification agent for hydrogen and ethanol generation at the gasification unit. The other objective of this study is to investigate the impact of changing system properties and operating conditions to maximize hydrogen and ethanol production as well as energy and exergy efficiency while minimizing detrimental syngas by conducting several parametric studies in a renewable energy-based multigeneration system. Furthermore, a molten salt storage system is available to minimize energy imbalances originating from renewable solar energy. The gas-steam combined cycle in the rest of the system aims to meet the community’s electricity and heating needs. In the last stage, the cooling required by the community is provided by a vapor absorption cooling system. The overall energy and exergy efficiencies are found as 61.1% and 56.4%, respectively.

An online parameter identification and real-time optimization platform for thermal systems and its application

Real-time performance optimization of thermal systems is crucial for energy conservation but also challenging because of the high system complexity and time sensitivity. Herein, an online parameter identification and real-time optimization platform for thermal systems is developed, and a gas-steam combined cycle cogeneration system is used to demonstrate its capability. The platform integrates data collection, parameter identification, system simulation, and real-time optimization modules. The data preprocessing and parameter identification modules collects real-time operation parameters for optimization. The system simulation module applies the heat current method to model the cogeneration system precisely, and a high-efficiency simulation procedure is proposed using the hierarchical and categorized (H&C) algorithm. The system optimization module introduces the artificial neural network technology to ensure the response time of real-time optimization. Meanwhile, the H&C algorithm and genetic algorithm are combined to update the database to improve the optimization performance gradually. The platform is first validated on three typical conditions. It is further deployed at a power plant, where a field test is conducted for the practical verification. Field test results show that the standard coal consumption of the cogeneration system could be reduced by 0.415 g/kWh by using the platform, which proves its practicability.

Thermo-conversion of a physical energy storage system with high-energy density: Combination of thermal energy storage and gas-steam combined cycle

Electrical energy storage (EES) systems are of great significance for the widespread use of renewable energy and peak shaving of power grids. The EES system with high-energy density is one of the current research hotspots. In this paper, a novel type of EES system with high-energy density, pressurized water thermal energy storage system based on the gas-steam combined cycle (PWTES-GTCC), is presented. The proposed system could achieve the coupling of thermal energy storage (TES) and gas-steam combined cycle (GTCC) through the cracking reaction of methanol. In discharging process, methanol is cracked after absorbing thermal energy, and the cracked gas is burned to drive GTCC for generating electricity. By constructing the thermo-dynamic model of the system, performance of the system and each component are discussed in detail. The results show that the energy storage density of the proposed system reaches 36.5 kWh/m3, and it is the most sensitive to the temperature of the high-pressure water with a sensitivity coefficient of 5.7. Furthermore, the efficiency of the PWTES-GTCC is expected to reach 53.1% as the efficiency of the GTCC and the electrical efficiency of the pressurized water thermal energy storage (PWTES) achieve 55.4% and 42.6%, respectively. These three efficiencies are most sensitive to the inlet temperature of the gas turbine.

Thermodynamic analysis of a combined gas-steam cycle without and with afterburner

Currently in power plants what is sought are higher thermal efficiencies, which is why combined cycle plants have been chosen, since they make better use of fuel, producing greater net power, all this It has led to innovative modifications to combined cycle power plants, improving their performance. In this article the thermodynamic analysis of a combined cycle (Gas-Steam) without and with Afterburner is carried out, in said analysis adequate thermodynamic indices have been used and the calculations have been carried out taking into account the state of the art for gas turbines and the typical values for steam cycle quantities. The purpose of this study is to analyze the combined plants where the exhaust gas at the outlet of the gas turbine is used in a waste heat recovery boiler to produce steam that is expanded in a turbine and discharged in a condenser. Since the air-fuel ratio in the combustion chamber of a gas turbine is higher than the stoichiometric, fuel can be added in the boiler (Afterburner) to increase steam production or to improve the quality of the steam produced.

Research on Selection of Heating Extraction Point for H Class Gas-Steam Combined Cycle Unit in Zengcheng， Guangzhou

Introduction To find out the best extraction heating scheme according to the medium pressure heating steam parameters of large capacity combined cycle unit. Method Combined with the heat load characteristics of Zengcheng project， this paper discussed and analyzed in detail the system configuration， initial investment， load adaptability， unit efficiency and power output of various extraction heating schemes applied to gas steam combined cycle units. Result The analysis results showed that， compared with hot section extraction and IP cylinder extraction， cold section extraction has higher unit power generation output， power generation efficiency and comprehensive energy utilization， and the initial investment was the lowest. Conclusion Cold section steam extraction is a kind of medium pressure steam extraction heating scheme with better parameter matching adaptability， stronger ability to adapt to variable operating conditions of units， better thermal economy and initial investment， and more suitable for large capacity combined cycle units. This scheme can be used for reference for similar engineering designs.

Technical and Economic Analysis of the Supercritical Combined Gas-Steam Cycle

Combined cycle power plants are characterized by high efficiency, now exceeding 60%. The record-breaking power plant listed in the Guinness Book of World Records is the Nishi-Nagoya power plant commissioned in March 2018, located in Japan, and reaching the gross efficiency of 63.08%. Research and development centers, energy companies, and scientific institutions are taking various actions to increase this efficiency. Both the gas turbine and the steam turbine of the combined cycle are modified. The main objective of this paper is to improve the gas-steam cycle efficiency and to reach the efficiency that is higher than in the record-breaking Nishi-Nagoya power plant. To do so, a number of numerical calculations were performed for the cycle design similar to the one used in the Nishi-Nagoya power plant. The paper assumes the use of the same gas turbines as in the reference power plant. The process of recovering heat from exhaust gases had to be organized so that the highest capacity and efficiency were achieved. The analyses focused on the selection of parameters and the modification of the cycle design in the steam part area in order to increase overall efficiency. As part of the calculations, the appropriate selection of the most favorable thermodynamic parameters of the steam at the inlet to the high-pressure (HP) part of the turbine (supercritical pressure) allowed the authors to obtain the efficiency and the capacity of 64.45% and about 1.214 GW respectively compared to the reference values of 63.08% and 1.19 GW. The authors believe that efficiency can be improved further. One of the methods to do so is to continue increasing the high-pressure steam temperature because it is the first part of the generator into which exhaust gases enter. The economic analysis revealed that the difference between the annual revenue from the sale of electricity and the annual fuel cost is considerably higher for power plants set to supercritical parameters, reaching approx. USD 14 million per annum. It is proposed that investments in adapting components of the steam part to supercritical parameters may be balanced out by a higher profit.

Liquefied natural gas re-gasification cold energy hybrid system integration in gas-steam combined cycle power plant model: Enhancement in power generation and performance

• Hybrid system integration that uses a secondary chilled water circuit is proposed. • Significant enhancement of power output occurs at higher ambient temperature. • The hybrid system produces higher cooling duty. • The efficiency gain is at best marginal and depends on the integration approach. The liquefied natural gas (LNG) cold energy utilization for inlet air cooling (IAC) to augment combined cycle power output is widely recognized as a feasible and sustainable alternative. However, issues with flexible operation and hybrid system integration still remain in warm climate region. To take the edge off from such kind of issues and to enhance the power generation and the performance, few possible opportunities are explored for a gas-steam combined cycle power plant (CCPP) with thermal integration of LNG re-gasification cold energy. Three integration approaches, such as 1st gas turbine IAC, 2nd condenser water cooling (CWC) in steam turbine cycle and 3rd combined approach of both IAC and CWC are proposed. Thermodynamic modeling and simulation-based method is adapted for CCPP model identification and thermodynamic performance comparison. Moreover, the results are established as a function of relative humidity and ambient temperature along with off design power generation of the proposed system. The result shows that the CCPP relative power improved from 1.01% to18.48% (for third integration approach) and 0.17% to 0.217% (for second integration approach), in the ambient temperature range of 13–45 °C and relative humidity of 90–40% respectively, compared to that of non-integrated CCPP. In third integration approach the relative efficiency enhancement is observed in the range of 0.05–0.40%, particularly in higher range of ambient conditions. In second integration approach the CCPP efficiency enhanced from 0.17% to 0.22% in ambient temperature range of 13–45 °C and relative humidity 40–90%.

Thermo-economic analysis of the integrated bidirectional peak shaving system consisted by liquid air energy storage and combined cycle power plant

Natural gas peak shaving power station with gas-steam combined cycle is widely used to meet the demand of peak load regulation of the power grid. However, the exhaust heat of the system and the high-grade cold energy from the nearby liquified natural gas terminal are not fully utilized. Liquid air energy storage is a load leveling method suitable for grid scale but the system efficiency needs to be further improved. Therefore, a system that flexibly integrates the combined cycle power plant and liquid air energy storage to maximize the recovery of the wasted heat and cold energy is proposed, achieving the bidirectional peak shaving. The system realizes the cryogenic compression during the charging process and adequate exploitation of the exhaust heat from the power station during the discharging process. The effects of compressor and air turbine inlet temperatures, ambient temperature and natural gas pressure on the system are investigated by the thermodynamic analysis. The highest system efficiency can reach 99.39%. Also, it is demonstrated that the integrated system is economically preferable. Moreover, within the inlet temperature ranges of the compressor and air turbine studied, the systemic economics performance deteriorates as the temperature increases.

Numerical Analysis of Influence Factors on Operation Performance of an Axial Exhaust Condenser

Taking the axial exhaust condenser of one gas-steam combined cycle unit as the research object, the steam flow in the shell side of the condenser was simulated under summer operating conditions. The flow distribution of the condenser in the shell side was obtained. Through the extraction of simulation data, the pressure of the condenser was obtained. The simulation results of single factor influence showed that the main factors leading to high operating pressure of the condenser under summer working condition were steam load, circulating water inlet temperature, circulating water flow and vacuum tightness.

Research on Metal Supervision and Inspection Standards for Gas-steam Combined Cycle Units

Domestic gas-steam combined cycle units start and stop frequently, and the load changes greatly, which accelerate the expansion of defects, such as fatigue, cracks, and organizational deterioration of metal components. In view of the problems caused by the material selection characteristics of gas-steam combined cycle units and the daily shutdown mode, several common typical cases of gas-steam combined cycle units are analyzed, such as compressor blade fatigue fracture, main steam combined valve body fatigue cracks, pipeline and pressure vessel weld fatigue cracks. As well, the gas-steam combined cycle unit metal supervision content and inspection emphasis are studied and supplemented.

Data modelling and simulation control of steam heat circulation system in coal-fired power plant

To make up for the lack of domestic research on the dynamic model of the unit in a gas-steam combined cycle power plant, the thesis researched and established a real-time digital simulation model of the combined cycle power plant unit. Firstly, the theory found a non-real-time digital simulation model in MATLAB/SIMULINK environment. Then the paper converts it into C language code and uses the C Builder tool to encapsulate it into a simulation model that can run in real-time. Finally, the thesis conducted a simulation test on the model on real-time digital simulation and compared it with the field test results. The simulation results show that the combined cycle power plant unit model we have established can meet the real-time simulation requirements of the power system in terms of computational efficiency and model accuracy.