Water-steam Cycle Research Articles

Thermal efficiency and performance analysis of 50 MW concentrated solar power plant

This study evaluates the operational efficiency and performance of the Shagaya 50 MW Concentrated Solar Power (CSP) plant in Kuwait that has been operational since February 2019. Utilizing Parabolic Trough technology, the plant incorporates a large Solar Field (SF) comprising 8 platforms with total of 206 solar-collector loops. Thermal energy captured by the SF is utilized in a Low Temperature Rankine Cycle to generate electricity via water-steam cycle and heat exchangers, with a nominal turbine capacity of 50 MW. Supported by a thermal energy storage (TES) system capable of storing 1200 MWht energy in molten salt. Through a comprehensive assessment spanning 41 months, real-time operational data is analysed to evaluate the CSP-TES system's efficacy within Kuwait's climatic conditions. Various performance parameters are examined, providing insights into CSP technology's practical implications and operational strategies. Driven by the annual difference in downtime and TES availability, comparative analysis of the plant's annual electricity production over the three years reveals notable variations: 74.99 GWh in 2019, 160.62 GWh in 2020, and 140.04 GWh in 2021, corresponding to capacity factors of 19 %, 40.75 %, and 35.53 %, respectively. The findings underscore the strong correlation between the SF and TES system in determining overall plant efficiency. The study also highlights the impact of high wind speeds on plant operation, triggering shutdowns on 9 days during the assessment period. Additionally, soiling losses in the SF are assessed through daily reflectivity measurements, guiding cleaning efforts using semi-automated armed trucks. Seasonal peaks in cleanliness factor coincide with local spring season, underlining the detrimental effect of reflectivity losses on plant output due to higher dust mass densities. A design flaw causing frequent breakdowns of receiver tubes under high winds is identified and addressed.

Numerical investigations of transient thermal loading of steam turbines for SMR plants

One of the well-known technologies that fit well into the goal of reduction of greenhouse gas emissions is nuclear energy. In particular, the change in approach to the design and construction of nuclear power plants led to the development of small modular reactors (SMRs), which are characterized by a broader range of possible applications than large nuclear reactors and the ability to flexibly operate as per load demand. This paper presents an analysis of the thermal loads of a steam turbine rotor operating in a power plant with SMR. Steam-water cycle and turbine train of a 300 MW unit are presented. High-pressure steam turbine rotor and its thermal loading due to varying steam conditions are investigated for a cold startup designed with consideration of the thermal characteristics of nuclear reactors. It was shown by numerical simulations that steam condensation on rotor surfaces plays a crucial role in determining its thermal behaviour. Comparison with conventional rotors has shown that the thermal loading of nuclear turbine rotors is lower and more stable than that of conventional turbines.

Supercritical CO2 power cycle

The article is focused on summarizing the issue of energy circuits working with supercritical carbon dioxide sCO2. Carbon dioxide is currently coming to the forefront of many research institutions with regard to its possible use in its supercritical conditions, thanks to which higher efficiency and compactness of equipment can be achieved compared to conventional steam-water cycles. The article describes the basic properties of this medium, including a description of sCO2 cycles (Brayton, Rankine, etc.). Furthermore, the possible use of energy cycles with sCO2 is discussed, especially in solar and nuclear power plants and in power plants burning fossil fuels. In the case of solar power plants, the sCO2 Brayton cycle can offer higher cycle efficiencies than using super-critical steam cycles. The use of sCO2 in nuclear or coal power plants in turn increases efficiency and reduces water consumption. In addition, the use of the sCO2 circuit in new nuclear reactors of the IV generation is currently being considered, in which the operating temperatures are in the range of 500 - 900 °C, i.e. they are generally higher than operating water-cooled reactors. Even though the use of CO2 refrigerant in power systems has been known for a long time (e.g. use in the first Czechoslovak power plant in Jaslovské Bohunice), they are still not used commercially in the energy industry. One of the reasons is the ongoing research into the behavior of materials at high temperatures in sCO2, corrosion protection, or the effect of carbon dioxide purity on behavior in the supercritical region.

Construction of a Test Facility and the Test of an Active Tritium Permeation Barrier

In future fusion or fission reactors, tritium permeation may present a serious challenge. In order to separate the water steam cycle from gas streams containing significant amounts of tritium, a permeation barrier is necessary. Tritium permeation into the environment through steam generators and heat exchangers can be a significant hazard regarding radiation and environmental safety. In the scope of the project TRANSversal Actions for Tritium (TRANSAT), a facility has been set up to perform tests on various scaled and functioning permeation barrier mock-ups at the Tritium Laboratory Karlsruhe (TLK). The facility was built in a standard glove-box unit in accordance to the technical terms and requirements of tritium handling at TLK. The behavior of an active permeation barrier was investigated. Within the first series of TRANSAT experiments, four different mock-ups have been tested for tritium permeation. Migrated tritium is oxidized to tritiated water (HTO) using Carulite reactors and molecular sieves for HTO trapping. This paper will present the construction, setup, and commissioning of the facility as well as the first series of TRANSAT experiments including their evaluation.

Feasibility Study of Scheme and Regenerator Parameters for Trinary Power Cycles

Natural gas-fired combined cycle plants are nowadays one of the most efficient and environmentally friendly energy complexes. High energy efficiency and low specific emissions are achieved primarily due to the high average integral temperature of heat supply in the Brayton–Rankine cycle. In this case, the main sources of energy losses are heat losses in the condenser of the steam turbine plant and heat losses with the exhaust gases of the waste heat boiler. This work is related to the analysis of the thermodynamic and economic effects in the transition from binary to trinary cycles, in which, in addition to the gas and steam–water cycles, there is an additional cycle with a low-boiling coolant. A method for the feasibility study of a waste heat recovery unit for trinary plants is proposed. The schematic and design solutions described will ensure the increased energy and economic performance of combined cycle power plants. Based on the results of the thermodynamic optimization of the structure and parameters of thermal schemes, it was found that the use of the organic Rankine cycle with R236ea freon for the utilization of the low-grade heat of a trinary plant’s exhaust gases operating from a GTE-160 gas turbine makes it possible to achieve a net electrical efficiency of 51.3%, which is a 0.4% higher efficiency for a double-circuit combined cycle gas turbine plant and a 2.1% higher efficiency for a single-circuit cycle with similar initial parameters. On the basis of the conducted feasibility study, the parameters and characteristics of the heat exchangers of the regenerative system of the waste heat recovery unit are substantiated. The use of plain fin-and-tube heat exchangers in the regenerative system of the utilization cycle is the most promising solution. It was found that the level of allowable pressure loss in the regenerator of 10 kPa and the degree of regeneration of 80% allow for maximum economic efficiency of the waste heat recovery unit.

Nuclear Magnetic Resonance Analysis of Hydrothermal Reactions of Ethyl- and Octylamine in Sub- and Supercritical Water

Hydrothermal reactions of aliphatic amines have recently gained importance in relation to the application of amines as film-forming corrosion inhibitors for steam-water cycles. The kinetics and mechanism of the hydrothermal reactions of ethylammomiun cation (EtAH+) and n-octylammonium cation (OctAH+) were studied for comparison with the corresponding neutral amines to elucidate their reaction products and pathways at sub- and supercritical temperatures of 300-400 °C as model reactions of aliphatic ammonium cations. We analyzed the reaction of 13C-15N-labeled EtAH+ using NMR spectroscopy and revealed that the initial hydrolysis to ethanol, known as the main path, is followed by the elimination reaction producing ethene and the disproportionation reaction giving diethylammonium cation. The OctAH+ yields octene and octanol, each of which isomerizes to thermodynamically more stable species as the major products. Comparisons were made between the reactions of the neutral amines and ammonium cations to highlight their different reactivity. The hydrolysis, alkene formation, and dehydration of alcohols to alkenes were all found to be accelerated at low pH. The formation of low-molecular-weight organic acids such as acetic acid and formic acid was not observed. These results indicate that the corrosion protection effect of film-forming amines will be maintained under practical conditions with pH values as high as around 9 to 10, and hence side reactions involving byproducts will be suppressed.

Dynamics of large-scale bubbling fluidized bed combustion plants for heat and power production

Bubbling fluidized bed combustion (BFBC) plants for combined heat and power (CHP) production have traditionally been dispatched under slow load changes. As the amount of variable renewable electricity increases in energy systems worldwide, knowledge regarding the transient capabilities of the gas and water-steam sides of BFBC plants is required. The aim of this work is to investigate the dynamic performance of large-scale BFBC plants when accounting for both the gas and water-steam sides. To do so, this paper presents a dynamic model of BFB-CHP plants that result from connecting a model of the gas side to a process model of the water-steam side. The plant model output is validated by comparisons with operational data measured in a 130-MWth BFBC plant that produces electricity, district heating (DH) water and steam for industrial clients. The validation shows that the model can satisfactorily describe both multi-load steady-state operation and load transients. The simulation results highlight the fact that the water-steam cycle achieves stabilization more rapidly after changes in the DH line and steam delivered to customers, as compared to changes in the combustor load. The timescales of the plant outputs for different changes have been calculated, with stabilization times ranging from 2 to 15 min for the power production versus 2–25 min characterizing the DH production. Compared to the stabilization times of the gas side, the water-steam side is an order of magnitude slower, thereby limiting the transient operation capabilities of BFB-CHP plants.

Dependence of Na+ leakage on intrinsic properties of cation exchange resin in simulated secondary environment for nuclear power plants

Material corrosion in nuclear power plant (NPP) is not controlled only by amine injection but also by ion exchange (IX) which is the best option to remove trace Na+. This study was conducted to understand the Na+ leakage characteristics of IX beds packed with ethanolamine-form (ETAH-form) and hydrogen-form (H-form) resins in the simulated water-steam cycle in terms of intrinsic behaviors of four kinds of cation-exchange resins through ASTM test and Vanselow mass action modeling. Na+ was inappreciably escaped throughout the channel created in resin layer. Na+ leakage from IX bed was non-linearly raised because of its decreasing selectivity with increasing Na+ capture and with increasing the fraction of ETAH-form resin. Na+ did not reach the breakthrough earlier than ETAH+ and NH4+ due to the increased selectivity of Na + to the cation-exchange resin (H+ < ETAH+ < NH4+ ≪ Na+) at the feed composition. Na+ leakage from the resin bed filled with small particles was decreased due to the enhanced dynamic IX processes, regardless of its low selectivity. Thus, the particle size is a predominant factor among intrinsic properties of IX resin to reduce Na+ leakage from the condensate polishing plant (CPP) in NPPs.

The comprehensive solution to decrease cooling wall temperatures of sCO2 boiler for coal fired power plant

Compared with water-steam cycle, supercritical carbon dioxide (sCO2) cycle has higher efficiency when applied in coal fired power plant. However, it also introduces challenges in boiler: because of the higher working fluid temperature and the lower convective heat transfer coefficient in boiler tubes, the cooling wall is more prone to overheating and bursting due to higher wall temperatures. Here, based on fundamental consideration of the thermal coupling between 3D radiation heat flux in furnace side and CO2 fluid in cooling wall tubes, we propose a comprehensive solution to decrease cooling wall temperatures. The solution includes four consecutive techniques: improved coupling in furnace width direction (CWD), flue gas recirculation for heat flux reduction (FGR), improved coupling in furnace height direction (CHD), and enhanced heat transfer in cooling wall tubes (EHT). A comprehensive thermal-hydraulic model is developed for a 1000 MWe power plant. It is found that the new solution can reduce the cooling wall temperatures from 670.5 °C to 635.0 °C, among which CWD, FGR, CHD and EHT contribute to the decrement of cooling wall temperatures by 13.3 °C, 4.4 °C, 6.8 °C and 11.0 °C, respectively, concluding that CWD and EHT are more effective than other techniques.

Performance Analysis of a Waste-to-Energy System Integrated with the Steam–Water Cycle and Urea Hydrolysis Process of a Coal-Fired Power Unit

An innovative hybrid energy system consisting of a waste-to-energy unit and a coal-fired power unit is designed to enhance the energy recovery of waste and decrease the investment costs of waste-to-energy unit. In this integrated design, partial cold reheat steam of the coal-fired unit is heated by the waste-to-energy boiler’s superheater. The heat required for partial preheated air of waste-to-energy unit and its feedwater are supplied by the feedwater of CFPU. In addition, an additional evaporator is deployed in the waste-to-energy boiler, of which the outlet stream is utilized to provide the heat source for the urea hydrolysis unit of coal-fired power plant. The stand-alone and proposed designs are analyzed and compared through thermodynamic and economic methods. Results indicate that the net total energy efficiency increases from 41.84% to 42.12%, and the net total exergy efficiency rises from 41.19% to 41.46% after system integration. Moreover, the energy efficiency and exergy efficiency of waste-to-energy system are enhanced by 10.48% and 9.92%, respectively. The dynamic payback period of new waste-to-energy system is cut down from 11.39 years to 5.48 years, and an additional net present value of $14.42 million is got than before.

Evaluation methodologies of damage related issues for heat exchangers in the thermal storage energy system

Thermal oil is used as a heat transfer fluid in many thermal solar power systems, while molten salts are used to store thermal energy. The oil absorbs solar energy and transports it to a water-steam cycle via heat exchangers, where it is transformed into electric energy via a turbo-generator or stored in a thermal energy storage device for subsequent transmission to the water-steam cycle. The complexity of these thermal solar plants is rather significant, as they mix conventional engineering used in power stations (water-steam cycle) or petrochemical (oil pipeline) with modern solar (parabolic trough collector) and heat storage (molten salts) technology. This paper focuses on modelling in heat exchanger tubes in molten salt energy storage systems, and it offers a comprehensive model of the process. By developing such a model, the groundwork for future study into heat exchangers model failure analysis is established.

A new heat supply strategy for CO2 capture process based on the heat recovery from turbine exhaust steam in a coal-fired power plant

A new heat supply strategy for the CO2 capture process based on the heat recovery from turbine exhaust steam was proposed and evaluated. A water-steam cycle, a CO2 capture unit, a CO2 compression unit, and an enhanced two-stage heat pump were simulated for a 600 MW coal-fired power plant using Aspen Plus. Effects of the working medium, the exhaust pressure of the turbine, and reboiler temperature on the heat pump efficiency were studied. The integrated configurations were simulated and the effects of reboiler duty, exhaust steam pressure, and reboiler temperature on the thermodynamic performance of the plant station were discussed. Results indicated that the utilization of internal heat exchangers improved effectively the coefficient of performance (COP) of the two-stage heat pump by 13.3–22.0%; the heat pump recovered effectively the latent heat of exhaust steam, and a lower CO2 desorption temperature would significantly contribute to a higher COP of the heat pump system and greater thermodynamic performance of the proposed integrated configuration with heat pump. A net electric efficiency penalty of 7.07% and a fuel utilization efficiency of 51.58% were obtained when the reboiler temperature was 90 °C.

Research Process on Water Treatment Agent of Boiler for Preventing Metal Corrosion in the Steam-water Cycle

The safe and economical operation of boiler is influenced significantly by the metal corrosion in the steam-water cycle. It is the most common way to add the water treatment agents into the boiler water to prevent metal corrosion. In this paper, the application situation and limitations of the traditional boiler water treatment agents were summarized. Then the research process of the film-forming amines was elaborated. First, the structure and composition of film-forming amines, their properties and the interaction mechanisms with metal materials were described. Second, the industrial application of the film-forming amines was considered. Third, the existing problems of film-forming amines were discussed. Finally the future development of the novel film-forming amines was prospected.

Corrosion study on low molecular organic acids in the initial condensation zone of steam turbines

Purpose The purpose of this study was to investigate the corrosion of low molecular organic acids from water-steam cycles such as acetic acid and formic acid in mental parts of steam turbine initial condensation zone. Design/methodology/approach The corrosion behavior of gray cast iron in initial condensate containing different concentrations of acetic acid and formic acid was studied by weight loss test, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Findings The results indicated that gray cast iron had a certain degree of corrosion in the simulated initial condensate containing acetic acid and formic acid, but the acid corrosion of gray cast iron was not only caused by low molecular organic acid but also affected by inorganic anions such as Cl−. When Cl− existed, after removing corrosion products, surface analysis results proved that the surface of gray cast iron was rough and uneven with many cracks, which was corrected more serious. Originality/value The corrosion behavior of thermal equipment by low molecular organic acids and inorganic anions in water-steam cycles was studied. The research results can provide theoretical guidelines for corrosion control of steam turbine in power plants.

Operation and Sensitivity Analysis of a Micro-Scale Hybrid Trigeneration System Integrating a Water Steam Cycle and Wind Turbine under Different Reference Scenarios

Renewable energy sources, such as solar, wind, biomass, and geothermal energy, are being more and more adopted in small and micro-scale distributed generation systems. In this context, different hybrid configurations and layouts that may adopt, lead to different energy and economic performance of energy generation systems. In micro-scale applications, biomass and solar energy sources are more frequently investigated in literature compared to other combinations as biomass and wind energy. The analysis of the performance of a novel small-scale trigeneration system is presented in this paper. The system includes biomass boiler, water steam turbine, absorption chiller, and wind turbine, and it is linked to the electric grid by means of a bidirectional connection, allowing to the store virtually the electrical energy produced in excess, and use when needed. For the proposed system, a zootechnical farm and a residential building are considered as case study, including different scenarios for the reference energy system. The Transient System Simulation (TRNSYS software is used to model, simulate, and investigate the system performance under realistic operation conditions. Energy and economic performance of the system is assessed by means of a daily, weekly, and yearly analysis. The effect of the main design parameters, as steam and wind turbine power on the system performance, is investigated by means of a sensitivity analysis. The investigations show that the Simple Pay Back time of the proposed system is below 6 years, when the biomass is free, capacities of steam and wind turbines lower than 4 kW are selected, and a reference system with a natural gas boiler and electrical grid is considered. The system allows one to achieve satisfactory energy and economic performance under the considered conditions, when a proper design of the system component capacities is adopted.

Systematic evaluation of efficiency improvement options for sCO2 Brayton cycles

Supercritical CO2 (sCO2) based power cycles have gained an increased attention because of their potential to offer a higher cycle efficiency combined with improved process economics and operational flexibility. The potential for further development and commercialization is determined by the right balance between cycle efficiency, design complexity, and economics. The present study analyzes different pathways to improve the design of generic sCO2 Brayton cycles for power generation based on a structured pattern known from conventional water-steam cycles. Starting from a simple cycle design, different options such as preheating, intercooled compression, reheating, and split-compression are investigated. The application of an exergy analysis for each design provides the possibility to identify the location and magnitude of thermodynamic inefficiencies for each design option. With the use of a complexity metric, the offset between efficiency improvement and increase in system size and complexity can be quantified in the absence of appropriate economic data. The results show the inherent trade-off between the increase in efficiency and complexity with the best cycle improvement options being preheating by recuperation, split-compression, and intercooled compression. In principle, the suggested complexity metric approach is useful when evaluating similar systems and provides tangible results for subsequent, more detailed studies.

Aluminum compound forms in the Al–H2O system as applied to operating conditions of Dry Cooling Towers

One of important indicators of reliable operation of the steam-water cycle at power plants is water chemistry. Special chemicals are used to adjust properties of working fluids. At designing a new unit the chemicals are selected on the basis of parameters of water, steam and materials, used in different parts of the cycle.Another indicator is minimizing the cooling water loss. Typical loss of cooling water is about 5% of total water amount. This loss is associated with evaporation, droplet carry-over, and blowdown in cooling towers.For power plants, it is typically recommended to use dry cooling towers for minimizing the cooling water loss. In dry cooling systems, cooling water with low amount of impurities goes to mixing condenser, where turbine steam condensation occurs. Then one portion of mixed water flow at the condenser outlet is supplied to the boiler or steam generator feed water loop. Another portion is returned back to the cooling tower. Inside the cooling tower, water is cooled down by passing through air-cooled heat exchangers manufactured of aluminium or steel alloys.On the basis of Pourbaix diagram it is proposed to evaluate the influence of water chemistry on the forms of existence of aluminium compounds in dry cooling towers. The results of calculations are compared with the experimental data.

The Vapor of Thermal Deaerators as a Factor of their Energy Efficiency

The effect of the vapor of thermal deaerators on the energy efficiency of these heat-and-mass transfer apparatus and the thermal power plant as a whole is considered. Problems of reducing the vapor flow rate and its use in design and operation of Russian thermal power plants are neglected. Unjustified fuel losses in thermal deaerators of poor design and the lack of control over the vapor and its recovery are exemplified. The theoretical vapor flow rates necessary for different flow patterns of deaerated water and desorbing agent in deaerators are determined. A significant advantage in the energy efficiency of the countercurrent design over the once-through design is demonstrated. It is shown that the standardized specific vapor flow rates for thermal deaerators of different types are justified inadequately. The possibility of effective deaeration of water at a specific vapor flow rate that is substantially lower than the standard one and very close to the theoretically necessary value is proved based on experimental data. It is demonstrated that there is a wide margin to improve the energy efficiency of thermal power plants by rationally using the vapor heat of thermal deaerators. A necessary condition for increasing the energy efficiency of thermal power plants is shown to be the recovery of the vapor heat and mass of thermal deaerators. To this end, the vapor coolers should be made of corrosion-resistant materials and the vapor condensate should be used in the water-steam cycle of the power plant. Another important way to improve the efficiency is to maintain the vapor flow rate consistent with the operating mode of the deaerator, which can most effectively be done by monitoring the residual content of corrosive gases in the deaerated water. A schematic of a deaeration plant with the vapor flow rate controlled by monitoring the residual oxygen content in the deaerated water is proposed. The vapor flow rate in such a plant is kept necessary and sufficient to maintain the rated desorption efficiency of dissolved oxygen in all thermohydraulic deaeration modes, thus preventing the operation of the deaerators at insufficient or excessive vapor flow rate.

Modeling and Energy Efficiency Analysis of Thermal Power Plant with High Temperature Thermal Energy Storage (HTTES)

This paper presents the recent research on the study of the strategies for the flexible operation of the thermal power plant to meet the requirement of load balance. The study aimed to investigate the feasibility of bringing the High Temperature Thermal Energy Storage (HTTES) to the thermal power plant steam-water cycle, to identify the suitable HTTES in the cold (hot) section of the reheating pipeline and to test the efficiency of the HTTES integration to increase the flexibility of peak shaving and energy efficiency via thermal power plant with HTTTES modelling and simulation. Thermoflex was adopted to perform the simulation and a 300 MW subcritical coal-fired power plant model was implemented onto the software platform. The simulation results show that it is feasible to extract steam from the steam turbine to charge the HTTES, and to discharge the stored thermal energy back to the power generation process, and to analyse the improved capability of the plant flexible operation with HTTES. Then the study was extended to analyse the effect of thermal energy temperature, the opening of the regulating valve, and the pipeline pressure loss aspects on thermal efficiency of the whole plant. The study is beneficial to achieve more economic operation of the thermal power plant with HTTES integration. It is concluded that the introduction of the HTTES can improve the consumption of wind power, and these ideas and methods for solving the energy consumption of the renewable energy and reducing the peak energy consumption are provided.

A novel approach to improving load flexibility of coal-fired power plant by integrating high temperature thermal energy storage through additional thermodynamic cycle

This work presents a novel approach to improving the load flexibility of coal-fired power plant by integrating high temperature thermal energy storage (HTTES) through additional thermodynamic cycle. It aims to investigate the feasibility of introducing an HTTES-aided additional cycle into the steam-water cycle of conventional coal-fired power plant and to test how a high round-trip efficiency can be achieved with the HTTES integration. The thermal system and operation mode of an HTTES-aided coal-fired power plant were described. The performance evaluation model was built and its performance was discussed based on a 600 MW subcritical coal-fired power plant model. The results show that the proposed approach is feasible to improve the load flexibility of the conventional coal-fired power plant. An additional net power can be obtained while the original unit works at its rated condition. The initial steam pressure of the additional cycle is the determining factor for the round-trip efficiency and a round-trip efficiency of 44.18% can be obtained. This work is expected to provide a detailed reference on the use of HTTES system to improve the load flexibility of coal-fired power plants and further to relieve the serious problem of the curtailment for fluctuating renewable power generation in China.