Water-steam Cycle Research Articles

Heat Pump and Steam Accumulator Electrical Energy Storage System (Esheatpac System)

Esheatpac is an electricity storage system that combines heat pump, steam accumulator, and steam-water cycles technologies. It includes a heat pump, powered by an electric compressor, which produces saturated steam that is stored in steam accumulators as pressurized liquid water. Later, this steam produces electricity in a turbo-generator. Combination of efficiency of heat pump and Rankine cycle heat rate allows reaching efficiencies of up to 100% or higher, without requiring any auxiliary fuel. Efficiencies of up to 124.5% can be achieved by providing natural gas, with the combination of heat pumps with COP equals 2.65 and Rankine cycles with heat rate of 47%. The above means that it is possible to extract from the system the same or higher amount of electricity that enters it, after remaining stored for the time required, up to almost 25% more. Esheatpac is an optimal solution for when it is required to store large amounts of electricity and medium discharge times. Today, the only storage systems that meet these conditions are pumped hydro storage (PHS) and compressed air energy storage (CAES). Compared to PHS, Estheapc presents the advantages of its better performance, a maximum of 85%, and less environmental and public opposition problems, in addition to the limitations to find suitable locations. Compared to CAES, it presents the advantages of its better performance, 50% in current plants, and much lower storage capacities, on the order of seven times less, which also means a lower material investment.

Response characteristics of ship steam power system under switchover of turbine feed water pump

Objectives The switching performance of turbine feed water pump is a key technical indicator to decide the operation stability of ship steam power system, and it is of great significance to the safety of navigation. Methods Using the Modular Modeling System(MMS) thermal engineering system simulation software, a simulation model of ship steam turbine power system based on the switching principle of turbine feed water pump is established. Meanwhile, the accuracy of the simulation model is verified by experiment data. The dynamic response of turbine feed water pump to steam-water cycle of steam turbine power system is analyzed under high-speed and low-speed conditions. Results The calculation results show that switchover of turbine feed water pump can meet the water supply demand of supercharged boiler under high-speed and low-speed conditions. After switching, the system can run stably under low-speed condition, but the operation of the system is unstable after switching under high-speed condition. It shows that the water level of the condenser rapidly rises to an extremely high level, and the water level of the deaerator drops sharply to an extremely low level. Severe pressure fluctuation occurs in exhaust steam and micro superheated steam. Conclusions The research results can provide theoretical support for the optimization of the switching scheme of the steam turbine feed water pump.

Study of supercritical power plant integration with high temperature thermal energy storage for flexible operation

Abstract The paper presents the recent research in study of the strategies for the power plant flexible operation to serve the requirement of grid frequency control and load balance. The study aims to investigate whether it is feasible to bring the High Temperature Thermal Storage (HTTS) to the thermal power plant steam-water cycle, to identify the suitable thermal charge and discharge locations in the cycle and to test how the HTTS integration can help support grid operation via power plant dynamic mathematical modelling and simulation. The simulation software named SimuEngine is adopted and a 600 MW supercritical coal-fired power plant model is implemented onto the software platform. Three HTTS charging strategies and two HTTS discharging strategies are proposed and tested via the simulation platform. The simulation results show that it is feasible to extract steam from the steam turbine to charge the HTTS, and to discharge the stored thermal energy back to the power generation processes. With the integration of the HTTS charge and discharge processes, the power plant simulation model is also connected to a simplified GB (Great Britain) grid model. Then the study is extended to test the improved capability of the plant flexible operation in supporting the responses to the grid load demand changes. The simulation results demonstrate that the power plant with HTTS integration has faster dynamic responses to the load demand changes and, in turn, faster response to grid frequency services.

A mathematical model of an existing gas-steam combined heat and power plant for thermal diagnostic systems

Systems of thermal diagnostic of an operation require computational tools, including mathematical models. These models should have a simple structure and short computing time. Therefore, often analytical-empirical models are used which encompass both mass and energy balances as well as additional empirical functions whose coefficients are estimated on the basis of measurement results. As a result, changing technical conditions of modelled machines are taken into account. This paper presents the simulation model of an existing gas-steam combined heat and power plant, which has a modular design and is divided into three partial models of: the gas turbine unit with rated power of 125.4 MW, the double-pressure heat recovery steam generator and the steam-water cycle with steam turbine rated 65 MW. The simulation models allow to calculate non-measured operating parameters and energy assessment indicators. They also have the capability of adapting to the changing technical conditions of the modelled machines. The developed models were validated by the use of measurements. Model predictive quality was verified with the determination factor and root mean square error. The models were also used to simulate the behavior of the analyzed gas-steam CHP plant under different operating conditions. Exemplary calculations have been presented.

Development and application of a multi-domain dynamic model for direct steam generation solar power plant

Direct Steam Generation (DSG) concentrated solar plants are promising but complex power systems. This latter feature originates both from the variety of physical phenomena and the dynamic nature of the boundary conditions at play during plant operation. A representative yet computationally efficient numerical simulator is a valuable tool to assist engineers in the proper design, control and operation of such specific water-steam cycle. The present communication reports on the development of a multi-domain dynamic model representing a DSG plant. To do so, we followed a code-coupling approach and relied on the domain-decomposition paradigm. More specifically, we built three sub-models respectively in the thermal-hydraulic, the optical and the control-command domains and coupled them through an in-house co-simulation platform called PEGASE. We used the CATHARE system code to solve the thermal-hydraulic problem and the more generalist DYMOLA software to model the convective and radiative heat exchanges within the solar receiver. As an example, we then applicate the simulator to elaborate an efficient controller for the steam separator level.

Economic Analysis of Electricity Storage Based on Heat Pumps and Thermal Storage Units in Large-Scale Thermal Power Plants

In this paper the financial viability of a novel storage concept, referred to as ‘integrated pumped-heat-electricity storage’, is assessed for both a coal-fired and a combined cycle (CC) power plant located in Germany, as well as for a concentrated solar power (CSP) plant located in Spain. The rationale of this concept is to use electricity during times of cheap wholesale market prices, e.g. stemming from a high supply of renewable energies, in order to generate thermal energy via a heat pump, since thermal energy can be stored at comparatively low cost. If the electricity demand rises again, the stored thermal energy is used to power a conventional water-steam cycle, thereby reducing the amount of fossil fuels used or enlarging the operating time of a CSP plant. A mixed integer linear program, considering the day-ahead wholesale market electricity prices and remunerations of offering tertiary control power in Germany, is employed to find an approximation of the optimal schedule for the generation in the power plant as well as for the purchase and the sale of electricity. The financial viability is assessed using net present value (NPV) and real options analysis. Storing electricity to profit from temporal arbitrage is found to be unprofitable, since the (conservatively estimated) costs of thermal storage units are still too high. The largest part of the revenues stems from the remunerations of offering tertiary control power. Therefore, while the utilization of heat pumps, which are estimated to have rather high costs, is not profitable, employing electric heaters without storage units is found to be economically viable for a coal-fired and a CC power plant in Germany. Here, NPV and real options analysis yield the same result, i.e. to invest immediately in such an application. In Spain, offering tertiary control power is presently not remunerated, but only the call-offs of tertiary control energy, which are not considered in the mixed integer linear program. Consequently, employing electric heaters in CSP plants in Spain is found to be not financially viable either.

Modelling and simulation of a coal-fired power plant for start-up optimisation

The increased impact from fluctuating energy sources like wind and photovoltaics significantly affects the operational regime of conventional power plants. In the near future, even former base load power plants such as the large-scale lignite plants in Germany will need to start and shut down to balance the electricity system. As frequent starts were not in the focus of optimisation in the past, an extensive potential can be expected to reduce start-up costs and environmental impacts. In order to investigate such optimisation potentials, a comprehensive dynamic simulation model has been developed including process components such as boiler and water-steam cycle but also the power plants control system along with start-up sequence control. After successfully reproducing a reference start of the power plant, the model has been used to identify restrictions for faster start-ups, less fuel consumption and less emission while keeping the thermal and mechanical stress, caused by higher ramp rates, within acceptable bounds.

Using of Pourbaix diagram for evaluation of water chemistry recommended for ultra-supercritical parameter of water coolant

An important indicator the reliable operation of the steam-water cycle at power plants is water chemistry. Special chemicals are used to correct water chemistry. At designing a new unit the selection of the chemicals is determined by the parameters of the water and steam and materials, used in different parts of the cycle. Oxygen and ammonia are used to correct water chemistry at units with supercritical parameters In the presence of these reagents the protective film is formed on the surface of the metal.The transition to ultra-supercritical parameters requires the using of new materials, used in the water-steam cycle. Austenitic steels are recommended to replace on inconel steels. Oxygenated treatment and all-volatile treatment under oxidizing conditions were recommended to apply at units of ultra-supercritical parameters. However to select the optimum water chemistry is necessary to have date on the conditions of formation the protective film on the inconel surfaces.On the basis of Pourbaix diagram is proposed to evaluate the influence of water chemistry on the forms of existence the oxides of nickel and chromium on the surface of inconel at high parameters of water coolant. The results of calculations are compared with the experimental data.

Decomposition characteristics of humic acid in boiler make-up water in power plants

The organic matter (OM) entering the water–steam cycle of a power plant has been considered as one potentially serious contaminant in the industry. Therefore, the thermal decomposition characteristics of humic acid (HA) were investigated at an elevated temperature in a stainless steel autoclave through ion chromatography and total organic carbon analysis methods. The concentrations of the impurity anions varied with the changes in HA concentration and pyrolysis time. In addition, the different contents of thermal decomposition products in the vapour–liquid environment were evaluated. Results show that the major inorganic decomposition products of humic acid at 350°C are chloride, sulfate, nitrate and fluoride ions. The experimental results are expected to contribute significantly to the quality control of feed and make-up water in power plants.

Modelling and Dynamic Simulation of the 2nd Generation Oxy Fired Power Plant – Oxidant Fan Failure Case

In large and complex processes use of simulators will take place more and more in the future to avoid and learn about transients and unexpected situations. There are plenty of dynamic simulation tools in the markets but most of them have been developed and used for quite specific and limited application areas. At the moment there are just few simulation tools which are capable to handle dynamically in the same simulation case challenging process areas like combustion, distillation, chemistry and control of very large process areas. For this reason, in this study, there was a need to carry out co–simulation where two dynamic simulation tools Apros and Aspen Plus Dynamics were combined together by using Matlab Simulink as an interface. The co–simulation approach was a way to construct large dynamic process simulation environment, where typical operational transients and failure situations of an oxy fired power plant were possible to test and analyze.Under EU 7th Framework Programme (FP7) the FLEXI BURN CFB project an oxy firing concept based on circulated fluidized bed (CFB) combustion and supercritical once-through (OTU) water steam cycle was developed and successfully demonstrated [1]. This project also generated a dynamic simulation model of the 1st generation oxy firing concept, as we call it. In the EU 7th Framework Program's project O2GEN (Optimization of Oxygen-based CFBC Technology with CO2 capture), the 2nd generation concept of CFB based oxy firing was developed. The target of the project was, at first, to increase O2 content in recirculated flue gas to see what kind of effect it has to the heat exchange and corrosion in the boiler. Secondly, the target was to carry out exergy analysis to increase the whole concept efficiency by decreasing energy consumption in the boiler, Air Separation Unit (ASU) and CO2 -purification unit (CPU). Based on these steady state analysis means the refined concept was then modelled for dynamic simulations which were carried out by using Apros and Aspen Plus Dynamics dynamic modelling tools in a co–simulation mode.This paper deals with dynamic simulation of the 2nd generation 600 MW oxy fired CFB once trough boiler. In this paper we will present the dynamic model which includes oxy fired CFB boiler, turbine island, ASU and CPU with all needed equipment like heat exchangers, pipes, pumps, air and fuel feeding systems, distillation columns and sequestration vessels. Automation like measurements, controllers and actuators are included in the model. The simulation case selected for this paper presents an analysis what happens when one of the oxidant fans trips on boiler full load operation and how to handle this kind of failure by decreasing the boiler load to sufficient level of regarding the available oxidant feeding capacity. There were several items which were taken into account in the boiler, turbine island, ASU and CPU side when this kind of failure takes impact. The main findings in the failure analysis will be presented. Finally, discussion and future aspects of the simulation approach described will be given.

THERMODYNAMIC ANALYSIS OF USE OF FLUOROCARBON WORKING FLUIDS IN POWER GENERATING UNITS OF SMALL SCALE POWER PLANTS

Estimation is given of thermodynamic efficiency of flow diagrams for small scale power plants with a working substance of fluoroorganic composition. A review of existing organic Rankine cycle (ORC) 4 technologies with working media other than those of the fluorocarbon composition has been given. As an object of comparison and replacement by a nonaqueous power plant, a small scale biomass fuelled power plant has been chosen using solid bark waste biomass as a fuel. This plant design is based on the traditional water-steam Rankine cycle. The calculated analysis of thermodynamic efficiency of multicircuit flow diagrams, with staged heat utilization circuits, as well as consecutive heat transfer from one circuit to another, proposed as an alternative to the traditional cycle, has been provided. The efficiency of steam-turbine cycles of the proposed arrangement has been analyzed for octafluoropropane (C 3 F 8 ) and decafluorobutane (C 4 F 10 ). The calculation of cycles and processes for new power generating units involved using experimentally substantiated state equations obtained by the authors earlier. The influence on internal cycle efficiency of new small scale power generating units depending on initial live steam pressure at turbine inlet and condensing temperature has been studied. A significant increase of thermal efficiency is noticed for the staged heat utilization arrangement, compared to the water-steam cycle. A number of technological and design advantages have been noted that can be achieved through applying working fluids of the fluorocarbon composition as the working media for small scale thermal power plants.

Transport of corrosion products in the steam-water cycle of supercritical power plant

The operational reliability of thermal power plant boilers is significantly influenced by corrosion processes and by the formation of deposits on heat transfer surfaces. The basis of this problem is the transport of corrosion products in the steam-water cycle. In this study, the source of corrosion products was discussed. The effect of the water parameters on the transport of corrosion products was analysed. The generation (or deposition) ratio of corrosion products on the main components was evaluated. The corrosion of carbon steel was found to be the main source of transported corrosion products, wherein about 85% of the corrosion products transferred in the fluid was derived from the feed-water train and about 90% of the corrosion products deposited on the boiler tubes. Consequently, a micro-oxygenated treatment method for supercritical power plant was proposed to restrain the transport of corrosion products.

Combined Cycle Performance Evaluation and Dynamic Response Simulation

Power plants operating in combined cycle present higher thermal efficiency (over 60%) and increased power generation when compared to traditional simple cycles, such as gas or steam turbines operating alone. Considering that the power plant evaluated in this paper is already operational, a further development concerning to the power plant control system is required in order to evaluate disturbances and frequency variations, generated by the electrical grid during normal operation, as the loads applied to the turbines are intrinsically associated to the grid frequency. A computer program able to simulate the control system was developed to cope with these instabilities and to guarantee the necessary protection to the power plant operation. The develop program was made using MATLAB Simulink®. The main components of the power plant consists of 2 gas turbines of 90 MW each and a steam turbine of 320 MW, totalizing 500 MW. Firstly, the power plant main components were constructed separately. Once obtained stable models, the exhaust from the gas turbine was connected to the water-steam cycle through the heat recovery steam generator. The main parameters necessary to adjust the model such as gains, limits and constants were obtained from the power plant operational data. The simulation results allowed the evaluation of some key parameters; others are possible but not shown, such as power, exhaust gas temperature, fuel flow and variable stator angles during grid instabilities. The studies were conducted by testing the robustness, response time, transient analysis, steady state analysis and reliability of the proposed model.

Potential of Exergy Efficiency Improvement of Coal Power Plants in Sri Lanka: a Case Study

In the context of energy utilization it is required to harvest maximum possible potential from the available energy sources. Therefore analysis, monitoring and optimization of available energysources and in particular those related to power plants are major requirement in the sector. Generally the energy performances of power plant are evaluated using criteria based on 1st law of thermodynamics. However, subsequent development in the field of thermodynamic studies in particular the exergy analysis was identified as a useful method to design, evaluation, optimization and improvement of power plant performance. It is based on 2nd law of thermodynamics. In this study, it is aimed to find out the potential of exergy efficiency improvement opportunities in coal power plants through exergy flow analysis. A methodology was developed to estimate exergy flows in coal power plants and efficiencies of major equipment in power plant employing 2nd law or exergy analysis. This was done according to general equations which are used in thermodynamics. As a result, set of equations pertaining to the thermodynamics behaviours was established to analyse exergy flows in coal power plants. The methodology was then applied to unit 01 of Lak Vijaya power station (LVPS) in Sri Lanka as a case study. In the process, thermodynamic properties of water-steam cycle of LVPS unit 01 under both design and actual calculation were used to evaluate exergy values of critical states of the cycle as well as the resulting exergy flows and related efficiencies of major equipment. Boiler was identified as the major exergy destruction equipment in power plant and consequently it has less exergy efficiency. Hence boiler sub system was analysed to identify potential of exergy efficiency improvement in coal power plants. The main parameters of boiler were used to identify the exergy flow behaviours of the boiler. An economic analysis was also done for the boiler to identify the benefits. Not only steam generating cost saving in power plant but also reduction of hazardous CO2 emission calculations were carried out.

Investigation of Different Operation Strategies to Provide Balance Energy With an Industrial Combined Heat and Power Plant Using Dynamic Simulation

Intermittency of renewable electricity generation poses a challenge to thermal power plants. While power plants in the public sector see a decrease in operating hours, the utilization of industrial power plants is mostly unaffected because process steam has to be provided. This study investigates to what extent the load of a combined heat and power (CHP) plant can be reduced while maintaining a reliable process steam supply. A dynamic process model of an industrial combined CHP plant is developed and validated with operational data. The model contains a gas turbine (GT), a single pressure heat recovery system generator (HRSG) with supplementary firing and an extraction condensing steam turbine. Technical limitations of the gas turbine, the supplementary firing, and the steam turbine constrain the load range of the plant. In consideration of these constraints, different operation strategies are performed at variable loads using dynamic simulation. A simulation study shows feasible load changes in 5 min for provision of secondary control reserve (SCR). The load change capability of the combined cycle plant under consideration is mainly restricted by the water–steam cycle. It is shown that both the low pressure control valve (LPCV) of the extraction steam turbine and the high pressure bypass control valve are suitable to ensure the process steam supply during the load change. The controllability of the steam turbine load and the process stability are sufficient as long as the supplementary is not reaching the limits of the operating range.

Optimizing integrated reference cases in the OCTAVIUS project

Adding a carbon capture plant to a power plant reduces the efficiency of said power plant. In order to keep this drop in efficiency as small as possible, several optimisation studies are performed in the OCTAVIUS project. Based on the work of the European Benchmarking Task Force—EBTF within the CESAR, CAESAR, and DECARBit projects, two reference power plants are modelled in Ebsilon®Professional. The first is an 800MWe coal case, the second a 430MWe natural gas combined cycle (NGCC) case. For each power plant two separate capture plants are considered: one using 30wt% MEA as solvent system, the other with CESAR1, a mixture of AMP and PZ as solvent system. This results in four different reference cases which are optimized by varying different process parameters and evaluating process modifications. In a second step, the integration of the capture plant into the power plant is evaluated. This is important especially for the coal fired power plant, where integration of waste heat from the capture plant or the CO2 compressor intercoolers can lead to a significant increase in overall efficiency. The configuration of intercoolers for the CO2 compressor is adapted to achieve the highest overall efficiency. For the natural gas combined cycle plant, integration is not that beneficial, since there is no heat sink available in the water steam cycle. In the end, the cost of electricity and cost of CO2 avoided is calculated for all four cases. While the CESAR1 solvent system in a conventional absorber–stripper scheme is less costly (almost 17%) than the MEA solvent system in a process with Lean Vapour Compression for the coal cases, the result is the opposite for the two NGCC cases though the difference is not substantial.

Experience in Preservation of the Water Steam Cycle in CCPP (Combined Cycle Power Plants) with ODA (Octadecylamine)

Based on the changes in the European energy market and EU goals for CO2 reduction, the fossil fired power plants, especially the high effective combined cycle power plants, are faced with new challenges. Flexible load requirements associated with frequent shutdowns especially in plants with peak load area are the results. In addition, large reserve capacities have to be retained for short-terms needs which can be quickly start operation. For this reason, preservation procedures play an increasingly important role. They should provide a good protective effect with the most simple handling and flexible management system. The preservation using FFA (film forming amines), for example, octadecylamine become more and more attraction. With the lecture, a first insight into the preservation process using octadecylamine will be given to the operators of boiler and turbine plants. Especially in the view of the further increase in supply of renewable energy and related flexibility requirements in the existing power plants, an efficient and sustainable preservation technology will be presented. Based on the feed-in priority of electricity from renewable energy sources, fossil fueled power plants have to deal with sinking electricity prices on the one hand and rising fuel costs on the other. Even the economic operation of highly efficient combined cycle power plants is more difficult. The results are frequent starts and stops and shutdowns with unknown duration. Even coal-fired power plants must cope with flexible load requirements and longer run-times in low and part load operation. In contrast, higher reserve capacities, which are often needed quickly, must be made available. For these reasons, preservation procedures have become more and more important. Because of different methods, the operator must decide to what

Energetic and exergetic analysis of Rankine cycles for solar power plants with parabolic trough and thermal storage

The paper analyzes the “secondary” circuit (for thermodynamic conversion) of a Concentrated Solar Power (CSP) plant with thermodynamic cycle, whose mirrors field supplies a thermal power, averaged over a sunny day, of about 100 MW heat. We study the case of parabolic trough solar collector using silicone oil in the “primary” circuit, which limits the peak temperature below 400 °C. The “primary” circuit uses thermal storage, allowing a delay between the power generation in rapport with the solar energy capture. We choose a water-steam cycle, type Hirn. For increasing its efficiency, it has regenerative feed water preheating and steam reheating. We compared, energetic and exergetic, two types of cycles, using a numerical model with iterative structure, developed by the authors. The results showed that the simplified design achieves practically the same thermodynamic performances with the advanced one.

Effect of Ethanolamine, Ammonia, Acetic Acid, and Formic Acid on Two-Phase Flow Accelerated Corrosion in Steam–Water Cycles

Effects of ethanolamine, ammonia, and acetic and formic acid on two-phase flow-accelerated corrosion were investigated in an experimental loop simulating the conditions found in a water-steam cycle. Results indicate that the effects of acetic acid and ethanolamine on the corrosion rate neutralize each other. The effect of acetic acid on the corrosion rate was most pronounced at the highest tested steam quality. A model simulation for liquid film pH at 90% steam quality suggests that at very high steam qualities the protection ethanolamine provides increases, while the protection provided by ammonia goes down. A linear relation between calculated liquid film pH and the measured corrosion rate was found for 24% steam quality within a pH range from 5.6 to 6.3. Formic acid was thermally unstable at the tested temperatures and had no effect on the corrosion rate.

Energy, exergy analysis and working fluid selection of a Rankine cycle for subsea power system

In this paper, a subcritical/transcritical Rankine cycle for subsea power system is investigated. By balancing the pressure between the inner and outer side of the rotary seal, the dynamic sealing problem for the subsea power system is minimized. This Rankine cycle is electrical heated and utilizes the surrounding deep seawater as the cooling source. The mathematical model was established based on the first and second law of thermodynamics and the simulation validation was made. Water–steam, CO2, C9H20, C10H22 and C12H26 are selected as the working fluid and the comparison was made. The results show that the subsea Rankine cycle can obtain a higher thermal efficiency as the working depth increases between 1000 and 5000m. The thermal efficiencies are obtained as: 19.4–26.7% for water–steam cycle, 9.6–31.2% for CO2 cycle, 9.1–14.7% for C9H20 cycle, 8.0–13.5% for C10H22 cycle and 6.3–11.8% for C12H26 cycle, depending on the working depth. With the same working depth, the water–steam cycle has a higher thermal efficiency, exergy efficiency and turbine power output but requires higher total energy input; while the CO2 cycle can obtain a high thermal efficiency, exergy efficiency with lower energy consumption but produces less turbine power output. In addition, it is found exergy destruction mainly occur in the boiler and condenser, accounting for more than 90% in total.