Feedwater Heater Research Articles

The performance of a Solar Aided Power Generation plant with diverse “configuration-operation” combinations

Solar Aided Power Generation is an efficient way to integrate solar thermal energy into a fossil fuel fired power plant for solar power generation purposes. In this particular power plant, the solar heat is used to displace the extraction steam to preheat the feedwater to the boiler. The heat exchanger, which facilitates the heat exchange between the solar heat carried by the heat transfer fluid and the feedwater, is termed a solar preheater. Four possible configurations of the solar preheater, namely Parallel 1, Parallel 2, Series 1 and Series 2, are proposed in this paper. In this type of plant, the extraction steam flow rates must be adjusted according to the solar input. The ways to control the extraction steam flow rates are termed solar preheater operation strategies. Three typical strategies: the Constant Temperature control, Variable Temperature control with high to low temperature feedwater heater displacement and Variable Temperature control with low to high temperature feedwater heater displacement have been identified. Each configuration can be operated with one of the three strategies, resulting in twelve “configuration-operation” combinations/scenarios (shown in Table 1). Previous assessments and modelling of such a plant have only been based on a single combination. In this paper, a Solar Aided Power Generation plant, modified from a typical 300MW power plant, is used to understand the plant’s performance for all twelve of the available combinations. The results show that the instantaneous and annual technical performances of such a plant are dependent on the combinations used. The scenario 10 (Table 1) is superior to the other combinations in terms of the plant’s instantaneous technical performance, while the scenarios 2, 5, 8 (Table 1) has the best plant’s annual technical performance.

Thermodynamic Modeling and Validation of a 210-MW Capacity Coal-Fired Power Plant

This paper presents the thermodynamic modeling and validation of a 210-MW subcritical coal-fired power plant situated in North India. In the era of high computing facilities available, modeling and simulation have become a very pertinent tool for design and development. As such, the objective of the present work is not to enhance the thermal conversion efficiency, but to represent the thermal system in a simplistic yet functional manner. The thermal performance module consists of the following main sections such as steam boiler, economizer, superheater, reheater, steam turbine, condensate extraction pump, boiler feed pump, feedwater heaters and condenser. Thus, a semi-empirical module has been developed to predict thermal performance of coal-fired power plant. It includes the mass balance, energy balance, thermodynamic property relations for working substance followed by empirical correlations for steam bled pressure and thermodynamics of a steam power cycle. By using the MATLAB calculation tool, a process-based computer program of the coal-fired power plant has been successfully validated for thermal efficiency, steam flow rate and coal consumption rate at wide plant load range. The predictions were compared with operating data of 210-MW thermal power plant at different power output levels. The predicted results agree with plant operating data.

Exergetic analysis of a natural gas-burning steam power plant

An exergetic analysis of the main subsystems of a steam power plant was undertaken. The product of the entropy generation rate and the effective temperature (modified Gouy–Stodola law) was used to calculate the real power/exergy loss due to various irreversibilities present in the subsystems. The use of the effective temperature was deemed appropriate because its derivation depends on the dynamics of the subsystem(s) under consideration. The results of our analysis showed that the highest rate of entropy generation occurred in the condenser while the maximum rate of entropy generation for the feed-water heaters was observed in the Heater6. The reasons for these observations were discussed in the relevant sections of this study. The greatest power/exergy loss was observed in double-flow low-pressure turbine. This could be due to the fact that the inlet steam was split and flows axially in opposite directions through the turbine blades, thereby creating a lot of irreversibilities. According to the results of this study, it can be concluded that the most irreversible unit in the system is the condenser with loss and followed by the high-pressure turbine with a power/exergy loss of . It was observed that when environmental temperature was used in the calculation of power/exergy loss, the results always underestimated the real power/exergy loss. Finally, the results of this study have highlighted the areas where the various subsystems of the power plant can be improved. The analyses show where the largest quantities of power/exergy loss are being dissipated within the plant, thus pointing to areas where improvement in energy usage can be made. The use of exergy as a potential design and retrofit tool was also pointed out.

Thermoeconomic and environmental analyses of a low water consumption combined steam power plant and refrigeration chillers – Part 1: Energy and economic modelling and analysis

Two novel configurations are proposed to replace the conventional Rankine cycle based steam power plants (SPP) with natural draft wet cooling towers (NDWCT) as cooling units. Closed feedwater heater unit of the base SPP-NDWCT system is eliminated in order to combine a vapor compression refrigeration (VCR) and an absorption heat pump (ABHP) with the base SPP-NDWCT system. Both VCR-SPP-NDWCT and ABHP-SPP-NDWCT systems are integrated to decrease the NDWCT load which could result in water losses decrease. In part one of the presented two-part paper, model-based energy and economic analyses are performed to compare systems performance and applicability. The temperature difference at pinch point and temperature difference between the hot and cold sides of the heat exchangers which were used for systems integration in VCR-SPP-NDWCT, and the absorber pressure and temperature in ABHP-SPP-NDWCT system are studied using parametric analysis procedure. A water-fuel management strategy is also introduced for the ABHP-SPP-NDWCT system according to the influence of the absorber pressure changes on system water and fuel consumption. In part 2, environmental and thermoeconomic analyses are performed to complete a comprehensive study on designing steam power plants. The results of part 1 showed that water losses and total annual costs decreased by 1–18% and 0–4.7% for the ABHP-SPP-NDWCT system but increased by 11% and 60% for the VCR-SPP-NDWCT system, respectively.

Thermoeconomic Optimization of a 450 MW Natural Gas Burning Steam Power Plant

The theory of thermoeconomics and local optimization were used to investigate how the cost of the resources consumed by a 450 MW power plant varies with the unit cost of the resources consumed, the technical production coefficients of the productive structure and/or the external demand for the products. In order to accomplish this, the costs of exergy of the productive structure were analyzed under three different conditions by using the relevant characteristic equations. In general, it was found that the thermoeconomic cost of a flow consists of two parts, namely the monetary cost of the fuel exergy (natural gas in the present study) needed to produce the flow, that is, its thermoeconomic cost and the costs due to the productive process (cost of capital equipment, maintenance, etc.). The results show that the steam leaving the boiler has the lowest exergy cost, while the condenser has the highest. The sequential quadratic programming (SQP) algorithm was used to obtain the optimized solutions of each major component of the plant. It was found that substantial operational and capital cost benefits were realized by optimizing most of the major plant equipment (boiler, turbines, feedwater heaters and the pumps). However, optimization of the condenser did not yield any cost benefit in capital equipment cost, but did produce some savings in operational cost.

Coupling performance analysis of a solar aided coal-fired power plant

Coal-fired power plants are the dominant form for power generation in many countries, even though they are the main contributor to the current environmental crises. The solar aided coal-fired power plant is an attractive new way to reduce the coal consumption by using solar energy. From the perspective of operational mechanism and coupling property, an all-condition mechanism model of the solar aided coal-fired power plant is proposed in this paper. The operation of an N600-24.2/566/566 supercritical coal-fired power plant hybridized with parabolic trough solar collectors is simulated using Matlab/Simulink in the fuel saving mode. And a new evaluation index of solar energy is proposed to reasonably assess solar energy contribution to the solar aided coal-fired power plant. When the solar steam is used to replace the extraction steam in the feedwater heating system, the change of the main steam, the reheat steam, and the extraction steam are discussed as the coupling property is taken into account. Furthermore, thermal economic analysis is carried out to optimize the solar steam replacement and the entrance of inlet feedwater to the solar field. Moreover, the efficiency and output power of the high pressure cylinder, the intermediate pressure cylinder, and the low pressure cylinder are discussed when the extraction steam is replaced by the solar steam in the feedwater heating system. Finally, the output power shock of the solar aided coal-fired power plant caused by the fluctuation of Direct Normal Irradiance is assessed. It is found that the strong fluctuation of Direct Normal Irradiance affects the power quality of the solar aided coal-fired power plant significantly.

Simulation and parametric optimisation of thermal power plant cycles

Summary The objective of the paper is to analyse parametric studies and optimum steam extraction pressures of three different (subcritical, supercritical and ultra-supercritical) coal fired power plant cycles at a particular main steam temperature of 600 °C by keeping the reheat temperature at 537 °C and condenser pressure at 0.09 bar as constant. In order to maximize the heat rate gain possible with supercritical and ultra-supercritical steam conditions, eight stages of feed water heater arrangement with single reheater is considered. The system is optimized in such a way that the percentage exergetic losses are reduced for the increase of the exergetic efficiency and higher fuel utilization. The plant cycles are simulated and optimized by using Cycle Tempo 5.0 simulation software tool. From the simulation study, it is observed that the thermal efficiency of the three different power plant cycles obtained as 41.40, 42.48 and 43.03%, respectively. The specific coal consumption for three different power plant cycles are 0.56, 0.55 and 0.54 Tonnes/MWh. The improvement in feed water temperatures at the inlet of steam generator of respective cycles are 291, 305 and 316 °C.

Power-Augmented Steam Power Plant in a Cogeneration Cement Factory

AbstractCement factories have more potential to generate power from waste heat compared to other industries. Pressurized water flashing into wet steam at the end of a boiler’s economizer augments 15% of the plant’s output by increasing waste heat recovery compared to a regular steam power plant (Rankine cycle with a deaerator). A double-flash steam power plant is considered for theoretical demonstration of power augmentation with a cement factory’s waste heat recovery compared to a regular steam power plant. The hot water from the final flash chamber is used for feedwater heating and the saturated steam from the two flash chambers is supplied to the turbine. The current work is focused on selection of heat-recovery steam generator’s (HRSG) pressure and location of the high-pressure flasher (HPF) and low-pressure flasher (LPF). The flash fluid mass can be analyzed for better heat recovery as it influences the exhaust gas temperature. A low pressure has been recommended for the HRSG as it increases the heat...

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.

The development of a thermo-economic evaluation method for solar aided power generation

In this paper, a method is derived for evaluating the thermo-economic performance of solar aided power generation (SAPG) hybrid systems. These systems can achieve emissions reduction and energy savings compared to conventional coal-fired power generation systems. In the discussed model of SAPG hybrid system, various stages of heating feed-water in a conventional coal-fired power plant steam Rankine system are replaced by steam injected from solar direct steam generation (DSG). In order to determine the thermo-economic viability of SAPG compared to conventional power generation, convenient methods are required for evaluating the performance of SAPG systems. Therefore, an analysis method is developed which involves defining a generalized steam–water distribution matrix equation. This matrix approach simplifies the traditional thermal calculation and has a one-to-one correspondence with the system structure. As a case study, the proposed method is successfully used to solve the case of a 600MW power generation system with the integration of DSG. A comparison of the case study system with (SAPG) and without (non-SAPG) the integration of the solar DSG shows thermo-economic benefits to the hybridised system. If the state parameters are taken as variables, this method can be used to study the effects of changes in system, equipment, operation, and load on the thermal economy of the integrated system.

Performance of flow and heat transfer in vertical helical baffle condensers

The feed water heaters in power plants are actually the condensers using turbine extracting steam to heat feed water. The vertical feed water heater occupies less area than the horizontal one and convenient to lift tube bundles out in maintenance. However, the lower heat transfer coefficient due to thick condensate film limits its application. A novel trisection helical baffled vertical condenser (feed water heater) is proposed with liquid dams and gaps for facilitating condensate drainage. The flow and condensation heat transfer characters of two vertical condensers with variable angled trisection helical baffles of both single-thread and dual-threads and a variable spanned segmental baffled one were numerically studied with Mixture model of Fluent software. The distributions of velocity, pressure, volume fraction of condensate, and local heat transfer coefficient in these heat exchangers were demonstrated. The simulation results show that the inclined baffles with liquid dam and drainage gaps could drain condensate effectively from tube bundle surfaces and prevent liquid film from entraining into vapor, and that the variable angled trisection helical baffled vertical condenser with dual-threads could greatly improve the condensation heat transfer coefficient up to 35.7% higher than that of the variable spanned segmental baffled one.

To analyse the combined effect of different extraction line pressure drops on the performance of coal-fired thermal power plant

ABSTRACTIn this research paper, work is done on a 120 MW coal-fired thermal power plant. Power plants are used for power generation, but during the process, some amount of steam is extracted from steam turbines to increase the feed water temperature, and steam extraction changes power generation/output from the power plant. The power generation also depends upon the pressure drop in the extraction lines/pipes. So, different case studies have been done for all feed water heaters. Then the power generation and the heat rate have been found for different extraction line pressure drops. These case studies indicate that if the extraction line pressure drop varies, then the power output and the heat rate also vary. The correction factor curves for power and heat rate have also been generated for the combined effect of extraction line pressure drop. Thus, the performance of the plant has been evaluated.

Second Law Based Thermodynamic Performance analysis of Steam Power Cycle

The generation of mechanical power had been a challenge for mechanical engineers and a great deal of attention has been focused on designing system for power generation. Thermal power cycles are important devices used in practical engineering application for thermal power generation and control of environment. Several thermodynamic approaches are possible to analyze the performance of these cycles. The most traditional approach is the first law of thermodynamics or energy balance analysis; however, this concerned only with the conversion of energy, and therefore it can not be show how or where irreversibility in a system or process occur. Second law analysis is another well-known method used to analyze thermodynamic cycles, but to some, it may be still new. Unlike first law analysis, second law analysis determines the magnitude of irreversible processes in a system, and thereby provides an indicator that the points the direction in which the engineers should concentrate their efforts to improve the performance of thermodynamic systems. This thesis is an attempt to physically understand and evaluate the internal irreversibilities due to heat transfer and fluid flow in various thermal power cycle used for power generation. This thesis present investigations on thermodynamic modelling and effects of irreversibilities in thermal power cycles using the concept of exrgy analysis and entropy generation. Detail literature review on second law analysis of thermal power cycles is reported in Section I.0 First and second law analysis of stem power cycle, gas turbine cycle, combine Brayton/Rankine power cycle, indirect fired air turbine multi stage…. have been carried out. Analytical expressions for the performance parameters involving the relevant variables for these systems under given conditions, corresponding to available power output and exergy destruction in the system, have been obtained. Detailed parametric study has been done and result are presented. This study include the effect of pressure ratio, cycle temperature ratio, number of reheat stages, pressutre drop in heat transfer devices, and the refrigeration temperature on the performance parameters of the thermal power cycles. Second law based performance assessment of regenerative-reheat steam power cycle has been carried out in terms of irreversibility analysis. The reduction in irreversible losses with the addition of backward, cascade type feed water heater and a reheat options are compared with a conventional first-law assessment. The second law indicate that the maximum exergy is destroyed in the boiler and that these thermodynamic losses are significantly reduced by incorporating feed water heater. The incorporation of feed water heating results in a reduction of total irreversility rate of the plant by 18%. The corresponding improvement in thermal efficiencies is 12%. These two values are enhanced to 24% and 14% respectively, by the incorporation of reheat in addition to regeneration.

Thermodynamic Evaluation of Repowering Options for a Small-size Combined Cycle with Concentrating Solar Power Technology

The increasing penetration of low-carbon technologies and enhancements in fossil-fuelled power plants efficiency are some of the most important and up to date research topics.Renewable energy, in particular solar, has the potential of meeting the world energy needs while addressing environmental concerns, but technological advances in renewable energy electricity production are necessary to become competitive with conventional technologies.New opportunities to increase the penetration of renewables energies, smoothing out renewables variability and intermittency problems, come out from the hybridization concept. Hybrid renewable-fossil fuel systems join the advantages of both renewable energies and programmable devices. Among all the renewable technologies available for hybridization, Concentrating Solar Power (CSP) with parabolic trough is the most diffused because of its relatively conventional technology and ease of scale-up. CSP hybrids are well established worldwide, predominantly with natural gas: the hybridization options for CSP ranging from feed water heating, reheat steam, live steam to steam superheating.Based on a detailed thermodynamic cycle model of a reference small-size one pressure level Combined Cycle (CC) plant, the impact of CSP addition is thoroughly evaluated. Different hybrid schemes are evaluated and compared considering CC off-design operation. The goal of this study is to evaluate, from a thermodynamic point of view, three repowering options of a small-size CC with a CSP system in a hybrid system configuration and to quantify their potential benefits in terms of system's performance increase. In particular, the optimal size of CSP plant is shown for each investigated hybrid repowering options. The changes in CC steam cycle operating parameters are presented together with CC performance increase. It is shown that solar hybridization into an existing CC plant may give rise to a substantial benefit from a thermodynamic point of view.

Optimization of Solar Integration in Biomass Fuelled Steam Plants

This paper is focused on solar-biomass integration and presents a thermodynamic analysis of solar power utilization replacing the steam bleeds of a regenerative Hirn cycle plant, biomass fuelled, in feedwater pre heating process. In solar-biomass integrated configuration an energy conversion efficiency of solar energy has been evaluated in order to compare the use of solar energy in solo and hybrid configurations. Such efficiency has been adopted as optimization parameter for the best hybrid plant configuration, varying steam pressure and regeneration parameters.

A techno-economic analysis of partial repowering of a 210 MW coal fired power plant

This paper presents a techno-economic analysis of a partial repowering scheme for an existing 210 MW coal fired power plant by integrating a gas turbine and by employing waste heat recovery. In this repowering scheme, one of the four operating coal mills is taken out and a new natural gas fired gas turbine (GT) block is considered to be integrated, whose exhaust is fed to the furnace of the existing boiler. Feedwater heating is proposed through the utilization of waste heat of the boiler exhaust gas. From the thermodynamic analysis it is seen that the proposed repowering scheme helps to increase the plant capacity by about 28% and the overall efficiency by 27%. It also results in 21% reduction in the plant heat rate and 29% reduction in the specific CO2 emissions. The economic analysis reveals that the partial repowering scheme is cost effective resulting in a reduction of the unit cost of electricity (UCOE) by 8.4%. The economic analysis further shows that the UCOE of the repowered plant is lower than that of a new green-field power plant of similar capacity.

The Use of Flashing Drums and Microchannel Heat Exchangers to Generate Steam in Large Integral Light Water Reactors

Integral pressurized water reactors are innovative reactors in which all of the components typically associated with the nuclear steam supply system of a nuclear power station are located within the reactor pressure vessel. In order to facilitate this modification in large [~1000-MW(electric)] light water reactors (LWRs), compact heat exchangers such as microchannel heat exchangers must be used. Previous attempts at using microchannel heat exchangers were unsuccessful since they are prone to vapor locking and crud blockage when the primary coolant boils. Therefore, the authors propose the use of a flashing drum to facilitate boiling in conjunction with a primary microchannel heat exchanger for a large integral LWR. The integral inherently safe light water reactor (I2S-LWR) is used as a basis for the implementation of this novel concept. The high-temperature, high-pressure secondary water generated in the secondary loop through heating in the microchannel primary heat exchanger of the I2S-LWR is sent to a flashing drum where 99.9% pure vapor is extracted and sent to the turbines. This prevents boiling in the primary heat exchanger that in turn reduces crud deposition, flow instabilities, and the potential for channel blockage or vapor locking in the small channel sizes of microchannel heat exchangers. The benefits and disadvantages of this approach are presented in this paper. Unfortunately, this innovative approach to nuclear steam generation for integral LWRs is challenged by a potential decrease in thermodynamic efficiency. Therefore, a sensitivity study is presented that explores the impact of several design variables on the thermodynamic efficiency of the plant. As part of this study, a simple and a complex Rankine cycle were modeled in order to determine the impact that system design modifications can play in recovering thermodynamic efficiency lost by the steam drum. Both cycles utilize turbines, condensers, and condensate/recirculation pumps, while the complex Rankine cycle utilizes a four-stage turbine with subsequent separation and open feedwater heaters. The optimized efficiencies for the simple and complex Rankine cycles are 31% and 33%, respectively, indicating that additional system enhancements to the power conversion system could compensate for the inclusion of a flashing drum.

Theoretical Investigation on the Partial Load Feedwater Heating System with Thermal Vapor Compressor in a Coal-fired Power Unit

When a coal-fired unit operates at a partial load, the decrease at regenerative steam pressure leads to a decrease in boiler feedwater temperature, affecting not only the thermal economical efficiency, but also the selective catalytic reduction (SCR) denitrification effect and the boiler combustion stability. A feedwater system with the thermal vapor compressor has been studied in the present paper. The high pressure regenerative steam is injected by the live steam to heat boiler feedwater to increase its temperature. Mathematical models of the thermal vapor compressor, boiler and turbine regenerative system are established to calculate the performance of a 660MW supercritical air cooling unit at a 60% load. It was found that although the energy-saving effect is small, it is positive to improve the SCR denitrification effect and stabilize the boiler combustion.

Estimation of Scale Deposition in the Water Walls of an Operating Indian Coal Fired Boiler: Predictive Modeling Approach Using Artificial Neural Networks

Application of computational intelligence for predicting industrial processes has been in extensive use in various industrial sectors including power sector industry. An ANN model using multi-layer perceptron philosophy has been proposed in this paper to predict the deposition behaviors of oxide scale on waterwall tubes of a coal fired boiler. The input parameters comprises of boiler water chemistry and associated operating parameters, such as, pH, alkalinity, total dissolved solids, specific conductivity, iron and dissolved oxygen concentration of the feed water and local heat flux on boiler tube. An efficient gradient based network optimization algorithm has been employed to minimize neural predictions errors. Effects of heat flux, iron content, pH and the concentrations of total dissolved solids in feed water and other operating variables on the scale deposition behavior have been studied. It has been observed that heat flux, iron content and pH of the feed water have a relatively prime influence on the rate of oxide scale deposition in water walls of an Indian boiler. Reasonably good agreement between ANN model predictions and the measured values of oxide scale deposition rate has been observed which is corroborated by the regression fit between these values.

ENERGY AND EXERGY ANALYSIS OF A 250MW COAL FIRED THERMAL POWER PLANT AT DIFFERENT LOADS

In this present investigation exergy and energy efficiencies of a coal fired 250 MW thermal power plant operating in eastern part of India are determined both for 100% and 90% load based on actual operating data. The efficiencies are evaluated for the overall plant as well as for different equipments like boiler, turbine, all feed water heaters and condenser. Similarly effectiveness of the feed water heaters is evaluated for both the loads. Exergy destruction % for each of the equipment are also given for clear understandingof the loss of available energy due to irreversibilities involved in the processes for each equipment and the whole plant. It is observed that a major irreversibility or, exergy destruction takes place at boiler though 1st law energy efficiency is quite high. This signifies that there might have further scope of improvement in this equipment. Similar analyses are carried out for other equipments. The results obtained in present analysis are compared with those of other investigators.