Feedwater Preheating Research Articles

Game theoretic approach for the synthesis and optimization of economically optimal coalitions in integrated renewable energy and polygeneration networks

This study presents the generation of an integrated resource network that encompasses a bioenergy supply chain and a polygeneration hub. The resource network is designed using a superstructure that comprises 3 layers. The first layer is a supply chain network of seasonally available renewable and non-renewable energy sources and is connected to the second layer by a transport system comprised of rail, road, and pipeline. The second layer, which is the polygeneration hub, comprises a boiler to produce high-pressure steam, steam turbines for generating power, a multi-effect evaporation system for desalinating salt-water and an absorption refrigeration system to produce chilled water. The option of connecting the boiler to a solar-thermal and heat storage subnetwork for feedwater pre-heating is included in the second layer. Piping and electrical cables connect the polygeneration layer to the third layer, which comprises industrial heat demand, represented by heat exchanger network, and electrical power demand. The model is applied to a case study in which the subnetworks in the overall integrated superstructure layers are considered as individual players in an industrial symbioses network with the possibility to be in a cooperative game. The objective function of the model, which is represented as a mixed integer nonlinear programming model, involves the minimization of the summation of the players' marginal contribution, with equal weighting applied for each player, to the coalition's total annual cost. The result obtained involves preference for a coalition among participating subnetworks that include combined heat and power, multi-effect evaporation, and heat exchanger network.

A novel solar-aided lignite-fired power generation system with calcium looping CO2 capture, lignite pre-drying and feedwater preheating

Integrating solar heat and calcium looping (CaL) process into the existing lignite-fired power generation system is a promising technology to control CO2 emission. However, the heat released from carbonation process led to the temperature increase of exhaust flue gas together with heat losses in boiler. To recover the waste heat from the exhaust flue gas, this paper proposed a solar-aided lignite-fired power generation system with CaL process CO2 capture, lignite pre-drying and feedwater preheating (i.e., design III). Besides, design I without waste heat recovery and design II with only lignite pre-drying were simulated for comparison. Through the case study based on a solar-aided 330 MW lignite-fired power generation system, thermal and techno-economic performance of design III was the best on the design condition. Its standard coal consumption rate was 374.44 g/kWh, which was 61.12 g/kWh and 8.24 g/kWh lower than design I and design II, respectively. With the new design, the annual net profit of design III is $18.2924 M, with $0.5652 M higher than design II. The sensitivity analysis indicated that the thermal performance of design III was also the best under various conditions of CO2 capture efficiency and integrated solar heat.

Novel integration of thermoelectric distiller with direct contact membrane distillation

A thermoelectric distiller (TED) integrated with a direct contact membrane distillation (DCMD) unit was proposed and numerically investigated. The mathematical models of the hybrid TED--–DCMD system were developed and validated. In the proposed hybrid system, the TED provides the heating demand of the DCMD desalination unit in four novel configurations of TED-DCMD integration. The first configuration integrates the TED-DCMD by adding a DCMD heat exchanger coil inside the condensation tank of a TED, while the second configuration involves two TED condensation tanks with each tank containing a DCMD heat exchanger coil. The third configuration also consists of two TED tanks with an external heat exchanger where thermal energy from the TED produced water is transferred to the DCMD feed stream. The fourth configuration is a modification of the second configuration with a thermal recovery from TED produced water for inlet feed water preheating. To investigate the performance (distillate productivity, specific energy consumption, coefficient of performance, and ratio of TED productivity) of each integrated TED-DCMD configuration, the effects of different operating parameters such as DCMD feed flow rate, TEM current, number of TEMs, and TED produced water temperature were examined. Findings indicated that the third configuration is the most energy efficient, with specific energy consumption (SEC) reaching a minimum value of 217 kWh/m3 at low current operation of 2.1 A, and feed flow rate of 4.0 L/min for 8.0 TEMs in the TED. A maximum freshwater productivity and COPh of 2.74 kg/s and 3.24, are attained by the 4th and 3rd configurations, respectively. Results also indicated that elevating the current input encourages higher water productivity. Meanwhile, higher values of SEC and water productivity are attained when operating TED at saturation temperature.

An assessment of renewable energy generation in a conventional steam power plant with geothermal feedwater preheating

Hybrid steam power plant with geothermal feedwater preheating enables conversion of low temperature geothermal resources into electricity. The paper presents results of calculation of some performance parameters for 200 MWe fossil power unit associated with geothermal well. The paper gives separation rule of renewable energy from conventional one at hybrid power plant output. An influence of geothermal fluid temperature on hybrid power plant performance is discussed in a study and illustrated in several charts.

Integrated Wastewater and Waste Heat Recovery System in Coal-Fired Power Plants Using Reverse Osmosis to Produce Clean Water and Increase Thermal Efficiency

Indonesian electricity supply is still dominated by coal-fired power plants (CPP) by more than 50%. Water consumption for CPP in Indonesia reaches 222 million kL/year. Meanwhile, 10% of Indonesia's population is predicted to experience a clean water crisis in 2045. Most of the water consumed by CPP will be disposed of as wastewater, such as cooling tower blowdown and boiler blowdown. Boiler blowdown temperature is still relatively high. Thus, it wastes a high-quality of energy. Therefore, these conditions open the opportunity for innovations in improving clean water supply and increasing CPP’s thermal efficiency. In this research, a novel system that integrates wastewater recovery and waste heat recovery in CPP using reverse osmosis is proposed to produce clean water while increasing the CPP’s thermal efficiency. In this system, the boiler blowdown is streamed to a heat exchanger as the feedwater preheater. Then, the boiler blowdown flows to a Pelton turbine to generate electricity. The boiler blowdown will then be mixed with the cooling tower blowdown and streamed to a reverse osmosis system to produce clean water. The brine is converted by an electrolyzer into NaClO and H2. Thermodynamic and economic analyses are performed to assess the proposed system’s technical and economic feasibility. Based on the thermodynamic analysis calculation using the Engineering Equation Solver, the system is able to produce 162 kL/hr of clean water and the thermal efficiency of the coal-fired power plant increases by 0.4%. The economic analysis showed that the additional system is feasible with a payback period of 4.9 years.

Novel feedwater preheating system for parabolic trough solar power plant

Several improvements in the referenced parabolic trough power plant (PTPP) model (Andasol II) have been implemented by APROS software. The main advantage of this novel feedwater preheating system is to improve electricity production and evening operation hours at a low cost for modifying an existing PTPP in Spain. This in turn leads to less dependence on fossil fuels during the evening and cloudy periods. The reference model is improved by an increase in the collector loops in the reference solar field (SF) model to 208 loops rather than 156 loops to increase the absorbed thermal power, increasing the capacity of the thermal storage system (TSS) from 1017 MWth h to 1,360 MWth h to improve the night operating period, replacing the Feedwater/Steam circuit with a Feedwater/HTF circuit using five shell and tube counter-current heat exchangers that are used instead of condenser heat exchangers. The HTF enters the fifth low-pressure preheater with 128 kg/s and 393 °C in the daytime and 377 °C at night. The main advantage of this improvement is to use the entire generated steam within the steam turbine and not to heat the feedwater in the feedwater circuit. In addition, the control circuits are modified and added new controllers with new limitations for controlling the new operating conditions. This development is the first attempt in the field of research to use a Feedwater/HTF circuit in the PTPP in order to enhance performance. This improvement (optimization 1) in turn leads to a raise in the total HTF mass flow and the quantity of stored molten salt, as well as increasing the mass flow of HTF to the power block (PB). According to optimization 1, no steam will be taken out of the HP and LP-turbine toward the feedwater circuit. Therefore, the feedwater fed through new preheaters is heated by thermal oil instead of steam extractions. The predictions obtained from this optimization are compared to the simulated results that were previously extracted from the reference model on clear and cloudy days for evaluation of the behaviour of the optimized PTPP. It should be mentioned here that it can be used the same turbine and generator in the actual power plant to achieve this increase in the performance of the power plant, according to the technical data of manufacturers. Finally, an economic study of the cost was conducted for referenced and the optimized PTPP depending on the levelized energy cost (LEC). The findings reveal that the levelized energy cost of the optimized PTPP with storage energy is about 10.5% lower than that of the referenced PTPP.

Thermo-economic analysis of integrated gasification combined cycle co-generation system hybridized with concentrated solar power tower

Integrated gasification combined cycle (IGCC) systems have the ability to utilize low-quality coal with reduced emissions and multiple co-generation capabilities (i.e., power, chemicals and fuels). Integration of solar power tower (SPT) with IGCC co-generation can provide an opportunity to use lignite coal with lowest greenhouse gas emissions. In this work, thermodynamic and economic evaluations of solar-IGCC 100% power (power only) hybrids and co-generation (electricity, methane and ammonia) hybrids have been performed using Aspen Plus® V.11 and system advisor model (SAM). Two designs (i.e., large and medium solar) of the SPT have been simulated and optimized for Pakistani weather conditions. Thermodynamic evaluations include, net electrical efficiency, effective energy efficiency and solar-to-electric efficiency of hybrid plants. Economic estimations include, levelized cost of energy, total plant costs, operating and maintenance costs for hybrid plants. Specific CO2 emissions after hybridization are also evaluated. Total annualized revenue at flexible market scenarios and production scenarios have also been evaluated. The net boosted electrical efficiency of 100% power (Hyb-1A) is 38.77%, and the improved efficiency after flue gas integration with SPT for the pre-heating of boiler feed water is 39.10%. The minimum specific CO2 emission achieved from one hybrid combination (Hyb-4A) is 42.1 kg/MWhnet.

Techno-economic and GHG mitigation analyses based on regional and seasonal variations of non-concentrating solar thermal collectors in textile sector of Pakistan

SDG implementation in the industrial sector of Pakistan is significant for its economic growth, sustainable industrialization, innovation, and sustainable production. Integration of solar thermal collectors in the textile industry will encompass sustainable development goals (SDG 7,9,12,13). Meeting these goals in the thermal sector of Pakistan is becoming increasingly challenging due to the limited resources and harmful emissions from conventional fuels. In this study, the technical feasibility of two non-concentrating collectors, Flat Plate Collector (FPC) and Evacuated Tube Collector (ETC) was investigated for the application of preheating of feedwater of boilers. Choosing the better performing collector for a range of regional and climatic variations across Pakistan, a comparative analysis of three fuels (coal, oil, and natural gas) has been carried out by using TRNSYS and RETScreen for economic analysis and GHG emission mitigation, respectively. The overall best results have been observed in Quetta. For this city replacement of coal has shown the highest GHG emission mitigation potential of 182,326 tonnes of CO2 and the highest NPV for oil (1509.4 million PKR) among the three fuels studied. Based on the results, it can be deduced that this work can be further extended to concentrating thermal technologies as well. Since real-time industrial data has been used, the insights will promote solar thermal technology in Pakistan.

Novel Feedwater Preheating System for Parabolic Trough Solar Power Plant

Novel Feedwater Preheating System for Parabolic Trough Solar Power Plant

Supercritical Carbon Dioxide Cycles for Concentrated Solar Power Plants: A Possible Alternative for Solar Desalination

This manuscript investigates the supercritical carbon dioxide (sCO2) power cycle employed in the power block of concentrated solar power (CSP) plants—solar tower—as an alternative for solar desalination, developed with either distillation or reverse osmosis. This concept is investigated as a possible up-scaling of the SOLMIDEFF project, originally based on a hot-air micro gas turbine combined with a solar dish collector. For the upscaled concept, five different sCO2 cycles are considered, chosen amongst the best-performing configurations proposed in the literature for CSP applications, and modelled with Thermoflex software. The influence of ambient conditions is studied, considering two minimum cycle temperatures (35 °C and 50 °C), corresponding to Santa Cruz de Tenerife and Abu Dhabi, respectively. The results show that the low temperatures at the inlet of the heat rejection unit compromise the viability of distillation technologies. On the other hand, the high thermal efficiency achieved by these cycles, especially with the recompression and partial cooling layouts, reduces the specific energy consumption when combined with reverse osmosis (RO), below that of photovoltaic (PV)+RO. Feed-water preheating is explored as a solution to further reduce energy consumption, concluding that its actual interest is not clear and strongly depends on the location considered and the corresponding water quality standards.

Combination of passive and active enhancement methods for higher efficiency of waste-fired plants; flue gas and solar thermal processing

This article presents a novel and applied solution for increasing the efficiency and cost-effectiveness of waste-fired power plants and comprehensively analyzes the proposal from thermodynamic, economic, and environmental aspects. The idea is centered around the simultaneous use of passive (flue gas condensation) and active (solar thermal heaters comprising evacuated tube collectors and parabolic trough collectors) for feedwater preheating. In this way, the extracted heat from the turbines for this purpose could be used directly for power generation, and thus, higher waste-to-power efficiency of the cycle. The proposed configuration and the base-case power plant are both simulated in TRNSYS software for dynamic modeling and comparison of the results over an entire year of operation of the power plants. For making the results more reliable for real-life operation conditions, the simulations are run for a real case study in Qassim city, Saudi Arabia. The results of exergy analysis show that the waste incinerator with the annual exergy destruction of 128.3 GWh is the main source of irreversibility in both models. The results further indicate that the proposed novel system is the more suitable option with 11.36 GWh and 68.18 GWh more annual produced electricity and heat, respectively. With these numbers, although the unit product cost of the proposed novel system is 2.2 $/MWh higher than the conventional plant due to the high cost of solar systems, the new system results in a 205.08 ton/GWh lower CO2 emission index which is extremely important and even of high economic value preventing large emission taxes.

Improving waste incineration CHP plant efficiency by waste heat recovery for feedwater preheating process: energy, exergy, and economic (3E) analysis

In this work, waste heat recovery, as a passive technique with low cost, is used for increasing the efficiency of a waste incineration CHP plant via an innovative way. Here, the recovered thermal energy is suggested to be used for the feedwater preheating process instead of steam extractions of turbines or any other auxiliary heat input for this purpose. For investigating the effects of the proposal, three different scenarios are considered and compared to each other. The first scenario is an old design waste CHP plant with a fuel-burning preheating process; the second scenario is a CHP plant with steam extractions from turbines for feedwater preheating; and the last scenario is when both of the previous preheating tools are removed from the cycle and instead, the energy of the exhaust gas of the incinerator is recovered and utilized for feedwater preheating. The energy, exergy, and economic analyses of the three scenarios are carried out, and the main performance factors of these power plants are compared. The results show that the efficiency of the heat recovered case considering both heat and power outputs can reach about 94% while the plants with old-fashion design and with steam extraction lines could give only 77% and 82% efficiencies. The exergetic efficiency of the proposed solution reaches the top value of 81% among the three scenarios, and its unit product cost will be lowest among all with a value of below 11 $/GJ. In the end, the effects of several operating parameters on the efficiency of the proposed system are investigated and reported.

Compound parabolic solar collector – Performance evaluation as per standard test method and actual field conditions for industrial process heat application in Indian context

Industrial process heating has been identified as a potential field for solar thermal applications. In this paper, a comparative study was carried out on the performance of an individual solar collector under laboratory conditions and performance of the collector array under field condition. Compound Parabolic Concentrator (CPC) has been used as a solar collector for the application of boiler feed water preheating. The characterization of CPC has been done in liquid phase with water as a working fluid as per the standard, IS 16648 (Part-5):2017. The optical efficiency of the CPC is found to be 64.8% under standard test conditions. In the field, total 200 number of CPCs, each having 3 m2 area, were installed. The performance monitoring and evaluation of the actual installation was carried out over a period of 10 months. The system was designed to supply average 448,500 kWh- Thermal/year, saving the equivalent amount of fossil fuel. The comparative study of the performance of CPC collector under standard conditions and actual operating conditions in the field shows significant variation. The average variation in the performance was about 9% with a maximum variation of 14.7%. The major reasons behind the lower performance output than expected, attribute to the heat losses through the collector manifold and piping (3.9%), soiling of reflector and absorber of CPC (1.72%), uncertainties of instruments (1.49%) and other unaccounted losses like dislocation of the evacuated tubes from the original position, loss of vacuum through evacuated tubes, shadow effect, heat utilization pattern etc. (1.89%), which should be considered while designing the solar field to meet the required output.

A novel means to flexibly operate a hybrid concentrated solar power plant and improve operation during non-ideal direct normal irradiation conditions

Hybridization of concentrated solar power (CSP) with other energy sources can drastically increase how much solar energy is harnessed and potentially expand the current geographical deployment of CSP installlations. In this study, a novel operation strategy referred to as flexible heat integration (FHI), is proposed and applied to a hybrid CSP-natural gas power plant. The proposed plant, modeled in Simulink, employs a solar central receiver (SCR) and dual-source gas boiler to drive a steam Rankine power cycle. FHI involves collecting and dispatching solar energy at modified temperatures during off-design direct normal irradiance (DNI). During low-grade (<100 W/m2) and medium-grade (100–500 W/m2) levels of DNI, molten salt is used for steam boiling and feedwater preheating, respectively, rather than superheating usually seen in SCR steam plants. Hybrid gas-firing supplies energy to bypassed systems. FHI is applied to a hybrid plant over the course of a day from each season for a plant located in Salt Lake City, Utah, an unconventional location due to off-design DNI variability. A spring day exhibiting variable DNI is used as the main case study to demonstrate the dynamics and robust operation under the FHI framework. The operation of the plant over the winter day shows the largest improvement in solar-to-electric (STE) efficiency whereas the summer day exhibits the smallest improvement. Monthly results follow a similar trend with FHI improving STE from 15.3% and 16.3% to 17.0% and 16.7% in January and July, respectively. Yearly results show FHI improving STE efficiency from 16.1% to 17.1% relative to standard hybrid operation. Overall, the proposed concept expands the current understanding of energy management in hybrid SCR-natural power plants under non-ideal DNI conditions and locations that have lower DNI by applying FHI.

Full repowering of an existing fossil fuel steam power plant in terms of energy, exergy, and environmen for efficiency improvement and sustainable development

In this study, the feed-water-heating method is studied due to its numerous advantages for the repowering of 320 MW units at Isfahan power plant. In this method, only low-pressure heat exchangers or only high-pressure heat exchangers can be replaced with a new gas–water heat exchanger, or both can be replaced by two high-pressure and low-pressure heat exchangers. It is also possible to do the preheating of boiler feed water in parallel with existing heat exchangers and new heat exchangers. Each of this method has its own characteristics that have advantages and disadvantages. We first analyze the energy and exergy of the existing cycle and then analyze the methods used to feed-water-heating repowering. Various gas turbines are used for this work, and the results are expressed. Energy and exergy efficiencies are considered as objective functions, and finally, while considering other limiting parameters, it is recommended for each method of optimal gas turbine. The characteristics of the new heat exchangers are also described. In the first method, net efficiency of energy and exergy is increased relatively to 8.25% and 8.4%, respectively, and in the second method net efficiency of energy and exergy is increased relatively to 10.96% and 11.56%, respectively.

Thermodynamic analysis and life cycle assessment of supercritical pulverized coal-fired power plant integrated with No.0 feedwater pre-heater under partial loads

With ever increasing share of renewable energy sources in the electricity mix, pulverized coal-fired power plants (PCPP) have to participate in peak load regulations frequently and thus, they regularly operate under partial loads. The energy efficiency and eco-efficiency are both significantly affected by such operating patterns. Therefore, the present work aims to establish an overall concept for the estimation of environmental impacts from PCPP under nominal and partial loads with combined thermodynamic analysis and life cycle assessment (LCA) methodology. A 1000 MW supercritical PCPP was modeled using commercial simulation software (GSE for thermodynamic simulation and SimaPro for LCA analysis). Results indicated that global warming was the predominant environmental impact of PCPP, while ozone formation, acidification and eutrophication were also serious concerns attributed to NOx emissions in electricity generation process. The mechanisms of formation, migration and removal of different kinds of pollutant emissions significantly influenced the LCA results. Particularly, the total environmental impact potential considerably increased by approximately 90% under partial/low loads due to reductions in the plant thermal efficiency and NOx removal efficiency. A novel partial load No.0 feedwater preheating system driven by steam ejector was thus proposed for NOx reduction improvement. Operation optimization was carried out based on the guidelines of the LCA framework. It was found that the total environmental impact could be effectively reduced by up to 27.3%. Therefore, the implementation of the No.0 feedwater pre-heater was favorable for environmental performance improvement under partial/low loads.

Failure Analysis of Carbon Steel Tubes in a Reformed Gas Boiler Feed Water Preheater

This study involves the failure analysis of carbon steel tubes in a reformed gas boiler feed water preheater unit operating at an ammonia plant. It was determined that the incipient failure mechanism in the carbon steel tubes was pitting corrosion at the inner surface of the failed tube transporting boiler feed water. The spectroscopic and microscopic analysis revealed the presence of iron oxides, including magnetite (Fe3O4), on the surface of a hole inside a pit formed in the inner surface. A significant thickness reduction in the internal wall due to subsequent erosion–corrosion led to the formation of the hole. No voids/cracks were present in the grain boundaries in the (ferritic and pearlitic) microstructure of the carbon steel tube (A214). Due to the recurrent nature of the failure of the carbon steel tubes in the preheater unit, SS304L tubes are recommended to be used throughout the waterside of the preheater.

Multi-objective optimization of feed-water heater arrangement options in a steam power plant repowering

In this paper, the full repowering of a steam Power Plant with a capacity of 320 MW in Iran was evaluated technically and economically. Implementation of this plan for the target power plant was selected because of its over 30 years of age. Due to the presence of steam flash feed water preheaters and the possibility of preheating feed water entirely or partially prior to entering heat recovery steam generator, the effect of using or not using these low and high pressure equipment was evaluated in different cases. To do this, five different cases were proposed and reviewed. Considering the available gas turbines in Iran, the gas turbines models Siemens V94.2 and V94.3A were selected. In each case, the optimum point is obtained in terms of the lowest cost of electricity generation. Finally, after reviewing the results of all cases, full repowering plan with parallel feed water heating was selected as the best alternative in terms of energy and exergy efficiencies and the price of generating electricity. If two heat recovery steam generators and two V94.3A gas turbines are used, the net exergy and energy efficiencies for the cycle can reach 54.49% and 52.98%, respectively. Moreover, the power capacity of a repowered unit is equal to 700.44 MW with electricity generation price of 0.05986 $/kWh.

COMPARATIVE ENERGY AND EXERGY ANALYSIS OF A POWER PLANT WITH SUPER-CRITICAL AND SUB-CRITICAL

The aim of this study that how to effect live steam parameters reheat and feed water preheater numbers on efficiencies of energy and exergy at coal-fired power plants. Moreover, two desuperheaters and a regenerative turbine are added USCPP (Case 3) to approach best results. Soma Power Plant (Case 1) consists of one reheat stage, two HPRHs and four LPRHs with one DEA. It is operated sub-critic and coal is used for a fuel. Live steam conditions of Soma Power Plant set at 13,92 MPa and 540 °C, and the reheat steam is reheated to 540 °C. Supercritical Power Plant (Case 2) consists of the same main components of Case 1. However, steam parameters of Case 2 are increased to 262.5 Bar and 600 °C to determine impact of the steam parameters on power plant efficiencies. USCPP which consists of two reheat stages, four HPRHs, six LPRHs with one DEA is designed to generate live steam under nominal conditions of 30 Bar and 600 °C. Besides, reheat steam are heated to 620 °C. Simulations have been carried out Ebsilon Professional software and pressure drops at preheaters and reheats are also considered. Some assumptions are made in the analysis. The thermal and exergy efficiencies of USCPP increase by 9.241 and 8.06 percentage points compared with Soma power plant, respectively. The results of this study that live steam parameters which are increased from sub-critical values to super-critical values have enormous influence on energy and exergy efficiencies. Secondly, adding second reheat stage has positive impact to improve power plant efficiencies. Finally, augmenting feed water preheater number, adding two desuperheater and one regenerative turbine increase power plant efficiencies. However, optimum numbers of feed water preheaters are determined considering economic parameters.

Thermoeconomic analysis and multi-objective optimisation of MED-TVC and MED-TVC.FH systems using ABC algorithm

In this study, 4E analysis for feasible integrated systems for cogeneration of fresh water was investigated. Steam generation provided by a steam boiler, designed to supply the thermal heat requirements of MED-TVC and MED-TVC.FH systems. Parametric analysis is made to determine CO2 emission rate, gain output ratio, exergy destruction rate and special heat rate for each system. By using Artificial Bee Colony algorithm, systems were optimised for maximum exergy efficiency and minimum cost of the produced distilled water. The results showed that by selecting final optimum solutions, the distillated water cost reduced by 18.1% and 28.8% for MED-TVC and MED-TVC.FH systems respectively. Also exergy efficiency increased from 3.2% and 4.04% in the base case to 3.63% and 4.47% for MED-TVC and MED-TVC.FH respectively in the optimum case. The system with feed water preheater, has more exergy efficiency and less CO2 emission, also the cost of distilled water reduced by 7.86%.