Steam Generator Design Research Articles

Influence of the steam generator on the exergetic and exergoeconomic analysis of solar tower plants

Solar power tower plants differ from conventional power plants in the steam generator design due to the higher heat duty. In this work, the influence of the steam generator heat exchangers (preheater, evaporator, superheater and reheater) on a solar power plant with molten salt receiver and thermal storage is studied for the first time. Energy, exergy and exergoeconomic analyses give a complete view of the cost flows within the system. The pinch point temperature difference in the evaporator is used as the main variable as it changes the steam generator design and the operating conditions of the plant, such as the inlet temperature of the receiver and the salt mass flow. All heat exchangers are designed and optimized at minimum cost for each pinch point to fulfill the thermomechanical limitations of TEMA standards and Pressure Vessel code. The field of heliostats, molten-salt receiver and the power-block (110 MWe) designs are kept constant throughout the paper. A low pinch point should be used to minimize the plant exergy destruction while the exergoeconomic approach obtains an optimum pinch point around 2-3 °C. Furthermore, the low exergoeconomic factor values show that the heat exchangers of the SG are crucial for the plant operation.

Numerical investigation of the separation performance of full-scale AP1000 steam-water separator

The steam-water separator is a crucial equipment supplying high-quality steam for the turbines in the AP1000 nuclear power station. It is comprised of the gravity separation space, primary separator (swirl-vane separator), secondary separator (wave-type vanes separator) and auxiliary equipment. In the present study, full-scale three-dimension modeling and simulation are conducted using the Euler-Lagrange approach based on the AP1000 steam generator design drawing to investigate the steam-water separating mechanism and the separation performance of the AP1000 separator. The details of steam-water separation efficiency and pressure drop are obtained in the gravity separation space, primary separator and secondary separator under various operating conditions. The numerical results indicate that the separation efficiency increases rapidly as the steam velocity increases and the relative humidity at the outlet of the AP1000 steam-water separator is less than 0.1% which satisfies the design standard of the AP1000 power station. In addition, the head cover and diffuser assembly structure into the upper of the primary separator greatly increases the steam-water separation efficiency though the pressure drop increases somehow as well, compared to the geometric model without head cover and diffuser assembly. Finally, the inlet velocity distribution of the secondary separator, resulting from the arrangement of the orifice plate in front of the secondary separator, affects the separation efficiency with ±9% discrepancy compared to the uniform inlet distribution.

Steam generator performance improvements for integral small modular reactors

Abstract Background Steam generator (SG) is one of the significant components in the nuclear steam supply system. A variety of SGs have been designed and used in nuclear reactor systems. Every SG has advantages and disadvantages. A brief account of some of the existing SG designs is presented in this study. A high surface to volume ratio of a SG is required in small modular reactors to occupy the least space. In this paper, performance improvement for SGs of integral small modular reactor is proposed. Aims/Methods For this purpose, cross-grooved microfins have been incorporated on the inner surface of the helical tube to enhance heat transfer. The primary objective of this work is to investigate thermal–hydraulic behavior of the proposed improvements through modeling in RELAP5-3D. Results and Conclusions The results are compared with helical-coiled SGs being used in IRIS (International Reactor Innovative and Secure). The results show that the tube length reduces up to 11.56% keeping thermal and hydraulic conditions fixed. In the case of fixed size, the steam outlet temperature increases from 590.1 K to 597.0 K and the capability of power transfer from primary to secondary also increases. However, these advantages are associated with some extra pressure drop, which has to be compensated.

Numerička simulacija dvofaznog strujanja i razmene toplote u vertikalnom generatoru pare

U radu je predstavljen dvodimenzijski termohidraulički model strujanja dvofazne mešavine oko snopa cevi vertikalnog generatora pare, kao i model za proračun toplotnog fluksa između predajnika i prijemnika toplote. Model dva fluida je primenjen za simulaciju strujanja dvofazne mešavine na strani prijemnika toplote i zasnovan je na jednačinama bilansa mase, količine kretanja i energije za svaku fazu pojedinačno. Procesi na međufaznim razdelnim površinama su modelirani na osnovu odgovarajućih konstitutivnih korelacija. Takođe, u radu su predstavljeni različiti načini modeliranja sile međufaznog trenja, koji se koriste u komercijalnim softverskim paketima za CFD simulacije i programima za analize sigurnosti nuklearnih reaktora. Predviđanje toplotnog fluksa izvršeno je modelom razmene toplote, koji obuhvata mehanizme jednofazne konvekcije, pothlađenog ključanja i razvijenog mehurastog ključanja. Rezultati dobijeni numeričkom simulacijom su upoređeni sa izmerenim vrednostima dostupnim u literaturi. Razvijeni model predstavlja podršku pri projektovanju generatora pare, a rezultati pružaju detaljan uvid u termohidrauličke parametre procesa.

Thermo-economic optimization of molten salt steam generators

This paper presents a methodology to guide the design of heat exchangers for a steam generator in a solar power tower plant. The low terminal temperature difference, the high fluid temperatures and the high heat duty, compared to other typical shell and tube heat exchanger applications, made the design of the steam generator for molten-salt solar power towers a challenge from the thermomechanical point of view. Both the heat transfer and the thermal stress problems are considered to size the preheater, evaporator, superheater and reheater according to the TEMA standards and ASME Pressure Vessel code. An integral cost analysis on the steam generator design effects on the power plant performance reveals an extremely low value for the optimum evaporator pinch point temperature difference. Furthermore, an optimization using genetic algorithms is performed for each heat exchanger, which leads to economical and feasible designs.A 110MWe solar power tower plant is studied. Two configurations of the steam generator are proposed: with one or two trains of heat exchangers. The results show that the optimum pinch point temperature differences are very close to 2.6°C and 3°C for the steam generator with one and two trains, respectively. The proposed design of the steam generator consists of a U-shell type for superheater and reheater, a TEMA E shell forced circulation evaporator and a TEMA-F shell preheater. Also, the approach point temperature difference analysis is performed to avoid subcooled flow boiling in the preheater. An economic study to compare forced and natural circulation evaporator designs is carried out.

Configurations and pressure levels optimization of heat recovery steam generator using the genetic algorithm method based on the constructal design

In last two decades, there was a great deal of attention on the optimum design and performance improvement of the heat recovery steam generator (HRSG) units. In the present work, considering different objective functions and utilizing the constructal design method, three configurations of HRSG are compared. The design method is based on the constructal theory and optimization technique is carried out by varying the geometric design parameters and steam pressure levels for different values of the exhaust gas temperatures. Optimum conditions of HRSG are obtained with the help of the genetic algorithm under the fixed total volume constraint. For each configuration of HRSG, optimal distribution of the heat surfaces (sizes) subject to the total volume constraint are derived such that the objective function is optimum. It is shown that how the geometric and thermodynamic design variables of HRSG can be achieved, simultaneously. Features that resulted from the constructal design are the number of tubes, configurations and aspect ratios for the main sections, the tube diameters and rate of the steam production at each pressure level. The results revealed that variations in different objective functions are strongly affected by the hot gas inlet temperature. In addition, the use of several pressure levels in HRSGs causes a considerable increase in the power production, declines irreversibility in HRSGs and allows producing higher steam flow rate for all values of the inlet gas temperature. The constructal principle invoked in this paper represents that geometrical form of systems can be deduced from a single principle.

Experimental study on thermal-hydraulic behaviour of LBE and water interface

For the design and safety studies of steam generator in the China LEAd-based Reactor (CLEAR) project, it is necessary to investigate the consequences of a Steam Generator Tube Rupture (SGTR) accident which could result in a reaction between Lead-Bismuth Eutectic (LBE) and highly pressurised water. Some experiments have been conducted to investigate the thermal-hydraulic behaviour of the molten LBE/water interface; the whole fragmentation processes of these experiments were visually observed with a high-speed video camera, and the transient pressure histories were measured by high-frequency piezoelectric pressure sensors. The effects of LBE temperature, water temperature, nozzle diameter and injection velocity were investigated. Visualisation films indicated that the explosion phenomenon happened readily at lower water temperature. The peak pressure decreased with increasing water temperature, nozzle diameter and injection velocity. However, the peak pressure first increased and then decreased as the LBE temperature increased. The shape of the debris became round at higher water temperature, and a needle-like shape was observed at lower temperatures. Debris analysis results showed that the debris sizes of 2.8–6.7 mm had the largest mass fraction. By comparison with the theoretical calculation, it was found that the fragment diameters measured in the present study agreed well with Weber number theory. Thus, it was demonstrated that the fragmentation mechanism was controlled by shearing stress under the present experimental conditions.

Constructal design and optimization of a dual pressure heat recovery steam generator

Optimum design of the Heat Recovery Steam Generator (HRSG) has noticeable effects on the thermal efficiency of the combined cycle power plants. In this paper, constructal design of a dual pressure HRSG is proposed. It is shown how to simultaneously optimize the operating and geometric design parameters of the HRSG by using the constructal theory. Considering the minimum total entropy generation as objective function, optimum parameters of the HRSG unit are derived by using the genetic algorithm method under the fixed total volume condition. The optimized total volume, aspect ratios of the units, the number of tubes through the length and width, the heat transfer area of the HRSG and thermodynamic properties are significant features of the flow configuration resulted from constructal design. Optimal aspect ratios of the units are correlated to the pressure and temperature and effects of these variables on the main geometric characteristics of HRSG are obtained. The results show that there is an optimum value for total volume of the HRSG and most of the overall heat transfer coefficient (UA) are allocated to the evaporators. Also, number of the tubes in the longitudinal direction are fewer than the number of tubes in the transverse direction.

Cost-based design optimization of the heat exchangers in a parabolic trough power plant

This paper addresses two important concerns of the design of steam generators of parabolic trough power plants: cost minimization and component reliability. A thorough economic analysis of the heat exchangers of the steam generator and oil-to-salt heat exchangers of a 50 MWe parabolic trough power plant is presented. The heat exchanger design is realized following TEMA standards and optimized using a genetic algorithm. Two design strategies are compared: the minimization of the total heat transfer area and the minimization of the total annualized cost. It is seen that the second approach provides substantial savings over the lifetime of the plant.The economic analysis reveals a global optimum with an outlet temperature of the heat transfer fluid of 293 °C and an evaporator pinch point of 4.85 °C. The best design of the steam generator consists of a TEMA-H shell superheater and preheater and a TEMA-F shell reheater. The best design of the oil-to-salt heat exchangers includes six TEMA-F shell heat exchangers in series, with a log mean temperature difference of 7 °C and the molten salt on the shell-side. Lastly, a TEMA-X recirculation evaporator is proposed with a considerably reduced wall thickness when compared to a kettle evaporator.

J-resistance curves for Inconel 690 and Incoloy 800 nuclear steam generators tubes at room temperature and at 300 °C

The structural integrity of steam generator tubes is a relevant issue concerning nuclear plant safety. In the present work, J-resistance curves of Inconel 690 and Incoloy 800 nuclear steam generator tubes with circumferential and longitudinal through wall cracks were obtained at room temperature and 300 °C using recently developed non-standard specimens' geometries. It was found that Incoloy 800 tubes exhibited higher J-resistance curves than Inconel 690 for both crack orientations. For both materials, circumferential cracks resulted into higher fracture resistance than longitudinal cracks, indicating a certain degree of texture anisotropy introduced by the tube fabrication process. From a practical point of view, temperature effects have found to be negligible in all cases. The results obtained in the present work provide a general framework for further application to structural integrity assessments of cracked tubes in a variety of nuclear steam generator designs.

Safety Analysis of Pb-208 Cooled 800 MWt Modified CANDLE Reactors

Safely analysis of 800MWt Pb-208 cooled fast reactors with natural Uranium as fuel cycle input employing axial-radial combined Modiified CANDLE burnup scheme has been performed. The analysis of unprotected loss of flow(ULOF) and unprotected rod run-out transient overpower (UTOP) are discussed. Some simulations for 800 MWt Pb-208 cooled fast reactors has been performed and the results show that the reactor can anticipate complete pumping failure inherently by reducing power through reactivity feedback and remove the rest of heat through natural circulations. Compared to the Pb-nat cooled long life Fast Reactors, Pb-208 cooled reactors have smaller Doppler but higher coolant density reactivity coefficient. In the UTOP accident case the analysis has been performed against external reactivity up to 0.003dk/k. And for ULOHS case it is assumed that the secondary cooling system has broken. During all accident the cladding temperature is the most critical. Especially for the case of UTOP accident. In addition the steam generator design has also consider excess power which may reach 50% extra during severe UTOP case..

Accident Analysis Simulation in Modular 300MWt Gas Cooled Fast Reactor

Safety analysis of 300MWt helium gas cooled long-life fast reactors has been performed. The analysis of unprotected loss of flow(ULOF) and unprotected rod run-out transient overpower (UTOP) are discussed. Some simulations for 300 MWt He gas cooled fast reactors has been performed and the results show that the reactor can anticipate complete pumping failure inherently by reducing power through reactivity feedback and remove the rest of heat through natural circulations. GCFR relatively has hard spectrum so it has relatively small Doppler coefficient. In the UTOP accident case the analysis has been performed against external reactivity up to 0.002dk/k. In addition the steam generator design has also consider excess power during severe UTOP case..

Maximizing the Efficiency of a Heat Recovery Steam Generator for Solid Oxide Fuel Cell-Based Trigeneration Systems

In this study, a complete strategy for the optimum design of a heat recovery steam generator (HRSG) is outlined. The performance of the heat recovery steam generator is examined by modelling a trigeneration system based on an ethanol-fuelled solid oxide fuel cell in Aspen Plus. To maximize the HRSG efficiency, the performance of the HRSG at different steam product specifications is investigated in terms of the exergy efficiency and exergy destruction. The result shows that to minimize exergy destruction in the HRSG, the temperature difference across the HRSG should be maintained at a minimum and superheated condition should be avoided. Heat recovery steam generator with double pressure levels shows the maximum efficiency when utilizing 10 - 30 % of recovered heat for cooling application and employing the remaining heat for heating devices at nearly saturated condition.

Development and verification of the TR-BN software for substantiation of normal operation modes of BN reactors

Substantiation of design parameters of sodium-cooled fast reactor facilities (BN RF) in normal operation modes represent an important task solution of which is necessary for determining safe and optimal reactor operation conditions. Software tools existing for the purpose allow implementing calculation analysis of separate types of equipment (for example, steam generators) or of circulation loops (secondary and tertiary cooling loops). The TR-BN software developed for the purpose of complex analysis of thermal hydraulic parameters is intended for determination of the main design characteristics (temperature, pressure) for all heat removing loops (including the primary cooling circuit) and for optimization of algorithms of BN RF operation in normal operation modes on different power levels.Brief description of the software and of the calculation methodology, as well as of possible calculation options depending on the steam generator design is given. Verification and cross-verification of the TR-BN software were implemented by way of comparison of calculated results with operational characteristics of BN-600 reactor facility and with results of calculation of BN-800 steam generator obtained using the Korsar/GP computer code. Analysis of the obtained results demonstrated satisfactory agreement with maximum discrepancy for temperature not exceeding 7.5% for sodium and 14.2% for steam. Standard uncertainties of parameters calculated using the TR-BN software and characterizing the accuracy of the performed calculations were determined. Possibility was demonstrated to use the software in the normal operation modes in the substantiation of safety of the BN RF.

Numerical simulation of dryout and post-dryout heat transfer in a straight-pipe once-through steam generator

Accurately predicting dryout and post-dryout heat transfer characteristics is critical for proper design of once-through steam generators. This paper provides a reasonable and simple method for this prediction by introducing a two-fluid, three-flow-field mathematical model and improving the dryout criterion-critical quality, and conducts a numerical simulation of dryout and post-dryout heat transfer in a once-through steam generator to prove the model’s performance. The results show that the critical quality in a once-through steam generator is about 0.82, with the heat transfer capacity significantly reducing and the wall temperature sharply increasing in a non-linear form by approximately 30K when dryout occurs. Part of the steam is superheated in the post-dryout region, resulting in a deviation from thermodynamic equilibrium between the vapor and liquid phases. Dryout and post-dryout heat transfer in the once-through steam generator operate between complete deviation from thermodynamic equilibrium and complete thermodynamic equilibrium. Therefore, the presence of droplets has a significant influence on the mass, momentum and energy transfer between the film and vapor phases.

A discrete and continuous mathematical model for the optimal synthesis and design of dual pressure heat recovery steam generators coupled to two steam turbines

This paper addresses the optimal arrangement and design of a dual pressure heat recovery steam generator coupled to two steam turbines. A superstructure that embeds various alternative configurations is optimized considering the following two single objective functions: (a) the maximization of the total net power generation for a given total heat transfer area and (b) the minimization of the total heat transfer area for a given total net power. The optimal number of heat exchangers and pumps and how they should be connected are the discrete decisions. The dimensions and operating conditions are the continuous decisions. A discrete and continuous mathematical model is developed and logical propositions are used for discrete decisions. The results are compared with a reference case reported by other authors. The results indicated that the optimization of the proposed superstructure allowed to find a more efficient HRSG configuration. The obtained configurations differ from the configuration of the reference case in how the heat exchangers and pumps are connected. A considerable increase in about 8% of the total net power generation in (a) and a significant reduction in about 24% of the total heat transfer area in (b) are achieved when compared to the reference case.

Study on the Structure Optimization and the Operation Scheme Design of a Double-Tube Once-Through Steam Generator

A double-tube once-through steam generator (DOTSG) consisting of an outer straight tube and an inner helical tube is studied in this work. First, the structure of the DOTSG is optimized by considering two different objective functions. The tube length and the total pressure drop are considered as the first and second objective functions, respectively. Because the DOTSG is divided into the subcooled, boiling, and superheated sections according to the different secondary fluid states, the pitches in the three sections are defined as the optimization variables. A multi-objective optimization model is established and solved by particle swarm optimization. The optimization pitch is small in the subcooled region and superheated region, and large in the boiling region. Considering the availability of the optimum structure at power levels below 100% full power, we propose a new operating scheme that can fix the boundaries between the three heat-transfer sections. The operation scheme is proposed on the basis of data for full power, and the operation parameters are calculated at low power level. The primary inlet and outlet temperatures, as well as flow rate and secondary outlet temperature are changed according to the operation procedure.

Thermal–hydraulic design and analysis code development for steam generator of CFR600

China Fast Reactor (CFR) with 600MW electric power is under development in China. Lots of efforts are being made to its Research and Development (R&D). The CFR600 steam generator with straight tubes consists of the evaporator and the superheater. Phase change exists in the water/steam side and the thermal–hydraulic behavior is difficult to predict. It is challenging to design such a steam generator. Therefore, a suitable thermal–hydraulic code is necessary to assist its design and analysis. A steady-state thermal–hydraulic model is derived based on the mass, energy and momentum equations. The characteristic tube is divided into four regions: subcooled region, nucleate boiling region, film boiling region and superheated region. Equal node enthalpy increment in a region is applied to enhance the numerical accuracy. The model is verified with the design results of design code SG-33 and CEFR. It is proven that the code developed can be used to design and analyze the thermal–hydraulic behavior. Sensitivity analysis is performed to investigate the influence on the heat transfer from key parameters. A preliminary design of CFR600 steam generator is presented using the developed code and reasonable results are obtained.

Investigations for performance enhancement of dual pressure HRSG in gas/steam combined cycle power plants

ABSTRACTA heat recovery steam generator (HRSG) is the vital equipment in a gas/steam combined cycle power plant (CCPP) which plays an important role in enhancing the overall performance of the plant. An HRSG is designed on the basis of the size of the gas and steam turbines used in the power plant. Therefore, the HRSG directly affects the performance of the CCPP and its optimisation based on physical design can improve the plant performance. In the present study, the plant data of the CCPP of NTPC Ltd. at Auraiya (U.P.), India, has been considered for study. A segmented finned model has been chosen as it is the preferred arrangement [Ganapathy, V. 2003. Industrial Boiler and Heat Recovery Steam Generator Design, Application and Calculation. New York: Marcel Dekker Inc.] and thermodynamic investigations have been carried out upon a dual pressure HRSG in a gas/steam CCPP from the perspective of maximum heat recovery and minimum pressure loss. The performance investigations of varying physical parameters of a dual pressure HRSG with segmented fins are useful for CCPP designers and for all those who are engaged in the area of heat recovery.

일체형 원자로용 관류식 직관형 증기발생기 열수력 해석 코드 개발

관류식 직관형 증기발생기의 열수력 설계와 성능분석을 위한 해석코드를 개발하였다. 개발한 물리적 모델과 수치 해석 코드를 검증하기 위해 설계 제원이 공개되어 사용되고 있는 관류식 직관형 증기발생기를 개발된 코드를 이용해 해석하고 설계 자료와 비교하였다. 또한 동일한 증기발생기를 최적 열수력 안전해석코드인 MARS를 이용하여 해석한 뒤 비교분석하였다. 열전달면적, 압력 및 온도분포 등의 계산 결과는 설계 자료 및 MARS 코드의 계산 결과와 대부분 일치하게 나타났다. 최종적으로 개발된 코드가 직관형 증기발생기의 열적 설계 최적화 및 민감도 분석을 목적으로 폭넓게 사용될 수 있음을 확인하였다. A thermal-hydraulic design and performance analysis computer code for a once-through steam generator using straight tubes is developed. To benchmark the developed physical models and computer code, an once-through steam generator developed by other designer is simulated and the calculated results are compared with the design data. Also, the same steam generator is analyzed with the best-estimate thermal-hydraulic system code, MARS, for the code-to-code validation. The overall characteristics of heat transfer area, pressure and temperature distributions calculated by the developed code show general agreements with the published design data as well as the analysis results of MARS. It is demonstrated that the developed code can be utilized for diverse purposes, such as, sensitivity analyses and optimum thermal design of a once-through steam generator.