Corrosion and corrosion prevention in heat exchangers

In many industries and processes, heat exchangers are of vital importance as they are used to transfer heat from one fluid to another. These fluids can be corrosive to heat exchangers, which are usually made of metallic materials. This paper illustrates that corrosion is an important problem in the operation of heat exchangers in many environments, for which no straightforward answer exists. Corrosion failures of heat exchangers are common, and corrosion often involves high maintenance or repair costs. In this review, an overview is given of what is known on corrosion in heat exchangers. The different types of corrosion encountered in heat exchangers and the susceptible places in the devices are discussed first. This is combined with an overview of failure analyses for each type of corrosion. Next, the effect of heat transfer on corrosion and the influence of corrosion on the thermohydraulic performances are discussed. Finally, the prevention and control of corrosion is tackled. Prevention goes from general design considerations and operation guidelines to the use of cathodic and anodic protection

Feasibility Study on the Replacement of Traditional Heat Exchanger by ALFA LAVAL COMP ABLOC in PETRONAS OPUs.

Selection of a heat exchanger for a certain application is a considerable decision making. The performance of the selected heat exchanger should meet the maximum demand of the operation unit involving the heat exchanger and also the cost factor is of high importance since it consist the maintenance and the running cost. In the present work, analysis had been carried out to investigate the possibility of replacing existing traditional heat exchanger with compact types. The study is based on the performance analysis to meet the operational requirement of PETRONAS OPU. Also a cost analysis has been conducted to compare between the traditional and the compact heat exchanger. The results obtained have shown that COMPABLOC require less heat transfer area than the STHE at the same thermal duty. On the cost analysis part, the analysis reveals that the replacement is feasible and justified

Failure Analysis of Heat Exchangers with a Valid CFD Simulation

Energy efficiency, safety and stable operation of units are the most crucial aspects in every industrial process. In this study, Computational Fluid Dynamics (CFD) simulations were used to study heat transfer in a laboratory-sized tubular heat exchanger. A partly 2D axisymmetric and mainly 3D model of the heat exchanger was created and validated with several simulation in different operating points of heating capacity and volume flow. The results of the simulations were compared to experimental data to validate the model. The inlet and outlet temperatures were measured with Pt100 temperature probes, and the surface temperatures were measured with an infrared camera. The heat transfer coefficient was determined based on the surface measurements The validated model was applied for the investigation of performance losses of heat exchanger due to fouling caused by particle deposits along the tube which caused reduced heat transfer surface or performance and a failure of heating wire which caused reduced heating performance, hence altered heat and flow characteristics through the equipment. The results provide useful information not only in the design processes but the operational lifetime as well

THERMAL-HYDRAULIC STUDY IN SUPPORT OF THE DESIGN OF THE DEMO BALANCE OF PLANT

The European Research Roadmap to the Realisation of Fusion Energy, foresees that the Demonstration Fusion Power Reactor (DEMO) is going to be the successor of ITER reactor in the pathway towards the exploitation of nuclear fusion to produce electric energy on an industrial scale. It will, hence, have to deliver hundreds MW of electric power ensuring an adequate availability and reliability of operation over a reasonable time span. EU-DEMO pre-conceptual design is being conducted by research institutions and universities from 26 countries of European Union, Switzerland and Ukraine, with the main aim to provide electric energy to the grid from nuclear fusion reactions by 2050. However, where exactly DEMO should be located in between ITER and a commercial fusion power plant depends on the resources, the gaps towards a commercial plant as well as the development risks that can be accepted and the time scale to fusion deployment. It is worth to say that, due to the inherent different mission between the two machines, some of the technical solutions adopted for ITER are not DEMO relevant and a return of design and operational experiences cannot be expected from ITER in certain fields. For instance, as DEMO has been conceived to deliver net electric power to the grid, the reactor design must be more oriented toward the Balance of Plant (BoP) issues than it is in ITER, where the heat power, available at a rather low temperature level, will be wasted to the environment heat sink without any energy conversion intended to civil applications and/or exploitation. Therefore, since the early phase of the DEMO project, emphasis has been given to those engineering aspects and design integration issues that actually affect the architecture of a nuclear power plant, e.g. technology readiness, power conversion features, safety and related licensing aspects etc. Within the framework of the R&D activities DEMO-oriented, promoted and supported by the EUROfusion Consortium, it has been carried out the research activity relevant to the XXXII cycle of the Ph.D. course in Energy and Information Technologies. In particular, the main objective of the theoretical research campaign has been to outline a pre-conceptual design of the Primary Heat Transfer System for the helium-cooled Breeding Blanket concept. The choice of the Breeding Blanket option, thus of the primary coolant, plays a pivotal role in the whole reactor Balance of plant architecture having a strong influence on plant operation, safety and maintenance. The studies have been articulated in two main phases: in the first part of the work it has been carried out a thermal-hydraulic and mechanical design of the main system components following and developing analytical/semi-analytical procedures by the adoption of the methodologies commonly used for this purpose; the second half of the activities has intended to verify the effectiveness of these procedures as well as the robustness of the design, therefore an assessment of the thermal-hydraulic behaviour of the primary heat transfer system has been made by means of a theoretical-computational approach based on the Finite Volume Method and adopting suitable releases of both 1-D and 3-D codes. The Ph.D. activities, which were led from the end of 2016 to the second half of 2019, are going to be extensively described in this thesis

HYDROPHOBIC COATINGS BASED ON COMMERCIAL PERFLUOROPOLYETHERS FOR FOULING MITIGATION. APPROACH ON A PILOT HEAT EXCHANGER PLANT

This work concerns the mitigation of fouling in heat exchangers, by means of the modification of the interaction between the foulant particles and the solid surfaces involved in the fouling phenomenon. To achieve this goal, hydrophobic coatings containing commercial perfluoropolyethers (PFPE) and metal oxides were prepared. Specifically, three typologies of coatings were prepared for the protection of stainless steel surfaces: commercial \u3b1,\u3c9-inorganic substituted PFPE coatings, multilayer coatings containing the commercial PFPE and metal oxides nanopowders, and hybrid coatings containing sol-gel metal oxides networks and the commercial PFPE. All the coatings prepared were fully characterized in order to assess their morphology, composition and thickness. The wettability of the coatings was measured by contact angle (CA) determination, and all the coatings resulted to be hydrophobic, with CA>120\ub0. The chemical and mechanical stability of all the coatings prepared was investigated by means of particular resistance tests, performed in liquid environments. Hybrid coatings appeared as the most resistant coatings against the erosion induced by chemical aggressive liquids, high temperature liquids (343 K), or shear stresses induced by the flowing of water upon the coated surface (0.17 m/s). The experimentation on a heat exchanger pilot plant confirmed the ability of the hydrophobic hybrid coatings to mitigate crystallization fouling on stainless steel heat transfer surfaces. In the condition adopted (transient flow regime and heat exchanging fluids at temperatures of 291-293 K and 318-323 K), the hybrid coating was able to delay the fouling step of about 200 hours and to promote the removal of the fouling deposits progressively formed on the heat transfer surfaces

Solar thermochemical process interface study

The design and analyses of a subsystem of a hydrogen production process are described. The process is based on solar driven thermochemical reactions. The subject subsystem receives sulfuric acid of 60% concentration at 100 C, 1 atm pressure. The acid is further concentrated, vaporized, and decomposed (at a rate of 122 g moles/sec H2SO4) into SO2, O2, and water. The produce stream is cooled to 100 C. Three subsystem options, each being driven by direct solar energy, were designed and analyzed. The results are compared with a prior study case in which solar energy was provided indirectly through a helium loop

Feasibility Study on the Replacement of Traditional Heat Exchanger by ALFA LAVAL COMP ABLOC in PETRONAS OPUs.

Selection of a heat exchanger for a certain application is a considerable decision making. The performance of the selected heat exchanger should meet the maximum demand of the operation unit involving the heat exchanger and also the cost factor is of high importance since it consist the maintenance and the running cost. In the present work, analysis had been carried out to investigate the possibility of replacing existing traditional heat exchanger with compact types. The study is based on the performance analysis to meet the operational requirement of PETRONAS OPU. Also a cost analysis has been conducted to compare between the traditional and the compact heat exchanger. The results obtained have shown that COMPABLOC require less heat transfer area than the STHE at the same thermal duty. On the cost analysis part, the analysis reveals that the replacement is feasible and justified

Design and dynamic analysis of steam generators of concentrating solar power plants

Mención Internacional en el título de doctorCommercial concentrating solar power (CSP) plants normally use an indirect steam generation system due to the advantages provided by use of the heat transfer fluid (HTF), which allows the installation of cost‐effective storage systems. However, the pinch point temperature difference limitation imposed by the indirect steam generator (SG) systems has a great influence on the overall plant performance because it sets the mass flow rate of the HTF. As a consequence, a trade‐off is obtained between the investment cost of the heat exchangers and the operational pump cost of the heat transfer fluid. CSP plants need to increase their flexibility in order to be competitive in the current electricity markets. The SG has a great influence on the flexibility of CSP plants due to the thermal stresses on thick‐walled components that limit the start‐up and load changes ramps. Furthermore, the cycling operating conditions of CSP plants may cause fatigue damage. For this reason, the dynamic analysis of SG is mandatory to assure its lifetime. This PhD thesis consists of the design and dynamic analysis of SG for CSP plants. A methodology for the design of the SG and oil‐to‐salt heat exchangers of a 50 MWe parabolic trough power plant (PTPP) is presented. The heat exchanger design is made following TEMA standards and ASME Pressure Vessel code. The economic analysis of SG is made using as main variables the evaporator pinch point and the HTF outlet temperature, in order to take into account the total operational HTF pump cost and the investment cost of the SG heat exchangers. The heat exchanger design is made using genetic algorithms to obtain feasible and optimized results. Two design strategies are compared: the minimization of the total heat transfer area and the minimization of the total annualized cost. The results show that the second approach leads to substantial savings. A recirculation evaporator specially designed for PTPP is modeled and compared with kettle design. A methodology for heat exchanger design of a solar power tower plant (SPTP) is also proposed. The special operating conditions with high fluid temperatures and the high heat duty make this issue a non‐typical heat exchanger design problem. For this reason, heat transfer and thermal stress requirements are considered in the heat exchanger selection of superheater, reheater, evaporator and preheater. The economic analysis consists of the evaporator pinch point temperature difference optimization taking into account its impact on the global plant performance. Two SG configurations are studied: with one or two parallel trains of heat exchangers. The results show extremely low optimum pinch point values. A preliminary economic study is also made to compare forced and natural circulation evaporator designs. The section of the thesis corresponding to dynamic study deals about the offdesign analysis of the proposed design of SG for a SPTP. For that purpose, transient models are developed to the single phase heat exchangers and the recirculation evaporator with steam drum. Furthermore, different models are proposed to estimate the transient temperature field and stresses on critical parts of shell‐and‐tube heat exchangers such as: tubesheets ligaments and tubesheet junction. Two SG start‐up initial conditions are studied. The first considers non‐isothermal temperature profiles on the heat exchangers at the beginning of the start‐up whereas the second considers isothermal initial conditions. For both scenarios are proposed a start‐up procedure where the main allowable temperature fluid ramps to operate the SG on safety‐side are calculated. The dynamic analysis of the SG proposed for a PTPP is also presented. The dynamic response of the heat exchangers is estimated developing transient models for TEMA F and TEMA H. The thermal stresses are calculated on the critical zones such tubesheets, head‐nozzle junctions, steam drum‐downcomer junction and U‐bend regions. In addition, the analytical stress models are validated by means of different finite element simulations. A SG start‐up is performed using temperature ramps to not overpass the ratcheting and magnetite protection stress limits. Lastly, a study is made to compare the dynamic behavior between kettle and recirculation evaporators. Finally, it is presented the fatigue analysis of the SG for a PTPP. The fatigue analysis is performed following ASME Pressure Vessel code for the start‐up, shutdown and load change of the SG.Las centrales termosolares normalmente utilizan sistemas de generación de vapor indirectos debido a las ventajas producidas por la utilización de un fluido caloportador, que permite la instalación de eficientes sistemas de almacenamiento térmico. Sin embargo, los sistemas de generación de vapor indirectos están limitados por la diferencia de temperaturas mínima en el evaporador, que fija el caudal de fluido caloportador, y por tanto tiene un gran impacto en el funcionamiento de la planta. Como consecuencia, se obtiene un compromiso entre los costes de inversión de los intercambiadores de calor y los costes de bombeo del fluido caloportador. El estado actual de los mercados eléctricos promueve la necesidad de incrementar la flexibilidad de las centrales termosolares. El sistema de generación de vapor tiene una gran influencia en la flexibilidad debido al estrés térmico en los componentes de pared gruesa que limitan las rampas de arranque y cambio de carga. Además, la operación cíclica de las centrales termosolares pueden producir daño a fatiga y por tanto conducir a un fallo prematuro del material. Por esta razón, el análisis dinámico del sistema de generación de vapor es necesario para asegurar su vida útil. Esta tesis doctoral está basada en el diseño y análisis dinámico de sistemas de generación de vapor de centrales termosolares. En primer lugar se ha desarrollado un metodología para el diseño del sistema de generación de vapor de centrales termosolares de 50 MWe de cilindro parabólico, incluyendo también el diseño de los intercambiadores sales‐aceite. El diseño de los intercambiadores de calor se ha realizado acorde con la normativa TEMA y el código ASME. El análisis económico se ha realizado tomando la diferencia de temperatura mínima en el evaporador y la temperatura de salida del fluido caloportador como principales variables. De este modo, se tienen en cuenta los costes de bombeo del fluido caloportador y los costes de inversión de los intercambiadores de calor. Por otro lado, dos estrategias de diseño son comparadas: minimización del área de transferencia de calor y minimización de los costes anualizados. Obteniendo con la segunda opción un considerable ahorro de los costes de operación. Además, se ha desarrollado un evaporador de recirculación especialmente diseñado para centrales termosolares de cilindro parabólico. Por otro lado, también se ha desarrollado una metodología para el diseño del sistema de generación de vapor de una central termosolar de tipo torre. Las condiciones especiales de operación con altas temperaturas y grandes calores de intercambio hacen de esta tarea un problema atípico en el diseño de intercambiadores de calor. Por esta razón, se han tenido en cuenta consideraciones de transferencia de calor y estrés térmico para la selección del tipo de intercambiador para sobrecalentador, recalentador, evaporador y precalentador. El análisis económico se ha realizado tomando como principal variable la diferencia de temperaturas mínima en el evaporador por su influencia en el funcionamiento global de la central. Dos configuraciones del generador de vapor son estudiadas: con un tren y con dos trenes en paralelo. Los resultados muestran que los valores óptimos se obtienen para diferencias de temperaturas mínimas en el evaporador muy bajas. Además, un análisis económico preliminar se ha realizado para comparar los evaporadores con circulación forzado y natural. El estudio dinámico comienza con el análisis transitorio del sistema de generador de la central termosolar de tipo torre. Para ello, son desarrollados diferentes modelos dinámicos para los intercambiadores monofásicos, y para el conjunto evaporador y calderín. Además, se han desarrollado modelos para el cálculo de los campos temperaturas y del estrés en partes críticas de intercambiadores de tubo y carcasa como los ligamentos de placa de tubos y las uniones de la placa de tubos. Para el estudio dinámico del arranque del generador de vapor son considerados dos escenarios. El primero considera perfiles de temperatura no isotérmicos en los intercambiadores al principio del arranque, mientras que el segundo considera perfiles isotérmicos. Para ambos escenarios son calculadas las rampas de temperatura del fluido caloportador y del evaporador para operar el generador de vapor por el lado de la seguridad. Además también se ha presentado el análisis dinámico del sistema de generación de vapor de una central termosolar de cilindro parabólico. Para ello, se han desarrollado modelos dinámicos para intercambiadores TEMA F y TEMA H. Los estreses térmicos son calculados en zonas críticas como: la placa de tubos, uniones de cabeza y tobera, las uniones tipo T del calderín y los tubos en U. Además, los modelos de estrés son validados por medio de diferentes modelos en elementos finitos. El análisis dinámico del arranque del sistema de generación se ha realizado para rampas de temperatura que no sobrepasan los límites de estrés impuestos por la integridad estructural y la protección de la capa de magnetita. Finalmente, se ha realizado un estudio comparando el comportamiento dinámico entre evaporador tipo kettle y de recirculación. En último lugar, se ha realizado el análisis a fatiga del sistema de generación de vapor de una central termosolar de cilindro parabólico. El análisis a fatiga se ha realizado conforme al código ASME para las operaciones de arranque, apagado y cambio de carga del generador de vapor.Programa Oficial de Doctorado en Ingeniería Mecánica y de Organización IndustrialPresidente: David Sánchez Martínez.- Secretario: Antonio José Rovira de Antonio.- Vocal: Rafael Eduardo Guédez Mat

Design of a Heat Exchanger for a Supercritical CO2 Turbine System

This research aims at designing a shell and tube heat exchanger which will drive a turbine operated on supercritical CO2. Hot gases from boiler (simulated using air) at 1500 K is introduced into the shell to heat up the supercritical CO2 at 10 MPa flowing within tubes from 450 K to 1050 K. The design was done using selected shell and tube heat exchanger empirical equations at predefined boundary conditions. The effect of shell and tube diameter on other design parameters was examined. It was observed that the number of tubes, tube external and internal side surface area, volumes of shell and tube, overall surface area and mass of tube material increases as the shell diameter increases from 6 m to 18 m at 2 m interval and this is due to the increase in cross sectional area. The shell length, the number of baffles, overall heat transfer coefficient, the pressure drop in both shell and tube sides all decreases as shell diameter increases at same rate as described previously, and this is attributed to a reduced velocity caused by the increased cross section area of tubes and baffle space. The increase in tube diameter from 0.0092 m to 0.12 m at 0.02 m intervals however leads to an increase in shell length, volume of tube material, number of baffles, shell side pressure drop, tube side pressure drop, overall area of the device ,tube external side surface area and tube internal side surface area. However, the overall heat transfer coefficient, total length of tubes and number of tubes decreases as the tube diameter increases at same rate as described previously. A decision was made on the selected heat exchanger based on fewer tubes, reduced mass of tube materials , low shell and tube pressure drop, and a high heat transfer coefficient. A selected of shell diameter 8 m, shell length 51.62 m, tube diameter 0.102 m, number of tubes 1509 and overall heat transfer coefficient 60.51 W/m2K was considered. A CFD analysis was conducted using ANSYS 18.1 on the prototype of the selected heat exchanger device. The device was built using the design modeler and it consist of the shell, tubes, air fluid, CO2 fluid and baffles The meshing and naming of unit parts was done while the set-up stage was achieved with the predefined boundary conditions and properties. The temperature distribution and thermal analysis of the heat exchanger was reported

Comparison of Thermal Effectiveness and Crevice Corrosion Risk of Fin Geometry on All-Aluminum Microchannel Heat Exchangers

Article all-aluminum microchannel heat exchangers have recently gained popularity in the heating, ventilation, and air conditioning industry. Despite their attractive thermal performance design, these heat exchangers make coils used in automotive, commercial, and residential applications prone to crevice corrosion. This study uses high-fidelity conjugate heat transfer simulations to model a micro channel heat exchanger system that includes fins and tubes with crossflow to compare their thermal effectiveness to gain insight into potential crevice corrosion of the MCHE alloy