Boiler Heat Exchanger Research Articles

Condition-based inspection policies for boiler heat exchangers

This study considers the inspection and maintenance of boiler heat exchangers, which are examples of a system composed of degrading, non-repairable components in series whose operation can be restored by removing failed components from service (albeit at a performance loss). For such systems, the increased failure risk due to component degradation may be managed through inspections and preventive removal of high failure risk components from service (again at a performance loss for remaining life of systems). In this study, a new joint inspection and preventive maintenance policy is developed, which uses condition information obtained at an inspection to optimize decisions regarding maintenance and future inspections to optimally balance the risks of system failure, future performance losses, and maintenance costs. The policy is optimized using the Markov Decision Process paradigm and is applied to a case study of a boiler heat exchanger operating in an Australian sugar factory. The results show that the proposed policy yields significant savings compared to benchmark policies that represent the factory's current practice.

A void fraction of high-viscosity air-water flow in capillary pipes with a slope of 30 degrees to the horizontal positio

Two-phase flow is a flow that is composed of several combined substances, namely liquid and gas. Two-phase flow is found in industrial processes, such as in boiler systems, reactors, heat exchangers, geothermal and others. The phenomenon of two-phase flow is also often found in nature, such as fog, snow, clouds, and rain. The purpose of this study was to obtain the characteristics, length, and frequency of flow patterns in two phases based on the experimental value of the fraction in a two-phase flow of a mixture of water-glycerin and air in a capillary tube with a slope of 30˚. The study used a 1.6 mm diameter capillary tube with a working fluid which mixed air and water mixed with glycerin with glycerin concentrations of 40%, 50%, 60%, and 70%. Void fraction values were analyzed using digital image processing methods with the MATLAB R2014a application program. The results showed that the void fraction value was determined by the surface velocity of the liquid and air. The greater the superficial air velocity, the value of the vacuum fraction will develop, while the greater the superficial velocity of the liquid, the vacuum fraction will decrease. The flow pattern of bubbles and plugs is strongly influenced by fluid viscosity. Therefore the higher the viscosity, the velocity of the bubble and plug flow patterns will decrease, conversely if the viscosity of the fluid decreases, the velocity of the bubble and plug flow patterns will increase. The length and flow of the bubble pattern are strongly influenced by homogeneous values (β). If the homogeneous value (β) is higher then the length of the flow pattern will increase. In the stopper flow pattern obtained a high enough frequency, it will produce a high enough void fraction value. Keywords: Two-phase, fluid, void fraction, viscosity, flow pattern.

Mechanical and surface morphology study of Monel – Copper joint by rotary friction welding

The demand for of dissimilar metal joints is increasing day by day in many industrial applications like automobile, aero space, boiler accessories, defence and structural components. Recently many of researchers have focussed on monel base dissimilar weld joints because, it has played a main role in the fabrication of hydraulic, boiler components such as valve, pump, casing, fin, pipe and shaft. So, the present experimental work is to join Monel (K-500) – Copper (ETP) by rotary friction welding technique under a spindle speed of 1500 rpm for boiler heat exchanger applications. Totally 16 joints were prepared with varied process parameter like frictional pressure (20, 25, 30 and 35 bar), Upset pressure (15, 20, 25 and 30 bar) and constant feed rate (9 mm/s) was maintained. Finally, all the joints were evaluated to find its mechanical and micro structural properties such as micro hardness, yield and ultimate strength as per ASTM standards. The interface (inertial bonding structure) and Heat Affected Zone (HAZ) of weld joint were examined by scanning electron beam microscope and its level of monel – copper layer was identified through X-ray diffraction technique.

Two-step numerical procedure on the removal process of gaseous potassium chloride generated from waste incineration via the injection of sulfate-based additives

Gaseous potassium chloride (KCl) that constitutes a relatively large portion of the combustion gas of municipal solid waste can condense on the surface of boiler heat exchanger tubes, causing severe corrosion attacks. To reduce the chlorine-induced high-temperature corrosion, sulfate-based additives have been used. In this study, a two-step numerical procedure is proposed to quickly predict the effect of the injection of sulfate-based additives on the removal of gaseous KCl. A computational fluid dynamics (CFD) simulation is first carried out to obtain the temperature distribution. Then, the thermal decomposition of sulfate additives, sulfation of gaseous KCl, and condensation of K2SO4 are calculated to predict the species concentration profiles at the temperature conditions given by the CFD simulation. After validation with a laboratory-scale experiment using NH42SO4, the procedure is applied to a pilot-scale boiler to examine the effects of NH42SO4, Fe2SO43, and Al2SO43. The calculation results show that each additive has an optimal injection temperature range: approximately 800 °C for NH42SO4 and 1000 °C for both Fe2SO43 and Al2SO43, which are consistent with the values reported in the literature. The expressions for the stoichiometric KCl removal efficiency of each additive are derived and compared with the calculated efficiencies.

Simulating growth of ash deposit in boiler heat exchanger tube based on CFD dynamic mesh technique

Ash deposition on heat transfer surfaces is still a significant problem in existing conventional utility boilers. Understanding the formation of ash deposit is thereby very important, which is helpful to optimize the design and operation procedure of boilers. In this study, a dynamic numerical method based on the commercial software ANSYS FLUENT was developed to predict the growth of ash deposit on the deposition probe in a 300 kW slagging test furnace fired with Zhundong coal. Based on the CFD dynamic mesh technique, both shape variations and surface temperature variations of ash deposit with time were predicted. Time-dependent deposition behaviors on the deposition probe with different initial metal wall temperatures were presented. The simulation results (e.g. thickness, heat flux, surface temperature, and shape of ash deposit) are in good agreement with the experimental data. It shows that increased surface temperature of ash deposit can significantly increase ash deposition mass. It was also determined that the shape variation of ash deposit can obviously reduce the impact mass and deposition mass during ash deposition by the comparative studies. The developed simulation method is proved to be a useful tool to predict ash deposition behavior with more detailed information.

ПІДВИЩЕННЯ ЕНЕРГОЕФЕКТИВНОСТІ ВОДОГРІЙНИХ КОТЛІВ ЗА ДОПОМОГОЮ ІНТЕНСИФІКАЦІЇ ТЕПЛООБМІНУ

In the work the research of the efficiency of the heat exchange intensification in the gas-tube heat exchanger of the water heating boiler was carried out, the analysis of the obtained results was carried out. It was noted that for heat pump gas boilers the problem of heat transfer intensification is especially important, since the coefficient of heat transfer from gases to the wall in the channels without intensification is rather small, and the temperature of the waste gases and the efficiency coefficient depend on the heat transfer intensity of the heat exchanger. The review of literary information, which showed that in modern water-heating boilers of small and medium power intensifiers are used: wired inserts of various configurations, ring grooves, spiral inserts, band swirls, screw turbulators, plates of different configurations, combined methods. As part of the course design, the design of a heat generator on wood chips with a rated power of 550 kW was developed. For this design, numerical studies of the influence of the installation of intensifiers on the performance of the boiler on the full and partial load are carried out. To study the boiler's energy characteristics, a mathematical model has been developed, which is supplemented with dependencies for the calculation of the intensified heat transfer in the boiler heat exchanger. Influence of installation of the intensifier on the temperature of flue gases at the output from the boiler and on the efficiency coefficient is investigated. It is shown that the greatest reduction of the temperature of the exhaust gases is observed for the intensifier in the form of a twisted tape, a combined method, an intensifier of the original construction and a bent plate with different geometric parameters. It is noted that when choosing a method for intensifying heat exchange in a boiler for solid fuels and parameters of intensifiers, it is necessary to carry out a detailed thermal and aerodynamic calculation when changing the boiler's thermal power and to estimate the ranges of rational work, which will exclude significant cooling of flue gases, and the effect of installing the intensifiers will exceed the cost of overcoming the additional hydraulic resistance in the heat exchanger.

Key issues and practical design for cooling wall of supercritical carbon dioxide coal-fired boiler

When supercritical carbon dioxide (S–CO2) Brayton cycle is used for coal-fired power plants, the significantly increased mass flow rate and endothermic temperature of S–CO2 boiler leads to the over-temperature and high pressure drop on the cooling wall (CW). This paper presents a mathematic flow and heat transfer model of S–CO2 in combustion chamber CW. The results show that reducing the tube diameter can effectively reduce the temperature difference in cooling wall and reduce the effect of high heat flux on the temperature difference. The pressure drop decreases exponentially with the increase of tube diameter and boiler expansion factor. Increasing partial flow numbers will decrease the boiler pressure drop and improve system cycle efficiency in spite of increasing the temperature difference of CW. The change of flow direction has no obvious effect on temperature distribution of CW and has opposite effect on gravity and buoyancy force. Three boiler layout strategies, including partial flow strategy, flow symmetry strategy and boiler local expansion strategy are proposed in order to coordinate the pressure drop and uneven temperature distribution, which can not only decrease boiler heat exchange surface temperature difference but also reduce the boiler pressure drop to prevent the over-temperature and improve system performance.

Data Driven Leakage Detection and Classification of a Boiler Tube

Boiler heat exchange in thermal power plants involves tubes to transfer heat from the fuel to the water. Boiler tube leakage can cause outages and huge power generation loss. Therefore, early detection of leaks in boiler tubes is necessary to avoid such accidents. In this study, a boiler tube leak detection and classification mechanism was designed using wavelet packet transform (WPT) analysis of the acoustic emission (AE) signals acquired from the boiler tube and a fully connected deep neural network (FC-DNN). WPT analysis of the AE signals enabled the extraction of features associated with the different conditions of the boiler tube, that is, normal and leak conditions. The deep neural network (DNN) effectively explores the salient information from the wavelet packet features through a deep architecture instead of considering shallow networks, such as k-nearest neighbors (k-NN) and support vector machines (SVM). This enhances the classification performance of the leak identification and classification model developed. The proposed model yielded a 99.2 % average classification accuracy when tested with AE signals from the boiler tube. The experimental results prove the efficacy of the proposed model for boiler tube leak detection and classification.

Preliminary design assessment of supercritical CO2 cycle for commercial scale coal-fired power plants

The concept of the supercritical CO2 power cycle has been widely proved to be effective by previous studies. However, more specific system layout and key components design analysis is still imperative to demonstrate the technology feasibility of large scale utility. In the present paper the technology adaption of supercritical CO2 power cycle for commercial scale coal-fired power plant was evaluated in terms of both the whole thermodynamic cycle layout and the preliminary assessment of key components. The effect of several key factors such as turbine inlet parameters, compressor inlet parameters and two split flow ratios were analyzed by an in-house code for the purpose of optimization design of a 300 MW commercial scale coal-fired power plant. Furthermore, the preliminary design assessment of key components such as boiler, turbomachines and compact heat exchangers were performed to demonstrate the technology feasibility of commercial scale utility. The results showed that the proposed cycle can achieve 50.2% net efficiency. However, in order to achieve this high efficiency, the key components should be carefully designed to meet the high standard requirements and coal-fired system integration constraints: For boiler, split flow economizer is required to fully recover the flue gas residual energy with over 500 °C. A highly effective compact heat exchangers with pinch temperature as low as 5 °C are mandatory. The compressors and turbines are also required to achieve the high industry level with compressors efficiency of 89% and turbines efficiency of 94%.

Fire-tube boiler heat exchange surfaces fouling formation

The paper deals with the main types of foulings on the boilers heating surfaces. The mathematical modelling of the fire-tube boiler processes including the fouling formation was carried out. The fire tube design making it possible to reduce the fouling formation velocity is proposed.

Design assessment of a 5 MW fossil-fired supercritical CO2 power cycle pilot loop

Abstract The concept of the supercritical CO2 (S-CO2) power cycle has been widely proved to be effective by several small scale test loops. However, more specific system layout for fossil-fired power generation and key components design assessment is still imperative to demonstrate the technology feasibility of commercial scale utility. The S-CO2 power cycle must be optimized to deal with fossil-fired system integration constraints. In the present study the technology adaption of S-CO2 power cycle for fossil-fired power plant has been evaluated in terms of both the whole thermodynamic cycle layout and the preliminary assessment of key components. The design considerations and selections of key parameters such as turbine inlet parameters, compressor inlet parameters and split flow ratios were analyzed by a self-developed code for the purpose of optimization design of a 5 MW fossil-based S-CO2 pilot test loop. The proposed recompression and reheat cycle with two split ratios tailored for fossil-fired power plants can achieve 33.49% net efficiency. As a first step to the final recompression cycle, the design of simple recuperated and reheat cycle after carefully considerations of the specific design assessment of core components such as boiler, turbines, compressor and compact heat exchangers has been accomplished and currently under construction.

Degradation modeling and condition-based maintenance of boiler heat exchangers using gamma processes

Boiler heat exchanger tubes erode over time, leading to costly leaks and capacity loss as damaged tubes are taken out of operation. These losses can be recovered by replacing the heat exchanger, albeit at significant capital cost. Deciding when to replace the heat exchanger is greatly aided by prediction of the future capacity and downtime losses associated with tube thickness degradation. However, current thickness loss models study a single phenomenon and therefore provide oversimplified point predictions of thickness loss. Additionally, the available models do not account for uncertainty in the degradation process and therefore cannot provide information on future tube failure probabilities required for decision making.In this paper a novel degradation model is presented using a physical erosion model and a Gamma process to account for the uncertainties in the thickness degradation process. Subsequently, new algorithms are presented to predict the probability of key events in boiler operation: the bursting of a tube during operation and the plugging of a tube preventively during a scheduled shutdown. Finally, a condition-based maintenance methodology is presented based on the new degradation model and applied to a real-world case study of a boiler operating in a real Australian sugar production facility.

Lattice Boltzmann simulations of rising bubble driven by buoyancy in a complex microchannel

The movement of bubbles in the viscous fluid is a typical process in many industrial applications, such as in evaporators of refrigeration cycles, petroleum refining, boiling process, steam bubble rising in boiler tubes and heat exchangers, etc. It is an important research problem in engineering and physics. Although this kind of problem has been extensively studied, their flow details are largely unknown due to the complexity of the interface dynamics, which hinders the understanding of the physical mechanism. In order to further study underlying physics of the issue, a gas bubble rising under buoyancy in a complex micro-channel is investigated by using a gas-liquid two-phase flow lattice Boltzmann method. Initially, the model as well as a classical problem of bubble rising in a smooth vertical microchannel is tested by Laplace law. Then it is then applied to the study of a bubble rising in a complex micro-channel. Specially, the dynamic behaviors of the bubble deformation, breaking up, coalescence, and the following movement in the micro-channel are presented. The rising velocity, terminal velocity and residual mass of the bubble under the influence of micro-channel surface wettability, buoyancy force, obstacle size and the initial position of bubble are examined. The simulation results show that the surface wettability of the obstacle has a significant influence on the bubble motion. For smaller values of the contact angle, the whole bubble passes through the channel with obstacles successfully. For higher values of contact angle, the bubble is attracted to the obstacle surface of the micro-channel in the movement process. In this case, an appreciable deformation of the bubble is observed. After detachment, part of the bubble is attached by the obstacle surface, so only the rest of the bubble can go through the micro-channel, which leads the the bubble residual mass to decrease. Correspondingly, the rising velocity and terminal velocity of the bubble decrease with the wettability of the micro-channel obstacle increasing. On the other hand, with the increase of buoyancy force the detachment and coalescence phenomenon happen easily, and the bubble residual mass and terminal velocity increase logarithmically. Furthermore, as the radius of the obstacle structure increases, the bubble clings more tightly to the obstacle surface when it rises in the micro-channel. And the bubble residual mass decreases first slowly and then rapidly, while the bubble terminal velocity approximately decreases linearly. Finally, the numerical results also show that when the bubble is located at the sidewall initially, the variation trend of bubble rising velocity, terminal velocity and residual mass are consistent with that of initial position placed in the middle of the micro-channel, however all of the corresponding values decrease and the bubble deformation is more significant in the rising process.

Operation characteristics of external heat exchangers in the 600 MW supercritical CFB boiler

In this paper, experiments were carried out to obtain the actual operation characteristics of external heat exchangers (EHEs) in the first 600MW supercritical CFB boiler. The furnace temperatures and some operational parameters in EHEs were measured and the heat transfer coefficients of heating surfaces in EHEs were calculated. The results showed that by controlling the solid flow rates to the EHEs, the furnace temperature were adjusted for good performance at various boiler loads and the bed temperature were maintained stable at full load. The heat transfer coefficients in EHEs were mostly over 200W/(m2∙K), which contributed to the flexible temperature regulation. The tube panel wall temperatures were found to be a saddle-shaped distribution, which was high in the bed center but low near the wall. Packet renewal theory was used to explain such uneven temperature distribution. These results confirm the importance of EHEs to the furnace temperature control of the supercritical CFB boilers, but the uneven tube wall temperatures need to be well solved in the future.

Analysis of Fouling Degree of Individual Heating Surfaces in a Pulverized Coal Fired Boiler

The paper presents the method of fouling degree evaluation of the heating surfaces in pulverized coal-fired boiler during coal combustion and biomass co-combustion. The fouling processes have a negative impact on the boiler operation by reducing the steam outlet temperature, increasing the mass flow rate of cooling spray water, and may be the reason for overheating of the superheater (SH) tube material. This leads to a reduction of the boiler efficiency and can cause shortening of a lifetime as well as damage of boiler heat exchangers, in particular, the steam SH. The basis of fouling degree assessment method are the dimensionless coefficients, which represent current values of heat absorbed by an individual heat exchanger in comparison to the value for a clean surface. The coefficients are determined based on the calculated heat power of individual heat exchanger taking into account the adjustment resulting from the flue gas temperature inside a combustion chamber. The results of the analysis showed a significant reduction of the amount of heat absorbed by the convection SH during continuous boiler operation. The next important conclusion is a large increase of the heat amount transferred to the radiant SH, which may result in exceeding the permissible temperature of the tube material. The proposed method together with on-line monitoring system installed on the boiler is used to calculate the fouling degree of individual heating surfaces. Accurate monitoring of boiler heating surface conditions can be used to optimize soot blowers operation and finally to improve process efficiency.

Increase of efficiency and reliability of liquid fuel combustion in small-sized boilers

One of the ways to increase the efficiency of using fuels is to create highly efficient domestic energy equipment, in particular small-sized hot-water boilers in autonomous heating systems. Increasing the efficiency of the boiler requires a reduction in the temperature of the flue gases leaving, which, in turn, can be achieved by installing additional heating surfaces. The purpose of this work was to determine the principal design solutions and to develop a draft design for a high-efficiency 3-MW hot-water boiler using crude oil as its main fuel. Ensuring a high efficiency of the boiler is realized through the use of an external remote economizer, which makes it possible to reduce the dimensions of the boiler, facilitate the layout of equipment in a limited size block-modular boiler house and virtually eliminate low-temperature corrosion of boiler heat exchange surfaces. In the article the variants of execution of the water boiler and remote economizer are considered and the preliminary design calculations of the remote economizer for various schemes of the boiler layout in the Boiler Designer software package are made. Based on the results of the studies, a scheme was chosen with a three-way boiler and a two-way remote economizer. The design of a three-way fire tube hot water boiler and an external economizer with an internal arrangement of the collectors, providing for its location above the boiler in a block-modular boiler house and providing access for servicing both a remote economizer and a hot water boiler, is proposed. Its mass-dimensional and design parameters are determined. In the software package Boiler Designer thermal, hydraulic and aerodynamic calculations of the developed fire tube boiler have been performed. Optimization of the boiler design was performed, providing the required 94% efficiency value for crude oil combustion. The description of the developed flue and fire-tube hot water boiler and the value of the main design and technical and economic parameters are given.

Laser Cladding of Ni50Cr: A Parametric and Dilution Study

The increasing use of biomass as a fuel is leading to higher fireside corrosion of the heat exchangers in boilers due to the high chlorine and alkali metal content in the fuel. Laser cladding of Ni50Cr is a promising technique to enhance fireside corrosion resistance of boiler tubes from this aggressive environment. A parametric study is carried out on the blown powder based laser cladding of Ni50Cr on 304 stainless steel. Successful deposits were generated and the effects of the various process parameters on clad geometry and dilution are reported. The various commonly used techniques for determination of clad dilution are compared and some guidelines for their use are suggested.

火力発電プラントの高効率肉厚計測技術 ケーブルレスインナーUT

火力発電プラントの高効率肉厚計測技術 ケーブルレスインナーUT

Investigation of transient behaviour of combi boiler type appliances for domestic hot water

Combi boiler type appliances heating both space and water demanded for use and consuming natural gas as the energy source are one of the most common branches of the household goods. This study touches mainly on two types of combi boiler concepts to investigate only domestic hot water (DHW) heating function since highly efficient condensing appliances have been manufactured in terms of space heating. First concept has the normal working configuration of the heat exchangers of a standard combi boiler; whereas, the second has the opposite operation order of the heat exchangers. 1D transient energy equations have been constructed with the help of the laws of thermodynamics in order to model the heat exchangers in a standard combi boiler. After obtaining a general mathematical model for the standard combi boiler, the energy equations have been discretised with finite difference scheme, and solved numerically in Matlab®. Subsequently, numerical results are validated experimentally in different working modes of a standard appliance. As the last step, similar results are obtained for the second proposed concept using the related equations of the standard combi model to compare both concepts on a numerical basis.

Research on Mechanical Engineering with the Design and Implementation of Thermal Power Boiler Soot Blowing Control System

Ash deposition and slagging on boiler heat exchange surfaces is a common phenomenon in fossil fuel fired power plants. In this dissertation, author focuses on the building of soot blowing control system and all of the work is based on a 300MW boiler. This dissertation introduces the endangerment of soot deposition on boiler heat exchange surfaces. In order to reduce the loss due to fouling of the heat exchange surfaces and improve the economic efficiency of the boiler. In this dissertation, author finds the reason about the fouling form and makes analysis on the damage about the soot to thermal power boiler. On the other hand, author make design and implementation of the thermal power boiler soot blowing control system including hardware system design and software system design, and it will be the fundament of soot blowing optimization. The hardware can connect the equipment about the boiler together, and it is the foundation of the control system for thermal power boiler. Based on the data from DAS of power plant and using heating balance theory, this software system puts forwards some graphical user interfaces and that can configure the setting data and monitor the information about thermal power boiler. In this dissertation, author will design and realize the control system about thermal power boiler.