Boiler Heat Transfer Research Articles

Research on the Mechanism and Preventive Measures of Heat Transfer and Coking in Boilers

Boilers are one of the most important power supply sources in the chemical industry. The irreplaceable nature of its products requires boilers to maintain stable long-cycle operation during the production process. However, boiler failures occur from time to time and necessary measures need to be taken to reduce the chances of failure. Among these failures, metal corrosion and tube failures are particularly prominent. Due to the fact that the thermal calculation results do not match the actual; the coefficients in the design are not reasonably selected, and the hearth and boiler shape are not properly selected; the structural design of the superheater system and the arrangement of the heated surface are not reasonable; and the wall temperature calculation method is not perfect, which leads to the improper selection of materials and so on. These will make the fire-side heat exchange system produce wall temperature super-high, tube bundle burst and other failure phenomena. These phenomena cause a certain degree of hidden danger to the safe production of the boiler.

Influence of Exhaust Temperature and Flow Velocity of Marine Diesel Engines on Exhaust Gas Boiler Heat Transfer Performance

Due to the relatively cheap price of diesel, most Marine engines use diesel as Marine fuel, but its emissions contain a lot of carbon. To reduce carbon emissions, International Maritime Organization (IMO) has established an Energy Efficiency Design Index (EEDI) and Energy Efficiency Existing-Ship Index (EEXI). Currently, a popular way is to reduce EEDI by optimizing the heat transfer performance of exhaust gas boilers on new ships, but there is little research on the EEXI index of existing ships. For operating ships, the thermal conductivity of exhaust gas boiler materials and other parameters has been fixed, so the main factors affecting the heat transfer coefficient of the exhaust gas boiler are exhaust gas temperature and flow velocity. Therefore, this paper studies the influence of engine exhaust temperature and flow rate on boiler heat transfer coefficients and optimizes it to achieve the EEXI value required by IMO. Firstly, based on the conservation of mass and energy as the basic equation, a heat exchange model of the exhaust gas boiler is established by using the hybrid modeling method and lumped parameter method. Secondly, for the given boiler, since other parameters are basically unchanged, the input temperature and flow rate of the model are changed by the control variable method, and the temperature of the boiler outlet is simulated by the test algorithm. Through the simulation operation of an Aalborg OC-type boiler, the results show that when the exhaust gas flow velocity is 15 m/s, 17.2 m/s, 22.4 m/s and 25 m/s, respectively, the heat transfer coefficient at each flow velocity increases first and then slowly decreases with the increase of temperature, and there is an optimal temperature at each velocity, which is 230 °C, 227 °C, 225 °C and 224 °C, respectively. The innovation of this study lies in the research on the inlet temperature and flow rate of the exhaust gas boiler of the operating ship based on the EEXI, and the relevant results are obtained, which provides theoretical guidance for the operation management of the exhaust gas boiler of the operating ship.

Optimal operating strategy of ash deposit removal system to maximize boiler efficiency using CFD and a thermal transfer efficiency model

Ash deposits generated during the combustion process on the outer tube surface of a boiler reduces the boiler’s efficiency. In most boilers, ash deposits are physically removed with high-pressure steam using an ash deposit removal system, sootblower. However, most sootblowers spray steam with excessive pressure, without considering the characteristics of the ash deposit, resulting in problems such as waste of steam energy and damage to equipment. In addition, an optimal operation strategy based on the position of the sootblower and the injection angle of the steam nozzle are not considered, leading to a lowered efficiency of ash deposit removal and steam waste. Hence, this study proposes a novel method to determine the optimal operating conditions of a sootblower using computational fluid dynamics (CFD) and a thermal transfer efficiency model considering the properties of the ash deposits. This method was developed based on a commercial recovery boiler, and consists of (i) a sootblowing steam velocity model that considers the ash deposit characteristics, (ii) a three-dimensional CFD model considering the interior design of the boiler, and (iii) a thermal transfer efficiency model that calculates the thermal resistance depending on the amount of ash deposit removed.Case studies were performed to calculate the amount of ash deposit removed for various ash deposit thicknesses, and sootblower positions and angles using this methodology. The boiler heat transfer efficiency was calculated using the calculated ash deposit removal amount and thermal transfer efficiency model, and the optimum operating conditions for the sootblower with the optimum heat transfer efficiency were derived. This study presents a guideline for efficiently operating sootblowers according to the ash deposit characteristics, and can be applied not only to recovery boilers but also to other boilers in which ash deposits are generated.

Design and Performance Analysis of Air Pre heater for Water Tube Boiler to improve its Efficiency

Air preheater is a heat transfer surface in which air temperature is raised by transferring heat from other media such as flue gas which is coming from boiler exhaust. The paper presents the design of regenerative –air preheater to designed to meet specific performance requirements, using the software application CFD (Computational Fluid Dynamics) / CADD. An analytical study was planned to find out the various heat transfer performance parameters like outlet and inlet air temperature of the air preheater and the boiler, Pressure drop inside the Air preheater and the boiler heat transfer coefficients, heat transfer rate, overall heat transfer coefficient and Velocity of the air and flue gas also Conduction and convection modes of heat transfer were found. These heat transfer parameters are critical in designing and functioning of the air Preheater and to calculate the efficiency of the boiler.

Effects of Different Turbulators on Heat Transfer in Smoke Tube Boilers and Modeling of These Effects with Machine Learning Algorithms

In smoke pipe boilers, the thermal efficiency of the boiler depends on the smoke pipe diameter, smoke pipe length and the heat transfer between the smoke pipe and the outlet chimney. If the heat in the smoke pipes is effectively transported through the pipes, the heat distribution on the surfaces is balanced and the thermal efficiency of the boiler increases. In this study, the improvement of heat transfer in a solid fuel boiler with 125,000 kcal / h heat capacity with a diameter of 42 mm, chimney diameter of 230 mm and water inlet and outlet diameters of 65 mm was investigated by using 4 different types of strip turbulators. Experiments were carried out with turbulators placed in all the smoke pipes in the boiler. Firstly, experiments were carried out without placing a turbulator inside. In the second step, by placing turbulators in the smoke pipes, experiments were made for each type and heat transfer was calculated. In the experiments, the flow rate of the fan was changed with the help of damper and the reynolds number was calculated between 18000 and 28000. Turbulator experiments for heat transfer improvement have increased by at least %15 and at most %41 compared to turbulator free experiments. For the heat transfer increase values obtained because of calculations, predictive models were obtained using machine learning algorithms SVM (support vector machine) and decision tree (M5P model tree). The resulting models have been analyzed for error analysis and have been shown to successfully predict heat transfer increase values.

Numerical analysis and modified thermodynamic calculation methods for the furnace in the 1000 MW supercritical CO2 coal-fired boiler

Supercritical carbon dioxide (S–CO2) coal-fired power generation technology is considered as the transformative technology in the energy sector due to its high efficiency, simple turbomachinery and high power density though the concept design of S–CO2 boiler is still in the infancy stage. This study constructs a modified combustion and heat transfer thermodynamic calculation method of the S–CO2 boiler adapted for multi-zone furnace. The effects of parameters and configurations on the characteristics of the S–CO2 boiler are compared and analyzed. The results show that the increase in the separated over-fired air ratio can effectively equalize the heat duty distribution. And the increasing of the furnace wall temperature will affect the furnace radiation heat transfer performance, which increases the flue gas average temperature. The boiler configurations including the flue gas recirculation, double furnace strategy, thermal insulation strategy and boiler local expansion strategy have the positive effects on decreasing the furnace heat duty to ensure the boiler safety. Finally, the novel S–CO2 boiler configurations are proposed and the comprehensive evaluations are conducted on the boiler combustion, heat transfer and burnout characteristics, which show that the novel S–CO2 boiler performance is promising and can provide a basis for the design of S–CO2 boiler.

Development of a New Burner Device Based on Injection-Radiation Method for Gas Fuel Combustion

This paper presents the results of designing a promising burner device that combines injection and radiation methods for gaseous fuel combustion. Infrared radiation from the heated surface of nozzle of radiation burner provides intensive heat transfer in furnaces and boilers, specifies their high efficiency at low flue gas temperatures, and very low NOx emissions. Effective gas combustion is facilitated by additional heating of the initial fuel mixture during filtration through the hot walls of porous nozzle. The new design of radiation burner has high performance characteristics, provides effective combustion of gaseous fuel up to 99% and meets high environmental standards and requirements.

Study on dynamic measurement of fouling thermal resistance in a boiler

A fouling thermal resistance method is introduced, for evaluating water quality in real time through measuring fouling thermal resistance on heat transfer surface. A simple device as a boiler heat transfer model was designed for measuring the deposition of dirt by the fouling thermal resistance method. The change in the thermal resistance of the fouling was measured with regard to samples with different water quality. The temperature-time curves were plotted with respect to the measured data of various temperatures over the whole process of temperature rise and fall to examine the feasibility of the method in evaluating the thermal resistance of the fouling contributed by the hardness of the water, finding that the fitted curve can characterize the fouling deposition of high hardness water. It has been shown that this experimental device can be improved further in the hope of being applied in practical use.

Heat transfer calculation methods in three-dimensional CFD model for pulverized coal-fired boilers

Computational fluid dynamics (CFD) has been used extensively to study the combustion characteristics of coal-fired boilers. However, very limited of the boiler CFD studies were used to quantitatively predict the heat transfer distributions in practical boiler applications. This paper presents a systematic description on the heat transfer calculation methods in three-dimensional CFD model for coal-fired boilers. The primary objective is to provide a set of heat transfer submodels that can be easily employed to solve and analyze large scale practical boiler problems. All types of boiler heating surfaces are considered with particular focus on the heat transfer calculation of furnace water wall. It is implemented in the CFD model in terms of a thermal boundary condition (B.C.) describing the energy balance between the boiler’s fire side heat transfer and water side heat absorption. The physical significance of the associated B.C. parameters and their accurate prescription are discussed in detail in this paper. It is found that furnace wall heat transfer is largely affected by the wall ash deposit conditions such that the heat transfer coefficient of furnace wall can be determined based on the thermal properties of ash. Although ash thickness may vary dramatically over furnace wall and is extremely difficult to predict, its thermal conductance was found to only vary within a small range for normally operated coal-fired boilers. Establishing the connection between the thermal conductance of wall ash deposits and the heat transfer calculation of furnace wall bypasses the tremendous difficulty and uncertainty incurred in predicting the ash thickness, and thereby, greatly simplifies the wall heat transfer calculation process. The heat transfer calculation methods introduced in this study embody the key physics associated with boiler’s heat transfer process while making a reasonable balance between the level of model complexity and their applicability to practical boiler problems. In this paper they are illustrated and validated on a 330 MW tangentially-fired subcritical boiler. The results show that the predicted boiler heat transfer distributions are in close agreement with the boiler’s operating data.

ANALISIS KINERJA BOILER DI PT. PLN (PERSERO) WILAYAH KALIMANTAN SELATAN KALIMANTAN TENGAH SEKTOR PLTU ASAM - ASAM

Boiler is a tool that serves to convert water into pressurized steam. In the heat causes heat boiler heat transfer through the water into pressurized steam that is heated from the fuel in the furnace.And often a problem of burning in the boiler is less than the maximum. Because the incoming energy is energy derived from the fuel, there is some energy lost during the combustion process it happens because the fuel has a low heat so that the combustion is not maximal cause the boiler performance is reduced. To avoid this, it is necessary to maintenance for the boiler component in order to improve performance. Direct method is "input - output method" because this method uses only the heat in the fuel and steam coming from the boiler output. Boiler efficiency of research results from the date of March 27, 2017 until the date of 10 April 2017 with a total average - average efficiency were analyzed, namely 74.4%. On April 3, 2017 the calculated efficiency of 76.57% indicates that the boiler performance is still feasible to operate but on April 4, 2017 the boiler efficiency becomes 71.59%. Boiler efficiency at commissioning, with boiler efficiency of 85.13% and in 2017 done the boiler efficiency calculation theoretically on 27 March until 10 April 2017 with total average 74.4% where the efficiency decrease equal to 10.73%. Factors affecting the efficiency ratio are in the coal content used. Keywords:Boiler, Performance, Direct Method

Emittance of typical ash minerals: Influence of particle size and mixtures of carbonates and sulfates

The current paper presents measurements of the normal spectral and total emittances of mixtures of different powdery material, all typical constituents of coal ashes. Measurement of sample surface temperature, a key parameter for the calculation of emittance, is carried out by thermocouples and by two-colour pyrometry. Two size fractions of 0 to 32 µm and 125 to 160 µm were examined. The influence of particle size on emittance is investigated by measurement of mixtures of different size fractions of SiO2. In addition, mixtures of CaCO3, CaSO4, K2SO4, Fe2O3 are examined. Measurements were made from 500 up to 1000 °C. The spectra were recorded from 1.6 µm to 12 µm, the major wavelength range for radiative heat transfer in boilers. The results show that the larger the particle size, the higher the emittance. In carbonate/sulfate mixtures absorption bands are visible in the spectra. Fe2O3 shows no absorption bands and seems to dominate the spectra when mixed with carbonates or sulfates.

Role of Sodium in Coal in Determining Deposition Rates

The alkali content in the ash is commonly thought to be the “bad actor” in determining coal ash deposition rates on boiler heat transfer surfaces. This paper reports results of 16 tests in which ash aerosol deposition rates were measured for three coals, burned under air- and oxy-fired combustion conditions. A 100 kW down-fired laboratory combustor coupled with a specially designed deposition probe was employed. Ash aerosol particle size distributions and size-segregated compositions were measured using electric-mobility, light-scattering, and low-pressure impactor techniques. Net sodium vaporization (assumed to be the fraction of sodium collected as a <0.6 μm fume) was compared to literature data. For ash deposition rates, emphasis was on the tightly bonded “inside” deposits rather than the loosely bound “outside” deposits, which could not be collected or weighed precisely. Over a limited range of these tests, where PM1 was indeed greatly enriched in sodium, deposition rates did correlate with the sodium...

Process for Dewatering of Water-Containing Oil Sludge

There was considered a scheme of formation, recovery and involvement in the production of oil sludge. There were outlined the most widely used combination of methods of disposal and recycling of oil sludge and negative consequences of the use of watered fuels for heat and power equipment. For efficient dewatering of water-containing waste oil there was offered a method of dewatering on the basis of low-grade waste heat boiler heat transfer. The final dehydrated product may be used as additives for boiler fuel without substantially reducing of thermo technical characteristics of the combustion process.

Characterization of Microstructure and Thermal property of Ash Deposits on Fire-side Boiler Tube

Ash deposition of heat exchange boiler, caused mainly by accumulation of particulate matter, reduces heat transfer of the boiler system. Heat and mass transfer through porous media such as ash deposits mainly depend on the microstructure of deposited ash. Therefore, in this study, we investigated microstructural and thermal properties of the ash deposited on the boiler tube. Samples for this research were obtained from the fuel economizer tube in an industrial waste incinerator. To characterize microstructures of the ash deposit samples, scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES), X-ray diffraction (XRD) and BET analysis were employed. The results revealed that it had a porous structure with small particles mostly of less than a few micrometers; the contents of Ca and S were 19.3, 22.6% and 18.5, 18.7%, respectively. Also, the results showed that it consisted mainly of anhydrite (CaSO₄) crystals. - The thermal conductivities of the ash deposit sample obtained from the economizer tube in industrial waste incinerator were measured to be 0.63 and 0.54 W/mK at 200℃, which were about 100 times less than the thermal conductivity (61.32 W/mK) of the boiler tube itself, indicating that ash deposition on the boiler tube was closely related to a decrease in boiler heat transfer.

Системно структурированная адаптация теплопередачи в котлах

E.V. Toropov, evtor@mail.ru South Ural State University, Chelyabinsk, Russian Federation Торопов Евгений Васильевич, д-р техн. наук, профессор, заслуженный деятель науки и техники РФ, профессор кафедры «Промышленная теплоэнергетика», Южно-Уральский государственный университет, г. Челябинск; evtor@mail ru.

100 MWe급 순산소연소 발전소 보일러계통 공정설계 및 운전변수 민감도 예측

The oxy-fuel combustion is <TEX>$CO_2$</TEX> capture technology that uses mixture of pure <TEX>$O_2$</TEX> and recirculated exhaust as oxidizer. Currently some Oxy-fuel power plants demonstration project is underway in worldwide. Meanwhile research project for converting 125 MWe Young-Dong power plant to 100 MWe oxy-fuel power plants is progress. In this paper, 1 D process analytical approach was applied for conducting process design and operating parameters sensitivity analysis for oxy-fuel combustion of Young-Dong power plant. As a result, appropriate gas recirculation rates was 74.3% that in order to maintain normal rating superheater, reheater steam temperature and boiler heat transfer patterns. And boiler efficiency 85.0%, CPU inlet <TEX>$CO_2$</TEX> mole concentration 71.34% was predicted for retrofitted boiler. The oxygen concentration in the secondary recycle gas is predicted as 27.1%. Meanwhile the oxygen concentration 22.4% and moisture concentration 5.3% predicted for primary recycle gas. As the primary and secondary gas recirculation increases, then heat absorption of the reheater is tends to increases whereas superheater side is decreased, and also the efficiency is tends to decrease, according to results of sensitivity analysis for operating parameters. In addition, the ambient air ingression have a tendency to lead to decline of efficiency for boiler as well as decline of <TEX>$CO_2$</TEX> purity of CPU inlet.

Experimental Study of Soot Volume Fraction Applied in Laminar Diffusion Flames

The soot emission has been the focus of many studies due to applications in industry and the prejudicial effects caused to the environment. The presence of soot is important to the heat transfer in boilers and combustion chambers, contributing significantly to efficiency increases. In controversy, the inhaled soot may cause respiratory system damage and even cancer. Another important point is the contribution to the greenhouse effect. Therefore, the aim of this work is to analyse the soot emission in laminar diffusion flames produced from commercial fuels stabilized on a burner representative of industrial applications. Methane, vehicular natural gas and liquid petroleum gas are considered as fuels. An experimental setup was constructed to implement the technique of laser light extinction and laser-induced incandescence. These non-intrusive techniques provide instant information, in real time, about soot volume fraction. The measurements were calibrated and validated using methods and results of studies available in the literature, and also the uncertainty is analysed and suitably minimized. The results will contribute to the database for projects of combustion systems optimization, aiming to increase the efficiency and soot emissions control.

Combustion Characteristics of the External Circulation Loop on Baima’s 300 MWe Circulating Fluidized Bed Boiler

Local measurements of concentrations of O2, CO, SO2, and NOx were carried out inside Baima’s 300 MWe circulating fluidized bed (CFB) boiler. Custom-made probes with a length of 4.8 m were used to take samples from the boiler’s external circulation loop, especially from the cyclones and fluidized bed heat exchangers (FBHEs). Eighteen points were used to introduce the probes, and the penetration depth inside the boiler was up to 3.7 m. Solid particles at the entrance and exit regions of both the cyclones and FBHEs were also sampled for analyzing the particle size distribution and carbon content. Results implied that there was significant combustion in the boiler’s external circulation loop, and most of the combustion was from the cyclones. The flue gas temperature at the cyclone outlet could be 135 °C higher than that at the cyclone inlet. The ratio of the oxygen consumption in the cyclone to that of the entire combustion process of the boiler was nearly 12%. The O2 consumption rate might mainly come from the burn-out of char particles rather than the combustible gas. With regard to the FBHEs, the inside combustion phenomenon was not as severe as that in the cyclones. Obvious differences of gas concentrations were observed at the outlet between those FBHEs with different functions. The experimental results can provide information for adjusting and designing the heat-surface arrangement and lay a foundation for modeling the flow structure, combustion, and heat transfer in similar large-scale CFB boilers.

Prediction of silica carry-over and solubility in steam of boilers using simple correlation

Abstract Silica content of the boiler water is critical for steam turbines and scaling of boiler heat transfer surfaces. Silica (SiO2) can volatilize with the steam in sufficient concentrations to deposit in steam turbines leading to scale formation on boiler surfaces. In this work, a simple correlation is presented to predict silica (SiO2) solubility in steam of boilers as a function of pressure and water silica content. The solubility of silica in steam directly depends on both the density and temperature of steam. With decreasing temperature and density, solubility of silica reduces. As the pressure affects steam density which has a strong bearing on steam temperature, it has an important effect on the solubility of silica in steam. The proposed correlation predicts the solubility of silica (SiO2) in steam for pressure up to 22,000 kPa and boiler water silica contents up to 500 mg/kg. The predictions from the proposed correlation have been compared with reported data and found good agreement with average absolute deviation being around 4%. This simple-to-use correlation can be of immense practical value for the engineers to have a quick check on silica (SiO2) solubility in steam of boilers as a function of pressure and water silica content at various conditions without performing any experimental measurements. In particular, personnel dealing with the utility boilers would find the proposed approach to be user friendly involving no complex expressions with transparent calculations.

Prediction of amount of entrained droplets in vertical annular two-phase flow

Prediction of amount of entrained droplets or entrainment fraction in annular two-phase flow is essential for the estimation of dryout condition and analysis of post dryout heat transfer in light water nuclear reactors and steam boilers. In this study, air–water and organic fluid (Freon-113) annular flow entrainment experiments have been carried out in 9.4 and 10.2 mm diameter test sections, respectively. Both the experiments covered three distinct pressure conditions and wide range of liquid and gas flow conditions. The organic fluid experiments simulated high pressure steam–water annular flow conditions. In each experiment, measurements of entrainment fraction, droplet entrainment rate and droplet deposition rate have been performed by using the liquid film extraction method. A simple, explicit and non-dimensional correlation developed by Sawant [Sawant, P.H., Ishii, M., Mori, M., 2008. Droplet entrainment correlation in vertical upward co-current annular two-phase flow. Nucl. Eng. Des. 238 (6), 1342–1352] for the prediction of entrainment fraction is further improved in this study in order to account for the existence of critical gas and liquid flow rates below which no entrainment is possible. Additionally, a new correlation is proposed for the estimation of minimum liquid film flow rate at the maximum entrainment fraction condition. The improved correlation successfully predicted the newly collected air–water and Freon-113 entrainment fraction data. Furthermore, the correlations satisfactorily compared with the air–water, helium–water and air–genklene experimental data measured by Willetts [Willetts, I.P., 1987. Non-aqueous annular two-phase flow. D.Phil. Thesis, University of Oxford]. However, comparison of the correlations with the steam–water data available in literature showed significant discrepancies. It is proposed that these discrepancies might have been caused due to the inadequacy of the liquid film extraction method used to measure the entrainment fraction or due to the change in mechanism of entrainment under high liquid flow conditions.