Water Wall Surface Research Articles

An Effective Strategy for Monitoring Slagging Location and Severity on the Waterwall Surface in Operation Coal-Fired Boilers

It is of great importance to obtain the exact location and severity of slagging deposits on the waterwall surface of an operational boiler to avoid aimless soot-blowing and reduce steam consumption. In this paper, an effective waterwall surface temperature monitoring method is proposed to determine the slagging locations. It has been noted that the temperature difference of the waterwall surface before and after soot-blowing varied with the waterwall location, with more than 80 °C covered with slag and less than 20 °C found clean. According to this, a slagging temperature index was developed to describe the severity of slagging deposits on the waterwall surface. Results indicated that the process of slagging deposit growth included four stages, with the slagging temperature fluctuating in the range of about 90–110 °C in stage III, followed by a rapid drop below 60 °C in stage IV. Furthermore, a digital image monitoring system was used to validate the slag growth process and study the relationship between deposit thickness growth and area expansion. This novel approach provides automated and accurate guidance for each soot blower around the furnace, which reduces soot-blowing steam consumption and avoids serious slagging on the waterwall surface.

Condition Assessment of Boiler Water Wall Tubes using Robotics

Boiler tube failures continues to be the primary cause for forced outages in boilers. To get the boiler back on line and reduce (eliminate) future forced outages due to tube failure, it is extremely important to determine and correct the failure root cause. Detecting and sizing flaws before they cause failures is of critical importance in boiler maintenance. Localized and general wall thinning due to corrosion & erosion in boiler water-wall tubing is a significant inspection concern for boiler operators. There are at least four (4) other methods used for the inspection of Boiler Water walls. These methods are Spot Check UT, A-Scan UT, EMAT, and Scanning Thermograpy. Spot Check UT only gives thickness readings and gets very minimal coverage of the total surface area of the furnace water walls; the chances of finding I.D. flaw mechanisms using Spot Check UT are minimal at best. If Boiler Water walls have been sandblasted, A-Scan UT may be used to inspected larger areas of the furnace walls; in these cases, a steady flow of water is most often used as the couplant. The EMAT technique requires that any Boiler Water wall surfaces be sandblasted. This paper will present a discussion on the deployment of robotic wall crawler using electromagnetic technique to inspect boiler water walls from outside of the tube together with the theoretical background of the technique which explains the quantitative nature of the inspection. Further, case studies will be presented for the technique that allows the extraction of tube wall thickness information from the inspection data.

Effect of metal anti-wear device on the water wall erosion in CFB boiler

The erosion of water wall tube induced by the flushing of ash is one of the safest factors in the operation of the circulating fluidized bed (CFB) boiler. The reasonable installation of a metal anti-wear device on the water wall provides an effective protection method for reducing particle erosion on the wall surface. Seven metal anti-wear devices were designed and evaluated by comparing the erosion distribution of the local water wall surface in this work. The results show the type with an angle between the windward side and the water wall greater than 90° and the leeward side perpendicular to the water wall can obtain a good anti-wear effect. The erosion rate of water wall increases correspondingly with the increasing inlet velocity and particle size, but decreases to some extent by adding cohesive particles. The height of the ash deposition zone decreases correspondingly with the decreasing particle diameter and proportion of cohesive particles. The type G metal anti-wear device was preferably applied and tested in a CFD boiler for half a year according to its simple structure and its behavior of reducing erosion rates. The Type G anti-wear device can well protect the water wall of CFB boilers at the power plants.

Адаптация степени черноты продуктов сгорания топлив к интервалу температур 1000…2000 К

The accuracy of calculations of heat transfer caused by the emission from a high-temperature gas flow during the combustion of natural fuels significantly depends on the accuracy and representation of data on thermal and physical properties of gases, as well as the value of a radiant heat flux. Th reliable experimental data helped to generate the dependencies that allow performing calculations of emissivity factor for combustion products. The accuracy of the calculable approximation of experimental data in the two-factor function – optical density of the gas and its temperature - has been determined. The adaptation of parameters in a ratio for calculating the attenuation ratio and the Buger number has been carried out based on the updated experimental data. The range of application of the obtained results for the intense combustion zone as well as for the main combustion chamber volume of a boiler unit has been considered. This gives the possibility to determine boundary conditions for these zones of the boiler unit. Previously developed mathematical model with a triple-component pattern, which allows dividing the influence of flare continuum and combustion gases, is applicable for the intense combustion zone. The heat transfer in the main combustion chamber volume is described within the heat transfer paradigm, which allows accounting for the configuration of the combustion chamber as well as the efficiency of heat emission to the waterwall surfaces.

Regularities pertinent to heat transfer in the gas layers of a torch in steam boiler fireboxes. Part III. Examples of heat transfer calculations in torch furnaces and steam boiler fireboxes

A procedure for calculating heat transfer in steam boiler fireboxes is developed proceeding from the scientific discovery of laws pertinent to radiation from torch gas layers. By using this procedure, it is possible to determine the distribution of heat flux densities both along the height and perimeter of all waterwall surfaces in a firebox and to calculate the maximal densities of incident heat fluxes. Examples of heat transfer calculation in a torch furnace and steam boiler firebox carried out using the procedure developed on the basis of the above-mentioned discovery are given. The calculation results are in satisfactory agreement with the results of heat transfer measurements in a torch furnace and steam boiler firebox. The difference between the calculated data and measurement results does not exceed 12%.

Numerical Simulation for Residual Stress and Deformation of Surface Welding on Membrane Water-Wall

Automatic MIG was adopted to weld Inconel 625 alloy on 20 G Membrane Waterwall, which can improve the capacities of high temperature corrosion resistance and wear resistance. To study the influence of Membrane Waterwall surface welding sequences on residual stress and residual deformation, this paper utilized finite element software ABAQUS and segmented moving heat source model to simulate the sequence welding, balanced welding from the middle to sides, balanced welding from sides to the middle, balanced skip welding from middle to sides and balanced skip welding from sides to the middle and studied their residual stresses and deformations. The simulation results indicated that there was a great influence of welding sequences on the residual stress and deformation. The optimal welding sequence was balanced skip welding from middle to sides and balanced skip welding from sides to the middle, which could change the stress distribution, decrease the welding residual stress by 17%, realize the even deformation of the whole welding section and decrease the bending deformation by 50%.

Study on Calculation Method for Partition of Heat Transfer in an Ultra-supercritical Boiler

Use a 1000MW ultra-supercritical tower boiler as the research object. On the basis of one dimensional model, simplify the tube heat transfer model and the radiation heat transfer model; establish the two-dimensional area calculation model with the regional method; summarize the heat load distribution of flue gas temperature and water wall surface; and compare with the measured data. The error range of the result is acceptable on the project. The distribution of water wall surface heat load along the furnace width and the area where heat transfer deterioration cause easily along the furnace height direction are studied with the model and algorithm on different boiler load conditions. All these provide the reference for the design and operation of the ultra supercritical boiler.

Analysis of the Method for Furnace Thermal Calculation with Radiation Intensity Attenuation

Based on the network method for radiant heat transfer, a radiant space resistance ke R /4F1 was proposed, the radiant heat transfer network diagrams which subjects to the radiation attenuation was given in this paper, this method is helpful to accurately analyze the zero-dimensional radiant heat transfer. Simulation results show that, due to the radiant space resistance kR /4F, the total thermal resistance between the flame and the water wall surface is degraded, radiation attenuation from the flame center to water wall surface should not be ignored. It is also shown that,when the radiation attenuation is involved, the furnace outlet flue gas temperature utilizing the furnace ɛf syn blackness is more accurate than the Soviet Union 1973 calculation standard.

Heat Flux Measurement in Boiler Furnaces: Methods, Sensors, First Results

New methods to measure local heat flux per unit area over the waterwall surface of a close-coupled furnace of a power boiler are proposed. A new class of heterogeneous gradient heat flux sensors (HGHFS) based on the transverse Seebeck effect is presented. The theory of HGHFSs, their design, and application in boiler technology are described. Laboratory tests of heat flux sensor modules are performed. For the first time, gradient heat flux measurements have been made in the furnace of the boiler (total power − 210 tons of water steam per hour) at Thermal Electric Power Plant No. 4 in the Kirov city, Russia. The efficiency of a HGHFS during continuous operation, as well as its ability to be an indicator of fouling and cleaning of the furnace surface is confirmed.

Corrosion of Carbon Steel Tubes in the Mid-Furnance of Kraft Recovery Boilers--Environmental Characterization

Carbon steel tubes in the mid-furnace of kraft recovery boilers have experienced accelerated corro-sion in recent years. Gaseous environments in the mid-furnace of kraft recovery boilers were generally considered to be oxidizing and not very corrosive to the carbon steel waterwall tubes. However, mid-furnace corrosion has occurred above the cut line where composite tubes that have a stainless steel outer layer used in the lower furnace are welded to the carbon steel waterwall section. This study characterized the local environments in three boilers to find the reasons for accelerated corrosion of waterwalls in the mid-furnace. Gas sampling ports were installed in the mid-furnace with high and low corrosion rates of carbon steel waterwall tubes. During boiler operation, gases were sampled and analyzed using a specially designed gas chromatograph. In each boiler, the areas with higher corrosion rates had higher concentrations of reducing gases and sulfur-containing gases at the waterwall surface than in the low-corrosion areas. Results from this study indicate that accelerated mid-furnace corrosion likely results from changes in the boiler operation, such as decreases in the air supply at the lower air port levels of the furnace. These changes also might result in higher local gas temperatures and local thermal cycling in the mid-furnace of boilers.

Numerical modeling of axial bed-to-wall heat transfer in a circulating fluidized bed combustor

The water-wall surfaces located above the secondary air inlet within the circulating fluidized bed (CFB) combustor are exposed to the axial bed-to-wall heat transfer process. In the current work, the axial bed-to-wall heat transfer coefficients are estimated for three different axial voidage profiles (covering three widely occurring average particle concentrations) in order to investigate the effect of voidage, time, initial and fixed temperature of the bed and annulus, and gas gap between wall and solid particles; on the axial heat transfer process. A 2D thermal energy balance model is developed to estimate the axial heat transfer values for the gas–solid suspension along the height of the riser column with horizontally changing mass distribution. The gas–solid mass distribution is fixed with time thus providing a spectrum of changes in axial bed-to-wall heat transfer profile with time. The current work provides an opportunity to understand the axial heat transfer relationship with particle concentration and instantaneous behaviour. The results from the work show that: (i) first few seconds of the suspension temperature near the wall has maximum energy thus providing a small time frame to transfer more heat to the surface (CFB wall); (ii) both axial and horizontal particle concentrations (influenced by the operating conditions) affect the axial heat transfer locally; (iii) initial temperature of the bed between average and maximum values provide end limits for the axial heat transfer; (iv) annulus region has higher thermal energy than the core due to increased particle presence; and (v) a particle-free zone near the wall (gas gap) having a maximum thickness of 1 mm, tends to reduce up to 25% of axial heat transfer value. The model trends have close agreement with experimental trends from published literature; but the model values differ when correlating with real values due to inconsistencies in riser diameter and nature of variation in parameters.

Visual experiment research of the inhaled particle thermophoresis deposition rule in the rectangle turbulent flow tube

In order to solve the problem of removing inhaled particle caused by the combustion source, the dynamics characteristics of the inhaled particle in additional temperature field have to be studied. The dynamics characteristics of the inhaled particle in temperature field are measured in designed and processed a rectangle experiment channel by the PDA instrument. This method is visual. The dynamic characteristic of the particle at 0.15 mm near by water wall surface in boundary layer can be measured through the direction change of beam of PDA light. The movement rules of the inhaled particle in the additional temperature field are obtained through the experiment. The experiment results show that the thermophoresis force has strong influence on the particle which diameter is about 6 μm and the experience formulas are put forward to calculate the thermophoresis deposition efficiency. The thermophoresis deposition efficiency formulas obtained from this experiment is consistent with Batchelor and Shen formulas. The research shows that the PM 2.5 thermophoresis deposition efficiency is direct proportion to the temperature ratio between the inlet temperature and the water wall surface but is not the temperature difference in the rectangle channel.

Effect of dilute and dense phase operating conditions on bed-to-wall heat transfer mechanism in a circulating fluidized bed combustor

In the present paper investigations are conducted on bed-to-wall heat transfer to water-wall surfaces in the upper region of the riser column of a circulating fluidized bed (CFB) combustor under dilute and dense phase conditions. The bed-to-wall heat transfer depends on the contributions of particle convection, gas convection and radiation heat transfer components. The percentage contribution of each of these components depends on the operating conditions i.e., dilute and dense phase bed conditions and bed temperature. The variation in contribution with operating conditions is estimated using the cluster renewal mechanistic model. The present results contribute some fundamental information on the contributions of particle convection, gas convection and radiation contributions in bed-to-wall heat transfer under dilute and dense phase conditions with bed temperature. This leads to better understanding of heat transfer mechanism to water-wall surfaces in the upper region of the riser column under varying load conditions i.e., when the combustor is operated under dilute and dense phase situations. The results will further contribute to understanding of heat transfer mechanism and will aid in the efficient design of heat transfer surfaces in the CFB unit.

04/02025 Industrial waste combustion boiler installed at paper mill - EBARA internally circulating fluidized bed boiler (ICEB) & gasifier (ICFG): Tsukamoto, K. and Miyoshi, N. Kami Pa Gikyoshi, 2003, 57, (5), 645–653. (In Japanese)

In the present paper investigations are conducted on bed-to-wall heat transfer to water-wall surfaces in the upper region of the riser column of a circulating fluidized bed (CFB) combustor under dilute and dense phase conditions. The bed-to-wall heat transfer depends on the contributions of particle convection, gas convection and radiation heat transfer components. The percentage contribution of each of these components depends on the operating conditions i.e., dilute and dense phase bed conditions and bed temperature. The variation in contribution with operating conditions is estimated using the cluster renewal mechanistic model. The present results contribute some fundamental information on the contributions of particle convection, gas convection and radiation contributions in bed-to-wall heat transfer under dilute and dense phase conditions with bed temperature. This leads to better understanding of heat transfer mechanism to water-wall surfaces in the upper region of the riser column under varying load conditions i.e., when the combustor is operated under dilute and dense phase situations. The results will further contribute to understanding of heat transfer mechanism and will aid in the efficient design of heat transfer surfaces in the CFB unit.

Furnace water-wall slag deposition testing in a 0.5 MW t combustion pilot plant

This article presents combustion pilot-plant test results obtained using newly developed ash deposition probes (ADPs) designed to measure both the thermal and mechanical properties of furnace ash deposits. The ADP measurements are obtained at multiple elevations in the furnace to provide detailed heat absorption and ash deposition time constant profiles for 8 h soot-blowing cycles. Profiles of incident radiation are also presented. Results are presented for four different coal types representing major steam-coal-producing regions in the United States. The furnace heat absorption profiles are distinctly different for each coal type and also vary significantly with furnace elevation. Combined furnace heat absorption and time constant data are used to recommend optimal use of soot-blowing resources, or to specify soot blower and water-wall surface addition and location according to coal type.

Fouling and heat transfer in a furnace under variable load of a liquid slag removal boiler

The physical parameters that characterize the fouling dynamics of the water wall surfaces of the chamber furnace when its heat load varies are determined. The effect of the variable heat transfer conditions in the furnace on the working surface of steam generating tubes is substantiated.

Heat transfer from a circulating fluidized bed to membrane waterwall surfaces

AbstractAverage and local heat transfer coefficients were measured for transfer from circulating fluidized beds of sand particles (mean size 188 and 356 μm) to two water‐cooled membrane wall surfaces located on one face of a 152 mm square by 7.3 m tall column. The measurements cover a range of superficial gas velocities from about 4 to 7 m/s, suspension densities from about 8 to 130 kg/m3, suspension temperatures from 150 to 400°C, and secondary‐to‐primary air ratios of 0 to 1.5. Heat transfer coefficients, averaged over a 1.53 m length of the membrane waterwall surfaces, depend strongly on suspension density, but show almost no separate dependence on gas velocity, bed temperature, or secondary‐to‐primary air ratio for the conditions studied. For the surface nearest the top of the unit, the coefficient decreases with distance measured downward from the top, suggesting that particles travel downward along the surface. As a result, averaged coefficients are lower and the influence of particle size is less than for previously reported circulating fluidized bed heat transfer measurements where miniature heat transfer surfaces were employed.

Evaluation of Equivalent Radiant Heating Surface of Block-Covered Water-Walls.

The heat absorption of block-covered water-walls is less than that of the ideal cases when the surface temperatures are equal to the inside water temperatures, because of the resistance to heat conduction between the water-wall surface and the inside boiler water. We investigated on the heat resistance by measuring the electric resistance of suitably constructed models and then corrected the results by the actual temperature distribution data, and thus determined a method of calculation. The coefficient showing the proportion of actual heat flow to the ideal case can easily be found by using the diagram presented in the paper. For usual bare-faced cast-iron blocks, the coefficient falls between 0·92 and 0·98, and we recommend 0·95 for approximate calculations.

Evaluation of Effective Radiant Heating Surface and Application of the Stefan-Boltzman Law to Heat Absorption in Boiler Furnaces

Abstract In the first section of this paper a method has been developed for converting well-known types of furnace heat-absorbing surfaces into an equivalent effective radiant heating surface. It concerns the evaluation of this effective radiant heating surface as controlled by (1) various spacings of waterwall tubes, (2) various kinds of blocks on the waterwall tubes, (3) various amounts of slag on the waterwall tubes or blocks, and (4) the emissivity of the waterwall surface exposed to the flame. The second section deals with the fraction of heat supplied to the furnace that is given up by the gases in the furnace which is solved most simply and practically by the use of the Stefan-Boltzman radiation law. Results computed in this manner have been compared with results reported in a paper entitled, “An Experimental Investigation of Heat Absorption in Boiler Furnaces”. It is found that for large pulverized coal, and oil-fired and gas-fired furnaces, the assumption of an effective furnace emissivity of unity leads to results which are in substantial agreement with experimental data. For stoker-fired furnaces in general, the effective furnace emissivity appears to be less than unity.