Furnace Wall Temperature Research Articles

Numerical study of a tangentially fired boiler for reducing steam tube overheating

A comprehensive numerical and experimental study on a 200MW tangentially fired boiler firing metallurgical gases was conducted. A three-dimensional Computational Fluid Dynamics (CFD) model was developed to simulate the flow characteristics and combustion process inside the boiler. The eddy dissipation concept combustion model was applied to take into account detailed turbulent interactive reacting chemical reactions. Field experiments were also conducted on the original tangentially fired boiler under different operation conditions. Flame profiles videos were captured during experiments. A quick comparison of the experimental flame profile with numerical simulation results shows good agreement. Wall steam tubes overheating problem was observed, and the hot spots were identified based on a wide range of typical operation conditions. The effect of total fuel input and natural gas percentage on the furnace wall temperature were investigated.

Combustion characteristics of a four-wall tangential firing pulverized coal furnace

The furnace core temperature (FCT), wall temperature, and tangential circle diameter in a 1 MW four-wall tangential firing furnace (FWTF(F)) were investigated in detail. The FCT and wall temperature of the primary air section of corner tangential firing furnace (CTF(F)) were also studied for comparison. Results show that compared with CTF that exhibited higher temperature distribution in the center of the furnace wall and lower at the corner where the burners are installed, FWTF is more conducive for gas-powder mixture timely ignition and burnout because of the higher temperature and heat flux in the burner zone. FWTF can efficiently prevent slagging in the burner zone because of the small temperature difference of the primary air section. The wall temperature in FWTFF exhibited uniformity, became an uneven parabola-like distribution, and exhibited uniformity again along the flue gas. The maximum temperature difference in CTFF was 1.48 (anthracite) and 3.65 (bituminous) times of that in FWTFF. The actual tangential circle diameters of anthracite and bituminous in FWTFF were approximately 3 and 7.6 times of imaginary tangential circle diameter, respectively.

A comprehensive study on co-pyrolysis of bituminous coal and pine sawdust using TG

A sample consisting of woody biomass and bituminous coal was pyrolyzed in a lab-scale furnace in a nitrogen atmosphere with the temperature increasing by different heating rates of 5, 10, and 50 °C min−1 until the furnace wall temperature reached 900 °C. Five blending ratios (BRs) of coal–biomass were tested. For each BR, the mass loss of the sample and mole fractions of the gaseous species evolved from the sample were measured using a thermogravimetry (TG) and a real-time gas analyzer (GA). Reactivity, product yield, and activation energy were considered as index parameters to co-pyrolysis. While synergy (the difference between the experimental data and calculated results obtained using an additive model) of the reactivity of co-pyrolysis was observed only at specific temperatures, the TG results showed synergy at temperatures between 450 and 500 °C compared to between 450 and 600 °C seen with the GA method for all pyrolyzed gases, and especially between 350 and 650 °C for H2. While there was no synergy in the char yield of the co-pyrolysis, the liquid and total gas exhibited synergy for all three BRs. The pre-exponential factors and the activation energies of BRs of 0.25, 0.5, and 0.75 were obtained using a kinetic study of co-pyrolysis.

N<sub>2</sub>雰囲気におけるエマルジョン燃料噴霧流の二次微粒化挙動と粒径分布（二次微粒化挙動に及ぼす雰囲気温度の影響）

In this study, secondary atomization of emulsified fuel spray was visualized, and the effect of ambient temperature on secondary atomization in spray flow was investigated. The W/O emulsified fuel was prepared by adding 10 wt% water and 0.75 wt% emulsifying agent (sorbitan monooleate) to n-dodecane. A shadow imaging system consisting of high-speed video camera (125,000 fps) and metal halide lamp was used to visualize secondary atomization of spray droplets. As a result, it clearly showed that secondary atomization of spray droplet was caused by vapor production inside the spray droplet due to the rapid evaporation of dispersed water. When the furnace wall temperature (Tw) was 823 K, there is no significant difference between the size distribution of emulsified fuel spray and that of n-dodecane spray because the droplet temperature was too low to produce vapor inside the spray droplet, leading to decreasing secondary atomization effect. Meanwhile, at Tw = 923 K and 973 K, the size distribution of emulsified fuel spray droplets was shifted to smaller than that of n-dodecane spray droplets. This is because the droplet temperature was enough to produce vapor inside the droplet and secondary atomization was enhanced. It was indicated that ambient temperature was important in the occurrence of secondary atomization.

Thermal decomposition kinetics of sodium carboxymethyl cellulose: Model-free methods

Thermal analysis techniques such as thermogravimetric analysis (TGA) have been widely used because they provide rapid quantitative determination of various processes under isothermal or non-isothermal conditions. It allows the estimation of effective kinetic and thermodynamic parameters for various decomposition and thermal reactions. In this article, thermal degradation of sodium carboxymethyl cellulose (SMC) is investigated by means of dynamic thermogravimetric/derivative thermogravimetry (TG/DTG) in helium atmosphere with the flow rate 100 mL/min at the heating rate of 10-30 °C/min until the furnace wall temperature reached 700 °C. The non-isothermal degradation of SMC found to be taking place occurred major one step and minor two steps. Using a non-isothermal kinetic method based on a TGA data, kinetic parameters ( E and ln A ) are calculated by Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO) and Friedman methods. The results of studied polymer demonstrated that E and ln A is varied with function of conversion (α), which is in good agreement with literature data.

Modeling thermal response of steel–concrete floor systems in a furnace

A methodology was developed to predict the thermal exposure from a furnace onto a floor assembly specimen. In furnaces with low conductivity wall linings and gas fired burners with complete combustion, the gas attenuation effects were determined to be small indicating that radiation between surfaces and convection are the dominant modes of heat transfer. This was modeled by assigning the internal furnace wall temperature to the furnace time–temperature exposure and performing a three-dimensional heat transfer analysis on the specimen. The furnace exposure model predicted heat transfer to the specimen surface that was within 5–14% of measured heat fluxes. The proposed furnace exposure methodology was used to predict the temperature rise of steel in a floor assembly where the test specimen can view itself as well as the furnace, making radiation exchange an important aspect of the problem. Predictions were within 5–10% of the measured values, which was within the experimental uncertainty.

Model-Based Sensitivity Analysis and Experimental Investigation of Perlite Grain Expansion in a Vertical Electrical Furnace

The new vertical electrical furnace which has been designed and operated at NTUA successfully produces expanded perlite of superior quality, unleashing its potential for high-performance thermal and acoustic insulation applications in the manufacturing and construction industries. A detailed sensitivity analysis has been performed on the basis of our dynamic model for perlite grain expansion, in order to quantitatively understand and systematically evaluate the effect and relative importance of feed quality and operating conditions on macroscopic (grain velocity and temperature evolution) and microscopic (steam bubble pressure, grain size) perlite particle state variables. Experimental campaign observations illustrate furnace efficiency and are in acceptable agreement with the model. Perlite feed quality (origin, chemical composition, effective water content, initial particle size distribution) is critical for adequate expansion and must be determined in advance of high-temperature processing. Process operating conditions (air feed flow rate and temperature, heating chamber wall temperature) are instrumental toward adequate expansion of a given perlite feed. Ambient air injection accomplishes sufficient expansion of the finer raw perlite fractions only, while preheated air injection achieves coarse fraction expansion but induces a risk of grain overheating and disintegration. Process efficiency increases dramatically when the furnace wall temperature is maintained within the 1100–1200 °C range.

Mathematical modeling and process simulation of perlite grain expansion in a vertical electrical furnace

Expanded perlite is a lightweight material with remarkable thermal and acoustic insulation properties, rendering it widely useful in the construction and manufacturing industries. Currently applied perlite expansion technology suffers numerous technical disadvantages, which adversely affect product quality and limit the range of its applications. To overcome these established drawbacks, a new perlite expansion process has been designed on the basis of a vertical electrically heated expansion furnace. The novel furnace enables precise control of experimental conditions, in order to allow for efficient adjustment of particle residence time and internal temperature. The quality of expanded perlite strongly depends on raw material thermophysical properties as well as furnace operating conditions, and the experimental investigation of the isolated effect of each parameter on expanded product quality is technically cumbersome and extremely time-consuming and expensive.A mathematical model for perlite grain expansion has been developed in order to perform a detailed numerical investigation of process efficiency, toward the optimization of the expansion process in the novel pilot-scale furnace. The dynamic model consists of ordinary differential equations for both air and particle heat and momentum balances, as well as nonlinear algebraic equations for both air and perlite melt thermophysical and transport properties, probing the air temperature distribution within the vertical electrical furnace as well as the particle velocity, temperature and size along its trajectory inside the heating chamber. The effect of raw material physical properties (raw feed origin, initial particle size, effective water content) as well as operating parameters (air inlet temperature and flowrate, furnace wall temperature) on evolution of the particle state variables is presented and discussed. Model results indicate perlite expansion is strongly affected by raw ore feed origin, size and water content. Moreover, operating conditions affect expansion considerably, and furnace wall temperature has the strongest effect on the final particle expansion ratio attained. The new dynamic model is instrumental towards achieving a detailed comprehension of perlite expansion in the vertical electrical furnace towards multi-parametric sensitivity analysis, process optimization and efficient control.

Pyrolysis Characteristics of Phoenix Dactylifera Date Palm Seeds Using Thermo-Gravimetric Analysis (TGA)

Mass losses of Phoenix dactylifera date palm seeds (DPSs) were measured using a thermo-gravimetric analyzer (TGA). Six-milligram-sample of six varieties of DPSs were pyrolyzed in an inert condition (argon atmosphere) with a constant flow rate of 100 ml/min for the entire range of experiments. The experiments were conducted under non-isothermal conditions and at a heating rate of 20°C/min until the furnace wall temperature reached 900°C. The moisture (M), ash (ASH), volatile matter (VM) and fixed carbon (FC) of the selected date seeds were determined by means of proximate analysis. The weight percentages of carbon (C), hydrogen (H), oxygen (O), nitrogen (N), sulfur (S) and atomic ratios (H/C and O/C) were determined through the ultimate analysis. The heating value, bulk and particle density of DPSs were also measured using a bomb calorimeter and ultra-pycnometer, respectively. The yield of the liquids was obtained by subtracting the total gaseous mass from the DTG data. The experiments demonstrated that there were significant differences in physiochemical properties of selected DPSs. The findings also revealed that DPSs contain much volatile compounds. DPSs energy densities were found to be among the high-quality biological feedstocks.

Aerosol fabrication of thermosensitive nanogels and in situ hybridization with iron nanoparticles

Collison atomized n-isopropylacrylamide (NIPAM) droplets were thermally treated with different furnace wall temperatures to form nanogels in an aerosol state. The size of the aerosol nanogels decreased from 40.3 nm to 32.8 nm by increasing the temperature from 40 °C to 90 °C due to the coil-to-globule transition of the NIPAM. A serial reactor consisting of a spark generator coupled to a collison atomizer was further employed to efficiently (>90% in production yield) fabricate biocompatible (78.8% in cell viability)-magnetic (30.3 emu g−1 in saturation magnetization) hybrid nanogels of NIPAM and iron nanoparticles.

Numerical Simulation of a Coke Oven

At present, the CFD numerical simulation, combined with an experiments involving heat transfer has become an important approach to studying coal carbonization. The aim of this paper is to illustrate how a standard CFD package may be modified so it can be used to simulate temperature distribution, coking time and carbonization processes that occur in coke oven charge. Content of volatile matters and moisture have important influence on heating rate during carbonization. Further, heating rate have effects on char structure an inner coking condition, as well as the carbonization time. In addition, furnace wall temperature have important effects on carbonization, because they can change the coking time. Our simulation results for the coke oven model are in agreement with experimental and virtual data.

CO 2 effects on near field aerodynamic phenomena in 40 kW, co-axial, oxy-coal, turbulent diffusion flames

The effects of oxy-coal combustion on the near-field aerodynamics of simple, co-axial turbulent diffusion flames have been investigated. Experiments were carried out in a specially designed 40 kW (100 kW nominally) combustion test rig. Results from two sets of experiments are presented, with each set using once-through CO 2, without H 2O, plus added O 2 for the oxidant stream. The first set consists of screening experiments that revealed: (i) how replacement of dilution N 2 by CO 2 (as in oxy-coal combustion) affected NO x emissions at equivalent adiabatic flame temperatures; (ii) how, for oxy-coal combustion at constant P O 2 , primary , changes in P O 2 , secondary affected lengths of both the standoff distance and the luminous zone, and (iii) how the luminosity of oxygen-enriched air flames compared to that of aerodynamically similar oxy-coal flames at similar adiabatic fame temperatures. These screening experiments also allowed for the evolution of a methodology for quantifying flame standoff distance from video images. This methodology involved photo-image processing and probability density functions (PDFs) that represented observed fluctuations in the near-field aerodynamic region. The second set consists of final experiments after the data processing techniques had been refined. Results presented here focus on the relationship between the flame shapes, as seen by an observer, to the PDFs used to quantify the fluctuating flame standoff distance. The latter was taken to be an essential characteristic of the near-field aerodynamics of oxy-coal flames. Flame images (yielding practical, but qualitative information) and the concomitant PDFs (yielding fundamental, and quantitative data) are presented showing the separate effects of primary P O 2 , secondary P O 2 , transport diluent composition, furnace wall temperature, and secondary stream preheat temperature. A simple model in which ignition was controlled by the rate of molecular diffusion of O 2 through a gas film composed of the primary jet transporting fluid appeared to correlate some of the data. These experimental data provide not only a quantitative insight into mechanisms of ignition of coal in turbulent oxy-coal flames of practical relevance, but also (with uncertainty quantification) a quantitative basis for validation of future detailed simulations of this process.

Study of coal pyrolysis by thermo-gravimetric analysis (TGA) and concentration measurements of the evolved species

Mass losses of coal and the mole fractions of evolved species were measured during coal pyrolysis using a thermo-gravimetric analyzer and a real-time gas analyzer, respectively. Coal samples from Shin-Wha, China were pyrolyzed using a lab-scale furnace in a nitrogen atmosphere under non-isothermal conditions at heating rates of 5, 10, 20, and 30 °C/min until the furnace wall temperature reached 900 °C. Using a non-isothermal kinetic method based on a first-order model, experimental data from the thermo-gravimetric analysis (TGA) and real-time gas analysis (GA) were interpreted using a single model and a parallel model, respectively. Using the TGA data, the activation energy E and pre-exponential factor A were 130 kJ/mol and 3.19E + 07 min −1, respectively. Using both TGA and GA data, the calculated activation energies for CO {1}, CO {2}, H 2{1}, H 2{2}, total gaseous hydrocarbon(THC), and the liquids (tar and water) were 67.0, 204.2, 72.0, 43.8, 78.7, and 97.0 kJ/mol, respectively, where subscripts {1} and {2} refer to the first and second peaks of GA data. The yield of the liquids was obtained by subtracting the total gaseous mass from the derived thermo-gravimetric (DTG) data. The yields of the total gases, liquids, and char ranged from 20 to 30%, 10 to 15%, and 62 to 64%, respectively. The thermal lag effect and the promotion of lighter species by the slower heating rate were observed using the TGA and the GA, respectively. The cold gas efficiency ( CGE) ranged from 0.37 to 0.52. Slower heating conditions enabled extended residence time for volatiles within the particles, and thus promoted the generation of lighter species. The Brunauer, Emmett, and Teller (BET) surface increased (5–10 °C/min) as the heating rate increased, reached a maximum, and then decreased (10–30 °C/min).

Experimental Study on the Heat Flux Distribution of a Laboratory-Scale Wall-Fired Furnace

We investigate the effect of different operating conditions on the combustion process of the wall-fired furnace. The flue gas temperature, furnace wall temperature, and spatial distribution of local heat flux on the wall of a laboratory-scale, gas fuel front wall-fired furnace are measured experimentally. Different combinations of operating conditions including swirl intensity (SI), air supply (AS), and burner combination (BC) are considered, and their influences on the combustion, heat-transfer, and heat flux distribution characteristics are explored. Among the operating conditions studied in this paper, the combustion process can be improved with the increase of SI as well as the inner secondary air (ISA) rate. Detailed local heat flux data are obtained and analyzed under various operating conditions. The results illustrate complicated variations over the entire furnace wall. The decrease in SI conditions significantly enhances the local heat fluxes near the bottom of the furnace (adjacent to the combus...

Effect of the lining design on the temperature of the outer wall of the metal frame of pyrolysis furnaces

The requirements of different standards for the temperature of the external surfaces of pyrolysis furnace walls in petrochemical plants and the real values are reported. A different approach to determining the boundary conditions in thermal calculation of the furnace lining is noted, which makes it difficult to evaluate operation and select lining material. The outer wall temperature of pyrolysis furnaces with linings of different design was analyzed. A conclusion was drawn concerning the necessity of unifying the approach to calculating the furnace wall temperature with consideration of external conditions. Recommendations are given on designing linings and selecting materials for manufacturing them.

Study of the pyrolysis of biomass using thermo-gravimetric analysis (TGA) and concentration measurements of the evolved species

The mass losses of biomass and the mole fractions of evolved species during biomass pyrolysis were measured using a thermo-gravimetric analyzer and a real-time gas analyzer, respectively. Each biomass sample (sawdust) was pyrolyzed in a lab-scale furnace, in a nitrogen atmosphere under non-isothermal conditions at heating rates of 5, 10, 20, and 30 °C/min until the furnace wall temperature reached 900 °C. Using a non-isothermal kinetic method based on a first-order model, the experimental data from the thermo-gravimetric analysis (TGA) and real-time gas analysis (GA) were interpreted using a single model and a parallel model, respectively. Using the TGA data, the activation energy ( E) and pre-exponential factor ( A) were 145 kJ/mol and 2.67E+11 1/min, respectively. Utilizing both the TGA and GA data, the calculated activation energies for CO, H 2{1}, H 2{2}, THC, and the liquids (tar + water) were 41.7, 39.6, 51.1, 37.6, and 128.4 kJ/mol, respectively. By subtracting the total gaseous mass from the DTG (derived thermo-gravimetric) data, the yield of the liquids was obtained and was found to be higher (58–64%) than the yields of the pyrolyzed gas (20–25%) or of the char (10–12%). The cold gas efficiency (CGE) ranged from 0.38 to 0.47.

MODELLING ON DIRECTIONAL SOLIDIFICATION OF SUPERALLOY BLADES WITH FURNACE WALL TEMPERATURE EVOLUTION

Ni-based superalloy turbine blades produced by Bridgman directional solidification technology are widely used in both aeronautic and energy industries as key parts of the gas turbine engines. Because of existence of complex heat radiation between the shell surface and the furnace wall, precise control of the temperature distribution within the blade is a challenging task. A modified model based on the Monte Carlo ray tracing method was proposed for the three dimensional temperature simulation of the turbine blades during directional solidification process, in which the furnace wall temperature evolution was considered and calculated. Ray refinement in normal direction was applied to improve the heat radiation calculation precision. Three dimensional finite differential grids for turbine blades and two dimensional differential grids for furnace wall were used together to increase simulation efficiency and save memory consumption. Heat transfer calculation of the blades with the modified model was performed and compared with that of the simplified model in which the furnace wall temperature was treated as constant. Experiments were carried out to validate the proposed model in this paper. It was demonstrated that the modified model revealed the furnace wall temperature change during the withdrawal process and its impact on the blade, and simulated the temperature distribution of the turbine blade with a higher accuracy.

Effect of coal-over-coal reburn on furnace temperature and heat flux distributions in 1 MW tangentially fired furnace

The furnace temperature and heat flux distributions of 1 MW tangentially fired furnace were studied during coal-over-coal reburn, and the influences of the position of reburn nozzle and reburn fuel fraction on furnace temperature and heat flux distributions were investigated. Compared with the baseline, the flue gas temperature is 70–90 °C lower in primary combustion and 130–150 °C higher at furnace exit, and the variations of the flue gas temperature distributions along furnace height are slower. The temperature distribution along the width of furnace wall decreases with the increase of the relative furnace height. In the primary combustion zone and the reburn zone, the temperature and heat flux distributions of furnace wall are much non-uniform and asymmetric along the width of furnace wall, those of furnace wall in the burnout zone are relatively uniform, and the temperature non-uniformity coefficients of the primary combustion zone, the reburn zone and the burnout zone are 0.290, 0.100 and 0.031, respectively.

211 炭化物燃焼炉の開発(循環型廃棄物処理技術(3))

We have developed the combustion furnace for pulverized wooden charcoal .Wooden charcoal has similar properties of Anthracite. It has a little volatile matter and a lot of fixed carbon. It was expected that it is difficult to combust it stably. It is important for stable combustion of wooden charcoal to describe as follows. (1) Even solid fuel including a little volatile matter can be combusted stably (2)Temperature of furnace wall is always kept lower than the softening point of fly ash from wooden charcoal combustion and slagging must be controlled (3) Growth of NOx in the high temperature combustion zone msut be restrained. We have achieved the development of the combustion furnace for pulverized wooden charcoal with abilities of controlling slagging and growth of NOx by way of slow combustion and flue gas recirculation and in-furnace NOx reduction.

Temporal Variations in Gas Temperature in an Atomization Stage of Cadmium and Tellurium Evaluated by Using the Two-line Method in Graphite Furnace Atomic Absorption Spectrometry

In order to discuss the atomization process of an analyte element occurring in a graphite furnace for atomic absorption spectrometry, we measured variations in the characteristic temperature with the progress of an atomization stage, by using a two-line method under the assumption of a Boltzmann distribution. For this purpose, iron was chosen as the analyte element. Also, the atomic absorption of two iron atomic lines, Fe I 372.0 nm and Fe I 373.7 nm, was simultaneously monitored as a probe for the temperature determination. This method enables variations in the gas temperature to be directly traced, yielding a temperature distribution closely related to the diffusion behavior of the probe element in the furnace. This temperature variation was very different from the furnace wall temperatures, which were monitored in conventional temperature control for atomic absorption spectrometry. Correlations between the gas temperature and the charring/atomizing temperatures in the heating program of the furnace were investigated. The atomization of cadmium and tellurium was also investigated by a comparison between the gas temperature with the wall temperature of the furnace. The atomic absorption of cadmium or tellurium appeared to be apart from the absorption of iron while the gas temperature was still low. Therefore, the analyte atoms could be atomized through direct contact with the wall of the graphite furnace, which has a much higher temperature compared to the gas atmosphere during atomization. Their atomization would be caused by conductive heating from the furnace wall rather than by radiant heating in the furnace.