Actual Boilers Research Articles

A novel online method incorporating computational fluid dynamics simulations and neural networks for reconstructing temperature field distributions in coal-fired boilers

Three-dimensional (3D) reconstructions of temperature distributions can be used to effectively design power plants and ensure production safety. Typically, 3D temperature reconstruction based on the flame image processing technology and finite element calculation of furnace combustion using computational fluid dynamics (CFD) simulation are performed to obtain the furnace temperature field. In this study, a novel online method that overcomes the defects of image detection devices was proposed for reconstructing the temperature field with improved evaluation accuracy. Numerical simulations were used to perform numerous calculations. In this method, deep neural network (DNN) models were used for reconstructing the 3D temperature distribution. The training set was derived from offline CFD simulations that were set for a specific boiler and a series of typical working conditions. Based on established DNN models, the online calculation of 3D temperature distribution was realized for current operating conditions. The result revealed that the furnace temperature field could be accurately reconstructed online in a 350-MW tangentially fired boiler. Compared with the numerical simulation results, the mean absolute percent error under the tilt angles of 0°, 10°, and −10° were 3.61 %, 4.25 %, and 4.52 %. The proposed integrated method was applied to actual boilers with average error 3.448 % and achieved feasible solutions within 20 s.

Structure and reactivity of chars prepared from low-volatile coal under O2/N2 and O2/CO2 conditions in a flat-flame assisted entrained flow reactor

Accurate assessment of the structural characteristics and reactivity of coal char is crucial for the design of burners. Chars from low-volatile coal were prepared under O2/N2 (ON) and O2/CO2 (OC) conditions in a flat-flame assisted entrained flow reactor, with bituminous coal as a reference. Both the heating rate and residence time were carefully selected to mimic the conditions used in actual industrial boilers. The physical-chemical structures and reactivities of all chars were characterized using Raman and FTIR spectrometers and thermogravimetric analysis. The physical structure results indicated that a high CO2 content inhibited the char yield and specific surface area of chars from low-volatile anthracite coal, while, for chars from high-volatile bituminous coal, CO2 increased the char yield and specific surface area. For chemical structures, the degree of disorder in the carbon skeleton structures and active functional group contents of all chars prepared under OC conditions were greater than those of chars prepared under ON conditions. Moreover, the apparent reactivity results demonstrated that the physical structure characteristics of coal char played a leading role in the apparent reactivity under investigative conditions.

Improving the heat transfer efficiency of a direct-flow recycling boiler using organic fluid

This paper considers the problem of studying the heat transfer exchange during boiling in a direct-flow recycling boiler using an organic coolant. The study was conducted using numerical modelling in the ANSYS software package. Asaresultofthestudyavisual picture eofvaporphasedistributionwasobtained. This picture shows that the studied heat-exchange surface can be conditionally divided into two areas: the area of intense vaporization and the area in which the degree of dry vapor varies insignificantly. Analysis of changes in the heat transfer coefficient along the length of the heat-exchange surface led to the conclusion that heat transfer in the second area is inefficient. Based on the results of the study, it was concluded that intensification of heat transfer is necessary, for which it is proposed to install a separator at the boundary between the selected areas. The subject of the study is the dependence of the variationin the heat transfer coefficient along the length of the pipe and the determination of the boundary between the selected areas at various values of the defining parameters. Numerical simulation for therange of variationofthe defining parameters corresponding to the actual temperature regimeof power steam boilers and the conditions for the implementation of heat recovery in organic Rankine cycle unitswas performed.

Simultaneous state and fuel property estimation in biomass boilers - theory and practice

A key factor for the further distribution of biomass boilers in modern energy systems is the capability of changing the applied feedstock during normal plant operation. This is only possible with the application of advanced control strategies that utilize knowledge about the state variables and varying fuel properties. However, neither the state variables nor the fuel properties are measurable during plant operation and, thus, need to be estimated. This contribution presents a method for the simultaneous real-time estimation of the state variables and the fuel properties in fixed-bed biomass boilers which is a novel approach in the field of biomass boilers. The method bases on an Extended Kalman Filter using a nonlinear dynamic model and measurement data from the combustion process. The estimated variables are the masses of dry fuel and water in the fuel bed as well as the fuel’s bulk density, water content, chemical composition and lower heating value. The proposed method is easy to implement and requires moderate computational effort which increases the potential of its application at actual biomass boilers. The proposed method is verified with simulation studies and by test runs performed at a representative small-scale fixed-bed biomass boiler. The estimation results show a good agreement with the actual values, demonstrating that the proposed method is capable of accurately estimating the biomass boiler’s state variables and simultaneously its fuel properties. For this reason, the presented method is a key technology to ensure the further distribution of biomass boilers in modern energy systems.

Evaluation of ash melting behavior in pulverized coal-fired furnace from proportion of amorphous phase in fly ash

Molten ash in pulverized coal-fired boilers has significant effects on the generation of high-strength clinkers, which cause issues in boiler operations. To predict ash melting behavior in actual utility boilers is difficult because the melting behavior is influenced by various factors such as ash chemical composition, temperature, gas composition, etc. In this study, coal combustion and ash deposition experiments were conducted in a 760 kW coal combustion furnace to develop a method for investigating the ash melting behavior. Additionally, the proportion of the amorphous phase in the fly ash obtained from a bag filter was investigated by the Rietveld quantitative analysis of X-ray diffraction data. As a result, the proportion of the amorphous phase in the fly ash was high when high-strength clinkers with molten surfaces were generated. The results indicated that most of the molten phase in the fly ash particles transformed into the amorphous phase because they were cooled rapidly by being transported into the bag filter, resulting in the inhibition of their crystallization. Hence, we concluded that the proportion of the amorphous phase in the fly ash captured by cold ash collectors represents the ash melting behavior in the actual environments. The proposed method can be used to evaluate the effects of fuel or boiler-operating conditions on ash melting behavior. The applications of the method on actual utility boilers will be considered in further studies.

Enhanced sodium adsorption capacity of kaolinite using a combined method of thermal pre-activation and intercalation-exfoliation: Alleviating the problems of slagging and fouling during the combustion of Zhundong coal

The thermal utilization of low-rank coal with high sodium content easily leads to severe fouling and slagging in actual boilers. To alleviate this problem, a combined method of thermal pre-activation and intercalation-exfoliation was developed in order to modify the kaolinite and thus control the release of sodium vapor during the combustion of Zhundong coal. The results show that the sodium capture efficiency of kaolinite increased from 3.59 mg g−1 to 4.62 mg g−1 when employing the combined modification method. This modified kaolinite can be used more effectively, alleviating fouling and slagging in actual boilers that burn high sodium solid fuels. The experimental data regarding the crystal structure, functional groups, Si/Al-coordination and micromorphology of kaolinite indicate that two modification methods had different effects on the structure of kaolinite, which were closely associated with the sodium adsorption capacity of the modified kaolinite. By thermal pre-activation, metakaolinite formed after dehydroxylation, resulting in the hexa-coordinated Al (VI) being converted to unsaturated Al. During the process of intercalation-exfoliation, the lamellar structure of kaolinite was broken, leading to a decrease in its crystallinity. The combining method contributed to the highest degree of structural disorder and promoted the conversion of Al (V) to Al (IV), thus creating more active sites for sodium fixation. In this case, the chemical sodium adsorption efficiency of kaolinite increased significantly regardless of the purity of raw kaolinite and the temperatures of pre-calcination. Based on a multistage analysis of the modified kaolinite, a relationship between the structure and adsorption capacity was developed, providing a new method of adsorbent modification.

Simultaneous investigation into the yields of 22 pyrolysis gases from coal and biomass in a small-scale fluidized bed reactor

Flash pyrolysis gas yields from bituminous coal and torrefied biomass have been investigated in the temperature range between 873 and 1273K for 22 different gas species simultaneously. Recording a larger number of species gives a more detailed insight into pyrolysis of solid fuels than it is provided by other studies in literature, where typically smaller numbers of species are tracked. As processes utilizing biomass are designed for lower process temperatures, literature data for biomass pyrolysis are scarce in the temperature range between 1023 and 1273K. This work, aiming at investigating potential fuels for pulverized solid fuel combustion, approximates pyrolysis conditions in the ignition zone of actual power plant boilers, where possible.Thus, based on results of a literature review, an experiment was designed using a small-scale fluidized bed reactor (FBR) to simultaneously analyze the pyrolysis gas yields for 22 species and to close the temperature gap found for biomass. Small batches of pulverized torrefied biomass from poplar wood and pulverized Colombian bituminous coal (Mina Norte) were rapidly pyrolyzed in the reactor. The two fuels were chosen as exemplary conventional and alternative energy sources for pulverized fuel fired power plants. Experiments have been carried out under atmospheric pressure in pure nitrogen atmosphere.Product gas analysis was carried out by Fourier transform infrared spectroscopy (FTIR) including two different sampling techniques. As a novelty, offline measurements have been used exclusively to improve the gas species selection procedure and reliability of detection. In case of offline measurements, the gas flow to the FTIR gas cell is stopped and the gas is enclosed in the cell allowing longer scan times of the captured gas mixture and thereby enlarging the signal-to-noise ratio (SNR). In succession, regular measurements with continuous flow (online) were performed for the simultaneous quantitative analysis of total pyrolysis yields for 22 selected gas species.Obtained pyrolysis yields show good agreement with available literature data. The larger number of investigated species provides an extended data set also covering minor pyrolysis species, for which quantitative data are scarce. Additionally, trends in the gas yields for biomass agree well with those found by other authors outside the mentioned temperature gap between 1023 and 1273K.

Numerical analysis on effect of furnace scale on heat transfer mechanism of coal particles in pulverized coal combustion field

To investigate the effect of the furnace scale on the heat transfer mechanism of coal particles, numerical simulations of coal combustion fields in three different scale furnaces (915MWth actual large scale boiler, 2.4MWth and 0.76MWth test furnaces) were conducted. High accuracy of simulation methods was validated with the measured data. From the comparison of numerical simulations between three different scale furnaces, it was clarified that the particle residence time with high particle temperature for a small scale furnace is shorter than that for a large scale furnace even if the particle residence time passing the high temperature gas is the same. This is caused by the insufficient heat gain of particles for a small scale furnace due to the lower radiation heat transfer because of the thinner flame thickness in the small furnace. The sphericity of ash particles from small scale furnaces is lower than that for large scale furnaces due to the shorter particle residence time with high particle temperature. These findings should be considered when the usability of coal brands for actual large scale boilers is evaluated by the fly ash properties from a small scale experimental furnace.

Controlling Factors of Localized Corrosion in Boiler Combustion Gas Environments

Localized corrosion (LC) sometimes appears in boiler tubes exposed in severely corrosive combustion gases including Cl, S and O, but prediction and on-site maintenance of LC is actually difficult in many cases. Therefore understanding the cause of LC is considered to be important to maintain safety services and estimate lifetime in high temperature facilities. This LC occurs due to formation of partially different corrosive conditions due to fuels, condition of combustion, designing of boilers, and materials. In this paper, investigation results of macroscopic LC and influenced factors formed in actual boilers were described with the four cases of fossil fuel, biomass and WTE boilers, and also described against any coatings. Mechanisms of each LC were considered individually by using cut-off samples of damaged tubes, detailed analyses of corrosive environments and results of laboratory tests. From these considerations, protective oxide layers and not only static factors but also dynamic factors arising in operated conditions such as temperature and composition fluctuations were concluded to be important for the accurate lifetime evaluations of tube materials and coatings.

Method for Identifying Areas of Sulfidation on Water-Wall Tubes in Coal-Fired Boilers

In Japan, pulverized-coal-fired thermal power plant boilers are operated with a high two-stage combustion ratio to reduce NOx emissions. This combustion ratio forms a strongly reducing atmosphere containing H2S at the burner zone. Water-wall tube materials, such as low-alloy steel, sulfidize severely in such an atmosphere. In the past few years, wastage of the tubes observed in limited areas. However, the sulfidation area tends to extend and/or to shift along with changes in combustion conditions and coal properties. As a result, large-area inspections are necessary to identify the sulfidation areas. Several methods for identifying sulfidation areas have been developed, but these methods have various drawbacks, including (a) long inspection times to adequately assess large areas and (b) a need for descaling, which can act to accelerate tube wastage. Accordingly, a new approach is required for quick identification of sulfidation areas in large commercial boilers without any need for wall descaling. Toward this end, we investigated coal ash chemistry, scale structure/composition, and combustion conditions at several pulverized-coal-fired boilers in Japan. The results show that severe sulfidation occurs in areas where coal-ash deposits contain a comparatively high Zn content. In a reducing atmosphere with sufficient sulfur potential, only a limited amount of Zn contained in coal is sulfidized to form ZnS. At the combustion temperature (about 1300 °C), ZnS is present as a gaseous phase. It presumably solidifies on the tube surface, the temperature of which is about 500 °C. Continuous deposition of ZnS acts to increase the Zn content in the coal ash on tube surfaces. A relatively high level of Zn on the tube surface can be an “indicator” for a sulfidation area. With this as an indicator, the entire region of actual boilers can be easily evaluated without descaling and within several hours by the use of a handheld X-ray fluorescence analyzer.

Air-Staged Combustion Characteristics of Pulverized Coal under High Temperature and Strong Reducing Atmosphere Conditions

It is of great importance to clarify the effect of the combustion temperature in actual boilers on air-staging combustion of coals. In this work, a novel vertical tandem-type drop-tube furnace system was set up, in which a temperature of as high as 1600 °C can be achieved. Experimental investigations were performed thoroughly with particular attention to NOx formation and unburned carbon in ash. The results indicate that, to maximize NOx removal efficiency by air-staged combustion, the reducing zone should be under high temperature and strong reducing atmosphere (HT&SRA) conditions. A remarkably low NOx emission and high coal burnout can be attained concurrently by creating HT&SRA conditions in the fuel-rich zone. The NOx emission for high-volatile coals can be below 150 mg/m3. The special role of the temperature is discussed in detail in terms of the difference of NOx formation between the reducing zone exit and burnout zone exit. For comparison, the NOx emission in Ar/O2- and oxy-fuel-staged combustion was also studied. Staged combustion is as effective for NOx reduction in Ar/O2 and oxy-fuel as in air combustion. However, for oxy-fuel-staged combustion, the effect of HT&SRA conditions presents some differences, which are closely related with the oxygen proportion in the gas atmosphere. In addition, it is also found that the temperature in the burnout zone (800–1200 °C) has a weak effect on NOx generation, but CO emission would drastically increase when it is below 1100 °C.

Thermal Stability of Zinc Compounds

Zn and Cl have been found in deposits in municipal solid waste (MSW) boilers and industrial boilers. This leads to the general belief that ZnCl2 may play a role in corrosion of heat-transfer tubes, owing to its low melting temperature and high corrosivity. In this study, the thermal stability of the compounds ZnCl2, ZnSO4, and ZnO as well as mixtures of ZnCl2 and NaCl/KCl was investigated by means of thermogravimetric analysis/differential scanning calorimetry (TGA/DSC). The reactions of the Zn compounds with SO2/SO3 and HCl were also investigated. The results obtained show that ZnCl2 melts at 320 °C. Above 400 °C, ZnCl2 vaporizes and is partly oxidized to ZnO. ZnSO4 is stable up to 680 °C, at which it decomposes and, subsequently, forms ZnO above 900 °C. ZnO is stable at a much higher temperatures but can be chlorinated to ZnCl2 in the presence of HCl at temperatures around 300 °C. In the presence of a large amount of NaCl/KCl, which is typically the case in actual boilers, ZnCl2 reacts with NaCl/KCl to form 2NaCl·ZnCl2 and 2KCl·ZnCl2, respectively. These compounds melt at temperatures lower than NaCl and KCl but higher than ZnCl2. The findings show the significance of understanding the thermal stability of various zinc compounds, how they interact with one another, and whether they react with alkali chlorides and other compounds in the deposits to assess the role of Zn in deposit formation and corrosion in boilers burning Zn-containing fuels.

Experimental Study on the NO and N2O Formation Characteristics during Biomass Combustion

In the present study, the NO and N2O formation characteristics during combustion of five biomass fuels (rice straw, wheat straw, corn stalk, sugarcane leaf, and eucalyptus bark) and one bituminous coal, as a comparison, were investigated in a horizontal fixed-bed reactor. It showed that there was still a considerable degree of N2O conversion for biomass fuels, although NO was formed in a much larger amount. Most of NO and N2O were formed during the devolatilization stage for biomass fuels; therefore, optimizing the supply of air and fuel during biomass combustion in actual boilers can be expected to achieve ultralow emissions of nitrogen oxides. There was no clear correlation between the NO and N2O yields and fuel N content, which indicated that the nitrogen functionality and other components, such as inherent mineral matter, present in biomass must have great influence on the nitrogen transformation during thermal processing. When rice straw was co-fired with eucalyptus bark, nonlinear behavior could be ...

Effects of fine ash particles and alkali metals on ash deposition characteristics at the initial stage of ash deposition determined in 1.5 MWth pilot plant tests

The purpose of this study was to evaluate the effect of fine ash particles and alkali metals on the decreasing heat flux at the initial stages of ash deposition which has a significant effect on heat transfer characteristics during the whole ash deposition process. For this purpose, a series of slagging tests were conducted in a 1.5MWth pilot plant. The heat transfer characteristics of four bituminous and three sub-bituminous coals were studied using a slagging probe set in the high temperature zone simulating the water wall in actual boilers. The heat flux through a slagging probe was calculated and the decreasing rate of heat flux per unit weight fraction of ash (dq/dt-ash) was compared for each coal. Deposits on the slagging probe were sampled and analyzed after each test run. Analysis results showed that particle fractions with a diameter less than 10μm (R10under) of bituminous coals varied in wide range: from 5 to 45wt.%, while those of sub-bituminous coal did not change greatly: from 16 to 30wt.%. In terms of alkali components, the inner layer of deposits of bituminous coals tends to enrich Al, Fe and Ca. In the case of sub-bituminous coals, refractory compounds of Si, Al and Ti, alkali compounds of Na, K, Fe and P. To evaluate the influence of factors on the decreasing rate of heat flux at the initial stage of ash deposition quantitatively, a multiple regression analysis of heat flux data (dq/dt-ash) was performed using the following parameters: R10under, and also Na2O and K2O values in each parent coal. Calculation using a regression equation agreed well with experimental data.

Staged combustion properties for pulverized coals at high temperature

Staged combustion properties for pulverized coals have been investigated by using a new-concept drop-tube furnace. Two high-temperature electric furnaces were connected in series. Coal was burnt under fuel-rich conditions in the first furnace, then, staged air was supplied at the connection between the two furnaces. Reaction temperature (1800–2100 K) and time (1–2 s) were similar to those used in actual boilers. When coal was burnt at the same stoichiometric ratio as in actual boilers, similar combustion performance values as for actual boilers were obtained regarding NO x emission and carbon in ash. The most important factor for low NO x combustion was to raise the combustion temperature above the present range (1800–2100 K) in the fuel-rich zone. The NO x emission was significantly increased with decrease of burning temperature in the fuel-rich zone when the temperature was lower than 1800 K. But, NO x emission was cut to around 100–150 ppm, for sub-bituminous coal and hv-bituminous coal, in the latest commercial plants by forming this high-temperature fuel-rich region in the boilers. If the temperature and stoichiometric ratio could be set to the most suitable conditions, and, burning gas and air were mixed well, it would be possible to lower NO x emission to 30–60 ppm (6% O 2). The most important NO x reduction reaction in the fuel-rich zone was the NO x reduction by hydrocarbons. The hydrocarbon formation rate in the flame was varied with coal properties and combustion conditions. The NO x was easily reduced when coals which easily formed hydrocarbons were used, or, when burning conditions which easily formed hydrocarbons were chosen. Effects of burning temperature and stoichiometric ratio on NO x emission were reproduced by the previously proposed reaction model. When solid fuel was used, plant performance values varied with fuel properties. The proposed drop-tube furnace system was also found to be a useful analysis technique to evaluate the difference in combustion performance due to the fuel properties.

二段燃焼用空気ノズル形状が及ぼす燃焼性能への影響評価(熱工学,内燃機関,動力など)

We examined relations between the shape of the staged air nozzle (after air port) and the mixing performance in the furnace for two staged combustion. Four different shapes of ports, 1 hole, 4 holes, 9 holes, Lobe shape, with the same open area of nozzle outlet were used to examine the effect on the NO_x and CO performance. The gas velocity in the furnace and the air ratio were fixed at the values near the operating condition of the actual boilers as much as possible. NO_x and CO performance was correlated with the mixing performance in the downstream side of the after air port. CO decrease when the standard deviation of the local air ratio in the furnace become small. This is because extremely low oxygen concentration region is hard to be formed in the furnace. On the other hand, NO_x increase if the standard deviation of that is small. The overall air ratio was set at 1.15 for the experimental condition. Under this condition, improvement of mixing performance brings an increase of thermal NO_x because of higher gas temperature. We also examined the nozzle design criteria in order to predict its mixing performance beforehand. It was found that the circumference length of the jet flow had a good correlation with the standard deviation of the local air ratio. When a nozzle has a longer circumference length, mixing performance of it becomes better.

Computational intelligence approach for NOx emissions minimization in a coal-fired utility boiler

The current work presented a computational intelligence approach used for minimizing NOx emissions in a 300 MW dual-furnaces coal-fired utility boiler. The fundamental idea behind this work included NOx emissions characteristics modeling and NOx emissions optimization. First, an objective function aiming at estimating NOx emissions characteristics from nineteen operating parameters of the studied boiler was represented by a support vector regression (SVR) model. Second, four levels of primary air velocities (PA) and six levels of secondary air velocities (SA) were regulated by using particle swarm optimization (PSO) so as to achieve low NOx emissions combustion. To reduce the time demanding, a more flexible stopping condition was used to improve the computational efficiency without the loss of the quality of the optimization results. The results showed that the proposed approach provided an effective way to reduce NOx emissions from 399.7 ppm to 269.3 ppm, which was much better than a genetic algorithm (GA) based method and was slightly better than an ant colony optimization (ACO) based approach reported in the earlier work. The main advantage of PSO was that the computational cost, typical of less than 25 s under a PC system, is much less than those required for ACO. This meant the proposed approach would be more applicable to online and real-time applications for NOx emissions minimization in actual power plant boilers.

Development of a Thermal-Hydraulic Analysis Code in the Distributed Parameter System for Furnace Water Wall Tubes of Fired Boilers

For design optimization of the furnace water wall of pulverized coal-fired boilers, a thermal-hydraulic analysis code to calculate the flow rate and wall temperature distribution in the water wall has been developed. The code can be applied to complex flow networks for two-phase flow consisting of many tubes and headers for both steady and transient states in the distributed parameter system. The detailed flow conditions at any tube position, such as temperature, quality, velocity, etc. can be calculated stably and quickly by the developed algorithm using a matrix solver. The results of 3-D combustion analysis are used as one of the boundary conditions for this code. The performance of the code was verified using steady and transient states data of temperature distribution in the furnace water wall tubes of actual boilers. The results of both steady and transient states analyses showed good agreement with measured data. The new algorithm decreased the calculation time for steady-state analysis significantly compared with the previous algorithm. For transient-state analysis with a high performance computer, it can calculate tube temperature faster than the real transient time.

船用低圧ボイラ水中におけるMg硬度の挙動

It is very important to investigate accurately the behavior of sea water component, especially of Mg hardness, for the boiler water qualtiy control of marine boilers. And also, important to investigate the behavior of PO43-, especially when Mg2+ and OH- coexist with it, for making the automatic control method proposed by the authors more feasible and reliable. Accordingly, this paper studies experimentally the behavior of Mg hardness when OH- and/or PO43- coexist, and when silica is mixed. Experiments were carried out at the condition of the same solution level with the water quality criterions adopted for actual boilers, by the use of an autoclave of which temperature and pressure adjusted as the same level with actual auxiliary boilers. The obtained results are summarized as follows.(1) In the reaction model developed so far, It has been thought so far that almost all Mg hardness reacts to form Mg (OH) 2 in the boiler water when the phosphate concentration is controlled appropriately by the alkali treatment. In this experiment, however, it was found that Mg reacts not only with OH-but also with PO43-, and the mole ratio of reaction products Mg (PO4) 2 and Mg (OH) 2, increases with the decrease of pH, that is, 0 at pH=12.0, and around 2 on pH 10.5.The mole ratio is hardly affected by the PO43- concentration and the reaction temperature in the range of 1MPa-3Mpa.(2) If SiO2 is mixed together with Mg hardness in the feed water, MgSiO3 is formed in boiler water. Its quantity increases with the increase of SiO2. The rest of Mg hardness unreacted with SiO2 is considered to react to form [Mg3 (PO4) 2] n⋅Mg (OH) 2 as mentioned above, and it is resulted in that pH and PO43- concentration are decreased.

Combustion Characteristics and Pollution Minimum Technology for VR (Vacuum Residue) Fired Boiler.

An experimental study on the combustion of extra heavy oil has been performed using a cylindrical test furnace. Recently, light oil such as gasoline is almost exclusive ly demanded as liquid fuel made from petroleum. In order to produce light oil in a high yield, extra heavy oil, which is called as VR(Vacuum Residue), remains after refinement under reduced pressure. VR features extremely high viscosity, as well as high percentages of sulfur, nitrogen, heavy metals, and resident carbon in fuel. Regarding the use of VR as a fuel for actual commercial boilers, a number of serious problems must be overcome. These include high- and low-temperature corrosion of metal materials, and the need to meet environmental regulations calling for low NO x and a low unburned carbon ratio in exhaust gas. In the present study, accordingly, a firing test has been conducted to accumulate the basic characteristics of VR combustion. From the test results, stable ignitability was ascertained, and both NO x emission and the unburned carbon ratio in exhaust gas were found to be at the same level as for bituminous coal combustion. Also, the reactivity and the carbon structure of the sampled soot and char were chemically examined in detail, and the reaction rate with oxygen was formulated. Furthermore, numerical simulation of combustion in one dimensional furnace was conducted, and the calculated results were compared with the experimental data.