Unburnt Char Research Articles

Entropy generation analysis of a three-dimensional coal-fired furnace: A realistic study

An analysis of the entropy generation by radiative heat transfer in a three-dimensional virtual coal-fired furnace is performed. The gases, including CO2 and H2O, and particles, including soot, unburnt char and ash, are considered as a participating medium. The radiative transfer equation for a non-grey medium was solved by the discrete ordinate method, in which the radiative properties of the gases, soot, unburnt char and ash were obtained by using the statistical narrow-band correlated-k model, Rayleigh's theory, and Mie theory, respectively. The distributions of the local volumetric rate of entropy generation and the local rate of entropy generation at the wall are calculated. The contributions of various media in coal-burning furnaces to the radiative entropy generation rate (REGR) are evaluated, and the effects of several important factors, such as the oxidizer atmosphere, burnout rate, and the volume fraction of soot, unburnt char and ash on the REGR and dimensionless entropy generation were also investigated. The numerical results show that the irreversibility of the particle radiation contributes more than 80% of the volumetric radiative entropy generation. The concentration of particles also has an important effect on REGR, which decreases by 41% when the concentration of unburnt char and ash increases from 10 ppm to 50 ppm and decreases by 70% when the concentration of soot increases from 1 ppm to 6 ppm in a real-size furnace such as an optically thick furnace.

Competition between NH3-O2 reaction and char-O2 reaction and its influence on NO generation and reduction during char/NH3 co-combustion: Reactive molecular dynamic simulations

To reduce CO2 emissions in power plants, the co-firing of ammonia (NH3) and coal in boiler has received increasing attention in industry and academia. In this work, char/NH3 co-combustion behaviors and NO generation and reduction characteristics under different temperatures, O2 equivalence ratios and NH3 co-combustion ratios are studied via the reactive molecular dynamic (ReaxFF MD) simulations. The initial reaction mechanisms of char oxidation and NH3 oxidation revealed by ReaxFF MD simulations conform to the models that have been proposed, which proves the accuracy of ReaxFF MD method in studying char/NH3 co-combustion. The char/NH3 co-combustion simulation results show that NH3 will compete with coal char for O2, resulting in an increase of NH3 oxidation rate and a decrease of char oxidation rate. The competition between NH3-O2 reaction and char-O2 reaction during char/NH3 co-combustion are largely depended on temperature, O2 equivalence ratio and NH3 co-combustion ratio. Compared to NH3 combustion, the concentration of O and OH radicals are higher while the concentration of NH2, NH and NNH intermediates are lower during char/NH3 co-combustion due to the competition between NH3-O2 reaction and char-O2 reaction, which enhances the NO generation reactions but weakens the NO homogeneous reduction reactions. Under oxygen-lean conditions, the homogeneous reduction of NO by NNH and the heterogeneous reduction of NO by unburnt char play an important role in reducing NO emissions, especially at high NH3 co-combustion ratios. The reaction paths of NO reduction by char during char/NH3 co-combustion are revealed. The results indicate that both the carbon atoms and the nitrogen atoms in char are responsible for NO reduction.

Incineration of Aviary Manure: The Case Studies of Poultry Litter and Laying Hens Manure

The industrial incineration of aviary manure is still far from the concept of using its ash residuals for nutrient uptake by plants and most of these materials are landfilled under futile fixed cost. Aviary manure includes poultry litter mixed with different aviary bedding materials or laying hens manure, which may be burned using different incineration technologies and conditions. This study aims to determine the comparative characterisation of P-rich ash residues sampled at Güres Energy (Turkey) fluidized bed combustion of laying hens manure and at Campoaves (Portugal) chain grate stoker combustion of rice husk poultry litter. The effect of different fuels and different combustion systems on P speciation in ash was investigated: the characterisation of global samples (bottom ash (BA), economiser fly ash (FAECO), cyclone fly ash (FACYC)) and respective size-fractions were done chemically (proximate and elemental analysis by X-ray fluorescence–XRF–and Inductively Coupled Plasma Mass Spectroscopy – ICP-MS), morphologically (detailed imaging and X-ray micro analysis by Scanning Electron Microscopy—Energy-Dispersive X-ray spectrometry–SEM−EDS) and mineralogically (X-ray diffraction–XRD). Phosphorus was detected in Güres ashes mainly as hydroxyapatite crystals alongside with CaCO3 relics and CaO, while Campoaves ash fractions contained P also as Na–K-Mg phosphate and major amounts of rice husk relics including unburnt char and silica phases. Both Güres and Campoaves ashes are complex but the combustion of aviary manure under these setting conditions appears to be promising for P recovery owing to their high P content and limited trace elements respecting the limitations imposed by EU legislation for fertilisers applications.

Effect of ZnS/PbS deposits on high temperature corrosion of waterwall tubes in reducing atmosphere

Zn- and Pb-rich deposits have been observed on the waterwall at fireside in three tangentially coal-fired boilers. This work aims to clarify the influence of ZnS or PbS deposits on sulfide corrosion behavior with the help of field and corrosion testing analyses. The characterization of field samples shows that the enrichment of various metal elements (Pb, Zn, Ga, Se, etc.) in the corroded layer is mainly attributed to vaporization-condensation of metal vapors, and gaseous migration of metal elements remained in unburnt char. In laboratory 12Cr1MoVG specimens were exposed to ZnS or PbS deposits in a mixed gas of 0.1%H2S-0.1%O2–5%CO-N2 at 400 or 500 °C for 120 h. The results show that pyrite is identified only at 400 °C while marcasite appeared at 500 °C needs a longer exposure time. Iron can be oxidized in the regions in which PbOx is stable, while in the regions where PbS is stable iron can only be sulfided. PbS and ZnS deposits could decrease the corrosion rate of specimens. But the capacity of PbS for hindering corrosion attacks is slightly weaker than ZnS, due to the generation of Pb(g) and more active S migrating into corrosion side.

Numerical investigation of the effects of size segregation on pulverized coal combustion in a blast furnace

Pulverized coal combustion in a blast furnace raceway can play a critical role in blast furnace iron-making operations. This research study integrated the particle combustion and the raceway formation processes using a refurbished coupling method based on computational fluid dynamics (CFD). The CFD model was validated, and there was good agreement between the simulation results and the two sets of experimental data. The combustion behaviors of pulverized coal particles in an industrial blast furnace were also simulated over a wide size range. The simulation results showed that size segregation occurred along the vertical direction in the raceway. Along the coal plume, the effectiveness of the size segregation process can be significantly reduced by the turbulence generated owing to the existence of the lance, the expansion of the gas jet near the tuyere tip, and the gas recirculation at the front end of the raceway. The burnout rate of particles smaller than 60 μm was also shown to be sensitive to the degree of weakening of the size segregation. The particle distribution in the coke bed indicated that the group of particles with diameters equal to 52.5 μm was associated with the largest proportion of unburnt char. This research extended the applicability of the existing numerical methods and provided a better understanding of the pulverized coal injection (PCI) process from the viewpoint of size segregation, which is beneficial to the further optimization of PCI usage

A full spectrum k-distribution based non-gray radiative property model for unburnt char

By using the concept of weighted sum of four gray particles and spectrum k-distribution (WSGP-SK), a non-gray radiative property model for unburnt char particles is developed. Based on the carbon burnout kinetic model for structure during oxidation, and the linear mixed approximation theory for complex index of refraction, spectral radiative properties of unburnt char particles are first calculated as function of the burnout ratio by Mie theory. Referring to the full spectrum k-distribution model, k-distribution is applied to reorder absorption and scattering efficiencies of particles. Then, weighting factors and efficiency factors of the non-gray radiative property model are directly obtained from Gaussian integral points of k-distribution. The model is validated against the benchmark solutions of line-by-line (LBL) model. Maximum relative errors of this model are 3% and 15% for radiative heat fluxes and source terms in non-isothermal inhomogeneous particulate media, respectively. The assumption of linearly varying radiative properties with burnout ratio (Lockwood et al. 1986) will result in a predicted deviation of 53% for radiative source terms. Results also show that this non-gray model is remarkably better than the Planck mean method. Moreover, a satisfactory comparison with LBL solutions is achieved in the gas and particle mixture by combining the non-gray WSGG-SK model (Guo et al. 2015). As a radiation sub-model, this non-gray radiative property model can significantly improve prediction accuracy of radiative heat transfer in oxy-fuel combustion.

Prevention of boiler performance degradation under large primary air ratio scenario in a 660 MW brown coal boiler

To study how to prevent the boiler performance degradation under large primary air ratio (PAR) condition, a three dimensional computational fluid dynamics model was established on the basis of a 660 MW wall-fired brown coal boiler. Accuracy of simulation models was established by carrying out a mesh independence test and a comparison with real-life data. Then it was used to investigate the effects of proposed measures on boiler performance. The distribution profiles of combustion temperature, heat flux, CO mass fraction and unburnt char particles were selected to analyze the boiler performance under different cases. Results show that boiler performance deteriorates evidently when PAR is increased to 0.425, and the overall heat flux decreases by 37.0 MW. The three proposed measures can indeed improve the boiler performance that has been deteriorated when PAR is increased, and the overall heat flux was increased by 6.42 MW, 6.59 MW and 15.53 MW respectively. Among the proposed measures, the method of closing part of secondary air nozzles is recommended in regular boiler operation, due to its operability and convenience. The findings of this research and recommended measures can be used as guidelines in the actual operation in brown coal power plant.

A reduced order mathematical model of the blast furnace raceway with and without pulverized coal injection for real time plant application

Pulverized coal is injected into blast furnace tuyeres to reduce coke consumption as well as to reduce hot metal production cost. Knowledge of the combustion behavior of pulverized coal in the blast furnace raceway zone and accumulation of unburnt char are of paramount importance. To alleviate the problem of high computational time of a multidimensional model, a reduced order raceway model of the blast furnace has been proposed for real time plant application. The model is capable of predicting radial temperature and gas composition profiles in the raceway zone with and without pulverized coal injection (PCI). Influence of all the key operating process parameters such as PCI rate, blast temperature, blast volume, oxygen enrichment and steam addition on the raceway combustion behavior, temperature and gas composition profiles as well as raceway depth have been investigated and validated with literature and plant database, wherever possible. It has been observed that with increasing PCI rate on a fixed fuel rate basis, the peak gas temperature (PGT) decreases and the location of PGT tends to shift toward tuyere nose. The present model is an efficient computational tool to predict the raceway process variables for online application, in synchronization with plant operation.

Interaction mechanism between coal combustion products and coke in raceway of blast furnaces

The interaction mechanism between the combustion products of pulverized coal injected and coke in the raceway of blast furnace was studied through thermodynamic calculation and experiments. The results indicated that additives significantly affected the melting property of coal ash in high temperature zone. Although the unburnt char, raw coal ash, and catalyzed coal ash failed to wet the coke surface, the wettability of the catalyzed coal ash on the coke was greater than that of the raw coal ash. Since the unburnt char had weak reaction with the coke surface, it showed little influence on the surface morphology of the coke. The interaction between the raw coal ash and the coke gave rise to the increase in the pore size on the coke surface. However, the raw coal ash only affected the coke surface and the entrances of the pores owing to its poor fluidity. After being melted, the catalyzed coal ash was expected to immerge into the inside part of the coke and then react with the coke, resulting in an expansion and increase of coke cavities. The raw coal ash and the unburnt char reduced the coke reactivity, while the catalyzed coal ash improved the coke reactivity. Thereinto, the coal ash containing Fe2O3 exhibited a larger influence on the reactivity than that containing CaO.

高炉下部におけるプラスチック粒子の移動挙動

Injection of plastics into blast furnaces as an alternative reducing agent has been carried out for the purpose of mitigation of carbon dioxide emissions. Several studies on the pyrolysis of plastic particles have been reported, however flow behavior of plastic particles or unburnt char in actual blast furnace is not clear. In this study, hotmodel experiments and thermogravimetry analysis were conducted for the modeling of gasification behavior of plastic particles, then flow behavior of plastic particle and unburnt char in a blast furnace was calculated by numerical simulation. According to the observation results of gasification experiment, volatile matter of plastics seems to be evolved at the surface of the particles. Regarding reaction of char derived from plastics, thermogravimetry analysis showed that rate of gasification of unburnt char depended on the rate of heating. Gasification rate in the case of rapid heating condition tended to increase. As the results of numerical simulations, initial diameter of plastics and char diameter determined the flow behavior in the blast furnace. When relatively small plastic was injected or diameter of unburnt char was small, unburnt char went upward along with gas flow and most of it might be consumed at the cohesive zone. On the other hand, when relatively coarse plastics was injected and diameter of unburnt char was relatively coarse, it was suggested that unburnt char accumulated around the deadman. Therefore, it is considered that fine plastics injection is desirable for the stable operation of blast furnace.

Numerical Modeling and Experimental Investigation on the Use of Brown Coal and Its Beneficiated Semicoke for Coal Blending Combustion in a 600 MWe Utility Furnace

In this paper, coal blending combustion performance in a 600 MWe supercritical boiler has been investigated through a series of on-site measurements and computational fluid dynamic modellings. A bituminous coal was used as reference, which was blended with brown coal or brown coal semicoke in an indirect way, i.e., different coals being fed separately into the boiler without prior mixing in the mill. The coal blending combustion behavior was assessed upon varying brown coal injection location, brown coal blending ratio, air staging ratio, and the use of brown coal pyrolysis-derived semicoke. ANSYS FLUENT 15.0 was employed for numerical simulations. Upon a successful validation, the model was further used to predict the influence of individual variables. The main conclusions achieved include (1) the bituminous coal-designed mill can be used safely for brown coal, at the expense of an increased mass ratio of primary air to coal, a decreased temperature for the outlet of the mill, and an incomplete drying of brown coal. (2) The allocation of brown coal in the middle burner zone is the best option that ensures a relatively long residence time of bituminous coal particles in the boiler, as well as provides sufficient heat to bituminous coal particles for a quicker ignition and burnout. (3) The 50 wt % blending ratio for brown coal is optimum, striking a good balance between the feeding amounts of combustible hydrocarbons and inherent moisture into the burner. (4) The separate over fire air of 30% ratio is beneficial in reducing total NOx emission through increasing the unburnt char quantity in the NOx reduction zone. (5) The high heating value of beneficiated Victorian brown coal and its semicokes ensures a lower feeding rate for each of them to be used as a substitute fuel. The high volatile-O2 and char-O2 oxidation reactivity of these samples also ensured a strong heat provision from their flame to the bituminous coal allocated in both the bottom and top of the burner zones. (6) The use of brown coal and semicoke is in favor of the reduction in NOx, particularly fuel-NOx, due to the generally low nitrogen content within these samples, relative to bituminous coal.

Evaluation of combustion behaviour of coal blends for use in pulverized coal injection (PCI)

Generally, coal blends show unexpected combustion performance which cannot be explained on the basis of individual coal properties particularly coal rank and volatile matter. The current study investigates the combustion behaviour of four coals and their blends at different proportion under high oxygen concentrations more than 21% for use as feed coal in pulverized coal injection (PCI) in the blast furnace. Three different high rank coals blended with one relatively low rank coal in different proportions and combustion behaviour of the individual coals and their blends were studied in thermogravimetric analyser (TGA) and drop tube furnace (DTF) with enriched oxygen concentration. The results suggest that coal D is most suitable for PCI injection. The other three higher rank coals are not suitable for PCI and if charged singly, they can lead to significant proportions of unburnt char in the stack of the blast furnace. To accommodate wide variety of coals of different rank and types, blending of coal is considered as a suitable option for the PCI injection. Results of thermogravimetric analysis showed that low rank coal influenced the ignition temperatures of blends whereas high rank coals influenced their burnout behaviour. Both TGA and DTF study shows that blends containing up to 10% of high rank coal gives better combustion performance even that of low rank coal.

Evaluation of catalytic combustion of pulverized coal for use in pulverized coal injection (PCI) and its influence on properties of unburnt chars

In order to investigate the influences of applying catalysts on pulverized coal injection (PCI) and blast furnace (BF) operations, the catalytic combustion of two kinds of pulverized coals by three oxides (MnO2, CaO and Fe2O3) was simulated by using a drop tube furnace (DTF), and variation of structures as well as the reactivity of unburnt chars were examined. For bituminous, the relative active sequence of catalysts to the burnout rate was: CaO>Fe2O3>MnO2. For anthracite, it is as follows: Fe2O3>CaO>MnO2. These three catalysts exhibited better catalytic effect on anthracite than bituminous coal. In addition, the structural study results imply that the chemical reactions on char particle and pore surface were enhanced greatly by catalysts. On the other hand, the X-ray diffraction analysis shows that chars became more ordered with catalysts addition. Nevertheless, unburnt chars formed from catalytic combustion still have a higher reactivity than pure unburnt char, which is most probably due to the lower activation energy. Consequently, these results imply that the catalytic combustion in PCI operation facilitates the combustion process of pulverized coal in raceway, as well as the following consumption of unburnt char out of raceway.

CFD Modelling and Analysis of Pulverized Coal Injection in Blast Furnace: An Overview

AbstractIn order to understand the complicated phenomena of pulverized coal injection (PCI) process in blast furnace (BF), several mathematical models have been developed by the UNSW and BSR cooperation. These models are featuring from coal combustion in a pilot‐scale test rig, to coal combustion in a real BF, and then to coal/coke combustion in a real BF, respectively. This paper reviews these PCI models in aspects of model developments and model applicability. The model development is firstly discussed in terms of model formulation, their new features and geometry/regions considered. The model applicability is then discussed in terms of main findings followed by the model evaluation on their advantages and limitations. It is indicated that the three PCI models are all able to describe PCI operation qualitatively. The model of coal/coke combustion in a real BF is more reliable for simulating in‐furnace phenomena of PCI operation qualitatively and quantitatively. Such model gives a more reliable burnout prediction over the raceway surface, which could better represent the amount of unburnt char entering the coke bed. These models are useful for understanding the flow‐thermo‐chemical behaviours and then optimising the PCI operation in practice.

Experimental Investigation of the Combustion of Bituminous Coal in Air and O2/CO2 Mixtures: 1. Particle Imaging of the Combustion of Coal and Char

Combustion of a low-volatile bituminous coal in air versus two O2/CO2 mixtures (21/79 and 27/73, v/v) was conducted at two furnace temperatures of 800 and 1000 °C in a lab-scale drop tube furnace (DTF). Through in situ photographic observation and measurement of overall coal burnout rate, CO emission profile, and unburnt char properties, a variety of distinct phenomena relating to oxy-fuel combustion has been revealed. Consistent with the literature, the significant thermal effect of CO2 due to its large product of Cpρ (specific heat capacity and density) relative to that of N2 retarded volatile ignition in the two O2/CO2 mixtures. As a result, the volatiles released in O2/CO2 remained as a thick protective sheath on char surface for a relatively long duration, which mainly converted into CO through partial oxidation in 21% O2/79% CO2. Increasing the O2 fraction to 27% in CO2 triggered the ignition/oxidation of the unburnt volatiles once their concentrations were critically accumulated on char surface in ...

Effect of hot reducing gas (HRG) injection on blast furnace operational parameters: theoretical investigation

The injection rate of fossil fuels in the blast furnace is limited because of a drop in the flame temperature in the raceway as well as problems in deadman region and the cohesive zone owing to the unburnt char. An alternative option for coke saving, a clean deadman as well as increase in blast furnace productivity is injection of hot reducing gases (HRG) which are produced by low grade coal gasification or top gas recycling after CO2 and N2 removal. Calculations using a mathematical model show that HRG injection at higher temperature is desirable. Hot reducing gas injection is possible up to 300 Nm3 thm–1, above which the top gas temperature shoots up beyond practical limits. Furthermore, it also shows that if the flame temperature is maintained constant by varying steam and oxygen injection, the productivity is increased by 16% and coke rate is reduced by 84 kg thm–1 with the replacement ratio of 1˙4 kg coke/kg gasified coal at 300 Nm3/thm of HRG injection. It was also observed that the complete replacement of pulverised coal (PC) injection with HRG injection is more effective over the coinjection of PC and HRG in terms of coke rate saving. However, oxygen enrichment is possible up to 75% with the coinjection of HRG and PC, with a resultant of rise in productivity. Injection of HRG in the form of top gas (blast furnace gas) is more effective over the injection of HRG generated from coal gasification. The productivity is increased by 25% and coke rate is reduced by 83 kg thm–1 with the replacement ratio of 1˙7 kg coke/kg HRG at 250 Nm3 thm–1 of HRG injected from top gas.

Combustion of bio-oil ethanol blends at elevated pressure

This paper reports an investigation on the combustion performance of bio-oil/ethanol blends. Experiments were conducted in a constant volume vessel operating at a pressure of 25 bar and temperature 1100 K. Bio-oil produced via the fast pyrolysis of a spruce feedstock was blended to ethanol to form three stable blends containing 10%, 20% and 40% bio-oil by weight. In addition, ethanol and standard automotive grade diesel were tested as reference fuels. Measured vessel pressure was used in a single-zone heat release analysis, while two-colour optical pyrometry was used to investigate particle loading and temperature. Results show that for similar injections of fuel energy, use of up to 20% bio-oil in ethanol has limited impact on the performance of ethanol while 40% bio-oil in ethanol produced instability in the pressure trace near the end of the combustion process. Burning rates are similar for blends and ethanol. Addition of bio-oil to ethanol was found to increase combustion generated particle load, and this increased with bio-oil concentration, but remained much lower than particle concentration in diesel. Addition of bio-oil also resulted in formation of char particles that appear as luminous clusters outside the boundary of the spray. This suggests these particles will cool rather than oxidize. The presence of unburnt char particles in large numbers may have consequences for bio-oil as an alternative diesel fuel.

Problems in PFBC boiler (2): characterization of bed materials found in a commercial PFBC boiler at different load levels

Bed materials sampled from a commercial pressurized fluidized bed combustion (PFBC) of coal boiler at different loads of 270 and 285 MW output levels (bed materials; namely BM270 and BM285, respectively) were characterized in term of their morphology, composition, and thermal properties, since the operation at a little higher output suffered the problem of poor fluidization, resulting in a shutdown due to the slagging at the bottom of the boiler. BM270 was uniform grains with diameter around 3–5 mm, consisting principally of CaCO 3 grains, which carried fine calcium aluminosilicate particles on their surface. In contrast, BM285 carried much larger grains among grains similar to BM270. The larger grains were classified into two groups, sintered egg (SE) and agglomerated grain (AG). The former grains were fused as well as adhered fine particles of calcium oxide and aluminosilicate, while the latter grains were adhered ones without extensive fusion. Higher temperature at a particular location occurring in 285 MW output operation may accelerate the calcination of CaCO 3 forming CaO. Yellow particles present dominantly in BM285 adhered each other to form AG. Low viscosity of melted calcium aluminosilicate formed the smooth surface of BM285 yellow particles that carried more numbers of very fine aluminosilicate. CaO particles successively adhered through SO 2 absorption to the half-solidified surface, forming porous surface of CaSO 4 found over AG. AG was degraded into fines particles when saved in the air atmosphere. CaO particles which bridged the BM285 yellow particles in AG may lose their binding force through their hydration into Ca(OH) 2 by absorbing humidity. Bed materials and ash particles are locally heated and softened to form SE through softening and adhesion of powder materials such as very fine calcium oxide, alumina, and silicate particles into a compact grain. Unique properties of very fine particles must be clarified. Unburnt char particles were found among the BM285, providing with another evidence of poor fluidization once larger grains are produced. A little more charge rate of feed at 285 MW output may critically increase the chance of poor heat dispersion at some locations, causing the agglomeration of bed materials and coal ash, which leads to the poorer fluidization first locally and then in the whole boiler.

Assessing the internal state of the raceway/dead man part of the blast furnace at low coke rate : Negro, P. et al. European Commission, [Report] EUR, 2002, 1–309

The principal aims of this project were to study the blast furnace hearth and raceway behaviours in case of low coke and high coal rates operations. The different partners of this project have used their own possibilitiesand devices installed on several industrial blast furnaces. Using the tuyere coke sampling devices, it has been established that : - with coal injection rates ranging from 50 to 200 kg/thm, significant differences were apparent in the drill core structures. In the cases of lower coal injection rates, the drill cores incorporated lower levels of coke fines and iron/slag and were much less compacted than those achieved in cases of high coal injection rates. With high coal injection, the fines content increases just behind the bird nest ; - with high coal injection the raceway length becomes lower showing that the permeability of the dead man boundary becomes also lower ; - the fines sampled along the coal along the tuyere radius when using different coke qualities did not show any accumulation of unburnt coal in the dead man or at the outer shell of the dead man. However, the fines are made of three carbon phases with different level of organisation as graphite and coke. The graphite content in the fines was higher with high coal injection rates, near the raceway and in the smaller fraction. Nevertheless, the origin of the graphite fines is till now uncertain ; - the study of the unburnt char by sampling dust and gas at different positions along the height at the wall and the radius at the top of the furnace when using different coke qualities showed very different results : - the Coke contents in dust rise in the blast furnace from top to bottom in accordance with the increasing thermochemical demand on the coke, when using feed coke with low CSR values. In the case of using coke with high CSR values there is no increase in the Cake content in the dust, i.e. this coke shows a lower degradation mainly in the lower part of the furnace. This has been also confirmed by calculation of the coke degradation inside the blast furnace issued from coke core borings results. More over, hot strength measurements on coke from the tuyere level show higher values with higher CSR values of feed coke in the raceway, in the transition zone and in the dead man. This fact is of great importance because the stress on coke is not finished in the tuyere level ; - in the case of centre coke charging operations, the maximum C c o a l contents in the dust appear in the lower furnace area and in the upper shaft. Both maximum contents are attributable to transverse flows from the furnace centre, where the highest concentrations of unburnt coal particles are measured. The trials with feed coke with a higher hot strength show lower C c o a l contents in the dust despite of higher coal rates. This means a more uniform gas flow when charging cokes with high CSR values.

E208 PREDICTION OF INFLUENCE OF OPERATING CONDITIONS ON GASIFICATION PERFORMANCE OF ENTRAINED FLOW AIR BLOWN COAL GASIFIER

Deeply understanding of phenomena in a coal gasifier is very useful for an assessment gasifier performance and for an optimization of a design and operation parameters. In this paper, influence of operating conditions, such as oxygen concentration in oxygen enriched air as a gasifying agent and steam flow rate, on gasification performance of an entrained flow air blown coal gasifier is discussed. A numerical simulation, three-dimensional gas-particles reacting flow calculations were carried out to predict gasification performance of the gasifier. As a target of this simulation, the 2 tons/day (T/D) coal gasifier of CRIEPI was selected. The gas phase properties are calculated by three dimensional time-mean Eulerian conservation equations. The turbulent flow field is determined by the κ-ε two equations model. Radiative energy transfer is calculated by the discrete transfer radiation model. The pulverized coal and ash particle behavior is modeled via a Lagrangian manner. Coal gasification reaction model is constited by three chemical processes in the current model; a pyrolysis, a char gasification and gas phase reactions. Per pass gasification performance were only taken into account in the calculation (without unburnt char recycle system). The model result of the per pass carbon conversion efficiency increases as the oxygen concentration in gasifying agent increases. The per pass carbon conversion efficiency hardly changes even if the steam flow rate increases in the same oxygen concentration condition. The current model is potentially powerful tool for the evaluation of gasification performance.