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The outlet velocity field of the pulverized coal burner is one of the important factors affecting its operating characteristics. In this article, cold tests were carried out for a new swirl burner ...

The differences in the gas thermophysical properties (including heat capacity, thermal conductivity and diffusivity) between char combustion in wet and dry environments have remarkable influences o...

In order to explain the influence of the coal ash on the combustion characteristics of coal, the physical and chemical structures of pulverized coal with different ash contents were compared and analyzed, and the combustion characteristics and kinetics of pulverized coal were systematically studied by non-isothermal thermogravimetric analysis. The results show that the physical and chemical structure of the deashed coal is not significantly changed compared with the raw coal. The combustion process of the deashed coal gradually moves to the high temperature zone, and the combustion performance is obviously weakened. The comprehensive combustion characteristic parameters of the three samples can be arranged as: raw coal > primary deashed coal > secondary deashed coal. In this study, the RNGM model was used to analyze the combustion kinetics of pulverized coal, and the fitting effect is good. And there is a significant kinetic compensation effect in the combustion process. After calculation, the activation energy value of the samples is between 16.15~29.51 kJ/mol. The RNGM model can effectively characterize the various stages of the combustion reaction and validate the experimental results.

An improved experimental methodology is presented that provides combustion data of single pulverized coal and biomass particles with a high level of detail. This is the first part of a two-article ...

In the present article, CFD simulation of various oxy-fuel combustion cases has been performed to find out the influences of oxy-fuel combustion environment on temperature distribution, char consum...

Carbon capture and storage employing oxy-fuel combustion is one of the most promising options to reduce greenhouse gas emission. For the transition from conventional air-fired combustion to oxy-fue...

In the tangential combustion of a pulverized coal boiler, the swirl number is the key design index for evaluating the flue-gas temperature deviation at both sides of the furnace outlet. However, th...

Aiming at the wide adoption of flue gas recirculation (FGR) in coal power plants for NOx removal and CO2 capture, and the imperfect removal of particulate matters (PMs), especially ultrafine PMs wh...

The surrounding atmosphere of coal particles changes continually during the combustion process in pulverized coal boilers. A part of noncombustible mineral composition in char will be melted under ...

Four-wall tangential firing (FWTF) is a newly developed furnace arrangement used in supercritical and ultra-supercritical 600-MW boilers. In this study, flow characteristics of the flue gas in furnace of a 660-MW boiler firing pulverized coal with FWTF arrangement were investigated through numerical simulations. The variation characteristics of the tangential circle size of the furnace and flue gas bias at the furnace exit were determined. The results show some differences in the flue gas characteristics between the FWTF and traditional four-corner tangential firing (FCTF) in the furnace. In the FWTF, the variation in the actual sizes of the tangential circle in the burner zone is insignificant; the maximum size with respect to geometric limitations is largely maintained. Hence, unlike conventional FCTF, the size of the tangential circle cannot be used as a reliable parameter to analyze the variation in flue gas characteristics in the FWTF. Moreover, the flue gases are uniform and have high fillin...

A numerical study of flameless combustion with mixtures of methane and a sub-bituminous pulverized coal was carried out. The analyzed mixtures were 0%, 25%, 50%, 75%, and 100% pulverized coal (ener...

The pyrolysis characteristics of pulverized-coal particles in a hot turbulent nitrogen jet were investigated using large-eddy simulation (LES). In the present study an advanced pyrolysis model, the chemical percolation devolatilization (CPD) model, has been incorporated into LES in real time. The simulation results of the developed online-CPD-coupled LES were used to calibrate the kinetic parameters of the conventional single first-order reaction model (SFOM). Through the comparison between the CPD-coupled LES and the LES using the SFOM model, the CPD-coupled LES approach is found to be able to give a better prediction on particle pyrolysis in the high-temperature turbulent flow. Finally, the effects of important parameters, including the particle diameter, coal type, coal-feeding rate, carrier-phase velocity, and pyrolysis temperature, on the pulverized-coal pyrolysis process were investigated through parametric studies using the online-CPD-coupled LES method.

Two Pakistani crop residues bagasse (B) and wheat straw (WS), both with high ash content, were milled to

The unburned carbon (UBC) content of ash from coal-fired thermal power stations and plants that use massive amount of coal can sometimes be 6-7% or more; this simply means loss of carbon and decrease in efficiency. Carbon loss not only causes a decrease in efficiency but is also an economical issue. Decreasing the carbon content would provide the usage of ash from thermal power stations as cement additives. Many factors cause low combustion efficiency and a high amount of UBC. In the course of this study, fly ash and bottom ash were divided into size fractions and accumulation of UBC at coarser size fractions was observed. In this study, a ground coal sample from a mill was sieved, and the accumulation of UBC at coarser size fractions was associated to a lack of grinding of pulverized coal. Ground coal has a size distribution where 54.45% was below 75 µm, and 45.55% was still over this critical size. A significant amount (35.48%) of the UBC accumulated in the size fraction over 75 µm in fly ash, whereas almost 70% accumulated in the size fraction over 0.5 mm in bottom ash. Coal and ash samples were observed under a microscope to deduce origins of UBC. © 2016 Taylor & Francis.

The main objective of this study was to conduct the combustion process of selected wood fuels in a low-temperature bottom-combustion water boiler, while analyzing combustion gases for the presence of CO, NOx, and SO2 at respective combustions stages. In research conditions, substantial CO, NO, and SO2 emissions to the atmosphere were observed, especially during the combustion of fuels characterized by finer grains (sawdust) and susceptible to the evaporation of volatile content—coniferous-tree wood. Nevertheless, the first and third stages of combustion when using biomass for power generation, under counter-current combustion conditions in bottom-combustion boilers, are accompanied by problematic emissions—mainly of CO. Therefore, such heating devices require an improved airflow, and, in the case of using an electronic combustion controller, more-precise algorithms controlling airflow to the boiler should be devised.

An online coal calorific value prediction method through combustion radiation monitoring for industrial boilers was presented. Multiband combustion radiation signals in visible, infrared, and ultraviolet ranges were monitored. Multi-scale variables were extracted from the signals as flame radiation features in time and frequency domains. Principal component analysis (PCA) was used to eliminate information redundancy and noise disturbance. Correlation between obtained key principal components and the coal calorific value was established by training a support vector regression (SVR) model. Particle swarm optimization (PSO) and genetic analysis (GA) methods were used to search for the best SVR construction parameters. Performance test results showed that the optimized PCA+SVR model-based coal calorific value prediction results had a mean error of 110.9 kcal/kg relative to the lab analysis results, while the standard deviation (STD) was 151.9 kcal/kg. In order to reveal dynamic correlations among the multi-sc...

Coal ash deposits were collected in a 160 kWth, down-fired oxy-coal reactor under staged and unstaged conditions for four different coals at two locations. The deposits were embedded in epoxy for imaging and element composition analysis using scanning electron microscopy equipped with energy dispersive spectroscopy (SEM-EDS). Particles were found to be categorized into four groups: non-porous non-molten mineral matter, unburned coal/char, porous non-molten mineral matter, and molten mineral matter. Near burner deposits on the upstream side of tubes in cross-flow contained all four types of particles. Downstream deposits contained primarily molten mineral matter, approximately an order of magnitude smaller in size. No measureable chlorine (greater than 1%) was found in the deposits. Sulfur was observed to correlate with coal calcium content in oxidizing regions. The only major difference between the air and oxy-combustion deposits measured previously was the sulfur concentration; deposits collected with ox...

Using an IFA300 constant temperature anemometer system, cold air experiments on a quarter-scaled burner model sited in a 300 MWe down-fired boiler were conducted to investigate the influence of various inner secondary air vane angles on the flow characteristics in the burner nozzle region. By increasing vane angles, no central recirculation zone appeared, the axial velocity decay rate increased, radial velocities increased at the jet boundary, and tangential velocities clearly increased in the inner secondary air zone. Industrial experiments were also performed on a down-fired pulverized-coal 300 MWe utility boiler with swirl burners. Gas temperature, concentrations of gas components (O2, CO, and NOx) in the burning region, and carbon content in the fly ash were measured with inner secondary air vane angles of 42°, 47°, 53°, and 60°. By increasing vane angles up to 53°, NOx emission and boiler efficiency increased; when vane angles were increased to 60°, NOx emission increased, but boiler efficiency decre...

To overcome the problem of high carbon content in the fly ash of down-fired utility boilers using low-volatility coals, the combustion system of a 660 MWe full-scale down-fired boiler was retrofitted, with the direction of the secondary air under the arch being changed from horizontal to an angle of declination of 20°. Industrial experiments were performed using the boiler before and after the retrofit to determine the reconstruction effect. Data are reported for the gas temperature distribution along the primary air and coal mixture flow, furnace temperature, gas compositions, such as O2, CO, CO2, and NO x , and gas temperatures in the near-wall region. Comparisons between the two cases were made, and the results show that with the angled secondary air under the arches, ignition of the primary air and pulverized coal mixture was brought forward in the boiler. Gas temperatures rose in the fuel-burning zone, and the residence time of pulverized coal in the fuel-burning zone was extended. Thus, the quantity...

The major drawbacks of coal combustion are connected with the large emission of particulate matter. This paper deals with the experimental investigation of ultrafine (D100nm) and nano (D10nm) ashes formed during conventional high temperature pulverized coal combustion on a laboratory-scale reactor. The reactor consists of an atmospheric pressure laminar premixed flame homogeneously doped with pulverized coal particles, monodisperse in size. It allows the investigation of the early stage of ash formation. Generated aerosols, sampled using high dilution probes, are conveyed into high resolution Differential Mobility Analyzers (DMA) to perform on-line measurements of the size distribution function of ultrafine ashes. Two DMA systems are used: the first is equipped with a Faraday cup electrometer detector and identifies particles as small as 1nm, and the second is equipped with a condensation nucleus counter and exhibits 3nm lower detection limit. Measurements have been performed at several dilution ratios to understand the nature and behavior of detected particles. Results indicate that nanosized coal ashes are formed during pulverized coal combustion. They are the most abundant in number and also a significant fraction of ultrafine ash mass, implying they should be detected at the exhaust of pulverized coal furnaces.

A new approach to modeling NOX under oxy-fuel combustion conditions in a simple staged-oxidizer flow field is presented. The approach is centered on the combination of devolatilization and char oxidation models with a detailed kinetic mechanism for light hydrocarbon combustion. NOX chemistry is included by the user's selection of the detailed mechanism, while the devolatilization model consists of the chemical percolation devolatilization (CPD) model modified to be independent of oxidizer composition. Literature-based correlations provide elemental composition of the volatiles. Model predictions were compared to experimental measurements with good agreement in several respects. The model provides insights for the interpretation of experimental oxy-fuel combustion NOX results, and recommendations are given for computational fluid dynamics (CFD) modeling of NOX in oxy-fuel combustion.

Numerical analysis was used to study the deposition and burning characteristics of combining co-combustion with slagging combustion technologies in this paper. The pyrolysis and burning kinetic models of different fuels were implanted into the WBSF-PCC2 (wall burning and slag flow in pulverized co-combustion) computation code, and then the slagging and co-combustion characteristicsespecially the wall burning mechanism of different solid fuels and their effects on the whole burning behavior in the cylindrical combustor at different mixing ratios under the condition of keeping the heat input samewere simulated numerically. The results showed that adding wood powder at 25% mass fraction can increase the temperature at the initial stage of combustion, which is helpful to utilize the front space of the combustor. Adding wood powder at a 25% mass fraction can increase the reaction rate at the initial combustion stage; also, the coal ignitability is improved, and the burnout efficiency is enhanced by about 5% of suspension and deposition particles, which is helpful for coal particles to burn entirely and for combustion devices to minimize their dimensions or sizes. The results also showed that adding wood powder at a proper ratio is helpful to keep the combustion stability, not only because of the enhancement for the burning characteristics, but also because the running slag layer structure can be changed more continuously, which is very important for avoiding the abnormal slag accumulation in the slagging combustor. The theoretic analysis in this paper proves that unification of co-combustion and slagging combustion technologies is feasible, though more comprehensive and rigorous research is needed.

An experimental work was performed to investigate the co-firing of pulverized coal and premixed gas/air streams in a double swirl combustor. The results showed that the NOx emissions are affected by the relative rates of thermal NOx formation and destruction via the pyrolysis of the fuel-N species in high temperature fuel-rich zones. Various burner designs were tested in order to vary the temperature history and the residence time across both coal and gas flames inside the furnace. It was found that by injecting the coal with a gas/air mixture as a combined central jet surrounded by a swirled air stream, a double flame envelope develops with high temperature fuel-rich conditions in between the two reaction zones such that the pyrolysis reactions to N2 are accelerated. A further reduction in the minimum NOx emissions, as well as in the minimum CO concentrations, was reported for the case where the coal particles are fed with the gas/air mixture in the region between the two swirled air streams. On the othe...

Measurements were performed in a 300-MWe wall-fired pulverized-coal utility boiler. Enhanced ignition-dual register (EI-DR) burners and centrally fuel rich (CFR) swirl coal combustion burners were installed in the bottom row of the furnace during experiments. Local mean concentrations of O2, CO, CO2 and NO x gas species, gas temperatures, and char burnout were determined in the region of the two types of burners. For centrally fuel rich swirl coal combustion burners, local mean CO concentrations, gas temperatures and the temperature gradient are higher and mean concentrations of O2 and NO x along the jet flow direction in the burner region are lower than for the enhanced ignition-dual register burners. Moreover, the mean O2 concentration is higher and the gas temperature and mean CO concentration are lower in the side wall region. For centrally fuel rich swirl coal combustion burners in the bottom row, the combustion efficiency of the boiler increases from 96.73% to 97.09%, and NO x emission decreases fro...

This article describes an experimental and numerical investigation of a black liquor recovery boiler from a pulp industry. Measurements are reported for major gas-phase species concentration and temperature in a representative horizontal plane across the furnace cross-section for different operating conditions. Overall, the experimental data reveal that the use of an interlaced secondary air distribution mode leads to important gradients from the back wall to the boiler nose, while the use of a rotational air distribution mode leads to more important differences between the left and right side of the furnace, in spite of the values being more uniform. A numerical model, previously available to simulate pulverized coal combustion, was adapted to simulate the combustion process of black liquor. The simulation of the droplets decomposition is based on empirical models from literature followed by the consideration of heterogeneous reactions for both the entrained droplets and the ones that fall on the smelt b...

This work pertains to the high-temperature combustion of pulverized coal chars under oxygen-enriched atmospheres. Single char particles were burned in a drop-tube furnace, electrically-heated to 1300–1500 K, in 21%, 50% and 100% O2, in a balance of N2. Their luminous combustion histories were observed with two-color ratio pyrometry. A solution of the Planckian ratio-pyrometry equation for temperature was implemented, extending on Wien's approximation. The temperature and time histories for 45–53 µm bituminous chars experienced wide particle-to-particle disparity, and varied depending on oxygen mole fraction and furnace temperature. Average char surface temperatures increased from 1600–1800 K in air, to 2100–2300 K in 50% O2, to 2300–2400 K in 100% O2, at gas temperatures of 1300–1500 K, respectively. Combustion durations decreased from 25–45 ms in air, to 8–17 ms in 50% O2, to 6–13 in 100% O2. Thus, average particle temperatures increased by up to 45%, whereas burnout times decreased by up to 87%...

This study formulates a global NOX submodel for deployment in CFD simulations from a database on flames of three diverse coals at pressures to 3.0 MPa for broad ranges of stoichiometric ratio (S.R.). A new reaction scheme was formulated from a sensitivity analysis of simulations based on detailed reaction mechanisms for all tests. It shares many elements in common with commercial submodels, yet it correctly predicts that (1) less coal-N is converted into NO; and (2) HCN persists to higher S.R. for progressively higher pressures. Explicit dependences on O2 concentrations are responsible for the first feature, because the variations in O2 concentrations mimic the ways that the oxyhydroxyl radical pool shrinks at progressively higher pressures, which shifts HCN conversion toward N2 production. The second feature was depicted by resolving the intermediate products of HCN decomposition in the global scheme. Discrepancies surfaced when the new submodel was applied to different coals without re-adjustin...

This paper describes an experimental and numerical investigation on the co-combustion of propane with pulverized coal, pine shells, and textile wastes. Measurements have been performed in a large-scale laboratory furnace fired by an industrial-type swirl burner. Data are reported for in-flame major gas-phase species concentration, including NOx, in-flame gas temperature, and overall char burnout for three flames: a propane/coal flame, a propane/pine shells flame, and a propane/textile wastes flame. For comparison purposes, data are also reported for a pure propane flame. The experimental results show that CO and unburned hydrocarbon emissions from propane cofiring with pine shells and textile wastes can be important due to the relatively large sizes of the solid particles and that NOx emissions data reproduce the impact on them of the fuel nitrogen content via fuel-NO formation for the three solid fuels studied. Also, the cofiring of propane with pine shells and textile wastes yields particle burnout valu...

In an air-particle test facility, a three-dimensional particle-dynamics anemometer was used to measure air particle flows in the near-burner region of the radial bias combustion burner. With the increase of nonswirling secondary air (SA) ratio, the air and the particle divergent angles greatly decrease. Both the diameter and the length of the central recirculation zone decrease and the peak value of particle volume flux near the burner axis increases. The reacting flow experiment shows that oxygen concentration decreases while CO and NO x concentrations increase in the burner central zone when the nonswirling SA ratio increases. The application of the nonswirling jet of the secondary combustion air results in a substantial reduction in carbon-in-ash content.

The thermochemistry of the combustion of a blend of coal and 5% petroleum coke was analyzed. Thermodynamic modeling and microscopic techniques were used to study the behavior of the inorganic constituents upon combustion of the blend of coal and petroleum coke. The chemical composition and phase constitution of the combustion products, as well as the deposits at several temperatures corresponding to those at the various parts of the boiler, were deduced by free-energy minimization. These results were compared with actual results obtained from a commercial pulverized fuel boiler fired with coal and petroleum coke blend. The deposits on the fireside surfaces of the boiler tubes in the various parts (water walls, platen superheater, final superheater, economizer, and electrostatic precipitator) of the commercial pulverized fuel boiler fired with coal and 5% petroleum coke were characterized by particle size analysis, chemical analysis, x-ray diffraction, optical microscopy, and scanning electron microscopy. ...

The amount of unburned carbon in ash is an important performance characteristic in commercial boilers fired with pulverized coal. Unburned carbon levels are known to be sensitive to fuel selection, and there is great interest in methods of estimating the burnout propensity of coals based on proximate and ultimate analysis--the only fuel properties readily available to utility practitioners. A simple numerical model is described that is specifically designed to estimate the effects of coal selection on burnout in a way that is useful for commercial coal screening. The model is based on a highly idealized description of the combustion chamber but employs detailed descriptions of the fundamental fuel transformations. The model is validated against data from laboratory and pilot-scale combustors burning a range of international coals, and then against data obtained from full-scale units during periods of coal switching. The validated model form is then used in a series of sensitivity studies to explore the ro...

An integrated method is evaluated for simultaneously reducing NO x , SO 2 , and particulate emissions from power plants. The method combines dry-sorbent injection for SO 2 concentration reduction, coal injection for NO x emission reduction, in conjunction with a ceramic honeycomb filter for particulate capture. The filter is mounted in an elevated temperature region where it retains sorbent particles for prolonged periods of time and facilitates their utilization until it is regenerated (cleaned). The performance of low-cost commercial sorbents, such as calcium carbonate, CaCO 3 ; calcium hydroxide, Ca(OH) 2 ; calcium oxide, CaO; and sodium bicarbonate, NaHCO 3 , was evaluated in the laboratory. The sorbent powders were blended with three types of pulverized coal to achieve NO x reduction (bituminous, subbituminous, and lignite coal) and results were contrasted with the performance of the higher-cost porous sorbent calcium formate, Ca(COOH) 2 . The sorbents were injected in a simulated effluent gas contai...

Measurements have been performed in a 300-MW e , front-wall-fired, pulverized-coal utility boiler. New data are reported for local mean gas species concentrations of O 2 , CO, CO 2 , and NO x , gas temperatures, and charburnout measured at several ports in the boiler including those in the burner region. They complement previously obtained data in the same utility boiler before being retrofitted with low-NO x burners and over-fire air ports. During the current experimental work, a considerable effort was made to assure minimum variations on boiler operating conditions and coal chemical and particle size characteristics so that the data presented are especially useful for three-dimensional mathematical model evaluation and development. The main conclusions are as follows: (1) As compared with our previousmeasurementsin this boiler, prior to the retrofitting, the results show lower local mean O 2 and higher CO concentrations and temperatures in the boiler as a consequence of the lower stoichiometry in the m...

Experimental and modeling investigations have been performed on the co-combustion of a traditional fossil fuel and a tire residue. The experimental runs have been carried out using a pilot-scale vertical furnace (0.5 MW) with a burner for pulverized solid fuels. Different conditions have been set up for the co-combustion of a medium volatile bituminous coal and a tire residue. The scope was to test the feasibility of burning secondary fuels (biomasses and residues) with coals using a low NO x burner developed for pulverized coal in the ENEL Research Centre. A co-combustion model was developed for interpreting the results and extrapolating kinetic parameters to practical conditions. It considers the effect of the particle size distribution, the different reactivity, and, in general, the different combustion behavior of each fuel fed to the furnace. The kinetic scheme adopted is simple and the introduced assumptions allow easy coupling with computational reactive fluid dynamic codes. Fuel conversion, oxygen...

This paper discusses the development of specialized subroutines used in a Computational Fluid Dynamics code (FLUENT™) to accurately predict temperature, velocity, and species profiles in a down-fired, pilot-scaie, pulverized coal combustor and in the t-fired industrial boiler. A Lagrangian particle tracking algorithm, along with an advanced char burnout kinetic (CBK) model, was used to accurately predict the representative particle trajectories, as well as the loss of carbon from coal particles. The devolatilization and burnout parameters for the full-scale industrial combustion model were generated using the first principles and the combination of drop-tube/pilot-scale experiments. Additionally, the moisture that evolved from coal/biomass char heating is included via surface reactions, which accounts for char

A numerical study for simulating a swirling pulverized coal combustion in axisymmetric geometry is carried out here by applying the weighted sum of gray gases model (WSGGM) approach with the discrete ordinate method (DOM) to model the radiative heat transfer equation. In the radiative transfer equation, the same polynomial equation and coefficients for weighting factors as those for gas are adopted for the coal/char particles as a function of partial pressure and particle temperature. The Eul-erian balance equations for mass, momentum, energy, and species mass fractions are adopted with the standard k-ϵs turbulence model, whereas the Lagrangian approach is used for the particulate phase. The eddy-dissipation model is employed for the reaction rate for gaseous mixture, and the single-step first-order reaction model for the devolatili.ation process for coal. By comparing the numerical results with experimental ones, the radiation model used here is confirmed and found to provide sound alternative for simula...

The Australian Coal Industry Research Laboratory (ACIRL) furnace is scaled to simulate slagging and fouling in operating boilers. This requires that the gas and target temperatures, the heat flux, and the flow pattern be the same as those in real boilers. The gas and target temperatures are maintained by insulating the wall and cooling the target respectively. The flow pattern of a small burner cannot be the same as a large furnace. However, this flow pattern is partially compensated for by placing the slagging panels in three vertical locations. The paper develops the models of radiant heat transfer from the flame to the deposits both in pilot-scale and full-scale furnaces. They are used to compare the effective radiant heat transfer of the pilot- and full-scale furnaces. The experimental data both from the pilot- and full-scale furnaces are used to verify the incident heat flux and temperature profiles in the pilot- and full-scale furnaces. The results showed that the thermal condition in the pilot-scale furnace meets the requirements for studying the slagging regarding the gas temperature and the incident heat flux, particularly for the panel #1. The gas temperature in the convective section also meets the requirement for studying the fouling.

The effect of the Precessing Jet flow-field on the coal burnout, gas species concentrations (CO, NO, SO2, N2O) and gas temperature of a pulverised coal flame was investigated. Two burner arrangements were used with a central Precessing Jet nozzle for air or gas supply inside an annulus for coal delivery. Four flames were examined of heal input of 110-140 kW. The flames were compared with 110 kW flames from the literature. It was deduced that the Precessing Jet nozzle can be used to make a monochannel flame approach the profiles of coal bumout, concentration of CO and gas temperature of a swirl-stabilised flame, without the need for swirling the secondary air and quarl application. Furthermore, the flue gas emissions of NO did not exceed 43% of the levels expected for a swirt-stabi-lised coal flame of similar thermal load, while the emissions of N2O were negligible.

A new type of pulverized-coal combustor, called "Wall-Protecting-Jets Combustor" (hereafter, WPJC has been proposed, designed and studied with both CFD (Computational Fluid Dynamics) and experimental methods. The WPJC is based on a novel concept in which all inlet jets are along the combustor wall. Pilot combustion experiments were conducted to investigate the combustion performance of WPJC. Two-phase flows and pulverized-coal combustion were simulated to study the mechanism of),WPJC using the commercial software FLUENT. The results show that the WPJC has many remarkable advantages: wall-protection by the cold jets without the use of refractory materials; low-temperature and three-stage combustion with low NOx emission; negligible ash/slag-deposition; multiple functions with convenient switching between them; effective adjustment of the combustion intensity and the ignition position.

Blended coal that consists of 70% anthracite and 30% bituminous coal is cheaper than pure bituminous coal, but it is very difficult to bum in the revolving cement kiln. To bum the blended coal, a new kind of burner, which is called the burner with velocity difference jets, is used. The combustion processes in the revolving cement kiln are simulated by means of improved multi-fluid model for two-phase turbulent flows with reaction. The better burner construction is decided by simulation, which should not only ensure the ignition and stable combustion for blended coal but also restrain the expansion of pulverized coal flow and make flame not touch the slagging layer of kiln. The results of integral simulation show that the ignition of blended coal is slower than that of bituminous coal, but the flame of blended coal is longer than that of bituminous coal. Thus the use of blended coal not only reduces the cost but also suits wet kiln better

A low volatile coal was burned with oxygen-enriched air in a drop tube furnace at 1223 and 1523 K, either as single particles or as small batches added as a pulse. The particle temperatures and burnout times at the two furnace temperatures were recorded for each test. The ignition / combustion processes were recorded by pyrometer and video camera. The pulsed batch burnout times were ten to twenty times longer than the single particle times, indicating that cloud combustion was taking place. A mathematical model of the transient behaviour of the batch combustion process was developed, based on plug flow. Effects arising from volatile combustion were apparent in the visualisations but were ignored in the modelling. Burning was predominantly under diffusion control especially at high oxygen concentrations. The effect of particle segregation due to feeder performance and aerodynamic drag was simulated. From the dispersion of the particles, values of the local cloud combustion number G during burnout ...

Based on the influence of chemical equivalence ratio on the combustion stability of utility pulverized coal-fired boilers and the control theory about system stability, a combustion stability index, CSI, which refers to the maximum reduction ratio of the fuel mass flow rate that can be overcome by the stable combustion process under a constant air mass flow rate, was proposed to assess quantitatively the combustion stability in the boilers. MLO, the Minimum Load of Operation with stable combustion not supported by firing oil, and MCQ, the Minimum Coal Quality, which gives the lowest heat values of coals with different volatile matter contents for stable operation of boilers, are defined on the basis of CSI. In order to predict MLO and MCQ, a simple chemical reaction system model has been modified by means of the concept of lean flammability of gaseous fuels. A three-dimensional combustion simulation code integrated with the modified model was used to study the stability of combustion process in a...

Previous coal combustion models using assumed-shape PDF's to treat turbulence-chemistry interactions have used only one progress variable to treat products from coal reactions. This assumes that the products of all coal reactions have the same composition. However, the composition of the combustion products of coal particles is known to vary with burnout, especially between devolatilization and char oxidation. In this work, two progress variables were implemented which distinguish between the products of devolatilization and those of char oxidation. This new approach requires as input the specified volatile content and elemental release during devolatilization. The values for these parameters were estimated based on elemental release data obtained in flat-flame burners. Predictions of the new and the old approaches for the major variables of the field were not appreciably different. However, NO pollutant predictions of the new method were, in general, better than those of the old method, particul...

A two-color Laser Doppler Anemometer (LDA) was used to obtain axial and tangential velocity information in a 0.2 MW pulverized coal flame. In addition to the reacting flow data, a study on the accuracy of using coal as a seed panicle to measure gas phase velocity using LDA was performed. Non reacting flow velocity measurements were also obtained near the fuel inlet and in the quarl region of a geometrically identical burner to identify the velocity profile at several burner settings and to assist in establishing modeling inlet conditions. Both the reacting and non reacting velocity data were obtained at three or more swirl settings and various axial positions allowing a study of the affect of swirl on inlet turbulence and flame structure. The velocity results were compared with effluent NOx measurements. At the flow rates and accelerations experienced in this study, the coal particles were shown to be useful as seed particles for LDA gas phase velocity measurements. The coal-flame velocity indicated a cen...

A study of detailed species, velocity and temperature data of a pulverized coal flame is important to understanding the mechanisms which sustain the flame and lead to the formation of various pollutants such as NOx. The data can be particularly useful when compared to comprehensive combustion models which encapsulate the sub-models and processes of combustion. This data set contains in-situ axial and radial temperature, velocity and species concentrations for three swirl ratios of a pulverized coal flame located in a cylindrical, down-fired, 0.2 MWt reactor. Species measurements include CO, CO2, NO and O2. Velocity measurements were obtained using Laser Doppler Anemometry (LDA) and are summarized here after the method and results were reported in detail in a companion paper. The data show the change in structure of the coal flame as swirl is increased. At zero swirl the flame was located along a centerline jet, but as swirl increased, a recirculation zone was created which carried the combustion products ...

A novel pulverized coal fired burner, called “main burner with double primary air channels for pulverized coal”, is presented in this paper. Such a burner can burn various kinds of coals, including bituminous coal, low grade coal, lignite, semianthracite, anthracite, satisfying stability of combustion, controllability of the ignition location of pulverized coal, high efficiency, and low NO x , emission, thereby eliminating the unstable combustion caused by variation of coal quality and low load operation. It has not only solved the problem of low load operation and the combustion without oil assisting of Jiafu anthracite, which is the most difficult coal to burn in China, but also first successfully conducted the normal combustion in a tangentially pulverized anthracite fired furnace, as in a W-shaped flame furnace. According to the low load test on a tangentially pulverized coal fired furnace of 1025 t/h of anthracite combustion, its stability is superior to that of a W-shaped flame furnace with the same...

This is a laboratory investigation on the emissions from batch combustion of waste tire-derived-fuel (TDF) and coal in fixed beds. The goal was to compare the magnitude of the emissions of this mode of combustion to that of continuous combustion of streams of particles of the same fuels in pulverized form, conducted previously (Levendis et al., 1996; Levendis et al., 1998). In the experiments herein waste tire chunks (in the range of 3-9 mm), tire crumb (180 212 μm) and bituminous coal (63-75 μm) were burned in a horizontal muffle furnace, at a gas temperature of 1000°C. The fuel mass loading in the furnace was varied; the residence time of the post-combustion gases was 1 s. At the exit of the furnace CO, CO 2 , NO,, polynuclear aromatic hydrocarbon (PAH) and particulate emissions were measured. Results showed that the PAH emissions from batch combustion of tire chunks were higher than those from tire crumb, which in turn were an order of magnitude higher than those from coal, under similar combustion conditions. Increasing the mass loading for both tire crumb and pulverized coal, increased the specific emissions of PAHs. Increasing the segmentation of the tire, at a fixed mass loading also increased the specific PAH emissions. Emissions of particulates closely followed the trend of PAH emissions. Batch combustion of tire chunks resulted in higher particulate yields than tire crumb, with pulverized coal a distant third. Specific CO emissions from batch combustion of TDF were an order of magnitude higher than those from coal combustion. For both fuels, CO emissions were detected during the release and combustion of the volatiles only. On the other hand, specific CO 2 , and, especially, NO x emissions from batch combustion oftire crumb were lower than those from coal. The comparison of the emissions of batch combustion of pulverized fuels in fixed beds with those of continuous combustion of streams of particles was conducted under laminar flow conditions, similar gas temperatures and similar post combustion residence times. Results showed that (i) the PAH and CO emissions of tire crumb were much lower in the latter mode of combustion, even at bulk equivalence ratios as high as 1.4; (ii) to the contrary, for coal the mode of combustion had little influence on the PAH and CO emissions.

By initiating chain reactions that consume NOx, CHi radicals play an important role in natural gas reburning. In conventional reburning, most of the methane is consumed in reactions with oxygen to form CO, and does not produce CHi- radicals as intermediate products, which limits NO reduction efficiency. Activating natural gas externally to the boiler may generate a mixture of CHi radicals by passing CH4 through a discharge before injection into the reburning zone. Five activation technologies are reviewed: microwave heating and discharge plasmas, electron beam irradiation-induced plasmas, corona discharge induced plasmas, and thermal plasmas. Wall, cyclone and tangentially fired boilers were considered in the economic assessment. From preliminary capital and operating cost estimates, pulse corona and electron beam techniques appear to be the most promising activation techniques

Particle data on a 160 MWe corner-fired, pulverized-coal fired boiler operated by New York State Electric and Gas (NYSEG) were collected as part of a comprehensive series of measurements taken to better understand the complex phenomena involved in pulverized-coal combustion, and to develop information suitable for model validation of comprehensive combustion codes. Changes in operating conditions involved variations in coal type, the amount of overfire air, load, and burner tilt. The measurements discussed include those of particle size, velocity, concentration, and an analysis of the concentration probability density function. The particle data were collected using the laser-based PCSV (Particle Counter Sizer Velocimeter) probe. PDF calculations were based on particle velocity distributions measured with the PCSV probe and particle data rate statistics measured with a frequency-to-voltage converter connected to the signal processing system. Measurements for this test series were collected primar...

In pulverised coal flames, the most important volatile nitrogen component forming NOx, is HCN. To be able to model the nitrogen chemistry in coal flames it is necessary to have an adequate model for HCN oxidation. The present work was concerned with developing a model for HCN/NH3/NO conversion based on systematic reduction of a detailed chemical kinetic model. Models of different complexity were developed and tested under conditions similar to those in a pulverised coal flame. Comparisons of the models were made for ideal chemical reactors simulations (plug flow reactor and well-stirred reactor). Provided that the CO/H2 chemistry was described adequately, the reduced HCN/NH3/NO model compared very well with the detailed model over a wide range of stoichiometries. Decoupling of the HCN chemistry from the CO/H2 chemistry resulted in over-prediction of the HCN oxidation rate under fuel rich conditions, but had negligible effect on the CO/H2 chemistry. Comparison with simplified HCN models from the l...