Coal-fired Furnace Research Articles

Calcium magnesium acetate and urea advanced reburning for NO control with simultaneous SO 2 reduction

Calcium magnesium acetate (CMA) shows potential as a reductant for simultaneous NO x and SO x removal from coal-fired combustion plant. The performance of urea co-injection with CMA on NO reduction in an ‘advanced reburn’ (AR) configuration has been investigated with a view to optimization of the process in a pulverized coal-fired furnace operating at 80 kW. The impact on SO 2 reduction has also been investigated. Urea/CMA solution was sprayed into the reburn zone of the furnace using twin-fluid atomizers over a range of reductant/NO stoichiometric ratios (NSR). The influence on NO reductions of primary zone stoichiometry ( λ 1) was investigated for a range of CMA reburn feed rates (Rff) and reburn zone stoichiometry ( λ 2). In addition, the effect of temperature on the SNCR performance of urea was investigated. Optimum process conditions were categorized either by maximizing NO and SO 2 reductions (Modes A and B, respectively) or maximizing reductant utilization efficiencies (Modes C and D). NO control was best performed at λ 1=1.05, but SO 2 reductions were greatest at more fuel-lean primary zone conditions ( λ 1=1.15). Highest NO reductions of 85% under AR-rich conditions were achieved under Mode A, but were only slightly higher compared with reductions of 79% under Mode B, where SO 2 reductions were optimized at 85%. N-utilization was also at an acceptable level of 25% compared to the maximum utilization efficiency which was obtained at NSR=1.5 of 30% for the same conditions of stoichiometry operating in Mode C. Operation at this lower level of reburn (9.6%) could significantly reduce the consumption of CMA with some impact on NO reduction (73%). SO 2 removal performance would be compromised severely with reductions lowered from 75% at Mode A to 35% at Mode C. Optimizing Ca utilization (Mode D) resulted in poor NO and SO 2 reductions, at 61 and 22%, respectively, and can be discounted as a viable option. The technique offers flexibility of operation depending on the emission control requirements.

Modeling Sorbent Injection for Mercury Control in Baghouse Filters: II—Pilot-Scale Studies and Model Evaluation

Activated carbon injection for Hg control in a 500-lb/hr pilot-scale coal-fired furnace equipped with a fabric filter for particulate control was evaluated at different operating conditions. The pilot-scale tests showed that Hg removal was improved at lower temperatures and higher C/Hg ratios. The two-stage mathematical model developed to describe Hg removal using powdered activated carbon injection upstream of a baghouse filter was used to obtain Langmuir isotherm parameters as a function of temperature by fitting the model to a subset of experimental data. The predictive capability of the model was then tested by comparing model calculations with additional experimental data from this system obtained using different operating temperatures and sorbent to Hg ratios. Model predictions were in good agreement with experimentally measured Hg removal efficiency. Based on the model predictions, Hg removal in the duct appears to be limited and higher C/Hg ratio, lower operating temperature, and longer cleaning cycle of the baghouse filter should be utilized to achieve higher Hg removal in this system.

Computational modeling of no x reburning by hydrocarbons in a coal furnace with reduced kinetics

Reduction technology of kinetic mechanisms has greatly increased the possibility of the detailed kinetic modeling of practical combustion problems and offers potential improvement of modeling accuracy in comparison with using global mechanisms. The current work applies a mechanism-reduction technology in conjunction with the CHEMKIN library and develops a reduced kinetics for NO x reburning with methane in coal-fired furnaces. Based on the full mechanism GRI 3.0 with 325 reactions and 53 species, a 38-species/100-reaction skeletal mechanism, and, further, a 16-species/12-step reduced mechanism were established. The reduced mechanism was implemented into the three-dimensional Computational Fluid Dynamics (CFD) program AIOLOS, which deals predominantly with pulverized-coal combustion processes. The eddy dissipation concept (EDC) model was used to consider the influence of turbulence on chemistry. A simulation series of the CH 4 reburning process in a coal-fired reactor was carried out. The modeling results are discussed and compared with experimental data. It is shown that the reduced mechanism and the comprehensive modeling give quite satisfactory results in a fairly wide parameter range, and that the computing time of the current reduced mechanism is approximately three times that using the traditional global mechanism.

Present status and tendency of the industrial furnaces for forging in China : Wang, B. Gongye Jiare, 2002, (1), 1–4. (In Chinese)

In the paper, the author presents the technical status of the fuels, furnace structure, burning devices, recuperation of residual heat refractories and thermal control etc. of the industrial furnaces for forging, as well as the tfendency of the reformation of coal-fired furnace and the high performace industrial furnaces for forging.

Detailed modeling of hybrid reburn/SNCR processes for NO X reduction in coal-fired furnaces

Mechanism reduction has made the detailed kinetic modeling of combustion problems much easier; it also offers potential improvement of modeling accuracy and flexibility in comparison to global mechanisms. The present work applies mechanism reduction in conjunction with the CHEMKIN library and develops an automatic reduction program code. Regarding the hybrid re-burn/selective non-catalytic reduction (SNCR) (“advanced re-burning”) conditions in coal-fired furnaces and based on a full mechanism “GADM98,” a skeletal mechanism with 39 species, 105 reactions, and further a 10-step/14-species reduced mechanism were established. The reduced mechanism was implemented into a 3D-combustion computational fluid dynamics (CFD) code. The eddy-dissipation-concept model was used to describe the influence of turbulence on the combustion chemistry. A large number of simulations for reburning and hybrid reburn/SNCR processes in a coal-fired reactor were executed; the predicted results were compared with experimental measurements. The reduced mechanism and the comprehensive modeling give quite satisfactory results over a wide range of mole ratios for β = [NH 3]/[NO] and air/fuel equivalence ratios λ 2 in the reburn zone. From the modeling results, it was found that adding ammonia premixed with reburn fuel (CH 4) effects no further reduction of NO x or even impairs the reduction efficiency compared to pure reburning, and in contrast, staged addition of ammonia downstream of the CH 4 injection in the reburn zone provokes a significant further reduction of NO x over a wide range of parameters. According to the predictions, NO x-reduction rates of 50–60% and of 70–80% can be achieved through pure reburning and hybrid reburn/SNCR approaches, respectively, at λ 2 = 0.95 and β = 1.5. Concerning the computational procedure, essential measures were taken to optimize convergence and computing time. The computing time with the present reduced mechanism is ∼2.5 times that with the traditional global mechanism for the same iteration number. Tabulation of the rate constants reduced the computing time of the reaction kinetics by ∼50%.

Experience with an ODS high-temperature heat exchanger in a pilot-scale HiPPS plant

A very high-temperature heat exchanger (HTHX) composed of MA754 alloy is being tested in a coal-fired slagging furnace system at the University of North Dakota Energy & Environmental Research Center. The HTHX was designed and built by the United Technologies Research Center. It is composed of three 6-foot-long by 2½-inch-od tubes which were originally protected from the products of combustion by ceramic panels. It was used to produce process air at 950°C and 150 psig over 2000 hours of testing with a variety of coals. For a short time, conditions of 1100°C and 100 psig were reached. In later tests the bare alloy tubes were exposed directly to the products of combustion which increased heat exchange coefficients by five times suggesting the HTHX cost would be only 1/10 as much as with the ceramic panels. Laboratory tests of the alloy exposed directly to the coal slag showed recessions of 5–10 mils per year at up to 1150°C. The data suggest that a cost competitive power system could be built employing this technology.

Numerical simulations of coal-fired furnaces using a vectorized Lagrangian particle model coupled with the discrete ordinates method

Numerical simulations of coal-fired furnaces using a vectorized Lagrangian particle model coupled with the discrete ordinates method

Materials science aspects of coal

Various semicokes were obtained from medium-low temperature pyrolysis of Dongrong long flame coal. The proximate analysis, calorific value and Hardgrove grindability index (HGI) of semicokes were determined, and the ignition temperature, burnout temperature, ignition index, burnout index, burnout ratio, combustion characteristic index of semicokes were measured and analyzed using thermogravimetry analysis (TGA). The effects of pyrolysis temperature, heating rate, and pyrolysis time on yield, composition and calorific value of long flame coal derived semicokes were investigated, especially the influence of pyrolysis temperature on combustion characteristics and grindability of the semicokes was studied combined with X-ray diffraction (XRD) analysis of semicokes. The results show that the volatile content, ash content and calorific value of semicokes pyrolyzed at all process parameters studied meet the technical specifications of the pulverized coal-fired furnaces (PCFF) referring to China Standards GB/T 7562-1998. The pyrolysis temperature is the most influential factor among pyrolysis process parameters. As pyrolysis temperature increases, the yield, ignition index, combustion reactivity and burnout index of semicokes show a decreasing tend, but the ash content increases. In the range of 400 and 450 °C, the grindability of semicokes is rational, especially the grindability of semicokes pyrolyzed at 450 °C is suitable. Except for the decrease of volatile content and increase of ash content, the decrease of combustion performance of semicokes pyrolyzed at higher temperature should be attributed to the improvement of the degree of structural ordering and the increase of aromaticity and average crystallite size of char. It is concluded that the semicokes pyrolyzed at the temperature of 450 °C is the proper fuel for PCFF.

308 石炭焚き火炉におけるバーナ最低負荷予測手法の考案

We present a basic idea for the prediction of burner minimum loads for different coal-fired furnaces. Our idea is using the equation expressed by heat loss ratio and radiation intensities. We measured radiation intensities near the burner exit and studied the radiation profiles with decreasing burner load at 25MJ/h single burner test furnace. Radiation intensity decreases with decreasing load and the intensity at the burner minimum load is approximately 150kW/m^2. To get the equation for the prediction, quantities of heat transferred to the flame stabilization region at full and minimum loads are studied theoretically. We compared the decreasing radiation profile with the predicted profile by the equation at 25MJ/h test furnace and got good agreement. Next, we predicted the minimum loads for different types of coal at 150MJ/h test furnace. The assessment using data shows that our equation can be used to predict burner minimum load for the low-stabilized condition from the high-stabilized condition with an error of about 12%.

Transformations of Coal-Derived Soot at Elevated Temperature

Coal pyrolysis experiments were performed in the post-flame region of a CH 4 /H 2 /air flat-flame burner operating under fuel-rich conditions, where the temperature and gas compositions were similar to those found in the near-burner region of an industrial pulverized coal-fired furnace. Volatiles released from the coal particles formed a cloud of soot particles surrounding a centrally fed coal/char particle stream. Soot samples were collected from the cloud at different residence times using a water-cooled, nitrogen-quenched probe. The soot samples were then analyzed for their elemental compositions of carbon, hydrogen, nitrogen, sulfur, and (by difference) oxygen plus inorganic matter. Soot from three parent coals (Pittsburgh #8, Illinois #6, and Utah Hiawatha) and two gaseous hydrocarbon fuels (propane and acetylene) were investigated at temperatures of 1650, 1800, and 1900 K. The results reveal that the yield of coal-derived soot decreases with increasing reactor temperature, even though the total volatiles yield increased only slightly with temperature. The coal-derived soot yield at each reactor temperature condition also increased slightly with residence time. The carbon content in the coal-derived soot decreased with increasing particle residence time (at a given reactor temperature) and with increasing reactor temperature (at a given residence time) for all three coals. Carbon content remained constant with residence time for the gaseous hydrocarbon-fuel-derived soot. It is suggested that the observed decrease in coal-derived soot yield with increasing temperature is due to reactions of radical species from the flame with the soot precursors (i.e., the tar molecules). The slight increase in coal-derived soot yield with increasing residence time is due to attachment of light gas species such as acetylene which are richer in hydrogen than the local soot particles. The different behavior of soot from coal and the gaseous hydrocarbon fuels is explained in terms of their different chemical structures; coal-derived soot molecules have more aliphatic attachments and heteroatoms than soot from acetylene or propane. Carbon/hydrogen ratios in the soot samples were observed to be significantly different for the different soot types depending on parent fuel.

00/02691 Thermodynamic evaluation for combined combustion of wastes in coal-fired furnaces

00/02691 Thermodynamic evaluation for combined combustion of wastes in coal-fired furnaces

00/02821 Thermodynamic evaluation for combined combustion of wastes in coal-fired furnaces

00/02821 Thermodynamic evaluation for combined combustion of wastes in coal-fired furnaces

00/02288 Investigation of desulfurization and sulfur analysis method in hydropyrolysis of coal

Calcium magnesium acetate (CMA) shows potential as a reductant for simultaneous NOx and SOx removal from coal-fired combustion plant. The performance of urea co-injection with CMA on NO reduction in an ‘advanced reburn’ (AR) configuration has been investigated with a view to optimization of the process in a pulverized coal-fired furnace operating at 80 kW. The impact on SO2 reduction has also been investigated. Urea/CMA solution was sprayed into the reburn zone of the furnace using twin-fluid atomizers over a range of reductant/NO stoichiometric ratios (NSR). The influence on NO reductions of primary zone stoichiometry (λ1) was investigated for a range of CMA reburn feed rates (Rff) and reburn zone stoichiometry (λ2). In addition, the effect of temperature on the SNCR performance of urea was investigated. Optimum process conditions were categorized either by maximizing NO and SO2 reductions (Modes A and B, respectively) or maximizing reductant utilization efficiencies (Modes C and D). NO control was best performed at λ1=1.05, but SO2 reductions were greatest at more fuel-lean primary zone conditions (λ1=1.15). Highest NO reductions of 85% under AR-rich conditions were achieved under Mode A, but were only slightly higher compared with reductions of 79% under Mode B, where SO2 reductions were optimized at 85%. N-utilization was also at an acceptable level of 25% compared to the maximum utilization efficiency which was obtained at NSR=1.5 of 30% for the same conditions of stoichiometry operating in Mode C. Operation at this lower level of reburn (9.6%) could significantly reduce the consumption of CMA with some impact on NO reduction (73%). SO2 removal performance would be compromised severely with reductions lowered from 75% at Mode A to 35% at Mode C. Optimizing Ca utilization (Mode D) resulted in poor NO and SO2 reductions, at 61 and 22%, respectively, and can be discounted as a viable option. The technique offers flexibility of operation depending on the emission control requirements.

A parametric study of radiative heat transfer in pulverised coal furnaces

The P-1 approximation and the Monte Carlo method are applied in cylindrical coal-fired furnaces. The absorption and scattering efficiencies and the phase function of coal, char and fly-ash particles are obtained from Lorenz-Mie theory and wavelength dependent optical properties based on measurements available in the literature. The influence of each kind of particle on the radiative heat transfer is investigated. Comparisons between the P-1 and the Monte Carlo methods are performed for various particle size distributions and mass concentrations. Isotropic and neglecting of scattering are evaluated against anisotropic scattering as potential simplifications in engineering applications.

A Radiation Model for the Numerical Simulation of Coal-Fired Furnaces Using Body-Fitted Grids

A model for predicting radiative heal transfer in coal-fired furnaces is presented. The radiative transfer equation is modelled by the discrete ordinates method for body-fitted coordinates using the S4-approximation. The gas absorption coefficient is determined by a weighled-sum-of-grey-gases model, the radiative properties of coal and ash particles are derived from the specific area and a mean efficiency factor of the particle cloud. The scattering phase function is modelled by the Delta-Edding-ton approximation. The entire radiation model is adopted for vector and parallel computers guaranteeing numerical efficiency. It is tested at an idealized squared combustion chamber with black walls filled by an emitting, absorbing medium with constant absorption coefficient. The computations are carried out on several curvilinear non-orthogonal grids using different boundary conditions. On all grids the computed radiative source terms and wall heat fluxes are in very good agreement with the analytic solution. Furthermore, the model is validated at a coal-fired lest facility. Apart from the near burner region the computed temperature distribution only slightly deviates from the measured values.

00/00444 Thermodynamic evaluation for combined combustion of wastes in coal-fired furnaces

00/00444 Thermodynamic evaluation for combined combustion of wastes in coal-fired furnaces

99/02018 Separation of solids using perforated metal foils after brown coal-fired furnaces: Winkler, B. Fortschr.-Ber. VDI, Reihe 3, 1998, 544, (i–ix), 1–161. (In German)

99/02018 Separation of solids using perforated metal foils after brown coal-fired furnaces: Winkler, B. Fortschr.-Ber. VDI, Reihe 3, 1998, 544, (i–ix), 1–161. (In German)

99/00409 On the simulation of the gas-solid flow in pulverized coal-fired furnaces

99/00409 On the simulation of the gas-solid flow in pulverized coal-fired furnaces

A New Wave in CFD

The convergence of virtual reality, parallel processing, and Internet access is enabling computational-fluid-dynamics (CFD) codes to model complex problems in the process and petroleum industries. Improved user interfaces are making it easier for non-specialists to use CFD to investigate the conditions under which flammable or poisonous gases, to investigate the conditions under which flammable or poisonous gases, for example, might build up around an oil platform. CFD rests on the sure foundation of the scientific laws that deal with mass, momentum, and energy. Engineers used CFD in the design of a coal-fired furnace whose burners produce a swirling flow, enhancing the efficiency of the combustion process. CFD codes simulate the processes in four key stages: ignition, laminar-flame propagation, turbulence generation, and turbulence-controlled combustion. The ignition process is usually represented by the sudden temperature increase of a small body of gas, such as in a single computational cell. Most CFD codes seeking to simulate explosions use variants of one of these models.

98/02506 Analysis of thermal radiation in coal-fired furnaces : Miles, J. J. et al. Proc. SPIE-Int. Soc. Opt. Eng., 1997, 3056, 20–32

98/02506 Analysis of thermal radiation in coal-fired furnaces : Miles, J. J. et al. Proc. SPIE-Int. Soc. Opt. Eng., 1997, 3056, 20–32