Coal-fired Furnace Research Articles

97/05196 Radiative properties of particle clouds in coal-fired furnaces: Liu, L. et al. Heat Transfer Sci. Technol. 1996, [Int. Symp. Heat Transfer], 4th., 1996, 287–292. Edited by Buxuan, W., Higher Education Press, Beijing, People's Republic of China

97/05196 Radiative properties of particle clouds in coal-fired furnaces: Liu, L. et al. Heat Transfer Sci. Technol. 1996, [Int. Symp. Heat Transfer], 4th., 1996, 287–292. Edited by Buxuan, W., Higher Education Press, Beijing, People's Republic of China

The performance of pulverized-coal flames in a simulated combined cycle unit

Measurements have been taken in a pulverized coal-fired furnace to evaluate the combustion characteristics of a combined cycle unit—a coal-fired boiler coupled with a gas/oil-fired turbine. Results are presented for two aerodynamically distinct laboratory scale burners—the single annular orifice and the single central orifice (SAO and SCO) in a 0.5 MW furnace. The combined cycle is simulated through the vitiation of combustion air delivered to the burners. Under unvitiated-air conditions, both laboratory burners offer similar combustion performance in regard to particle burnout. The SAO burner, representative of wall-fired practice, exhibits much higher NO x emissions due to the almost immediate evolution of the fuel's volatiles in an oxygen-rich shear zone immediately downstream of the burner. Its counterpart (SCO burner) gives less NO x due to a manipulation of the aerodynamics, with the volatiles being liberated in the oxygen-lean internal recirculation zone. Vitiated-air conditions produced by increasing the flue-gas recirculation, altered the burner's performance. The NO x reduction in the faster mixing burner is substantial, from 667 to 171 ppm, with some reduction seen in burnout. For the slower mixing burner, with aerodynamics more appropriate to staged combustion, low-NO x operation is observed with a reduction from 356 to 250 ppm. More importantly, the stability limits of this burner are increasingly restricted with air vitiation. A mathematical model of coal combustion was also used to predict the observed trends of flame stability and to establish a single criterion for flame stability on both the fast and slow mixing burners operating under nonvitiated, as well as vitiated-air conditions. Flame stability strongly depends on combustion aerodynamics in the burner, while, under vitiated-air conditions, the local concentration of oxygen becomes a dominant factor. For all the operating conditions simulated by the mathematical model, it was found that the appropriate criterion for defining a stable flame is that the axial temperature profile reaches its peak value (more than 900°C) within a distance of approximately 10 burner diameters. This is the condition under which volatiles are well released from the coal and burnt in the heat-confined environment to sustain a high temperature. The model overpredicts the stability limit; this indicates a limitation of the k − ε model for flow with a high swirl number. It is suggested that the slow mixing of fuel and oxidant associated with low-NO x burner technology in a combined cycle operation would prevent it from achieving its expected capabilities. The results of this study suggest that a burner offering less stratification of air and fuel would be more appropriate.

An efficient computational technique for radiative heat transfer in axisymmetric enclosures

One of the most important mechanisms of heat transfer in furnaces and other similar equipment is radiation. Radiative heat transfer can be rigorously described by the radiative transfer equation, which is a six-dimensional integro-differential equation in a phase space. The most popular and widely adopted techniques for solving the radiative transfer equation are the P1 approximation and the S4 method. Although the P1 approximation solves the radiative transfer equation with a decent amount of computer time, it yields somewhat inaccurate results for the cases of optically thin media. On the contrary, the S4 method yields accurate results for all ranges of optical thickness but it requires a large amount of computer time and memory. Moreover, the number of iterations in the S4 method, and consequently the computer time, increases as the value of the scattering albedo increases when the extinction coefficient is not small. In the present work, a new algorithm is devised to solve the radiative heat transfer equation efficiently. This algorithm consists of separating the radiation intensity into two parts i.e., wall emission and medium emission according to the modified differential approximation. Then the wall emission is treated by the S4 method, which can satisfy the wall boundary conditions exactly, and the medium emission is treated by the P1 approximation. The scattering term which increases the iteration number in the S4 method is taken care of by the P1 approximation. The present algorithm solves the radiative heat transfer equation accurately and efficiently for all ranges of optical thickness when compared with conventional techniques, and may be adopted in the analysis of many engineering systems with a significant amount of radiative heat transfer such as pulverised coal-fired furnaces.

97/03060 Modeling combustion and fly ash production in a pulverized coal-fired furnace

97/03060 Modeling combustion and fly ash production in a pulverized coal-fired furnace

An On-line Identification Method for the Slagging Factor in Coal-Fired Furnaces

An On-line Identification Method for the Slagging Factor in Coal-Fired Furnaces

97/02239 Industrial testing of an electric and coal-fired furnace for manufacture of ferrosilicon

97/02239 Industrial testing of an electric and coal-fired furnace for manufacture of ferrosilicon

Role of Sulfur in Reducing PCDD and PCDF Formation

Past research has suggested that the presence of sulfur (S) in municipal waste combustors (MWCs) can decrease the downstream formation of chlorinated organic compounds, particularly polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). Thus, co-firing a MWC with coal, because of the S species from coal, may reduce PCDD and PCDF emissions. Experiments were carried out to test this hypothesis and to determine the role of S. A field-sampled MWC fly ash was injected into the EPA's pilot-scale reactor, doped with hydrogen chloride (HCl). The tests involved either natural gas or coal combustion. Besides the combustion environment, MWC fly ash injection temperature and sulfur-to-chlorine ratio (S/Cl) were varied. Flue gas was sampled and analyzed for PCDD and PCDF to determine in-flight formation. In the natural-gas-fired reactor, when S was added (as sulfur dioxide, SO2), the PCDD and PCDF formation decreased dramatically at S/Cl ratios as low as 0.64, and with varying furnace conditions, the inhibitory effect was consistent for S/Cl ratios of about 1. In tests with the coal-fired furnace, the S inhibitory effect was again observed at S/Cl values of 0.8 and 1.2, respectively, for the two coals tested. S inhibition mechanisms were studied in a bench-scale reactor. Results show that the depletion of molecular chlorine (Cl2), an active chlorinating agent, by SO2 through a gas-phase reaction appears to be a significant inhibition mechanism in addition to previously reported SO2 deactivation of copper catalysts.

96/01905 Experimental and computational study of turbulent heat transfer characteristics in serrated channel flow

Measurements have been taken in a pulverized coal-fired furnace to evaluate the combustion characteristics of a combined cycle unit—a coal-fired boiler coupled with a gas/oil-fired turbine. Results are presented for two aerodynamically distinct laboratory scale burners—the single annular orifice and the single central orifice (SAO and SCO) in a 0.5 MW furnace. The combined cycle is simulated through the vitiation of combustion air delivered to the burners. Under unvitiated-air conditions, both laboratory burners offer similar combustion performance in regard to particle burnout. The SAO burner, representative of wall-fired practice, exhibits much higher NOx emissions due to the almost immediate evolution of the fuel's volatiles in an oxygen-rich shear zone immediately downstream of the burner. Its counterpart (SCO burner) gives less NOx due to a manipulation of the aerodynamics, with the volatiles being liberated in the oxygen-lean internal recirculation zone. Vitiated-air conditions produced by increasing the flue-gas recirculation, altered the burner's performance. The NOx reduction in the faster mixing burner is substantial, from 667 to 171 ppm, with some reduction seen in burnout. For the slower mixing burner, with aerodynamics more appropriate to staged combustion, low-NOx operation is observed with a reduction from 356 to 250 ppm. More importantly, the stability limits of this burner are increasingly restricted with air vitiation. A mathematical model of coal combustion was also used to predict the observed trends of flame stability and to establish a single criterion for flame stability on both the fast and slow mixing burners operating under nonvitiated, as well as vitiated-air conditions. Flame stability strongly depends on combustion aerodynamics in the burner, while, under vitiated-air conditions, the local concentration of oxygen becomes a dominant factor. For all the operating conditions simulated by the mathematical model, it was found that the appropriate criterion for defining a stable flame is that the axial temperature profile reaches its peak value (more than 900°C) within a distance of approximately 10 burner diameters. This is the condition under which volatiles are well released from the coal and burnt in the heat-confined environment to sustain a high temperature. The model overpredicts the stability limit; this indicates a limitation of the k − ε model for flow with a high swirl number. It is suggested that the slow mixing of fuel and oxidant associated with low-NOx burner technology in a combined cycle operation would prevent it from achieving its expected capabilities. The results of this study suggest that a burner offering less stratification of air and fuel would be more appropriate.

Conversion of coal tar to soot during coal pyrolysis in a post-flame environment

Coal pyrolysis experiments were performed in the postflame 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 in the near-burner region of a large-scale coal-fired furnace. Volatiles released from the coal particles formed a cloud of soot particles at high temperatures in the absence of oxygen. The soot particles in the cloud were collected at different residence times using a water-cooled, nitrogen-quenched suction probe. Test variables included the reaction temperature and coal type. Soot yields in terms of weight percentage of dry ash-free coal were measured based on bulk soot collection experiments. The measured soot yields were related to coal rank, reaction temperature, and residence time. Size changes of soot particles due to soot agglomeration were also observed. The information obtained about coal-derived soot is useful in predictions of radiative heat transfer and pollutant formations in the near-burner region of pulverized coal-fired furnaces.

95/04954 The properties of thermal effects of ash deposits in coal-fired furnaces: A review

95/04954 The properties of thermal effects of ash deposits in coal-fired furnaces: A review

Computerized Analysis of Low-NOxCoal-fired Utility Boilers

Abstract Mathematical modelling and simulation can be used to assess the effect of modifications of the combustion process and pollutant formation. In this paper two pulverized coal combustion plants are considered. The first plant is a bituminous coal-fired furnace with eight swirl burners and a thermal power of 490 M W. In order to reduce NO x -formation, the furnace system was modified using a different burner design and a modified burnout air arrangement for realizing the staging of combustion air. Both cases were investigated. The second plant is a brown coal-fired furnace with an electric power of 150 MW. The goal was to reduce CO-emissions and to improve the burnout of the coal. For a more flexible discretization of the domain a method was developed which allows that each burner can be discretized by an independent grid system. Using this method, details of the burner geometry can be considered and the governing processes of pollutant formation in the near-burner zone may be described in more detail.

Excavations at the 17th-century glasshouse at Haughton Green, Denton, near Manchester

AbstractThe remains of a glasshouse dating approximately from 1615 to 1653 were located in the valley of the river Tame at Haughton Green, Denton, south-east of Manchester (SJ/942946), and were excavated between 1969 and 1973. The glasshouse was one of the first provincial coal-fired furnaces established under the monopolist Sir Robert Mansell; it was leased to Isaac du Houx, a member of the aristocratic Huguenot family of glass-makers from Lorraine. Only partial excavation of the site was possible, but the main furnace was fully excavated and three subsidiary furnaces exposed nearby. The main furnace probably held four pots, with two pots resting on parallel sieges, the main feature being a deep passage running beneath the sieges which fed air to the central iron grid which would have supported the coal fuel. The subsidiary furnaces were probably annealing furnaces for cooling the glass. The products included good quality forest style vessel glass in green, black and blue glass with moulded and applied f...

5158024 Combustion control apparatus for a coal-fired furnace: Shinji Tanaka, Tatsuy Miyatake, Kazuyoshi Yamamoto, Yuichi Miyamoto, Tokyo, Japan assigned to Kawasaki Jukogyo Kabushiki Kaisha

5158024 Combustion control apparatus for a coal-fired furnace: Shinji Tanaka, Tatsuy Miyatake, Kazuyoshi Yamamoto, Yuichi Miyamoto, Tokyo, Japan assigned to Kawasaki Jukogyo Kabushiki Kaisha

The influence of near burner region aerodynamics on the formation and emission of nitrogen oxides in a pulverized coal-fired furnace

Detailed measurements have been performed for two distinct pulverized-coal-fired burners in a large-scale laboratory furnace. Comparative in-flame data are archived and include gas temperature, O 2, CO concentration, and an inventory of stable fuel nitrogen species and solids (HCN, NH 3, N 2O, NO, nitrogen release, mass flux, and particle burnout). A significant decrease in the NO concentration in the near burner region and a substantial decrease in the furnace exit values are observed when the “central tube” from a single annular orifice burner jet (normally the location of a gas or oil burner for light-up purposes) is replaced with a single central orifice burner jet of same cross-sectional area. The latter burner exhibits the delayed combustion phenomena normally associated with a tangentially fired system. The particle burnout remains unaffected due to the longer particles' residence time in the all-important oxygen lean internal recirculation zone. The difference in NO emissions is not reflected in the on-line N 2O emission values that are found to be low (2–3 ppm) for both flames. Data recorded nearer to either burner configuration, however, reveal that the maximum N 2O values for both burners are found in the flame region and are between 1%–2% of the corresponding maximum NO concentrations.

An Efficient Method for Predicting Unburned Carbon in Boilers

Abstract A model was developed to predict unburned carbon in pulverized coal-fired furnaces and industrial and utility boilers. The model is a one-dimensional description of the complex processes: flow. combustion and heat transfer. Models for devolatilization and char oxidation, turbulence and gas-phase combustion are used to simulate a test furnace and industrial and utility boilers. A total of 39 examples were evaluated and show good agreement of predictions with data. The results clearly indicate the approach has potential as an engineering tool to evaluate unburned carbon in boilers.

Combustion characteristics of carbonaceous residues from heavy oil fired boilers

The combustion of solid carbonaceous particles generated in residual oil-fired furnaces has been investigated. These particles are large ash-rich cenospheres that are not completely burned in the furnace and end up in the effluent gases, creating problems associated with both emissions and reduced operating efficiency. To study the reactivity of these chars, single-particle combustion experiments were conducted where the particle temperature and burnout times were measured by near-infrared two-color pyrometry. The results show that the particle temperature-burn time traces exhibited higher particle-to-particle variability than those of coal-derived char particles, but the overall burnout times were of the same order of magnitude as coal chars of similar size. Taking into account random particle-to-particle property variations, and using a particle combustion model, reaction rate parameters were estimated. Two limiting forms of the model were used for this estimation. The first assumed the particles to burn as shrinking cores, with all reaction concentrated very near the external particle surface. The second assumed the particles to burn at constant radius, with increasing void fraction. Using first-order kinetics, the shrinking core model gave an average apparent activation energy of about 18 kcal/(g mol), with a corresponding average preexponential factor of approximately 37 g/(cm^2 s atm of O_2. These values are similar to the respective parameters estimated for lignite and bituminous chars burned under similar conditions, indicating that these particles can be burned at temperatures and residence times similar to those existing in coal-fired furnaces. The constant radius model gave an intrinsic activation energy of 40 kcal/(g mol), with a preexponential factor of 550 g/(cm^2 s atm of O_2). The constant radius model gave a slightly better fit to the experimental data.

Experimental studies of a hybrid heat wheel

A hybrid heat wheel has been developed by combining the designs and incorporating the advantages of a metallic and a ceramic heat wheel. The final heat wheel has loose ceramic packings inside a metallic basket rotating around a vertical axis. It has been operated with maximum stream flow rates up to 350 nm 3/h and hot gas inlet temperatures up to 860 °C. It may not be suitable for attachment to a coal-fired furnace because of possible clogging of packing voids by non-combustible coal ash.

Effects of particulate concentrations on temperature and heat flux distributions in a pulverized-coal fired furnace

A simple methodology for numerical modelling of total heat transfer in an axisymmetric, cylindrical pulverized coal-fired furnace is introduced. The solution for the flow field and energy equations are coupled with the solution of the radiative transfer equation. The SIMPLER code is employed to solve all the equations numerically. The radiation part is modelled using the first-order spherical harmonics approximation. The radiative properties of the gases and particulates such as soot, coal/char and fly-ash are obtained locally to account for the temperature and concentration distribution effects. Using a k - e model, the turbulence closure is obtained. Parametric studies are performed and are presented graphically to demonstrate the effects of particulate concentrations on the distributions of medium radiative and physical properties, temperature, and the wall total and radiative heat fluxes.

Combustion Measurements in a Pulverised Coal-Fired Furnace

Abstract Combustion measurements are being performed in a laboratory cylindrical pulverised coal fired furnace as part of a continuing research programme, The data are primarily intended to assist the validation of mathematical models ultimately intended for the prediction of full scale plant. In this paper gas-species concentration and temperature data are presented and discussed for a bituminous coal fuel fired at two excess air levels and two swirl numbers.

National nuclear policies in FR Germany

Measurements have been taken in a pulverized coal-fired furnace to evaluate the combustion characteristics of a combined cycle unit—a coal-fired boiler coupled with a gas/oil-fired turbine. Results are presented for two aerodynamically distinct laboratory scale burners—the single annular orifice and the single central orifice (SAO and SCO) in a 0.5 MW furnace. The combined cycle is simulated through the vitiation of combustion air delivered to the burners. Under unvitiated-air conditions, both laboratory burners offer similar combustion performance in regard to particle burnout. The SAO burner, representative of wall-fired practice, exhibits much higher NOx emissions due to the almost immediate evolution of the fuel's volatiles in an oxygen-rich shear zone immediately downstream of the burner. Its counterpart (SCO burner) gives less NOx due to a manipulation of the aerodynamics, with the volatiles being liberated in the oxygen-lean internal recirculation zone. Vitiated-air conditions produced by increasing the flue-gas recirculation, altered the burner's performance. The NOx reduction in the faster mixing burner is substantial, from 667 to 171 ppm, with some reduction seen in burnout. For the slower mixing burner, with aerodynamics more appropriate to staged combustion, low-NOx operation is observed with a reduction from 356 to 250 ppm. More importantly, the stability limits of this burner are increasingly restricted with air vitiation. A mathematical model of coal combustion was also used to predict the observed trends of flame stability and to establish a single criterion for flame stability on both the fast and slow mixing burners operating under nonvitiated, as well as vitiated-air conditions. Flame stability strongly depends on combustion aerodynamics in the burner, while, under vitiated-air conditions, the local concentration of oxygen becomes a dominant factor. For all the operating conditions simulated by the mathematical model, it was found that the appropriate criterion for defining a stable flame is that the axial temperature profile reaches its peak value (more than 900°C) within a distance of approximately 10 burner diameters. This is the condition under which volatiles are well released from the coal and burnt in the heat-confined environment to sustain a high temperature. The model overpredicts the stability limit; this indicates a limitation of the k − ε model for flow with a high swirl number. It is suggested that the slow mixing of fuel and oxidant associated with low-NOx burner technology in a combined cycle operation would prevent it from achieving its expected capabilities. The results of this study suggest that a burner offering less stratification of air and fuel would be more appropriate.