Investigation of wear pattern in a complex coal pulveriser using CFD modelling

In this study, we have constructed a commercial-scale pulveriser and simulated motion of air and coal particles inside the pulveriser to investigate the effect of air passage on the wear pattern. Simulations were carried out using Eulerian–Lagrangian approach. The results indicated that the primary air entering into the pulveriser under the bowl via splitters, exited the pulveriser vanes to the left with the highest velocity. This validates the constructed model as the nozzle ring above the bowl has vanes that run clockwise making most of the primary air to exit the vanes to the left. Additional simulations with modified inlet duct geometry led to a possible solution for making the airflow distribution even at the base of the mill, which is expected to reduce the wear pattern. The results presented in the paper provides impetus for the modification of the airflow path using baffle splitters in the primary air duct, which could prove valuable to designers for the optimisation of airflow and the potential reduction of wear on the components within the coal pulveriser.     

Numerical simulation of coal gasification in entrained flow coal gasifier

This paper presents modeling of a coal gasification reaction, and prediction of gasification performance for an entrained flow coal gasifier. The purposes of this study are to develop an evaluation technique for design and performance optimization of coal gasifiers using a numerical simulation technique, and to confirm the validity of the model. The coal gasification model suggested in this paper is composed of a pyrolysis model, char gasification model, and gas phase reaction model. A numerical simulation with the coal gasification model is performed on the CRIEPI 2 tons/day (T/D) research scale coal gasifier. Influence of the air ratio on gasification performance, such as a per pass carbon conversion efficiency, amount of product char, a heating value of the product gas, and cold gas efficiency is presented with regard to the 2 T/D gasifier. Gas temperature distribution and product gas composition are also presented. A comparison between the calculation and experimental data shows that most features of the gasification performance were identified accurately by the numerical simulation, confirming the validity of the current model.     

气流床煤气化辐射废锅内多相流动与传热

采用多相流动与传热模型耦合的数值方法,对气流床煤气化辐射废锅内多相流场与传热过程进行了数值模拟。在Euler坐标系中采用组分输运模型计算气体组分扩散过程,并通过realizable k-ε湍流模型计算炉内流场,煤渣颗粒运动轨迹在Lagrange坐标系中计算,并考虑了气固相间双向耦合。利用灰气体加权和模型与离散坐标法相结合,计算了炉内辐射传热过程,并考虑了煤渣颗粒的热辐射特性。结果表明：炉体入口存在张角约为10°的中心射流区,其流速和温度均较高,且周围存在明显回流区,回流区内部分颗粒富集;大部分颗粒直接落入渣池,且粒径越大落入渣池时温度越高;炉内温度分布除中心射流区,整体分布均匀,且随壁面灰渣厚度的增加而升高;计算结果与实验测量结果及文献值基本一致。     

CFD based investigations into optimization of coal pulveriser performance: Effect of classifier vane settings

In coal-fired power plant, pulveriser is the first major component, whose performance dictates the total power plant efficiency. Uniform flow rate and desired size fraction at outlet pipes along with higher classifier efficiency are three important measures which decide the pulverizer performance. Optimization of pulverizer at its best operating conditions has been considered as a potential area that needs to be addressed for improving unit performance, emissions, operations, and maintenance. The best operating conditions are optimum air velocity and classifier vane settings. In this investigation, numerical simulations of a typical pf coal based pulveriser have been carried out for different classifier vane settings to evaluate uniform flow rate and desired size fraction at outlet pipes along with high optimum classifier efficiency. The optimum opening for the vanes has been determined based on the above measures, which not only reduces unburnt CO, SO_x and NO_x emissions at boiler end but also minimise energy consumption of mill (in terms of reductions in regrinding cost). Computational Fluid Dynamics (CFD) simulations of the coal classifier physical model indicate good agreement with the plant data, in terms of internal flow patterns, particle collection efficiency and desired cut size. From the simulation studies, optimum opening for the vanes is found to be 65% for selected utility which leads to closest uniformity with 60% classifying efficiency wherein 70% particles pass through 75 μm sieve.     

Modeling and simulation of an entrained flow coal gasifier

A mathematical model has been developed to simulate the Texaco downflow entrained-bed pilot-plant gasifier using coal liquefaction residues and coal-water slurries as feedstocks. This model describes the physical and chemical processes occurring in an entrained coal gasifier. The gasification kinetics describes different complex reactions occurring in the gasifier and the hydrodynamics describes mass, momentum and energy balances for solid and gas phases. Temperature, concentration and velocity profiles along the reactor height were obtained by solving the mass, momentum and energy balances. Parameter studies were made to provide a better understanding of the reactor performance for various inlet feed conditions utilizing the model.     

Multiphase flow at the edge of a steam chamber

The use of steam‐assisted gravity drainage (SAGD) to recover bitumen from Athabasca deposits in Alberta has been growing. Butler [Butler, J. Can. Pet. Tech. 1985;24:42–51] derived a simple theory to calculate the production rate of oil during SAGD in an ideal reservoir. This simple and useful theory made several assumptions about the properties of the reservoir and operating conditions of the process. The theory also assumed that the highest mobility oil is at the edge of the steam chamber and that the oil phase velocity is highest at the chamber edge and reduces with distance into the oil sand. This research examines flow conditions at the edge of the steam chamber. Specifically, a new theory is derived that takes into account the impact of oil saturation and relative permeability on the oil mobility profile at the edge of a steam chamber. It is shown that the flow behaviour at the edge of a steam chamber is more complex and is not fully represented by Butler's theory. Contrary to Butler's theory, the oil mobility has its maximum some distance away from the edge of the steam chamber. The results reveal that the higher the thermal diffusivity of the oil sand, the deeper the location where the oil phase velocity is maximum. The developed model has been validated against published experimental and field data.     

Multiphase flow with unequal granular temperatures

Multiphase kinetic theory has been generalized to include rotation of particles with unequal masses and diameters. Inelastic binary collisions of particles with normal and tangential restitution coefficients are considered. New expressions for number of binary collisions, viscosities and conductivities were developed. Collision integrals produced new expressions for energy dissipation involving tangential and normal restitution coefficients. Computed radial profiles of granular temperatures of 530 and 156 μm glass beads flowing in a two story riser matched the experimentally measured profiles of granular temperatures using a particle image velocity technique without rotation. The measured and the computed particle concentration profiles were nearly flat in the central portion of the riser without rotation. Computations show that rotation can alter these profiles. Sufficient particle spin can drive the particles to concentrate near the center of the tube.     

潮湿细煤气流分级机内气固两相流的CFD模拟

以CFD计算软件FLUENT为平台,采用Realizablek-着湍流模型和欧拉-拉格朗日方法的离散相模型对实验室研制的潮湿细煤气流分级机内的空气流场进行数值模拟,得到分级机中流场的气流速度、流场静压、流场湍动能的分布情况,以及不同粒径细粒煤在分级机中的运动轨迹。数值计算结果表明:分级机内多孔层的设置可造成压强和流速阶跃,增强多孔层上方区域的流速,提升气体对细粒煤的携带作用;导流板的设置使入料口到细料出口间出现了较强的流带,有利于细粒煤分离;导流板和倾斜多孔层的设置使分级机内压差最大且湍流较弱,有利于颗粒分散,实现小颗粒与大颗粒的分离,提高分级效率同时也有利于中等粒径团聚体的破碎、分散,但对大粒径团聚体的分裂破坏作用有限。     

Oxygen in coal ash: a simplified approach to the analysis of ash and mineral matter in coal

Oxygen was determined accurately in eight U.S. Bureau of Mines coal ash samples A, B, D, F, G, I, and J, NBS coal fly ash 1633 reference material, and two low-temperature ashes (LTA) from lllinois State Geological Survey. The method uses fast-neutron activation (FNA) analysis employing a dual counting and irradiation system which is essentially free from interferences. The stoichiometric balance based on analyses of the ashes performed by the USBM is calculated and summations given in oxide and element percent. Excellent agreement is found with the chemical data obtained by classical silicate analysis methods. Accurate oxygen determination for coal ash and LT-ash (or mineral matter) is important for calculation of data in the ultimate analysis of coal as such. Knowledge is required for recalculation of the data on a dry and dry-ash-free basis. The routinely used ‘oxygen by difference’ values are inadequate for accurate work. In order to determine the organic oxygen in coal one also has to correct for oxygen in mineral matter and oxygen in the water removed as moisture. The Parr formula and other methods of empirical estimation are inadequate and may be replaced in some cases by the oxygen determination. The complete data provide a quantitative basis for stoichiometric interpretation of coal analyses. It was found that the eight coal-ash samples analysed contained 45.5 ± 3% oxygen. Since these ashes represent a large variety of U.S. coals, this figure can be used as an estimate for recalculation and evaluation of the proximate and ultimate coal analyses. It is better, however, to use values actually determined in ash by the rapid fast-neutron activation method. This permits a better estimation of the sum of cations plus sulphates in the ash.     

煤等离子热解制乙炔热流场模拟的对比研究

简要介绍了煤热解制乙炔反应器的流程以及该工艺存在的结焦严重,热能损失较大,连续稳定运行时间短,整体反应器效率低,负荷小等缺陷,为了减少或抑制煤这种不足,利用GAMB IT前处理和FLUENT数值模拟软件针对工艺在不同保护气速度下进行了热流场的优化模拟及对比研究(默认等离子的温度5 000 K),并最终得出了保护气速度为70 m/s,煤热解的反应空间是最大的,有利于反应的充分进行,热量的利用率较高,此时出口截面的温度约为3 700 K,出口截面的速度约为18 m/s,防止结焦的效果最好。     

Pore-level numerical simulation of methane-air combustion in a simplified two-layer porous burner

A simplified two-dimensional model of two-layer porous burner based on pore level is developed.The heat transfer of solid phase in porous burner is seen as the synergistic effects of conduction through con-necting bridges and surface radiation between the solid particles in the model.A numerical simulation study on the characteristics of flow,combustion and heat transfer in the two-layer porous burner is car-ried out using the pore level model,and the effects of the control parameters such as the inlet velocity and solid thermal conductivity on thermal non-equilibrium are investigated.The results show that the flame structure is highly two-dimensional based on pore level.Obvious thermal non-equilibrium in the burner for the two phases and solid phase are observed,the largest temperature difference between the gas and solid phases is observed in combustion zone,while the temperature difference inside the solid particles is largest near the flame front.The results also reveal that thermal non-equilibrium of por-ous burner is much affected by the inlet velocity and solid thermal conductivity.     

CFD simulation and experimental validation of co-combustion of chicken litter and MBM with pulverized coal in a flow reactor

The influence of co-combustion of solid biomass fuels with pulverized coal on burnout and CO emissions was studied using a flow reactor. The thermal input on a fuel feeding basis of the test rig was approximately 7 kW. Accompanied with the measurements, a reactor model using the CFD code AIOLOS was set up and first applied for two pure coal flames (with and without air staging). Reasonable agreement between measurements and simulations was found. An exception was the prediction of the CO concentration under sub-stoichiometric conditions (primary zone). As model input for the volatile matter release, the HTVM (high temperature volatile matter as defined by IFRF [IFRF, www.handbook.ifrf.net/handbook/glossary.html. [1]]) was used. Furthermore, a relatively slow CO oxidation rate obtained from the literature and the ERE (Extended Resistance Equation) model for char combustion were selected. Furthermore, the model was used for simulating co-firing of coal with chicken litter (CL) and meat and bone meal (MBM). The conditions applied are relevant for future co-firing practice with high thermal shares of secondary fuels (larger than 20%). The major flue gas concentrations were quite well described, however, CO emission predictions were only qualitatively following the measured trends when O₂ is available and severely under-predicted under substoichiometric conditions. However, on an engineering level of accuracy, and concerning burnout, this work shows that co-combustion of the fuels can reasonably well be described with coal combustion sub-models.     

Three-dimensional flow simulation of a film-casting process

Three-dimensional flow simulation of a film-casting process was performed using a finite element method assuming an isothermal and steady Newtonian flow. The simulation was carried out under industrial operation conditions. The neck-in and the edge bead phenomena could be simulated. The effects of draw ratio, air gap length, and die width on these phenomena are discussed. The neck-in and the edge bead phenomena were affected by the draw ratio and air gap length and not by the die width. The neck-in value, which was defined as the difference between the die width and film width at the chill roll, increased with the draw ratio and air gap length.     

Kinetics of donor-vehicle coal liquefaction in a flow reactor

Development of the Exxon Donor Solvent process has necessitated studies to more clearly define the influence of liquefaction conditions on coal conversion. Process studies were conducted in a 22.7 kg/day (fifty-pound-per-day) integrated pilot plant. Illinois No. 6 coal was liquefied at temperatures from 644 to 756 K, pressures of 10 and 17 MPa, and a tenfold range of residence time. A kinetic model was developed in terms of an empirical classification of four reactive coal constituents. The reactive classes are an incorporation of concepts published in other coal-liquefaction kinetic studies. The effect of vehicle vaporization on actual residence time was used in evaluating the kinetic parameters for this study in a tubular flow reactor. The kinetic model accurately predicts distillation bottoms yields, which ranged from 41 to 72 wt % on coal. Material-balanced quadratic equations are presented for other liquefaction products.     

GSP气化炉内多相湍流反应流动模拟研究

采用涡耗散概念(EDC)模型,对某化工厂的GSP气化炉内多相反应流场进行了数值模拟研究.计算中采用Realizable k-ε湍流模型对雷诺平均后的N-S方程进行封闭;采用离散相随机轨道模型来模拟气化炉内煤颗粒的弥散运动;采用P1模型对燃烧的辐射传热进行模拟.计算结果表明:气化炉内为强旋射流流场,颗粒在气化炉顶部回流区...     

Simulation of pulverized coal combustion in a turbulent flow

A numerical model has been developed for calculating pulverized coal combustion in a two-dimensional turbulent axisymmetric flow on a gaseous oxidant. The radiation is considered in the four-flow model. Satisfactory agreement with the available experimental data is obtained.Institute of High Temperatures, Russian Academy of Sciences, Moscow 127412. Translated from Fizika Goreniya i Vzyrva, Vol. 30, No. 4, pp. 46–52, July–August, 1994.