Numerical simulation on optimization of structure and operating parameters of a novel lean coal decoupling burner

Due to its low volatile characteristics of lean coal,it is difficult to catch fire and burn out.Therefore,high temperature is needed to maintain combustion efficiency,while,this leads to high nitrogen oxide emission.For power plant boilers burning lean coal,stable combustion with lower nitrogen oxide emission is a challenging task.This study applied the 3D numerical simulation on the analysis of a novel de-coupling burner for low-volatile coal and its structure and operation parameters optimization.Results indicate that although it was more difficult for lean coal decoupling burner to ignite lean coal than high volatile coal,the burner formed a stepwise ignition trend,which promoted the rapid ignition of lean coal.Comparison of three central partition plate structure shows that in terms of characteristics of the flow field distribution,rich and lean separation and combustion,the structure with an inclination of 0°showed good performance,with its rich-lean air ratio being 0.85 and concentration ratio being 22.94,and there was an apparent decoupling combustion characteristic.Finally,the structure of the selected burner was optimized for its operational conditions.The optimal operating parameters was determined as the primary air velocity of 24.9 m·s^-1 and the mass flow rate of pulverized coal of 2.5 kg·s^-1,in which the pyrolysis products were utilized as reductive agent more fully.Eventually,the nitrogen oxide was efficiently reduced to nitrogen,which emission concentration was 61.88%lower than that in the design condition.

Experimental simulation and numerical analysis of coal spontaneous combustion process at low temperature

The characteristic of coal spontaneous combustion includes oxidative property and exothermic capacity. It can really simulate the process of coal spontaneous combustion to use the large scale experimental unit loading coal 1 000 kg. According to the field change of gas concentration and coal temperature determined through experiment of coal self ignite at low temperature stage, and on the basis of hydromechanics and heat transfer theory, some parameters can be calculated at different low temperature stage, such as, oxygen consumption rate, heat liberation intensity. It offers a theoretic criterion for quantitatively analyzing characteristic of coal self ignite and forecasting coal spontaneous combustion. According to coal exothermic capability and its thermal storage surroundings, thermal equilibrium is applied to deduce the computational method of limit parameter of coal self ignite. It offers a quantitative theoretic criterion for coal self ignite forecasting and preventing. According to the measurement and test of spontaneous combustion of Haibei coal, some token parameter of Haibei coal spontaneous combustion is quantitatively analyzed, such as, spontaneous combustion period of coal, critical temperature, oxygen consumption rate, heat liberation intensity, and limit parameter of coal self ignite.

Effect of turbulent fluctuation on the ignition of millimeter particle:Experimental studies and numerical modelling with a new correlation of nusselt number Author links open overlay panel

Understanding the influencing mechanism of turbulent fluctuation on the ignition characteristics of millimeter coal particles is essential.In this work,to study the effect of turbulent fluctuation on ignition time,millimeter coal particles are subjected to a specific flow field,generated in a furnace with symmetric fans.A one-dimensional model with the new proposed correlation and the Ranz-Marshall(R-M)correlation for Nu(Nusselt number)is established to simulate the coal ignition process.In addition,the effects of fan speed,temperature,particle diameter,particle distance and coal type on the ignition time are investigated.It is found that an increase in fan speed from 0 to 3000 rpm leads to a particle Reynolds number Re_(p)increase from 0 to 22.5,and a turbulent particle Reynolds number Re_(t)*increase from 0 to 71.5.With a consideration of the fluctuation effect,the new correlation of Nu gives a better prediction of ignition time compared to the R-M correlation.Moreover,the ignition time is revealed to decrease with an increasing fan speed and an elevating temperature.While the ignition time shows merely an initial boost with enlarging particle distance,it exhibits a linearity with the term of particle diameter dp1.3-1.7 and Reynolds numbers(Nu*/Nu)-0.6(Nu*is turbulent Nusselt number).Based on this relationship,the difference of predicted ignition time is calculated at different Re_(p)and Re_(t)*.It is shown that at low Re_(p)or high Re_(t)*values,the new correlation should substitute for the R-M correlation.

Fast Ignition and Stable Combustion of Coarse Coal Particles in a Nonslagging Cyclone Combustor

A combustion set-up of an innovative nonslagging cyclone combustor called 'Spouting-Cyclone Combustor (SCC)' ) with two-stage combustion, organized in orthogonal vortex flows, was established and the experimental studies on the fast ignition and stable combustion of coarse coal particles in this combustor were carried out. The flame temperature versus ignition time and the practical faSt ignition procedure were obtained; The stable coal combustion can be achieved after a short period ignition, and the temperature fields in SCC were obtained. These results show that it is possible to obtain highly efficient and clean combustion of unground coal particles by using this technology.

Numerical simulation of bituminous coal combustion in a fullscale tiny-oil ignition burner： Influence of excess air ratio

The progression of ignition was numerically simulated with the aim of realizing a full-scale tiny-oil ignition burner that is identical to the burner used in an 800 MWe utility boiler. The numerical simulations were conducted for four excess air ratios, 0.56, 0.75, 0.98 and 1.14 （corresponding to primary air velocities of 17, 23, 30 and 35 m/s, respectively）, which were chosen because they had been used previously in practical experiments. The numerical simulations agreed well with the experimental results, which demonstrate the suitability of the model used in the calculations. The gas temperatures were high along the center line of the burner for the four excess air ratios. The flame spread to the bumer wall and the high- temperature region was enlarged in the radial direction along the primary air flow direction. The O2 concentrations for the four excess air ratios were 0.5%, 1.1%, 0.9% and 3.0% at the exit of the second combustion chamber. The CO peak concentration was very high with values of 7.9%, 9.9%, 11.3% and 10.6% for the four excess air ratios at the exit of the second combustion chamber.

RESEARCH THE CHANGE RULE OF OXIDATION ZONE WIDTH CAUSED BY NITROGEN INJECTION IN GOB

On the basis of heat transfer and chemical kinetics theory, both connections coal self ignite with oxygen concentration and range of oxidation zone with air leak intensity are analyzed, and calculating method is deduced to gain the lower limit of oxygen concentration and the range of oxidation zone. The change rule of correlative parameter is quantitatively researched between before nitrogen injection and after nitrogen injection in gob, such as oxygen concentration, oxidation zone width, etc. According to theoretical calculation, the relation position and flow of nitrogen injection with oxidation zone width is conformed, and computational formulas of the best flow and position of nitrogen injection are obtained. It offers a theoretic criterion for preventing and controlling float coal self ignite by nitrogen injection in gob.