Distribution of spontaneous combustion three zones and optimization of nitrogen injection location in the goaf of a fully mechanized top coal caving face

In order to effectively prevent and control spontaneous combustion of residual coal in the goaf and reduce the waste of nitrogen caused by setting the position of nitrogen injection, 1303 fully mechanized coal caving faces of the Jinniu Mine are studied. By deploying a bundle tube monitoring system in the inlet air side and return air side of the goaf, changes in gas concentration in the goaf are continuously monitored. In addition, the distribution area for spontaneous combustion three-zone in the goaf is divided into heat dissipation zone, oxidized spontaneous combustion zone, and suffocation zone. Simulations from the COMSOL Multiphysics 5.3 software provide insight based on the three zones division standard of spontaneous combustion in the goaf. The gradual deepening of the nitrogen injection position into the goaf affects the lower limit of the oxidized spontaneous combustion zone significantly, but the impact on the upper limit of the oxidized spontaneous combustion zone is not obvious and is negligible. With regard to the width of the oxidized spontaneous combustion zone, it initially decreases followed by a gradual increase. Numerical calculations suggest the optimal nitrogen injection position is 40 m from the roof cutting line, with an oxidized spontaneous combustion zone width of 28 m. Based on the simulation analysis results, nitrogen injection controlling measures have been adopted for spontaneous combustion of residual coal in the goaf of the 1303 fully mechanized coal caving faces, and coal self-ignition in the goaf has been successfully extinguished.

Research on determining reasonable negative pressure based on the control of the goaf

In order to study the law of spontaneous combustion in goaf under the condition of gas extraction, the method of beam tube monitoring and numerical analysis is adopted to obtain three dimensional distribution of oxygen concentration and contour map under the condition of different negative pressure. Based on the way of regression analysis, reasonable negative pressure are determined. The results show that with the increase of negative pressure, the spontaneous combustion “three-zone” in goaf: the heat dissipation zone and the spontaneous combustion zone become wider and the suffocation zone narrows. At the same time, the trend of spontaneous combustion zone presents to the deep part of the goaf; the amount of gas extraction increases first and then decreases with the increase of negative pressure. Combined with the trend of spontaneous combustion zone and the amount of gas extraction in goaf, and the reasonable negative pressure value is 32kpa and verified.

DEVELOPMENT OF CONCEPTUAL TECHNICAL SOLUTIONS AND METHODS OF THEIR IMPLEMENTATION DURING THE DESIGN OF A DUST COAL STEAM GENERATOR OF SUPER-SUPER CRITICAL PARAMETERS OF STEAM 28 MPa / 600 °С / 600 °C FOR 300 MW ENERGY UNIT. PART 2

In the second part of the work, using the mathematical model described in first unit, a direct-flow pulverized coal boiler with supercritical steam parameters of 28 MPa /600 °C /600 °C was calculated for a 300 MW power unit at loads of 50–70 %. It is shown that: a) the temperature of contaminated screens 1234 °С in the active combustion zone, where 92 % of the initial fuel burns out, is lower than the temperature of slagging beginning (1268 °С) of ДГ-100 coal, which indicates the slag-free operation of the screens of the lower radiation part (LRP) b) over the entire range of the boiler load change of 50–100 %, the temperature at the exit from the active combustion zone will be higher than the minimum permissible temperature of 1250 °C, below which the flame is attenuated; c) upon transition to 50 % load, the temperature of gases at the outlet from the active combustion zone decreases from 1506 °C to 1342 °C, as a result of which the specific thermal stress of the LRP screens decreases by 1.469 times, while the feed water consumption at the inlet of the boiler falls by 2 times, which leads to an increase in the temperature of the LRP steam, the middle and upper radiation parts, screens of the ceiling and rotating chamber; d) to reduce the thermal stratification of the inlet stage of the secondary steam superheater (ППП1), and as a consequence, the pipe wall temperature, it is necessary to divide the ППП1 surface into two packets, installing an intermediate mixing manifold between them with full steam mixing. Bibl. 5, Fig. 13, Tab. 3.

EFFECT OF THE EMBER ELEMENT IN INCREASING THE EFFICIENCY OF LPG STOVES

The purpose of this study is to attempt to increase the efficiency of LPG stoves by using an ember element made of woven nickel wire arranged in layers. It is supposed that high-temperature embers can burn more fuel around the wire, thereby increasing the area of complete combustion. Testing was conducted by means of a Water Boiling Test (WBT) and the number of ember layers varied from one to four. It was found that the use of elements of fire without reflectors could increase efficiency by 8.32%, with the highest efficiency being with the use of a single layer ember element of the fire, of 61.71%. However, the use of elements of fire in the finned heat reflectors causes efficiency to decrease, as the pattern to put elements of fire interfere with the reflectivity. This means the heat reflection is blocked by the pattern and trapped between the reflector and pattern elements. As a result, the heat energy from the reflector reflection cannot be forwarded to the combustion zone. The test results also show that the temperature distribution from ember element use can increase the area of complete combustion.

SOME TEMPERATURE CHARACTERISTICS SUB-LAYER AEROSOL EXTINGUISHING OF ALCOHOLS

Problem Statement: Nowadays, the process of sublayer aerosol quenching has not been studied at all, and its basic parameters, such as changes in flame temperature, liquid surface layer, tank sides, and approximate time of alcohol quenching and quenching, are unknown. The purpose of the work is to determine the parameters of sublayer aerosol quenching - flame temperature, the surface layer of liquid, tank sides, and the impact on the efficiency of sublayer quenching of aerosols dispersion – as one of the main parameters characterizing the process of alcohol quenching. The scientific novelty of the work is that for the first time the parameters of sublayer aerosol quenching at different sizes of aerosol bubbles were determined and it was found that at smaller bubbles the surface layer temperature decreases to 15%, aerosol distribution on the liquid surface is more uniform and a heterogeneous system is formed, which contains both aerosol solid particles – K2CO3, KOH, KNSO3, NH4HCO3, gases – CO2, N2, H2O, alcohol vapors, and the alcohol itself in the vapor and liquid phases. The main results of the study: The paper describes the developed installation and methodology for determining the parameters of sublayer aerosol quenching at different stages of the aerosol release process. The values of the flame temperature reduction and its behavior when the aerosol enters the flame are established. The established values are plotted and it is determined that when the aerosol enters the flame, the flame temperature begins to decrease actively and in 40 seconds reaches about 600 degrees Celsium. It was also found that the flame turns orange, which indicates that the combustion zone is the thermal dissociation of potassium salts, the flame size decreases, which indicates a decrease in the amount of alcohol vapor entering the combustion zone. The rate of cooling the sides at the exit of the aerosol from different-sized holes was also determined and it was found that the amount of cooling of the tank side is slightly higher at smaller hole diameters with a more uniform distribution of the aerosol on the surface. The range of reduction of liquid and board temperatures for each of the alcohols is less than the boiling point by 30-40 degrees Celsium. The decrease in temperature occurs at approximately the same rate and slows down until the end of the aerosol release. Analysis of the experimental results showed that the action of fire-extinguishing aerosol when it comes to the surface leads to intensive alcohol cooling due to bubbling of the aerosol through the alcohol layer, with active mixing of alcohol layers and the rise of cold liquids to the surface. This phenomenon leads to further cooling of burning surface of the liquid, which can have a temperature of 60 degrees Celsium to 97 degrees Celsium, as well as the sides of the tank as a result of alcohol on them and its intense evaporation. The result is the establishment of the parameters of the sublayer aerosol quenching – the temperature of the liquid surface, the temperature of the sides of the tank, the rate of aerosol to the surface, and the flame temperature when the aerosol enters the combustion zone.

Computational modeling of flow field in boiler before and after urea injection under different conditions

In order to achieve ultra-low NOx emissions, the effects of total excess air coefficient, air coefficient in main combustion zone, blended-coal combustion and ammonia nitrogen molar ratio on a 330 MW coal-fired boiler combustion were studied by numerical simulation. The results show that the velocity field and temperature field in the furnace have synergy, the better the synergy is, the faster the temperature rises, and the more NOx it generates. Compared before and after urea spraying, the NOx concentration decreased with the decrease of the total excess air coefficient, the optimum total excess air coefficient is about 1.15, and the denitrification rate is as high as 76.2%. The smaller the air coefficient in the main combustion zone is, the smaller the NOx concentration is. The optimum air coefficient in the main combustion zone is about 0.92, and the denitrification rate is 85%. After urea injection, the denitrification rate of high volatile coal combustion is higher than that of low volatile coal combustion, and the reasonable blending mode of coal can reduce NOx emissions. The larger the ammonia-nitrogen molar ratio is, the lower the NOx concentration is. When the ammonia-nitrogen molar ratio is greater than 2, the amount of ammonia escape at the flue outlet exceeds the standard. When the ammonia-nitrogen molar ratio is less than 1, the NOx concentration at the flue outlet is greater than that before urea injection. The optimal ammonia-nitrogen molar ratio is about 2.

Efficiency of fire extinguishing with general purpose fire extinguishing powder in case of non-stationary interaction of its particles with burning material

Evaluation of the effectiveness of fire extinguishing by jet systems of powder fire extinguishing in conditions of non-stationary heat exchange processes and heterogeneous inhibition of active flame centers by powder particles was the aim of the work. The theoretical dependence of the amount of heat, absorbed by the particles of fire extinguishing powder, and the reaction rate of heterogeneous active centers of flame, inhibiting them, in non-stationary conditions of heat transfer, as well as inhibition reaction for fire extinguishing ink jet systems were obtained. The extinguishing of a flame with a fire extinguishing powder under non-stationary conditions is more effective, the smaller is the effective size of the powder particles, the longer is their stay in the combustion zone, and the shorter are the characteristic times of heat transfer and inhibition reaction. Comparison of the estimates of the characteristic duration of heat transfer and inhibition reaction for widely used fire extinguishing powders has shown a large inertia of the thermal mechanism of fire extinguishing, which greatly reduces its effectiveness at high speeds of powder particles in the combustion zone.