A new theory of chemical method to prevent spontaneous combustion of coal

In order to prevent spontaneous combustion of coal from the source,based onthe study on the mechanism of spontaneous combustion of coal,especially the process ofcoal to self-ignite and different activate structures have different activation for oxidization,the new theory and mechanism with chemical inhibition that can change the tendency ofspontaneous combustion of coal and let the activate structures deactivate were broughtforward.Therefore,coal was not self-ignited under a certain temperature when beingchemically inhibited.

The shortest period of coal spontaneous combustion on the basis of oxidative heat release intensity

It’s necessary to forecast the shortest spontaneous combustion period for preventing and controlling the coal spontaneous combustion.During the experimental process,a calculating model of the SSCP is established on the basis of the oxidative heat release intensity and thermal capacity at different temperatures.According to the basic parameters of spontaneous combustion,heat of water evaporation and gas desorption,the SSCPs of different coals are further predicted.Finally,this study analyzed the relationships of the SSCP and the judging indexes of the self-ignite tendency.The result shows that the SSCP non-linearly increases with the decrease of dynamic oxygen adsorption and increase of activation energy.Compared with the practical fire situation of mine,this reliable method can meet the actual requirement of mine production.

Characteristics of coal re-oxidation based on microstructural and spectral observation

In order to investigate the characteristics of re-oxidation of residual coal in goafs in close coal seam mining,scanning electron microscope and infrared spectrometer are used to study the changes of coal microstructure and chemical reaction of functional groups of eight coal samples at different ranks.Result shows that after initial oxidation,the surface morphology of pore are different,and the porosity of coal is increased and the oxygen adsorption capacity of coal is improved.The change of coal molecular structure and presence of a large amount of active oxygen-containing functional groups lead to increasing tendency of coal to further oxidation.In addition,the higher lever of the initial oxidation is,the easier the re-oxidation occurs.

Changes in active functional groups during low-temperature oxidation of coal

Using Fourier Transform Infrared (FTIR) combined with an adiabatic oxidation test, temperature-programmed oxidation and gas analysis, we studied the changes of active functional groups during low-temperature oxidation of lignite, gas coal, fat coal and anthracite. During slow low-temperature heat accumulation, aliphatic hydrocarbons, such as methyl and methylene, are attacked by oxygen atoms absorbed by pores on coal surfaces, generating unstable solid intermediate carbon-oxygen complexes, which then decompose into gaseous products (CO, CO2) and stable solid complexes. At the accelerated oxidation stage, the stable complexes begin to decompose in large amounts and provided new active sites for further oxidation, while the aliphatic structures gained energy and fell from the benzene rings to produce CxHy and H2.

Prediction of oxygen concentration and temperature distribution in loose coal based on BP neural network

An effective method for preventing spontaneous combustion of coal stockpiles on the ground is to control the air-flow in loose coal. In order to determine and predict accurately oxygen concentrations and temperatures within coal stockpiles, it is vital to obtain information of self-heating conditions and tendencies of spontaneous coal combustion. For laboratory conditions, we designed our own experimental equipment composed of a control-heating system, a coal column and an oxygen concentration and temperature monitoring system, for simulation of spontaneous combustion of block coal （13-25 mm） covered with fine coal （0-3 mm）. A BP artificial neural network （ANN） with 150 training samples was gradually established over the course of our experiment. Heating time, relative position of measuring points, the ratio of fine coal thickness, artificial density, voidage and activation energy were selected as input variables and oxygen concentration and temperature of coal column as output variables. Then our trained network was applied to predict the trend on the untried experimental data. The results show that the oxygen concentration in the coal column could be reduced below the minimum still able to induce spontaneous combustion of coal - 6% by covering the coal pile with fine coal, which would meet the requirement to prevent spontaneous combustion of coal stockpiles. Based on the prediction of this ANN, the average errors of oxygen concentration and temperature were respectively 0.5% and 7 ℃, which meet actual tolerances. The implementation of the method would provide a practical guide in understanding the course of self-heating and spontaneous combustion of coal stockpiles.

Bulking factor of the strata overlying the gob and a three-dimensional numerical simulation of the air leakage flow field

The present study examines the results of the researches related to the gob bulking factor carried out at home and abroad.A mathematical function of a three-dimensional gob bulking factor is described based on a three-dimensional gob model.The method of taking value for interstice and permeability ratios is also proposed.The law of air leakage of fully mechanized top coal is researched in this study.The results show that the speed of air flow near the upper and lower crossheadings is higher than that in the central section of the gob at the same distance from the working face.When the amount of air at the working face exceeds a critical amount,the width of the spontaneous combustion zone in the upper and lower crossheadings is also larger than that in the central section.In this situation,the key is preventing the coal left in the upper and lower crossheadings from self-igniting.Reducing the amount of air at the working face can decrease the width of the spontaneous combustion zone,especially the width near the upper and lower crossheadings.This also moves the spontaneous combustion zone in the direction of the working face.It can prevent the coal in the gob from self-igniting by making the coal left in the crossheadings to be inert and by effectively controlling the amount of air at the working face.

Production and Properties of a Thickener with Ability of Suspending Sand

To overcome the shortcomings of pouring sands, a thickener with the ability to suspend sands was developed. It is mixed with sands to form densified slurry, and can insure the sands against deposition, jamming pipelines and de- hydration. The chemical structure of the thickener is introduced in this paper and the production process is studied. The main processes include immersion, decomposition, dilution and addition of additives. In order to produce a thickener with high viscosity to suspend sands, key factors must be controlled in each process: the immersion time is 2 h; the mass fraction of formaldehyde is 0.01% and mass of NaCO3 accounts for 15% of dry material; the water temperature is 65 ℃ in summer and 72 ℃ in winter and the decomposition time is 2 h in the reaction; the densified decomposition so- lution should be diluted to 1% mass fraction; the additives of calcium ions and pH indicators must be added to the di- luted liquid; the mass fraction of CaCl2 is 0.048% and the pH value of the solution is 7.5. The thickener is a gel with three-dimensional network structure, a liquid with non-Newtonian behaviour and the characteristics of pseudo-plastic material, a solution with little resistance and the ability to revive its oral primary viscosity. It has been successfully ap- plied in Shendong Mines and has great value and wide-spread prospective use.

Experimental research on inorganic solidified foam for sealing air leakage in coal mines

In order to efficiently seal air leakages and control spontaneous combustion of coal, solidified foam was developed by adding a certain compound additive to fly coal ash and cement as the main materials. It was prepared basing on the foaming characteristic through physical and mechanical system. We studied the effects of the different types of foaming agents, the mass ratio of cement to fly ash, and the mass ratio of solid to water and content of cellulose on the performance of solidified foam. The results show that when adding the composite protein, surfactant and cellulose foaming agents. The cement-fly ash ratio of 0.75:1, the water solid ratio as large as 2:1, and the solidified foam with high properties and density of only 516 kg/m 3 and compressive strength of up to 12.68 MPa were prepared. But the initial setting time, identity and compressive strength may be changed by varying the water solid ratio and/or the additives. We theoretically analyzed the influence mechanism of foam density, compressive strength and water solid ratio. The solidified foam is especially suitable for sealing surface leakage channels and filling the goaf with a wide application prospects.

A new forecast model for the carbon-monoxide concentration in the upper corner of mining face

The CO gas in the upper comer along with the work of mining face in different coal-seam of Lingwu coal-field has deeply affected judgment for the degree of the coal spontaneous combustion and safety work. For this issue, a new calculation and forecast model of the carbon monoxide concentration in the upper comer of mining face was deduced for analyzing and calculating the date from the lab and test-in-place, during this course using the knowledge of heat transfer, fluid dynamics, and mathematics. The model took into account the characteristics of the coal spontaneous combustion, coal mining conditions, and other correlate factors, so the CO concentration of the upper comer safe under the normal condition, and it is in danger when the coal reached spontaneous combustion, which can be calculated accurately with the model and compared with the measured concentration with a tolerance of less than 12%.

Influence of fly ash and sewage sludge application on wheat biomass production,nutrients availability,and soil properties

The influence of fly ash(FA)applied alone and/or with sewage sludge(SS)on wheat(Triticum vulgare)grain yield,biomass production and soil properties was studied in a field experiment.The results showed that both FA and SS significantly increased grain yield and plant biomass.FA applied alone increased significantly soil pH and EC while FA applied together with SS did not significantly affect them compared to mono FA treatment.Soil pH and EC values increased with time in FA and FA-SS treatments.SS increased soil organic matter and total N content and SS applied together with FA increased also available soil B.From the plant nutrients tested only tissue N concentration was increased significantly in all treatments compared to control.Copper,Zn,Mn,Ni,and Pb at both available and total concentrations are significantly affected.

Improved Sorting Scheme of Microstructure of Fly Ash

Aiming at the problem of the existing sorting for microstructure of fly ash, an improved scheme was put forward in this paper. First, fly ash particles are divided into four groups as low calcium, iron, high calcium and char particle according to the substance components of fly ash. Then fly ash particles are divided into 14 sub groups, for example: cenospheres, plerospheres, solid spheres, porous char and dense char based on their chemical composition, shape and the characteristics of inner structure of fly ash. It has a distinct difference in granule configuration, inner structure and substance components. Some disadvantages of the existing scheme such as unilateralism and imprecision have been overcome in the advanced schemes.