| Early prediction is the key to a comprehensive disaster prevention of spontaneous combustion of coal. Currently, the indirect method, by collecting and analyzing gas samples and being compared to index gas, is used to determine the status of coal combustion, and CO is a sort of common and effective index gases. However, practice shows that spontaneous combustion of coal is not the only source of CO in the coal mine; CO concentration in coal-bed methane being over the "Coal Mine Safety Regulations" standard is continuously detected during a very long period of time in many low-level coal mine mining process. Among them, some of which are caused by spontaneous combustion of coal, however, there is no spontaneous combustion occurs in other cases, which is mostly caused by primal carbon monoxide generating with the coal-forming process. This problem has seriously affected the normal development of coal mine production safety work. Currently, it is generally believed that CO overrun mainly due to blasting word or coal spontaneous combustion in coal mine, and there is little emphasis on the reason of primal CO adsorption and emission, the research on the generation, occurrence and the adsorption and desorption law of primal CO is not enough, there is no clear understanding of the generation mechanism of coal CO, and no sound measuring method of CO emission after coal mining. Therefore, researching the generation mechanism and measuring method of coal primal CO and analyzing the adsorption characteristics and emission law after coal crushing of CO are with important scientific significance to improve the accuracy of forecasting coal spontaneous combustion and ensure the normal and safe production of coal mining enterprises and safety of miners.CO generation and dissipation were studied from the perspective of coal formation through literature research and theoretical studies. It is conclutied that primal CO in coal seam is mainly generated by three phases and methods-biogenic, thermogenic and abiogenetic. Thermogenic CO is mainly produced in the early stage of thermal degradation- "long flame coal to gas coal" stage, the concentration of CO in this stage is relatively high. The primal CO was found in widespread geographical distribution all over our country, coal types were maily lignite, low metamorphic long flame coal-gas coal and tectonic coal, magma intrusion coal is a typical example. Based on available information, occurrence characteristics of primal CO were analyzed and the difficulties of primal CO measuring were studied. It is believed that the primal CO is easily confused with there types CO sources, which include CO generated by coal crushing decarbonylation, CO generated by coal reacting with oxygen under normal temperature and CO generated by local high-temperature for short-time friction, drlling process is a typical example for the last case. The main difficulty for measuring primal CO is the existence of above cases, but in addition, difficulty, amount and concentration level of CO desorption and other factors also affect the actual operation of theoretical approaches.This paper conducted an investigation on relevant primal CO measureing method which has been carried out in our country. Based on this, considering the purpose and requirements of measureing, physical and chemical properties of coal, simple process, safe experiment, high test precision and ease of automation, functional analysis was carried out of the experimental system. Experimental system was divided into seven parts- sealed nitrogen crushing and sampling device, direct gas desorption apparatus, external heating thermostat, the desorbed gas collecting apparatus, the gas component concentration measuring means, gas line and gas distribution and the experimental control and data acquisition device. And a preliminary analysis of the hardware configuration according to functional of subsystems was carried out to form the original content of coal seam gas composition and emission testing analysis platform. This system mainly consists of nitrogen sealed sample cans, ball mill, underground gas desorption instrument, temperature-programed oven, laboratory drainage gas gathering deviece, gas composition and concentration detector, gas distribution and gas path, experiment control and data acquisition deviece, coal sample weighing and screening devices. The establishment of the platform laid a foundation for subsequent experimental research.Based on the platform, this paper gave the testing method for the original gas composition and content changes over time after crushing and studied the calibration method of gas amount and the best mill rotation rate. According to this testing method, 6 coal samples of Xingtao coal mine in Shuozhou(XT), Donghuantuo coal mine in Tangshan(DHT), Linnancang coal mine in Tangshan(LNC), Xixizhuang coal mine in Zhangjiakou(XXZ1# and XXZ5#) and Dashucun coal mine in Handan(DSC) were tested. Testing of the original gas component content of coal samples and their changes over time were carried out under six different conditions- grinding 3 hours accompanied by introduction of nitrogen under the best working conditions at ambient temperature 25?(L3), grinding 2 hours accompanied by introduction of nitrogen under the best working conditions at ambient temperature 25?(M2), grinding 3 hours accompanied by introduction of nitrogen under the best working conditions at ambient temperature 30?(M3), grinding 3 hours accompanied by introduction of nitrogen under the best working conditions at ambient temperature 35?(H3), grinding 3 hours accompanied by introduction of air under the best working conditions at ambient temperature 30?(AM3), grinding 4 hours accompanied by introduction of nitrogen under the best working conditions at ambient temperature 30?(M4). It is concluded that component and concentration of original gas for different coal samples are not the same, the introduction of air has an impact to gas component and emission after coal crushing. At last, the SPSS software was used to make numerical fitting of CO concentration varing with time for 6 coal samples under M3 condition, and a conclutsion was obtained that the relationship between testing concention of CO and time basically follow the exponential distribution.Measuring method and analysis indicators of content and emission law of primal CO were studied, which includes the initial concentration of CO emission(Ic), emission attenuation coefficient(Ia), 10 h emission amount(IQ10) and 10-24 h emission amount(IQ10-24). The differences of emission laws between primal CO, CO2 and CH4 were analyzed, it is believed that attenuation of CO and CH4 is much larger than the CO2 within 10 h, attenuation of CH4 and CO is similar and emission of CO, CO2 and CH4 respectively follow exponential, logarithmic and exponential distribution. The relevance between emission characteristics of primal CO and intrinsic parameters of coal(industrial composition, element content and porosity characteristics) was studied, it is believed that intrinsic parameters have a certain impact on primal CO emission and the effect is overall the result of the combined effects of many parameters. The relvevance between emission characteristics of primal CO and the external environment was studied, it is believed that the ambient temperature mainly have impact on the attenuation coefficient and release amount and no significant effect on the initial concentration emission, degree of fragmentation will affect the amount and initial concentration of emission, CO generation of low-temperature oxidation for different coal samples vary greatly. The relvevance between emission characteristics of primal CO and coal rank and geological conditions was studied, it is believed that the genertation of coal primal CO is casued by the two factors together. Primal CO is most likely to produce at gas coal stage; closed extrusion and friction are prone to CO production. Coal seams with large amount of primal CO in this paper structurally complex, there is enclosed area due to the presence of tectonic movement, coal seams simply being in the right metamorphic stage does not guarantee the occurrence of primal CO, complex geological conditions may be a necessary condition for the occurrence of primal CO, appropriate degree of metamorphism and sealed structure existing simultaneously(LNC) may cause a lot of primal CO occurrence.Fourier transform infrared spectroscopy was used to test the sample surface functional groups under four conditions(in turn four conditions)- original untreating, atmospheric desorption 72 h in nitrogen, 25? oxidation 72 h in ambient air and100? oxidation 10 h in ambient air. Analyzing the infrared spectra of different rank coals, it is showed that Carbonyl(710-1700 cm-1 and 1736-1722 cm-1) peak intensity of the spectrum is very low and alkyl ethers(1050-1030 cm-1) and aromatic ether(1264-1255cm-1) peak intensity of the spectrum is high, which Show that in addition to hydroxy ether bonds account for the major portion of the oxygen-containing functional groups, is an important form of coal macromolecules bridge between the basic cell structure,the oxygen-containing functional groups including ether oxygen bonds show a descreasing trend with the deeping of metamorphic grade. It is showed by Infrared spectra under different conditions that the surface active groups of original coal samples did not significantly change at atmospheric nitrogen desorption conditions, this indicates that chemical reaction does not occur or the degree of reaction is undetectable. Low rank coal reacted with oxygen in the air at room temperature conditions, the surface functional groups obviously changed, predominantly aliphatic hydrocarbon content is reduced, parts of the oxygen-containing functional groups increase or slightly decrease, however, the extent of reaction for high rank anthracite is very low. Significant chemical reaction occurred in all coal samples at 100 ?, significant raction occurr in low rank lignite,the extent of reaction for high rank anthracite is very low, predominantly aliphatic hydrocarbon content is reduced, oxygen-containing functional groups are significantly changed, which shows that surface active groups are the intermediary in the oxidation reaction before entering the combustion stage. Finally, this paper analyzed the formation mechanism of CO in coal seam based on previous studies, it is believed that in addition to physical desorption CO, carbonyl groups and carboxyl groups may products CO by self-reaction under non-oxidizing conditions. The generation courses of CO by the oxidation of 6 kinds of typical groups were theoretically studied, it is believed that coal generating CO is very complex in the low temperature oxidation process, there are many active groups' generation and consumption during this process, however, and finally CO is mainly generated by the carbonyl group or carboxyl group, there are also transition and the participation of other groups such as hydroxyl.Pressure method is applied to adsorption and desorption experiments of XXZ 5# and LNC coal samples, concentration of CO, CO2 and CH4 is 5000×10-6 and He is the balance gas in standard gas. Experiments carried out under four differents conditionssimply using the standard gas and respectively pressurized with He, CO2 and CH4 after injecting 1MP satanderd gas. Adsorption characteristics of low concentration multi-gas containing CO was studied maily by analyzing concentration changes of three absorptional gases during adsorption- desorption process, and the adsorption characteristics of CO and its relvevance with other gas components were futher intensively studied. It is showed that at low concentrations, although the amount of adsorption of three gases rise with pressure and there is a certain slowing trend, but it is less than that of the late stage of pure gas adsorption, adsorption volume of desorption process is greater than that of adsorption process at the same pressure, there is a certain "Delay" feature, which is much more obvious than that of pure gas adsorption. At low concentrations, CO and CH4 adsorption capacity is similar, but CO is a little weaker than CH4, adsorption capacity of both two gases is significantly weaker than CO2 at low concentration. The adsorption and desorption process of CO is largely affected by high concentrations of CH4 and CO2 under condeitons of standered gas-CH4 and standered gas-CO2. Impact of unadsorptive gas He is mainly reflected in the dilution effect, which influence adsorption and desorption equilibrium. The adsorption characteristics of CO, CH4 and CO2 can be well expressed by pure standered gas and standered gas-He adsorption process. There is not only differnts of adsorption capacities but also influence and constraints between the three gases duting the adsorption process, high concentrations of CO2 and CH4 have a significant displacing effect on CO adsorption, among which the effect of CO2 is the most prominent. |
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