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Technical Measures and Selections for Reducing Flue Gas Heat Loss of Large Coal-Fired Boilers
The main technologies for reducing flue gas heat loss of pulverized coal-fired boilers are introduced,and the suitability of these technologies for boiler operation and the principles for selection of these technologies are explored.The main conclusions are:1) the non-equilibrium control over flue gas flow rates at the inlet of the air heater and the reversal rotation of the air heater rotator should be popularized as regular technologies in large boilers; 2) increasing the area of the air heater to reduce the flue gas heat loss in pulverized coal-fired boilers should be the top option and increasing the area of the economizer be the next choice; 3) lowpressure economizer technology could save energy under special conditions and should be compared with the technology of increasing economizer area in terms of techincal economics when the latter is feasible; 4) the hot primary air heater is only suitable to the pulverizing system with a large amount of cold air mixed....
2020-06-12 16:19:11浏览：1403
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The Influence of CO on the Carbon Isotopic Composition of CH4 in Closed Pyrolysis Experiment With Co
A low-mature coal (Ro=0.4%, from the Manjia'er depression, Tarim Basin, China) was subjected to closed system pyrolysis, in sealed gold tubes, under isothermal temperature conditions. The carbon isotopic compositions of the pyrolyst fractions (hydrocarbon, CO2, CO, etc.) at two temperature points (350°C and 550°C) were measured. The results showed that δ13CCH4 value is generally heavier at 350°C than that at 550°C, because the high abundance of CO generated at low temperature would greatly influence δ13CCH4 value, and the retention time of CO in gas chromatograph is close to that of CH4. But CO is formed through chemical reaction of the oxygen-containing functional group C=O, e.g. Lactones, ketones, ether, etc. At low temperature, while CO2 comes mainly from zecarboxylization.The carbon isotopic composition of coal gas from Lanzhou Coal Gas Works was definitely different from that of thermally pyrolysed products from coal. Theδ13CCH4 value of coal gas was abnormally heavier than δ13CCO. At the same time, the reversed sequence (δ13C-1＞δ13C-2) of δ13C1 and δ13C2 happened. The bond energy of free ions generally decides the sequence of generation of hydrocarbon fractions according to the chemical structure, whereas the stability of pyrolysate fractions and their carbon isotope fractionation are affected by the C-C bond energy....
2020-06-12 16:19:07浏览：1435
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Natural Gas and Indoor Air Pollution: A Comparison With Coal Gas and Liquefied Petroleum Gas
The study was designed to compare the combustion products of coal gas, liquefied petroleum gas and natural gas in relation to indoor air pollution. Methods Regular pollutants including B(a)P were monitored and 1-hydroxy pyrene were tested in urine of the enrolled subjects.Radon concentrations and their changes in four seasons were also monitored in the city natural gas from its source plant and transfer stations to final users. To analyze organic components of coal gas,liquefied petroleum gas and natural gas, a high-flow sampling device specially designed was used to collect their combustion products, and semi-volatile organic compounds contained in the particles were detected by gas chromatograph-mass spectrograph (GC/MS). Results Findings in the study showed that the regular indoor air pollutants particles and CO were all above the standard in winter when heating facilities were operated in the city, but they were lowest in kitchens using natural gas;furthermore, although NO2 and CO2 were slightly higher in natural gas, B(a)P concentration was lower in this group and 1-hydroxy pyrene was lowest in urine of the subjects exposed to natural gas.Organic compounds were more complicated in coal gas and liquefied petroleum gas than in natural gas. The concentration of radon in natural gas accounted for less than 1‰ of its effective dose contributing to indoor air pollution in Beijing households. Conclusion Compared to traditional fuels, gases are deemed as clean ones, and natural gas is shown to be cleaner than the other two gases....
2020-06-12 16:19:06浏览：1426
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Principle and engineering application of pressure relief gas drainage in low permeability outburst c
With the increase in mining depth, the danger of coal and gas outbursts increases. In order to drain coal gas effectively and to eliminate the risk of coal and gas outbursts, we used a specific number of penetration boreholes for draining of pressure relief gas. Based on the principle of overlying strata movement, deformation and pressure relief, a good effect of gas drainage was obtained. The practice in the Panyi coal mine has shown that, after mining the Cllcoal seam as the protective layer, the relative expansion deformation value of the protected layer C13 reached 2.63%, The permeability coefficient increased 2880 times, the gas drainage rate of the C13 coal seam increased to more than 60%, the amount of gas was reduced from 13.0 to 5.2 m3/t and the gas pressure declined from 4.4 to 0.4 MPa, which caused the danger the outbursts in the coal seams to be eliminated. The result was that we achieved a safe and highly efficient mining operation of the C 13 coal seam....
2020-06-12 16:19:02浏览：1402
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Failure characteristics of surface vertical wells for relieved coal gas and their influencing factor
Based on data from through-hole and logging, we studied the failure characteristics of surface drainage wells for relieved coal gas in Huainan mining area and its influencing factors. The results show that the damaged positions of drainage wells are mainly located at the thick clay layer in the low alluvium and the lithological interface in the upper section of bedrock in west mining area. The failure depth of casing is 244-670 m and concentrates at about 270-460 m deep. These damaged positions are mainly located in the bending zone according to three zones of rock layers in the vertical section above the roof divided. Generally, the casing begins to deform or damage before the face line about 30-150 m. Special formation structure and rock mass properties are the direct causes of the casing failure, high mining height and fast advancing speed are fundamental reasons for rock mass damage. However, the borehole configuration and spacing to the casing failure are not very clear....
2020-06-12 16:18:47浏览：1395
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A new technology for coal and gas control based on the in situ stress distribution and the roadway l
An auxiliary gas control technology is described that can reduce coal and gas outburst accidents when there is no existing protective coal seam and gas pre-draining is not effective.Numerical simulation methods were used to study the Stress distribution ahead of the roadway face for different in situ stresses.The results from the simulation can then provide a new gas control technology.The results show that a high stress concentration,high stresses,and high displacement gradients appear ahead of the roadway face when the maximum in situ stress is aligned perpendicular to the roadway axis.The risk of gas outburst is higher when the stresses decrease rapidly over distance and when the release of more energy occurs immediately after driving the roadway.The gas outburst risk is much smaller when the in situ stress is aligned parallel to the roadway axis.During design of the coal mine most of the coal roadways should be arranged to parallel the maximum in situ stress.This will decrease the outburst risk in general and may be considered a new gas outburst prevention method....
2020-06-12 16:18:28浏览：1431
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Partitioning characteristics of gas channel of coal-rock mass in mining space and gas orientation me
In order to research the influence of coal-rock mass morphology of mining space on the flow law of gas, the laboratory physical model and numerical computation methods were adopted to simulate coal min-ing activities. The simulation results indicate that, after coal seam mining, the loose rock accumulation body of free caving, ordered rock arrangement body of plate damage rich in longitudinal and transverse fractures and horizontal fissure body formed by rock mass deformation imbalance are formed from bottom to top in the mining space. For these three types of accumulation bodies, there are essential differences in the accumulation state, rock size and gas breakover characteristics. According to this, the coal-rock mass in the mining space is classified into gas turbulence channel area, gas transitional flow channel area and gas seepage channel area. In the turbulence channel area, the gas is distributed trans-versely and longitudinally and gas diffuses in the form of convection with Reynolds number Re more than 100;in the transitional flow channel area, one-way or two-way gas channels are crisscross and gas is of transitional flow regime with Re between 10 and 100. In the seepage channel area, there are a few vertical gas channels with Re less than 10. In this paper, the researches on the gas orientation method in different partitions were further carried out, gas orientation methods of low-level pipe burying, middle-level interception and high-level extraction were determined and an on-site industrial test was conducted, achieving the effective diversion of gas and verifying the reasonableness of gas channel partition....
2020-06-12 16:18:24浏览：1428
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Resarch and Development of Hot Primary Air Heater for Coal-Fired Boilersin Power Plant
The reasons of introducing cold air into pulverizer are analyzed for boilers with large capaciiy and high parameters.The temperature rises of the exhaust gas are calculated when varying the amount of the cold air.The hot primary air heater,a new technology,is developed to eliminate the cold air from the pulverized coal system.The applications,advantages and disadvantages are introduced in detail for the new device and system.It is concluded that introducing cold air into pulverizer is one of the major factors that causes the exhaust gas temperature of boilers with large capacity to be high.The amount of the cold air could be reduced significantly,even to zero in some cases by adopting the hot primary air heater,which drops the exhaust gas temperature of the boiler effectively.The hot primary air heater,which could play part roles of the steam-air heater or the hot air recirculation system,could also be used to adjust the exhaust gas temperature within the range of 20 ℃ by controlling the flow rate of the cooling medium.Moreover,the startup period of the steam-air heater or the hot air recirculation system will be shortened,which is a unique advantage of the hot primary air heater among the measures to drop the exhaust gas temperature....
2020-06-12 16:18:21浏览：1453
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Upgrading of Yi'an gas coal by low temperature pyrolysis under different atmospheres
The quality of Yi'an gas coal before and after low temperature upgrading under either a N2 or H2 atmosphere was examined by thermogravimetric and infrared analyses.The effect of upgrading on the prepared coke quality was analyzed.The results show that the carboxyl and phenolic hydroxyls in the coal molecular structure are removed after upgrading by low temperature pyrolysis under either N2 or H2 atmospheres.This improves coal caking properties to a certain extent.The upgrading effect under a H2 atmosphere is remarkably better than the effect observed after upgrading under N2.Compared to coke obtained from raw coal,the compressive- and micro-strength of the cokes obtained from upgraded coal are greatly improved.The effect on coke reactivity with CO2 is not significant.The best upgrading temperature for Yi'an gas coal under either a N2 or H2 atmosphere is 250 or 275 ℃ respectively....
2020-06-12 16:17:52浏览：1419
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Secondary biogenic coalbed gas in some coal fields of China
The secondary biogenic coalbed gas, a new genetic and energy source type of coalbed gas in China, has been found in Xinji, Liyazhuang and Enhong areas. The essential characteristics of this type of gas are: (i) the major component of the gas is methane, with C1/C1-5 value higher than 0.99, indicating that the gas is part of dry gas; (ii) the δ13C1 value is in the range of -61.7‰ to -47.9‰, mostly lower than -55‰, which is much lower than the estimated δ13C1 value of thermogenic methane according to the thermal evolution degree of the coal rocks (with Ro value from 0.87%to 1.43%), showing the characteristics of the secondary biogenic gas; (iii) the δD value of methane ranges from -244‰to -196‰; (iv) δ13C 2 value ranges from -26.7‰ to -15.9‰and δ13C 3 value ranges from -10.8‰ to -25.3‰, indicating that the heavier hydrocarbons have a thermogenic origin; (v)the content of CO2 is very low, and δ13Cco2 value changes greatly, reflecting a characteristic of secondary change; (vi)δ15N2 value ranges mainly from -1‰ to +1‰, indicating N2derived significantly from air. The negative linear correlation between the contents of N2 and CH4 reflects the activity of bacteria bearing surface water infiltrating into coal beds.The comprehensive tracing indices show that the coalbed gas in the studied areas is the mixed gas of primarily secondary biogenic gas and a part of remnant thermogenic gas. The uplift of coal beds and the development of faults in the studied areas create favorable conditions for the formation of the secondary biogenic gas....
2020-06-12 16:17:49浏览：1407
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Prognosis of residual coal gas capacity made by the 'Express' method
An easy, reliable, and inexpensive method, called ‘Express' method, was described to determine the residual gas capacity of deep mines using results from an air and gas balance. Air and gas balances are common elements of mine management and must be performed periodically. Using the process described here to obtain balance results, it is straightforward to obtain the residual gas capacity, which is an important parameter for decision-making in current mine operations. After a mine is closed, the residual gas capacity becomes a dominant factor used to select methods to protect against gas emissions from the closed underground area or perhaps to provide information for the use of purpose to date....
2020-06-12 16:17:48浏览：1453
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Research on forced gas draining from coal seams by surface well drilling
Surface drilling was performed at the Luling Coal Mine, in Huaibei, to shorten the period required for gas draining. The experimental study was designed to reduce the cost of gas control by efficiently draining gas from the upper protected layer. The structural arraignment and technical principles of pressure relief via surface drilling are discussed. Results from the trial showed that gas drained from the surface system over a period of 10 months. The total amount of collected gas was 248.4 million m3. The gas draining occurred in three stages: a growth period; a period of maximum gas production; and an attenuation period. The period of maximum gas production lasted for 4 months. During this time the methane concentration ranged from 60% to 90% and the average draining rate was 10.6 m3/min. Combined with other methods of draining it was possible to drain 70.6% of the gas from middle coal seam groups. The amount of residual gas dropped to 5.2 m3/ton, and the pressure of the residual gas fell to 0.53 MPa,thereby eliminating the outburst danger in the middle coal seam groups. The factors affecting pressure relief gas draining by surface drilling were analysed....
2020-06-12 16:17:44浏览：1433
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A general solution and approximation for the diffusion of gas in a spherical coal sample
The square root relationship of gas release in the early stage of desorption is widely used to provide a simple and fast estimation of the lost gas in coal mines. However, questions arise as to how the relation-ship was theoretically derived, what are the assumptions and applicable conditions and how large the error will be. In this paper, the analytical solutions of gas concentration and fractional gas loss for the dif-fusion of gas in a spherical coal sample were given with detailed mathematical derivations based on the diffusion equation. The analytical solutions were approximated in case of small values of time and the error analyses associated with the approximation were also undertaken. The results indicate that the square root relationship of gas release is the first term of the approximation, and care must be taken in using the square root relationship as a significant error might be introduced with increase in the lost time and decrease in effective diameter of a spherical coal sample....
2020-06-12 16:17:40浏览：1421
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Conversion Excess Coal Gas to Dimethyl Ether in Steel Works
With the technical progress of metallurgical industry, more excess gas will be produced in steel works. The feasibility of producing dimethyl ether by gas synthesis was discussed, which focused on marketing, energy balance, process design, economic evaluation, and environmental protection etc. DME was considered to be a new way to utilize excess coal gas in steel works....
2020-06-12 16:17:28浏览：1430
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Microseismic Monitoring Data Fusion Algorithm and Coal and Gas Outbursts Prediction
The prediction study on coal and gas outbursts is carried out by monitorisng some indices which are sensitive to the initiation of coal and gas outbursts.The values and changing rules of the irdices are the foundations of coal and gas outbursts prediction.But now,only the data of one key monitoring station is used in the coal and gas outbursts prediction practice,and the other data are ignored.In order to overcome the human factor and make full use of the monitoring information,the technique of multi-sensor target tracking is proposed to deal with the microseismic information.With the results of microseismic events,the activities of geological structure,fracture-depth of roof and floor,and the location of gas channel are obtained.These studies indicate that it is considerably possible to predict the coal and gas outbursts using microseismic monitoring with its inherent ability to remotely monitor the progressive failure caused by mining....
2020-06-12 16:17:21浏览：1429
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