| The UCG mass and energy balance model is established by combing the distribution characters of “three zones”, including oxidation zone, reduction zone and dry distillation zone, in the UCG process with the balance model of coal gasification system on the ground. Through the pyrolysis experiments of different coals at different end temperature, the transfer formulas of elements in the raw coal were obtained. Through the UCG model test where the structure of gasification channel, injection way and composition of gasification agents and volume flow rate of water influx were different, the control formula and constant η of carbon transfer ratio and water-gas-shift(WGS) equilibrium constant Kp were obtained at the base of the area ratios of “three zones”. The UCG mass and energy balance model softeare was developed, when the model was applied in UCG field test, the calculations of the syngas concentration and heat efficiency was exact enough, the accuracy and the value of application were good. The maim research purposes, methods and results are as follows:1、 In the atmosphere of N2 the lignite, bituminous coal and anthracite coal were heated at low heating rae of 10℃/min and ordinary pressure. The end temperature of pyrolysis were as follows: 500℃, 600℃, 700℃, 800℃, 900℃.The product output and constitution were analysed. According to the conservation law of element, transfer ratios of elements can be calculated from raw coal to pyrolysis products. The results showed that:(1)At different end temperatures, C element in lignite and bitumimous coal mainly transfered into gasification carbon and tar, a(C,gasification carbon) and a(C,tar) of bituminous coal were higher, the transfer formulas were as follows: y = 1E-05x2-0.0371 x + 93.908, y = 2E-07x3- 0.0005x2 + 0.3624x- 68.835,(y-transfer ratio, x-end temperature). C element in anthracite coal mainly transfered into gasification carbon and CH4, the transfer formulas were as follows: y = 2E-07x3- 0.0004x2 + 0.2528 x + 47.888, y =-3E-05x2 + 0.0496x- 17.089. a(C, gasification carbon) decreased with the increasing temperature, at 600 ℃ a(C,tar) was maximum for each coal.(2)H element mainly transfered into residue, tar, H2 O, CH4, H2. a(H, residue) and a(H, H2) of anthracite coal were highest, the transfer formulas were as follows: y =-0.1725 x + 179.09, y = 0.1237x- 63.067. a(H, tar) of bituminous coal was highest, the transfer formulas was: y =-4E-09x4 + 1E-05x3- 0.0126x2 + 5.9058x- 999.05. a(H,H2O) and a(H, CH4) of lignite were highest, the transfer formulas were: y = 6E-08x3-0.0004x2 + 0.4065x- 101.71, y = 0.0528x- 17.602. a(H, hydrocarbon gases) decreased when the side chains, bridge bond and low molecular compound decreased with the increasing coal rank; for a(H,NH3), a(H,HCN) and a(H,H2S), with the increasing temperature the gas permeability of the pyrolysis products of bituminous coal was bad, and the pyrolysis of gas occurred twice for the high diffusion resistance, so the a(H,NH3), a(H,HCN) and a(H,H2S) were less.(3)O element mainly transfered into residue and H2 O, a(O,H2O) of bituminous coal was highest, the transfer formulas was: y = 0.0338 x + 35.221. a(O, residue) of lignite was highest, the transfer formulas was: y = 0.0003x2- 0.544 x + 217.22. N and S elements mainly transfered into residue, a(N, residue) of lignite was highest, the transfer formulas was: y = 5E-05x2- 0.0924 x + 128.57. a(S, residue) of anthracite was highest, the transfer formulas was: y = 0.0004 x + 98.95.2、 At the base of model test, the control constant η and equilibrium formula of carbon transfer ratio were obtained at the base of the area ratios of “three zones”mainly in different gasification processes. So in the model test Ulanqab lignite, Xinjiang candle coal and Ezhuang bituminous coal were gasified with air, rich oxygen, CO2 and H2 O. In these UCG processes, the expansion of “three zones” was monitored, and the area ratios of “three zones” changed for the structure of gasification channel, injection way and composition of gasification agents. The results showed that:(1)Through the confirmation of the correlation between the area ratios of “three zones” and syngas components, in the UCG process of lignite and candle coal, the temperature ranges for three zones were divided as follows: oxidation zone: over 900°C, reduction zone: 600–900°C, dry distillation zone: 300–600°C, for bituminous coal, oxidation zone: over 1200°C, reduction zone: 600–1300°C, dry distillation zone: 200–600°C.(2)when the coal was gasified with air, rich oxygen and CO2, rich oxygen and H2 O, rich oxygen respectively, the correlation formulas between η and area ratios of “three zones” were as follows: η= 5.2358x2- 32.528 x + 60.551, η= 0.2983x- 5.9551(free channel) and η=-0.0914 x + 4.6132(percolation channel), η=-0.1084 x + 5.932(retracting injection point), η= 0.0005x2- 0.0761 x + 4.8828, at the same time the ranges of η were as follows: 9.99~38.87, 1.95~2.32(free channel) and 2.51~3.02(percolation channel), 2.06~4.21(retracting injection point), 2.7~3.06.(3)Besides, compared with the gasification in the free channel, the porous medium structure of percolation channel showed a higher convective mass transfer rate of gasification agent. Compared with the gasification in the percolation channel, the injection point was retreated in DCRA process, which improved the oxygen concentration on the gasification working face, a series of cavity can be formed, at the same time, the energy can be absorbed by the cavity downstram, the temperature of which could keep higher for a long time. So the gasification efficiency of retracting injection point was best, and percolation channel was better than free channel. When the oxygen concentration is 65%, the ranges of the area ratio of oxidation zone and η were similar, the medium and high heating value gas can be produced stabely by gasifier.3、 In UCG process, the gasification channel is long in favor of exothermal reaction, the concentration of H2O(g) is high for water influx through the strata roof, and the catalysis of the alkali metal and its oxide in ash is valid for WGS, so WGS reaction occurrs in the gasification channel. In the model tests, the catalysis of two types of ash was analysised, one was produced by the coal gasificatin with rich oxygen and CO2, the other one with rich oxygen and H2 O. Kp was calculated by means of syngas concentration. The temperature Tp at the end of gasification channel was an intermediate variable, which can correlate the area ratios of “three zones” with Kp, then the correlation formula between Kp and the the area ratios of oxidation zone and reduction zone was eatablished. The results showed that:(1)The catalysis of ash was influenced by the composition of gasification agent, the catalysis of the former one was better. In the gasification process the pore structure on the surface of ash was changed for the composition of gasificaitn agents, so in the fixed-bed catalysis reactor, 1# and 2# ash were produced by the coal gasification with rich oxygen/H2 O and rich oxygen/CO2, CO and H2 produced by the 2# ash may released simultaneously, but H2 released slower than CO in WGS reaction of 1# ash, therefore, the catalysi of 2# ash was better, the inversion of CO for 2# and 1# ash were 72.46% and 30% respectively.(2)Moreover, the Kp were 3.3 and 1.5 respectively in the gasification with rich oxygen/CO2 and rich oxygen/H2 O, for the injection point was retreated in DCRA process, the temperature in the gasification channel was higher when the coal was gasified with rich oxygen and H2 O, so Kp was less. The minimum temperature of WGS was higher than 400℃. When the coal was gasified with rich oxygen and H2 O, the correlation formula between Kp and the the area ratios of oxidation zone and reduction zone was as follows:4、 Water influx occurs in the UCG process, the temperature field distribution will change for heat is absorbed by water, at the same time, the area ratios of “three zones” also change. Because on the gasificatin working face the area ratio of oxidation zone αox decides the heat supply, αox/αred can reflect the state of heat supply and requirement, the effective ranges of αox and αox/αred should be obtained at a volume flow rate of water influx in order to keep the process stable. In the mode test, when the coal was gasified with rich oxygen, CO2 and H2 O, the influence of water influx on the expansion of “three zones”was analysised, the correlation formulas between the flow rate of water influx, αox and αox/αred were obtained, then η and Kp in the process can be calculated. The results showed that:(1)With the increase of the flow rate of water influx, when the coal was gasified with rich oxygen and CO2, the ranges of αox and αox/αred were as follows: 10.79%~18.96%, 2.26~3.72. The correlation formulas were as follows: αox = 0.8683x2-15.143 x + 76.743, αox/αred =-0.2107x2 + 3.8614x- 13.965.when the coal was gasified with rich oxygen and H2 O, the ranges of αox and αox/αred were as follows: 21.82%~31.99%, 1.58~2.49, in addition, the influence of water influx on the area ratio of oxidation zone was less, the heating value of syngas was higher, and the stability of the process was better. The correlation formulas were as follows: αox =-0.4589x2 + 8.8913x- 12.056, αox/αred = 0.1658x2- 3.0004 x + 14.643.(2)Compared with the gasification process with rich oxygen and CO2, the way of water influx influenced the oxidation intensity less. the area ratio of oxidation zone was higher, which can ensure the temperature for gasification reaction, meanwhile, the expansion rate of the oxidation zone can be controlled. the range of αox/αred was from 1.58 to 2.49, so the energy produced by the oxidation zone was adequate enough for the reduction zone. Therefore, the high heating value syngas can be produced in the DCRA process s Tab.ly, the gasification time and efficiency were long and high.5、 UCG mass and energy balance model was developed as a software at the base of MVC and VS2013 architecture, the datas and documents of model can be saved on No Sql database, the software was simplified and run fast on the platform of Matlab.The UCG balance model was applied to the field test, where the Ulanqab lignite was gasified with rich oxygen and CO2, first the volume flow rate of water influx in the model test was calculated according to the field test, then the area ratio of “three zones”, η and Kp were obtained in the balance model, the elements transfer ratio also can be found at 600 ℃, at last these parameters can be input into the mass and energy balance model and the results output fast, the field test data was compared with the calculation of balance model, the fractional error of syngas concentration except CH4 and heat efficiency were less than 20%, so the accuracy and the value of application were good enough. |
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