Theoretical calculation of water effect on power plant flue gas adsorption by goaf coal
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摘要: 为研究电厂烟气注入采空区时，煤中含水率和烟气中水分对于封存温室气体CO2和抑制煤自燃的影响，建立干煤和湿煤结构模型，采用巨正则系综蒙特卡洛方法，计算了不同水分含量的烟气组分CO2/O2/N2/H2O在干煤以及不同含水率的湿煤中的吸附行为。结果表明，烟气中CO2竞争性最强吸附量最大，O2的物理吸附量极小，烟气中H2O含量不影响CO2、N2和O2的吸附量，可不进行干燥处理直接将电厂烟气注入采空区。随着煤中含水率增加，水分占据孔隙空间，范德华作用减弱，H2O-H2O之间的氢键作用增强且提供了额外吸附位。H2O的等量吸附热升高，吸附位移向吸附作用更强的低相互作用能区域，吸附大量水形成水团簇，与CO2竞争吸附位，并且占据吸附空间抑制CO2、O2、N2的吸附，使其吸附量降低50%以上，因此，注入烟气时应充分考虑采空区煤体的含水率问题。Abstract: To investigate the effect of water content in flue gas and moisture in coal on the greenhouse gas CO2 storage and coal spontaneous combustion when injecting power plant flue gas into goaf, the dry and wet coal structural models were established. The adsorption behavior of flue gas mixtures of CO2/O2/N2/H2O with different water contents by dry coal and wet coal with various moisture contents was simulated using Grand Canonical Monte Carlo method. The result shows that the competitive adsorption ability and capacity of CO2 in flue gas are the strongest, while the physical adsorption amount of O2 is the least. The H2O content in flue gas has little effect on the adsorption amount of CO2, N2 and O2. So the power plant flue gas can be directly injected into the goaf without drying. As the water content in the coal increases, the pore space is occupied by water, the Van der Waals force decreases, and the hydrogen bonding between H2O-H2O increases to provide additional adsorption sites. However, because the isosteric heat of H2O increases and the adsorption sites move toward a lower interaction region where the adsorption is stronger, a large amounts of water is adsorbed to form water clusters and compete the adsorption sites and space with CO2, O2, N2, leading to a decrease in gas adsorption amount by more than 50%. Therefore, the water content in goaf coal should be fully taken into account when the flue gas is injected.
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Key words:
- power plant flue gas /
- coal /
- water /
- adsorption /
- Monte Carlo
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图 1 退火优化过程中煤的密度及能量变化
Figure 1 Density and energy changes of coal during annealing process
图 3 纯水与烟气中水在干煤中的吸附量对比
Figure 3 Comparison of adsorption capacity between pure water and water in flue gas on dry coal
■: 298.15K pure H2O; ◆: 298.15K H2O in flue gas; ●: 303.15K pure H2O; □: 303.15K H2O in flue gas; ▲: 313.15K pure H2O; ○: 313.15K H2O in flue gas; ▼: 318.15K pure H2O; ◇: 318.15K H2O in flue gas
图 4 烟气各组分在干煤中的吸附量
Figure 4 Adsorption amount of flue gas components on dry coal
(a): □: 298.15K CO2; △: 313.15K CO2; ○: 303.15K CO2; ∇: 318.15K CO2; ■: 298.15K N2; ▲: 313.15K N2; ●: 303.15K N2; ▼: 318.15K N2
(b): ◀: 298.15K O2; ◁: 298.15K H2O; ▷: 303.15K O2; ▷: 303.15K H2O; ◆: 313.15K O2; ◇: 313.15K H2O; ★: 318.15K O2; ☆: 318.15K H2O
图 5 烟气各组分间在干煤中的吸附选择性
Figure 5 Adsorption selectivity of flue gas components on dry coal
□: 298.15K CO2/N2; ○: 303.15K CO2/N2; △: 313.15K CO2/N2; ∇: 318.15K CO2/N2; : 298.15K CO2/O2; : 303.15K CO2/O2; : 313.15K CO2/O2; : 318.15K CO2/O2; ■: 298.15K CO2/H2O; ●: 303.15K CO2/H2O; ▲: 313.15K CO2/H2O; ▼: 318.15K CO2/H2O
图 6 烟气中各组分在不同含水率湿煤中的吸附量
Figure 6 Adsorption amount of flue gas components on wet coal with different moisture
■: dry coal; ●: coal with 1.0% H2O; ▲: coal with 2.9% H2O; ▼: coal with 4.8% H2O; ◀: coal with 6.5% H2O; ▶: coal with 8.3% H2O
图 7 烟气组分在不同含水率煤中的吸附量和等量吸附热
Figure 7 Adsorption amount and isosteric heat of flue gas components on coal with different moisture
: H2O; : CO2; : N2; : O2
图 8 烟气在不同含水率湿煤中吸附的能量变化
中文注解
Figure 8 Energy variety of flue gas in various moisture of wet coal(CO2/O2/N2/H2O=15/5/77/3)
: van der waals energy; : electrostatic energy; : interaction energy; : intramolecular energy
图 9 烟气在不同含水率湿煤中的吸附密度分布图
Figure 9 Probability density distribution of flue gas in various moisture of wet coal
(a) moisture 1.0%; (b) moisture 2.9%; (c) moisture 4.8%; (d) moisture 8.3%
图 10 H2O和CO2在不同含水率煤中吸附时的能量分布
Figure 10 Energy distribution of H2O and CO2 adsorbed in different moisture coal(CO2/O2/N2/H2O=15/5/77/3)
■: H2O in 1.0% moisture coal; ●: H2O in 2.9% moisture coal; ▲: H2O in 4.8% moisture coal; ▼: H2O in 8.3% moisture coal; □: CO2 in 1.0% moisture coal; ○: CO2 in 2.9% moisture coal; △: CO2 in 4.8% moisture coal; ∇: CO2 in 8.3% moisture coal
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