## 4 Discussion
### Effect of Mixed Coal Mass Ratio on Gas Adsorption Constant
#### 4.1.2 Effect of Mixed Coal Mass Ratio on Gas Adsorption Constant \(b\) Value  
According to the experimental results, the data describing the relationship between the adsorption constant \(b\) and the mass ratio of tectonic coal to virgin coal were fitted and plotted on a graph, as shown in Figure 7. The curve has a high fit degree (0.974). For mixed samples of hard tectonic coal in this mine, the adsorption constant \(a\) meets the fitting formula. For mixed samples of tectonic coal and virgin coal, adsorption constant \(b\) also meets the fitting formula.  
\[b=0.0394x^{2}-0.3026x+1.0196 \tag{4}\]  
where \(x\) is the mass ratio of tectonic coal to virgin coal.  
In the formula for Langmuir monomolecular layer adsorption, the adsorption constant \(b\) is a pressure coefficient, and it is inversely proportional to the gas pressure in the pores of the coal. The change tendency of the value of adsorption constant \(b\) with the change of the mass ratio of tectonic coal to virgin coal is shown in Figure 8. The change trend of the Langmuir adsorption constant \(b\) is a parabola opening upward with the mass ratio change of tectonic coal to virgin coal.  
Figure 8: Curve of the relationship between the adsorption constant \(b\) and the mass ratio of hard to soft coal.  
The formation of tectonic coal in the early stage, the quality of virgin coal is relatively high, so it puts a lot of pressure on the tectonic coal. Although the adsorption capacity of mixed coal is not dominated by virgin coal, virgin coal has a large mass and more heat, which increases the dynamic viscosity coefficient of the pore gas in mixed coal. Furthermore, it greatly increases the amount of gas retention in the pores, resulting in increased pressure. Meanwhile, overlying virgin coal puts pressure on tectonic coal and increases its pore resistance, causing the adsorption constant \(b\) value to show a decreasing trend. When the qualities of tectonic coal and virgin coal were approximately equal, the adsorption constant \(b\) reached its minimum. After that, with the further increase in the quality of tectonic coal, the methane adsorption was dominated by tectonic coal. Due to the high adsorption capacity of tectonic coal, the heat generated by the adsorption process also increased. When the temperature reached the equilibrium point, the coal began to exchange heat with the outside world, which caused the temperature of the coal to be drastically reduce. The viscosity coefficient of the gas in the pores of the coal became smaller due to the temperature's influence, so that the gas pressure in the pores of the coal decreased and the adsorption constant \(b\) gradually increased. The change tendency of the adsorption constant \(b\) revealed that the rising rate after the maximum was reached was lower than the declining rate before the maximum was achieved. This was determined by finding the slope of the tangent of a certain experimental point before and after the maximum value.  
From previous studies [47; 48; 49; 50], we know that coal seam porosity is sensitive to the effects of stress, as well as to the strength coefficient. The results obtained in this study give new insight into the mechanisms of coal seams containing different layers.