The combustion process of ventilation air methane (VAM) with air in a tangential coal-fired boiler was investigated by the component transport model. The influence of VAM with different volume fractions of methane (CH4) on the combustion characteristics of the boiler was analyzed. The results indicated that the maximum average temperature in the main combustion area increases to 102K, with the increasing volume fraction of CH4 in the VAM. Under the same conditions, the distribution of oxygen (O2) volume fraction showed a trend of decay in the main combustion zone, while carbon monoxide (CO) started to increase. Meanwhile, the NO emission at the over-fire air (OFA) decreased from 974.8mg/m3 to 436.3mg/m3, with a reduction rate of 55.24%. When the VAM with the CH4 volume fraction of 0.75% was fed into the boiler for combustion in different ways, the furnace temperature would rise and the NO emission would decrease. The concentration of CH4 in the VAM should not be less than 0.01%. The analysis results demonstrated that adding the VAM into the boiler combustion can not only save resources and protect the environment but also help to reduce the emission of nitrogen oxides.
Regarding the three expansion modes of hydraulic fractures at the interface of a coal measure composite reservoir (arrested, deflection, and penetration), based on the coupling theory of fluid flow and solid elastic deformation, a criterion that considers the influences of the injection parameters (fracturing fluid injection rate and viscosity) is established to predict the propagation path of hydraulic fractures at the interface of a composite reservoir. The criterion judges the propagation behavior of the fractures by comparing the water pressure in the wellbore and the critical seam pressure of the penetration and deflection. The controlled variable method is used to analyze the influences of the various factors on the propagation behavior of hydraulic fractures at the interface between layers. The results show that the differences in in situ stress, the interface cohesion, and the included angle mainly affect the critical seam pressure of the fracture deflection. The differences in elastic modulus, fluid injection rate, and fracturing fluid viscosity directly affect the water pressure in the wellbore. The difference in the fracture toughness mainly affects the crack propagation path by affecting the critical seam pressure of the deflection. The smaller the difference in the in situ stress is, the more likely it is that the hydraulic fractures will penetrate the layer. Larger differences in the fracture toughness between layers, interfacial cohesion, fluid injection rate, and fracturing fluid viscosity are more conducive to the hydraulic fractures penetrating the layer. When the angle between the hydraulic fractures and the interface is 25–55°, the hydraulic fracture is more likely to expand along the interface. This criterion takes into account the influences of the injection parameters and is of great significance to gaining a better understanding of the propagation behavior of hydraulic fractures at an interlayer interface.
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