煤炭地下气化点火阶段正庚烷着火及燃烧数值模拟研究

Numerical Simulation of N-heptane Ignition and Combustion in the Ignition Stage of Underground Coal Gasification

煤炭地下气化技术将地下煤层以天然气形式开采出来,是一种清洁、高效的能源利用方式。点火是开启气化反应的第一步,对化学点火过程中燃料着火与燃烧特性的分析将有助于高效气化。该文选取正庚烷为点火燃料,采用离散相模型模拟庚烷雾化过程,建立庚烷液滴与氧气共流燃烧模型,探究庚烷着火温度及燃烧火焰特性,并对影响初始点火过程的关键因素进行分析。结果表明:随压力升高,庚烷着火温度降低,10 MPa时达到670 K;液滴粒径在0.1~0.4 mm范围内时,着火温度随粒径减小而小幅上升;提高氧化剂中氧气浓度可显著提高火焰温度,但会导致火焰长度变短;为避免煤的熔融问题,氧气浓度控制在20%~30%附近较为合适,对壁面最高温度在1200~1530 K内。贫氧燃烧时,火焰温度较低,但过量空气系数处于0.6~0.8时,对壁面的加热温度及加热长度均高于富氧燃烧,在点火过程中能更高效利用燃料。结果可为煤炭地下气化点火过程燃料及氧化剂参数控制提供一定参考。

Underground coal gasification extracts underground coal seams in the form of natural gas,which is a clean and efficient way of using energy.Ignition is the first step to start the gasification reaction,and it is necessary to analyze the ignition and combustion characteristics of fuels during chemical ignition.N-heptane is selected as the ignition fuel,and the Discrete Phase Model is used to simulate the atomization process of n-heptane.The co-flow combustion model of heptane droplets and oxygen is established.The ignition temperature and combustion flame characteristics of heptane are explored,and the key factors affecting the ignition process of underground coal gasification are analyzed.The results show that with the increase of pressure,the ignition temperature of heptane is lower,and it reaches 670 K at 10 MPa.When the droplet particle size is in the range of 0.1–0.4 mm,the ignition temperature increases slightly with the decrease of particle size.Increasing the oxygen concentration in the oxidant can significantly increase the flame temperature,but it would lead to a shorter flame length.In order to avoid the melting problem of coal,it is more appropriate to control the oxygen concentration around 20%~30%,and the maximum temperature of the wall surface is within 1200~1530 K.The flame temperature is lower during lean combustion,but when the excess air coefficient is 0.6~0.8,the heating temperature and heating length of the wall surface are higher than that of oxy-fuel combustion,which can make more efficient use of fuel in the process of ignition.