Research on the variation of CO concentration and temperature in the directional drilling process

During drilling operations, the drill bit continuously rubs against the coal seam, generating heat and releasing CO gas, which may lead to severe CO poisoning accidents. To address this issue, we construct an experimental monitoring platform to analyze the variations in CO concentration and temperature during coal seam drilling under different drilling feed rates and drilling rig rotational speeds. The results indicate that no CO is produced at the initial stage of drilling. Subsequently, CO concentration increases linearly, accompanied by an increase in the CO generation rate, which leads to an exponential increase in CO concentration. A higher drilling rig rotational speed results in a faster CO generation rate and higher CO concentration. Similarly, a higher drilling feed rate also accelerates the CO generation rate. Specifically, at a drilling rig rotational speed of 990 r/min and a drilling feed rate of 0.5 cm/s, the CO concentration reaches a peak of 29.6 ppm. The temperatures of both the drill bit and coal body initially increase rapidly and then stabilize. Higher drilling rig rotational speeds lead to faster temperature rises in both the drill bit and coal body, causing them to enter the steady growth phase earlier and resulting in higher final temperatures. In contrast, higher drilling feed rates cause the drill bit temperature to rise more rapidly, while the coal body temperature increases at a slower rate. As a result, both temperatures reach the steady growth phase earlier but lead to a lower final temperature. At a drilling rig rotational speed of 990 r/min and a drilling feed rate of 1.5 cm/s, the drill bit and coal body temperatures enter the steady growth phase earliest, at 30 s. At a drilling rig rotational speed of 990 r/min and a drilling feed rate of 0.5 cm/s, the highest temperatures for the drill bit and coal body are reached, 118.2 °C and 68.2 °C, respectively. The temperature rise in both the drill bit and coal body follows a linear relationship with the average CO generation rate. This study provides valuable insights for ensuring safety during coal seam drilling operations.