Underground coal gasification (UCG) is a safe, low-carbon coal mining and utilization technology with broad prospects. To promote the low-carbon development and utilization of coal, it is necessary to improve the efficiency of coal combustion and reduce pollutants. Tar is a typical pollutant in the coal gasification process, and its polycyclic aromatic hydrocarbons (PAHs) pose a threat to the environment and human health. The key to tar control lies in the regulation of the internal temperature field, and swirl injection is an effective strategy. In this work, an ex-situ experimental system with swirl injection was constructed. The system captures the temperature of coal block inside the reactor through a thermal imager, collects the generated tar through outlet filters, and detect the gas composition and content in real time with a gas analyzer. In addition, the tar samples are subjected to detailed compositional analysis using GC-MS method. By comparing the tar yield under traditional straight (Cases 1~4) and swirl (Cases 5~8) injection methods, it is found that swirl injection can significantly reduce tar production at the same oxygen and steam flow rates, with a tar reduction rate of up to 50%. The increase in oxygen content and steam content leads to an increase in tar concentration. However, the effect of steam temperature on tar concentration varies under different mixed atmospheres of oxygen and steam. This work demonstrates that swirl injection technology can significantly reduce the generation of pollutants in the UCG process, and it has broad application potential in industrial situation.

underground coal gasification; tar; temperature field regulation; swirl flow injection; traditional straight flow injection