Experimental study on thermal environment and pollutant distribution during the cooling stage in a graphitization plant with an ultra-large surface pollution source

· The indoor environment in the plant during graphitization cooling was tested. · The cooling process is divided into 3 stages based on pollutant emission intensity. · Radiation heat dissipation during cooling is 49.4%–58.0% of total dissipation. · SO 2 and particle concentrations are mainly from the initial cooling phase. To investigate the thermal environment and pollutant distribution in industrial plants with large-area pollution sources, on-site measurements were conducted in a naturally ventilated graphitization workshop. During different cooling stages, the surface temperature of pollution sources, indoor thermal parameters, and concentrations of SO 2 and particulate matter (PM 2.5 and PM 10 ) were recorded. In addition, the micro-morphology, elemental composition, and particle size distribution of the collected particulates were analyzed. The field test results indicate that the cooling process can be divided into three stages: the initial, middle, and final stages. During these stages, radiative heat dissipation accounts for 49.4% to 60.0% of the total heat loss. The current natural ventilation rate is 25.3% lower than the theoretical requirement, and the wet-bulb globe temperature (WBGT) at the post ranges from 25 °C to 32 °C. The results of the Kruskal-Wallis test indicate that the differences between parameters at different cooling stages are statistically significant. In the initial cooling stage near the source, the concentrations of SO 2 and PM 2.5 are 0.95 to 2.68 times and 2.1 to 3.5 times higher, respectively, compared to the middle and final stages. During the testing period, the ratio of PM 2.5 to PM 10 ranges from 12.72% to 62.52%. A positive correlation is observed between the thermal environment parameters of the factory and pollutant concentrations, with the strongest correlation occurring in the early cooling stage. The correlation coefficients between air temperature and SO 2 , PM 2.5 , and PM 10 are 0.67, 0.59, and 0.51, respectively. Laboratory analysis reveals that the particles exhibit irregular shapes, such as block-like and flake-like forms. The cumulative particle size distribution follows the Rosin-Rammler distribution, with a characteristic size of 53.618 μm. This study provides valuable references for CFD simulation parameter settings and ventilation system optimization in the indoor environment control of factories with large surface pollution sources.