Abstract: The fire tube waste heat boiler in the de-oiled asphalt gasification process has serious scaling problems, which not only affect the heat transfer efficiency of the fire tube boiler, but also threaten the safe operation of the boiler. In view of the special ash composition and large temperature difference between inlet and outlet in de-oiled asphalt, combined with the melting liquid phase ratio model, critical velocity model and shedding model, the CFD method is used to segmentally simulate the ash deposition distribution, deposition surface temperature and outlet temperature changes in industrial fire tube boilers, and explore the related impact of synthesis gas inlet flow. The entire fire tube is divided into seven segments A-G. The study found that the ash deposition in the fire tube boiler mainly concentrated in segments A and B, with a maximum deposition thickness of 6.34 mm. The ash deposition caused the synthesis gas outlet temperature to rise by 7.07 K. The ash deposition process had a small impact on overall heat transfer performance, but significantly deteriorated local heat transfer performance, with average deposition surface temperatures in segments A and B rising by 232.77K and 211.08 K respectively. In addition, when increasing the synthesis gas flow rate, the ash deposition and temperature distribution in the fire tube boiler showed significant changes, with a decrease in deposition thickness and temperature in segment A, followed by continuous warming in subsequent segments. When investigating the impact of synthesis gas flow rate on deposition and heat transfer behavior, when the flow rate increases to 120%, the tube wall temperatures in segments B and C approach the maximum working temperature of 773 K of the material.