THERMODYNAMIC ANALYSIS AND NUMERICAL SIMULATION OF VERTICAL REDUCING HELICAL COILED FIRE-TUBE WASTE HEAT BOILER IN GASIFICATION

摘要

The problems of over-temperature and tube damage occurred in a vertical reducing helical coiled fire-tube waste heat boiler in the gasification process when the feedstock was changed from residual oil to natural gas. A heat transfer model was employed to investigate the effects of many factors on the performance of the boiler. Numerical simulation was carried out to analyze the temperature and velocity fields in a full-size fire tube used in practical production. The calculation results were compared with the operating conditions. The results of our research show that the fouling resistance in fire tubes is the crucial thermal resistance in heat transfer. Moreover, the fouling resistance has a significant effect on the outlet syngas temperature and little influence on the steam output; increasing inlet syngas temperature will decrease the gas side fouling resistance and lead to lowering the outlet temperature. Results of numerical simulation show that the reason for the tube damage is the superposition of the high temperature, high velocity, and high viscosity of the syngas. This superposition is caused by the effects of the fire-tube structure and the temperature-dependent syngas properties.