Abstract: Aimed at solving the antifreezing problem of the wet purification device of biomass gasification station due to the installation of the firewall in winter time of north China， a waste-heat recovery system based on fan & double-tube is proposed. The Fluent and k-ε model is used to simulate the unsteady state of heating. The results indicate that the antifreezing requirement can be met in 90 or 40min when the inlet air velocity is 9 or 13m/s， respectively. Then the feasibility of the technique can be proved. The heating effects of different inlet air velocities of 5， 9， 13m/s at different times are also simulated. It shows that the heating effect can be raised and the time needed to reach the antifreezing requirement can be shortened and the temperature distributed in purification room can be more even by increasing the fan air volume. But the air speed should be restricted according to the corresponding standard and the energy consumption considerations.

Key words: biomass gasification, heating, fan, double-tube, numerical simulation