The Study On Characteristic Of Diffusion Flame And Slag Deposit And Heat Transfer In Water Wall Entrained Flow Gasifier

The entrained flow gasification technology with water wall is a better choice in large coal gasification field. According to "principle of slag resistence", slag deposited on water wall can protect water wall from high temperature ablation. The slag deposit and heat transfer of water wall nearly have relations with flow field of gasifier, operating temperature and ash physicochemical property etc. Base on the background of water wall entrained flow gasification technology, the study on characteristic of diffusion flame and slag deposit and heat transfer was carried out.(1) The gasification diffusion flame is primary character in entrained flow gasifier and effect total temperature distribution of gasifier. The morphological analysis is mainly direction on flame investigation. The results indicate that in open space the effect of oxygen in air on flame configuration is finite, flame shape is gradually determined by oxygen from burner with increasing oxygen flux from burner. The burner structure of multi-jet can effectively improve mixture of fuel and oxygen, flame length of multi-jet burner is shorter than that of coaxial two-channel burner. In low oxygen velocity, the flame of two-channel burner is related to fuel primary atomization. The rule of primary atomization in combustion is similar with that in cold condition, but the critical velocity in combustion is higher. The structure of single flame is maintained before arriving to impinging region, but rapidly disappear in impinging region. With the increase of impinging velocity, impinging region become larger and unstable, the distribution of single flame is more continuous and homogeneous.There is a fractal characteristic in impinging gasification flame boundary. The fractal dimension decreases in ignition stage and increases from two-burners to four-burners. During the increase of load, the fractal dimension increases, however, the difference-value of the fractal dimension in two burner pattern reduces.(2) The results of study on bench-scale and pilot-scale water wall gasifier indicate that the slag deposit is related to flow filed, operating temperature and slag physicochemical property etc. Slag can deposit on all water wall surface and protect water wall from ablation. Compared with bench-scale study, slag deposit is more homogeneous in pilot-scale gasifier. With consumption scale per water wall surface increasing heat loss of water wall can play down. The dry feed flow, the ratio of oxygen and coal and drum pressure respectively can effect the heat transfer of water wall, but the level of effect is different. (3) The results of simulation based on water wall heat transfer and stress model is approximately consistent with experimental measure. According to simulation, the distribution of temperature and stress is achieved and further understand water wall heat transfer and slag cracking. The results show that the temperature gradient of slag layer is maximal, slag layer can effectively reduce bulk temperature of water wall. Temperature fluctuation in gasifier will result in thermal stress, the thermal stress is distinct for different material. The maximal thermal stress is located in slag layer, thermal stress of tube and pin is minimal. The possibility of slag crack increase with slag porosity increasing. When a load is applied in slag surface that there is a crack, stress distribution is very concentrative near crack tip and stress located in crack tip is several times than applied load. Once away from crack tip, stress distribution return to normal.