Hydrodynamics Simulation And Feed System Pressur Analysis Of Bubbling Fluidized Bed In TBCFB

Circulating fluidized bed is a good choice for the conversion and utilization of coal. Most of the traditional circulating fluidized beds are composed of combustion bed and gasification bed. Among them, during coal pyrolysis process, the produced tar, light hydrocarbon gases and inorganic gases seriously hinder further gasification of coal on the gasification bed, and then reduce utilization efficiency of coal. The combination of combustion, pyrolysis and gasification together forms a new coupling technology of low rank coal gasification on the triple-bed circulating fluidized bed(TBCFB), which can effectively avoid the occurrence of these problems. For the TBCFB, The implementation of high solid circulation flux is the key to its efficient and stable operation. In TBCFB, continuous feeding/unloading bubbling fluidized bed involves the import and export of solid particles, having more complex structure than conventional bubbling fluidized bed. Although the import and export help to achieve the efficient recycling of energy, but limit the realization of high solids circulation flux. Among them, export restrictions have been resolved to a certain extent through the addition of gas seal bed, import restrictions need for further study.In this paper, the numerical simulation study was conducted by using eulerian-eulerian two-fluid model with CFD software on a continuous feeding/unloading bubbling fluidized bed, which belongs to the TBCFB. In this paper, the gas-solid mixing characteristics is mainly explored under these conditions: the feeding pipe length, the feeding pipe diameter, the superficial velocity solid mass circulation flux and particle diameter, and by measuring the height and pressure drop, evaluates quantitatively fluidization quality is good or bad. Simulation results show the change condition of the bed by using velocity vector diagram, solid volume fraction images and origin graph. The results show that preferable fluidization quality appears when the feed pipe length is 1.1m, the feed pipe diameter is larger than or equal to 0.1m and the superficial velocity is less than or equal to 0.22m/s; with the increasing solid mass flux, solid holdup near the feed port increases as well as the solid holdup and the height of bubbling fluidized bed, preferable fluidization quality appears when solid mass circulation flux is 100kg/m2 s and 1000kg/m2s; with particle diameter increasing, larger gas velocity are required to maintain the best fluidization quality. In order to study how to design a feeding tube will not hinder normal operation of the system under the high solid mass circulation flux, a feeding system pressure balance model is built. From the point of theory, the influence on solid particles stack height in feed pipes is studied under these conditions: the solid mass circulation flux, solid particles and the feed pipe wall friction coefficient, the feed pipe diameter and feed pipe buried in the depth of bubbling fluidized bed. The results show, with solid mass circulation flux increasing in a lower range, which will not hinder the whole system circulation; when solid mass circulation flux surpass a certain range, solid particles stack height in feeding pipe will increase rapidly, reach the extent for hindering the entire system cycle soon. This results are consistent with the experimental phenomenon in the literature. The pipe wall friction coefficient has little effect on solid stack height of the feed pipe while other factors affect more obviously. When excessive accumulation of solid particles in feeding pipes hinders the normal cycle operation of the system, the appropriately increasing the feed pipe diameter or decreasing the depth of feed pipe embedment in bubbling fluidized bed can reduce the solid stack height of feeding pipe, restoring normal operation of system.