Cold State Experiment Study On Two-stage Separation Return Circulating Fluidized Bed

Coal gasification is one of the strategic development directions of efficient and clean utilization of coal.Circulating fluidized bed coal gasification technology is widely used in coal chemical industry,metallurgy,ceramics,building materials and other industries with the advantages of wide coal adaptability,low investment and operation cost and environmental friendliness.With the increase of operating pressure and circulating flow rate,there are some problems in the operation of circulating fluidized bed,such as unbalanced pressure of circulating circuit,low gas-solid separation efficiency and unstable operation of return feeder.This subject proposes a new process technology of graded separation return circulating fluidized bed,in order to realize the popularization and application of pressurized coal gasification technology in engineering field.In order to study the operation characteristics of two-stage separation return circulating fluidized bed,two sets of cold test devices with different solid-gas ratio range are built in this paper,We carried out tests on the effects of bed material particle size distribution,furnace operating wind speed,solid-gas ratio at the inlet of the primary separator,inlet speed and other factors on the two-stage material distribution,pressure balance distribution and pressure fluctuation;Combined with numerical simulation and experimental research,the flow field and particle separation characteristics in the primary separator are obtained,which provides an experimental basis for the return process of staged separation.The test results show that:In the two-stage separation return circulating fluidized bed,the solid-gas ratio at the inlet increases from 3kg / kg to 6kg / kg and the gas velocity at the inlet of the primary separator increases from 8m / s to 15 m / s,the proportion of the mass flow rate of the primary circulating circuit increases,the pressure fluctuation of the primary circulating circuit is strong,the primary circulating circuit dampens the pressure fluctuation of the furnace,the pressure fluctuation of the secondary circulating circuit is small,and the secondary circulating circuit operates stably;Compared with the single-stage separation return circulating fluidized bed system,the two-stage separation return circulating fluidized bed system has a higher system circulation mass flow rate,but the separation system has a higher high pressure drop and requires greater power equipment.Compared with the low solid-gas ratio test device,the high solid-gas ratio test device has a lower proportion of the mass flow rate of the primary circulating circuit under the same operating bed material particle size and the inlet gas velocity of the primary separator,and the material distribution is more reasonable;The high solid-gas ratio test device has little effect on the pressure balance distribution of the secondary circulating circuit,and the secondary circulating circuit operates stably.The primary separator is the key component of two-stage separation return circulating fluidized bed When the inlet solid-gas ratio increases from 3kg / kg to 6kg/ kg,the separation efficiency of the separator increases.When the inlet solid-gas ratio increases from 6kg / kg to 11 kg / kg,the area of particle concentration layer increases,the particle dispersion distribution in the cylinder increases and the separation efficiency decreases;When the diameter of the cylinder decreases,the turning stagnation point of the air flow moves down,the axial velocity of the air flow in the cone decreases,the area of the annular area at the top of the particle impact decreases,and the separation efficiency decreases;The inlet of the primary separator with a cylinder diameter of 210 mm is a tangential connecting cylinder.The tangential air flow at the inlet of the separator destroys the particle concentration layer,forms a particle cavity area and weakens the separation efficiency.Through numerical simulation and experimental study of the flow field in the first stage separator,it is concluded that the increase of the attenuation gradient of the inlet velocity of the gas phase flow field,the increase of the tangential velocity of the gas phase flow field in the cone and the increase of the particle dispersion distribution in the cylinder are conducive to the separation of particles;The increase of concentration layer area,axial velocity of gas phase flow field in cone section and horizontal rebound angle of particles are not conducive to particle separation.