Study On The Characteristics Of Solid Internally Circulating In The CFB-FGD

The industry of flue gas desulfurization has large market and expanded space. The CFB-FGD is widely applied with its advantage. Internally circulating of a large number of solid is important in CFB-FGD, which can increase the particle concentration in the bed and increase the desulfurization efficiency and the utilization of the calcium sorbent. There are many methoad to enhence the internally circulating of the particle. Different types of method have different effect to the desulfurization reaction process. One of the important tasks is to discuss the validity of the internally circulating and realize the effective internally circulating of the sorbent.The separator in the outlet of the CFB is mainly used in desulfurization technology. The process of particle flow in the top of the bed is investigated in this thesis. Ways to improve uniformity of CFB-FGD are discussed in cold experimental apparatus. The falling particle is effected by the gas flow. The gas and solid flow in the CFB can be divided three regions: the back flow zone, back mixing and acceleration zone and the main flow zone. The max length of the particle falling decrease in exponential type with the increase of the superficial gas velocity. The pariticle concentration in top of the bed is heigher than the bottom. More solid concentrated in the middle and top of the bed., which decrease the validity of the sorbent to desulfurization reaction. In order to increase the utilization of sorbent, the calcium sorbent should be send to the bottom of the bed.Ways to inprove the validity of pariticle is studied in cold experimental apparatus. When superficial gas velocity decrease to 0.68m/s, the phenomenon of solid sedimentation is obvious. Core-annular flow pattern appears. In the bottom of the bed, the ratio of maximum of the concentration to minimum reach 80. The average concentration increased 220% than the condition of the superficial gas velocity is 1.34m/s. so the validity of the solid invrease with the decrease of the superficial gas velocity.Composite fluidization of tangential swirl-once through flow is put forward to. It adds tangential swirl flow under the once-through fluidized of venturi. This is a valid way to improve the validity of the particle. The characteristics of flow under composite fluidization are studied The characteristics of gas-solid two-phase flow and particle circulation is studied in cold experimental apparatus.With the increase of the swirling flux, reflux appears near the wall. The gas turbulence and the mixing of the gas and the solid is enhenced. In the zone of r/R is 0.7 to 1.0, the solid concentration is higher. In the case of x=30%, the ratio of concentration near the wall to that in the core of the bed is 180. The zone of higher solid concentration become larger with the increase of the swirling flux, thus the validity of solid also increase. When the inlet particle concentration increase, the average concentration of particle also increase. The solid tend to aggregate, and can be easily separated with the centrifugal force. The internally circulating of particle is enhenced. The average particle size in the center is larger than that near the wall. In the area of 0.8R to 1.0R, the particle size peak value appears. Most of the larger particle concentrated in the bottom of the bed.A new internally circulating FGD tower is put forward to based of the experiment. In the bottom of the tower, new type of swirl structure is adopt. The resistance pressure character is studied. The most pressure drop is the venturi throat and the swirl region whose pressure drop is 60%-80% of the all. When shut off part of the swirling inlet, the swriling flow rate decrease. In the case of load of the power plant decrease, the swirling inlet can be shut off to increase the gas velocity in the bottom of the tower.The new internally circulating desulfurization tower was applied in a 140MW power plant. The distribution of the flow and solid concentration is studied in this power plant. The uniformity can be got more quickly. The solid concentration near the wall is 43% higher than that of inlet, when the power load is 120MW. With the decrease of the load, the extend of solid concentration increase become larger. When the desulfurization sytem is running, the size of the particle become larger and the solid concentration improed rapidly.