| The circulating fluidized bed for flue gas desulfurization (CFB-FGD) is a one of flue gas desulfurization technologies applied in thermal power stations widely. With the enlargement of the flue gas desulfurization device, it becomes more and more important to how to adapt to the requirement of boiler variable load operation and reduce the system operation resistance. In this paper, in order to provide the basis for the design and operation of a CFB-FGD system, a mathematical model of gas-solid two-phase flow was established and the effects of structural parameters, operation parameters and other factors on the gas-solid flow characteristics in a desulfurization tower and a baghouse filter of CFB-FGD process for a260t/h boiler were studied by using the Fluent numerical simulation platform. The main research contents and conclusions are listed as follows:1) Mathematical model of the gas-solid two phase flow for CFB-FGD process was set up based on Euler-Lagrange method combined with the gas turbulence model, and a method of porous jump media model was put forward to simplify and simulate the flow of gas distributors and filter bags. The governing equations of the gas phase field were discretized by using finite volume method and solved by using SIMPLE algorithm, and the DPM model was applied to deal with the discrete particle phase.2) The fuel gas flow characteristics of the CFB-FGD single-throat desulfurization tower was simulated by using the k-ε turbulence model. The effects of Venturi structure parameters on the desulfurization tower resistance and its pressure field were analyzed. The obtained results indicated that more than90%resistance of desulfurization tower system comes from the Venturi. The system resistance decreased and the pressure field in the desulfurization tower became more and more symmetrical with the decreasing of expanding-angle of the Venturi. The ratio of Venturi throat’s height to its diameter had little influence on the total pressure drop of the desulfurization tower. Venturi’s resistance loss decreased with the decreasing of the reducing-angle of the Venturi. Compared with the structure of hyperboloid type Venturi and the original Venturi, the resistance loss of desulfurization tower with the whole-surface type Venturi decreased significantly. The resistance loss of Venturi tube has the relationship of a quadratic function with the throat velocity approximately.3) The fuel gas flow characteristics of the CFB-FGD seven-throat flue gas desulfurization tower was simulated by using the k-ε turbulence model. The effects of structural and operation parameters on resistance loss and fuel gas flow field of the seven-throat CFB-FGD desulfurization tower were analyzed. The simulated results indicated that the installment of baffles in the CFB-FGD smoke chamber will result in increasing the total pressure drop of the desulfurization tower slightly, but improve the flow field distribution uniformity of the desulfurization tower significantly. the design of the pure cylindrical outlet of desulfurization tower with the value of Hm37/Hm3=0.65, and two90°elbows with radiuses of2400mm and1555mm respectively, is very helpful to the inner material loop and decrease the system resistance. The system resistance of desulfurization tower has the relationship of a quadratic function with the load.4) The effects of diameter, quantity and installation location of the bypass pipe in a bypass type CFB-FGD seven-throat desulfurization tower on flow field characteristics, load adjusting and resistance loss were simulated. The results showed that increasing diameter and quantity of bypass pipe will improve the symmetry of the flow field of the desulfurization tower. The flow rate of CFB-FGD bypass increases with increasing diameter of bypass pipe at the same bypass quantity. The load of a desulfurization tower increased by20%at designed rsistance loss, which can enlarge the system load range of the desulfurization tower to50%-130%. The resistance loss characteristics of bypass type desulfurization tower are the same with those of a non-bypass type desulfurization tower; however the total pressure drop decreases significantly at the same operating flue gas flowrate. Compared with the original desulfurization tower, the trajectory distribution of the particle phase of the bypass type desulfurization tower is more uniform, and which is consistent with the analysis result of the flue gas phase field.5) The inertial duster, the bag-filter and the integrated duster for CFB-FGD system were simulated. The effects of the number of guiding-baffles, the opening ratio of flue gas distributor and its installation position, etc. on the flow field of the dust collector, the operation resistance and the handling capacity of the filter bag group and so on were anlyzed. The results are listed as follows:(1) The utilization rate of inertial filter improves significantly and the system total pressure drop decreases slightly through installment of guiding-baffles and decrasing the height of flue gas distributors.(2) Better flow field distribution is obtained and the total resistance loss decreases while a straight-pipe type flue gas inlet of the filter-bag is replaced by gradul-expanding one and the opening ratio of the flue gas distributor with10%in the middle and35%in both sides.(3) The best flow field can be achieved while two flue gas distributors with the opening ratio of50%was installed on the right side wall of the chamber and2300mm away from it in the integrated duster. The uniformity of the filter bag group’s handling capacity with installment of two pieces of flue gas distributor is better than that with one flue gas distributor, and the system resistance increases slightly. The uniformity of handling capacity of gradual-expanding type filter chamber is also better than that of original type and the system resistance loss decrease significantly.(4) The system total pressure drops of two types of dusters (the inertial duster+the bag-filter, the integrated duster) all have an approximate relationship with the load of a quadratic function. The particle phase flow patterns of optimized duster are better than those of the original one, which is consistent with the results of the flue gas fields. |
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