Low-pressure-drop fluidized-bed distributor

The compressor power required to maintain fluidization is one of the high cost factors in the application of fluidized bed combustors. Good uniform fluidization can be obtained if the distributor air injector tubes are so small that they cause a pressure drop of at least 20% and better if 40% of the pressure drop in the bed. By designing the distributor air injector tubes with a crossflow at their inlets it has been demonstrated that uniform fluidization can be obtained with a distributor pressure drop of only 10% of that in the bed. The pressure wave caused by the collapsing bubble above the distributor travels upstream in the tubes and gets blown away by the crossflow at its inlets. This reduces the distributor local flow rate fluctuations and in turn minimizes the bed instability and flow nonuniformity. The stabilizing effect of the crossflow was experimentally verified by operating two nearly identical cold fluidized beds side by side, one with and the other without crossflow at the tube inlets. The performance difference between the two beds was significantly reduced when caps were added to the tube outlets to prevent weeping bed material into the distributor plenum. One disadvantage of the reducedmore » turbulence in the jets emerging from the injector tubes is the thickening of the stagnant zone of the bed. An experiment with a nonuniform bed geometry shows that such a technique can improve circulation and reduce the thickness of the stagnant zone.« less