This invention relates to an improved method for injecting particulate material into a fluidized bed reactor.
Fluidized bed processes are used commercially for the chlorination of titanium containing materials, ore roasting or refining, petroleum processing and refining, combustion of solid carbonaceous material such as coal, etc.
In such processes, particulate material, a suitable fluidizing gas such as air, oxygen or other oxidizing agents are fed into a reaction chamber, and the desired temperature and pressure are maintained. As necessary, the flow rates are adjusted so that the particulate material becomes fluidized, i.e., it is maintained in a state of suspension and has the appearance of boiling.
A good example of a commercial fluidized bed process is that for chlorinating titanium containing material. In such process, particulate coke, particulate titanium containing material, chlorine and optionally oxygen or air are fed into a reaction chamber, and a suitable reaction temperature, pressure and flow rates are maintained to sustain the fluidized bed. Gaseous titanium tetrachloride and other metal chlorides are exhausted from the reactor chamber. The gaseous titanium tetrachloride so produced can then be separated from the other metal chlorides and used to produce titanium dioxide pigment or titanium metal.
Fluidization has many advantages, but also can present certain problems. For example, if the particle size distribution is wide, a gas flow sufficient to fluidize the large particles may blow unreacted small particles out of the fluidized bed. Conversely, a gas flow just sufficient to fluidize the fine particles may not be sufficient to fluidize the large particles. Commonly used pneumatic feed, where significant amounts of air or other gas is used to transport the particulate materials to the fluidized bed reactor, can also be a problem. For example, the air or gas injected can aggravate the problem of fines being blown out of the reactor.
Another problem is that many industrial fluidized beds are operated at greater than atmospheric pressure. To inject the particulate material into such beds, there is often used pneumatic feed and/or a mechanical injection device such as a screw feeder. The pneumatic feed is undesirable because of the reasons previously mentioned. In addition, the mechanical feed devices are undesirable because they can have significant wear and maintenance costs.
The following information is disclosed that may be of interest to this invention: U.S. Pat. No. 5,320,815 discloses a process for feeding fine, particulate material to a fluidized bed. U.S. Pat. Nos. 5,325,603 and 5,175,943 disclose a process and an apparatus for feeding particulate material to a fluidized bed reactor. "Effects of System and Geometrical Parameters on the Flow of Class B Solids in Overflow Standpipes, R. A. Sauer", I. H. Chan, and T. M. Knowlton, American Institute of Chemical Engineers Symposium Series No. 234, Vol. 80, (1983) discloses various parameters for operating standpipes.