Various processes require that material be treated with an elemental sulfur-containing gas. This treatment process frequently involves a "bed" of material to be treated, with a sulfur-containing gas rising through the bed to treat the material. Material may be continually input to and removed from a chamber in a sulfider, and the treatment may occur at a high temperature provided by the incoming material. Sulfider equipment is thus well suited for a continuous flow-through process rather than a batch process. Fluid injector tubes have long been used to input the hydrogen-containing gas into the lower portion of the bed within the treatment chamber, while an upper portion of the sulfider acts as a settling chamber to allow treated material fines to settle by gravity back to the bed.
Those skilled in the cracking of hydrocarbon feedstock have long recognized the value of various solid catalyst to yield more valuable end products. These catalysts typically may be manufactured from various synthetic crystalline materials, and are utilized in powder form with particle sizes ranging from 1 to 100 microns. The solid catalyst become contaminated or poisoned by "metals" during the hydrocarbon conversion, with the term "metals" referring to contaminants in the form of either free metals or relatively non-volatile compounds. U.S. Pat. No. 3,140,253 and U.S. Pat. No. Re. 27,639 generally disclosed techniques for preparing a suitable catalyst for cracking hydrocarbon feedstocks.
Various techniques have been devised for removing metals from the hydrocarbon conversion catalyst so that the catalyst can be returned to service. One commonly used technique is to chlorinate a contaminated catalyst at elevated temperatures. According to the technique described in detail in U.S. Pat. No. 4,686,197, the contaminated catalyst is demetalized by contacting the catalyst with at least one chlorine-contaminating component. Vapor phase chlorination is preferred at a temperature of approximately 600.degree. F., followed by an inert gas purge by approximately 1000.degree. F. Chlorination can be effective to move vanadium from the catalyst, and also for placing nickel poisons into a form soluble in an aqueous solution. After chlorination and washing, the demetalized catalyst may then be returned to a fluid bed reactor vessel for cracking hydrocarbons.
As disclosed in the '197 patent, contaminated catalyst from the fluid bed catalytic cracking operation may be passed through an initial sulfiding process for enhancing the removal of nickel and vanadium during the subsequent chlorination and washing processes. During the sulfiding step, the poisoned catalyst is contacted with elemental sulfur vapors, such as H.sub.2 S, at a temperature of from 500.degree. F. to 1500.degree. F. According to the prior art, this sulfiding step is preferably performed using an in-line or continuous flow-through process by passing the heated catalyst into a sealed reactor having metal walls. H.sub.2 S is introduced into the bottom of the reactor and passed upward through the fluid bed formed by the catalyst.
The injection tubes or nozzles in catalyst sulfiders have been of a conventional design for fluid bed reactions. A central injection pipe was passed through a lower end of the sulfider, and a plurality of tubes or nozzles extended horizontally outward from a header at the upper end of the pipe. The plurality of tubes thus resembled spokes which effectively covered the cross-sectional area of the sulfider with the injected gas. Each tube has a series of drilled ports in its lowermost surface, and the injected fluid was directed downwardly to increase its effectiveness at treating all of the material in the bed.
The hydrogen sulfide generator, the flow line from the generator to the injector tubes, and the injector tubes themselves produce scale or debris which tend to plug the ports of the injection tubes. When these ports plug, the material in the bed is not efficiently treated by the hydrogen sulfide. The sulfide accordingly must be shut down, the bed of catalyst removed, the ports in the injector tubes cleaned, and the catalyst bed again formed to allow continued treatment. It was not uncommon to operate a sulfider for approximately one month, then shut the sulfider down for a period of one week or more to clean or replace the injection tubes. Maintenance costs for the sulfider are thus high, and more importantly, extensive hydrocarbon cracking equipment must operate at the reduced efficiency while the sulfider is down, or extra sulfiders must be constructed to treat catalysts while the injector tubes of a sulfider are cleaned and the sulfider returned to service.
The disadvantages of the prior art are overcome by the present invention, and improved methods and apparatus are hereinafter disclosed for substantially minimizing repair and maintenance costs for injector tubes used to introduce a sulfur-containing gas into a bed of material to be treated. The techniques of the present invention are particularly well suited for reducing the maintenance and plugging problems of a sulfider used in hydrocarbon cracking operations to assist in demetalizing catalysts by subjecting the contaminated catalyst to the sulfur-containing gas.
USPTO Backgrounds
USPTO Backgrounds