Fluid cracking regenerator

Fluid cracking retained the moving bed concept of the catalyst transported regularly between the reactor and regenerator. And as with the air-lift systems, the fluid plant rejected mechanical carrying devices (elevators) in favor of standpipes through which the catalyst fluid traveled. 

The work just cited refers to beds of small diameter. Designers and operators of large-scale catalytic fluid beds of Group A powders now appreciate that all of these beds function beyond the Lanneau-Kehoe-Davidson transition (Avidan, 1982 Squires et al., 1985). Most are turbulent beds Sasol reactors and some fluid catalytic cracking regenerators are fast beds. Sasol engineers reported successful development of a turbulent bed for hydrocarbon synthesis (Steynberg et al., 1991). 

The poisoning of fluid cracking catalysts (FCC) by vanadium is well known (7, 2). In general, vanadium is deposited on the cracking catalyst as coke by vanadyl porphyrins in the feed. During regeneration, the coke is burned off, and vanadium can be oxidized to the V+5 oxidation state. Woolery et al. (3) have shown that the oxidation state of the vanadium can alternate between +4 to +5 in... 

Chemical composition of waste plastic cracking products depends on shares of the individual polymers (PE, PP, PS) in the feed and process parameters. This fact decides the technological application of the final products. Important products of the cracking process, both petroleum fractions and waste plastics, are coke residues. Coke residue yield increases considerably, up to 10 wt%, in cracking of municipal and industrial waste plastics since they contain various inorganic impurities and additives. It can be applied as solid fuel, like brown coal. In the fluid cracking the solid residue is continuously removed from the process by combustion in a regenerator section. 

Distribution of Regeneration Heat in a Commercial Fluid Cracking XJnit ... 

The relationship between the principal variables involved in an overall heat balance around the reactor and regenerator of a fluid cracking unit is illustrated in Figure 34. This plot shows the reactor temperatures obtainable at various combinations of feed-preheat temperature and... 

Luckenbach, E. C. (1978) U.S. 4,081,508, to Exxon Research and Engineering Co. Process for reducing flue gas contaminants from fluid catalytic cracking regenerator. 

MTO was first scaled up in MRDC s 4 B/D fluid-bed pilot plant in Paulsboro, New Jersey. Following successful completion of the 100 B/D MTG project, the project was extended, and the plant modified to demonstrate MTO (refs. 16, 17). The plant is shown schematically in Fig. 4. Methanol is converted in a turbulent fluid bed reactor with typical conversions exceeding 99.9%. The products are recovered in a simple gas plant. Coked catalyst is continuously withdrawn from the reactor, and the coke is burned in a fluid-bed regenerator. Coke yield and catalyst circulation are an order of magnitude lower than in fluid catalytic cracking. 

The catalyst is employed in bead, pellet, or microspherical form and can be used as a fixed bed, moving bed, or fluid bed. The fixed-bed process was the first process used commercially and employs a static bed of catalyst in several reactors, which allows a continuous flow of feedstock to be maintained. The cycle of operations consists of (/) the flow of feedstock through the catalyst bed (2) the discontinuance of feedstock flow and removal of coke from the catalyst by burning and (J) the insertion of the reactor back on-stream. The moving-bed process uses a reaction vessel, in which cracking takes place, and a kiln, in which the spent catalyst is regenerated and catalyst movement between the vessels is provided by various means. 

The most dominant catalytic process in the United States is the fluid catalytic cracking process. In this process, partially vaporized medium-cut petroleum fractions called gas oils are brought in contact with a hot, moving, freshly regenerated catalyst stream for a short period of time at process conditions noted above. Spent catalyst moves continuously into a regenerator where deposited coke on the catalyst is burnt off. The hot, freshly regenerated catalyst moves back to the reactor to contact the hot gas oil (see Catalysts, regeneration). 

A. P. Kreuding, "Power Recovery Techniques as AppHed to Fluid Catalytic Cracking Unit Regenerator Flue Gas," presented at 79thFEChE... 

Catalytic Pyrolysis. This should not be confused with fluid catalytic cracking, which is used in petroleum refining (see Catalysts, regeneration). Catalytic pyrolysis is aimed at producing primarily ethylene. There are many patents and research articles covering the last 20 years (84—89). Catalytic research until 1988 has been summarized (86). Almost all catalysts produce higher amounts of CO and CO2 than normally obtained with conventional pyrolysis. This indicates that the water gas reaction is also very active with these catalysts, and usually this leads to some deterioration of the olefin yield. Significant amounts of coke have been found in these catalysts, and thus there is a further reduction in olefin yield with on-stream time. Most of these catalysts are based on low surface area alumina catalysts (86). A notable exception is the catalyst developed in the former USSR (89). This catalyst primarily contains vanadium as the active material on pumice (89), and is claimed to produce low levels of carbon oxides. 

Cataljdic reactions performed in fluid beds are not too numerous. Among these are the oxidation of o-xylene to phthalic anhydride, the Deacon process for oxidizing HCl to CI2, producing acrylonitrile from propylene and ammonia in an oxidation, and the ethylene dichloride process. In the petroleum industry, cataljdic cracking and catalyst regeneration is done in fluid beds as well as some hydroforming reactions. 

Fluid catalytic cracking units present formidable emission control problems. Contaminants are present in both reactor product gas and regenerator flue gas. The reactor product contains hydrogen sulfide, ammonia, and cyanides, plus combined sulfur and nitrogen in the liquid products. Hydrogen sulfide, ammonia and cyanides are handled as part of the overall refinery waste water cleanup. The combined sulfur and nitrogen may be removed by hydrotreating. 

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