Cyclone reaction vessel

The cyclone separators are placed in the disengaging space in the top of each reaction vessel, the collected solids being returned to the dense phase of catalyst through internal standpipes (diplegs) that extend below... 

Catalyst recovery. Catalyst losses in downflow units are typically in the range of 0.2 to 0.4 Ib./barrel of feed (100,234). Cyclones recover most of the catalyst from vapors leaving the reaction vessels. Catalyst that escapes from the reactor cyclones is recovered in the bottoms from the fractionating tower. The upflow units and the early downflow units were equipped with Cottrell electrostatic precipitators to recover en-i rained catalyst from the flue gas leaving the regenerator cyclones. It... 

Marty et al. have reported a complete pilot-plant reactor/separator system for carrying out enzymatic reactions in SCFs. The plant comprises a continuously operated tubular reaction vessel followed by four cyclone separators. The separators may be put in descending pressure order by adjusting needle valves between each vessel. Liquid products are recovered from the bottom of each vessel discontinuously [15]. 

Steam Explosion Steam explosion was conducted in a two-cubic foot batch digester equipped with steam injection and ball valves providing for rapid decompression. Approximately 2 kg of yellow poplar (Liriodendron tulipifera) wood chips were loaded batchwise into the vertical reaction vessel and treated with live steam (232 C) for 2.5 minutes. Using the method of Overend and Chomet (34), these conditions corresponded to a severity of log R 4.3. Following decompression, the exploded fibrous mulch was collected from a cyclone steam separator. 

Modern technology is considerably different, particularly since the introduction, in the early sixties, of synthetic crystalline zeolite catalysts. These were so active that the cracking mainly or entirely took place in the riser, so that the reaction vessel caused overcracking into undesired light gases and coke. A recent version of a catalytic cracker is shown in Fig. 13.2.2-1. The catalyst is completely entrained in the riser-reactor, to reduce the contact time. The former reactor vessel is now essentially reduced to a vessel containing cyclones and a stripping section. 

Fresh butane mixed with recycled gas encounters freshly oxidized catalyst at the bottom of the transport-bed reactor and is oxidized to maleic anhydride and CO during its passage up the reactor. Catalyst densities (80 160 kg/m ) in the transport-bed reactor are substantially lower than the catalyst density in a typical fluidized-bed reactor (480 640 kg/m ) (109). The gas flow pattern in the riser is nearly plug flow which avoids the negative effect of backmixing on reaction selectivity. Reduced catalyst is separated from the reaction products by cyclones and is further stripped of products and reactants in a separate stripping vessel. The reduced catalyst is reoxidized in a separate fluidized-bed oxidizer where the exothermic heat of reaction is removed by steam cods. The rate of reoxidation of the VPO catalyst is slower than the rate of oxidation of butane, and consequently residence times are longer in the oxidizer than in the transport-bed reactor. 

Fluidized bed reactors typrcally are vertical cylindrical vessels equipped with a support grid and feed sparger system for adequate fluidization and feed distribution, internal cooling coils for heat removal, and either external or internal cyclones to minimize catalyst carryover. Fluidizauon of the catalyst assures intimate contact between feed and product vapors, catalyst, and heat-transfer surfaces, and results in a uniform temperature within the reactor. Reaction heat can be removed by generating steam within the cooling coils or by some oilier heat-transfer medium. 

In the process (Figure 8-12), the feedstock is vaporized upon contacting hot regenerated catalyst at the base of the riser and lifts the catalyst into the reactor vessel separation chamber where rapid disengagement of the hydrocarbon vapors from the catalyst is accomplished by both a special solids separator and cyclones. The bulk of the cracking reactions takes place at the moment of contact and continues as the catalyst and hydrocarbons travel up the riser. The reaction products, along with a minute amount of entrained catalyst, then flow to the fractionation column. The stripped spent catalyst, deactivated with coke, flows into the Number 1 regenerator. 

The short contact time is accomplished by using a transfer line between the regenerator and the reactor vessels. Most of the reaction occurs within the riser section.912,14 A termination device can be used to separate the catalyst from the products that are taken quickly as overhead. The main reactor vessels contain cyclone separators to remove the catalyst from the products and provide additional space for cracking the heavier fraction of the feed. 

Many chemical processes recirculate solids. Catalytic systems recirculate catalyst in a reaction/regeneration cycle. First the catalyst is used to supply heat or a reactant to the process it is then transferred to a separate vessel to regenerate the catalyst, and then it is returned to the reactor. Circulating fluidized bed combustors recirculate fuel and ash around a loop to burn the fuel completely. A system with a cyclone collecting entrained solids above a fluidized bed and returning the solids to the bed via the cyclone dipleg is also a recirculating solid system. All of these recirculation systems employ standpipes. 

At the termination of the riser it is important to have quick separation of reaction mix from spent catalyst. After the riser, the reaction mix can remain in the reactor vessel for over 20 seconds before it enters the reactor cyclones and is separated from the spent catalyst. Typically, catalyst densities between riser outlet and cyclone inlet average only 1 to 3 Lb/Ft. During that 20+ seconds additional conversion can occur, but since the catalyst is spent the conversion is thermal in nature and not selective to gasoline. Ross (1990) reports commercial information (Figure 15) for a simple riser turndown that shows a 4 LV % FF conversion gain between riser outlet and cyclone inlet. Even though conversion increased, gasoline yield went down. 

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