Two fluidized bed

All the foregoing pertains to sohds of approximately the same physical characteristics. There is evidence that sohds of widely different characleristics wih classify one from the other at certain gas flow rates [Geldart, Baeyens, Pope, and van de Wijer, Powder Technol., 30(2), 195 (1981)]. Two fluidized beds, one on top of the other, may be formed, or a lower static bed with a fluidized bed above may result. The latter frequently occurs when agglomeration takes place because of either fusion in the bed or poor dispersion of sticl feed solids. 

Circored A DR process using hydrogen made by reforming natural gas. Two fluidized beds are used. Developed by Lurgi in 1995 and first installed in Trinidad in 1998. 

There have been attempts to use catalysts in order to reduce the maximum temperature of thermal decomposition of methane. In the 1960s, Universal Oil Products Co. developed the HYPROd process for continuous production of hydrogen by catalytic decomposition of a gaseous hydrocarbon streams.15 Methane decomposition was carried out in a fluidized bed catalytic reactor from 815 to 1093°C. Supported Ni, Fe and Co catalysts (preferably Ni/Al203) were used in the process. The coked catalyst was continuously removed from the reactor to the regeneration section where carbon was burned off by air, and the regenerated catalyst returned to the reactor. Unfortunately, the system with two fluidized beds and the solids-circulation system was too complex and expensive and could not compete with the SR process. 

Cooper, P, F., The Two Fluidized Bed Reactor for Wastewater Treatment, Chap. 11 in Process Engineering Aspects of Immobilized Cell Systems, pp. 179-204. Instn. Chem. Engrs. (London), 1986. 

FBD [Fluidized Bed Dehydrogenation] A catalytic process for converting alkanes to alkenes. Two fluidized beds are used a reactor and a regenerator. The catalyst beads are recirculated from the regenerator to the reactor, providing heat to the reactor. The catalyst is chromia on alumina. 

Fluid-Bed Process Union Carbide and Shell technologies are combined in this process Two fluidized-bed reactors are used in series to produce impact-resistant polypropylene. As with other processes, reaction conditions are 50-100°C and 10-40 bar, with particle residence times between 1 and 4 hours. 

The liquid-like flow of particles allows continuous controlled operations with easy handling. In particular, the circulation of solids between two fluidized beds makes it possible to remove or add the high quantities of heat produced or needed in large reactors as well as to substitute part of the (sticky or agglomerated) bed material with fresh solids. 

Uranium(IV) oxide is the starting material for uranium(lV) fluoride production in which uranium(lV) oxide is generally reacted with anhydrous hydrogen fluoride. This difficult to carry out exothermic reaction proceeds either in a fluidized bed, in moving bed reactors, or in screw-reactors. To achieve as complete as possible reaction in fluidized bed reactors, two fluidized bed reactors are connected in series. Screw-reaetors are also preferably connected in series. In moving bed reactors the reduction zone and the hydrofluorination are arranged above one another in a plant. The uranium(IV) oxide produced by the reduction of uranium(VI) oxide with hydrogen is very reactive and is eompletely reaeted with HF at temperatures between 500 and 650°C to uranium(lV) fluoride. 

In the dry process, introduced by Allied Chemical Corp., the uranium concentrate is pelletized and directly reduced with hydrogen to uranium(IV) oxide at temperatures between 540 and 650°C in a fluidized bed reactor. Hydrofluorination to uranium(IV) fluoride proceeds in two fluidized bed reactors connected in series. After fluorinating the uranium(IV) fluoride formed in a production unit consisting of a flame-reactor and a fluidized bed reactor, the uranium(Vl) fluoride produced is purified in a two stage pressure distillation process. This distillative purification process is necessary, because, in contrast with the wet process, no purification is carried out in earlier stages. 

The finding by Lewis and Gilliland (see Kunii and Levenspiel, 1991) that solids circulation between two fluidized beds (usually a reactor and a regenerator) and in the transport lines connecting them can occur stably... 

A particularly interesting use of seeds is in the resolution of the isomers of methy l-dopa as practiced by Merck Co., Inc. In this process two fluidized beds operate in tandem, each of which is seeded with one of the optical isomers. Supersaturation is controlled to minimize nucleation so that growth of each isomer occurs on the existing crystals in their respective beds (see Section... 

Since the late 1990s, there has been ever increasing interest in BFB combustion. The two fluidized-bed technologies are similar. Both use a bed of inert material (most typically sand) that is fluidized by high-pressure combustion air. The primary differences are that the BFB unit normally operates in a reducing atmosphere (less air than is needed for combustion), does not have as great an ability to absorb sulfur dioxide, and normally is used to bum lower-quaUty fuels with high-volatile matter. Further, the BFB unit keeps most of the sand in the lower furnace. 

Fluidized bed reactors are used for the gas phase polymerization of olefins to produce LLDPE and HDPE (Unipol PE, Innovene and Spherilene processes [22]) as well as for the manufacture of polypropylene (Unipol PP process [22]). The residence time distribution of a fluidized bed reactor is close to that of a well mixed continuous reactor. Therefore, the use of a single fluidized bed reactor leads to a broad particle size distribution and to large variations in the catalyst productivity from particle to particle. The use of two fluidized bed reactors in series narrows the residence time distribution leading to a more uniform product. 

The Mitsui Hypol process is based on two stirred autoclave reactors followed by two fluidized-bed gas-phase reactors (Figure 2.41). The gas-phase reactors are also used in homopolymerization, enabling polymer with better properties to be made. In the more up-to-date Hypol II process, the stirred autoclaves are replaced by loop reactors giving higher throughput and further reducing capital costs. 

In yet another modification, Minet and coworkers [14,17,18] employed two fluidized beds in series. The two steps of the process are chlorination (reaction of CuO with HCI at 200-280°C) and oxidation (reaction of CuCh with oxygen at 340-380°C). Again, the sum of the two reactions is the same as Deacon chemistry ... 

In parallel to the Lurgj fixed bed MTP process, Tsinghua University proposed a fluidized bed MTP (FMTP) process based on the SAPO-18/34 zeo-hte catalyst. It was declared that this catalyst can limit the formation of the compounds of C4 and beyond, and thus prompt the yield of ethylene and propylene. FMTP process has two fluidized bed reactors. The first one is used to convert methanol to light olefins, and the second one is mainly for further converting ethylene and butylenes to propylene. In 2008, Tsinghua, together with its partners, built a FMTP demonstration unit (capacity of 30 kt/a of methanol feed) in Anhui, China. In September 2009, the demonstration unit was started up. The experimental data shows that the methanol conversion is almost 100%, and the propylene yield is close to 67.3% (CH2 basis). FMTP has not been industrialized so far. 

The eireulations of solids between two fluidized beds allows eontinuous eatalyst regeneration. 

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