Multistage system with recycle

Contiuous biomass-producing systems are usually single-stage reactors without recycle. Waste treatment systems usually use multistage systems with recycle. They frequently use step feeding of several stages to improve system stability. 

The conventional DBA and MDEA split-flow/flash amine systems operated at 900 psia. The circulating solutions were 30% DBA and 50% MDEA. Acid gas in both systems was released at 25 psia. The multistage membrane system consisted of an initial membrane bulk removal unit followed by a two-.stage permeation system with recycle. 

The scheme of commercial methane synthesis includes a multistage reaction system and recycle of product gas. Adiabatic reactors connected with waste heat boilers are used to remove the heat in the form of high pressure steam. In designing the pilot plants, major emphasis was placed on the design of the catalytic reactor system. Thermodynamic parameters (composition of feed gas, temperature, temperature rise, pressure, etc.) as well as hydrodynamic parameters (bed depth, linear velocity, catalyst pellet size, etc.) are identical to those in a commercial methana-tion plant. This permits direct upscaling of test results to commercial size reactors because radial gradients are not present in an adiabatic shift reactor. 

Figure 6.16 shows results for a 20% increase in recycle flow FR. The production rate is changed by only 10%, which is less than observed for the single adiabatic reactor. Thus the recycle flowrate is not an effective manipulating variable for changing the production rate in this multistage adiabatic reactor system with intermediate cooling. 

Often in practice, several membranes for gas separation are cascaded with recycle streams to effect a multistage system for increasing the separation factor to an effective level, particularly when the individual gases in the mixture have similar permeabilities. 

Figure 6.19. Different types of multistage CSTR operation (a) single-stream multistage system, (b) multistream multistage system, (c) multistage with recycle.

The unit has virtually the same flow sheet (see Fig. 2) as that of methanol carbonylation to acetic acid (qv). Any water present in the methyl acetate feed is destroyed by recycle anhydride. Water impairs the catalyst. Carbonylation occurs in a sparged reactor, fitted with baffles to diminish entrainment of the catalyst-rich Hquid. Carbon monoxide is introduced at about 15—18 MPa from centrifugal, multistage compressors. Gaseous dimethyl ether from the reactor is recycled with the CO and occasional injections of methyl iodide and methyl acetate may be introduced. Near the end of the life of a catalyst charge, additional rhodium chloride, with or without a ligand, can be put into the system to increase anhydride production based on net noble metal introduced. The reaction is exothermic, thus no heat need be added and surplus heat can be recovered as low pressure steam. 

Multistage/multistep combinations of two-step and two-stage processes can be designed but are seldom used in commercial systems—their complexity makes them uncompetitive with alternative separation technologies. More commonly some form of recycle design is used. 

Description In the Classic process, EB is catalytically dehydrogenated to styrene in the presence of steam. The reaction is carried out at high temperature under vacuum. The EB (fresh and recycle) and primary steam are combined with superheated steam, and the mixture is dehydrogenated in a multistage reactor system (1). An interheater reheats the process gas between stages. Reactor efflu-... 

The multistage liquefaction process (Figure 19.17) involves the liquefaction of crushed, dried coal which is slurried with an aromatic recycle solvent and the whole is then charged to a reactor at 415°C-440°C (VSOT-STST) at approximately 2000 psi. An expanded bed reactor system is employed to circumvent the problems that arise through reactor plugging, catalyst deactivation, and inequitable liquid distribution. 

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