Sieve tray reactors

In this condenser, part of the stripper off-gases are condensed (the heat of condensation is used to generate low pressure steam). The carbamate formed and noncondensed NH and CO2 are put into the reactor bottom and conversion of the carbamate into urea takes place. The reactor is sized to allow enough residence time for the reaction to approach equiUbrium. The heat required for the urea reaction and for heating the solution is suppHed by additional condensation of NH and CO2. The reactor which is lined with 316 L stainless steel, contains sieve trays to provide good contact between the gas and Hquid phases and to prevent back-mixing. The stripper tubes are 25-22-2 stainless steel. Some strippers are still in service after almost 30 years of operation. 

Gas-liquid reactions form an integral part of the production of many bulk and specialty chemicals, such as the dissolution of gases for oxidations, chlorin-ations, sulfonations, nitrations, and hydrogenations. When the gaseous reactant must be transferred to the liquid phase, mass transfer can become the rate-limiting step. In this case, the use of high-intensity mixers (motionless mixers or ejectors) can increase the reaction rate. Conversely, for slow reactions a coarse dispersion of gas, as produced by a bubble column, will suffice. Because a large variety of equipment is available (bubble columns, sieve trays, stirred tanks, motionless mixers, ejectors, loop reactors, etc.), a criterion for equipment selection can be established and is dictated by the required rate of mass transfer between the phases. 

The synthesis section of the Stamicarbon (STAC) process is shown in Figure 11.3. An updated version of this process, Urea 2000plus, is offered by DSM (Stamicarbon s parent company)108,110. In this process NH3 and CO2 are converted to urea via ammonium carbamate at a pressure of 140 bar and a temperature of lSt/ C to 185°C. An NH3-to-C02 molar ratio of 2.95 is used in the reactor to give a CO2 conversion of 60%, and an NH3 conversion of 41%. The reactor is lined with 316L stainless steel. It contains sieve trays to provide... 

From a simulation viewpoint units SO, S6 and S7 may be considered blackboxes. On the contrary, SI to S5 are simulated by rigorous distillation columns, as sieve trays. In the steady state all the reactors can be described by a stoichiometric approach, but kinetic models are useful for Rl, R2 and R4 in dynamic simulation [7, 8]. As shown before, the reaction network should be formulated so as to use a minimum of representative chemical species, but respecting the atomic balance. This approach is necessary because yield reactors can misrepresent the process. 

A, = minimum cross-sectional area for downcoming liquid flow in finite-stage tower, ft2 Ar cross-sectional area of flow reactor, ft2 A, = bubble-cap slot area, perforation sieve-tray area, or valve-opening valve-tray area, ft2 A, = total cross-sectional area of tower, ft2 b = width of slot at base, ft B = nB/N0 in Eqs. (48), (49), (52), and (54) c = height of slot, ft C = Ncl/N0 in Eqs. (48) to (53)... 

Trays, fractionating assembly of sieve trays, 428 bubblecap, 428,430-433 capacity, F-factor, 429 capacity, Jersey Critical, 432 capacity, Souders-Brown, 432 cartridge, 428 design data sheet, 429 dualflow, 426 efficiency, 439-456 Linde, 430 ripple, 426 sieve, 428,429 turbogrid, 426 types, 426 valve. 429.430.432 Trickle reactors, 576, 607 Tridiagonal matrix, 407 Trommels, 335... 

A steady-state Plant Simulation Model of an existing plant helped to calibrate the base-case model on a representative operating point. Some details of an industrial process were skipped, but the omission of these details does influence neither the plantwide material balance nor the process dynamics. The units SO, S6 and S7 may be considered black-boxes. Contrary, SI to S5 are rigorous distillation columns, modelled as sieve trays. In steady-state all the reactors are described by stoichiometric approach, but kinetic models are used for Rl and R4 in dynamic simulation. 

Figure 7.1 Conventional equipment used for fluid-fluid reactions (columns (a) multistage agitated column, (b) packed column, (c) sieve tray column, (d) buss loop reactor, (e) tubular reactor, and (f) static mixer)...

Hirata (22) also studied the behaviour of an Oldershaw column, a packed column and a sieve-tray column as distillation reactors for the esterification of ethanol and acetic acid. He found reflux ratio to be an important factor affecting not only separation but also conversion. 

Figure 12.16 Illustration of possible types of slurry bubble column reactors, (a) Simple bubble column, (b) cascade bubble column with sieve trays, (c) packed bubble column, (d) multishaft bubble column, and (e) bubble column with static mixers [61].

In terms of catalyst utilization, the most relevant reactor hardware is the distributor tray as it is responsible for the liquid distribution across the catalyst bed. In general, traditional distributor designs such as sieve trays, chimney trays, and bubble cap trays are known for their poor performance, whereas state-of-the-art distributors facilitate complete irrigation of the catalyst bed (e.g.. Sheiks HD tray, Topsoe Vapor-Lift tray, Exxon s Spider Vortex technologies, Akzo Nobel s Duplex tray, and Fluor s Swirl Cap tray) [65]. 

Figure 1. Fluid bed and related reactors, (a) Bubbling bed (with or without internals) (b) turbulent bed (c) pneumatic transport (riser and fast bed) (d) countercurrent baffle column (e) plate column (sieve trays, bubble caps, etc,) (f) packed column (bubble flow or trickle flow).

Continuous reactors are at work all the time. This means newly introduced reactants mix to some extent with products. This extent is termed backmixing. A tower has many plates or baffles in it and experiences less backmixing as, for instance, a tank with no plates. Continuous reactors can then be found within towers and columns. Towers may be packed or plate (bubble cap or sieve tray) type. Optimum reactor design attempts to curtail the amount of dead space or areas where no reaction is taking place. It is also possible to have reactants take a shorter path than is necessary for optimum reaction. This is called shortcircuiting. 

Tray-type reactors. Intemally, a variety of different tray types may be used. The descriptive terms for these trays include bubble cap trays, flexitrays, ballast tra5 , float tray, sieve trays, turbogrid, and kittel trays. They use a variety of techniques, including sieve slots and holes, as well as caps or fitted mini skirts, to alter the residence time of the fluid that passes over them, thereby enabling a more complete reaction. 

Relationships Between Objects, Processes, and Events. Relationships can be causal, eg, if there is water in the reactor feed, then an explosion can take place. Relationships can also be stmctural, eg, a distiUation tower is a vessel containing trays that have sieves in them or relationships can be taxonomic, eg, a boiler is a type of heat exchanger. Knowledge in the form of relationships connects facts and descriptions that are already represented in some way in a system. Relational knowledge is also subject to uncertainty, especiaUy in the case of causal relationships. The representation scheme has to be able to express this uncertainty in some way. 

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