Solution single stage

The urea solution is evaporated in a two-stage system (99.8%) if the final product is prills, and a single-stage system (+95%) if granules are to be provided. 

The urea solution out of the stripper bottom flows to a single-stage low pressure recirculation section (0.4 MPa, 4 bar). The stripper off-gas is sent to the carbamate condenser. 

The urea solution stream is then fed to the vacuum concentrator unit which operates at 17.3 kPa (130 mm Hg abs) and produces 88.7 wt % urea. It then goes to either two-stage evaporators if prills are made, or a single-stage unit for granule production. 

After a single-stage liquid-liquid contact the phase remaining from the feed sohition (raffinate) can be contacted with another quantity of fresh extraction solvent. This crosscurrent extraction scVieme (Fig. 15-4) is an excellent laboratoiy procedure because the extrac t and raffinate phases can be analyzed after each stage to generate equihbrium data. Also, the feasibility of solute removal to lowTevels can be demonstrated. 

Petroleum products may be treated with various solvents for the removal by selective solubility of undesirable constituents or for the recovery of by-products. The solvent and solute must be separated to yield the desired product and to recover the solvent for reuse. The solvents normally boil at a lower temperature than the products from which they are to be removed and so are generally distilled off as overhead products. The pipe stills used for this service may be single-stage or multi-stage units, depending on the service involved. Some solvents can be removed by the use of steam heated stills. In other cases, the high temperature required necessitates the use of fired heaters and vacuum towers. 

These 11 equations describe the performance of the single-stage RON. For a given Qf, Cf and there are 12 unknown variables (Cr, Cr, Cs, n, N ,ater, solute, Qr> AP). Therefore, by fixing one variable the whole... 

This does not pose a constraint for the single stage, as the concentration of solute (C2) will be that of the final concentrate (20 kg/m3). 

While offering a more inherently realistic method of solution, however, the technique may cause some additional problems in the numerical solution, since high values of Kl can lead to increased stiffness in the differential equations. Thus in using this technique, a compromise between the approach to equilibrium and the speed of numerical solution may have to be adopted. Continuous single-stage extraction is treated in the simulation example EQEX. Reaction with integrated extraction is demonstrated in simulation example REXT. 

An infinitely large volume of solvent is needed to achieve complete extraction of a solute in a single stage. This necessitates application of multistage extraction. It allows essentially complete recovery deploying a limited volume of the solvent. In the countercurrent proc-... 

Reverse osmosis is particularly useful when it is necessary to separate ionic material from an aqueous solution. A wide range of ionic species is capable of being removed with an efficiency of 90% or greater in a single stage. Multiple stages can increase the separation. 

In the single-stage batch process illustrated in Figure 13.1, the solvent and solution are mixed together and then allowed to separate into the two phases—the extract E containing the required solute in the added solvent and the raffinate R, the weaker solution with some associated solvent. With this simple arrangement mixing and separation occur in the same vessel. 

As described in Section 15.2.1, eutectic systems can be purified in theory by single-stage crystallisation, whereas solid solutions always require multistage operations. Countercurrent fractional crystallisation processes in column crystallisers are described in Section 15.4.3. 

All freeze separation processes depend on the formation of pure solvent crystals from solution, as described for eutectic systems in Section 15.2.1. which allows single-stage operation. Solid-solution systems, requiring multistage-operation, are not usually economic. Several types of freeze crystallisation processes may be designated according to the kind of refrigeration system used as follows . 

In order to increase the recovery of adsorbate by adsorption, and to reduce the amount of adsorbent required to attain a specific recovery, a multistage adsorption operation can be used. In such an operation (as shown in Figure 11.3), a liquid solution is successively contacted at each stage with the adsorbent. In such a scheme, the relationship given by Equation 11.7 can be applied to each stage, with assumptions similar to the single-stage case, and the concentration ofthe adsorbate in the... 

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