Two feed streams

Hquid—Hquid-phase spHt the compositions of these two feed streams He oa either side of the azeotrope. Therefore, column 1 produces pure A as a bottoms product and the azeotrope as distillate, whereas column 2 produces pure B as a bottoms product and the azeotrope as distillate. The two distillate streams are fed to the decanter along with the process feed to give an overall decanter composition partway between the azeotropic composition and the process feed composition according to the lever rule. This arrangement is weU suited to purifying water—hydrocarbon mixtures, such as a C —C q hydrocarbon, benzene, toluene, xylene, etc water—alcohol mixtures, such as butanol, pentanol, etc as weU as other immiscible systems. 

The issue is to design an industrial SMB system capable of processing these two feed streams, and to compare them in order to select the most adapted solution. The working pressure should not exceed 10 bar. 

Two feed streams each containing one of the reactants at a concentration of 0.2 kmoles/m3 of benzene and each at 25 °C are to be rapidly mixed and fed to a tubular reactor. 

As discussed earlier, acid-base reactions are always nonpremixed. For example, a semi-batch reactor could initially be filled with base at concentration B0 and acid is added with concentration A0. Likewise, a continuous reactor could be run with two feed streams one for acid and one for base. For both of these examples, the degree of mixing between the acid stream and the rest of the reactor contents can be quantified by introducing the mixture fraction , which obeys... 

The difference between the catalyst responses in the two feed-streams may be related to factors which are yet unknown in addition to SO- poisoning of the water-gas shift reaction. Instruments which have 10%-to-90% response times of less than 0.1 s are required to measure the dynamic response of a catalyst in engine exhaust. 

Figure 5.8. The mixture-fraction PDF in turbulent flows with two feed streams (binary mixing) can be approximated by a beta PDF. 

Figure 5.9. The unmixed mixture-fraction PDF in turbulent flows with two feed streams has two peaks that can be approximated by a beta PDF. However, with three feed streams, the unmixed PDF has three peaks, and is therefore poorly approximated by a beta PDF. 

Perhaps the simplest Lagrangian micromixing model is the interaction by exchange with the mean (IEM) model for a CSTR. In addition to the residence time r, the IEM model introduces a second parameter tm to describe the micromixing time. Mathematically, the IEM model can be written in Lagrangian form by introducing the age a of a fluid particle, i.e., the amount of time the fluid particle has spent in the CSTR since it entered through a feed stream. For a non-premixed CSTR with two feed streams,100 the species concentrations in a fluid particle can be written as a function of its age as... 

Multi-environment presumed PDF models can also be easily extended to treat cases with more than two feed streams. For example, a four-environment model for a flow with three feed streams is shown in Fig. 5.24. For this flow, the mixture-fraction vector will have two components, 2 and 22- The micromixing functions should thus be selected to agree with the variance transport equations for both components. However, in comparison with multi-variable presumed PDF methods for the mixture-fraction vector (see Section 5.3), the implementation of multi-environment presumed PDF models in CFD calculations of chemical reactors with multiple feed streams is much simpler. 

Assuming each reaction is linearily dependent on the concentrations of each reacr-tant, derive a dynamic mathematical model of the system. There are two feed streams, one pure benzene and one concentrated nitric acid (98 wt %). Assume constant densities and complete miscibility. 

Another very common example of this type of system is in controlling two feed streams to a reactor where an excess of one of the reactants could move the composition in the reactor into a region where an explosion could occur. Therefore, it is vital that the flow rate of this reactant be less than some critical amount, relative to the other flow. Multiple, redundant flow measurements would be used, and the highest flow signal would be used for control. In addition, if the differences between the flow measurements exceeded some reasonable quantity, the whole system would be interlocked down until the cause of the discrepancy was found. 

To illustrate the PFR unit representation, let us consider the representation of a PFR with five CSTRs shown in Figure 10.1. Figure 10.1 illustrates a PFR with five CSTRs and two feed streams. These feed streams can represent fresh feed (e.g., feed 1) and the outlet stream of another reactor (e.g., feed 2). Note that the feed streams are allowed to distribute to any of the CSTRs. Also note the incorporation of by-passes around each CSTR unit. 

Twenty stream variables need to be specified in order for a unique solution to exist. In principle, any 20 stream variables could be supplied however, the usual solution strategy requires that the process feed streams be specified. Specifying the flow rate of each of the eight components, plus the temperature and pressure of the two feed streams (ethylbenzene and steam) reduces the number of variables to 150. Hence, a unique solution is available. 

Figure 1 shows the equipment used. The tubular reactor was 240 ft (73m) long, 0.5 inch (1.27cm) OD, Type 316 stainless steel. The reactor was placed in an agitated, constant temperature water bath. Two gear pumps were used to give metered flow of the two feed streams-an emulsion of styrene in an equal volume of water, and a solution of potassium persulfate in water. Table 1 shows the recipe used for polymerization. 

The following flowchart shows a distillation column with two feed streams and three product streams ... 

Specific enthalpies of the two feed streams and the product stream are obtained from the steam tables and are shown below on the flowchart. 

Thus, three specifications would have to be provided in the problem statement, following which the system equations could be solved for all remaining unknowns. Specifying values of three of the variables would suffice, as would giving values for two of the variables and a relationship between the masses of the two feed streams. (Convince yourself—choose values for any three variables and mentally go through the calculation of the remaining three from the system equations.)... 

SOLUTION Since ihree streams are mixed in the process but the MIX routine can only handle two feed streams,... 

The packing promotes good contact between the phases by dividing the two feed streams into many parallel interconnected paths. Ideally, you would like the liquid to flow downward as a thin film over the surface of the packing. This would give the maximum surface area of contact between the gas and liquid. 

Essentially the mixing point gives the composition of a hypothetical single-phase mixture formed from the two feed streams. According to a mass balance, this is the same mixture which would be formed by mixing the two product streams. In other words, M is the mixing point for either Lq and V2 or Lj and Vj. 

This will also be the mixing point for the two product streams L and Vj, although these streams are not coming from the same stage (i.e. they contain the same material as in the two feed streams). Assuming all the stages in the cascade are equilibrium stages, we also know that the points L and Vj lie somewhere on the equilibrium curve, but not necessarily on opposite ends of the... 

Step 3 Knowing the flowrates and compositions of the two output streams for stage 1, we can calculate the mixing point Mj using the method of Example 1. This is also the mixing point for the two feed streams Eg and 2-... 

Solve Problem 6.8 graphically or analytically with the column having two feed streams Stream 1, 80 kmol/h, 50% mole benzene, and 50% mole toluene, saturated liquid, sent to stage 3 Stream 2, 20 kmol/h, 30% mole benzene, and 70% mole toluene, saturated vapor, sent to stage 5. Use any other necessary data as given in Problem 6.8, and find the product compositions at a reflux ratio of 2 and a distillate rate of 50 kmol/h. 

Two mixtures of toluene and xylene are separated into toluene and xylene using one column consisting of 36 theoretical stages, including a partial condenser and a reboiler and operating at a pressure of 140 kPa. The two feed streams are at the same temperature and pressure but are of different flow rates, compositions, and phase (Table 9.9). The process requirements are a toluene recovery of 99.9% in the overhead and a xylene recovery of 95.2% in the bottoms. Recoveries are based on total feed. 

Figure 3.6 shows a non-adiabatic (heat is either lost to or gained from the environment surrounding the control volume) two-phase equilibrium-based process. There are two feed streams and two exit streams. The exit streams are in thermodynamic equiUbrium. 

The analysis begins with mixing of the solvent and diluent streams, as follows. Imagine two liquid streams O and V) which may contain any or all of components A, B and C. These two streams are mixed to form a third stream, F). The streams O, V and F may be single phase or two phase. Note that the control volume isn t necessarily an equilibrium-limited stage. The compositions and flowrates of the two feed streams are known (remember that for 0 xa+ Xb + xc = 1, for V ja + Jb + Jc = 1, and for F za+ Zb + Zc = ) Po not be confused about the notation the x s and y s are used to differentiate between the compositions of the two feeds, but the y s do not mean that stream V is vapor. Both feed streams are liquid.]... 

When applied to extraction problems, the two feed streams V and O are equivalent to the incoming feed and solvent streams. The stream F would represent a two-phase mixture, which would separate into the raffinate and extract phases. The component A is usually the solute and the component B is usually the diluent, although the lever-arm rule will work no matter how the axes of the diagram are arranged. When solving extraction problems graphically, it is really useful to remember equations ... 

Figure 6.2 shows a basic flow diagram for either an absorption or a stripping column. The process differs from distillation in that one stream enters with a contaminant and exits clean while a second enters clean and exits with the contaminant. Hence, there are two feed streams, the solute carrier and the mass-separating agent, which enter the column at opposite ends. This creates a flow pattern similar to distillation in which a gas phase flows countercurrent to a liquid phase. An absorption column is equivalent to the rectifying section of a distillation column. 

FIGURE 12.21 Typical reactive distillation configuration showing two feed streams and a reaction zone that can comprise multiple beds. 

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