Partial Heat Integration

Partially vaporized feed reverses these effects. For a given separation, the feed conditions can be optimized. No attempt should be made to do this at this stage in the design, since heat integration is likely to change the optimal setting later in the design. It is usually adequate to set the feed to saturated liquid conditions. This tends to equalize the vapor rate below and above the feed. 

For the study of the process, a set of partial differential model equations for a flat sheet pervaporation membrane with an integrated heat exchanger (see fig.2) has been developed. The temperature dependence of the permeability coefficient is defined like an Arrhenius function [S. Sommer, 2003] and our new developed model of the pervaporation process is based on the model proposed by [Wijmans and Baker, 1993] (see equation 1). With this model the effect of the heat integration can be studied under different operating conditions and module geometry and material using a turbulent flow in the feed. The model has been developed in gPROMS and coupled with the model of the distillation column described by [J.-U Repke, 2006], for the study of the whole hybrid system pervaporation distillation. 

Heat integration, multiple feed and withdrawal, partial splits, and medium recoveiy fractions in distillation column sequencing. 

Pinch Point Analysis starts with the input of data. The first step is the extraction of stream data from a flowsheet simulation, which describes typically the material balance envelope (Reactors and Separators). Proper selection and treatment of streams by segmentation is a key factor for efficient heat integration. The next step is the selection of utilities. Additional information regards the partial heat transfer coefficients of the different streams and segments of streams, and of utilities, as well as the cost of utilities and the cost laws for heat exchangers. 

To find temperature profiles for the constant flux case, simply replace q = -kdT/dx and integrate partially with respect to x. To do this, we need to call upon material in Chapter 4. If the temperature far from the heated surface is denoted by Tq = T(oo, t), then partial integration yields... 

T. loannides and X. E. Verykios, Development of a novel heat-integrated wall reactor for the partial oxidation of methane to synthesis gas, Catal. Today, 1998, 46, 71-81. 

We begin with the THF-water system. A comparison of systems with no heat integration, with partial heat integration and with complete heat integration will be presented. The phase equilibria for this system and a nonheat-integrated system have been discussed in Chapter 5. 

Figure 6.1 Flowsheet conditions with partial heat integration.

With complete heat-integration, the heat removal in the condenser of the high-pressure column Qc2 must be equal to the heat input to the reboiler of the low-pressure column. Therefore, a degree of freedom is lost, and we can only set the reflux ratio on one column, not both as is the case with partial heat integration or no heat integration. 

In the following sections the fuUy heat-integrated system is compared with a completely nonheated-integrated system and with a partially heat-integrated system. 

TABLE 6.2 Controller Tuning Parameters No Heat Integration and Partial Heat Integration THF-Water. 

Notice in the faceplates shown at the bottom of Figure 6.23 that the setpoints of the two temperature controllers are different in the partially heat-integrated case fiom those used in the fully heat-integrated system because the temperature profiles are slightly different. Of course the TCI temperature controller must be retuned since its output signal is a ratio. 

The second column in Table 6.2 gives tuning parameters. The TC2 temperature controller is also retuned because of the somewhat small heat duty in the high-pressure column with partial heat integration. These tuning parameters are very similar to those found in the completely nonheat-integrated system, so we anticipate that control should be good. 

Figure 6.26 Feed flowrate disturbances partial heat integration.

These results show that there is no control penalty for going to the partial heat-integrated systems when auxiliary reboilers or condensers are added. This result is to be expected because there is no loss of control degrees of freedom. 

Pressure-swing systems are very amenable to heat integration because of the inherent temperature differences in the two columns. Complete heat integration is the most economical from a steady-state economic point of view. However, a considerable dynamic controllability penalty can occur, which can be greatly reduced by using partial heat integration. 

In this section we compare the steady-state design and the dynamic control of heat-integrated extractive and pressure-swing processes. The same numbers of trays used in the base-case designs are used in both systems. The systems have not been reoptimized for heat integration. Only partial heat integration is considered in which an auxiliary reboiler is used. 

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