Process Flowsheets

To this end, we have partially process-integrated the generic Microsoft Excel application [844] for the user-triggered calculation of the mass flow in streams of flowsheet process groups. In a similar manner, a partial integration between the flowsheet editor and the MOREX dedicated simulation tool [147] has been realized for the transfer of information concerning the simulation of compounding extruders. 

Process integration offers the potential to couple other tools participating in the design with the central flowsheet editor. We show, how a method fragment can guide the export of flowsheet process group information to the Excel tool for the calculation of the mass balance of the process. 

FLOWSHEETER = Process diagram calculation software package. Examples ASPEN , PROII , HYSIS . 

In the following sections we will discuss a number of important aspects of adsorption technology, inc I tiding adsorbents, criteria for when to use adsorption, a description of various ndsorption process flowsheets, criteria for choosing a process flowsheet, process-design considerations, and speculations on new and expended uses for adsorption processes. 

At the outset of the flowsheeting process, we know what final products are to be manufactured from what raw materials. Then the first step of PNS is to identify all plausible operating units and concomitant intermediate materials, which can participate in implementing the transformation of the raw materials to the final products. 

Kehat, E., Shacham, M. (1973) Chemical Process Simulation Programs. 11. Partitioning and tearing system flowsheets. Process Technol. 18, 115-118. 

All of the data obtained thus far from the process flowsheets, process survey forms, control equipment survey forms, stack survey forms, photographs, correspondence, discussions, and the plant tour can now be organized to develop an emission survey plan. This plan must indicate the quantity of emissions estimated from each source, with possible variations due to season, time of day, feed materials, and similar variables. The emissions characterization should identify all important parameters affecting control of the pollutants and possible sampling techniques. These data will be used to review the compliance status for each source. These programs will describe the plans that will be implemented by the company to achieve or maintain compliance, and should contain the following increments of progress or milestones ... 

Once the flowsheet structure has been defined, a simulation of the process can be carried out. A simulation is a mathematical model of the process which attempts to predict how the process would behave if it was constructed (see Fig. 1.1b). Having created a model of the process, we assume the flow rates, compositions, temperatures, and pressures of the feeds. The simulation model then predicts the flow rates, compositions, temperatures, and pressures of the products. It also allows the individual items of equipment in the process to be sized and predicts how much raw material is being used, how much energy is being consumed, etc. The performance of the design can then be evaluated. 

Grossmann, I. E., Mixed Integer Programming Approach for the Synthesis of Integrated Process Flowsheets, Camp. Chem. Eng., 9 463, 1985. 

Kocis, G. R., and Grossmann, I. E., A Modeling/Decomposition Strategy for MINLP Optimization of Process Flowsheets, paper no. 76a, AIChE Meeting, Washingtonj D.C., 1988. 

The decisions made in the reactor design are often the most important in the whole flowsheet. The design of the reactor usually interacts strongly with the rest of the flowsheet. Hence a return to the decisions made for the reactor must be made when the process design has progressed further and we have fully understood the consequences of those decisions. For the detailed sizing of the reactor, the reader is referred to the many excellent texts on reactor design. 

However, factors such as this should not he allowed to dictate design options at the early stages of flowsheet design because preheating the cold feed hy heat integration with the rest of the process might be possible. 

The introduction of an extraneous component as a heat carrier aflfects the recycle structure of the flowsheet. Figure 4.6a presents an example of the recycle structure for just such a process. 

Where possible, introducing extraneous materials into the process should be avoided, and a material already present in the process should be used. Figure 4.6h illustrates use of the product as the heat carrier. This simplifies the recycle structure of the flowsheet and removes the need for one of the separators (see Fig. 4.66). Use of the product as a heat carrier is obviously restricted to situations where the product does not undergo secondary reactions to unwanted byproducts. Note that the unconverted feed which is recycled also acts as a heat carrier itself. Thus, rather than relying on recycled product to limit the temperature rise (or fall), simply opt for a low conversion, a high recycle of feed, and a resulting small temperature change. 

Clearly, the time chart shown in Fig. 4.14 indicates that individual items of equipment have a poor utilization i.e., they are in use for only a small fraction of the batch cycle time. To improve the equipment utilization, overlap batches as shown in the time-event chart in Fig. 4.15. Here, more than one batch, at difierent processing stages, resides in the process at any given time. Clearly, it is not possible to recycle directly from the separators to the reactor, since the reactor is fed at a time different from that at which the separation is carried out. A storage tank is needed to hold the recycle material. This material is then used to provide part of the feed for the next batch. The final flowsheet for batch operation is shown in Fig. 4.16. Equipment utilization might be improved further by various methods which are considered in Chap. 8 when economic tradeoffs are discussed. 

Figure 4.16 Final flowsheet for the production of butadiene sulfone in a batch process.

Example 6.1 The flowsheet for a low-temperature distillation process is shown in Fig. 6.19. Calculate the minimum hot and cold utility requirements and the location of the pinch assuming AT, m = 5°C. 

Consider again the simple process shown in Fig. 4.4d in which FEED is reacted to PRODUCT. If the process usbs a distillation column as separator, there is a tradeofi" between refiux ratio and the number of plates if the feed and products to the distillation column are fixed, as discussed in Chap. 3 (Fig. 3.7). This, of course, assumes that the reboiler and/or condenser are not heat integrated. If the reboiler and/or condenser are heat integrated, the, tradeoff is quite different from that shown in Fig. 3.7, but we shall return to this point later in Chap. 14. The important thing to note for now is that if the reboiler and condenser are using external utilities, then the tradeoff between reflux ratio and the number of plates does not affect other operations in the flowsheet. It is a local tradeoff. 

The best way to deal with a hazard in a flowsheet is to remove it completely. The provision of safety systems to control the hazard is much less satisfactory. One of the principal approaches to making a process inherently safe is to limit the inventory of hazardous material, called intensification of hazardous material. The inventories we wish to avoid most of all are flashing flammable liquids or flashing toxic liquids. 

Once the process route has been chosen, it may be possible to synthesize flowsheets that do not require large inventories of materials in the process. The design of the reaction and separation system is particularly important in this respect, but heat transfer, storage, and pressure relief systems are also important. 

Starting irom the original flowsheet, LinnhofT and Parker have shown that it is possible by a combination of distillation modifications and network improvements to reduce the energy consumption of this process by approximately 60 percent. 

The design of the reactor usually interacts strongly with the rest of the flowsheet. Hence a return must be made to the reactor when the process design has progressed further. 

The synthesis of reaction-separation systems. The recycling of material is an essential feature of most chemical processes. The use of excess reactants, diluents, or heat carriers in the reactor design has a significant effect on the flowsheet recycle structure. Sometimes... 

As the flowsheet becomes more firmly defined, the detailed process... 

Since the discovery of petroleum, the rational utilization of the fractions that compose it has strongly influenced the development of refining processes as well as their arrangement in refining flowsheets. 

With the introduction of new antipollution standards as well as limitations envisaged for the chemical composition of finished products, current refining flowsheets and especially those beyond the year 2000 will have to adapt to the new specifications using new processes. 

Fig. 1. A typical process flowsheet for acrolein manufacture. A, Fixed-bed or fluid-bed reactor B, quench cooler C, absorber D, stripper E and F,...

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