Utility Flowsheets

Over a period of years, the Titania A/S flowsheet has changed as the ore in the plant changed. The flowsheet that is currently being used is shown in Figure 25.6. This flowsheet utilizes a two-stage flotation method, where in stage 1, pyrite and apatite are recovered, followed by ilmenite flotation in stage 2. 

Modular simulators are frequently constructed on three levels. The lowest level consists of thermodynamics and other physical property relations that are accessed frequently for a large number of flowsheeting utilities (flash calculations, enthalpy balances, etc.). The next level consists of unit operations models as described above. The highest level then deals with the sequencing and convergence of the flowsheet models. Here, simultaneous... 

Figure 1. Basic glassmaking flowsheet utilized in waste flxation...

A schematic of a flowsheet utilizing the ternary azeotrope phenomenon to sepa-... 

A schematic of a flowsheet utilizing the ternary azeotrope phenomenon to separate components A and B is shown in Figure 10.5. The required amount of entrainer may be added either to the fresh feed or directly to the azeotropic column as reflux. In this process the entrainer is added as reflux to the azeotropic column. The ternary azeotrope is taken as column overhead and condensed, whereupon it separates (in the receiver) into two liquid phases, one rich in the entrainer and the other rich in component B. Compositions below the curve in the ternary diagram (Hgure 10.5) form two coexisting liquid phases, and those above the curve form one liquid phase. The tie lines connect compositions in the two liquid phases at equilibrium with each other. 

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. 

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. 

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. 

Preliminary Process Flowsheet. This will show major equipment and lines, preliminary equipment details (vessel diameter, number of trays, pump flow and driver horsepower, etc.), major instrumentation, and, it is hoped, have a material balance at the bottom of each drawing with flows keyed to a numbering system on the diagram. The process flowsheets should cover both the process and utility sides of the plant. 

Many s)mbols are pictorial which is helpful in representing process as well as control and mechanical operations. In general, experience indicates that the better the representation including relative locating of connections, key controls and even utility connections, and service systems, the more useful will be the flowsheets for detailed project engineering and plant design. 

The two types of lines on a flowsheet are (1) those representing outlines and details of equipment, instruments, etc., and (2) those representing pipe carrying process or utility liquids, solids, or vapors and electrical or instrument connections. The latter must be distinguished among tliemselves as suggested by Figure 1-21. 

The process designer must also consider the corrosive nature of the fluids involved when selecting construction materials for the various process and utility service lines. Some designers attach these materials designations to the line designation on the flowsheets, while others identify them on the Line Summary Table (Figure 1-24D). Some typical pipe materials designations are ... 

The Zircaloy Conversion Process (24, 25, 26) is a concept whereby one waste stream, Zircaloy fuel hulls, can be utilized in the stabilization of a second waste stream. The process flowsheet which is conceptual in nature, details the steps required to convert the fuel hulls to sodium zirconate to be used in the solidification of liquid high level waste. 

TBP is a sufficiently powerful extractant for actinides that it may be used in diluted form. Dilution improves the hydrodynamic properties of the solvent, allowing more complete and rapid phase disengagement. Typically concentrations of 20-30 v/o TBP in OK are used in process flowsheets. Although TBP is relatively stable as an extractant, radiolysis does lead to the formation of some acidic phosphate esters, HDBP and H2MBP, which can impair process performance.289 An aqueous alkali wash of the recycled solvent is usually carried out to remove those by products. Radiolytic degradation of the diluent in the presence of nitric acid can result in the formation of hydroxamic acids,290 which can lead to fission product retention by the organic phase. Again the solvent wash is used to prevent the accumulation of such species. A comprehensive account of the industrial utilization of TBP has recently been published.291... 

By assigning, for instance, binary variables to represent the existence or not of process units in a total process system, the potential matches of hot and cold streams so as to reduce the utility consumption or the existence of trays in a distillation- based separation system, the resulting total number of binary variables can grow to 1000 or more which implies that we have to deal with a large combinatorial problem (/. ., 21000 process flowsheets). 

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