Example Process Flowsheets

These examples ask for the construction of flowsheets from the given process descriptions. Necessary auxiliaries such as drums and pumps are to be included even when they are not mentioned. Essential control instrumentation also is to be provided. Chapter 3 has examples. The processes are as follows  

Visbreaking is a mild thermal pyrolysis of heavy petroleum fractions whose object is to reduce fuel production in a refinery and to make some gasoline. 

A side stream is withdrawn at the tenth tray from the top of T-2 and proceeds to steam stripper T-3 equipped with five trays. Steam is fed below the bottom tray. The combined steam and oil vapors return to T-2 at the eighth tray. Stripper bottoms are pumped with J-6 through E-2A (on crude) and E-2B (on cooling water) and to storage as heavy gasoline.  

Overhead of the fractionator T-2 is partially condensed in E-1A (on crude) and E-IB (on cooling water). A gas product is withdrawn overhead of the reflux drum which operates at 15 psig. The light gasoline is pumped with J-5 to storage and as reflux. 

Include suitable control equipment for the main fractionator 

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The process engineer identifies heat exchange equipment in a process by the operation or function it serves at a particular location in the flow cycle. For example, the bottom vaporizer on a product finishing distillation column is usually termed Finishing Column ReboUer E-16, or Reboiler E-16 the overhead vapor condenser on this column is termed Condenser E-17 etc. The usual operations involved in developing a process flowsheet are described in Table 10-11, or Chapter 1, Volume 1. 

In this example the flowsheet of the EDTA process has been modified by removing the following valves vlO, vll, vl3, and v20. The result of the modifications is shown in Fig. 17. 

By way of an example, one may consider the case of hydrometallurgical reactors. Leaching is the most important of the different unit operations, and is prominently placed and assigned due emphasis in a typical hydrometallurgical process flowsheet. A representative list of the various types of reactors used for agitation leaching is given in Table 1.21. 

Commercial-scale application of solvents coming under the category of neutral reagents is largely found as applied to the nuclear industry materials, as in example, for the separation and refining of uranium, plutonium, thorium, zirconium, and niobium. A process flowsheet for extracting niobium and tantalum from various resources is shown in Figure 5.23. It will... 

A simplified process flowsheet for Example 2.1 (from Madron, 1985). 

Let us introduce a simple example to illustrate the previous concepts. The simplified process flowsheet presented in Fig. 1 (Madron, 1985) consists of four units interconnected by eight streams. We are interested in the estimation of the total flowrates of the system. If these variables are measured for streams 1, 7, and 8, then the measurement matrix C is of dimension (Z x g), where Z = 3 and g = 8. 

If the total flowrates of streams 1, 4, 7, and 8 are measured for the process flowsheet presented in Example 2.1, the matrix M is defined as follows ... 

FIGURE 8 Process flowsheet for Example 3.6 (adapted from Kretsovalis and Mah, 1988b). 

Let us consider the well-known Vaclavek s example (Vaclavek and Loucka, 1976) the process flowsheet and measured variables are presented in Fig. 5 and Table 3, respectively. It consists of six units and four components. In this case, the concentrations of a stream are assumed to be either all measured or all unmeasured. 

Process flowsheet for Example 4.5 (from Vaclavek and Loucka, 1976). 

Many consumer products are produced, at least in part, using chemical processes. A characteristic chemical process involves a chemical and/or physical transformation of raw materials into products or intermediates that are then further processed. Process flowsheets or process flow diagrams are used by process engineers to depict the flow of process streams through the basic unit operations involved in a chemical manufacturing process. A unit operation typically refers to a vessel where a chemical or physical transformation occurs. Examples include chemical reactors and distillation columns. 

The final example to illustrate our plantwide control design procedure comes from Luyben and Tyreus (1998), who present design details of an industrial process for the vapor-phase manufacture of vinyl acetate monomer. This process is uniquely suited for researchers pursuing process simulation, design, and control studies. It has common real chemical components in a realistically large process flowsheet with standard chemical unit operations, gas and liquid recycle streams, and energy integration. 

Example 1-4 Liquid-Phase Industrial Process Flowsheet... 

As was described in the review of previous work, over the last ten years MINLP optimization models have been reported for the synthesis of process flowsheets, heat-exchanger networks, separation sequences, reactor networks, utility plants, and design of batch processes. Rather than describing in detail each of these works, we will briefly highlight several examples from our research group at Carnegie Mellon to illustrate the capabilities and the current limitations of the MINLP approach. 

All the previous material balance examples have been steady-state balances. The accumulation term was taken as zero, and the stream flow rates and compositions did not vary with time. If these conditions are not met, the calculations are more complex. Steady-state calculations are usually sufficient for the calculations of the process flowsheet (Chapter 4). The unsteady-state behavior of a process is important when considering the process startup and shutdown, and the response to process upsets. 

To avoid cluttering up the flowsheet, it is not normal practice to show the utility (service) headers and lines on the process flowsheet. The utility connections required on each piece of equipment should be shown and labeled, for example, CT W for cooling tower water. The utility requirements for each piece of equipment should be tabulated on the flowsheet. 

The symbols used to show the equipment, valves, instruments, and control loops will depend on the practice of the particular design office. The equipment symbols are usually more detailed than those used for the process flowsheet. A typical example of a P and I diagram is shown in Figure 5.29. 

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