Engineering flowsheets

Figure 2.6. Engineering flowsheet of a gas treating plant. Note the tabulation of instrumentation flags at upper right (Fluor Engineers, by way of Rase and Barrow, Project Engineering of Process Plants, Wiley, New York, 1957).

Figure 10.3 Outline flowsheet for the production of isopropyl alcohol by direct hydration of propylene. (From Smith and Petela, Chem. Eng., 513 24, 1991 reproduced by permission of the Institution of Chemical Engineers.)...

Process engineer usually the chemical engineer who developed the flowsheet. 

Process Flowsheet Batch vs. Continuous operation Detailed unit operations selection Control and operation philosophy Information above plus process engineering design principles and experience... 

Figure 7.7 Flowsheet of the CE case study (from El-Halwagi et at, 1996. Reproduced with permission of the American Institute of Chemical Engineers. Copyright 1996 AIChE, All rights reserved).

Chemical engineering performance design for specific items of equipment required for a flowsheet, and mechanical interpretation of this to a practical and reasonable specification. Here the process requirements are converted into hardware details to accomplish the process end results at each step in the product production process. 

From the basic process-containing flowsheet other engineering specialties develop their own details. For example, the instrument engineer often takes the requirements of the process and prepares a completely detailed flowsheet which defines every action of the instruments, control valves, switches, alarm horns, signal lights, etc. This is his detailed working tool. 

O Donnell [9] has described the engineering aspects of these special flowsheets. 

Since the flowsheet is the primary reference for all engineers working on a project, it must contain all of the decisions, data, flow connections, vents, drains etc., which can reasonably be included without becoming confusing and difficult to read. 

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. 

To aid in readability by plant management as well as engineering and operating personnel, it is important that a set of symbols be developed as somewhat standard for a particular plant or company. Of course, these can be improved and modified with time and as needed, but with the basic forms and letters established, the sheets can be quite valuable. Many companies consider their flowsheets quite confidential since they contain the majority of key processing information, even if in summary form. 

Some equipment code systems number all items on first process flowsheet with 100 series, as C-101, C-102, P-106 to represent compressors number 101 and 102 in different services and pump 106 as the sixth pump on the sheet. The second sheet uses the 200 series, etc. This has some engineering convenience but is not always clear from the process view. 

As a direct companion of the completed flowsheet, the line schedule sheet transmits the process and mechanically necessary details for proper interpretation of the piping aspects of the flowsheet (see Figures 1-24A, B, C, D). These schedules are initiated by the process engineer to further explain the requirements of the process as shown on the flowsheets. They are often and perhaps usually cooperatively completed by other engineers, particularly the piping, mechanical and instrumentation groups. 

In some cases, they may be anticipated by a knowledge of the status of the process data prior to the start of engineering acthity. The larger projects are somewhat easier to group than the smaller ones. Process engineering is not always handled as completely for the small jobs. This is to say that flowsheets may be simplified, detailed equipment and line schedules may not be required, and the over-all project can be completely visualized at the outset, which is not the case with large projects. 

Figure 1-36. Process engineering costs (1975), based on process engineering charged at 14 per manhour. Chemical plant engineering operations, includes flowsheet development and drafting, material and heat balances, equipment designs, ratings, checking, and bid reviews and selection of equipment. By permission, E. E. Ludwig [7].

O Donnell, j. P., Flow Flowsheets Communicate Engineering Information," Chem. Eng, Sept. 1957. 

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. 

---