Figure 14.6a Heat and material balance-established material and thermal requirements [9].

      14.5.3 Piping Flowsheet or Mechanical Flow Diagram, or Piping and Instrumentation Diagram (P&ID)

This is used to present “mechanical-type” details to piping and mechanical vessel designers, electrical engineers, instrument engineers, and other engineers not directly in need of process details (Figures 14.7 and 14.8). Piping and Instrument Diagrams (P&IDs) are graphical summary of the actual hardware elements in a petroleum refining and chemical process plant and their inter relationships of connections to form an operable, safe and reliable plant. The P&IDs include vessels (columns and tanks), pipe sizes, schedule (thickness), materials of construction, all valves (sizes and types), pumps, heat exchangers, reactors, furnaces, compressors, expanders, relief and drain valves, traps, filters, conveyors, hoppers, purchased subsystems, sensors, insulation requirements (thickness and type), controllers (flow, pressure, temperature, level), spares and other manufactured items, all in a logical configuration. The P&IDs do not include piping lengths and bends. In some engineering systems, detailed specifications cannot be completed until this flowsheet is basically complete.

      Figure 14.6b Process flow diagram of (feed and fuel desulfurization sections) [9].

Figure 14.6c Process flow diagram of atmospheric fractionator.

Figure 14.7 Mechanical detail flow diagram [9].

Figure 14.8 Piping and Instrumentation (P & ID) diagram for ammonia plant [9].

      14.5.4 Combined Process and Piping Flowsheet or Diagram

This is used to serve the same purpose of both the process and piping flowsheets (Figures 14.9 and 14.10). This necessarily results in a drawing with considerably more detail than either of types 2 and 3 just discussed. However, the advantage is in concentrating the complete data and information for a project at one point. It does require close attention in proper reading and often opens data to larger groups of persons who might misinterpret or misuse it.

      Some companies do not allow the use of this sheet in their work primarily because of the confidential nature of some of the process data. Where it is used, it presents a concise summary of the complete process and key mechanical data for assembly. This type of sheet requires more time for complete preparation, but like all engineering developments preliminary issues are made as information is available. Often the sheet is not complete until the piping and other detailed drawings are finished. This then is an excellent record of the process as well as a worksheet for training operators of the plant.

      14.5.5 Utility Flowsheets or Diagrams (ULDs)

Utility line diagram (ULD) includes hardware details of the steam, water piping and control systems (Figures 14.11 and 14.12). Used to summarize and detail the interrelationship of utilities such as air, water (various types), steam (various types), heat transfer mediums such as Dowtherm, process vents and purges, safety relief blow-down, etc., to the basic process. The amount of detail is often too great to combine on other sheets, so separate sheets are prepared. These are quite valuable and time saving during the engineering of the project. They also identify the exact flow direction and sequence of tie-in relationships for the operating and maintenance personnel. The distribution of a utility such as steam is by a common distribution pipe, with each unit requiring the utility drawing its supply from that pipe. When a unit has taken its requirement, the utility distribution pipe can then be reduced in size as it continues to the next unit requiring the utility. The order of servicing units is affected by layout, and utility line sizes are affected by the order.