Читать книгу Automation of Water Resource Recovery Facilities - Water Environment Federation - Страница 124

Instrumentation and controls (I&C) systems represent an integral part of designing a new or upgraded water resource recover facility (WRRF). As such, process and instrumentation diagrams (P&IDs) are an important part of the process.

Process and instrumentation diagrams are schematics that illustrate all the components of a WRRF. A P&ID typically provides enough information for the project team and stakeholders to understand how the treatment process will be measured and controlled, but leaves out details that require a specialist’s expertise. These details are covered in related specifications, data sheets, instrument lists, logic diagrams, and installation details.

Design engineers have various philosophies on how to use P&IDs in WRRF design. Some engineers, for example, use them to develop piping and equipment designs. However, this approach can make other design documents too dependent on P&IDs and can actually hinder their progress.

A more common approach is to use P&IDs to develop instrumentation and electrical designs. In this instance, P&IDs would include all instrumentation connections, control panels, workstations, signal lines, and electrical power needs. For example, it would show which instruments and control panels need 120 VAC and which control valves and other elements need air supply. It also might include other equipment’s power needs, motor control centers (MCCs), variable-frequency drives (VFDs), and power distribution. Electrical engineers would then use P&IDs to develop power-distribution drawings for all equipment.

Mechanical engineers use P&IDs to develop piping designs. (The precursor to P&ID development is a process flow diagram [PFD], which is described later in this chapter.) As such, they need the diagrams to show all wall-mounted, panel-mounted, and freestanding instruments, in addition to in-line devices (e.g., magnetic flow meters and pressure taps) mounted on the process equipment (e.g., tanks, centrifuges, and scrubbers). Analytical instruments such as water quality analyzers, gas detection analyzers, and so on are also included in P&IDs. Sometimes, P&IDs also include instruments that are part of a vendor-supplied skid-mounted package. These details are necessary to ensure that piping, including required straight runs before and after a meter, is configured properly. For more information on all the documents included in a complete automation design, see Chapter 3.