Heuristics Rules for Process Equipment

    Provided that they are updated when appropriate to keep them relevant, time-tested heuristics rules based upon experience, also referred to as rules of thumb, can be useful for the design, specifying and operation of several kinds of equipment used in process plants. The first and foremost heuristic rule is that the engineer should not shy away from using heuristics – and the second rule is that he or she should not rely blindly upon them. Presented here are a wide range of heuristics, classified according to major kinds of typical process equipment or activity.   Fluid handling   Fans are suitable for raising gas pressures moderately (for instance, by 3%, or by 12 in. of water); for higher pressures up to about 40 psig, blowers are suitable; for yet higher pressures, employ compressors (however there is overlap between the operating ranges of blowers and compressors)   Typical polytropic efficiencies for large centrifugal compressors are about 76 to 78%; rotary compressors normally have efficiencies around 70%, except for liquid-sealed ones, which have efficiencies around 50%   For pipe lines of diameter D in inches, typical fluid velocities and pressure drops are as follows: (a) for pump…