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Comment PDF Processing & Handling

Gas Handling: Process Control for Compressible Flow

By Walt Prentice, Applied Flow Technology |

Controlling flow in gas-handling applications can present challenges because of the fluids’ compressibility. This article presents an overview of how compressible gases behave in response to interacting variables Gas-handling operations are common in almost every sector of the chemical process industries (CPI). Some examples are obvious, and others not as much so. Process plants may have heating, ventilation and air conditioning (HVAC) systems for recirculating air; auxiliary steam systems for heating unit operations; or even compressed air for pneumatic valve and tool operation, among others. While controlling parameters such as flowrate and pressure in a gas-handling process may be an intuitive goal, the methods of achieving it may not be. There are certainly physiochemical reasons to control flow and pressure, but there are regulatory reasons as well. For example, controlling pressure drop to keep the sound levels from getting too high in a process plant is a major topic in the Occupational Safety and Health Administration’s (OSHA; Washington, D.C.; www.osha.gov) Technical Manual. Figure 1. Since gases are compressible, variable densities alter volumetric flowrate and velocity. This compressible flow presents unique challenges…
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