Speed manages streams

摘要

The case for variable frequency drives as a final control element spreads. The concept of using variable frequency drives to control electric-driven centrifugal pumps is distinguished. But they seldom work in the petroleum industry. Why? The reasons given range from misinformed economic data and an unease of using unfamiliar electrical technology to an ignorance of how these devices react as control devices. One still sees the majority of flow, pressure, and temperature control happening through constant-speed centrifugal machines that a control valve throttles to provide the desired control of fluids. The use of variable frequency (VF) drives—adjustable frequency drives or variable speed (VS) drives—on electric motors driving centrifugal pumps offers many advantages over using control valves for controlling the fluid flow. Some of the advantages are energy savings, efficiency, power factor, installation, specification, ability to control, maintenance, fugitive emissions, and reduced wear on the bearings and seals of the pumps. Although this method of control has gained wide acceptance in general industry, there is still reluctance to use it in the petroleum industry. The reasons for this vary, but the most common reasons are: (1) a lack of understanding about how these devices work in comparison to the more commonly used control valve (2) a common misconception that these devices are expensive compared to control valves (3) a reluctance to use these devices on explosionproof motors found in petroleum facilities (4) a fear of the reliability of these fundamentally electronic devices (5) a lack of knowledge about the failure modes of these devices for the hazard and operability analysis There is no doubt that in the early days of development of the variable frequency drive some of the issues were true. However, over time the cost, reliability, functionality, and knowledge of these devices has improved to a point where we believe they should be viable final control elements for petroleum facilities.