Valve Magazine - Fall 2010

An added benefit of not using instrument air offshore is the weight savings realized by eliminating air compressors, receivers, dryers and other peripheral equipment. Because an electric actuator can run from an existing generator, having none of this additional equipment represents a significant weight savings, which means a reduction in the support structure (or jacket) cost.

In the offshore gas production fields of North West Australia, the most recent platforms built are unmanned and use an all-electric actuator configuration, including the control valve actuators.

In the oil fields of Lake Maracaibo in Venezuela, electric actuators replaced the air-powered control valves a decade ago, eliminating a major availability and maintenance headache.

Carbon Concerns: Many industrial nations are concerned with the carbon footprint of their industrial facilities. A carbon footprint relates to the weight of carbon generated in producing a product and is a measure of the amount of greenhouse gases produced and the associated environmental impact. Some manufacturing facilities that see a continuing demand for their products are feeling pressure to reduce their carbon footprints when producing those products.

One major European consumer products manufacturer, for example, has declared it will double its production over the coming 10 years, but yet will maintain the same carbon footprint or even reduce it. A key part of that company’s strategy is to eliminate use of instrument air in its facilities. Because air compressors and associated equipment are inefficient for moving power from one point to another, ceasing use of such compressors represents a significant energy savings. It is generally accepted that reducing energy used gives a corresponding reduction in the carbon footprint.

With the advent of modern electric
control valve actuators, many facilities
have no need for instrument air supplies,
since they were needed only to provide
the motive power to move actuators.
Electric actuator installations are signifi-
cantly more efficient, so major gains can
be made in reducing energy consumption
and thereby the carbon footprint.

A high precision valve being used for chemical dosing in a water treatment plant.

trol valve positioning can eliminate friction and overshoot effects. This gives improved control performance when valves with high seat or packing friction are used.

Smart positioners have made a significant difference in overcoming the inherent resilience of the air power medium in these circumstances and provide a good benchmark against which to measure the latest electric actuators.

Furthermore, the electric control valve actuator offers another benefit in this situation. When using pneumatic control valve actuators in such applications, some basic designs of positioner may need to be recalibrated at regular intervals because of “drift” in the position settings. This recalibration is time consuming, inconvenient and costly. Because there is no external linkage on an electric control actuator and all feedback and control is internal to the actuator, there is no drift. This eliminates the need for routine recalibration.

SUMMARY

While traditional spring diaphragm actuators are preferred in many situations, the list of applications where electric control valve actuators can be a better choice is growing. The new generation of electric control valve actuators can provide extremely precise operation, reduce labor-intensive maintenance costs, and often can operate better in bitter cold and other challenging environments. VM