Actuators & Controls
- Published on Tuesday, 08 July 2014 07:48
- Written by Chris Warnett
The conventional perception of a motorized valve is one of a large isolating valve with a heavy-duty valve actuator, usually powered by a three-phase electrical supply. However, many processes require smaller valves, and those valves often call for small electric actuators for isolating and modulating applications. As a result, the number of these smaller actuators is steadily growing.
The HVAC industry has used small electric actuators on valves and dampers for some time. However, the increased need for smaller size automation for heavier industrial applications that operate in hazardous or hostile environments has created an additional need.
In recent years, valve actuator manufacturers have improved small electric actuators’ performance. Part of the reason is that new technologies in electric motor design and more robust micro control circuitry make those improvements possible. As a result, reliability has increased and costs have decreased.
These improvements allow the demands of some applications to be met with both a commercially attractive and practical solution using motor-operated valves (MOVs), sometimes controlled from a considerable distance.
The higher efficiency of these actuators also means less power is needed to operate the valves. This is particularly important for applications in remote areas where the power distribution lines may not stretch. Even where power is available, it is often significantly less expensive to run low-voltage, single-phase or DC power lines compared to higher voltage, three-phase lines.
OIL AND GAS PRODUCTION
As energy and raw materials take on increased significance to the global economy, the search for new sources has spread into more remote locations. Oil and gas production and other industries are employing new technologies to exploit these less-accessible resources, and all of this has a direct impact on the production facilities and their associated control and instrumentation.
The rapid development of unconventional oil and gas sources also means more wells drilled in areas where there is no infrastructure to support conventional technology. These areas may be a considerable distance from a conventional electricity supply grid.
Previously, oil and gas well heads could use the gas produced from those wells to provide a power source to operate chokes and shutoff valves. However, environmental and economic concerns have decreased this practice. The environmental issues arise because the venting of natural gas is severely restricted in many countries to reduce greenhouse gas emissions. As for economic concerns, vented gas has a commercial value, so using it for power at the well site represents lost revenue to the producer.
Some installations have used solar-powered instrument air systems so they could avoid the use of gas. This has met with varying degrees of success, however.
Remote installations have been capable of control from a distance using telemetry powered by solar panels for some time because the power demand of the remote terminal unit is low enough to make this practical. However, to maintain continuous control of wellhead pressure and flow rates, regular adjustment of the control choke valve is often required, which necessitates the use of an actuator.
Several companies manufacture small electric actuators that can be powered by a solar power pack. These actuators are DC-powered and can operate many different types of control chokes and other valves.
In applications where many sites are spread over a wide area, each site requires its own solar power pack. The larger the solar pack, the more expensive it is. For this reason, equipment that has a relatively high power demand carries a high commercial penalty.
The key constraint for these applications is efficiency of the power source available. This means that low-power-draw actuators are almost a necessity.
Two main factors impact the power draw of the MOV assembly: the force demand of the valve and the efficiency of the actuator. Some members of the control choke valve industry (which is centered in North America with a majority of manufacturers in the Gulf region) are currently developing control chokes that require less torque to operate. This allows a smaller actuator to be used that not only reduces the power usage, but also the cost of the actuator.
Existing infrastructure often can be retrofitted to improve or extend its operating life. While this reality applies to any of the individual industries that make up this infrastructure, one place where inexpensive compact actuators are making a difference is with old plants and the power and control mechanisms that run them.
For example, in many cities around the world, water distribution systems have been in place for many decades. Leakage is inevitable and rampant with many of these systems, and as systems age, the leakage rates increase. In fact, estimates are that over 1 million miles of leaking water distribution pipes in the United States need replacing. The problems associated with these leaking systems are not limited to the loss of water but also include wasted energy and physical damage from erosion.
Leaks can be mitigated by reducing pressure during off-peak, low-demand hours. By reducing system pressure, the rate of flow through a leak can be reduced. To orchestrate this pressure management, close control of the multiple regulating valves in a system is required.
Here’s where compact electric actuators come into play. These smaller actuators are ideal for precisely controlling the pilot pressure activation of larger pressure-reducing valves in the distribution system. The physical constraints of sub-surface valve pits, as well as the damp environment, combine to require robust, compact electric actuators that can operate frequently and reliably to adjust the main valve position. These valves then can be controlled from a central location to reduce leakage in an entire municipal area.
Ultimately, the best way to reduce leaks is to repair or replace the miles of leaking distribution pipes. But this requires time and resources. Meanwhile, the control of pressure in the system can be implemented relatively quickly and cheaply. By using centralized control of hundreds of pressure-regulating valves, a municipality can implement leak mitigation in a shorter time frame.
As these two examples of industry use show, there are many processes and places today where smaller electric actuators are coming into play. To respond to those needs, manufacturers are using new technology to develop actuators that can make a difference.