Valve Automation Solutions (3)

POWER/ENERGY SOURCES

All ESD/PSD actuators that require a motion, a reaction or that must lock-in-last to a “trip signal” (not just a fail in place) need some type of power source to transfer that energy into a form that can drive a valve to its pre-determined ESD/PSD position or safe state. Generally that power source, in conjunction with valve type, must be established before significant automation progress can begin. Rather than simply listing the three primary energy sources, the following is a summary of the power sources or combined power solution ideas that may be found in the shale field for typical ESD/PSD actuator use. These ideas or methodologies are certainly not all inclusive, but they represent possible out-of-the-box automation solutions.

Manual power (human effort): This source can be used to generate energy, often in the form of a manual hydraulic pump which in turn can compress a spring (in a spring return actuator).

Pneumatic or gas supply to directly compress a mechanical spring: This can take the form of instrument air supply (compressed air), a gas supply derived from the media in the valve (such as natural gas), a nitrogen bottle or any suitable pressure vessel such as an air fail-safe tank.

Pneumatic or gas stored supply: This source can be used in an adequately pressurized volume so it powers an actuator through an ESD/PSD function. This can be a gas motor or other gas-powered actuator (e.g., a gas-over-oil unit.)

Hydraulic or hydraulic power unit: Direct hydraulic power, which normally requires an electrical supply to power a hydraulic pump, can compress a spring or store hydraulic energy in a storage vessel (hydraulic accumulator).

Electric (AC, DC, including solar panel derived): Pure, electrically powered units are not normally found in ESD applications, except for situations in which a charged battery storage bank provides a backup power source or when smaller, spring return, quarter- or part-turn units are involved.

Electric hybrid: Electro-hydraulic actuators typically use an electric power source to create hydraulic pressure used to compress a mechanical spring.

FAIL MODE TRIP

Automation solutions can be configured many ways to respond to a trip and ESD or PSD signal. The most common methods used in shale fields include:

Shutdown by ESD/PSD signal to a solenoid valve: The system can be remotely or locally shutdown by an electrical signal, typically through de-energizing the solenoid valve or valves.

Loss of supply pressure: This is usually a piloted control valve with functionality similar to the solenoid valve.

High- and/or low-pressure shutdown: This is often one or two pressure pilot valves (high and/or low). Pilots or pressure sensors are installed on the flowlines at various points to automatically trigger the valve shutdown in the event the preset pressure range is exceeded (which is called an Overpressure Pipeline Protection System) or falls below a given value or range. Versions of this are also available to measure pressure drop over time, allowing for temporary pressure fluctuations within a pre-determined period of time to avoid spurious trips.

High-temperature shutdown: This is often a fusible plug device or temperature sensing device that can typically vent a motive pressure.

Wireless: A newer technology is available for monitoring the valve and flow lines and transmitting an alarm or monitoring signal for position recognition in the field. Generally, wireless transmitters are not yet considered suitable for ESD on basic process control system functions.

A mix: One or more of the above methods are combined including redundant or sequentially interrelated.

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