Sarah Kellet reports on an electric process control actuator that assisted a ‘one day install’ for LNG separator skids
A modulating actuator was recently installed on a ‘one day install’ (ODI) wellhead gas/water separator skid bound for the giant Queensland coal seam gas-to-liquified-natural-gas (LNG) project in Australia.
These remotely sited wellhead separators are designed to operate under a wide range of conditions. They include an automated control system with instrumentation and communication/telemetry to a central control room to enable operator assisted start up, shut down and monitoring.
Traditional skid designs take an average of two weeks to commission but, as the name suggests, the operator believes that, once delivered to site, the ODI skid can be operational within a day. The ODI design has attracted a lot of attention from all the major players in the Australian LNG industry.
Previously, produced gas was used as the operating medium for the actuators, but in some areas this is not feasible, so the operator searched for an economical and reliable electric alternative, capable of operating in remote areas from renewable power sources.
Fulfilling this requirement, the compact Rotork CMA actuator is available in linear, part-turn and multi-turn versions. They facilitate the economical operation of numerous types of control valve, damper and pump stroke adjuster applications. Single-phase or DC electrical power supply is all that is required for control valve actuation, saving the on-going costs associated with the operation and maintenance of instrument air supplies.
The maintenance-free CMA drivetrain, environmentally protected to IP67 and permanently lubricated for operation, even in sub-zero temperatures, can be mounted in any orientation.
Accepting an industry-standard 4-20mA control signal, the CMA provides accurate, repeatable and backlash-free positional control.
Resolution is 0.2% on linear and quarter-turn applications, two degrees on the multi-turn models. All CMA actuators have output speeds that are adjustable down to 50% of full speed in 10% increments and manual operation is provided as standard. Network compatibility encompasses Rotork Pakscan, HART, Profibus, Modbus, DeviceNet and Foundation Fieldbus.
Local controls offer manual operation at the valve, combined with a vivid LCD display of valve position that also incorporates critical and non-critical fault symbols. Control selection knobs enable selection of Local, Stop or Remote operation and Open or Close input commands in the Local control mode. Each mode can be locked in place to prevent unauthorised operation. The LCD display shows the valve position as a precise percentage of total valve travel.
For fail-to-position performance, a reserve power pack provides the actuator with the ability to perform a predetermined action on power failure. The power pack also preserves position indication on the LCD display during power failure. Upon restoration of mains power, the power pack is swiftly recharged to ensure continued fail-to-position functionality. Action on power loss is easily configured with the standard CMA HMI interface as part of the user-friendly actuator set-up menu.
Sarah Kellett is with Rotork.