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Electric Valve Actuators in Process Plant Operations

Precision flow control using electric valve actuators

Process plant operation requires precise control of valves, and so the modulation of flow throughout the system depends on the operation of the valve actuator. Taken across their range of operations, these critical pieces of equipment may have to perform under extremes of conditions – very high, very low temperatures, in arid or high rainfall environments, in remote situations in deserts or arctic tundra or reliably rebuffing the corrosive effects of high humidity or salinity.

When they operate in potentially explosive atmospheres, there is a requirement for explosion protection, failsafe and fireproof operation.

By Paul Hopkins – MD, AUMA Actuators Limited

Paul Hopkins – MD, AUMA Actuators Limited

This article considers electric valve actuation, so in addition to the core function of opening and closing the valve, the actuator often forms the crucial interface between the process and the control system, providing integration into whichever distributed control system (DCS) is in use.

And, at a time where the IIoT and Edge Computing is gaining more and more momentum, electric actuators equipped with powerful electronics play a key role as information hubs providing direct access to a wide variety of both process and diagnostics data.

Fixed speed, variable speed, modulating? Electric Valve Actuation comes in many forms

Electric Valve Actuators have to be able to operate the full range of valves - gate valves, ball valves and others, to control flow of both gas and liquids. Typically, ball or butterfly valve actuation requires part-turn actuators providing a swivel movement of generally 90° for full travel. Gate valves, on the other hand, typically need multi-turn actuators providing several complete actuator turns to operate the valve from open to close and vice versa.

​Further distinction between open/close and modulating duty must be made. Actuators for open-close duty are required to infrequently open or close shut-off valves. Modulating (positioning) actuators, on the other hand, provide enhanced positioning accuracy for control valves in order to precisely modulate the flow within pipes.

An example from the oil and gas world is gas receiving terminals in gas pipelines where pressure control valves have to operate frequently and precisely to reduce the gas pressure.

​For ultimate control and process protection, a variable speed actuator offers a number of additional benefits. Valves, and pipe flanges, can be protected by slow initial and final valve velocity, while a higher speed through the middle of the cycle reduces the total open/close time, and fine adjustments can be made if a modulating duty version is specified.

In many ageing plants, and particularly in cold weather, exposed pipes and flanges can be prone to cracking, and so a ‘sympathetic’ actuation cycle can protect the integrity of the process. Variable speed operation also reduces power usage at the beginning of the cycle, so operation by solar PV power becomes a genuine option.

Modular Electric Valve Actuator Approach

It is not unusual for different automation processes within a pipeline to require a different actuation solution for each individual application. To support the customer, consistency of user interfaces and device handing is needed: from installation to commissioning, operation and maintenance.

​A modular actuator concept meets varied demands with a set of standard components. A broad range of multi-turn and part-turn actuators are available for different torque ranges, for different power supply sources, different valve attachments, etc. At control level, a choice between basic or intelligent actuator controls provide cost-efficient solutions for both simple and the most complex process control tasks.

​Modular design combined with a flexible actuator geometry allows easy on-site adjustment of mounting positions, making sure that operating elements such as local controls and display are always easily accessible, even if space is scarce.

​Case study – Limited space application for Saudi Aramco KAEQC pipeline

Space constraints are often an issue for filtration skids due to their very compact design. This is illustrated in figure 1, showing a filtration skid for the Saudi Aramco KAEC Pipeline Project.

AUMA supplied the actuators for the main line valves and filtration skids for this project. The actuators could be mounted in various orientations to meet the customer’s space requirements, while assuring optimum positioning of cable entries, hand wheel and local controls.

Variable speed electric actuator with modulating duty for ‘sympathetic’ actuation and fine control

Variable speed electric valve actuator with modulating duty for ‘sympathetic’ actuation and fine control

​​As an additional benefit, a modular concept dramatically reduces the amount of inventory required, as only a small number of standard/core components needs to be stocked by the end user.

​Combining standard actuators with a complementing gearbox portfolio allows very large valves to be operated, achieving torques of up to 675,000 Newton metres.

​Case study – Modulating actuator for Copenhagen District Heating Network

The 48-inch butterfly valve supplied by KOSO Kent Introl is the largest they have supplied and has a Cv of 59,531. It features a profiled vane that dissipates the energy as a valve works across a large pressure drop, reducing the chance of cavitation. The AUMA SEVEN HiMod, in conjunction with the GS gearbox, delivers a torque of 90,000Nm.

A variable speed (modulating) actuator means, clearly, that the speed of movement of the valve can vary throughout its travel, moving quickly throughout the majority of the cycle and slowing as it closes to reduce wear on the mechanical components. Variable speed also gives the opportunity for a ‘soft’ start, reducing energy usage.

Modular electric actuator design helps to meet the tight space constraints at a Saudi Aramco filtration skid.

Modular electric valve actuator design helps to meet the tight space constraints at a Saudi Aramco filtration skid.

Explosion Proofing and failing safe

Explosion-proof actuators are designed so that they will not act as ignition source for a potentially explosive atmosphere. They will neither generate sparks nor hot surfaces. All the electrical, mechanical and electronic components of the actuator are integrated into a single housing.

To maintain the correct separation from a potentially explosive atmosphere the ideal solution is a flameproof enclosure, so the enclosure must be able to withstand the pressure that may develop during an internal explosion to prevent it from being transmitted to an explosive gas surrounding the enclosure.

Additional requirements can call for actuators in fireproof versions that reliably maintain all functionality, even under the direct impact of fire. Meeting these demands, actuators can be equipped with a fireproof enclosure that meets the requirements of UL 1709.

In the event of a fire, the enclosure absorbs the heat and ensures reliable actuator operation at ambient temperatures up to 1,100 °C for 30 minutes, enabling the fire to be blocked and preventing spread of fire by closing the valve.

For more general failsafe operation, electric actuators can be backed up by mechanical failsafe devices such as AUMA’s FQM. The AUMA FQM works by tensioning up a ‘mainspring’. If power is lost, then the spring releases, safely moving the valve to the safe position, either valve open or valve closed.

Systems Integration with Intelligent Electric Valve Actuator Controls

Electric actuators are, in most cases, equipped with intelligent integral controls, which assume communication between DCS and actuator. Controls are available with various interfaces to the DCS – allowing both parallel signal transmission and fieldbus communication.

Supported are, for example, Profibus DP, Modbus RTU, Devicenet, Foundation Fieldbus as well as HART and WirelessHART. Embedded advanced diagnostics functions enable preventive maintenance and integration of actuators into asset management systems.

Electric Valve Actuators with patented K-Mass coating remain fully functional for 30 minutes even when subjected to temperatures up to 1,100 °C

Electric Valve Actuators with patented K-Mass coating remain fully functional for 30 minutes even when subjected to temperatures up to 1,100 °C

​Latest developments also include interfaces for the Industrial Ethernet standards Profinet and Modbus TCP/IP. Thanks to an unprecedented connectivity and real-time data transmission these standards are especially suitable for integrating actuators into IIoT/ Edge applications.

​Electric valve actuators can play a key role in these systems: On one hand, they operate remotely, opening and closing valves. On the other, powerful electronics allow electric actuators to act as information hubs for both process-related data, for example valve position feedback, and actuator-related data, based on advanced self-diagnostics.

For instance, intelligent algorithms monitor actuator characteristics to indicate when maintenance should be carried out. Asset management based on device-specific data boosts plant reliability and reduces unexpected downtime.

All information is directly available on the IT network and can be used for process visualisation, statistics, advanced modelling, or simulation to improve process performance.

AUMA offers TÜV-certified electric valve actuators suitable for applications up to SIL 2/SIL 3.

AUMA offers TÜV-certified electric valve actuators suitable for applications up to SIL 2/SIL 3.

​Empowering the User

As devices, including actuators, become more sophisticated, they need more in terms of set-up, and when things do go wrong, an expert understanding of their operation. On a large site, where there may be hundreds of valves and actuators in operation, this can cause headaches, especially when diagnosing a fault has to take into consideration the distinct possibility that any issue may lie with the mechanical operation of the valve rather than its actuator. That can result in significant service and repair costs and downtime that may well be unnecessary.

​One approach, as an alternative to using a manufacturer’s in-house service department, is to empower and train the user to work on the equipment themselves. Recognising that an instrument engineer will tend to want to be able to handle requirements themselves, at AUMA we have instituted a protocol for training staff and support engineers, called AUMA Certified Engineers, or ACE.

A dedicated training suite has been established at our UK head office and, via a secure log-in, accredited ACE technicians can access a raft of resources through our UK web portal. These include wiring diagrams, specific ‘how-to’ support and a library of short videos that support and reinforce training. The video below gives you a flavour of how they work.

​​Optical fibre communication for long distances

To cope with the long distances between the devices frequently encountered in pipeline projects and the high demands for data transmission security, data transmission via optical fibres can present a viable solution. Low attenuation of signals in optical fibre cables allow long distances between participants and, unlike copper cables, optical fibre cables are resistant to electromagnetic interference; so separate installation of signal and power cables is not necessary.

Case study: Optical fibre data transmission in Trans-Adriatic Oil Pipeline

Optical fibres proved to be a suitable solution for the Trans-Adriatic Pipeline (TAP) project. The pipeline will transport gas from the Turkish-Greek border via Greece and Albania across the Adriatic Sea to Italy, enhancing security of supply as well as diversification of gas suppliers for the European markets.

For the first phase, compressor stations in Greece and Albania are required, together with a metering station at the Greece/Albania border. The TAP system is controlled from the main supervisory control room at the pipeline receiving terminal in Italy, where the pipeline ends and the gas enters into the Snam Rete Gas (SRG) Network.

​The pipeline uses a SCADA system featuring a ring of fibre-optic cables laid along the whole pipeline route. Fibre optic components also have to meet strict directives if they are to be deployed in explosion hazard areas, as the luminous power, under certain conditions, represents an explosion risk.

AUMA therefore implemented a solution that uses fibre optic converters that fulfil EN 60079-28 for inherent optical radiation ("Op is") in accordance with the ATEX directive. These FO converters were installed within the Ex d enclosure of the actuator’s electrical connection.

A modular approach allowed this solution to be rolled out across all applications, which included high torque applications using actuators combined with part-turn gearboxes as well as linear applications using actuators combined with linear thrust units.

Electric valve actuators have to withstand extreme environmental conditions

Electric valve actuators have to withstand extreme environmental conditions.

Fieldbus and the Future

The challenges and opportunities presented by IIoT, Edge computing and big data are complex, but at their heart lies a simple truth. The flow of materials throughout the process industries will all be expressed as data with ever increasing granularity. Where there is data, that data can be used and manipulated.

​Once everything is measurable, and data security and internet reliability issues are fully addressed, as they will be, then new ways of using that data will emerge. At the same time, more will be expected from sensors and other elements of the control infrastructure in terms of local control and remote management. Actuators, because they are present throughout any distributed flow process, will be key enablers in the data revolution to come.

AUMA Actuators Ltd

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