“The future of anti-surge control valves (ASCV) lies in electric actuation, like the servomechanism that Shell developed with Festo. It is less complex than pneumatic actuation and so requires less maintenance and less expertise to set up.”
^ Birds’ eye view of one of Shell’s refineries
Article by Lucien Joppen
Willem van Rijs, Senior Automation Engineer at Shell Global Solutions, with expertise in automated valves, has been working for the Anglo-Dutch company since 2014. He previously spent 38 years with valve maker Masoneilan before moving to the end-user side of the industry.
At Shell, one of Van Rijs’s tasks is to communicate current as well as future expectations to the company’s valve and actuator suppliers. According to Van Rijs, the future of valves and actuators will be electric and digital. “There are a number of reasons for this strategic choice. First of all, pneumatic actuators are complex systems that are difficult to adjust properly and can be sensitive to extraneous parameters. Therefore, these systems require careful monitoring and regular inspection and maintenance.
In practice, this often necessitates flying in specialists from OEMs - a costly affair in terms of man hours, but also in regard to downtime. We also see that the number of experts available to work on pneumatic actuators systems is decreasing. In other words, it will become increasingly more difficult and expensive to employ or hire experts in this field.” Van Rijs says that electric actuation can also help to improve safety, efficiency and reduce costs in the oil and gas industry.
Electric actuators also offer more opportunities to be incorporated in automated systems than pneumatic actuators. Van Rijs: “Electric actuation makes it possible to monitor various parameters more precisely, such as voltage, current, frequencies, vibrations and so on. These data can be combined with other data for various purposes such as predictive maintenance. With pneumatic actuation, for example, an ASCV, has few parameters to monitor as most of the time it is ‘dormant’. The only signal is: ‘I am here’.”
Van Rijs mentions the ASCV as a telling example because it performs a vital function in the field, namely preventing compressor surge. “ASCVs are also among the most complex systems in our operations, yet they are rarely activated. But when needed, these systems have to work as the costs of compressor repair/replacement and downtime are high.”
Huge installed base
ASCVs are typically based around pneumatic actuation. Van Rijs states that this is a tried and tested technology that has proven its worth over many decades. “The installed base worldwide for pneumatic ASCVs is huge and it won’t disappear in the coming decades.”
But pneumatic actuation in this application has its disadvantages, one of these being dead time. To build up or blow off pressure requires up to a couple of seconds in which nothing happens. With electric actuation, in particular the servo-actuator which has been co-developed with Festo, Van Rijs states the ASCV can be monitored and operated faster and more precisely. “As mentioned before, electric actuation facilitates data transfer much better, making it easier for Industry 4.0 concepts.”
Outside the box
The rough idea for an electrical, digital servoactuated valve came up in Van Rijs’s mind while visiting a trade show which featured robotic and mechatronic applications. “The expo wasn’t geared specifically towards the oil and gas sector, but it became clear to me that some concepts on display could be put to use in our business. Servo-actuators have the potential to work quicker and deliver a more controlled movement, which should make it more effective in protecting compressors. Ideally, the ASCV control system would be able to predict surges on the basis of relevant data.”
Eventually Van Rijs’ brainstorm led to the Festo ASCV patent that lists him and mechanical principal technical expert Alfred Kruijer from Shell as the inventors. As Festo explains (see pages 73, 74 and 76), the challenge was to develop a servoactuator based on existing equipment to make the concept more accessible to the market. The idea was also to eliminate, as much as possible, the various process steps (from electricity to compressed air to actuation) which are usually associated with pneumatic systems. By reducing these complexities, the ASCV should be easier to operate and maintain, resulting in a higher efficiency and longer life span, Festo states.
Apart from the servo-actuator, the other innovation in the ASCV is a mechanical fail-safe solution that safeguards the protective function of the ASCV in case power is unavailable. As Van Rijs stresses, the ASCV has two roles: control and protection. For the latter function, the ASCV has to be kept open in a predefined position. This position will protect the compressor without compromising safety and will give personnel the time to intervene without having to shut down the operation.
According to Van Rijs, the mechanical fail-safe system is designed to fulfil the role of the solenoids used with pneumatic actuators. With the mechanical fail-safe unit, electro-magnetic energy is used to hold a spring in an energized position. In case of an emergency, the electro-magnetic energy is deactivated, the spring’s energy is released and the actuator moves to its predefined position. As the mechanical failsafe patent is still pending, Van Rijs cannot disclose any specific details at this stage.
Based on a demo model, two prototype servo-actuated valves have been designed and built. Shell intends to conduct field tests with them in Q1 and Q2 of 2019 in The Netherlands. Van Rijs says a final decision has yet to be made, but the test location will most likely be in an existing asset. “We are looking for confirmation and assurance that the servo-actuated ASCV performs as expected in real life. It also gives us the opportunity to learn and, if needed, adjust certain aspects of the configuration. All in all I am very positive about the outcome.”
Van Rijs is also optimistic about the integration of the servo-actuator in the industry. “We have contacted several ASCV suppliers and they all expressed interest in this development. It is important that new developments are picked up by the industry. Collaboration is key and can only accelerate acceptance and facilitate further improvements to the concept. Ultimately, the entire sector will benefit from solutions that are more efficient and less costly. Having said this, the implementation of new concepts require time as work processes have to be developed and validated. It also requires new skills and expertise from our employees.”