“With our unique Adaptive PID Loop we can assure performance of 0.1 per cent on valves,” says Rotex Director Ms. Mitali Shah

Out with the old, in with the new!

Upgrading a single component can sometimes make a huge improvement in the performance of an entire system. Such was the case when a refinery in India recently decided to replace an Electrohydraulic Actuator with a model that could offer much better accuracy.
^ “With our unique Adaptive PID Loop we can assure performance of 0.1 per cent on valves,” says Rotex Director Ms. Mitali Shah

Article by David Sear

With facilities at several locations throughout the country, Bharat Petroleum is one of India’s key oil and gas corporations. Faced with unsatisfactory control valve performance at their Oil Receiving Station at Karur, BPCL turned to Mumbai-based Rotex Automation for a solution.

Rotex Director Ms. Mitali Shah takes up the story. “Bharat Petroleum asked us to provide an Electrohydraulic Actuator for installation on a control valve located on a pump output pressure balance system. This was required to replace a competitor’s model that was unable to deliver sufficiently accurate performance. The refinery had observed, for example, that the control valve had a deadband of over 1.5 per cent. In their specifications, they stipulated that our actuator should ensure a deadband with a maximum of 0.1 per cent.”

Further discussing the specifications, Ms. Shah says that the new Electrohydraulic Actuator delivered by Rotex has a thrust of 4700kg, a stroke of 90mm, is a fail-safe close model and can cycle from 0.5 to 100 per cent in under four seconds. “Like all our products this actuator was purpose-built to suit the exact specifications. However, thanks to our modular concept we were able to build this actuator using standard parts and components.”

As part of the contract, Bharat Petroleum requested Rotex to provide an end to end solution. Rotex therefore also undertook the installation and commissioning, which was fully completed in less than four hours. “During that time our staff fully dismantled the old actuator from the valve, fitted the new one, went through the calibration process, and also ensured the actuator was properly functioning with the DCS,” adds Ms. Shah.

Having discussed the project, Ms. Shah was kind enough to furnish extra details about the general benefits of Electrohydraulic Actuators. “Electrohydraulic actuators offer a fail-safe electric solution and do not require any external media such as air. Taking our models as an example, they are self-contained as they feature a built-in power pack, offer a life expectancy of around 25 years, and benefit from lower power consumption, consuming less than 25 watts in the steady state condition.  Moreover, performance drift is less than 1% over 25 years.”

Rotex is determined to live up to its motto of ‘Engineering for the Future’, states Ms. Shah. This is evident in the many features that can be identified in its SIL 3 certified Electrohydraulic Actuators. For example, a single hydraulic block contains all components including the power pack, solenoid valves, limit switch and the electronics module, all internally wired. This eliminates the need for any external tubing, reducing any possibility of cabelling faults or leakages due to tubing. This arrangement also simplifies maintenance.

Another benefit, continues Ms. Shah, is that the Rotex motor does not need to run 24X7 to maintain the position of the valve. “Our motor kick starts only after few positioning movements to build back the pressure, which saves a lot of energy. Moreover, the unique Adaptive PID Loop delivers accuracy, a low deadband, and hysteresis of under 0.1 per cent. That is why we are able to assure performance of 0.1 per cent on valves.”

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