Reliability restored

Paul Boughton

Mark Stone explains how actuated valves saved the day after a hot water flood in Denmark.

The Metropolitan Copenhagen Heating Transmission Company (CTR) operates the largest district heating system in Denmark. Seven combined heat and power (CHP) and two waste incineration power plants, supported by 14 peak load power plants, supply heat to the CTR transmission system, consisting of over 100km of mostly underground pipelines with diameters up to 800mm. Water is pumped around the system at a pressure of 25 Barg and a temperature of 115°C. Along the transmission pipelines, 29 exchange and pump stations transfer the heat to the local district heating systems, serving more than 250,000 households and nearly one million citizens of five municipal areas of Copenhagen.

A problem in an adjacent area recently caused a remotely controlled underground valve chamber to be flooded with very hot water. Although the problem was quickly rectified, all the electric valve actuators installed in the chamber had been completely submerged in the near-boiling water. Subsequent inspection revealed that the robust double-sealed design of the Rotork IQ actuators installed in the chamber had protected them from any damage and maintained the integrity of their IP68 temporarily submersible enclosure specification. By comparison, actuators from another manufacturer had been badly damaged by the effects of the hot water reaching internal electric and electronic components.

Replacement actuators would be required as soon as possible to minimise potential disruption to routine operations, but integration with the centralised control system demanded the inclusion of special interlocks in each new actuator to ensure the correct operational sequence of main and bypass valves.

In the valve chamber, the design of the Rotork actuators had proved to be superior by protecting them from the damage that was inflicted on the other actuators. Rotork produced a wiring diagram with customised interlocks to suit the application and confirmed that new IQ3 actuators meeting this specification could be delivered in less than four weeks. CTR therefore agreed to place an order for these actuators.

The site wiring interface with the old actuators utilised plug-and-socket connections. To retain these, separate plug-and-socket housings were installed, locally sited by each new actuator and connected to the actuator terminal compartment. As well as retaining the double-sealed environmental integrity of the Rotork IQ3 actuator design, the plug and socket connectors have also enabled the actuators to be retrofitted with minimal modification to site wiring.

In addition to double-sealing, IQ3 actuators incorporate many other features that ensure long term reliability and uninterrupted operation. Secure, non-intrusive wireless commissioning and data transfer, using the hand-held setting tool and easy to follow menus displayed on the actuator screen, mean that once the actuator has been site wired there is no need to remove any electrical covers ever again. Internal electrical and electronic components are permanently protected. Commissioning itself can be performed with or without mains power connected.

Piezo torque sensing, unlike disc springs or other mechanical devices, is accurate throughout the life of the actuator and unaffected by the effects of wear on moving parts. A patented absolute encoder, with only four moving parts, provides constant sensing and reporting of valve position, even if the actuator is moved manually with the power disconnected.

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Mark Stone is with Rotork Controls.

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