Valve automation at solar power plants includes retrofit upgrade

With a generating capacity of 432 MW, Spain is now the world’s largest generator of electricity from solar power plants. Spanish solar energy plants utilise parabolic trough technology combined with a thermal storage system using molten salt batteries to maximise their power generating capacity.

Rotork IQ intelligent electric valve actuators with Rotork Pakscan two-wire digital control systems are in widespread use throughout these plants, as is the case at the recently completed La Dehesa and La Florida installations in the state of Badajoz.

Rotork Iberia has worked closely with the plants’ owner, Renovables SAMCA, to integrate an economical and efficient IQPro actuation and control system. The decision to use Rotork’s Pakscan P3 control system was assisted by its extremely long range bus capabilities and cost savings. Each Pakscan P3 master station can operate a bus loop of up to 20 kilometres in length with no deterioration in communication performance or the need for repeaters, making it ideal for the spacious environment of a solar power plant.

Rotork is now back on site for a retrofit project on the plants’ HTF (Heat Transfer Fluid) pipework. The HTF pipes carry the heat transfer oil between the parabolic mirrors, the steam plant and the power generation circuits. At each site Rotork is now installing 168 actuators and four Pakscan P3 master stations for the automation of 3 inch globe valves, to introduce remote control of the HTF temperature.

The application demands very high mechanical output resolution from the actuator in response to minimal signal changes from the controller. The linear stroke of each valve is 30mm and the requirement is to move a minimum of only 1% of this stroke, resulting in discrete movements of only 0.3mm. To achieve this, Rotork is supplying a linear version of the IQTF multi-turn actuator, which operates at a relatively low output speed to provide maximum resolution and accuracy. The positional monitoring and control signal is provided by the Pakscan P3 system, using Modbus RTU protocol, over a two-wire, twisted pair bus loop. Automatic, inbuilt redundancy of the field network is an integral part of the Pakscan design, ensuring that control is maintained even in the event of equipment or cable failure.

In common with all Rotork IQPro actuators, data loggers within the IQTF units facilitate valve diagnostics by recording historical operating data and valve torque trends. Using Rotork’s IQ-Insight software this data can be analysed on a PC to predict any potential operating issues, enabling maintenance to be planned in advance without interruption to normal plant operations.

The retrofit project is being carried out by Rotork Site Services, a dedicated organisation within the Rotork Group that supports all the actuator operations with a range of activities including retrofitting, maintenance, repair, extended scope projects and life of plant programmes.