Product category:
Valve positioners and actuators
News Release from: Festo | Subject: Copar DRD/DRE and DLP in Athens
Edited by the Processingtalk Editorial
Team on 26 September 2005
Pneumatic upgrade for sewage treatment
valves
Europe's largest sewage treatment facility makes extensive use of Festo pneumatic valve actuators to provide intrinsically safe and maintenance-free valve operation
The Psyttalia Wastewater Treatment Plant is Europe's largest sewage treatment facility, and makes extensive use of Festo pneumatic valve actuators to provide intrinsically safe and maintenance-free operation The plant originally discharged effluent to sea, but was upgraded to meet the EU Urban Wastewater Treatment Directive, in time for the Olympic Games last year
This article was originally published on Processingtalk on 3 Feb 2004 at 8.00am (UK)
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The upgrade involved the addition of a large-scale biological treatment plant, comprising 12 fermentation tanks with a capacity of almost 300,000 cubic metres.
The treatment plant occupies almost the whole of the island of Psyttalia in the Saronic Gulf, just outside the Athens harbour area of Piraeus.
The plant handles the majority of Athens wastewater - amounting to about 1 million cubic metres a day, or 12 cubic metres a second - which is transferred to the island via nine huge Archimedes screw pumps.
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After treatment and dewatering, the waste sludge, amounting to about 800 tonnes per day, is shipped back to the mainland for disposal in landfill sites.
To ensure that the plant will operate reliably for many years, the construction companies in this joint venture (Themeliodomi, Aktor and Athena from Greece, Giovanni Putignano and Figli from Italy and Passavant Roediger Products from Germany), chose pneumatic automation technology.
According to George Lousis, the mechanical engineer responsible for the construction of the plant on behalf of the consortium: "It is vital that the actuators used to open and close the shut-off valves offer explosion protection, particularly in the area of the fermentation tanks, where the high-temperature sludge fermentation process generates gases such as methane and carbon dioxide.
It is laborious and costly to configure electrical drives for operation in potentially explosive atmospheres".
Nicholaos Zaminos, a system planner for the project, also points out that the long service life and overload tolerance of pneumatic drive technology are important factors.
"Pneumatic drives are maintenance-free, and with a service life of more than a million operating cycles, will outlive any process valve.
In this application, accumulated or dried material on the valves may make their breakaway torque much higher than normal.
Pneumatic drives are 'overload-tolerant', while electrical drives run up against torque limiters if required to deliver exceptionally high torque or force.
With pneumatic drives, it is easy to increase the operating pressure and thus the force and torque generated".
As most process valves in sewage plants are operated in a simple open/close mode or manually, the use of pneumatic technology has made it possible to achieve a significant rationalisation effect.
With electrical drives, in contrast, it is necessary for control system planners to include monitoring functions for values such as overtemperature, torque, switching frequency and servicing and maintenance intervals, which means a vast number of inputs and outputs to wire up.
The flow of sludge into the fermentation tanks is controlled by a total of 50 Copac DLP pneumatic linear actuators supplied by Festo.
These actuators are ideal for the control of gate valves as they act directly on the gates, making it possible to position them precisely.
The flow control system for the biogas generated in the fermentation tanks employs 40 quarter-turn Copar DRD/DRE actuators from Festo.
These actuators are used for open/close functions, and in conjunction with standard position controllers to achieve precise positioning of ball valves, stopcocks, shut-off and flow control valves.
The biogas produced during the fermentation process in the tanks is used as an energy supply for the sewage treatment plant.
The Copar actuators also control the distribution of hot water for the heat exchangers which are used to maintain a temperature of 33C in the fermentation tanks to dry the sludge. Request a free brochure from Festo ...
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