Automation project completed for sewage facility

Edited by the Engineeringtalk editorial team Sep 20, 2007

The hoists and chains were replaced with threaded rising stems, operated by Rotork IQ Pro Model 35 actuators and IB7 bevel gearboxes.

Rotork has completed an automation upgrade on the main inlet penstocks at the Thames Water Beckton Sewage Treatment Works, involving motorisation with IQ Pro intelligent electric actuators.

The contract was performed by Rotork Site Services, whilst the IQ Pro actuators were specified for the application within the terms of the framework agreement which Rotork holds with Thames Water.

Beckton is the largest sewage treatment works in the UK.

Situated on the north shore of the River Thames in the London Borough of Newham, the site treats the sewage from 3.4 million London residents and businesses.

The first stage of sewage treatment is fine screening to remove solids and debris.

A total of twelve inlet and outlet penstocks are installed in the screening plant to enable the flow to be diverted and screens to be isolated for routine maintenance.

The substantial penstocks, each measuring approximately 150 by 300cm, were fitted with electric hoists and chains to lift them out of the inlet channels.

The hoists, which had provided satisfactory service for many years, were reaching the end of their operating life and required replacement to prevent potential interruptions and reliability issues.

In addition, operation of the electric hoists was a relatively labour intensive process that could only be performed locally and a more up to date and automated solution was therefore required.

Engineers from Rotork Site Services first carried out a survey of the existing plant and then designed the new drive systems and top works on which the new actuators are mounted.

The hoists and chains were replaced with threaded rising stems, operated by Rotork IQ Pro Model 35 actuators and IB7 bevel gearboxes.

In addition to precise and reliable operation, the new actuators also enable a particular operating characteristic of the penstocks - which used to be performed manually - to be now carried out automatically, thanks to the flexible functionality built in to the Rotork IQ Pro control package.

When the penstocks are in the shut position sludge, debris and solids settle out on the bottom of the channel adjacent to the penstocks over a period of time.

If a penstock is opened in one uninterrupted movement, this concentrated build up would rush through onto the screening equipment and potentially overwhelm it.

Therefore, it had always been the practise to raise each penstock by approximately 10% of its travel and then stop it for a set period, which enabled the build up of sludge to disperse slowly before the penstock was fully opened.

The successful completion of this sequence used to rely on the eye of the operator but is now automatically performed by the Rotork actuators.

Each actuator is programmed to communicate a signal to its supervisory PLC when it reaches the 10% position of opening travel, at which point the PLC stops further travel for a preset time before asking the actuator to complete the opening operation.

During original project discussions this sequence of operations was to be triggered by external position switches attached to the penstocks themselves, but Rotork's Site Services engineers were able to demonstrate that using the standard features inherent in the IQ Pro control package provided a solution that is more reliable, less expensive and more flexible.

For example, it is easy to programme the actuator to pause at a different opening position if operating experience dictates.

The alternative would be to physically move the external switch on the penstock.

Rotork Sites Services' contract encompassed the survey, design of new adaptation and topworks, installation and actuator commissioning.

Completion was achieved on time and on budget.