Articles & Case Studies
ABB dissolved oxygen meters help Thames Water cut energy consumption for compressed air by 10%
Posted: Tuesday 17th July 2012
Dissolved oxygen meters from ABB are helping Thames Water to reduce energy consumption by roughly 10% in its compressed air blowers at the giant Beckton sewage treatment works in the London Borough of Newham.
The meters are part of a new control system designed to optimise the amount of compressed air used to treat the sewage. At Beckton, like virtually all sewage treatment works, oxygen is used in the process to break down organic matter by injecting oxygen in the form of compressed air into the sewage. But substantial sections of the site date back to the 1960s and previously included no instrumentation to match the supply of compressed air to the variable oxygen demand of the sewage.
“We compared the dissolved oxygen meters from a number of vendors and chose the ABB meters as the most cost-effective solution,” says Howard Smith, Instrumentation, Control and Automation Manager on the project for main contractor, Laing O’Rourke. “We were also working to a tight programme and the key was to deliver as fast as possible.”
The new installation includes 28 dissolved oxygen systems in total, made up of 16 AX480 single-input analysers and 6 AX488 dual-input analysers. All the systems are controlled from a central computer using on-board Profibus communications. The rugged design of both analysers makes them suitable and safe to use in harsh environments. They are also simple to install and use and require minimum maintenance, which makes them ideal for fully automated control schemes such as the installation at Beckton.
Beckton is already one of the largest sewage treatment works in Europe, serving 3.5 million people and discharging its effluent into the River Thames. The new control system is part of a £190 million programme upgrade that will enable the site to treat up to 60% more sewage by the end of March 2014. This will enable it to handle storm water as well as a growing population, helping to safeguard the Thames.
ABB’s AX400 Analyzers incorporate the latest technology providing highly reliable, flexible, feature-packed devices that satisfy a diverse range of process monitoring and control applications. The complete range encompasses solutions for pH/Redox (ORP), conductivity and dissolved oxygen.
AX48x instruments enable continuous measurements of one or two dissolved oxygen points with simultaneous local display and retransmission. AX48x can be used with the 9408 Series immersion, submersion and self-cleaning floating-ball sensors providing measurements with exceptional accuracy and performance.
AX400 Series analyzers are available for either wall-/pipe- or panel-mounting and are rated to IP65. All versions are supplied with two, fully-isolated current outputs as standard, which can be assigned to the measured parameter, sample temperature or any appropriate calculated variables. The analyzer range also comes with PROFIBUS DP capability, providing users with remote access to a greater range of process data at the field level.
Operating with dual inputs, the AX488 can monitor two continuous measurements thus reducing initial expenditure, saving space and minimizing installation costs when compared to using two individual analyzers. This capability provides on-line validation of the process measurement. Making two simultaneous measurements and configuring one of the set points as a difference alarm provides continuous on-line checking and early warning of malfunction of the measurement. Alternatively, both measurements can be compared and an average value calculated and transmitted via the analog output.
To complement the well-proven design, unrivalled accuracy and reliability in service of the dissolved oxygen sensor, the entire sensing loop is regularly self-monitored for short circuits and temperature element faults. The instrument incorporates a nonvolatile memory, eliminating the need for battery back-up, and line-voltage supply filtering to minimize the effects of mains borne interference.