Articles & Case Studies

Emerson’s Innovative Measurement System Uses Solar and Wind Energy to Gather Flow Data in Remote Landfill Location

Posted: Tuesday 6th January 2009

System helps East Sussex County Council evaluate cost-effective, environment-friendly leachate treatment process.

Emerson Process Management has implemented an innovative flow measurement solution for East Sussex County Council. A wind and solar powered system is being used to assess flows of leachate from the remote Castlewood landfill site, with a view to replacing regular tanker removal with local treatment.

Castlewood landfill site was closed in 1979. The area is now backfilled and grassed over. It is a pleasant rural spot surrounded by trees, to the west of East Grinstead.

Leachate from the Castlewood site is collected by tanker and transported to the local treatment works 17 miles away. East Sussex County Council has tankers do the 34-mile round trip through the local country lanes, five times a day, Monday to Friday, removing about 75m3 from the lagoon each day.

“Most of the leachate collected on site is believed to comprise mainly of rainfall and groundwater rather than leachate generated from the waste, therefore it is not highly concentrated,” explains Raymond Smith, Engineering Officer for East Sussex County Council. “If we could treat it locally and discharge it directly into the watercourse, we could make a significant reduction in the environmental impact of the process, and save money.”

Before any such decisions can be made, East Sussex County Council needs reliable flow data for the site, including diurnal, monthly, seasonal and annual figures. Since the nearest mains power is more than 500m away, the solution was not immediately obvious.

“We knew what we wanted to achieve, but without power to drive a pump system we didn’t know how it could be done,” says Smith. “We took the problem to the Emerson team, and they came up with this clever, environment-friendly solution.”

The Castlewood system does not use pumps at all. Instead, to keep power consumption to a minimum, each inlet flow (there are two) is held back by control valves until the respective sump level rises to operate a float switch. This triggers power to a Rosemount® magnetic flow meter and opens the control valve. Similarly, when the sump level drops sufficiently, the float switch closes the control valve and switches off power to the flow meter. The system is efficient because it only powers the flow meter when there is flow to be measured.

The Rosemount magnetic flow meter was chosen for its robust housing, built-in diagnostic capabilities and wide flow turndown (40:1).

Solar panels and a small wind turbine are used to trickle charge four 12V batteries, which provide a 24V dc supply. “We opted for both because the system was to be installed in a shady spot among the trees and we were not convinced that solar would provide enough power on its own,” explains Vernon Baber of the Emerson team that installed the system. “The addition of a wind turbine means we benefit from most weather conditions. Together they generate a total of about 3.5A. There is no reason to think the batteries will ever need replacing.”

Flow from the lagoon to the tankers is also measured using another flow meter powered from the same supply via a Mobrey® ultrasonic level switch. The data is logged locally, and downloaded to a PC at regular intervals.

By installing an appropriately scaled treatment plant on site at Castlewood, East Sussex County Council will avoid the need for regular tanker trips through the rural area and increasing treatment volumes at the main water treatment works.

“The system has been up and running since April 2008. Once we have got a full year’s worth of data we will be able to make an informed decision about the optimum size and form for the new treatment plant,” said Smith. “It is all part of our commitment to continuous improvement of water and waste management in the area.”

Tel: +44 (0) 1753 756600.
Fax: +44 (0) 1753 787109
www.mobrey.com




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