ABB drives help cut power consumption by a third at landfill site
Patersons Quarries use ABB variable-speed drives to allow more energy to be sold into grid
PATERSONS Quarries’ landfill site at Mount Vernon, near Glasgow, has saved a third of the power used by motors to pump gas, following the installation of two ABB variable-speed drives (VSDs). Methane gas extracted from decaying waste at the site is used to generate electricity and the 45kW VSDs efficiently control the speed of the motors running the gas compressor pumps, which were previously operated ‘direct-on-line’.
According to ABB, maintaining the correct gas pressure from the pumps allows more efficient operation and this means an extra 199,368kWh per year can now be exported back on to the grid by Patersons Quarries – increasing their revenue by nearly £17,000.
The solution uses two ABB general-purpose drives to provide constant gas pressure to the generators. This is achieved by utilizing pressure transducers that feed back the gas pressure to the drives and allows them to control the speed of the motors to maintain the pressure at the correct level.
The 91ha landfill site produces 40,000MW of green electricity a year, enough to power up to 4,000 homes. This is sold by Patersons to Scottish Power Distribution, creating a significant income stream for the business. The gas management compound has four 45kW motors which are used to boost gas pressure up to 100 mbar, ensuring correct combustion is provided across five on-site generators. Two of these motors are used at any one time to provide gas for all of the generators.
‘The main problem was that the motors were running at 100% speed all the time, whether they needed to or not,’ explained Alan Hoggins, site manager at Mount Vernon. ‘Because the motors run on the electricity we generate on site, this was obviously wasteful of energy that we could otherwise sell.’
In response, Patersons wanted to gain better control of this process to ensure they could always maintain the correct gas pressure. The company approached EDC, the ABB’s authorized value provider for Scotland, who recommended the use of VSDs to control the pumping of water. EDC performed an energy assessment on the booster pumps and logging revealed that using VSDs to run the compressor pump motors could save a third of the energy used.
Another challenge was that the existing star/delta enclosures were too small to take the VSDs. To resolve this, EDC designed custom enclosures to house the drives and other components. These were located next to the existing enclosures, with interconnections between them.
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