Case Study 2 - Paterson's Quarries
Paterson's Quarries Greenoakhill Landfill Mount Vernon
Gas Plant Inverter Booster Fans March 2016
The UK waste management sector has always been quite strained, leading to the landfill sites across the country reaching close to capacity. Sustainable solutions were required to limit the environmental impact of these sites and one such solution, regulated by the government, is to flare the methane and carbon dioxide gases produced by the various types of waste on these landfill sites before they can reach the atmosphere.
Paterson's Quarries Greenoakhill Landfill site covers 91 hectares and has been developed for landfill purposes in stages so it now consists of four zones. Each zone consists of a series of cells which have been engineered to operate independently of each other so that gas and other materials cannot migrate from one part of the site to another.
Patersons go over and above the government requirement to flare the methane gas and have put in place a fenced gas management compound which brings in gas from the zoned sections of the landfill site and burned in gas generators to convert into electricity. Patersons sells this electricity to the Scottish Power Distribution system via a cable connecting the site to the grid.
The Mount Vernon landfill site produces approximately 40,000MW of green electricity per year, enough to power 3,000- 4,000 homes.The electricity generation has proved extremely profitable and this now makes Patersons more profit from the sale of electricity as it makes from tipping by waste contractors.
The existing gas management compound involves four 45kW motors with star/delta starters used to boost the gas pressure to achieve desired value to burn in the generators, two of these 45kW motors are run at any one time with each set of motors boosting the pressure feeding a set of 5 generators. Without these motors there wouldn’t be enough gas pressure to run the generators thus no profitable electricity production.
In Oct 2015 EDC performed an Energy Appraisal on the Booster Fans and proposed fitting variable speed drives to provide constant gas pressure to the engines, and reduce parasitic energy consumption, enabling them to increase generation.
Patersons decided to go ahead with the variable speed drive option due to the following benefits:
• Less mechanical stress on motors and fans
• Process Improvements through utilizing pressure transducers in closed loop control to maintain constant gas pressure to the engines
• Energy/Cost Saving of 99,684 kWh per year which is now exported back onto the grid.
However the existing star/delta enclosures were too small to take the variable speed drives, so EDC designed custom made enclosures housing the drives and other necessary components and situated these next to the existing enclosures making all the required modifications to interconnect both.
• Energy logging before and after the VSDs were installed shows a reduction of one third on the power consumed by each motor.
• Cost effective installation.
• Higher gas plant availability.
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