Case studies 

Stone Pit Landfill Site, Dartford, UK 
 
Stone Pit 1 is a large historic landfill site located near the Dartford Crossing in Kent. Site owner, UK land specialist, Land Logical, began the first stage of a site restoration project in May 2015. Land Logical inherited a large and complex buried landfill gas management system which had grown ‘organically’ over many years with little being available in the way of installed plans or schematics. The system had a number of separate gas flows with different methane levels and a legacy landfill gas flare which was not operational. 
 
Landfill Systems supplied Land Logical with a conventional elevated hire flare for pumping trial purposes. The poor condition of the legacy gas management system meant that uninterrupted flaring was difficult to achieve because of low methane levels. The main sustainable gas flow was estimated to be around 600m3/hr at 20% methane. Landfill Systems designed and constructed an LC1250 Low Calorie flare which was installed in April 2017. The flare was installed and commissioned in one working day. A sustainable gas flow of 455m3/hr at 14% methane was quickly established. 
 
Now with sustainable flaring on the site, Land Logical were better able to understand the complexities of their inherited gas management system. Many improvements and replacements were made resulting in the establishment of two distinct gas flows; one with relatively high methane content suitable for power generation and one with lower methane content which needed to be flared to maintain environmental control. 
Renewable energy company, NewEnCo, were brought in to supply and install a Capstone micro turbine which is operated under the UK Government’s micro generation scheme, exporting 50kWe and attracting 1.8 ROC’s per MWh. Because of the separated nature of the gas flows on the site, Landfill Systems designed and constructed a stand-alone booster package to supply higher calorie gas to the Capstone engine. The package automatically diverts the gas flow to the flare when the micro-turbine is stopped. 
 
Land Logical invested further in their gas management system, resulting in a significant increase in the higher calorie gas flow. It became apparent that more gas was available than the micro turbine could use and so NewEnCo supplied and installed a Scania spark ignition engine to use the excess gas flow. Landfill Systems designed and converted a standard ISO container to package the Scania engine. Another, larger booster package was also supplied to pump gas to the new engine. 
 
By embracing the many years of landfill gas experience and know how provided by Landfill Systems and NewEnCo, Land Logical have achieved: 
• Full control of their gas management system. 
• World class site emissions levels. 
• Maximum financial benefit from the production of renewable energy from their landfill gas resource. 
 
Landfill Systems and NewEnCo continue to support the installations at Stone Pit with regular maintenance regimes and full remote access and monitoring services. 
 
 
Low Calorie flare replaces an elevated flare on a timer. 
 
A Local Authority have operated an elevated (‘candle’) flare at a remote small historic landfill since it was installed in 1992. Within weeks of the original installation, the gas flow reduced in flow and methane content to such an extent that the flare could only be operated on a daily timer. Initially the flare ran for 8 hours in every 24 but within a few years the running time reduced to 2 hours per day. This made it difficult to control landfill gas migration to a sensitive receptor. Latterly, the flare was operated in vent mode as combustion of the gas was no longer possible due to low methane levels. 
 
Following a pumping trial using the original flare operating in vent mode, sufficient gas flow information was gathered to enable the maximum capacity of a suitable low calorie flare to be assessed. Landfill Systems designed, built and installed an LC50 low calorie flare, which has a thermal capacity of 50kW (equivalent to 10m3/hr. at 50% methane). The flare was installed and commissioned, and the original flare was removed for disposal, all on the same day. 
 
The new flare is operating continuously with a combustion temperature of over 1,000*C with no support fuel, at a gas flow of 11m3/hr. and 12% methane (equivalent to 13.2kWth). Continuous gas extraction means that gas migration from the site is now firmly controlled. As a result, site visits will be reduced from weekly to monthly, helped by the comprehensive remote telemetry and data logging systems on board. 
 
The highly efficient flare design means that there will be little or no increase in the energy consumption of the site, even though the new flare is operating on a 24/7 basis. 
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