The Landfill Gas Management System at the Sudbury Landfill Site
The Waste Management Systems Plan identified the Sudbury Landfill Site as the long term waste disposal site for Greater Sudbury (formerly the Regional Municipality of Sudbury). This decision required City staff to apply for an expansion of the site under Ministry of the Environment (MOE) regulatory requirements. The final MOE Certificate of Approval (license) was received in February 2002. The Certificate of Approval outlined the requirement for the design and installation of a landfill gas collection and flaring system.
Knowing that a landfill gas collection and flaring system would be required, staff included the review of various landfill gas utilization processes as part of the 2004 Waste Optimization Study. Several options were reviewed and the final recommendation was to use the landfill gas to generate electricity. Council supported this concept in principle in February 2005. Council subsequently supported staff's recommendation to commence negotiations to sell the landfill gas to Genco (a subsidiary of Greater Sudbury Utilities Inc.). In March 2005 and in 2006, Council supported staff's recommendation to finalize the agreement with Genco.
What is Landfill Gas?
Landfill Gas (LFG) is produced as a result of the biological decomposition of organic wastes placed in a landfill. The composition of the LFG is highly variable, and depends upon a number of site-specific conditions including solid waste composition, density, moisture content, and age. In general, LFG is primarily composed of methane (CH4) and carbon dioxide (CO2), 50 percent each by volume, with trace quantities of other gases such as hydrogen sulphide (H2S), mercaptans, and non-methane organic compounds (NMOC).
Landfill Gas Concerns
Due primarily to pressure gradients, LFG may migrate through either the landfill cover or the adjacent soil, enter the atmosphere, and can contribute to adverse air emission issues, such as Greenhouse Gas (GHG), health and toxic effects, and nuisance odour. Combustion of LFG at high temperatures oxidizes methane to carbon dioxide thereby reducing the impact on the atmosphere (methane is a potent GHG which has 21 times the global warming potential of carbon dioxide).
Sudbury Landfill Site Landfill Gas Management System
The Landfill Gas Management System at the Sudbury Landfill Site was commissioned in November 2005. The primary objective of this system is to provide long-term control of potential methane-related LFG emissions. The system is comprised of the following three major components.
1) Landfill Gas Collection Field
The purpose of the LFG Collection Field is to provide access to the waste mass to collect the LFG from within the waste disposal area through horizontal collection trenches and to transport the LFG to the LFG Control Facility. The collection field consists of approximately 4700 metres of horizontal gas collection trenches buried an average of three metres below the waste. Each collection trench holds a 150 millimetre (mm) diameter perforated high density polyethylene (HDPE) pipe.
At the end of each run of horizontal gas collection trenches is a Valve Chamber (VC) which houses control valves to balance the collection field, and sample ports for monitoring gas quality and gas velocity. HDPE laterals, 100 mm in diameter, connect the valve chamber and the LFG collection field to the LFG collection header. The 300 mm HDPE diameter LFG collection header connects to the LFG Control Facility (i.e. blower, flare).
2) LFG Control Facility
The purpose of the LFG Control Facility is to extract, transport and combust the LFG collected from the LFG collection field; it houses the mechanical and electrical components required to extract and destroy the LFG (i.e. LFG blower and enclosed flare).
The Blower applies a vacuum on the LFG collection field and draws the LFG to the flare; it has a maximum flow rate of 800 cubic feet per minute (cfm). A variable frequency drive (VFD) controls the LFG flow rate to the flare, the speed of which may be manually adjusted.
The Flare is an enclosed drum flare and consists of a steel shell surrounding a refractory-lined combustion chamber which is equipped with a waste gas burner, an automatic propane ignition system igniter, control panel, and a stack with an internal lining. In accordance with it's Certificate of Approval, the flare must operate at a minimum temperature of 871°C with gas residence time of at least 0.75 seconds.
The facility also includes a programmable logic controller (PLC) which continuously monitors for the presence of a flame, flare temperature, LFG composition (methane and oxygen), and any operational faults registered by the system.
3) Condensate Management
Generally, LFG is saturated with water vapour and condensate (i.e. condensation) may form within components of the LFG management system. The purpose of the Condensate Management is to remove and collect any condensate forming in the LFG header piping and the piping within the LFG control facility and direct the condensate to the leachate collection system for disposal as leachate.
Two Condensate Traps (CT), connected to the LFG header piping, collect condensate and pump it via a forcemain and gravity drain to the leachate collection system, via manholes. An additional CT and a moisture separator is located prior to the blower.
Landfill Gas to Electricity Project
In September 2007, Greater Sudbury Utilities launched the Landfill Gas Generation System. Greater Sudbury Utilities has an agreement with Toromont Energy Limited to operate and maintain the landfill gas generation plant for a 20 year term matching that of the Provincial Standard Offer Agreement between Greater Sudbury Utilities and the Ontario Power Authority.