Solid Waste & Recycling

Feature

Landfill Gas Utilization

BFI Canada's Lachenaie landfill is the nearest landfill facility serving the waste disposal needs of Montreal, Quebec -- a community of 3.5 million people. The Lachenaie landfill site is located on th...


BFI Canada’s Lachenaie landfill is the nearest landfill facility serving the waste disposal needs of Montreal, Quebec — a community of 3.5 million people. The Lachenaie landfill site is located on the north shore adjacent to the extreme east of Montreal Island, crossed by highways 40 and 640. The annual capacity of the landfill handles about a third of Montreal’s waste; the city disposes approximately 3.8 millions tonnes of non-hazardous solid waste annually.

In 1994, BFI designed and built a landfill gas extraction system at the landfill. The following year it constructed a power plant that features a 4-megawatt (MW) reciprocating Waukesha 7042 GL engine plant to produce electricity. This power plant benefited from the company’s experience designing and building seven such installations in the United States.

The company established a 25-year agreement with Hydro-Quebec for the purchase of the electricity generated by the landfill biogas — the first such operation in Quebec. The plant generates enough electricity to power approximately 2,500 homes.

An important side benefit of the energy project is that it reduces greenhouse gas emissions. The reduction (approximately 600,000 tonnes of carbon dioxide equivalent) is roughly equal to the amount of carbon dioxide emitted by 160,000 cars in a year.

The idea for the project grew in tandem with an aggressive action plan from the Quebec government that decided in 1998 to recycle waste at a rate of 67 per cent by 2008. (This included municipal waste, as well as industrial, commercial and institutional [IC&I] waste and construction/demolition [C&D] debris.) By 2001 the City of Montreal achieved a recycling rate of 17 per cent for its municipal solid waste stream. The annual quantity of biogas generated from waste buried in the landfill was projected with estimates that used the recycling rate objectives of the Quebec government. The calculations determined the total airspace that is likely to be available in the landfill (which will be used up in 40 years).

According to the company, around 50 per cent of the total waste received at the Lachenaie landfill is municipal solid waste, 43 per cent is IC&I and the remainder is C&D debris and sludge from municipal wastewater treatment plants.

Landfill design and gas collection

The Lachenaie landfill cell is built like a vault in clay. The design leaves at least 10 meters of clay under the bottom of the cell, exceeding proposed provincial regulations that require a minimum six meters of clay. A state-of-the-art system collects leachate and the bottom of the cells is covered with sand that filters solid particles from the leachate.

The leachate is pumped through a treatment system comprised of three lagoons. The first pond acts as an anaerobic system; the other two use aerators to reduce organic pollutants before discharge to the municipal wastewater treatment facility (owned by the Townships of Terrebonne and Mascouche).

Eventually the maximum height allowed by the facility’s certificate of approval issued by the Quebec Ministry of the Environment is reached for each cell. Clay excavated from a new cell is then used to cap each completed cell. This occurs after the final drainage cap is installed over the last layer of buried solid waste. To complete the structure, topsoil is added above the clay cap and seeded.

Landfill gas is extracted via a number of wells drilled into the waste. The wells extend to approximately two meters above the bottom of the waste. Well installation is an ongoing process with new wells added to the gas collection system as landfill cells are filled and capped. Currently, about 250 wells are in place. The well risers are constructed of high-density polyethylene (HDPE) pipe. Each wellhead is equipped with sampling ports and a valve to allow measurement, to control extraction vacuum and to limit oxygen ingress into the waste (to avoid an underground fire).

BFI conducts an environmental survey each year of the ambient air, the groundwater, the treated leachate, the emissions from the power plant, and noise. This program will be continued for at least 30 years after the landfill is closed.

Gas treatment

The gas extracted from the site is directed to the power plant where it is pretreated to remove particulates, moisture and any trace contaminants. Pretreatment of the gas protects the engines and reduces downtime and maintenance costs. The gas passes through a microfiltration unit after it’s compressed, chilled, and reheated to remove moisture. Moisture removed from the gas, known as condensate, is discharged back into to the landfill’s leachate treatment system.

The treated gas is then injected into engines coupled to generators. Combustion of the gas in the engines powers the generators and produces electricity that is then delivered to the electrical grid.

The power plant is equipped with four Waukesha 7042 GL reciprocating engines that are specifically designed to operate on landfill gas. Each engine/generator set is rated to produce roughly 1,000 kilowatts of electricity. The power plant’s net output capacity is roughly 3.7 kilowatts, after operating loads.

In 2003, BFI captured around 5,000 scfm of landfill gas of which 1,600 scfm was used to generate power. The excess (3,400 scfm) was destroyed in three enclosed flares. This represents approximately 8 MW of wasted energy. BFI has proposed a power-plant expansion for a future gross capacity of 12 MW of power generation. This electricity could then be sold to Hydro-Quebec or other customers outside the province.

Through the customers’ base of Gaz Metropolitain, some companies and utilities located in the neighborhood of Lachenaie landfill are interested in using the excess gas (after moisture is removed) to replace in whole or in part other energy sources like natural gas or fuel. The gas would have to be delivered via a dedicated pipeline, but these potential customers would avoid the cost of natural gas compression and transport from Western Canada.

Says Yves Normandin, Vice President of BFI Usine de Triage Lachenaie Lte, “Such generation of green energy from landfill gas uses a resource that would otherwise be wasted and is an environmentally friendly source of renewable power.”

Guy Crittenden is editor of this magazine.


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