How can we reduce greenhouse gas emissions? In western France, Le Mans Metropolis repurposes waste from 400,000 households into thermal and electrical energy.
“The plant produces the equivalent of the annual electricity consumption of 3,500 households and provides 18,000 housing units with renewable energy for heating.”
In the fight against global warming, cities and local authorities in general are on the frontline and implementing solutions. For instance, in western France, Le Mans Metropolis has decided to recover the heat generated by its waste incineration to produce electricity and heat. To this end, the Sarthe urban community has relied on the services of Syner’Val, a Veolia group subsidiary, since 2016.
140,000 metric tons of waste
Each year, the Le Mans Waste-to-energy plant (WTEP) recovers 140,000 metric tons of non-recyclable waste. This waste is produced by the 400,000 inhabitants of Le Mans and the surrounding agglomerations.
Once transported to the treatment plant, the waste is burned in one of the plant’s two huge furnaces.
Its incineration produces heat at a temperature greater than 850°C, which passes through a boiler composed of a network of tubes containing water. Under the action of heat, water turns into steam and drives an electricity-generating turbine.
In addition to powering the plant, the vast majority (80%) of the electricity produced is reinjected locally into the power grid, corresponding to the equivalent of 3,500 households’ annual consumption. Part of the heat produced also supplies a network of 18,000 housing units in Allonnes and Le Mans South with heating and hot water. And — in a world first — a newly installed heat pump allows waste heat from the process to be recovered to meet peaks in demand in the district heating network.
Clinker and offgas
However, the waste recovery process has been taken to the limit. Like a wood-burning stove, waste incineration generates ash, or clinker, along with offgas.
The clinker goes through several separation steps to recover the metals found in it. It is then repurposed in conventional recycling channels. The rest, known as “processed bottom ash,” is used for sub-base roads or as quarry backfill.
The offgas undergoes a decontamination treatment before being released into the atmosphere. The dust remaining once the offgas has been treated is rendered inert and stored in landfill.
This is the only “final” — i.e. non-recyclable — waste generated by the entire cycle. It represents around 3% of the amount of waste processed.
Clean energy and purchasing powerIn this way, this process enables 46,000 metric tons of CO2 emissions to be avoided annually, which is equivalent to 8,500 fewer vehicles on the roads each day. With a total energy efficiency of 98% — corresponding to the ratio between the value of the energy produced and that consumed during a process such as combustion, the Le Mans WTEP is “one of the state-of-the-art waste-to-energy plants,” said its Director, Sébastien Mathey.
As well as helping reduce greenhouse gas emissions, the plant’s energy production represents savings of €200 per year per household on their electricity or heating bills.
“It offers increased purchasing power for our fellow citizens,” stated Renée Kaziewicz, councilor responsible for clean public spaces for Le Mans Metropolis, where a second heating network is hoped to be installed to supply the north of the city.
Credits: Main picture © Veolia