Eli5, Why do landfills merely burn off ex bytra gas into flames, why can’t they generate electricity or something with that gas?
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Depends on the landfill. The one in Bishopville SC has a gas capture system and the resulting power is enough to run the whole place.
Some do, either to create electricity, or to run the garbage trucks on the off gas. The problem is that all that equipment to collect, store, refine that gas is pretty expensive. Some really big landfills will do it because they’re big enough for it to make sense, but for smaller landfills it isn’t cost effective.
[Waste-to-energy](https://en.wikipedia.org/wiki/Waste-to-energy_plant) power plants exist, but they are not common. The cost of building and operating them is greater than the cost of fossil-fuel and nuclear plants.
Some do, directly run huge piston engines ( I’m talking ship size here ) Inturn run electric generators.
Some do. I live in a 400,000 person city and the dump generates about $2,500,000 of electricity a year. The plant is now at capacity and needs upgrades, but hard to justify for the amount of money it produces.
Some do. But setting up a power plant that can do that has extra equipment/costs associated with it compared to a power plant that runs straight off natural gas. So the amount produced needs to be enough that the savings from using landfill gas offset the cost of extra equipment.
As an example, the Keele Valley landfill was 3rd largest in North America. A power plant was built in 1994 to use the methane. It had a gas turbine and two boilers that powered a steam turbine. It also had sets of large blowers in order to draw the gas from the landfill and send it to the system at a useable rate/pressure.
By the time I did a college work placement there ~20 years later, they were removing the gas turbine which hadn’t been used in years. The boilers required a fairly large amount of natural gas in addition to the landfill gas in order to operate at full capacity. Gas power plants can last for 40 years, so this was halfway through it’s life cycle.
Basically what a lot of the answers here are already saying, there are some that do. The reason you wouldn’t is often a question of economics – the quantity of gas is either not sufficient to be useful for anything, or the cost to capture is higher than the payout on capturing it.
Lots of answers discuss how some do use gas capture systems but no answers as to why it’s relatively rare.
Gas from landfills and waste treatment plants is not pure methane. There are other contaminants like water vapor and Hydrogen Sulfide that need to be separated. Hydrogen Sulfide becomes sulfuric acid in the presence of water so it’s very corrosive. You need specialized equipment.
There’s one at my city landfill that produces like 1-5MW which is not a lot but arguably more useful than any other use for landfill gas.
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