I had a colleague who briefly worked with a mad scientist intent on bringing a “trash laser beam” — that’s what we called the plasma furnace — to market. In What a Difference a Day Makes, Robert X. Cringely describes the technology and its potential:
Until the late 1960s most American cities burned their trash, which was highly efficient at reducing the trash volume by more than 90 percent, yielding ash that was relatively small and easy to dispose of under the prevalent rules of that time. Then came the Clean Air Act, which made burning asbestos and DDT and PCBs and various heavy metals a no-no, so we started burying our trash in landfills, which requires a lot more effort and a lot more land — so much land that many large cities are running out of places to stash their trash. Recycling helps reduce the volume of trash, but it requires labor, costs more than it earns, and most of the stuff that could be recycled is missed. We need something better than burying our trash in landfills.As an aside, many products that were designed in the 1960s for easy incineration are designed today for easier digestion in landfills. Disposable diapers are a good example of such a product.
Eric and Andrew Day propose going back to burning our trash, but instead of using open-air incinerators or even high-temperature Basic Oxygen furnaces, they like the idea of burning our crap in electric plasma furnaces at temperatures in excess of 15,000 degrees Celsius. Take everything that would have gone to the landfill, add to it, if you like, everything that would have been recycled, and even leave in the really bad stuff like medical waste, toxic waste, heavy metals, and radioactive waste. Grind it all up into little chunks, some of which could be in a chemical or water slurry, and pump it into the plasma furnace.
Plasma furnaces have been around for decades and are already used for disposing of medical waste in Japan. Most such furnaces are fairly small, though the Days have found one manufacturer that can make a plasma furnace capable of burning 100 tons of trash per day.
The plasma furnace, operating in a closed loop, generates a form of synthetic gas that can be burned as a fuel as well as a glasslike inert material that can be used as aggregate in concrete. That’s what happens when you run your Pampers and plutonium and anthrax and last Sunday’s chicken dinner through a 30,000-degree Fahrenheit flame that breaks everything down to single atoms. The manufacturer of the plasma furnace (it’s in this week’s links) says the syngas can be burned to generate more power than the furnace uses, making it self-sufficient.
The Days propose building not just a plasma furnace but a chemical plant around it:
The purpose of the system is to simultaneously produce hydrogen, electricity, oxygen, biofuels/biomass, syngas, and other useful products from waste.Now, with one of the heroic oversimplifications I am known for, I’ll explain that the rest of the Day Cycle involves injecting steam into the syngas to create even more hydrogen along with lots of carbon dioxide. The carbon dioxide can be used to grow algae, yielding both biomass and oxygen in copious amounts. The final outputs of the plant are whatever can be made from the algae (biodiesel, ethanol, or — what the heck — SwiftFuel). All heat is recycled, no carbon dioxide is released (that’s the theory) and all that gets pumped out of the plant is some excess electricity (not sure how much of that), hydrogen, all those algae products, and of course oxygen.
Their claimed net production from each ton of municipal solid waste:
112 pounds of hydrogen
55 gallons of biodiesel
a little electricity
926 pounds of oxygen
One of the commenters, an Ed Underwood, notes that there’s nothing new here:
There have been companies selling plasma incinerators for years. They do a good job of greatly reducing a trash pile but they will not normally generate much energy. The water content of trash greatly reduces the efficiency of the system. Even if you break it into oxygen and hydrogen and burn it — you still dump a huge amount of energy into it to do that and you don’t get energy back to make up for that loss. Also when dealing with toxic trash , no matter how many times you feed the exhaust gases back into the system — you will still have to have a scrubber for exhaust — those require a lot of energy and are expensive to maintain.
In his opinion, you can reduce the volume of trash, but you won’t produce an energy surplus in the process.