Plasma Arc Waste Disposal

[Cutlass]

http://en.wikipedia.org/wiki/Plasma_arc_waste_disposal

Plasma arc gasification is a waste treatment technology that uses high electrical energy and high temperature created by an electrical arc gasifier. This arc breaks down waste primarily into elemental gas and solid waste (slag), in a device called a plasma converter. The process has been intended to be a net generator of electricity, depending upon composition input wastes, and to reduce the volumes of waste to being sent to landfill sites.

http://discovermagazine.com/2007/may/the-ultimate-garbage-disposal

The Ultimate Garbage Disposal
A power station eats up dirty landfill and churns out clean electricity.

What could be better than a power station that eats up dirty landfill and churns out clean electricity? One facility in Utashinai, Japan, has been doing just that since 2003, using plasma—an electrically induced stream of hot, charged particles—to process up to 220 tons of municipal solid waste a day. Now a bigger and better $425 million plant is scheduled for completion by 2009 in Saint Lucie County, Florida. The operator, Atlanta-based Geoplasma, expects it to generate 160 megawatts of electricity—enough to power 36,000 homes—from a daily diet of trash.

Here are the unanswered questions:

There are many metals in the waste stream, including toxic heavy metals. How do you extract the metals from the output from the plasma for reuse?

The plasma breaks all chemical bonds down to individual atoms, but the gases are at extreme temperatures at which it is possible that they will recombine into complex chemicals as they cool. How can that be managed?

 

[GenMarshall]

So this is an advanced tech for a Waste to Energy power plant?

 

[Cutlass]

Yes. By running garbage through a 10,000 volt field of electricity and the chemical bonds are broken and all of the material is heated to a plasma. This destroys all complex chemicals.

 

[Masquerouge]

Wow I never knew waste disposal could be so cool!
Or, I never knew plasma arc could be so trivialized!

 

[Genocidicbunny]

This is actually quite old news ( I have either a Discover or PopSci with an article on this from 2006) but it is still an amazing idea.

As for managing it, typically chemicals will combine to form the simplest structures, but a screening method for bad ones could be implemented. Put a filter at the 'exhaust' that only allow the good gas through ( There was one the magazine article mentioned specifically, but I can't remember what they called it). From there, you pump the bad gases back into the chamber until they dont recombine into unwanted things.

 

[zxcvbnm]

This is almost as great news as transmutation

 

[alexer]

I had never heard about this technology. It is really cool and interesting.






Waste Disposal London

 

[Samez]

I am nor sure what the real advantage of the plasma burning is (just the destruction of high complexity molecules can't be so uber).
There are several issues with this way of waste treatment:
- working with up to ~17000 K there are probably high temperature material problems.
- Plasma must be in a stable state which would either require an enormous control mechanism or very homogeneous waste.
- Process produces a heavy metal rich vitreous slag which is nearly impossible to process any further and must be disposed on a toxic waste dump.
- process may produce dioxin and other toxic lc molecules.
-(probably) more expensive than conventional waste incineration with exhaust filtering

Of cause many issues also concern conventional waste incineration but I still don't see the point

 

[Cutlass]

The problem with other waste burning is that it doesn't destroy complex chemicals. They remain persistent. The waste from this cools to a glass like substance. This solidifies and so won't leach out anything trapped in it like ash would. It would contain metals, but there may be a way to process it further and reclaim them.

 

[4thState]

working with up to ~17000 K there are probably high temperature material problems.

There's really no need to operate at that high of a temperature. You only need it hot enough to turn heavy metals into a gas, which is around 6,000C/10,000F. Also, there is a variety of ceramics and other refractory types on the market that can insulate this level of heat with no problem.

Plasma must be in a stable state which would either require an enormous control mechanism or very homogeneous waste.

The power to the plasma torch is what needs to be stable. A steady 500kW DC supply can generate the temperatures needed. The waste composition is really irrelevant in terms of destruction and vaporization. Dealing with an unpredictable gas mixture can present other issues downstream though.

Process produces a heavy metal rich vitreous slag which is nearly impossible to process any further and must be disposed on a toxic waste dump.

This is partially true. Some metals will end up in the slag and others will end up in trace amounts in filters and scrubbers downstream. But the slag is completely non-leachable, therefore not a negative landfill product. Also, since it has many of the properties of glass/sand, it can be used to make construction pavers or added to asphalt mixes.

process may produce dioxin and other toxic lc molecules.

This isn't true. Dioxins can't form at the temperatures we're talking about since there is no combustion. Other potentially toxic particulates are captured in filters and scrubbers.

(probably) more expensive than conventional waste incineration with exhaust filtering

The costs are comparable, but since the EPA pretty much isn't allowing any other incinerators to be permitted it doesn't really matter.

The overall benefit of using plasma is that it gives you control of a very wide temperature range. Dialing in the optimal temperature to sublimate the feedstock, at which point you're dealing with mostly gases, is the key to an efficient operation.

 

[Samez]

There's really no need to operate at that high of a temperature. You only need it hot enough to turn heavy metals into a gas, which is around 6,000C/10,000F. Also, there is a variety of ceramics and other refractory types on the market that can insulate this level of heat with no problem.

You're right about the high temperatures. They are only necessary directly in the plasma arc (generating a plasma arc will result in high temperatures). Still dealing with 6,000C/10,000F is not the easiest thing as refractory metal based materials are expensive and difficult to process. Using ceramics combined with a proper cooling system should probably work.

The power to the plasma torch is what needs to be stable. A steady 500kW DC supply can generate the temperatures needed. The waste composition is really irrelevant in terms of destruction and vaporization. Dealing with an unpredictable gas mixture can present other issues downstream though.

If the waste composition changes the waste gas will also do so. My idea was now that the waste gas might influence the plasma stream so the power required to ignite the plasma will vary. But perhaps it's enough to increase the pressure of the injected inert gas

This isn't true. Dioxins can't form at the temperatures we're talking about since there is no combustion. Other potentially toxic particulates are captured in filters and scrubbers.

The German wiki article stated that furans and dioxins might be a process product. As furans are flammable the info was probably crap....