PyroGenesis Plasma Arc Waste Disposal System
Photo courtesy of PyroGenesis ©2006
PyroGenesis Plasma Arc waste disposal system

At these temperatures, garbage doesn't stand a chance. Molecules break down in a process called molecular dissociation. When molecules are exposed to intense energy (like the heat generated by a plasma torch), the molecular bonds holding them together become excited and break apart. What's left are the elemental components of the molecules. With cyanide, for example, you'll end up with atoms of carbon and nitrogen.

Organic molecules (those that are carbon-based) become volatilized, or turn into gases. This synthetic gas (syngas) can be used as a fuel source if properly cleaned. Inorganic compounds melt down and become vitrified, or converted into a hard, glassy substance similar in appearance and weight to obsidian. Metals melt down as well, combining with the rest of the inorganic matter (called slag).

 

Unlike incinerators, which use combustion to break down garbage, there is no burning, or oxidation, in this process. The heat from plasma converters causes pyrolysis, a process in which organic matter breaks down and decomposes. Plasma torches can operate in airtight vessels. Combustion requires oxidization; pyrolysis does not.

Plasma waste converters can treat almost any kind of waste, including some traditionally difficult waste materials. It can treat medical waste or chemically-contaminated waste and leave nothing but gases and slag. Because it breaks down these dangerous wastes into their basic elements, they can be disposed of safely. The only waste that a plasma converter can't break down is heavy radioactive material, such as the rods used in a nuclear reactor. If you put such material in a plasma furnace, it would probably catch on fire or even explode.

In the upcoming sections, we will look at what makes up a typical plasma waste converter, examine the byproducts produced from the gasification process, and discuss the benefits and concerns about plasma converters.

Currently, plasma plants aren't standardized. Many different companies are designing plasma facilities, and for the moment each facility is essentially custom-built. Still, most converters have the following components in common:

A pre-treatment and feeder system

Conveyor system
In order to feed garbage into the converter, almost all plasma facilities have a conveyor system. Garbage is loaded on the conveyor and is pushed into the furnace (or pre-treatment system if the plasma facility uses one) by a plunger.

Pre-treatment mechanism
Although a plasma torch can break down waste without any special pre-treatment, most plasma facilities employ some sort of pre-treatment process to make the entire system more efficient. Some designs use grinders or crushers to reduce the size of the individual pieces of garbage before moving in to the furnace. The plasma torch can break down the smaller pieces faster.

A plasma furnace

Furnace
Here's where the magic happens. Furnaces have an airlock system to allow garbage to come in while preventing the hot gases in the furnace from escaping into the atmosphere. The furnace houses at least one plasma torch; many furnaces have multiple torches to break down all the matter. These torches are usually placed a little lower than halfway down the furnace. The furnace also features a drainage system to tap off the slag as it accumulates and a vent system to vent out the gases. In order to withstand the intense heat, furnaces are lined with refractory material and often have a water-cooling system as well.

Plasma torch
The plasma torches used in these facilities are custom-built. The amount of energy they consume, the lifespan of the electrodes it uses, the gas used for ionization (most torches just use ordinary air), the downtime it takes to replace an offline torch and the size of the plasma field it generates all depend on the specific manufacturer. Plasma torches are water-cooled.