Plasma gasification has the potential to be a breakthrough technology. It can serve not only as a method of producing fuels, but also as a method for effectively dealing with hazardous wastes. In fact, the technology was initially developed to be a method for waste disposal, and the energy production potential was just a side benefit.
Plasma gasification was one of the more exotic methods that was discussed as a precursor for the Coskata process for ethanol production. Coskata’s method takes a stream of carbon monoxide and hydrogen (known as syngas) and feeds it through a bioreactor vessel where specialized strains of bacteria feed on the syngas and metabolize it to produce ethanol (or other alcohols, depending on the strain of bacteria in the reactor). There are numerous methods for producing syngas, some more than a century old, but others, such as the plasma gasification method, sound like the stuff of science fiction.
Plasma gasification uses extremely high energy plasma (at a temperature of 30,000 degrees (F), three times as hot as the surface of the Sun). The plasma torch inside the containment vessel is directed by an operator to break down whatever material is fed into it. It acts much like contained, continuous lightning, and everything that is fed into the system is broken down to its constituent atoms. Because the plasma torch so thoroughly annihilates anything that is fed into it, it is also an excellent means of dealing with dangerous and hazardous waste. In fact, the first contracts signed for plasma systems were intended for primarily for waste disposal. “In 1997 the U.S. Army became Startech’s inaugural customer, buying a converter to dispose of chemical weapons at the Aberdeen Proving Ground in Maryland. A second reactor went to Japan for processing polychlorinated biphenyls, or PCBs, an industrial coolant and lubricant banned in the U.S since 1977 (‘really nasty stuff,’ Longo says).”
Plasma torches could also be used to deal with other hazardous materials that are too difficult to recycle by other means. Biological hazards would also be completely broken down with such a system. Ordinary waste incineration has been used to reduce the volume of municipal wastes, although they certainly pose their own set of problems. Incinerators are also typically open systems, dumping pollution into the air, rather than keeping it in a closed system. Furthermore, there are concerns that incinerators can create dioxins as a by-product of incineration. A plasma system could be used to break down hazardous dioxins as well as any other feedstock, and, by using a closed system to contain the effluent gas, it can be treated in such a fashion that the conditions for the formation of dioxins are avoided.
While the plasma torch would seem to demand huge amounts of energy to operate, in fact, it produces a surplus of electricity from its operation. Once it has started, the system can run a generator turbine from the high temperature gas coming out from the plasma vessel and produce enough energy to keep itself operating as long as it is kept fed with feedstock to keep the process going.
Not only does plasma gasification represent a technology that can be used to deal with a wide range of waste problems in a contained and highly effective manner, but it also does so in a way that produces useful byproducts of electricity, syngas, and slag, which can be used by the abrasives industry. Metals can also be recovered from the solid output, and could then be refined and reused. Other possibilities for fuel production can also be accommodated with plasma gasification technology, as well. Hydrogen, one of the components of syngas, could be refined from the system and used directly, if hydrogen were to become more prevalent as a fuel.
Image Source: StarTech