RE:RE:RE:RE:RE:RE:LKAB ...Nice catch Casavantghost. Thanks for sharing. That was a paper presented in 2013 at the 4th International Symposium on High-Temperature Metallurgical Processing.
THERMAL PLASMA TORCHES FOR METALLURGICAL APPLICATIONS
L. Rao , F. Rivard and *P. Carabin
PyroGenesis Canada Inc., 1744 rue William, Suite 200, Montreal, QQ H3J1R4
(^Corresponding author: pcarabin@pyrogenesis.com)
ABSTRACT
Advances in thermal plasma torches have resulted in this technology becoming a commercially viable solution for chemical and metallurgical processes. The main advantages of plasma are its ability to control process chemistry and to build small footprint reactors due to its high energy density and reactivity of the free radicals that are produced. This paper focuses on thermal plasmas produced by DC torches and their applications for waste treatment, production of high purity metals, and nanomaterials. Both transferred and non-transferred torches have been used as either a source of heat or as a reagent in various industrial processes. Retrofitting plasma torches in place of fuel oil burners lead to lower operating costs, capital cost and greenhouse gas emissions.
Figure 4 - Carbon nanotubes produced with an RPT torch (Photo courtesy of McGill University)
ADVANTAGES OF PLASMA TORCHES OVER CONVENTIONAL BURNERS
As demonstrated previously, plasma torches offer high energy densities making them suitable in a wide variety of applications. In addition, they can be retrofitted in applications where fossil fuel burners are used to provide heat to a process, with the advantages of lower operating costs and greenhouse gas emissions. With the current and forecasted increases in oil prices, there is growing interest in solutions that allow replacing the expensive fuel with more economic alternatives. In this context, plasma torches offer a very interesting option since they use electricity as a source of energy.
Table 1 shows the operating costs of a 2 MW net fuel oil burner (bunker C or fuel oil no. 6) vs. a 2 MW net air plasma torch. As can be seen, there is a significant reduction in operating costs with the use of an air plasma torch. Considering applications such as iron ore pellet induration furnaces, cement kilns and various metallic ore roasters, which usually include multiple burners and sometimes more than 100 burners per plant, the costs savings becomes even more interesting. 63
Table 1 - Operating costs of a 2 MW net bunker C burner vs. an air plasma torch Fuel Oil Cost (S0.5/L) Electricity Cost ($0.03/kWh) Replacement Parts Cost Total % Reduction Fuel Oil Burner $ 923,000 $ 9,000 $ 0 $ 932,000 Plasma Torch $0 $600,000 $38,000 $638,000 32%
Although the use of a plasma torch increases the global electricity cost, it reduces the electrical power required by the off-gas treatment system (exhaust fans, scrubbers, particulate filters) because the off-gas flow rate is much lower than with a burner. Indeed, there is about an 80% off-gas flow rate reduction when using a plasma torch instead of a burner. Not only does this reduce operating costs of the off-gas treatment system in existing plants, it also reduces the capital cost for future plants because a smaller and less complex off-gas treatment system can be purchased. In addition to the important costs incurred by the operation of a fuel oil burner, there is also a large amount of greenhouse gases (GHG) that is emitted due to the combustion of non renewable fossil fuel. With the increasing concerns towards the emission of GHG and the establishment of emissions trading programs (cap-and-trade) all over the world, solutions that also allow the reduction of GHG emissions are of particular interest. Depending on how it is produced, the use of electricity as a source of energy, as is the case for plasma torches, represents a great potential to reduce GHG emissions. While a bunker C fuel oil burner emits about 115 kg of carbon dioxide equivalents (CC^e) per gigajoule of net energy considering the combustion of the fuel as well as its extraction, production and distribution, a plasma torch powered with electricity generated by hydropower emits only about 1 kg C02e/GJ. Therefore, for a 2 MW plasma torch retrofitted in place of a burner, this would lead to yearly reductions of more than 7,000 metric tonnes of C02e. Again, considering there can be more than 100 of these burners per plant, the GHG reductions are even more interesting.
CONCLUSIONS
An overview of PyroGenesis DC torches and their applications was presented for use in waste treatment, production of high purity metals, and nanomaterials. The RPT provides twice the enthalpy level of the Minigun and also runs with any non oxygen containing gas as a plasma forming gas. It boasts very low erosion rates, making it very useful in the production of high purity materials. The APT was originally developed for waste treatment. It typically uses air as the main plasma forming gas, but, due to the use of a shroud gas for the cathode, allows for a wide choice of plasma forming gas, including oxidizing gases. In addition to its application for waste treatment, this plasma torch system can be used for other applications such as gas heating, plasma assisted ignition and combustion, plasma melting, scrap melting, ladle heating, and chemical synthesis. The SPT uses steam (water vapour) as the main plasma forming gas. The high reactivity of the hydroxyl ions produced by the ionization of steam allows for the destruction of highly stable hazardous substances such as chlorofluorocarbons and brominated hydrocarbons. Other applications of steam plasma include: steam reforming, coal gasification, steam arc cutting, and rapid decontamination of large surfaces. The replacement of fuel oil burners by plasma torches provides considerable operating costs reduction for existing plants as well as a capital cost reduction for future plants. The off-gas flow rate generated by a plasma torch being much less than that generated by a burner, the off-gas treatment system can be downsized significantly. In addition, plasma torches allow a major GHG reduction by avoiding the combustion of substantial amounts of fossil fuel in burners.