International designer and supplier of high capacity furnaces and complete smelting plants, Tenova Pyromet has patented a new technology for the high temperature cleaning of furnace offgas generated in a closed ferroalloy smelting process.
The technology, developed in-house by Tenova Pyromet, part of Tenova Mining & Minerals, will enable smelter operators to use the cleaned gas more easily in a number of cogeneration plant options.
Tenova Pyromet technology manager Piet Jonker says the new method and process to cool and clean the mainly carbon mon- oxide-rich furnace offgas has been developed through a combination and modification of current technologies and suc- cessfully addresses the short- comings of traditional wet scrubbing systems.
These include reducing the solid content in the cleaned process offgas to below 5 mg/Nm3. Moisture in the cleaned process gas is reduced by decreasing or eliminating the use of water, preventing condensation of tars on colder surfaces for certain process offgases by operating above the tar dew point of the process gas, and eliminating the wet scrubber liquor water treatment system, which can be problematic when a process offgas with tars present is to be treated.
The technology was internationally patented in April and presented in June at the thirteenth International Ferro Alloy Conference, in Almaty, Kazakhstan.
Tenova Pyromet sales and marketing GM Andre Ester-huizen explains that the principle of the new development is to clean the process gas at the highest temperature possible using filtration separation technology. Solids are separated and collected from the process gas by passing it through high temperature filtration elements, which are periodically cleaned using an inert gas.
“The resultant solid gas content of the cleaned gas is below 5 mg/Nm3, as opposed to the 10 mg/Nm3 to 50 mg/Nm3 of wet scrubbing systems, and is suitable for direct use in any power generation or heating system. If high volatile reductants are used, the hot gas with tar in vapour form passes through the filtering section for cleaning before entering a suitable tar removal system, prior to being used in a power generation system or heating system. The collected tars from the tar removal systems can be used as a fuel or safely disposed of,” states Esterhuizen.
The process is, therefore, applied beneficially as an alternative to conventional wet gas cleaning system in a number of applications. These include applications where there are medium offgas volumes at high gas temperatures, offgas containing unwanted components, such as tars, and where specific clean gas properties are required, such as low moisture content, low solid content and a gas temperature above the dew point for further processing or cleaning.
Tenova Pyromet MD Chris Oertel says the technology is an important development for ferroalloy producers, as the industry is facing increasing challenges in terms of harder to access and lower-grade carbon reductants, compounded by escalating power costs, as well as increasing legislative and social pressure to reduce impact on the environment.
“The increasing cost and diminishing supply of metallurgical grade coke as the main source of carbon for reduction reactions in closed ferroalloy smelting have led producers to use alternative sources of carbon, such as coal with a high volatile matter. When a high percentage of this lower grade coal is used, tar vapours can be present in the furnace off- gas, which, in wet gas cleaning, will condense when the gas is in contact with colder surfaces or water, creating operating, maintenance and water treatment problems,” he explains.
The rise in electricity prices, Oertel adds, has made it neces- sary to consider using all off-gases as a source of fuel for producing electrical energy in a cogeneration installation.