In an important development for the ferroalloy industry, a new, patented technology developed by Tenova Pyromet (part of Tenova Mining & Minerals) for the high temperature cleaning of furnace off gas generated in a closed ferroalloy smelting process, will enable smelter operators to use the cleaned gas more easily in a number of co-generation plant options. The new method and process to cool and clean the mainly carbon monoxide rich furnace off gas has been developed through a combination and modification of current technologies, successfully addressing the shortcomings of the traditional industry method of wet scrubbing systems.
These include reducing the solid content in the cleaned process off gas to below 5 mg/Nm3, reducing moisture in the cleaned process gas by reducing or eliminating the use of water, eliminating condensation of tars on colder surfaces for certain process off gases 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 off gas with tars present is to be treated.
The principle of the new development is to clean the process gas as hot as 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 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.
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 is medium off gas volumes at high gas temperatures, off gas 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/cleaning.
“This new 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 minimise impact on the environment,” says Chris Oertel, Managing Director of Tenova Pyromet.
“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.”
“In addition, the rise in electricity prices has made it necessary to consider utilising all the gases as a source of fuel for producing electrical energy in a co-generation installation.”
Tenova Pyromet is a leading company in the design and supply of AC and DC furnaces for the production of ferroalloys, platinum group metals, base metals, slag cleaning and alloy refining. Tenova Pyromet also designs and supplies plant equipment that is associated with furnaces such as material handling and pre-treatment, alloy conversion and refining, granulation of metal, matte and slag, furnace off-gas fume collection and treatment and treatment of hazardous dusts and waste. Tenova Pyromet provides feasibility studies, construction and commissioning supervision and training and also, provides several technologies to reduce operating costs and increase production efficiencies.