Smelter engineering firm Metix, part of the international SMS Siemag Group, has developed energy-saving solutions that enable cogeneration of power for the local furnace industry.As the persistent rise in the cost of electricity in South Africa continues to place industries under increased pressure to save energy, Metix has launched an integrated combined heat and power (CHP) energy system that enables the cogeneration of electricity and heat from a single fuel source, such as process gas or waste heat from metallurgical processes. Metix deputy sales director, Klaus Schmale, explains that up to 40% of the energy generated during the smelting process in a furnace escapes with off-gases, which are always hot and loaded with energy. “Metix offers energy recovery systems for the steelmaking and ferroalloy industries, which can benefit by saving up to 55% of this waste energy.” Schmale notes that CHP systems can be modified to the requirements of the end user. “Owing to their higher efficiency, CHP systems use less fuel to produce a given energy output. What’s more, higher efficiency results in reduced emissions, increased reliability and a higher power quality. These efficiency benefits also lead to economic benefits, which is apparent in reduced energy costs.” In ferroalloy production, Schmale points out that semi-closed type and closed type submerged arc furnaces (SAF)are ideally suited for energy recovery. “The carbon monoxide(CO) and hydrogen (H2) generated by semi-closed type furnaces are completely burned away as a result of the false air that enters the furnace via the doors and other openings,” he explains. “In these applications, large amounts of fully combusted off gas with high amounts of sensible heat are generated at temperatures of about 650°C. The off-gas of closed type furnaces is up to 1 800°C, and contains large amounts of chemical energy in terms of CO and H2.”
According to Schmale, Metix is able to generate power by using this offgas with a process gas-fired boiler combined with a turbine and a generator unit.“The boilers burn low calorific value process gas with special burners in a combustion chamber. Our standardised boiler is a two-pass boiler – the first pass is the combustion chamber, while the heat exchangers such as superheaters, evaporators and economisers are located in the second pass.”Following this process, Schmale explains that the superheated steam runs the turbine island to produce steam, and boilers using up to 360 tph of steam at 540oC can produce up to 160 MW of electrical energy, depending on the heat source. “Cogeneration ensures a directly controllable and constant price of energy, as opposed to sourcing electricity from the national grid.” Although the Metix CHP system has not been adopted in South Africa to date, Schmale points out that a Turkey-based ferrochrome producer ordered the energy recovery solution. It will be connected to two of its semi-closed SAFs. “The system is expected to start up early in 2013 and will produce steam, which will be used in a steam turbine with an attached power generation unit to produce 5 MW of electrical energy. The client expects an amortisation period of less than three and a half years, while the energy recovery unit is expected to save over 25 000 t of direct CO2 emissions yearly.” Looking to the future, Schmale is optimistic that the Metix CHP system will add considerable value to the South African market in the long-term. “We also plan to approach Eskom to present the features of the technology and discuss how it can help overcome the shortfall in electrical energy. We are hopeful that Eskom will support the introduction of the Metix energy recovery system as part of its range of energy saving initiatives in the long-term future,” he concludes.