Staged COmbustion for energy REcovery in Ferroalloy industry

The project SCORE, Staged Combustion for energy recovery in ferroalloy industry has been initiated in autumn 2013 and finalized in Dec. 2017. In the early phase of the project, the principal design of laboratory and pilot scale equipment has considered and detailed engineering has been performed. The design process was an integration of comprehensive modelling work and design reviews to design a system which can be implemented in an industrial setting. Fundamental laboratory scale experiments are performed which improved the data basis for the condensation of SiO and deposition of dust from the gas phase. The experimental work has been extended also to include industrial measurements of particle and condensation phenomena; these measurements are performed at Wacker Chemicals Holla. During the project new simulation models for PAH/tar breakdown and NOx-formation have been developed and implemented in a CFD-environment. Further a modelling framework to describe precipitation form fluids is developed to model scaling and fouling on surfaces of pipes and ducts. A fastloop has been designed to verify operation conditions in a transport pipe from the exhaust of a FeMn furnace to the combustion unit. The unit was successfully tested at the ERAMET Sauda plant and gave valuable insight into necessary design changes for the pilot unit and to minimize risks. The loop confirmed that the chosen shutdown strategy is sufficient for safe operation. The combustion unit has been assembled, completed and commissioned at the end of 2016 including comprehensive testing of the safety and shutdown system. In 2017 the combustion unit was installed at ERAMET Sauda for performing two experimental campaigns. The two campaigns showed that the designed combustion unit performed in-line with the given design framework. Emissions from the combustion unit were lower than comparable industrial state-of-the-art system whereas energy recovery efficiency is on the same level. Further, the unit demonstrated that the current PAH/tar containing sludge stream can be entirely removed; instead of sending a sludge stream to landfill the generated dry dust can be subjected to alternative recycling methods and valorisation. Finally, a technical and economical evaluation of the industrial implementation of the designed system has been performed. The new system is benchmarked to existing industrial solutions both with respect to the efficiency of energy recovery and the economical potential of the system. It is verified that the system will perform under standard economical consideration.

The Norwegian ferroalloy industry cooperates in the field of environmental challenges and is internationally renowned for sustainable production. The innovation is therefore on a national and international level. An innovation step change in design of fer roalloy furnaces is envisaged. A new concept for off-gas processing for the ferroalloy industry will be assessed, tested and evaluated. The concept consists of a combination of a traditional submerged arc furnace combined with a dedicated combustion chamb er for controlled heat recovery. Implementation will be based on experiences from other industries, such as waste incineration and steel industries, but its implementation to the ferroalloy industry is novel and has never before been tested. Should the co ncept prove to be successful, it may lead to other innovations in the process such as redesign of the furnace itself, closing the furnace hood (Si/FeSi) to facilitate stoichiometric combustion of SiO, tars, hydrocarbons and CO, and conversion of today's waste streams (dust/sludge from filter systems) into valuable products. The generic concept can be employed for both ferromanganese and ferrosilicon furnaces. In order to assess the benefits of the new concept, best available techniques (BAT) will be deve loped. Optimized conventional off-gas units are used for benchmarking of the new concept. The implementation of optimized heat recovery on existing furnaces will represent an incremental innovation.