- Interview with Dr. Iñigo Ortega Fernández, engineer at CIC ENERGIGUNE within the RESLAG Pilot system 2, focused on investigating the possibilities of using slag for storing and recovering heat
In addition to leading the entire RESLAG project, the Basque Energy Storage Research Centre (CIC ENERGIGUNE), located in Vitoria (Spain), heads the Pilot system 2, which focuses on the use of steelworks slag as a storage material for the recovery of waste heat in the steel industry.
Research so far has revealed that steel slag particles are indeed a very promising heat storage material, which would open up a new recovery route for this by-product. The next few months will be key in the search for definitive conclusions about this technology.
QUESTION. They lead RESLAG Pilot 2, which focuses on the research of steel slag as thermal energy storage material for waste heat recovery in the steel industry. How did the rehearsals and demonstrations go?
ANSWER. At this moment we are completing the commissioning of the demonstrator at ArcelorMittal steelworks in Sestao, hence no clear conclusions can be drawn yet. However, experiments carried out in a test rig available at CIC energiGUNE showed the produced steel slag particles as very promising heat storage material in terms of energy density, thermal performance in packed bed systems and cost-effectiveness.
Q. What are your expectations for the remaining months of the project?
A. In the coming months we will face the most interesting activities related to the pilot. In January 2019 the involved members of the consortium, CIC energiGUNE, ArcelorMittal, Novargi and IK4-Azterlan, will start the experimental campaign of the demonstrator in the steelworks. The final objective is to carry out as much as possible thermal cycles in the demonstrator, until the end of the project, in such a way realistic conclusions can be drawn about the technology, in terms of waste heat recovery potential, overall process efficiency or the stability of the produced slag pebbles, among other relevant parameters.
Q. What have been the main difficulties you have faced in this Pilot?
A. Up to now, the project consortium had to deal mainly with two difficulties related with the Pilot:
- Harsh nature of the electric arc furnace exhaust gases: the gases expelled by the furnace, which are used to charge the heat storage unit, are characterized by a high dust content and explosion risk due to hydrogen content. The later made necessary a sophisticated design of the heat exchanger in order to avoid performance losses or blocking of this component. And, the former required a careful revision of the layout incorporating protections to avoid explosions in all the demonstrator components.
- Mechanical stability of the slag pebbles: in the determination of the slag pebbles specifications it was found that important mechanical stresses may be generated in the pebbles due to the packed bed configuration and the thermal cycling. This issue made necessary to design specific tests for determining and confirming the long-term mechanical stability of the produced pebbles.
Q. What would the use of steel slag as a heat storage material represent for the steel industry?
A. The use of steel slag as thermal energy storage material may have two main benefits for the steel sector:
- It opens a new valorisation route: even though it exists many applications for the valorisation of this by-product, currently not 100% of the generated steel slag is reused. In this regard, this may represent a new market opportunity for the steelworks.
- Energy savings with the introduction of a cost effective heat recovery system: even if some solutions can be found for heat recovery from the electric arc furnace exhaust gases, no real implementation has been attained, by far, in the steelworks. The main barriers for the development of this type of alternatives are associated to poor thermal efficiencies and economically very expensive solutions. In contrast, the system proposed in the Reslag project could represent a clear step forward on thermal efficiency values together with a reduced economic effort for the steelworks.
The combination of both benefits, the valorisation of a by-product, the steel slag, by using it in the same plant for heat recovery purposes, boost the steel production sector towards the circular economy policy, that is currently promoted from the European Commission.
Q. Is the proposed system exclusive to the steel industry or could it be ‘exported’ to other sectors?
A. The proposed system is an adaptable solution that can be extended to any energy intensive industry were gases at high temperature are generated. These industries include the production of glass, cement, pulp, etc.
Q. What is your general assessment of the RESLAG Project?
A. Overall, my general assessment of the REslag project is very positive. On one hand, the large number of members forming consortium (20 partners) combined with a good balance between universities, research centres and companies have permitted the creation of a very enriching environment at both, research and personal levels. On the other hand, the results attained up to now from the investigated technologies are very promising, what indicates that at the end of the project new routes for the valorisation of the steel slag will be available in the market. These results are very interesting not only for the project consortium or the steel sector in particular, but also for the society in general.