Oliver Järvik

PhD project at Tallinn University of Technology (TalTech), Estonia This PhD project investigates how CaCO3-rich feedstock ash can be used to modify Fe2O3/Al2O3 oxygen carriers for chemical-looping hydrogen production. The research combines thermodynamic analysis, laboratory experiments, thermogravimetric testing, fluidised-bed reactor studies, and Aspen Plus process modelling to understand how calcium transfer from ash influences oxygen transfer, hydrogen yield, and long-term carrier stability. The project is linked to the EU-funded HELIA project and is based at TalTech’s Department of Energy Technology. It is co-supervised by Tenured Associate Professor Oliver Järvik and Tenured Associate Professor Abhishek Agarwal. The research environment includes expertise in thermochemical conversion, redox materials, fluidised-bed systems, reactor operation, and process modelling, with access to pilot-scale facilities and advanced gas/emissions analysis equipment. Scientifically, the project focuses on phase evolution during repeated redox cycling of iron-based oxygen carriers. It will examine whether calcium introduced through ash can beneficially alter phase formation, potentially promoting calcium-containing phases and improving oxygen-carrier behaviour, rather than being treated solely as an impurity. The work will also assess the roles of silicon, sulphur, chlorine, and alkali metals in affecting phase formation, particle behaviour, and material degradation. Planned tasks include thermodynamic analysis of Fe-Al-Ca-O-C-H equilibria, preparation and characterisation of oxygen carriers and ashes, reduction/steam oxidation/air regeneration experiments, controlled CaCO3/CaO addition studies, cyclic testing in a laboratory-scale fluidised-bed reactor, and characterisation using XRD, SEM-EDS, and BET. Experimental results will be used to build and validate an Aspen Plus model describing reactors and mass/energy balances, calcium accumulation, and oxygen-carrier activity. The position is a 4-year, full-time paid PhD employment with social security. The project offers an interdisciplinary research topic with international collaboration opportunities, professional development, conference travel support, and a strong experimental/computational environment. Applicants should have a relevant master’s degree, high-temperature experimental experience, modelling and thermodynamics knowledge, and English proficiency at B2 level or above. Applications are open from 16 September 2026 to 7 October 2026.