The present paper focuses on the production of a below zero emission reducing gas for use in raw iron production. The biomass-based concept of sorption-enhanced reforming combined with oxyfuel combustion constitutes an additional opportunity for selective separation of CO2. First experimental results from the test plant at TU Wien (100 kW) have been implemented. Based on these results, it could be demonstrated that the biomass-based product gas fulfills all requirements for the use in direct reduction plants and a concept for the commercial-scale use was developed. Additionally, the profitability of the below zero emission reducing gas concept within a techno-economic assessment is investigated. The results of the techno-economic assessment show that the production of biomass-based reducing gas can compete with the conventional natural gas route, if the required oxygen is delivered by an existing air separation unit and the utilization of the separated CO2 is possible. The production costs of the biomass-based reducing gas are in the range of natural gas-based reducing gas and twice as high as the production of fossil coke in a coke oven plant. The CO2 footprint of a direct reduction plant fed with biomass-based reducing gas is more than 80% lower compared with the conventional blast furnace route and could be even more if carbon capture and utilization is applied. Therefore, the biomass-based production of reducing gas could definitely make a reasonable contribution to a reduction of fossil CO2 emissions within the iron and steel sector in Austria.

In many industrial processes, the climate-damaging gas CO2 is produced as undesired by-product. The dual fluidized bed biomass gasification technology offers the opportunity to tackle this problem by using the produced CO2 within the process as gasification agent. Therefore, a 100 kWth pilot plant at TU Wien was used to investigate the use of CO2 as gasification agent by converting softwood as fuel and olivine as bed material into high-valuable product gas. A parameter variation was conducted, where the typically used gasification agent steam was substituted stepwise by CO2. Thereby, the amount of CO and CO2 increased and the content of H2 decreased in the product gas. These trends resulted in a declining H2/CO ratio and a decreasing lower heating value when CO2 was increased as gasification agent. In contrast to these declining trends, the carbon utilization efficiency showed an increasing course. As second part of this work, a temperature variation from 740 to 840 °C was conducted to investigate the change of the main product gas components. With increasing temperature, CO and H2 increased and CO2 decreased. To determine the degree of conversion of CO2 in the DFB reactor system, two approaches were selected: (1) a carbon balance and (2) a hydrogen balance. This way, it was found out that a certain amount of CO2 was indeed converted at the investigated process conditions. Furthermore, under certain assumptions, the reverse water-gas shift reaction was identified to be the predominant reaction during CO2 gasification.

The present work describes the results achieved during a study aiming at the full replacement of the natural gas demand of an integrated hot metal production. This work implements a novel approach using a biomass gasification plant combined with an electrolysis unit to substitute the present natural gas demand of an integrated hot metal production. Therefore, a simulation platform, including mathematical models for all relevant process units, enabling the calculation of all relevant mass and energy balances was created. As a result, the calculations show that a natural gas demand of about 385 MW can be replaced and an additional 100 MW hydrogen-rich reducing gas can be produced by the use of 132 MW of biomass together with 571 MW electricity produced from renewable energy. The results achieved indicate that a full replacement of the natural gas demand would be possible from a technological point of view. At the same time, the technological readiness level of available electrolysis units shows that a production at such a large scale has not been demonstrated yet.

Power-to-Liquid (PtL) plants can viably implement carbon capture and utilization technologies in Europe. In addition, local CO2 sources can be valorized to substitute oil and gas imports. This work’s aim was to determine the PtL efficiency obtained by combining a solid oxide electrolyzer (SOEC) and Fischer–Tropsch synthesis. In addition, a recommended plant configuration to produce synthetic fuel and wax at pilot scale is established. The presented process configurations with and without a tail gas reformer were modeled and analyzed using IPSEpro as simulation software. A maximum mass flow rate of naphtha, middle distillate and wax of 57.8 kg/h can be realized by using a SOEC unit operated in co-electrolysis mode, with a rated power of 1 MWel.. A maximum PtL efficiency of 50.8% was found for the process configuration without a tail gas reformer. Implementing a tail gas reformer resulted in a maximum PtL efficiency of 62.7%. Hence, the reforming of tail gas is highly beneficial for the PtL plant’s productivity and efficiency. Nevertheless, a process configuration based on the recirculation of tail gas without a reformer is recommended as a feasible solution to manage the transition from laboratory scale to industrial applications.

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