Project objectives
Within the 2030 Climate Target Plan, the European Union has set the objective to reduce greenhouse gas emissions by 55% and to become climate neutral by 2050. Application of hydrogen will form the backbone of the steel industry’s transformation to become climate neutral. In the longterm, for the vast majority of the roadmaps communicated by the different steel producers, the technical solution will be to replace the traditional blast furnace (BF) plants with direct reduction (DR) plants which will utilise hydrogen. The injection of hydrogen is also widely discussed to decrease the carbon dioxide emissions of BFs in the short to mid-term. Compared to carbon-based injectants (pulverised coal (PC) at the BF and natural gas (NG) in DR) hydrogen has a much lower density. This will play a major role in hydrogen injection applications with respect to the penetration depth into the packed bed and the resulting process efficiency. The injected gas must flow through the small voids of the packed bed between the solid particles, which introduces strong pressure drops close to the injection location (due to the high gas velocities at this position). The high pressure drop limits the penetration depth of the injected gas.
Multiple shaft gas injection tests at the BF e.g., in the ULCOS [1] project but also in later work showed that even with carbon-based gases the penetration depth is only a few meters or less. Generally, the penetration depth depends on the impulse of the injected gas (i.e. mass and velocity). Compared to carbon monoxide, hydrogen has only 1/14 of the molar mass.
Due to the relatively low resulting impulse, it is by far more challenging to reach the centre of the packed bed with hydrogen injection. Figure 1 shows a simulation of an injection of hydrogen in the BF shaft with 3-6 m³/s. The hydrogen stays close to the wall and thus only has very local effects on the process Simulations of DR columns with hydrogen as reductant also show a wall to centre process zone difference [2].
Figure 1: Simulation of hydrogen shaft injection in the BF [3]
For injection of hydrogen in the BF shaft, the hydrogen utilisation for reduction is poor. A larger part of the hydrogen will leave the process in the top gas without benefit and even hamper operational safety. Whilst hydrogen is only available in small quantities, optimal efficiency of hydrogen utilisation by guaranteeing sufficient gas penetration depths is of utmost importance. For hydrogen operated DR furnaces, poor penetration depth will increase the inhomogeneity of reduction and finally cause lower metallisation towards the centre, with increasing severity as furnace size increases.
To overcome these gas penetration depth problems, thyssenkrupp AT.PRO tec has developed the Sequence Impulse Injection technology (SIP). This technology is already matured and under operation for an injection of oxygen in the raceways via the tuyeres at an industrial scale BF.
The objective of this proposal is to adapt this injection technology for the new application of pulsed hydrogen injection into the furnace shaft (i.e. directly into packed beds and above the cohesive zone in case of the BF (cf. Figure 2). The project will therefore validate the functionality and the gas penetration
depth of the hydrogen impulse injection (H2II) technology at an industrial BF and therefore in a relevant environment. The application of such a technology will improve the reduction gasflow, the efficiency of hydrogen reduction and the CO2 mitigation by hydrogen shaft gas injection.
Figure 2: Concept for the H2II application for shaft injection at a BF
The injection trials will take place at a BF of voestalpine in Linz. The trials will demonstrate the applicability of the technology at a BF where it serves as a bridge technology for short- to mid-term CO2 mitigation. Following the roadmaps of European steel producers, most plants will have at least one BF still in operation until 2040 or beyond. As the BF will account for the main part of CO2 emissions of a steel plant during this time, it is highly important to minimise these CO2 emissions. H2II will provide all the basic needs to replace a significant part of carbon-based reduction by hydrogen reduction. The potential of CO2 mitigation by hydrogen in the BF process was calculated to be in the range of 20% [4]. In the medium-to long-term (as soon as industrial DR plants and large amounts of hydrogen are available) the technology can be easily transferred to hydrogen operated DR plants (H2-DR) to increase their efficiency. Summarising, the main objective of the H2II project is to substantially mitigate CO2 emissions by innovative shaft gas injection technology, enabling maximum injection rates and best possible hydrogen utilisation efficiency. This will rapidly support CO2 mitigation from steel production across numerous existing BF-BOF sites. It is easily transferable to the upcoming H2-DR technology, hence will also support future breakthrough decarbonisation. This is fully in line with the objective
stated in Article 8 of the research objectives for steel concerning low-carbon steelmaking. The decrease of CO2 emissions will support in mitigating climate change in line with the objectives of Article 10, being protection of the environment. As decarbonisation is also the key concern of the European Green Deal, the project’s expected impact is also fully compliant with the Green Deal objectives.
Starting point of the project is the technologically very similar SIP device from thyssenkrupp AT.PRO tec for oxygen impulse injection. This is already in operation in full scale at an industrial BF under continuous operation. This technology will be adapted to the application of hydrogen impulse injection directly into packed beds. The workflow within the project delivers step by step and in a straightforward manner, all devices and knowledge required for a successful validation of the technology.
It will start with a planning phase delivering first basics of the impulse injection unit (e.g. design & security, functionality test), proceed with test rig trials and finish with injection trials at a BF. Both the trials at the test rig and at the BF will be accompanied by simulations. The whole methodology of the project is in depth described in section 1.2. Each of those steps will generate measurable results (e.g. availability of the planning documents, availability of the H2II unit, data from the test
rig, benchmark data from the simulation, data from the penetration depth validation, etc.). The corresponding sub-objectives are defined in detail related to the work packages in section 3.2. Important sub-objectives are the layout and security concept of the impulse injection unit, an experimental lab test rig, two sophisticated simulation models (a detailed CFD-DEM model for particle movement and pulsed flow close to the injection location and a steady-state model covering all BF process zones), injection trials at an industrial BF and a large number of dissemination activities including a blog, a web-workshop and several open access papers. This approach ensures that these objectives are at all times measurable and verifiable.
The final validation of the technology at an industrial BF will allow verification of the functionality of the technology in an operational environment. The validation will be accompanied by suitable measurements to proof the accomplishment of the claimed main technical objective, which is to achieve a high penetration depth in the range of at least 2 m of the new shaft gas injection technology. All parts of the project start with existing, validated concepts and tools such that the achievement of the objectives is very realistic. On the other hand, the enhancement and combination of the concepts and tools delivers the breakthrough technology: Hydrogen shaft gas impulse injection.
References
1 ULCOS top gas recycling blast furnace process (ULCOS TGRBF), Luxembourg, European Commission, 2014, 47 p. EUR 26414.
2 Rami, B., Hamadeh, H., Mirgaux, O. & Patisson, F. Carbon Impact Mitigation of the Iron Ore Direct Reduction Process through Computer-Aided Optimization and Design Changes. Metals (Basel). 1–12 (2020).
3 Li, J., Kuang, S., Zou, R. & Yu, A. Numerical Investigation of Burden Distribution in Hydrogen Blast Furnace. Metall. Mater. Trans. B 53B, 4124–4137.
4 Reiprich, N. Mit Wasserstoff zur klimaneutralen Stahlproduktion. stahl und eisen 6 (2021) 24–26.