Thermal Efficiency
Task 6 Team
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Prof. Cameron Pleydell-Pearce
Swansea University
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Dr Jon Elvins
Swansa University
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Nicola Thomas
Swansea University
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Geraint Howells
Swansea University
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Nigel Koungampillil
Swansea University
Introduction
According to the International Energy Agency (IEA), heating accounts for 66% of industrial energy demand, which itself makes up 20% of total energy demand. Steel production represents a significant proportion of that demand and as there are some fundamental thermodynamic limitations to consider, such as iron’s melting point (15380C) and its key solid state phase transformation temperatures (e.g. ɣ > ɑ at 9200C). Currently, a typical UK integrated plant loses 20PJ/yr through the largest heat vector. Task 6 of SUSTAIN looks to minimise loss through improved insulation, more efficient heat transfer and two key thermal energy harvesting technologies (fig. 1).
Figure 1: The approach to targeting thermal efficiency in steelmaking within Task 6 of SUSTAIN, addressing both demand reduction and utilization of waste heat (top left to bottom right: thermal image of refractory ladle (courtesy of J. Wilmott Sheffield University), gas fired burner and reheated steel slab, casting a novel thermo-electric generator, non-toxic earth abundant thermochemical storage medium).
Project Aims
Develop as multiscale ex-situ structural characterisation approach for refractories.
Improve understanding of structure-property relations in carbon bonded refractories.
Develop robust, cost effective Sn-Se thermoelectric materials / devices for integration into refractory linings.
Build UK academic skill base in the field of refractories.
Improve steel re-heating efficiency.
Develop robust, energy efficient thermochemical heat storage materials suitable for steel production
Utilisation of industrial waste heat
The MESH project (fig. 2) is investigating capturing waste heat from industry and transport this to an end use location, such as for low carbon domestic heating. Low carbon space heating is likely provided by a mix of technologies, including air and ground source heat pumps, improved gas mixes; natural gas bio-gas, hydrogen micro-CHP, solar thermal generators, heat networks & waste heat recovery and high efficiency boilers. Each of these generation technologies can be integrated with, and improved by thermal storage technologies.
A second generation Thermochemical Storage (TCS) material has been developed ,Alginate + CaCl2. This material has increased salt volume density, storage density, thermal conductivity and moisture uptake at 75% RH properties.
Plenty of waste heat is available from industrial processes, and research has found that it can be captured using thermal storage materials. These materials have undergone multiple charge and discharge cycles to prove the concept of this technology, and it has been found that hot (40-50°C) water can be generated from this.
Figure 2: MESH - Thermochemical heat storage
Continuous Temperature Measurement of Liquid Metal
Recent research on this area has investigated the influence of different parameters on argon purging of liquid steel. During argon purging, an inert gas is discharged into the molten steel from outside the furnace at a predetermined pressure. When the gas flow rate is adequate to keep molten steel from entering the nozzle, the gas from the nozzle forms a column in molten steel, and the height of this column is kept equal to or greater than a predetermined value. The part of molten steel to be studied, then creates a pseudo-blackbody known as a cavity blackbody, owing to repeated reflections of emitted light within the gas column. As a result, a theoretically optimal condition for radiation thermometry is realised.
This phenomenon allows for continuous temperature measurement of liquid steel using radiation thermometry by observing the molten steel through a tuyere nozzle at the bottom of the furnace. To ensure a consistent Blackbody Cavity, it is important to understand the interaction between argon and liquid steel as a function of different parameters.
The investigations based on a combination of physical modelling, computer vision technologies and computational fluid dynamics (fig. 3) have so far have led to some interested findings. Unlike Annular, Annular Slotted and Multi Hole plug, Single Hole Tuyeres didn’t exhibit Plume formation/Jetting Behaviour. Instead, a gas column was established which allowed for minimum ‘Washing’ at the inlet of the nozzle. However, no plume formation implies minimum stirring capabilities.
The volume of Plume generated before detaching from the inlet for the other three Tuyeres increased proportionally to the flow rates. However, at lower flow rates the plume formation/collapse frequency was significantly higher when compared to higher flow rates. The ‘Washing’ plays a significant role in the refractory wear near the inlet. This implies that the frequency and magnitude of differential change in plume width before detachment, is an important parameter when designing a robust Tuyere.
These results provide valuable design principles on which a stable port may be created between the liquid steel and non-contact sensor technology such that stable temperature and compositional measurements may be made.
Figure 3: Physical modelling (Helium in Water) quantified through computer vision (left hand side) and CFD modelling (right hand side) to understand Argon – liquid steel interactions.
Development of Refractory Coatings
This work aims to support steelmaking decarbonisation in a number of ways:
Using computer modelling alongside novel data collection and thermographic measurement techniques for refractory lined plant such as ladles and ladle lids.
Develop the understanding of the compositional and surface factors that influence and impact the performance of refractory linings.
Optimise the design, construction and refractory selection to maximise efficiency and conservation of heat within ladles and steelmaking assets.
Avoid temperature losses that can have a significant impact to the business in terms of process, quality and financial.
A great deal of research has been carried out into understanding and evaluating thermal profiles of ladle wall refractories. The plan is to carry out in-situ thermocouple measurements of lid lining refractories record the temperature profile of the lid whilst in use. This information will be used to further optimise refractory lining schemes and validate the FEM model.
Existing and alternative ladle lid refractory linings have been characterised using X-ray CT to better understand the variations between the internal structures of these (fig. 4). This information could allow the refractory castable to be further optimised to improve its performance with regards to particle size and distribution throughout the material matrix, potentially improving cost effectiveness.
Future work in this area that utilises the methods developed in our research will focus on the behaviour of refractories in hydrogen / moisture rich reducing environments. This is an area of significance in the context of the decarbonisation of global steelmaking.
Figure 4: Refractories - porosity analysis showing voids within the 3D volume