requirements. This facilitates short distances from the source to the recycling of the waste and a corresponding reduction in CO 2 during transportation. In addition, plants can be easily adapted or moved to another location if the volume of waste increases. Wildfire Energy therefore sees the MIHG process as a flexible addition to recycling in order to drive forward the transition to a circular economy for materials and products.
Challenges for the measurement technology Figure 3. The team from Wildfire Energy at the pilot plant site. that also aim to be competitive. One such example is the Australian start-up, Wildfire Energy, whose process is based on the familiar gasification process which takes place at over 800 °C, but differs fundamentally from conventional gasifier technologies in terms of plant design. In a process known as moving injection horizontal gasification (MIHG), oxygen is injected horizontally under the waste layer to enable particularly efficient conversion of the organic waste into syngas.⁶ The basic operating principle of MIHG is shown in Figure 1.
Higher overall efficiency, scalable plant engineering
According to Wildfire Energy, the MIHG process offers multiple advantages. Firstly, heterogeneous waste – which can be problematic for many of the processes in place – can also be treated without complex pre-processing (for instance sorting and shredding of waste fractions). Secondly, the process should ensure high WtX yields: this means that roughly 42 kg of hydrogen can be produced per t of feedstock (mixed waste with a calorific value of 12 MJ/kg). Alternatively, the CO and hydrogen components contained in the syngas can also be used for the production of fuels, methanol or ethanol. The various possible uses are shown in Figure 2. Wildfire Energy cites the more favourable GHG balance compared to sending untreated waste to landfill as a further advantage of its process: in the case of WtE, negative emissions of up to 850 kg CO2 eq/MWh could be achieved with MIHG by avoiding methane emissions. In this comparative calculation, the WtH path would also be CO2-negative and therefore have an advantage over conventionally produced grey hydrogen in terms of climate protection. Thanks to its modular design, the MIHG process should also open up the possibility of creating small, flexible plants. This is important for the competitiveness of the process with conventional waste incineration, which for the most part takes place in large plants far away from urban centres today. While typical capacities of large incineration plants are several hundred kilotonnes of waste per year, a MIHG reactor processes small quantities from 4000 tpy, whereby upscaling to approximatley 50 000 tpy is possible. Housed in standard containers, the number of modules can be customised to suit local
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Reliable measurement and monitoring of key process parameters such as temperatures, pressures and gas volume flows are central in optimising the process flow. When setting up its first pilot plant, Wildfire Energy therefore placed its trust in the Swiss measurement technology manufacturer, Endress+Hauser. One particular challenge was to ensure accurate measurement at very low pressure in the MIHG reactor – an important requirement for the precise calculation of the volume flow in the syngas and hydrogen production. In addition to flow meters with different measuring principles, temperature sensors, pressure transmitters and level switches for accurate level measurement were used in the Wildfire pilot plant. With this pilot plant, Wildfire Energy was able to demonstrate that MIHG technology delivers on the expected results. Production is currently being upscaled with the aim of commercialising the technology worldwide. Endress+Hauser is also involved in this next development stage as technology partner to guarantee a high yield and quality in the production of syngas and hydrogen. The measurement technology manufacturer also hopes to gain new insights and economic potential from participating in this groundbreaking project. If the Wildfire technology proves its worth in practice, this would not only open up new perspectives for thermal waste treatment as a whole, but also for emission-reduced hydrogen production. Wildfire Energy is confident that it will be able to achieve a favourable hydrogen price of US$2/kg and therefore create the conditions for widespread use of the MIHG process.
References
1. ‘Waste to Energy 2022/2023: Technologies, plants, projects, players and backgrounds of the global thermal waste treatment business’, (2022), https://ecoprog.com/de/publikationen/datawte 2. ‘What a Waste 2.0, A Global Snapshot of Solid Waste Management to 2050’, World Bank Group, (2018), https:// datatopics.worldbank.org/what-a-waste 3. ‘A critical review on the principles, applications, and challenges of waste-to-hydrogen technologies, Renewable and Sustainable Energy Reviews’, (2020), https://www.sciencedirect.com/ science/article/pii/S1364032120306535?via%3Dihub 4. ‘Sachstand zu den alternativen Verfahren für die thermische Entsorgung von Abfällen’, Umweltbundesamt, (2017), https:// www.umweltbundesamt.de/sites/default/files/medien/1410/ publikationen/2017-03-06_texte_17-2017_alternativethermische-verfahren_0.pdf 5. ‘Abfallverbrennung in der Zukunft (Waste Incineration in Future)’, Dechema Position Paper, (2022), https://dechema.de/dechema_ media/Downloads/Positionspapiere/2022+03_Positionspapier_ Abfallverbrennung+2022-p-20008505.pdf 6. Wildfire Energy, https://www.wildfireenergy.com.au