Hydrogen is a vital energy source in a renewable energy economy of the future: it has the potential to replace fossil resources and fuels in the medium to long-term, not only in the mining, minerals and metals industries, but also in transport. In addition to electrolysis using renewable electricity – the standard process for producing climate-neutral, ‘green’ hydrogen – other emissions-free or reduced-emissions methods of production could also have a major impact in the future. Today, approximately 98% of hydrogen is generated from fossil fuels, primarily through the steam reforming of natural gas (‘grey’ hydrogen).
The thermal recycling of municipal waste (and similarly composed waste) provides another possible source of hydrogen. In 2022, over 2600 waste treatment plants were in operation worldwide with a capacity of approximately 460 million tpy.¹ Up until now, this sector has been dominated by traditional incineration processes that fully utilise the energy content of the largely organic waste to generate electricity and/or heat. Given that, according to a forecast by the World Bank, the global volume of waste will continue to grow significantly from today’s approximate 2.1 billion tpy to 3.4 billion tpy in 2050, alternative treatment processes, which should ensure more efficient recycling of the waste and therefore a reduction in the landfill space required, are coming to the fore.² The reason for this is that the methane emissions from landfilled organic waste – about 25 times more harmful to the climate than CO2 – contribute significantly to the warming of the earth’s atmosphere. While 100% of municipal waste is thermally treated in Switzerland today, and only the residues that remain after incineration and cannot be used for other purposes are landfilled, the dumping of untreated waste is still widespread in developing and emerging countries. Approximately one seventh of global methane emissions can be traced back to landfill.³
Alternative methods for thermal waste treatment: waste-to-X
Alternative methods can be used either as a further treatment stage in addition to combustion, or as a stand-alone process. Examples include thermochemical processes such as pyrolysis and gasification: in this case, the feedstock is not fully oxidised, but partially converted to liquid and/or gaseous components (‘synthesis gas’ or ‘syngas’) at temperatures of up to 1200 °C.4,5 These components can then be thermally recycled or separated and used for secondary purposes, for example as a raw material in the chemical industry or as a fuel in transport – the hydrogen separated from the syngas can be used as a fuel for fuel cell vehicles, for example. While conventional incineration processes focus primarily on the generation of electrical energy (waste-to-energy [WtE]), a broader range of valuable end products can therefore be produced using alternative processes. Therefore, we generally speak of ‘waste-to-X’ (WtX) solutions in this case or, if the focus is mainly on hydrogen production, of ‘waste-to-hydrogen’ (WtH).
The aim of using alternative waste treatment technologies is to achieve higher energy efficiencies, higher-quality conversion products and/or lower emissions than would be achievable by simply incinerating the feedstock. For example, in terms of the energy balance, a WtH process must therefore be more efficient than electricity generation from a traditional incineration plant and subsequent electrolysis. These requirements generally call for significantly more complex, and therefore cost-intensive, plant technology compared to conventional combustion. Although they have been tested for approximately 50 years already, alternative methods have only become established under special conditions, in Japan for example.5 However, stricter climate protection regulations and increasing landfill costs could also be expected to lead to a change in the competitive situation in Europe and other densely populated regions of the world in favour of more efficient waste recycling.
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/data-wte
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_alternative-thermische-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
Written by Uwe Wagner, Endress+Hauser, Switzerland.
This article was originally published in the Winter 2023 issue of Global Hydrogen Review magazine. To read the full article, simply follow this link.