Wood ash: The topic has arrived in the industry
New regulations for the handling of wood ash have been in force for five years. With the support of the Federal Office for the Environment within the framework of the Wood Action Plan, the environmental technology association Svut and Holzenergie Schweiz developed corresponding principles within the framework of the "HARVE Wood Ashes" project.
At the end of the project "HARVE Holzaschen - Aufkommen, Verwertung und Entsorgung" organized by the Fachverband Svut and Wood energy Switzerland, supported by the Federal Office for the Environment (Bafu), recently held the first Swiss Wood Ash Congress as a webinar, which was attended by over 100 interested parties.
General conditions, ash quality, clean landfilling
As hosts of the symposium originally scheduled for Windisch, Professors Timothy Griffin and Peter Stuber presented the Institute for Biomass and Resource Efficiency and the Energy and Environmental Technology course at the University of Applied Sciences Northwestern Switzerland in Windisch. This showed for the wood energy sector that the synergies already used today could be further expanded.
Representing Kaarina Schenk from the Bafu Waste and Raw Materials Section, Maurice Jutz from Effizienzagentur Schweiz AG presented the current legal basis and the most important ongoing research projects with which the enforcement of the Waste Ordinance in the area of wood ashes is to be designed as expediently as possible. Important topics here are, for example, the stoichiometry of chromate reduction at slag landfills or the heavy metal recovery of fly ash from the incineration of waste wood, which will be mandatory from November 2023.
Beat Müller, Schmid AG energy solutions, made the exciting connection between wood ashes and the actual operation of wood energy plants. He impressively demonstrated that measures can be taken at the plants to improve the quality of the wood ashes produced, especially with regard to their future utilization. These measures are to a large extent congruent with measures to improve efficiency or pollutant emissions (e.g. avoidance of strong load fluctuations). With a better parameterization of the furnace to the respective fuel, the ash quality can be significantly improved. This applies to the minimization of foreign particles and impurities in the fuel.
"Don't stir up dust" - under this title and with great practical relevance, Toni Portmann, Amstutz Holzenergie AG, demonstrated that dust-free unloading of wood ash at the landfill is possible today. According to the expert, the prerequisite for this is to become familiar with the matter.
Stephan Fromm, Center for Sustainable Waste and Resource Utilization (ZAR), then went into more detail about fly ash processing from waste wood incineration after 2023. For grate furnaces, the admixture of waste wood fly ash to MSW filter ash is technically feasible. For fluidized bed furnaces, the co-treatment with MSWI filter ashes is challenging, but ecologically reasonable.
Ashes as fertilizer, ashes in the construction industry
Rainer Schrägle, Bundesgütegemeinschaft Holzasche e.V., Rutesheim (D), has been working for years on the utilization of wood ash as agricultural fertilizer. Thanks to the integration of the entire industry and a sophisticated testing procedure, wood ashes from the combustion of untreated wood in Germany can obtain a certificate that allows their application as fertilizer in agriculture and forestry.
Mathias Meier, Logbau AG, presented the Ragaz earth concrete REB, to which wood ashes from the combustion of natural wood have been added for several years. The aim was to close material cycles and to recycle materials instead of disposing of them. Although the project makes economic and ecological sense, it is not a sure-fire success.
According to the Waste Ordinance, wood ash may be used as an additive and aggregate in the production of cement and concrete. Peter Kruspan, Holcim (Switzerland) AG, presented the results of an extensive analysis of numerous wood ashes and derived three demands from the cement industry to the plant operators:
- Wood ashes must be dry and collected separately for grate, cyclone and filter ashes.
- The operating and combustion quality of the plants must be improved.
- Foreign parts and contamination of the fuel must be avoided.
Sokrat Sinaj, Agroscope, also dealt with the utilization of wood ashes. In his presentation, he showed that wood ashes are certainly suitable as agricultural fertilizer. This is mainly because the wood ashes contain heavy metals, but these are little or not at all available for the plants.
Josef Wüest, a research associate at the University of Applied Sciences Northwestern Switzerland, showed that the production of vegetable charcoal not only reduces the amount of ash by a factor of 10 to 50 compared to "conventional" wood-fired systems, but that it also allows CO2 to be stored in the soil for a long time.
Michael Tobler, Tobler Holz & Forst Consulting, presented the most important results of the HARVE project at the end. The quantities of wood ashes and their regional occurrence are well known today. Also, thanks to the surveys carried out in various cantons, information is available on the existing infrastructure, logistics, type of temporary storage, etc. The most important information can be found in the guide "Disposal of Wood Ash". The most important information is summarized in the guide "Disposal of Wood Ash".
Conclusion
The first Swiss Wood Ash Congress on November 12, 2020 was a success. The great interest, the dedicated use of the chat as well as the consistently positive feedback show that the topic has arrived in the industry and that there is a growing need for information and exchange. There is still a long way to go before all wood ashes can be recycled in a meaningful way. The congress has shown the wood energy industry where it still has homework to do along the way.
Source: Wood Energy Switzerland
