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ECN publication
Conversion of water plants to biomass fuel using torwash
Pels, J.R.; Bleijendaal, L.P.J.; Nijman, M.N.W.; Zandvoort, M.H.; Cieplik, M.K.
Published by: Publication date:
ECN Biomass & Energy Efficiency 8-7-2014
ECN report number: Document type:
ECN-M--14-037 Conference Paper
Number of pages: Full text:
9 Download PDF  

Invasive water plants are harvested in The Netherlands in order to keep waterways open. It is expected that due to improved water quality the growth of these water plants will increase significantly. Waternet, the watercycle company of Amsterdam and surrounding areas, wishes to turn this material into useful products. One of the investigated options was TORWASH, a technology under development by ECN for converting wet, salt-containing biomass into clean solid biofuel suitable for energy production, e.g. by co-firing in power plants. Elodea nuttalii and Cabomba caroliniana were harvested and directly processed. Samples were chopped into a slurry and then subjected to TORWASH conditions. The resulting product was filtered and pressed into disks. All inputs and outputs were weighed and analysed to make mass balances and to determine the fate of key elements like potassium, chlorine, nitrogen and phosphorus. The pressed disks were assessed for their suitability as solid biomass fuel. Both water plants are suitable feedstock for the TORWASH process. Chopping turns these plants into a slurry with 90% water and reduces the volume by a factor of four. Chopping and milling when applied onsite will therefore result in substantial lower transport costs. The slurry has the right consistency to be introduced into the TORWASH reactor. No addition of water is needed. After wet torrefaction the slurry can be mechanically dewatered to a level of more than 70% dry matter. The dewatered solids are suitable for direct combustion in a fluidized bed system. Alkali and chlorine content are in the same order as fresh wood chips. For applications in co-firing in a pulverized fuel plant, additional drying and probably an extra washing of the product is needed to further remove alkaline and chloride. It is recommended to investigate how sand and other inert ash-forming constituents can be removed. To make the fuel comparable to clean wood pellets, an extra washing to remove alkali and chloride may need to be included.

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