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Specialist article
15.05.2022  |  1696x
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Opportunities in torrefying low-value biomass residual flows

Klinkenberg Zaanstad B.V. investigated using low-value biomass streams for heat generation. End goal is a torrefaction plant at production scale, to generate energy from what is now waste.
Klinkenberg Zaanstad B.V. has carried out a study into the usability and availability of unused low-value biomass streams that can be used to generate heat.


By torrefying and then pelleting these biomass streams, an end product is created with a high energy density that has superior properties compared to the untreated biomass. With financial support from the province of Noord-Holland in the form of an MIT feasibility grant, ten bio-waste streams were investigated on the following aspects:
  • Conversion efficiency of the torrefaction process per biomass type
  • Availability of the biomass
  • Combustion properties
  • The total cost of processing the biomass into a torrefied end product.

Batch test reactor

Feasibility studies carried out by CCS Energie-advies show that torrefaction provides a positive business case for a number of biomass species. Klinkenberg designed and built a torrefaction batch reactor in order to determine the optimal torrefaction conditions for each biomass type. By torrefying several batches of the same biomass species, each time changing a single parameter (such as residence time and temperature of the reactor), the optimal conditions for each biomass species were determined.

Verge grass

A good example of an unused biomass species is verge grass that becomes available during tillage of natural areas. With the torrefaction batch tester, the roadside grass was torrefied, see images.
Research into the combustion properties showed that existing medium-sized combustion boilers fired with wood pellets/chips (for example, to heat greenhouses, swimming pools or a residential tower) are suitable for firing torrefied pellets with a few modifications.

Torrefaction screw reactor

The promising results of the feasibility study led to a follow-up study with the ultimate goal of designing a large-scale torrefaction screw reactor that can torrefy 4 tonnes of fresh biomass per hour. In order to design and realise this large system, research is needed into how biomass behaves in a screw reactor. Among other things, the flow characteristics of each biomass species and the corresponding heat transfer from the reactor to the various biomasses are unknown process parameters that need to be determined for each biomass species.

In order to be able to determine these unknown process parameters, a follow-up study has been started that is subsidised by an MIT-R&D subsidy from the Province of Noord-Holland. The follow-up research consists of designing and building a mobile biomass torrefaction screw reactor that can torrefy 50 kg of fresh biomass per hour. The aim of this system is to test different biomass species under different process conditions. By investigating the effect of each process parameter, the most optimal process conditions can be determined for each biomass species. Later, these parameters will be used to set up a torrefaction plant at production scale.

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