PyrOPT-Pyrolysis of wood optimized for production of energy and tailor-made biochar for silicon production

Elkem has a pronounced ambition to contribute to the pursuit of a zero emission society. As a part of this, the use of fossile reduction agents (coal and coke) should be reduced as much as possible. One solution is to convert to renewable carbon sources based on biomass. Elkem has well defined target shares of biochar in steps towards 2030.

Partners: Elkem, Sintef Energi, Paper and Fiber Research Institute (PFI).
Funding period: 2017-2021
Main goal: to develop  a production process for tailor made biochar reductant for the silicon and ferrosilicon production.

Traditional charcoal production has millennial roots and has in principle remained unchanged although many varieties of pyrolysis furnaces  have been used through time. Pieces of wood are heated without (or with very limited) access to oxygen. That drives off water and volatiles as vapours and leaves a charcoal typically containing 70-90% carbon. The volatiles can be burned to produce energy or condensed to produce other liquid products such as fuel or functional chemicals. The traditional charcoal production is called slow pyrolysis and favours carbon formation.

Metallurgical industry has so far been limited to the charcoal quality produced for the barbeque market. To create a biochar suitable for silicon production, an optimal process for a tailored biochar, where the negative properties are minimized, and the beneficial properties are enhanced needs to be developed. Furthermore, the production should take place in the most sustainable way.

This means that every kilogram of biomass must give maximum amount of usable solid carbon, all side streams must be utilized and energy demanding processes such as drying wood should be driven by available energy sources. It would thus make sense to put the biochar production at an existing smelter to integrate energy flows in a good way.

The project is also investigating the agglomeration of fines as a part of tailoring a biochar for metallurgical industry. That also opens up for looking at intermediate pyrolysis that is expected to yield more fines than slow pyrolysis but at the same time gives better conditions for upgrading the vapours.

The project has three main work packages:
1. Defining the perfect biochar.
2. Developing optimized pyrolysis process.
3. Investigate optimal utilization of vapours or condensate.