Visit to Green Carbon – part 1

You might ask, what is Green Carbon and why visit? From the name you might conclude that it has something to do with vegetable carbon, the thermal treatment of biomass, or biochar, right? With the current market and industry trends, it was worthwhile to investigate and describe a hidden gem in the POLYTECHNIK portfolio, located in the north of Germany. Yes, Green Carbon is the name of POLYTECHNIKs’ industrial process for carbonizing biomass. With so many technology companies vying for a space under the sun in this sector, pushing CDRs, energy and the multiple benefits of something called biochar it can be a confusing landscape to navigate. Biochar, charcoal, char, carbonized biomass, vegetable carbon…All of it boils down to either getting a clean, sustainable and stable natural carbon or a coal like fuel substitute. You will hear terms such as slow pyrolysis, flash pyrolysis, steam explosion, torrefaction, carbonisation and HTC (hydrothermal carbonization) to name a few… See what we mean. Challenging, for sure.

Green Carbon and the process behind it

Green Carbon is based on a proven concept. The R&D team settled on this design after about a 15-year development period. It is a high temperature slow pyrolysis. High temperature means we go up to 650 – 700 oC in the process and slow pyrolysis means that the pyrolysis takes around 2-4 hours. Now these are very important factors because they ensure that carbonization is taking place with a high-quality product as an outcome. Essentially it is a continuous process based on a retort – batch concept. POLYTECHNIK has secured it’s Know How and development with a patent on the so-called Green Carbon Process.

Feedstock

The plant is conveniently located in the countryside, around two hours to the west of Hamburg, surrounded by trees and wind turbines. The entrance to the site, right off the highway, opens through the truck access road and a weigh bridge where each delivery of feedstock is weighed. Furthermore, depending on the quality of the biomass delivered, the truck is unloaded in a certain designated area of the feedstock yard. You will find green biomass residues from garden, park and roadside maintenance, hog fuel and some round wood.

Interestingly enough, residents in the area are invited to dispose of their garden residues in the yard themselves. There were tree pruning’s, whole orchards of trees (taken out by farmers for new ones), but also high-quality round wood. This enables the operators to produce a variety of carbonized biomass products, simultaneously! More on this in one of the future newsletters describing the pyrolysis process.

The large amount of green material (leaves, needles and other herbaceous materials) can be a reliable source for the composting process in the feedstock yard. This is a seasonal by-product of the feedstock handling. However, this is not a prerequisite for Green Carbon, just a convenient project specific case for this location.

As the feedstock is sieved, several fractions are generated: soil, herbaceous residues and woody residues. The woody residues (tree branches, tree limbs, stumps, pruning’s) are headed for the Green Carbon pyrolysis while the rest is composted to produce potting soil or Terra Preta (with 10% biochar). Nothing is wasted. In retrospect, it is important to point out that the thought process behind the feedstock is the reverse of common practice. Here, the feedstock is determined in two ways: availability or desired biochar quality. The pyrolysis is defined by the input quality of the material. If the desired biochar quality is high, for example to be used in human consumption, as animal supplement or any other product with strict quality requirements then the feedstock also has to be of higher quality. So, having a chipper and log splitter is a useful prerequisite to prepare the higher quality feedstock on site. This also allows the operators to adjust the feedstock quality and size to meet the desired biochar quality.

This flexibility allows for a greater feedstock resource pool and supply chain, directly impacting the cost of production.

In one of the future newsletters, we will deal with the Green Carbon pyrolysis process itself, stay tuned.

Written by: Viktor Radic, dipl.ing.