Perhaps it is of little surprise that a country like Sweden, so rich in natural forests, is leading the way in technology to process residues and waste from its timber industry. But the fact that it has built a one of a kind wood chip processing plant is worthy of note.
What is different about this unit is that the technology is based on the processing of wood residue by gasification, where the process is carried out in two phases, and allows for much recycling in its own method.
In the first stage the feedstock (wood chip) is fed into a fluidized bed gasifier. Here it is heated to about 8,500C. At this point gasification occurs, induced by simultaneous injections of superheated steam (brought in from a separate combustion chamber). The resulting combustible gas is purified of tar, sulfur, and carbon dioxide.
In the second stage, the gas is drawn into methanization units, where the content of methane is condensed to more than 95% purity. The majority of this Bio-methane (bio-SNG) is sold to the gas grid or used in gas-fired power stations. A small percentage is set aside, and added to the feedstock for further processing.
Ash from gasification is used as fertilizer in the same forests where the biomass originated. Waste heat from both phases is used to make the superheated steam, as well as heat buildings close to the plant.
The process is interesting not only in the way that it utilizes a waste product (wood chips), but also in the amount of recycling of energy it performs inside its own process. At present, engineers are looking to utilize this process for different waste products, but to date this has not been achieved. This is due to the large amount of poisonous or hazardous substances that are created when wood chips are replaced with other waste products, and also because the process (due to its technological difficulty) can be prohibitively expensive.
However, as has been suggested in previous articles in this blog, waste is a huge challenge for the chemical industry of the 21st century. Developments like those being made in Sweden to recycle and reuse, show that we may be on the edge of a breakthrough.