The aim is to increase knowledge of how bark-borer-damaged and frozen softwood is best chipped and impregnated for an increased yield in forest industrial processes. Project partners are MoRe Research (RISE Research Institutes of Sweden) and Umeå University. The project is financed by the Kempestiftelserna.
The background to the project is based on a now completed doctoral thesis (Wood Chips for Kraft and Sulfite Pulping - Evaluation of Novel Forest-Industrial Drum-Chipping Technology) carried out by Jessica Gard Timmerfors within the framework of Umeå University's business research school. The new doctoral project picks up where it previously left off and builds on skills and infrastructure that have been established at Domsjö Development Area in recent years.
The plan for the doctoral project includes four sub-studies that concern both conventional forest industrial processes, such as the sulfate and sulfite process, and new biorefinery processes where wood raw material undergoes hydrothermal pretreatment, enzymatic saccharification and microbial fermentation (so-called biochemical conversion). The sulfate process is the dominant process for the production of chemical pulp. The sulphite process is less common, but has been shown to be particularly suitable in a biorefinery context, e.g. by Domsjö Fabriker and Borregaard. Today, there are several large-scale industrial initiatives with a focus on biochemical conversion of wood raw material, and SEKAB is a company that is well ahead in technology development for that type of process.
Chipping and impregnation of dry wood.
The increase in bark beetle-infested wood requires increased knowledge of chipping and impregnation of this significantly drier wood. It is possible that the problems with a high proportion of wood chips and shavings when chipping dry wood can be solved by using MCS's new drum chipping technology. Dry wood chips are more difficult to impregnate and can thus cause operational problems in a cooker as they tend to float. Initial trials have shown that pressurized impregnation significantly improves the impregnation of dry chips. Studies to increase knowledge about impregnation and cooking of dry chips will be carried out with an impregnation reactor and a cooking pilot.
(2) Pressurized impregnation Impregnation of pine heartwood is problematic for the sulphite process due to high levels of the extractive substance pinosylvin. This limits the use of pine as a raw material. Since pine is almost as common as spruce, it is of interest to increase knowledge about how this chip is best impregnated. A partial study in the aforementioned doctoral thesis showed promising results in pressurized impregnation of pine heartwood. An extended study with pine heartwood with a high content of pinosylvin is planned in part study 2.
Chipping of frozen wood
Chipping of frozen wood is normally expected to give rise to an increased proportion of wood chips and shavings. Preliminary results obtained with MCS pilot drumming showed that this technique appears to be able to reduce this problem. More detailed studies on different tree species comparing frozen and thawed wood are planned within part study 3.
Impregnation in connection with hydrothermal pretreatment
In the Nordic countries, softwood is the main raw material resource for biochemical conversion. Effective hydrothermal pretreatment of softwood requires the presence of acid catalyst. The most common acid catalyst is sulfuric acid, but sulfur dioxide has been shown to be superior especially for softwood. It may be that using a gas as an impregnating agent provides additional benefits. Although the benefits of sulfur dioxide have been known for a long time, the underlying causes have never been scientifically rigorously investigated. The question is not only of academic interest but is highly essential for industrial biochemical conversion if softwood is used as raw material. Among other things for work environment reasons, in industrial contexts it is preferable to use sulfuric acid rather than sulfur dioxide. Studies of the reasons behind differences can give rise to new industrially relevant impregnation processes.