Maryam Mahmoudkhani

Recycling of Solid Residues to the Forest: Experimental and Theoretical Study of the Release of Sodium from Lime Mud and Green Liquor Dregs Aggregates

In order to optimize the recycling of solid residues back to the forest, it is necessary to measure and characterize the dissolution rate of the product under well-defined conditions. In this study, inorganic solid residues from a kraft pulp mill were characterized physically and chemically. The effect of pH, as well as physical characteristics and chemical composition, on the leaching rate was investigated. It was shown that the leaching behaviour differed depending on the production method of the aggregates. A model based on mass transfer was fitted to the experimental leaching data. It was shown that the leaching rate for the easily soluble species was reasonably well described using the concentration gradient of these species within the pellet. It was also shown that mass transfer within and from the pellet/granule was the rate-determining step.

Scandinavian Hardwood Biorefinery Using “near-neutral” Hemicelluloses Pre-extraction- Energy Efficiency Measures

While in a conventional mill, the hemicelluloses and lignin fraction of the wood is burned in the recovery boiler to produce steam, in a biorefinery it can be used to produce added value products. In this paper, a comprehensive heat integration study for an average Scandinavian kraft model mill, as well as for a hemicelluloses extraction process with further utilization for ethanol production, is performed. The results show that when the total integration of the hemicelluloses utilization process with the mill is considered, the integrated biorefinery could become self-sufficient in terms of steam.

Energy Analysis for Conversion of a Kraft Pulp Mill into a Dissolving Pulp Mill

Currently, kraft pulp mills in Europe and North America are facing several challenges and have been forced to think along new products and new business areas. One opportunity is the conversion of chemical pulp mills into dissolving pulp mills by extracting hemicellulose prior to digesting via pre-hydrolysis. From the extracted wood chips, the more valuable dissolving pulp can be produced whereas the hydrolysate can be upgraded to high-value products. In this paper, pinch analysis is used to evaluate the consequences in the energy balance and utility system of a kraft mill converted into dissolving pulp production as well as to identify the potential for heat integration within the host mill itself, between the host mill and the pre-hydrolysis unit and with a hemicellulose upgrading process. The results show that proper heat integration within the host mill itself, and between the host mill and the pre-hydrolysis unit gives significant amounts of surplus steam which could be exported to a hemicelluloses upgrading process, used for power generation or to facilitate lignin extraction.

Enlarging the Product Portfolio of a Kraft Pulp Mill via Hemicellulose and Lignin Separation - Process Integration Studies in a Case Mill

Increased energy and raw material prices along with contracting markets for kraft pulp, have highlighted the need for the pulp industry to enlarge their traditional product portfolio with new value-added products via the implementation of biorefinery concepts. In this paper, we have investigated potentials for enlarging the product portfolio of a kraft pulp mill by extracting hemicellulose prior to digesting and in this way, converting to dissolving pulp production. A case study has been performed on a Swedish kraft pulp mill, in order to evaluate the consequences of the original mill configuration, level of heat integration and choice of by-products produced have on the overall profitability of the mill upon conversion to dissolving pulp production. For the mill studied, the batch digester is identified to be the bottleneck for both kraft and dissolving pulp production. If the digester capacity is increased by e.g. purchasing new effects, the pulp production could be maintained. The results from the energy study indicate that dissolving pulp production is more heat demanding than kraft production. However, by increasing the heat integration of the mill, it is possible to, not only become self-sufficient in terms of steam, but also to produce significant amounts of excess steam. The steam excess facilitates integration of a lignin separation plant or can be used for power generation. The net annual profit was evaluated for varying prices of electricity and lignin. For the economic conditions studied, lignin separation was always better than power generation, if lignin can be priced as oil.