Jessica Algehed

Evaporation of black liquor and wastewater using medium-pressure steam: Simulation and economic evaluation of novel designs

Abstract In this paper, novel evaporation plant designs that use medium-pressure steam and deliver low-pressure (LP) steam to the steam network as well as conventionally designed plants are simulated and evaluated from a technical and economic point of view. Both evaporation of black liquor only and combined evaporation of black liquor and wastewater are analyzed. The results show that the novel designs suggested in this work all have large potential to save live steam and that an additional 8 m3 of wastewater/ADMT (air dry metric ton) can be evaporated without increasing the mill’s total live steam demand. They also indicate that the demand for LP steam in the rest of the process is less important for the savings in live steam. The total cost for the novel designs and the relationship between that cost and the cost for conventional designs depend on the economic conditions assumed. If the investment in a more energy efficient evaporation plant is considered from a strategic point of view using an annuity factor of 0.1 and if the cost of the saved fuel is rather high in comparison to the electricity price, the total cost for the novel designs will have a lower total cost than the traditional designs.

Pathways to a sustainable European pulp and paper industry: Trade-offs between different technologies and system solutions for kraft pulp mills

Earlier studies have shown that for chemical pulp mills there are many technologies and system solutions which can increase energy efficiency and thus reduce the process energy demand and consequently also the global emissions of CO2. Which technology pathway (combination of technologies and system solutions) holds the greatest potential for future profits and reduction of global CO2 emissions depends both on mill-specific conditions and on the surrounding energy system through e.g. policy instruments and energy market prices. In this paper the trade-off, in terms of system revenue and global CO2 emission consequences, between different technology pathways for utilization of excess heat at chemical kraft pulp mills is investigated for a case depicting a typical Scandinavian mill of today. The trade-off is analysed for four future energy market scenarios having different levels of CO2 charge. The technology pathways included in this study are (1) increased electricity production in new condensing turbines, (2) production of district heating, (3) increased sales of biomass in the form of bark and/or lignin, and (4) carbon capture and storage (CCS). Lignin extraction and CCS are considered as new and emerging pathways and the other pathways are considered to be well-tried. The results show that well-tried pathways such as increased electricity production in new turbines, selling bark and district heating production are economically robust, i.e. they are profitable for all of the studied energy market scenarios. The new and emerging technology pathways such as carbon capture and storage and lignin extraction hold a larger potential for reduction of global CO2 emissions, but their economic profitability is more dependent on the development of the energy market. All in all, it can be concluded that to realize the larger potential of reduction of global CO2 emissions a high carbon cost alone may not be sufficient. Other economic stimulations are required, e.g. technology-specific subsidies.