Process integration of electric plasma calcination in pulp and paper plants: Techno-economic and greenhouse gas emission assessment including CO₂ utilisation options

Abstract

The calcination process within the Kraft pulping process is essential since it enables the recovery and reuse of pulp cooking chemicals. Currently, fossil fuels or biomass are used as fuel, making the calcination process one of the main emitters of carbon dioxide. An alternative calcination process using electric gas-plasma technology and steam slaking has been proposed and could provide several benefits compared to the conventional calcination process such as a fuel switch to electricity, as well as the production of a pure stream of carbon dioxide with renewable origin that enables cost-effective further utilisation. However, the integration of the new calcination concept into existing pulp and paper plants has not been investigated in detail. This project aims to investigate the impact of integrating electric plasma calcination with steam slaking into existing pulp and paper plants by using pinch analysis. Two existing mills, the stand-alone pulp mill Södra Cell Värö and the integrated pulp and paper mill Holmen Iggesund were used as models in case studies to illustrate the proposed assessment methodology. Possible energy savings, emission reductions and increased onsite electricity production were investigated along with an economic assessment comparing the total annualised cost of the conventional calcination concept with the new calcination technology. Furthermore, an inventory of possible CO2 utilisation options was created while two of the CO2 utilisation options were investigated more in detail; the production of electro-fuels and the extraction of lignin via the LignoBoost process. The results show that the implementation of the electric plasma calcination concept would require an input of 23.2 MW of electricity for the Iggesund mill and 37.9 MW for Värö. However, it was found that by heat integration of the new calcination process, it is theoretically possible to achieve hot utility savings of about 10% of the total utility demand together with a possible increase of the on-site electricity production. A fuel shift from biomass to electricity results in a net increase of greenhouse gas emissions with the energy market conditions of today. However, if the biomass saved by the fuel shift is used to replace fuels of fossil origin, there is great potential to achieve significant emission reductions. The investment cost of the new calcination technology was found to be in the same order of magnitude as the investment cost of the conventional lime kiln. With regard to the CO2 utilisation investigations, it was found that only a share of the available CO2 can be utilised due to limitations of available grid capacity for electro-fuel production while the recovery boiler operation is the limiting factor for the LignoBoost concept. The greenhouse gas emissions from the electro-fuels are highly depending on the emissions associated with the electricity production, but provided sustainable electricity production, there is high potential to reduce the greenhouse gas emissions with both CO2 utilisation options if they were to replace fuels of fossil source. The economic potential for both options was investigated with promising results with production costs in the same order of magnitude as the current market price for similar fuels, however, the uncertainties in the cost estimations and the lignin market should be emphasised.