Process integration of electric plasma calcination in pulp and paper plants: Techno-economic and greenhouse gas emission assessment including CO₂ utilisation options
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Examensarbete för masterexamen
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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.
Beskrivning
Ämne/nyckelord
Kraft pulp process, electric plasma calcination, pinch analysis, CO2 utilisation, techno-economic assessment, greenhouse gas assessment, electro-fuels, LignoBoost