Oxyfuel combustion of black liquor in Swedish recovery boilers

To limit global warming to a maximum of 1.5 °C, measures in terms of negative emissions of carbon dioxide (CO₂) are required. Negative emissions refer to the separation and permanent storage of CO₂ of biogenic origin, shortened BECCS (bio-energy with carbon capture and storage). In Sweden, there are approximately seventy larger plants that each release over 100,000 tons of biogenic CO₂ annually. Together, they contribute over 30 million tonnes of CO₂ to the atmosphere, of which the largest emission sources are found in the paper and pulp industry. Sweden thus has particularly good conditions for creating negative net emissions of CO₂ at these large point emission sources by implementing BECCS. Combustion of black liquor in the Swedish pulp and paper industry annually releases approx. 20 million tonnes of biogenic CO₂ into the atmosphere. By implementing oxyfuel combustion in existing soda ash boilers, it would be possible to create negative net emissions of CO₂ at these large point emission sources.

Oxyfuel combustion, which means that the combustion air is replaced with oxygen diluted with recirculated flue gases, results in a stream of easily accessible CO₂. In recent years, oxyfuel combustion has gained a lot of interest due to the improved possibilities for simple and cheap CCS (Carbon Capture and Storage). An advantage of the technology is that it can be implemented in existing boilers. After conventional flue gas purification and condensation of water vapor, only a highly concentrated stream of CO₂ remains, which can be compressed directly without further purification for further permanent storage. Oxyfuel combustion thus means that complicated, expensive, and energy-intensive CO₂ capture steps can be completely avoided.

This project creates the conditions  to implement new industrial solutions within the pulp and paper industry, which in the long term can result in significant technological leaps towards drastically reduced Swedish emissions of greenhouse gases. The project's objective is to produce essential knowledge for future implementation. Since the melting chemistry in the soda boiler affects the entire mill's chemical recycling, the project involves increasing the understanding of important chemical engineering challenges and opportunities that need to be considered before conversion to oxyfuel combustion. Some of the project's concrete goals are to:

• Carry out extensive experimental tests with black liquor under varying oxyfuel conditions
• Develop a model that describes the complex chemistry in the soda boiler under different oxyfuel conditions
• Estimate costs for future implementation of the oxyfuel concept at an existing Swedish soda boiler and calculate the potential for CO₂ reduction from the same, assuming a maintained steam production
• Make the sapience available through scientific publications