Practices to recover nitrogen and phosphorus in pulp production : Case study: Analysing nitrogen and phosphorus flows of a pulp mill
Vasama, Venla (2023)
Vasama, Venla
2023
Tekniikan ja luonnontieteiden kandidaattiohjelma - Bachelor's Programme in Engineering and Natural Sciences
Tekniikan ja luonnontieteiden tiedekunta - Faculty of Engineering and Natural Sciences
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Hyväksymispäivämäärä
2023-12-19
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:tuni-2023121911008
https://urn.fi/URN:NBN:fi:tuni-2023121911008
Tiivistelmä
As a result of climate change, the importance of the bioeconomy is growing, and bio-based products are increasingly developed to replace non-renewable materials. In the forest industry, wood serves as a renewable raw material. The pulp and paper industry is one of the world's largest industrial sectors, with significant emissions. Nitrogen and phosphorus released from kraft pulp mills have various environmental impacts, contributing to issues such as the eutrophication of water bodies and air pollution. This study examined the nitrogen and phosphorus flows of a specific kraft pulp mill and explored ways to enhance nitrogen and phosphorus recycling within the pulp mill.
In the chemical pulp production process, cellulose fibres are separated from raw materials using chemicals. The production of pulp can be divided into two main lines: one producing pulp from wood raw material, and the other being the recovery process. The recovery process aims to recycle chemicals from by-products generated during cellulose cooking back into a form suitable for use in cellulose separation. Additionally, the recovery process reduces the environmental impact of by-products and generates energy. During the recovery process at the pulp mill, over 95% of the nitrogen oxides emitted are nitrogen dioxide, with the remaining emissions being nitrogen monoxide. The wastewater generated in the pulp production process is nutrient-poor, requiring the addition of nitrogen and phosphorus to the biological wastewater treatment process. Nitrogen is commonly added in the form of urea or ammonia, and phosphorus is added as phosphoric acid.
The significant nitrogen and phosphorus flows from the studied pulp mill included ammonia and phosphoric acid that are added to the biological wastewater treatment process, nitrogen oxide emissions resulting from the recovery process, nutrients in the effluents, ashes, green liquor dregs and in wastewater sludge. Nitrogen oxide emissions could potentially be reduced using flue gas scrubbers. Furthermore, by using scrubber water as a nitrogen source in the biological wastewater treatment process, the need for additional urea or ammonia could be minimized. The nitrogen and phosphorus in the wastewater sludge could be recycled in a form suitable for use in the pulp mill's water treatment process.
This study identified methods to enhance nutrient recycling in the pulp mill. In this study, an illustration was created to visualize the nitrogen and phosphorus flows of a pulp mill. The figure included a simplified process diagram of the pulp mill and nutrient flows associated with different stages of the process.
In the chemical pulp production process, cellulose fibres are separated from raw materials using chemicals. The production of pulp can be divided into two main lines: one producing pulp from wood raw material, and the other being the recovery process. The recovery process aims to recycle chemicals from by-products generated during cellulose cooking back into a form suitable for use in cellulose separation. Additionally, the recovery process reduces the environmental impact of by-products and generates energy. During the recovery process at the pulp mill, over 95% of the nitrogen oxides emitted are nitrogen dioxide, with the remaining emissions being nitrogen monoxide. The wastewater generated in the pulp production process is nutrient-poor, requiring the addition of nitrogen and phosphorus to the biological wastewater treatment process. Nitrogen is commonly added in the form of urea or ammonia, and phosphorus is added as phosphoric acid.
The significant nitrogen and phosphorus flows from the studied pulp mill included ammonia and phosphoric acid that are added to the biological wastewater treatment process, nitrogen oxide emissions resulting from the recovery process, nutrients in the effluents, ashes, green liquor dregs and in wastewater sludge. Nitrogen oxide emissions could potentially be reduced using flue gas scrubbers. Furthermore, by using scrubber water as a nitrogen source in the biological wastewater treatment process, the need for additional urea or ammonia could be minimized. The nitrogen and phosphorus in the wastewater sludge could be recycled in a form suitable for use in the pulp mill's water treatment process.
This study identified methods to enhance nutrient recycling in the pulp mill. In this study, an illustration was created to visualize the nitrogen and phosphorus flows of a pulp mill. The figure included a simplified process diagram of the pulp mill and nutrient flows associated with different stages of the process.
Kokoelmat
- Kandidaatintutkielmat [8798]