Post-Combustion CO2 Capture in Kraft Pulp Mills - Technical, Economic and System Aspects

Doctoral thesis, 2008

As a result of increasing concerns about climate change, there is considerable research and activities around CO2 capture and storage. In this thesis it is studied what role the pulp and paper industry can play in mitigating climate change through CO2 capture and storage. The technique evaluated here is post-combustion CO2 capture using chemical absorption. This technique is chosen since it does not require any rebuilding of the recovery boiler. Two different absorbents are used, mono-ethanolamine (MEA) and chilled ammonia. CO2 capture from flue gases leads to a considerable energy penalty for the regeneration of the absorbent. Therefore the main objective of this thesis is how to supply the extra energy demand needed for the CO2 capture. This energy supply can be divided into four main categories: producing more steam, creating excess steam at the mill, using excess heat from the mill and creating an energy combine. The studied configurations are evaluated by calculating the avoidance cost using different possible future energy market scenarios. The results show that an increasing degree of heat integration leads to a lower avoidance cost for the CO2. This is due to a lower demand for external fuel. The results also show that chilled ammonia has a better performance compared to MEA, due mainly to a lower heat demand for regeneration of the absorbent, smaller gas volume and thereby smaller equipment and lower investment cost. The chilled ammonia capture process also opens up for very interesting ways of heat integration with the mill. However, there are alternative uses of the excess heat and excess steam. Therefore extensive analyses must be performed in order to identify the best use. Results presented here show that under certain conditions CO2 capture can be the best use of energy excess for the mill. Under these conditions CO2 capture and storage can be very profitable for the pulp and paper mills.