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Based on KAMa pulp and paper mill, a polygeneration system integrated with a black liquor gasifier is proposed. The effects of CO₂ captured by oxygen-fuel combustion and Selexol absorption on the performance of the polygeneration system are studied in terms of both thermodynamic performance and cost assessment. Using the Aspen Plus simulator, the performance of the studied polygeneration systems are analyzed from the perspectives of the first and second laws of thermodynamics. Compared with the reference system, the first law efficiency of the polygeneration system increased from 15.7% to 29.3%, with an investment increment of 17.9%. The investment incremental rates for CO ₂ capture by oxyfuel combustion and Selexol absorption are 15.1% and 16.7%, respectively. Energy penalty due to CO₂ capture and compression is 0.61 MJ electricity/kg CO₂, avoided in the oxygen-fuel method at a cost of $29.6/tonne CO₂. However, energy penalty can reach 1.03 MJ product (electricity and methanol) per kg CO₂, avoided in the Selexol absorption CO₂ capture process at a cost of $46.0/tonne CO₂.