Environmental assessment of biomass gasification combined heat and power plants with absorptive and adsorptive carbon capture units in Norway

Negative emissions through carbon capture processes integrated with bioenergy plants are frequently seen as an important option to stabilise climate at low temperature levels for reaching the two degree target in a cost effective way. Climate neutrality of biogenic CO₂ emissions is commonly assumed while assessing credits for these systems however this simplification may cause an overestimation of climate benefits for long rotation period woody biomass fuelled plants (time gap between emitted and sequestrated CO₂). Carbon capture processes and associated increase of material and energy demand can lead to environmental trade-offs due to higher values for other mid-point impacts while reducing climate change potential. In this work, a comparative life cycle assessment study is undertaken. Three configurations have been analysed: i) a combined heat and power (CHP 10 MW_th input gasification plant (BGP); ii) BGP with pre-combustion adsorptive carbon capture unit (ADS); and iii) BGP with post combustion absorptive carbon capture unit (ABS). For both configurations in which CCS processes are incorporated, negative values for climate change potential are reported. A decrease of 144.7% is observed for ADS and a decrease of 195% is estimated for ABS, when employing specially modelled characterisation factors that take into account the temporal asymmetry between CO₂ emission and removal fluxes. For most of the other environmental performance indicators analysed in this work, higher life cycle values have been quantified for the plants with installed CCS processes despite lower on site emissions for some stressors due to co-capture by the separation agents (H₂S, SO_x and PM for ADS). For the plant with post combustion solvent based unit, larger absolute (per kWh_e basis) and specific (per kg of captured CO₂) increases have been estimated thus exhibiting a worse environmental performance than the CHP plant with pre-combustion adsorption CO₂ capture technology.