Pulp-mill integrated biorefineries: a framework for assessing net CO2 emission consequences

There is currently much interest in producing biofuel-based transportation fuels. However, since biofuel is a limited renewable resource, it is important to assess whether such fuels are both produced and used as efficiently as possible. Efficient production can be achieved in the future by integrated biorefinery operations at pulp mill sites, co-producing pulp and biofuel-based energy products. This paper compares production of transportation fuel with other biorefinery options for future pulp mills. The comparison is based on net CO2 emissions, i.e. accounting for off-site consequences associated with changes in the net flows of electricity, biofuel and biofuel-based transportation fuel entering or leaving the mill. The most important conclusion is that system variables (e.g. assumptions regarding the reference fuel and engine efficiency for future transportation systems) are of decisive importance for the net CO2 emissions associated with pulp mill biorefinery operations. This paper illustrates such aspects and underlines the importance of a system perspective in process engineering research.