Integration of absorption heat pumps in a Kraft pulp process for enhanced energy efficiency

A preliminary feasibility study of the implementation of various absorption heat pump configurations in a Kraft pulping process has been performed. Three different cases were considered: (i) integration of a double lift heat transformer into the heat recovery circuit of the wood chips digesters to produce low pressure steam equivalent to 25% of the steam demand of the chemical pulping plant, (ii) a double effect chiller installed in the bleaching chemicals making plant to chill cooling water and produce middle pressure steam and, (iii) a heat pump installed on the steam extraction line of a turbine which, combined with the addition of a condensing unit, increases substantially the power output. The simple payback time and net present value were used to compare the three cases. Both indices are highly dependant upon steam prices. The net present value is, in all cases, positive, which indicates that the equipment is viable using the assumed cost and efficiency data in this study. Absorption heat pumps are increasingly attractive options for energy upgrading and conversion in a context of increasing energy costs.