Opportunities to Reduce Fossil Fuel Consumption & Greenhouse Gases Emerge from Study of Low Carbon Electrification Alternatives for Lime Kilns.
A study performed by PETech on behalf of a Northern Bleached Softwood Kraft (NBSK) pulp mill unveiled critical considerations, as the push for greener, more efficient practices continues.
The significant energy pulp mills require crucially impacts operating costs, carbon emissions, water consumption, and wastewater pollution. Growing interest in technical advancements is a necessary response to the pressures the pulp and paper industry currently faces. The challenge remains to introduce reduced energy needs while meeting output demands.
Inquiry into whether a single electric plasma generator could be a viable replacement for two lime kilns prompted the study; however, it was quickly discerned that the largest plasma kiln system would not support the required output at peak lime demand. A plasma system does not equate to a simple kiln replacement, thus requiring a multitude of system component changes to achieve maximum efficiency. Among the most notable of these changes is the need for a new high temperature steam slaker, new lime dryer, CO2 compressors, and numerous heat exchangers and density separators.
As the study progressed, it was discovered that a considerable benefit of the new process is the potential for heat recovery from the high temperature steam slaker, which is used to dry the incoming lime mud. Steam slaking is an alternative to the conventional method that is currently being developed, with the main advantages being the recapture of thermal heat at higher temperatures and eliminating the need for cooling the green liquor, as the lime will already be slaked at the time of green liquor addition. As a result of this finding, the slaker replacement with new steam slaker and lime mud dryer, without the plasma kiln replacement, was offered as a second alternative. Both options offer excellent emissions saving potential, but at an appreciable capital cost.
The analysis of current energy needs against industry advancements creates important opportunities for reduced operating costs and environmental impact. Detailed environmental studies by experienced engineers play a critical role in highlighting oversights and potential.