Increasing cogeneration in Canadian pulp and paper mills: PART Ⅲ - NEW INSTALLATIONS IN KRAFT MILLS

摘要

With Canada's 2050 net-zero emissions target, pulp mills must adapt to increased carbon taxes, potentially higher biomass costs, and the possibility of becoming a negative emissions industry. Cogeneration plays a central role in how mills can reduce production costs and find new revenue streams. In kraft mills with aging boilers, a promising option is to rebuild the boilers with re-heat configurations, for additional electricity generation between eight and 23 MW/ktpd (megawatts per 1000 tons per day of pulp production). A riskier option is to gasify the hog fuel and/or black liquor for hydrogen-based combined cycle cogeneration, for additional electricity generation between 27 and 120 MW/ktpd. In the long term, configurations that can capture carbon, operate intermittently to balance wind power, and/or export green hydrogen may have a competitive edge. Without rebuilding the boilers, the most promising option is to add indirect contact economizers to the boiler and lime kiln flue gases to preheat the boiler feedwater immediately upstream of the deaerators, for additional electricity generation of about 5.5 MW/ktpd by an existing condensing steam turbine. Gas turbine cogeneration is possible by reusing the turbine exhaust as combustion air for the lime kiln, but this application provides much less benefits.