Usable excess heat in future kraft pulp mills.
New environmental objectives will lead to changes in the future pulp and paper industry, water loop closures, new processes to remove non-process elements (NPE), and reduced fossil fuel consumption are possible results of these neat objectives. A first step toward reducing the fuel consumption in a mill is to energy-integrate existing processes. Then, by designing the secondary heat system differently, medium temperature (70[degrees]C-100[degrees]C) heat can be made available and used in the plant to replace live steam through process modification, thus further decreasing fuel consumption. With a higher temperature where heat can be made available, a commensurate amount of live steam can be replaced. The amount of heat that can be made available varies among mills. We investigated two model mills producing market pulp (2000 a.d. metric tons/day) to help quantify the expected amounts. Two different secondary heat systems are shown for each model mill, one reference design and one novel design where excess heat is made available. The heat made available in these model mills is used in fine evaporation plant to replace live steam. The investment cost for the novel secondary heat system making heat available and for using that heat in the evaporation plant compared to the investment cost for the reference system is between US$ 5-10 million for the two model mills. The total heat demand for the plant is lowered up to 17% when using the heat made available in the evaporation plant to replace live steam. That, together with the extra investment cost, results in a profit of US$ 0.6-1.5 million/year. S!
Wising is a Ph.D. student and Berntsson is professor in the Department of Heat and Power Technology, Chalmers University of Technology, 412 96 Goteborg, Sweden; Asblad is with CIT Industriell Energianalys AB, 412 88 Goteborg, Sweden; email Wising at firstname.lastname@example.org.
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|Publication:||Solutions - for People, Processes and Paper|
|Date:||Nov 1, 2002|
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