Laboratory Simulation of Modified Kraft Cooking Systems - A New Cooking System Enables Independent Temperature and Liquor Transfer Programs, 1994 Pulping Conference Proceedings

P.O. Tikka, K. K. Kovasin

A lot of work on kraft cooking R&D by mill trials, basket hanging cases and laboratory equipment led us to the conclusion that today’s cooking simulations in laboratory are not satisfactory. Regardless of the heat- and mass-transfer phenomena in mill scale, all laboratory work is being done using fast digester circulation which is no longer the case in any of the modified kraft cooking systems. The present paper discusses the weaknesses in conventional laboratory digester technology and describes the development of a new equipment design, where heat-transfer has been completely separated from cooking and liquor transfer sequences. This has been made possible by a jacketed digester design. The temperature profile is controlled by the water circulation. This provides correct temperature for the reactor and also for the incoming liquors by leading them through a heat exchange coil. A versatile piping and pumping system connects the digester unit to tank farms organizing the reception and delivery of cooking liquors. After half a year of daily operation the results show excellent accuracy and repeatability. We have been able to simulate different mill scale displacement kraft batch processes and carried out experiments which could not have been done by older techniques. Comparisons to conventional simulations have revealed more realistic alkali profiles and higher unbleached brightness.