ULTRA HIGH PRESSURE (10 - 12 bar) TMP AND IT'S ENERGY RECOVERY OPTIONS, 2007 International Mechanical Pulping Conference

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Traditionally TMP for graphic papers is produced at low chip preheating pressures of 1-2 bar(g) (or even at atmospheric pressure in the case of PRMP) for 1,5 to 3 minutes and at refining pressures of about 3,0 to 4,0 bar(g) in order to obtain adequate pulp properties at reasonable energy requirements and a recovered steam pressure which is high enough to be used in the dryer section of the paper machine without further compression. Many investigations have shown that the residence time of the chips at higher pressures/temperatures during preheating and refining has to be short and well controlled in order to avoid pulp discoloration and to keep the energy consumption at acceptable levels. Short preheating times, in the order of about 13 seconds and pressures/temperatures of about 5,5 bar(g)/162°C are used in the first refining stage of the RTS process.