Chemical and Pulping Ltd

The following information describes the increased performance of displacement cooking systems.

Displacement Digester Offers Higher Cooking Performance

Heating Efficiency

The DDS system pumps liquor through the bed of chips in the digester.  The digester and it's contents start at ambient temperatures. Liquor is pumped through the digester to increase the temperature of the contents until it reaches close to the cooking temperature.  The two phases of liquor pumping are referred to as the initial cook and the middle cook operations.  If needed, steam is added to the digester after the middle cook operation.  The digester then continues to cook until the target kappa number is reached.

Increased Strength

The liquors used in the initial cook and middle cook operations have reaction chemicals and enough heat energy to delignify the wood or bamboo furnish, despite not being at the final cooking temperature.  This activity removes up to 50% of the lignin in the furnish before the digester enters the time-at-temperature cooking phase.  Therefore, the final removal of lignin at the higher cooking temperature can occur with a lower alkali concentration.  The lower alkali concentration at the high cooking temperature does significantly less damage to the fiber compared to conventional cooking.  This is one of the reasons that the DDS system will produce higher strength fiber at the same kappa number or similar strength fiber at much lower kappa numbers compared to conventional cooking.

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