Chip Cooking Process

Chips from the storage silo are loaded into the digester, where they are cooked with cooking liquor (caustic soda) at a temperature of 170-175°C and a pressure of around 9 kg/cm². The cooking process is carried out using indirect heating to remove lignin and other organic compounds. Once the desired pressure and temperature are reached, the mixture is maintained at these conditions for 2 hours. After this period, the entire mass is blown to the blow tank under pressure. The vapors from the blow tank are utilized to heat water in the blow heat recovery system.

Vertical Stationary Digester with Preheater:

The digester features a cylindrical central portion with conical shapes at the bottom and top ends. It has screen plates at the top, middle, and bottom. The material of construction for the digester is SA 516 Gr. 70, with a thickness of approximately 36 mm. The designed pressure is 10.5 kg/cm², and the test pressure is 16.5 kg/cm². The screen plates are made of AISI 304. The digester has connections for introducing liquor in the center and discharging at the top and bottom. The blow line to the digester is connected at the bottom, from where the complete mass is blown out after the cooking cycle completes.

Since the cooking process uses indirect heating, digesters are connected to a liquor preheater. In the preheater, steam is injected into the outer body, and the liquor is circulated through the tubes by liquor circulation pumps.

Blow Heat Recovery System:

The blow heat recovery system is installed to condense the contaminated vapors originating from the blow tank during the blowing of pulp from the digesters. Water from the accumulator tank is circulated to condense these vapors and raise the water temperature. This hot water is then used to heat fresh water from ambient temperature to 70°C in a plate-type or tube-type heat exchanger. The heated fresh water is subsequently used in the washing section.