Here steamed chips and liquor are fed into the pressurized digester. The contents are heated up by various circulation systems as they move downwards. The cooked and partly washed pulp is fed out of the bottom of the digester.
The spent cooking liquor (black liquor) is separated by screens around the digester and is directed to the flash tanks where the pressure is decreased to below vapor pressure. The generated steam is used for steaming of the chips and the black liquor is sent to the evaporation process.
Continuous digesters predominantly use the sulphate process (often also referred to as the kraft process or kraft pulping)
Examples of NAF valves used in this process
- NAF Duball DL full bore ball valve – Chip feed into digester, digester blow valve, digester recirculation return, white liquor to digester, sand separator junk trap, digester pressure
- NAF Trunnball DL full bore ball valve – Chip feed into digester, feeding of MP-steam into digester, blow line isolation, cold blow pump
- NAF Setball V-port ball sector control valve- Feeding of MP-steam into digester, LP-Steam control,
- NAF Torex triple offset butterfly valve- Screen switching valve, fines separator drain valve
- NAF Turnex pneumatic actuator- For all control and on/off service on NAF rotary valve
- NAF Duball DL Pocket ball valve- Sand separator dump valve
- NAF Check- general service check valve service for pulp, steam, black liquor lines
- NAF Triball– drain valves, sampling valves
- NAF Serie 48 gate valve- any tank service