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1. WO2020109667 - ARRANGEMENT AND METHOD FOR DEGASSING A PUMP

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[ EN ]

CLAIMS:

1. Arrangement for controlling a gas flow separated from a suspension of medium consistency pulp, which is treated in a pulp treatment apparatus comprising at least a first pump and a second pump, wherein the second pump is a degassing centrifugal pump provided with a degassing system which comprises

- a degassing conduit in which a degassing valve is arranged for regulating a pressure difference between an inlet of the second pump and the degassing conduit, characterized in that the degassing system further comprises a pressurized degassing vessel working under overpressure and having an inlet and an outlet, wherein the outlet of the vessel is connected to a pressure control valve for maintaining an overpressure in the vessel.

2. Arrangement according to claim 1 , characterized in that the pressurized degassing vessel is a pipe disposed horizontally, and the inlet of the pipe is connected to the degassing conduit and the outlet of the pipe is connected to an outlet conduit where the pressure control valve is located.

3. Arrangement according to claim 2, characterized in that the degassing system further comprises a water separator, which is connected to the outlet conduit and which is an unpressurized chamber provided with a vent conduit in the upper part thereof and a drainage conduit for adjusting a water level in the separator.

4. Arrangement according to claim 1 , characterized in that the pressurized degassing vessel is a pressurized water separator chamber having a liquid level and a gas space above the liquid level, and a vent conduit, in which the pressure control valve is arranged to maintain a required overpressure in the chamber, and the chamber further comprises a

drainage conduit, which is provided with a valve for regulating the liquid level in the chamber.

5. Arrangement according to claim 2 or 3, characterized in that a diameter of the pipe is at least 50 mm, preferably over 80 mm.

6. Arrangement according any of claims 1-5, characterized in that a

volume of the pressurized degassing vessel is in a range of 0.01-1.0 m3, preferably 0.02-0.2 m3.

7. Arrangement according any of claims 1-6, characterized in that the pressurized degassing vessel is arranged to operate at a pressure of 0.1- 4.0 bar(g).

8. Method for controlling a gas flow separated from a suspension of

medium-consistency pulp, which is treated in a pulp treatment apparatus so that it is pumped by at least a first pump and a second pump for raising the pressure of the pulp, and gas is separated from the pulp in the second pump, the separated gas flow is discharged to a degassing conduit, wherein a pressure difference is determined between the inlet of the second pump and the degassing conduit and the pressure difference value is maintained within a given range by a degassing valve connected to the degassing conduit, characterized in that the separated gas is fed to a pressurized degassing vessel located downstream of the degassing valve and connected to the degassing conduit, wherein a overpressure is maintained in the pressurized degassing vessel by a pressure control valve located downstream of the vessel in order to decrease a volume of the gas flow.

9. Method according to claim 8, characterized in that water is separated from the gas flow so that the water separation is carried out in a separate chamber after the pressurized degassing vessel.

10. Method according to claim 8, characterized in that water is separated from the gas flow so that the water separation is carried out in the pressurized degassing vessel.

11. Method according to claim 8, 9 or 10, characterized in that a liquid level is controlled during the water separation.

12. Method according to claim 8, 9, 10 or 11, characterized in that pressure in the pressurized degassing vessel is adjusted to a range of 0.1- 4.0 bar (g), preferably 0.3 - 3 bar (g).

13. Method according to any one of claims 8- 12, characterized in that the overpressure in the pressurized degassing vessel and volume of the vessel allow damping pressure changes over the degassing valve.

14. Method according to any one of claims 8- 13, characterized in that the medium consistency pulp from which gas is separated in the second pump is oxygen delignified.

15. Method according to any one of claims 8- 13, characterized in that the medium consistency pulp from which gas is separated in the second pump is treated before pumping with a gaseous bleaching chemicals, such as ozone or peroxide.