FI73022B - FOERFARANDE OCH ANORDNING FOER AVLUFTNING AV EN FIBERSUSPENSION. - Google Patents

Description

Method and apparatus for separating air from a fiber suspension Förfarande och anordning för avluftning av en fibersuspension 73022

Divided by application 810795 (publication 67591)

Avdelad frän ansökan 810795 (utlä.ggnirgsskrift 67591)

The present invention relates to a method and apparatus for separating a gas, such as air, from a fiber suspension. The method and the device are especially intended for high-density masses, e.g. 8 to 1.7%.

The air in the pulp especially hinders the pumping of the thick pulp by a centrifugal pump. The higher the air content of the pulp, the higher the inlet pressure the pump needs to function well. If the available inlet pressure is too low, the air in the mass will form bubbles which accumulate on the inlet side of the impeller, thus interfering with the operation of the pump.

The object of the present invention is to eliminate the above-mentioned difficulties by using a device by means of which air is efficiently separated from the pulp before it is introduced into the pump: impeller. The device can also be used without a pump if the available pressure difference is sufficient to move the mass from one place to another.

The present invention relates to a method for separating gas from a fiber suspension by rotating it by means of rotor blades so as to form a gas core surrounded by the fiber suspension, from which gas is removed to a separate gas space from which degassing is performed in an adjustable manner. The method according to the invention is characterized in that the desired pressure difference between the incoming fiber suspension and the outgoing fiber suspension is maintained by controlling the gas discharge from the gas space.

? 73022

The invention relates to a system for carrying out the method, comprising a device with a rotor having gases to which the gas separated in the rotor can be led and which is connected to a degassing pipe provided with a valve H.

The device according to the invention is characterized in that it comprises measuring and control devices for adjusting the pressure difference between the inlet and the outlet of the fiber suspension and for controlling the valve.

It is already known to use the rotational motion of a liquid to separate gases. Thus, a centrifugal pump is known from UF patent 3,597,904, in which the degassing pipe extends through the inlet channel of the pump up to the inlet of the impeller. The impeller of the pump is fitted with rotor blades which extend longitudinally into the degassing tube near its open end. As the vanes rotate, a central air core is formed surrounded by the liquid, from which gas is removed through a degassing pipe connected to a vacuum source.

The device according to the present invention does not have a gas outlet pipe which would cause flow-impeding friction in the pump inlet duct. Since there is no degassing pipe in the inlet of the device, the inlet can be in direct connection with the pulp tank. It can be used instead of any standard pump without. the piping needs to be changed in no way.

U.S. Pat. No. 3,323,465 discloses a method of controlling a pump having a degassing tube extending into the air core formed on the inlet side of the pump and having impeller blades extending into the inlet of the pump. The pressure difference between the liquid near the inlet wall and the liquid near the center line is measured. The pressure difference is controlled by a valve in the pump pressure pipe. The purpose of the adjustment method presented in this reference is to obtain a sufficient suction head in time to ensure that the 3 73022 impeller remains filled with liquid. However, the flow varies and cannot be adjusted to meet the requirements of the process.

Swiss patent 571,655 discloses a centrifugal pump having several vanes attached to the rear plate of an impeller. The rear plate also has several openings near the impeller shaft through which the liquid and gas in the foam are conducted. Liquid and gas are separated from the foam on the back of the impeller and removed separately.

However, such a pump cannot pump high-density fiber suspensions, as the fibers would block the pump inlet.

Swedish patent 363,363 discloses a degassing method in which the pump used is similar to the pump disclosed in U.S. patent 3,597,904. The gas space at the pump inlet communicates with the vacuum device.

However, this publication does not disclose any devices capable of adjusting the vacuum to the inlet pressure.

The invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 shows an embodiment of a device used in the method according to the invention in longitudinal section, Figure 2 shows a section of Figure 1 along line AA, Figure 3 shows a section of Figure 1 along line PE, Figure 4 shows another embodiment 5 shows a third embodiment, and Figures 6, 7 and 8 show some systems for carrying out the method according to the invention.

73022 4

The device shown in Figures 1-3 comprises a housing 1 with a rotor bore 2 and an adjacent gas space 3. In the partition wall 4 between them there is a centrally located opening 5, through which the rotor chamber and the gas space communicate with each other. The housing has an inlet 6 through which the fiber suspension flows into the rotor chamber and an outlet 7. The gas space has a gas outlet 8. The rotor chamber has a rotor 10 with vanes 9. The rotor has a tubular inner part 11 to which the vanes are attached and has openings 12. the aperture-side end is closed by a conical tip portion 13, and at its other end there is a plate 14 perpendicular to the rotor shaft with openings 15. The rotor plate 14 is attached to the medicine housing 16 on a shaft 17 not mounted as further defined herein. Shaft actuators are not shown in the figures.

The device can be attached to the bottom of the pulp tank 19 so that the rotor 10 is partially inside the tank, as in Fig. 1. As the rotor rotates, the adjacent pulp fluidizes and flows through the outlet 6 into the rotor chamber 2. In the rotor chamber, the rotor 10 , forming a central mass surrounded by an air core. Air can be removed through the interconnected openings 12, 15 and 5 to the gas space 3, from where it can be led out via the degassing opening 8. The pulp from which the air has been separated is removed through the outlet 7.

The purpose of the vanes 18 in the gas space is to disintegrate and remove the mass accumulated in the gas space during downtime.

In the embodiment shown in Figure 4, vanes 23 are attached to the rear of the plate 14 of the rotor 10.

The purpose of the wings is to separate the mass coming from the openings 15 of the plate 14 with the air. The separated mass is removed through a duct formed by the partition 4 of the plate 14 and 5 73022, whereby the air flowing into the gas space through the opening 5 is almost massless. The radial distance of the outer edges 24 of the wings 23 from the axis of rotation must be greater than the outer edges 26 of the wings 9. In this case, the diameter of the air core increases before the opening 5 of the wall 4 and the mass is prevented from entering the gas space.

In the embodiment of the invention shown in Fig. 5, a rotor which fluidizes the pulp and separates air therefrom is arranged in the centrifugal pump inlet duct 27 before the impeller 78 and fixed thereto so as to form a unitary rotor comprising a first part 10A in communication with the distance from the axis of rotation of the rotor is small, and the second part 10B communicating with the outlet opening 7, the radial distance of the outer edges 29 of the blades 9B of which from the axis of rotation is large. In the first part 10A of the rotor, the mass moves mainly in the axial direction, and in the second part 10B in the radial direction.

It has been found that the magnitude of the pressure difference between the inlet of the fiber suspension and the degassing channel substantially affects the operation of the device. When the pressure difference is too small, the air core becomes so large that it interferes with the operation of the pump. If, on the other hand, the pressure difference is too large, the air core decreases so that part of the mass escapes with the air through the openings 12, 15 and 5. When using a device to remove pulp from a tank, the inlet pressure of the pump changes as the height of the pulp surface changes. To standardize the pressure difference between the pump head and the exhaust air, the device is equipped with pressure control devices according to Figures 6-8. The optimum pressure difference for deaeration depends on the consistency and temperature of the pulp. It has been found experimentally that it should be from 0 to 0.7 bar, preferably from 0.2 to 0.5 bar.

In the system shown in Fig. 6, the air separator pump according to Fig. 5 attached to the bottom of the pulp tank is indicated by reference number 303030. The exhaust pipe attached to its outlet has a flow meter 31 and a control valve 32 by means of which the pump flow can be adjusted. The pressure difference between the pump inlet and the outlet (pump head) is measured by a differential pressure gauge 33. An outlet line 34 connected to the gas outlet of the device is fitted with an air tank or expansion section 35, a vacuum pump 36 and a control valve 37. The air outlet pressure is measured and adjusted . with a DP controller 38 connected to the differential pressure gauge 33 and the control valve 37. The differential pressure control regulates the size of the air bubble in the pump inlet duct by means of the control valve i 1 in 3 "1 so that the pump head setpoint is reached. a water line 39 for rinsing, and a compressed air line 40 connected to the air tank 35, by means of which air of controlled pressure and volume can be supplied during the start-up phase and, if necessary, to change the pressure difference quickly.

A slightly simpler system than the previous one, in which the differential pressure control of the deaeration is eliminated, is shown in Fig. 7. Here, the pressure difference between the pump inlet and the outlet is measured and controlled by a DP controller 41 connected to the deaeration control valve 37. However, the presetting of the vacuum system is slightly more cumbersome and the start-up is more prone to interference than the solution shown in Fig. 6, which is thus better but more efficient.

Figure 8 shows a solution suitable for use in cases where the inlet pressure of the pump is constant. In the embodiment shown in the figure, the height of the surface of the pulp in the tower is kept constant by means of a compensating meter 42 connected to the tower and a control valve 43 arranged in the pump outlet pipe.

: The pressure in the pump outlet pipe is measured with a pressure gauge 44 and; is controlled by the deaeration control valve 37.

Claims (4)

73022 A method for separating gas from a fibrous slurry by rotating it by means of rotor blades to form a gas core surrounded by a fibrous slurry degassing into a separate gas space from which the degassing is performed in a controlled manner, characterized by maintaining a desired pressure difference removal from the gas space. A method according to claim 1, characterized in that the pressure difference is maintained by adjusting the pressure difference between the incoming fiber suspension and the outgoing gas. Method according to Claim 2, characterized in that the pressure difference between the incoming fiber suspension and the outgoing gas is 0 to 0.7 bar, preferably 0.2 to 0.5 bar. A system for carrying out the method according to claims 1-3, comprising a device with a rotor having a gas space into which the gas separated in the rotor can be led and connected to a degassing pipe with a valve, characterized in that it comprises an inlet (6) and an outlet ( 7) measuring and regulating devices (DP, DPC) for adjusting the pressure difference between the valve and controlling the valve (37).