Pumps – Processes
Patent
1993-06-14
1994-11-22
Bertsch, Richard A.
Pumps
Processes
417 69, 417 90, 4151691, F04C 1900, F04D 2902
Patent
active
053663470
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a pump for pumping a suspension of cellulosic fibrous material, comprising a housing having an inlet and an outlet for the suspension, said outlet being substantially perpendicular to the inlet, a shaft rotatable about an axis of rotation with which the inlet is concentric, a fluidizing rotor for fluidizing the suspension, a first impeller for pumping the fluidized suspension, and a gas evacuation pump of liquid ring type comprising a pump housing with a cylindrical chamber and a second impeller rotating therein for evacuating gas collecting in front of said first impeller via a system of channels, said chamber having an inlet for said gas and an outlet for said gas which is displaced circumferentially substantially 180.degree. in relation to the inlet, and said chamber containing a liquid ring which rotates together with the second impeller and which defines blade pockets between itself and the blades of the second impeller to transport gas from the inlet to the outlet, the rotor and said two impellers being mounted on said shaft and rotating therewith.
BACKGROUND OF THE INVENTION
A suspension pump with a built-in gas evacuation pump of the type described above is previously known through U.S. Pat. No. 4,776,758, however, the gas evacuation pump functions only as a vacuum pump. Since the vacuum pump and the suspension pump are driven by a common shaft the vacuum pump cannot be disconnected in those cases when no gas is separated out from the suspension- The vacuum pump must therefore operate under extremely varying conditions, both in different installations and in one and the same installation. Suspension pumps in down pipes containing pulp of medium consistency at a low level and much air require a vacuum pump with high capacity in order to be able to evacuate sufficiently large quantities of air at low pressure on the inlet side of the suspension pump. Suspension pumps operating with high pulp levels on the inlet side, e.g. a suspension pump installed at the bottom of a storage tower, need only be de-aired when the pulp level drops below 15 m. At higher levels the vacuum pump works towards a closed outlet and contributes to unnecessary power consumption, however other problems may arise as will be clear below.
When the level of pulp in a storage tower is high, normally above 15 m, the pressure at the inlet to the pump is high, e.g. 2 bar, and no air will therefore be separated out from the pulp. The pressure inside the pump, at the centre of the impeller is considerably above atmospheric pressure. Under such operating conditions--high inlet pressure and no air separation--the vacuum pump will be filled with pulp and its outlet must be closed. When the vacuum is operating against a closed outlet in this way, and is filled with pulp, considerable pressure variations occur which lead to cavitation and mechanical stress.
When the level of the pulp is mid-way in the storage tower, usually 7-15 m, the pressure at the inlet to the pump will be correspondingly lower, e.g. 1 bar, and some of the air will therefore be separated out in the pump, disturbing the pumping process. The pressure at the centre of the impeller is still above atmospheric pressure, and it is difficult to evacuate air without the fibre suspension being pressed out at the same time. The outlet from the vacuum pump must therefore be throttled. However, such throttling causes the outlet to become blocked by fibres and to solve this problem the outlet is flushed clean with water from a pipe which is connected to the outlet before the throttle valve.
When the level of the pulp is low in the storage tower, usually below 7 m, the pressure at the inlet to the pump will be correspondingly lower, atmospheric pressure and below, so that large and varying amounts of air in the pulp will be separated out in the pump, disturbing the pumping process. The pressure at the centre of the impeller is now below atmospheric pressure, and the air is withdrawn by means of the vacuum pump. Since the amount
REFERENCES:
patent: 3072057 (1963-01-01), Esau de Silva Rosa
patent: 4776758 (1988-10-01), Gullichsen
patent: 4921400 (1990-05-01), Niskanen
patent: 4981413 (1991-01-01), Elonen et al.
patent: 5078573 (1992-01-01), Peroaho et al.
patent: 5228290 (1993-07-01), Speggiorin
Bertsch Richard A.
Kamyr Aktiebolag
McAndrews, Jr. Roland G.
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