Air lift pump

Abstract

 An air lift pump having two or more stages (11, 17) where the first stage (11) pumps liquid to a level above the surface of the body of liquid to be pumped. Next stage (17) pumps from this level to a still higher level. Further stages can be added to increase the pumping height or improving the pumping efficiency.

Description

The present invention relates to an air lift pump.

[0001] A major problem with prior art air lift pumps is that the pumping efficiency becomes low when the submergence ratio, i.e. the ratio between the length of the pump pipe submerged into a body of liquid and the total length of the pump pipe, is low. The efficiency of an air lift pump is almost always considered to be too low at a submergence ratio of 0.6 and does not work theoretically as a true air-lift pump below 0.5. The efficiency becomes even lower if pumping the heavier layer of a density stratified liquid. Such a liquid could be water with a layer containing water mixed with silt.

[0002] The object of the present invention is to create an air lift pump which can be efficiently used for low submergence ratios, in particular if the liquid to be pumped is density stratified. The invention is defined by the subsequent claims.

[0003] The invention is exemplified below with reference to the accompanying drawing in which fig 1 shows a two stage air lift pump according to the invention. Fig 2 shows a three stage air lift pump according to the invention. Fig 3 shows another embodiment of a two stage air lift pump according to the invention.

[0004] The two stage air lift pump shown in fig 1 comprise.s a pump pipe 11 partly submerged into a body of liquid 12. The liquid is normally water. The pump pipe is provided with an inlet opening 13 which often is situated close to the bottom 10 of the body of liquid. The pump pipe is at its lower end provided with means 14 for supplying gas, preferably compressed air, to the interior of the pump pipe. This means could be in form of a ring having holes for the exit of gas. This ring is also connected to a supply of gas through a not shown conduit. The pump pipe also comprises an outlet opening 15 positioned above the surface 21 of the body of liquid 12. The ratio between the distance between surface 21 and inlet opening 13 and the distance between outlet opening 15 and inlet opening 13 is called the submergence ratio of pump pipe 11. The gas-liquid mixture leaving pump pipe 11 through outlet opening 15 enters a receptacle 16 at an upper level. Receptacle 16 has an upper end 22 and a lower end 23 of which the latter is closed, e.g. through contact with bottom 10 as shown and end 22 is open to allow the gas of the gas-liquid mixture of the discharge to escape so that only liquid is present in receptacle 16. A further pump pipe 17 is positioned in receptacle 16. The further pump pipe is provided with an entry opening 18, a discharge opening 20 and means 19, connected to a source of gas, for supplying gas to the interior of the further pump pipe 17.

[0005] The embodiment of the invention shown in fig 2 is a three stage air lift pump. Of the three stages the first two correspond to the two stages of the embodiment according to fig 1. Therefore, the same reference numerals have been used. Gas-liquid mixture leaving discharge opening 20 enters a further receptacle 24 at an upper level. The further receptacle has an upper end 29 and a lower end 30 of which the latter is closed and end 29 is open to allow the gas of the gas-liquid mixture of the discharge to escape so that only liquid is present in receptacle 24. A pump pipe 25 is positioned in the further receptacle. Pump pipe 25 is provided with an inlet opening 26, a discharge opening 28 and means 27, connected to a gas supply, for supplying gas to the interior of pump pipe 25.

[0006] The embodiment shown in fig 3 differs from the one shown in fig 1 only by the fact that the second stage pump pipe is situated beside the receptacle. The fig 3 air lift pump comprises a pump pipe 41, a receptacle 45 and a further pump pipe 48. Pump pipe 41 is provided with an inlet opening 42, an outlet opening 44 and means 43, connected to a gas supply, for supplying gas to the interior of pump pipe 41. Receptacle 45 has an upper end 46 and a lower end 47 of which the latter is closed and end 46 is open to allow the gas of the gas-liquid mixture of the discharge to escape so that only liquid is present in receptacle 45. The further pump pipe 48 is provided with an entry opening 49, a discharge opening 51 and means 50, connected to a gas supply, for supplying gas to the interior of the further pump pipe 48.

[0007] The three embodiments shown in the drawing operate in the same way. The number of stages to be used is determined such that a sufficiently high pumping efficiency, i.e. a high ratio between liquid flow and gas flow, is obtained for a given total submergence ratio. This latter ratio is the ratio between the height to the final discharge from the inlet and the distance that the first inlet is submerged into the body of liquid. By splitting up the lifting height of the air lift pump into two or more stages it has been made possible to use the air lift pump principle for low submergence ratios, below 0.5, and to improve the pumping efficiency in general for submergence ratios below 0.95

[0008] One case where an air lift pump according to the invention is particularly efficient is when a density stratified liquid is to be pumped. In this case the whole height of the first pump stage is filled with a mixture of the denser liquid and gas whereas the height outside the pump pipe is occupied with lighter liquid. In the second and further stages, however, the receptacle is filled to the height of the outlet from the next preceding stage with the denser, liquid only. It is, therefore, preferable when pumping density stratified liquid to choose a higher submergence ratio for the first pump stage than for the second and further stages.

[0009] The increased efficiency of an air lift pump according to the present invention depends on the fact that the liquid level causing the pressure at the inlet of the second or further stages is situated above the surface of the body of liquid. This level is the level of the outlet from the next preceding stage.

Claims

1. An air lift pump comprising a pump pipe (11) being partly submerged into a body of liquid (12), said pump pipe having an inlet opening (13) for the entry of liquid into the pump pipe at a lower level thereof, means (14) for supplying gas to the interior of the pump pipe (11) near its lower level and an outlet opening (15) positioned above the body of liquid (12) for the exit of gas-liquid mixture from the pump pipe,
characterized in
that the air lift pump comprises a receptacle (16) for receiving the gas-liquid mixture from the outlet opening (15) at an upper level where the gas supplied is vented away to the atmosphere and a further pump pipe (17) having an entry opening (18) at a lower end for the entry of medium from a lower level inside the receptacle (16), said further pump pipe being provided with means (19) for supplying gas to the interior of the further pump pipe (17) near the lower end and a discharge opening (20) being positioned at a level above said outlet opening (15), whereby said inlet opening (13) and said entry opening (18) are positioned at substantially the same level.

2. An air lift pump according to claim 1,
characterized in
that the further pump pipe (17) is positioned in the receptacle (16).

Drawing