GB2227057A

GB2227057A - Screw pumps

Info

Publication number: GB2227057A
Application number: GB8830027A
Authority: GB
Inventors: Raymond Anthony Leon Goodridge
Original assignee: MULTIPHASE SYSTEMS PLC
Current assignee: MULTIPHASE SYSTEMS PLC
Priority date: 1988-12-22
Filing date: 1988-12-22
Publication date: 1990-07-18
Anticipated expiration: 2008-12-22
Also published as: GB2227057B; GB8830027D0

Abstract

A screw positive displacement pump for pumping comingled fluids (liquid and gas) has a body (130) provided with a pump chamber and having an inlet (131) and an outlet (133). The pump chamber contains intermeshing screw pumping members and has an inlet and a discharge port (132), a first passage for conducting fluid from the inlet (131) to the chamber inlet port and a second passage for conducting fluid from the chamber outlet port (132) to the body outlet (133). Between the chamber outlet port (132) and the body outlet (133) are provided vapour condensation and liquid collection means (135, 136 and 138 to 143), whereby passage of fluid from the chamber outlet part (132) to the body outlet (133) causes some vapourised fluid to be condensed and condensed liquid to be returned to a reservoir (137) for providing liquid to assist sealing of the pump chamber and the screw members. <IMAGE>

Description

IMPROVEMENTS IN PUMPS This invention relates to pumps for pumping comingled flows, such as mixtures of liquid and gas. A commercially important comingled flow is a mixture of oil and gas from an oil well, which poses particular problems since the proportion of gas to oil will vary from time to time, and a pump for pumping such mixtures must be able, for example, when passing almost entirely gas, suddenly to accept 100% oil.

We have proposed already the use of a screw positive displacement pump for handling comingled flows in our Patent GB 2165890 in which is described both a conventional screw positive displacement pump and a screw positive displacement pump according to the invention of that Patent which has enhanced efficiency.

Where particularly high gas fractions, notably in the 95% to 100% region, are concerned, there can be a difficulty with pump configurations as shown in GB 2165890 since insufficient liquid may be present to provide a seal between screws of the pump and the pump chamber wall.

According to the invention there is provided a screw positive displacement pump for pumping. comingled material, the pump comprising a body having a chamber therewithin, body inlet means and body outlet means for respective admission of fluid to and discharge of fluid from the body, the pump chamber having chamber inlet means and chamber outlet means, first passage means for conducting fluid from the body inlet means to the chamber inlet means and second passage means for conducting fluid from the chamber outlet means to the body outlet means, a plurality of intermeshing screw members mounted for rotation within the pump chamber for transporting the comingled material from the chamber inlet means to the chamber outlet means, vapour condensation means between the chamber outlet means and the body outlet means whereby passage of fluid from the chamber outlet means to the body outlet means causes some vaporised fluid to be condensed, said condensed liquid returning to liquid reservoir means within the body for providing liquid to the pump chamber to assist sealing of the pump chamber and the screw members.

The vapour condensation means may be provided by the chamber outlet means lying remote from the body outlet means, whereby an increase in length of the second passage means is achieved relative to the known art. Where the pump chamber has a single central outlet, the chamber outlet means is preferably arranged on the side of the pump chamber remote from the body outlet means.

Alternatively or additionally, the vapour condensation means may comprise baffle means provided in the second passage means for restricting flow of vaporised liquid from the pump, liquid collected by the baffle means returning to the liquid reservoir means.

The second passage means preferably comprise an unrestricted first flow path through which liquid can flow unhindered by the baffle means, and a second flow path in which the baffle means lie. The first flow path may pass below the pump chamber and the second flow path may pass above the pump chamber.

The baffle means may comprise a plurality, preferably a multiplicity, of baffle plates extending into and substantially normal to the flow path. The plates may be curved.

The baffle means may include baffle plates extending upwardly from a wall defining the pump chamber. The baffle plates may include passageways therethrough to allow condensed liquid to pass therethrough and hence to the reservoir means. The baffle means may include baffle plates extending towards the pump chamber from a body wall spaced outwardly from the pump chamber.

The chamber outlet means may be one central outlet and the chamber inlet means may be two inlets, one at each end of the pump chamber. Alternatively, the chamber inlet means may be a central inlet and the chamber outlet means two outlets, one at each end of the pump chamber. One set of screw members is preferably mounted for rotation in the pump chamber on each side of the central outlet or inlet, for providing hydraulic balance to the screw members.

Where the pump has a central inlet, the baffle means may comprise baffle plates partially obstructing the passage means in the region of the body outlet means.

The pitch of the screw members at the outlet end thereof may be smaller than the pitch of the screws at the inlet end thereof to cause compression of gaseous material being transported, in which case clearance is provided between the screws and between the screws and the walls of the chamber to allow sufficient leakage of the material towards the inlet when the material is in the liquid phase, to avoid a liquid lock.

The second passage means may be within a portion of the body formed in one piece, or alternatively the second passage may be in a portion of the body formed in a plurality of pieces and secured together. For example, the body outlet means may be provided by an outlet element secured, for example by bolting, to an outlet from a main body portion. The outlet element may include the vapour condensation means.

By way of-example, four embodiments of a pump according to the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a sectional view of a conventional screw positive displacement pump of constant screw pitch; Figure 2 is a diagrammatic sectional view of a pump similar to that of Figure 1; Figure 3 is a sectional view along the lines A-A in Figure 2; Figure 4 is a sectional side view of a first embodiment of a pump according to the invention; Figure 4a is a sectional side view of a modified pump of Figure 4.

Figure 5 is a sectional side view of a second embodiment of a pump according to the invention; Figure 6 is a sectional view of a third embodiment of a pump according to the invention; Figure 7 is a sectional view along the lines A-A in Figure 6.

Figure 8 is a sectional view along the lines VIII-VIII in Figure 9 of a fourth embodiment of a pump according to the invention, the axis of the pump screw members being vertical; and Figure 9 is a sectional view along the lines IX-IX in Figure 8.

Figure 1 shows a known screw displacement pump 10 having a body 11, and a chamber 12 within the body. The drawing is used here to illustrate typical constructional features of such pumps so that illustration of the embodiments of pumps according to the invention can be simplified.

Within the chamber 12 are mounted two screw shafts 13, 14 arranged to intermesh. The screw shafts 13, 14 are mounted for rotation in bearings 15, 16 and timing gears 17 on the screw shafts intermesh to ensure that the screw shafts 13, 14 rotate at the same speed in opposite directions.

Each screw shaft 13, 14 has two threaded portions one on each side of a central threadless portion, the two threaded portions of the screw shaft 14 having reference numerals 22 and 23 and the two threaded portions of the screw shaft 13 having reference numerals 20 and 21. The two threaded portions of each screw shaft are of opposite hand, and the meshing threads of the screw shafts 13 and 14 are of opposite hand.

Inlet to the chamber 12 is at each end thereof from an inlet plenum chamber 30, the screw shafts 13, 14 drawing fluid to the centre of the chamber where fluid is discharged through discharge opening 31.

Figure 2 is a sectional view illustrating flow paths of fluid through the pump of Figure 1, Figure 2 being a diagrammatic representation. As shown in Figure 2, comingled material enters through an inlet 120, the flow dividing as illustrated by curved arrows in Figure 2 to arrive at outside, inlet ends of two pump chambers 121, 122. The comingled material is pumped by intermeshing screws within the chambers 121 and 122 and leaves through liner discharge port 123 (Figure 3). As can be seen in Figure 3, the conventional route for material leaving the liner discharge port is to travel straight to outlet opening 124 from body 125 which surrounds the pump chamber.In this way, if a high gas fraction is present in the comingled material, there is no restriction on oil droplets or vapour leaving the pump and this can cause the pump to run dry of oil, thereby causing there to be insufficient oil to act as a seal between the screws and the pump chamber wall.

Figure 4 shows in sectional side view (similar to the view of Figure 3) a first embodiment of a pump according to the invention.

In the Figure 4 embodiment, comingled material enters pump body 130 through an inlet 131 and travels in a way similar to that of the embodiment of Figures 2 and 3 to outside inlet ends of pump chambers both containing pairs of intermeshing screws. However, the discharge configuration is quite different from the conventional one shown in Figure 3. There is a central liner discharge port 132 as before but this is arranged on the side of the pump chambers remote from body outlet 133, thereby increasing the path length of material leaving through the liner discharge port 132. On an inside body wall 134 are provided two downwardly extending baffle plates 135, 136 designed to catch droplets of oil (or the liquid being pumped) and return them to a reservoir 137 beneath the pumping chambers.It will be noted that the space around the pumping chambers has been increased relative to the conventional pump of Figures 1 to 3. Material in the gas and vapour phase tends to follow the curved arrow in Figure 4 and passes over the pumping chambers where it encounters further baffles in the form of baffle plates 138, 139, 140 and 141. Droplets of oil or condensed vapour fall back to the reservoir 137, base holes 145 being provided in the baffle plates 138, 139, 140 and 141 to allow passage of liquid, assisted by gas flow over the chambers. Circumferential baffle plate 144 guides retained liquid towards the reservoir 137. Finally, two futher baffle plates 142 and 143 extend downwardly from the wall of the outlet 133 to collect further droplets of oil (or other liquid) for return to the reservoir 137.

Where liquid is being pumped, it will emerge from the liner discharge port 132 and flow beneath the pumping chambers and leave predominently via the reservoir 137 through an unobstructed passageway. Thus, while high liquid fractions have an unimpeded flow to the outlet port 133, higher gas fractions can be handled than with the embodiment of Figures 2 and 3 since more liquid is retained in the reservoir 137 in the Figure 4 embodiment.

Figure 4a shows the pump of Figure 4 modified to include a body outlet element 200 bolted to an outlet from a main body portion of the pump. The body outlet element 200 has a baffle 201 and a reservoir well 202 to increase the liquid reservoir of the body. .It will be appreciated that the body element 200 could be provided with all the vapour condensation means of a particular pump, thus allowing an existing pump to be improved by adding a suitable outlet element to produce a pump according to the invention. It will be appreciated that the body outlet element 200 may be formed integrally with the main portion, for example by casting.

Figure 5 shows a second embodiment of a pump according to the invention in sectional view similar to the views of Figures 3 and 4. Inlet arrangements to a pump chamber defined by walls 150 are similar to those of Figure 4 but liner discharge port 151 is slightly different in profile from that of the Figure 4 embodiment. Nevertheless, as with the Figure 4 embodiment, the liner discharge port 151 is at a side of the pump chamber remote from outlet 152 from body 153. In the Figure 5 embodiment, baffle means in the form of a baffle rib 154 and baffle plates 155, 156 and 157 extend downwardly from an inside wall of the body 153 to collect liquid droplets or vapour for return to a reservoir 158 to maintain a necessary fluid level within the pump chamber.

A third embodiment of a pump according to the invention is shown in Figures 6 and 7 in which flow through the pump chambers is reversed such that there is a central inlet 160 and pump chambers 161 and 162 exit outwardly as indicated by curved arrows in Figure 6.

Material merges again as outlet port 163 is approached, at which stage upper flows encounter baffle plates arranged in two sets of three, either side of the outlet port 163.

The baffle plates are arranged symmetrically about the pump centre line and consist of an inner pair 164, a central pair 165 of lesser depth and an outer pair 166 shallower still. Additionally, a pair of baffle plates 167, 168 lie in the outlet port 163, all the baffle plates contributing to retain liquid within a reservoir 170.

In the embodiments of Figures 4 to 7, the screw axes have been arranged horizontally, with the reservoir lying beneath the pump chambers in each case. A fourth embodiment of a pump according to the invention is shown in Figures 8 and 9, and has screw axes arranged vertically.

In the embodiment of Figures 8 and 9, a body 180 has an inlet for comingled material 181. Within the body 180 is a pump chamber 182 in which are mounted two pairs of intermeshing screws (not shown) which may be of fixed pitch, or variable pitch to generate compression.

Coming led material enters the pump chamber at pump chamber inlets 183, 184 respectively above and below the chamber 182. As can be seen clearly in Figure 9, the two pairs of screws are arranged either side of a central chamber outlet 185 to provide hydraulic balance for the pump.

The outlet 185 is located on the side of the pump chamber 182 remote from an outlet 186 for material from the body. Comingled material flowing from the body inlet 181 to the chamber inlets 183, 184 is separated from comingled material flowing from the chamber outlet 185 to the body outlet 186 by a wall 187, providing a generally annular passage 188 between the chamber outlet 185 and the body outlet 187.

Comingled material leaves the chamber 182 in the direction shown by arrows in Figure 8 and encounters baffle plates 189 in an upper part of the passage 188.

These plates 189 assist in condensing liquid, which then drops to the bottom of the passage 188, to assist in providing a liquid reservoir in which the screw members sit.

These embodiments have an advantage that liqud retention is achieved by means within the pump casing and that liquid flow is unhindered. Liquid burn-off is made up naturally by the flow stream and the arrangement assists in keeping temperature differentials to acceptable limits.

It will be appreciated that the foregoing description is by way of example only and that modifications and alterations may be made within the scope of the invention. For example, numbers and profiles of baffle plates may be altered to suit particular requirements, and baffle plates may be omitted completely where adequate condensation is achieved by virtue of the fluid path length achieved by locating the chamber outlet remote from the body outlet.

Claims

1. A screw positive displacement pump for pumping comingled material, the pump comprising a body having a chamber therewithin, body inlet means and body outlet means for respective admission of fluid to and discharge of fluid from the body, the pump chamber having chamber inlet means and chamber outlet means, first passage means for conducting fluid from the body inlet means to the chamber inlet means and second passage means for conducting fluid from the chamber outlet means to the body outlet means, a plurality of intermeshing screw members mounted for rotation within the pump chamber for transporting the comingled material from the chamber inlet means to the chamber outlet means, vapour condensation means between the chamber outlet means and the body outlet means whereby passage of fluid from the chamber outlet means to the body outlet means causes some vaporised fluid to be condensed, said condensed liquid returning to liquid reservoir means within the body for providing liquid to the pump chamber to assist sealing of the pump chamber and the screw members.

2. A screw positive displacement pump as claimed in Claim 1 wherein the vapour condensation means are provided by the chamber outlet means lying remote from the body outlet means.

3. A screw positive displacement pump as claimed in Claim 2 wherein the pump chamber has a single central outlet arranged on the side of the pump chamber remote from the body outlet means.

4. A screw positive displacement pump as claimed in any one of Claims 1 to 4 comprising baffle means in the second passage means for restricting flow of vaporised liquid from the pump, liquid collected by the baffle means returning to the liquid reservoir means.

5. A screw positive displacement pump as claimed in Claim 4 wherein the second passage means comprise an unrestricted first flow path through which liquid can flow unhindered by the baffle means and a second flow path in which the baffle means lie.

6. A screw positive displacement pump as claimed in Claim 4 or Claim 5 wherein the baffle means comprise a plurality of baffle plates extending into and substantially normal to the flow path.

7. A screw positive displacement pump as claimed in Claim 6 comprising a multiplicity of baffle plates.

8. A screw positive displacement pump as claimed in Claim 6 or Claim 7 wherein at least some of the plates are curved.

9. A screw positive displacement pump as claimed in any of Claims 4 to 8 wherein the baffle means include baffle plates extending upwardly from a wall defining the pump chamber.

10. A screw positive displacement pump as claimed in Claim 9 wherein the baffle means include passageways therethrough to allow condensed liquid to pass therethrough and hence to the reservoir means.

11. A screw positive displacement pump as claimed in any one of Claims 4 to 10 wherein the baffle means include baffle plates extending towards the pump chamber body from the body wall spaced outwardly from the pump chamber.

12. A screw positive displacement pump as claimed in any one of Claims X, 2 and 4 to 11 wherein the chamber outlet means comprises one central outlet and the chamber inlet means comprises two inlets, one at each end of the pump chamber.

13. A screw positive displacement pump as claimed in any one of Claims 1 to 11 wherein the chamber inlet means comprises a central inlet and the chamber outlet means comprise two outlets, one at each end of the pump chamber.

14. A screw positive displacement pump as claimed in Claim 13 as dependent on any one of Claims 4 to 11 whereas the baffle means comprise baffle plates partially obstructing the passage means in the region of the body outlet means.

15. A screw positive displacement pump as claimed in any preceding claim wherein the pitch of the screw members at the outlet end thereof is smaller than the pitch of the screw members at the inlet end thereof to cause compression of gaseous material being transported, clearance being provided between the screws and between the screws and the walls of the chamber to allow sufficient leakage of the material towards the inlet when the material is in the liquid phase, to avoid a liquid lock.

16. A pump as claimed in any one of Claims 1 to 15 wherein the second passage means is within a portion of the body formed in a plurality of pieces and secured together.

17. A pump as claimed in Claim 16 wherein the body outlet means is provided by an outlet element secured to an outlet from a main body portion.

18. A pump as claimed in Claim 17 wherein the outlet element includes the vapour condensation means.

19. A screw positive displacement pump substantially as hereinbefore described with reference to and as shown in Figure 4 or in Figure 5 or in Figures 6 and 7 or in Figures 8 and 9 of the accompanying drawings.