Degassing Apparatus

Abstract

An apparatus for degassing fluids, particularly drilling muds, comprising a vessel having an inlet and an outlet for the intake and discharge of the fluid to be treated, a centrifugal pump connected to the vessel for circulating the fluid through the vessel and means for removing gas from the region of the impeller means in the centrifugal pump. The invention also includes a centrifugal pump designed for handling gas laden fluids, the pump having a means for removing gas from the region of the pump impeller. The invention further includes a centrifugal pump for handling corrosive and/or abrasive fluids wherein said fluids are prevented from contacting the pump seal by means of a gas pressurized compartment adjacent the seal.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a system for degassing fluids and more particularly to a system for degassing drilling muds, said system including a novel centrifugal pump for circulating the fluid or mud therethrough.

In numerous industrial operations there exist situations in which it is desirable to substantially remove gas from a fluid being processed. A prime example of this is in the oil well drilling industry where the drilling mud used frequently becomes contaminated, in the well, with natural gas or air. Since it is uneconomical to continuously supply a source of new mud, it is necessary that the mud be recycled. However, the presence of the natural gas or air in the drilling mud decreases its weight and viscosity, thus markedly diminishing its effectiveness in preventing blow outs. Accordingly, it becomes necessary to degasify the drilling mud prior to recycling it to the well.

Numerous prior art systems have been proposed as systems for degassing drilling muds. Characteristically these systems utilize a vacuum tank having some sort of baffle structure over which the mud flows in a thin film, the vacuum in the vessel serving to allow the gas to escape from the thin film of mud. The released gas is thus vented from the vessel as waste or if economically feasible to a gas recovery system. In mud degassing systems employing the above described baffled-vacuum tank, it is necessary to utilize some form of prime mover to circulate the gas laden mud through the vacuum vessel. Numerous pumping systems have been proposed in this respect as for example the jet-type pumping systems shown in U.S. Pat. Nos. 2,748,884 and 3,241,295 and the mechanical pumping system shown in U.S. Pat. No. 3,226,916. From the point of view of economy, simplicity of operation, and ease of maintenance, a mechanical pumping system such as one employing a centrifugal pump is most desirable. However, prior art systems employing centrifugal pumps have not been completely successful due partially to vapor lock of the pump which of course results in a diminished supply of clean mud to the well. Moreover, prior art vapor-vented centrifugal pumps such as that shown in U.S. Pat. No. 2,815,717 are not suitable for use in mud degassing systems because rapid wearing of the seals due to the abrasiveness of the mud results in frequent and expensive repair.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a system for degassing fluids and more particularly for degassing drilling muds.

It is a further object of the present invention to provide a fluid degassing system which employs a novel centrifugal pump.

Still a further object of the present invention is to provide a fluid degassing system employing a centrifugal pump which is substantially free from vapor lock.

An important object of the present invention is to provide a fluid degassing system for use in degassing drilling muds which system employs a novel centrifugal pump in which the pump seal is kept substantially free from contact with the drilling mud.

Another object of the present invention is to provide an improved centrifugal pump for handling gas laden fluids particularly gas laden drilling muds.

Yet another object of the present invention is to provide a centrifugal pump for handling corrosive and abrasive liquids such as drilling muds in which the pump seal is kept substantially free from contact with the drilling mud.

These and other objects of the present invention will become apparent from the drawings, the description given herein and the appended claims.

In accordance with the above stated objects, the present invention provides a fluid degassing system including a vessel having in inlet and an outlet for the intake and discharge of the fluid being treated and a centrifugal pump connected to the vessel for circulating the fluid therethrough the centrifugal pump including an impeller means and means rotatably mounting the impeller within the pump and a means for removing gas from the region of the impeller to thereby prevent vapor lock. In one form of the system, the pump is provided with a means for providing a gas barrier for preventing the fluid being handled by the pump from contacting the pump seal through which the pump shaft extends.

In one embodiment of the present invention, the degassing vessel is operated under vacuum and the centrifugal pump is connected to the outlet of the vessel while in another embodiment, the centrifugal pump is connected to the inlet of the degassing vessel which is at substantially atmospheric pressure and the fluid to be degassed is forced under pressure into the vessel.

The above objects are further accomplished by a centrifugal pump for handling gas laden fluids, the pump having a housing with an inlet and an outlet for the intake and discharge respectively of the fluids, an impeller means, means for rotatably mounting the impeller means in the housing and means for venting gas from the region of the impeller means. The novel centrifugal pump may further include, when a pump seal is employed, a means for preventing the fluid being handled by the pump from contacting the seal. In a preferred embodiment of the centrifugal pump the fluid is prevented from contacting the seal means through the use of a gas filled compartment adjacent the seal, the gas filled compartment serving to form a gas barrier between the fluid and the seal. The novel gas barrier principle of preventing the fluid from contacting the seal permits the centrifugal pump to be used for handling corrosive and/or abrasive materials which would otherwise cause excessive wear and damage to the seal.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic elevation, partly in section, of the novel fluid treating system of the present invention.

FIG. 2 is an elevational view, partly in section, showing a modified centrifugal pumping means for use with the system shown in FIG. 1.

FIG. 3 is a view similar to FIG. 2 of yet another modification of a centrifugal pumping means for use with the fluid treating system shown in FIG. 1.

FIG. 4 is a view taken along the line 4--4 of FIG. 3.

FIG. 5 is a view similar to FIG. 2 of another embodiment of a centrifugal pumping means for use with the fluid treating system shown in FIG. 1.

FIG. 6 is a slightly modified variation of the centrifugal pumping means shown in FIG. 1.

FIG. 7 is a variation, shown in elevation, of the novel fluid treating system of the present invention.

FIG. 8 is a view, reduced in size, taken along the line 8--8 of FIG. 7.

FIG. 9 is an elevational view, in section, of another embodiment of the novel fluid treating system of the present invention.

FIG. 10 is a top view, partly broken away, of the system shown in FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the description that follows, the present invention will be described with reference to the degassing of drilling muds. It is to be understood however, that the system can be used for degassing other fluids containing entrained or dissolved gas.

Referring then to FIG. 1, there is shown a conduit 10 leading from an oil well (not shown) which feeds a return mud tank 11 with used drilling mud 12 contaminated with drill cuttings, other solid materials and gas. Return mud tank 11 communicates with clean mud tank 13 by means of a restricted conduit 14 thereby assuring that a constant supply of mud is always available to be fed into the well. Mud to the well is supplied via pump 15 and conduit 16 which extends down into clean mud tank 13 to thereby draw in clean mud 17 contained therein. Since the function of the drilling mud in oil well drilling operations is well known, it is not necessary for purposes of describing the invention that the process be described. It is however noteworthy to point out that one of the prime functions of drilling mud is to provide a fluid head in the well which will resist the discharge from the well of fluid from a high pressure zone resulting in a blow out. Because of this latter function, it is important that the returned, contaminated mud 12 be freed of gas which may be dissolved or entrained with the mud since the presence of such gas in excess quantities reduces the specific gravity of the mud thus lightening the fluid head in the well annulus. The apparatus herein described and claimed is designed to effectively degas and otherwise treat the returned drilling mud 12 thereby making it suitable for continuous recycle in the drilling operation.

Leading from returned mud tank 11 is a pipe or conduit 19 which opens into a second conduit 19a which in turn opens into the top of a vacuum treating vessel 20. The open end of conduit 19a is provided with a threaded cap 19b to allow access into conduit 19a if necessary. It should be noted that while in the embodiment shown mud is delivered through the top of vessel 20, the system can be designed such that it is delivered into vessel 20 from the side closely adjacent the top.

While vessel 20 can assume any shape, in the embodiment shown herein, it has a generally cylindrical sidewall 21, flat top wall 22 and downward sloping bottom walls 23 and 24 somewhat axially displaced from one another so as to form an opening 25 near the bottom of vessel 20. Vessel 20 has a base portion consisting of a lower extension 21a of sidewall 21, flat bottom portion 26 and a lower vertical side section 27 which allows vessel 20 to rest upon skid 28, vessel 20 being secured thereto by means of an angle iron bracket 29 which extends around the lower part of the vessel. Skid 28 rests upon supports 30 and 31 so as to allow the entire treating system to be moved adjacent mud tanks located above the surface of the ground.

Mounted within vessel 20 closely adjacent the top thereof is a baffle 32 consisting of a cylindrical upper section 33 adjoined to an inverted truncated conical lower section 34, truncated conical section 34 containing an opening 35 at its inverted apex. Also contained within vessel 20 is a float 36 secured to upper and lower spindles 37 and 38 respectively. Lower spindle 38 is slidably mounted in lower sleeve 39 secured to the bottom wall 24 of vessel 20, a stop 39a secured to spindle 38 serving to limit the downward movement of float 36 should the fluid level drop too low. Spindle 37 extends through flexible diaphragm 40 which is secured at its periphery between an inwardly extending annular shoulder 19c and the inner end of cap 19b. Diaphragm 40 is secured to spindle 37 by being clamped between an annular shoulder 37b and a washer 40a and retaining nut 40b on the threaded end of spindle 37. A passageway 37a in spindle 37 leads from the space above diaphragm 40 to vessel 20 below valve member 41 thus ensuring equal pressure above diaphragm 40 and below valve member 4. Affixed to upper spindle 37 by means of a collar 41a is a disc shaped member 41 which has an area substantially equal to or somewhat greater than the cross-sectional area of conduit 19a at the point where it opens into vessel 20. Disc shaped member 41 serves the function of a control valve such that if float 36 is caused to move upwardly as the level of fluid in vessel 20 rises, member 41 will effectively reduce the size of the opening from conduit 19a into vessel 20 as much as necessary to regulate the flow of fluid into vessel 20.

To maintain sub-atmospheric pressure within vessel 20, a vacuum pump 42 is connected via a conduit 43 which opens into vessel 20 at a point always above the liquid level. To control the level of vacuum within the vessel 20, float 44 is connected through a linkage 44a to a check valve 45. Check valve 45 is located in conduit 43 between vacuum pump 42 and the end of conduit 43 which opens into vessel 20. Upward movement of float 44 closes valve 45 while downward movement opens valve 45.

Connected to the outlet 25 of vessel 20 is a centrifugal pump shown generally at 46. In the embodiment shown in FIG. 1, the pump housing comprises a generally cylindrical side wall 47, a flat top wall 55 and an impeller housing 51 which faces impeller 50. Shaft 48 extends through top wall 55 and is aligned generally concentrically with side wall 47. The outlet 49 of pump 46 leads from the impeller housing 51. On the lower end of shaft 48 is mounted impeller 50, impeller 50 being secured to shaft 48 by hub 51a. Shaft 48 is rotatably mounted at its upper end through a seal 52, seal 52 acting as a barrier against fluids entering the bearing section 52a. Shaft 48 is driven by a motor (not shown) which connects by means of a belt 53 to a pulley 54 secured to shaft 48.

Spaced axially from the upper wall 55 and toward impeller 50 is a baffle 56 which has an opening 57 through which shaft 48 extends. Opening 57 has a cross-sectional area larger than the cross-sectional area of shaft 48 such that shaft 48 does not fit snugly therein. Baffle 56 along with the upper portion of side wall 47 and top wall 55 serve to form a compartment 58 adjacent seal member 52. A conduit 59 having one end which opens into vessel 20 is in open communication with the interior of pump 46 below partition 56. Conduit 59 can open into vessel 20 either above or below the liquid level therein. A baffle 59a is mounted in vessel 20 above the end of conduit 59 and forms a pocket 59b adjacent the open end of conduit 59 in vessel 20. This arrangement allows gas escaping through conduit 59 to vent into vessel 20 more easily. Moreover, when little or no gas is venting through conduit 59, the pocket 59b maintains a pressure sufficient to prevent fluid from flowing up into the pocket and down conduit 59. The result is that the flow through opening 25 into pump 46 is very uniform.

As can be seen from the above description, pump 46 is vertically mounted, i.e., cylindrical side wall 47 and concentrically disposed shaft 48 are aligned such that their long axes are substantially vertical, the drive mechanism of pump 46 being attached to the uppermost end of shaft 48 and the pumping mechanism i.e., impeller 50, being mounted at the lowermost end of shaft 48. It is this vertical, axial displacement of the pump drive mechanism from the pumping mechanism per se which permits the unique operation of the system shown in FIG. 1 and hereinafter described.

In operation, the system described above and shown in FIG. 1 works as follows. Contaminated mud 12 from the well flows through line 10 into tank 11 from whence it is drawn up through a conduit 19 by means of pump 46 into vessel 20. As the mud enters vessel 20, it impinges upon disc shaped member 41 and because of its velocity upon entering vessel 20 and the restricted space between member 41 and the opening of conduit 19a into vessel 20, it sprays radially outward in fine droplets towards the cylindrical wall 33 of baffle 32, where it flows in a relatively thin film downwardly falling through outlet 35 in baffle 32 onto float 36 where it again flows in a thin film and finally into the lower portion of vessel 20. Since vessel 20 is under sub-atmospheric pressure, any gas dissolved or entrained in the mud is released to the space above the liquid in vessel 20 and is pumped via conduit 43 to atmosphere or if economical to a gas collecting system.

To ensure that the mud level in vessel 20 does not exceed a volume which can be effectively handled by pump 46, the level controller consisting of float 36 and valve member 41 is employed. When the level of mud in vessel 20 becomes too great, float 36 will move upwardly causing disc shaped valve member 41 to partially seal off conduit 19a, thus regulating the flow of mud into vessel 20. Diaphragm 40 aids in eliminating pressure surges in conduit 19 and accordingly prevents pressure surging acting against valve member 41.

In order to control the sub-atmospheric pressure existing in vessel 20, float 44, linkage 44a, and valve 45 in conjunction with vacuum pump 42 is employed. When the level of mud in vessel 20 rises to a certain level, float 44, via linkage 44a will act to close check valve 45 thus cutting off the suction from pump 42. This of course will prevent excessive reduction of pressure in the upper part of vessel 20 above the liquid level and will in effect maintain an adequate pressure in vessel 20 to permit pump 46 to more easily draw mud from the bottom vessel 20.

The mud which has been degassified and which is in the bottom portion of vessel 20 is pulled into pump 46 via inlet 60, being ejected by impeller 50 from pump 46 through outlet 49 into clean mud tank 13. The unique construction of pump 46, i.e., with the seal 52 axially displaced from impeller 50 along shaft 48 results in a generally cylindrical void in the vicinity of shaft 48. The cylindrical void allows any gas which is collecting in the eye of impeller 50 to move upwardly adjacent shaft 48, a part passing through opening 57 in baffle 56 and eventually filling compartment 58, the greater portion entering conduit 59 and passing through conduit 59 into pocket 59b formed by baffle 59a and then into vessel 20 to thereby be removed via conduit 43 and pump 42. Besides the above described functions, the gas pocket collected in baffle 59a prevents direct access of fluid into conduit 59 during the time when there is little or no gas in the pumped fluid. It should be noted that at all times a pocket of gas will be maintained in compartment 58 adjacent to seal 52 thus forming a gas barrier or seal which substantially prevents any fluid from entering the space between shaft 48 and seal 52 causing damage to the latter. At the same time, the unique construction of pump 46 which results in the formation of the cylindrical void around shaft 48 provides a means whereby gas collecting in the eye of the impeller will be allowed to escape thus increasing the efficiency of pump 46. The degassified and cleaned mud 17 contained in tank 13 is then returned to the well via conduit 16 and pump 15.

As will be readily appreciated from the above description, while the pump shown in FIG. 1 has been described as being vertically mounted, i.e., with the long axis of pump shaft 48 and cylindrical side wall 47 in a generally vertical position, it is to be understood that vertical disposition is not necessary. It is only necessary that pump 46 be disposed at some angle to the horizontal such that the seal means is elevated above the impeller means such that gas collecting near the impeller will flow upwardly through the pump housing and be allowed to enter compartment 58 thus forming a gas barrier or seal and preventing any fluid from entering the space between shaft 48 and seal 52 causing damage to the latter. Thus while mechanical convenience and design dictates generally vertical disposition of shaft 48, such is not necessary to enable pump 46 to operate in the fashion described.

Turning now to FIG. 2, there is shown a modification of the pump system shown in FIG. 1. In this embodiment, the centrifugal pump shown generally as 61 comprises a bearing casing 62 through which extends the pump shaft 63 rotatably mounted by means of bearings 64 and 65. Shaft 63 is driven by suitable motor (not shown). Shaft 63 extends into the impeller housing 66 in which is contained impeller 67 secured to the end of shaft 63. Fluid is taken into pump 61 via inlet 68 and forced out of pump 61 through outlet 69 into the return mud tank 13. To prevent gas from accumulating in the eye of impeller 67 thereby reducing the efficiency of pump 61, a conduit 70 extends into pump 61 opening on one end closely adjacent the central region of impeller 67 and opening on the other end into the space in vessel 20 above the liquid level.

In the cases shown in FIGS. 1 and 2, the gas being removed from the region of impellers 50 and 67 respectively, is vented back to the sub-atmospheric region of vessel 20. It is to be understood however, that in those cases and in all other embodiments of the present invention, the gas being removed from the region of the impeller need only be drained to a region of lower pressure than that existing in the pump.

In FIGS. 3 and 4 are shown slightly modified embodiments of the system in FIG. 1. Pump 46 is connected to vessel 20a by horn-shaped inlet 72 formed by substantially flat horizontal bottom 73 which also forms the bottom of vessel 20a, substantially flat, vertical side wall 72b, substantially flat, vertical side wall 72c and a substantially flat horizontal upper wall 72a. Side walls 72b and 72c converge towards one another at the inlet to pump 46 and diverge at the point where they adjoin vessel 20a thus forming the horn-shaped inlet 72. Side wall 47a of pump 46 rather than being substantially cylindrical as the embodiment of FIG. 1 is distorted such that it has a snail shell appearance when viewed in a plane normal to pump shaft 48. Vertical side wall 72b adjoins pump side wall 47a approximately at the point where the distance between shaft 48 and wall 47a is greatest while vertical side wall 72c adjoins pump side wall 47a at approximately the point where the distance between shaft 48 and side wall 47a is minimal. As will be observed the overall effect of such a configuration is to funnel the fluid leaving vessel 20a into pump 46a in such a fashion that it flows tagentially into pumP 46 up against the inner surface of side wall 47a. This tagential funneling action coupled with the action of impeller 50 serves to form a vortex having a void 107 in the immediate vicinity of shaft 48. This vortexing also results in a gas space 108 in open communication with void 107 and the open space above the level of the fluid in vessel 20a. Thus, gas which collects in the eye of impeller 50 moves upwardly through void 107 adjacent shaft 48 passing through annular opening 57 in partition 56 where it is trapped in compartment 58 thus causing a gas barrier and preventing the ingress of fluid through opening 57 into compartment 58 from where it would eventually splash into the space between shaft 48 and seal 52 thus causing wear on the latter. As will also be observed, excessive gas escaping from the eye of impeller 50 and moving up void 107 will collect under upper wall 72a in space 108 and move counter flow to the liquid into the space in vessel 20a above the liquid level. Thus it is seen that the embodiment in FIG. 3 also provides a pumping system wherein the eye of the impeller is continuously freed from any gas which might build up thereby reducing the pump's efficiency. Unlike the case shown in FIG. 1, however, the outlet 49 from pump 46 is not disposed below the level of the liquid in the clean mud tank 13. Rather the degassed mud is transferred via pipe 74 to the clean mud tank. This of course is necessitated by the fact that the casing or lower portion 51 of pump 46 has its upper surface substantially flush with the bottom 73 of vacuum tank 20a.

As will be observed, the embodiments shown in FIGS. 1 and 3 are quite similar in that the pump shaft is generally vertically disposed and there is a compartment displaced axially along the pump shaft from the impeller which serves as a means for maintaining a gas barrier between liquid being handled by the pump and the spacing between the pump shaft and the seal. As we noted above for the pump design shown in FIG. 1, it is not absolutely necessary in the embodiment of FIGS. 3 and 4 that the shaft of the pump be vertically aligned.

Reference is now made to FIG. 5 for yet another embodiment of the present. An S-shaped conduit 74a leads from the bottom portion of vacuum vessel 20b to the intake 76 of pump 75. Pump shaft 77, driven via pulley 77a attached to a motor (not shown), is rotatably mounted in bearings 78 and 79 which are in turn secured by a suitable mounting bracket 80. Impeller 81 is secured to the end of shaft 77 and faces wear plate 82 attached to one end of conduit 74a. A bleed line 83 extends into pump 75 having one open end disposed closely adjacent the central region or eye of impeller 81. Bleed line 83 extends upward out of clean mud tank 13 through a flanged fitting 84 mounted on the side of vessel 20b and then into vessel 20b, the other open end of bleed line 83 being disposed this time in the space above the liquid level in vessel 20b. As before in the other embodiment, bleed line 83 serves the purpose of allowing gas which may accumulate in the eye of impeller 81 to escape to the vacuum of vessel 20b thus maintaining the overall efficiency of pump 75.

Referring now to FIG. 7, there is shown a still further embodiment of the degassing apparatus of the present invention. Vacuum vessel shown generally at 20c mounted on legs 85 and 86 has a generally hemispherical bottom 87 adjoined to a cylindrical side wall 88. For purposes of simplicity, only the lower section of vessel 20c is depicted, it being understood that the inlet and liquid level-controlling systems employed but not shown are substantially the same as those shown in the previous embodiments with the exception of a slightly modified float design hereinafter described. Connected to the lowermost section of vessel 20c and preferably made integral therewith is an impeller housing 89, the interior of housing 89 and the interior of vessel 20c being in open communication via an aperture 20d comprising the outlet of vessel 20c and the inlet of housing 89. Mounted in housing 89 is an impeller, shown at 90, secured to a shaft 91 by a suitable retaining nut 92. Shaft 91 is rotatably mounted in bearings 92 and 93 and extends through the end of bearing casing 94, shaft 91 having affixed to the end extending from casing 94 a pulley 95 driven by a motor (not shown) via belts 96. Bearing casing 94 is removably secured to impeller housing 89 by means of bolts 97.

Impeller 90, which is disposed closely adjacent aperture 20d, comprises vanes 97 affixed to and extending upward from disc 98 and has extending from the bottom side of disc 98 a shroud 99 which forms a cavity 100 partially partitioned by an annular upwardly extending projection 101 from bearing casing 94. The radially innermost portion of cavity 100 forms a seal compartment in which is mounted a seal 102 secured to and rotating with shaft 91, non-rotating seal ring 103 being supported by resilient seal 104, a spring in seal 102 urging seal 102 against ring 103 to effect adequate sealing. Leading from impeller housing 89 is a discharge pipe 105 through which the degassed fluid flows into tank 13.

Secured to the bottom of vessel 20c are a plurality of spiral fins 109. Connected to several of the spiral fins 109, although, if desired, to all of fins 109 are brackets 110 which extend inwardly toward the center of vessel 20c where they are commonly connected to a guide spindle 111 which is slidably mounted in a suitable passageway 112 in the underside of float 113. Float 113 unlike float 36 shown in FIG. 1 has a concave surface 114 on its underside resulting in the formation of a cavity 115 which forms an air pocket under float 113. Leading from cavity or air pocket 115 is a conduit 116, one end of which opens into cavity 115 the other of which opens above the level of fluid in tank 20c. Spiral fins 109 while acting to induce a fluid flow pattern hereinafter described also serve the purpose of acting as a stop to limit the downward movement of float 113 should the level of liquid in vessel 20c drop too low. As explained, the diaphragm and valve system plus the means used to control the vacuum in the system in FIG. 7 is identical with that shown in FIG. 1.

In operation, the system described in FIG. 7 works as follows: fluid in vessel 20c is drawn through opening 20d by impeller 90. Because of the presence of spiral fins 109, the fluid is diverted into a clockwise flow pattern as it leaves vessel 20c. As the fluid enters impeller housing 89, it is immediately thrust radially outward away from the eye of impeller 90. The combination of the clockwise induced flow and the action of impeller 90 results in the formation in vessel 20c of a vortex having a void 106 up through which gas present in the fluid and being disengaged at the impeller 90 escapes and collects in space 115 where it passes via conduit 116 to the air space in vessel 20c. Since the action of impeller 90 in the system shown in FIG. 7 is to move the fluid being handled radially outward away from the eye, an annular lower pressure region is formed on the underside of disc 98 adjacent shaft 91. Any gas which enters impeller housing 89 will migrate to this lower pressure region on the underside of plate 98 and will in fact gather in cavity 100 thus forming a gas barrier and effectively preventing any fluid within impeller housing 89 from contacting the seal comprised of components 102 and 103. Although impeller 90 is seen as having a shroud 99 extending from the underside of plate 98, the presence of such is not necessary in order to ensure that any gas entering impeller housing 89 will collect on the underside of plate 98 and be trapped in cavity 100. Such a shroud however aids in maintaining gas which has collected under impeller plate 98 in cavity 100. In effect, the operation of the system is similar to a centrifuge where the heavier materials, i.e., the degassed liquid, is thrown radially outward by the impeller whereas the lighter material, i.e., the gas, migrates to the central region thus providing the gas barrier necessary to prevent contact of the seal means with the fluid being handled by the system.

Reference is now made to FIG. 9 and 10 for an embodiment of the present invention in which the degassing vessel is not operated under sub-atmospheric pressure conditions. The degassing vessel, shown generally at 120, comprises a cylindrical upper section 121 and an inverted, truncated conical lower section 122. A conduit 123 leads from the inverted apex of conical section 122 and has an opening 124 through which degassed mud discharges into clean mud tank 125. A second conduit 126 extends up through the central portion of vessel 120 forming inlet 127 to vessel 120. A vent pipe 128 leads from the interior of vessel 120 through flat top wall 129 thus providing substantially ambient pressure operation of vessel 120. A removable hatch 130 secured to wall 129 provides access to the interior of vessel 120, hatch 130 being secured by a threaded connection, bolting or some other such means of removably fastening it to wall 129. Affixed to the underside of hatch 130 and extending into vessel 120 is a downwardly projecting member 131 having a longitudinally extending slideway 132 which opens into vessel 120. Slidably positioned in slideway 132 is a spindle 133 which on one end is secured to disc shaped plate 134. Disc shaped plate 134 is also secured to one end of a coil spring 135, the other end of which is attached to the underside of hatch 130, spring 135 being concentrically disposed about member 131, slideway 132 and spindle 133. As will be seen, removal of hatch 130 results in removal of the assemblege consisting of spring 135, disc 134 and member 131.

The inlet 127 to vessel 120 is closely adjacent the bottom side of disc 134 such that fluid being forced into vessel 120 impinges on the underside of disc 134 and because of the restricted nature of the opening between the end of conduit 126 and disc 134, is sprayed out radially from opening 127 in fine droplets whence it impinges on walls 121 and 122 and then flows in a thin film to the bottom of vessel 120 eventually passing out through outlet 124. Since disc 134 is resiliently biased by coil spring 135, it serves somewhat as a flow regulator to the extent that if the flow through conduit 126 becomes large, disc 134 will be moved upwardly against the biasing of spring 135 thus allowing a greater flow of fluid into vessel 120 while still ensuring that the fluid entering vessel 120 will flow radially outwardly in fine droplets in the manner herein before described. It should also be noted that spring biased disc 134 is not necessary for operation of the system shown in FIG. 9. Indeed, the apparatus shown in FIG. 9 can be somewhat simplified by moving the inlet 127 to vessel 120 closer to the top wall of vessel 120 and fabricating top wall 120 of relatively thin sheet metal which has some degree of flexibility and therefore a built in biasing characteristic.

Extending from the cylindrical side wall 121 of vessel 120 is a bracket 136 secured to an I-beam 137. Extending from I-beam 137 are bearing mounting brackets 138 and 139. Secured to the lower portion of I-beam 137 is a centrifugal pump shown generally at 140 comprised of an open ended, cylindrical, upper wall section 141, a truncated, conical, intermediate wall section 142 and a cylindrical lower wall section 143. Cylindrical lower wall section 143, which forms a housing for the pump impeller 154, has extending tangentially therefrom pump outlet 144, pump outlet 144 being in open communication with conduit 126. Extending radially outward from the lowermost edges of conical wall section 142 is an annular flange 145, the outside diameter of annular flange 145 being approximately the same as the outside diameter of cylindrical lower wall section 143. An impeller wear plate 146 having a generally centrally disposed aperture 147 is secured at its outer edges to the uppermost edge of wall section 143. Extending vertically upward from and attached to the top surface of wear plate 146 are a series of radially disposed spiral vanes 148, vanes 148 being connected at their upper edges to the underside of annular flange 145. It will thus be observed that wear plate 146 serves to divide pump 140 into an upper chamber 149 and a lower chamber 150, upper and lower chambers 149 and 150 respectively being in open communication via aperture 147. A circumferentially extending inlet 151 is formed between the underside of annular flange 145 and the upper surface of wear plate 146, the only impediment to flow of fluid through inlet 151 being the spiral vanes 148 disposed therein.

A shaft 152 rotatably mounted in upper and lower bearings (not shown) held in upper and lower bearing brackets 138 and 139 respectively extends substantially vertically down into pump 140, passing through aperture 147 in wear plate 146 and terminating in lower chamber 150. Secured to the end of shaft 152 in chamber 150 by means of a hub 153 is impeller 154 having upwardly projecting vanes 155. Attached to the uppermost end of shaft 152 is a drive pulley 156 which is driven by means of belt 157, motor pulley 158, shaft 159 and motor 160. Motor 160 is secured to motor mounting bracket 161 suitably attached to the mounting assembly comprised of members 136 and 137. Pump 140 is disposed in return mud tank 161 such that, when the system is operating, the intake 151 will be submerged below the level of mud in tank 161. A right angle conduit 162 connects clean mud tank 125 and return mud tank 161 and serves to ensure that return mud tank 161 will always have a supply of fluid. When the level of mud in clean mud tank 125 reaches a certain level, it will begin to flow back into return mud tank 161 thus ensuring that a supply of mud will always be available for pump 140 to circulate.

In operation, the used mud is drawn into the circumferential inlet 151 of pump 140 where vanes 148 cause a clockwise flow to be imparted to the mud. The momentum of the spiraling fluid is conserved as it is drawn into the lower chamber 150 by impeller 154 which acts to thrust the mud radially outwardly, the mud eventually passing through tangential outlet 144, conduit 126 and into degassing vessel 120. The combined action of the spiral vanes 148 and impeller 154 serve to produce a vortex having a void 163 disposed generally concentrically about shaft 152 and up through which gas being disengaged at impeller 154 is vented to atmosphere through the open end 164 of pump 140. The fluid being pumped through conduit 126 and discharged into vessel 120 impinges on the underside of disc 134 as it enters vessel 120. Due to its velocity upon entering vessel 120, and because of the fact that the discharge area into vessel 120 is relatively confined, the fluid is forced to spray radially outwardly towards the walls of vessel 120 and subsequently flows in a relatively thin film downwardly over the inside of vessel 120. Because of the large surface area exposed, any gas entrained or dissolved in the mud is allowed to escape therefrom and is vented to atmosphere through vent pipe 128. Thus, the mud flowing out of vessel 120 and into clean mud tank 125 is essentially free of any dissolved or entrained gas and may then be returned to the well. As in the other embodiments shown, the system shown in FIG. 9 and 10 provides a degassing system wherein the centrifugal pump employed to circulate the fluid through the degassing vessel contains a means whereby gas being disengaged from the fluid in the region of the impeller can be vented.

As can be seen from the desciptions given above of the various embodiments of the present invention, the degassing systems all are provided with means whereby gas accumulation occurring in the region of the pump impeller can be reduced. While in all cases shown, gas is removed from the eye or central region of the impeller, it is to be understood that it may be desirable to provide a gas vent radially outward from the eye of the impeller, i.e., near the ends of the vanes such that any gas accumulating in the vanes will be dispelled. This could be accomplished, for example, by providing a vent in the top plate of impeller housing 51 (FIG. 1) and running a conduit from the vent back through the pump housing 47, and allowing the end of the conduit to open closely adjacent shaft 48. Gas thus removed from above the vanes of the impeller would move up the cylindrical void counter flow to the liquid around shaft 48 in the manner above described.

It is well known that gas accumulation in centrifugal pumps can cause vapor lock thus reducing the efficiency of the pump. In cases such as oil well drilling where it is absolutely necessary that a source of mud be available at all times to maintain a sufficient head in the well annulus to prevent a well blow out, the pump being used to pass the used mud through the treating system must operate effectively and continuously. In prior art degassing systems employing centrifugal pumps of conventional design, it has been noted that the liquid output is intermittent to the extent that when much gas is present in the liquid, very little liquid is pumped out of the system because of the fact that the gas has no where to escape and accordingly must be discharged by the pump into the clean mud tank. The system of the present invention circumvents this problem because of the fact that the gas is allowed to escape counter flow through the liquid being handled by the pump such that it is not necessary for the pump to discharge such gas through the discharge outlet into the receiving tank. This of course results in a virtually continuous and constant quantity of mud or other such liquid being delivered by the system rather than an intermittent delivery of mud or liquid from the system as is usually the case with the prior art systems.

As explained above, while the system has been described with particular reference to the degassing of drilling muds, the pump embodiments shown in FIGS. 1, 3, and 6 are particularly suitable for handling abrasive and/or corrosive fluids containing virtually no gas. In pumping such materials, a common source of trouble is the wearing of the pump seal due to the seepage of the abrasive or corrosive material between the seal and the pump shaft and the sliding or movable members of the seal. The utilization of the gas barrier in compartment 58 acts as a means to prevent such materials from seeping into the space between the shaft and the seal. Thus in cases where gas free abrasive and/or corrosive materials are being handled, an external source of gas can be supplied. For example, in the embodiment shown in FIG. 6, line 71 could be used as a means to introduce a gas into compartment 58 thereby building up a pressure sufficient to prevent the seepage of the abrasive and/or corrosive material through space 57 into compartment 58. Likewise, such provisions could be carried out with the embodiment shown in FIG. 1 and FIG. 3, simply by providing a means to introduce gas into compartment 58 and pressurizing it sufficiently to prevent any back flow of fluid into compartment 58. Likewise a conduit could be disposed to lead from cavity 100 (FIG. 7) to atmosphere whereby air would be drawn in forming the gas barrier.

Claims

I claim:

1. In a system for degassing fluids, the combination which comprises:

a degassing vessel having an inlet and an outlet,

centrifugal pump means connected to said vessel for removing fluid from said vessel, said pump means including an impeller housing having an inlet and an outlet, an impeller means and means for mounting said impeller means in said impeller housing for rotation about a substantially vertical axis.

chamber defining means defining a chamber having an inlet and an outlet, said chamber being disposed adjacent said impeller housing, said inlet to said impeller housing being in open communication with said outlet of said chamber, said impeller means serving to induce vortexing of said fluid in said chamber whereby at least a portion of the gas accumulating in the central region of said impeller means is vented through the central portion of the vortex substantially counterflow to the direction of feed of fluid to said impeller means.

2. The system of claim 1 including means for maintaining sub-atmospheric pressure within said degassing vessel.

3. The system of claim 1 wherein said means for rotatably mounting said impeller means includes a rotatable shaft having said impeller means mounted thereon and seal means surrounding said shaft and there are means for preventing fluid being handled by said pump means from contacting said seal means.

4. The system of claim 1 including means for controlling the flow of fluid into said vessel.

5. The system of claim 4 wherein said means for controlling the flow of fluid into said vessel includes valve means in said inlet of said vessel.

6. The system of claim 2 including means for controlling the degree of vacuum within said vessel in accordance with the fluid level within said vessel.

7. The system of claim 6 including means responsive to the level of fluid in said vessel for controlling said valve means.

8. The system of claim 7 wherein said means for controlling said valve means includes a float operatively connected to said valve means.

9. The system of claim 8 including means operatively connected to said valve means for reducing pressure surging in the inlet of said vessel.

10. The system of claim 2 including means for conducting gas vented from the region of said impeller means to said vessel.

11. The system of claim 3 wherein said means for preventing said fluid from contacting said seal means comprises means for forming a gas barrier adjacent said seal means.

12. The system of claim 11 wherein said means for forming a gas barrier adjacent said seal means is in open communication with said chamber whereby at least a portion of the gas being vented from said impeller means forms said gas barrier.

13. The system of claim 2 wherein said means for rotatably mounting said impeller means includes a rotatable shaft having said impeller means mounted thereon and seal means surrounding said shaft and there are means for preventing fluid being handled by said pump means from contacting said seal means.

14. The system of claim 13 wherein said seal means is axially displaced along said shaft and substantially vertically above said impeller means, said means for preventing fluid from contacting said seal means includes means forming a compartment adjacent said seal means, said compartment being in open communication with said chamber whereby at least a portion of said gas being vented from said impeller means through said chamber is retained in said compartment to thereby form a gas barrier against said fluid contacting said seal means.

15. The system of claim 13 wherein said chamber is formed within said vessel and is disposed substantially vertically above said impeller housing, said impeller housing having an axial inlet and a radial outlet for the intake and discharge respectively of said fluid, said inlet of said impeller housing and said oultlet of said chamber being closely adjacent one another, said outlet means being displaced axially along said shaft below said impeller means, and said means for preventing fluid from contacting said seal means comprises means forming a compartment adjacent said seal means, said compartment having a downwardly facing opening, said impeller means being mounted in said impeller housing closely adjacent the inlet of said impeller housing such that fluid being removed from said chamber is substantially simultaneously thrust radially outwardly away from the central region of said impeller means whereby at least a portion of the gas present in said fluid within said impeller housing migrates to the central region of said impeller means and collects in said compartment to thereby form a gas barrier against said fluid contacting said seal means.

16. In a system for degassing fluid, the combination which comprises:

a degassing vessel having an inlet and an outlet,

centrifugal pump means connected to said vessel for introducing fluid into said vessel, said pump means including an impeller housing having an inlet and outlet, an impeller means and means for mounting said impeller means in said impeller housing for rotation about a substantially vertical axis,

chamber defining means defining a chamber having an inlet and an outlet, said chamber being disposed adjacent said impeller housing, said inlet to said impeller housing being in open communication with said outlet of said chamber, said impeller means serving to induce vortexing of said fluid in said chamber whereby at least a portion of the gas accumulating in the central region of said impeller means is vented through the central portion of the vortex substantially counterflow to the direction of feed of fluid to said impeller means.

17. The system of claim 16 wherein said chamber inlet extends substantially circumferentially around said chamber defining means.

18. The system of claim 17 wherein there are vertically disposed spiral vanes disposed in said chamber, said spiral vanes serving to impart spiral flow to said fluid being drawn into said chamber.