Patent GB-1408054-A (GB)
Title: Apparatus for degassing fluids and centrifugal pumps for handling gas-laden fluids
IPC: E21B21/06
Filed: 1972-09-21
Abstract: 1408054 Degassing; centrifugal separation SMITH INTERNATIONAL INC 21 Sept 1972 [27 Sept 1971] 43844/72 Headings B1M and B2P [Also in Division F1] Apparatus for degassing fluids comprises a degassing vessel and a centrifugal pump for pumping fluid through the vessel; the pump comprising an impeller rotatably mounted in a housing having an inlet and an outlet; a chamber having an inlet and an outlet, the outlet of the chamber being also the inlet to the housing; the impeller being arranged in such a way that rotation thereof induces a. vortex in the fluid in the chamber at the eye of which vortex gas accumulates, and means are provided allowing at least a portion of the accumulating gas to be vented through the eye of the vortex in a direction contrary to the general flow of fluid in the chambers. In the embodiment shown in Fig. 1, drilling mud from an oil well, contaminated with drill cuttings and other solids and gas, is returned via a pipe 10 to a return mud tank 11 which communicates with a clean mud tank 13 via a restricted pipe 14. Mud is transferred from tank 11 to tank 13 by a centrifugal pump 46 which is connected to tank 11 via a conduit 19 and a degassing vessel 20. The level of mud in the vessel 20 is controlled by a valve 41 operated by a float 36. Mud entering the vessel 20 impinges upon the valve 41 and is sprayed outwards in fine droplets and then flows in a thin film, firstly over a conical wall 34 and then over the float 36. Since the vessel 20 is maintained at sub-atmospheric pressure by a vacuum pump 42, any gas dissolved or entrained in the mud is released into the space above the liquid level in the vessel 20, whence it is removed by the vacuum pump. A valve 45 controlled by a float 44 controls the subatmospheric pressure in the vessel 20. A generally cylindrical void around the pump shaft 48 is formed within a vortex caused by rotation of the impeller 50. Gas collecting at the eye of the impeller 50 of the pump 46 rises through the void around the pump shaft 48, and part of it passes through the gap between the shaft and an annular baffle 56 to enter a compartment 58 between the baffle and a shaft seal 52, whereby liquid is kept away from the seal. The remainder of the gas is vented to the vessel 20 via a conduit 59 (or may instead be vented to some other low-pressure region). A pocket of returned gas collecting below a baffle 59a prevents liquid from flowing down the conduit 59. The compartment 58 may be vented to atmosphere. The pump 46 may be disposed at an angle to the vertical, provided the seal 52 is at a higher level than the impeller 50. In a modification, Figs. 2 and 3 (not shown), the pump (46) is located outside the tank (13) and closely adjoining the degassing vessel (20a), the mud flowing from the vessel to the pump via a scroll-shaped casing which promotes a gas-releasing vortex around the shaft (48). The released gas passes to the vessel above the level of the mud flowing from the vessel to the pump, Fig. 5 shows an arrangement in which the pump is mounted immediately below an exit opening 20d from the degassing vessel 20c and discharges the mud to the tank 13 via a pipe 105. A vortex is set up in the mud flowing from the vessel to the pump by the combined effect of spiral fins 109 and the impeller rotation, whereby a void 106 is produced. The gas released at the impeller eye passes through the void 106 into a space 115 afforded by the concave bottom 114 of a float 113 which replaces the float 36 of Fig. 1, and then passes via a conduit 116 to the air space above the liquid level in the vessel. The pump 140, Fig. 7, may be mounted within the return mud tank 161, discharging via a pipe 126 to the degassing vessel 120, which in turn discharges the degassed mud through an opening 124 into the clean mud tank 125. Mud is drawn into the pump through a circumferential inlet 151 having vortex-inducing vanes 148, the gas released at the impeller eye being vented to atmosphere via the open end 164 of the pump casing. A spring-biased valve 134 performs the same functions as the float-operated valve 41 of Fig. 1. The gas released in the vessel 120 is vented to atmosphere via a vent 128. The valve 134 may be omitted, its functions then being performed by a flexible top wall of the vessel 120, the exit end 127 of the pipe 126 then being located close to this top wall.