Impeller-type liquid ring compressor
An impeller-type liquid ring compressor having a particular posture configuration. This type of posture arrangement can completely support the impeller since it rotates, eliminating many of the issues inherent in the prior art layouts without changing the general overhung impeller design. This may allow the impeller-type liquid ring compressor to be easily retrofitted in present use environments, such as, for instance, oil and gas processing facilities, oil refineries, and petrochemical processing centers. In some exemplary embodiments, a thrust bearing may be located on the front face of the impeller, or radial bearings may be disposed between the vanes of the impeller. A radial bearing and thrust bearing may further be disposed on the rotating side of the impeller near the impeller itself. The compressor could be configured so the process fluid carries heat away from each one of those bearings.
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Centrifugal pump systems have been implemented for use in a huge variety of applications. Existing centrifugal pump systems normally make use of an overhung impeller. In a standard centrifugal pump system, fluid enters the impeller through the”eye” of the impeller, and is then”centrifuged” into the impeller periphery by the continuous rotation of the impeller, generally with assistance from the impeller vanes. In some designs, impellers may be open or closed, and might have one vane, manyvanes, or no vanes in any way.
One specific variant of this centrifugal pump process is the liquid-ring pump. Liquid-ring pumps are most frequently used as vacuum pumps or gas compressors. At a liquid-ring pump, liquid (usually water) is fed into the pump, and is formed intoa transferring cylindrical ring round the inside of the casing by the action of a multi-vane impeller. This liquid ring creates a succession of seals in the spaces between the impeller vanes, which form compression chambers. The multi-vane impeller is locatedslightly off-center from the casing of this liquid-ring pump, like the eccentricity between the impeller’s axis of rotation and the geometric axis of the casing results in a cyclic variation of the volume enclosed by the vanes of the impeller and bythe liquid ring. This is used to pump gas (typically air) through the pump; gas is drawn into the pump through an inlet port on one end of the casing, trapped in the compression chambers, reduced in volume by the impeller rotation, and discharged in theother end of the casing.
In current overhung impeller designs for liquid-ring pumps, the radial bearing is located outside of the compressor casing and in some distance from the impeller. Basically, it follows that the most critical section of the weight of theimpeller is cantilevered at some distance away from the point of aid. The weight of the impeller being cantilevered this way away from the point of support creates a moment in the shaft, located between the radial position and the thrust bearings.This triggered moment could be observed at the depiction of a prior art overhung impeller design, shown at exemplary FIG. 1. In current designs, this moment makes a radial load on the thrust bearings, which may lead to premature failure of the thrustbearings.
To further explain the present impeller designs, the impeller is typically attached to the rotating shaft via collar and key, and with an impeller nut. The shaft is typically attached to the center of the impeller. The impeller, as shown, issignificantly bigger in diameter than the shaft.
During operation, the compressor operates with a specific quantity of water inside the casing. After the impeller is active, this water is spun against the face of the shell. However, when the impeller is idle or inactive, this water sits in thebottom of this compressor casing. After the impeller is initiated from an inactive state, the impeller must turn through the water in the bottom of the compressor casing so as to properly remove it around the inside of the shell of the compressor.This water makes a substantial quantity of drag on the impeller.
Nonetheless, in a startup state, the top of the impeller is encompassed by gas or vapor, which has less viscosity compared to water at the bottom of the impeller. This usually means that there is far less drag on the top of the impeller ascompared to the bottom of the impeller. Likewise, the gasoline on peak of the impeller has far less mass than the water at the bottom of the impeller, and therefore the gas has much less inertia resisting the movement of the impeller compared to water.These two variables, combined with the radial bearing to impeller space, means that the gap in the inertial forces on the impeller which may be required at startup may cause the impeller to”wobble” within the casing until the impeller reaches asufficient rate to produce the necessary rotational movement to distribute the water through the casing.
Similar issues may arise when the impeller is to be closed down, even though in reverse in this case. As the impeller slows, it will slow beyond the stage where it may create the necessary rotational movement to distribute the water through thecasing, and the water will sink into the bottom of the casing. This may cause the bottom section of the impeller to be slowed more quickly by the inertial force of the water acting on the impeller vanes, again inducing wobble from the impeller.
In typical pump layouts, the clearance between the impeller and the interior of the casing (specifically, between the impeller and the gas distributor located inside the casing) are very small, often on the order of 0.02″. It follows that, whenthe impeller is opened up or shut down and trigger to wobble, there is a possibility of effect between the impeller and the gas distributor, which may typically damage the distributor, the impeller, or even both.
Further, common pump designs as understood in the prior art are often expensive to fabricate and function. A bearing arrangement to get a present liquid ring pump expects that the bearing housing be manufactured and installed on the compressor. Italso requires this posture be supplemented with an external bearing lubrication procedure, such as oil, grease, or petroleum jelly, which requires monitoring and regular refilling, and limits the positioning of liquid ring pumps to points where they could beeasily obtained with this necessary maintenance.
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