JP2756118B2 - Single shaft multi-stage centrifugal compressor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-pressure, high-speed, single-shaft, multi-stage centrifugal compressor. [Prior Art] A labyrinth structure of a conventional fluid machine will be described using a single-shaft multi-stage centrifugal compressor as an example. FIG. 3 shows a longitudinal sectional view of a single-shaft multi-stage centrifugal compressor. The handling gas sucked from the suction nozzle 7 is sequentially compressed by the multi-stage impeller 1 and is discharged from the discharge nozzle 8. The internal leak from the impeller outlet to the inlet is a mouth labyrinth 3, the leak between stages is a stage labyrinth 4, the leak from the last stage to the suction is a balance labyrinth 6, and the shaft end leak is prevented by an end labyrinth. I have. [Problems to be Solved by the Invention] In the above-mentioned prior art, no consideration has been given to the point of the fluid vibration generated by the spring action and the damping action of the labyrinth part in a high-pressure and small-sized high-speed machine. That is, as shown in FIG. 4, the flow in the labyrinth gap has a rotational direction component U under the influence of the rotor surface. Due to the flow of the rotation direction component, the labyrinth seal portion has a characteristic of supporting the rotor with a spring action and a damping action. In large machines, this characteristic is dominated by the characteristics of the rotor bearing system and can be ignored. However, when it comes to high-speed compact and high-pressure machines, the characteristics of the rotor bearing system
The properties of the seal cannot be ignored. Moreover, the spring and the damping of the seal portion have a component for rotating the rotor, so that the vibration characteristics of the rotor become unstable. That is, unstable labyrinth whirl generally causes unstable vibration, which makes it difficult to operate the machine. As a method of solving the above-mentioned problem, a method of discharging gas from the outside to the labyrinth chamber in a direction opposite to the rotation direction of the rotor is known. However, power consumption due to gas consumption and a casing structure become complicated. However, there is a problem in terms of cost, such as the necessity of external piping. The present invention has been made in view of the above-described circumstances, and an object thereof is to suppress labyrinth whirl without requiring external suction gas, to reduce total energy loss, and to achieve simple operation. An object of the present invention is to provide a single-shaft multi-stage centrifugal compressor using a labyrinth structure having a configuration. [Means for Solving the Problems] In order to achieve the above object, in the present invention, a labyrinth member having a plurality of annular projections and a groove formed between the annular projections is provided in a casing, In a single-shaft multi-stage centrifugal compressor that forms a labyrinth with a rotatable rotor to which an impeller is attached, among the plurality of annular protrusions, the rotor corresponding to the protrusion closest to the impeller, A plurality of grooves spirally twisted with respect to the axis of the rotor and a helically twisted ridge formed between the grooves are provided, and the torsional direction of the grooves is determined with respect to the leakage direction of the fluid leaking the labyrinth. The upstream side is advanced with respect to the downstream side by an angle θ in the rotation direction of the rotor, and the angle θ is defined as ω · cos θ> u, where the relative flow velocity ω of the gas and the flow velocity u of the groove portion are given by: Specially to satisfy Sign. [Operation] With the above configuration, a swirl component in a direction opposite to the rotation direction of the rotor can be given to the gas in the labyrinth seal portion, and the labyrinth whirl is suppressed in the single-shaft multistage centrifugal compressor using the labyrinth seal. be able to. Embodiment An embodiment of the present invention will be described below with reference to FIGS. 1 and 2. FIG. 1 shows an example in which the present invention is applied to a balance seal portion of a centrifugal compressor as an example of a structure of a labyrinth portion of a fluid machine. The handled gas is discharged from the discharge nozzle after leaving the final impeller 1, and a part thereof passes through a gap between the balance seal portion, that is, the balance labyrinth 6 and the surface of the rotor 2, and a secondary side (low pressure side) portion (for example, a suction side). Nozzle). At the inlet of the balance seal portion, there are a slit (groove) 11 and a ridge 13 provided on the rotor side. The slit is configured such that the high pressure side of the labyrinth seal has a phase advance in the rotation direction with respect to the rotor rotation axis than the low pressure side. Further, the inclination angle (phase lead amount) of the slit 11 is determined as follows. The angle at which the slit is inclined from the high pressure side to the low pressure side is θ, and the peripheral speed of the slit portion is u.
The axial component of the gas flow after exiting the slit is obtained by the following equation from the flow rate Q obtained from the equation for calculating the amount of leakage of the labyrinth and the cross-sectional area A of the slit portion. From the above θ and Cm, the relative flow velocity ω of the gas at the slit exit can be obtained by the following equation. ω ≒ Cm / sinθ (2) Therefore, the absolute flow velocity C of the gas at the exit of the slit is
It is obtained by equation (3). C = {ω ² + u ² −2ω · u · cos θ} ^1/2 (3) This absolute flow velocity C is opposite to the rotor rotation direction if the slit inclination angle θ satisfies the expression (4). Can be ω · cos θ> u (4) That is, in the present invention, by forming the slit such that the slit inclination angle θ satisfies the expression (4), the gas to the labyrinth seal portion is directed in the direction opposite to the rotor rotation direction. Can be provided. This eliminates the spring and damping characteristics of the labyrinth seal portion in the rotor rotation direction, thereby suppressing labyrinth whirl. FIG. 2 shows an example in which the slit is provided on a stator side (for example, a balance labyrinth). In principle, this is the same as the above-described embodiment (FIG. 1), and has an effect that the unstable phenomenon due to the labyrinth seal can be suppressed as in the previous example. [Effects of the Invention] According to the present invention, the labyrinth whirl of a high-speed small-sized and high-pressure fluid machine can be suppressed without blowing gas from the outside, so that the total energy loss is small and the structure is simple. It has the effect of being economical.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing one embodiment of the present invention, and FIG. 2 is an explanatory diagram of another embodiment of the present invention. FIG. 3 is a longitudinal sectional view of a single-shaft centrifugal compressor, which is a conventional example of a fluid machine, and FIG.
It is an enlarged view which shows the structure of the balance seal part of the figure. DESCRIPTION OF SYMBOLS 1 ... Impeller, 2 ... Rotor, 3 ... Mouse labyrinth, 4 ... Stage labyrinth, 5 ... Casing, 6
… Balance labyrinth, 7… suction nozzle, 8… discharge nozzle, 11… slit, 12… slit.

Claims (1)

(57) [Claims] A single-shaft multi-stage centrifugal compressor in which a labyrinth member having a plurality of annular projections and a groove formed between the annular projections is provided in a casing, and a labyrinth is formed between a rotatable rotor to which a plurality of impellers are attached. In the plurality of annular projections, the rotor corresponding to the projection closest to the impeller is formed with a plurality of grooves spirally twisted with respect to the axis of the rotor, and between the grooves. A helically twisted ridge is provided, and the torsion direction of this groove is such that the upstream side with respect to the leakage direction of the fluid leaking the labyrinth is advanced by an angle θ in the rotation direction of the rotor with respect to the downstream side. The angle θ satisfies ω · cos θ> u when the relative flow velocity ω of the gas and the flow velocity u of the groove are satisfied.