JP2006177242A - Overhang type centrifugal compressor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce thrust load at a time of start without reducing heat insulation efficiency in an overhang type centrifugal compressor. <P>SOLUTION: The overhang type centrifugal compressor is provided with a start thrust reduction means. The start thrust reduction means includes a thrust load air gap 21 formed by sealing a gap between an inner circumference surface of an inner circumference surface of an impeller operation chamber 4 and a front surface side outer circumference surface of the impeller 5 by a sealing means, and applies thrust load opposing start thrust load on a compressor rotor 1 by thrust load pressure generated in the thrust load air gap according to pressure of gas to be compressed or supplied. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an overhanging centrifugal compressor used for gas compression and air supply in various process plants and the like, and more particularly, to a reduction in thrust load at startup in a compressor rotor of an overhanging centrifugal compressor.

  FIG. 2 shows a conventional general configuration of an overhang type centrifugal compressor. The overhanging centrifugal compressor includes a compressor rotor 1. The compressor rotor 1 is composed of a rotating shaft 2 and an impeller (centrifugal impeller) 5 that is attached to the tip of the rotating shaft 2 and is accommodated in an impeller working chamber 4 formed in the casing 3. . The rotary shaft 2 is supported in the radial direction by radial bearings 6 provided at two locations in the intermediate portion, and is also supported in the thrust direction by a thrust bearing 7 provided at the rear end portion. A shaft sealing device 8 is attached to the rotary shaft 2 so that gas entering the impeller working chamber 4 does not leak outside along the rotary shaft 2. The impeller 5 has a structure having a hollow blade portion 13 surrounded by the core plate portion 11 and the side plate portion 12, and a space between the outer peripheral surface of the core plate portion 11 and the inner peripheral surface of the impeller working chamber 4. A labyrinth seal 14 seals the gap between the outer peripheral surface of the side plate 12 and the inner peripheral surface of the impeller working chamber 4. Since the impeller 5 is attached to the tip of the rotary shaft 2, the impeller 5 has a cantilever structure with respect to the support of the rotary shaft 2 by the radial bearing 6. For this reason, it is called an overhang type.

  Such an overhang type centrifugal compressor has a problem of a thrust load (thrust load at start-up) applied to the compressor rotor 1 at start-up. A constant pressure (set ring pressure) is applied to the impeller working chamber 4 by the process gas even when the compressor is stopped. The settling pressure of the process gas applies a thrust load corresponding to the shaft diameter D1 of the rotary shaft 2 to the impeller 5 in the right direction in the state shown in the figure. That is, when the compressor rotor 1 is stopped, the settling pressure of the process gas acts uniformly in the impeller working chamber 4, so that the thrust load is offset against the side plate portion 12 of the impeller 5. do not do. On the other hand, in the core plate portion 11 of the impeller 5, the settling pressure acting area on the outer peripheral surface is reduced according to the shaft diameter D <b> 1 of the rotating shaft 2. Acts in the right direction. As a result, at the time of start-up, a thrust load corresponding to the shaft diameter D1 of the rotary shaft 2 is applied to the compressor rotor 1.

  For this reason, it is necessary to set the load capacity of the thrust bearing according to the settling pressure of the process gas in a process plant that uses a compressor. The thrust bearing becomes larger and compressed as the settling pressure of the process gas increases. This will increase the size and cost of the machine. In addition, the thrust load at start-up leads to an increase in start-up torque. Therefore, the compressor rotor drive unit needs a drive unit with a rated output larger than the output in normal operation, which also leads to an increase in size and cost of the compressor.

  After starting, the pressure of the gas increases due to compression by the compressor rotor 1, and the increased pressure is applied to the core plate 11 of the impeller 5, so that a thrust load in the direction opposite to that at the time of stopping or starting is impeller. It will take car 5. It is possible to cope with this thrust load by appropriately setting the radial position D2 of the labyrinth seal 14 in the core plate portion 11 so as to be a load corresponding to the load capacity of the thrust bearing 6.

  Patent Document 1 discloses a technique for reducing the thrust load at start-up caused by the process gas settling pressure as described above. In the technique of Patent Document 1, a boss whose internal cavity pressure can be adjusted is fixed to the casing with guide vanes and provided at the tip of the rotating shaft, and the internal pressure of the boss is applied to the rotating shaft at the time of startup. The thrust load is offset and reduced.

JP-A-6-129392

  As described above, the overhang type centrifugal compressor has a problem in that it causes an increase in size and cost in order to cope with a thrust load at start-up caused by the inherent pressure inherent in the gas to be compressed or supplied. was there. With respect to this problem, the technology disclosed in Patent Document 1 enables the thrust load during startup to be effectively reduced, thereby avoiding an increase in size and cost.

  However, although the technique of Patent Document 1 enables reduction of the thrust load at the time of startup, it causes a problem that the heat insulation efficiency of the compressor is reduced. In the technique of Patent Document 1, a boss provided at the tip of the rotating shaft is fixed to the casing with guide vanes in order to reduce the thrust load at startup. These structures are inevitably provided in the gas passage due to their functions, but as a result, they impede the passage of gas, thereby generating a pressure loss and the compressor. This will reduce the heat insulation efficiency.

  The present invention has been made in the background as described above, and the purpose of the present invention is to make it possible to effectively reduce the thrust load during startup without incurring problems such as a decrease in heat insulation efficiency for an overhang type centrifugal compressor. Is to do

  To achieve the above object, the present invention includes a compressor rotor configured by attaching an impeller to the tip of a rotating shaft, a casing formed with an impeller working chamber in which the impeller is accommodated, In an overhang type centrifugal compressor having a start-up thrust reduction means for reducing a start-up thrust load applied to the compressor rotor at the start-up by the pressure of the gas to be supplied, the thrust reduction at the start-up The means includes a thrust load gap formed by closing a gap between an inner peripheral surface of the impeller working chamber and an outer peripheral surface on the front side of the impeller by a sealing means, and the thrust load gap includes the thrust load gap. The compressor rotor can be loaded with a thrust load that opposes the thrust load at the start-up by a thrust load pressure generated according to the gas pressure. It is characterized in that.

  Further, in the present invention, in the overhang type centrifugal compressor as described above, the thrust load gap is formed so as to allow leakage of the gas from the impeller working chamber, and the leaked gas to the thrust load gap Is released from the thrust load gap to the outside through the pressure adjusting means, thereby generating the thrust load pressure.

  According to the present invention, the thrust load at start-up can be effectively reduced, and the start-up thrust reducing means does not become an obstacle to the passage of gas in the impeller working chamber, and the heat insulation efficiency is lowered. The problem of can also be avoided.

  Hereinafter, embodiments of the present invention will be described. FIG. 1 shows the configuration of an overhanging centrifugal compressor according to an embodiment. The overhanging centrifugal compressor of this embodiment also has a common configuration with the conventional overhanging centrifugal compressor described above with reference to FIG. In the following, the thrust reduction means at start-up, which is a characteristic configuration of the present embodiment, will be mainly described. Constituent elements common to those of the prior art are denoted by the same reference numerals as those in FIG. Omitted as necessary.

  The startup thrust reduction means includes a thrust load gap 21, a communication path 22, and a pressure adjustment system 23. The thrust load gap 21 is a portion where the outer peripheral surface of the side plate portion 12 of the impeller 5, that is, the front surface side outer peripheral surface of the impeller 5 and the inner peripheral surface of the impeller working chamber 4, specifically, the outer peripheral surface of the side plate portion 12. And a portion provided with a labyrinth seal 15 for sealing between the inner peripheral surface of the impeller working chamber 4 is formed. More specifically, in addition to the labyrinth seal 15 provided as a seal for preventing the high pressure gas compressed by the impeller 5 from leaking to the low pressure side, the labyrinth seal 24 is connected to the side plate portion 12 and the impeller working chamber. 4 is provided between the inner peripheral surfaces of the four blades, and a thrust load gap 21 in a closed state is formed in the gap between the inner peripheral surface of the impeller working chamber 4 and the outer peripheral surface of the side plate portion 12 of the impeller 5 by both the sealing means. is doing.

  The communication path 22 is formed in a state of penetrating the solid portion of the casing 3, and has one end communicating with the thrust load gap 21 and the other end opened to the outer peripheral surface of the casing 3. Such communication paths 22 are provided at two locations as communication paths 22a and 22b.

  The pressure adjustment system 23 includes a pressure adjustment valve 25 and pressure detection means 26 which are pressure adjustment means. One side of the pressure regulating valve 25 communicates with the thrust load gap 21 via the pipe 27 and the communication path 22a, and the other side communicates with the atmosphere side or the low pressure side of the process gas. The pressure detection means 26 can detect the internal pressure of the thrust load gap 21 through the communication path 22b.

  The starting thrust load is reduced by the starting thrust reducing means as follows. The thrust load gap 21 is closed by sealing with a labyrinth seal that allows a certain amount of leakage. For this reason, the process gas which is applying the set ring pressure P1 to the impeller working chamber 4 at the time of start-up leaks into the thrust load gap 21, whereby a certain pressure is applied to the thrust load gap 21. The pressure detection means 26 detects the pressure in the thrust load gap 21 and outputs a pressure value signal corresponding to the detected pressure. The pressure value signal from the pressure detecting means 26 is input to the pressure regulating valve 25 to control the opening degree of the pressure regulating valve 25. When the pressure control valve 25 has an opening degree corresponding to the pressure value signal, gas is released from the thrust load gap 21 to the atmosphere side or the low pressure side of the process gas according to the opening degree. The pressure is lowered to a predetermined thrust load pressure P2 lower than the process gas settling pressure, that is, the pressure P1 generated in the impeller working chamber 4. That is, the opening degree control of the pressure regulating valve 25 by the pressure value signal is performed so as to keep the pressure of the thrust load gap 21 caused by the leakage of the process gas at a thrust load pressure P2 lower than the pressure P1 of the impeller working chamber 4 by a certain amount. The

  By maintaining the pressure of the thrust load gap 21 at the thrust load pressure P2 in this way, a thrust load corresponding to the pressure difference between P1 and P2 is applied to the impeller 5 leftward in the state shown in the figure. It will be. The thrust load applied by the thrust load gap 21 is in the opposite direction to the thrust load at start-up, and works to reduce the start-up thrust load. Therefore, by appropriately setting P2, it is possible to cancel the starting thrust load with the thrust load caused by the thrust load gap 21 so that the starting thrust load is not substantially generated.

  As described above, the start-up is performed in a state in which the thrust load at the time of start-up is reduced, and when the steady operation is started, the pressure regulating valve 25 is closed. For this reason, the process gas does not leak through the thrust load gap 21 during steady operation. However, even if the pressure regulating valve 25 is closed, the pressure in the thrust load gap 21 is a pressure P3 that is smaller than the pressure P1 in the impeller working chamber 4, and the thrust load due to this is applied to the impeller 5. Will be. This thrust load is the same kind as the thrust load due to the increase in gas pressure after activation, and it is possible to cope with appropriately setting the radial position D2 of the labyrinth seal 14 in the core plate part 11.

  As described above, according to the present invention, it is possible to effectively reduce the thrust load at the time of starting, thereby enabling reduction in size and cost of the compressor. In addition, since the thrust load gap 21 utilizing the gap between the inner peripheral surface of the impeller working chamber 4 and the outer peripheral surface of the side plate portion 12 of the impeller 5 is used, the thrust load at the time of activation is reduced. There is no obstacle to the passage of gas in the working chamber 4, and the problem of a decrease in heat insulation efficiency can be avoided.

  In the above embodiment, the labyrinth seal is used as the sealing means for the thrust load gap 21, but an abradable seal or the like can be used instead.

  INDUSTRIAL APPLICABILITY The present invention can effectively reduce the starting thrust load without reducing the heat insulation efficiency of the overhanging centrifugal compressor, and can be widely used in the field of overhanging centrifugal compressors.

It is a figure showing composition of an overhang type centrifugal compressor by one embodiment. It is a figure which shows the general structure in the conventional overhang type centrifugal compressor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Compressor rotor 2 Rotating shaft 3 Casing 4 Impeller working chamber 5 Impeller 15, 24 Labyrinth seal 21 Thrust load gap 25 Pressure control valve

Claims (2)

In addition to a compressor rotor constructed by attaching an impeller to the tip of the rotating shaft, it has a casing formed with an impeller working chamber in which the impeller is accommodated, and further has a gas to be compressed or supplied. In an overhang type centrifugal compressor provided with a starting thrust reduction means for reducing a starting thrust load applied to the compressor rotor at the time of starting by the pressure being applied,
The starting thrust reduction means includes a thrust load gap formed by closing a gap between an inner peripheral surface of the impeller working chamber and an outer peripheral surface on the front side of the impeller by a sealing means, An overhanging centrifugal compressor characterized in that a thrust load that opposes the thrust load at the time of start-up can be applied to the compressor rotor by a thrust load pressure generated in a thrust load gap according to the pressure of the gas. . The thrust load gap is formed to allow leakage of the gas from the impeller working chamber, and the leaked gas to the thrust load gap is discharged from the thrust load gap to the outside via a pressure adjusting means. The overhanging centrifugal compressor according to claim 1, wherein the thrust load pressure is generated.

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