RU2472043C1 - Centrifugal compressor unit - Google Patents

Abstract

FIELD: engines and pumps.

SUBSTANCE: unit includes compressor comprising the shaft with blades, which is installed in the housing on bearings, and gas dynamic seals installed on the shaft, and actuator connected by means of connecting element to compressor shaft. Actuator is located outside the housing. One of gas dynamic seals is located between bearing and connecting element. Gas supply channels to bearings are connected at least to one suction branch pipe, and impellers are installed on rotary part of bearings.

EFFECT: avoiding the problems related to use of electric motors in designs of compressor units; avoiding additional cooling circuits and costs on their arrangement.

3 cl, 1 dwg

Description

The invention relates to the field of compressor engineering, mainly to centrifugal compressors with a high-frequency electric drive without lubrication in the bearings of the rotor, in particular oil-free vacuum circulation compressors of gas-dynamic lasers.

In a number of closed-loop processes, there is a need:

- the complete exclusion of oil in the process gas;

- maintaining the constancy of the component composition of the gas in the gas-dynamic circuit;

- minimize leakage of process gas into the atmosphere (to complete tightness);

- maintaining a vacuum in the gas-dynamic circuit.

There are known designs of centrifugal compressor units containing a compressor, including a shaft with blades mounted in a housing on bearings and gas-dynamic seals mounted on a shaft, a drive also installed in the housing and connected to the compressor shaft by means of a connecting element (see, for example, patent RU 2333398, published 09/10/2008; Internet site www.s2m.fr or www.converteam.com). The construction scheme “MOPICO sealed” or “HOFIM sealed” used in this way allows us to satisfy the above requirements.

However, there are a number of problems associated with the use of high-frequency electric drives in such designs.

1. Cooling of a rotor of a high-frequency electric motor.

In these schemes, the rotor of the electric motor and compressor is in the process gas environment. If heat removal from the stator part can be carried out by a liquid, in particular water, then cooling of the rotor part (including electromagnetic bearings) is possible only with process gas. Since the high-frequency electric motor, and accordingly its rotor, are smaller, which is an advantage compared to an asynchronous electric motor of the same power but normal speed (3000 rpm), and the amount of heat to be removed from the rotor is approximately the same, the heat exchange surface area of the high-frequency rotor due to the smaller size is insufficient for the same parameters (flow rate, initial temperature and pressure) of the cooling process gas for normal cooling of the mouth pa. The rotor will heat up. For vacuum compressor units, the cooling problem is exacerbated due to a decrease in the heat transfer coefficient of rarefied gas. For successful cooling of the rotor of a high-frequency electric motor, either an increase in the heat transfer surface or additional cooling of the process gas directed to cooling the rotor is necessary.

The first way is associated with an increase in the length of the rotor of the electric motor, because the rotor diameter cannot be increased from the strength condition. But this leads to the development of a new electric motor, new electromagnetic bearings (EMF), an increase in dimensions, mass, and, accordingly, cost, i.e. to the loss of the advantage that originally had a high-frequency electric motor.

The second way is additional energy costs for cooling the process gas. The gas supplied for cooling must be well prepared and thoroughly cleaned. But the development and creation of a cooling system also leads to an increase in the cost of the installation and a decrease in its operational reliability.

2. Additional (lengthy or equivalent) tests of materials (including insulation) in contact with the process gas under the influence of an electromagnetic field.

Actual process gases passing through the compressor and flowing around the rotor and stator parts of the electric motor can contain various types of impurities, including water, condensate, hydrogen sulfide, vanadium, potassium, mercury and other chemical elements of the periodic table, as well as corrosive agents, abrasive inclusions, including sand. The raw gas causes a rapid formation of deposits on the hot parts of the electric motor, destroys it, exposes the stator windings to the inevitable risk of a short circuit, and leads to failure of the magnetic bearings.

Materials testing will require additional time and additional funding to create a test bench and conduct tests.

3. All high-frequency sealed electric motors are of single production and have a high cost.

Also known are the designs of oil-free centrifugal compressor units made according to the “HOFIM tight” scheme, containing a single sealed compressor housing and a high-frequency electric motor with a single rotor with electromagnetic bearings (see, for example, V.V. Durymanov, S.A. Leontyev, V. V. Sedov “On land and under water: encapsulated compressor unit STC-ECO of SIEMENS”. Turbines and diesel engines / March-April 2010. P.10-14).

The stator of the electric motor is separated from the direct effect of unclean gas by a special insulating “glass” (capsule). The stator insulating cup, which is installed in the gap between the stator and the rotor, is a non-metallic composite shell that also prevents the formation of eddy currents. The stator cooling system in this case is performed by a double-circuit, complicated, with additional equipment. The windings of the squirrel-cage rotor of an induction motor are embedded and fixed inside the shaft and have a special protective coating.

In hermetic compressor units, all active EMFs are hermetically isolated from the working gas.

The placement of additional equipment with a control system for its operation, as well as an increase in the dimensions of the stator part of the electric motor (to compensate for the effects of the insulating cup) will lead to an increase in the dimensions of the electric drive, i.e. again to the loss of a number of advantages of the high-frequency electric drive.

The objective of the invention is to eliminate the problems associated with the use of electric motors in the design of compressor units according to the schemes "MOPICO tight" and "HOFIM tight", the exclusion of additional cooling circuits and the costs of their organization.

The technical result of the invention is as follows:

- the complete exclusion of oil in the process gas;

- maintaining the constancy of the component composition of the gas in the gas-dynamic circuit;

- minimize leakage of process gas into the atmosphere;

- maintaining a vacuum in the gas-dynamic circuit.

The technical result of the invention is achieved due to the fact that the centrifugal compressor unit comprises a compressor, including a shaft with blades mounted in the housing on bearings and gas-dynamic seals mounted on the shaft, and a drive connected by a connecting element to the compressor shaft, one of the gas-dynamic drives being located outside the housing gasket is located between the bearing and the connecting element, while at least one suction pipe is connected to the gas supply channels and to the bearings, and on the rotor part of the bearings impellers are installed.

In addition, a filter separator can be installed on each gas supply channel.

In addition, the connecting element can be made in the form of a dry coupling.

The invention is illustrated in the drawing, which shows a structural diagram of a centrifugal compressor unit, explaining the proposed design solution.

The centrifugal compressor unit contains a compressor 1, including a housing 2, inside of which a shaft 4 with working blades 5 is mounted on electromagnetic bearings 3 (EMF) 5. Compressor 1 also includes suction 6 and discharge 7 nozzles. The unit contains a drive 8 located outside the housing 2, which is an oil-free, multiplier-free high-frequency electric motor with electromagnetic rotor bearings and with its own cooling system (air or liquid) of the stator and rotor (not shown). The drive 8 is mechanically connected to the compressor shaft 4 by means of a connecting element 9, made in the form of a dry coupling. Between the connecting element 9 and the EMF 3 in the housing 2 of the compressor 1 there is a gas-dynamic (dry, oil-free) seal 10, designed to prevent air from entering the atmosphere into the process gas and to minimize leakage of the process gas into the atmosphere.

Channels 11 for supplying gas to the stator parts of the EMF 3 are connected to the suction nozzles 6 of compressor 1, each of which has a filter separator 12, while impellers 13 (impellers) are installed on the rotor part of the EMF 3, which serve to create excess pressure of the process gas used for cooling EMF 3.

In operation, the actuator 8 is in an air atmosphere and is not in contact with the process gas. Own cooling system provides cooling of the rotor and stator of the electric motor and its EMF.

The EMF 3 of the compressor 1 is cooled by the process gas taken from the suction nozzles 6 of the compressor 1 through the channels 11. The cooled gas is purified in the filter separators 12 and the impeller 13 is fed into the EMF 3 cavity, from where it enters the impellers of the compressor 1, i.e. returns to the process.

A buffer gas of the same composition as the process gas is supplied to the dry gas dynamic seal 10 with a gas pressure for the vacuum unit that is slightly (for example, 10 Pa) higher than atmospheric.

The proposed design of the compressor unit allows you to use the purchased high-frequency electric motor without modifications, i.e. excluded:

- contact of the electric motor with the process gas;

- the problem of cooling and additional tests;

- the problem of ensuring the tightness of the electric motor.

The presence of a single dry seal halves the leakage of process gas into the atmosphere.

The location of the dry seal 10 from the flowing part behind the EMF 3 in the direction of the drive end of the shaft 4 allows you to organize the cooling of the EMF 3 of the compressor 1 directly with process gas.

Thus, the proposed design allows you to:

- apply purchased high-frequency electric motors of the usual, well-developed configuration;

- halve the number of gas-dynamic seals in comparison with typical compressor designs;

- reduce the cost of organizing EMF cooling;

- reduce dynamic axial loads.

Claims (3)

1. A centrifugal compressor unit comprising a compressor, including a shaft with blades mounted in a housing on bearings and gas-dynamic seals mounted on the shaft, and a drive coupled by means of a connecting element to the compressor shaft, characterized in that the drive is located outside the housing, one of the gas-dynamic seals is located between the bearing and the connecting element, while at least one suction pipe is connected to the gas supply channels to the bearings, and on the rotor part of the bearings impellers are installed. 2. The unit according to claim 1, characterized in that a filter separator is installed on each gas supply channel. 3. The assembly according to claim 1, characterized in that the connecting element is made in the form of a dry coupling.