AU2019440859B2

AU2019440859B2 - Vertical cryogenic liquid centrifugal pump

Info

Publication number: AU2019440859B2
Application number: AU2019440859A
Authority: AU
Inventors: Rui GE; Ruixiong HAN; Xiangzhen ZHANG
Original assignee: Institute of High Energy Physics of CAS
Current assignee: Institute of High Energy Physics of CAS
Priority date: 2019-04-17
Filing date: 2019-12-23
Publication date: 2023-04-27
Anticipated expiration: 2039-12-23
Also published as: WO2020211434A1; CN110017285A; AU2019440859A1

Abstract

A vertical cryogenic liquid centrifugal pump, comprising a rotating shaft (2), a motor assembly (1) located in a room temperature environment, a low-temperature heat-insulating protection structure (3) located in a low temperature environment, and an impeller assembly (4). The motor assembly (1) comprises support bearings (11), a dynamic seal structure (13), and a vacuum flange (14), the room temperature environment and the low temperature environment are separated by means of the vacuum flange (14), and the dynamic seal structure (13) is arranged at the vacuum flange (14); the support bearings (11) match one end of the rotating shaft (2); the other end of the rotating shaft (2) penetrates through the dynamic seal structure (13) and the vacuum flange (14) to extend to the low temperature environment so as to be connected to the impeller assembly (4); the low-temperature heat-insulating protection structure (3) is arranged on the periphery of the rotating shaft (2) between the impeller assembly (4) and the vacuum flange (14). The centrifugal pump can achieve the effects of low heat leakage, high efficiency, and high reliability.

Description

A Vertical Type Cryogenic Circulation Centrifugal Pump

TECHNICAL FIELD

The invention is for the transfer of the cryogenic fluid with a low boiling point. In detail, it is a

vertical type cryogenic centrifugal pump which is set in a vacuum chamber.

BACKGROUND

The cryogenic fluids are mainly liquid such as the nitrogen, hydrogen, helium of which the

boiling points are lower than 120 K. As the boiling points are very low and the vaporization latent heat

is small, the cost of the acquisition and storage is considerably high, and the consumption of the

long-distance transportation is considerably large. Normally, there are two methods for the cryogenic

fluids transportation. One is increasing pressure and the other is using mechanical pump. The

transportation method of increasing pressure would brought about the rise of investment cost and the

whole system complexity. While the method of mechanical pump can avoid the above problems, but it

requires the pump to have the high efficiency, the low heat load and the good reliability.

The existing cryogenic centrifugal pumps are mostly used in the field of air separation industry

and other occasions with large flow and non-rigid heat load application. The research and development

of centrifugal pump for the cryogenic liquid with small flow rate, high hydraulic head and low heat

load are less reported. Meanwhile, the existing patents about cryogenic pump mainly have the

following disadvantages: 1) The consumption of cryogenic liquid is large because of the heat transfer

from the room temperature; 2) The supporting bearing is located near the cryogenic liquid, which

causes the friction heat and the vaporization of the liquid. The bearing is easy to damage and hart to

repair; 3) The efficiency of the pump is low because that the impeller is partial flow type; 4) The

cryogenic medium is single and the application range is limited; 5) The scheme is too general to get

the details.

The invention with the publication number CN106224246A describes a low-scale cryogenic

centrifugal pump which is used in a cold box. The bearings of the drive shaft are close to the impeller

in the cryogenic environment. The heat load, which is generated from the friction, causes the large

consumption of the cryogenic liquid and large amounts of vapor will appear. As there is no adiabatic

structure in the transition part between the low and high temperature, the cold vapor will go up to the top flange, which causes strong heat convection. Meanwhile, the drive shaft is made of solid metal which causes a big heat conduction. The big heat transfer makes the room temperature part to be frosted, which influences the sealability at the room temperature.

The invention with the publication number CN108716469A describes a high speed cryogenic

centrifugal pump with a low heat load. The bearings are also close to the impeller of the low

temperature, which causes the friction heat and the vaporization of the cryogenic fluid. Although the

adiabatic structure is designed between the cold and room parts, large amounts of vapor still goes into

the motor in the room temperature and the heat convection is generated at the same time. The drive

shaft is designed to be split type where the metal section is connected to the nonmetal part. This

structural style reduces the mechanical stability of the drive shaft. Otherwise, the partial flow type

impeller decreases the efficiency of the centrifugal pump.

Therefore, these problems have to be solved through a new pump design.

SUMMARY

According to a first aspect, there is provided a vertical type cryogenic centrifugal pump

comprising a motor assembly, a rotating shaft, an impeller, an inducer, a volute and a heat insulation

protection, the motor assembly, which forms a closed container at room temperature, includes a coil,

two support bearings, a dynamic seal and a top flange, which is used to isolate the atmosphere and

lower temperature vacuum environment, the dynamic seal, which is fixed by the top flange, comprises

a top cover, a seal filler and a bottom plate, wherein the seal filler, which is a multilayer structure, is

composed of carbon rings and stainless steel rings inside a closed container which includes the top

cover and the bottom plate, the full-length rotating shaft includes two parts, one is solid part which is

located inside of the motor assembly at room temperature and supported by the two bearings, and the

other is hollow part which is connected with a full flow impeller and an inducer at the low temperature

vacuum environment, the impeller and its inducer inside the volute directly contact with the cryogenic

liquid, between the top flange and the volute, there is a heat insulation structure with many insulating

baffles at the low temperature vacuum environment.

In one form, the heat insulation protection structure is composed of an outer sleeve, an inner

sleeve and a number of horizontal protective baffles in the jacket between the two sleeves. Each of

horizontal protective baffles is connected with the inner sleeve respectively, and there is a small gap

between the horizontal protective baffles and the outer sleeve. Besides, there is a small gap between the inner sleeve and the rotating shaft.

In one form, the impeller includes a volute which is connected with the heat insulation structure.

The impeller and the inducer is inside the volute, a liquid inlet is set at the bottom of the volute and the

outlet at the side.

In one form, the inducer is the front stage of the impeller.

In one form, the full-length rotating shaft includes two parts, one is solid part which is located

inside of the motor at room temperature and supported by two bearings, and the other is hollow part

which is extended to the cryogenic environment and connected with an impeller and an inducer.

In one form, the impeller and the inducer are fixed at the end of the rotating shaft by a bolt with a

reverse thread.

In one form, the motor assembly, which forms a closed container at room temperature, includes a

coil, and two support bearings.

In one form, the motor assembly includes a frequency transformer, which is used to control the

frequency of the motor.

The vertical cryogenic centrifugal pump consists of the motor assembly, the impeller assembly,

the shaft between them and the cryogenic adiabatic protection assembly. The motor, the support

bearings and dynamic seal are set in the room temperature. The impeller, the inducer and the volute

are set in the cryogenic environment. The motor assembly is connected to the cryogenic impeller by

the drive shaft.

The invention is further designed as follows: the two support bearings for the drive shaft are

placed in the motor. The shaft starts from the room environment to the cryogenic region. The room

temperature part of the shaft is designed as a solid structure and the cryogenic part as hollow one.

By the technical solutions stated above, the motor assembly is set in the room environment and

the impeller assembly is immersed in the cryogenic fluid. The support bearings of the shaft is set in the

room temperature. The energy of the motor is transferred to the impeller by the shaft. The dynamic

seal near the flange and the adiabatic protection structure at the transition part prevent the vapor from

spreading to the inside of the motor.

The invention is further designed as follows: a dynamic seal structure is set close to the flange of

the motor. The cryogenic adiabatic protection structure is designed as the transition part between the

low and room temperature.

By the technical solution stated above, the cryogenic vapor evaporated from the liquid could be

stopped to form the vortex and spread to the upside, which reduces the effect on the motor. Meanwhile,

some vapor goes through the small gap of the dynamic structure into the motor, which has some

cooling effect on it. And the motor assembly is a closed cavity which has no leak to the atmosphere.

The invention is further designed as follows: the dynamic seal is designed to be the multilayer

form and connected to the vacuum flange.

By the technical solution stated above, the multilayer form can decrease the gas leakage rate and

prevent the cryogenic vapor from moving into the room temperature part. Then, the heat exchange

between the cryogenic vapor and external atmosphere is decreased to avoid the condensation and frost

of the moisture, which has a bad effect on the seal at the room temperature.

The invention is further designed as follows: the heat insulation protection structure is composed

of an outer sleeve, an inner sleeve and a number of horizontal protective baffles between the two

sleeves.

By the technical solution stated above, the inner and outer sleeves can decease the heat

conduction by big length and small crossing area. The horizontal protective baffles stop the cryogenic

vapor to go up, which reduces the heat convection.

The invention is further designed as follows: the impeller is the full flow type and the inducer is

its front stage.

By the technical solution stated above, the full flow type impeller can avoid the unbalanced axial

force and improve the flow efficiency. Meanwhile, the inducer can improve the absorption

performance of the pump.

The invention is further designed as follows: the cryogenic centrifugal pump is a vertical type and

the length of the drive shaft is optimized.

By the technical solution stated above, the vertical structure can decrease the transversal

displacement of the drive shaft end. The length of the drive shaft can be optimized according to the

cryogenic working medium and its parameter. The heat load of the low temperature can be reduced

and the mechanical stability can be improved.

The invention is further designed as follows: the rotation rate of the motor can be adjusted by the

frequency transformer.

By the technical solution stated above, by the frequency transformer, the motor speed can be changed based on the load of cryogenic liquid. Also, the electric power could be saved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective sectional view of the cryogenic liquid centrifugal pump.

FIG. 2 is the structure of low temperature heat insulation protection;

FIG. 3 is the assembly of the impeller, inducer and volute.

FIG. 4 is the structure of dynamic seal

DESCRIPTION OF EMBODIMENTS

The invention is described in detail in combination with the drawings and embodiments of the

cryogenic liquid pump.

A vertical cryogenic liquid centrifugal pump, as shown in Fig. 1, Fig. 2 and Fig. 3, comprises a

motor assembly 10, a rotating shaft 20, a heat insulation protection assembly 30 and an impeller

assembly 40. The motor assembly 10 includes mechanical rolling bearings 11, a variable frequency

drive (VFD) 12, a dynamic seal structure 13, a top flange 14, an outer shell 15 and a coil 16. And the

heat insulation protection structure 30 includes an outer sleeve 31, an inner sleeve 32 and several

horizontal protective baffles 33. The impeller assembly 40 includes an impeller 41, an inducer 42 and

a volute 43.

Referring to Fig. 1, when the cryogenic centrifugal pump works normally, the motor components

10 are at room temperature, the impeller 41 and its front stage inducer 42 inside the volute 43 contact

with the low temperature liquid, and the power of motor is transmitted to the impeller 41 and the front

inducer 42 by the rotating shaft 20. The top flange 15 isolate the atmosphere and the vacuum box. The

cryogenic fluid is limited in the volute 43.

As shown in Fig. 1, the internal moving parts of the motor 10, the mechanical rolling support

bearings 11 and the rotating shaft 20 are assembled firstly, and then they are assembled with the

external static parts of the motor. The finned shell of the motor 15 is made of aluminum alloy or brass

material to increase the heat exchange with the environment, and the motor is powered by a variable

frequency drive (VFD) 12 to adjust the speed.

As shown in Fig. 4, the dynamic seal structure 13, as a multilayer laminated design, which is

composed of a stainless steel bottom baffle 131, middle baffles 133, a top baffle 134, carbon rings 132,

a stainless steel top cover 136 and a bottom cover 138, etc. Particularly, the seal rings 132, contacting

with the rotating shaft 20, is made of wear-resistant graphite material. At the same time, the dynamic seal structure 13 is fixed on the top flange 14 and realizes the seal connection with the motor 10.

As shown in Fig. 1 and Fig. 3, the impeller 41 and the front stage inducer 42 are made of 316L

stainless steel or titanium alloy, which are combined together and connected with the rotating shaft 20

by a bolt. The material of the rotating shaft 20 is 316L stainless steel, the room temperature part is

solid structure 21, the low temperature part is hollow structure 22, and the two parts are welded and

then machined to ensure the mechanical accuracy. There is a hole with internal thread at the end of

rotating shaft 20 at the low temperature, and connected with the impeller 41 and the front stage

inducer 42 by a bolt 44. At the same time, the thread directions of the hole of rotating shaft 20 and the

bolt 44 are opposite to achieve self-locking effect.

As shown in Fig. 2, the material of the heat insulation protection structure 30 is 316L stainless

steel, the wall thickness of the outer sleeve 31 and the inner sleeve 32 is relatively thin, and several

horizontal protective baffles 33 are spot welded with the inner sleeve 32, while leaving a small gap

with the outer sleeve 31 for easy assembly.

As shown in Fig. 3, the material of the volute 43 is 316L stainless steel or aluminum alloy, which

is connected with the outer sleeve 31 of the heat insulation protection structure 30. The inlet of the

volute 45 is located at the bottom vertical position, and the outlet 46 is located at the horizontal radial

position. During normal operation of the centrifugal pump, the impeller 41 and inducer 42 are rotated

and driven by the motor 10, and the cryogenic liquid is suctioned from the inlet of the volute 45, and

then discharged from the outlet 46 after pressurization.

The motor 10 housing with supporting bearings 11 and dynamic seal structure 13 are integrated

and placed in the room temperature environment. The full flow impeller 41 and front stage inducer 42

are placed in the cryogenic liquid. The two supporting bearings 11 of the rotating shaft 20 are placed

in the room temperature environment. The other end of the rotating shaft 20 extends to the low

temperature environment and connects with the impeller 41 and the inducer 42 to form a vertical

"cantilever beam" supporting structure, which is placed vertically.

The low heat load can be realized by the following design: firstly, the supporting bearings of the

rotating shaft are all placed at room temperature and away from the cryogenic liquid environment, so

as to avoid the friction heat in the cryogenic liquid during operation. At the same time, the section of

rotating shaft extending to the low temperature is the form of hollow structure, so as to decrease the

heat conduction by reducing the cross-sectional area and increasing the heat conduction path. Besides, the dynamic seal structure at the room temperature and the heat insulation protection structure at low temperature can avoid gas vortex disturbance and stop the cold vapor to spread upward, so as to reduce the convective heat transfer.

The high efficiency can be realized by the following design: the full flow impeller and the inducer

are working together to improve the operation efficiency and suction performance. The small heat load

at low temperature can reduce the liquid consumption, which can improve the efficiency further.

The high reliability can be realized by the following design: the motor, the supporting bearing of

the shaft and the dynamic seal structure are all at the room temperature and away from the cryogenic

liquid, which can improve the reliability and prolong the operation cycle. What is more, the structural

characteristic of core pulling can be convenient for maintenance.

In summary, the significant advantages of the invention are shown below.

Firstly, the structural advantage: the motor, the support bearings and dynamic seal are set in the

room temperature. The impeller, the inducer and the volute are set in the cryogenic environment. The

two supporting bearings of the rotating shaft are at the room temperature, and the other end of the

rotating shaft extends to the low temperature and connects with the impeller and the inducer to form a

vertical "cantilever beam" supporting structure, which is placed vertically.

Secondly, the low heat load: the supporting bearings of the rotating shaft are all placed at room

temperature and away from the cryogenic environment, so as to prevent the friction heat from entering

into the cryogenic liquid during operation. Meanwhile, the section of rotating shaft extending to the

low temperature is the form of hollow structure, so as to decrease the heat conduction by reducing the

cross-sectional area and increasing the heat conduction length. Besides, the dynamic seal structure at

the room temperature and the heat insulation protection structure at low temperature can avoid vortex

disturbance caused by a large number of volatile low-temperature gas, so as to reduce the convective

heat transfer.

Thirdly, the high efficiency: the full flow impeller and the front inducer work together to improve

the operation efficiency and the suction performance. The low heat load can reduce the liquid

consumption, which can further improve the operation efficiency.

Fourthly, the high reliability: the motor, the supporting bearing of the rotating shaft and the

dynamic seal structure are all located in the room temperature environment, which can improve the

reliability and prolong the operation cycle. The core parts which can be pulled out is convenient for maintenance.

Although the present invention has been described in detail for the purpose of illustration, it is to

be understood that such detail is solely for that purpose and that variations can be made therein by

those in the art without departing from the spirit and scope of the invention.

Throughout the specification and the claims that follow, unless the context requires otherwise, the

words "comprise" and "include" and variations such as "comprising" and "including" will be

understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any

other integer or group of integers.

The reference to any prior art in this specification is not, and should not be taken as, an

acknowledgement of any form of suggestion that such prior art forms part of the common general

knowledge.

In some cases, a single embodiment may, for succinctness and/or to assist in understanding the

scope of the disclosure, combine multiple features. It is to be understood that in such a case, these

multiple features may be provided separately (in separate embodiments), or in any other suitable

combination. Alternatively, where separate features are described in separate embodiments, these

separate features may be combined into a single embodiment unless otherwise stated or implied. This

also applies to the claims which can be recombined in any combination. That is a claim may be

amended to include a feature defined in any other claim. Further a phrase referring to "at least one of'

a list of items refers to any combination of those items, including single members. As an example,

"at least one of a, b, orc" is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c.

It will be appreciated by those skilled in the art that the invention is not restricted in its use to the

particular application described. Neither is the present invention restricted in its preferred embodiment

with regard to the particular elements and/or features described or depicted herein. It will be

appreciated that the invention is not limited to the embodiment or embodiments disclosed, but is

capable of numerous rearrangements, modifications and substitutions without departing from the

scope of the invention as set forth and defined by the following claims.

Claims

1. A vertical type cryogenic circulation centrifugal pump comprising: a motor assembly, a rotating

shaft, an impeller, an inducer, a volute and a heat insulation protection; the motor assembly, which

forms a closed container at room temperature, includes a coil, two support bearings, a dynamic seal

and a top flange which is used to isolate the room temperature and low temperature vacuum

environment; the dynamic seal, which is fixed by the top flange, comprises a top cover, a seal filler

and a bottom plate, wherein the seal filler, which is a multilayer structure, is composed of carbon rings

and stainless steel rings inside a closed container which includes the top cover and the bottom plate;

the rotating shaft includes two parts, one is solid part which is located inside of the motor assembly at

room temperature and supported by the two bearings, and the other is hollow part which is connected

with a full flow impeller and an inducer at the low temperature vacuum environment; the impeller and

its inducer inside the volute directly contact with the cryogenic liquid; between the top flange and the

volute is a heat insulation protection with many insulating baffles at the low temperature vacuum

environment.

2. The vertical type cryogenic circulation centrifugal pump according to Claim 1, wherein the heat

insulation protection structure is further comprising: an outer sleeve, an inner sleeve and a number of

horizontal protective baffles between the two sleeves; each of horizontal protective baffles is

connected with the inner sleeve respectively, and there is a small gap between the horizontal protective

baffles and the outer sleeve; there is a small gap between the inner sleeve and the rotating shaft.

3. The vertical type cryogenic circulation centrifugal pump according to Claim 2, wherein the

impeller includes a volute which is connected with the heat insulation structure; the impeller and the

inducer is inside the volute; a liquid inlet is set at the bottom of the volute and an outlet at the side.

4. The vertical type cryogenic circulation centrifugal pump according to Claim 3, wherein the

inducer is the front stage of the impeller.

5. The vertical type cryogenic circulation centrifugal pump according to Claim 1, wherein the room

temperature part of the rotating shaft is designed as a solid structure and the low temperature part as

hollow one.

6. The vertical type cryogenic circulation centrifugal pump according to the Claim 5, wherein an

internal thread is set at the end of the rotating shaft; the impeller and the inducer are fixed at the end of the rotating shaft by a bolt with reverse thread.

7. The vertical type cryogenic circulation centrifugal pump according to Claim 1, wherein the motor

assembly, which forms a closed container at room temperature, includes a coil, and two support

bearings.

8. The vertical type cryogenic circulation centrifugal pump according to Claim 1, the motor

assembly includes a frequency transformer, which is used to control the frequency of themotor.