US20170254338A1

US20170254338A1 - Apparatus and method for surge prevention for centrifugal compressor

Info

Publication number: US20170254338A1
Application number: US15/446,666
Authority: US
Inventors: Joa Hyoung LEE
Original assignee: Electronics and Telecommunications Research Institute ETRI
Current assignee: Electronics and Telecommunications Research Institute ETRI
Priority date: 2016-03-02
Filing date: 2017-03-01
Publication date: 2017-09-07
Also published as: KR20170102736A

Abstract

Disclosed is an apparatus and method for surge prevention for a centrifugal compressor. An apparatus for surge prevention for a buffering vessel based centrifugal compressor according to the present invention includes a recycle pipe which connects a suction portion to a discharge portion of the centrifugal compressor, a cooler which cools compressed gas received according to an opening of a recycle valve disposed at the recycle pipe, a buffering vessel which stores the gas cooled by the cooler, and a compressor control unit which determines a surge occurrence condition to control opening and closing of the recycle valve and a buffer valve which is disposed at a rear stage of the buffering vessel.

Description

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to and the benefit of Korean Patent Application No. 10-2016-0025237, filed on Mar. 2, 2016, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Invention
The present invention relates to an apparatus and method for surge prevention for a centrifugal compressor.
2. Discussion of Related Art Performance of a centrifugal compressor is represented by a flow curve relative to a compression ratio, and it is possible to maximize the performance of the centrifugal compressor by increasing resistance in a discharge portion and lowering an input gas flow rate when a speed of an impeller is constant.
However, when the resistance is excessively high and the gas flow rate is lowered to such an extent that it can't overcome the resistance, a surge phenomenon occurs in which air or gas in the discharge portion backflows, which causes the impeller to be burdened and damaged.
A blow off method and a recycle method have been proposed to prevent such a surge phenomenon, wherein the blow off method has a problem in that efficiency thereof is degraded because compressed gas or air is wasted and the recycle method has a problem in that a delay occurs in increasing gas flow of a suction portion because output gas needs to go through a process having its temperature lowered before being re-input to the compressor.

SUMMARY OF THE INVENTION

The present invention is directed to providing an apparatus and method for preventing a surge by including a cooler and a buffering vessel, which stores gas whose temperature is lowered by the cooler, which are provided at a recycle pipe and by controlling a gas flow input to a suction portion of a centrifugal compressor and resistance generated at a discharge portion of a centrifugal compressor.
According to an aspect of the present invention, there is provided an apparatus for surge prevention for a buffering vessel based centrifugal compressor, including: a recycle pipe which connects a suction portion to a discharge portion of the centrifugal compressor; a cooler which cools compressed gas received according to an opening of a recycle valve disposed at the recycle pipe; a buffering vessel which stores the gas cooled by the cooler; and a compressor control unit which determines a surge occurrence condition to control opening and closing of the recycle valve and a buffer valve which is disposed at a rear stage of the buffering vessel.
According to another aspect of the present invention, there is provided a method for surge prevention for a buffering vessel based centrifugal compressor, including: checking a level value of a buffering vessel which receives and stores compressed gas through a recycle pipe; controlling opening and closing of a recycle valve according to the level value; determining a surge occurrence condition; and introducing the gas stored in the buffering vessel into a suction portion of the centrifugal compressor by opening a buffer valve when the surge occurrence condition is determined to be satisfied.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will become more apparent to those of ordinary skill in the art by describing exemplary embodiments thereof in detail with reference to the accompanying drawings, in which:

FIG. 1 is a graph illustrating a flow curve relative to a compression ratio which represents performance of a centrifugal compressor;

FIG. 2 is a view illustrating a gas flow of a centrifugal compressor in a normal state;

FIG. 3 is a view illustrating a gas flow of a centrifugal compressor in a surge state;

FIG. 4 is a view illustrating a recycle method according to a conventional technology;

FIG. 5 is a view illustrating a gas flow of a normal state in a recycle method according to a conventional technology;

FIG. 6 is a view illustrating a gas flow of a surge state in a recycle method according to a conventional technology;

FIG. 7 is a view illustrating an apparatus for surge prevention for a buffering vessel based centrifugal compressor according to an embodiment of the present invention;

FIG. 8 is a view illustrating a process of storing gas in a buffering vessel according to an embodiment of the present invention;

FIG. 9 is a view illustrating an open state of a buffer valve according to an embodiment of the present invention;

FIG. 10 is a view illustrating a state in which a recycle valve and a buffer valve are opened when pressure of a discharge portion is high according to an embodiment of the present invention; and

FIG. 11 is a flow chart illustrating a method of surge prevention for a buffering vessel based centrifugal compressor according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The above-described objectives, other objectives, advantages, and features of the present invention and methods of accomplishing them will be made apparent from the following detailed description of the embodiments with reference to the accompanying drawings.
The present invention may, however, be embodied in different forms and is not to be construed as limited to the embodiments set forth herein. Rather, the embodiments are provided to easily convey objectives, configurations, and effects of the present invention to those skilled in the art of the technical field to which the present invention belongs, and the scope of the present invention should be defined only by the appended claims.
Meanwhile, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well unless clearly indicated otherwise by context. It should be further understood that the terms “comprises” and “comprising” specify the presence of stated features, integers, steps, operations, elements, and/or components when used herein, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
Before describing exemplary embodiments of the present invention, a background of the present invention will first be described to facilitate understanding of those skilled in the art.
There are several types of compressors depending on methods of compressing air or gas, and a user selects a compressor according to field conditions.
Air compressors are classified into reciprocating compressors, rotary compressors (screw compressors), and turbo compressors according to a compression method, and turbo compressors are classified into centrifugal compressors and axial compressors.
A centrifugal compressor is an apparatus that compresses a fluid by rotating gas or air suctioned via a suction portion using an impeller to transfer kinetic energy thereto and converting the kinetic energy into pressure according to resistance at a discharge portion.
Performance of such a centrifugal compressor may be represented by a flow curve relative to a compression ratio as illustrated in FIG. 1.
The compression ratio of the centrifugal compressor increases as a speed N of an impeller increases, resistance R at a discharge portion increases, and an input gas flow rate Q decreases.
When the speed of the impeller is constant, it is possible to maximize the performance of the centrifugal compressor by increasing the resistance at the discharge portion and lowering the input gas flow rate, however when the resistance is excessively high and the gas flow rate is lowered to such an extent that the resistance cannot be overcome, a surge phenomenon occurs in which air or gas in the discharge portion backflows and causes the impeller to be burdened and damaged.
A gas flow in a normal state (when the gas flow is greater than pressure of the discharge portion) is shown in FIG. 2, and the gas flow in a surge state (the pressure of the discharge portion is greater than the gas flow) is shown in FIG. 3.
A state in which a surge may occur is referred to as a surge limit line (SLL), and a measure for preventing an occurrence of a surge is necessary because a surge may occur when a performance state of the centrifugal compressor approaches the SLL.
A blow off method and a recycle method have been proposed to prevent such a surge phenomenon, and the blow off method includes a blow off valve (BOV) installed in a discharge portion to adjust resistance of the discharge portion, and the BOV is opened to discharge gas to the outside when a possibility of an occurrence of a surge is high.
In a blow off method according to a conventional technology, although resistance in a discharge portion may be lowered by discharging air or gas compressed by a centrifugal compressor to the outside, efficiency is degraded because some of the gas or air compressed by the centrifugal compressor is wasted and there is a problem in that a production amount is decreased when the system is for gas production.
A recycle method according to a conventional technology proposed to resolve the problem of such a blow off method is as shown in FIG. 4.
The recycle method is a method in which gas output from a discharge portion is input back to a compressor instead of being discharged to the outside, and, referring to FIG. 4, is configured to include a cooler 10, a flow sensor 21 and a pressure sensor 22 which are disposed at a suction portion 20, a pressure sensor 41 disposed at a discharge portion 40, a recycle pipe 60 and a recycle valve 61 disposed thereat, and a compressor control unit 50 which controls opening and closing of the recycle valve 61.
As illustrated in FIG. 5, when a gas flow of the suction portion 20 is greater than pressure of the discharge portion 40, gas flows in a normal state and an input of output gas through the recycle pipe 60 is not performed.
As illustrated in FIG. 6, when a possibility of an occurrence of a surge is high, inputting output gas to a compressor 30 may not only lower resistance of the discharge portion 40 but also increase a gas flow input to the compressor 30, and thereby the recycle method may more effectively prevent a surge.
As described above, such a recycle method has an advantage in that a production amount is not reduced when compared to the blow off method because gas is not wasted and the output gas is re-input to the compressor 30, however the output gas that is re-input to the compressor 30 needs to go through a process of having a gas temperature thereof being lowered by the cooler 10.
Accordingly, there is a disadvantage in that a delay occurs in increasing the gas flow input to the suction portion 20, and a problem arises in that an immediate reaction is not easy even when a possibility of an occurrence of a surge is high.
An apparatus for surge prevention for a buffering vessel based centrifugal compressor according to an embodiment of the present invention proposed to resolve the above-described problem is shown in FIG. 7.
To prevent a surge from occurring at a centrifugal compressor, a gas flow rate input to a suction portion 200 needs to be increased or resistance generated at a discharge portion 400 needs to be lowered, and the present invention is directed to providing an apparatus and method which may immediately react when a surge is expected to occur by including a cooler 620 and a buffering vessel 630, which stores gas whose temperature is lowered by the cooler 620, which are disposed at a recycle pipe 600.
That is, according to the embodiment of the present invention, the cooler 620 and the buffering vessel 630 are installed at a front stage of the suction portion 200, and since a buffer valve 640 may be opened as needed after compressed gas is cooled by the cooler 620 and stored in the buffering vessel 630, there is an effect in that the problem of the delay time occurrence in the above-described recycle method according to a conventional technology is solved.
The buffering vessel based centrifugal compressor according to the embodiment of the present invention includes the recycle pipe 600 which connects the suction portion 200 to the discharge portion 400 of the centrifugal compressor.
In addition, the buffering vessel based centrifugal compressor includes the cooler 620 disposed at a rear stage of the recycle pipe 600 and configured to lower a temperature of a gas compressed by the centrifugal compressor according to an opening of a recycle valve 610 disposed at a frontstage of the recycle pipe 600.
In addition, the buffering vessel based centrifugal compressor includes the buffering vessel 630 which stores the gas cooled by the cooler 620 and a compressor control unit 500 which determines a surge occurrence condition to control the recycle valve 610 and the buffer valve 640 which is disposed at a rear stage of the buffering vessel 630.
The cooler 620 is a constituent element which lowers a temperature of the compressed gas received from the discharge portion 400, through which the compressed gas is output, through the recycle pipe 600.
The buffering vessel 630 stores the gas cooled by the cooler 620, conveys the stored gas to the suction portion 200 to increase a gas flow rate of the suction portion 200 when the gas flow rate of the suction portion 200 is lowered and a possibility of an occurrence of a surge is high, and thereby preventing the occurrence of a surge.
The compressor control unit 500 receives sensed values from a flow sensor 210 and a first pressure sensor 220 which are disposed at the suction portion 200 and a second pressure sensor 410 disposed at the discharge portion 400 to determine a surge occurrence condition, and controls opening and closing of the recycle valve 610 and the buffer valve 640.
FIG. 8 is a view illustrating a process of storing gas in a buffering vessel of an apparatus for surge prevention for a buffering vessel based centrifugal compressor according to an embodiment of the present invention.
As illustrated in FIG. 8, the compressor control unit 500 determines an amount of gas stored in the buffering vessel 630 by a level sensor 631 disposed at the buffering vessel 630.
When the amount of gas stored in the buffering vessel 630 is lower than a preset value and the buffering vessel 630 is determined to have available space, the compressor control unit 500 opens the recycle valve 610 and the buffering vessel 630 stores the gas cooled by the cooler 620.
Next, the compressor control unit 500 monitors a sensed value of the level sensor 631 and close the recycle valve 610 when the amount of gas stored in the buffering vessel 630 is equal to or more than the preset value (or when the buffering vessel is full).
FIG. 9 is a view illustrating an opening of a buffer valve of an apparatus for surge prevention for a buffering vessel based centrifugal compressor according to an embodiment of the present invention.
The buffer valve 640 is a constituent element which controls the gas input from the buffering vessel 630 to the suction portion 200.
The compressor control unit 500 opens the buffer valve 640 when the gas flow rate input to the suction portion 200 is lowered and a possibility of an occurrence of a surge is high.
According to the opening of the buffer valve 640, the gas stored in the buffering vessel 630 is introduced into the suction portion 200 to increase the gas flow rate of the suction portion 200.
In this manner, when the possibility of an occurrence of a surge is determined to be high, the gas cooled by the cooler 620 and stored in the buffering vessel 630 is immediately introduced into the suction portion 200 to increase the gas flow rate of the suction portion 200, thereby performing a quick reaction to the possibility of an occurrence of a surge.
FIG. 10 is a view illustrating a state in which a recycle valve and a buffer valve are opened when pressure of a discharge portion of an apparatus for surge prevention for a buffering vessel based centrifugal compressor according to an embodiment of the present invention is high.
When there is a possibility of an occurrence of a surge due to excessively high pressure of the discharge portion 400 even when the gas flow rate input to the compressor 300 through the suction portion 200 is increased, the compressor control unit 500 lowers the pressure of the discharge portion 400 by controlling the recycle valve 610 to be opened so that the compressed gas of the discharge portion 400 is stored in the buffering vessel 630 through the recycle pipe 600 and the cooler 620.
According to the embodiment of the present invention, the gas flow rate and the pressure of the suction portion 200 and the pressure of the discharge portion 400 are monitored to control the opening and closing of the recycle valve 610 and the buffer valve 640, and thereby the gas flow rate input to the suction portion 200 is increased and the resistance generated in the discharge portion 400 is lowered, resulting in an effect of preventing the occurrence of a surge.
According to the embodiment of the present invention, when there is available space in the buffering vessel 630, the recycle valve 610 is opened to enable the compressed gas to be introduced through the recycle pipe 600, cooled by the cooler 620, and stored in the buffering vessel 630, and when a possibility of an occurrence of a surge is high due to a low gas flow rate in the suction portion 200, the buffer valve 640 is opened so that the gas stored in the buffering vessel 630 may be quickly introduced into the suction portion 200.
In addition, in spite of the gas flow rate input to the suction portion 200 being increased, when the possibility of an occurrence of a surge is still expected due to excessively high pressure of the discharge portion 400, the resistance of the discharge portion 400 may be lowered by opening the recycle valve 610.
FIG. 11 is a flow chart illustrating a method of surge prevention for a buffering vessel based centrifugal compressor according to an embodiment of the present invention.
A method of surge prevention for a buffering vessel based centrifugal compressor according to an embodiment of the present invention includes, firstly closing a recycle valve and a buffer valve (S100).
Next, the method includes reading a sensed value from a level sensor disposed at a buffering vessel and checking a level value of the buffering vessel (S200).
As a result of the checking, the method includes maintaining a closed state of the recycle valve when gas is sufficiently stored in the buffering vessel, and opening the recycle valve to store compressed gas of a discharge portion when there is available space in the buffering vessel (S300).
Here, the compressed gas received through the recycle valve is cooled by a cooler before being stored in the buffering vessel.
S400 is an operation in which a possibility of an occurrence of a surge is primarily determined, and the possibility of an occurrence of a surge is determined using sensed values of a gas flow rate and pressure of a suction portion respectively input from a flow sensor and a first pressure sensor which are disposed at the suction portion and a sensed value of pressure of the discharge portion input from a second pressure sensor disposed at the discharge portion.
When the possibility of an occurrence of a surge is determined to be low in operation S400, the process returns to operation S200 in which the level value of the buffering vessel is checked.
On the other hand, when the possibility of an occurrence of a surge is determined to be high in operation S400, the buffer valve is opened to introduce the gas stored in the buffering vessel into the suction portion so that the gas flow rate of the suction portion is increased (S500).
As describe above, since the gas is cooled by the cooler before being stored in the buffering vessel, the gas flow rate of the suction portion may be increased without a time delay in operation S500.
Following the opening of the buffer valve, the possibility of an occurrence of a surge is secondarily monitored (S600), and when the possibility of an occurrence of a surge is determined to be low as a result of the monitoring, the process returns to operation S200 in which the level value of the buffering vessel is checked. On the other hand, when the possibility of an occurrence of a surge is determined to still be high in operation S600, the recycle valve is opened to enable the compressed gas in the discharge portion to be input to the cooler and the buffering vessel for reducing the resistance of the discharge portion (S700).
The apparatus and method for surge prevention for a buffering vessel based centrifugal compressor has an effect in which an occurrence of a surge may be prevented by including the cooler and the buffering vessel, which stores gas cooled by the cooler, which are provided at the recycle pipe and by quickly increasing the gas flow input to the suction portion when a possibility an occurrence of a surge is determined to be high.
The present invention has been described in connection with exemplary embodiments. Those skilled in the art should understand that various modifications may be made to the embodiments without departing from the spirit and features of the present invention. Therefore, the disclosed embodiments should be considered from an illustrative perspective rather than a restrictive perspective. The scope of the present invention is represented in the attached claims rather than the above-described description, and all technical differences within an equivalent scope thereof should be interpreted as being included in the scope of the present invention.


[Reference Numerals]

10: COOLER	200: SUCTION PORTION
210: FLOW SENSOR	220: FIRST PRESSURE SENSOR
300: CENTRIFUGAL	400: DISCHARGE PORTION
COMPRESSOR
410: SECOND PRESSURE SENSOR	500: COMPRESSOR CONTROL
	UNIT
600: RECYCLE PIPE	610: RECYCLE VALVE
620: COOLER	630: BUFFERING VESSEL
631: LEVEL SENSOR	640: BUFFER VALVE

Claims

What is claimed is:

1. An apparatus for surge prevention for a buffering vessel based centrifugal compressor comprising:

a recycle pipe which connects a suction portion to a discharge portion of the centrifugal compressor;

a cooler which cools compressed gas received according to an opening of a recycle valve disposed at the recycle pipe;

a buffering vessel which stores the gas cooled by the cooler; and

a compressor control unit which determines a surge occurrence condition to control opening and closing of the recycle valve and a buffer valve which is disposed at a rear stage of the buffering vessel.

2. The apparatus of claim 1, wherein the compressor control unit receives a sensed value from a flow sensor and a first pressure sensor which are disposed at the suction portion and a second pressure sensor disposed at the discharge portion to determine the surge occurrence condition.

3. The apparatus of claim 1, wherein the compressor control unit receives a sensed value from a level sensor disposed at the buffering vessel to control the opening and closing of the recycle valve.

4. The apparatus of claim 1, wherein the compressor control unit opens the buffer valve to enable the gas stored in the buffering vessel to be introduced into the suction portion when an occurrence of a surge is expected.

5. The apparatus of claim 4, wherein the compressor control unit opens the recycle valve when a surge is expected to occur due to pressure of the discharge portion in spite of a gas flow rate of the suction portion being increased by opening the buffer valve.

6. A method for surge prevention for a buffering vessel based centrifugal compressor comprising:

checking a level value of a buffering vessel which receives and stores compressed gas through a recycle pipe;

controlling opening and closing of a recycle valve according to the level value;

determining a surge occurrence condition; and

introducing the gas stored in the buffering vessel into a suction portion of the centrifugal compressor by opening a buffer valve when the surge occurrence condition is determined to be satisfied.

7. The method of claim 6, further comprising closing the recycle valve and the buffer valve which is disposed at a rear stage of the buffering vessel before the checking.

8. The method of claim 6, wherein the controlling opens the recycle valve to store the gas in the buffering vessel when the level value is less than a preset value and close the recycle valve when the level value is equal to or higher than the preset value.

9. The method of claim 8, wherein the controlling enables the gas to be cooled by a cooler before being stored in the buffering vessel.

10. The method of claim 6, wherein the determining determines a possibility of an occurrence of a surge on the basis of a gas flow rate and pressure of the suction portion of the centrifugal compressor and pressure of a discharge portion of the centrifugal compressor.

11. The method of claim 6, further comprising, after the introducing, monitoring a possibility of an occurrence of a surge due to high pressure of a discharge portion in spite of opening the buffer valve.

12. The method of claim 11, further comprising introducing the compressed gas in the discharge portion of the centrifugal compressor into the buffering vessel by opening the recycle valve when the possibility of an occurrence of a surge is monitored in the monitoring.