Centrifugal compressor that recovers energy from the recirculation line

Abstract

A centrifugal compressor (21) is described and disclosed with an anti-surge return line (2), a radial expansion impeller (22) configured downstream of a compressor discharge (23), one or more flow regulators configured between the compressor discharge (23) and the radial expansion impeller (22), and a radial expansion impeller discharge (29) is connected to the anti-surge return line (2). A method for controlling surge in a compressor is also described, the method including directing at least a portion or a constant volume of a continuous flow of fluid from the compressor (21) to the radial expansion impeller (22) and the return line (2).

Description

[Technical Field]

[0001] This disclosure relates to centrifugal compressors, and more particularly to centrifugal compressors having an anti-surge control system. More specifically, this disclosure relates to a centrifugal compressor having a recirculation line that returns a portion of the discharge gas from the compressor outlet to the inlet, and means for recovering energy from the portion of the discharge gas. Embodiments disclosed herein relate, in particular, to a centrifugal compressor comprising a recirculation line and means for energy recovery configured and arranged along the recirculation line, together with suitable equipment for monitoring and control. [Background technology]

[0002] Centrifugal and axial compressors can experience a potentially destructive condition known as a surge.

[0003] A surge is defined as the operating point at which a centrifugal compressor reaches its peak head capacity and minimum flow rate limits. This condition occurs when the amount of gas being processed by the compressor is insufficient for the size of the compressor, causing the blades to lose their ability to transfer energy from the shaft to the fluid.

[0004] The operating principle of a centrifugal compressor is to create a pressure increase by adding kinetic energy / velocity to the continuous flow of fluid through the rotor, and then convert this kinetic energy into an increase in potential energy / static pressure by decelerating the flow through the diffuser. The pressure increase in the rotor is almost always approximately equal to the pressure increase in the diffuser. The fluid flow from the diffuser is then collected by the collector and sent downstream at the required pressure and flow rate.

[0005] It is known that a significant reduction in fluid flow through the compressor during startup or emergency shutdown can cause a surge, potentially preventing the compressor from meeting downstream flow requirements. The collector pressure can become higher than the compressor outlet pressure, causing the fluid to backflow, or even reverse, within the compressor. As a result, the collector pressure decreases, the inlet pressure increases, and the flow reverses again. This phenomenon occurs repeatedly in cycles where the frequency varies from 1 Hz to 2 Hz. The compressor loses its ability to maintain its peak head, and the entire system becomes unstable.

[0006] Surging can cause the compressor to overheat to a point where it exceeds the unit's maximum allowable temperature. Surging can also cause damage to the rotor's thrust bearings due to the rotor shifting back and forth from the working side to the non-working side. This is defined as a surge cycle in the compressor.

[0007] To avoid surges, an anti-surge control system is typically made available with the compressor to detect when the process compression stage is approaching a surge and then take measures to maintain stable operation by reducing the collector pressure and increasing the flow through the compressor. Referring to Figure 1, a schematic diagram of a centrifugal compressor including a prior art anti-surge control system is shown, which is typically achieved by providing a recirculation line 2 (also called an anti-surge line) with the compressor 1, which returns a portion of the discharge gas from the outlet 3 to the inlet 4 of the compressor 1. The anti-surge control system 5 is connected to temperature, pressure, and flow meters 6 on the outlet line 7 of the compressor 1 and temperature, pressure, and flow meters 8 on the inlet line 9 of the compressor 1. The operation of such an anti-surge control system 5 is performed by opening a control valve 10 (also called an anti-surge valve) in the recirculation line 2 via a valve control subsystem 10'. By returning a portion of the compressor's discharge gas to the inlet 4 of the compressor 1, a minimum necessary flow rate is always guaranteed at the compressor inlet 4. The gas flow returned to compressor 1 typically passes through a scrubber 11 configured upstream of the compressor 1 inlet 4. The scrubber 11 is usually required to prevent liquid from entering compressor 1. The gas flow returned to compressor 1 also passes through a cooling system 12 (chiller), which can be configured upstream or downstream of the anti-surge valve 10 and, in some cases, may be bypassed depending on the dynamics that need to be provided. Figure 1 also shows the compressor driver 13 and the cooling system 14 for the portion of the gas flow that is not returned to compressor 1 but is sent to a downstream service 15 or process. The driver 13 rotates the compressor 1 by providing the necessary mechanical power. The driver 13 can be an electric motor. In other embodiments, the driver 13 can be a mechanically powered turbomachinery such as a gas turbine engine or steam turbine. In yet another embodiment, the driver 13 can include a reciprocating internal combustion engine.

[0008] As a result of using the anti-surge control system, the compressor's operating state is maintained stably due to the dual effect of increasing the flow rate and reducing the discharge pressure that actually changes the system's resistance curve.

[0009] Furthermore, in some applications, an anti-surge line can be used to extend the compressor's operating range towards lower flow rates. Therefore, the anti-surge system can operate either during shutdown and startup, or during normal operation.

[0010] Regarding the effects of surging on the thrust bearings of the compressor, the following must also be considered:

[0011] A centrifugal compressor processes a certain volume of gas and increases its pressure. In particular, in a multi-stage compressor, the pressure gradually increases with each stage. As a result, under normal operation, the pressure downstream of the compressor is higher than that upstream, and the effect resulting from the compressor's operation is the generation of axial force on the rotor. In addition to differential pressure, the axial force is essentially also due to contributions from momentum fluctuations in various parts of the rotor.

[0012] Referring to Figure 2, a schematic diagram of the longitudinal section of a conventional centrifugal compressor is shown. In Figure 2, the same reference numerals represent the same or corresponding parts, elements, or components already illustrated in Figure 1 and described above, and are not described again here. In particular, Figure 2 shows a cross-section of half of the compressor 1 above the rotation axis z of the rotor 16. Figure 2 also shows the stator 17, the compressor gas inlet 4, and the outlet 3. The axial force on the rotor 16 is offset by a thrust bearing 18. To minimize the size of the thrust bearing 18, the compressor structure includes an axial thrust balancing system that reduces its size. The balancing system consists of a balance drum 19 attached to the rotor 16 and coupled to a stator seal 20 configured to be positioned downstream of the compressor outlet. A pressure drop occurs at the interface between the balance drum 19 and the stator seal 20, so in normal operation, the balance drum 19 counteracts the higher upstream pressure (typically the discharge pressure of the compressor 1) and the lower downstream pressure (typically the suction pressure of the compressor 1). The pressure difference across the front of the balance drum 19 balances other thrust contributions and generates a force that can be adjusted by the selection of the diameter of the balance drum 19. The fluid leaving the balance drum 19 is led through a pipe to a low-pressure source, which is typically the compressor suction port, but can be any other low-pressure point inside or outside the machine.

[0013] Therefore, an improved anti-surge control system to address the issues of instability and the risk of damage to the thrust bearings of current compressor technology would be beneficial and welcome in the technology. More generally, it is desirable to provide a system adapted to more efficiently address the problems associated with surging. [Overview of the Initiative]

[0014] In one embodiment, the subject matter disclosed herein is a centrifugal compressor in which a radially expanding impeller is configured and positioned on the end of the rotor shaft downstream of the compressor discharge port, and the discharge port of the radially expanding impeller is connected to a recirculation line, returning a portion of the compressor discharge gas to the compressor inlet.

[0015] In another aspect, the subject matter disclosed herein relates to an arrangement of a centrifugal compressor having a radial expander connected via a gas passage and a mechanical device, the expander being capable of performing a pressure expansion of a working fluid and generating useful mechanical power. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Many of the disclosed embodiments of the invention, and attendant advantages thereof, will be better understood and readily appreciated when considered in connection with the accompanying drawings, by reference to the following detailed description of the invention, from which a complete understanding may be easily obtained. [Figure 1] FIG. 1 is a schematic view of a centrifugal compressor including an anti-surge control system according to the prior art. [Figure 2] FIG. 2 shows a schematic longitudinal cross-section of a centrifugal compressor including a balance drum according to the prior art. [Figure 3] FIG. 3 shows a schematic longitudinal cross-section of a centrifugal compressor including a radial expansion impeller and a discharge gas recirculation line according to one embodiment. [Figure 4] FIG. 4 shows a schematic view of a centrifugal compressor including an anti-surge control system according to the present disclosure. [Figure 5] FIG. 5 shows a compressor operating map. DETAILED DESCRIPTION OF THE INVENTION

[0017] [[ID=3I]] According to one aspect, the subject matter is directed to a centrifugal compressor in which a centrifugal expansion impeller is arranged downstream of the compressor discharge port to convert the potential energy / static pressure of the discharge gas from the compressor into kinetic energy and balance the axial thrust of the compressor.

[0018] According to another aspect, the discharge port of the radial expansion impeller is connected to a recirculation line to return a portion of the discharge gas of the compressor to the inlet of the compressor and act as an anti-surge system.

[0019] According to one aspect, the subject matter includes a radial compressor that replaces the balance drum of a prior art centrifugal compressor with a radially expanding impeller.

[0020] According to another aspect, the nozzle system is configured to regulate the passage of gas through the expanding impeller and allow the passage of some or all of the compressor discharge flow.

[0021] According to yet another aspect, the diffuser is configured to convey the gas processed by the radially expanding impeller downstream to a discharge volute connected to a return line that feeds back to the compressor inlet.

[0022] According to a further aspect, the diffuser is alternatively oriented axially or radially.

[0023] According to another aspect, the radially expanding impeller is arranged along the rotor and, for example, projects outside a journal bearing. In particular, this configuration is convenient for configurations where fluid can be discharged to the atmosphere.

[0024] According to yet another aspect, the machine includes a gas journal bearing or an active magnetic bearing.

[0025] Hereinafter, embodiments of the Disclosure are given in detail, and one or more of these examples are illustrated in the figures. Each example is provided for illustrative purposes only and is not limiting to the Disclosure. It will be apparent to those skilled in the art that various modifications and variations can be made to the Disclosure, as long as they do not deviate from the scope or spirit of the Disclosure. Throughout this Specification, any reference to “a certain embodiment,” “one embodiment,” or “several embodiments” means that a particular feature, structure, or characteristic described in relation to one embodiment is included in at least one embodiment of the subject matter disclosed. Thus, where the phrases “in a certain embodiment,” “one embodiment,” or “several embodiments” appear in various places throughout this Specification, they do not necessarily refer to the same embodiment. Furthermore, certain features, structures, or characteristics can be combined in any preferred manner in one or more embodiments.

[0026] When presenting elements of various embodiments, the articles "a," "an," "the," and "said" are intended to indicate that there is one or more of those elements. The terms "comprising," "including," and "having" are intended to be non-exclusive, meaning that additional elements other than those listed may exist.

[0027] Referring here to the drawings, particularly Figure 3, a schematic diagram of a longitudinal cross-section of a centrifugal compressor according to one embodiment is shown, and the same reference numerals indicate the same or corresponding parts, elements, or components already shown in Figures 1 and / or 2 and described above, which are not described again. In particular, Figure 3 shows a cross-section of half of the compressor 21 above the rotation axis z of the rotor 16. Figure 3 also shows the stator 17 and thrust bearing 18, as well as the gas inlet 4 and outlet 3 of the compressor.

[0028] The radially expanding impeller 22 is configured and positioned downstream of the compressor discharge port 23 and receives the gas flow directly from the compressor discharge volute 24 through the deswarler 25. The passage of the gas flow through the expanding impeller 22 is regulated by a system including one or more adjustable nozzles 26 configured to regulate the amount of gas flow passing through the radially expanding impeller 22. Thus, one or more nozzles 26 can be adjusted to allow 100% of the gas flow (i.e., the entire gas flow) to pass through the impeller 22, or to allow any amount less than 100% of the entire gas flow (i.e., a portion of the entire gas flow or volume) to pass through the impeller 22. One or more nozzles 26 can also control the flow rate of the gas flow, and in some embodiments where multiple nozzles 26 are used, the amount of gas flow through each nozzle and / or the associated gas flow rate through each nozzle may be the same for all nozzles 26 or may differ among any of the nozzles. When only a portion of the gas flow is allowed to pass through the impeller 22, the remaining amount, portion, or volume of the gas flow, i.e., the gas flow that does not pass through the expansion impeller 22, is discharged toward the downstream service or process 15 (e.g., pipeline, tank, chemical reactor, cavity, reservoir, heat exchanger, etc.) at the compressor design discharge pressure.

[0029] Referring also to Figure 4, which shows a schematic diagram of a centrifugal compressor including an anti-surge control system according to one embodiment, the adjustable nozzle 26 is automatically controlled to keep its operating point within a compressor stable operation map (as described below with reference to Figure 5) by an anti-surge control system 27 connected to temperature, pressure, and flow meters 6 on the outlet line 7 of the compressor 21, temperature, pressure, and flow meters 8 on the inlet line 9 of the compressor 21, and a nozzle guide vane control subsystem 27', the nozzle guide vane control subsystem 27' is connected to a nozzle guide vane actuator 28 to adjust the nozzle 26 of the expansion impeller 22 as needed.

[0030] The discharge port 29 of the radially expanding impeller 22 is connected to the diffuser 30 and then, via the recirculation line 2, to the inlet 4 of the compressor 21.

[0031] A centrifugal compressor including an anti-surge control system according to the present disclosure has the position of the input signal (compressor discharge volume) the same as the control action (the compressor discharge port and the recirculation inlet are in the same place), removing the delay due to the gas volume (piping and devices) between the compressor outlet of the prior art and the anti-surge control valve, thus shortening the reaction time of the system and providing more effective control.

[0032] Referring also to FIG. 5 showing a compressor operating map, that is, a map showing the operating state of the compressor as a function of the inlet flow rate x with the discharge pressure / suction pressure ratio, i.e., the points representing the head y of the compressor, the centrifugal compressor 21 of the present disclosure operates as follows. The compressor operating map shows several curves 31 specific to any compressor for different rotational speeds and is divided into three regions, namely, a stable operating region 32 to the right of the surge control line 33, a margin region 34 included between the surge control line 33 and the surge limit line 35, and an unstable operating region 36 to the left of the surge limit line 35. During normal operation, i.e., when the operating point is within the stable operating region 32 of the compressor operating map, the gas flow (G cc ) processed by the compressor 21 is divided into the flow (G out ) at the compressor outlet 3 and the flow (G exp ) to the expanding impeller 22. G cc = G out + G exp

[0033] During normal operation, the flow rate at the compressor outlet 3 is much higher than the flow rate processed by the expanding impeller 22, G out >> G exp (e.g., 96% and 4% of G cc respectively).

[0034] The anti-surge control system 27 continuously monitors the compressor inlet flow rate x and the relative discharge head y, and if it detects that the process compression stage is approaching a surge state or situation, for example, when the operating point 37 is on the surge control line 32, the anti-surge control system 27 communicates with the nozzle control subsystem 27' to operate the nozzle actuator 28, and subsequently opens the adjustable nozzle 26, allowing a larger portion or volume of the total gas flow from the compressor discharge port 23 to pass through the deswarra 25 to the expansion impeller 22, thereby converting the potential energy / static pressure of the expansion impeller 22 into kinetic energy.

[0035] During this stage, the flow rate processed by the expansion impeller 22 can vary from a small amount (minimal recirculation) to the entire compressor flow (complete recirculation) (for example, G cc 0% and 100% of that.

[0036] Energy E recovered by the expanding impeller 22 rec The capacity G of the expansion impeller 22 exp and its efficiency η exp It is proportional to.

number

[0037] In particular, assuming that the efficiency of the expansion impeller 22 is 0.8 and that 10% of the process flow is recirculated to the inlet of the compressor 21, the power wasted by a conventional anti-surge valve is 10% of the total compression power, but in comparison, the power loss due to the expansion impeller 22 is advantageously only 2% of the total compression power.

[0038] In addition, since the gas flow pressure downstream of the expansion impeller 22 decreases to the pressure value at the compressor inlet 4, the expansion impeller 22 effectively eliminates the pressure difference between the downstream and upstream pressures of the rotor 16 and the axial force generated on the rotor 16.

[0039] Next, the gas processed by the radial expansion impeller 22 is carried through the diffuser 30 and finally returned to the compressor inlet 4 through the return line 2.

[0040] As a favorable result, the radially expanding impeller 22 effectively performs the dual function of balancing the axial thrust of the compressor and recovering energy from the processed flow.

[0041] The power generated by the radially expanding impeller 22 contributes to driving the operating machine and, therefore, reduces the power absorbed by or required by the main driver 13 during normal operation.

[0042] The anti-surge control system can open the nozzle 20 during normal operation or when the equipment is stopped. In the first case, the power generated by the radially expanding impeller 22 is used to assist the operator 13 or to charge the battery system. In the case of anti-surge opening during trip or stoppage, the power generated by the radially expanding impeller 22 is no longer needed and can rather be stored by the battery for further use, so it does not have to be used to drive the compressor.

[0043] Please note that the configurations shown in Figures 3 and 4 can be combined in various ways.

[0044] While aspects of the present invention have been described in relation to various specific embodiments, it will be apparent to those skilled in the art that many modifications, changes, and omissions are possible without departing from the spirit and scope of the claims. In addition, unless otherwise specified herein, the order or arrangement of any process or method step may be changed or rearranged according to alternative embodiments.

Claims

1. A centrifugal compressor (21) comprising a compressor rotor (16), a compressor stator (17), a working fluid compressor inlet (4), a working fluid compressor outlet (3), and a driver (13), wherein the driver (13) rotates the compressor rotor (16) through the rotor shaft end (16'), a radial expansion impeller (22) configured and positioned on the rotor shaft end (16') downstream of the compressor rotor (16), the radial expansion impeller (22) having a radial expansion impeller inlet and a radial expansion impeller outlet (29), one or more flow regulators (26) configured and positioned between the working fluid compressor outlet (23) and the radial expansion impeller inlet to adjust the amount of working fluid that can pass through the radial expansion impeller (22), the radial expansion impeller outlet (29) being connected to the working fluid compressor inlet (4) through a return line (2), and The centrifugal compressor (21) further comprises a working fluid compressor outlet (3) and a driver (13), wherein the centrifugal compressor (21) further comprises an anti-surge control system (27) that communicates with temperature, pressure and flow rate measuring instruments (6) on the outlet line (7) of the compressor (21) and temperature, pressure and flow rate measuring instruments (8) on the inlet line (9) of the compressor (21), wherein the flow rate of the working fluid at the working fluid compressor outlet (3) is higher than the flow rate of the working fluid flowing through the radial expansion impeller outlet (29), and the anti-surge control system (27) is configured to increase the amount of the working fluid returned to the working fluid compressor inlet (4) via the radial expansion impeller outlet (29) by adjusting one or more flow regulators to increase the amount of the working fluid that can pass through the radial expansion impeller (22).

2. The centrifugal compressor (21) according to claim 1, wherein the compressor discharge volute (24) is configured and positioned downstream of the working fluid compressor discharge port (23), and the deswarra (25) is configured and positioned between the compressor discharge volute (24) and the radial expansion impeller inlet.

3. The centrifugal compressor (21) according to claim 1 or 2, wherein the diffuser (30) is configured to be positioned between the radial expansion impeller discharge port (29) and the return line (2).

4. The centrifugal compressor (21) according to any one of claims 1 to 3, wherein one or more flow regulators are adjustable nozzles (26).

5. The centrifugal compressor (21) according to claim 4, wherein the nozzle guide vane actuator (28) is configured to actuate the adjustable nozzle (26) and operate the compressor (26) in recirculation mode.

6. A method for controlling surges in a compressor, wherein the compressor causes a pressure increase relative to the continuous flow of the working fluid, The aforementioned method, Steps include providing a radial expansion impeller (22) downstream of the compressor discharge port, The step of providing one or more flow regulators (26) between the compressor discharge port and the radial expansion impeller (22), The step of providing a return line (2) downstream of the radially expanding impeller (22) in order to connect the radially expanding impeller (22) to the compressor, The flow rate of the working fluid at the outlet (3) of the working fluid compressor is higher than the flow rate of the working fluid flowing through the radial expansion impeller outlet (29) of the radial expansion impeller (22). The aforementioned method, A method comprising the step of adjusting one or more flow regulators (26) to direct at least a portion or a certain volume of the continuous flow of the fluid through the radially expanding impeller (22) to the return line (2), further comprising the step of adjusting one or more flow regulators (26) to increase the flow rate of the working fluid that can pass through the radially expanding impeller (22), thereby increasing the flow rate of the working fluid that is returned through the radially expanding impeller outlet (29) to the working fluid compressor inlet (4) connected to the radially expanding impeller outlet (29) through the return line (2).

7. The method according to claim 6, wherein one or more flow regulators (26) are adjusted to direct less than 100% of the continuous gas flow through the radial expansion impeller (22) to the return line (2).

8. The method according to claim 7, wherein a certain amount of the continuous gas flow not guided through the radial expansion impeller (22) is delivered to a downstream service or process (15) at the compressor design delivery pressure.

9. The method according to any one of claims 6 to 8, further comprising the step of passing the continuous gas flow through a deswarra (25) before the continuous gas flow is guided through the radial expansion impeller (22).

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