System and method for energy optimisation of compressors

Abstract

The invention relates to a method for operating a system (7), wherein the system (7) comprises a compressor (8) and an expander (24), wherein the outlet of the compressor (8) is fluidically connected to the inlet of the expander (24), wherein the outlet of the expander (24) is fluidically connected to the inlet of the compressor (8), wherein a control valve (26) is arranged between the inlet of the expander (24) and the outlet of the compressor (8), which control valve opens during an operation condition which the compressor (8) is in shortly before a pumping state and, as a result, the energy of the flow medium in the expander (24) is used.

Description

Description TITLE System and process for the energetic optimization of compressors TECHNICAL FIELD

[0001] The invention relates to a system comprising a compressor and an expander. BACKGROUND D

[0002] The surge line of a compressor describes a transition from an aerodynamically stable to an aerodynamically unstable operating mode. The term "stability" refers to the flow of a process fluid or flow medium in the intended flow direction. When a compressor surges, significant backflow occurs, causing pressure fluctuations and temperature increases. These pressure fluctuations and temperature increases can lead to damage after a relatively short period of operation in this condition. Reaching the surge line is often clearly noticeable, as the pressure fluctuations cause significant vibrations whose noise levels exceed those of normal operation.

[0003] The operation of a turbo compressor therefore requires measures to prevent reaching the surge limit and to limit the surge condition to the shortest possible time periods. Accordingly, the control of a compressor always maintains a defined safety margin from the surge limit of the operating map. In addition, a surge limit control valve is usually provided, which allows a reduction in pressure at the compressor outlet if a certain distance to the surge limit is undershot or if surge has already occurred. The surge condition, or a close proximity to the surge limit, is characterized by a reduced mass, Quantity or volume flow of the process gas to be conveyed and with a corresponding pressure ratio via the compressor.

[0004] Figure 1 shows a characteristic curve map 1 illustrating the operating mode of a compressor. The x-axis represents the mass flow through the compressor. The y-axis represents the compressor outlet pressure. Line 2, marked 100%, represents the speed during nominal operation. The lines marked with other percentages indicate correspondingly different speeds, for example, 90%, 80%, etc. of the nominal speed.

[0005] The higher the mass flow, the more advisable it is to increase the speed. If the speed remains constant and the mass flow is reduced, the operating point 6 moves towards a so-called surge limit line 3. If the operating point (mass flow, speed, outlet pressure) lies on the surge limit line 3 or even to the left of it, the surge condition described above can occur. Therefore, a control characteristic 4 is usually considered, which leads to specific measures when the operating point reaches this control characteristic 4. The goal of these measures is to prevent the operating point from shifting further to the left. In other words: Compressors, especially turbo compressors, have a permissible operating range, which is represented by the characteristic curve field 1 in Figure 1. It is sometimes desirable to operate a compressor permanently outside the limits of the characteristic curve field 1 over the course of its service life. Therefore, it is very often desired to operate the compressor with less than the minimum mass flow permitted by the characteristic curve field 1. This range is located to the left of the characteristic curve field 1 and is limited by the surge limit line 3 and the associated control curve 4. Such an operating requirement exists, for example, in the oil and gas industry when, as the service life of a gas source progresses, the production rate decreases or, for example, also in air separation, when the mass flow is lower due to lower plant capacity.

[0007] If it is desired to operate the compressor with less than the minimum mass flow permitted according to characteristic curve family 1, this is entirely possible. If the operating point (for example, operating point 6) is moved to the left in characteristic curve family 1, into the area of ​​decreasing mass flows, and reaches the control curve 4 upstream of the surge limit line 3, a blow-off valve or relief valve opens. This ensures that the dangerous and therefore undesirable operating condition of surge is avoided. However, operation with the blow-off valve or relief valve open is very energy-efficient. The gas compressed at the expense of power is expanded at a blow-off valve on the suction side of the compressor. At a relief valve, the gas compressed at the expense of power is released into the atmosphere. In both variants, the compression power used is wasted, thus drastically reducing the efficiency of the compressor. [GC08] There are plant configurations in which the compressor characteristic map is not determined by varying the speed, but by aerodynamic changes to the blade cascade or by changing the suction pressure in front of the compressor. (0009] In addition, there are system configurations that do not have a characteristic map range, but only a characteristic curve. In these cases, the blow-by is often used permanently to control the compressor. This is the worst possible control of a compressor in terms of energy efficiency.

[0010] It is desirable to provide a system with a compressor that is more energy-efficient. SUMMARY OF THE INVENTION The object of the present invention is therefore to provide a system with a compressor which has better energy efficiency.

[0012] The problem is solved by a system comprising a compressor and an expander, wherein the outlet of the compressor is fluidically connected to the inlet of the expander, wherein the outlet of the expander is fluidically connected to the inlet of the compressor.

[0013] The object is also achieved by a method for operating a system, wherein the system comprises a compressor and an expander, wherein the outlet of the compressor is fluidically connected to the inlet of the expander, wherein the outlet of the expander is fluidically connected to the inlet of the compressor

[0014] Advantageous embodiments are the subject of the dependent claims. The invention thus proposes recovering the power lost during operation of a compressor in bypass or blow-off mode. This is achieved by the energy inherent in the bypass or blow-off flow, which is normally simply destroyed, being fed back into the machine train in a direct, mechanically coupled way. This reduces the compressor's required drive power through the recovered power. This significantly improves the efficiency of operating points in terms of energy efficiency during bypass or blowdown.

[0016] This energy-efficient improvement of operating points could be applied primarily to existing machines. The existing machines would need to be upgraded with a service upgrade package.

[0017] According to the invention, it is therefore proposed to install a new pipeline parallel to the bypass or blow-off line. It must start before the surge limit valve and end after it.

[0018] By installing a new pipeline parallel to the existing bypass or blow-off line, it is possible to access the bypass or blow-off flow without negatively impacting the equipment required for machine protection. In some cases, it may be advisable to dimension the new pipeline not for 100% of the mass flow, but only for a partial mass flow. This makes it possible to operate energy recovery up to this partial mass flow without having to build pipelines up to the turbine position for the entire mass flow.

[0019] According to the invention, an expander is arranged in this pipeline. Various turbine types can be used. Examples include a radial expander stage, a single-stage or multi-stage backpressure turbine, or even a screw expander. The turbine is housed in a separate casing outside the compressor housing.

[0020] The expander enables the recovery of the energy present in the recirculation or blow-off flow. Its housing in a separate enclosure allows for flexible integration within the machine train, which is particularly advantageous for retrofitting.

[0021] According to the invention, a control valve is installed in front of the expander. The installed control valve allows the expander to be controlled in the bypass or blow-off flow. It should open first before the bypass or blow-off valve still present in the parallel line. This means that continuously running bypass or blow-off flows should pass through the expander. Bypass or blow-off flows for machine protection, for example, when pump surges are detected, flow through the bypass or blow-off valve in the main line.

[0023] According to the invention, the expander is positioned at a free location in the machine train or at a free location on the compressor.

[0024] The expander must be positioned in such a way that minimal modifications are required for the compressor or the compressor train. It is therefore advisable to utilize available installation spaces. This makes retrofitting possible for existing machines. Free installation spaces on the compressor, the shaft ends, or an intermediate gear unit are particularly preferred. The turbine can be flange-mounted to an existing compressor housing or positioned on individual components of the machine train.

[0025] According to the invention, the expander is mechanically connected to the machine train with a freewheel clutch.

[0026] The expander can be permanently mechanically coupled to the line and only delivers its power to the line when it is subjected to the bypass or blow-off flow. This is achieved by a one-way clutch.

[0027] A gearbox can optionally be installed between the expander and the machine train. An optional gearbox installed between the machine train and the expander ensures that the expander can run at its optimum speed even if the machine train's speed is too slow. Due to its small footprint, a planetary gearbox, for example, is a suitable option.

[0028] Optionally, the pipeline and expander can be subjected to a vacuum. In addition to conventional vacuum pumps, a gas jet pump, which is pressurized with process gas, can be used to create the vacuum. To create a sealed space that can be evacuated, a valve or flap must be installed behind the expander. If the pipeline is evacuated along with the expander, the expander can rotate without generating any significant power loss. This eliminates the need for a one-way clutch, for example.

[0030] According to the invention, a control logic is installed between the bypass or blow-off valve and the control valve for turbine control.

[0031] The control logic must simultaneously control the bypass or blow-off valve and the control valve. If operating points to the left of the characteristic curve are to be operated in the bypass or blow-off system, the control valve must be controlled so that the turbine can recover energy from the gas flow. If the purpose is to protect the machine, for example, if surges are detected, the bypass or blow-off valve is controlled. DESCRIPTION OF THE INVENTION

[0032] In a first advantageous development, a control valve is arranged between the outlet of the compressor and the inlet of the expander.

[0033] This makes the system easier to operate.

[0034] In a further advantageous development, the control valve is designed such that during operation the control valve opens when the flow conditions in the compressor are such that an operating point encounters a control characteristic curve 4, wherein the control characteristic curve 4 is arranged upstream of a surge limit line 3.

[0035] This allows the energy of the flow medium to be recovered.

[0036] In a further advantageous development, the expander is designed as a radial expander, as a backpressure turbine or as a screw expander.

[0037] In a further advantageous development, the compressor and the expander are coupled to each other in a torque-transmitting manner.

[0038] This allows the energy converted in the expander to be efficiently fed back into the system. The recovered power reduces the compressor's required drive power.

[0039] In a further advantageous development, the compressor has a compressor shaft and the expander has an expander shaft, wherein a freewheel clutch is arranged between the compressor shaft and the expander shaft. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] In the following, an embodiment of the invention is explained in more detail with reference to the following figures.

[0041] The above-described properties, features and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments, which are explained in more detail in connection with the drawings.

[0042] Identical components or components with the same function are marked with the same reference symbols.

[0043] Embodiments of the invention are described below with reference to the drawings. These are not intended to represent the embodiments to scale; rather, where useful for explanation, the drawings are presented in a schematic and / or slightly distorted form. For supplements to the teachings immediately apparent in the drawings, reference is made to the relevant prior art.

[0044] They show:

[0045] FIG 1 a schematic representation of a characteristic field

[0046] FIG 2 a schematic representation of a system according to the invention DESCRIPTION OF THE EMBODIMENT

[0047] Figure 2 shows a schematic representation of a system 7 according to the invention. The system comprises a compressor 8. The compressor 8 can It can be a turbocompressor and has a compressor shaft 9. A motor 10 transmits torque to the compressor shaft 9. The motor 10 can be an electrically driven motor or a steam turbine or similar. In any case, the drive power of the motor 10 must be sufficient to drive the compressor 8. The compressor 8 has an inflow 11. A flow medium or process gas to be compressed flows into the inflow 11 via a supply line 12. The flow medium passes through an inflow valve 13 to a separator 14, from where it then enters the supply line 12. Before entering the compressor 8, the flow medium has a temperature and a pressure. In addition, the flow medium has a mass flow with which it flows through the compressor 8. After the compressor 8, the flow medium flows out of the compressor 8 via an outlet line 15. The temperature and pressure of the flow medium flowing out of the compressor 8 are higher than the temperature and pressure of the flow medium flowing into the compressor 8. The flow medium flows out of system 7 via an outlet valve 16 for further processing. The operating point, i.e. the mass flow of the flow medium, the outlet pressure of the flow medium, and the speed of compressor 8, is determined by the characteristic curve field 1 in Figure 1. In the event that the operating point on the characteristic curve field 1 approaches or exceeds the surge limit curve 3 and the control characteristic curve 4, system 7 is designed in a conventional manner with the lines described below. Firstly, the energy-rich and compressed flow medium is blown off via a blow-off line 17, which opens into the outlet line 15, via a blow-off valve 18 located in the blow-off line 17.

[0050] On the other hand, a blow-by-pass line 19 is formed, which creates a fluidic connection between the outlet of the compressor 8 and the inlet of the compressor 8. A blow-by-pass valve 20 is arranged in this blow-by-pass line 19. The blow-by-pass valve 20 opens as soon as the Operating point is located in the left area of ​​the characteristic curve field 1. The above two lines (blow-off line 17 and blow-bypass line 19) are known in the prior art. For clarity, both the blow-bypass line 19 and the blow-off line 17 are shown in Figure 2. It will be clear to those skilled in the art that such systems are generally designed with either a blow-bypass line 19 or a blow-off line 17. According to the invention, the system 7 is now further developed in such a way that it is also possible to operate the system 7 with a reduced mass flow.

[0051] For this purpose, a line 21 is arranged at the outlet 22 of the compressor 8. The outlet 22 of the compressor 8 is fluidically connected to an inlet 23 of an expander 24. An outlet 25 of the expander 24 is fluidically connected to the inlet 11 of the compressor 8. As soon as the operating point of the system is such that it moves to the left of the characteristic curve field 1, the energy-rich flow medium is guided through the expander 24 via line 21. For this purpose, a control valve 26 is arranged in the line 21. The energy of the flow medium is converted into mechanical energy in the expander 24. The control valve 26 is arranged between the outlet 22 of the compressor 8 and the inlet 23 of the expander 24.

[0052] The control valve 26 is designed such that, during operation, the control valve 26 opens when the flow conditions in the compressor 8 are such that an operating point encounters a control characteristic curve 4, wherein the control characteristic curve 4 is located upstream of a surge limit line 3. In other words, the control valve 26 opens when the flow conditions in the compressor 8 are such that the compressor 8 is just before a surge condition. By means of this measure according to the invention, the system 7 can even be operated to the left of the characteristic curve field 1, for example at operating point 5 (to the left of the surge limit line 3).

[0054] The expander 24 can be designed as a radial expander, a backpressure turbine, or a screw expander. In any case, the expander 24 is designed designed to convert the energy of the flow medium into mechanical energy.

[0055] The mechanical energy of the expander 24 can be used to assist the engine 10. The drive power of the engine 10 can thereby be reduced. This is achieved by coupling the compressor 8 and the expander 24 to transmit torque. The expander 24 has an expander shaft (not shown), with a one-way clutch (not shown) arranged between the compressor shaft 9 and the expander shaft.

[0056] In an alternative embodiment, the system 7 can be designed such that the compressor shaft 9 and the expander shaft are rigidly coupled to one another. For this purpose, a shut-off valve or butterfly valve 28 is arranged in the line downstream of the turbine. The expander 24 is then subjected to a vacuum before the control valve 26 and the shut-off valve or butterfly valve 28 are opened. The vacuum is generated using a vacuum pump or a gas jet pump 29. In Figure 2, this alternative embodiment is enclosed by the dashed line 27. The vacuum pump or gas jet pump 29 is arranged within the dashed line 27.

Claims

Claims 1 . System (7) comprising a compressor (8) and an expander (24), wherein the outlet of the compressor (8) is fluidically connected to the inlet of the expander (24), wherein the outlet of the expander (24) is fluidically connected to the inlet of the compressor (8).

2. System (7) according to claim 1, with a control valve (26) arranged between the outlet of the compressor (8) and the inlet of the expander (24).

3. System (7) according to claim 1 or 2, wherein the control valve (26) is designed such that during operation the control valve (26) opens when the flow conditions in the compressor (8) are such that an operating point encounters a control characteristic curve (4), wherein the control characteristic curve (4) is arranged upstream of a surge limit line (3).

4. Plant (7) according to one of the preceding claims, wherein the expander (24) is designed as a radial expander, as a backpressure turbine or as a screw expander.

5. System (7) according to one of the preceding claims, wherein the compressor (8) and the expander (24) are coupled to one another in a torque-transmitting manner.

6. System (7) according to claim 5, wherein the compressor (8) has a compressor shaft (9) and the expander (24) has an expander shaft, wherein a one-way clutch is arranged between the compressor shaft (9) and the expander shaft.

7. A method for operating a system (7), wherein the system (7) comprises a compressor (8) and an expander (24), wherein the outlet of the compressor (8) is fluidically connected to the inlet of the expander (24), wherein the outlet of the expander (24) is fluidically connected to the inlet of the compressor (8).

8. The method according to claim 7, wherein a control valve (24) is arranged between the outlet of the compressor (8) and the inlet of the expander (24).

9. The method according to claim 8, wherein the control valve (24) opens when the flow conditions in the compressor (8) are such that the compressor (8) is shortly before a pumping state.

10. Method according to claim 8 or 9, wherein the control valve (26) only opens when, during operation, the flow conditions in the compressor (8) are such that an operating point encounters a control characteristic curve (4), wherein the control characteristic curve (4) is arranged upstream of a surge limit line (3) in a characteristic map.

11. Method according to one of claims 7 to 10, wherein the compressor (8) is formed with a compressor shaft (9) and the expander (24) is formed with an expander shaft, wherein the compressor shaft (9) is coupled to the expander shaft in a torque-transmitting manner.

12. The method according to claim 11, wherein the compressor shaft (9) and the expander shaft are coupled to one another by means of a one-way clutch.

13. The method according to claim 11, wherein the compressor shaft (9) and the expander shaft are rigidly coupled to one another, wherein the expander (24) is subjected to a vacuum before the control valve (26) opens.

14. The method according to claim 13, wherein the vacuum is generated using a vacuum pump or a gas jet pump.

Images