MX2012007457A - Dynamic thrust balancing for centrifugal compressors. - Google Patents

Abstract

Systems and methods for dynamically balancing axial loads in centrifugal compressors (10) to reduce residual axial loads on the bearings (20) used therein are described. A sensor or probe (42) detects a parameter associated with the axial load acting on the bearing (20). Based on the detected parameter, the pressure in a balance chamber (34) is controlled to adjust the compensating axial force generated by a balance drum (28).

Description

PUMP BALANCING DI NÁM ICO FOR COMPRESSORS CENTRIFUGES Ca m po of the I nve n c i on The present invention relates to centrifugal compressors and more specifically, to the swinging thrust in such compressors.

A nteced e nts of the I nven c i n n A compressor is a machine that increases the pressure of a compressible fluid, for example, a gas, through the use of mechanical energy. The compressors are used in several different applications, including operating as an initial stage of a gas turbine engine. Gas turbine engines, in turn, are used in a large number of industrial processes, including power generation, natural gas liquefying and other processes. Among the different types of compressors used in such processes and process plants are called centrifugal compressors, where the mechanical energy operates on the gas inlet for the compressor by means of centrifugal acceleration, for example, when rotating the centrifugal propeller.

Centrifugal compressors can be adjusted in a single impeller, i.e., a single-stage configuration, or with a plurality of centrifugal stages in series, in which case, they are often called multi-stage compressors. Each of the stages of a centrifugal compressor typically includes an inlet volume of gas to be compressed, a rotor that has the ability to provide the kinetic energy in the inlet gas and an outlet tube that converts the kinetic energy of the gas that leaves the propeller in pressure energy.

Multi-stage centrifugal compressors are subjected to axial thrust in the rotor caused by a pressure difference across the stages and the change of momentum of the gas rotating from the horizontal direction to the vertical direction. This axial thrust is normally compensated by a swing piston and an axial thrust bearing. Since the axial thrust bearing can not be loaded by the full thrust of the rotor, the swing piston is designed to compensate for most thrust, which leaves the bearing to handle any residual, remaining thrust. The swinging piston is normally implemented as a rotating disc or drum which fits over the arrow of the compressor, such that each side of the swinging disc or drum is subjected to different pressures during operation. The diameter of the swinging piston is selected to have a desired axial load to prevent its residual load from overloading the axial bearing. Conventional oil-lubricated bearings are typically designed to withstand axial thrust forces within the order of four times the maximum residual axial thrust expected to occur during abnormal, fault conditions.

However, when the gas conditions change during operation in the compressor, the compensation provided by the swing piston may not be sufficient to avoid overloading the bearing. Certain types of centrifugal compressors are more likely than others to experience such variations in gas conditions, for example, in gas storage applications for multi-stage centrifugal compressors that employ the parallel operation, where the difference in thrust axial between the first and second sections of the compressor, linked to the difference of flow coefficient, can not be easily compensated by the swing piston. Thus, conventional oil-lubricated bearings are typically designed to withstand axial thrust forces in the order of four times the maximum residual axial thrust that is expected to occur during abnormal conditions, or failure.

Another recent development involves replacing the active magnetic bearings (AMB) with conventional oil-lubricated bearings such as the axial (and radial) rotary support for the compressor shaft. The AMB operate on the basis of electromagnetic principles to control the axial and radial displacements within the compressor. Briefly, the AMBs include an electro-magnet driven by a power amplifier that regulates the voltage (and therefore, the current) inside the coils of the electro-magnet as a function of a feedback signal that indicates the displacement of the rotor of the compressor inside the device. AMBs have a desirable attribute that does not require oil as the lubricant, which reduces the maintenance of the compressor system and potentially removes the requirement to provide seals between the thrusters and the bearing. However, AMBs also have the disadvantage that they do not have the ability to handle both axial thrust and conventional oil-lubricated bearings.

In accordance with this, it would be desirable to design and provide methods and systems for dynamic thrust balancing in such compressors that overcome the aforementioned disadvantages of the existing balancing systems.

Brief Description of the Invention The exemplary embodiments are related to systems and methods for dynamically balancing axial loads in centrifugal compressors to reduce the residual axial loads in the beas used in them. A sensor or probe detects a parameter associated with the axial load acting on the bea. Based on the detected parameter, the pressure in a balancing chamber is controlled to adjust the axial compensation force generated by the balancing drum. The advantages in accordance with the exemplary embodiments described herein include, for example, a reduction in the residual axial forces acting on the beas through the different operating conditions. However, persons skilled in the art will appreciate that such advantages should not be considered as limitations of the present invention, except to the extent that they are explicitly described in one or more of the appended claims.

According to an exemplary embodiment, a centrifugal compressor includes a rotor assembly that includes at least one propeller, a bea connected with and to rotatably support, the rotor assembly, a stator, a balancing drum disposed between the rotor and the rotor. at least one propeller and the bea, the balancing chamber, defined at least in part by the outer side of the balancing drum, and having a rolling line connected thereto, a sensor for detecting a parameter that is associated with an axial load on the bea and a control valve to vary the pressure inside the roll chamber based on the detected parameter.

According to another exemplary embodiment, a method for dynamically balancing an axial load acting on a bea in a centrifugal compressor includes the steps of detecting a parameter associated with the axial load, and controlling the pressure in a roll chamber near the drum. of rolling in the centrifugal compressor based on the parameter detected by dynamically balancing the axial load acting on the bea.

Brief Description of the Drawings The accompanying drawings illustrate the exemplary modalities, in which: Figure 1 is a schematic view of a centrifugal compressor of the multi-stage type, which may be provided with dynamic balancing mechanisms in accordance with the exemplary embodiments.

Figure 2 illustrates the static axial load balancing in a centrifugal compressor.

Figure 3 illustrates the dynamic roll of axial load in a centrifugal compressor in accordance with an exemplary embodiment; and Figure 4 is a flow diagram illustrating a method for dynamically balancing a load in accordance with an exemplary embodiment.

Detailed description of the invention The following detailed description of the exemplary embodiments refer to the accompanying drawings. The same reference numbers in the different drawings identify the same or similar elements. Also, the following detailed description does not limit the invention. Rather, the a l ince of the n a nce n is defined by the re vic tions to nexes.

In order to provide some context for the following description related to thrust balancing systems in accordance with these exemplary embodiments, Figure 1 schematically illustrates a centrifugal, multi-stage compressor 1 0, where the thrust balancing systems can be employed. Therein, the compressor 20 includes a housing or housing (stator) 1 2 within which is mounted the rotary compressor arrow 14 which is provided with a plurality of centrifugal propellers 1 6. The rotor assembly 1 8 includes an arrow 14 and propellers 1 6 and is supported radially and axially by the beas 20 which is disposed on either side of the rotor assembly 18.

The multi-stage centrifugal compressor operates to capture the inlet process gas from inlet 22 of the duct, to increase the process gas pressure through the operation of the rotor assembly 1 8, and then expelling the process gas through the outlet 24 at an outlet pressure that is higher than its inlet pressure. The process gas, for example, can be one of carbon dioxide, hydrogen sulfide, butane, methane, ethane, propane, liquefied natural gas or a combination thereof. Between the rotors 1 6 and the bearings 20, the sealing systems 26 are provided to prevent the process gas from escaping to flow to the bearings 20. The housing 1 2 is configured to cover both the bearings 20 and the systems 26 of sealed, to prevent the escape of gas from the centrifugal compressor 1 0. In accordance with other exemplary embodiments of the present invention, the bearings 20 can be implemented as bearings lubricated with oil or magnetic active bearings. When active magnetic bearings are used as the bearings 20, then the sealing mechanisms 26 can be omitted.

The centrifugal compressor 10 also includes the swinging piston (drum) described above together with its corresponding labyrinth seal 30. A balancing line 32 maintains the pressure in the balancing chamber 34 on the outer side of the balancing drum at the same pressure (or essentially the same pressure) as those of the process gas entering through the inlet duct 22. However, in accordance with the embodiments described below, this balancing line 32 includes a control valve that can modulate the pressure in the balancing chamber 34 based on, for example, the detected axial load or near the bearing 20, as described below with reference to Figure 3.

Initially, however, it would be useful to describe the interaction of the different elements shown in Figure 1, since they relate to the axial load in general when describing Figure 2. There, the different axial load forces associated with the operation of the compressor 1 0 centrifugal are illustrated in conceptual form. As shown in Figure 2, the thrusters 16 impose an axial load (force) on the bearings 20 in the direction of the internal side (low pressure) of the compressor 10, due to, for example, differences between the stages, changes in the moment of gas, etc. Although not shown in Figure 2, the motor rotating the arrow 1 8 of the compressor will impose (essentially constant) an axial load in the opposite direction, that is, to the outside (high pressure) side of the centrifugal compressor 1 0. To counteract the remaining axial load of the thrusters 16, the roll drum 28 is designed to exert an axial force in the outward direction, the amount based on the expected axial load of the thrusters minus that of the engine. This is achieved, for example, by designing a system so that the pressure Pu of the process gas on the inner side of the sway drum 28 is greater than the pressure Pe on the outer side of the sway drum 28, and when selecting a drum of a size (diameter) appropriate to generate the desired rolling force. The pressure imbalance is developed and maintained by providing the roll line 32 between the roll chamber 34 and the main suction line associated with the inlet duct 22 so that the pressure in the roll chamber is essentially the same as the internal side of the thrusters 16.

Ideally, the axial thrust compensation provided by the roll drum 28 will essentially displace the axial load placed on the bearings 20 by the thrusters 16 or at least displace the axial load enough that any residual load is within the specification of the design of the bearings 20. However, as described above, the operational variations within such compressors and / or the use of the AMBs as the bearings 20 can cause the residual load to exceed the design tolerances of the bearings 20 for the axial load.

Consider for example, the following Table 1 illustrating the results of an axial load test of a six-throttle centrifugal compressor 10 having a roll drum 28 with a diameter of 231 mm rotating at 17,000 rpm. This test compressor was equipped with AMB as the bearings 20 which are rated nominally for axial load of +/- 9000 N.

TABLE 1 From Table 1 it can be seen that the flow rates of 73%, 1 30% and 141% of the designed nominal flow rate, the residual axial load, that is, the axial load placed in the AMB 20 of the compressor centrifugal, exceeded +/- 9000 N of the bearings using the configuration shown in Figure 2, that is, with an uncontrolled rolling line 32.

In accordance with the exemplary embodiments of the present invention, the control valve 40 is placed on the balancing line 32 to allow automated pressure control Pe to be exerted on the outer side of the balancing drum 28, as shown in FIG. Figure 3. There, the same reference numbers are used in Figures 1 and 2, refer to the same or similar components of a centrifugal compressor 20. The control valve 40 regulates the pressure in the roll chamber 34 to vary the reaction force generated by the roll drum 28 as a function of for example, the displacement of the bearing 20 or the axial load on the bearing 20 is measured by a sensor or probe 42.

The control valve 40 thus controls the value of the pressure Pe and accordingly, the amount of compensation axial load provided by the balancing drum 28. More specifically, upon closing the control valve 40, the pressure Pe increases, which reduces the amount of compensation axial load provided by the balancing drum 28. Alternatively, upon opening the control valve 40, the pressure Pe decreases, which increases the amount of axial load provided by the sway drum 28. When the control valve 40 is fully open, the maximum amount of compensation axial load is generated by the balancing drum 28. Since the amount of load provided by the balancing drum 28 is in accordance with the exemplary embodiment, variable in controlled manner, it may be desirable to design the balancing drum 28, so that its maximum axial load of compensation is higher than that provided by conventional static roll drums (i.e., by providing a larger roll drum 28 for the system), since it is possible, in these exemplary embodiments, to reduce the amount of compensation provided by closing the control valve 40 as desired.

As mentioned above, the control valve 40 is controlled based on a feedback signal from the probe or sensor 42 without considering the amount of axial load that the bearing 20 undergoes in a given time. The measurements can be made periodically by the probe or sensor 42 and reported back to the control logic 44 which is connected to the control valve 40 to implement any desired control algorithm to open and close the valve 40, as appropriate. necessary, to adjust the operational changes that result in more (or less) residual load of the bearings 20. An exemplary relationship between the detected axial load and the operation of the control logic 44 to control the gas pressure with the use of a valve 40 is described below with respect to Table 2. The control logic 44 can be implemented as an ASIC, FPGA, computer or other type of processor or can be implemented only in hardware, software or software. in some combination of them. The sensor or probe 42 can be of any type. For example, when the bearing 20 is an AMB, an inductive sensor or probe such as a linear potentiometer displacement transducer (LPDT) can be used to measure the displacement of the bearing 20 due to the axial load. Alternatively, when the bearing 20 is of the oil lubricated type of the bearing, a parasitic current sensor or probe may be an appropriate implementation of the sensor or probe 42. Other types of sensors may be used, for example, piezoelectric sensors or sensors They measure the pressure in the oil film in the bearing.

In accordance with an exemplary embodiment, the control logic 44 may include a proportional integral derivative controller (PID) that automatically, in a closed loop, changes the pressure in the drum chamber 34 as a function of the thrust measured in the machine . For example, for AMBs, the currents in the AMB coils are representative of the thrust that is controlled by the system. In particular, when the current in the thrust bearing coil of an AMB exceeds a certain value (threshold), the control logic 44 can act on the valve 40 through a simple PID controller. In accordance with the exemplary embodiments, the control system can be designed with a pulse (hysteresis value) to avoid any obturation of the thrust valve.

A test was developed to evaluate the arrangement in accordance with the exemplary embodiments illustrated in Figure 3 and to determine its ability to better control the residual load in the bearings 20. The test used the same type of centrifugal compressor 10 that was evaluated before to generate the results in Table 1, ie, six centrifugal compressors of the propeller running at 17,000 rpm, except that the drum 28 of roll increases from size to have a diameter of 247 mm to provide a slightly higher peak compensation axial load capacity in this dynamic balancing arrangement. The results of the test are shown in Table 2.

TAB LA 2 From Table 2 it can be seen that the pressure Pe in the roll chamber 34 varies by at least the majority of the different flow rates in the table under the control of the valve 40. The control valve is controlled by the sensor or probe 42 and control logic 44, so that it is closer to the higher flow velocities (the lower Pe pressure) and the more open to the lower flow velocities (the higher Pe pressure) . It can be seen in the residual load column that this has the effect of controlling the residual load on the bearing 20 to be within a much narrower range than was possible without the dynamic controls in accordance with the exemplary embodiments. In fact, the values are now within the design specifications for the axial load handling of the AMB (+/- 9000 N). It should be noted that in this example, the nominal pressure in the roll chamber (ie, when the control valve 40 is fully open) for this test group is 52 bar. Those skilled in the art will appreciate that the parameters used in the test settings associated with Tables 1 and 2 in all respects are merely illustrative.

Also, it should be appreciated that the exemplary embodiments allow the centrifugal compressors to be adjusted with smaller thrust bearings, since the axial load on such bearings can be better controlled. In addition, such compressors are expected to be more available by reducing the residual load on such bearings. A method for controlling the residual axial load in such compressor systems, in accordance with the exemplary embodiments, can be performed as illustrated in the flow chart of Figure 4. There, in step 1 00, a parameter associated with the axial load on the bearing. Then, in step 1 02, the pressure in the roll chamber near the roll drum in the centrifugal compressor is controlled based on the parameter detected to dynamically balance the axial load acting on the bearing.

The embodiments described above are intended to be illustrative in all respects, better than restrictive, of the present invention. Thus, the present invention can undergo many variations in the detailed implementation that can be derived from the description contained herein, by those skilled in the art. All variations and modifications are considered within the scope and spirit of the present invention as defined by the appended claims. No element, action, instruction used in the description of the present invention should be considered as critical or essential to the invention unless explicitly described otherwise. Also, as used here, the articles "a"; "a"; "the", "the" is intended to include one or more items.

Claims (15)

1. RECIPE N DICAC ION ES 1 . A centrifugal compressor (10) characterized in that it comprises: a rotor assembly (18) that includes at least one propeller (1 6); a bearing (20) connected with and to give rotary support to the rotor assembly (1 8); a stator (12); a balancing drum (28) disposed between the at least one impeller (1 6) and the bearing (20); a roll chamber (34) defined at least in part on an outer side of the roll drum (28) and has a roll line (32) connected thereto; a sensor (42) for detecting a parameter that is associated with an axial load on the bearing (20); Y a control valve (40) for varying the pressure within the balancing chamber (34) based on the detected parameter. 2. The centrifugal compressor according to claim 1, characterized in that it further comprises: a control logic configured to receive a sensor output and to control the control valve in accordance with a predetermined function. 3. The centrifugal compressor according to claim 2, characterized in that the predetermined function operates to increase the pressure in the roll chamber when the axial load on the bearing exceeds a predetermined value. 4. The centrifugal compressor according to any of the preceding claims, characterized in that the bearing is an active magnetic bearing. 5. The centrifugal compressor according to any of the preceding claims, characterized in that the bearing is a bearing lubricated with oil. 6. The centrifugal compressor according to any of the preceding claims, characterized in that the detected parameter is the displacement of the bearing. 7. The centrifugal compressor according to any of the preceding claims, characterized in that the detected parameter is the axial load on the bearing. 8. The centrifugal compressor according to any of the preceding claims, characterized in that the sensor is an induction sensor. 9. The centrifugal compressor according to any of the preceding claims, characterized in that the sensor is a piezoelectric sensor. 10. The centrifugal compressor according to any of the preceding claims, characterized in that the sensor in a stray current sensor. eleven . A method for dynamically balancing the axial load that it acts on a bearing (20) in a centrifugal compressor (10), the method is characterized in that it comprises: detect a parameter associated with the axial load; Y controlling a pressure in the balancing chamber (34) near the balancing drum (28) in a centrifugal compressor (10) based on the detected parameter to dynamically balance the axial load acting on the bearing (20). The method according to claim 1, characterized in that the step of controlling also comprises: open or close a valve connected to the balancing line that controls the pressure in the swing chamber. 13. The method according to claim 1 or claim 1, characterized in that the step of controlling operates to increase the pressure in the roll chamber when the axial load on the bearing exceeds a predetermined value. 14. The method according to any of claims 1 to 1, characterized in that the bearing is an active magnetic bearing. 15. The method according to any of claims 1 to 14, characterized in that the bearing is a bearing lubricated with oil.