Torque-based sensor and control method for varying gas-liquid fractions of fluids for turbomachines   

The invention relates generally to torque sensing and control systems and methods, and more specifically to a torque-based sensor and method for controlling machine speed or torque characteristics in response to varying gas-liquid fractions of fluids for a rotating flow machine.

Incoming fluid in many turbomachinery applications is comprised of two or more components such as water and air, or methane, water and sand. These incoming fluid compositions can vary significantly over time. In most cases, the gas-volume-fraction (GVF) is significantly larger than the liquid/solid-volume fraction. The gas-mass-fraction and the liquid-mass-fraction however, can be equally large. Small changes in volume fraction of one or the other phase can result in significant changes on the incoming overall mass to the turbomachine. This means that the shaft torque changes significantly due to the changes in gas-volume fraction.

Control of turbomachine operating conditions in some applications typically includes direct measurements of fluids comprised of multiple species that are difficult to ascertain, especially under dynamic conditions. Therefore, only temperatures are determined at some representative points on the casing of a turbomachine. The operating conditions are then adjusted according to calibration data obtained during tests. Fluid mechanical models are sometimes used to assist this calibration approach.

Other turbomachine control techniques employ venture nozzles and dual-energy fraction meters based on nuclear detection technology to assist in adjustment of turbomachine operating conditions. An external device comprising a multiphase flow meter is required to be calibrated to the drive-motor-compressor train including the inlet pipeline conditions when using the above described techniques.

It would be both advantageous and beneficial to provide a device that is able to quantify directly the impact of changing GVF on a turbomachine compressor such that the quantified information can be used to counteract disadvantageous turbomachine behavior associated with centrifugal compressors employed in the oil and gas industry. It would be further advantageous if the device could be just as easily applied to many types of rotating flow machines such as steam turbine, multiphase rotating pumps, and aircraft engines under rain conditions to quantify directly the impact of changing GVF on the respective rotating flow machine(s).

Briefly, in accordance with one embodiment, a method of controlling a rotating flow machine comprises:

measuring an inlet temperature of the rotating flow machine and predicting an outlet temperature of the rotating flow machine therefrom;

measuring rotating flow machine shaft torque and determining mass flow changes at an inlet to the rotating flow machine therefrom; and

controlling rotational speed or torque of the rotating flow machine shaft in response to the predicted outlet temperature and the mass flow changes into the rotating flow machine such that the rotating machine achieves desired operating conditions in association with changes in gas-volume-fraction at the inlet to the rotating flow machine.

According to another embodiment, a rotating flow machine control system comprises:

a flow machine having a rotational shaft;

a torque sensor configured to measure rotational shaft torque associated with the flow machine;

an algorithmic software configured to determine mass flow changes at an inlet to the rotating flow machine in response to the measured rotational shaft torque;

a temperature sensor configured to measure fluidic temperature at an inlet to the flow machine;

a temperature sensor configured to measure fluidic temperature at an outlet to the flow machine; and

a feedback control loop configured to control rotational shaft speed or rotational shaft torque of the flow machine in response to the mass flow changes, the fluidic temperature at the flow machine inlet, and the fluidic temperature at the flow machine outlet, such that the rotating machine achieves desired operating conditions in association with changes in gas-volume-fraction at the inlet to the rotating flow machine.

According to yet another embodiment, a rotating flow machine control system comprises:

a flow machine having a rotational shaft;

a torque sensor configured to measure rotational shaft torque associated with the flow machine;

an algorithmic software configured to determine mass flow changes at an inlet to the rotating flow machine in response to the measured rotational shaft torque;

a fluidic bypass actuator; and

a controller configured to control rotational shaft torque of the flow machine via causing the fluidic bypass actuator to vary the amount of fluid entering the inlet to the flow machine in real-time in response to the mass flow changes, such that the rotating machine achieves desired operating conditions in association with changes in gas-volume-fraction at the inlet to the rotating flow machine.

According to still another aspect of the invention, a method of controlling a rotating flow machine comprises:

measuring rotating flow machine shaft torque and determining gas-volume-fraction (GVF) changes at an inlet to the rotating flow machine therefrom; and

controlling rotational speed or torque of the rotating flow machine shaft in response to the GVF changes into the rotating flow machine such that the rotating machine achieves a desired operating point.

These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

FIG. 1 illustrates a rotating flow machine control system according to one embodiment of the invention; and

FIG. 2 illustrates a rotating flow machine control system according to another embodiment of the invention.

While the above-identified drawing figures set forth particular embodiments, other embodiments of the present invention are also contemplated, as noted in the discussion. In all cases, this disclosure presents illustrated embodiments of the present invention by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of this invention.

DETAILED DESCRIPTION

The torque of a rotating flow machine shaft such as a turbomachine shaft depends on the overall mass flow through the turbomachine and the specific enthalpy change through the machine. This can be described by the change in temperature for cases in which the fluid composition is known. In those cases, the measurements at the inlet and outlet of the turbomachine are relatively easy to obtain and are sufficient to determine the operating point of the turbomachine. The operating point of an electrical motor-driven compressor can easily be controlled by changing the rotational speed of the compressor. Undesired operating points, such as points close to or beyond the surge/stall limit of a compressor, can be avoided by changing the speed of revolution such as described below with reference to FIG. 1 or by bypassing parts of the fluid such as described below with reference to FIG. 2. Incoming and outgoing flow properties are not easily determined however, when multiphase flows are involved in the process.

The present inventors recognized that changes in the shaft torque itself can be used to determine the operating point, i.e. incoming changes in mass flow, provided that the principle fluid components do not change over periods of the order of the speed of revolution of the turbomachine, but only to the composition of the fluid, i.e. GVF. The changes in mass flow in this instance are related only to the changes of the fluid composition.

The exit temperature of the liquid compressed or expanded in a turbomachine is also a function of the GVF. Changes in the GVF at the inlet however, will be detected as changes in the exit temperature associated with larger time scales than the changes in mass flow caused by changes in the GVF. The latter can be detected almost instantaneously via a torque sensor; while changes in the exit temperature are on the order of the convection time of a particle that travels through the flow channel of a turbomachine.

This feature was recognized by the present inventors to provide a flow machine control system 10 described below with reference to FIG. 1. A fluid mechanical model is used to predict the temperature of the fluid composition exiting the turbomachine, including consideration of condensation or evaporation. This predicted temperature, together with the measured torque/GVF, is then used to determine the direction of change of rotation, i.e. speed-up or slow-down.

The actual exit temperature is then measured at the operating point, and is used together with the model based predictions to iterate the operating point and close an iteration loop. The minimum sensor information requirements therefore include temperatures at the inlet and exit of the compressor, as well as the rotational speed. Mass flow at an initial point in time, i.e. a dry gas calibration point, is only required since the technique described herein detects changes in the mass flow.

Looking now at FIG. 1, a rotating flow machine control system 10 is illustrated according to one embodiment of the invention. The rotating flow machine control system 10 includes a compressor 12; although the principles described herein are equally applicable to any type of rotating flow machine such as, without limitation, a turbomachine, i.e. steam turbine, multiphase rotary pumps, and aircraft engines under rain conditions.

Compressor 12 is driven by a suitable drive motor 14. A power control module 16 includes algorithmic software 18 described in further detail below, and is configured to control the rotational speed and/or torque characteristics of the drive motor 14.

A torque sensor 20 is configured to measure the torque on the motor/compressor shaft 22, while temperature sensors 24, 26 at the respective compressor fluidic input and output ports 28, 30 are each configured to measure its corresponding fluidic temperature.

The algorithmic software 18 is configured to determine mass flow changes at the inlet 28 to the compressor 12 in response to the measured rotational shaft torque.

A feedback control loop 32 is configured to control the rotational shaft 22 speed or rotational shaft 22 torque of the flow machine 12 in response to the mass flow changes determined via the algorithmic software 18, the fluidic temperature at the flow machine inlet 28, and the fluidic temperature at the flow machine outlet 30, such that the rotating machine/compressor 12 achieves desired operating conditions in association with changes in gas-volume-fraction at the inlet to the rotating flow machine 12.

In summary explanation, torque sensing and control methods detect varying gas-liquid fractions of a fluid entering a rotating flow machine 12 that operates with a fluid having variable liquid phases and compositions. A changing liquid composition results in a respective changing torque on the rotating shaft 22 of the rotating flow machine 12. The measured shaft torque is then used to detect the gas-liquid fraction; and this information is fed to a control algorithm 18 that controls the operating point of the rotating flow machine 12.

Setting the control algorithm 18 so that it can change the torque and therefore the rotational speed of the rotating flow machine 12 in response to information about the actual gas-liquid fraction is desirable to achieve safer operating conditions or conditions with higher efficiency or higher power output under varying liquid compositions that otherwise result in varying torque on the rotating shaft 22 of the rotating flow machine 12, leading eventually to damages to the rotating flow machine 12 under unwanted operating conditions sometimes close or beyond the stall or surge limit(s).

The rotating flow machine control system 10 is therefore based on high-speed torque acquisition that is used to determine the gas volume fraction at the rotating flow machine inlet 28. Moreover, the sensed signal from the torque sensor 20 is fed into a power control module 16 feedback control loop 32 to determine an improved operating point for the rotating flow machine 12 that better suits the needs of the new fluid composition.

FIG. 2 illustrates a rotating flow machine control system 50 according to another embodiment of the invention. The rotating flow machine control system 50 includes a compressor 12; although the principles described herein are equally applicable to any type of rotating flow machine such as, without limitation, a turbomachine, i.e. steam turbine, multiphase rotary pumps, and aircraft engines under rain conditions.

Compressor 12 is driven by a suitable drive motor 14. A controller 52 includes algorithmic software 54 described in further detail below, and is configured in combination with a shaft torque sensor 20 to control a fluid bypass actuator 56 in response to the rotational shaft 22 torque of the compressor 12.

The algorithmic software 54 is configured to determine mass flow changes at the inlet 28 to the compressor 12 in response to the measured rotational shaft torque. This information is then used to control the amount of fluid flowing through the compressor inlet 28 in real-time via a fluid bypass actuator 56, such that the rotating machine/compressor 12 achieves desired operating conditions in association with changes in gas-volume-fraction at the inlet 28 to the rotating flow machine 12. Although described in terms of a variable speed rotating machine, this technique applies equally well to fixed speed rotating machines.

Modern torque sensors based on magnetic shaft encoding can achieve a measurement repeatability of 99.99% and a signal bandwidth up to 30 kHz if all primary and secondary sensor design requirements are fulfilled, requiring an optimized design for each type of application. Considering and integrating the optimized sensor design during the design stage of the rotating flow machine control system 10 enables detection of even very small changes in volume fraction of one or the other phase in a reliable manner, allowing this information to be employed in advanced performance control circuits such as described herein.

A flow machine control system such as described herein with reference to the Figures can be configured, without limitation, for use with a variable speed motor to drive a compressor or for use with a variable speed energy generator to drive a turbine (or with fixed speed machines). The control system in each instance provides for fast reaction times suitable for changing mass flow, shaft speed and/or torque.

A fast reacting torque sensor for turbomachinery operated at 10,000 rpm requires a reaction within 6 msec, which equates to one rotational cycle. State of the art shaft encoded torque sensors have signal bandwidths up to 30 kHz, as stated above, meaning that they can detect events on a 30 microsecond time scale. Such sensors however may be limited in use as an input for control circuits since they may also be sensitive to electromagnetic or other disturbances.

Using the output of a torque sensing system in association with fast acting controls in one embodiment requires a special sensor design, especially if real-time behavior of the sensed signal is needed, i.e. improving the signal quality by filtering or standard signal processing methods cannot be applied. This sensor design according to one embodiment requires shielding of the magnetic field sensing coils against external electromagnetic disturbances. The magnetic field sensing coils, for example, must be positioned inside of a metallic tube (alternatively a cylindrical metallic cover around the shaft). In addition, multiple magnetic field sensor pairs according to one embodiment must be positioned around the shaft 22. They can be used to exclude that lateral movements of the shaft or external fields that impact the measurement result, e.g. in performing differential measurements, comparing and summarizing the relevant field components from different positions around the shaft, so that only true torque is measured at all times.

Alternatively, an integration based shaft power or torque measurement method could be used to generate a more reliable input signal for the control algorithm. Such a method may employ a number of magnetically encoded regions, induction coils and integration sections configured to provide a required time resolution for specific applications, e.g. 1 ms. Air core induction coils can be employed in a solution that allows their application in a much higher temperature range than permanent magnetic field sensing solutions.

In further summary explanation, a torque-based sensor and control method have been described for rotational flow control machines such as a turbomachine that operates on varying gas-liquid fractions of fluids. According to one aspect, a calibration event is provided at the beginning of the process. A feedback loop is provided that feeds the turbomachine shaft torque information back to a turbomachine control system. Temperature sensors are provided at an inlet and exit of the turbomachine. A torque sensor is provided that measures the rotational speed of the turbomachine. Known information about the liquid components, i.e. gas-type, liquid-type is provided. A fluidmechanical model of the turbomachine running under multiphase conditions is provided in which changes in GVF cause a change in overall mass flow. Turbomachine exit temperature(s) and pressure(s) are predicted based on the measured speed and inlet temperature(s). A new operating point is predicted via the fluidmechanical model; and if this operating point is unwanted, the rotational speed or a bypass mechanism or other installed means to influence the operating point of the turbomachine can be used to change the actual operating point. A continuous monitoring of the changes in the inlet and exit quantities then allows a stable settling of a new operating point.

While only certain features of the invention have been illustrated and described herein, many modifications and changes will occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.