WO2013048266A1

WO2013048266A1 - System and method for monitoring polytropic efficiency of a charge gas compressor

Info

Publication number: WO2013048266A1
Application number: PCT/PL2011/000098
Authority: WO
Inventors: Hua Xia; Larry VALERY; Giorgio Greco; Patrick LUCAS; Vincenzo SANGIORGIO; Salim JONES; Rafal JURKOWSKI; John LUNDE
Original assignee: General Electric Company
Priority date: 2011-09-29
Filing date: 2011-09-29
Publication date: 2013-04-04
Also published as: TW201326762A

Abstract

A system and method is provided for monitoring a charge gas compressor or compressor train operation conditions. The monitoring system includes a plurality of sensing modules having at least one fiber Bragg grating sensor for measuring a localized machine operating parameter adjacent to an inlet or an outlet of each compressor stage. The optical fiber- based sensing modules are operatively connected to a data acquisition system, or signal interrogator, wherein the signals from different fiber Bragg grating sensors are detected simultaneously. The data acquisition system is operatively connected to a controller, wherein the controller determines an estimated the polytropic efficiency for each compressor stage, and baseline all measured data from machine operation conditions with designed values and their variation range. Whenever a parameter is outside the operation limit, a control or optimization process will be operated.

Description

SYSTEM AND METHOD FOR MONITORING POLYTROPIC EFFICIENCY OF

A CHARGE GAS COMPRESSOR

FIELD OF THE INVENTION

The present invention relates to systems and methods for monitoring using sensing technologies and, more particularly, to monitoring using fiber optic sensing modules for measuring various operational parameters from charge gas compressor used in ethylene production facilities.

BACKGROUND OF THE INVENTION

It is well known that in an ethylene production unit, fouling is a phenomenon that may significantly limit the performance of the charge gas compressor and affect inter-stage coolers, and therefore the entire operation of the ethylene production unit. For most ethylene production plants, the operation of the charge gas compressor has historically been a critical bottleneck. The compressor often suffers from heavy fouling which requires a dedicated plant stoppage for cleaning purposes. Sometimes these cleanings are required on a yearly basis. Such fouling of the compressor reduces the efficiency of the compressor. Fouling control and prevention are, therefore, very critical processes, and several methods have been used to accomplish this goal, either alone or in combination. Whatever method is used to control fouling, or even when no fouling controls are in place, monitoring the machine performance and operation conditions of the charge gas compressor is of extreme importance for every ethylene producer, either in planning the production or in determining the maintenance schedule. Industrial compressors have shown frequent mechanical and thermal anomalies that significantly induce fouling formation and thereby reduce compressor polytropic efficiency. When fouling occurs, the turbine speed is increased in variable speed machines, or recycles are closed in fixed speed machines. Due to loss of the internal energy or heat due to fouling, the polytropic efficiency of a compressor very likely deviates from adiabatic condition. Such a loss of the heat could arise from the fouling formation that actually increases thermal resistance or flux. It becomes critical to continuously monitor the compressor's thermodynamic behavior in steady and transient temperature, pressure, and even vibration. Compressor polytropic efficiency, n^k-l)/k*LnP2/Pl)/Ln(T2/Tl), where k=C_p/C_v, the ratio of the constant-pressure specific heat over the constant-volume specific heat; T and P are suction and discharge temperature and pressure. This efficiency mainly depends upon cracked gas composition, suction/discharge temperatures and pressures. Any change from these parameters will affect its polytropic efficiency. If temperature, pressure, and gas composition can be monitored simultaneously, this enables by far a more accurate understanding of the machine condition, plus it allows the possibility of individuating the stages that are more subject to fouling severity. Existing temperature, pressure, and flow sensors have been used as basic system operation indicators. In general, simultaneously measuring both temperature and pressure from a compressor machine can be practically done with conventional pressure gauges and thermocouples.

Although the suction and discharge pressure and temperature are easily measured with existing detection technologies, it is relatively challenging to analyze gas composition in real time with gas chromatography (GC) or micro gas chromatography (MGC) because of time-consuming and complicated instrument field calibration. In a normal case, the gas analysis could take five to 10 minutes. In other cases, the gas samples are extracted and sent to remote laboratories for analysis, which may take hours or days. Moreover, three distinct instruments, namely, thermometers or thermocouples, pressure sensors, and gas chromatography, are required for compressor performance variation monitoring. Such a method proves difficult for providing online accurate measurement of the compressor efficiency and thereby cannot provide accurate information on the condition of the machine in real time. Therefore, a need exists for a system and method for monitoring of a charge gas compressor variables so as to determine the real-time operating condition and efficiency of the compressor. A need also exists for a system and method for monitoring a charge gas compressor using sensors that are capable of operating in harsh environments or are not subject to degradation due to chemical reactivity with the fluids and/or gases experienced in the measuring conditions.

BRIEF SUMMARY OF THE INVENTION

According to one aspect of the present invention, a charge gas compressor monitoring system for determining polytropic efficiency of a charge gas compressor or compressor train is provided. The charge gas compressor or compressor train includes a plurality of compressor stages fluidly connected in series and an inter-stage cooler positioned between adjacent compressor stages. The charge gas compressor monitoring system includes a plurality of self-calibratable sensing modules, wherein each of the sensing modules is positioned adjacent to an inlet or an outlet of each compressor stage. Each sensing module includes at least one fiber Bragg grating sensor positioned within a housing for measuring an operating parameter for a corresponding compressor stage, and each of the fiber Bragg grating sensors is functionalized to respond to one of temperature, pressure, gas density, flow rate, in either steady status or in dynamic event. The charge gas compressor monitoring system also includes a data acquisition system operatively connected to each of the plurality of sensing modules, wherein the data acquisition system includes an optical interrogator for receiving at least one signal from each of the sensing modules. The charge gas compressor monitoring system further includes a controller operatively connected to the data acquisition system, wherein the controller includes a processor and a software interface to determine an estimated polytropic efficiency of each compressor stage. According to another aspect of the present invention, a charge gas compressor monitoring system for determining polytropic efficiency of a charge gas compressor or compressor train is provided. The charge gas compressor or compressor train includes a plurality of compressor stages fluidly connected in series and an inter-stage cooler positioned between adjacent compressor stages. The charge gas compressor monitoring system includes a plurality of sensing modules, wherein each of the sensing modules is positioned adjacent to an inlet or an outlet of each compressor stage. Each sensing module includes a housing having a first fiber Bragg grating sensor embedded into elastic material, a second fiber Bragg grating sensor and a third fiber Bragg grating sensor attached to a cantilever beam, and a fourth fiber Bragg grating sensor positioned within the housing. The charge gas compressor monitoring system also includes a data acquisition system operatively connected to each of the plurality of sensing modules for receiving a signal from each of the sensing modules. The charge gas compressor monitoring system further includes a controller operatively connected to the data acquisition system, wherein the controller includes a processor and a software interface to determine real-time polytropic efficiency for each compressor stage. Advantages of the present invention will become more apparent to those skilled in the art from the following description of the embodiments of the invention which have been shown and described by way of illustration. As will be realized, the invention is capable of other and different embodiments, and its details are capable of modification in various respects. BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWINGS

These and other features of the present invention, and their advantages, are illustrated specifically in embodiments of the invention now to be described, by way of example, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 is a schematic diagram of a charge gas compressor monitoring system; FIG. 2 is another schematic diagram of a charge gas compressor monitoring system;

FIG. 3 is an embodiment of an integrated temperature, pressure and flow sensing module;

FIG. 4 is another embodiment of an integrated temperature and flow sensing module;

FIG. 5 is a chart representing the fiber Bragg grating temperature sensor response;

FIG. 6 is a chart representing the fiber Bragg grating pressure sensor response; FIG. 7 is a chart representing the fiber Bragg grating gas sensor response;

FIG. 8 is a chart representing the fiber Bragg grating vibration sensor response; FIG. 9 is a chart representing the gas effective molecular weight and gas density versus fiber gas sensor response amplitude in wavelength; and

FIG. 10 is a chart representing a compressor polytropic efficiency and gas effective molecular weight dependence. It should be noted that all the drawings are diagrammatic and not drawn to scale. Relative dimensions and proportions of parts of these figures have been shown exaggerated or reduced in size for the sake of clarity and convenience in the drawings. The same reference numbers are generally used to refer to corresponding or similar features in the different embodiments. Accordingly, the drawing(s) and description are to be regarded as illustrative in nature and not as restrictive.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 , a schematic of an exemplary embodiment of a charge gas compressor monitoring system 10 for monitoring the polytropic efficiency of a compressor 11 for use in an ethylene processing unit for providing a five-stage system is shown. Although a five- stage system is shown and described below, it should be understood that any number of stages can be used in conjunction with the concepts and systems described herein. In typical ethylene processing units, the charge gas compressor 1 1 has historically been the critical bottleneck in production. It should also be understood by one of ordinary skill in the art that the concepts for monitoring and controlling a compressor used in conjunction with cracked hydrocarbon gas, ethylene production, propylene production, or any other process utilizing a compressor.

Compressor polytropic efficiency depends directly upon gas composition, temperatures, and pressures at suction and discharge positions. Gas flow rate, fouling severity, and chemical treatment process also indirectly affect compressor polytropic efficiency variation and degradation tendency. Another parameter that can also be used in conjunction with these parameters to indicate increased fouling and surge, and decreased efficiency of a compressor includes vibration and surge of the compressor structure. Because these parameters vary between each of the compressor stages and are dominated by fouling severity, the resulting discharge temperatures, suction pressure, steam turbine speed, and driver horsepower can be increased, while the gas compression ratio and gas throughput can be decreased. Any change of these parameters will affect the efficiency of the compressor and also may cause compressor surge events. Existing temperature, pressure, and flow sensors have been used as basic system operation indicators, and these sensors are able to provide substantially real-time feedback of the conditions. However, gas composition measurement is extremely difficult to measure on a real-time basis. Although gas chromatography (GC) or micro gas chromatography (MGC) can be used to determine gas composition, these processes are time-consuming and require complicated instrument field calibration. As such, analysis of results from these methods may be overly time consuming and does not provide real-time efficiency results of the compressor. Because each of the stages of the compressor are subject to degradation of operating conditions, it is important to provide real-time monitoring of the operating conditions of the compressor at each stage. The charge gas compressor monitoring system 10 of the present invention is configured to monitor operating parameters relating to each stage of the compressor and continually compare those parameters to provide a real-time analysis of the efficiency at each stage to determine the overall efficiency of the compressor train so as to pinpoint the location of the least efficient stage of the compressor train. Real-time polytropic efficiency analysis can also allow for similar real-time control of various conditions of the compressor train so as to correct any decrease in operating efficiency.

This charge gas compressor monitoring system 10 includes a fiber Bragg grating-based (FBG-based) sensing module that can be used for monitoring pre-determined operating parameters for a gas charge compressor or compressor train. This sensing module allows online multi-parameter (fouling, temperature, pressure, flow, gas composition, vibration, etc.) to be simultaneously detected from sensors which are installed at the input and output of each compressor stage of a compressor or compressor train. Each sensor or sensing module is configured to measure at least one condition, including but not limited to: temperature, pressure, flow rate, gas density, as well as thermal and mechanical dynamic events. A network is constructed with a central data process unit that can be remotely accessible and configured to be operatively connected to each sensor or sensing module. The sensing modules are interconnected with the system by either TCP/IP fiber cables or wirelessly. A graphics user interface is designed to convert the measured system operation conditions received from the sensing modules to determine charge compressor train efficiency as well as to control and optimize operation of the compressor. Various types of sensing modules can be used to measure one or more operating conditions at each stage of a multi-stage compressor. In particular, fiber optic sensors, such as a fiber Bragg grating (FBG) sensor, are incorporated into a sensing module and deployed at each location in which pre-determined compressor parameters are to be measured. A FBG- based sensing module is packaged and functionalized to respond to a specific external measurand, or several measurands. In one embodiment, the FBG-based sensing module is a multi-functional physical sensing module that can simultaneously measure temperature, pressure, and flow rate.

The temperature can be determined by FBG sensor wavelength by ΔΤ(ι)=τ*Δλ(ϊ), where τ«10-12 pm/°C, while pressure is calculated by ΔΡ(ί)=γ*Δλ(ΐ), where γ~0.1-0.2 pm/psi. The flowrate sensor is made with two FBG integrated beam structure, which is bent via gas flow. The deflation of the beam induced elastic strain at the low-part of the beam can be detected by two FBGs. When gas flow pass the sensor probe window, the beam bent, one side will produce tensile strain and opposite side beam will produce compressed strain. The relative difference of two FBGs,

is proportional to flow rate, fr(t), where δ is flow sensitivity of the flow sensor in pm/(T/h). Meanwhile, the relative difference between two FBGs central wavelengths is calibrated with flow rate. And the central position, Δλ=(λ(ΡΒ01)+λ(ΡΒ02))/2=τ*ΔΤ, of the two FBGs is a function of the temperature. This FBG-based sensing module is packaged in a probe-like structure. In another embodiment, the FBG-based sensing module is configured for cracked hydrocarbon gas analysis that can also simultaneously measure gas density, gas temperature, and gas flow rate. This sensing module consists of thermally energized FBG- based sensors that are sealed in a thermal capacitor-like package. The gas density is detected when the compressed gas is flowed through the thermal capacitor cell which is measured by FBG-based thermal sensors. The relative wavelength shift of each fiber optic sensor is correlated and converted to an equivalent gas molecular weight, which is directly related to the compressor polytropic efficiency. The wavelength shift indicates the change in polytropic efficiency. Each of these sensing modules can be operated in either a steady status mode or a dynamic status mode. In FIGS. 1-2, the charge gas compressor monitoring system includes a compressor 11 having a plurality of compressor stages 12 that are fluidly connected in series. Compression of a gas causes the temperature of the gas to increase, so an inter-stage cooler 14 is positioned between each compressor stage 12 to maintain a substantially consistent gas temperature as the gas passes between stages such that the overall process is nearly adiabatic. A plurality of sensing modules 16 are positioned within or adjacent to the gas stream to measure operating conditions or parameters of the gas passing therealong. Each of the sensing modules 16 includes at least one fiber Bragg grating sensor 56, as will be explained below. Each of the sensing modules 16 is operatively connected to a junction box 20 in which the signal from each sensing module 16 is received. The data acquired by the junction box 20 is then transferred to a controller 22 that receives and processes the data to monitor the operational parameters of each stage along the charge gas compressor 1 1. The controller 22 is configured to continually monitor the operational parameters of each stage on a real-time basis. The controller 22 continually analyzes the operational parameter data to determine the polytropic efficiency of each compressor stage. The controller 22 analyzes all measured data from machine operation conditions with designed values and their variation range. Whenever a parameter is outside the operation limit, a control or optimization process will be trigged by the controller 22. The controller 22 is also configured to control the anti-fouling conditions of the compressor 1 1.

In an embodiment, the junction box 20 can be configured to include a data acquisition system (DAQ), a static and/or dynamic optical signal interrogator, a sensor signal processor, or a wavelength multiplexer alone or any combination thereof. The controller 22 can be configured to include data acquisition system(DAQ), a processor for collecting and processing collected data, an analyzer that compares and/or evaluates the collected data, and/or an operator for providing a feedback response to the compressor in view of the collected data and determined efficiency results. Moreover, the controller could trig an optimization process for improving compressor efficiency.

FIG. 3 illustrates an exemplary embodiment of an FBG sensor module 16. The sensor module 16 is bolted or otherwise attached to the compressor or tube wall 52 and extends at least partially as a probe into the gas flow stream through the compressor wall. The sensing module 16 includes an optical fiber 54 extending along the length of the module, wherein light is transmitted along the optical fiber 54 to and from the junction box 20 (FIGS. 1-2). In one case, the optical fiber 54 can be formed of silicon or any other material that is substantially inert with respect to gases that contain hydrocarbons. The pressure induced elastic strain variation on FBG is calibrated with a standard pressure gauge. In another case, the FBG pressure is hermetically sealed in a deformable small cylinder with internal pressure of P(0). Its difference from external pressure P(t) will modulate a pre- strain FBG wavelength. Once again, the modulated wavelength is calibrated with a standard pressure gage. The sensing module 16 can include a plurality of fiber Bragg grating sensors 56 formed on the optical fiber 54. In the illustrated embodiment, the sensing module 16 includes a first fiber Bragg grating sensor 56a, a second fiber Bragg grating sensor 56b, and a third fiber Bragg grating sensor 56c. Although the illustrated sensing module 16 shows only three sensors 56, it should be understood by one of ordinary skill in the art that any number of sensors can be positioned along the length of the optical fiber 54. Each sensor 56a, 56b, 56c consists of a fiber Bragg grating formed onto the optical fiber 54, and each sensor 56a, 56b, 56c is also configured to reflect a distinct peak wavelength through the optical fiber 54 that is different from the peak wavelength of the other sensors. In the illustrated embodiment, the first sensor 56a is configured to measure the localized temperature, the second sensor 56b is configured to measure the localized pressure, and the third sensor 56c is configured to measure the localized flow rate. The optical fiber 54 and the fiber Bragg grating sensors 56 are disposed within a housing 58 that is secured to the wall 52. The sensing module 16 is operatively connected to a junction box 20 that is configured to provide light through the optical fiber 54 to each of the fiber Bragg grating sensors 56, and the junction box 20 is also configured to receive the light reflected from the fiber Bragg grating sensors 56. The particular operating parameter being measured causes a change in the peak in the wavelength of light reflected back to the junction box 20, or wavelength shift, produced by the fiber Bragg sensor. The sensing module 16 illustrated in FIG. 3 may also include an additional FBG sensor for measuring the amount of localized vibration.

FIG. 4 illustrates another exemplary embodiment of a sensing module 16. The sensing module 16 includes a pair of optical fibers 54 disposed partially within a housing 58 that is configured to be attached to a wall such that the sensor module 16 is at least partially disposed within the gas flow between compressor stages. Each optical fiber 54 includes a first fiber Bragg grating sensor 56a and a second fiber Bragg grating sensor 56b formed thereon. The first FBG sensor 56a is configured to measure the pressure of the gas flowing through the sensing module 16, and the second FBG sensor 56b is a dual-mode sensor that is configured to measure both the flow rate and temperature. Although FIGS. 3-4 illustrate a single sensing module 16 that includes multiple fiber Bragg sensors integrated therein for measuring distinct operating parameters, it should be understood by one of ordinary skill in the art that multiple sensing modules 16 may be positioned adjacent to the same inlet or outlet of any single compressor stage such that each sensor module 16 measures fewer operating parameters than available sensors.

Another alternative sensing module is shown and described in related patent application entitled "Fiber Bragg Sensor Package for Measuring Polytropic Efficiency in a Compressor" filed the same day as the present application and having serial number xx/xxx,xxx, the entire contents of which are incorporated herein.

When a fiber Bragg grating sensor is packaged to respond to pressure, its package will be required to respond to the pressure-induced strain variation. In order to make precise measurements, a sensor package normally includes one FBG sensor for measuring pressure and a second FBG sensor as a temperature sensor. In this way, a pressure may have a thermal dependent sensitivity, but an additional FBG temperature sensor could be used to differentiate the thermal effect from the mechanical strain effect induced by external pressure variation.

FIG. 5 illustrates the relationship between the temperature sensor response with respect to the relationship between temperature and wavelength shift using a fiber Bragg grating sensor to measure the localized temperature. The relationship between the temperature and wavelength shift is substantially linear for T<500F, and slightly nonlinear afterwards. FIG. 6 illustrates the fiber Bragg grating pressure sensor response with respect to the relationship between pressure and response amplitude. FIG. 7 illustrates the fiber Bragg grating gas sensor response with respect to the relationship between the effective molecular weight of the gas and the response amplitude of the reflected light wavelength. FIG. 8 illustrates the fiber Bragg grating vibrational sensor response with respect to the relationship between the vibrational frequency and the amplitude. FIG. 9 illustrates the relationship between the effective molecular weight (EMW) of the gas relative to the wavelength shift using a fiber Bragg grating sensor using eight different hydrocarbon gas mixtures. FIG. 10 illustrates the relationship between the effective molecular weight of a gas composition and both the k-value as well as the polytropic, efficiency. While it is true that the first direct effect of the machine fouling is a decrease in the polytropic efficiency, the actual value alone of the polytropic efficiency does not provide enough information about the real conditions of the compressor. Variations in compressor efficiency can occur not only because of increased fouling, but also because of variation of input conditions such as pressure, temperature, flow rate, and gas compositions. The latter is increasingly becoming one of the most critical components in assessing the fouling severity. Increased flexibility in feedstock and cracking severity, the possibility of using different streams from an upstream integrated refinery, and recycling of streams from downstream plants are greatly increasing the variation of cracked gas compositions for the same plant, exacerbating the complexity of the fouling phenomena, as well as its interpretation.

The sensor modules 16 positioned along the change gas compressor 11 are configured to measure operating parameters at the inlet and outlet of each compressor stage 12. The polytropic efficiency of each compressor stage 12 is dependent upon the temperature, pressure, and density of the gas being compressed. Although the temperature and pressure have historically been fairly easy to measure in real-time, the gas density has posed much more difficult to measure in real-time. The fiber Bragg grating sensor provides measurements of operational parameters that can be used to calculate the gas density which is determined by the effective molecular weight of the gas. Very often, gas characteristics are not known, so also k value or Cp/Cv, is not known and a standard design value has to be used. If a constant k, i.e. a constant gas composition, is used, also the measure of flow with calibrated orifice is not very precise. Knowing gas characteristics, therefore, is also helpful in designing a better anti-surge system, limiting the safety margin and therefore saving energy. Using a standard k value leads to huge errors, ranging from 5 to 15%, in the calculation of the actual polytropic efficiency. Some other tool is therefore necessary to obtain information about gas composition and k.

Very often, gas characteristics are not known, so also k value is not known and a standard design value has to be used. If a constant k, i.e. a constant gas composition, is used, the measure of flow with calibrated orifice is not very precise. Knowing gas characteristics, therefore, is also helpful in designing a better anti-surge system, limiting the safety margin and therefore saving energy. Using a standard k value leads to huge errors in the calculation of the actual polytropic efficiency. It has been determined that for each processing plant, there should be some strict relation between gas effective molecular weight, i.e. gas density, and the k value.

The monitoring system for determining the real-time polytropic efficiency of a charge gas compressor or compressor train utilizes online fiber Bragg grating sensing instrumentation, as described above, which can first measure gas compositions from different compressor stages, and later extend monitoring capability to suction and discharge temperatures and pressures. Meanwhile additional machine operation conditions, flow, and turbine speed, for instance also can be simultaneously monitored and used for compressor efficiency control and optimization. The sensing instrumentation includes FBG-based sensors, such as temperature sensors, pressure sensors, flow sensors, gas sensors, anti-surge vibration sensors, and anti-fouling sensors that are integrated together with either wavelength- division-multiplexing or time-division-multiplexing platform. Each sensor is a plug-and- play type sensor module, and all the FBG-based sensors can be connected to the sensing network with standard telecom technology. Meanwhile, the sensing system can be remotely monitored and controlled via Ethernet, and the obtained data can be integrated with the existing control platform with a software-based user interface.

The method for remotely monitoring the polytropic efficiency of a charge gas compressor train includes continually collecting measured operating parameters of each compressor stage at the junction box and transmitting the collected measurements to a controller on a real-time basis. Data acquisition is done on a continuous basis, at the maximum sampling rate allowed by the data source, to ensure that a precise assessment of the machine condition can be made even during transient operation. Typical data frequencies are from lHz to 10 kHz. Data are stored in a local database. Analog data are stored at a given frequency, while alarms and events are stored on a "change detection" basis. The controller provides the calculation of the polytropic efficiency, its normalization according to the current process conditions of pressure, temperature, and flow rate (if available), as well as the evaluation of the expected efficiency, based on a real performance curve. The two values are then compared. Once the estimated polytropic efficiency is available, controller calculates the expected performance in the same process and mechanical conditions using the effective characteristics of the machine. Any deviation between actual data and the expected ones could then be associated directly to the fouling. While preferred embodiments of the present invention have been described, it should be understood that the present invention is not so limited and modifications may be made without departing from the present invention. The scope of the present invention is defined by the appended claims, and all devices, process, and methods that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.

Claims

CLAIMS:

1. A charge gas compressor monitoring system for determining polytropic efficiency of a charge gas compressor or compressor train having a plurality of compressor stages fluidly connected in series and an inter-stage cooler positioned between adjacent compressor stages, said charge gas compressor monitoring system comprising:

a plurality of self-calibratable sensing modules, wherein each of said sensing modules is positioned adjacent to an inlet or an outlet of each compressor stage, each sensing module comprising at least one fiber Bragg grating sensor positioned within a housing for measuring an operating parameter for a corresponding compressor stage, and each of said fiber Bragg grating sensors is functionalized to respond to one of temperature, pressure, gas density, and flow rate in either steady status or in dynamic event;

a junction box operatively connected to each of said plurality of sensing modules, said data acquisition system including both a static and a dynamic optical interrogator for receiving at least one signal from each of said sensing modules; and

a controller operatively connected to said data acquisition system, said controller including a processor and a software interface to determine real-time polytropic efficiency corresponding to each compressor stage.

2. The charge gas compressor monitoring system of Claim 1, wherein each sensing module includes at least one optical fiber positioned at least partially within said housing, and at least one of said fiber Bragg grating sensors is disposed along said at least one optical fiber.

3. The charge gas compressor monitoring system of Claim 2, wherein each of said optical fibers is directly connected to said data acquisition system with armored fiber transmission cables.

4. The charge gas compressor monitoring system of Claim 1, wherein at least one of said sensing modules includes a first fiber Bragg grating sensor functionalized to measure temperature, a second fiber Bragg grating sensor functionalized to measure pressure, and a third fiber Bragg grating sensor functionalized to measure flow rate.

5. The charge gas compressor monitoring system of Claim 4, wherein said static optical interrogator is configured to receive a signal from at least one of said first, second, and third fiber Bragg grating sensors with a data rate from one sample per second to one sample per minute.

6. The charge gas compressor monitoring system of Claim 4, wherein said dynamic optical interrogator is configured to receive a signal from only one of said first, second, or third fiber Bragg grating sensor with a data rate from one sample per second to ten thousand samples per second.

7. The charge gas compressor monitoring system of Claim 1 , wherein said both static and dynamic optical interrogators are wirelessly connected to said controller.

8. A charge gas compressor monitoring system for determining polytropic efficiency of a charge gas compressor or compressor train having a plurality of compressor stages fluidly connected in series and an inter-stage cooler positioned between adjacent compressor stages, said charge gas compressor monitoring system comprising:

a plurality of sensing modules, wherein each of said sensing modules is positioned adjacent to an inlet or an outlet of each compressor stage, each sensing module comprising a housing having a first fiber Bragg grating sensor embedded into elastic material, a second fiber Bragg grating sensor and a third fiber Bragg grating sensor attached to a cantilever beam, and a fourth fiber Bragg grating sensor positioned within said housing;

a data acquisition system which includes both a static and a dynamic optical interrogator, said data acquisition system being operatively connected to each of said plurality of sensing modules for receiving at least one signal from each of said sensing modules; and a controller operatively connected to said data acquisition system, said controller including a processor to determine an estimated polytropic efficiency for each compressor stage.

9. The charge gas compressor monitoring system of Claim 8, wherein said first fiber Bragg grating sensor measure temperature, said second and third fiber Bragg grating sensors measure compression and tensile strain in said cantilever beam to determine gas flow rate, and said fourth fiber Bragg grating sensor measures gas density that is calibrated to standard gas composition.

10. The charge gas compressor monitoring system of Claim 8, wherein said data acquisition system is an interrogation source that generates an interrogation signal, wherein upon interrogation of the fiber Bragg grating sensors by said interrogation signal, each sensing module generates a response data signal characteristic of a sensed temperature, pressure, flow rate, or gas density.

11. The charge gas compressor monitoring system of Claim 8, wherein said controller includes a signal acquisition, a data analysis system, and a control system, wherein said at least one signal from each of said sensing modules is acquired by said signal acquisition and said data analysis system to estimate said polytropic efficiency.