Abstract:
Method and apparatus for the detection and measurement of contaminant concentration within pressurized fluid flows in real-time. The provided method and apparatus allow for real-time detection of black powder contaminants in pressurized gas flows by irradiating the flow with electromagnetic waves generated by hermetically-sealed electromagnetic wave radiators and measuring wave characteristics. An image is rendered of the spatial distribution of black powder within the pipe cross section, and mass flow of the contaminated gas is measured.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application the non-provisional application of U.S. Provisional Application Ser. No. 62/039,258 entitled Method and Apparatus to Detect Contaminants in Pressurized Fluid Flows, filed on Sep. 5, 2014, the contents of which are incorporated herein by reference in their entirety for all purposes. 
     
    
     BACKGROUND 
       [0002]    Aspects of the present invention generally relate to the detection of undesired contaminants in fluid flows within structures such as pipelines and vessels, using electromagnetic waves. More specifically, aspects of the present invention relate to the real-time detection and monitoring of black powder contaminants within gas flows in natural gas pipelines. Conventional systems for detecting undesired contaminants generally function by transmitting and receiving an electromagnetic signal through a multiphase flow, and inferring the dielectric properties of the flow based on the amplitude and phase change of the received signal. Such detectors also function by deducing flow properties based on the shift of the resonance frequency as well as the quality factor in the transmitted signal. 
         [0003]    Pipelines and vessels are typically made out of either metallic materials (e.g., steel) or non-metallic materials (e.g., plastics and composites). Such structures are used extensively for fluid transmission in many industries including the oil and gas industry. When used for natural gas transmission, steel pipelines are susceptible to undesired solid contaminants in the form of black powder carried within the gas flow. Black powder is a general term used to describe dry or wet fine powder material, e.g., solid particles, consisting of various corrosion products such as iron oxides, iron sulfides, and other contaminants such as dirt and sand. Black powder is a recognized threat to the integrity and operation of transmission pipelines in many different regions around the world. 
         [0004]    Although the formation mechanism of black powder can vary, those skilled in the art believe that the initiation of black powder can be attributed at least in part to the hydrotesting phase during the pipeline commissioning stage. Regardless of how it originates, black powder adversely impacts the integrity of gas pipelines and the controls and instrumentation associated with the pipelines, which may lead to partial or even complete shutdown and lost production. For example, black powder accumulation causes valve damage, compressor failure, and instrumentation clogging leading to expensive repairs. In many instances, black powder contaminants propagate further to downstream processes and utility companies. In addition to potential physical asset damage, the propagation of the contaminants raises critical quality-of-service complaints and flow assurance concerns which may reflect negatively upon the image of the supplier. 
         [0005]    Black powder is currently only discoverable through examining the consequences of its presence in a given pipeline section, such as by end-user complaints, or by discovering the indications of black powder residuals by inspecting components such as a failed compressor, a clogged flow meter, or a due-for-replacement line filter. After detecting black powder in a particular pipeline, it is typically managed, i.e., removed from the victim line, through routine pipeline maintenance procedures using various well-established methods such as filtration, gel-based or surface active agents-based cleaning and aggressive pigging. This, however, does not solve the problem completely because the discovered black powder in the cleaned line might have originated from a different pipeline in the network and transported with the flow to the victim line. Due to the lack of effective black powder detection methods, the source of the black powder is rarely discovered and hence not treated. Consequently, the problem soon arises again and repairs on the victim lines must be repeated. 
         [0006]    The black powder flow in a gas pipeline is a two-phase (solid-gas) dielectric mixture. The presence of black-powder in the pipeline changes the effective medium in the pipe cross section. There is no doubt that the black powder particles have physical and chemical properties that are distinct from the host gas carrying the black powder. Such chemical or physical contrasts can be the basis for many detection methods. In principle, the contrast in the magnetic, electrical, electromagnetic, optical, thermal, and mechanical properties between the black powder and its host gas can be exploited to develop viable detection techniques. For instance, differential weight measurements have been used to measure black powder deposits in gas pipelines. Unfortunately, this method is not applicable for detecting the black powder in motion with the gas flow as desired in many applications. Ultraviolet and visual spectrometers have also been used to detect liquids in gas flows. 
         [0007]    Previously, microwave measurement techniques for multiphase mixture characterization and liquid flow metering have been employed in many multiphase metering technologies and liquid flow sensors, alone as well as combined with other methods such as gamma rays. Although microwave techniques are particularly promising for multi-phase component fraction measurements, current solutions are lacking. 
         [0008]    In general, determining multiphase component fractions using microwave methods is founded on the electromagnetic interaction between the electromagnetic waves and the dielectric medium in the pipe. Conventional methods of deducing the dielectric properties of the multiphase mixture at microwave frequencies are generally based on two approaches. In the first approach, the dielectric properties, i.e. permittivity, of the multiphase flow are inferred from amplitude and phase change of a microwave signal passing through the flow or reflected from the flow. In the second approach, these properties are deduced from the shift of the resonance frequency and change in the quality factor of a microwave resonant cavity containing the multiphase flow. 
         [0009]    These conventional techniques have several shortcomings. For example, they cannot be applied to detect black powder within pressurized natural gas flows. In particular, the techniques do not address the significant problem of coping with high pressure applications. Furthermore, they either use the pipeline as a waveguide cavity resonator, or they are based on resonant inserts placed in the flow, which tend to perturb the process flow and decrease measurement accuracy. Also, most of these methods are limited to metallic pipelines. 
         [0010]    Additionally, many techniques predict the flow properties from either detecting a shift in the resonance frequency, Doppler frequency shift, and/or detecting the attenuation of the microwave signal between two measurement points along flow direction. But these techniques have not been demonstrated as capable of detecting very small black powder flow rates, such as rates at less than 1 g/s typically encountered in practice 
       SUMMARY 
       [0011]    Briefly, aspects of the present invention permit detecting black powder inside gas pipeline networks in real time. As is understood by those skilled in the art, black powder should be detected as early as possible and its source should be localized and treated to avoid severe black powder consequences and to design cost-effective pipeline maintenance protocols. Aspects of the invention permit early detection of black powder in susceptible lines for efficient pipeline management and “Best in Class” maintenance. In this regard, aspects of the present invention provide a sensitive detection device that allows in-field evaluation of the installed filters to detect the presence of black powder and measure its concentration within the flow in its early stages. This not only enables cost-effective maintenance procedures but also allows for tracing the initiating source of the black powder, fully understanding its formation mechanism, and eliminating the problem completely from the origin. Moreover, aspects of the present invention embody improvements that permit black powder detection without requiring use of cavity resonators or resonator inserts and without requiring use of the pipeline as a waveguide for the microwaves. In this regard, detection is permitted in both metallic and non-metallic pipelines at an improved level of sensitivity, without involving any type of sampling for the gas-black-powder mixture. Aspects of the invention provide detection of very small black powder flow rates (less than 1 g/s) even under high temperature, high pressure, and/or high flow rate conditions. 
         [0012]    In an aspect, an apparatus characterizes multiphase flow in a pipe transporting a fluid under pressure. The apparatus includes a transmitter to generate a signal. A first antenna transmits the signal through a first transmission line to a fluid contained within a section of pipe, and is also configured for receiving a reflected portion of the signal. A second antenna receives a portion of the signal “transmitted through” the fluid. A first diode detector detects a standing wave in the first transmission line, the standing wave comprising the reflected portion of the transmitted signal and the original transmitted signal, producing a first voltage representing the standing wave. A second diode detector produces a second voltage based on the transmitted through signal received by the detector from the second antenna. A preamplifier/filter, a converter, and a monitoring processor further process the first and second voltages to identify characteristics of the flow. 
         [0013]    In another aspect, a method for detecting components within a pressurized gas flow mixture is provided. 
         [0014]    Other objects and features will be in part apparent and in part pointed out hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]      FIG. 1  depicts a microwave detection apparatus in accordance with one embodiment of the invention. 
           [0016]      FIG. 2  is an exemplary graph depicting dependency of the transmitted-through signal power on the volume fraction of black powder in a 3-inch pipe. 
           [0017]      FIG. 3(   a ) is a cross-sectional side view of an antenna constructed in accordance with one embodiment of the invention. 
           [0018]      FIG. 3(   b ) is a cross-sectional end view of the antenna of  FIG. 3(   a ). 
           [0019]      FIGS. 4(   a ) and  4 ( b ) are exemplary graphs depicting measurement results according to an embodiment of the invention. 
           [0020]      FIG. 5  depicts a microwave imaging system in accordance with an embodiment of the invention. 
           [0021]      FIG. 6  depicts exemplary microwave imaging of black powder sediment illustrating an obtained image representing black powder distribution. 
           [0022]      FIG. 7  depicts an array construction of a microwave imaging system in accordance with one embodiment of the invention. 
           [0023]      FIGS. 8(   a ) and  8 ( b ) depict perspective and front views of part of an in-line array for use in a pipe in accordance with an embodiment of the invention. 
           [0024]      FIGS. 9(   a ) and  9 ( b ) depict perspective and front views of another part of the in-line array for use with the part of  FIGS. 8(   a ) and  8 ( b ). 
           [0025]      FIGS. 10(   a ) and  10 ( b ) depict perspective and front views of an insert for use with the in-line array parts of  FIGS. 8(   a ) and  8 ( b ) and  FIGS. 9(   a ) and  9 ( b ). 
           [0026]      FIG. 11  is an exemplary graph depicting an array-produced response due to target movement in the cross section of the pipe. 
           [0027]      FIG. 12  is an exemplary flow diagram depicting a method of microwave detection and imaging in accordance with one embodiment of the invention. 
       
    
    
       [0028]    Corresponding reference characters indicate corresponding parts throughout the drawings. 
       DETAILED DESCRIPTION 
       [0029]    Aspects of the present invention relate to detection of undesired contaminants, namely, black powder. More specifically, improved methods and systems involving black powder detection are described. The presence of black powder in the pipeline changes the effective dielectric medium of the flow in the line. The dielectric properties (i.e., complex permittivity and permeability) of the black powder are significantly different than the host gas flow. Hence, the presence of the black powder, even in small concentrations, changes the effective dielectric properties of the flow considerably. Microwaves are sensitive to minute dielectric variations. Specifically, these waves undergo scattering (reflection) and attenuation as they impinge and pass through the cross section of the pipeline containing black powder. Two main embodiments that utilize this interaction are described in the following. 
       1. Microwave Detection Apparatus and Method 
       [0030]      FIG. 1  depicts a microwave detection apparatus in accordance with one embodiment of the invention. As depicted by  FIG. 1 , a pipeline  101 , which has a pipe wall  103 , carries a mixture of gas  105  and contaminants  107  within a flow  108  of process fluid. For instance, the contaminants  107  include black powder. Additionally,  FIG. 1  depicts a detection apparatus  110  according to a preferred embodiment. As depicted in  FIG. 1 , the apparatus  110  includes, among other components, a transmitter  113 , a transmitting antenna  115 , a receiving antenna  118 , a first transmission line  141 , a second transmission line  150 , a first diode detector  125 , and a second diode detector  153 . In an embodiment, the detection apparatus  110  of  FIG. 1  is hermetically-sealed for use in fluid environments. The transmitter  113  generates a microwave signal  128  carried by the second transmission line  150  to the transmitting antenna  115  as transmitted signal  155 . The transmitting antenna  115  in turn launches the supplied microwave signal  128  (i.e., transmitted signal  155 ) through the pipe wall  103  into the flow  108  inside the pipeline  101 . 
         [0031]    When microwaves impinge upon the gas  105  component of the flow  108  that carries black powder contaminants  107 , a portion of the incident wave reflects back towards the transmitting antenna  115  as a reflected wave  135 . The remaining wave portion passes through the flow  108  as a transmitted-through wave  138 . The transmitted-through wave  138  is picked up at the receiving antenna  118 , which is on the pipe wall  103  on the other side of pipeline  101 . The receiving antenna  118  delivers a signal  168  representative of transmitted-through wave  138  via a first transmission  141  line to a first diode detector  125 . The first diode detector  125  produces a voltage proportional to the power in the transmitted-through signal  168  (V T ) at node  144 . Also, the reflected wave  135  is picked up by the transmitting antenna  115  and propagates as a reflected signal  147  in a second transmission line  150  where it is superimposed on the opposite-traveling transmitted signal  155  creating a standing wave. The power in the formed standing wave is detected using a second diode detector  153  that produces a voltage proportional to this power (Vs) at node  156 . In the illustrated embodiment, a Pre-Amplifier/Filter  159  filters and amplifies the detected voltages before they are sampled using analog to digital converter  162 . A Processing Unit/Display  165 , which comprises a microprocessor, personal computer, or the like, processes and displays the digitized voltages. The Pre-Amplifier/Filter  159 , the analog to digital converter  162 , and the Processing Unit/Display  165  are powered by a power supply  171 . 
         [0032]    The presence of the black powder contaminants  107  within the flow  108  alters the phase angle and amplitude (power) of the complex reflected signal  147  and transmitted-through signal  168  in a specific way that is correlated to the concentration of the black powder contaminants  107  within the gas  105  that comprises the flow  108 . 
         [0033]    For instance,  FIG. 2  illustrates the dependency of the power of a transmitted-through signal (proportional to V T ) on the volume fraction of black-powder at 24 GHz in a 3-inch pipeline (“no-black-powder” case is set at 0 dBm as reference). As shown in  FIG. 2 , besides the induced change due to the presence of black powder (20 dB for 5% volume fraction), there is a one-to-one relation between the power of the transmitted through signal (in dB) with the black powder concentration. In this example, the detection dynamic range is 42 dB. Although, in this particular example, measuring the power of the transmitted through signal could be relied upon for detection and quantification, measuring more parameters as provided by the system shown in  FIG. 1  (two measurements: V T  and V S ) provides diversity to compact non-unique mappings that might arise in larger pipes, decrease the measurement uncertainties, and enhance the detection dynamic range. 
         [0034]    Based on the apparatus  110  shown in  FIG. 1 , a microwave detection device working at 24 GHz was realized using simple power detectors. To launch/receive the microwave signal into/from the pipe, a compact hermetically-sealed antenna that is properly coupled to the pipe was designed. The designed antenna is non-perturbing to the flow and isolated from it. Furthermore, the antenna construction and its coupling mechanism can withstand the pressure encountered typically in practice. As desired, the antenna uses a standard coupling mechanism such as tap holes and thread-o-lets similar to most standard sensors which are typically interfaced to the pipe based on such coupling. Since the antenna is configured with standard coupling, the apparatus  110  can be installed on spare pre-tapped locations typically found in the network for flow sampling and instrumentation purposes. 
         [0035]      FIGS. 3(   a ) and  3 ( b ) depict longitudinal and cross-sectional dimensions of an antenna (e.g., antenna  115  or antenna  118 ) constructed in accordance with one embodiment of the invention. To construct an antenna according to an embodiment with attributes that provide for the detection of black powder contaminants  107  as described above, a probe  300  comprising a circular waveguide as shown in  FIGS. 3(   a ) and  3 ( b ) is disclosed. In an embodiment, the circular waveguide works in the TE 11  mode region and is fed through TEM-to-TE 11  transition by a 50 ohm coaxial line. In another embodiment, the disclosed antenna is constructed by using a single block  304  of “type 303 stainless steel” or the like to machine both the transition (feed) section  302  as well as the circular waveguide  306  section from the same block of steel (cf.  FIG. 3(   a ) for dimensions) without creating weak joints. 
         [0036]    In an embodiment, a rod  308  comprised of a fluorocarbon solid or the like (e.g., TEFLON® polytetrafluoroethylene) is press-fit into the circular waveguide  306  section as well as into the feed  302  section to hermetically seal the probe  300  and to isolate the probe  300  from the flow  108 . In an embodiment, the rod  308  of  FIGS. 3(   a ) and  3 ( b ) is press-fit into portions of the probe  300  to surround and insulate a center conductor that comprises a standard coaxial feed. The standard coaxial feed  309  is communicatively connected to a coaxial line port  312 . In an embodiment, a matching flat bottom hole is machined into portions of the rod  308  to configure portions of the rod  308  for screwing into the feed  302  section structure. 
         [0037]    Finally, in an embodiment, the antenna probe  300  is configured to be fitted with a commercial bored-through fitting comprising a ⅜″ NPT (M) process connection suitable for high pressure applications. To install the transmitting and receiving antennas  115 ,  118 , respectively, two ⅜″ NPT (F) steel thread-o-lets are fitted on a flanged test section made out of standard 4-inch (˜101 mm) steel pipe (˜6.2 mm wall thickness) and PN16 flanges. The overall length of the antenna was ˜7.0 cm and it was designed such that the open-ended aperture of the waveguide, such as waveguide  306  section, is offset from the inner pipe&#39;s wall surface by 2 mm. 
         [0038]      FIGS. 4(   a ) and  4 ( b ) are exemplary graphs depicting measurement results.  FIG. 4(   a ) depicts a transmitted-through response for various black powder sample weights, demonstrating real-time detection and assessment of black powder contaminants  107 . In an embodiment, the detection apparatus  110  was used in a 3.6-m long experimental flow rig developed specifically for demonstration purposes. The experimental rig consisted of interconnected 4-inch ID (˜101 mm) horizontal acrylic pipes and a 120-W DC fan as an air source. The flow created by the fan was rotational and had a maximum speed of 12 m/s (at the pipe&#39;s wall  103 ). While the air was flowing from the fan, black powder samples with known weight were deposited through a sealed material inlet into the flow  108  before the inline test section. 
         [0039]      FIG. 4(   b ) depicts the correlation between the sample weight and the integral of the response curve for black powder and sand. It is evident that black powder flow rates as small as 0.2 g/s can be readily detected. To further demonstrate the measurement selectivity of the disclosed apparatus  110 , the black powder experiment was repeated using sand samples.  FIG. 4(   b ) illustrates a comparison between the detection response of black powder samples and the detection response of sand samples. 
         [0040]    The design of the microwave detection circuitry subsystems can be changed without departing from the scope of this invention. For instance, coherent detectors (measuring phase and magnitude) can be used to detect the reflected and transmitted-through signals. 
       2. Microwave Imaging Apparatus and Method 
       [0041]      FIG. 5  depicts a microwave imaging system  500  according to another embodiment of the present invention. It is sometimes desired to visualize the distribution of black powder in a pipe  501 . In addition to the microwave detection method described above, the imaging system  500  is capable of producing a visual rendering of black powder distribution within a cross section of the pipe  501 . The microwave imaging system  500  assumes access to the inside of pipe  501 . This can be accomplished by integrating an imaging array (e.g., see  FIGS. 8(   a )-(b),  FIGS. 9(   a )-(b)) within the pipe structure. The microwave imaging system  500  and its array of antennas are preferably non-perturbing to the flow in the pipeline and isolated from it. Microwave excitation is performed from localized points along the circumference and enclosing the test space. 
         [0042]    The imaging system  500  disclosed in  FIG. 5  comprises an N-channel microwave based imaging system based on a 2D imaging array working in the frequency range from 8-16 GHz. For instance, a uniform circular array embodies the 2D imaging array. Each antenna  503  is capable of transmitting and receiving a microwave signal in this frequency range. Hermetically-sealed wide band antennas are developed specifically for this purpose. In this particular embodiment, the array has an inner diameter of 4 inches, measured from a test section wall  506 . To avoid spatial aliasing in the frequency range up to 16 GHz, a total of N=32 elements are used in one embodiment. As shown in  FIG. 5 , an N-channel transmitter/receiver module  509  connected to each antenna  503  by way of transmission lines  515  is configured to provide data describing detection results to display/storage components  521 . In an embodiment, antenna  503  comprises transmitting antenna  115  and/or receiving antenna  118  as previously described. In another embodiment, the N-channel transmitter/receiver modules  509  are replaced by a single module (i.e., vector network analyzer) and a fast 1-to-32 microwave switch. As with the detection system, the array construction has means to withstand high pressures, providing for the detection of black powder contaminants  518 . 
         [0043]      FIG. 6  depicts exemplary results obtained from the microwave imaging of black powder sediment illustrating an obtained image representing black powder distribution. With switched excitation/reception, the system described in  FIG. 5 , for example, is configured to facilitate robust monostatic measurements. In an embodiment, after cycling over each antenna  503 , the detected signals (phase and magnitude) are processed to construct an image for the pipe cross section. In an embodiment, the image is representative of the gas flow mixture in the pipe  501  as a function of V T  and V S . 
         [0044]    Additionally or alternatively, various well-established imaging algorithms are used for the purpose of constructing the pipe cross section image. In one non-limiting example, a synthetic focusing algorithm is utilized and implemented to produce an image for an irradiated medium. To illustrate this concept, a microwave imaging algorithm based on a bi-focusing operator was simulated to produce an actual distribution for black powder sentiment in a 3 inch pipe. In another embodiment, an image (illustrated by  FIG. 6 ) is obtained for black powder sentiment in a 3 inch pipe, providing an image of a first detection region  554  that illustrates a greater presence of black powder sentiment in relation to a second detection region  557 . In yet another embodiment, second detection region  557  illustrates a greater presence of black powder sentiment in relation to a third detection region  560 . 
         [0045]      FIG. 7  depicts array construction of a microwave imaging system  700  of the type shown in  FIG. 5  in accordance with one embodiment of the invention. The imaging system  700  depicted by  FIG. 7  is comprised of one or more antenna arrays that further comprise a hermetically sealed waveguide array. For example, the waveguide array includes 32 staggered rectangular waveguide elements integrated within the pipe structure. The imaging system  700  is designed to provide efficient means to withstand high gas pressures. The designed array in this embodiment comprises a circular array of 32 antennas. In an embodiment, the designed array comprises a first antenna (e.g., antenna  503 ) located in a first array, a second antenna  703  located in the first array and across the pipe from the antenna  503  for receiving the transmitted microwave signal through the fluid contained within the section of the pipe, and a third antenna  706  located downstream of the second antenna  703  for receiving the transmitted microwave signal through the fluid contained within the section of the pipe, as described herein. 
         [0046]    In an embodiment, each antenna (e.g., antenna  503 , second antenna  703 , or third antenna  706 ) comprises a rectangular waveguide. In another embodiment, each rectangular waveguide has similar dimensions (width=0.5305 inch and height=0.2386 inch in one non-limiting example) filled with a fluorocarbon solid to isolate the element from the process, as previously described. The waveguide antennas  503 ,  703 ,  706  are configured specifically to provide for TM z  test section illumination (i.e., illumination of the electric field along the pipe axis  709 ). Each array&#39;s antennas, such as antennas  503 ,  703 ,  706 , are arranged into a concentric and identical circular array. For instance, each array of  FIG. 7  comprises 16 waveguide elements interspaced center to center by a 20 mm arc.  FIG. 7  illustrates the arrays by a first concentric circular array including antenna  503  and second antenna  703  and labeled  1 ,  2 ,  9 ,  15 , and  16 , respectively and a second, concentric, and identical circular array including antennas such as third antenna  706  labeled  17 ,  18 ,  24 ,  30 ,  31 , and  32 , respectively. In an embodiment, each concentric circular array is staggered by a uniform offset measurement. Additionally or alternatively, the circular arrays are interspaced by a uniform offset measurement along the pipe axis of 10.1 mm between each antenna (slightly larger than a quarter wavelength at 10 GHz). Additionally or alternatively, the concentric circular arrays are staggered by a uniform offset measurement of 11.25 degrees, as shown by  FIG. 7 . 
         [0047]      FIGS. 8(   a )-(b),  FIGS. 9(   a )-(b), and  FIGS. 10(   a )-(b) depict perspective and front views of array parts comprising a center part ( FIGS. 8(   a ) and  8 ( b )), a cover part ( FIGS. 9(   a ) and  9 ( b )), and a filling ( FIGS. 10(   a ) and  10 ( b )) in accordance with an embodiment of the invention. In an embodiment, each antenna (e.g., antenna  503 , second antenna  703 , or third antenna  706  as previously described) comprises a waveguide as described herein. For example, each antenna comprises a waveguide that is fed by a coaxial feed with TEM-to-TE 10  transition designed specifically to operate in the range from 8-16 GHz. The array parts are built on, for example, a custom made four inch pipe section. In an embodiment, a center part, such as shown in  FIGS. 8(   a ) and  8 ( b ), mates with a cover part, such as shown in  FIGS. 9(   b ) and  9 ( b ), to form a circular array of uniformly spaced rectangular waveguides. In the illustrated embodiment, fluorocarbon solid inserts, as shown in  FIGS. 10(   a ) and  10 ( b ), fill the waveguides. It is to be understood that multiple arrays (e.g., as shown in  FIG. 7)  can be constructed by arranging center sections back to back with associated cover sections. In this embodiment, a gasket is preferably arranged in-between the center sections. In another embodiment, the array parts further comprise two cover sections ( FIGS. 9(   b ) and  9 ( b )) arranged back to back with associated center sections. To reduce the cost of manufacturing, two identical center sections and covers are manufactured. For post-manufacturing alignment, M6 clearance holes  803  and M6 threads  805  are machined on a seven inch OD circle on each cover. Each M6 clearance hole  803  is offset from the threaded hole  805  by 11.25 degrees, in an embodiment. Aligned M6 clearance holes are machined into the center sections, in yet another embodiment. 
         [0048]    With further reference to  FIGS. 8(   a )-(b),  FIGS. 9(   a )-(b), and  FIGS. 10(   a )-(b), each antenna further comprising a waveguide is machined into the center part such that the back, bottom, and two side walls of the waveguide are completely embedded in the center part. The cover part provides the top waveguide wall once the array is assembled. A coaxial feed is inserted through a feed hole  809  from the back of the cover part into the fluorocarbon solid insert or filling of the waveguide. In an embodiment, various design specifications provide for an array structure capable of withstanding high pressures. The center sections are constructed with radial  812  and circumferential  815  tongues as shown in  FIGS. 8(   a ) and  8 ( b ). In another embodiment, the cover sections are constructed with radial  818  and circumferential  821  grooves as shown in  FIGS. 9(   a ) and  9 ( b ), resulting in a tongue-groove assembly allowing for the electromagnetic isolation of array elements (such as antenna  503  comprising a waveguide, for example) from each other as well as making the array structure withstand high pressure and avoid any fluid leakage. If needed, sealants can be used in the grooves without impairing the functionality of the array. 
         [0049]    Still referencing  FIGS. 8(   a )-(b),  FIGS. 9(   a )-(b), and  FIGS. 10(   a )-(b), each pair of cover and center parts are assembled together by inserting M3.5 and M2.5 screws through M2.5 hole  824  and M2.5 thread  827 , as well as M3.5 hole  830  and M3.5 thread  833 . This procedure results in two identical cover-center assemblies. These two assemblies are placed such that the center section&#39;s flat faces are parallel. Then, M6 screws should be inserted through the clearance holes  803  of one cover-center assembly and screwed into an aligned M6 thread  805  in the second cover-center assembly. 
         [0050]      FIG. 11  is a graph depicting an exemplary array-produced response due to target movement in the cross section of the pipe. Due to the unique tongue-groove assembly surrounding each antenna comprising an array element as described above, the disclosed array provides high isolation between the array elements. The symmetry in construction results in symmetric response. The sensitivity of the system to a target  903  within the pipe cross section is demonstrated in  FIG. 11 , which illustrates a typical measured response as a target  903  traverses the pipe cross section along a line  906  connecting any two elements. As demonstrated in  FIG. 11 , the phase and magnitude response as a function of the position of target  903  is indicative of the sensitivity of the apparatus as an imaging system. 
         [0051]    Placing a cylindrical nylon rod within the imaging array and displaced towards one of side of the pipe highlights the capabilities of the disclosed imaging system. To highlight the capability of the disclosed imaging system for detecting and localizing relatively small targets, a cylindrical nylon rod comprised of 0.78-inch OD was placed coaxially within the imaging array while displaced towards one of side of the pipe. A total signal bandwidth of 8 GHz (8-16) was used to produce an image for the target considered in this demonstration. The disclosed system can produce clear indication for the presence of the target (i.e., the rod) as well as render a clear image from which the location of the target can be readily estimated. 
         [0052]      FIG. 12  depicts a method for detecting components within a pressurized gas flow mixture, in accordance with an embodiment of the invention. The process begins at  1110 , comprising generating, by a transmitter, a microwave signal. Step  1115  comprises transmitting, via a transmitting antenna configured for receiving the microwave signal, an incident wave into a gas flow mixture contained within a pipe, said transmitting antenna being coupled to the transmitter via a transmission line. Next, at  1120 , the process comprises receiving, via the transmitting antenna, at least a portion of the incident wave reflected back to the transmitting antenna by the gas flow mixture. 
         [0053]    With further reference to  FIG. 12 , the process continues at  1125  with receiving, via a receiving antenna, at least a portion of the incident wave transmitted through the gas flow mixture, said receiving antenna being located substantially opposite the transmitting antenna across the pipe. Next, at  1130 , the process comprises producing a voltage (V T ) proportional to the power of the received portion of the incident wave transmitted through the gas flow mixture. The process further comprises producing a voltage (V S ) proportional to the power in a standing wave formed on the transmission line by superimposing the portion of the incident wave reflected back to the transmitting antenna by the gas flow mixture on the microwave signal, as illustrated by step  1135 . Finally, the process concludes at  1140  with; identifying one or more characteristics of the gas flow mixture as a function of V T  and V S . 
         [0054]    Still referring to  FIG. 12 , it is to be understood that the presence of black powder, even at a relatively small volume within the process flow, is manifested with considerable variations in the microwave transmission properties of the process flow rendering high overall detection sensitivity. Therefore, it is to be understood that the method described in  FIG. 11  allows for the identification of one or more characteristics of the gas flow mixture that in turn describe considerable variations in the microwave transmission properties of the pressurized gas flow mixture, resulting in high overall detection sensitivity. 
         [0055]    Advantageously, both the detection and imaging systems can be equipped with means to measure the mass flow rate. In the detection system, an addition of one or more probes (such as an antenna  503 , a second antenna  703 , or a third antenna  706 , each of the antennas further comprising a waveguide in an embodiment, as described herein) displaced along the axis of the pipe provides such a means. In the imaging system, since there are two arrays along the pipe axes, the relative measurements between these arrays can be readily used to measure the flow rate, and to construct an image that comprises the mass flow rate measurement. 
         [0056]    Moreover, the imaging system is a more general embodiment of the detection system. In an embodiment, a subset of the imaging system can be used to perform the detection and quantification of black powder. 
         [0057]    Both the detection and imaging system are configured to utilize conventional phase and/or magnitude modulation schemes as well common time- and/or frequency multiplexing techniques of the transmitted and/or received signals to enhance sensitivity, resolution, and/or reduce system complexity. 
         [0058]    Embodiments of the aspects of the invention may be implemented with processor-executable instructions. The processor-executable instructions may be organized into one or more processor-executable components or modules on a tangible processor readable storage medium. Aspects of the invention may be implemented with any number and organization of such components or modules. For example, aspects of the invention are not limited to the specific processor-executable instructions or the specific components or modules illustrated in the figures and described herein. Other embodiments of the aspects of the invention may include different processor-executable instructions or components having more or less functionality than illustrated and described herein. 
         [0059]    The order of execution or performance of the operations in embodiments of the aspects of the invention illustrated and described herein is not essential, unless otherwise specified. That is, the operations may be performed in any order, unless otherwise specified, and embodiments of the aspects of the invention may include additional or fewer operations than those disclosed herein. For example, it is contemplated that executing or performing a particular operation before, contemporaneously with, or after another operation is within the scope of aspects of the invention. 
         [0060]    When introducing elements of aspects of the invention or the embodiments thereof, the articles “a,” “an,” “the,” and “said” are intended to mean that there are one or more of the elements. The terms “comprising,” “including,” and “having” are intended to be inclusive and mean that there may be additional elements other than the listed elements. 
         [0061]    In view of the above, it will be seen that several advantages of the aspects of the invention are achieved and other advantageous results attained. 
         [0062]    Not all of the depicted components illustrated or described may be required. In addition, some implementations and embodiments may include additional components. Variations in the arrangement and type of the components may be made without departing from the spirit or scope of the claims as set forth herein. Additional, different or fewer components may be provided and components may be combined. Alternatively or in addition, a component may be implemented by several components. 
         [0063]    The above description illustrates the aspects of the invention by way of example and not by way of limitation. This description enables one skilled in the art to make and use the aspects of the invention, and describes several embodiments, adaptations, variations, alternatives and uses of the aspects of the invention, including what is presently believed to be the best mode of carrying out the aspects of the invention. Additionally, it is to be understood that the aspects of the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the drawings. The aspects of the invention are capable of other embodiments and of being practiced or carried out in various ways. Also, it will be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. 
         [0064]    Having described aspects of the invention in detail, it will be apparent that modifications and variations are possible without departing from the scope of aspects of the invention as defined in the appended claims. It is contemplated that various changes could be made in the above constructions, products, and process without departing from the scope of aspects of the invention. In the preceding specification, various preferred embodiments have been described with reference to the accompanying drawings. It will, however, be evident that various modifications and changes may be made thereto, and additional embodiments may be implemented, without departing from the broader scope of the aspects of the invention as set forth in the claims that follow. The specification and drawings are accordingly to be regarded in an illustrative rather than restrictive sense.