Abstract:
The present invention relates generally to an apparatus and method for sample analysis. More particularly, the invention encompasses a method and an apparatus for continuous, constant, flow sample introduction of fluid samples of varying viscosity and composition. The invention further includes the option of the apparatus being associated with at least one fluid analyzer system. A temperature controlled environment may also be provided for the processing and analysis of a fluid sample.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The instant patent application is related to U.S. Provisional Patent Application Ser. No. 60/941,304, filed on Jun. 1, 2007, titled “Technique for Continuous, Constant Flow Sample Introduction,” the disclosure of which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to an apparatus and method for sample analysis. More particularly, the invention encompasses a method and an apparatus for continuous, constant, flow sample introduction of fluid samples of varying viscosity and composition. The invention further includes the option of the apparatus being associated with at least one fluid analyzer system. A temperature controlled environment may also be provided for the processing and analysis of a fluid sample. 
     BACKGROUND INFORMATION 
     Fluid samples are often introduced to process analyzers with valves that provide a fixed amount of sample. Some process analyzers require a continuous, constant flow of sample. This can be achieved by ensuring that the flow rate of the sample remains constant while it is being introduced and processed by the analyzer. One way to achieve a constant flow rate is by passing a stable viscosity sample through a restrictor at constant pressure. This will not work for a sample whose viscosity is changing unpredictably. Any change in the composition of the fluid sample can result in a change in viscosity, and, hence a subsequent change in its flow rate through the restrictor. The nature of flare samples is that they frequently undergo unpredictable and dramatic compositional changes. This dramatic variation in the composition of the flare lines and the resulting changes in viscosity can make the control of the flow rate of a sample of flare line gas a difficult problem. 
     Ulrich Gokeler and Friedhelm Müller, in “On Line Monitoring Of Total Sulfur In Combustion Fuel Using Process Gas Chromatography”, 2001 ISA Analysis Division Proceedings, Houston, Tex., October 2001, the disclosure of which is incorporated herein by reference, describes an analytical system for an automatic online total sulfur analyzer based on a proven process gas chromatographic technique utilizing a new and unique system to vaporize small amounts of sample continuously. The vaporized sample is continuously burned in a Flame Ionization Detector (FID) flame to produce, various components of the sample, such as, for example, sulfur dioxide, water and carbon dioxide. The sulfur dioxide, represents the entire sulfur content in the sample, which is then separated using conventional gas chromatography and detected utilizing a Flame Photometric Detector (FPD). 
     U.S. Pat. No. 6,453,725 (Robert W. Dahlgren, et al.), the disclosure of which is incorporated herein by reference, discloses a multi-port, diaphragm sealed valve suitable for use as both a sampling and column switching valve. The valve is constructed to internally block fluid communication between one or more pairs of ports in a valve operating mode. Such blocking may be used to conserve carrier gas when the valve is in the ON position. 
     Even with these improvements, a need exists for an improved apparatus and method for fluid sample introduction. 
     Thus, a need exists for a method and an apparatus for a continuous, constant flow, sample introduction for compositionally unstable fluids. 
     A need also exists for associating at least one fluid analyzer system with an apparatus for a continuous, constant flow, sample introduction. 
     This invention also overcomes the problems of the prior art. The invention provides a method and an apparatus for an automatically compensating continuous, constant flow, sample introduction system. 
     PURPOSES AND SUMMARY OF THE INVENTION 
     The invention is a novel method and an apparatus for a continuous, constant flow sample introduction. 
     Therefore, one purpose of this invention is to provide a novel method and an apparatus for a continuous, constant flow, sample introduction. 
     Another purpose of this invention is to provide a method and apparatus where while one sample valve is being filled with a sample fluid at least a second sample valve is sending a sample fluid to be analyzed. 
     Yet another purpose of this invention is to have the fluid sample processed in a temperature controlled environment. 
     Still, yet another purpose of this invention is to have a continuous, constant flow of the fluid sample regardless of changes in the viscosity of the sample caused by unpredictable compositional sample changes. 
     Therefore, one aspect this invention comprises an apparatus for continuous, constant, flow sample introduction, comprising: 
     (a) at least one sample line having at least one sample fluid; 
     (b) at least one sampling system for processing said at least one sample fluid; 
     (c) at least one electronic pressure controller for processing at least one carrier fluid; and 
     (d) at least one first sampling valve and at least one second sampling valve, wherein said first sampling valve is connected to said second sampling valve in series, and wherein said first sampling valve and said second sampling valve are configured such that while said first sampling valve is processing said fluids to be analyzed the second sampling valve is being replenished with fluids to be analyzed, and wherein said fluids to be analyzed comprise said at least one sample fluid and said at least one carrier fluid. 
     Another aspect this invention comprises a process for continuous, constant, flow sample introduction, comprising: 
     (a) forwarding at least one sample fluid from at least one sample line to at least one first sampling valve or at least one second sampling valve via at least one sampling system; 
     (b) forwarding at least one carrier fluid to said at least one first sampling valve or at least one second sampling valve via at least one electronic pressure controller; 
     (c) processing a fluid to be analyzed in said first sampling valve or said second sampling valve, wherein said fluid to be analyzed comprises said at least one carrier fluid and said at least one sample fluid; and 
     (d) wherein said at least one first sampling valve and at least one second sampling valve are connected in series, and wherein said first sampling valve and said second sampling valve are configured such that while said first sampling valve is processing said fluids to be analyzed the second sampling valve is being replenished with fluids to be analyzed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The features of the invention that are novel and the elements characteristic of the invention are set forth with particularity in the appended claims. The drawings are for illustration purposes only and are not drawn to scale. Furthermore, like numbers represent like features in the drawings. The invention itself, both as to organization and method of operation, may best be understood by reference to the detailed description which follows taken in conjunction with the accompanying drawings in which: 
         FIG. 1A  is an exemplary continuous flow sample introduction apparatus which is used to illustrate a first embodiment of the present invention, in one state of operation. 
         FIG. 1B  is an exemplary continuous flow sample introduction apparatus which is used to illustrate a first embodiment of the present invention, in another state of operation. 
         FIG. 2  is an exemplary continuous flow sample introduction apparatus having at least one analyzer system associated therewith and is used to illustrate a second embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     This invention allows the continuous introduction of a fluid sample to an on-line analyzer at a constant flow rate, even if the viscosity of the sample changes due to changes in the sample&#39;s composition. The fluid sample is pushed through the analyzer with a carrier fluid at a constant flow rate. Preferably, at least two valves are used in series to introduce the fluid sample to the flowing stream. The valves are alternately switched so that while one valve is being filled with the sample fluid, the other valve is delivering the sample fluid to at least one fluid sample analyzer. The flow rate is determined by the flow of the carrier fluid which has a constant viscosity. Thus, the viscosity of the fluid sample does not affect the flow of the sample. For purposes of illustration only, an example of how this invention can be used is provided. The example, that is provided, only for the purposes of illustration of this invention, is the measurement of total sulfur in a petrochemical plant flare line. The illustrated example is for a vapor sample, however, it should be understood that the invention can also be used for any fluid sample, such as, for example, a liquid sample. 
       FIG. 1A  is an exemplary continuous flow sample introduction apparatus  23 , which is used to illustrate a first embodiment of the present invention, in one or first state of operation. 
       FIG. 1B  is an exemplary continuous flow sample introduction apparatus  23 , which is used to illustrate a first embodiment of the present invention, in another or second state of operation. 
     Referring to  FIGS. 1A and 1B , a sample introduction system  23 , has at least one sample introduction line  21 , having at least one sample to be analyzed  20 , or sample  20 , such as, for example, a flare line  21 , having a flare line sample  20 . The sample  20 , from the flare line  21 , is brought to a normal sampling system  22 , for filtration and simple flow control. The sample flow is then sent to two sampling valves, SV 1  (Sampling Valve  1 )  30 , and SV 2  (Sampling Valve  2 )  40 , which are preferably plumbed in series. 
     SV 1  (Sampling Valve  1 )  30 , is preferably a 6-port valve, comprising ports  31 ,  32 ,  33 ,  34 ,  35  and  36 , and where sample loop  37 , connects port  36  with port  33 . In an active state port  31  is connected to port  36 , port  32  is connected to port  33 , and port  34  is connected to port  35 , for the flow path, as shown in  FIG. 1A . However, in an inactive or relaxed state port  31  is connected to port  32 , port  33  is connected to port  34 , and port  35  is connected to port  36 , for the flow path, as shown in FIG. I B. It should be appreciated that the sample loop  37 , stores the sample to be analyzed  20 . 
     SV 2  (Sampling Valve  2 )  40 , is preferably a 6-port valve, comprising ports  41 ,  42 ,  43 ,  44 ,  45  and  46 , and where sample loop  47 , connects port  46  with port  43 . In an active state port  41  is connected to port  46 , port  42  is connected to port  43 , and port  44  is connected to port  45 , for the flow path, as shown in  FIG. 1B . However, in an inactive or relaxed state port  41  is connected to port  42 , port  43  is connected to port  44 , and port  45  is connected to port  46 , for the flow path, as shown in  FIG. 1A . It should be appreciated that the sample loop  47 , stores the sample to be analyzed  20 . 
     At least one calibration sample container or unit  25 , containing at least one calibration sample fluid  24 , is preferably connected to a calibration valve  26 , which is an either or valve  26 , so that calibration valve  26 , either allows the passage of calibration sample  24 , or the flare line sample  20 , from the sampling system  22 . 
     It is preferred that the calibration sample fluid  24 , is a non-interfering fluid  24 , or a non-reactive fluid  24 . The calibration sample fluid  24 , from the calibration sample unit  25 , is selected from a group consisting of argon, helium, propane, methane, ethane, nitrogen, or similar fluid, to name a few. Known amounts of one or more compounds of interest or compounds containing one more elements of interest are also present in the calibration sample fluid  24 , such as, for example, 500 ppmv carbonyl sulfide in propane. 
     At least one carrier fluid  10 , contained in a container or reservoir  11 , such as, a carrier gas  10 , for example, helium  10 , is also sent to the sampling valves SV 1   30 , and SV 2   40 . The flow of the carrier gas  10 , is preferably controlled by changing the pressure on a pressure regulator  12 , such as, an EPC (Electronic Pressure Controller)  12 . The flow of the carrier gas  10 , goes to at least one restrictor  14 , which is preferably located in a temperature controlled environment  50 , such as, an oven  50 . The EPC  12 , may also have at least one proportional solenoid valve  16 , for the management of pressure of carrier gas  10 , to the restrictor  14 . It is within the realm of a person skilled in the art to replace the EPC  12 , the proportional solenoid valve  16 , and the restrictor  14 , with an electronic flow controller (not shown) or a mechanical flow controller (not shown). 
     It is preferred that the carrier fluid  10 , is a non-interfering fluid  10 , or a non-reactive fluid  10 . The carrier fluid  10 , could be selected from a group consisting of Argon, Helium, Nitrogen, to name a few. 
     It is preferred that the restrictor  14 , is chosen to be of a high flow restriction relative to other restriction in the flow path. This high flow restriction will result in the flow rate of the sample  20 , through the sampling valves SV  130 , and SV 2   40 , to be high relative or compared to the flow of the carrier fluid  10 . A flow rate of about 200 mL/min is a preferable flow rate for the flow of sample fluid  20 , from the sampling system  22  , while, a flow rate of between about 1 to about 2 mL/min is a preferable flow rate for the carrier fluid  10 . It is preferred that the flow rate for the sample fluid  20 , is between about 150 mL/min to about 250 mL/min, and preferably between about  180  mL/min to about 220 mL/min, and more preferably about 200 mL/min. It is preferred that the flow rate for the carrier fluid  10 , is between about 0.50 mL/min to about 2.50 mL/min, and preferably between about 0.80 mL/min to about 2.20 mL/min, and more preferably between about 1.00 mL/min to about 2.00 mL/min. 
     To initiate the continuous, constant, sampling process any of the sampling valves are actuated. For the purposes of illustration only, sample valve SV 1   30 , is actuated to change the flow path of carrier fluid  10 , to go from port  31 , of the valve  30 , to port  36 , and then push the sample  20 , from the sample loop  37 , to port  33 , and then port  32 , and out to port  41 , of the SV 2   40 , as illustrated in  FIG. 1A . The sample  20 , is then processed through port  42 , and is then sent to at least one analyzer system  60 , via line  18 . 
     While SV 1   30 , is processing the sample  20 , the flow is being monitored by methods well known in the art. At an appropriate time, before the entire sample  20 , in the sample loop  37  has been used SV 1   30 , is de-actuated and SV 2   40 , is actuated. The carrier fluid  10 , then flows through port  31  to port  32 , of SV 1   30 , and out to port  41  to port  46  of SV 2   40 , which pushes the sample  20 , out of the sample loop  47 , to port  43  to port  42 , and then out to the analyzer system  60 , via line  18 , as more clearly illustrated in  FIG. 1B . Once again this flow of the carrier fluid  10 , is stopped and switched back to the sample loop  37 , prior to using up the entire sample  20 , in the sample loop  47 . 
     It should be appreciated that while the sample  20 , is being delivered from SV 1   30 , to the analyzer system  60 , the sample loop  47 , of SV 2   40 , is being replenished or reloaded with sample  20 , from the sample system  22 . After the sampling loop  47 , is reloaded with the sample  20 , the SSO (Sample Shut Off) Valve  28 , is actuated which will stop the flow of sample  20 , through SV 2   40 . At least one ARV (Atmospheric Reference Valve)  52 , is then actuated which allow the sample pressure to equilibrate with the atmospheric pressure. The ARV  52 , is preferably an either or valve  52 , so that the sample  20 , coming from SV 2   40 , is either sent to at least one ATM (Atmospheric Management) vent  54 , or sent to sample recovery  58 , via at least one flow indicator  56 . 
     It should be understood that when SV 1   30 , is de-actuated and SV 2   40 , is actuated the ARV  52 , and SSO valve  28 , are de-actuated for a period of time to allow the sample loop  37 , of SV 1   30 , to be reloaded with the sample  20 , from the sample system  22 . During this period the SSO (Sample Shut Off) Valve  28 , is actuated thus stopping the flow of sample  20 , through the SV 1   30 . The ARV (Atmospheric Reference Valve)  52 , is then actuated which allows the sample pressure to equilibrate with the atmospheric pressure. Thus, ARV  52 , equilibrates the sample loop  37  and  47 , with atmospheric pressure after the replenishment or reloading of the sample  20 , from the sample system  22 . 
     As stated earlier that the sample loop  37 , and the sample loop  47 , are primarily used to store the sample to be analyzed  20 , such that, as the sample to be analyzed  20 , is being used or exhausted in one sample loop, the other sample loop is actively being reloaded or replenished with the fluid sample to be analyzed  20 . It should also be understood that the driving force to move the sample to be analyzed  20 , from the sample loop  37  or  47 , to an analyzer  60 , more clearly discussed with reference to  FIG. 2 , is the carrier fluid  10 . 
     This process of introducing carrier fluid  10 , and sample fluid  20 , into SV 1   30 , and SV 2   40 , and alternating between SV 1   30 , and SV 2   40 , in a repeated manner essentially provides a continuous, constant, flow of sample fluid  20 , to the analyzer system  60 , at a constant flow rate regardless of sample viscosity or composition. In other words while one sample valve is being filled with the sample fluid  20 , the second sample valve is allowing the flow of the sample fluid  20 , thus creating the continuous, constant, flow of the sample fluid  20 , through the continuous flow sample introduction apparatus  23 . It should be understood that the flow rates, sample loop sizes, and timing can be adjusted to accommodate each application. 
       FIG. 2  is an exemplary continuous flow sample introduction apparatus  23 , having at least one analyzer system  60 , associated therewith and is used to illustrate a second embodiment of the present invention. As stated earlier this invention can be associated with a number of different types of analyzers, as it can provide a continuous flow sample to the analyzer system. 
     For the purposes of illustration only, the analyzer system  60 , as illustrated in  FIG. 2 , is used as an example in the determination of total sulfur in a flare gas line  20 . It is preferred that the gas sample  20 , is sent from the sample valves SV 1   30  and SV 2   40 , to an optional splitter valve  61 . For this particular application, a portion of the sample gas  20 , is introduced to a FID (Flame Ionization Detector)  63 , where the sample  20 , is burned in a hydrogen air flame. If hydrocarbons are present then the burning of the sample  20 , in a hydrogen air flame will produce water and carbon dioxide. If sulfur containing compounds are present then they will be converted into sulfur dioxide. If carbon is present in the sample  20 , then carbon dioxide will be produced during the burning of the sample  20 , in the hydrogen air flame. The burning of the sample  20 , in the hydrogen air flame creates an effluent sample  90 . The effluent sample  90 , from the FID  63 , is then sent to a FPD SV (Sample Valve)  70 . A portion of the effluent sample  90 , may be injected into a chromatographic column set where the sulfur dioxide is separated from the water, carbon dioxide, and nitrogen. The sulfur dioxide is measured with a FPD (Flame Photometric Detector)  66 . 
     FPD SV (Sample Valve)  70 , is preferably a 10-port valve, comprising ports  71 ,  72 ,  73 ,  74 ,  75 ,  76 ,  77 ,  78 .  79  and  80 , and where sample loop  87 , connects port  79  with port  72 . In an inactive or relaxed state port  71  is connected to port  72 , port  73  is connected to port  74 , port  75  is connected to port  76 , port  77  is connected to port  78 , and port  79  is connected to port  80 , for the flow path, as shown in  FIG. 2 , with solid lines. However, in an active state port  71  is connected to port  80 , port  72  is connected to port  73 , port  74  is connected to port  75 , port, and port  78  is connected to port  79 , for the flow path, as shown in  FIG. 2 , with dashed lines. It should be appreciated that port  76  and port  77  are never connected. However, for most applications, in an inactive mode or state the sample  90 , is sent from port  71  to port  72 , from port  72  to port  79  via sample loop  87 , and then from port  79  to port  80 , and is then sent to the vent  67 , via FPD  66 . Whereas, in an active mode or state the sample  90 , is sent from port  71  to port  80 , and is then sent to the vent  68 . 
     For some applications, sample  20 , from line  18 , is sent to a split vent  62 , via the splitter valve  61 . However, for all applications the splitter valve  61 , will send at least some of the sample  20 , to the FID  63 , via at least one restrictor  64 . It should be appreciated that portion of the sample  10  and  20 , is usually sent to the split vent  62 , via the splitter valve  61 , when the sample  10  and  20 , are too large for processing by the FID  63 . 
     A portion of effluent sample  90 , may be sent to at least one chromatographic column  1   86  where water is separated from the rest of the components in the effluent sample  90 . The rest of the components in the effluent sample  90 , which consist of mainly air, carbon dioxide and sulfur dioxide, are then sent to column  2   88 . After the air, carbon dioxide and sulfur dioxide have passed though column  1   86 , to column  2   88 , and the valve  70 , is activated. With column  1   86 , in the active state, water is back-flushed from column  1   86  through port  78 , to port  77  and restrictor  82  to the back-flush vent  84 . The sulfur dioxide continues to pass through column  2   88 , where the sulfur dioxide is separated from the other components in the sample and passed to the FPD  66  for processing, and then to vent  67 . 
     The FPD SV  70 , and related components are preferably located in a temperature controlled environment  100 , such as, an oven  100 . 
     It should be appreciated that in this invention the carrier fluid  10 , is known and the fluid flow of the carrier fluid  10 , is kept constant, while the sample fluid  20 , is unknown and changing, and the combination of the two fluids keep the sample flow constant while the unknown component of the sample fluid  20 , is analyzed in the analyzer system  60 , after being processed by either SV 1   30  or SV 2   40 . Thus, even with the viscosity changes or composition changes of the fluid sample  20 , the fluid flow rate within SV 1   30  or SV 2   40 , remains the same or constant. 
     The analyzer system  60 , can be calibrated by introducing a calibration mixture in the sample introduction system  23 , using a calibration valve  26 , from a calibration sample  24 , as illustrated in  FIGS. 1A and 1B . 
     The analyzer system  60 , that is illustrated in  FIG. 2 , is illustrated having at least one detector and wherein the detector is selected from a group consisting of a Flame Ionization Detector (FID)  63 , and a Flame Photometric Detector (FPD)  66 . However, the analyzer system  60 , could be selected from a group consisting of a UV Analyzer  60 , a chemluminescence analyzer  60 , an ultraviolet fluorescence analyzer  60 , a themoconductivity analyzer  60 , an X-ray fluorescence analyzer  60 , and a photo ionization analyzer  60 . 
     This invention allows for the analysis of a fluid sample  20 , whose viscosity may be changing, such that, the viscosity of the sample fluid  20 , processed at time t 1 , may be the same or may be different than the viscosity of a sample fluid  20 , processed at time t 2 . 
     Similarly, this invention allows for the analysis of a fluid sample  20 , whose material composition may be changing, such that, the material composition of the sample fluid  20 , processed at time t 1 , may be the same or may be different than the material composition of a sample fluid  20 , processed at time t 2 . 
     While the present invention has been particularly described in conjunction with a specific preferred embodiment, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. It is therefore contemplated that the appended claims will embrace any such alternatives, modifications and variations as falling within the true scope and spirit of the present invention.