Abstract:
Apparatus and methods are provided for testing and analyzing a plurality of stream sources to monitor for an upset condition in one of the stream sources. A manifold is provided having a plurality of manifold inlets and a manifold outlet. A plurality of sampling devices for sampling the plurality of stream sources are coupled to the manifold inlets to provide stream samples to the manifold. A controller is in electronic communication with each of the plurality of sampling devices for providing test samples in the manifold. The controller alternately operates the sampling devices in (1) a sequencing mode in which each test sample is a stream sample from one of the plurality of sampling devices or (2) an averaging mode in which each test sample is representative of an average of the stream samples from the plurality of sampling devices. An analyzer is coupled to the manifold outlet to receive the test samples from the manifold and analyze each test sample for the presence of the upset condition.

Description:
BACKGROUND 
   1. Field of Invention 
   The present disclosure relates to sampling methods and apparatus, and more particularly to sequencing and averaging multiple sampling methods and systems. 
   2. Prior Art 
   Continuous online analysis of components in liquid and gas streams is a common practice in industry today. For example, routine sampling and analysis is conducted in power plant smokestacks, liquid waste streams, industrial process streams, the head space in storage vessels and many other sources. Because analytical monitors and instrumentation are quite expensive, it is often desirable to share an analyzer bank with multiple sample streams. This is usually accomplished by one of two methods—sequencing or averaging. 
   In sequencing, the analyzer tests each sample in sequence, on a time share basis. A controller or multiplexer system may utilize a programmable logic controller (PLC), distributed control system (DCS) or a computer to sequence through multiple sample chambers, each obtaining samples via valve-controlled orifices. An example of a sequencing sampling system in shown in U.S. Pat. No. 4,325,910 (Jordan). Averaging systems involve feeding multiple input samples into a central manifold or header and mixing the samples prior to analyzing the mixture. A control device, such as a needle valve, is used to precisely control the flow of each sample into the manifold. The combined mixture is then analyzed to provide an average reading for all of the samples. 
   Either of the above two methods works fairly well in the absence of an upset condition. However, when a problem arises with one of the sampled streams, both prior art systems have difficulty in quickly locating the stream that is out of specification. In the case of sequencing, the upset condition will not be detected during the time that the analyzer is testing other samples. If the streams being analyzed are potent, toxic, flammable, radioactive or otherwise dangerous, the delay in detecting an upset condition could have serious consequences. An averaging system could also involve a substantial delay in finding an upset condition, because the samples are all mixed before being analyzed. Moreover, it may be difficult to even detect the presence of a problem sample because each sample is substantially diluted with other samples before being analyzed. Accordingly, new methods and apparatus are needed to quickly and accurately locate an upset condition in a stream flow using a multiple stream analyzer. 
   SUMMARY 
   In a first embodiment of the present disclosure, apparatus is provided for testing and analyzing a plurality of stream sources to monitor for an upset condition in one of the stream sources. A manifold is provided having a plurality of manifold inlets and a manifold outlet. A plurality of sampling devices for sampling the plurality of stream sources are coupled to the manifold inlets to provide stream samples to the manifold. A controller is in electronic communication with each of the plurality of sampling devices for providing test samples to the manifold. The controller alternately operates the sampling devices in (1) a sequencing mode in which each test sample is a stream sample from one of the plurality of sampling devices or (2) an averaging mode in which each test sample is representative of an average of the stream samples from the plurality of sampling devices. An analyzer is coupled to the manifold outlet to receive the test samples from the manifold and analyze each test sample for the presence of the upset condition. 
   In another embodiment of the present disclosure, a method is provided for testing and analyzing a plurality of stream sources having various flow rates or velocities to monitor for an upset condition in one of the stream sources. A plurality of samples are provided from the plurality of stream sources using a plurality of sampling devices coupled to a manifold. A controller electronically communicates with the plurality of sampling devices to provide test samples to the manifold, alternately operating in (1) a sequencing mode in which each test sample is a stream sample from one of the plurality of sampling devices or (2) an averaging mode in which each test sample is representative of an average of the stream samples from the plurality of sampling devices. The test samples are analyzed using an analyzer coupled to the manifold to determine the presence of the upset condition. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned features and other features and advantages of this disclosure will become more apparent and the disclosure will be better understood by reference to the following description of an exemplary implementation taken in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a schematic diagram showing the fluid flow arrangement of the sequencing and averaging apparatus according to an embodiment of the present invention; 
       FIG. 2  is a schematic diagram showing the electrical control arrangement of the sequencing and averaging apparatus according to the embodiment shown in  FIG. 1 ; 
       FIGS. 3 and 4  are plan drawings showing the sequencing and averaging apparatus according to the embodiment shown in  FIG. 1 ; and 
       FIG. 5  is a perspective view of manifold and valve apparatus according to the embodiment shown in  FIG. 1 ; 
       FIGS. 6 ,  7 ,  8  and  9  are flow diagrams showing methods of the sequencing and averaging apparatus according to the embodiment shown in  FIG. 1 . 
   

   Throughout the drawings, identical reference numbers may designate similar, but not necessarily identical, elements. The examples herein illustrate selected implementations of the disclosure in certain forms, and such exemplification is not to be construed as limiting the scope of the disclosure in any manner. 
   DETAILED DESCRIPTION 
   The embodiments described herein provide unique apparatus and methods for analyzing samples of various industrial sources, using a combination of sequencing and averaging methods to determine the presence of an upset condition in one or more of the sources. As used herein, the term “upset condition” refers to the sensing of one or more parameters in a source being monitored to determine the presence, absence, excessive amount or deficient amount in a quantity that deviates from a pre-selected standard by an unacceptable amount. Examples could be excessive amounts of contaminants, the presence of unacceptable toxic elements, or the absence of beneficial elements. 
   The apparatus and methods disclosed herein utilize the same hardware to carry out both the sequencing and the averaging methods, relying on software or programmed firmware to vary the sequencing and/or averaging processes, as needed. By utilizing both sequencing and averaging, the delay time in finding an upset condition is minimized, thereby lessening the possibility of damage to the related equipment, exceeding regulated standards or causing health-threatening conditions. Moreover, the use of the same apparatus for both sequencing and averaging methods substantially reduces monitoring costs, space requirements and maintenance. 
   The sequencing and averaging multiple sample system of the present invention is useful in monitoring a wide variety of industrial sources and processes. For example, the present system may be used to monitor exhaust gas flow from turbines or boilers, measuring oxygen or carbon monoxide output to control the fuel and air mixture in the burners. Combustion output may also be monitored to insure that products of combustion, such as sulfur oxides, nitrogen oxides, mercury, carbon monoxide, hydrochloric acid and hydrofluoric acid, are within prescribed limits. Liquid flow may also be monitored in a series of process streams to measure pH or to determine the level of toxic waste. In solid processes, coal conveyer belts may be monitored to sense the presence of carbon monoxide, indicating a fire that must be extinguished. Storage vessels and the head space in storage vessels, as well as many other sources may also be monitored and analyzed with the present system. 
   Referring now to  FIG. 1 , a schematic diagram discloses a simplified fluid flow arrangement according to an embodiment of the present invention. A manifold  20 , disposed within an enclosure (not shown), is adjacent to four fluid sample input connections  21 – 24 . Four three-way valves  31 – 34  each connect to one of ports  21 – 24 . Valves  31 – 34  each have output ports  35 – 38  that feed into the enclosure of manifold  20 . An output line  40  provides a sample in manifold  20  to sample outlet connection  42 . 
   Each of valves  31 – 34  also have constant flow ports  44 – 47  that are coupled to a common bypass line  48  which is connected to a bypass outlet connection  50 . Bypass line  52  is powered by a fluid pump  54  and checked by a flow meter  56  before being shunted to an output vent  58 . Likewise, a sample line  60  is coupled to sample outlet  42  and runs to a fluid pump  62 , a filter  64  and a flow meter  66  in series. The fluid sample in line  60  flows from flow meter  66  to an analyzer  70 , used for monitoring various parameters, as discussed above. An output line  72  also flows to output vent  58 . 
   Thus, as shown in  FIG. 1 , fluid flow samples are provided on input ports  21 – 24  from external sources (not shown). The three way valves  31 – 34  provide the samples into the manifold, where they are mixed (if in the averaging mode), the result test sample is sensed and is provided to the analyzer for the appropriate monitoring. The valves  31 – 34  may be mounted on the manifold  20  or disposed to stand alone. 
     FIG. 2  is a related schematic diagram showing the electrical control connections of the embodiment shown in  FIG. 1 . Valves  31 – 34  are each connected to and controlled by a programmable logic controller  80 , which also drives fluid pumps  54  and  62 . Pumps  54  and  62  may be a common pump device with two heads driving the bypass line  52  and the sample line  60 . Programmable logic controller  80  is connected to analyzer  70  to interrelate functions between controller  80  and analyzer  70 , as needed. 
     FIGS. 3 and 4  show side and front views, respectively, of an enclosure  90  that houses the sequencing and averaging system of the present embodiment. In  FIG. 3 , enclosure  90  includes sample inlet connections  21 – 24 . Sample output connection  42  is disposed near the bottom of enclosure  90 , adjacent to bypass outlet connection  50  and an atmospheric bleed connection  51 . A louvered fan vent  92  is also provided at the side of enclosure  90 . 
     FIG. 4  shows the front of enclosure  90  with a front door (not shown) removed. Sample inlet connections  21 – 24  are shown connecting to valves  31 – 34 . Fluid pumps  54  and  62  and filter  64  are mounted in the enclosure  90 . Flow meters  56  and  66  are mounted on an inner door  94  having a touch panel view window  96 . The programmable logic controller  80  (not shown) is mounted within enclosure  90  behind inner door  94 . 
   The analyzer  70  (not shown) may be also be located within enclosure  90  or at some location remote from enclosure  90  and in communication with manifold  20  and programmable logic controller  80 . Analyzer  70  may be a convention analyzer such as model number Ultramat  23  made by Siemens. Programmable logic controller  80  may by a conventional controller such as model number 06 made by Automation Direct. 
     FIG. 5  shows a perspective view of manifold  20  having openings  101 – 106  to accommodate six solenoid valves. The four three-way valves  31 – 34  are shown. The valves may be high-speed three-way solenoid valves, such as Type 6608 analytical solenoid valves made by Burkert Controlmatic USA in Irvine, Calif. Any number of valves may be mounted on a convention manifold or header, as needed. Outlet sample connection  42  and bypass connection  50  are also shown. Manifold  20  may be a convention manifold having chamber volume ranging from 5 ml to 100 ml, with 10 ml being a typical volume. 
   Referring now to  FIGS. 6 ,  7  and  8 , flow diagrams are provided showing methods carried out by the sequencing and averaging apparatus of the embodiments disclosed herein. The flow diagrams represent algorithms that may be programmed in software or firmware in the programmable logic controller  80 . As shown in  FIG. 6 , a system  120  is shown with multiple sources to be sampled. The programmable logic controller  80  is initially calibrated, at step  122 , for each valve  31 – 34  by pumping a calibration fluid through each sampling source and each valve to establish a flow rate and other parameters for each valve. In situations involving gas testing, a typical calibration gas might be sulfur dioxide or nitrogen oxide having nitrogen gas doped with the impurity to be tested. During calibration, the flow rate is determined for of each source being monitored, for a purpose to be discussed below. 
   Next, at step  124 , the system is operated in an averaging mode in the programmable logic controller  80  actuates each of the valves  31 – 34  to provide samples to the manifold  20  from each of the sources to be monitored. The samples are mixed to form an average test sample, which is sent to the analyzer  70  to be tested for the presence of a predetermined parameter. The averaging mode can be carried out in at least two different ways. The valves may be rapidly sequenced to provide samples from each source that are mixed in the manifold to form an average test sample. Alternately, the valves may be turned on simultaneously during a sampling period to provide samples that are mixed in the manifold to form an average test sample. 
   In either averaging sampling process, the valves may be actuated for different time periods, depending on the flow rate of each source being sampled. For example, if the flow rate of the sample obtained from valve  31  is twice the flow rate of the sample obtained from valve  32 , the sample time for valve  31  may be half of the sample time of valve  32 . In this manner, the same amount of each monitored sample is mixed in the manifold to obtain a true average test sample. 
   For example, in the sequential averaging process, a sample time of one second might be used. During that one-second sample time each valve is sequenced for a different fraction of one second corresponding to the ratio of the flow rate of the respective monitored source relative to a standard flow rate. Similarly, in the simultaneous averaging process, each valve may be actuated at the beginning of the one-second sample period. Then, each valve shuts off at the end of a predetermined fraction of the sample period, depending on the flow rate of the respective source being sampled. Sampling periods during the averaging mode may fall within a range of ⅕ seconds to 5 seconds. It is important to maintain the averaging mode sampling times relative short, in order to provide a true average test sample in a relatively small manifold chamber volume and to quickly detect an upset condition. 
   Next, at step  126 , analyzer  70  tests the average sample for an upset condition. If no upset condition is detected, the averaging mode of sampling is continued. If an upset condition is detected, the programmable logic controller  80  switches over to a sequencing mode, as shown at step  128 , to detect the problem valve, at step  130 , that is sampling a problem source. In this mode, the programmable logic controller  80  sequentially actuates each valve  31 – 34  for a period long enough to provide a test sample in the manifold  20  that can be sent to the analyzer  70  for testing. A typical sample time during the sequencing mode is 15 seconds. The sample time may vary over a wide range of as much as 10 seconds to 5 minutes, depending on the flow rates and the length of sample line of the sources being sampled. 
   Looking now at  FIG. 7 , an alternate method is shown for operating the sequencing and averaging system of the present embodiments. The method shown in  FIG. 7  is helpful, in situations, such as system  140 , where there are a large number of valves sampling a large number of sources. At step  142 , the programmable logic controller  80  is calibrated for each of the valves  31 – 34 , as previously discussed. At step  144 , the system is operated initially in the averaging mode and continues in that mode until an upset condition is detected, at step  146 . 
   At the time of upset condition detection, the programmable logic controller  80  divides the sampling valves into two equal groups. At step  148 , an averaging mode operation may then be carried out for the first group in which samples from each source in the group are mixed in the manifold  20  to form a first group test sample. This sample is then tested by the analyzer  70 , at step  150 , to determine whether the upset condition is in the first group. If so, the valves of the first group are sequentially sampled, at step  152 , to detect the problem sample source, as shown at step  154 . If the first group does not show an upset condition, then the problem is in the second group. Accordingly, as shown at step  156 , the second group is sequentially sampled to detect the problem sample source. It should be understood that the sampling valves may be divided in any number of groups to carry out the dividing process shown in  FIG. 7 . If more than two groups are selected, then additional averaging mode testing must be carried out to find the problem. 
     FIG. 8  shows one example of a system  160  having multiple groups involving a large number of valves and sources. In this situation, it might not be practical to average samples from all of the sources, as was done with systems  120  and  140  in  FIGS. 6 and 7 . Rather, after the calibration step  162 , the system might be separated into multiple groups, such as first, second and third groups shown. Then the system may be sequenced through each of the average samples of the groups to determine whether an upset condition had occurred. If so, then sequencing may be used to locate the problem. 
   Thus, at step  164 , the first group is averaged and the output sampled. If an upset condition is detected, at step  166 , the first group is selected for sequencing, at step  168 , to detect a problem, at step  170 . If an upset condition is not detected at step  166 , the second group is averaged and the output sampled, at step  172 . If an upset condition is detected, at step  174 , the second group is selected for sequencing, at step  168 . If an upset condition is not detected, at step  174 , the third group is averaged and the output sampled, at step  176 . If an upset condition is detected, at step  178 , the third group is selected for sequencing, at step  168 . If an upset condition is not detected at step  178 , the system sampling returns to the first group at step  164 . 
   In other situations, a system might be initially sequenced in a calibration mode to calibrate each valve. In the event that a valve is found to be out of calibration, an adjustment is made. The system may continue to sequence in the calibration mode until no calibration problems are detected or for a safe period of time, after which the system may go into a normal sampling process, such as those shown in  FIGS. 6 ,  7  and  8 . 
   For example, in a large boiler, several dampers may control the fuel-air mixture in various parts of the boiler. In the event that too little air is found to be going to a burner, the respective damper may signal an out-of-calibration condition, at which time the damper position may be changed to allow more air to the burner. After the dampers are all in calibration, or after a safe period of time, such as twenty minutes, the system may go into an averaging mode, pending the detection of an upset condition. 
     FIG. 9  shows an example of such a system  180 . At step  182 , the system conducts a calibration sequencing through each valve or damper to determine whether a valve is out of calibration. If a calibration problem is detected, at step  184 , the appropriate valve is adjusted to correct the problem, at step  186 . The system  180  then continues at step  182  with its initial calibration sequencing. After calibration has been completed, the system  180  moves on to an averaging step  188 , until an upset condition is detected, at step  190 . Then, at step  192 . the system sequences through each valve until a problem is detected at step  194 . 
   While this disclosure has been described as having preferred embodiments, the present disclosure can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this disclosure pertains and which fall within the limits of the appended claims.