Abstract:
Arrangements for withdrawing carefully controlled samples from an active flue gas source are disclosed. A testing assembly is provided for connection to downstream processing equipment to obtain a sample from a gas stream. Included is a probe, a flexible sample line and a coupler joining the probe and the flexible sample line. At least one externally controlled or self-regulating heating cable is put in heating communication with the flexible line. A receptacle engaging the coupler is also provided for positioning the probe with respect to the flue gas source.

Description:
FIELD OF THE INVENTION 
   The present invention relates to the testing of atmospheric emissions and, in particular, to testing equipment for withdrawing samples from a flue gas stream or other atmospheric discharge, especially on a continuous testing basis. 
   BACKGROUND OF THE INVENTION 
   Owners and operators of certain combustion devices are required to comply with a variety of environmental regulations pertaining to the maximum allowable emissions of a particular substance. One example of such regulations is directed to the concentration of a substance suspended in a waste gas, such as the flue gas of a combustion device, that discharges a waste gas stream into the atmosphere. In addition to specifying maximum allowable amounts or concentrations, environmental regulations at times specify how a waste gas stream is to be tested in order to determine regulatory compliance. Taking into account the different technologies and characteristics of substances involved, different testing techniques are often required for different types of substances, and additionally for different timing of such testing. For example, testing can be periodic or continuous. 
   One example of continuous emission monitoring regulations is found in part 75 of Title 40 of the Code of Federal Regulations, which pertains to the protection of the environment by way of continuous emission monitoring. Subpart I of these regulations is concerned with the continuous emission monitoring of mercury mass emissions of certain coal-fired units. Included in the regulations is a requirement as to how certain aspects of the continuous emission monitoring are to be carried out. 
   Compliance may be audited by a site visit for testing purposes, or a continuous monitoring program may be required. In either event, testing can require a substantial investment in capital and man-hours. Improvements in testing equipment, especially for repetitive (e.g. continuous) testing are continually being sought. 
   SUMMARY OF THE INVENTION 
   The present invention provides a novel and improved arrangement for withdrawing carefully controlled samples from an active flue gas source. Equipment provided by the present invention allows easy withdrawal of the sample material, while leaving associated equipment, such as vacuum pumps and line heaters, undisturbed. The present invention minimizes the disadvantages associated with prior art devices and materials related thereto. 
   One embodiment comprises a testing assembly for connection to downstream processing equipment to obtain a sample from a gas stream. Included is a probe having a first end with a gas inlet and a second end, a flexible sample line and a coupler joining the second end of the probe and the flexible sample line. The flexible sample line includes at least one gas channel comprising a flexible gas line coupled to the probe to transmit a sample from the probe inlet to the downstream processing equipment. At least one externally controlled or self-regulating heating cable is put in heating communication with the flexible line. The flexible sample line further includes an outer sheath surrounding the flexible gas line and the heating cable, and a thermal insulator is disposed within the outer sheath and surrounds the flexible line and the heating cable. 
   In another embodiment, a system for controlled positioning of a probe with respect to a gas stream is provided wherein the probe has a first end with a gas inlet and a second end for connection to downstream processing equipment to deliver a sample from the gas stream. Included is a flexible interconnect for connecting the probe to the downstream processing equipment, and a coupler for joining the second end of the probe and the flexible interconnect. The flexible interconnect includes at least one gas channel comprising a flexible gas line coupled to the probe to transmit a sample from the probe inlet to the downstream processing equipment. At least one externally controlled or self-regulating heating cable is put in heating communication with the flexible line. The flexible interconnect further includes an outer sheath surrounding the flexible gas line and the heating cable. A thermal insulator is disposed within the outer sheath and surrounds the flexible line and the heating cable. A receptacle for receiving the probe and the coupler includes a lever operated cam spaced a predetermined distance from the gas stream and engaging the coupler so as to position the gas inlet of the probe with a preselected relationship to the gas stream. 
   In a further embodiment, a flexible interconnect is provided for connecting a probe having a first end with a gas inlet and a second end, to downstream processing equipment to obtain a sample from a gas stream. Included is a coupler for joining to the second end of the probe, at least one gas channel comprising a flexible gas line having an inlet end for coupling to the probe, to transmit a sample to downstream processing equipment, and at least one externally controlled or self-regulating heating cable in heating communication with the flexible line. An outer sheath surrounds the flexible gas line and the heating cable, and a thermal insulator is disposed within the outer sheath so as to surround the flexible gas line and the heating cable. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings: 
       FIG. 1  is a schematic diagram of a testing system employing the present invention; 
       FIG. 2  is a schematic perspective view of a multi-channel probe shown installed in a flue gas stream; 
       FIG. 3  is an end view thereof; 
       FIG. 4  is an exploded perspective view thereof; 
       FIG. 5  is a side elevational view thereof; 
       FIG. 6  is a side elevational view thereof shown partly broken away; 
       FIG. 7  is a cross-sectional view taken along the line  7 - 7  of  FIG. 1 ; 
       FIG. 8  is a cross-sectional view taken along the line  8 - 8  of  FIG. 5 ; and 
       FIG. 9  is a schematic diagrammatic representation of a testing system. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENT 
   The invention disclosed herein is, of course, susceptible of embodiment in many forms. Shown in the drawings, and described herein in detail, is a preferred embodiment of the invention. It is understood, however, that the present disclosure is an exemplification of the principles of the invention and does not limit the invention to the illustrated embodiment. 
   For ease of description, a system for testing a gas stream such as a combustion flue gas stream embodying the present invention is described herein in its usual assembled position as shown in the accompanying drawings and terms such as upstream, downstream, inner, outer, upper, lower, horizontal, longitudinal, etc., may be used herein with reference to this usual position. However, the system may be manufactured, transported, sold or used in orientations other than that described and shown herein. 
   Flue gas sampling is one example of many industrial applications where it is necessary to maintain the physical and chemical integrity of a gas sample extracted from a process stream. Frequently, the temperature of the sampled gas must be maintained above a critical lower temperature while it is being transported through sampling lines to downstream measuring devices and other equipment, in order to avoid condensation or otherwise altering important properties of the gas sample. 
   Conventional gas sample extraction systems are known to include a sample probe to be inserted directly into a process stream, such as the flue gas stream of a smokestack. A heated sample line is provided to transport the sample to downstream equipment. In many applications, gas sampling systems must be carefully constructed from non-reactive materials capable of sustaining elevated temperatures. However, certain problems have been noted in the use of conventional equipment. For example, the junction where the sample probe and sample transport line are connected must be maintained at an elevated temperature and must be free of leaks, either entering or leaving the gas sample system. The junction is typically embodied in a junction box, in order to meet demanding criteria, such as the criteria discussed herein. 
   Referring now to the drawings, and initially to  FIG. 1 , a testing assembly is generally indicated at  100 . Included is a flexible sample line  102  and a generic probe  104 . If desired, probe  104  and sample line  102  could be made to carry only a single sampling channel. However, in the preferred embodiment, sample line  102  and probe  104  have the capacity to carry multiple separate, independent sampling channels, and are thus referred to herein as a multi-channel sample line and a multi-channel probe, respectively. As can be seen in  FIG. 1 , the sample line  102  and probe  104  are joined, preferably permanently joined, so as to form a single unitary testing assembly. 
   Probe  104  and sample line  102  preferably have multiple separate and independent gas sampling channels. In the preferred embodiment, the gas sampling channels include tubing of flexible, non-reactive material such as TEFLON or other engineered fluoropolymeric material. The flexible lines are indicated in  FIG. 1  at  110 ,  112 . Also included are connectors for a variety of auxiliary equipment such as sensors and heaters. Included are connectors  114 ,  116  associated with each flexible line and a connector  118  associated with instrumentation separate from the flexible lines. 
   Probe  104  can comprise virtually any type of probe known today, having either single or multiple channel capability. As mentioned, in a preferred embodiment, probe  104  has multi-channel gas sampling capability and includes a pair of gas sampling channels. Referring to  FIG. 2 , the gas sampling channels have inputs  120 ,  122 . A thermocouple  124  is also located adjacent gas inputs  120 ,  122 . In the preferred embodiment, probe  104  is designed to have a specialized gas sampling capability, to withdraw gas samples using absorbent material. In a preferred embodiment, probe  104  utilizes sorbent trap technology. 
   Referring briefly to  FIG. 4 , included in probe  104  is a sorbent trap  130  with an insert including sections  132  of sorbent trap material. Although not required, the sorbent trap insert  130  is received within an outer shell  136  of rugged stainless steel construction. A ferrule or frustoconical collar  138  is attached, preferably by welding or brazing, to the inlet end of shell  136 , and a nut or compression fitting  140  that threadingly engages a threaded nipple  142  which is fitted to an end cap  144  of a rugged stainless steel housing  146  of probe  104 . In a preferred embodiment, the compression fitting  140  can be removed for ready withdrawal of a sample cartridge  152  formed by the combination of sorbent trap insert  130 , outer shell  136  and, as an option, fitting  140 . The sorbent trap insert  130  may be easily withdrawn from shell  136  with the shell  136  either removed from housing  146  or left in place as shown, for example, in the adjacent gas sampling channel having input  122 . However, virtually any sample probe arrangement can be utilized with the present invention and removable inserts and/or removable cartridge assemblies are not required. 
   Referring to  FIGS. 5 and 6 , the downstream ends  150  of the sorbent trap inserts  130  are coupled to flexible lines  110 ,  112  (see  FIG. 1 ) in a manner (not shown) to form a continuous gas sampling passageway. As will be seen herein, auxiliary equipment such as thermocouples and heaters are combined with the gas passageways to form a pair of gas sampling channels. 
   Referring now to  FIG. 7 , a cross-sectional view of sample line  102  is shown. Included in the sample line  102  are two gas sampling channels generally indicated at  154 ,  156 . Included in each channel are flexible hollow lines  110 ,  112  which, as mentioned above, are preferably made of TEFLON material. Surrounding the flexible lines  110 ,  112  is an outer covering  162  of thermal barrier material such as fiberglass cloth, which is coated, wrapped or otherwise disposed about each flexible line. As indicated in  FIG. 7 , the channels  154 ,  156  are spaced apart and disposed within a rugged outer weatherproof jacket  166  of polyurethane material. The outer jacket  166  is preferably formed with a shrink-wrap process. The interior of sample line  102  is filled with a thermal insulator material such as glass fiber insulation and most preferably non-hygroscopic glass fiber insulation material indicated at  168 . 
   Also included in each gas channel is a externally controlled or self-regulating heater preferably in the form of electrical cables schematically indicated at  172 . Preferably, each flexible line is wrapped with two independent externally controlled or self-regulating electric resistance cable heaters. The length of the first heater cable is equal to the length of the flexible line that is inserted into the process stream. The second heater cable is wrapped around the length of flexible line that remains outside of the process stream. As indicated in  FIG. 7 , the heater cables are encapsulated in insulation material  168 . In the preferred embodiment, the two heaters for each gas channel provide an arrangement for maintaining two temperature zones. One zone is the section of the sample line that is covered by the probe sheath or outer probe housing  146 . This section is exposed to the process gas and must maintain the proper sample gas temperature while being exposed to the temperature of the process gases. The second heated zone is the section of the flexible line that transports the extracted sample to downstream equipment such as a gas conditioning and pumping system of the type generally indicated in  FIG. 9  to be discussed below. The second heated zone maintains the proper gas temperature while being exposed to ambient air temperature. 
   The section of the sample line  102  that is inserted into the process stream is wrapped with a high temperature protective jacket of silicone material. This section is placed inside the rigid stainless steel tube forming the outer housing  146 , shown in  FIG. 4 . As mentioned, the housing  146  at the free end of the probe is joined to an end wall  144 , preferably by welding, brazing, or other metallurgical joinder. That portion of sample line  102  that remains outside of the process gas is wrapped with the weatherproof protective jacket  166  (see  FIG. 7 ). 
   In a preferred embodiment, sample line  102  contains instrumentation for the operation of the testing assembly. Included are a number of thermocouples measuring different operating parameters. The thermocouples are accessed by connectors  114 ,  118  shown in  FIG. 1 . Referring again to  FIG. 7 , a line thermocouple  180  is provided to measure the internal temperature of sample line  102 . As mentioned with reference to  FIG. 2 , a thermocouple  124  is provided for sensing the temperature of the process gas and is placed in-situ in the gas stream adjacent gas inlets  120 ,  122 . The signal for this thermocouple is carried by electrical conductor  182  shown in  FIG. 7 . Connection with the thermocouple is made with connector  118  in  FIG. 1 . As mentioned, the sorbent trap inserts  130  are located in probe  104 . Preferably, the temperature of the sorbent traps are monitored by their own respective thermocouples, with signals being transmitted through electrical conductors  186 ,  188  to a pair of connectors  114  as shown in  FIG. 1 . 
   Referring now to  FIG. 8 , a section of probe  104  is shown schematically in cross-section. Included are the sorbent trap inserts  130 , preferably in the form of hollow glass tubes receiving sections of sorbent trap material  132 , separated from one another by separator sections  134  as shown for example in  FIG. 4 . Referring again to  FIG. 8 , the outer shell  136  of the sorbent trap cartridge surrounds the sorbent trap inserts  130 . Electrical conductors  192  for thermocouple  124  are located in the upper portion of  FIG. 8  and electrical conductors  194  are provided for additional instrumentation. The interior of the probe is filled with thermal insulation which, as mentioned, preferably comprises non-hygroscopic glass fiber insulation. As shown in  FIGS. 7 and 8 , is the outer jacket  166  is preferably located immediately inside of the rigid, stainless steel housing  146 . 
   There are many applications involving the direct insertion of sorbent traps into an industrial gas stream to measure properties of the gas stream. One application, for example, requires the measurement of a trace component, such as mercury concentrations, using sorbent traps. Sorbent traps may include, for example, glass tubes packed with iodinated activated carbon. As mentioned in greater detail herein, one protocol for this measurement is contained in the alternative mercury monitoring approach detailed in 40 C.F.R. 75, Appendix K. 
   Usually, sorbent trap sampling requires forming and maintaining a gas-tight seal between the traps and the physical device used to hold them in place during sampling, herein referred to as a sorbent trap module or probe. This arrangement allows a vacuum to be placed on the apparatus during sampling and any leakage between the trap and the apparatus could lead to erroneous sampling results. For example, in Appendix K applications, the gas seal, such as that provided by the present invention must be able to maintain leak tightness at a minimum vacuum of 15 inches Hg absolute pressure. Additionally, the seal provided by the present invention is able to withstand chemical and physical conditions of the environment inside the gas stream which, as will be apparent to those skilled in the art, may often times be hot, corrosive and/or dust-laden. 
   Sorbent trap modules or probes according to principles of the present invention allow sorbent trap inserts to be quickly inserted and removed from the probe without the use of tools. The trap or insert is pushed by hand into a removable module inside the probe, preferably in the form of cartridge  152  shown for example in  FIG. 6 . A leak-tight seal is made between the insert  130  and the shell  136  of cartridge  152  by a series of three o-rings  126 , preferably contained within interior grooved rings formed inside of cartridge shell  136  in the manner indicated in  FIG. 1 . The probe  104  and cartridge  152  preferably include outer housings made of stainless steel or another type of corrosion-resistant ridged material. Preferably, the o-rings  126  are made of a pliable, chemically resistant and thermally stable polymer such as silicone or VITON. The cartridges  152  are held in place within the probe and sealed to the probe using a threaded compression fitting and nut assembly  142 ,  138  and  140 , respectively. 
   Accordingly, the sorbent traps, i.e., sorbent trap inserts  130  can be inserted and removed without the need for tools such as wrenches or pliers. With the present invention, the sampling process is simplified and is made more time efficient. The sorbent trap module or cartridge  152  can be readily removed from probe  104  and replaced with a new one, as may be desired. The nut  140  used to hold the cartridge in place within probe  104  may be tightened and loosened with a wrench, but, according to a preferred embodiment, the cartridge  152  is not removed from the probe  104  except for periodic maintenance purposes, such as o-ring wear. In this regard, it is generally preferred in the present invention that three o-rings are provided to seal the sorbent trap insert  130  and to provide redundancy in case of failure of a particular o-ring. Further, as can be seen for example in  FIG. 1 , it is generally preferred that two o-rings be placed close to each other at the downstream end  150  of the sorbent trap insert and that a single o-ring be located at the forward or free end of probe  104 , adjacent the gas inlet end  120  of the sorbent trap insert. 
   With reference to  FIG. 6 , the test assembly  100  conveniently provides a multichannel, redundant testing capability which is often a condition for a regulatory body to allow self-testing programs implemented by the facility operator, rather than a designee or member of the responsible agency. In order to provide maximum benefits to an operator, the testing assembly should be relatively lightweight and for the most part reusable from one testing operation to another. This is particularly important where continuous or quasi-continuous monitoring is required. Several times a day, during continuous operation of the facility, examples are withdrawn from the gas stream, an operation often repeated during the life of the facility, especially since many large scale facilities are seldom completely shut down. 
   As mentioned above, the probe  104  is preferable made rigid and with locating fitting  218 , allows the accurate positioning of inlets for the gas sample channels within the gas stream flow to be tested. However, in light of the need for gas-tight seals to be continuously maintained during testing and the need for flexibility to allow the probe to be permanently joined to the sample line  102 , it is important that the sample line be made relatively flexible, without compromising leak-free integrity of the test assembly. The preferred construction described above with reference to  FIG. 7 , for example, allows sample line  102  to meet these criteria while being relatively lightweight. The materials and dimensions of one example of a testing assembly have been given herein and afford a relatively lightweight construction, typically on the order of three pounds per linear foot. 
   With testing assemblies according to principles of the present invention, the exposed portions of the trap inserts, at the inlet to the gas channels, may be carefully controlled and protected by an operator from accidental contact and breakage, when contacting a nearby object. It should be remembered, in this regard, that often testing facilities are not typically provided for during design and construction of the facility but rather are added later, where space and other conditions allow. Further, testing operations are conducted, in many instances, continuously, year-round. In very cold weather when gloves and other protective apparel are required, the ability to control the free end of probe  104  and the exposed glass tubes projecting therefrom, becomes even more important. The flexible sample line  102 , the construction of the rigid probe  104 , the precision positioning fitting  218  and the receptacle construction  202  all contribute to ensure that continuous testing programs and other testing procedures can be successfully carried out, even during extreme atmospheric conditions. 
   The testing assembly according to the principles of the present invention provides a compact, relatively lightweight arrangement which aids in obtaining gas samples in difficult work areas of restricted accessibility such as may be provided about a smokestack of an operating combustion facility. For example, in one preferred embodiment according to the present invention, the outer housing  146  of probe  104  has a 2.5 inch outer diameter and sample line  102  has an outer diameter of similar dimensions. The sorbent trap inserts  130  are made of hollow glass tubing having an outer diameter of about 0.39 inches and an inside diameter of approximately 0.32 inches. The walls of outer shell  136  of the cartridge  152  preferably have a thickness of approximately 0.09 inches and a length of approximately 8.5 inches. The flexible lines  110 ,  112  preferably have an approximate nominal external diameter of approximately one quarter inch. 
   Turning again to  FIG. 1 , a fitting assembly generally indicated at  202  is provided for support and control of depth insertion of the probe in the process stream. Included in assembly  202  is a port  204  and flange  206 . Connected to flange  206  is a pipe nipple  208  which preferably has a nominal internal diameter of 2.5 inches. Also included is a quick lock fitting  210  with an internal bore of approximately 2.5 inches, dimensioned to receive probe  104 . A pair of cam locks (not shown) protrude into the inner bore of fitting  210  and are operated by lever arms  212 . The cam members seat against a grooved portion  216  of a fitting  218  mounted at one end of probe  104  and are preferably rigidly connected thereto by welding, brazing or other form of metallurgical joinder. A flexible, high-temperature o-ring  211  (e.g., Viton) sits in a groove within the fitting  210  and seals against fitting  218  when the cam locks are engaged. 
   Fitting  218  is in turn connected to sample line  102  and a strain relief system  222  is provided to transfer support load to assembly  202 . In operation, probe  104  is inserted into fitting  210  so as to project into the process flow in the manner indicated in  FIG. 2 . Preferably, fitting  218  provides an approximate insertion limit by engagement with fitting  210 . The final insertion control is provided when the cam locks are operated by lever arms  212  with the cam locks received in groove  216  to provide a final, rigidly secure and accurately positioned engagement of the probe with respect to the process stream. 
   Although a particular probe construction has been described above, the testing assembly according to principles of the present invention can readily employ probes of different constructions and operating principles. Further, those skilled in the art will readily appreciate that the sample line can be readily modified to accommodate different numbers of gas channels to be monitored. For example, a single channel can be readily provided as can a system having three or more gas channels. Further, the present invention can be employed to test virtually any type of material. 
   Referring now to  FIG. 9 , a sample system suitable for use with the aforementioned probe, sample line and related equipment is generally indicated at  10 . Included is a duct wall  12  confining a gas stream which flows in the direction of arrow  14 . An entrance  16  formed in duct wall  12  is provided for probe  20 . In one example, probe  20  includes a sorbent trap  22  which is placed in the gas stream. A pump  26  draws flue gas through trap  22  and probe  20 . That portion of the gas stream passing through trap  22  is drawn through a chiller  30  and desiccant unit  32  before entering subsystem  34  which includes pump  26 . An isolation valve  40  and flow control valve  42  are provided along with a flow controller/data logger  44  which outputs data on port  46 . Gas stream leaving pump  26  passes through dry gas meter  50  and a rotating meter device  52  before being discharged at  54 . 
   The foregoing descriptions and the accompanying drawings are illustrative of the present invention. Still other variations and arrangements of parts are possible without departing from the spirit and scope of this invention.