Semi-continious non-methane organic carbon analyzer

Abstract

A filed portable analyzer capable of performing both the sampling and analytical procedures required by U.S. EPA Method 25 utilizing a small volume injection of sample onto a cryotrap cooled by a Stirling linear drive charged with helium to replace the field sampling condensate trap. The cryotrap is followed by the specified sorbent column/traps to ensure precise compatibility with prior reported compliance test results. The analytical system utilizes an oxidation catalyst and reduction catalyst to remove the potential for differing response factors on the FID from different compounds.

Claims

1. A device for measurement of Non-Methane Organic Carbons (NMOCs) including Volatile Organic Carbons (VOC's) in a sample stream without chromatographic separation of the NMOC's comprising a sample inlet for introducing a sample into the device a carrier inlet for introducing a carrier gas into the device a sampling and concentration system within said device, the sampling and concentration system comprising a cryotrap capable of rapid heating and cooling wherein said cryotrap removes heavy organic compounds from the sample stream an adsorbent trap capable of rapid heating and cooling wherein said adsorbent trap removes light organic compounds from the sample stream one or more multi-port valves in fluid communication with the cryotrap and the adsorbent trap to allow separation of carbon monoxide, carbon dioxide, and methane in the sample stream, thereby concentrating NMOC's and VOC's in said traps an oxidation catalyst downstream of the cryotrap and adsorbent trap wherein the oxidation catalyst converts NMOC's and VOC's to carbon dioxide a reduction catalyst downstream of the oxidation catalyst wherein the reduction catalyst converts carbon dioxide to methane and a detector to measure NMOC's and VOC's in the sample stream wherein the detector is selected from the group consisting of a flame ionization detector (FID) or an infrared spectrometer.

2. A device according to claim 1 wherein the multi-port valves comprise four, six, or ten port valves operating simultaneously with the trap.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a view of a Stirling cooler assembly as used in the cryotrap;

(2) FIG. 2 is a view of the core and coil in the assembly of the cryotrap of FIG. 4;

(3) FIG. 3 is an exploded view of the main components of the cryotrap incorporating the presently preferred embodiment of the invention;

(4) FIG. 4 is a view of the assembly of the main components of the cryotrap; coil, core, collar and Stirling cooler;

(5) FIG. 5A showing the plumbing pathways through the system using a 4 and 6 port combination;

(6) FIG. 5B is a diagram illustrating the operation of the cryotrap, with a 10 port control valve in the sampling position showing the two flow paths through the valve; and

(7) FIG. 5C is a diagram similar to that of FIG. 5A with a 10 port control valve in the injecting position showing helium carrier flow to the detector, and

(8) FIG. 5D is a diagram similar to that of FIG. 5C showing the flow of helium carrier to the detector with the valve in the backflush position.

DESCRIPTION OF THE PREFERRED EMBODIMENT

(9) In the cryotrap shown in FIG. 1, a core plate, apertured insulator plates, solid insulator plates, and a mounting plate are held together in a sandwich construction by rods and screws positioned at the corners of the plates. A core is positioned in the core plate and a gas expander is attached to the mounting plate by screws, with the tube of the gas expander extending through openings in the plates and into an axial opening in the core. A thermally conductive compound such as silver-loaded silicone grease may be applied to the end of the expander tube to improve the thermal connection to the core.

(10) The gas expander is part of a refrigeration system which provides for cooling of the core. In the preferred embodiment illustrated, a Stirling linear cooler is utilized, having a compressor connected to the gas expander. The Stirling linear cooler may be of conventional design, providing a closed cycle with helium being compressed at the compressor and with pressure pulses transferred through the helium to the expander. Cooling is obtained by cyclic out-of-phase motion of a compression piston and a displacer-regenerator located in the expander assembly. The compressor is operated for a time prior to the introduction of the sample to allow the core and tubing to reach the desired operating temperature. The compressor continues to operate during the time that the sample is passed through the trap tubing. The compressor is then turned off during the heating mode.

(11) The core preferably is a aluminum disc with a helical groove on the exterior. A length of tubing, preferably of stainless steel, is wound on the core in the helical groove. Temperature sensor may be positioned in openings in the core, preferably between the gas expander opening and the helical groove. The temperature sensor is connected to a control circuit by wires.

(12) The stainless steel tubing of the trap is heated via the electrical resistance of a DC current passing from one end through the other.

(13) During the cooling modes, the compressor control electronics hold the core temperature to a selectable preset temperature as sensed by the temperature sensor. The heater temperature controller also provides a display of the core temperature. Cooling and heating modes are controlled by the cryotrap sequence control electronics, with power from a DC power supply. Desirably, the core plate and insulator plates are formed of a low density, closed cell, rigid foam for thermal insulation, typically a polymethacrylimide foam. The individual plates preferably are about ½″ thick and about 4″ square. A layer of moralized plastic film, typically aluminized Mylar film, is positioned on each side of each plate, typically about 0.0005″ thick.

(14) A plurality of openings are provided in each of the core plate and insulator plates, typically about ½″ in diameter. Prior to applying the surface layers, the openings preferably are filled with crumpled metalized plastic film, typically aluminized Mylar film. Also, preferably the openings in adjacent plates are misaligned.

(15) In operation, the core is cooled by the gas expander rod in the opening of the core. Substantial insulation is provided around the core and the gas expander tube so there is minimal heating from the surrounding atmosphere. At the same time, heat is periodically applied to the tubing for thawing the frozen gas constituents. It has been found that the insulation construction using the foam plates, with the crumpled metalized film in the openings achieves an excellent balance between heating and cooling, permitting freezing of substantially all constituents in the gas while at the same time requiring a minimum of cooling energy and permitting a rapid cycle tune.

(16) It is desirable to cool the core quickly. Rapid cooling minimizes wear on the Stirling cooler and enables the cryotrap to complete a cooling/heating cycle quickly. To cool the core quickly it is necessary to minimize the amount of material that must be cooled. This includes the insulating material around the core, therefore insulating material is removed resulting in a plurality of openings in each of the core plates and insulator plates. The openings are typically ½″ in diameter leaving a “web” of foam insulation to support the core and providing a longer path through the foam from the core to the outside. To prevent air currents from circulating in these openings, the openings are filled with crumpled metalized plastic film, typically aluminized Mylar film. Metalized plastic film is also bonded to each side of the insulating plate. The metalized plastic film also serves to reflect external radiant energy away from the core.

(17) The cryotrap is utilized with a ten port valve which is movable between a sampling position shown in FIG. 5B and a flushing position shown in FIGS. 5C and 5D. A source of sample gas is connected to the valve through a line, and a vent for the sample gas is connected to the valve through another line. The carrier gas from an analyzer such as a gas chromatograph is connected to the valve by an incoming line and an outgoing line. The tubing is connected to the valve.

(18) During the sampling mode, the sample gas flows through the line, the valve, through the tubing, and back through the valve to the vent line, with the carrier gas flowing directly to and from the valve to the detector.

(19) With the valve turned to the flushing mode, the sample gas flows directly into and out of the valve, with the carrier gas flowing through the line to the valve, through the tubing and back to the analyzer through the valve and the line.

(20) The operation of the valve may be automatic, operating on a predetermined cycle or may be manually operated as desired.

(21) If a faster analytical cycle is desired, a second cryotrap assembly may be added along with a 6 port valve to switch between traps. In such a case one trap would be cooling while the other is used for the sampling and analysis.

REFERENCES

(22) Mitra S., Yun C. “Continuous gas chromatographic monitoring of low concentration sample streams using an on-line microtrap” J. Chromatogr. A 648, 415-421 (1993) Feng C. H., Mitra S. “Two-stage microtrap as an injection device for continuous on-line gas chromatographic monitoring” J. Chromatogr. A805, 169-176 (1998) Mita S. “Analytical apparatus and instrumentation for on-line measurement of volatile organic compounds in fluids” U.S. Pat. No. 6,112,602 Sep. 5, (2000) 40 CFR 60. Appendix A to Part 60 Method 25—Determination of total gaseous non-methane organic emissions as carbon

US Patent References

(23) U.S. Pat. No. 4,148,196, Apr. 10, 1979, French, et al., Multiple stage cryogenic pump and method of pumping U.S. Pat. No. 4,283,948, Aug. 18, 1981, Longsworth, Cryogenic air sampler U.S. Pat. No. 4,479,927, Oct. 30, 1984, Gelemt, Regenerable cold trap for aluminum chloride effluent U.S. Pat. No. 4,506,513, Mar. 26, 1985, Max, Cold trap U.S. Pat. No. 4,607,491, Aug. 26, 1986, Ishimaru, et al., Cooling trap for vacuum U.S. Pat. No. 5,073,896, Dec. 17, 1991, Reid, et al., Purification of laser gases U.S. Pat. No. 5,349,833, Sep. 27, 1994, Pardee, et al., Cryotrap for air pollution analyzer U.S. Pat. No. 5,537,833, Jul. 23, 1996, Matte, et al., Shielded cryogenic trap U.S. Pat. No. 5,596,876, Jan. 28, 1997, Manura, et al., Miniaturized cryogenic trap apparatus U.S. Pat. No. 6,477,905, Nov. 12, 2002, Mitra, Apparatus and instrumentation for measurement of TOC, NMOC and VOCs U.S. Pat. No. 7,370,482, May 13, 2008, Desbiolles, et al, Rapidly regenerating cryogenic trap U.S. Pat. No. 8,127,595, Mar. 6, 2012, Finlay, et al., Pre-concentrator and sample interface