Patent Application: US-201213616542-A

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 .

Description:
in the cryotrap shown in fig1 , 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 . 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 . 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 . the stainless steel tubing of the trap is heated via the electrical resistance of a dc current passing from one end through the other . 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 . 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 . 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 . 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 . the cryotrap is utilized with a ten port valve which is movable between a sampling position shown in fig5 b and a flushing position shown in fig5 c 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 . 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 . 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 . the operation of the valve may be automatic , operating on a predetermined cycle or may be manually operated as desired . 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 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