US 3910765 A
A chromatograph testing system with a plural filament thermal conductivity detector, a pressure detector safety device in one embodiment for protecting the detector filament, and improved means for maintaining constant testing temperatures. The system is designed to reach test temperatures up to 500 DEG F., to be compact, and to be easily maintained.
Description (OCR text may contain errors)
Oct. 7, 1975 United States Patent [191 Tinklepaugh et al.
XXX 33 ZZ HCR //3 in 77 22 3 33 22 Atwood et al, Heaton Dodd et al, Gaylemm. Luckey R E: in mm m n Primary Examiner-Robert M. Reese g -B: n Oil omp ny f Pennsylvania. Attorney. Agent, or FirmGe0rge L. Church; Donald Philade phi PH- R. Johnson; Gary V, Pack Dec. 2, 1974  Filed:
A chromatograph testing system with a plural filament thermal conductivity detector, at pressure detector safety device in one embodiment for protecting the detector filament, and improved means for maintaining constant testing temperatures. The system is de signed to reach test temperatures up to 500F, to be compact, and to be easily maintained.
8 6 m lw w Z 7 6 |11R-:5 0 C5 G4 4 5 5& 2 am n 4 .2 u 52 NR3 H 3 02 v MG WU H .m2 WWh R H c U HE mi s .2... l 2 C 0 S UhF Z QM S5 J 6] References Cited 6 Claims, 6 Drawing Figures m 2 N 7 S N E T. Am M Sm m s mm D l W% NH U7 7 4 m 9 2 US. Patent 0a. 7,1975 Sheet 2 of3 PROCESS GAS CHROMATOGRAPH ANALYZER The control valve and actuating mechanism disclosed herein is disclosed and claimed in a copending application, Ser. No. 528,756, filed of even date herewith.
This invention relates to gas chromatography, and more particularly to a design for a gas chromatograph which increases the accuracy and reliability of test results and decreases the time required for maintenance and repair.
One major concern in industry is to have its processes in continuous operation to assure maximum output. The gas chromatograph is often used as a monitor on many processes in a refinery or other industrial settings. A major problem develops when these chromatographs fail to operate properly because of the length of time required for repair. This invention discloses a design which features modularization of each component so that when part of the chromatograph stops operating, it can be easily replaced and the defective component can be returned to a shop for repair and analysis of the reason for failure.
All elements of this invention are designed for easy and quick replacement in the field of operation. The tubing for the column separator is wound tightly around a ring. thereby allowing replacement of a co' umn by merely disconnecting the two ends of the column separator tube and slipping the ring off of the heating block. Each detector filament is secured in a socket. thereby facilitating easy replacement. The ease of replacing the other components will become evident in the detailed description of this invention.
Several design features in the chromatograph help assure maximum accuracy in the test results. An essentially solid metal heating block houses the detector filaments. The mass of the metal comprising the heating block acts as a heat sink. maintaining a constant uniform temperature for the columns and detector components. This constant temperature provides more accu rate test results which can easily be plotted as a bar graph. These bar graphs have improved peak shapes that can be read by the process operator much easier than the conventional triangular plots.
An object of this invention is to improve a simple de sign for a gas chromatograph with easily interchangeable components.
Another object of this invention is to provide a gas chromatograph with the capability of maintaining constant temperature control of the sample gas and the detector components.
Another object of this invention is to provide a safety device to detect pressure losses in the chromatograph and to turn off the detector elements in the event of loss of pressure thereby preventing their burnout.
A still further object of this invention is to provide a gas chromatograph which can reach test temperatures to 500 and be able to sustain continuous testing at these high temperatures.
The objects of this invention are accomplished briefly in the following manner: A generally cylindrical metal heating block, housing a cartridge heater and the detector filaments, is maintained at the testing temperature desired. The columns are affixed around the heating block to be maintained at a constant operating temperature. A fourteen-port rotary control valve designed to withstand the high testing temperatures desired is used to provide all the switching and sampling requirements. A pair of steel bellows is used to actuate the rotary valve.
Further objects and advantages of this invention will become obvious in the following detailed description of the invention, taken in conjunction with the accompanying drawings, wherein:
FIG. I is a front view of the invention disclosed without the oven cover.
FIG. 2 is a top view of the invention with the heating block and adjoining components removed.
FIG. 3 is a sectional view of the heating block taken along line 33 of FIG. 1.
FIG. 4 is a sectional view of the heating block taken along line 44 in FIG. 1.
FIG. 5 is a sectional view of the heating block taken along line S5 in FIG. 1.
FIG. 6 is a flow diagram of the gas chromatography system in this invention.
Refer now to the figures provided. The entire chromatograph with the exception of its electronic controls is contained in an oven which is insulated on all sides. The top and the four sides are constructed as one sec tion (not shown) which rests tightly against the oven base 12.
Heating plate 13 rests on oven base 12 and is secured thereto by bolts 14. Embedded in heating plate I3 is heating element I5. Temperature sensor I6 and heat limiter switch 17 rest in passages embedded in heating plate 13. Resting on the upper surface area of heating plate 13 is the tubing for heat transfer coil 18.
FIGS. I and 2 illustrate one possible valve and valve actuation design. Control valve housing frame 21 is so cured by screws 22 to the upper surface of heating plate 13. Steel bellows 23 and 24 are mounted on one side of housing frame 21. Openings on housing frame 21 at the location where each steel bellows. 23 or 24 is mounted, allow for connection of steel bellows 23 and 24 to a pressure source (not shown) for actuation through tubing 25 and 26 and couplings 27 and 28 respectively. Rotary control valve 29 is securely mounted to the top side of housing frame 21 with valve drive shaft 31 of control valve 29 extending through opening (not shown) in the top side of housing frame 21. Drive shaft 31 is connected securely to the center of lever 33. One end of lever 33 is connected pivotally to push rod 34 of steel bellows 23 by pivot pin 35 and the other end of lever 33 is pivotally connected to push rod 36 of steel bellows 24 by pivot pin 37. Stop blocks 38 and 39 are secured to the side of housing frame 21 opposite steel bellows 23 and 24, respectively. The conduit connections to control valve 29, with the exception of heat transfer 18, are omitted from FIGS. 1 and 2 since these connections vary with the testing sequence used.
Rigid support pipe 40 passes through and is secured to heating plate I3. Explosion proof housing 41 is threadedly secured to and supported by support pipe 40. Heating block 42 is thrcadedly engaged to housing 41. Heating block 42, which serves as the body for thcrmal conductivity detector 58 (FIG. 6), is essentially solid with the exception of several channels. Cylindrical channel 43 spans the entire longitudinal axis of heating block 42, housing heating element 44. Stop plug 45 is threadedly engaged in the external end of channel 43. Four longitudinal filament chambers. 46 and 46'. of equal size are bored in the internal end of heating block 42. For clarity, only filament chamber 46 is shown in FIG. 3. A plug 47 is threaded into each filament chamber 46 and 46' in such a manner as to seal each filament chamber. Each plug 47 seals a detector filament 48 inside its respective chamber, having the detector filament electrical leads 73 pass through the plug itself. Four internal passages, 49 and 49', lead from the outside wall of heating block 42 at coupling 50 and 50', to their respective sealed longitudinal filament chamber 46, or 46', as seen in FIG. 4. Two inter' nal connecting passages, 51, connect filament chambers 46 to filament chambers 46 as shown in FIG. 5. Plugs 52 block the external end of each connecting passage 51. When the chromatograph is in operation, two streams of gas pass through the above passages. For example, carrier gas enters coupling 50, flows through internal passage 49 into filament chamber 46, through connecting passage 51 into filament chamber 46 and then flows out of heating block 42 by way of internal passage 49' and coupling 50'. The same flow pattern is followed for the other symmetrical combination of passages and sealed chambers.
A longitudinal opening 53 houses temperature sensor 54 and other longitudinal opening 55 houses heat limiter switch (not shown).
All the aforementioned electrical components housed in heating block 42 are placed in their respective opening in such a manner that their terminals run outside of heating block 42, but inside explosion proof housing 4] and can be connected to wires which run through the inside of support pipe 40 to electronic control systems (not shown) outside the oven. Explosion proof housing 41 has a housing cap 56 which is threadedly attached and can easily be removed for easy ac cess to the electrical connections contained therein.
The column separator 60, which typically comprises two columns arranged for series flow, is wound tightly around a generally cylindrical structure ring 61 and held firmly in place by clamping members 62 which are attached to structure ring 61 by screws 63. For operation, structure ring 61 is slid over the external end of heating block 42 and the ends of the tubing of column separator are coupled to the appropriate ports of control valve 29. In the center of heater block 42, capillary tubing 64 is wrapped tightly around the circumference of heating block 42 and held in place firmly by support members 65, which are secured to heating block 42 by screws 66.
For normal operations an electronic control system is needed to operate the chromatograph. Separate control systems that are connected to temperature sensors 16 and 54 are used to maintain the correct temperature in heating plate 13 and heating block 42. The heat limiting switches act as a fuse by turning off the heat if the temperature rises above a certain point. A timing system is needed for activating control valve 29. Electronic circuits above described are available and known to those skilled in the art and constitute no part of this invention.
There is no one preferred use of the design above described. Because of the versatility of the design and rotary valve used, several different types of tests can be set up. Adjustments for a different test are simple. The only changes needed are to switch the connections to the rotary valve, thereby changing the paths in which the tdst sample and carrier gas flow through. Generally, in many tests, the following sequence for sample and carrier gas flow takes place. Referring to FIG. 6, the sample enters the oven enclosure and passes through LII heat transfer coil 18 in which the sample temperature is raised to the operating temperature of the chromatograph. The sample then flows to control valve 29. In the normal mode of operation the sample fluid passes through control valve 29. For sampling, control valve 29 rotates quickly, catching small quantity of sample fluid in the control valve. This quantity of sample fluid is carried out of control valve 29 by the carrier gas and to a column separator. If the sample is a liquid, once it is inserted into the chromatograph system, it vaporizes because of its reduced partial pressure. Next, the sample is separated into its components by flowing through column separators 60. The number and sequence of column separators and direction of flow through the columns depend on the test. The separated sample next flows through control valve 29 and to heating block 42 of detector 58. By way of internal passage 49, the sepa rated sample and the carrier gas pass through the filament chamber housing detector filament 48. The separated sample continues to flow through heating block 42 by way of connecting passage 51 and into another filament chamber 46' housing a detector filament (not shown), eventually exiting heating block 42 through internal passage 49'. The separated sample is carried by the carrier gas to a pressure switch or a flow measurement device and then vented into the outside air. When the pressure switch detects a loss in line pressure or the flow measurement device detects a drop in the flow rate, the power to detector 58 is turned off to avoid burning out the detector filaments 48.
The carrier gas, such as helium for example, serves to push the sample gas throughout the entire test. The carrier gas enters the oven and flows through capillary tubes 64. The capillary tubes serve to provide a constant rate of flow of carrier gas, thereby resulting in more accurate test data. The carrier gas then passes through heating block 42 of detector 58, flowing through two different detector filaments exactly as explained for the separated sample and the carrier gas. The carrier gas then enters the control valve where it can be channeled to clean out the column separators between tests or carry the sample gas during tests.
Since the usual variations in the flow pattern relate to control valve 29 connections, no specific flow pattern through valve 29 is indicated in the diagram. Examples of flow patterns through the control valve can be found in Young, US. Pat. No. 3,223,123.
Actuation of control valve 29 is by carrier gas pressure applied to one of the steel bellows 23 or 24. A solenoid valve 71, activated by a timer (not shown switches the carrier gas pressure between each steel bellows. Normally, one steel bellows is in the expanded position, its push rod fully extended against its respective stop block, and the other steel bellows remains in its rest or deflated position. When the timer switches the solenoid, the solenoid changes the carrier gas pressure to the other steel bellows and returns to its original position after the sample gas has had sufficient time to be carried through the detector filaments by the carrier gas.
The chromatograph reading is determined with a conventional wheatstone bridge arrangement using the four detector filaments 48. However, a two filament wheatstone bridge can be used by replacing two of the filaments with fixed resistors. Various kinds of detector filaments can be used in the thermal conductivity detector, including thermistor and catalytic filaments.
Heater block 42 helps assure constant temperature of the gas when it enters the filament chambers, and prevents minute temperature changes which alter the resistivity of the detector filaments, thereby affecting the test results. Heating plate 13 heats the air in the oven in order to help assure a constant temperature in heating block 42. Heating plate 13 also controls the temperature of control valve 29 as well as the sample gas flowing through the chromatograph. Control valve 29 provides quick and accurate sample volumes. Small diameter columns and small sample volumes decrease the time for testing, which results in improved peak shapes of the test data. Because of the accuracy of the results obtained, accurate bar graphs can be plotted from the tests. This type of graph is much easier and much more accurate to read as compared to the conventional triangular shaped graph.
The design features also permit easy replacement of any part in the field avoiding long shutdown times or replacement of entire units.
This invention is particularly adaptable to use in remote areas. Regular household current is sufficient for the electrical requirements and the carrier gas also provides the pressure required for steel bellows 23 and 24 to actuate control valve 29. Low current lines of VDC or less are less susceptible to noise pickup over long distances and can be used to control the tests in many chromatographs from one central location.
From the above disclosure, it can be seen that there has been provided a gas chromatograph having a novel and improved design which combines the elements of the chromatograph in such a manner as to provide very constant test temperatures which permit accurate and reliable test data to be recorded. Also included in this design are features which allow quick and easy replacement of any part of the gas chromatograph.
The invention claimed is:
1. In a gas chromatography apparatus, a means for achieving more accurate test data by reducing temperature variations within the chromatograph components, comprising:
a. an insulated container,
b. an essentially solid heating block, having a plurality of internal passages and mounted inside the insulated container.
c7 a plurality of detector filaments embedded in the heating block, said internal passages providing fluid communication from the exterior of the heating block to the detector filaments,
d. heating means embedded in the heating block, and
e. tubing wound around the circumference of the heating block for use as column separators.
2. Apparatus claimed in claim 1 whereby the plurality of tubes are connected to the circumference of the 6 heating block by means comprising:
a. an annular ring with a size and shape that allows the ring to fit snugly around the circumference of the heating block, b. a plurality of tubes wound tightly around the annular ring, and c. means for securing the tubes to the ring. 3. Apparatus claimed in claim 1 which includes a means for heating the air surrounding the heating block as well as the sample gas, comprising:
a. an essentially solid metal heating plate, and b. heating means embedded in the heating plate. 4. In a gas chromatography apparatus, a thermal conductivity detector designed to maintain a constant temperature, comprising:
a. an insulated container, b. an essentially solid cylindrical heating block, having a plurality of internal chambers and passages and mounted inside the insulated container, 0. a plurality of detector filaments, d. a plurality of insulated plugs, holding their respective detector filament securely in each respective internal chamber ofthe heating block, said internal passages providing fluid communication from the exterior of the heating block to the detector fila merits and between the detector filaments, e. a means for heating the heating block and maintaining a constant preset temperature, comprising: i. an elongated heating element resting in an inter nal chamber spanning the longitudinal axis ofthe heating block, and
ii. means to detect the temperature of the heating block and for changing the temperature in the heating element as required, and
. a plurality of tubes wound tightly around the cir cumference of the heating block for use column separators and carrier gas flow control.
5. Apparatus claimed in claim 4, which includes a means for preventing burnout of the detector filaments comprising:
a pressure switch mounted in the chromatograph downstream from the detector, so installed that the power to the detector is switched off when the pressure in the chromatograph drops below a predetermined amount.
6. Apparatus claimed in claim 5 where said means for preventing burnout of the detector filaments com prises:
a flow measurement device downstream from the de tector, so installed that the power to the detector is switched off when the flow rate in the chromatoan H... "hm. M