Title:
SAMPLING VALVE FOR HIGH TEMPERATURE CORROSIVE GASES
United States Patent 3585860
Abstract:
A sampling valve receiving a continuous carrier gas and intermittent samples of high temperature, corrosive gases has a valve body of high-temperature material with two passageways through the valve body which are interconnected at two points where two valve chambers extend through the valve body so as to intersect the passageways. A portion of one passageway between the interconnections serves as a sample reservoir and the two valve chambers each support two valve stems, one in each end of the chamber. Housing means encloses packing means which in turn encloses each valve stem.


Inventors:
ALT FRANK B
Application Number:
04/797848
Publication Date:
06/22/1971
Filing Date:
02/10/1969
Assignee:
Diamond Shamrock Corporation (Cleveland, OH)
Primary Class:
International Classes:
G01N1/00; G01N30/20; (IPC1-7): G01N1/26
Field of Search:
73/422,421.5,422GC 137
View Patent Images:
US Patent References:
3205701Fluid analyzing systems1965-09-14Szonntagh
3186234Sampling valve1965-06-01Solnick et al.
3166939Sample valve1965-01-26Koeller et al.
3021713Fluid sampling valve1962-02-20Wright
1532781Stopcock and shut-off cock for pressure-fluid piping1925-04-07Schneider
Primary Examiner:
Prince, Louis R.
Assistant Examiner:
Yasich, Daniel M.
Claims:
I claim

1. An on-stream sampling valve for delivering a controlled volume of sample gas to be analyzed, and a continuous flow of a second inert carrier gas, through a delivery line to an analytical instrument, comprising a valve body, having in combination;

2. The sampling valve of claim 1 wherein said chamber and each of said channel means and said passageways are lined with a high-temperature material selected from the group consisting of nickel, the HASTELLOY series, the stainless steel 316 series, INCONEL AND MONEL.

3. The sampling valve of claim 7 wherein the tips of the valve stems are lined with a high-temperature material selected from the group consisting of nickel, the HASTELLOY series, the stainless steel 316 series, INCONEL AND MONEL.

4. The sampling valve of claim 6 wherein the valve body is a high-temperature material selected from the group consisting of nickel, the HASTELLOY series, the stainless steel 3l6 series, INCONEL and MONEL.

5. The sampling valve of claim 4 wherein the tips of the valve stems are lined with a high-temperature material selected from the group consisting of nickel, the HASTELLOY series, the stainless steel 316 series, INCONEL and MONEL.

Description:
BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a plural valve system arranged to mix intermittent samples of a first gas with a constant flow of second gas and deliver the mixture to a location external to said valve system. More particularly, this invention relates to a sampling valve for high temperature process gases which are corrosive at these temperatures, the valve having an improved, corrosion resistant construction for intermittently injecting into a continuously flowing stream of inert carrier gas a predetermined volume of sampled process gas.

2. Description of the Prior Art

The valve of this invention can be used for mixing intermittent volumes of one gas with an uninterrupted flow of another gas for any desired utilization of the mixture with one particularly preferred utilization being analysis of the intermittent gas by gas chromatography. Gas chromatography essentially is a process for separating complex mixtures of gas into their components. In order to accomplish the separation, a so-called partitioning or separating column is used. In gas chromatography, an inert sweep or carrier gas (such as helium or nitrogen) flows continuously through the separating column. This is the main fluid stream, usually having a flow rate of between 50 and 100 cc./minute. A small sample of a mixture to be analyzed (called the sample) is injected into the sweep or carrier gas stream, prior to the column. The chromatogram may be developed by elution, the different components of the sample having different retention times in the separating column.

In the design of fluid-sampling valves, it is desired to achieve certain ends among which are a valve having a quick, smooth operation so that the uniform flow of the carrier gas through the partitioning column is disturbed as little as possible. The valve should be as small and compact as possible so that it can be used where space is limited. The parts of the valve should be long wearing, to reduce to a minimum the cost and inconvenience of making repairs. The force required for operating the valve should be small.

Upon reviewing the valves used in this field, it was discovered that those available were not capable of withdrawing samples of process gases which would be at elevated temperatures when the samples were taken and which would be corrosive to many materials at those temperatures. Of particular contemplation are process gases having one or more of the following present in at least minor concentration at temperatures of 225° C. or greater: chlorine, fluorine, hydrogen chloride, hydrogen fluoride, sulfur dioxide, nitric oxide, nitrous oxide and hydrogen sulfide. Valves which have TEFLON surfaces contacting the process gas have not been able to perform at temperatures in excess of 225° C. in such corrosive, gaseous atmospheres for any length of time with reliability. Hence, the corrosive failure of these valves has necessitated rapid replacement, much down time for the process and generally unsatisfactory results due to labor costs in repair and replacement costs for parts. No other valves presently known were able to approach the desired lifetime for sampling corrosive process gases at temperatures sufficient to maintain all the components of these gases in the vapor state.

SUMMARY OF THE INVENTION

This invention makes possible the sampling of corrosive process gases at temperatures in excess of 222° C. where none of the gaseous components will condense from the sample and the combination of these samples of process gas with a constant flow of carrier gas to a chromatograph or other analytical instrument.

It is a primary object of this invention to have a sampling valve which is resistant to corrosion by samples of process gas having corrosive, gaseous components at temperatures insuring there will be no separation of the gaseous mixtures through condensation.

An associated object of this invention is to have a high temperature, corrosion-resistant valve capable of drawing intermittent samples of process gas for long periods of operation with minimal repairs so that periods of at least a year of operation without repairs are possible.

A further object of this invention is to have a valve construction with the foregoing features while having the smooth, quick action features and small, compact size of existing prior art devices.

A further object of this invention is to have a valve capable of mixing intermittent volumes of a gas with an uninterrupted flow of another gas, thus achieving a mixture of the two gases.

Other objects and advantages of this invention will become apparent from a reading of the following discussion and the appended claims and by reference to the attached drawings, wherein:

FIG. 1 is a section through a sampling valve which receives a continuous flow of carrier gas and intermittent samples of high temperature, corrosive, gaseous atmospheres, the valve being constructed in accordance with the teaching of this invention. The figure illustrates a point in the sampling sequence when the lower set of valve stems are not in contact with the valve body 10.

FIG 2 is a partial view of FIG. 1 showing the valve body with valve stems, packing and housing partially cut away at a different point in the sampling sequence when the upper set of valve stems are not in contact with the valve body 10.

FIG. 3 is a partial view showing the valve body with the valve stems, packing and housing partially cut away and all the valve stems are in contact with the valve body. This is the normal rest position of the valve stems prior to and after a sampling sequence.

FIG. 4 sets forth the sampling valve as integrated into an operating system whereby associated hardware provides energy pulses to operate the sampling valve system for taking samples to be combined with a sweep to pass to an analytical instrument.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and first to FIGS. 1 and 2 of the drawings, a valve body 10, whose outer configuration is substantially that of a rectangular prism, has therein, as positioned in the drawing, which position is not critical to the operation of the valve, two passageways which extend through the valve body in a generally horizontal direction, one passageway carrying a constant flow of a gas such as an inert, carrier gas and the other passage receiving an intermittent flow of another gas such as a process gas. The flow pattern of the first gas (carrier gas) is from a source CG through line 31 to valve body 10 where the line 31 is connected in an airtight seal to the threaded portion 15 of chamber 11. Chamber 11 connects to cavity 13 which in turn is connected to chamber 8. The gas flows from cavity 13 into chamber 8 which joins another cavity 14 which connects to chamber 6. Chamber 6 has a threaded portion 15a enabling line 33 to be connected thereto in an airtight connection with line 33 leading to an external location 34 such as a chromatograph. The flow pattern of the second gas (process gas) comes from a conduit 32 or reservoir into line 30 to valve body 10 where line 30 is connected in an airtight seal to the threaded portion 15b of chamber 12. Chamber 12 empties into cavity 13a which in turn is connected with chamber 28'. The gas flows in chamber 28', empties into chamber (sample port) 26 which is connected to chamber 29'. The process gas flows from chamber 29' into cavity 14a which is joined to channel 7. Channel 7 has a threaded portion 15c enabling an airtight connection with line 35 which enables the process gas to flow into the atmosphere, to pollution control equipment or to conduit means 32 downstream from line 30 (when a venturi, for example, is located downstream in conduit means 32). Intersecting the passageways are two chambers or bores which extend through the valve body or block 10, and as shown in FIG. 1, are positioned in a vertical direction. The bores have a constricted or small diameter central portion (channels 28 and 28' and channels 29 and 29') which serves to interconnect the two gas passageways. The bores are counterbored to provide larger diameter portions, the first larger diameter portions being 13, 13a, 14 and 14a, the next larger diameter portions being 13' and 14', and the largest diameter portions being 13" and 14" which open on the edges of the valve body 10. Channels 28 and 29 serve to interconnect the passageway carrying a constant flow of a gas with the passageway receiving an intermittent flow of another gas.

In cavities 13, 13a, 14 and 14a are positioned valve stems l6, l6a, 16b and 16c (there are four valve stems in all) so that the valve stems 16, 16a, 16b and 16c of cylindrical shape are slideably moveable and capable of being placed so as to fit tight against the valve body 10 or can be withdrawn from valve body 10. The tip of the valve stems 16, 16a, 16b and 16c are of such size that when brought against the valve body 10 at channels 28, 29, 28' and 29', respectively, no gas will pass from channel 11 into channel 28, from channel 29 into channel 6, from channel 12 into channel 28' or from channel 29' into channel 7. The upper two valve stems 16 and 16a have passageways 9 and 9', respectively, therethrough which enables gas from channel 11 to pass through stem 16 into channel 8 on the left side of the valve body 10 and from channel 8 into channel 6 on the right side of the valve body 10. Each valve stem can have a rounded rim on the outside of the stem at the junction of the conical tips and the cylindrical stems to better seal with the sleeves.

Enclosing a portion of each of the valve stems 16, 16a, 16b and 16c in a gastight seal is a packing means of a hollow cylindrical sleeve 17 (17a) one end of which rests in the expanded cavities 13' and 14' of the bores. The upper two sleeves 17 and 17a have openings 4 and 5, respectively, which enable gas to pass from the passageway 9 in valve stem 16 into channel 8 on the upper left side of the valve body and from channel 8 to passageway 9' in valve stem 16 on the upper right side of the valve body. Resting on the sleeve 17 and enclosing a small portion of each valve stem are a series of packing rings 19 and resting on the packing rings is a packing follower 20. Enclosing each sleeve 17, packing rings 19 and packing follower 20 is a hollow cylindrical housing (valve bonnet) 18, the housings being threaded externally on the end fitting the threading of bores 13" and 14' with the other end of each housing 18 being sealed off by a gland nut 21 which is threaded to fit the internally threaded end of the housing 18 which opens away from the valve body. This leaves the gland nut 21 holding the packing means including the packing follower 20 in position, and the gland nut 21 is hollow so as to enclose a portion of the valve stem 16 and provide a clearance to permit free movement of the valve stems.

The two valve stems 16 and 16a on the upper side of the valve body form one pair of valve stems called, for purposes of reference in this discussion, the upper pair of valve stems, with those on the lower side of the valve body forming another pair of valve stems (16b and 16c) called the lower pair of valve stems. As noted before, the positioning of the sampling valve is not critical to its operation. The upper pair of valve stems, 16 and 16a, is connected to an upper crossbar 22 and the lower pair of valve stems, 16b and 16c, is connected to a lower crossbar 24, with one form of connection being by crossbar nuts 23, as shown in the drawing, but other forms of fastening, such as by welding, could also be practiced. The upper crossbar 22 is in turn connected to a drive shaft 25 which receives energy inputs to slideably operate the upper set of valve stems 16 and 16a from a closed position where the tips of the stems 16 and 16a are in contact with the valve body 10 to an open position where the tips of the valve stems 16 and 16a do not contact the valve body 10. The lower crossbar 24 is connected to a drive shaft 27 which receives energy inputs to slideably operate the lower set of valve stems 16b and 16c from an open position where the tips of the valve stems 16b and 16c do not contact the valve body 10 to a closed position where the tips of the valve stems 16b and 16c are in contact with the valve body 10 and restrict the passage of fluid.

For proper valve action, it is necessary that free and unrestricted communication be established at certain times (depending upon the valve operation, as will later be described) between the conical tip of each of the valve stems 16, 16a, 16b and 16c and the valve body 10 at the respective seats formed by the juncture of channel 28 and cavity 13, channel 29 and cavity 14, channel 28' and cavity 13a, and channel 29' and cavity 14a. The channels 28, 29, 28' and 29' are of a diameter smaller than the diameter of each of the valve stems 16, 16a, 16b and 16c, so that the conical tips of these stems will partially fit into the channels 28, 29, 28' and 29', sealing off the passageways to the passage of fluid. In this manner, each set of the valve stems slideably moves through a small space by sliding as crossbars 22 and 24 receive energy inputs. When fully depressed, each set of stems mates with the valve body 10, but when withdrawn, the stems leave a path for a fluid to flow. In this manner, the valve stems act as a simple flow or no flow sequence for the passageways with regard to the flow of fluid through the valve body. But, as previously pointed out, the upper set of valve stems 16 and 16a have passageways 9 and 9' bored therein so that the carrier gas passes through these passageways 9 and 9' in stems 16 and 16a when the stems are seated on valve body 10.

A discussion of the operation of the sampling valve will be given by reference to FIGS. 1, 2 and 3, the discussion being adapted for sampling a process gas for analysis by an analytical instrument. At the point of beginning the sampling sequence, the upper set of valve stems 16 and 16a are positioned tight upon the valve body 10 sealing off channels 28 and 29 from channels 11 and 6, respectively, so that the carrier gas cannot enter channels 28 and 29 as shown in FIG. 3. First, a sweep of carrier gas is established from a source CG into conduit means 31 through the valve body 10 entering channel 11, passing through cavity 13, through passageway 9 in stem 16 and through passageway 4 in sleeve 17, reaching channel 8. From channel 8 the gas passes through opening 5 in sleeve 17a, through passageway 9' in stem 16a reaching channel 6 and exiting into conduit means 33 which reaches analytical instrument 34 to establish a background count in the instrument 34 due to the carrier gas alone. The flow of carrier gas is at a constant, established rate.

At the point of beginning the sampling sequence, the lower set of valve stems 16b and 16c are positioned tight upon the valve body 10 sealing off channels 28' and 29' from channels 12 and 7, respectively, as shown in FIG. 3. Further, valve 37 is turned to open position to enable gas to flow in line 30. Before withdrawing the lower set of valve stems 16b and 16c from contact with valve body 10, it may be desirable to back purge an inert gas through a channel 12', a channel similar to channel 12. The inert gas comes from channel 40 into cavity 13 through channel 12 and line 30 reaching a porous, metallic plate in the line at point 36 which opens into conduit 32. The back purging is optional but is desirable where solid matter may temporarily plug up the porous, metallic plate used in withdrawing the process gas from conduit 32. In order to start a flow of process gas through the valve body 10, the lower set of valve stems 16b and 16c are positioned away from the valve body 10 so that the process gas will freely flow into channel 12 in valve body 10 from line 30 (See FIG. 1). Then the process gas passes into cavity 13a up channel 28' into sample port (channel) 26, down channel 29' into cavity 14a. From cavity 14a the gas enters channel 7 and passes out of the valve body 10 into line 35.

As previously described, line 35 can return downstream to the main process gas stream in large conduit means 32, exit into the atmosphere or a pollution control unit as desired. The process gas is allowed to flow for a short time so that the process gas in channel 26 of valve body 10 is representative of that currently in the process gas stream, then energy is applied to the lower drive shaft 27 which moves the shaft 27, the associated lower crossbar 24 and the lower set of connected valve stems 16b and 16c into contact with the valve body 10 at channels 28' and 29' of valve body 10 (typically one-eighth inch to one-fourth inch in movement). This traps the process gas in the sample port 26 as the stems 16b and 16c form a gastight seal when they are in contact with the valve body 10.

Next, while maintaining the sweep of carrier gas as previously described, energy is applied to the upper drive shaft 25 to move the associated crossbar 22 and connected upper set of valve stems 16 and 16a away from the valve body 10 for a controlled distance (typically one-eighth inch to one-fourth inch) so that passageways 9 and 9' through stems 16 and 16a in the upper set of valve stems are blocked off by the sleeves 17 and 17a which forces the sweep of carrier gas entering cavity 13 from passageway 11 down through the channel 28 into the sample port 26; from there the sweep of carrier gas goes up channel 29 into cavity 14 and out passageway 6 to conduit means 33 and analytical instrument 34. This corresponds to the position of the sampling valve shown in FIG. 2. After the sweep has removed the trapped process gas to the analytical instrument 34, the upper set of valve stems is returned to contact with the valve body 10 so that the sweep again passes from passageway 11 into cavity 13, through passageway 9 of stem 16 and passageway 4 of sleeve 17 into channel 8, from channel 8 the gas passes through passageway 5 of sleeve 17a and passageway 9' of stem 16a into channel 6, out channel 6 into line 33 to analytical instrument 34. Also, the lower set of valve stems 16b and 16c are left in contact with the valve body 10 until the next flow of the process gas into channel 12 of valve body 10. This position of the valve is shown in FIG. 3. At this point, the sampling cycle is complete. In summary by reference to the figures, the sampling cycle is as follows: It starts with FIG. 3, has the bottom set of valve stems withdrawn from the valve body as shown in FIG. 1 to let the process gas flow in and then the set is placed against the valve body to trap a sample in the sample port. Then the upper set of valve stems is withdrawn from the valve body 10 as shown in FIG. 2 until the carrier gas has flushed the process gas in channel 26 to the instrument 34 and then all stems are returned to contact with the valve body 10 as shown in FIG. 3. From the foregoing, the person skilled in this art could integrate various circuits which could either be operated on a manual basis or a timed sequence coordinated with processing cycles, etc.

From the foregoing, it is readily apparent that a minimal number of parts and limited surface area are in contact with the high temperature, corrosive, process gas. In particular, channels 12, 28', 28, 26, 29, 29', 6 and 7, along with cavities 13a and 14a and the tips of the valve stems 16, 16a, 16b and 16c, have the most contact with the process gas. Minimizing the number of parts and the surface area of these parts coming in contact with the process gas is important as these areas are fabricated of specially suited materials.

The valve body 10 (or a lining for the channels 12, 28, 28', 26, 29, 29', 6 and 7 and cavities 13a and 14a of the valve body 10 coming into contact with the process gas) and the tips of the valve stems 16, 16a, 16b and 16c (or a lining for the tips) are usually fabricated of high temperature, corrosion-resistant materials, preferably nickel or the HASTELLOY A and B series of nickel-containing alloys, but the high quality stainless steel 316 series, INCONEL and MONEL have also proven satisfactory. The sleeves 17 (17a) surrounding each valve stem are usually pressed graphite or carbon, but other materials will work, such as available high temperature, self-lubricating compositions. The other parts of the valve can be made of lower cost, conventional materials, as these parts do not come into contact with the high temperature, corrosive, process gas. The valve bonnet, gland nuts, crossbars, crossbar nuts and drive shaft can be made of conventional metallic alloys, such as steel, aluminum, etc. The packing rings and followers are typically made of carbon or pressed graphite. The conduit means coming in contact with the process gas (e.g., 30, 33, 35) are selected from existing supplies of nickel tubing. Those conduit means not contacting the process gas (e.g., 31) can be selected from conventional stainless steel or nickel alloy tubing.

In greater detail, a typical system for operating the sampling valve for sampling the corrosive gases at very high temperatures as described in this invention is given in FIG. 4. In this figure, 40 represents either manually operated electrical pulsing means for operating solenoid valve 42 or a timer for operating solenoid valve 42 at a predetermined time sequence through electrical energy transmitted on wires 41. A source of air 44 travels in line 43 which splits into three lines, 46, 47 and 48 at point 45. When the solenoid valve 42 is energized, this valve starts air motor 50 with air in line 49, which drives gear box 51 by means 52, one example of which is a belt drive. Gear box 51 turns shaft 53 and the attached cams 54 55, 56 and 57 thereon with these cams being designed to operate four different three-way valves, 58, 59, 60 and 61 in a sequence given below. The three-way valve 58 keeps the air motor 50 running through a complete cycle (usually about 60 seconds) by allowing the air in line 47 to drive the air motor 50. The three-way valve 59 opens diaphragm valve 64 to back purge sample line 30 and the porous plate at 36 for about 20 seconds and then closes. A suitable purge gas, such as for example nitrogen, is supplied from a source not shown, through line 66. The three-way air valve 60 applies air under diaphragm 70 which pulls the connected set of stems 16b and 16c away from valve body 10 to allow the process gas to flow through sample port 26 for a period of 30 seconds, and then lets the set of stems 16b and 16c seat upon valve body 10 trapping a sample of process gas in the sample port 26. Then cam 57 operates the three-way valve 61 which allows air from line 71 to operate air-to-open valve 73. As the diaphragm 74 of this valve 73 is depressed, drive shaft 25 is pulled away from valve body 10 which in turn moves crossbar 22 and the associated set of valve stems 16 and 16a so that the tips of the valve stems no longer seal off the channels 28 and 29 (in FIG. 1) in the valve body, but now the carbon sleeves 17 and 17a seal off the passageways 9 and 9' in the valve stems 16 and 16a. When this is completed, the sweep of carrier gas from line 31 enters channel 28 from passageway 11 to flush the process gas in sample port 26 out of the sample port 26, up through channel 29 to the passageway 6 into conduit means 33 leading to analytical instrument 34. In normal practice, this proceeds for about 4 seconds for the flush of the carrier gas to remove the process gas in the sample port. As shaft 53 returns to rest, the air-to-valves 73 and 69 are closed. This leaves both set of stems 16 in contact with the valve body 10.

The valve operation described (i.e., the operation from a position where both sets of valve stems are in contact with the valve body as in FIG. 3 to the FIG. 1 position through FIG. 2 position and returning to a position where both sets of valve stems are in contact with the valve body as in FIG. 3) takes place very rapidly, so that the time during which all four valve stems are not in contact with the valve body is only a very small fraction of time. Thus, the interruption of the flow of sweep gas is only slight and not noticed by the analytical instrument 34. Also, the valve shown in FIGS. 1 through 3 may be enclosed in an insulated box and heated so that the valve body and components are maintained at a desired elevated temperature during sampling.

The sampling valve of this invention is rather simple to manufacture; the only critical machining operations are those for the surfaces involved for channels 11, 8, 6, 7, 26 and 12, the bores 28-28', 29-29', 13, 13a, 13', 13", 14, 14a, 14' and 14" and the tip of the valve stems 16. Channels 8 and 26 are drilled into the valve body 10 from one side with welding or solid screws being used to fill the extra area cut away from the side of the block to the beginning of channels 8 and 26. Also, the air pressure required to operate the valve is very small. The stems in practice are only moved a fraction of an inch (typically one-eighth inch to one-fourth inch), preferably 1/8-inch maximum, when being removed from contact with the valve body or being brought into contact with the valve body. If preferred, channels 11, 12, 6 and 7 may be drilled at a right angle to channels 8 and 26 instead of in a line as shown in FIGS. 1 through 3.

The valve of this invention is very small in size. By way of example, the dimensions from the outer face of the upper gland nut 21 to the outer face of the lower gland nut 21 may be 13 inches ±2 inches; the overall width of the valve body may be 21/4 inches ±1 inch with a depth dimension for the valve body of 21/4 inches ±1 inch. The gas conducting passageways 11, 8, 6, 7, 26 and 12 through the valve body of this invention are made small, as analytical instruments can give very accurate readings on a small volume of sample. However, the size of sample port 26 can be readily varied by using different size drills where larger volume is desired. As a result of the gas conducting paths being so small, any necessary dead space is kept to a very small volume, when compared to the sample volume.

One valve model has successfully sampled process gas from a vapor phase reaction of isophthalonitrile and chlorine for six months without failure. The valve body is made of nickel and the bottom one-half inch of all the valve stems are made of nickel with the packing being a pressed carbon. The temperatures of the process gas brought into the valve range from 300° to 400° C. The process gases analyzed have included the following constituents: chlorine, hydrogen chloride and tetrachloroisophthalonitrile. Examination of the valve parts, when disassembled, has revealed a minimum of corrosion; in fact, the valve was still judged capable of operation for at least a similar period of time before any further replacement of components would be needed.

It is to be understood that although the invention has been described with specific reference to particular embodiments thereof, it is not to be so limited, since changes and alterations therein may be made which are within the full intended scope of this invention as defined by the appended claims.