US 3357256 A
Description (OCR text may contain errors)
R. J. BURCH 3,357,256
SAMPLING LINE FOR CRYOGBNIC LIQUID MIXTURES Dec. 12, 1967 INVENTOR ROBERT J. BURCH ATTORNEY United States Patent 3,357,256 SAMPLHNG LINE FQR CRYOGENIC LIQUID MIXTURE Robert J. Burch, Chatham, N.J., assignor to Air Reduction Company, Incorporated, New York, N.Y., a corporation of New York Filed Aug. 16, 1965, Ser. No. 486,073 5 Claims. (Cl. 73421) This invention relates to an arrangement for sampling liquefied gas, and more particularly to a sampling line constructed and arranged to effect removal of a true sample of a cryogenic liquid mixture from a vessel over the full range of temperatures and pressures encountered in cryogenic work.
Various arrangements have heretofore been proposed for Withdrawing a sample of a liquefied gas from a container for the purpose of determining the composition thereof by analyses. In general, such arrangements comprise withdrawing fluid from the container, through a tube, and passing such fluid into an evaporator through a throttling valve. However, in prior arrangements of this type, an uncontrolled evaporation of the fluid occurs in the tube ahead of the throttling valve. Hence, gas and liquid flow alternatingly and intermittently through the valve, whereby the sample ultimately received by the analysis apparatus is not identical with the composition of the liquid contained in the vessel from which the sample has been taken.
One prior arrangement directed to the provision of a vaporized sample having the same composition as the liquid in the vessel, comprises a capillary tube passing through a wall of the vessel, which tube extends outwardly of the wall for a short distance and terminates in a heated evaporator. The stream of liquid is completely vaporized within the heated evaporator and the vapor is caused to flow into a vaporization chamber. However, this arrangement does not always yield a true sample of a liquefied gas mixture since there is no assurance that vaporization of the liquefied gas does not occur in the capillary tube, particularly in that portion which protrudes into the vaporization chamber, which can give rise to backfiow of the gas and liquid into the vessel. Further, the requirement that the capillary tube extend outwardly of the vessel for only a short distance, minimizes the usefulness of such arrangement, since it is not often feasible to mount the vaporization chamber close to the wall of the vessel containing the liquefied gas.
An object of this invention is the provision of an improved sampling line for obtaining a true sample of a liquefied gas mixture for purpose of analyses.
An object of this invention is the provision of a sampling line to effect removal of a true sample of a liquefied gas mixture from a vessel over the full range of temperatures and pressures encountered in cryogenic work and for most vessel designs and modes of operation.
An object of this invention is the provision of a sampling line for withdrawing and vaporizing a sample of a cryogenic liquid mixture from a vessel, which arrangement is constructed and arranged to minimize vaporization of liquid in the sampling line, to prevent backfiow of any gas which may result from incipient vaporization of the liquid, to revent backfiow of any liquid from which gas has been vaporized, to remove small, undissolved particles from the sample stream, and to prevent precipitation of low boiling point components during the vaporization of the mixture.
An object of this invention is the provision of an arrangement for effecting removal of a true sample of a cryogenic fluid from a vessel, which arrangement comprises a capillary tube having an end extending into the liquid and the other end terminating in a minute orifice extending into a vaporization chamber, means refrigerat- 3,357,256 Patented Dec. 12, 1967 ing the portion of the capillary tube external of the vessel, means increasing the linear velocity of the fluid after it enters the capillary tube, and means to further increase the linear velocity of the fluid over the length of the capillary tube where the temperature changes from the refrigerated value to the temperature of the vaporization chamber.
These and other objects and advantages will become apparent from the following description when taken with the accompanying drawing. It will be understood, however, that the drawing is for purposes of illustration and is not to be construed as defining the scope or limits of the invention, reference being had for the latter purpose to the claims appended hereto.
Reference now is made to the single figure of the draw ing which is a diagrammatic illustration of apparatus made in accordance with this invention. The reference numeral 1! identifies the wall of a vessel containing a liquefied gas mixture 11. A capillary tube 12, made of stainless steel, and having an internal diameter of approximately 1.18 mm., extends through an opening formed in the wall of the vessel and passes through a larger tube 13. The capil lary tube may have any length required for the removal of the sample. One end of the capillary tube is enlarged and formed into a helical coil 14 disposed in the liquid mixture. The other end of the capillary tube has connected thereto a hypodermic tube 15, which extends into a vaporization chamber 16 provided with a flow control valve 17. The hypodermic tube also is made of stainless steel and has an internal diameter of approximately 0.2 mm. Disposed between the end of the larger tube 13 and the chamber 16 is a thermal barrier 18, which barrier may be a suitable, solid heat-insulating material or a vacuum space. The hypodermic tube passes through the thermal barrier.
A portion of the capillary tube 12 is flattened, as indicated by the numeral 19, such flattened portion and the contiguous unflattened tube portions being enclosed within a rod 20 made of a metal having a good thermal conductivity. During use of the sampling line, a refrigerant, in liquid or vapor form, is pumped through the tube 13, said tube being provided with openings 21 for exit of the refrigerant. Thus, the portion of the sampling line which is external of the vessel 10 is refrigerated up to the point where the hypodermic tube 15 passes through the thermal barrier 18.
The helical coil 14,
which is immersed in the liquefied gas 11, allows a liquid sample to be withdrawn while the sample is refrigerated at the exact temperature of the liquefied gas 11, and without a pressure drop, so that there is no vaporization of the liquid components within the coil. A porous plug inserted into a somewhat enlarged line may be used in place of the helical coil, but the latter is simpler to construct and install.
The refrigeration of the capillary tube 12 to a temperature sli htly below the temperature of the liquid 11 insures that only liquid will be present throughout the length of this tube. This is particularly important since the sampling line must handle varied combinations of liquefied mixtures, such as solids in liquids, liquids in liquids and gases in liquids. Refrigeration may be effected by using pumped liquid nitrogen, or cold nitrogen gas. Also, refrigeration may be effected by using the liquefied gas 11 when a throttling valve is used in place of the exit holes 21, or by using the larger tube 13 as a vapor sampling line.
The rod 20 provides a means for smoothing out tem-- perature oscillations due to uneven flow of the refrigerant, which is particularly important for gas-liquid refrigerants. The flattened portion of the sampling line increases the linear velocity of the liquid mixture after it has passed well into the sampling line, inhibits the backflow of any gas which may result from incipient vaporization of the liquid and, further, serves to remove small, undissolved particles.
The hypodermic tube, passing through the thermal barrier, further increases the linear liquid velocity thereby to prevent vaporization of the sample over the critical length Where the temperature changes from that of the refrigerant to that of the vaporization chamber and, also, prevents precipitation of those dissolved components of the liquefied gas mixture having a high boiling point. Further, such high linear velocity of the fluid through the hypodermic tube provides for a visual indication, by means of a flow meter and pressure drop, that the sampling line is, indeed, filled with the liquid mixture at all times during the sampling period.
A sampling line made in accordance with this invention is particularly adapted for use with cryogenic liquid mixtures, for example, mixtures of solid krypton and liquid oxygen, and mixtures of neon and helium gases in liquid nitrogen, and functions to provide a true sample of the particular mixture for purposes of analysis.
Having now described the invention, those skilled in this art will be able to make various changes and modifications without thereby departing from the spirit and scope of the invention as recited in the following claims.
1. A sampling line for a liquefied gas mixture contained within a vessel, comprising,
(a) means forming a refrigerated zone external of the vessel,
(b) means forming a flow path for the flow of liquid from the vessel through said refrigerated zone and into a vaporization zone,
(c) means to increase the linear velocity of the liquid within said refrigerated zone, and
(d) means forming a thermal barrier between the refrigerated and vaporization zones.
2. The invention as recited in claim 1, including means to further increase the linear velocity of the liquid just before and as it exits from said refrigerated zone through the thermal barrier.
3. In an arrangement for obtaining a sample of a liquefied gas mixture contained within a vessel, the combination of,
(a) a tube extending through a wall of the vessel, said tube having one end disposed in the liquid within 5 the vessel and the other end connected to a hypodermic tube of reduced cross-sectional area,
(b) means to increase the linear velocity of the liquid in said tube prior to passage thereof to the said hypodermic tube, and
(c) means refrigerating the entire length of the tube within which the linear velocity of the liquid is increased.
4. A sampling arrangement for a cryogenic liquid mixture contained within a vessel, said arrangement comp (a) a first tube passing through a wall of the vessel and having an inner end disposed in the contained liquid, said tube having a flattened intermediate portion external of the vessel,
(b) a vaporization chamber,
(c) a second tube spaced from and surrounding the external portion of the said first tube,
(d) a thermal barrier zone between the said second tube and the vaporization chamber,
(e) a hypodermic tube connected to the other end of the said first tube, said hypodermic tube passing through the said thermal barrier zone and extending into the vaporization chamber, and
(f) a refrigerant fiowing through the said second tube.
5. The invention as recited in claim 4, including a member surrounding and in contact with the said flattened portion of said first tube, said member being made of a metal having a good thermal conductivity.
728,134 11/1942 Germany.
LOUIS R. PRINCE, Primary Examiner.
S. C. SWISHER, Assistant Examiner.