US3680388A

US3680388A - Sampling of gaseous atmospheres

Info

Publication number: US3680388A
Application number: US867759A
Authority: US
Inventors: Derek Critchley; Frank Dawber; Kenneth Frederick Grainger
Original assignee: Pilkington Brothers Ltd
Current assignee: Pilkington Group Ltd
Priority date: 1968-11-01
Filing date: 1969-10-20
Publication date: 1972-08-01
Anticipated expiration: 1989-08-01
Also published as: GB1275905A; DE1954426A1; FR2022374A1

Abstract

The content of a water-insoluble gas in an atmosphere is analyzed by drawing a sample of the atmosphere into an analyzer by means of a steam ejector pump, the pressure of the steam supply being regulated so that the sample is drawn into the analyzer at a pressure greater than atmospheric pressure.

Description

United States Patent Critchley et al. [45] Aug. 1, 1972 [54] SAMPLING OF GASEOUS 2,987,921 6/1961 Kraftson ..73/42l.5 A ATMOSPHERES 3,106,843 10/1963 Luxl ..73/421.5 A 1 144 718 6/1915 Meier ..417/l72 [72] Inventors. Derek CrItchley, St. Helens, Frank Dawber Uphonand near wigan; 2,041,803 5/1936 Wolff ..417/172 Kenna Frederlck FOREIGN PATENTS OR APPLlCATlONS Helm an ofEngland 516 70s 9/1955 c d 73/421 ana a .5 [73] Asslgnee: Bmhers Llver' 951,467 3/1964 Great Britain ..73/421.5 A

pool, England [22] Filed: Oct. 20, 1969 Primary ExaminerLouis R. Prince Assistant Examiner-Daniel M. Yasich [21] Appl' 867759 AttorneyBurns, Doane, Swecker & Mathis [30] Foreign Application Priority Data [57] ABSTRACT Nov. 1, 1968 Great Britain ..51,863/68 The content of a water-insoluble gas in an atmosphere is analyzed by drawing a sample of the atmosphere [52] U.S. Cl. ..73/42l.5 R into an analyzer by means of a steam ejector pump, [51] Int. Cl. ..G01n l/24 the pressure of the steam supply being regulated so [58] Field of Search.,..73/42l.5 A, 421.5 R; 417/172 that the sample is drawn into the analyzer at a pressure greater than atmospheric pressure. 56 R f C't d 1 e erences l e 14 Claims, 4 Drawing Figures UNITED STATES PATENTS 2,934,958 5/1960 Kingma ..73/421.5 A

SAMPLING OF GASEOUS ATMOSPHERES BACKGROUND OF THE INVENTION 1 Field of the Invention This invention relates to the sampling of gaseous atmospheres, for example, the atmosphere existing in the headspace of a glass melting furnace, and is particularly applicable to the testing of gaseous atmospheres to measure the content of constituents thereof which are insoluble or only slightly soluble in water.

2. Description of the Prior Art It is known to effect gas sampling by inserting a probe into the atmosphere to be sampled and withdrawing a sample of the atmosphere through the probe. Mechanical pumps are conventionally used to withdraw the sample through the probe.

These samples are under negative pressure which can result in atmospheric oxygen being drawn into the sample. Such pumps fail to give satisfactory service in practice where the gas being sampled contains corrosive agents or is at a high temperature. In the particular case of a furnace such as is used in the manufacture of glass, the waste gas temperature may typically be in the region of 1,600 C. and, moreover, corrosive agents tend to be carried-over in the waste gases.

It is a main object of this invention is to provide a gas-sampling probe which is capable of working satisfactorily under such arduous conditions.

SUMMARY The invention provides a method of analyzing an atmosphere in respect of a given gas which is insoluble in water. A sample of atmosphere is drawn into a sampling probe by means of a steam ejector pump, and the pressure of the steam supply is regulated so that entrained atmosphere is at a pressure greater than atmospheric pressure. The content of the gas in the entrained atmosphere is then determined.

A useful application of the invention is to the quantitative sampling of the oxygen content of furnace waste gases, for example the waste gases of an oil-fired furnace, as used in the batch-melting of glass. The oxygen content of the waste gases provides an indication of the combustion conditions in the furnace burners; in an automatically controlled furnace the measured oxygen content of the waste gases, sampled continuously, can be utilized in a closed loop servo-system for controlling combustion in the furnace by controlling the air and/or fuel supply thereto.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagrammatic axial cross-section through a gas-sampling probe according to the invention,

FIG. 2 is an axial cross-section on an enlarged scale of the nozzle block employed in the probe of FIG. 1,

FIG. 3 is a transverse cross-section of the probe on an enlarged scale, taken on line III-Ill in FIG. 1, and

FIG. 4 is a diagrammatic representation of gas analyzing apparatus employing the sampling probe of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, a gas-sampling probe indicated generally at 1 is adapted to be inserted through the wall of a furnace, for example an oil-fired furnace of the kind used for melting the batch for supplying molten glass to glass fiber drawing apparatus into the furnace atmosphere, which atmosphere will in general contain the combustion products of the furnace.

The probe 1 comprises a sampling tube 2 which is closed at its inner end, shown on the left-hand side of FIG. 1, which is to be inserted in the atmosphere to be sampled. Adjacent its inner end the tube 2 is provided with lateral openings 3 (two in number in this example) which communicate with the probe exterior (that is, with the atmosphere to be sampled in use of the probe) through respective laterally extending inlet pipes 4 (FIG. 3).

A steam supply line 5 extends coaxially within the sampling tube 2 and terminates in the region of the lateral openings 3 in a nozzle block 6, shown in further detail in FIGS. 2 and 3. The nozzle block 6 has a generally cylindrical outer surface and fits within the sampling tube 2, the block extending at least partially across the lateral openings 3. The external surface of the nozzle block 6 is recessed with two parallel flat surfaces 7 (FIG. 3) disposed opposite the respective openings 3 to define respective clearances 8 between the nozzle block 6 and the internal surface of the tube 2 at the respective openings 3.

The nozzle block 6 is formed in two parts, comprising a nozzle plate 10 and a cap 11, both made from a heat-and-acid-resistant alloy, for example that known as Incoloy 825. The plate 10 has an axially extending peripheral flange 12 which is internally threaded and which receives an externally threaded part of the cap 11. An annular sealing gasket 14 of copper is interposed between the end surface of the flange l2 and an axially facing surface provided on a flange formed on the cap 1 1.

The steam supply line 5 communicates with a central inlet 15 in the nozzle plate 10. The surface of the cap 11 directly opposite the plate 10 is concave towards the plate 10 and symmetrical about the axis of the inlet 15, so that an internal chamber 16 is defined within the nozzle block 6. The nozzle plate 10 is formed with a plurality of ejector nozzles comprising axially extending bores 17 in the plate 10 arranged in an annular array concentrically surrounding the inlet 15 and communicating with the chamber 16.

The sampling tube 2 is surrounded coaxially by a cooling jacket comprising an outer cylindrical wall 18 and a cylindrical partition 20 interposed between the wall 18 and the tube 2. The inner end of the wall' 18, that is, the end adapted to be inserted in the atmosphere to be sampled, is closed and spaced from the closed inner end of the sampling tube 2, the inner end of the partition 20 being open and spaced from the closed end of the wall 18. Inner and outer

coolant flow passages

21, 22 respectively, of annular cross-section, are thereby defined between the wall 18, the partition 20 and the outer surface of the tube 2, the two inlet pipes 4 extending through the

passages

21, 22 and projecting a short distance outwardly of the outer surface of the wall 18.

The respective

coolant flow passages

21, 22 are closed at their outer ends and communicate with laterally extending coolant outlet and

inlet pipes

23, 24 respectively. Similarly, the sampling tube 2 communicates at its outer end with a lateral sample supply conduit 25.

In operation, the probe 1 is inserted into a furnace atmosphere to be sampled through a suitable seal in the furnace wall 26a, shown diagrammatically in FIG. 4, so that the lateral inlet pipes 4 are disposed in the said atmosphere while the various connections to the probe 1 are disposed outwardly of the furnace wall 26a.

Steam is supplied to the steam supply line 5, enters the chamber 16 of the nozzle block 6 and emerges as a plurality of jets directed axially towards the outer-end of the sampling tube 2 through the bores 17 of the nozzle plate 10. The reversal of the direction of steam flow in the chamber 16 is assisted by the concave internal surface of the cap 11. The ejector effect of the steam jets causes a pressure reduction at the lateral openings 3 adjacent the nozzle block 6, and in consequence gas is withdrawn from the furnace atmosphere through the inlet pipes 4 and the lateral openings 3.

The steam, mixed with the sampled gas, passes outwardly along the sampling tube 2 and into the sample supply conduit 25. The conduit 25, which includes a shut-off valve 26, passes the steam and gas mixture into a condenser 27 where the mixture comes into contact with pipes through which cooling water is circulated. The steam is condensed in the condenser 27, and is removed as water, together with any entrained solid particles, through a drain outlet 28.

The gas sample, after removal of the steam therefrom in the condenser 27, is passed through a filter device 30 to remove solid particles from the gas. The filter device 30 conveniently comprises two filters of the PALL type connected in respective parallel flow lines, so that either filter can be replaced, after shutting off flow through the respective flow line, without disrupting the gas flow through the filter device 30 as a whole.

After passing through the filter device 30 the gas sample passes through a flow-meter 31 to an analyzer 32, in which the content of a particular gaseous waterinsoluble constituent in this case oxygen is measured continuously. Any convenient known type of analyzer may be used. By measuring the oxygen content of the furnace waste gases the combustion conditions of the furnace burners can be deduced. Moreover, the analyzer 32 may be operatively associated with a closed loop servo-system for controlling the fuel-air ratio of the furnace burners so as to control the burners automatically and maintain a predetermined oxygen content in the furnace waste gases.

It is important that the steam supplied to the steam supply line should be dry and free from impurities. The steam supply line therefore preferably includes filters 33 and a steam/water separator or drier 34 of the SPYRAX (Registered Trade Mark) type.

During the operation of the probe coolant fluid, conveniently water, is circulated in the cooling jacket. In the illustrated example the coolant is supplied through the inlet pipe 24, passes outwardly through the outer flow passage 22, returning through the inner flow passage 21 and the outlet pipe 23. This direction of circulation of coolant is preferred in practice where the furnace waste-gas temperature is of the order of 1,600 C. of higher.

Because of the high working temperature of the probe the exposed parts thereof, particularly the cooling jacket wall 18, are made of a temperature-resistant alloy, preferably immaculate 5T stainless steel. Parts which are also exposed in operation to steam and furnace waste gas condensate at high temperature are fabricated in an acid-resistant alloy such as that known as lncoloy 825: such parts include the nozzle block 6, the steam supply line 5 (at least the inner end thereof) and the sampling tube 2.

In operation of the probe 1 corrosive (acidic) products tend to condense on the exposed surfaces of the probe and would in the course of time obstruct and corrode the inlet pipes 4 and lateral openings 3. To prevent undesirable accretions on these parts, the shutoff valve 26 is periodically closed for brief periods, for example for a few minutes every 24 hours. This has the effect of blocking the steam and gas outlet from the probe 1, and causes steam to be blown from the nozzle block 6 through the openings 3 andthe pipes 4, clearing out any accretions in the latter. The valve 26 may be manually operated, but alternatively may be operated by a conventional timer-operated solenoid 35 to be closed automatically for a predetermined time interval at pre-set intervals.

Further with a view to reducing the accumulation of condensates on the probe 1, the latter is preferably mounted so that it extends into the furnace with an upward inclination, for example at about 15". to the horizontal, as shown in FIG. 4.

We claim:

1. A gas-sampling probe comprising a sampling tube having a closed inner end for insertion in an atmosphere to be sampled, the tube being formed with lateral openings near said closed inner end for communication with the atmosphere, a steam supply line extending axially within said sampling tube, a nozzle block within the sampling tube and at least partly disposed opposite said lateral openings, which nozzle block comprises a nozzle plate fitted on the steam supply line and formed with a plurality of ejector nozzles spaced in an annular array surrounding the steam supply line, and a cap fixed to the nozzle plate and defining therewith an internal chamber communicating with the steam supply line and with said annular array of nozzles, the external surface of the nozzle block opposite each said lateral opening being recessed to provide a clearance between the nozzle block and the internal surface of the sampling tube at each said lateral opening.

2. A probe according to claim 1, wherein the cap has an internal concave surface facing the nozzle plate.

3. A probe according to claim 1, including a filter and a drier through which steam is supplied to the steam supply line, so that steam supplied is substantially free of particles and water.

4. A probe according to claim 1, including a shut-off valve communicating with said sampling tube for shutting off the flow of steam and entrained gas through the tube.

5. A probe according to claim 4, including means for closing said shut-off valve automatically for predetermined intervals of time at separated times during operation of the probe.

8. A method of sampling an atmosphere comprising the steps of:

positioning a closed-end portion of a sampling tube within the atmosphere;

supplying a flow of steam toward said closed end through a steam line positioned within said sampling tube; causing the flow of steam to exit said steam line and enter said sampling tube in a direction away from said closed end by a reversing nozzle block positioned at the end of said steam line in the range of at least one lateral opening in said sampling tube;

causing the flow of steam directed away from said closed end to create a pressure reduction at said at least one lateral opening to draw atmosphere into said sampling tube; and

blocking-off fluid flow from an outlet end portion of said sampling tube while continuing to supply steam through said steam line, to cause steam to exit through said at least one lateral opening to clear out accretions of corrosive products tending to obstruct and corrode said at least one lateral opening.

7. The method according to claim 6 and further including the step of:

circulating cooling water entirely around the portion of the sampling tube positioned within the atmosphere.

8. A gas-sampling probe comprising:

a sampling tube having a closed inner end, at least the closed-end portion of said tube being adapted to be inserted in an atmosphere to be sampled, the tube being formed with at least one lateral opening near said inner end for communication with said atmosphere; steam supply line extending into said tube and being directed toward said closed inner end from within said tube, said steam supply line terminating in the region of said lateral opening; and a reverse-steam ejection nozzle block positioned at the end of said steam line in the region of said at least one lateral opening, said nozzle block having at least one steam ejector nozzle communicating with said steam line and being directed into said tube away from said inner end in a direction generally parallel to and opposite the direction of steam flow through said steam line; said at least one lateral opening being positioned adjacent the outlet portion of said at least one nozzle such that steam ejected from said at least one nozzle causes a pressure reduction at said at least one lateral opening to draw atmosphere into the sampling tube.

9. A probe according to claim 8 wherein the portion of said sampling tube positioned in said atmosphere has a substantially constant cross-section throughout its length. v

10. A probe according to claim 9 wherein a cooling jacket is provided completely surrounding the portion of the sampling tube located within the atmosphere, the cooling jacket having a substantially constant annular cross-section throughout the length thereof positioned within the atmosphere; and an atmosphere inlet pipe is provided extending through the jacket from said lateral opening.

11. A probe according to claim 8, comprising a cooling jacket surrounding the tube and having an inlet and an outlet or coolant flu'd spaced from said inner end of the samp ing tube, an an atmosphere in et pipe extending through the jacket from said lateral opening.

12. A probe according to claim 11, wherein the cooling jacket comprises two coaxial tubular walls defining inner and outer passages of annular cross-section, said passages communicating with each other at the inner end of the sampling tube, and respective coolant fluid connections communicating with the inner and outer passages remotely from said inner end.

13. A probe according to claim 8, wherein the nozzle block is formed with an internal chamber communicating centrally with the steam supply line, and includes a nozzle plate constituting one wall of the chamber and formed with a plurality of ejector nozzles spaced apart in an annular array surrounding the steam supply line, which nozzles communicate with the internal chamber.

14. A probe according to claim 13, the nozzle block is formed with an internal concave end wall facing the nozzle plate.

Claims

7. The method according to claim 6 and further including the step of: circulating cooling water entirely around the portion of the sampling tube positioned within the atmosphere.

8. A gas-sampling probe comprising: a sampling tube having a closed inner end, at least the closed-end portion of said tube being adapted to be inserted in an atmosphere to be sampled, the tube being formed with at least one lateral opening near said inner end for communication with said atmosphere; a steam supply line extending into said tube and being directed toward said closed inner end from within said tube, said steam supply line terminating in the region of said lateral opening; and a reverse-steam ejection nozzle block positioned at the end of said steam line in the region of said at least one lateral opening, said nozzle block having at least one steam ejector nozzle communicating with said steam line and being directed into said tube away from said inner end in a direction generally parallel to and opposite the direction of steam flow through said steam line; said at least one lateral openIng being positioned adjacent the outlet portion of said at least one nozzle such that steam ejected from said at least one nozzle causes a pressure reduction at said at least one lateral opening to draw atmosphere into the sampling tube.

8. A method of sampling an atmosphere comprising the steps of: positioning a closed-end portion of a sampling tube within the atmosphere; supplying a flow of steam toward said closed end through a steam line positioned within said sampling tube; causing the flow of steam to exit said steam line and enter said sampling tube in a direction away from said closed end by a reversing nozzle block positioned at the end of said steam line in the range of at least one lateral opening in said sampling tube; causing the flow of steam directed away from said closed end to create a pressure reduction at said at least one lateral opening to draw atmosphere into said sampling tube; and blocking-off fluid flow from an outlet end portion of said sampling tube while continuing to supply steam through said steam line, to cause steam to exit through said at least one lateral opening to clear out accretions of corrosive products tending to obstruct and corrode said at least one lateral opening.

9. A probe according to claim 8 wherein the portion of said sampling tube positioned in said atmosphere has a substantially constant cross-section throughout its length.

11. A probe according to claim 8, comprising a cooling jacket surrounding the tube and having an inlet and an outlet for coolant fluid spaced from said inner end of the sampling tube, and an atmosphere inlet pipe extending through the jacket from said lateral opening.