DE2040593A1 - FLUID SAMPLING DEVICE - Google Patents

Description

PATENT Attorney *
t I 1 (
t MUNICH 2
VAL 33
TEL. 0311/228894
235051
CABLES: THOPATENT
TELEX: FOLQT Dipi.-chem. Dr. D. ThotTisen Dipi.-mg. H. Tiedtke
Dipi.-chem. G. Bühüng FRANKFURT (MAIN) 50
FUCHSHOHL 71
TEL. 0611 / H «M Dipi.-mg. W. Weinkauff

Reply requested to: Please reply to:

8000 Munich 2 August 14, 1970 T 3790 - case AE&CI 228

African Explosives and Chemical Industries Limited Johannesburg, South Africa

Device for pluid sampling

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The invention relates to a device for sampling from a fluid or fluid, for Example dust or droplet-laden exhaust gases from chemical or industrial plants, and in particular to a isokinetic sampling probe for taking samples from these Oases.

Sampling probes for the determination of the dust O or mist or droplet content of chimney gases often produce or are unreliable

difficult to handle and a hindrance in terms of air pollution legislation in many Countries routine analyzes of waste gases, analyzes carried out with regard to these legal provisions have to. It is therefore important that the device be simple in structure and easy to use.

The previous device for sampling waste gases has a sampling probe with a shaped Nozzle that is inserted into the gas stream to be examined. The gas is pumped through with the help of a vacuum or suction pump the probe and a sampling kit drawn from a Filter, a cyclone separator or electrostatic separator, a subsequent condenser, a collecting pot and a Rotarneter.

The particulate matter is retained in the filter, while water vapor, if any, is retained in the filter condenses in the condenser.

The gas sample must be collected under isokinetic conditions, i.e. the speed of the in the The gas entering the probe must be equal to the speed of the gas flow from which the sample is taken, otherwise the sample is not truly representative of the effluent gas stream. To ensure these conditions, the speed of the gas flow must be monitored continuously and in the case of

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Deviations the sampling rate can be adjusted accordingly. This is usually done by using pitot tubes, the readings obtained with the aid of the device enclosed slide rules or homograms in speeds being transformed. At the end of the sampling period, the weight of particulate matter collected in the filter becomes determined and based on the volume of the gas taken as a sample, the impurity concentration in the chimney gas to investigate.

An improved device for fluid sampling uses a so-called "zero point probe", ie a probe which has a specially designed nozzle through which the static pressures inside and outside the nozzle can be measured by means of holes ₅ in the inner and outer walls of the nozzle assembly. If the pressures on the inside and outside are kept the same, isokinetic conditions are achieved. The use of these nozzles eliminates the need to individually measure the velocity of the gas flow and the sampling rate. Nevertheless, it was found that the static pressures measured via the feeler holes on the inside and outside of the nozzle are influenced by the nozzle shape. The shape or form of the nozzle causes turbulent flows and eddy formations on the outside as well as a pressure loss on the inside of the nozzle. As a result, erroneous results will be obtained using these nozzles.

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Another disadvantage is that these nozzles are not readily interchangeable, so that at high or low gas velocities the sampling rates either are very high or extremely low.

The aim of the invention is therefore to create a zero point sampling probe that essentially or entirely does Difficulties as they occur in the prior art eliminated.

It was found that the undesirable influences which, because of the shape of the nozzle, the static pressures are disadvantageous affect, can be avoided by keeping the static pressures on the outside and at the inlet of the nozzle determined. This is achieved by using a double tube that has two concentric tubes or tubes that have an axial bore and provide an annular channel surrounding the wall of the bore. This new feature is used as part of a zero point probe, which is called the "double metatic tube".

Accordingly, an apparatus for sampling a fluid stream in a conduit is provided which has a sampling probe and a double static tube that sits axially within the nozzle and extends over the nozzle opening extends out and ends in a closed, aerodynamically shaped end, the outer wall of the elongated

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Cut the pipe with first and second openings is that with the bore or the annular channel of the pipe in connection stand, while the opposite end of the bore and the annular channel of the pipe at a distance from the elongated Section connected to a push button device to the static pressure of the fluid flow outside the nozzle and the static pressure of the fluid stream entering the nozzle mouth to feel.

The first holes or openings of the double static pipe for determining the pressure outside the nozzle are advantageous at a distance of at least 13 pipe diameters of located at the streamlined end of the tube to avoid any turbulence or eddy formations within the fluid or fluid to avoid that could be formed at the end of the pipe when flowing past.

The second openings or holes for detecting the pressure of the fluid stream entering the nozzle advantageously on or near the outside of the plane of the mouth the nozzle. This position is used to avoid a pressure drop within the nozzle. In addition, these second openings are at a distance of at least 21 pipe diameters from the streamlined end of the pipe to avoid possible mutual Avoid interference as a result of the first openings.

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The push button openings in the tube have a diameter which is advantageously no more than one tenth of the outer diameter of the tube.

The nozzle forming part of the probe can be replaced without difficulty as the pushbutton devices are not in the body of the nozzle.

The invention is illustrated in the following with the aid of a schematic Drawings explained in more detail using an exemplary embodiment.

Pig. 1 is a cross section through a sampling

probe according to the invention; ■

i FIG. 2 shows an enlarged scale in cross section _;

the double tatikrohi that forms part of the ■ probe.

According to FIG. 1, the sampling probe 1 has a detachable nozzle 2 and a double static tube 3. The first push-button openings

k and the second push button openings 5 in the central channel j

of the extended section of the double static rotary 3 surrounding Wall stand with a push button device (not shown) above j a line arrangement 6 and pipes 7 in connection. :

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ORIGINAL INSPECTED

The Pig. 2 shows in detail the structure of the double static tube 3 and illustrates the position of the push button openings ί * and 5 in relation to the streamlined end 9 of the tube. The front section 8 of the tube can be made of solid material be.

The device is used in conjunction with a standard ',

• ι filter, a cyclone separator or electrostatic separator

and a suction pump used. Any sensitive tactile device can be used for measuring the pressure difference between the first and second tactile openings are used.

The size of the nozzle used depends on the speed of the QasB stream and is advantageously chosen so that that it provides a sampling flow rate between 5 and 6 cubic meters per hour under isokinetic conditions, so | that the sampling periods for the collection of a representative the sample should be between 5 and 10 minutes.

If water vapor is present in the gas flow, it can condense in cold parts of the sampling probe and J. a heated jacket 10 can be placed around these parts,

to prevent this condensation. i

The probe was 'acquisition speeds in the range of 5 to 25 meters per second tested in a test run with sample' and were used to cover this range four

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^0WG '^, _NSPecreo

DUsen dimensions used.

The sampling flow rate was measured on an accurate rotameter, the difference between this like its flow rate and that from the speed and the DU area calculated flow rate is the sampling error.

The results of this test are given in Table I.

Table I.

Sampling sampling

correctness of nozzle Mr. rate m ³ / h error %

5.0 22 6.3 0

7.5 16. 5.3 O

10.0 16 6.3 2

12.5 13 5.3 2

15.0 13 6.3 2

17.5 · 10 3.8 1

20.0 10 H, k 1

22.5 10 5.2 1

25.0 10 5.5 1

The accuracy of the device according to the invention is higher than that of the currently available known devices.

One advantage of the device according to the invention lies in interchangeable nozzles, a further advantage being that the device is suitable for routine sampling of waste gases can be used by unskilled operators.

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Claims (6)

Claims 1.) Device for taking samples from a fluid stream in a line, characterized by a sampling probe (1) with an aerodynamically shaped nozzle (2) and a double static tube (3), which lies axially inside the nozzle and extends beyond the nozzle mouth and in a closed, aerodynamically shaped end ends with the outer wall of the elongated section of the tube with first and second Openings (4,5) is provided with the bore and the annular channel of the pipe are connected, which are spaced or ent-. remotely connected from the extended portion to a pushbutton device with which the static pressure of the fluid flow; outside the nozzle and the static pressure in the nozzle mouth ■ entering positive flow is detectable. 2. Apparatus according to claim 1, characterized in that j that the first openings (4) for determining the static j Pressure outside the nozzle at a distance of at least 13 _; Rdhrdurc hnessern are arranged from the end of the tube. 109809/1840 - ίο - 3. Apparatus according to claim 1 or 2, characterized in that the second openings (5) for determining the static pressure inside the nozzle in the plane of the nozzle mouth or near this plane but outside the nozzle and in are arranged at a distance of at least 21 pipe diameters from the pipe end. t \. Apparatus according to any one of the preceding claims, characterized in that each of the push button openings in the tube has a diameter no more than one tenth the outer diameter of the tube. 5. Device according to one of the preceding claims, · characterized in that the nozzle (2) of the probe (1) is detachable j connected and with other nozzles of different dimensions gen and shape is interchangeable. | 6. A method for the production of isokinetic states in the fluid sampling with the aid of a probe provided with a nozzle, characterized in that the static Measures the pressure outside and at the inlet of the nozzle. 109809/1840 Blank page