GB2288344A

GB2288344A - Dust Sampling Device

Info

Publication number: GB2288344A
Application number: GB9507413A
Authority: GB
Inventors: Horst Bytel; Juergen Keitel; Heinrich Thuermer; Dieter Beckmann; Lothar Juenemann; Karl-Heinz Sauermann; Elmar Hahne
Original assignee: Institut fuer Bioprozess und Analysenmesstechnik eV
Current assignee: Institut fuer Bioprozess und Analysenmesstechnik eV
Priority date: 1994-04-15
Filing date: 1995-04-10
Publication date: 1995-10-18
Anticipated expiration: 2015-04-10
Also published as: FR2718847B1; FR2718847A1; GB2288344B; DE4413525A1; DE4413525C2; GB9507413D0

Description

Dust sampling device 2288344 The invention relates to a dust sampling

device using an electrically polarized fleece filter and a suction unit.

is For evaluating the dust situation in the environment, more particularly in the work environment it is known to use appliances which produce specimens and appliances which give direct indications or registrations.

In the case of appliances producing specimens, a certain amount of sample air is drawn in and the dust separated off in filters. The dust specimen is then evaluated by various different weighing techniques, by counting, photometry or by various different chemical or crystallographic analysis methods. These appliances make it possible to provide evidence on the concentration of the dust particles in the air (mg/in) fractionated according to particle size and on the chemical-crystallographic composition of the dust.

Devices are also known which work on the two-phase gravimetric process. Thus from DD-PS 89 496 a device is known for removing samples of suspended substances from gases for the purpose of subsequently determining the concentration of suspended substances and the material composition of the suspended particles. This device is fitted with two filters and a suction assembly. With this device the coarse particles are first separated off in a cyclone as a preliminary separator with a defined separation characteristic. The air is then sucked in through a fine dust filter in which the fine particle fractions are separated of f. This filter consists of an electrically polarized coarse fibre fleece.

With the device according to DD-PS 89 496 owing. to the:

P1524. P3 6 April 1995 substantially constant filter resistances the through-flow measurement and regulation is dispensed with which in unfavourable cases can be connected with greater deviations from the ideal value of the through- flow. Also with other known devices known up until now with ventilators as aspirators the demand for keeping the operating volume stream constant is not met.

The known devices have the drawback that they do not carry out the currently demanded 3-phase particle size fractionating according to DIN-EN 481 which allows a physiologically better differentiation of the dust deposition in the breathing tract.

With the arrangements known up until now flywheel anemometers, hot wire or hot ball anemometers, nominal diaphragms or Venturi nozzles are used as the f low meter which in the actual sense represent mass flow sensors.

Under normal conditions, ie with only a slight deviation of the room temperature and air pressure from the normal conditions which lead to no significant change in the air density, a proportionality is provided between the mass and volume flow. The volume flow is the pre-requirement for the representative imitation of the human breathing tract.

Under actual conditions of use the normal conditions do not prevail, ie during use underground there are considerable other pressures or in the ceramic and metal-producing industries there are considerable temperature deviations.

Therefore when measuring this mass flow it is necessary to carry out temperature and pressure compensation with corresponding sensor systems in order to produce a volume flow measurement in relation to the operating volume.

The object of the invention is to provide a dust sampling device which has a three-phase particle size separation P1524. P3 6 Anril 1995 is according to DIN-EN 481 which under real conditions of use requires no expensive regulation for keeping the operating volume f low constant, which is characterized by a small structural volume and which in the event of breakdown in its pneumatic circuit is automatically switched off.

According to the invention, there is provided a dust sampling device using an electrically polarized fleece filter and a suction unit characterised in that three separating phases are provided wherein two centrifugal force separators are provided in front of the electrically polarized fleece filter and that one device for the volume f low measurement is provided on the principle of the Karman vortex path.

A dust sampling device using an electrically polarized fleece filter and suction unit has according to the invention three separation phases wherein two centrifugal f orce separators are mounted in f ront of the electrically polarized fleece filter and there is in addition a device for the volume flow measurement (operating volume) working on the principle of the Karman vortex path. Furthermore regulation is provided to achieve a constant volume flow.

With this arrangement a three-phase separation is achieved which comes extremely close to the required separation characteristic. This provides a separation into three particle size fractions corresponding to the place of their deposit in the human body. The separation of the coarsest dust fraction (nasopharyngeal fraction) is carried out in the said first centrifugal force separation, the separation of the medium fraction (bronchial fraction) is carried out in the second centrifugal force separation and the separation of the fine dust fraction (alveolar fraction) is carried out in the electrically polarized coarse fibre P1524. P3 6 April 1995 - 4 fleece filter.

is By applying the principle of the Karman vortex path direct measurement of the operating volume flow is possible. As opposed to the previously known indirect volume flow measurement through proportionality to the mass flow it is no longer necessary to correct density deviations which are caused by temperature or pressure deviations, ie the expensive compensation of the temperature and pressure influences is eliminated. Good processable digital signals are produced, and the measurement of the volume flow only requires simple mechanics.

The dust masses detected with this device are related to the evaluated operating volume for proper determination of the gravimetric dust concentration. This operating volume is produced from the product of the volume flow and the operating time. The regulated volume flow (operating volume) which is necessary for obtaining the operating volume makes it necessary to use a sensor which evaluates the operating volume.

A lamellar separator is provided as the f irst centrifugal force separator and a cyclone as the second centrifugal force separator. The lamellae of the lamellar separator are preferably mounted in a curved flow channel. The curvature of the lamellae runs according to the curvature of the flow channel.

The air which is obtained through suction into the opening of the lamellar separator receives as a result of its curved flow channels a radial component of movement which leads to inertia-conditioned collision of the dust particles of the predetermined fraction.

P1524. P2 6 April 1995 71 The lamellae should preferably be wetted with a medium which allows the separated dust particles to stick, eg with silicon oil.

The separation is carried out with the same characteristics as with a plate elutriator of specific geometry. The separating behaviour is determined through the channel width between the lamellae, the f low speed and the amount of directional change.

is In order to produce the f low guide in the cyclone it is further expedient to attach a pseudo immersion pipe in the area of the inlet opening. It is advisable to f it the immersion pipe in the bottom of the cyclone in order to be able to arrange the separating units one after the other in the direction of the suction intake unit. The housing of the adjoining fine dust filter which normally has the shape of a flat cylinder, is coupled to the immersion pipe of thecyclone so that the air flows in tangentially and thus flows through the filter evenly distributed over the circumference of the fine dust filter ring.

To measure the volume flow a disruptive body is provided in the suction intake channel in front of the suction unit and in front of a measuring unit which detects the vortices released at the disruptive body. The measuring device for detecting the vortex can be for example a measuring device for counting the released vortex and/or for measuring the vortex frequency. An ultrasound measuring device can be provided as the measuring device for the vortex frequency.

In order to achieve a compact structural shape it is advisable if the lamellar separator, the cyclone and the fine dust filter are mounted in a first apparatus part from which they can be readily removed after the sampling. A P1524. P3 6 AiDril 1995 high voltage module for the filter is provided in the remaining free space between these structural groups. By positioning the high voltage module in the filter head it is possible to eliminate the danger through damage to the pipes.

The lamellar separator, cyclone and filter are mounted easily replaceable in the housing and can be formed independently of each other f or transport of the specimen and as weighing container.

According to the invention the two preliminary separator phases and the housing of the filter as well as the additional cover of the high voltage module which originally serves to protect this module against the ef f ects of dust are equally designed as a Faraday cage which protects the support of the apparatus against the damaging ef f ects of the high voltage.

For a compact structural f orm it is further expedient to mount the electronic structural groups required for operating the dust sampling apparatus in a second apparatus part which also contains the suction assembly. When using a radial ventilator with an associated suction intake pipe it is expedient if the conductor plates for the electronic elements are mounted around the suction intake pipe wherein the electronic structural elements of each two conductor plates lie opposite one another.

A micro processor undertakes the regulation of the volume flow through frequency or impulsewidth modulated excitation of the motor by means of a setting member.

To detect the breakdown levels in the pneumatic circuit of the test sampling apparatus, eg by bending or tearing the P1524.P3 6 April 1995 k hose connection between f ilter head and suction unit a threshold switch is provided for detecting the motor voltage as a measure for the permissible speed range which operates a main switch through a micro processor. Through this the apparatus is switched off in the case of a breakdown.

The invention will now be explained in an embodiment illustrated with reference to the drawings in which:

Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 is a diagrammatic view of the structure of the dust sampling apparatus according to the invention; is a sectional view through the centrifugal force separator according to Figure 1; is a sectional view through the suction assembly; is a sectional view through the apparatus for the volume flow measurement; is a sectional view turned 90 degs. relative to the sectional view of Figure 4 through the apparatus for the volume flow measurement; and is a block circuit diagram of a circuit for switching off the dust sampling apparatus in the event of breakdown in the pneumatic circuit.

With the dust sampling apparatus according to the invention the dustcharged air is sucked in through a suction intake pipe 1 and first passes into a lamellar separator 2 in which a first dust separation is carried out. In this first phase dust of the particle size of 100 = to 10an which settles in the human body in the nose and throat is separated. The separation takes place on the lamellae, two of which, 15,16 are shown, which are provided in a curve of the lamellar separator 2. The sucked-in air receives in the curve a radial component of movement which causes collision of the dust parts of the said particle size.

P1524. P3 6 April 1995 1 is From the lamellar separator 2 the air passes tangentially into a cyclone 3 in which a second dust fraction is separated off as a result of centrifugal forces. Here dust of the particle size of 10 pm to 4 an is separated off, which is also called bronchial dust. The air thereby enters tangentially into the cyclone at the top and leaves it at the bottom through an immersion pipe 18. The separated dust is collected laterally by the tangential pipe in a dust deposit area 19.

From the immersion pipe 18 the air enters tangentially into a filter capsule 4 in which an electrically polarized filter 5 is mounted. As a result of the tangential entrance of the air the filter is biased evenly with air at the circumference. As filter material can be used tangled fibre filter fleece of polypropylene which has a high degree of separation with a low pressure drop and a high dust storage capacity. In this filter the third dust fraction is separated off having particle sizes < 4pm. Dust of this particle size is also termed alveolar dust.

The air passes from outside into the filter, through same, is sucked off inwards and passes through a channel 6' into a suction channel 6 which is connected by a hose connection to the apparatus part which contains the suction unit. In this apparatus part the volume flow measurement is carried out according to the Karman vortex principle. For this purpose a disruptive body 7 is provided in the suction intake channel of same so that vortices are split up from same. The number of vortices and vortex frequency are a measure for the volume or volume flow. In order to measure the vortex frequency an ultrasound transmitter 8 is provided in the present embodiment in the f orm of a pair of piezo elements to which an input signal is supplied with a frequency of about 150 kHz through supply lines 10 wherein P1524. P3 6 Anril 1995 k - 9 is a low frequency signal of 300 Hz resulting from the frequency of the continuous flow vortex is superimposed on the input signal f requency. A f requency-modulated output signal is supplied through leads 11 via an ultrasound receiver 9 in the f orm of a piezo element to a signal production unit 26 where the 150 kHz carrier frequency is f iltered out. The received signals are converted after amplification and demodulation into digital electric signals whose frequency is proportional to the volume flow.

A micro processor 27 undertakes the task of digitally regulating the suction assembly to the preset ideal value of the volume flow through frequency or impul s e -width -modulated control of the setting member 29.

In order to detect the breakdown conditions in the pneumatic circuit of the sampling apparatus such as eg bends or tears in the hose connection between filter head and suction unit the motor voltage when the setting member 29 is opened is additionally evaluated by the micro processor 27 through threshold value switches 28 as a measure for the permissible speed area and in the event of breakdown the apparatus is switched off through a main switch 30.

A radial ventilator 20 is provided for sucking in the air.

This ventilator is driven by a motor 14. The air is sucked in through a suction intake pipe 12 and a ring gap 13.

In order to achieve a compact construction of the dust sampling device the high voltage module for operating the filter 5 is mounted in the space between the suction intake pipe 1, the lamellar separator 2, cyclone 3 and filter capsule 4. This space which is available in any case in the apparatus is expediently utilized in this way.

P1524. P3 6 April 1995 is A compact construction is further reached in that the necessary analog conductor card 21 and computer conductor card 22 are provided in the area of the suction intake pipe 12 of the radial ventilator 20. The computer conductor card 22 has a recess 24 which corresponds to the outer dimensions of the suction intake pipe 12 so that it can be pushed over same. The analog conductor card 21 has a recess 25 which corresponds to the outer dimensions of the motor 14 so that it can be pushed over this. The conductor cards are arranged so that the electronic component parts 26 located on same lie opposite one another, thus are on the inside. Accumulators or primary elements can be provided as a source of current.

With the measures according to the invention it is possible for the first time to provide a portable dust sampling device which meets both the demands for a measurement statement three-phase separation with close approximation to a separating characteristic which comes close to the human breathing tract and which is also laid down in DINEN-481; sufficiently large volume flow which allows use even in the case of small concentrations; high storage capacity; easy extraction of specimens in the case of analyses; and also meets the ergonomical demands for a small, lightweight and physically correct structural shape.

P1524. P3 6 April 1995

Claims

CLAIMS is 1. Dust sampling device using an electrically polarized fleece

filter and a suction unit characterised in that three separating phases are provided wherein two centrifugal force separators are provided in front of the electrically polarized fleece filter and that one device for the volume flow measurement is provided on the principle of the Karman vortex path.
2. Dust sampling device according to claim 1 characterised in that a lamellar separator is used as the first centrifugal f orce separator and a cyclone is used as the second centrifugal force separator.
3. Dust sampling device according to claim 2 characterised in that the lamellae of the lamellar separator are provided in a curved flow channel.
4. Dust sampling device according to claim 3 characterised in that the curvature of the lamellae runs according to the curvature of the flow channel.
5. Dust sampling device according to at least one of the preceding claims characterised in that the lamellae are wetted with a medium which allows the separated dust particles to stick.
6. Dust sampling device according to at least one of claims 2 to 4 characterised in that the lamellae are wetted with silicon oil.
7. Dust sampling device according to at least one of the preceding claims characterised in that in the suction intake channel in front of the suction unit is a disruptive body P1524. P3 6 April 1995 - 12 after which is mounted a measuring device for detecting the vortex which is released at the disruptive body.
8. Dust sampling device according to at least one of the preceding claims characterised in that a measuring device is provided to count the released vortices and/or for measuring the vortex frequency.
is g. Dust sampling device according to at least one of the preceding claims, characterised in that an ultrasound measuring device is provided as measuring device f or the vortex frequency.
10. Dust sampling device according to at least one of the preceding claims characterised in that a pseudo- immersion pipe is provided in the area of the inflow opening of the cyclone.
11. Dust sampling device according to at least one of the preceding claims, characterised in that the immersion pipe of the cyclone is fixed tangentially on the filter housing.
12. Dust sampling device according to at least one of the preceding claims, characterised in that the immersion pipe is provided in the base of the cyclone.
13. Dust sampling device according to at least one of the preceding claims, characterised in that the lamellar separator, cyclone and filter are mounted in a first compact apparatus part and that a high voltage module for the filter is provided in the remaining free space between these structural groups.
14. Dust sampling device according to at least one of the preceding claims characterised in that the lamellar P1524. P3 6 April 1995 1 r - 13 separator, the cyclone and filter are mounted readily exchangeable in the housing.

is
15. Dust sampling device according to at least one of the preceding claims, characterised in that the lamellar separator, cyclone and filter are designed independently of each other f or transporting the specimen and as weighing containers.
16. Dust sampling device according to at least one of the preceding claims, characterised in that the two centrifugal force separators, the housing of the filter and a further cover of the high voltage module which originally serves to protect this module against the effects of dust, are designed as a Faraday cage.
17. Dust sampling device according to at least one of the preceding claims characterised in that the electronic structural groups required for operating the dust sampling device are mounted in a second device part which also contains the suction unit.
18. Dust sampling device according to claim 12 characterised in that when using a radial ventilator with an associated suction intake pipe the conductor plates for the electronic components are mounted around the suction intake pipe wherein the electronic components of each two conductor plates lie opposite one another.
19. Dust sampling device according to at least one of the preceding claims, characterised in that a micro processor and a setting member are arranged for regulating the volume flow through frequency- or impulsewidth-modulated excitation of the motor.

P1524. P3 6 April 1995
20. Dust sampling device according to at least one of the preceding claims, characterised in that a threshold value switch is provided for detecting the motor voltage as a measure for the permissible speed area, which is associated with a main switch which is controlled by a micro processor.
21. Dust sampling device substantially as herein described with reference to the accompanying drawings.

n P1524. P3 6 A1Dril 1995