DE3244892A1 - Optical method and device for measuring the consistency of a paste - Google Patents

Description

^ f. December 3rd, 1982 - ph

File: VA 1007

Applicant:

VALMET OY
Punanotkonkatu 2
001.30 Helsinki 13
Finland

Optical method and device for measuring the consistency of pulp

Finding area

The present invention relates to a new method and method new device for measuring the consistency of mixtures of Pulp and water of various types (of pulps). the Invention is based on optical phenomena in pulp-drum blends and on the use of this phenomenon in the Measuring the consistency of such mixtures.

Background of the invention

In the pulp and paper industry, during the papermaking process, individual wood fibers are separated from whole wood either mechanically or chemically, or by a combination of the two. The 30 wood fibers produced are mixed in with rfasser, so that a pulp mass is created, which typically consists of more than 80% tfasser. In order to achieve good quality control of the defibering process and to consistently produce an end product (paper) that meets the prescribed standards, it is essential to know the ratio of the amount of wood fiber to the total mass at every point in the process (this ratio is known in the trade as "consistency "). For example, for quality control purposes, it is important to be able to measure the consistency of the material mass when passing through a

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Tube or in a column or chamber where the movement of the The crowd is extremely slow or where it is completely motionless at times is. Bs is of the same density, the consistency of Hasse with chemical Hasse (bleached or unbleached), more thermomechanical Hate, wood pulp, mixes of different masses or auqh the consistency of the hate during the bleaching process to be able to determine.

Most of the transmitters currently used in the industry to determine the consistency of barrel-pulp mixtures (of pulps) work mechanically. Such mechanical encoders sometimes measure the force with which the movable frame acts on a mechanical arm, a plate or the like. These mechanical encoders have their well-known limitations, such as distortions due to the speed of the ¹ Hasse, the influence of different types of wood and freedom (irrigation). Furthermore, such mechanical transmitters cannot be installed with ease in a column or chamber in which the mass moves slowly or stands still. Mechanical encoders are also limited to specific mass consistencies and do not accurately measure mass consistencies below about 1% as well as above about 5 %.

A chlorination agent is available on the market, the insensitivity which causes variations in consistency. (Dieeer Geber is described in U.S. Patent No. 3,994,602 to John J. Howarth, 30.11.1976 specified and claimed). This donor basically aims at regulating the chlorination and accomplishes this by measuring the transmittance in the visible and near-infrared part of the electromagnetic spectrum (dee light). These The patent also teaches measuring consistency by seeing the permeability of the mass of fabric at various distances from the radiation source. A second device uses a combination of reflection and fluoroscopy at the same time Purpose. Neither method uses specific filtration of radiation as a key to determining the Consistency.

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Summary of the invention

The invention aims to produce an optical device and procedures that are able to maintain the consistency of pulp of different qualities (regardless of the wood fiber ” type) to measure accurately and the measurement under different process conditions with different geometries, e.g. in pipelines, columns or chambers, regardless of the Speed as well as within the entire temperature range of 0 to 100 C.

The measuring principle is based on the unique properties of light (electromagnetic radiation) in the range from about 200 nm to about 5000 nm, on the emission of such light against a mass of matter and detection of that reflected by the fibers in the mass Light on. The consistency measurement builds directly on it on that the water in the substance mass weakens light of different wavelengths in the mentioned range to different degrees.

The reflectivity of the mass is measured using "water sensitive" and "water insensitive" wavelengths and by comparing these signals mathematically. The result is that the measuring method is sensitive to changes in the amount of water in the mass, but largely insensitive to it various other factors that would normally interfere or impair the measurement. Which in itself is based mainly because these "disruptive" factors are both affect measured wavelengths in the same way - such Common disruptive factors can be e.g. the brightness, the type of wood or the chemicals that are dissolved or in the waas part of the mass are present.

The invention relates to a process for measuring consistency of pulp, composed mainly of wood pulp and water, and this process involves the blasting of electromagnetic radiation against the substance mass and measurement dea relative absorption and the relative reflectance of the

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reflected electromagnetic radiation.

The wavelength of the electromagnetic radiation can be in the range from about 200 nm to about 5000 nra. Tighter areas can are within about 400 nm to about 1600 nm and about 700 nm to about 1250 nm, respectively.

The process of determining the consistency mainly from wood pulp and water existing mass of matter can comprise the following: a) the emission of electromagnetic radiation against the haters » b) receiving reflected electromagnetic radiation from the Hasse, c) splitting the reflected electromagnetic radiation Radiation in components and d) Measurement of the relative intensities of the reflected wavelengths of the components the water absorption factors according to.

The reflected electromagnetic radiation can be divided into two components be divided.

Han can be the first component of the reflected electromagnetic Pass radiation through a band pass filter with a nominal Hitt wavelength at about 960 nm. Han can be the second component of the reflected pass electromagnetic radiation through a bandpass filter, which has a nominal Hitt wavelength of about 800 nm.

Han can alternatively use the first component of the reflected electromagnetic Radiation through a bandpass filter with a nominal Hitt wavelength about 1200 nm and the second component of the reflected electromagnetic radiation can be passed through a bandpass filter with a Hitt wavelength of about 1060 nm.

Han can alternatively use the first component of the reflected Measure electromagnetic radiation at a wavelength that corresponds to a haximura of water absorption in the spectral range of about 200 nm to 3 corresponds to about 2000 nm, and the second component of the reflected electromagnetic radiation can be seen in a Measure wavelengths which have a much lower value of the rfas-

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aerabsorption corresponds to al3 for the first component.

The device for measuring material mass consistency can include: a) Device for directing electromagnetic
Radiation against one mainly made of wood fiber and off
Water existing mass of matter, b) devices for receiving
electromagnetic radiation that has been reflected by Der Hasse, c) devices for breaking down the reflected electromagnetic radiation into components, d) first filtering means for filtering out one of the two components of the reflected electromagnetic radiation, e) second filtering means for filtering out a further component of the reflected electromagnetic radiation
Radiation, f) first photodetector devices for sensing the
electromagnetic filtered off by the first filter means
Radiation and thereby for generating a proportional electronic signal, g) second photodetector devices for perceiving the electromagnetic radiation filtered off by the second filtering means and thereby for generating a proportional one
electronic signal, h) means for amplifying the first and second photodetector signals; and i) means for dividing the two reflected signals to produce a ratio of the two reflectances.

One can select the first filter means (d) so that it
mainly allows electromagnetic radiation with such a wavelength to pass through, which corresponds to one of the maximum absorption ranges of water, and one can select the second filtering means (e) so that it mainly passes electromagnetic radiation with such a wavelength at which the water absorption is significantly less than at the wavelength of the first filter agent is.

The central wavelength of the first filter medium (d) can be about 960 nm and the central wavelength of the second filter medium (e)
can be at a wavelength at which water absorption
is considerably less than that of the first filter medium.

The second filter means (e) can have electromagnetic radiation

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at the wavelength at which the water absorption The water absorption is more than five times lower than that of the first filter means (d) transmitted electromagnetic radiation.

The device (a) for emitting electromagnetic radiation can be electromagnetic falling in the range of about 200 to about 5000 nm Radiate radiation.

drawings

In the drawings

Fig. 1 describes the attenuation of electromagnetic radiation in Vfasser as a function of the wavelength,

Fig. 2 shows an optical consistency generator in a lateral sectional drawing,

3 is an electronic block diagram of the components making up the make optical consistency givers,

Figure 4 is a graphical representation of eleven trials carried out to demonstrate the consistency generator signal plotted against the substance mass concentration, namely for half-bleached Force mass and

Figure 5 is a graphical example of six experiments carried out to demonstrate minimizing the change in brightness the influence exerted on the consistency generator signal.

Detailed description of the invention

The reflectance of electromagnetic radiation from a mass (which is a two-phase mixture of liquid-solids) becomes usually directly influenced by the amount of liquid present, since the mass usually consists of rfaeaer. This applies to

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Pulp pulp, and accordingly the yeflectance becomes more electromagnetic Radiation from the mass of matter mainly through affects the amount of water present. In the speculum from about 200 nm to about 5000 nm shows the absorption of the radiation in Water peaks and valleys at different wavelengths.

Since the mass of matter consists mainly of water, old one insignificant amount of dissolved and suspended components, light directed against the mass will pass through most of the time liquid component of hate will happen with little disability. However, some of the light is reflected. The crowd reflects light from fibers close to the surface and, to a large extent, from individual fibers deeper below the surface lie. Therefore, the permeability of the water or the bulk liquid becomes a key factor with regard to the degree to which which a given mass as a whole will reflect electromagnetic radiation of a given wavelength.

The reflectance of wood fibers is also dependent on the wavelength of the incident radiation dependent. At wavelengths above 800 nm, the yeflectance of electromagnetic radiation on wood fibers is relatively insensitive to changes in wavelength. in the In contrast, water shows clear variations in absorption at wavelengths above 800 nm. Pig. 1 showing the values of electromagnetic Represents absorption in relation to the wavelength, it can be seen that water has an absorption maximum (a peak) about 960 nm. Bs has an absorption minimum (a valley) at one Wavelength of about 1060 nm. Again, at about 1200 nm, the water absorption reaches a maximum (a peak). The same cyclical The trend continues at wavelengths of electromagnetic radiation over 1200 nm with alternating maxima and minima. this means that other wavelengths can also be used for the purpose of the invention.

I have made the discovery that these absorption peaks and valleys can be used to measure the amount of water in the Mass of matter (and therefore "consistency") can be measured by looking at light

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n with a relatively large bandwidth, e.g. about 200 nm to emits about 5000 nm, whereby one selects and uses such filters that the reflected electromagnetic radiation only at certain preselected wavelengths through. By choosing the filters so that the one filter is matched to the wavelength of the light absorption maximum, and by taking the ratio thereof to the signal from another filter, which is matched to the wavelength of the light absorption minimum, I have found that it is possible to obtain a measurable result which is not particularly dependent or influenced by those properties of the Hasse which normally affect the reflectance spectrum in the chosen wavelength range. The result is against it Consistency changes sensitive to. This can be seen from the graphs in Figs. 4 and 5, which show the experimental measurement results at different masses in the case where the two filters have a wavelength of 960 and 960 respectively. 800 nm with a bandwidth of 5 nm.

Fig. 2 and 3 illustrate the construction of the encoder. Electromagnetic radiation (light) from an incandescent lamp (5) with tungsten wire, the light in the spectral range from about 200 nm to about 5000 nm generated, is passed through a fiber optic light cable (2) and sent through a window (14) into a mass of material that is located on the other side of the window. I am part this light passes through the mass, while a part in Direction to the window (14) and is thrown back through the same.

A second fiber optic cable (2a) is parallel to the cable (2) and collects and guides the substance through the window (14) reflected light to a lens (13) and finally to two photodetectors (11) and (Ha). One beam splitter (7) and two separate filters (8) and (8a) split the reflected light that has passed through the line (13) so that each photodetector (11) or (.11a) only receives about half of the reflected light.

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9 The photodetectors (11) and (I1a) «earth excited by light and generate signals that are amplified and using an electronic Divisors can be edited to obtain the ratio of the two reflectances at two particular wavelengths. That The ratio signal is converted into a current signal of 4 20 mA, which is used for industrial processing, regulation and evaluation e.g. by means of a computer.

The cables 2 and 2a are housed in a transmitter shaft (1). A light cable holder (3) holds the ends of the two cables in place and Job. The optical and electronic devices a are in housed in a transmitter housing (10). The encoder shaft (1) is attached to the encoder housing (1O) by a flange (4) »The optics is attached to an optics mounting block (6) and is used by worn this. The two filters (8) and (8a) are held by a pair of filter holders (9). The electronic district map (12) is also housed in the housing (10). The effects of scattered light are achieved through the use of light-tight packings (15) various crucial connection points have been prevented.

The two filters (3) are chosen so that both are fairly tight Bandwidth, e.g. have a pass bandwidth of 5 nm. The tiittwavelength (the wavelength that corresponds to the greatest permeability) is equal to an absorption peak in one of the filters of water, e.g. at a wavelength of 960 nm or 1200 nm chosen lying.

The other filter (8a) is then chosen so that it has a central wavelength as close as possible to the wavelength of the first filter, but at the same time a wavelength at which the water absorption is substantially less, preferably more than five to ten times less, such as a wavelength of 800 nm or of 1060 nm.

Consequently, if one measures reflectance from the mass of material, the signal from the first filter becomes far stronger from the amount of water present per unit of volume influenced than the signal from the second filter

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(8a). On the other hand, both signals have almost the same effect Instruct the remaining phenomena of hate that have an effect on the Have reflectance. This wj ^ erum means that the ratio (or the output νοα encoder) is highly sensitive to the variation in consistency and factors other than consistency variation is largely insensitive to.

Figure 5 graphically illustrates six experiments that were carried out to demonstrate how a brightness disturbance is caused by the Sensor is suppressed. It can be seen that the sensitivity to consistency is significantly higher than the response to Changes in brightness. Here the two examples represent the practical extreme cases of brightness. Under actual litigation conditions, such vigorous changes hardly ever occur.

A second aspect to consider when choosing a filter is, is that sometimes one disturbance factor can surpass all others in strength. For example, the brightness! fairly constant, while changes in wood species are frequent and are unpredictable. In such cases the second wavelength is chosen, so that the greatest insensitivity to the one in question standing interfering factor results, and this is done by taking measurements on samples of the present Hasse and selects the second filter to be possibly one of the normal choice of the second filter has a slightly different wavelength.

A number of modifications to the basic design can be made to achieve results that are as good or a little worse than those obtained with the encoder described above are. These are the following:

1. Han can omit the fiber optic cable by removing the light source, the radiation absorber, the filters and the detector directly attaches to the window in the top of the encoder.

2. One can light source using light emitting

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Execute diodes (LKDa). This is how the construction takes shape and the implementation of the encoder is simpler, but it is less adaptable to the respective process conditions; for example need very narrow band filters of a specific wavelength are used to compensate for disturbances. Hit the further advancement of LSD technology is likely to do so with consideration for simplicity and Costs are becoming an attractive alternative.

3 · You can use multiple filters, or you can measure the carry out the entire spectrum in question to obtain the same result, but with greater freedom in the choice of wavelength and regarding the various compensations.

4. Instead of the two-signal ratio, one can apply calculations of the following kind in order to obtain a useful result under certain conditions To achieve ratios:

a) the difference between the two signals,

b) dividing one signal by the sum of both,

c) a signal alone (this variant becomes more useful with consistencies higher than 4-5 % and with high brightness of the mass) and

d) a signal + a constant divided by the sum of the second signal and a constant.

5 The filters can be built on a filter wheel,

6. One or more electromagnetic detectors can be used depending on the number of filters and whether a filter wheel used or not.

7. You can use different processing elements instead of the divisor insert. For example, a microprocessor could be used to advantage.

The above list is not claimed to be complete; it is only exemplary.

A result similar to the one described above can be can be achieved by using wavelengths which all coincide with absorption maxiina of water, and then the summed up individual signals. In such a case, however, the advantage of compensating for the influence of other disruptive phenomena in the reflectance spectrum is largely lost.

Some of the benefits of my invention are currently in use the existing donors are:

a) little need for maintenance;

b) a measuring range of 0.05 to 15 % consistency is made possible by using one and the same basic encoder;

c) it is possible to install the encoder through a ball valve, to allow easy inspection later;

d) the measurement is largely independent of the flow velocity (compared to mechanical devices);

e) From a practical point of view, the donor can be used at any point in the process be installed where there is minimal flow and enough space for the light to reflect off the hatch;

f) the geometry of the pipe laying and the physical containers have no influence on the measurement.

It will be apparent to those skilled in the art that various modifications of the Embodiment that is described and illustrated in the drawings can be made without getting lost from the idea and the Scope of the invention as defined in the claims below.

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Claims (1)

13th Claims . 1. ) Method for measuring the consistency of pulp, which consists mainly of wood pulp and water, characterized in that electromagnetic radiation is emitted onto the pulp and the relative absorption and the degree of reflection of the reflected electromagnetic radiation are measured. 2. The method according to claim 1, characterized in that the wavelength of the electromagnetic radiation is about 200 nm to about 5000 nm. 3. The method according to claim 1, characterized in that the Wavelength of the electromagnetic radiation in the range of about 1 + 00 nm to about 1600 nm. k. Method according to claim 1, characterized in that the wavelength of the electromagnetic radiation is in the range from about 700 nm to 1250 nm. 5. A method for measuring the consistency of a substance consisting mainly of wood pulp and water, characterized in that that the procedure includes: a) emitting electromagnetic radiation to the mass, b) receiving reflected electromagnetic radiation from the mass, c) dividing the reflected electromagnetic radiation into components, d) measuring the relative intensities of the reflected wavelengths of the components according to the Wasserabsorptionsfaforen. 6. The method according to claim 5 , characterized in that the reflected electromagnetic radiation is divided into two components. 7- method according to claim ^r ), characterized in that dn.:;i; the wavelength of the electromagnet, i see radiation about? 00 um bti; is about 5000 nm. BATH ORIGINAL Jj ' ^ k. 9. The method according to claim 5, characterized in that the The wavelength of the electromagnetic radiation is in the range from about 100 nm to about 1600 nm. 9. The method geraäss claim 5, characterized in that the Wavelength of the electromagnetic radiation in the range of about 700 nm to about 1250 nm. 10. The method according to claim 6, characterized in that the first component of the reflected electromagnetic radiation is passed through a band pass filter with a nominal center wavelength of about 960 nm. 11. The method according to claim 10, characterized in that the second component of reflected electromagnetic radiation is passed through a band pass filter with a nominal center wavelength of about 800 nm. 12. The method according to claim 6, characterized in that the first component of the reflected electromagnetic radiation is passed through a band pass filter with a nominal center wavelength of about 1200 nm. 13. The method according to claim K), characterized in that the second component of the reflected electromagnetic radiation through a bandpass filter with a central wavelength of about 1060 nm is directed. '\H. The method of claim 6 wherein _T, dar.s the first component of the reflected s ektromagnet I i:; chen radiation is like to eat at a wavelength corresponding to a maximum nm of water absorption in Bpektralbereich of about POO nm to about 5000th 15. The method according to claim 1h, characterized by the fact that the second component of the ref I ckt ieri.cn el e.ktromagnol, ical radiation at a wavelength is ßememieti, · 1 \ <· '' because, / ', eringereu Wasaerabsorpl. ifii.i.-iwfirt old ·. 1><· ί ₍ | ι »ι · e» r: .it>'u component en (-: tpricht. OR! G! NAL 15th 16. Device for measuring the consistency of pulp, thereby characterized as comprising the following: a) means for emitting electromagnetic radiation onto an existing mainly from wood pulp fibers and water St off mass, b) devices for receiving electromagnetic radiation reflected from the substance mass, c) Devices for splitting the reflected electromagnetic Radiation in components, d) first filter devices for filtering out one of the two components of the reflected electromagnetic radiation, e) second filter devices to filter out a second component the reflected electromagnetic radiation, f) first detector devices for detecting the signals provided by the first Filter devices filtered reflected electromagnetic radiation and thus to generate a proportional electronic Signals, g) second detector devices for detecting the signals provided by the second Filter devices filtered reflected electromagnetic radiation and thus to generate a proportional electronic signal, h) means for amplifying the first and second photodetector signals , i) Devices for dividing the two reflected signals to produce a ratio of the two reflectances. 17 · Device according to claim 16, characterized in that the first filter device (d) is chosen such that it mainly emits electromagnetic radiation with such a wavelength through which one of the maximum absorption areas of water is equivalent to. 18. The device according to claim 17, characterized in that the second filter device (s) is chosen such that it mainly lets through electromagnetic radiation with a wavelength at which the wastierabsorpt ion knowingly gi-ringcr as is at the wavelength of the first filter device. 16. 19. The device according to claim i6, characterized in that the center wavelength of the first filter device (d) about 960 nm amounts to. 20. The device according to claim 19, characterized in that the central wavelength of the second filter device (e) is at a wavelength at which the water absorption is significantly lower than that of the first filter device. 21. The device according to claim 20, characterized in that the second filter device (s) electromagnetic radiation from at such a wavelength at which the water absorption more than five times less than the water absorption of the electromagnetic radiation transmitted by the first filter device is. 22. The device according to claim 16, characterized in that the electromagnetic radiation emitting device (a) emits electromagnetic radiation which is in the range of about 200 to about 5000 nm. 23. The device according to claim 16, characterized in that the electromagnetic radiation emitting device (a) emits electromagnetic radiation in the range of about i + 00 nra to about 160 nm. 2k. Device according to claim 16, characterized in that the device (a) emitting electromagnetic radiation emits electromagnetic radiation which is in the range from about 700 nm to about 1250 nm. BAD ORiGiNAL