METHOD FOR DETERMINING THE AMOUNT OF SOLID MATERIAL AND / OR LIQUID CONTAINED IN A TWO-PHASE CURRENT WITH AN AGENT
GASEOUS TRAILER Description of the Invention The invention relates to a method for determining the amount of solid and / or liquid material contained in a biphasic stream with a gaseous entrainer. A preferred field of the application of the invention is the determination of the amount of coal dust transported pneumatically in the combustion ducts of a power plant operated by coal. The transport of solid and / or liquid materials that exist in the form of small or tiny particles in a biphasic stream with gaseous entraining agent is often carried out in turbulent streams in order to obtain a sufficient transport speed and a sufficient quantity of water. the solids and / or liquids that are transported. Particularly in the case of the transport of tiny solid particles, it is not possible to avoid in the real transportation systems that in what is known as higher density tufts the transport channel is formed. Such tufts can on the one hand be geometrically very stable and localized, but on the other hand they can also appear stochastically at the most diverse sites and modify their extension as well as their density, or migrate within the transportation channel. In particular at the bifurcation points very irregular distributions of the solids can occur and with this considerable differences in the amount of the material transported within the individual channels due to the formation of tufts. Therefore, it is a big problem to determine the amount of material transported in a pneumatic transportation system, in
In particular, the amount of material transported in the individual transportation channels in the case of bifurcated systems. Known methods, such as isoquinetic suction tubes at various measuring points
Often, they give very falsified measurement values, because the tufts are detected with difficulty or by chance. To this must be added the slowness of these measurements, which often yield measurement results after hours and therefore
are discarded to be used in a regulating circuit. In order to control pneumatic transportation processes and regulate the amount of material transported in bifurcated systems, systems are required
fast measuring. Therefore, it has been a long time since
Try to apply the microwaves to these measurement tasks. For this purpose, the microwaves of a given frequency are coupled to a section of the channel prepared as a measurement section, and at the end of the measurement section the change of amplitude and phase of the microwave is recorded. The physical background of this measurement principle lies in the fact that the loading of the entrained gas with solids and / or liquids leads to a modification of the complex dielectric constant within the transport channel, and that the microwaves suffer attenuation and a displacement of the phase as a function of this dielectric constant. A corresponding method is described, for example, in EP 0717269, EP 669522 or also in US 5177444. However, the sensitivity of the known measurement methods by using microwaves is not sufficient for pneumatic transport systems , in particular when as a consequence of the bifurcated transport channels, different amounts of material are transported in the individual channels or channel sections, or there are considerable differences in the concentration of solid and / or liquid material per m 3 of spatially distributed trawl gas within the system of tubes or channels due to the aforementioned formation of tufts. For example, a resolution of the measurement of 1 g of coal dust per m3 of trawl gas is required for a sufficiently precise regulation of the feeding of coal dust to a combustion system of a boiler of a power plant . Such small differences in charge only cause a very small modification of the complex dielectric constant, and therefore have little influence on the attenuation and phase of the microwave. Furthermore, the use of microwaves for the measurement of the load in pneumatic transportation systems causes considerable problems due to the disturbing influences due to the reflected microwaves. Especially in the case of reduced loads, the attenuation of the microwaves is very low, so that in the channel system they are conducted over very long distances as in a hollow conductor and are reflected in the constrictions, bifurcations or extremes. There can be superpositioning between the waves that come and go and consequently considerable distortions of the measurement results. Furthermore, the known methods by the use of microwaves suffer from the additional disadvantage that they require a considerably complex apparatus. In general, it is necessary to insert into the channeling system a channel segment to be prepared as a measuring section having a high geometric precision, and suitable transmitting and receiving antennas. It is also known to install coupling windows as emission and reception devices in existing channel sections, which must correspond to a pre-established geometry. The object of the invention is to create a method for determining the amount of solid and / or liquid material contained in a biphasic stream with a gaseous entrainer that can also be used in the case of small loads or small differences in the load and does not require substantial intervention in existing channel systems. For this purpose, the task consists of developing a method that is characterized by a minimum resolution of the measurement of 1 g of material per m3 of entraining agent and does not impose excessive requirements on the geometry of the measurement section. According to the invention, this task is solved by a method according to claim 1 of the invention, the subsequent claims describe advantageous improvements of the invention. The invention is based on the known physical relationship that the attenuation of an alternating electric field as a function of frequency has a relatively linear, nearly inclined transition similar to a jump function from a high attenuation value to a low attenuation value as along a constant stretch below the characteristic limit frequency for the
wave diffusion. This transition remains substantially unchanged in relation to its shape (jump function) starting from the no-load state, that is to say a drag-gas without solid and / or liquid load, until arriving at that with relatively high loads.
large. However, the frequency range within which the transition takes place is shifted to lower frequencies as a function of the load, and the amount of frequency displacement represents a measure of the charge of the entrained gas with solid material.
and / or liquid. The essence of the method according to the invention is to excite an alternating electric field within a section of tube or channel and detect the interference of this alternating field along a stretch
of the path that is in the flow direction or against the flow direction of the loaded gas stream, being that the frequency shape and range of said attenuation transition in the discharged state is first defined, and then the
frequency deviation of this transition towards
^ m ii ^ i? ^^^ »^^^, ^ lower frequencies as a result of the load, in order to calculate the load of the entrainment gas with solid and / or liquid material based on known ratios. For this purpose, an approximately linear area is defined within the transition, which is delimited by a higher attenuation threshold value with its respective lower frequency and a lower attenuation threshold value with its respective higher frequency, with the use of a receiver real with finite sensitivity, within this approximately linear area there is an inversion point of the attenuation curve over the frequency that can be determined simply mathematically and technically. Within this approximately linear area small frequency variations are related to large variations in attenuation. It is therefore possible to detect or determine with high precision the points or areas within this approximately linear area. Technically it is possible to conceive various variants on how to carry out the essence of the invention. Thus, for example, it is possible to select within the approximately linear area a characteristic attenuation value with its respective frequency in the discharged state, and to define the load to vary (increase) to
i * ^ to? fc * h'¿;, M¿-j --- •• J from a starting frequency the frequency of the alternating electric field coupled until the attenuation measured in the loaded state shows the same value as the one selected at the beginning. As a starting frequency, a frequency that is less than or equal to the lower frequency of the approximately linear area is chosen in the case of the maximum load that occurs in the respective application case. This starting frequency can be defined by subtracting from the lower frequency of the approximately linear area in the discharged state the maximum deviation? F of the frequency, that is, the one that appears with the maximum load. This deviation? F of the frequency can be easily calculated according to the relation? F - fo (1-1 / Vμrer), where f0 is the cycle of the cutoff frequency of the system of tubes or channels discharged and μr the permeability relative to the relative dielectric constant of the gaseous entrainer mixture and the amount of solid and / or liquid material contained therein. The frequency difference between the frequencies corresponding to the selected characteristic attenuation value in the unloaded and loaded state is then a measure of the load. It can be easily understood that in order to reach a maximum sensitivity of the method, the chosen attenuation should be within the most inclined range, ie, that which is approximately linear, since for technical reasons the inversion point of the attenuation curve would be pre-defined. In order to accelerate the measurement process, it is convenient to increase the step frequency from the aforementioned starting frequency, calculated from the difference of the upper and lower frequency of the approximately linear area., until the measured attenuation is within the approximately linear area. The frequency differential between the frequency corresponding to the attenuation measured in the unloaded state and the measured frequency is the measurement of the load, as mentioned above. Naturally, it is also possible to recalculate to another selected characteristic attenuation value the measured attenuation within the approximately linear area as well as the frequency corresponding to it based on the linear equation describing this approximately linear area, to then determine the deviation of the frequency of this characteristic attenuation value of the state discharged to the charged state. An essential advantage of the method according to the invention resides globally in that extreme requirements with respect to the roundness of the tube are not imposed.
of the measurement section along which the attenuation of the electric alternating field is defined. The measurement can be carried out, for example, in conventional tubes corresponding to the DIN standard. The sensitivity of the measurement method is remarkably good also in the case of these tubes, and is found in less than 1 g of material per m 3 of trawl gas. Another advantage of the method is that the excitation of the alternating electric fields is carried out through short mismatched radiators. The reception antennas are designed in the same way. This results in abrasions only insignificantly influencing the measurement method and only a replacement of the antennas at greater intervals due to wear is necessary. In addition, short hertzian radiators can be installed in existing tube or channel systems without incurring substantial expense. The invention can also be used preferably when tufts are formed within a pipe system. To detect and take into account the strands in the result of the measurement it is necessary to excite two alternating electric fields rotated one with respect to another azimuthally by 90 °, and to define the frequency deviation of the approximately linear area of the curve of
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attenuation of these alternate fields along a pre-established measurement section as already described above. A variant of the method consists in alternately exciting in time both alternating fields rotated one with respect to the other azimuthally by 90 °, and defining in the manner described the frequency deviation of the approximately linear area of the attenuation curves by receiving antennas transposed by a pre-established distance, equally rotated by 90 degrees with respect to one another and aligned axially flush with respect to the emitting antennas. The tufts that appear will lead to different deviations of the frequencies of the attenuation curves of the alternating fields rotated by 90 ° one respect to the other. By means of the formation of average values that are conveniently carried out until other measurements no longer lead to a substantial variation of the result, a deviation of the frequency is obtained which corresponds to an average load density that contains the lock. But by means of the method according to the invention it is also possible to define the spatial location and intensity of a lock within a tube. For this purpose, two alternating electric fields of equal frequency and the same phase are excited in the same way inside the tube.
* 8 * * 2tí £ * ia-_sa_S "i" "sw rotated relative to each other azimutially by 90 °, and defines the frequency deviation of the approximately linear area of the attenuation curve of these alternating fields along the A pre-set measurement segment 5 In this case the excitation and the definition are carried out simultaneously, both alternating fields are superimposed to obtain a resulting alternating field, in a similar way a deviation of the frequency of the approximately linear range of the attenuation curve as
measurement of the load in the azimuthal direction of the resulting alternate field. By varying the amplitudes of the alternating fields rotated with respect to each other azimuthally by 90 °, the resulting alternate field can be rotated azimuthly, and the amplitude of the field
The resulting alternate should preferably be kept constant. Now, the azimuthal spin of the resulting alternate field defines the maximum and minimum deviation of the frequency of the approximately linear area of the attenuation curve. The maximum and minimum deviations of the
The frequency is rotated azimuthally by 90 ° in the case of a lock. The position of a lock can be calculated from the corresponding azimuthal directions, the result being ambiguous because the alternating electric field is axially symmetrical. This
means that the azimuthal alignment of the electric field
MA ^^ ^^^^^ & ^^^^., ^^ alternate in the case of a maximum deviation of the frequency corresponds to the azimuthal position of the lock in the following manner: aSt - aF + n 180 °, where aSt - the azimuthal angle of the lock, aF - the azimuthal angle of the alternate electric field and n an element of the natural numbers. In other words, a strand detected in this way can always be found in two quadrants that are pinpointed with respect to each other. For the ratio of the minimum deviation to the
maximum deviation of the frequency can be directly defined the ratio of the minimum to maximum field intensity that passes through the lock. Based on the quantitative distribution of the field strength of the alternating electric field in the tube, the radial position can be determined
of the lock. In order to allow an unambiguous azimuthal location of the tuft it is necessary to define half of the circular section of the tube in which the tuft is located in an additional stage of the method. In accordance with the
This invention is carried out by evaluating the alternating voltage induced in a receiving antenna rotated azimuthally by 90 ° with respect to the emitting antenna. If the position of the emitting antenna is set azimuthally by 0 °, then in the position of 180 ° you can check a
alternating electric field of equal field strength but
It is the opposite polarity. In the case of a homogeneous load, in the position of 90 ° the field strength and consequently the alternating voltage induced in the receiving antenna are equal to zero. When a strand appears in the tube half of the emitting antenna, the alternating electric field is distorted in such a way that an electric field strength of opposite polarity appears in the receiving antenna transposed by 90 °. This induces an electrical alternating voltage that is opposite phase to the alternating voltage that feeds the emitting antenna. If the strand is in the pipe half away from the emitting antenna, an equi-phasic voltage is detected in the transmitting and receiving antennas. Conveniently this measurement is repeated by exchanging the transmitting and receiving antennas in order to detect with sufficient security also the tufts that are in the immediate vicinity of the transmitting antenna or the receiving antenna. In addition to this, the method according to the invention makes it possible to measure the transport speed of the transported material. For this purpose, temporary variations in charge density are recorded, which are always due to the turbulent flow at two axially transposed sites with respect to the excitation site of the alternating electric field, preferably in and against the direction of flow of the transported material, and the temporal asymmetry "* of both temporal sequences is evaluated by means of a correlation filter.For the temporal asymmetry and the axial distance of the measurement sites, the transportation speed of the transported material can be determined. The material according to the invention will be explained in more detail below on the basis of an exemplary embodiment, the corresponding drawings show in: FIG. partial section of a system of pipes of the feeding conduit of the burners of a electric entral operated by means of carbon, figure 2 the attenuation curve as a function of the frequency in the range of the inclined transition from a high attenuation to a low attenuation, figure 3 the alternating electric field resulting from the existence of a lock within the conduit of power to the burners (azimuth direction 0 °), figure 4 the resulting electric field alternately when there is a lock inside the supply conduit to the burners (azimuthal direction 90 °). There is the task of defining the quantity of fine-grained coal transported in the air stream in a supply conduit 1 of the burners of a coal-fired power plant, with circular section and a diameter of 500 mm, as well as to detect eventual tufts. The temperature of the burner supply line 1 is set as temporarily constant. First, in a straight segment of the conduit 1, two perforations axially aligned flush at a distance of 1000 mm are produced in which a short hertzian radiator (length 5 cm) is mounted respectively. For this purpose, for example, normal coaxial passage nozzles can be used. It is convenient to use such short mismatched antennas because they are on the one hand exposed to less mechanical wear and on the other hand only the sensitivity of the electrical system is negligibly influenced due to the appearance of mechanical wear. The first radiator 2 in the flow direction of the air-carbon mixture serves as the emitting antenna, the second 3 as the receiving antenna. In order to suppress the upper harmonic waves capable of diffusion in the tube, a vertical flank filter whose cutting frequency cycle is just above the cutting frequency cycle of the conduit 1 is placed before the antennas, respectively. The parameters of the measuring section are first recorded in the discharged state by the attenuation of the alternating electric field along the measurement distance as a function of frequency. For this purpose an alternating electric field is excited through the emitting antenna 2 inside the supply conduit 1 to the burners, and the
interference of this alternating field in the receiving antenna 3 as a function of the frequency. It is a typical development of the curve shown in Figure 2, in which, within a frequency range of approximately 1.3 MHz, the attenuation falls relatively
inclined approximately linearly. Within this transition range from high attenuation to low attenuation, an approximate linear reference area is now defined, which lies between a higher attenuation threshold value of approximately 45 dB with a
lower frequency of approximately 348.5 MHz, and a lower attenuation threshold value of approximately 20 dB with a higher frequency of approximately 349.3 MHz. Within this reference area a reversal point of the attenuation curve can be checked at a
frequency of approximately 349.3 MHz and an attenuation of
t -.- lb-Liij ÍMte- '»a s. M ffiggjÉ | approximately 32 dB. It is within this approximately linear area that the fall of the attenuation curve has its greatest inclination, which means that with small variations of the load at a constant measurement frequency a large variation of the attenuation is caused. The absolute values of the upper and lower attenuation threshold values are a function of the alternating electric field excited as well as the sensitivity of reception. From Figure 2, a value of about 350 MHz can be determined as the cycle of the cut-off frequency fo below which a wave diffusion no longer takes place. In the case of the present application, a maximum load of 1500 g of fine-grained coal per m 3 of air can be counted. This results in a relative dielectric constant er of 1.003 for the air-carbon mixture. The relative permeability μr is found in 1. Through the relation? F - f0 (l-l / Vμrer) an amount? F of the frequency of 523 kHz is calculated. To define the amount of fine-grained coal contained in the air stream, an alternating electric field is now excited in the charged state with a starting frequency of approximately 347.9 MHz (the lower frequency corresponding to the upper threshold value of the attenuation in the
'^^^^^^^^^^^ j ^^^^^^^^ discharged state less the amount? f of the frequency) through the emitting antenna 2, and through the receiving antenna 3 the attenuation is defined that takes place along the measurement stretch. This first will be first above the approximate linear reference area. The frequency of the alternating electric field is then stepped up until the corresponding attenuation is within the approximate linear reference area. The diagrammatic representation of the attenuation values determined in the charged state at different frequencies is contained in Figure 2 as a dashed curve. At a frequency of 348.2 MHz the alternating electric field results in an attenuation of 44 dB in the charged state. This attenuation is within the approximate linear reference area. In the unloaded state, this attenuation is reached at 348.6 MHz. This moves the approximately linear area of the attenuation curve in the charged state by 0.4 MHz with respect to that of the discharged state. Through the relation? F - fo (l-1 / μrer) it is possible to calculate the load of the air stream with fine-grained carbon through the variation of the relative dielectric constant er of the air-carbon mixture from the deviation? f of the frequency of the approximately linear area. In this the relative permeability μr is found in 1. According to this it can be
> - «- **,« -calculate a load of 0.16 g of carbon per m3 of air. To increase the sensitivity of the method, it is convenient to select within the approximately linear area the point of inversion as a reference point, and in determining the amount of fine-grained carbon contained in the stream of air change the frequency of the alternating electric field until the corresponding attenuation corresponds to the attenuation of the inversion point. This represents an advantage because it is at the point of inversion where the approximately linear area has the greatest verticality and where consequently the highest sensitivity is achieved. To speed up the development of the measurement it is convenient from the starting frequency defined for the maximum load increase this for the second measurement point by the differential amount between the upper and lower frequencies of the approximately linear area, in the present example by 1.3 MHz. This is achieved with a minimum number of measurements to safely find a measurement point with an attenuation within the approximately linear area. Based on this measurement point, the frequency deviation of the approximately linear area can be directly defined, or a calculation of the inversion point in the loaded state is first performed through the linear equation of the approximately linear area, and then a calculation of the frequency deviation of the approximately linear area in the charged state with respect to that of the discharged state based on both reversal points. To detect the tufts in the result of the
measurement, it is necessary to insert another transmit and receive antenna 3 and 4 into the segment of the burner supply line 1. These are rotated azimutially by 90 ° with respect to the antenna of emission and reception 2 and 3, but axially at the same height as the latter (axially aligned flush). To define an average load that takes into account the tufts, by alternate electric fields is alternately defined by the antennas of emission and reception 2 and 3 and 3 and 4 1a load of the air stream
with fine-grained carbon as described above, and a mean value is formed from the two measurements. This then takes into account an existing lock. Multiple repetition of this cycle with medium value formation can improve accuracy
of the measurement result. It is convenient to repeat the cycle until the average value formed globally no longer varies or only insignificantly. To detect strands, two alternating electric fields are excited through the emitting antennas 2 and 4.
equal frequency and equiphasic. These are superimposed inside
l - ?? ^ of the burner supply conduit 1 to give a resultant alternating electric field. Through the receiving antennas 3 and 5, the mutual interference of both alternating fields of equal frequency and equiphasic is recorded, with the attenuation of the resulting alternating electric field being defined along this measurement stretch. By varying the amplitudes of alternating electric fields of equal frequency and equiphasic (coupled with phase immobilization) can be rotated azimuthly by a maximum of 90 ° the direction of the alternating electric field resulting from the superposition of both alternating fields rotated by 90 ° with respect to one another. By means of the additional phase inversion of an alternating electric field, the turning sector of the resulting alternating electric field can be expanded to 180 °. In the present example of a burner supply conduit 1 with a diameter of 500 mm, through the antennas 2 and 4 with an attenuation of +20 dBm (corresponds to an emission power of approximately 100 mW) a field is excited alternating electric power inside the burner supply duct. To perform an azimuthal turn in steps of 22.5 ° of the alternating electric field resulting from the superposition of the individual fields that are excited azimuthally rotated by 90 °, the supply ducts of the antennas are attenuated with the values indicated in
tM-ft-fflW-f ^ y-MSf-Hlffffll fc lai ítety ^ table,
Direction Antenna 2 Antenna 4 azimuth 0 ° 0 dB -50 dB 22.5 ° -1 dB -9 dB
45 ° -3 dB -3 dB 67.5 ° -9 dB -1 dB
90 ° -50 dB 0 dB 112.5 ° -9 dB (phase inversion by 180 °) -1 dB
135 ° -3 dB (phase inversion by 180 °) -3 dB 157.5 ° -1 dB (phase inversion by 180 °) -9 dB
In the indicated individual azimuthal directions of the resulting alternate electric field the definition of the deviation of the frequency of the linear range is carried out and through this the calculation of the load of the air stream with fine-grained carbon as described with anteriority. The determined frequency deviations are summarized in the following table:
Azimuth direction Deviation of frequency 0 ° 125 kHz 22.5 ° 177 kHz 45 ° 200 kHz
J ^ £ agj gg? G? ^^ continuation of
Azimuth direction Deviation of frequency 67.5 ° 266 kHz 90 ° 376 kHz 112.5 ° 260 kHz 135 ° 192 kHz 157.5 ° 160 kHz
It is possible to unequivocally check a maximum value of the deviation of the frequency and thus of the load by 90 °. This means that in the azimuthal direction at 90 ° there must be a lock. Figures 3 and 4 illustrate the resulting alternating electric field within the burner supply conduit 1 in the case of the azimuth direction of 0 ° (Figure 3) and the azimuthal direction of 90 ° (Figure 4). The relation between the maximum deviation of the frequency (maximum load) and the minimum deviation of the frequency (minimum load) can be conjectured about the radial position of the lock. In the present case, that is, in a ratio of 1: 3, the lock is near the wall of the tube. The more this proportion moves 1 the closer the lock of the central point of the circular section of the tube is to 1. A strand that is directly and centered at the center point of the circular section of the tube can not be detected. Naturally, a tuft detection only makes sense if the tuft is relatively stationary, that is, if it is almost stationary in relation to the time of the measurement. In the case of actual measurement times of a few milliseconds, this is generally the case in practice. The purpose of the tuft detection in the present example is in any way the measures to remove the tuft. Regarding this, only the quasi-stationary tufts have significance.