FI121557B - Arrangement and method for monitoring bed state of a fluidized bed reactor and fluidized bed reactor - Google Patents

Description

ARRANGEMENT AND METHOD FOR MONITORING THE FLOORED BED REACTOR PED'S STATUS AND FLOATED BED REACTOR

The present invention relates to an acoustic emission-measuring arrangement of a bed of a fluidized bed reactor, in particular a fluidized bed bed boiler, whereby changes in the fluidized bed state, in particular the particle size, can be detected in real time.

Fluidized bed reactors are widely used for a variety of purposes such as combustion, gasification, chemical and metallurgical processes. Fluidization refers to the state in which fine solid 10 is fluidized by gas or liquid. Depending on the process, various solid bed materials are fluidized and / or recycled in the systems. In combustion processes in the fluidized bed boiler, the bed material is typically sand or the like. In a fluidized bed boiler, fluidization is achieved by blowing air through a solid bed material on the air distribution grate. The fluidized bed may contain particulate fuel such as carbon, coke, wood, waste or peat, as well as other particulate matter such as sand, ash, sulfur adsorbent, catalyst or metal oxides. The coarse fraction of fuel ash, stones, etc., build up in the bed, which requires their removal. Elements of fuel also accumulate in the bed material, which results in aggregate formation in the bed. Eventually, the presence of too coarse material may lead to the collapse of the entire floating bed and thus prevent the entire process from working. In order to guarantee the operation of the fluidized bed process, the particle size of the fluidized bed material must be kept within certain limits. Therefore, it is important to continuously monitor the bed condition, change conditions, and thus prevent excessive build-up and accumulation of coarse material in the bed.

From WO 2005/038420 there is known a method for monitoring the content of fluidized bed bed material by determining the temperatures at the top and bottom of the bed and monitoring the change in the difference between these temperatures. The increase in temperature difference is an indication of the increasing proportion of coarse material. At the same time, it is advantageous to take samples from the bed to determine the coarse material, especially when the temperature difference indicates that the coarse material content is above a certain value.

EP 1106984 defines agglomerates in a reaction vessel, such as an olefin polymer fluidized bed reactor, by installing a detector rod whose extent of elongation / deflection is measured when the agglomerates collide with it. The rod is mounted at an angle of 20 to 70 degrees with respect to the flow of gas and particles.

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WO 00/43118 discloses a method in which the condition of a fluidized bed is monitored by determining the pressure across the fluidized bed segment at various levels in the vertical direction.

One of the problems with the above methods is probably the inaccuracy due to e.g.

5 material that attaches to the measuring sensor, which makes it difficult to measure the correct size.

US 5022266 discloses a method wherein e.g. flow uniformity / unevenness in the fluidized bed can be monitored. Sensors (typically an accelerometer or pressure sensor) attached to the outer wall of the process vessel measure wall vibration and determine the power spectrum as a function of frequency. Measurements are made at several points around the circumference of the vessel and, in addition, at each point the power spectrum area containing the resonance peak at each measuring point is determined. Later a new measurement is made and compared to the previous one. The basic measurement is made immediately after the start of the process when it is known that the flow in the bed is uniform. This measurement is indirect and intermittent and thus does not produce data continuously.

The object of the present invention is to provide a more reliable arrangement for continuous monitoring of the bed state of a fluidized bed reactor, such as a fluidized bed boiler. In particular, the purpose is to determine and monitor the proportion of coarse material in the fluidized bed.

To accomplish these purposes, the arrangement of the present invention is characterized in that it comprises at least a sensor for measuring acoustic emission from fluidized bed particles, the sensor comprising a rod-like waveguide spaced at a distance 25 inside the reactor and a second end outside the reactor provided with piezoelectric a transducer portion for converting the received emission into an electrical analog signal, wherein the reactor internal waveguide portion comprises an uninsulated portion for receiving the emission and an isolated portion; and - means for processing the received signal to determine a frequency spectrum and / or a curve for monitoring changes in the fluidized bed within a certain frequency range.

The method is characterized by: - continuously receiving acoustic emission caused by collisions of bed particles with a sensor extending into the reactor interior, the internal reactor 3 part comprising an uninsulated part for receiving emission and an isolated part, - transforming the received emission into a digital signal; a curve 5 in a specific frequency range suitable for the application and comparing it with the corresponding frequency spectrum of the bed normal state and / or the envelope to detect changes in the bed state.

The invention also relates to a fluidized bed reactor employing and applying the arrangement and method of the invention.

The invention is based on the idea that the condition of the fluidized bed is monitored by installing a transducer transducer (waveguide) to receive the acoustic emission, or high-frequency oscillation wave, caused by particle collisions at the inner end of the transducer. The rod passes the oscillation waves to a piezoelectric transducer sensor associated with the rod, which measures the selected frequency and converts the high-frequency energy applied to the rod directly into an electrical signal. The electrical signal is passed through an analog filter and an amplifier to an A / D converter, from which the resulting digital signal is filtered and processed for data processing.

From the filtered digital signal, a real-time Fourier (FFT) transform is calculated, which is a frequency spectrum that shows instantaneous, rapid changes and can be used as a criterion for estimating the instantaneous situation. Over a longer period, an averaged-curved envelope is calculated to monitor natural bed change, comminution, or agglomeration.

In preliminary experiments, the frequency spectra of three fluidized beds with known different roughnesses were determined. There was a clear difference in the spectra, especially within a specific frequency band. The Kar-30 had the strongest peaks in the spectrum, while the spectrum in the finest bed had a smoother spectrum. Determining the averaged envelopes of these spectra shows that there are substantial differences between the envelopes of the different coarseness. By setting the envelope in this manner for a suitable period of time, it reliably indicates changes in the fluidity of the fluidized bed.

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The bed monitoring method of the invention responds consistently to the characteristics of the bed state, such as fluidization rate (energy level of particle collisions), suspension density (collisions / unit of time, second) and fluidity of the fluid (collision energy). Indirectly through the above quantities, the measurement results are also influenced by e.g.

5 position, length, shape and hardness, grain shape, surface texture of the detector rod.

The arrangement according to the invention preferably comprises the following elements: 10 waveguide (detector bar) - piezoelectric sensor - filter - amplifier - A / D converter - digital filtering - FFT conversion - data processing - user interface.

The invention will be described in more detail with reference to the accompanying drawings, in which Fig. 1 shows a preferred structure of a waveguide rod, Fig. 2 shows a typical frequency spectrum (intensity / frequency) and corresponding curves of a fluidized bed, and Fig. 3 shows a coarse and fine fluidized bed.

The structure of the waveguide is illustrated in Figure 1. An elongated rod-shaped waveguide 2 having a length L1 is mounted through a wall 4 of a reactor, such as a fluidized bed boiler, into a bed in the boiler. The rod material must be heat and abrasion resistant. Part of the waveguide rod is provided with an insulator 3 in the reactor to prevent acoustic emission at this point of the rod. The length (L2) of the uninsulated part, which influences the "sampling distance", that is, how far the rod is able to collide with the particle, is optimized according to the target (each bed). On the other hand, the width and length of the uninsulated part determine the sampling area, that is, the number of collisions per unit area / m2. The dimensions of the rod thus determine the specificity of the measurement.

The shape of the rod (cross-sectional shape; massive / hollow) affects the flow resistance 30 and the angle of impact of the particles. The waveguide rod must not be shaped in such a way that it adversely affects the flow locally and thereby interferes with the operation of the bed. Excessive resistance also increases adhesion of the moth material to the rod. All in all, excess material should be prevented from sticking to the waveguide rod as much as possible because the excess material will passivate the waveguide, change the area of measurement, and finally the waveguide will not be able to measure if completely covered. The shape of the waveguide also influences the angle of collision between it and the particle. The shape is such that the 5 particle collision angle to the surface of the waveguide rod should be greater than 0 degrees, preferably 45 to 90 degrees, most preferably close to 90 degrees, or about 90 degrees, since the perpendicular impact on the waveguide provides the best energy level. The waveguide position relative to the bed flow should also be such that the collision angle of the particle 5 is preferably 45 to 90 degrees, most preferably about 90 degrees. At an angle of 90 degrees to the flow, a "" pure collision "is obtained.

The length L3 of the insulated part is determined by e.g. where the bed is the measuring point, that is, how deep into the reactor the rod must reach to reach the desired measuring point (location and length of uninsulated section 10).

The waveguide rod must also be insulated from the reactor core so as not to interfere with the measurement. At the pass-through, the rod in the reactor wall is protected by a pass-through sleeve 5 and a vibration isolation 6, which eliminates the interference of the reactor body vibrations with the bed monitoring. Adequate support and the duration of the pressure difference between the reactor core and the environment are also taken into account. The rod thus installed is also easy to check and replace if necessary.

The piezoelectric sensor 7 is not mounted inside the reactor and is preferably not mounted directly on the wall of the reactor but at a distance from it. This allows this sensor to be installed outside the thermal insulation, facilitates maintenance and calibration work, and prevents the sensor from overheating.

In an analog filter, high pass, low pass, or band pass are made as needed. It selects the best correlating frequency range according to the application and filters out any interfering frequencies. After filtering, the signal is passed through an analog amplifier and amplified at the intensity required by the application. The signal is then converted to digital in the A / D converter for ease of processing.

The converted signal is digitally filtered in an optimum manner selected for the application so that one or more selected frequency bands are highlighted and the result is a system for optimal tracking of bed roughness. The frequency range is selected so as to best represent the frequency range in question. changes in the fluidized bed state of the process. Preliminary experiments can determine the optimal frequency range for each process, i.e., in which region the changes in the pro-35 process, especially the changes in bed roughness, are most evident.

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Typically, a plurality of sensor gauge waveguides are installed in the fluidized bed reactor at process-optimal locations. In this way, the bed can be monitored in height and width at different points in the bed. The location of the waveguide is selected so that it is in the optimum range for currents as described above, whereby the risk of adhesion is also minimized.

The information from the sensor at each measuring point is derived as a filtered digital signal. The processed signal is output to the user interface in the manner selected, e.g., as a continuous frequency spectral display, as a long-term envelope, or simply by printing over the preset alarm thresholds 10.

Figure 2 shows a typical frequency spectrum as well as a corresponding envelope for three fluidized beds of known roughness. The coarsest bed has the strongest spectrum and envelope.

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Figure 3 shows the envelopes of the coarse and fine beds when measuring at two levels in the bed. The intensity of the coarse bed is stronger than that of the fine bed. There is a significant, essential difference in intensity. The intensity of a finer bed is on average half that of a coarse bed. Thus, the continuous monitoring of bed state in ai-20 chicken in a finer bed indicates an increase in intensity indicating an increase in particle size, i.e. coarseness. When the intensity value exceeds a certain threshold value defined for each application, the conditions in the fluidized bed reactor are changed. For each application, the frequency range with the highest intensity and difference is preferably selected for continuous bed monitoring.

In the method of the invention, the frequency spectrum and envelope curves are the actual tools for analyzing bed roughness. The curve, which is determined for a sufficiently long time, reliably and clearly indicates the change in the roughness of the bed. In tests, it has been found by measuring the acoustic emission from particle collisions that it has a direct, clear correlation to bed conditions: 30 - Correlation to bed fluidization rate - Correlation to bed size - Correlation to bed roughness and change - Correlation of waveguide band / bed current.

The present invention achieves the following advantages: 7 - Acoustic emission (AE) measurement can be used to monitor the state and changes in the state of the fluidized bed; the system can be trained to recognize normal situations and alert for abnormal changes in the bed; 5 - Combining other normal process data with AE data avoids unnecessary alarms during normal changes to the driving situation.

The invention is not limited to the exemplary embodiments, but can be modified and applied within the scope of the inventive idea as defined in the claims.

Claims (8)

An arrangement for monitoring the bed state of a fluidized bed reactor, in particular for monitoring the content of coarse material in the bed material, characterized in that the arrangement comprises at least 5 sensors for measuring acoustic emission from fluidized bed particles, comprising a rod-shaped waveguide (2) the outside end of the reactor is provided with a piezoelectric sensor portion (7) for converting the received emission into an electrical analog signal, wherein the inside of the reactor waveguide comprises an uninsulated portion 10 for receiving the emission and an insulated portion (3); and means for processing the received signal to determine a frequency spectrum and / or a curve curve for monitoring changes in the fluidized bed within a certain frequency range. Arrangement according to Claim 1, characterized in that the means for processing the electronic analog signal comprises at least an analog filter and an amplifier, an A / D converter and a digital filter. Arrangement according to Claim 1 or 2, characterized in that the dimensions of the uninsulated part of the waveguide (2) 20 determine the sampling area, that is, the number of collisions per unit area per time unit. Arrangement according to one of the preceding claims, characterized in that at least two waveguides (2) are arranged at different positions in the reactor in the height and / or in the horizontal direction. Arrangement according to one of the preceding claims, characterized in that the waveguide rod (2) is of such a shape and position that it does not substantially interfere with the flow in the bed, such that the particle has an impact angle to the surface of the waveguide rod 45 to 90 degrees, and the position of the waveguide relative to the bed flow is three-dimensional such that the particle collision angle is preferably 45 to 90 degrees. Arrangement according to one of the preceding claims, characterized in that the collision angle of the bed particle-35 coils with respect to the rod (2) is such that it raises the signal energy level, whereby the collision angle of the particle relative to the waveguide surface. A method for monitoring the bed state of a fluidized bed reactor, in particular monitoring changes in the bed material roughness, characterized by: - continuously receiving acoustic emission from bed particle collisions with a sensor extending into the reactor interior, the sensor reactor interior comprising an insulated part transforming the received emission into a digital signal, and - determining a real-time frequency spectrum and / or envelope of the digital signal in a specific frequency range suitable for the application and comparing it with the corresponding frequency spectrum and / or envelope of the bed normal state. 15 Fluidized bed reactor, such as a fluidized bed boiler, characterized in that it comprises an arrangement according to claims 1-6 for monitoring the bed state. 20