FI64747C - SAETT ATT STYRA RENSFOERLOPPET VID RENSNING AV FILTERMATERIALET VID TEXTILA SPAERRFILTER - Google Patents

Description

ra1 ANNOUNCEMENT, _ 1¾ (11) uTLAGG N I NCSSKRI ft 6 4 747 t®) Patent tieddelat ^ ^ (51) Kv.lkp / Int-CI. 3 B 01 D 46/04 FINLAND — FINLAND (21) P * t «nttlh * k« mu * —Pttenttiueknk »* 80032t (22) HtkeeihplW — AiMMoilnptfag 04.02.80 (EN) (23) Alkuptfrt — Glklghetsdag 04.02.80 ( 41) Tullut iulkheksl - Bllvit offwitllg 13 · 08.80

National Board of Patents and Registration / 44) Date of Nihttviksipuion and KuLjuikabu. -

Patent · och registerstyrelsen Araetun utbgd och uti. «Krift * n public end 30.09 · 83 (32) (33) (31) Pyydetty« tuolkeu * —Begird prloritet 12.02.79

Sweden-Sweden (SE) 7901181-3 (71) Fläkt Aktiebolag, Sickla Alle 13, Nacka, Sweden-Sweden (SE) (72) Roland Apelgren, Växjö, Sweden-Sweden (SE) (74) Oy Kolster Ab (54) The present invention relates to a method for controlling the cleaning activity in the cleaning of the filter material of textile filters according to the preamble of claim 1. The present invention relates to a method for controlling the cleaning activity in the cleaning of the filter material of textile filters according to the preamble of claim 1.

In a conventional control system, the hose filter cleaning system is usually controlled by the pressure drop of the plant from flange to flange. Both inlet and outlet dampers as well as duct losses are included in the pressure drop from flange to flange. Cleaning begins when the limit value for the pressure drop from flange to flange is reached. The Interval of Purifications is thus dependent on the dust container of the gas. The method is well suited for processes where the operating conditions, i. the gas flow, gas temperature, and dust content are essentially unchanged.

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However, when the gas flow and dust concentration vary, the gas flow tends to largely control the control system described above, which is clearly unsuitable from a separation point of view.

Because the pressure drop from flange to flange is always proportional to the gas flow, cleaning can begin without being dependent on the layers of dust in the hoses, due to short-term increases in flow. The result is over-cleaning, i.e. the dust cake breaks and the filter media remains open to the gas stream. Emissions as well as hose wear and residual resistance increase because a fine portion of the dust vcL is easier to penetrate through the open filter media.

The opposite use case can also occur, i. high dust content and low gas flow, resulting in a brisk growth of the dust cake without starting cleaning. Thus, the growth of dust layers is not in itself sufficient to reach the limit value for starting cleaning with a lower gas flow. As the gas flow increases, cleaning starts immediately, but then the cleaning power (impulse pressure) is not adjusted for the thicker dust cake. As a result, many cleanings are required to clean the filter, which consumes more hoses and shortens service life. In extreme cases, it may even happen that the operating point of the plant moves to an upper working point, which is associated with a greater pressure drop and a lower gas flow. The upper working point concerns the intersection between the system plant and the fan curve. When a plant includes a pulse-cleaned filter, the plant curve takes the form of an obliquely upward parabola with a "tip" corresponding to the maximum possible filter flow. Once the upper operating point is reached, the plant must be restarted to return it to the lower operating point, which is associated with a lower pressure drop and a higher load.

It is also known to control the cleaning operation of a hose filter by initiating cleaning impulses at a predetermined interval, which is then adapted to provide the required cleaning in the case of use where the load is greatest. The control then takes place by means of a time clock arrangement. It is clear that when the load on the filter falls below the maximum load, the system requires cleaning when cleaning is not necessary, resulting in high filter media wear and higher emissions.

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Po. it is an object of the invention to provide an improved control system which eliminates the disadvantages of known methods. This is achieved as defined in claim 1. The invention is thus based on the realization that the dust layer on the filter medium, usually the filter hoses, must control the cleaning system, so that regardless of variations in gas flow and dust content, cleaning always starts when the hoses have the same dust layer. Claims 2 and 3 define a suitable procedure which takes into account the viscosity of the gas, which is expedient when, in addition to the flow variations of the gas to be purified, there are variations in its temperature. Claims 4 to 7 define alternative ways of controlling the cleaning power of a cleaning system by influencing parameters relevant to the cleaning power.

The invention will now be described in more detail in connection with the accompanying drawing, which shows a cross-section of a filter device.

In the drawing 1 shows a filter housing in which filter chambers 2 with cassettes 3 or packages containing several rows of hose filter hoses 4 are placed. In the filter housing, the raw gas is led through the duct 7 to the raw gas inlet 8 of the filter chamber and thus penetrates through the filter hoses 4, whereby the dust remains on the surface of the filter medium. The purified gas is led from the clean gas side of the filter chamber through the clean gas outlet 9 to an outlet duct 10 in the filter housing connected to the clean air duct 6. The filter shown includes a plurality of non-shown filter chambers connected to common ducts 7 and 10. sealing filter palms as necessary for inspection, filter replacement, etc. For this purpose, an elevator device 13 is used, with which the cassette is lifted up from the filter chamber. The filter chamber shown on the right in the figure is closed by the damper 12. The left filter chamber is in use, as shown by the position of the damper 11, and the gas flow is indicated by arrows indicating the flow direction.

To clean the filter hoses, a cleaning device 14 is used. This comprises, in the form shown, a pressure vessel 15 for the cleaning medium, i.e. compressed air, a valve 16 for supplying the cleaning medium to a distribution channel 17 provided with a nozzle tube 18.

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The operation and embodiment of the cleaning device shown in the figure will not be described in more detail here, but it should only be mentioned here that they are am. of the type described in U.S. Patent 4,033,732. Cleaning is accomplished by directing a pressure push down into the hose, allowing the filter media to accelerate and decelerate, causing dust to detach from the filter media and accumulate in the dust bag 19. This cleaning procedure has been thoroughly tested and the parameters affecting cleaning performance are well known.

According to the invention, the cleaning system is controlled as follows. By means of the probe 20 placed in the flue gas duct 5, the total pressure and the static pressure of the gas are measured, whereby the pressure transmitter 21 can register the dynamic pressure of the gas and its variation in time. Since the dynamic pressure is a function of the gas flow, a measure of the variation of the gas flow is thus obtained, and when the the duct area and the total surface area of the filter medium, the appropriate filter processing gives the filter load vf as an output signal from the pressure transducer 21. In the determination, the filter load is thus a quotient between the gas flow (m / s) and the filter area 2 (m) 06 m / s.

The pressure sensor 22 is located on the raw gas side of the filter chamber (at the raw gas inlet 8) and its known pressure is transferred to the pressure transducer 23. The second pressure sensor 24 is located at the clean gas outlet 9 of the filter chamber. . The separation pressure p ^ is then pressure drop through filter media. In common applications it ranges from 0.75 to 2.5 kPa. Output signals from pressure transducers 21 and 23, i.e. v ^ and p ^, are fed to the electronics unit 25 for further processing. According to the invention, the filter resistance S is calculated here, which is defined as the quotient between the pressure drop p 1 through the filter medium and the filter load v 1. The usual values of S are 15-50 kPa (m / s). The output signal S from the electronics unit is applied to a limit value unit 26, where a comparison is made with the target value So of the filter resistance and which gives a signal C for filter cleaning when the filter resistance S has risen to the set target value So. The signal C is fed to the control electronics unit 29, which provides the signals required by the cleaning sequence node 14 to perform the cleaning. In this way, the compressed air compressor is started and, in addition, a grate-mechanical valve operates, which opens the valve 16 via the control valve and thus starts the cleaning operation.

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Process applications often occur where the temperature of the gas varies greatly over time. In this case, the viscosity of the gas also changes, which affects the pressure drop through the filter medium without changing the dust cake deposited on the filter medium. Since, according to the principle of the invention, only the size of the dust layer can affect the control of the cleaning system, the invention comprises a suitable procedure for normalizing the determination of the filter resistance by means of a check temperature To when the gas temperature and thus the viscosity varies. This is done so that the temperature sensor 27 senses the temperature of the gas and transmits the value of the absolute temperature T of the gas to the electronic unit 25 via the transducer 28. When calculating the filter resistance S, the quotient is multiplied here by the value p ^ / v (To / T) **, where To is the control temperature ° K and T is temperature ° K.

A \ is a constant with a value of 0.7 6 at temperatures below 200 ° C.

According to the invention, the cleaning operation is controlled by changing one of the parameters that are relevant to the efficiency of the cleaning operation. The most suitable way for the practical application of the invention is to control the cleaning power by changing the cleaning interval or the mutual interval of the cleaning pulses.

In this connection, it should be noted that the cleaning of the cartridge containing the filter hose usually takes place line by line and that the cleaning interval refers to the time from the start of cleaning of one filter line of the cartridge to the time when the filter lines are cleaned and the next cleaning cycle is started. Thus, the cleaning cycle may imply a rapid purge of the filter package and the time to the next cleaning interval is controlled accordingly. In the second case, the cleanings take place line by line without interruption after the cleaning of the cassette and instead the time between the cleaning pulses is changed. When heavy dust settles on the filter medium, cleaning begins at short intervals, and when little dust settles, corresponding intervals are formed for a long time.

Since the cleaning power is dependent on the pressure of the cleaning medium or pulse, so that the high pressure gives a stronger cleaning power than the low pressure, the pressure of the cleaning pulse can be changed according to an alternative method to adjust the cleaning power. In this case, the time interval between pressure pulses is preferably constant, and before each purge the system emits a signal that affects the purge pressure so that the incoming purge pulse 6,64747 is just as strong as necessary to achieve the required purge. The control of the impulse pressure itself can take place in various ways, e.g. by controlling the pressure in the tank, which is well understood by a person skilled in the art. Alternatively, the purge power of the purge impulse can be adjusted by changing its duration. If the impulse is switched off early, a lower cleaning power is obtained than if it is allowed to act as a whole. In practice, this can be done by changing the duration of the signal C.

To illustrate the invention in more detail in the following application example. The experiment was performed in a hose filter plant that cleaned the gas after an electric arc furnace. In these plants, the gas flow varies a lot during operation and in addition the temperature varies. The flow through the filter ranged from 300,000 Nm / h to 440,000 Nm3 / h and the temperature ranged from 20-100 ° C. The filter plant consisted of four compartments, each with 336 hoses, each with a length of 5 m and a diameter of 0.127 m. The total filter area totaled 2,286 m. Compared to normal use, the use according to the invention resulted in an increase in the average purification interval of 33% from 1.25 minutes to 1.65 minutes. Then, in addition to the gas temperature variation was taken into account, the purification interval was further extended from 1.65 , To 85 minutes.

The advantages obtained by using the invention and compared with the conventional technique are summarized as follows. Filter hoses are cleaned whenever the hoses have a certain layer of dust, thus avoiding excessive cleaning, which would consume the hoses more. In this way, the hoses achieve a longer service life. The total emission of the filter plant is reduced because the hoses are not cleaned too much, and there is always a dust cake left on the filter media. This also prevents the fine dust from penetrating deep into the filter medium, which gives a lower residue resistance and thus a lower average pressure drop through the filter hoses. This means significant energy savings in the form of less fan operation. In addition, the lower number of cleanings results in a reduction in the energy consumption of the cleaning system itself.

Claims (7)

64747 7 A method for controlling cleaning operations by cleaning filter media from textile barrier filters, mainly hose filter-type filters, in which the contaminated gas is fed into the filter chamber through a raw gas inlet and the gas passes through the filter medium in the filter chamber, leaving is achieved by applying a compressed air impulse to the filter medium from a cleaning system controlled by the control system, characterized in that the control system measures the pressure drop (p ^) through the filter medium and the filter load (v ^), which is the quotient between the gas flow and the filter area; forms the quotient between p ^ jn and v ^, i.e. a filter resistor (S) which, when compared to the target value (So) of the filter resistor, provides a signal for controlling at least one parameter which affects the power at which the cleaning system cleans the filter medium. Method according to Claim 1, characterized in that the control system measures the absolute temperature (T) of the gas and the temperature in question by means of temperature sensors. in the calculation of the filter resistance, taking into account the the temperature is corrected by a ratio which determines the change in viscosity of the gas with respect to the control temperature T. "o Method according to Claim 2, characterized in that the correction is effected by calculating the product of the quotients p ^ / v ^ and (T / T) α, where To is the check temperature ° K and a is constant. Method according to Claims 1 to 3, characterized in that it affects the time between cleanings. Method according to Claims 1 to 3, characterized in that the control system controls the cleaning power of the cleaning system by influencing the time interval between the cleaning pulses. Method according to Claims 1 to 3, characterized in that the control system controls the cleaning efficiency of the cleaning system by influencing the cleaning pressure of the cleaning impulse. A method according to claims 1-3, characterized in that the control system controls the cleaning power of the cleaning system by influencing the duration of the cleaning impulse.