SE458988B - PROVIDED IN AN ELECTROSTATIC SUBSTITUTE DETERMINANT TO CHANGE A CHANGE IN SUBSTANCE DISPOSAL - Google Patents

Description

458 988 to a precipitation electrode, where a dust layer is built up. Usually that the higher the voltage that occurs between the electrodes, the better and more efficient the dust separation takes place.

However, it is known that such a voltage can not be selected too high, since too high values will create undesirable estimates between the electrodes.

It is therefore common for the voltage between emission electrodes and precipitation electrodes are not kept constant but are periodically varied, from ex. 80% of the voltage at which the previous estimate occurred, with a slow increase until the next estimate occurs.

This ensures that changes in operating conditions lead to a adjustment of the voltage in the dust collector.

The present invention finds a particularly suitable application in such electrostatic precipitators which are adapted to separate quantities of dust from a gaseous medium and therefore dust the separator of several units, with one for each unit, separately controllable current and / or voltage supply circuit, and an associated control equipment, which enables a separate control of each unit current and / or voltage values. ' With such an electrostatic precipitator, it is previously known to sow affect any control equipment that the controllable current and / or voltage The supply circuit supplies the electrodes of the unit with a maximum voltage. and / or current that the electrode array or device can withstand without an unacceptable number of estimates occurs per unit of time.

It is further known that certain types of dust lead to limitations in the efficiency of the separator by an excessive current per unit area against the precipitating electrodes charge the dust layer faster than it is discharged against the precipitation electrodes. Such a charge of the layer then leads to 458 988 breakthrough in the dust layer itself, whereby dust is thrown out into the gas again, s.k. re-radiate nine ng.

It is also known that the degree of separation in a given dust separator is depending on the composition of the substance as far as possible separation as separation at a given energy supply. This leads to a certain oversizing of most dust collectors to this should not limit, for example, the selection of suppliers.

In some cases, the emission of dust via the chimney can be less than one tenth of the prescribed limit values if the separator is used to the maximum.

This result may seem desirable but is obtained at the price of worthwhile energy losses.

With the help of smoke density meters in the chimney, the operating parameters for the electrostatic precipitator is adjusted so that the current emission the dust content is below the limit value set by the authorities but not so far below that unnecessary energy loss occurs. An optimization of F ~ the parameters of the individual units 1 the dust collector is difficult to do p.g.a. that i.a. a change in an entity leads to changes in holdings in all downstream units.

Furthermore, the distance to the smoke density meter is often 100 m or more and the time constants in regulation are therefore quite low.

The optimization of the parameters for the individual units is also made more difficult of the fact that the dust separation is very different in the different ones the units with large quantities of separated dust in the first unit and significantly less in the downstream units.

U.S. Pat. No. 4,490, 159 discloses a method that in a electrostatic precipitator, of the above nature, try create conditions for efficient dust separation at low energy needs by for each of the units, these in turn and order is added to a changed energy supply, with a pre-determined 458 988 value, and then the energy supply is returned to the original league value. In addition, it is determined by the changed energy supply caused the change in the dust separation for each of the said units, so that in an evaluation of the results for all units can it and only the unit alternatively the units where a changed energy supply provides the conditions for the most efficient dust separation at the lowest energy requirement, is switched on without having to exceed a predetermined maximum value of the dust emission.

Finally, it is also known that electrostatic precipitators, such as usually supplied with high voltage direct current, in most cases requiring less energy for a given degree of separation if the current is supplied in the form of pulses. These pulses can vary in length from about 10 us to 10 ms and can come one by one or in groups. The residence time can vary from about 1 ms to Is. In these cases, there will be significantly more parameters to regulate and thus the search for the best working point becomes more complicated.

TECHNICAL CONSIDERATIONS, WHICH BASIS FOR THE CURRENT INVENTION The invention is based on the insight that in an electrostatic dust separators with several identical units placed one after the other in the gas flow , supplied with the same current, the voltage is highest in the first unit and successively, decreasing in downstream units. ' The reason for this decreasing voltage is that the dust contained in the gas provides a space charge with an opposite voltage as a result. The more dust the higher the counter-voltage and consequently this counter-voltage decreases then the gas is gradually purified.

The momentarily occurring voltage thus provides for each, unit, one indication of how much dust is coming into the unit in question or the existing gas contains, and the concentration and concentration of variations are reflected as an altered voltage, if the current is maintained constant, or in any other case as a change in the relationship between lan current and voltage. 458 988 If the incoming gas becomes cleaner, the voltage drops and if the gas becomes more polluted, the voltage rises, provided the current is kept constant.

Since all dust in the gas flow through the dust collector contributes to the The evaluation makes the evaluation of the voltage change significantly safer estimation of changes in dust concentration than a smoke density measure tare, which only measures along the narrow path through which the light beam passes.

A smoke density meter is therefore often provided with an integrating average formers, whose time constant can be over 30s. so as not to be too uncertain and momentarily strongly fluctuating values must be recorded.

This insight is used according to the invention to control, maximize or optimize the operation of a unit in the dust collector by power and / or voltage is measured.

With a constant current supply, you can thus in principle get a measure of instantaneous dust concentration in a unit by evaluating the voltage value for that device.

DESCRIPTION OF THE PRESENT INVENTION TECHNICAL PROBLEM Taking into account the prior art, as described above joke, it must appear as a technical problem to with simple means be able to quickly evaluate the current degree of separation for a unit and This is especially true when the degree of separation is to be evaluated for each and every one one of, or one or more selected, included in the dust collector devices.

Taking into account the previous state of the art, it must also get is considered to be a technical problem to be able to determine by simple means instantaneous degree of separation or dust concentration and hence opti- be able to control current and / or voltage values for each of the units in an electrostatic precipitator.

It is also a technical problem to be able to evaluate in a simple way the importance of the various operating parameters for the instantaneous separation 458 988 degree, especially in a dust separation system, which is followed downstream by multiple devices.

It is also a big problem to be able to create such opportunities one can quickly see the change in the degree of separation in a unit without install smoke density meters also between the units to reduce stand from the unit to the detector.

Furthermore, it is a very qualified technical problem to be able to evaluate their dust concentration in the gas as an average over a substantial part of the cross section of the channel, instead of measuring along just one line with the help of ex. a ray of light.

It is a particularly qualified technical problem to meet the above desire without the use of special instruments, which require costly maintenance and are expensive to purchase.

It is also a technical problem to do the evaluation using only that on the electrostatic precipitator usually already existing equipment.

It is of course a technical problem to make the evaluation independent which operating parameter is also varied in pulse-fed systems.

It is also a technical problem to do the evaluation of a device operating point independent of the dust concentration of the incoming gas.

It is a qualified technical problem to realize that changes in the degree of separation in a unit affects downstream units so that the effect of operating parameter changes in the upstream unit can assessed using the relationship between certain operating parameters in one or several downstream units.

It must also be considered as a qualified technical problem that using a device's current and / or voltage supply circuit to monitor 458 988 changes in the dust concentration occurring in the device itself through to let the circuit evaluate the relationship between instantaneous (or mean formed) current and voltage values in the device itself.

It will then be possible to achieve a monitoring that can take place independently of whether the change in dust concentration is due to one or more upstream located dust function of the unit or on changes of dust concentrations incoming to the dust collector.

LUSNINGEN The present invention now provides a solution of one or more of the above specified technical problems by indicating a method of dust collector, with an inlet for receiving a quantity of dust gas stream and an outlet to discharge one in the dust collector to some extent dust purified gas stream, and with a number, in succession, provided with separately controllable current and / or voltage supply circuits, units create the conditions to be able to quickly determine a change in the dust separation rate for one or more of said units.

In this connection, the invention directs that in order to determine said change in the dust separation in the said one unit utilizes occurring changes in current and / or voltage values applicable to a downstream, representative esvis in an almost downstream, located unit.

Said change in the dust separation in said one unit can also determined in a number of downstream units.

As previously reported, this means a change in the energy supply to an upstream unit, that in a downstream, preferably one immediately downstream, the unit may be affected by the changed energy supply. caused the change in the dust compartment of the upstream unit separation is quickly evaluated as an increase in voltage with increasing dust concentration and a decrease in stress at a decreasing dust concentration ration, if this is fed with constant current. Also other relationships between current and voltage can be evaluated. 458 988 When adjusting or changing the operating point of a first unit for example, the current in the other unit is kept constant and each end ring in the first unit, which results in an improved separation, manifests itself as a voltage drop in the other unit while each change that manifests itself as a degraded dust separation in the first the unit provides a voltage increase in the other unit.

If one or more downstream units are supplied with a constant current changes in voltage that have occurred can be evaluated in order to make changes in the dust concentration of the gas leaving it upstream unit and which is subject to the said changed energy feed.

Furthermore, the invention indicates that one or more units located downstream must be able to be supplied with a constant voltage and that its current variation evaluated or that simultaneous variations in current and voltage evaluations are evaluated.

The voltage supply to a device can also be regulated so that the voltage over a downstream unit, with constant current supply, is minimized alternatively, a current supply to a device can be regulated so that the voltage over a downstream unit, with constant current supply, is minimized.

If a device is supplied with a pulsed voltage, whose repetition rate and / or pulse energy content is regulated, so here too the voltage can exceed a downstream unit, with constant current supply, is minimized.

It has been found to be particularly suitable to allow current and voltage the values of the downstream unit, prior to the evaluation of the changes, be set at such values where neither types or characteristics with negative resistance are present.

The possibility of reaching a first unit then falls within the scope of the invention brought to the desired, optimal or maximum, function, an adjustment procedure is repeated by adjusting a second unit with the corresponding 458 988 evaluation 1 a third entity. The last unit cannot be tuned in this way, but there the difference in the operating conditions is compared with the penultimate unit quite small due to small dust concentration and it can, for example, be given the same setting as the penultimate.

The method according to the invention is useful for both direct current and heart rate monitors and can be used regardless of driving strategy. Its fold- most likely application is when maximum efficiency in desired and with appropriate evaluation, both the limit of as the appropriate bounce rate is determined.

The method is well adapted for automatic operational monitoring and is feasible easily computerized.

BENEFITS _ The benefits that can primarily be obtained are considered to be associated with a way in in accordance with the present invention is that it has thereby been created conditions for in an electrostatic precipitator, with a plurality between the inlet and the outlet arranged with separately controllable power and / or voltage supply circuits provided, devices, much be able to quickly detect changes in dust separation at one or several of these devices and thus create the conditions to get one rapid regulation of current dust separation.

BRIEF DESCRIPTION OF FIGURES A presently proposed embodiment, having the present significant characteristics of the present invention, will be further described by reference to the accompanying drawing therein; figure 1 shows in perspective view an installation, which shows one multiple units with only one transformer rectifier unit arranged For one of the units and shown one paragraph above the unit, 458 988 10 Figure 2 shows a circuit diagram of a transformer rectifier unit for a current and / or voltage supply circuit intended for one unit, figure 3 schematically shows a number of units connected in series, each provided with a circuit according to the figure 2, u Figure 4 shows a voltage / current diagram for those conditions which may be considered to exist at the three shown in Figure 3 the units, Figure 5 shows a voltage / current diagram for those conditions which can be considered to exist at the three shown in Figure 3 the units and where the breakpoints for re-radiation are showed, Figure 6 shows a proposed pulse rate valid for each and every one one of the devices and Figure 7 shows in strong simplification a separate control of the units. only current and / or voltage supply circuits orderly control unit.

DESCRIPTION OF THE NOW FURESLAGEN EXECUTION FORM Thus, Figure 1 shows in an perspective view an example of an electrostatic dust separator 1, consisting of a plurality connected one after the other four units, designated A, B, C and D, each equipped with an electrode group. A transformer / rectifier unit is required for each of these units, but 1 figure 1 has only one transformer / rectifier unit vi- sentence, and this has been given the reference numeral 3 and is illustrated cooperating with unit D. The orientation of the four units A, B, C and D is such that the output of a device is connected directly to the input time for subsequent unit, i.e. a pure series connection.

The reference numeral "D" illustrates the last unit and this one is, as Figure 1 shows, connected with its outlet Sa to a chimney 4. 458 988 11 Although an electrostatic precipitator constructed of is illustrated here a number of units, it should be considered that the invention may be used in even when each of these units can be considered as one separate electrostatic precipitator.

An electrostatic precipitator 1, of the type described here, shall: separate from air or gas, which carries particles, said particles. The the particulate gas stream is connected to an inlet 5 for the first unit "A" and allowed to pass through the first and then in turn and order other units "B", "C" and "D".

In the first unit "A", as in the others, the particles will electrically charged by an electric field, which is trained between built-in precipitation electrodes, which are placed next to each other as plates, and emission electrodes, placed between the plates. One dust particle entering this field becomes electrically negatively charged and this particle is attracted to the positive precipitation electrode and repelled by the negative emission electrode and thereby comes the particles to collect to the precipitation electrode.

Thus comes the dust-laden gas stream, which is connected to the inlet 5, to be purified more and more as the gas stream passes through the unit. "A", "B", "C" and "D" for the electrostatic precipitator, after which thus purified and separated gas stream from particles passes through the outlet 5a to the chimney 4.

As a result, the electric field thus comes electric charged dust particles to accumulate preferably to precipitate electrons. trod and forms there a coating or a layer on the tiles. When this coating or layer achieves a predetermined thickness the layer is mechanically pushed away from the precipitation electrode and falls downwards.

The particles therefore normally accumulate in one arranged under each unit dust pocket, and for the "A" unit, the dust pocket has been assigned a reference the designation "a". 458 988 12 Figure 2 illustrates a simplified circuit diagram for a transformer. tor / rectifier unit intended for the unit "D", but also other units have a similar unit, which shows that a line 6a, for alternating current supply is connected to two thyristors 8, 8a, connected in the opposite direction ning. Each thyristor is equipped with its own control electrode and these have assigned the reference numerals 8 'and 8a', and these are further used closed to an energy control circuit 7, shown as a block, only indicated in Figure 2.

The circuit 7 may preferably be of a type which is known in principle and which is already shown and described in detail in U.S. Pat 4,486,704.

The transformer winding "T1" cooperates with the transformer winding "T2", which is connected to a rectifier bridge 9. Negative rectified voltage which can be considered equalized due to the capacitances that are present between the grounded precipitating electrode 11 and the emission electrode 10, is connected to the emission electrode 10 for e.g. the device "D".

To control the instantaneous voltage acting between the electrode groups included in the unit 2 for dust separation, the circuit 7 requires information over the instantaneous DC voltage level and the magnitude of the current in the the separator. The level of the instantaneous voltage is obtained via line 12 while the instantaneous current value is obtained via line 13. The time torque when the AC voltage exceeds zero is evaluated via line 14.

The main purpose of the circuit 7 is to control the signals on the conductors 8 'and 8a 'to thereby allow a control and regulation of the current and / or voltage appearing in the electrode group "D".

A circuit, of the type shown in Figure 2, is thus connected to each and one of the various units, which form the indicated electrostatic the dust separator. 458 988 13 It should be noted that the present invention is not limited to one special number of units. For simplicity, it is assumed in the following the description that there are only three units, which are assigned here the reference numerals "A", "B" and "C".

One reason for such simplification is that the last unit "D" does not separates a lot of dust and that according to the invention this unit would can very well be set to the same values that apply to the unit "C".

Figure 1 shows that the unit "A" is the first of four units. and in which the major proportion of dust is separated, unit "B" er of the other, the one immediately downstream, in which one smaller the proportion of dust is separated, and the units "C" and "D" are made up of the third and the fourth unit, in which even smaller proportions of dust are separated.

Now when the units "A", "B" and "C", as Figure 3 illustrates via their circuits 7a, 7b and 7c, are supplied with a constant current, the unit "A", "B" resp. "C" is assigned a change in its energy supply by a hand determined value from a first energy level or voltage level to a second energy level or voltage level and then the energy supply can returned to the first energy level or voltage level.

Such a change in the energy supply to a unit results in a change in the dust separation, usually so that an increased energy gives an increased dust separation and a reduced energy results in a reduced dust separation in this device.

According to the invention, it is important to be able to set, for example, the dust supply resulting from the energy supply change the distinction change.

For this purpose, the invention is based on the insight that at a constant power for each of the downstream units, dust will the proportion change through said unit to cause a voltage change of 458 988 14 such that a larger dust concentration gives a higher voltage and a lower dust concentration gives a lower voltage.

However, it should be noted that the magnitude of the voltage change depends on the nature and concentration of the substance, but this risk is evaluated.

As long as relative considerations are performed, the absolute value does not need determined.

Also within the scope of the invention is the embodiment that without a di- directly forced energy supply change for the upstream unit current dust concentration in a unit can be detected and when this dust concentration exceeds or falls below a predetermined value the device can provide control signals to the electrical circuit of the current unit to change the energy supply there.

Figure 4 indicates the characteristic relationship between current and voltage in the three units "A", "B" and "C". The curves describe how tense increases with increasing current in a certain unit as it works with constant incoming gas flow with constant parameters (temperature, moisture content, dust content, etc.). The designations 20a, 20b, 20c indicate three different only working points for the dust collector's three units "A", "B" and "C", when everyone is fed with the same current.

When the unit "A" is given a changed (reduced) power supply, it will work in point 20a '.

This change in the current value of unit A makes it less separable dust and thus the dust concentration in downstream units "B" and "C" to increase. This change in dust concentration changes the the point for unit "B" to 20b 'and for unit "C" to 20c'. After- as these units "B" and "C" are still supplied with constant current the working point is taken vertically in the diagram. With implied relationships it gives new working point increased emission of dust through the chimney. 458 988 15 Figure 5 simply shows the relationship between current and voltage which applies when dust with high resistivity is to be separated. When the current rises gives above a limit value 30a "the voltage drops with increasing current. Already at a significantly lower value of the current, however, re-radiation begins from the precipitating electrodes to impair the separation. A reduction in current but in unit "A" so that the working point is moved from 30a to 30a 'can thus giving an improved separation and thus a voltage reduction in the unit "B" and "C" which are damaged by the movement of the working points to 30b 'resp. 30c '. In this case, maximum separation is easily sought in unit "A" by minimizing the voltage across unit "B" at constant current. The unit "B" may be fed during the evaluation of unit "A" with reduced current, so that no re-radiation in unit "B" may interfere with the measurement.

Figure 6 shows at the top the time course of a full-wave rectified voltage when the the magnitudes 8, Ba emit all half-wave pulses to the transformer "T".

The other two show the time course of the voltage when every third or every fifth pulse is passed to the transformer "T" to pulse supply the dust separator ren 2.

Under conditions which give a characteristic according to Figure 5, it is as rule favorable to supply the energy pulsed to the electrostatic the dust separator. It can t.o.m. be so that the degree of separation then increases the energy supply is reduced to one third or one fifth, as in figure 6.

If the size of the individual pulses increases when the number per unit of time decreases the degree of separation is usually even better. Even these conditions is evaluated very quickly according to the method indicated according to the invention.

A number of parameters affect the degree of separation in an electrostatic dust separator. The temperature and moisture content of the gas are of great importance, as is the gas speed is a critical quantity. While this complicates long-term comparisons can also be used as an error indicator. Deviations from normal 458 988 16 values that cannot be returned indicate that something is not working in the process before the dust collector.

If all units of the dust collector "A", "B", "C" and "D" are monitored of a central computer system, which then communicates with all units the operation of the dust collector is optimized in a very short time by successive adjustment of the various units. Normal operation is disturbed in many ways small degree, resulting in small extra losses of energy and small dust emissions release compared to the adjustment made so far with it relatively remove and slow down the smoke density meter.

In particular, the present invention proposes that said dust concentrator variations depending on the current and / or voltage variations shall be detectable in the immediately downstream unit "B", because that's probably the biggest change.

Via the separately controllable current and / or voltage supply circuit 7b for the downstream unit "B", where said unit is fed with constant current, said change in dust separation is evaluable as a value corresponding to the change in voltage value corrected by one factor applicable, for example, to the nature of the dust and / or the concentration. tion.

Alternatively, via said current and / or voltage supply circuit can be supplied with a constant voltage, said change in the dust separation is valuable as a value corresponding to the change in current value as well if necessary corrected as above.

It is obvious that the description shown has been concentrated on one lowering of the energy level of the unit "A" and that one of the lowered the energy supply corresponding voltage increase or decrease is evaluated in a or several downstream units, but the invention may, of course is utilized and used even when the changed energy supply refers to one increase from an energy level to a higher energy level and thereby evaluate the lowering or raising of the voltage that will occur in one or 458 988 17 several downstream units due to the changed dust separation which this higher energy supply may cause.

With reference to Figure 7, a control unit 21 is shown in strong simplification.

Via a time circuit 22 included in the control unit 21, switches 23a, 23b can and 23c are controlled to be connected during different time sections "t1" and "t2" and so on. to each of the units "A" and "B".

During the time section "t1" the switch 23a is activated and during the same time sections are sensing circuits 24b and 24c, to determine the torque tane the voltage value in the unit "B" and "C", connected. _ An alternative is to only sense occurring instantaneous values in the devices.

Via a calculation unit 25, the variation of the dust concentration can be determined possibly, using a pre-programmed correction factor.

There is nothing to prevent the voltage value changes from being exploited for both units "B" and "C" to determine therefrom within the time period "tl" occurring variations in the dust concentration from the unit "A".

This averaging can take place for a maximum of 1 minute, preferably less than 15 seconds.

Furthermore, it is proposed, especially in pulse feeding, that the dust concentrate The relationship should be evaluated by averaging a plurality of occurring current and / or voltage values.

The invention is of course not limited to that exemplified embodiment but may undergo modifications within the scope of the invention. idea illustrated in the appended claims.

Claims (10)

458 988/8 / PATENT REQUIREMENTS 1. Set in an electrostatic precipitator (1), with an inlet (5) to receive a dust-laden gas stream and an outlet (Sa) to emit a gas stream purified to some extent from dust, and with a number, connected one after the other , equipped with separately controllable current and / or voltage supply circuits, units (A, B, C, D), determine a change in the dust separation in one of said units (A), characterized in that for determining said change in the dust separation in said one unit (A) utilizes occurring changes in the current and / or voltage values applicable to a downstream unit (B, C or D). 2. A method according to claim 1, characterized in that said change in the dust separation in said one unit (A) is determined in a unit located downstream (B). 3. A method according to claim 1, characterized in that said change in the dust separation in said unit (A) is determined in a plurality of downstream units (B, C). 4. A method according to claim 1, 2 or 3, characterized in that one or more downstream units (B, C) are supplied with a constant current and that occurring changes in the voltage are evaluated to thereby determine changes in the dust concentration for the gas leaving the upstream unit (A). 5. A method according to any one of the preceding claims, characterized in that one or more downstream units (B, C) are supplied with a constant voltage and that its current variation is evaluated. 6. A method according to any one of the preceding claims, characterized in that for the downstream unit (B) the simultaneous variation of occurring current and voltage values is evaluated. 458 988 7. According to claim 1, characterized in that a voltage supply to a unit (A) is regulated so that the voltage across a downstream unit (B), with constant current supply, is minimized. 8. A claim according to claim 1, characterized in that a current supply to a unit (A) is regulated so that the voltage across a downstream adjacent unit (B), with constant current supply, is minimized. 9. According to claim 1, characterized in that a unit is supplied (A) with a pulsed voltage whose repetition frequency and / or pulse energy content is regulated so that the voltage across a downstream unit (B), with constant current supply, is minimized. 10. A claim according to claim 1, characterized in that the current and voltage values of one or more downstream units (B, C) are, prior to the evaluation of behavioral changes, dependent on such values where neither characteristic with negative resistance nor - iigger.