WO1993010901A1

WO1993010901A1 - Method of removing dust from flue gases

Info

Publication number: WO1993010901A1
Application number: PCT/EP1992/002815
Authority: WO
Inventors: Horst Onland
Original assignee: Veba Kraftwerke Ruhr Ag
Priority date: 1991-12-06
Filing date: 1992-12-05
Publication date: 1993-06-10
Also published as: DE59203312D1; CZ61494A3; SK33294A3; ATE126455T1; PL169619B1; SK281289B6; DE4140228C2; DE4140228A1; EP0615466A1; ES2096780T3; EP0615466B1; CZ284410B6

Abstract

The invention concerns a method of removing dust from flue gases by means of an electrostatic filter (E). The filter (E) is located in the flue-gas flow (R), and a d.c. voltage is applied across the filter to ionize the dust particles flowing through it. In order to optimize the operation of the filter, from both the environmental and the economical point of view, the invention calls for the dust concentration to be continuously measured at the filter outlet, upstream of the desulphurization unit. An upper limit and a lower limit are set for the dust concentration, and process parameters previously determined experimentally by a comparator (V) from a memory (S) to optimize the process as regards the degree of dust removal and efficiency are derived as signals to control the filter.

Description

Process for dedusting flue gases

The invention relates to a method for dedusting flue gases by means of an electrostatic precipitator, in which a direct voltage U is applied to the electrostatic precipitator positioned in the flue gas to ionize the dust particles passing through it.

Such a method is used in particular for the dedusting of flue gases in coal-fired power plants. As is known, the flue gases generated at the power plant block are first dedusted using an electrostatic precipitator before they reach a flue gas desulfurization system. The dust is separated on the electrostatic precipitator by ionizing it with a high voltage. For economic reasons, the operation of the electrostatic precipitator should be such that it is just below the Breakdown voltage is operated. Current and voltage in the electrostatic filter are measured by means of measuring sensors. In accordance with the property of the wipers occurring in the electrostatic filter, the voltage reduction magnitude and the rate of rise are predetermined by the filter voltage regulator s such that the area shortly below the breakdown voltage is reached as quickly as possible. The breakdown voltage should not be reached if possible, since wipers will occur again. In the known arrangement, the full power is always on the electrostatic precipitator, even if there is only a low dust concentration in the flue gas. The known method is therefore uneconomical.

The invention is based on the object to provide a method for dedusting flue gases, which is improved in terms of economy.

This object is achieved in a method of the type mentioned in that

- the dust concentration is measured continuously at the outlet of the electrostatic precipitator,

- An upper setpoint and a lower setpoint for the dust concentration are specified, the upper setpoint being determined by the maximum permissible dust concentration and the lower setpoint by the lower limit of the dust concentration which is tolerable for economical operation, and

- From a comparator for the setpoint / actual value difference from a memory (S) experimentally on a process with regard to dedusting efficiency and efficiency optimal process parameters previously determined as signals for the Regulation of the electrostatic precipitator can be derived, the stored values being composed of several parameter groups, each forming individual regulating stages, with the increasing number of ordinal stages of the regulating stages resulting in a decreasing energy input to the electrostatic precipitator, so that the current regulating stage is maintained when the dust concentration lies within the nominal values and that Exceeding the upper setpoint di parameters of the next lower control level and when falling below the lower setpoint, the parameters of the next higher control level are selected.

The invention is characterized in that the mode of operation of the electrostatic filter is determined by a control process which receives default values from different control stages as a function of the control difference (setpoint / actual value difference). These default values are experimentally determined process parameters which have been identified as optimal by experiment with different process states on an operating power plant block. D control stages are constructed so that in the lowest control stage the maximum power is delivered to the electrostatic precipitator, while the highest control stage corresponds to the experimentally determined setting of the electrostatic precipitator b to operate with the lowest energy costs. The optimal control stage is selected depending on the load condition of the power plant block. The control level is selected under the influence of the specification of two setpoints, namely an upper setpoint, which from an operational point of view corresponds to the maximum permitted dust concentration of the flue gas desulfurization system and a lower setpoint, which corresponds to a dust concentration that is so low that it is a tolerable one represents lower dust concentration. The lower setpoint limit thus represents a limit given by economic factors. Depending on the location of the measured dust concentration - i. -

With regard to the two setpoints mentioned, the gradual adaptation to the most economical mode of operation takes place according to the invention.

It is advantageous here that the level of the measured direct current and voltage is used to regulate the electrostatic precipitator, and the options available in the voltage regulators for setting the voltage reduction magnitude and rate of increase after wipers have occurred and the ability to suppress alternating voltage periods (clock ratio) are used.

According to a preferred embodiment of the invention it is provided that the functions "pre-cleaning, medium cleaning and post-cleaning" of the electrostatic filter are each assigned separate storage sections in which the control stages are switched over in a coupled manner.

The optimization of the electrostatic filter process can be further improved in this way, since the regulation can be refined by dividing it into several function blocks.

If, in a method of the type mentioned in which a plurality of electrostatic precipitators are connected in series, the control stages are coupled in the memories or memory sections assigned to the individual electrostatic filters, the actual value for the dust concentration, which is relevant for the control, being arithmetically averaged to the dust concentrations measured at the respective filter outputs, use of the method according to the invention can also be achieved when several electrostatic precipitators are coupled, and the economy of the overall system can thus be further improved. It is preferably provided that the dust concentration of the flue gas entering the chimney is measured as a further process variable and that the lowest control level is selected when this value exceeds a predefinable limit value. This is a safety monitoring that is activated if, for example, the failure of the

Flue gas desulfurization system the dust concentration at the chimney becomes impermissibly high, so that in this case the electrostatic precipitators are operated with the greatest possible electrical power consumption.

It is also necessary to switch the electrostatic precipitator to the maximum possible electrical power consumption when starting and stopping the power plant block. This takes place according to the invention in that the feed water quantity in the power plant is measured as a further process variable and in that when this falls below a predetermined lower limit value, the lowest control level is selected. On the basis of the value falling below the minimum value of the feed water quantity, it is recognized in the method according to the invention that a transition from the regular working state to the start-up mode must be carried out.

According to a further variant of the invention, the switchover from one control stage to the other takes place only after a predeterminable waiting time has elapsed. This prevents short-term fluctuations in the dust concentration leading to undesirable oscillation of the control. This increases the stability of the control.

The invention is explained in more detail below with reference to a drawing:

Show FIG. 1 shows a basic circuit diagram to explain the dedusting method according to the invention,

Figure 2 is a functional diagram for explaining the structure of a system for performing the dedusting method according to the invention

FIG. 3 shows a flow chart for the dedusting process according to the invention,

Figure 4 is a table of values of the memory for the experimentally predetermined process parameters, divided into 14 control stages

and

FIG. 5 shows a measurement protocol to explain the function of the dedusting method according to the invention.

1, an electrostatic filter E is arranged in a flue gas flow denoted by R. The

Electro filter E is from a

High-voltage supply device H supplied, which in turn is fed by a two-phase network. The

The high-voltage supply device H is controlled via a comparator circuit V, which contains a measurement signal from a sensor as an actual value

Flue gas flow is arranged on the output side of the electrostatic precipitator E. The sensor thus measures that at the outlet of the electrostatic filter

E existing dust concentration. The comparator circuit V also contains two inputs, at which an upper setpoint

Setpoint and a lower setpoint setpoint can be entered max min. One is assigned to the comparator circuit

Storage device S, in which parameter values are stored, which are experimentally based on a

Economy optimal sample process were determined. The parameters are grouped into several directorial levels. The lowest control level 1 contains those process parameters which have been determined to be optimal for a full dedusting performance of the electrostatic filter E. As the ordinal number of the control stages increases, the electrical outputs that the electrostatic filter E uses by means of

High-voltage supply device H are supplied successively. After all, the highest control level corresponds to the lowest electrical consumption of the electrostatic filter

The parameter groups stored in the memory S influence the following output variables of the high-voltage supply device:

- Size of the DC output voltage

- Size of the output direct current

- Value of the rate of voltage rise after wipers occurred

- Value of the voltage reduction variable after wiping and

- duty cycle of the output DC voltage

1 shows a basic illustration of the dedusting method according to the invention, a more specific embodiment is now described with reference to FIGS. 2 and 3, which differs from the basic circuit diagram shown in FIG. 1 in that, on the one hand, z electrostatic filters El and E2 connected in series in the flue gas stream R. are present and furthermore because each electrostatic filter El, E2 is divided into three functional zones, namely pre-cleaning (pre-cleaning), Medium cleaning (medium) and after cleaning (after).

The basic structure of the control system is formed by first feeding the process variables to be measured to an analog-digital converter. The measured process variables are:

- the dust concentration at the outlet of the electrostatic filter 1,

- the dust concentration at the outlet of the electrostatic filter 2,

- the total feed water volume of the associated power plant unit

and

- The dust concentration in the chimney, i.e. where the dedusted smoke gases escape into the environment.

The measured values converted in the analog-digital converter are fed to a control circuit, the function of which will be explained in detail later. The output of the control circuit is an interface, at the output of which command data are output, which select the corresponding parameter group of the individual control stages as current process parameters for individual zones (pre-cleaning, medium cleaning and post-cleaning) of the respective electrostatic filters El and E2.

The function of the control loop is as follows:

After pressing the start button 1, the lowest control level in each zone is selected as the start value for the control method in program level 2. The high-voltage supply device is thus pre-cleaned in relation to both electrostatic filters and to all three zones, Medium cleaning and post-cleaning operated with the highest possible electrical output.

In program stage 3, the process data output by the output of the analog / digital converter is transferred to the control loop and subsequently queried as follows:

First, in program stage 4, the question is asked whether the dust concentration in the chimney exceeds a specified upper limit. This is further below the limit that is maximally permissible from an environmental point of view. If this is the case, the program via the feedback loop to stage 2 is selected in such a way that control stage 1 is set independently of the previously selected control stage. If this is not the case, the program step 5 below asks whether the total feed water quantity is less than a predetermined minimum value. If this is the case, this indicates that the power plant block in question is in the start-up or shutdown mode. Since economic considerations play less of a role than a possible good dedusting, control level 1 is also selected when the minimum value of the total feed water quantity is undershot in order to operate the electrostatic precipitators with the greatest possible electrical output.

If this is not the case, it is first checked in program step 6 whether the actual values measured by the sensors for the dust concentrations at the outlet of the respective electrostatic filters E1, E2 have possibly failed. If this is the case, the control process first runs through a waiting element with a dead time of ten minutes, so that short-term failures of the measured values do not affect the entire process. If there is still a failure of the actual values after the waiting time has elapsed, it becomes independent of the previously selected control level by means of the program level 16 via the feedback to the program level 2, the control level 2 is selected as an "emergency program" before the program sequence is interrupted in program level 17 and an error message is given in the program level 18 for waiting.

After the fault has been rectified, the program sequence can be restarted with a step.

If it is determined in program stage 6 that the actual values for the dust concentration of the electrostatic precipitators E1, E2 are present, the mean value is subsequently formed in program stage 7 from the two actual values of the dust concentrations. This mean value is considered as the actual control variable in the following:

First, a query is made in program stage 8 as to whether the

Average dust concentration is greater than the upper one

Target value (cf. input variable target in comparator stage V max of FIG. 1). If this is the case, it means that di

Plant operated with too low dedusting capacity so that in the end the output variables of

High-voltage supply device H for supplying the

Electrofilter El, E2 must be changed so that a higher power is output. However, in the short term

To rule out fluctuations in the dust concentration, the program first runs through a waiting element 10, which has a time delay of, for example, one minute.

If after the one-minute waiting period the

Correction result of program level 8 is corrected such that the upper setpoint is no longer exceeded

(logic output "No" from program level 10) there is no change in the control level.

However, if this is the case, the previously selected control level is reduced by one step in program level 12, that is, who should drive with gradually increased performance. The parameter groups belonging to the newly selected control level are called up via program level 14. The parameterizations are selected so that the highest possible degree of dust separation with a possible low electrical power consumption can be expected from results previously determined experimentally in the optimal process.

If, on the other hand, it is determined in program stage 8 that the mean value of the dust concentration is lower than de the upper target value, program stage 9 queries whether the lower target value (target at the input of the min comparator circuit V in FIG. 1) is undershot.

The lower setpoint is set so that it represents an economic limit, i.e. a low one

Dust concentration, if at all achievable, can only be achieved with intolerably high expenditure. So it's there

The control system endeavors not to let the dust concentration drop below the economically tolerable lower setpoint.

If the value does not fall below the lower setpoint limit, the control remains in the selected control level. If, however, this value is undershot, a waiting time element is first run through again in order to avoid that short-term shortfalls in the lower setpoint value would lead to instability in the control process. If, after the waiting time has elapsed, the below displayed lower setpoint value is not confirmed, the selected control level remains unchanged.

However, if program stage 11 confirms that the lower setpoint has been undershot, the control stage is increased by one step in subsequent program stage 13, so that the energy supplied to the electrostatic filters is increased step by step is reduced and thus a corresponding saving in energy costs is achieved.

As described above, depending on the measured process variables, there is therefore an automatic adaptation of the electrical power supplied to the electrostatic filters with regard to the necessary dedusting.

An example of the parameterization of the individual control stages can be seen in FIG. 4. From this it can be seen that 14 control levels are provided in a vertical order and that individual parameter sets for pre-cleaning (2nd column), medium cleaning (3-column) and post-cleaning (. Column) are assigned to these 1 control levels and are assigned the program names F, 0 , 1,2,3,4 are designated.

For example, control stage 1 for the pre-cleaning shows that the full direct voltage (100%), the full direct current (100%), a 70% voltage rise rate, a 10i voltage reduction variable and a clock ratio are used such that three alternating voltage periods are masked out. Corresponding parameter sets apply to the middle and subsequent cleaning. In the transition from control stage 1 to control stage 13, FIG. 4 shows that the control parameters i of the pre-cleaning and also in the middle cleaning are not changed, while in the post-cleaning the cycle ratio of the DC voltage is changed from 3 to 2. Only the functional section "post-cleaning" thus requires an increase in energy, while the other functional sections remain unchanged.

According to the parameter values shown in FIG. 4, only the parameters of one of the three always change when the selected control level is changed Function blocks, at least until control level 2 is reached In the subsequent control level for the greatest possible performance (control level 1), on the other hand, the parameterization in all three function blocks is changed.

FIG. 5 finally shows a measurement protocol which was recorded during a practical test of the dedusting method according to the invention in a typical load case of a power plant block. The column shows the time and the following four columns the corresponding values of the actual values recorded by the analog-digital converter in FIG. 2. On the basis of the feed water, it can be seen that a maximum of the power to be provided by the power station bloc is between 7:00 p.m. and 7:30 p.m.

The following column "Filter performance" corresponds to compliance with the permissible dust values for the electrical energy required to supply the El and E2 electrostatic filters, which are each divided into three zones: pre-cleaning, central cleaning and post-cleaning. The following columns show the respective programs in the individual filter zones of the two filters 1 and 2. The program numbers correspond to those in the "Progr." of Fig. 4. The last column shows the control level selected at the respective time. From this it can be seen that in times of low load the economic control level 14 to about 18.35 is sufficient. The output of the electrostatic precipitator is then gradually increased until the highest output at Loadf is reached at around 6:52 p.m. (control level 3) - then the dedusting performance provided in the electrostatic precipitators can be reduced again until finally the most economical control stage 14 around 8:30 p.m. is achieved.

Claims

ΛPATENT CLAIMS

1. A method for dedusting flue gases using an electrostatic precipitator (E.E1.E2), in which the electrostatic filter positioned in the flue gas (R) is subjected to a direct voltage U to ionize the dust particles passing through it, characterized by the following features:

- The dust concentration is continuously measured at the outlet of the electrostatic filter (E, E1, E2),

- An upper target value and a lower target value for the dust concentration are specified, the upper target value being determined by the maximum permissible dust concentration and the lower target value by a predeterminable lower limit of the dust concentration and

- A comparator (V) for the setpoint / actual value difference is used to derive experimentally determined process parameters from a memory (S) on a process that is optimal in terms of dedusting efficiency and efficiency as signals for the control of the electrostatic filter (E), the stored values being derived from several, in each case individual control stages forming parameter groups are put together, and with increasing ordinal number of control stages a decreasing energy exposure of the electrostatic filter (E) takes place in such a way that with an inner the current control level is maintained according to the setpoint dust concentration and that the parameters of the next lower control level are selected when the upper setpoint is exceeded and the parameters of the next higher control level are selected when the value falls below the lower setpoint.

2. The method according to claim 1, d a d u r c h g e k e n n z e i c h n e t that the height of the DC voltage, the rate of increase, the lowering variable and the clock ratio are used to regulate the electrostatic precipitator (E).

3. The method of claim 1 or 2, d a d u r c h g e k e n n z e i c h n e t that the functions "pre-cleaning, central cleaning and post-cleaning of the electrostatic filter (E) are each assigned separate memory sections in which a switching of the control stage is carried out coupled.

4. The method according to claim 1, 2 or 3 in which more electrostatic filters are connected in parallel, characterized in that the switching of the control stages is coupled in the memories or memory sections assigned to the individual electrostatic filters, the relevant actual value for the regulation of the dust concentration by arithmetic The dust concentrations measured at the respective filter outputs are averaged.

5- Method according to one of the preceding claims, characterized in that the dust concentration of the flue gases entering the chimney is measured as a further process variable and that if this value exceeds a predeterminable limit value, the lowest control level is selected. From

6. Method according to one of the preceding claims, that the feed water quantity in the power plant is measured as a further process variable and that, if this exceeds a predetermined lower limit value, the lowest control stage is selected.

7. The method according to one of the preceding claims that the switch from one control stage to the other takes place only after a predeterminable waiting time has elapsed.

8. The method according to any one of the preceding claims, characterized in that monitoring for a failure of the measured value for the dust concentration is carried out in such a way that the lowest control level is selected if the measured value does not exist after a predeterminable further waiting time.

CHANGED REQUIREMENTS

[Received at the International Bureau on April 8, 1993 (April 8, 1993); original claim 1 amended; all other claims unchanged (2 pages)]

1. A method for dedusting flue gases by means of an electrostatic precipitator (E, E1.E2), in which the electrostatic precipitator positioned in the flue gas (R) is subjected to a direct voltage U to ionize the dust particles passing through it, the dust concentration being continuously at the outlet of the electrostatic precipitator (E , E1, E2) is measured, an upper setpoint and a lower setpoint for the dust concentration are specified and compared in a comparator (V), and the upper setpoint is determined by the maximum permissible dust concentration and the lower setpoint by a predeterminable lower limit of the dust concentration are defined, characterized in that the comparator (V) for the setpoint / actual value difference from a memory (S) is experimentally derived in advance on a process with regard to dedusting efficiency and efficiency optimal process parameters as signals for the control of the electrostatic filter (E), whereby the memory values from several, each s individual control stages forming parameter groups are composed, and with increasing ordinal number of control stages a decreasing energy exposure of the electrostatic filter (E) takes place in such a way that with a dust concentration lying within the target values the current one O

Control level is maintained and that when the upper setpoint is exceeded, the parameters of the next lower control level and when the value falls below the lower setpoint, the parameters of the next higher control level are selected.