DE102009017025B3 - Method for removal of mercury from flue gas of e.g. waste incinerator, involves evaluating measuring signals such that monitoring of steep rising edge/deviation of mercury content is recognized by specific criteria - Google Patents

Abstract

The method involves evaluating measuring signals such that monitoring of a steep rising edge/deviation of mercury content is recognized for increasing capacity, the existence of the steep rising edge/ deviation by specific criteria. The criteria are increase of a value of less than 5 microgram per meter cube in a period of less than 10 minutes is measured as a triggering feature and/or an extension of higher dose lasts as long as it remains above an absolute value, when measurement of the absolute value is 10 microgram per meter cube.

Description

The The invention relates to a method for improved separation of Mercury from flue gases, in particular from flue gases fossil fired Power plants, coal or waste incineration plants, wherein an addition to reduce the mercury content in the flue gas performed by stove coke and the clean gas is monitored for short-term changes in the mercury content becomes.

at the incineration of household waste and commercial waste comes, according to the legal requirements, a flue gas cleaning for use. The aim of the flue gas cleaning is that in the flue gas contained below the legally required minimum values to reduce.

in the present case, HOK is metered into the flue gas in the swirling process, to adsorb Hg. about a sample gas line in the chimney will provide the required measured values the clean gas side determined. Correspond to the measured in the clean gas Values for Hg gets over on the raw gas side a controller HOK dosed into the vortex chamber. The in the vortex chamber contained amount of HOK thus represents the filter medium for Hg.

Garbage as fuel does not have constant properties, even in a narrow range.

Already a gripper filling (about 5 t) in the feed can at the readings in the clean gas generate significant fluctuations. The system technology used in terms of process and control must control these fluctuations.

The Practice shows, especially at Hg, sudden steep increases in the Measured values in the range of about 1 to 10 minutes. This problem is also in other waste incinerators known. The conventional Regulation is overwhelmed here. An increased Dosage is inevitable here even at an already elevated Measured value coupled, as thus only a large error occurs. Added to this is the time factor of the regulation. An addition in such a case should be done immediately if possible.

reacts at a steep gradient, the control is not fast enough consumes the amount of HOK contained in the vortex chamber. The Filter hits by. Hg deposited on the clean gas side and is by the Emission measurement evaluated as current measured value. That leads then to injuries from half-hourly mean values [HMW] to injury the daily average [TMW]. HMW and TMW are in the 17th BlmSchV established.

Hg measurements on the raw gas side would improve the control behavior. Such measurements are indeed existent, but deliver in practice for a regulation is not reliable Values.

A method is known for improving the Hg removal capacity in an exhaust gas purification process, wherein an aqueous suspension of a basic absorbent in a drying chamber of a drying-absorption zone is atomized in fine droplets into the hot flue gas, the water of these drops evaporates and leaves dry fine particles and a part of the harmful components of the gas (sulfur oxides, hydrogen halides, nitrogen oxides and mercury) are sorbed by the drops and the fine particles at the same time ( DE 692 03 350 T2 ). The flue gas is then passed, together with the entrained fine particles, to the particle collector where contact between the particles and the flue gas takes place for additional sorption of harmful constituents wherein the amount of chloride added to the drying-absorption zone is increased to an extent, which is sufficient to improve the Hg removal capacity of the process. The addition of chloride can be carried out in solid form to the coal or in the form of gaseous chloride in the flue gas.

Furthermore, a method for the separation of metallic mercury from reducing gases and gas mixtures is known in which an adsorption of mercury takes place on an adsorbent ( DE 197 31 639 A1 ). The adsorbent consists of a mixture of naturally occurring zeolites and contains 1 to 10 wt .-% Ag, Cu, Sn, Pb, Zn and / or Cd. In this method, the mercury-containing gas above its dew point with the adsorbent at a temperature of 50 to 150 ° C for a reaction time of 0.5 to 10 sec. reacted, wherein the mercury-laden adsorbent then regenerated at 350 to 500 ° C. The process can be carried out in a fly-flow reactor, in a circulating fluidized bed or in a fixed bed reactor and serves, in particular, for removing mercury from natural gas or from the gas mixture obtained during garbage gasification or garbage pyrolysis.

In addition, a method and apparatus for purifying mercury-containing exhaust gases is known that the dedusted flue gas before it enters an acid scrubber at a temperature between 50 and 80 ° C by means of a suspension of a powdered, mercury adsorbent product in a concentration between 0, 5 to 6 g / l is moistened, whereby between 50 and 100% of the mercury present in the dedusted smoke is removed ( DE 603 14 119 T2 ).

From the US 5,787,823 A It is known to improve the reduction of the Hg content in the flue gas by extending the reaction time of mercury with an adsorbent. Activated carbon can be used as adsorbent, among other things. The extension of the reaction time should be achieved by a recirculation of the adsorbent. The reduction in the Hg content should be achieved exclusively by procedural measures. A control engineering solution is not included.

Of the Invention is based on the object, the control behavior of existing Installations in the removal of mercury from flue gases in such a way to change, that a penetration of the filter medium - preferably Herdofenkoks - avoided becomes.

• – ein Anstieg mit einem erhöhten Wert von > 5 μg/m³ in einem Zeitraum von < 10 Min. als auslösendes Merkmal gemessen wird und/oder
• – in Messwertzyklen mehrere Anstiege mit steigenden Anstiegswerten hintereinander als auslösendes Merkmal gemessen werden,

und falls ein Messwert über einem Absolutwert von 10 μg/m³ gemessen wird, eine Verlängerung der erhöhten Dosierung solange anhält, wie dieser über dem genannten Absolutwert bleibt.This object is achieved with the features of claim 1. Advantageous embodiments thereof are mentioned in the further claims. According to the invention, this is achieved in that
in addition, short-term changes in the mercury content are monitored on the clean gas side,
wherein an increase in the capacity of hearth furnace coke to a proportion of 90 to 100% of the maximum flow rate in a period of 10 to 60 min., Preferably 15 min., And maximally to below a maximum level of mercury from 3 ug / m ³ to 10 μg / m ³ , preferably 4.7 μg / m ³ , is carried out,
wherein in the context of the flue gas measurement / monitoring, the measurement signals are evaluated so that the monitoring is directed to at least one steep rising edge / deviation of the mercury content
and to increase the delivery rate, the presence of the steep rising edge / deviation is recognized by the following criteria:

• A rise with an increased value of> 5 μg / m ³ in a period of <10 min. Is measured as a triggering characteristic and / or
• - in measured value cycles, several increases are measured successively with increasing rise values as a triggering characteristic,

and if a reading above an absolute value of 10 μg / m ^{3 is} measured, prolonging the increased dose as long as it remains above said absolute value.

A steep rising edge of the measured value is detected when a measured value rises very high within a short time and reaches a value change of> 5 μg / m ³ in a time interval of <1 to 10 min.

At the third criterion is the size (the Value) of the increase is not relevant. Only the fact counts that the new reading greater than is the old (previous) reading. If this reading increase several times in succession, there are several (smaller or larger) climbs to recognize one behind the other. As a period in this regard is the Period until the presence of the next Measured value.

For one Measurement cycle is an interval of <1 to 5 min., Preferably 1 min. set.

By Fluctuations in coal and / or waste will not be allowed increases permissible maximum mercury content in the clean gas, by using a Regulator an increase or reduction of the hearth furnace coke addition on the raw gas side realized becomes.

Advantages of the invention:

• - the Fluctuations in waste or coal compositions be effectively balanced, so that no puncture on the Clean gas side and no overruns the maximum values of mercury pollution
• - the Method is variable and control technology in existing systems implantable as well as various Parameters adaptable to almost any system
• - elaborate constructive changes at the plants are usually not necessary
• - the Method reacts very fast to changing gradients
• - the Control behavior of the system is effectively improved

embodiment

The Invention will be explained below with reference to an exemplary embodiment.

there demonstrate:

1 - the procedure as a flowchart

2 - The measured value course with HOK dosing in the normal course

3 - Measured value profile and HOK dosing, measured value peak without edge detection

4 - Measured value profile and HOK dosing, measured value peak with edge detection (example 1)

5 - Measured value profile and HOK dosing, measured value peak with edge detection (example 2)

The present method is integrated into the process control system [PLS] and comprises the components described in detail below (US Pat. 1 ):

1

free running clock generator

2

Reading Pipeline

3

subtractor

4

comparator Measured value change (with parameter 1)

5

comparator Absolute value (with parameter 2)

6

comparator Threshold for Release counter (with parameter 3)

7

comparator Old value / new

8th

Counter measured value increases (with parameter 4)

9

AND gate for release increase counter (8th)

10

OR gate to interconnect the criteria

11

AND gate to release the timer

12

timer (with parameter 5)

13

AND gate Reset timer

14

Setpoint changeover HOK dosage (with parameter 6)

• Parameter 1: 5 [μg/m3]
• Parameter 2: 12 [μg/m3]
• Parameter 3: 4,7 [μg/m3]
• Parameter 4: 6 [Anstiege]
• Parameter 5: 900 [s]
• Parameter 6: 95 [%]

The parameters 1 to 6 can be changed and adapted to the respective system. For the embodiment apply:

• Parameter 1: 5 [μg / m3]
• Parameter 2: 12 [μg / m3]
• Parameter 3: 4.7 [μg / m3]
• Parameter 4: 6 [increases]
• Parameter 5: 900 [s]
• Parameter 6: 95 [%]

The emission measurement delivers a new measured value every minute. All measured values are sent via the freewheeling clock generator ( 1 ) into the measured value pipeline ( 2 ) pushed. This results in an old measured value [old value] and a new measured value [new value].

The old value is stored in the subtractor ( 3 ) deducted from the new value. The result is the difference between the two measured values and is sent to the comparator of the measured value change ( 4 ). In ( 4 ), parameter 1 defines a maximum limit of the measured value change. If this limit is exceeded, criterion 1 is met.

In the comparator ( 5 ), the current measured value is compared with parameter 2. If the current measured value is greater than parameter 2, the additional criterion is fulfilled.

About the comparator ( 7 ) the old value is compared with the new value. If the new value is less than the old value, the counter ( 8th ) decreased by 1. If the new value is greater than the old value and, in addition, the condition for comparators ( 6 ) is met with parameter 3, the counter ( 8th ) increased by 1. Comparator ( 6 ) with parameter 3 forms a marginal limit. Below the limit value with parameter 3, the counter ( 8th ) not increased. Has the counter ( 8th ) reaches the limit with parameter 4, criterion 2 is met. The counter ( 8th ) is not bound to any absolute value of the measured value. It is bounded down with zero and up with parameter 4.

All criteria are determined via the OR gate ( 10 ) the timer release ( 11 ). The release to ( 11 ) is fulfilled when the timer ( 12 ) is not active.

Is the release of ( 11 ), we are the timer ( 12 ) started with parameter 5. The timer ( 12 ) is now active for the length of time specified by parameter 5. During this period, the setpoint switching ( 14 ) the setpoint for HOK dosing is switched to the value set with parameter 6.

• 1. Die Zeit des Zeitgliedes (12) mit Parameter 5 ist abgelaufen.
• 2. Über Vergleicher (6) wird festgestellt, dass der aktuelle Messwert bereits vor Ablauf des Zeitgliedes (12) die Geringfügigkeitsgrenze von Vergleicher (6) unterschritten hat. In diesem Fall erfolgt ein Reset des Zeitgliedes über Reset Zeitglied (13).

For the downshift to the normal value of the HOK dosage two criteria are relevant:

• 1. The time of the timer ( 12 ) with parameter 5 has expired.
• 2. Via comparator ( 6 ), it is determined that the current measured value already exists before the end of the timer ( 12 ) the de minimis limit of comparator ( 6 ) has fallen below. In this case, a reset of the timer via reset timer ( 13 ).

Is after expiration of the timer ( 12 ) on the merger of the criteria ( 10 ) yet another criterion, the timer ( 12 ) started again.

1 : Overview of the interconnection of the individual control components.

The presentation is considered an overview. In reality, special links are required depending on the PLS used. FIG. 2: Ordinate 1 [Hg]: Measured value mercury, maximum 50 μg / m3, limit value HMW 17. BlmSchV Ordinate 2 [HOK]: Control value HOK dosage, maximum 100% delivery HOK Abscissa [t]: Time, period 24 h

Course in garbage task without abnormalities. Condition old, without edge detection. The mercury concentration is well below 5 μg / m3. The normal control is engaged and keeps a basic dose close to 30%. FIG. 3: Ordinate 1 [Hg]: Measured value mercury, maximum 50 μg / m3, limit value HMW 17. BlmSchV Ordinate 2 [HOK]: Control value HOK dosage, maximum 100% delivery HOK Abscissa [t]: Time, period 6 h

Course in garbage with abnormalities. Condition old, without edge detection. The mercury concentration increases continuously. The rise period is relatively large, here about 20 minutes. The normal regulation starts very late. The limit value of 50 μg / m3 according to 17th BimSchV is violated before the maximum of the HOK dosing capacity is reached. At about 80% delivery rate, the staff recognizes the problem and sets by hand adjustment 100%. See steep falling edge of the delivery rate, here is the resetting of the manual intervention on the normal HOK controller. FIG. 4: Ordinate 1 [Hg]: Measured value mercury, maximum 50 μg / m3, limit value HMW 17. BlmSchV Ordinate 2 [HOK]: Control value HOK dosage, maximum 100% delivery HOK Abscissa [t]: Time, period 6 h

course at garbage disposal with abnormalities. Condition new, with edge detection.

The illustration shows two increases in concentration. The mercury concentration increases continuously. The rise period is relatively large. The rise of the measured value is detected by the edge detection. The HOK dosage is immediately switched to the value set with parameter 6. Penetration of the filter is prevented. In the first case, the marginality limit (parameter 3) is detected and before the expiration of the timer ( 12 ) returns to the normal regulator. In the second case, the end of the timer (parameter 5) is reached. Further criteria are not available at this time. The normal HOK controller will then remain the leader. FIG. 5: Ordinate 1 [Hg]: Measured value mercury, maximum 50 μg / m3, limit value HMW 17. BlmSchV Ordinate 2 [HOK]: Control value HOK dosage, maximum 100% delivery HOK Abscissa [t]: Time, period approx. 3 h

Course in garbage with abnormalities. Condition new, with edge detection. The illustration shows two increases in concentration. The mercury concentration increases rapidly with very steep flanks. The rise period is about 1 minute in the first case and about 3 minutes in the second case. The rise in the measured value is detected by the edge detection, here by criterion 1. The HOK dosage is immediately switched to the value set with parameter 6. Penetration of the filter is prevented. In the first case, the end of the timer ( 12 ) with parameter 5. Subsequently, no new trigger criteria are available. The normal HOK controller remains the leader. In the second case, the increase of the measured value is also detected by the edge detection and the HOK dosage is switched to the value defined with parameter 6. However, here after the expiration of the timer ( 12 ) again criteria, here additional criterion, measured value greater than parameter 2. The timer is triggered multiple times, the HOK dosage of the edge detection remains leading. The now sufficient HOK dosage leads to a drop in the measured value for mercury. The filter does not crack.

Claims (4)

Method for the improved removal of mercury from flue gases, in particular from flue gases from fossil-fired power plants, coal or waste incineration plants, to reduce the mercury content of the flue gas from a combustion chamber, wherein in a fluidized bed with a raw gas side and a clean gas side on the clean gas side measured values as measured signals of the mercury content are determined, is metered on the raw gas side via a controller Herdofenkoks of less than 30% of a maximum flow, in addition to short-term changes in the mercury content are monitored on the clean gas side, with an increase in flow rate of hearth furnace coke to a share of 90 to 100% of the maximum Flow rate in a period of 10 to 60 minutes, preferably 15 minutes, and at most to below a maximum level of mercury from 3 ug / m ³ to 10 ug / m ³ , preferably 4.7 ug / m ³ is performed, being under the smoke gas measurement / monitoring the measurement signals are evaluated so that the monitoring is directed to at least one steep rising edge / deviation of the mercury content and to increase the flow rate, the presence of the steep rising edge / deviation is detected by the following criteria: - a rise with a increased value of> 5 μg / m ³ in a period of <10 min. is measured as a triggering feature and / or - in measured value cycles, several increases with increasing ascent values are measured successively as a triggering characteristic, and if a measured value exceeds an absolute value of 10 μg / m ³ , an extension of the increased dosage as long as it remains above the said absolute value. A method according to claim 1, characterized in that is detected on a steep rising edge of the measured value when a measured value rises above average and a value change of> 5 micrograms / m ³ in a time interval of <1 min. A method according to claim 1, characterized in that the measured value cycle of each one set measuring technology is dependent and is usually selected in a range of <1 to 5 minutes, preferably 1 minute. Method according to claims 1 to 3, characterized by that by fluctuations of the fossil coal and / or the garbage shares no above average increases the maximum mercury content in the clean gas is allowed, by over a regulator an increase or lowering the hearth furnace co-addition on the raw gas side of the combustion chamber is realized.