JP7203711B2 - Exhaust gas treatment device and exhaust gas treatment method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an exhaust gas treatment apparatus and an exhaust gas treatment method.

Exhaust gas containing mercury may be generated when waste such as municipal waste is incinerated. In this case, a mercury adsorbent is supplied to the exhaust gas to remove mercury in the exhaust gas. The supply amount of the mercury sorbent is controlled based on the mercury concentration. On the other hand, the mercury contained in the exhaust gas mainly consists of zero-valent atomic mercury (hereinafter referred to as "zero-valent mercury") and divalent mercury (hereinafter referred to as " It exists as divalent mercury.) Conventionally, in measuring the concentration of mercury contained in exhaust gas, the divalent mercury in the exhaust gas taken in is reduced to zerovalent mercury, and the zerovalent mercury obtained by reducing the divalent mercury and the zerovalent mercury originally contained in the exhaust gas The total concentration of mercury (hereinafter collectively referred to as "total mercury") is detected as the mercury concentration.

Patent Document 1 discloses a mercury measuring apparatus capable of separating and continuously measuring zero-valent mercury (metallic mercury) and divalent mercury in gas. In the device, the first column and the second column are connected in parallel. In the first column, divalent mercury contained in the gas is collected by the first fixed catalyst, and only zerovalent mercury is sent to the mercury measuring instrument. In the second column, the divalent mercury in the gas is reduced to zero-valent mercury by the second fixed catalyst, and the reduced zero-valent mercury and the zero-valent mercury previously present in the gas are used as total mercury (total mercury). of mercury measuring instruments. The two mercury measuring instruments measure the concentration of zero-valent mercury and the concentration of total mercury, respectively, and the concentration of divalent mercury is obtained by subtracting the concentration of zero-valent mercury from the concentration of total mercury.

JP 2004-354067 A

By the way, since the mercury measuring device of Patent Literature 1 requires two concentration acquisition units (mercury measuring devices), the manufacturing cost of the device increases. Therefore, it is conceivable to switch between a zerovalent mercury measurement state for measuring the zerovalent mercury concentration and a total mercury measurement state for measuring the total mercury concentration using only one concentration acquisition unit. With such a mercury concentration meter, it is possible to reduce manufacturing costs. On the other hand, in the exhaust gas generated by incinerating wastes, etc., the concentration of total mercury may increase for a long time after the concentration of zero-valent mercury decreases. In this case, in the exhaust gas treatment apparatus using the mercury concentration meter, the total mercury concentration is measured when controlling the supply amount of the mercury adsorbent based on the zerovalent mercury concentration of the mercury concentration meter, which is in the zerovalent mercury measurement state. I can't. As a result, in the above case, the mercury concentration in the exhaust gas cannot be lowered appropriately.

The present invention has been made in view of the above problems. is intended to be reduced to

The invention according to claim 1 is an exhaust gas treatment apparatus comprising: an adsorbent supply unit that supplies a mercury adsorbent to the exhaust gas in a flue through which the flue gas flows; and an adsorbent that collects the mercury adsorbent in the flue. a zerovalent mercury measurement state arranged upstream in the flue with respect to the adsorbent trapping portion in the flow direction of the exhaust gas to measure the concentration of zerovalent mercury in the exhaust gas; and the exhaust gas. a mercury concentration meter capable of switching between a total mercury measurement state of measuring the total concentration of zero-valent mercury obtained by reducing the divalent mercury in the exhaust gas and the total concentration of zero-valent mercury originally contained in the exhaust gas as the total mercury concentration; and controlling the supply amount of the mercury adsorbent by the adsorbent supply unit based on the zerovalent mercury concentration of the mercury concentration meter in the zerovalent mercury measurement state, wherein the zerovalent mercury concentration is higher than a first threshold An evaluation value indicating the integrated amount of zerovalent mercury in the exhaust gas is acquired for a large period based on the zerovalent mercury concentration, and when the zerovalent mercury concentration becomes equal to or less than the first threshold following the period, The evaluation value is compared with a second threshold, and if the evaluation value is greater than the second threshold, the mercury concentration meter is switched to the total mercury measurement state, and the mercury adsorption is performed based on the total mercury concentration. and a control unit for controlling the supply amount of the agent.

The invention according to claim 2 is the exhaust gas treatment apparatus according to claim 1, wherein when the total mercury concentration is equal to or lower than a third threshold value, the control unit detects the mercury in the total mercury measurement state. The densitometer is switched to the zero-valent mercury measurement state, and the supply amount of the mercury adsorbent is controlled based on the zero-valent mercury concentration.

The invention according to claim 3 is the exhaust gas treatment apparatus according to claim 1 or 2, wherein in the flue, the further comprising a downstream mercury concentration meter that measures the total concentration of zerovalent mercury obtained by reducing divalent mercury in the exhaust gas and the total concentration of zerovalent mercury originally contained in the exhaust gas as a downstream mercury concentration; When the mercury concentration is greater than the fourth threshold, the control unit shifts control of the supply amount of the mercury adsorbent from control based on the zerovalent mercury concentration or the total mercury concentration to at least the downstream mercury concentration based control.

According to a fourth aspect of the present invention, there is provided an exhaust gas treatment method in an exhaust gas treatment apparatus, wherein the exhaust gas treatment apparatus includes an adsorbent supply section that supplies a mercury adsorbent to the exhaust gas in a flue through which the exhaust gas flows, and the flue. and an adsorbent trapping unit for trapping the mercury adsorbent in the flue, which is arranged upstream in the flow direction of the exhaust gas with respect to the adsorbent trapping unit in the flue, and measures the concentration of zero-valent mercury in the flue gas. and a total mercury measurement state in which the total concentration of the zerovalent mercury obtained by reducing the divalent mercury in the exhaust gas and the total concentration of the zerovalent mercury originally contained in the exhaust gas is measured as the total mercury concentration. and a mercury densitometer capable of switching between and, wherein the method for treating exhaust gas is based on the 0valent mercury concentration of the mercury densitometer that is in the 0valent mercury measurement state, and the mercury adsorbent supplied by the adsorbent supply unit. and acquiring an evaluation value indicating the integrated amount of zerovalent mercury in the exhaust gas based on the zerovalent mercury concentration during a period in which the zerovalent mercury concentration is greater than the first threshold value. and comparing the evaluation value with a second threshold when the zerovalent mercury concentration becomes equal to or less than the first threshold following the period, and if the evaluation value is greater than the second threshold, the mercury switching the densitometer to the total mercury measurement state and controlling the supply amount of the mercury adsorbent based on the total mercury concentration.

ADVANTAGE OF THE INVENTION According to this invention, even when the total mercury concentration increases for a long time after the concentration of zero-valent mercury in the exhaust gas has decreased, the mercury concentration of the exhaust gas can be appropriately reduced in the exhaust gas treatment apparatus.

It is a figure which shows the structure of an incineration facility. It is a figure which shows the structure of an upstream mercury concentration meter. FIG. 4 is a diagram showing an upstream mercury concentration meter in a zero-valent mercury measurement state; FIG. 4 is a diagram showing an upstream mercury concentration meter in a total mercury measurement state; It is a figure which shows the change of the zero valent mercury concentration and the total mercury concentration. It is a figure which shows the change of the zero valent mercury concentration and the total mercury concentration. It is a figure which shows the flow of exhaust gas processing in an exhaust gas processing apparatus. It is a figure which shows the other example of exhaust gas treatment in an exhaust gas treatment apparatus.

FIG. 1 is a diagram showing the configuration of an incineration facility 1 according to one embodiment of the present invention. The incineration facility 1 is a facility for incinerating waste such as municipal waste. The incineration facility 1 includes an incinerator 21 , a flue 3 , an exhaust gas treatment device 4 and a chimney 22 . The incinerator 21 burns waste and combustible gas generated from the waste. The flue 3 is a gas flow path connecting the incinerator 21 and the chimney 22 . In FIG. 1, the flue 3 is indicated by a thick solid line. The exhaust gas treatment device 4 is provided in the flue 3 . An induced draft fan (not shown) is also provided in the flue 3 . Exhaust gas (combustion gas) generated in the incinerator 21 is discharged into the flue 3 by the induced draft fan and guided to the chimney 22 via the exhaust gas treatment device 4 . In the incineration facility 1 , the exhaust gas generated from the incinerator 21 flows through the flue 3 from the incinerator 21 toward the chimney 22 , while the exhaust gas treatment device 4 performs predetermined treatment on the exhaust gas. A denitration device or the like may also be provided in the flue 3 . In the following description, it is assumed that the inside of the chimney 22 is also considered part of the flue 3 .

The exhaust gas treatment device 4 includes a control section 40 , an adsorbent supply section 41 , a bag filter 42 , an upstream mercury concentration meter 45 and a downstream mercury concentration meter 46 . The control unit 40 is, for example, a computer including a CPU, etc., and is responsible for overall control of the exhaust gas treatment device 4 . The control unit 40 may also serve as the control unit of the incineration facility 1 . A bag filter 42 is provided in the flue 3 . In the flue 3, an intake port of the upstream mercury concentration meter 45 and a supply port of the adsorbent supply unit 41 are provided upstream of the bag filter 42 (incinerator 21 side). An inlet for the downstream mercury concentration meter 46 is provided on the downstream side (the chimney 22 side). In FIG. 1 , the inlet of the downstream mercury concentration meter 46 is provided in the chimney 22 .

The upstream mercury concentration meter 45 measures the concentration of mercury contained in the flue gas flowing through the flue 3 . Details of the upstream mercury concentration meter 45 will be described later. The adsorbent supply unit 41 has, for example, a table feeder or the like, and supplies (injects) powdered mercury adsorbent into the flue gas flowing through the flue 3 . A mercury sorbent is, for example, activated carbon. Impregnated activated carbon obtained by impregnating the surface of activated carbon with iodine or sulfur, for example, may be used as the mercury adsorbent. The exhaust gas treatment device 4 may be provided with an alkaline chemical supply unit that supplies an alkaline chemical to the exhaust gas on the upstream side of the bag filter 42 . The alkaline chemical is a chemical for desalting and desulfurization, such as powdery slaked lime.

The bag filter 42 is of a filtration type, and collects fly ash contained in the exhaust gas with a filter cloth. Mercury adsorbent supplied by the adsorbent supply unit 41 is also collected by the filter cloth. Fly ash and mercury sorbents deposit on the filter cloth. The bag filter 42 is an adsorbent collecting portion that collects the mercury adsorbent in the flue 3 . Inside the bag filter 42, when the exhaust gas passes through the filter cloth, the mercury adsorbent deposited on the filter cloth adsorbs mercury contained in the exhaust gas. Adsorption of mercury in the mercury adsorbent also occurs in the flue 3 . The mercury adsorbent may further adsorb dioxins and the like contained in the exhaust gas. In addition, when the already-described alkaline chemical is supplied, the alkaline chemical is also collected by the filter cloth. A reaction between the acid gas (hydrogen chloride, sulfur oxides, etc.) contained in the exhaust gas and the alkaline agent on the filter cloth causes the acid gas to be removed from the exhaust gas.

In the bag filter 42, fly ash, mercury adsorbent, etc. deposited on the filter cloth are removed by backwashing using compressed gas. In the backwashing operation, compressed gas (pulse jet) is supplied to the filter cloth from the downstream side toward the upstream side in the flow direction of the exhaust gas. Compressed gas is, for example, compressed air. A plurality of filter cloth groups are provided in the actual bag filter 42, and the above-described backwashing operation is performed individually for each filter cloth group. During the normal time of exhaust gas treatment, which will be described later, the backwashing operation is sequentially performed on a plurality of filter cloth groups at a set cycle. The fly ash and mercury adsorbent, etc., which have been shaken off from the filter cloth, that is, the substances collected by the bag filter 42 are discharged to a discharge processing section (not shown). In the discharge processing section, chelate processing or the like is applied to the collected matter as necessary.

FIG. 2 is a diagram showing the configuration of the upstream mercury concentration meter 45. As shown in FIG. The upstream mercury concentration meter 45 includes a first intake port 51 , a second intake port 52 , a reduction section 53 , a concentration acquisition section 54 and a switching section 55 . The switching unit 55 includes a first flow path 551 , a second flow path 552 , three three-way valves 553 to 555 , a first auxiliary flow path 556 and a second auxiliary flow path 557 . The first inlet 51 and the second inlet 52 are attached to the flue 3 . The first intake port 51 is connected to the concentration acquisition section 54 by a first channel 551 . The second intake port 52 is connected to the concentration acquisition section 54 by a second channel 552 . Specifically, in the vicinity of the concentration acquisition unit 54, the first channel 551 and the second channel 552 merge via a three-way valve 555 to form one channel. The concentration acquisition unit 54 acquires a measured value of mercury concentration based on zero-valent mercury (metallic mercury) by an ultraviolet absorption method or the like. The mercury concentration measurement value is output to the control unit 40 .

In the first flow path 551 , a filter 591 , a return section 53 and a three-way valve 553 are provided in this order from the first inlet 51 toward the three-way valve 555 . The filter 591 removes fly ash contained in the exhaust gas (sampling gas) taken in from the first intake port 51 . The reduction unit 53 includes a reduction catalyst that reduces divalent mercury to zero-valent mercury. The reducing portion 53 is constantly heated to a predetermined temperature (eg, 350 to 400° C.) by the heating portion 531 . The reducing unit 53 may be provided with a scrubber for removing hydrogen chloride and the like. One end of the first auxiliary flow path 556 is connected to the three-way valve 553 . The other end of the first auxiliary flow path 556 is connected to the flue 3 downstream of the first inlet 51 . In the three-way valve 553 , the path of the gas flowing through the first flow path 551 is switched between the flow path toward the three-way valve 555 and the first auxiliary flow path 556 .

A filter 592 and a three-way valve 554 are provided in this order from the second inlet 52 toward the three-way valve 555 in the second flow path 552 . The filter 592 removes fly ash contained in the exhaust gas taken from the second intake port 52 . One end of a second auxiliary flow path 557 is connected to the three-way valve 554 . The other end of the second auxiliary flow path 557 is connected to the flue 3 on the downstream side of the second inlet 52 . In the three-way valve 554 , the path of the gas flowing through the second flow path 552 is switched between the flow path toward the three-way valve 555 and the second auxiliary flow path 557 .

The upstream mercury concentration meter 45 measures the concentration of zero-valent mercury contained in the exhaust gas flowing through the flue 3 (hereinafter referred to as "concentration of zero-valent mercury"), and measures the concentration of zero-valent mercury and divalent mercury contained in the exhaust gas. It is possible to selectively measure the total concentration of (hereinafter referred to as "total mercury concentration"). In other words, it is possible to switch between the zerovalent mercury measurement state for measuring the zerovalent mercury concentration and the total mercury measurement state for measuring the total mercury concentration. The zero-valent mercury measurement state and the total mercury measurement state in the upstream mercury concentration meter 45 will be described below.

FIG. 3 is a diagram showing the upstream mercury concentration meter 45 in a zero-valent mercury measurement state, and FIG. 4 is a diagram showing the upstream mercury concentration meter 45 in a total mercury measurement state. In FIGS. 3 and 4, out of the three triangles representing the three-way valves 553-555, two triangles are filled to show the flow paths connected by the three-way valves 553-555.

In the zero-valent mercury measurement state, as shown in FIG. 3, the exhaust gas taken in from the first intake port 51 and flowing through the first flow path 551 is led to the first auxiliary flow path 556 by the three-way valve 553, and the flue. Return to 3. Further, the exhaust gas taken from the second intake port 52 and flowing through the second flow path 552 is guided by the three-way valve 554 to the three-way valve 555 side, and further guided by the three-way valve 555 to the concentration acquisition section 54 . As a result, the concentration acquisition unit 54 acquires the measured value of the concentration of zerovalent mercury originally contained in the exhaust gas (that is, the concentration of zerovalent mercury) in a state in which the divalent mercury contained in the exhaust gas is not reduced to zerovalent mercury. be done. Thus, in the zero-valent mercury measurement state, zero-valent mercury is detected, but bivalent mercury is not detected. Therefore, it is possible to omit the time required to reduce divalent mercury to zero-valent mercury and quickly acquire the measured value of the mercury concentration.

In the state of total mercury measurement, as shown in FIG. 4, the exhaust gas flowing through the second flow path 552 is guided by the three-way valve 554 to the second auxiliary flow path 557 and returned to the flue 3 . Further, the exhaust gas flowing through the first flow path 551 is guided by the three-way valve 553 to the three-way valve 555 side, and further guided by the three-way valve 555 to the concentration acquisition section 54 . As a result, the concentration acquisition unit 54 acquires the measured values of the total concentration of zero-valent mercury obtained by reducing the divalent mercury in the exhaust gas and the total concentration of zero-valent mercury originally contained in the exhaust gas (that is, the total mercury concentration). be done. In this way, in the total mercury measurement state, both zero-valent mercury and divalent mercury are detected, so it is possible to obtain an accurate measurement value of the mercury concentration.

As described above, the exhaust gas taken in through the first intake port 51 flows into the reducing section 53 not only in the total mercury measurement state but also in the zerovalent mercury measurement state. That is, while the exhaust gas flows through the flue 3 , the exhaust gas always flows into the reducing section 53 . Therefore, immediately after switching from the zero-valent mercury measurement state to the total mercury measurement state, the concentration acquisition unit 54 can stably acquire the measured value of the total mercury concentration. Similarly, the exhaust gas taken in through the second intake port 52 flows into the second flow path 552 not only in the zero-valent mercury measurement state but also in the total mercury measurement state. Therefore, the second flow path 552 can be constantly warmed by the exhaust gas, and it is prevented or suppressed that the measured value of the zerovalent mercury concentration becomes unstable immediately after switching from the total mercury measurement state to the zerovalent mercury measurement state. be.

The downstream mercury concentration meter 46 in FIG. Measure the total concentration of zero-valent mercury contained. The downstream mercury concentration meter 46 has, for example, a configuration in which the second flow path 552, the first auxiliary flow path 556 and the second auxiliary flow path 557 are omitted from the upstream mercury concentration meter 45 of FIG. A value measured by the downstream mercury concentration meter 46 is output to the control unit 40 . As described above, in the example of FIG. 1, the inlet of the downstream mercury concentration meter 46 is provided in the chimney 22 . In the following description, the total mercury concentration measured by the downstream mercury concentration meter 46 is referred to as "downstream mercury concentration".

5 and 6 are diagrams showing changes in the concentration of zero-valent mercury and the concentration of total mercury in the exhaust gas. Here, instead of the upstream mercury densitometer 45, a mercury densitometer for measuring the concentration of zero-valent mercury and a mercury densitometer for measuring the total mercury concentration, that is, using two mercury densitometers, We also measured the mercury concentration in the flue gas on the upstream side. 5 and 6, solid lines L1 and L3 indicate the concentration of zero-valent mercury, and dashed lines L2 and L4 indicate the concentration of total mercury. Further, FIG. 5 shows changes in concentration for 4 hours, and FIG. 6 shows changes in concentration for 1 hour.

It was confirmed by the measurement using the above two mercury concentration meters that the changes in the concentration of zero-valent mercury and the concentration of total mercury were classified into a first pattern and a second pattern. In the first pattern, as shown in FIG. 5, after a sharp protrusion P1 is detected on the zerovalent mercury concentration line L1, a broad protrusion P2 is detected on the total mercury concentration line L2. In the second pattern, as shown in FIG. 6, after a sharp convex portion P3 is detected in the zerovalent mercury concentration line L3, a broad convex portion like the convex portion P2 in FIG. 5 is detected in the total mercury concentration line L4. No protrusion is detected. Further, as will be described later, when the integrated amount of zero-valent mercury is calculated based on the zero-valent mercury concentration corresponding to the height and width of the protrusions P1 and P3 and the period, etc., the protrusions in the first pattern The integrated amount of zero-valent mercury corresponding to the portion P1 is sufficiently larger than the integrated amount of zero-valent mercury corresponding to the convex portion P3 in the second pattern. Calculation of the integrated amount of zero-valent mercury will be described later. As described above, the scales of the horizontal axes in FIGS. 5 and 6 are different.

As will be described later, during normal exhaust gas treatment, the amount of mercury adsorbent supplied by the adsorbent supply unit 41 is controlled based on the concentration of zero-valent mercury. That is, when the concentration of zero-valent mercury is relatively high, the amount of mercury adsorbent supplied is increased, and when the concentration of zero-valent mercury is relatively low, the amount of mercury adsorbent supplied is decreased. Therefore, in both the first pattern and the second pattern, the supply amount of the mercury adsorbent is increased in accordance with the sharp protrusions P1 and P3 of the zerovalent mercury concentration, and when the zerovalent mercury concentration decreases, the mercury adsorbent supply is reduced.

At this time, in the second pattern shown in FIG. 6, after the concentration of zero-valent mercury decreases, the total mercury concentration also decreases. It is possible to appropriately reduce the mercury concentration of On the other hand, in the first pattern shown in FIG. 5, after the zerovalent mercury concentration decreases, the total mercury concentration increases over a long period of time. It is not possible to adequately reduce the mercury concentration in the flue gas passing through the As described above, in the actual exhaust gas treatment apparatus 4, since the upstream mercury concentration meter 45 switches between the zero-valent mercury measurement state and the total mercury measurement state, the upstream mercury concentration meter 45 in the zero-valent mercury measurement state When controlling the supply amount of the mercury adsorbent based on the concentration of zero-valent mercury, the total mercury concentration cannot be measured. Therefore, it is impossible to detect the first pattern by measuring the total mercury concentration. Exhaust gas treatment in the exhaust gas treatment device 4 capable of appropriately reducing the mercury concentration of the exhaust gas in both the first pattern and the second pattern will be described below.

FIG. 7 is a diagram showing the flow of exhaust gas treatment in the exhaust gas treatment device 4. As shown in FIG. The exhaust gas treatment in the following description is a process of controlling the amount of mercury adsorbent supplied by the adsorbent supply unit 41 to reduce the mercury concentration of the exhaust gas. In the exhaust gas treatment device 4, in principle, measurement of the mercury concentration (zero-valent mercury concentration or total mercury concentration) by the upstream mercury concentration meter 45 and measurement of the downstream mercury concentration by the downstream mercury concentration meter 46 are continuously performed. done. FIG. 7 shows control using only the upstream mercury densitometer 45, and control using the upstream mercury densitometer 45 and the downstream mercury densitometer 46 will be described later. Hereinafter, the term "total mercury concentration" simply means the total mercury concentration measured by the upstream mercury concentration meter 45. FIG.

During normal exhaust gas treatment, the concentration of zero-valent mercury is measured by the upstream mercury concentration meter 45, which is in the state of measuring zero-valent mercury, and the controller 40 supplies the adsorbent based on (the measured value of) the concentration of zero-valent mercury. The amount of mercury adsorbent supplied by the unit 41 is controlled (see step S18 described later). In the following description, the control of the supply amount of the mercury adsorbent based on the concentration of zero-valent mercury is simply referred to as "control based on the concentration of zero-valent mercury" (control based on the total mercury concentration described below and control based on the downstream mercury concentration The same applies to control.). In the control based on the concentration of zerovalent mercury, for example, when the concentration of zerovalent mercury is relatively high, the supply amount of the mercury adsorbent is increased, and when the concentration of zerovalent mercury is relatively low, the supply amount of the mercury adsorbent is increased. reduced. When the mercury adsorbent is activated carbon, the activated carbon also adsorbs dioxins. Therefore, it is preferable that a predetermined amount or more of the mercury adsorbent is always supplied to the flue 3 while the exhaust gas flows through the flue 3 .

Here, adsorption of mercury by the mercury adsorbent mainly occurs in the bag filter 42 . Further, in the control based on the concentration of zero-valent mercury, the concentration of zero-valent mercury obtained on the downstream side of the bag filter 42 is not used, but the concentration of zero-valent mercury obtained on the upstream side of the bag filter 42 is used. Therefore, it can be said that control based on the concentration of zero-valent mercury is feedforward control (FF control). The same applies to control based on the total mercury concentration, which will be described later.

As described above, no time lag due to reduction of divalent mercury occurs in the zero-valent mercury measurement state. As a result, in the control based on the concentration of zero-valent mercury, the supply amount of the mercury adsorbent can be rapidly adjusted to the change in the concentration of zero-valent mercury in the exhaust gas flowing in the vicinity of the second intake port 52, that is, with good responsiveness. control becomes possible. The zero-valent mercury concentration used for control in the control unit 40 may be a moving average or the like for a certain period of time (the same applies to the total mercury concentration and the downstream mercury concentration).

The control unit 40 compares the zerovalent mercury concentration with a predetermined first threshold in parallel with the control based on the zerovalent mercury concentration. The first threshold is, for example, 10 to 50 μg/m ³ N (converted to 12% oxygen). When the concentration of zero-valent mercury becomes greater than the first threshold value due to incineration of waste containing a large amount of mercury (step S11), integration of the amount of zero-valent mercury in the exhaust gas is started (step S12). The amount of zero-valent mercury is integrated, for example, at regular time intervals ΔH [h]. The value A [μg/m ³ N] of the concentration of zero-valent mercury and the flow rate B [m ³ N/h] of exhaust gas are constantly input to the control unit 40, and the integration of the amount of zero-valent mercury is The integrated amount of zero-valent mercury from the start of integration to the present is obtained from Σ(A×B×ΔH). The integrated amount of zero-valent mercury is an evaluation value used for the determination described later. Accumulation of the amount of zero-valent mercury is performed in parallel with control based on the concentration of zero-valent mercury.

When the concentration of zero-valent mercury becomes equal to or lower than the first threshold (step S13), the evaluation value is compared with a predetermined second threshold. Typically, the evaluation value is the integrated amount of zero-valent mercury itself, and as described above, the integration period is equal to or less than the first threshold from the time when the concentration of zero-valent mercury becomes greater than the first threshold. It is the period immediately before, that is, the period in which the concentration of zero-valent mercury is higher than the first threshold. The second threshold value is, for example, 0.5 to 2 g when the waste processing amount is 100 t/day. A 2nd threshold value is changed in proportion to the refuse processing amount of an incineration facility. The evaluation value may be other than the integrated amount of zerovalent mercury over the entire period, and as described later, it is determined whether the change in the zerovalent mercury concentration indicates the first pattern or the second pattern. If possible, it may be an integrated amount in a part of the above period. Also, the evaluation value may be another value that is correlated with the integrated amount of zero-valent mercury. In this way, the evaluation value may be a value indicating the integrated amount of zerovalent mercury in the exhaust gas during an integration period including at least part of the period during which the concentration of zerovalent mercury is greater than the first threshold value. In the following description, it is assumed that the evaluation value is the integrated amount of zerovalent mercury over the entire period.

When the evaluation value (here, the integrated amount of zero-valent mercury) is equal to or less than the second threshold (step S14), the integrated amount of zero-valent mercury is returned to 0 and reset (step S15). Also, returning to step S11, the zero-valent mercury concentration is compared with the first threshold value. At this time, since the concentration of zero-valent mercury is equal to or lower than the first threshold value, the supply amount of the mercury adsorbent is also relatively small. As will be described later, the second threshold value is for determining which of the first pattern and the second pattern the change in the concentration of zero-valent mercury for which the evaluation value was obtained. If it is equal to or less than the second threshold, it is assumed that the change in the concentration of zero-valent mercury exhibits the second pattern. In the second pattern, as shown in FIG. 6, after the zerovalent mercury concentration decreases, the total mercury concentration also decreases. Therefore, even if the control based on the concentration of zero-valent mercury is continued, it is possible to appropriately reduce the concentration of mercury in the exhaust gas.

On the other hand, when the evaluation value is greater than the second threshold (step S14), the upstream mercury concentration meter 45 is switched to the total mercury measurement state. As a result, control of the supply amount of the mercury adsorbent is switched from control based on the zerovalent mercury concentration to control based on the total mercury concentration (step S16). In control based on the total mercury concentration, the supply amount of the mercury adsorbent is controlled based on the total mercury concentration. Therefore, when the total mercury concentration is relatively high, the supply amount of the mercury sorbent is increased, and when the total mercury concentration is relatively low, the supply amount of the mercury sorbent is decreased.

As described above, the integrated amount of zero-valent mercury corresponding to the protrusions P1 in the first pattern is sufficiently larger than the integrated amount of zero-valent mercury corresponding to the protrusions P3 in the second pattern. In the exhaust gas treatment device 4, by comparing with the evaluation value indicating the integrated amount of zerovalent mercury, it is determined whether the change in the concentration of zerovalent mercury for which the evaluation value is obtained indicates the first pattern or the second pattern. A second threshold for determination is set in advance. If the evaluation value is greater than the second threshold, it is assumed that the change in the 0valent mercury concentration exhibits the first pattern. In the first pattern, as shown in FIG. 5, after the concentration of zero-valent mercury decreases, the total mercury concentration increases over a long period of time. By controlling the supply amount of , it is possible to appropriately reduce the mercury concentration in the exhaust gas. In addition, since an accurate mercury concentration can be obtained in the state of total mercury measurement, control based on the total mercury concentration makes it possible to control the supply amount of the mercury adsorbent to a lesser extent.

The control unit 40 compares the total mercury concentration with a predetermined third threshold in parallel with the control based on the total mercury concentration. The third threshold is, for example, 50 to 200 μg/m ³ N (converted to 12% oxygen). Typically, the third threshold is greater than the first threshold. If the total mercury concentration is greater than the third threshold (step S17), control based on the total mercury concentration is continued. When the total mercury concentration becomes equal to or less than the third threshold (step S17), the upstream mercury concentration meter 45 is switched from the total mercury measurement state to the zerovalent mercury measurement state. As a result, control of the supply amount of the mercury adsorbent is switched from control based on the total mercury concentration to control based on the zerovalent mercury concentration, and is returned to normal control (step S18).

At this time, in the bag filter 42, since the mercury adsorbent on the filter cloth has adsorbed a large amount of mercury, it is preferable that the backwashing operation is performed at a cycle shorter than the set cycle at normal times. Thereby, it is suppressed that mercury desorbs from the mercury adsorbent on the filter cloth and the downstream mercury concentration increases. In addition, since the mercury concentration (total mercury concentration) on the upstream side of the bag filter 42 is low, the exhaust gas with a high mercury concentration passes through the filter cloth on which the mercury adsorbent is not deposited due to the backwashing operation. A rise in the lateral mercury concentration is suppressed.

The controller 40 resets the integrated amount of zero-valent mercury (step S15). Then, returning to step S11, the zerovalent mercury concentration is compared with the first threshold value. In the exhaust gas treatment device 4, while the exhaust gas is flowing through the flue 3, the treatment shown in FIG. 7 is continuously performed.

As described above, the upstream mercury concentration meter 45 of the exhaust gas treatment device 4 is switchable between the zero-valent mercury measurement state and the total mercury measurement state. As a result, the concentration of zero-valent mercury and the concentration of total mercury can be selectively measured using one concentration acquisition unit 54, and the manufacturing cost of the upstream mercury concentration meter 45 can be reduced. In the exhaust gas treatment by the exhaust gas treatment device 4, the supply amount of the mercury adsorbent is normally controlled based on the zero-valent mercury concentration of the upstream mercury concentration meter 45, which is in the zero-valent mercury measurement state. Further, an evaluation value indicating the integrated amount of zerovalent mercury in the exhaust gas is acquired based on the zerovalent mercury concentration during the period when the zerovalent mercury concentration is greater than the first threshold value. After the period, when the concentration of zero-valent mercury becomes equal to or lower than the first threshold, the evaluation value is compared with the second threshold. Then, when the evaluation value is larger than the second threshold value, the upstream mercury concentration meter 45 is switched to the total mercury measurement state, and the supply amount of the mercury adsorbent is controlled based on the total mercury concentration. As a result, even if the total mercury concentration increases for a long period of time after the concentration of zero-valent mercury in the exhaust gas decreases (see the first pattern in FIG. 5), the exhaust gas treatment device 4 can appropriately adjust the mercury concentration of the exhaust gas. can be lowered to

Further, when the total mercury concentration becomes equal to or less than the third threshold value, the upstream mercury concentration meter 45 in the total mercury measurement state is switched to the zerovalent mercury measurement state, and the supply amount of the mercury adsorbent is based on the zerovalent mercury concentration. is controlled. As a result, after the total mercury concentration becomes low, it is possible to return to the control based on the zero-valent mercury concentration and control the supply amount of the mercury adsorbent with good responsiveness.

Next, control using the upstream mercury densitometer 45 and the downstream mercury densitometer 46 will be described. FIG. 8 is a diagram showing another example of exhaust gas treatment in the exhaust gas treatment device 4. As shown in FIG. Steps S19 to S21 in FIG. 8 are processes performed between steps S17 and S18 in FIG. Hereinafter, the processing after the control of the supply amount of the mercury adsorbent is switched from the control based on the zerovalent mercury concentration to the control based on the total mercury concentration in step S16 will be described.

The control unit 40 compares the total mercury concentration with the third threshold in parallel with the control based on the total mercury concentration. When the total mercury concentration becomes equal to or less than the third threshold (step S17), the downstream mercury concentration obtained by the downstream mercury concentration meter 46 is compared with a predetermined fourth threshold. The fourth threshold is, for example, 20 to 50 μg/m ³ N (converted to 12% oxygen). Here, in the control based on the concentration of zero-valent mercury and the control based on the total mercury concentration, the supply of the mercury adsorbent normally keeps the downstream mercury concentration low. When the downstream mercury concentration is equal to or lower than the fourth threshold, that is, when the downstream mercury concentration is kept low (step S19), the upstream mercury concentration meter 45 changes from the total mercury measurement state to the zero valent mercury measurement state. state can be switched. As a result, control of the supply amount of the mercury adsorbent is switched from control based on the total mercury concentration to control based on the zerovalent mercury concentration, and is returned to normal control (step S18). As in the process of FIG. 7, when the total mercury concentration becomes equal to or less than the third threshold value in step S17, even if the bag filter 42 performs the backwashing operation at a cycle shorter than the set cycle at normal time, good.

On the other hand, when the mercury adsorbent on the filter cloth of the bag filter 42 contains a large amount of mercury and mercury is desorbed from the mercury adsorbent, the comparison between the downstream mercury concentration and the fourth threshold shows that the downstream The side mercury concentration becomes larger than the fourth threshold (step S19). In this case, in the control unit 40, control of the supply amount of the mercury adsorbent is switched from control based on the total mercury concentration to control based on the downstream mercury concentration (step S20). In the control based on the downstream mercury concentration, when the downstream mercury concentration is relatively high, the supply amount of the mercury sorbent is increased, and when the downstream mercury concentration is relatively low, the supply amount of the mercury sorbent is decreased. be.

Control based on the downstream mercury concentration does not use the zero-valent mercury concentration or the total mercury concentration obtained upstream of the bag filter 42, but uses the downstream mercury concentration obtained downstream of the bag filter 42. Therefore, it can be said that control based on the downstream mercury concentration is feedback control (FB control). Control based on the downstream mercury concentration makes it possible to more reliably reduce the mercury concentration in the exhaust gas discharged into the atmosphere. Note that the upstream mercury concentration meter 45 may be switched from the state of measuring total mercury to the state of measuring zero-valent mercury along with the switching to the control based on the downstream mercury concentration.

Switching from feedforward control using the upstream mercury concentration (zero-valent mercury concentration or total mercury concentration) of the bag filter 42 to feedback control using the downstream mercury concentration (downstream mercury concentration) is performed by the operator. may be done manually by For example, during control based on the total mercury concentration, when the total mercury concentration is equal to or less than the third threshold and the downstream mercury concentration is greater than the fourth threshold (steps S17 and S19), the control unit 40 performs feedback A notification prompting the operator to switch to control is provided. The notification prompting the switching is performed, for example, by display on a display, output of sound, or the like. The exhaust gas treatment device 4 is provided with a changeover switch for instructing switching from feedforward control to feedback control, and the operator operates the changeover switch in response to a notification prompting the changeover, whereby the feedforward control is changed to the feedback control. Switching to control is performed (step S20).

In the control based on the downstream mercury concentration, the mercury concentration (zero-valent mercury concentration or total mercury concentration) obtained by the upstream mercury concentration meter 45 may be used. That is, in step S20, feedforward control may be switched to control using both feedforward control and feedback control. Switching to control using both may also be performed manually.

The controller 40 compares the downstream mercury concentration with a predetermined fifth threshold. The fifth threshold is, for example, 20 to 50 μg/m ³ N (converted to 12% oxygen). The fifth threshold may be the same as the fourth threshold. When the downstream mercury concentration is higher than the fifth threshold (step S21), control of the supply amount of mercury adsorbent based on the downstream mercury concentration is continued. When the downstream mercury concentration becomes equal to or lower than the fifth threshold (step S21), control of the supply amount of the mercury adsorbent is switched from control based on the downstream mercury concentration to control based on the zerovalent mercury concentration ( step S18). That is, the control in the exhaust gas treatment device 4 is returned to normal control.

As described above, in the exhaust gas treatment of FIG. 8, when the downstream mercury concentration is greater than the fourth threshold, the control unit 40 changes the supply amount of the mercury adsorbent from control based on the total mercury concentration to , is switched to control based on the downstream mercury concentration. As a result, it becomes possible to more reliably lower the mercury concentration in the exhaust gas discharged into the atmosphere.

In the exhaust gas treatment of FIG. 8, the control based on the total mercury concentration is switched to the control based on the downstream mercury concentration. In this case, control of the supply amount of the mercury adsorbent may be switched to control based on the downstream mercury concentration. Further, as described above, in the control based on the downstream mercury concentration, not only the downstream mercury concentration but also the zerovalent mercury concentration or the total mercury concentration may be used. As described above, in the exhaust gas treatment apparatus 4, when the downstream mercury concentration is greater than the fourth threshold (for example, the zerovalent mercury concentration and the total mercury concentration are equal to or less than a predetermined threshold, and the downstream mercury concentration is fourth threshold), the control of the supply amount of the mercury adsorbent is preferably switched from the control based on the zero-valent mercury concentration or the total mercury concentration to the control based on at least the downstream mercury concentration. As a result, it is possible to more reliably lower the mercury concentration in the exhaust gas discharged into the atmosphere.

Various modifications are possible in the exhaust gas treatment device 4 .

Another bag filter may be arranged between the incinerator 21 and the adsorbent supply unit 41 in the exhaust gas treatment apparatus 4 of FIG. 1 . In this case, the fly ash contained in the exhaust gas is collected by the other bag filter, and the bag filter 42 uses the mercury adsorbent supplied to the flue 3 by the adsorbent supply unit 41 (when an alkaline chemical is also supplied, Mercury adsorbents and alkaline agents) are mainly collected.

In the flue 3 , the inlet of the upstream mercury concentration meter 45 may be arranged at any position on the upstream side of the bag filter 42 in the flow direction of the exhaust gas. In addition, the inlet of the downstream mercury concentration meter 46 may be arranged at an arbitrary position on the downstream side of the bag filter 42 in the flow direction of the exhaust gas.

The exhaust gas treatment device 4 may be used in equipment other than the incineration equipment 1 .

The configurations in the above embodiment and each modified example may be combined as appropriate as long as they do not contradict each other. In addition, the numerical values in the text are regulatory values for Japan, and when applying to other countries, it is necessary to correspond to the regulatory values of that country.

3 flue 4 exhaust gas treatment device 40 control unit 41 adsorbent supply unit 42 bag filter 45 upstream mercury concentration meter 46 downstream mercury concentration meter S11 to S21 Steps

Claims (4)

An exhaust gas treatment device,
an adsorbent supply unit that supplies a mercury adsorbent to the exhaust gas in a flue through which the exhaust gas flows;
an adsorbent collecting unit that collects the mercury adsorbent in the flue;
In the flue, a zerovalent mercury measurement state that is arranged upstream in the flow direction of the exhaust gas with respect to the adsorbent collection unit and measures the concentration of zerovalent mercury in the exhaust gas, and a divalent mercury in the exhaust gas. a mercury concentration meter capable of switching between a total mercury measurement state for measuring the total concentration of the reduced zero-valent mercury and the total concentration of the zero-valent mercury originally contained in the exhaust gas as the total mercury concentration;
The amount of the mercury adsorbent supplied by the adsorbent supply unit is controlled based on the zerovalent mercury concentration of the mercury concentration meter in the zerovalent mercury measurement state, and the zerovalent mercury concentration is greater than a first threshold. During the period, an evaluation value indicating the integrated amount of zerovalent mercury in the exhaust gas is obtained based on the zerovalent mercury concentration, and when the zerovalent mercury concentration becomes equal to or less than the first threshold following the period, the An evaluation value is compared with a second threshold, and if the evaluation value is greater than the second threshold, the mercury concentration meter is switched to the total mercury measurement state, and the mercury adsorbent is measured based on the total mercury concentration. a control unit that controls the amount of supply of
An exhaust gas treatment device comprising: The exhaust gas treatment apparatus according to claim 1,
When the total mercury concentration is equal to or less than a third threshold value, the control unit switches the mercury concentration meter in the total mercury measurement state to the zerovalent mercury measurement state, and An exhaust gas treatment apparatus characterized by controlling the supply amount of a mercury adsorbent. The exhaust gas treatment device according to claim 1 or 2,
In the flue, it is arranged downstream in the flow direction of the exhaust gas with respect to the adsorbent collection part, and zero-valent mercury obtained by reducing divalent mercury in the exhaust gas, and originally contained in the exhaust gas Further comprising a downstream mercury concentration meter that measures the total concentration of zero-valent mercury as the downstream mercury concentration,
When the downstream mercury concentration is greater than a fourth threshold, the control unit shifts control of the supply amount of the mercury adsorbent from control based on the zerovalent mercury concentration or the total mercury concentration to at least the downstream side An exhaust gas treatment apparatus characterized by switching to control based on mercury concentration. An exhaust gas treatment method in an exhaust gas treatment apparatus,
The exhaust gas treatment device is
an adsorbent supply unit that supplies a mercury adsorbent to the exhaust gas in a flue through which the exhaust gas flows;
an adsorbent collecting unit that collects the mercury adsorbent in the flue;
In the flue, a zerovalent mercury measurement state that is arranged upstream in the flow direction of the exhaust gas with respect to the adsorbent collection unit and measures the concentration of zerovalent mercury in the exhaust gas, and a divalent mercury in the exhaust gas. a mercury concentration meter capable of switching between a total mercury measurement state for measuring the total concentration of the reduced zero-valent mercury and the total concentration of the zero-valent mercury originally contained in the exhaust gas as the total mercury concentration;
with
The exhaust gas treatment method is
a step of controlling the supply amount of the mercury adsorbent by the adsorbent supply unit based on the zerovalent mercury concentration of the mercury concentration meter in the zerovalent mercury measurement state;
a step of acquiring an evaluation value indicating an integrated amount of zerovalent mercury in the exhaust gas based on the zerovalent mercury concentration in a period in which the zerovalent mercury concentration is greater than a first threshold;
When the zerovalent mercury concentration becomes equal to or lower than the first threshold following the period, the evaluation value is compared with a second threshold, and if the evaluation value is greater than the second threshold, the mercury concentration switching the meter to the total mercury measurement state and controlling the supply amount of the mercury adsorbent based on the total mercury concentration;
An exhaust gas treatment method comprising:

Images