JP2010127597A - Treated object combustion treatment system and method of removing mercury in exhaust gas - Google Patents

Abstract

[PROBLEMS] To reduce the amount of fly ash generated when a processing object such as flammable waste is combusted and to reduce the amount of mercury contained in exhaust gas and discharged.
[MEANS FOR SOLVING PROBLEMS] Powdered activated carbon is sprayed at the entrance of a desalting bag filter (7) and mercury having a high concentration in the "return line process" is discharged to the outside of the system (14) by switching a switching damper (9) By starting, the mercury concentration in the exhaust gas is drastically reduced within a predetermined time, and after the predetermined time has elapsed, spraying of the powdered activated carbon at the entrance of the desalting bag filter 7 is stopped and switched to the “return line process”. As a result, it is possible to prevent the mercury concentration from abruptly increasing and to appropriately manage the mercury concentration.
[Selection] Figure 1

Description

  The present invention relates to a combustion treatment system (for example, combustible waste or pyrolysis gas) having a device for removing mercury in a part of the system, and a method for removing mercury in exhaust gas.

  Conventionally, as a method of removing mercury in exhaust gas, powdered activated carbon is sprayed at the entrance of a bag filter to exhaust gas generated by a combustion treatment apparatus that burns pyrolysis gas, etc., and mercury in the exhaust gas is adsorbed on the activated carbon. A so-called dry method (Patent Document 1) that collects and removes by a bag filter is known. In the dry method described in Patent Document 1, metal mercury contained in exhaust gas is converted into mercuric chloride (converted into a form that is easily physically adsorbed by activated carbon), and then the activated carbon is added and adsorbed on the activated carbon. Thus, the mercury removal rate by the activated carbon is improved.

Here, the collected matter by the bag filter is a mixture of fly ash, organic chlorine compounds such as dioxins contained in the fly ash, heavy metals, activated carbon adsorbing the organic chlorine compounds and mercury. In the dry method described in Patent Document 1, a method is described in which the collected matter is detoxified with a heavy metal fixing agent or cement to be disposed of, but the collected matter by the bag filter is returned to the return line. There is known a processing method in which the fly ash and heavy metal are melted and slagged and returned to the combustion melting furnace, and the organochlorine compound is decomposed (Patent Document 2).
JP 2006-263513 A JP 2004-298777 A

In the detoxification treatment of the collected matter according to Patent Document 1, a heavy metal fixing agent, cement, and the like are required, and the amount of fly ash generated increases, so that there is a problem that post-treatment costs increase.
On the other hand, if the molten slag conversion process of Patent Document 2 is used, fly ash and heavy metal in the collected matter become molten slag, so that the amount of fly ash generated can be reduced. However, since mercury has a melting point of −39 ° C., it becomes mercury vapor in the combustion melting furnace and cannot be removed as molten slag. Therefore, after the mercury in the collected matter is returned to the combustion melting furnace, it returns to the exhaust gas passage again. Then, the mercury returned to the exhaust gas passage is collected again from the exhaust gas by the bag filter, returned to the combustion melting furnace, and circulated back to the exhaust gas passage again. When this operating condition is continued, mercury is gradually concentrated.

  That is, if the exhaust gas treatment for returning the collected matter by the bag filter to the combustion melting furnace is continued, the mercury concentration in the exhaust gas flow channel upstream of the bag filter gradually increases. As a result, the mercury concentration in the exhaust gas passing through the bag filter gradually increases, and there is a problem that the amount of mercury discharged from the chimney mixed with the gas increases.

  The present invention has been made in view of such circumstances, and reduces the processing amount of fly ash and the like generated when a processing object such as combustible waste is combusted, and is included in the exhaust gas and discharged. The purpose is to reduce the amount of mercury.

  In order to achieve the above object, a processing object combustion processing system according to a first aspect of the present invention includes a combustion melting processing apparatus for combusting pyrolysis gas and char generated by heat processing a processing target, Provided in a first bag filter that allows the exhaust gas generated in the combustion melting processing device to pass through, a second bag filter that allows the exhaust gas that has passed through the first bag filter to pass, and an exhaust gas flow path downstream of the second bag filter A mercury concentration detector, a return line for returning the collected matter by the first bag filter to the combustion melting apparatus, and a switching portion for discharging the collected matter to the outside of the return line. A mercury removing material first adding means for adding a mercury removing material into or upstream of the first bag filter, and a mercury removing material second additive for adding a mercury removing material into or upstream of the second bag filter. And when the mercury concentration detection unit detects a preset value, the switching unit switches the collected matter to a direction to discharge out of the return line, and the mercury removing material second The addition means is switched from the non-addition state of the mercury removing material to the addition state, and after a predetermined time has elapsed, the switching unit is configured to return the collected matter from the discharge direction to the return line. It is characterized by that.

  According to this aspect, the fly ash or the like in the collected matter is again combusted by returning the collected matter by the first bag filter to the combustion melting treatment device through a return line for returning the collected matter to the combustion melting treatment device. The effect of reducing the processing amount of fly ash and the like in can be obtained.

  By returning the collected matter by the first bag filter to the combustion melting processing apparatus through the return line, the mercury adsorbed on the activated carbon also returns to the combustion melting processing apparatus, and the mercury concentration in the exhaust gas flow path of the combustion processing system Will rise. According to this aspect, when the mercury concentration detection unit detects a preset set value, the switching unit discharges the collected matter from the return line to the outside of the return line (outside the system). The mercury in the collected material is also discharged out of the return line (outside the system).

  Depending on the scale of the system, it will take more than a certain amount of time until the collected matter with the increased mercury concentration reaches the outside of the system. The mercury concentration in the collected material is reduced to the initial amount (first action).

The mercury concentration in the exhaust gas continues to rise until the collected matter whose mercury concentration has risen completely leaves the system. Therefore, the mercury concentration in the exhaust gas passing through the first bag filter and going to the second bag filter also continues to increase. According to this aspect, since the mercury removing material is added from the second removing means of the mercury removing material in the second bag filter or in the upstream portion thereof, the mercury contained in the exhaust gas that has passed through the first bag filter is further removed. (Second action).
That is, by both the first action and the second action, the amount of fly ash generated when the object to be treated such as combustible waste is burned is reduced, and it is contained in the exhaust gas. Can reduce the amount of mercury emitted.

  Further, by returning the collected matter by the first bag filter to the combustion melting processing apparatus through the return line, the fly ash in the collected matter can be changed to molten slag and discharged out of the system, and the fly ash It is also possible to decompose harmful substances such as dioxin contained in the ash etc., resulting in the effect of reducing the processing amount of fly ash and the like.

A processing object combustion processing system according to a second aspect of the present invention is the processing object combustion processing system according to the first aspect, wherein the mercury removing material from the mercury removing material second addition means after the predetermined time has elapsed. It is characterized by being comprised so that addition of may be stopped.
According to this aspect, in addition to the effects of the first aspect, the mercury removing material is added from the mercury removing material second addition means only for a predetermined time until the collected matter whose mercury concentration has risen completely out of the system. Therefore, the amount of mercury removal material used can be minimized.

A processing object combustion processing system according to a third aspect of the present invention is characterized in that in the processing object combustion processing system according to the first aspect or the second aspect, the mercury removing material is activated carbon.
According to this aspect, in addition to the effect of the first aspect or the second aspect, mercury in the exhaust gas can be effectively removed by the adsorption ability of the activated carbon.

The method for removing mercury in the exhaust gas according to the fourth aspect of the present invention is an exhaust gas for removing mercury in the exhaust gas generated by a combustion melting treatment apparatus that burns a pyrolysis gas and char generated by heat-treating a processing object. The first mercury removing step of adding a mercury removing material upstream of the first bag filter through which the exhaust gas is passed, and the collected matter by the first filter are returned to the combustion melting processing apparatus. A collected matter discharging step for discharging out of the return line and a second mercury removing step for adding a mercury removing material upstream of the second bag filter for passing the exhaust gas that has passed through the first bag filter, In the waste discharging step, the collected matter is discharged out of the return line for a predetermined time after a preset set value is detected by a mercury concentration detector provided in the exhaust gas flow path downstream of the second bag filter. Craft , And the second mercury removal process, when the setting value is detected, characterized by starting the addition of the mercury removing material.
According to this aspect, the same effect as the first effect can be obtained.

The mercury removal method in the exhaust gas according to the fifth aspect of the present invention is characterized in that, in the mercury removal method in the exhaust gas according to the fourth aspect, the addition of the mercury removal material is stopped after the predetermined time has elapsed.
According to this aspect, the same effect as in the second aspect can be obtained.

  According to the present invention, in the processing object combustion processing system, the processing amount of fly ash generated when the processing object such as flammable waste is combusted is reduced and discharged in the exhaust gas. The effect that the amount of mercury can be reduced is obtained.

Hereinafter, a mercury removal method in a processing object combustion processing system and a processing object combustion processing system according to the present invention will be described with reference to the drawings.
First, an embodiment of the present invention will be described with reference to FIG. In addition, this invention is not limited to the following embodiment.

  As shown in FIG. 1, the processing object combustion processing system according to the present invention heats a processing object to generate a pyrolysis gas, and heats the pyrolysis gas 1 as a pyrolysis device that burns the pyrolysis gas. A combustion melting furnace 2 as a combustion processing device, a high temperature air heater 3 as a heat recovery device for recovering summer from high temperature exhaust gas generated in the combustion melting furnace 2, and an exhaust gas heat recovered by the high temperature air heater 3 Waste heat boiler 4 as a heat source, a temperature reducing tower 5 for cooling the exhaust gas further used for heat in the waste heat boiler 4, and a first bug that allows the exhaust gas cooled by the temperature reduction tower 5 to pass through A dust removal bag filter 6 as an example of a filter, a desalination bag filter 7 as an example of a second bag filter that passes the exhaust gas that has passed through the dust removal bug filter 6, and an exhaust gas flow path downstream of the desalination bag filter 7 Provided in And a mercury concentration meter 8 as mercury concentration detection unit.

  Furthermore, a return line 12 for returning the collected matter 13 by the dust removal bag filter 6 to the combustion melting furnace 2 and a discharge direction and a return line provided in the return line 12 for discharging the collected matter 13 outside the system 14. A switching damper 9 for switching the direction of feeding into the carbon 12, a carbon hopper 10 for mixing the collected material 13 with pyrolytic carbon in the middle of the return line 12, and pyrolysis generated from the pyrolysis drum 1 And a separation device 11 for separating the residue and taking out the pyrolytic carbon.

  Further, a mercury removing material first adding means 15 for adding powdered activated carbon as a mercury removing material to the exhaust gas flow path between the temperature reducing tower 5 and the dust removing bag filter 6, the dust removing bag filter 6 and the desalting bag filter. 7 is also provided with a mercury removal material second addition means 16 for adding powdered activated carbon, which is a mercury removal material, to the exhaust gas flow path between the exhaust gas passage 7 and the exhaust gas flow path. In FIG. 1, reference numeral 17 indicates a known desalting agent addition means, and reference numeral 18 indicates a storage unit for a solid matter that is a collected matter by the desalting bag filter 7.

  Then, when the control unit 19 detects a preset value set by the mercury concentration detector 8, the collected substance 13 is discharged to the outside 14 outside the return line 12 by the switching damper 9. The mercury removal material second addition means 16 is switched from the non-addition state of powdered activated carbon to the addition state, and mercury removal processing is executed. After a predetermined time has passed, the collected matter 13 is removed by the switching damper 9. It is configured to return from the direction of discharging to the outside of the system 14 to the direction of sending into the return line 12.

  Here, as the “set value”, a value with no problem is used as the concentration of mercury released into the atmosphere. The set value is preferably as small as possible from the viewpoint of environmental protection, but if it is smaller than necessary, the switching operation of the switching damper 9 is frequently performed, and the amount of fly ash discharged outside the system 14 is reduced. Since it increases, it is preferable to set to the magnitude | size which can aim at environmental protection, suppressing the generation amount of fly ash.

  First, the waste (object to be treated) is put in the pyrolysis drum 1 and pyrolyzed. The pyrolysis residue and pyrolysis gas generated by the pyrolysis treatment are sent to the separation device 11 for the pyrolysis residue and iron, aluminum, etc. are removed as metal residues, while the pyrolysis gas is heated in the combustion melting furnace 2 at a high temperature. (For example, 1100 ° C. to 1300 ° C.) Combustion treatment is performed.

  Next, the high-temperature exhaust gas generated from the combustion melting furnace 2 is introduced into the high-temperature air heater 3 and used for heating the air. The air heated by the high-temperature air heater 3 is taken into a device (for example, a rotary kiln) having the pyrolysis drum 1 and used as a heat source for indirect heating of the pyrolysis drum 1. On the other hand, the exhaust gas used for heating the air in the high-temperature air heater 3 is recovered by the waste heat boiler 4 and used, for example, for power generation of electric power used in the system system.

The exhaust gas (temperature of about 300 to 400 ° C.) recovered by the waste heat boiler 4 is introduced into the temperature reducing tower 5 and cooled (temperature of about 150 to 200 ° C.), and then removed by the dust bag filter 6 and then removed. Through the salt bag filter 7, HCl, SOx, and the like contained in the exhaust gas are desalted and removed, and the purified gas is discharged from the chimney to the atmosphere.
In addition, as a desalting agent, the chemical | medical agents conventionally known as a desalting agent, such as calcium hydroxide (slaked lime) and sodium hydrogencarbonate (bicarbonate), can be used. For example, when removing hydrogen chloride contained in exhaust gas, a method of adding sodium bicarbonate to the exhaust gas and reacting with hydrogen chloride to produce solid sodium chloride, which is collected and separated by a bag filter. Is mentioned.

  Here, the mercury removal method in the system system in the processing object combustion processing system will be described in detail.

  The exhaust gas cooled by the temperature reducing tower 5 contains mercury derived from waste in a gas state. In order to remove this mercury, in this embodiment, powdered activated carbon is sprayed into the exhaust gas from the mercury removing material first addition means 15 at the entrance of the dust bag filter 6, and the powder activated carbon is adsorbed to the powder. The dust collecting bag filter 6 collects the activated carbon together with the activated carbon. The mercury removal rate here can usually be increased to about 99%. Therefore, the remaining 1% mercury passes through the dust bag filter 6.

  When only the desalting agent is added to the exhaust gas at the entrance of the desalting bag filter 7, only about 10% of the 1% mercury that has passed through can be removed. That is, the amount of mercury discharged outside the system is about 0.9% of the total.

  On the other hand, in the present invention, the powdered activated carbon is sprayed from the mercury removing material second addition means 16 at the entrance of the desalting bag filter 7, so that 99% of the 1% mercury that has passed can be removed. That is, mercury discharged outside the system can be reduced to about 0.01% of the total. Therefore, if the activated carbon powder is sprayed when the mercury concentration set in the mercury concentration meter 8 exceeds the set value, the mercury discharged outside the system system is reduced from 0.9% to 0.01% as described above. It becomes possible to reduce at a stretch.

  The mercury collected in the dust bag filter 6 together with the powdered activated carbon is put into the carbon hopper 9 through the return line 12 together with the fly ash contained in the exhaust gas also collected in the dust bag filter 6 and separated. It is mixed with the pyrolytic carbon separated and taken out by the apparatus 10 and returned to the combustion melting furnace 2. At this time, the switching damper 9 controls the flow of the collected matter 13 in a direction (return line 12) in which the collected matter 13 collected by the dust removing bag filter 6 is sent to the combustion melting furnace 2 through the carbon popper 10. .

  For this reason, in the combustion melting furnace 3, mercury contained in the newly generated exhaust gas and mercury contained in the collected product 13 sent from the return line 12 to the combustion melting furnace 2 are added to increase the mercury concentration. Yes.

  In addition, the fly ash etc. which are contained in the collection thing 13 are processed by the combustion melting furnace 2 at high temperature (for example, 1300 degreeC), are made into molten slag, and harmful substances, such as dioxin, are decomposed | disassembled.

The exhaust gas discharged from the combustion melting furnace 3 contains high-concentration mercury and fly ash, while the high-temperature air heater 3, the waste heat boiler 4, the temperature reducing tower 5, and the mercury removal material first addition means 15. It is introduced into the dust removal bag filter 6 through a spraying process of powdered activated carbon. Therefore, as described above, 99% of the mercury in the exhaust gas is removed, but since the mercury concentration is high, the exhaust gas that has passed through the dust removal bag filter 6 contains a higher concentration of mercury than the first. Thus, the mercury concentration in the exhaust gas measured through the desalting bag filter 7 increases.
On the other hand, the collected matter 13 collected by the dust bag filter 6 is sent again to the combustion melting furnace 3 through the return line 12 as described above.

  In this way, when the process of returning the collected matter 13 collected by the dust removal bag filter 6 to the combustion melting furnace 3 through the return line 12 (hereinafter referred to as “return line process”) is repeated, The amount of fly ash contained is reduced by melting slag in the combustion melting furnace 3, and harmful substances such as dioxin are also decomposed and reduced, but the concentration of mercury contained in the exhaust gas rises, and finally the mercury concentration The set value (management target value) set in total 8 is exceeded (FIG. 2).

Therefore, when the mercury concentration meter 8 detects the set value, the activated carbon powder is sprayed from the mercury removing material second addition means 16 at the entrance of the desalting bag filter 7, thereby reducing the concentration of mercury discharged out of the system system. At the same time, the switching damper 9 is switched to a direction in which the collected matter 13 collected by the dust removing bag filter 6 is discharged to the outside of the system 14 outside the return line 12, thereby being adsorbed by the powdered activated carbon and the collected matter 13. Mercury contained therein is discharged out of the system 14. This process reduces the mercury concentration in the system at once (FIG. 4). At this time, it is necessary to keep the switching damper 9 switched in a direction for discharging to the outside of the system 14 outside the return line 12 for a predetermined time. The reason for this is that, at the beginning when the switching damper 9 is switched from the direction inside the return line 12 for returning the collected matter 13 to the outside of the system 14 outside the return line, it is still inside the return line 12 from the switching damper 9 toward the combustion melting furnace 2. This is because the collected matter 13 containing high-concentration mercury remains, and it takes time until the collected matter 13 is collected by the dust bag filter 6 through the combustion melting furnace 3 and discharged out of the return line. This time varies depending on the scale of the system, but is usually 2 to 5 hours.
After the predetermined time has elapsed, the system is operated by switching the switching damper 9 toward the return line 12 for returning the collected matter 13 collected by the dust removing bag filter 6 to the combustion melting furnace 2 (FIG. 4).

  FIG. 3 shows a change in mercury concentration when only the powdered activated carbon is sprayed from the mercury removing material second addition means 16 at the entrance of the desalting bag filter 7 (in the case without the switching damper 9). When powdered activated carbon is sprayed at the entrance of the desalting bag filter 7, the mercury concentration rapidly decreases. However, when the spraying of the powdered activated carbon is stopped after a predetermined time, there is a disadvantage that the mercury concentration rapidly increases.

  This is because the “return line process” is repeated and mercury in the “return line process” is not removed and the mercury concentration increases. As shown in FIG. 3, when the spraying of the powdered activated carbon is stopped, the mercury concentration rapidly increases, and the exhaust gas passing through the dust removal bag filter 6 and passing through the desalting bag filter 7 contains high concentration mercury. become.

  Therefore, as in the present invention, powdered activated carbon is sprayed from the mercury removing material second addition means 16 at the entrance of the desalting bag filter 7, and the mercury that has become high in the “return line process” is replaced with the switching damper 9. By switching and starting discharge to the outside of the system 14 outside the return line, the mercury concentration in the exhaust gas is drastically reduced within a predetermined time compared with the case where powdered activated carbon is merely sprayed at the entrance of the desalting bag filter 7. (FIG. 4). In addition, even after stopping the spraying of powdered activated carbon at the entrance of the desalting bag filter 7 after a predetermined time, and switching to the “return line process”, almost no mercury remains in the “return line process”. There is no sudden increase in mercury concentration (Fig. 4).

  The mercury collected together with the powdered activated carbon in the desalting bag filter 7 is taken out into the solid container 18 and solidified with other collected substances (salts and the like) and discarded. A general known technique can be used for the solidification treatment. For example, a heavy metal fixing agent and water are added to the collected material, kneaded, solidified by a pressure molding machine, and discarded. Examples of the heavy metal fixing agent include chelating agents. Further, the mercury collected together with the powdered activated carbon contained in the collected matter of the dust removal bag filter 6 discharged to the outside of the system 14 outside the return line is solidified together with the fly ash and discarded. . About the solidification process, it can carry out by the method similar to the case where the collected matter collected by the desalting bag filter 7 mentioned above is solidified.

  As described above, according to the present invention, mercury in the processing object combustion processing system can be removed and the concentration of mercury discharged out of the system can be adjusted.

The block diagram of the process target object combustion processing system which concerns on embodiment of this invention. The figure which shows the relationship between elapsed time and mercury concentration in the case of not spraying powdered activated carbon at the 2nd bag filter (desalination bag filter) entrance. The figure which shows the relationship between elapsed time and mercury density | concentration at the time of spraying powdered activated carbon at the 2nd bag filter (desalting bag filter) entrance, and stopping spraying after progress for a predetermined time. Spray activated carbon powder at the entrance of the second bag filter (demineralized bag filter) and discharge the collected matter in the first bag filter (dust removal bag filter) to the outside of the return line. The figure which shows the relationship between elapsed time and mercury concentration at the time of switching to a return line process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pyrolysis drum, 2 Combustion melting furnace, 3 High temperature air heater, 4 Waste heat boiler, 5 Temperature reduction tower, 6 Dust removal bag filter (1st bag filter), 7 Desalination bag filter (2nd bag filter), 8 Mercury concentration meter, 9 switching damper, 10 carbon hopper, 11 sorting device, 12 return line, 13 collected product, 14 outside system, 15 mercury removing material first adding means, 16 mercury removing material second adding means, 17 desalting Agent addition means, 18 solid matter storage section, 19 control section

Claims (5)

A combustion melting processing apparatus for burning pyrolysis gas and char generated by heat-treating a processing object;
A first bag filter that allows the exhaust gas generated in the combustion melting apparatus to pass through;
A second bag filter that passes the exhaust gas that has passed through the first bag filter;
A mercury concentration detector provided in an exhaust gas flow path downstream of the second bag filter;
A return line for returning the collected matter by the first bag filter to the combustion melting processing apparatus;
A switching unit provided in the return line, for discharging the collected matter outside the return line;
A mercury removal material first addition means for adding a mercury removal material in or upstream of the first bag filter;
A mercury removal material second addition means for adding a mercury removal material in or upstream of the second bag filter,
When a preset set value is detected by the mercury concentration detection unit, the switching unit switches to a direction in which the collected material is discharged out of the return line, and the mercury removing material second addition unit is configured to remove mercury. The material is switched from the non-added state to the added state, and after a predetermined time has elapsed, the switching unit is configured to return the collected matter from the discharge direction to the return line. Processing object combustion processing system.   The processing object combustion processing system according to claim 1, wherein after the predetermined time has elapsed, the processing is characterized in that the addition of the mercury removing material from the second mercury removing material adding means is stopped. Object combustion treatment system.   The processing object combustion processing system according to claim 1 or 2, wherein the mercury removing material is activated carbon. A method for removing mercury in exhaust gas, which removes mercury in exhaust gas generated by a combustion melting treatment device that burns a pyrolysis gas and char generated by heat-treating a processing object,
A first mercury removing step of adding a mercury removing material upstream of the first bag filter through which the exhaust gas passes;
The collected matter discharging step for discharging the collected matter by the first bag filter to the outside of the return line that returns to the combustion melting processing device, and the mercury removal upstream of the second bag filter that passes the exhaust gas that has passed through the first bag filter. A second mercury removing step of adding a material,
In the collected matter discharging step, the collected matter is returned to the return line for a predetermined time from when a preset set value is detected by a mercury concentration detector provided in an exhaust gas flow path downstream of the second bag filter. Is a process of discharging to the outside,
The method for removing mercury in exhaust gas, wherein the second mercury removing step starts addition of a mercury removing material when the set value is detected. The method for removing mercury in exhaust gas according to claim 4, wherein addition of the mercury removing material is stopped after the predetermined time has elapsed.

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