JP2001096134A - Treatment method of combustion gas containing heavy metal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a combustion gas treatment method for efficiently and economically removing heavy metals such as mercury from an exhaust combustion gas containing heavy metals. SOLUTION: In a treatment method for an exhaust combustion gas containing heavy metals and discharged out an incinerator for wastes, before dust collection treatment is carried out by a highly efficient dust collecting apparatus, an incinerator ash slurry produced from a heavy metal stabilization agent, incinerator ashes and water is sprayed to the exhaust combustion gas to adsorb the heavy metals of the exhaust combustion gas in the slurry. Alternatively, prior to the foregoing treatment, the exhaust combustion gas containing heavy metals and discharged out an incinerator is subjected to dust collection treatment by a hot cyclone or a ceramic filter at a temperature not lower than the boiling point of the heavy metals as to take out incinerator ashes having lower harmfulness without transferring heavy metals with low boiling points to the incinerator ashes.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for treating a flue gas containing a heavy metal, which can remove mercury and other heavy metals contained in the flue gas efficiently and at low cost.

[0002]

BACKGROUND ART Harmful heavy metals such as mercury, lead, and arsenic are contained in flue gas discharged from waste incinerators. As a method for treating such flue gas containing heavy metals, dust collectors, It is common to use a scrubber or the like to remove heavy metals, and the heavy metals in the removed combustion exhaust gas are discharged into incinerated ash, air, scrubber drainage, and the like. At present, emissions of heavy metals in incineration ash and wastewater are regulated, and in the case of incineration ash, it is necessary to clear the elution standard value.

On the other hand, it is said that the concentration of heavy metals in exhaust gas, particularly mercury, will be regulated in the future. However, since mercury has two water-soluble and non-water-soluble forms, scrubbers use water-soluble. There is a problem that mercury is removed but non-water-soluble mercury is not removed and is discharged into the atmosphere. In addition, the need to stabilize heavy metals in incinerated ash has increased with the tightening of the elution standard value for incinerated ash after dust collection.However, kneading of heavy metal fixing agents into incinerated ash, cement solidification, In the stabilization method by the conventional method such as melting and solidification, since it is necessary to perform the entire incineration ash, there is a problem that the processing cost is increased. Further, as a treatment means for preventing the discharge of heavy metals such as mercury into the atmosphere, an adsorption removal method using activated carbon, an adsorbent or the like is known, but there is a problem that extra treatment cost is required.

[0004]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned conventional problems and enables the dust collection process to be performed efficiently and at low cost. The present invention has been completed for the purpose of providing a method for treating combustion exhaust gas containing heavy metals, which can be performed at low cost without requiring activated carbon or an adsorbent for the removal of mercury having two forms.

[0005]

Means for Solving the Problems The present invention made to solve the above-mentioned problems is directed to a method for treating combustion exhaust gas containing heavy metals discharged from a waste incinerator. Before application, incineration ash slurry obtained from a heavy metal fixing agent, incineration ash and water is sprayed on the combustion exhaust gas, and the heavy metal in the combustion exhaust gas is adsorbed on the slurry. Before performing the above treatment, the combustion exhaust gas containing heavy metals discharged from the incinerator is subjected to dust collection at a temperature higher than the boiling point of the heavy metals by a hot cyclone or a ceramic filter, and the heavy metals having a low boiling point are transferred into the incineration ash. It is preferable to take out the incinerated ash with low toxicity without causing the treatment efficiency to be significantly increased. In addition, it is preferable that a high-efficiency dust collector and a scrubber are sequentially arranged at the subsequent stage of the reaction tower, and an incineration ash slurry is obtained from the heavy metal fixing agent, the incineration ash collected by the high-efficiency dust collector, and the scrubber wastewater. Furthermore, the gaseous heavy metal element is adsorbed and removed by passing the combustion exhaust gas exiting the reaction tower through a primary filtration layer formed of a mixture of incineration ash and a heavy metal fixing agent formed in a filter in a high-efficiency dust collector. You can also. Note that a ceramic filter or a bag filter may be used as the high-efficiency dust collector.

[0006]

Preferred embodiments of the present invention will be described below with reference to the drawings. The drawings are schematic views showing an example of a processing apparatus provided for the present invention. In the drawing, reference numeral 1 denotes a waste incinerator such as a fluidized-bed furnace, and 2 denotes a dust collecting apparatus for collecting combustion exhaust gas discharged from the incinerator 1. The hot cyclone 3 for the treatment is a Venturi-type or cyclone-type reaction tower for adsorbing heavy metals in the combustion exhaust gas not collected by the hot cyclone, and the hot cyclone 2 and the reaction tower 3 are disposed between the hot cyclone 2 and the reaction tower 3. A preheater 4a for preheating the flowing air and a preheater 4b for preventing white smoke are provided. Reference numeral 5 denotes a high-efficiency dust collector such as a ceramic filter or a bag filter for collecting dust from the combustion exhaust gas containing incineration ash from the reaction tower 3, and 6 denotes a circulation for further removing heavy metals from the combustion exhaust gas of the dust collector 5. The mold scrubber, 7 is a chimney. An incineration ash slurry tank 9 for slurrying the incineration ash collected by the dust collector 5 and the drainage from the scrubber 6 and the heavy metal fixing agent such as a polymer chelating agent and a sulfide agent introduced from the chemical injector 8 is provided. The slurry is provided to be supplied to the reaction tower 3.

Next, a description will be given of a process of treating the combustion exhaust gas by the above-described processing apparatus. First, the combustion exhaust gas containing heavy metals such as mercury, lead, and arsenic discharged from the incinerator 1 is subjected to dust collection by the hot cyclone 2 to remove ash having large particles. At this time, hot cyclone 2 is 700
It is in a high temperature field of about 850 ° C., and heavy metals such as mercury are not collected in the hot cyclone 2 because they are in the form of fine particles or gas having a particle diameter of about 10 μm or less. Therefore, the hot cyclone 2 can collect a large amount of harmless incinerated ash that does not contain harmful heavy metals. In the subsequent steps, only the flue gas containing ash-reduced heavy metals needs to be treated, so that it is efficient. Processing can be performed.

Next, the combustion exhaust gas discharged from the incinerator 1 passes through a preheater 4 a for preheating the flowing air and a preheater 4 b for preventing white smoke, and is brought to about 350 ° C., and is introduced into the reaction tower 3. . During the cooling process in the reaction tower 3, heavy metals in the combustion exhaust gas are condensed, and the heavy metals are adsorbed and fixed on the slurry supplied into the reaction tower 3 so that the heavy metals are efficiently removed in a stable state. Becomes At this time, in the illustrated apparatus, the incinerated ash collected by the dust collector 5 and the drainage from the scrubber 6 at the subsequent stage of the reaction tower 3 and the incinerated ash for slurrying the heavy metal fixing agent supplied from the chemical input device 8 are used. Since the slurry tank 9 is provided, and the incinerated ash slurry obtained here is configured to be supplied to the reaction tower 3, the processing can be performed at low cost. As the heavy metal fixing agent, a polymer chelating agent for forming a chelate compound or a sulphidating agent such as sodium sulfide or sodium hydrosulfide for sulphidizing is used, and is mixed in the range of 1 to 10% with respect to incinerated ash. In addition, the wastewater from the scrubber 6 is 10
Mix in a range of ~ 100 times.

Next, the combustion exhaust gas discharged from the reaction tower 3 is further subjected to dust collection processing by a highly efficient dust collector 5 such as a ceramic filter or a bag filter. Here, the combustion exhaust gas passes through a primary filtration layer formed of a mixture of incineration ash and a heavy metal fixing agent formed on the filter, so that heavy metal elements such as mercury in a gaseous state are efficiently adsorbed and removed by the heavy metal fixing agent. It will be. Further, by removing a water-soluble heavy metal element such as mercury by a scrubber 6 in the next step, the gas is finally discharged from the chimney 7 to the atmosphere as a safe purified gas having a reference value or less. The heavy metal removed by the scrubber 6 is introduced into the incineration ash slurry tank 9 and is stabilized by reacting with the heavy metal fixing agent.

As described above, before performing dust collection processing by the dust collector 5, the incineration ash slurry obtained from the heavy metal fixing agent, the incineration ash, and the water is sprayed on the combustion exhaust gas, and the heavy metal in the combustion exhaust gas is adsorbed on the slurry. By doing so, the heavy metal can be stabilized and the dust collection process can be performed efficiently and at low cost. In the first stage, the flue gas is subjected to dust collection in a hot cyclone 2 at a temperature equal to or higher than the boiling point of heavy metals, thereby taking out as harmless incinerated ash containing almost no heavy metals from the flue gas. The harmful heavy metal is removed by the high-efficiency dust collector 5 and the scrubber 6, so that efficient and low-cost processing can be realized.

In addition, the incineration ash collected by the hot cyclone 2 and the incineration ash collected by the high-efficiency dust collector 5 after the treatment of the sewage sludge combustion exhaust gas by the above-mentioned treatment method are notified to the Environment Agency Notification No. 13 As a result of performing a dissolution test for heavy metals based on the results, it was confirmed that all were below the standard value for dissolution of harmful substances (see Table 1). It was also confirmed that the concentration of heavy metals in the combustion exhaust gas discharged from the scrubber 6 was below the detection limit. In addition, as a result of performing the same treatment on the flue gas of municipal garbage, it was confirmed that all of them cleared the reference value (see Table 2). In this case, in particular, incineration ash was separated by hot cyclone 2. It was confirmed that the mercury was removed satisfactorily without any treatment.

[0012]

[Table 1] Elution of sewage sludge incineration ash

[0013]

[Table 2] Leaching of fly ash from incineration of municipal waste

[0014]

As is clear from the above description, the present invention can perform the dust collection process efficiently and at low cost, and has two water-soluble / water-insoluble forms of mercury. The removal can be performed at low cost without requiring activated carbon or an adsorbent. Furthermore, in the first stage, the flue gas is subjected to dust collection in a hot cyclone to remove it from the flue gas as harmless incineration ash containing almost no heavy metals, and the remaining flue gas is collected only for efficient treatment. In addition, low-cost processing can be realized. Therefore, the present invention greatly contributes to the development of industry as a method for treating combustion exhaust gas containing heavy metals that has eliminated the conventional problems.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a processing apparatus provided for an embodiment of the present invention.

[Explanation of symbols]

1 incinerator, 2 hot cyclone, 3 reaction tower, 5
High efficiency dust collector, 6 scrubbers, 9 incineration ash slurry tank.

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 3K070 DA01 DA11 DA17 DA24 DA29 DA45 3K078 AA05 BA03 BA21 CA24 4D002 AA28 AA29 AC04 BA04 BA12 BA13 BA14 CA01 DA02 DA15 DA35 DA61 DA66 GA02 GA03 GB02 GB03 GB08 4K056 AA05 CA20 DB07 DB13

Claims (5)

[Claims] 1. A method for treating a combustion exhaust gas containing heavy metals discharged from a waste incinerator, wherein the combustion exhaust gas is obtained from a heavy metal fixing agent, incineration ash, and water before being subjected to dust collection by a high-efficiency dust collector. A method for treating a combustion exhaust gas containing a heavy metal, comprising spraying an ash slurry and adsorbing the heavy metal in the combustion exhaust gas to the slurry. 2. The method according to claim 1, wherein the flue gas containing heavy metals discharged from the incinerator is subjected to dust collection at a temperature higher than the boiling point of the heavy metals by a hot cyclone or a ceramic filter to remove heavy metals having a low boiling point. The method for treating a combustion exhaust gas containing heavy metals according to claim 1, wherein the ash is taken out as incineration ash having low harm without being transferred into the incineration ash. 3. A reactor, a high-efficiency dust collector, and a scrubber are sequentially arranged at a stage subsequent to the incinerator, and an incineration ash slurry is obtained by using a heavy metal fixing agent, incineration ash collected by the high-efficiency dust collector, and drainage of the scrubber. A method for treating a combustion exhaust gas containing a heavy metal according to claim 1. 4. A gaseous heavy metal element is adsorbed and removed by passing a flue gas discharged from a reaction tower through a primary filtration layer formed of a mixture of incinerated ash and a heavy metal fixing agent formed on a filter in a high efficiency dust collector. Claim 1 or 2 wherein
Or a method for treating a combustion exhaust gas containing a heavy metal according to item 3. 5. A high efficiency dust collector using a ceramic filter or a bag filter.
Or a method for treating a combustion exhaust gas containing a heavy metal according to 4.