JP7272382B2 - Combustion exhaust gas treatment method and combustion exhaust gas treatment device - Google Patents

Description

The present invention relates to the treatment of flue gas containing harmful acidic gases such as hydrogen chloride and sulfur oxides generated from combustion facilities such as municipal waste incinerators, industrial waste incinerators, power generation boilers, carbonization furnaces, and private factories. It relates to a method and a flue gas treatment device.

Combustion exhaust gas emitted from waste incinerators for municipal waste, industrial waste, etc., and combustion facilities such as thermal power plants contains carbon dioxide, water vapor, oxygen, nitrogen, hydrogen chloride, sulfur oxides ( _SOx ), Since it contains nitrogen oxides ( _NOx ), heavy metal compounds, and dust, it is necessary to remove these substances from the viewpoint of air pollution prevention prior to release into the atmosphere.
Flue gas containing harmful hydrogen chloride and sulfur oxides is generally sprayed with an alkaline agent such as slaked lime (calcium hydroxide) against the flue gas in front of the dust collector of the incinerator, as in Patent Document 1. Then, after a step of neutralizing acid gases such as hydrogen chloride and sulfur oxides, the dust is removed by a dust collector such as a bag filter and discharged from a chimney. On the other hand, fly ash collected by a dust collector contains harmful heavy metals such as lead and cadmium, and is disposed of in landfills after stabilizing these harmful heavy metals.

As an efficient neutralization treatment method for acidic gas, for example, Patent Document 2 uses calcium hydroxide having a specific specific surface area and apparent density based on the concentrations of hydrogen chloride and sulfur oxides in the combustion exhaust gas before the dust collector. A method and Patent Document 3 propose a method of adjusting the supply amount of the alkaline agent based on the gas analysis measurement results of either or both of the upstream side and the downstream side of the dust collecting means.

On the other hand, methods for treating heavy metals in fly ash removed by dust collectors include insolubilization using chelate heavy metal fixatives such as piperazine dithiocarbamate and diethyldithiocarbamate, as well as recycling of heavy metals at final disposal sites. From the viewpoint of elution prevention, in recent years, as in Patent Document 4, a method using a phosphoric acid-based compound such as phosphoric acid, which converts heavy metals into the form of hydroxyapatite, which is an inorganic mineral, has been disclosed as a heavy metal fixing agent. In addition, a method of adding an acidic neutralizing agent such as hydrochloric acid and aluminum sulfate, a method of adding a silicon dioxide-containing compound such as an aqueous solution of sodium silicate and powdered silicon dioxide; In that case, a method is known in which an iron-containing compound such as ferrous chloride or polyferric sulfate is added to prevent the elution of these heavy metals.

JP-A-9-99215 Japanese Patent No. 4194001 Japanese Patent Application Laid-Open No. 2002-361040 Japanese Patent Publication No. 4-61710

The means for neutralizing the acid gas in the flue gas with an alkaline agent is a reaction between the gaseous acid gas and the solid alkaline agent, so the reaction efficiency is poor. Therefore, in order to neutralize the acid gas with the stricter regulation of the acid gas, more alkaline agent than the neutralization reaction equivalent is added to the combustion exhaust gas. Therefore, after the neutralization treatment, the fly ash collected by the dust collector contains unreacted alkaline components. When the fly ash is treated with a heavy metal fixing agent, in order to optimize the effect of heavy metal treatment, the concentration of alkaline components in the fly ash is analyzed, and the required amount of heavy metal fixing agent is determined according to the concentration of the alkaline component. It is necessary to calculate and add the required amount of heavy metal fixing agent to the fly ash.
However, when analyzing the concentration of alkaline components in fly ash in this way, the analysis takes time and effort, and it is necessary to analyze at an analysis frequency that follows the fluctuation of fly ash. was unsuitable.

The present invention has been made in view of the above circumstances, and it is possible to grasp the concentration of unreacted alkaline components in fly ash in real time without the need to analyze the concentration of alkaline components in fly ash. It is an object of the present invention to provide a combustion exhaust gas treatment method and a combustion exhaust gas treatment apparatus capable of more accurately, safely and simply treating fly ash with heavy metals.

As a result of intensive studies, the present inventors measured the concentration of acidic gas in combustion exhaust gas before dry acidic exhaust gas treatment, and calculated the unreacted alkaline agent concentration in fly ash based on the measurement results. Without the need to analyze the concentration of alkaline components in fly ash, the concentration of unreacted alkaline agents in fly ash can be grasped in real time, and heavy metal treatment of fly ash can be performed with higher accuracy. I found
That is, the present invention provides the following [1] to [11].
[1] A dry treatment step of adding an alkaline agent to untreated flue gas containing acid gas to neutralize the acid gas to obtain alkali-treated flue gas;
A dust collection step of supplying the alkali-treated flue gas to a dust collector to collect fly ash;
a heavy metal fixing step of discharging the fly ash from the dust collector and adding a heavy metal fixing agent to the fly ash to fix heavy metals in the fly ash;
measuring the concentration of the acid gas in the untreated flue gas;
Based on the measured value of the acid gas concentration, the amount of the alkali agent to be added to the untreated flue gas is calculated and added, and the unreacted alkali agent concentration in the fly ash discharged from the dust collector. to calculate
A method for treating combustion exhaust gas, wherein the amount of the heavy metal fixing agent to be added to the fly ash is calculated and added based on the calculated value of the concentration of the unreacted alkaline agent.
[2] The heavy metal fixing step includes a storage step of storing the fly ash discharged from the dust collector in a storage silo, and extracting the fly ash in the storage silo and supplying it to a kneader. a kneading step of adding the heavy metal fixing agent to fix heavy metals in the fly ash;
The method for treating combustion exhaust gas according to [1] above.
[3] Store temporal data of the unreacted alkaline agent concentration in the fly ash supplied from the dust collector to the storage silo, calculated based on the measured value of the acid gas concentration in the untreated flue gas,
Based on the temporal data and the supply flow rate when the fly ash is extracted from the storage silo and supplied to the kneader, the unreacted alkali agent concentration in the fly ash supplied to the kneader and processed over time calculate the change,
The method for treating combustion exhaust gas according to [2] above, wherein the addition amount of the heavy metal fixing agent is controlled over time based on the change over time to fix the heavy metals in the fly ash.
[4] The method for treating combustion exhaust gas according to [2] or [3] above, wherein in the kneading step, an acidic neutralizing agent is further added to the kneader.
[5] Measuring the acid gas concentration in the combustion exhaust gas before the dry treatment, and based on the measured value, in the dry treatment step, the alkali agent is added in an amount of 1 to 3 equivalents with respect to the acid gas concentration. The method for treating combustion exhaust gas according to any one of [1] to [4] above.
[6] The acid gas according to any one of [1] to [5] above, wherein the acid gas contains hydrogen chloride and sulfur oxides, and the total concentration of the hydrogen chloride and sulfur oxides is measured as the acid gas concentration. A method for treating flue gas.
[7] The method for treating combustion exhaust gas according to any one of [1] to [6] above, wherein the alkaline agent contains at least one basic salt of an alkali metal or an alkaline earth metal.
[8] The method for treating combustion exhaust gas according to any one of [1] to [7] above, wherein the heavy metal fixing agent is an inorganic heavy metal fixing agent.

[9] A dry treatment apparatus for adding an alkaline agent to untreated flue gas containing acid gas to neutralize the acid gas to obtain alkali-treated flue gas;
a dust collector that is connected to the dry processing apparatus and collects fly ash in the alkali-treated flue gas;
a heavy metal fixing device connected to the dust collector for fixing heavy metals in the fly ash by adding a heavy metal fixing agent to the fly ash;
a measuring device for measuring the concentration of the acid gas in the untreated flue gas;
an alkali agent addition amount calculation unit that calculates the addition amount of the alkali agent to be added to the untreated flue gas based on the measured value of the acid gas concentration; and an unreacted fly ash discharged from the dust collector. an unreacted alkali agent concentration calculation unit that calculates the concentration of the alkali agent; and a heavy metal fixative calculation unit that calculates the amount of the heavy metal fixative to be added to the fly ash based on the calculated value of the unreacted alkali agent concentration. a computing device having
an alkali agent addition device for adding the alkali agent to the untreated flue gas in the dry processing unit based on the calculated value of the addition amount of the alkali agent calculated by the arithmetic unit; and a heavy metal fixing agent addition device for adding the heavy metal fixing agent based on the calculated value of the addition amount of the heavy metal fixing agent.
[10] The heavy metal fixing device includes:
A storage silo connected to the dust collector and storing fly ash discharged from the dust collector;
a kneader connected to the storage silo;
The combustion exhaust gas according to [9] above, which has a feeding device for extracting fly ash in the storage silo and supplying it to the kneader and a heavy metal fixing agent adding device for adding the heavy metal fixing agent to the kneader. processing equipment.
[11] A memory for storing temporal data of the unreacted alkaline agent concentration in the fly ash supplied from the dust collector to the storage silo, which is calculated based on the measured value of the acid gas concentration in the untreated flue gas. Unreacted alkaline agent in the fly ash to be supplied to the kneader and processed based on the part, the temporal data, and the supply flow rate when the fly ash is extracted from the storage silo and supplied to the kneader an arithmetic device comprising: an arithmetic unit for calculating a change in concentration over time; and an arithmetic unit for calculating an addition amount of the heavy metal fixing agent to the fly ash based on the change in the concentration of the unreacted alkaline agent over time;
a heavy metal fixing agent adding device for adding the heavy metal fixing agent based on the calculated value of the amount of the heavy metal fixing agent to be added to the fly ash;
The apparatus for treating combustion exhaust gas according to the above [10], having

According to the method and apparatus for treating combustion exhaust gas of the present invention, it is possible to grasp the concentration of unreacted alkaline components in fly ash in real time without the need to analyze the concentration of alkaline components in fly ash. Fly ash can be treated with heavy metals more accurately, safely and easily.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing an embodiment of a combustion exhaust gas treatment method and a combustion exhaust gas treatment apparatus according to the present invention; It is a graph which shows the time-dependent change of the hydrogen chloride density|concentration and sulfur oxide density|concentration in untreated flue gas in front of a dust collector. It is a graph which shows the time-dependent change of the unreacted slaked lime density|concentration in fly ash. It is a graph which shows the time-dependent change of the unreacted slaked lime density|concentration in the fly ash added to a kneader, and the time-dependent change of the addition amount of the heavy metal fixing agent added to a kneader. FIG. 2 is a conceptual diagram in which the change over time of the concentration of unreacted slaked lime in fly ash accumulated in a storage silo is converted into calculation of the amount of addition of a heavy metal fixing agent in the heavy metal fixing step.

[Method for treating combustion exhaust gas]
The flue gas treatment method of the present invention includes a dry treatment step of adding an alkaline agent to untreated flue gas containing acidic gas to neutralize the acidic gas to obtain alkali-treated flue gas; A dust collection step of supplying treated flue gas to a dust collector to collect fly ash, discharging the fly ash from the dust collector, and adding a heavy metal fixing agent to the fly ash to remove heavy metals in the fly ash. and a heavy metal fixing step for fixing,
The concentration of the acid gas in the untreated flue gas is measured, and the amount of the alkaline agent to be added to the untreated flue gas is calculated and added based on the measured value of the concentration of the acid gas. At the same time, the unreacted alkaline agent concentration in the fly ash discharged from the dust collector is calculated, and the amount of the heavy metal fixing agent added to the fly ash is calculated based on the calculated value of the unreacted alkaline agent concentration. It is a method for treating combustion exhaust gas that is added. Hereinafter, the method for treating combustion exhaust gas of the present invention may be abbreviated simply as "the treating method of the present invention".
According to the treatment method of the present invention, the concentration of acidic gas is measured before dry acidic exhaust gas treatment of combustion exhaust gas, and the concentration of unreacted alkaline agent in fly ash is calculated by calculation based on the measurement result. The concentration of unreacted slaked lime in the fly ash can be determined in real time without the need to analyze the concentration of alkaline components in the fly ash, and the heavy metal treatment of the fly ash can be performed with higher accuracy.

In the treatment method of the present invention, as the heavy metal fixing step, preferably, the fly ash discharged from the dust collector is stored in a storage silo, and the fly ash in the storage silo is extracted and supplied to a kneader. and a kneading step of adding the heavy metal fixing agent to the fly ash in the kneader to fix heavy metals in the fly ash.
In this way, the fly ash is stored in the storage silo, the fly ash in the storage silo is extracted, and the heavy metals in the fly ash are fixed. It is possible to fix heavy metals after being stored, fix heavy metals collectively at a speed faster than the speed at which fly ash flows into the storage silo, or adjust the timing of fixing heavy metals. .

Then, in the treatment method of the present invention, preferably, the unreacted fly ash in the fly ash supplied from the dust collector to the storage silo is calculated based on the measured value of the acid gas concentration in the untreated flue gas. Time-lapse data of the concentration of the alkaline agent is stored, and the fly ash supplied to the kneader and processed based on the time-lapse data and the supply flow rate when the fly ash is extracted from the storage silo and supplied to the kneader. This is a method of calculating a change in the unreacted alkaline agent concentration in the ash over time, and controlling the addition amount of the heavy metal fixing agent over time based on the change over time to immobilize the heavy metals in the fly ash.
As a result, after the fly ash in the storage silo is stored to some extent, the heavy metals are fixed, or the fly ash is collectively fixed at a speed faster than the fly ash flowing into the storage silo, and the heavy metals are fixed. Even if the timing of processing is adjusted, an appropriate amount of heavy metal fixing agent can be added according to the change over time of the unreacted alkali concentration in the fly ash extracted from the storage silo. It is possible to grasp the unreacted slaked lime concentration in the fly ash in real time without the need to analyze the concentration of the alkaline component in the fly ash, and to perform the heavy metal treatment of the fly ash with higher accuracy.

[Combustion exhaust gas treatment device]
FIG. 1 is a schematic diagram showing an embodiment of a flue gas treatment apparatus for carrying out the treatment method of the present invention. In the flue gas treatment apparatus 100 of FIG. 1, the flue gas containing acid gas generated in the incinerator 11 is passed through the pipe 1, the boiler 12 that utilizes the heat of the flue gas, and the gas cooling tower 13 via the pipe 2. It is cooled and introduced into dust collector 14 via flue 3 . An alkali agent is supplied from the alkali agent addition device 51 , and the flue gas containing acid gas and the alkali agent are mixed in the flue 3 . Alkali-treated flue gas is sucked out from the dust collector 14 by the suction fan 15 via the gas discharge path 4 and discharged from the chimney 16 .
On the other hand, the fly ash collected in the storage silo 21 is discharged from the dust collector 14 via the fly ash discharge path 5, and the fly ash in the storage silo 21 is extracted by the fly ash supply device 22 and is sent via the pipe 6. The fly ash is supplied to the kneader 23 , and after the heavy metal fixing agent is supplied to the fly ash from the heavy metal fixing agent addition device 52 immediately before the kneader 23 , the fly ash is discharged into the ash pit 24 .

The flue gas treatment apparatus 100 of FIG. 1 according to the embodiment of the present invention further includes an acidic gas concentration measuring device provided in the flue 3 in order to treat the acidic gas in the flue gas discharged from the incinerator 11. The unit 30 and the arithmetic device 40 are included, and together with the alkaline agent adding device 51, constitute a dry processing device.
Here, the acid gas concentration measuring device 30 includes a hydrogen chloride concentration measuring device 30a and a sulfur oxide concentration measuring device 30b. The hydrogen chloride concentration measuring device 30a continuously measures the hydrogen chloride concentration in the untreated flue gas flowing through the flue 3, while the sulfur oxide concentration measuring device 30b measures sulfur in the untreated flue gas flowing through the flue 3. The oxide concentration is continuously measured and output to the arithmetic unit 40 as a hydrogen chloride concentration signal S1 from the hydrogen chloride concentration measuring device 30a and a sulfur oxide concentration signal S2 from the sulfur oxide concentration measuring device 30b. The types of the hydrogen chloride concentration measuring device 30a and the sulfur oxide concentration measuring device 30b are not limited as long as they are measuring devices capable of measuring the hydrogen chloride concentration and the sulfur oxide concentration, respectively. Hydrogen chloride gas concentration can be measured by an ion electrode method, single absorption line absorption spectroscopy using a laser, etc., and sulfur oxide gas concentration can be measured by a non-dispersive infrared absorption method, an ultraviolet fluorescence method, or the like.

Arithmetic device 40 includes an alkali agent addition amount calculator 41, an alkali agent amount signal S4 including the total value of hydrogen chloride concentration and sulfur oxide concentration and the amount of added alkali agent output from the calculator 41, and fly ash. and an unreacted alkaline agent concentration calculator 42 for calculating the concentration of unreacted alkaline agent in the fly ash based on the generation amount of the unreacted alkaline agent concentration signal S5 output from the calculator 42 and a heavy metal fixing agent addition amount calculation unit 43 for calculating the addition amount of the heavy metal fixing agent to the kneader 23 based on the above. Here, the fly ash includes the ash from the waste to be incinerated and the alkaline agent that is put into the waste to be incinerated, and the amount of fly ash generated is calculated as a constant value (approximately 3% by mass) with respect to the amount of waste. be able to.

The alkali agent addition amount calculation unit 41 calculates the concentration of acidic gas in the flue gas based on the measured value of the acid gas concentration, which is the total value of the hydrogen chloride concentration and the sulfur oxide concentration, based on the hydrogen chloride concentration signal S1 and the sulfur oxide concentration signal S2. The amount of alkaline agent to be added per unit time to neutralize the acid gas is calculated and output as an alkaline agent addition signal S3.
The alkaline agent addition device 51 is a device that adds an alkaline agent to the untreated flue gas flowing through the flue 3 based on the alkaline agent addition signal S3.

The unreacted alkaline agent concentration calculator 42 calculates the unreacted alkaline agent concentration in the fly ash discharged from the dust collector 14 and supplied to the storage silo 21 based on the signal S4 calculated by the alkaline agent addition amount calculator 41. A calculation unit that stores the concentration of the unreacted alkaline agent, a storage unit that stores the concentration of the unreacted alkaline agent, the concentration of the unreacted alkaline agent, and the supply flow rate when extracting the fly ash from the storage silo 21 and supplying it to the kneader 23. and a calculation unit for calculating the unreacted alkaline agent concentration in the fly ash supplied to and processed by the machine 23 .
In the unreacted alkaline agent concentration calculation unit 42, the unreacted alkaline agent concentration in the fly ash supplied to the storage silo 21 is preferably stored in the storage unit as temporal data of the unreacted alkaline agent concentration. Further, the unreacted alkaline agent concentration in the fly ash supplied to and processed by the kneader 23 is preferably calculated as the amount of change over time of the unreacted alkaline agent concentration.

The heavy metal fixing agent addition amount calculation unit 43 calculates the amount of the heavy metal fixing agent to be added to the fly ash based on the signal S5 including the calculated value of the concentration of the unreacted alkali agent in the fly ash supplied to the kneader 23 and processed. Calculate the amount to be added.
Preferably, the heavy metal fixing agent addition amount calculation unit 43 extracts the time data of the unreacted alkaline agent concentration in the fly ash supplied to the storage silo 21 and extracts the fly ash from the storage silo 21 and supplies it to the kneader 23. The heavy metal to be added to the fly ash is fixed based on the signal S5 including the calculated value of the change over time of the concentration of the unreacted alkali agent in the fly ash that is supplied to the kneader 23 and processed, based on the supply flow rate at the time. Calculate the amount of agent to be added. More preferably, the temporal data of the unreacted alkaline agent concentration, the amount of fly ash generated per unit time (that is, the amount of fly ash stored in the storage silo), the capacity of the storage silo, and the supply flow rate (per unit time From the fly ash processing amount of the kneader), based on the temporal data of the unreacted alkaline agent concentration, considering the fly ash processing capacity and operating conditions of the heavy metal fixing device, the heavy metal fixing agent to be added to the fly ash Calculate the amount of addition.

The heavy metal fixing device in the combustion exhaust gas treatment apparatus according to the embodiment of the present invention supplies the heavy metal fixing agent immediately before the storage silo 21, the fly ash supply device 22, the kneader 23, the arithmetic device 40, and the kneader 23. A heavy metal fixative adder 52 is included.
The heavy metal fixing agent addition device 52 adds the heavy metal fixing agent to the fly ash immediately before the kneader 23 based on the heavy metal fixing agent addition signal S6 from the heavy metal fixing agent addition amount calculation unit 43 constituting the arithmetic unit 40. It is a device.

[Dry treatment process]
In the treatment method of the present invention, first, a dry treatment step is performed in which an alkaline agent is added to untreated flue gas containing acidic gas to neutralize the acidic gas, thereby obtaining alkali-treated flue gas.
The flue gas to which the treatment method of the present invention can be applied is not particularly limited. For example, flue gas containing acid gases such as hydrogen chloride, sulfur oxides, and nitrogen oxides generated in combustion facilities such as municipal waste incinerators, industrial waste incinerators, power generation boilers, carbonization furnaces, and private factories mentioned.
The alkali agent for removing acid gases in flue gas preferably contains at least one basic salt of an alkali metal or an alkaline earth metal.
Examples of such alkaline agent include slaked lime (calcium hydroxide), sodium hydroxide, potassium hydroxide, magnesium hydroxide, sodium hydrogen carbonate, sodium carbonate, calcium carbonate, calcium oxide, dolomite hydroxide [Ca(OH) ₂ ·Mg (OH) ₂ ], or mixtures thereof.

From the viewpoint of ensuring reactivity with acid gases such as hydrogen chloride and sulfur oxides and avoiding a decrease in collection efficiency in a dust collector and an increase in differential pressure, the alkali agent should have a specific surface area of 20 m ² /g or more. and a median diameter (d50) of 5 to 30 μm.
These alkaline agents are further blended with other components, such as activated carbon for treating dioxins in flue gas, diatomaceous earth used as a filter aid for bag filters, etc., within a range that does not impede the effects of the present invention. good too.

The alkaline agent is preferably added before the dust collector such as a bag filter after cooling the combustion exhaust gas in the temperature reducing tower and measuring the acid gas concentration, from the incinerator main body to the dust collector.
The means for adding the alkaline agent to the combustion exhaust gas is not particularly limited. For example, the alkaline agent put in the chemical storage tank of the alkaline agent addition device 51 is introduced into the combustion exhaust gas of the flue 3 from the nozzle installed in the flue 3. be sprayed. The alkali agent may be used in the form of powder, or may be used in the form of a dispersion liquid by dispersing the powder of the alkali agent in a dispersion medium in which the alkali agent is not dissolved, such as ethanol or isopropanol. The alkaline agent can be added intermittently or continuously.
There is no particular limitation on the temperature of the flue gas when adding the alkaline agent. Since the alkaline agent reacts with the acid gas in the dust collector, the temperature of the flue gas immediately before the dust collector is preferably 100 to 300°C, more preferably 130 to 230°C.

In the treatment method of the present invention, the alkaline agent is determined by measuring the acid gas concentration in the untreated combustion exhaust gas, preferably the total amount of hydrogen chloride and sulfur oxide concentrations, as the acid gas concentration. Based on the measured value, the addition amount of the alkaline agent to be added to the untreated flue gas is calculated and added.
The amount of alkali agent added is an amount that can reach the target value for acid gas treatment, and is such that the acid gas (chloride Hydrogen and sulfur oxides) is most preferably controlled to a constant equivalence in response to changes in the measured concentration over time.
More specifically, the amount of the alkali agent to be added is 1 to 3 equivalents of the alkali agent with respect to the total concentration based on the measured values of the concentrations of the acid gases, particularly hydrogen chloride and sulfur oxides, in the combustion exhaust gas. It is preferable to add so that the equivalent amount is 1.5 to 2.5 equivalents. Addition of such an amount of the alkaline agent reduces the amount of the heavy metal fixing agent to be added, making it easy to reduce the amount of fly ash that is finally disposed of.

[Dust collection process]
The treatment method of the present invention has a dust collection step of collecting fly ash in the alkali-treated flue gas. Dust collection of fly ash can be performed with a known dust collector such as a bag filter connected to the dry processing apparatus.
The dust collector is connected to a heavy metal fixing device that adds a heavy metal fixing agent to the fly ash to fix heavy metals in the fly ash.

[Heavy metal fixation step]
The treatment method of the present invention has a heavy metal fixing step of adding a heavy metal fixing agent to the fly ash collected in the dust collection step to fix heavy metals in the fly ash.
In the treatment method of the present invention, the addition amount of the alkaline agent to be added to the untreated flue gas is calculated based on the measured value of the acid gas concentration in the untreated flue gas in the dry treatment step. The unreacted alkali agent concentration in the fly ash discharged from the dust collector is calculated, and the amount of the heavy metal fixing agent added to the fly ash is calculated based on the calculated value of the unreacted alkali agent concentration. It is characterized by calculating and adding.
The amount of alkaline agent to be added to the untreated flue gas is calculated based on the measured concentration of the acid gas in the untreated flue gas, and from the added amount, the measured concentration of the acid gas is calculated. , the theoretical reaction amount of the alkaline agent is subtracted to calculate the concentration of the unreacted alkaline agent in the fly ash discharged from the dust collector. That is, without the need to analyze the concentration of alkaline components in the fly ash, highly accurate, safe and simple fly ash treatment can be performed in real time.

A representative example of heavy metals in the collected fly ash is lead, and others include cadmium, chromium, arsenic, selenium, and mercury.
Inorganic heavy metal fixing agents and chelate heavy metal fixing agents are known as heavy metal fixing agents, but in the processing method of the present invention, it is preferable to use inorganic heavy metal fixing agents.
The heavy metal fixing agent may be used in the form of powder, or may be used in the form of liquid by dissolving or dispersing the powder in water or the like.
Inorganic heavy metal fixing agents include phosphoric acid-based compounds, silicon dioxide-based compounds and iron-containing compounds.

Phosphate-based compounds exhibit long-term elution prevention effects of heavy metals in disposal sites, and are effective materials from the viewpoint of environmental protection. Phosphate-based compounds react with, for example, lead, which is a heavy metal, to form lead chloropyromorphite and lead pyromorphite, fix lead in the form of minerals, and prevent elution of lead. As the phosphoric acid-based compound, any phosphoric acid-containing compound can be used without particular limitation, and may be a phosphate or a mineral.
Phosphoric acid compounds include, for example, orthophosphoric acid (orthophosphoric acid), polyphosphoric acid, metaphosphoric acid, hypophosphoric acid, phosphorous acid, hypophosphorous acid, pyrophosphoric acid, superphosphoric acid, monobasic sodium phosphate, Sodium diphosphate, sodium tertiary phosphate, potassium phosphate dibasic, potassium phosphate tertiary, potassium phosphate tertiary, calcium phosphate dibasic, magnesium phosphate dibasic, magnesium phosphate dibasic, magnesium phosphate dibasic, Ammonium monophosphate, di-ammonium phosphate, lime superphosphate, sodium tripolyphosphate, potassium tripolyphosphate, sodium hexametaphosphate, potassium hexametaphosphate, sodium pyrophosphate, potassium pyrophosphate, sodium phosphite, potassium phosphite, Examples include sodium phosphite and potassium hypophosphite.
Among others, minerals in the form of orthophosphate, monophosphate, diphosphate, tertiary phosphate, tripolyphosphate, hexametaphosphate, pyrophosphate, hydroxyapatite, especially apatite (apatite compound) shows a good heavy metal elution prevention effect.
Phosphate-based compounds are particularly useful for preventing elution of lead among heavy metals.

The silicon dioxide-containing compound has the effect of generating a calcium silicate mineral (3CaO 2SiO ₂ 3H ₂ O) by reacting the calcium component in the fly ash with silicon dioxide, and confining heavy metals in the mineral. In addition, silicon dioxide acts directly on heavy metals to form sparingly soluble heavy metal silicates ( _PbSiO3, etc.), which is thought to have the effect of preventing the elution of heavy metals. The silicon dioxide-containing compound is easily affected by the alkali content in the fly ash, and when the alkali content in the fly ash is large, the necessary addition amount for producing the reaction product increases. Therefore, the treatment method of the present invention can significantly reduce the amount of silicon dioxide-containing compound that is required to be added.

The silicon dioxide-containing compound can be used without any particular limitation as long as it is a compound having a SiO ₂ component, and may be silicon dioxide itself, a salt, or a mineral.
Silicon dioxide-containing compounds include silicates containing alkali metals and alkaline earth metals such as sodium silicate and potassium silicate, silica fume, silica gel, activated clay, zeolite, bentonite, kaolinite, halloysite, antigorite, and pyrosilicate. Wright, talc, montmorillonite, sabonite, permiculite, muscovite, balagonite, illite, phlogopite, biotite, margarite, xanthophyllite, donpasite, sudouite, clinochlore, chamosite, sepiolite, palygorskite, imogolite, allophane and hisingerite silicate minerals such as
Silicon dioxide-containing compounds are particularly useful for preventing elution of lead among heavy metals.

The iron-containing compound may contain iron, and examples thereof include ferrous chloride, ferric chloride, ferrous sulfate, ferric sulfate, polyferric sulfate, and iron powder. Iron-containing compounds are particularly useful for preventing the elution of hexavalent chromium, arsenic, selenium and mercury, among other heavy metals.

An acid neutralizing agent may be added to the inorganic heavy metal fixing agent for use in the treatment method of the present invention. Since the acidic neutralizer has the role of reducing the amount of heavy metals eluted, from the viewpoint of further suppressing the elution of heavy metals, it is recommended to add an acidic neutralizer to the inorganic heavy metal fixing agent, that is, to use both together. is preferred. The acid neutralizing agent is also affected by the alkali content remaining in the fly ash, and when the alkali content in the remaining fly ash is large, the required addition amount increases. Therefore, according to the present invention, the necessary addition amount of the acidic neutralizing agent can be greatly reduced.
Examples of acidic neutralizers include hydrochloric acid, sulfuric acid, nitric acid, aluminum chloride, polyaluminum chloride, aluminum sulfate, iron sulfate, and iron chloride.
The combined use of an inorganic heavy metal fixing agent and an acidic neutralizing agent is preferable in that the amount of the expensive inorganic heavy metal fixing agent used can be reduced.

The heavy metal fixing step preferably includes a storage step of storing the fly ash discharged from the dust collector in a storage silo, and extracting the fly ash in the storage silo and supplying it to the kneader. and a kneading step of adding the heavy metal fixing agent to fix the heavy metals in the fly ash.
Preferably, in the treatment method of the present invention, the unreacted alkaline agent in the fly ash supplied from the dust collector to the storage silo is calculated based on the measured value of the acid gas concentration in the untreated flue gas. The temporal data of the concentration is stored, and the fly ash supplied to the kneader and processed based on the temporal data and the supply flow rate when the fly ash is extracted from the storage silo and supplied to the kneader. is calculated, and based on the time-dependent change, the addition amount of the heavy metal-fixing agent is controlled over time to immobilize the heavy metals in the fly ash.

The method of adding the heavy metal fixing agent to the fly ash is not limited, but the components in the liquid state can also be added by mixing with water, which will be described later. When adding an acidic neutralizing agent to the inorganic heavy metal fixing agent, both can be mixed with water and added. In addition, the component in the powder state can be added together with the fly ash by installing a constant supply device at the fly ash inlet of the kneading device.
As a kneader, a known kneader such as a twin-screw bench kneader mixer, a pan-type granulation mixer, and a vibrating mixer can be used.
The amount of fly ash processed per hour by a kneader is usually designed to exceed the amount of fly ash generated. The running and stopping states are controlled accordingly.

Water is preferably added to the kneader along with the heavy metal fixative. In addition to dissolving the heavy metal fixing agent, water facilitates kneading and distributes the heavy metal fixing agent evenly in the fly ash.It also reacts with calcium chloride and calcium oxide in the fly ash to generate heat of hydration. It has a role to express.
The amount of water added is preferably 5 to 40 parts by mass, more preferably 10 to 30 parts by mass, per 100 parts by mass of fly ash. When the amount is 5 parts by mass or more, the above-mentioned effects are easily exhibited, and when it is 40 parts by mass or less, the fly ash becomes muddy and prevents deterioration in handleability due to an increase in weight, and surplus water absorbs the heat of hydration. It is possible to prevent the temperature from being hindered by the

In this way, the amount of unreacted alkaline agent in the collected and discharged fly ash is calculated based on the measured value of the concentration of acid gases (hydrogen chloride and sulfur oxides) in the untreated flue gas, By calculating the amount of heavy metal fixing agent to be added to fly ash based on the calculated concentration of unreacted alkaline agent, it is possible to reduce the amount of heavy metal fixing agent used and reduce the amount of fly ash discharged to the final disposal site. It is possible to extend the period of use of the final disposal site.

[Example of method for calculating the amount of heavy metal fixing agent added]
First, based on the measured value of the acid gas concentration, the amount of alkali agent to be added to the untreated flue gas is calculated and added, and the unreacted alkali agent concentration in the fly ash discharged from the dust collector is calculated. .
For example, the amount of hydrogen chloride in the untreated flue gas is A mol/m ³ and the amount of sulfur oxide is B mol/m ³ , and the total of these is measured as the acid gas concentration, and all such acid gases are neutralized. As described above, when adding slaked lime as an alkali agent in an amount equivalent to 3 times the acid gas, the amount of alkali agent added to the combustion exhaust gas is 3 × (1/2A + B) mol / m ³ , and among them, The amount of unreacted alkaline agent is 2×(1/2A+B) mol/m ³ . Furthermore, when the amount of dust in the combustion exhaust gas is Ckg/ ^m3 , the unreacted alkaline agent concentration X [mol/kg-fly ash ] can be calculated as follows.
X = {2 × (1/2A + B)} / {C + 2 × (1/2A + B)} [mol/kg-fly ash]
In addition, since the amount of acid gas in the untreated flue gas changes depending on the operating conditions of the upstream combustion facility, etc., the unreacted alkaline agent concentration X [mol/kg- fly ash] also changes over time.

Next, time-dependent data of the unreacted alkaline agent concentration in the fly ash supplied from the dust collector to the storage silo, which is calculated based on the measured value of the acid gas concentration in the untreated flue gas, is stored.
For example, the fly ash having an unreacted alkaline agent concentration of X [mol/kg-fly ash] obtained as described above is supplied to the storage silo, and the unreacted alkaline agent concentration in the supplied fly ash is Store temporal data.

Next, based on the temporal data α of the unreacted alkaline agent concentration in the fly ash supplied from the dust collector to the storage silo and the supply flow rate when the fly ash is extracted from the storage silo and supplied to the kneader , the time-dependent change β of the unreacted alkaline agent concentration in the fly ash supplied to and processed by the kneader is calculated.
For example, when the flow rate of fly ash extraction from the storage silo is Y times the flow rate of fly ash supply to the storage silo, the concentration of unreacted alkaline agent in the fly ash supplied to the kneader and processed changes over time β is Y times the time-dependent change of the time-dependent data α of the unreacted alkaline agent concentration in the fly ash supplied from the dust collector to the storage silo.
In this way, even if the flow rate of fly ash extraction from the storage silo is Y times the flow rate of fly ash supply to the storage silo, unreacted fly ash supplied to the kneader and processed The time-dependent change β of the alkali agent concentration is grasped, and an appropriate amount of heavy metal fixing agent is added to the fly ash supplied to the kneader according to the time-dependent change β. Can be added to the ash.

For example, assume:
Amount of fly ash generated (flow rate of fly ash supplied to storage silo): _GFA kg/hr (always generated)
Fly ash processing amount of kneader: _MFA kg/hr
Storage silo level sensor low to high capacity: Vkg
In addition, the kneader is stopped until the level of the storage silo reaches a high level from a low level (suspension process), and after the level of the storage silo reaches a high level, the fly ash is extracted from the storage silo and supplied to the kneader. It is assumed that the process of starting fly ash treatment at the same time and stopping the fly ash treatment when the level returns to a low level (fly ash treatment step) is repeated.
In that case, the time T _S (hr) required for the stopping process is given by the following formula.
T _S (hr) = V/G _FA
In addition, the time T _M (hr) required for the fly ash treatment process is expressed by the following formula.
T _M (hr) = V/(M _FA - G _FA )
In other words, _TS is the time from when the fly ash treatment in the kneader is already completed to the start (time during which the kneader is stopped), and _TM is the time after the start of fly ash treatment in the kneader. It is also the time required for completion (time during which the kneader is operated).
Here, assuming that the sum of one stop process and one fly ash treatment process is one interval, the time required for one interval is T _S +T _M (hr). Moreover, the fly ash stored in the storage silo during the one interval (T _S +T _M (hr)) is processed by the kneader for T _M (hr). That is, the fly ash stored in the storage silo over _TS + _TM (hr) (fly ash generated between _TS and _TM ) is processed by the kneader in _TM (hr) time. become. That is, the time for processing the fly ash by the kneader is T _M /(T _S +T _M ) of the time for storing the fly ash in the storage silo.
Further, the breakdown of the processing time T _M (hr) by the kneader is as follows.
Processing time for fly ash generated during the stop process: T _M × {T _M / (T _S + T _M )}
Processing time of fly ash generated during the fly ash processing process: T _M × {T _S / (T _S + T _M )}
In other words, the temporal data α of the unreacted alkaline agent concentration in the fly ash supplied from the dust collector to the storage silo, stored as described above, is compressed by T _M /(T _S +T _M ) times, It can be used to control the amount of weight fixing agent added to the fly ash supplied to the kneader.

EXAMPLES Next, the present invention will be described in more detail with reference to examples, but the present invention is not limited by these examples.

[Example 1]
In ^a continuous incinerator (processing capacity 160 t/day), a hydrogen chloride measuring instrument (Kyoto Denshi Kogyo HL-22, manufactured by Horiba, Ltd.) and a sulfur oxide concentration measuring device (Horiba, Ltd., PG-337) are installed to measure the hydrogen chloride concentration and sulfur oxide concentration in the untreated flue gas. It was recorded as a moving average concentration for 30 minutes. FIG. 2 shows changes in hydrogen chloride concentration and sulfur oxide concentration over time over 24 hours.

The total of the recorded hydrogen chloride concentration and sulfur oxide concentration was taken as the acid gas concentration, and the amount of slaked lime to be added was calculated so as to be 3 equivalents of the acid gas concentration, and slaked lime was added to the flue in front of the bag filter as a dust collector. . Here, the combustion exhaust gas temperature in front of the bag filter was 170° C., and the fly ash generation amount ( _GFA ) was 200 kg/h.
The generated fly ash was collected by a bag filter, discharged and accumulated in a storage silo with a storage capacity (V) of 3600 kg.
The temporal data of the concentration of unreacted slaked lime in the fly ash was calculated based on the amount of added slaked lime and the measured value of the acid gas concentration in the untreated flue gas. FIG. 3 shows the change over time of unreacted slaked lime concentration in fly ash.

Next, the fly ash in the storage silo is extracted, and the fly ash is supplied to a kneader with a fly ash processing capacity (M _FA ) of 800 kg / h. (trade name “Ashnite R303”, phosphoric acid-based (acidic) compound) was added together with water (the amount of water added to 100 parts by mass of fly ash: 20 parts by mass).
The amount of the heavy metal fixing agent added to the kneader was calculated as follows, and the heavy metal fixing agent addition device was controlled.

First, from the fly ash generation amount G _FA , the storage capacity V of the storage silo, and the fly ash processing capacity M _FA of the kneader per unit time, the time until the fly ash is stored in the storage silo up to the capacity V, that is, the kneader Determine the time (T _S ) from when the fly ash treatment at is already finished to when it starts. On the other hand, the time (T _M ) required from the start to the end of fly ash treatment in the kneader is determined.
Next, when the heavy metal fixing process of fly ash by the kneader starts, the temporal data of the unreacted slaked lime concentration in the fly ash between _TS and _TM is output, and using this temporal data, the fly ash The unreacted slaked lime concentration of _TS ( _TM / ( _TS + _TM )) and _TM ( _TM / ( _TS + _TM )) are processed as time conversions and converted into the addition amount of the heavy metal fixing agent. was calculated and the amount of heavy metal fixative added to the kneader was controlled continuously. The amount of the heavy metal fixing agent to be added was calculated on the assumption that the fly ash stored in the storage silo is naturally deposited without being agitated in the storage silo, and that there is a concentration distribution in the vertical direction.

FIG. 4 shows changes over time in the concentration of unreacted slaked lime in fly ash and changes over time in the amount of heavy metal fixing agent added to the kneader.
In addition, FIG. 5 shows the time-dependent change in the concentration of unreacted slaked lime in the fly ash accumulated in the storage silo in the heavy metal fixing process. is converted by compression and converted into addition amount calculation of heavy metal fixing agent.

100: Combustion exhaust gas treatment device 1: Piping 2: Piping 3: Flue 4: Gas discharge path 5: Fly ash discharge path 6: Piping 11: Incinerator 12: Boiler 13: Gas cooling tower 14: Dust collector 15: Suction fan 16 : Chimney 21: Storage silo 22: Fly ash supply device 23: Kneader 24: Ash pit 30: Acid gas concentration measuring device 30a: Hydrogen chloride concentration measuring device 30b: Sulfur oxide concentration measuring device 40: Arithmetic device 41: Alkaline agent Addition amount calculation unit 42: Unreacted alkali agent concentration calculation unit 43: Heavy metal fixing agent addition amount calculation unit 51: Alkali agent addition device 52: Heavy metal fixation agent addition device S1: Hydrogen chloride concentration signal S2: Sulfur oxide concentration signal S3: Alkali agent addition signal S4: Alkali agent amount signal S5: Unreacted alkali agent concentration signal S6: Heavy metal fixing agent addition signal

Claims (13)

a dry treatment step of adding an alkaline agent to untreated flue gas containing acid gas to neutralize the acid gas to obtain alkali-treated flue gas;
A dust collection step of supplying the alkali-treated flue gas to a dust collector to collect fly ash;
A heavy metal fixing step of discharging the fly ash from the dust collector and adding a heavy metal fixing agent to the fly ash to fix heavy metals in the fly ash;
and
measuring the concentration of the acid gas in the untreated flue gas;
Based on the measured value of the acid gas concentration, the amount of the alkali agent to be added to the untreated flue gas is calculated and added, and the unreacted alkali agent concentration in the fly ash discharged from the dust collector. to calculate
A method for treating combustion exhaust gas, wherein the amount of the heavy metal fixing agent to be added to the fly ash is calculated and added based on the calculated value of the concentration of the unreacted alkaline agent. The heavy metal fixing step includes:
A storage step of storing fly ash discharged from the dust collector in a storage silo;
A kneading step of extracting the fly ash in the storage silo and supplying it to a kneader, adding the heavy metal fixing agent to the fly ash in the kneader to fix the heavy metals in the fly ash;
The method for treating flue gas according to claim 1, comprising: Store temporal data of the concentration of unreacted alkaline agent in the fly ash supplied from the dust collector to the storage silo, calculated based on the measured value of the acid gas concentration in the untreated flue gas,
Based on the temporal data and the supply flow rate when the fly ash is extracted from the storage silo and supplied to the kneader, the unreacted alkali agent concentration in the fly ash supplied to the kneader and processed over time calculate the change,
3. The method for treating flue gas according to claim 2, wherein the amount of the heavy metal fixing agent added is controlled over time based on the change over time to fix the heavy metals in the fly ash. The flow rate of the fly ash extracted from the storage silo is Y times the flow rate of the fly ash supplied to the storage silo, and the change over time of the unreacted alkaline agent concentration in the fly ash supplied to the kneader and processed β 4. The method for treating flue gas according to claim 3, wherein is Y times the change over time of the unreacted alkaline agent concentration data α in the fly ash supplied from the dust collector to the storage silo. The kneader is stopped until the level of the storage silo reaches a high level from a low level (stopping step), and after the level of the storage silo reaches a high level, fly ash is extracted from the storage silo and supplied to the kneader. Repeat the process of starting fly ash treatment and stopping fly ash treatment when the level returns to a low level (fly ash treatment process),
The time TS (hr) required for the stopping step is as follows,
TS (hr) = V/GFA
4. The method for treating flue gas according to claim 3, wherein the time TM (hr) required for the fly ash treatment step is as follows.
TM (hr) = V/(MFA-GFA)
(however,
Amount of fly ash generated (flow rate of fly ash supplied to storage silo): GFA kg/hr,
Fly ash processing amount of kneader: MFA kg/hr,
storage silo level sensor low to high capacity: V kg,
is. ) The method for treating combustion exhaust gas according to any one of claims 2 to 5, wherein in said kneading step, an acidic neutralizing agent is further added to said kneader. The acid gas concentration in the combustion exhaust gas before the dry treatment is measured, and based on the measured value, in the dry treatment step, an alkali agent is added so that the concentration is 1 to 3 equivalents with respect to the acid gas concentration. The method for treating combustion exhaust gas according to any one of claims 1 to 6 . The flue gas treatment according to any one of claims 1 to 7 , wherein the acid gas contains hydrogen chloride and sulfur oxides, and the total concentration of the hydrogen chloride and sulfur oxides is measured as the acid gas concentration. Method. The method for treating flue gas according to any one of claims 1 to 8 , wherein the alkaline agent contains at least one basic salt of an alkali metal or an alkaline earth metal. The method for treating flue gas according to any one of claims 1 to 9 , wherein the heavy metal fixing agent is an inorganic heavy metal fixing agent. a dry treatment apparatus for adding an alkaline agent to untreated flue gas containing acid gas to neutralize the acid gas to obtain alkali-treated flue gas;
a dust collector that is connected to the dry processing apparatus and collects fly ash in the alkali-treated flue gas;
a heavy metal fixing device connected to the dust collector for fixing heavy metals in the fly ash by adding a heavy metal fixing agent to the fly ash;
a measuring device for measuring the concentration of the acid gas in the untreated flue gas;
an alkali agent addition amount calculation unit that calculates the addition amount of the alkali agent to be added to the untreated flue gas based on the measured value of the acid gas concentration; and an unreacted fly ash discharged from the dust collector. an unreacted alkali agent concentration calculation unit that calculates the concentration of the alkali agent; and a heavy metal fixative calculation unit that calculates the amount of the heavy metal fixative to be added to the fly ash based on the calculated value of the unreacted alkali agent concentration. a computing device having
an alkali agent addition device that adds the alkali agent to the untreated flue gas in the dry processing unit based on the calculated value of the addition amount of the alkali agent calculated by the arithmetic unit;
a heavy metal fixing agent adding device for adding the heavy metal fixing agent based on the calculated value of the amount of the heavy metal fixing agent to be added to the fly ash;
Combustion exhaust gas treatment device. The heavy metal fixing device includes:
A storage silo connected to the dust collector and storing fly ash discharged from the dust collector;
a kneader connected to the storage silo;
A supply device for extracting fly ash from the storage silo and supplying it to the kneader;
12. The flue gas treatment apparatus according to claim 11 , further comprising a heavy metal fixing agent adding device for adding the heavy metal fixing agent to the kneader. a storage unit for storing temporal data of the unreacted alkaline agent concentration in the fly ash supplied from the dust collector to the storage silo, which is calculated based on the measured value of the acid gas concentration in the untreated flue gas; Based on the temporal data and the supply flow rate when the fly ash is extracted from the storage silo and supplied to the kneader, the unreacted alkali agent concentration in the fly ash supplied to the kneader and processed over time an arithmetic device comprising: an arithmetic unit for calculating a change; and an arithmetic unit for calculating the amount of the heavy metal fixing agent to be added to the fly ash based on the temporal change of the concentration of the unreacted alkaline agent;
a heavy metal fixing agent adding device for adding the heavy metal fixing agent based on the calculated value of the amount of the heavy metal fixing agent to be added to the fly ash;
13. The flue gas treatment apparatus according to claim 12 , comprising:

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