JP2021178283A - Flue gas treatment material and flue gas treatment method - Google Patents

Abstract

To provide a flue gas treatment material that can achieve both removal of an acidic gas in a flue gas and elution suppression of heavy metals with a use amount equal to or less than before, and treat the flue gas.SOLUTION: A flue gas treatment material of the present invention contains calcium dihydrogen phosphate powder and calcium hydroxide powder, and in which a volume-based cumulative 50% particle diameter D50, measured by laser diffraction scattering type measurement, of the calcium dihydrogen phosphate is less than 180 μm. The present invention also provides a method for treating the flue gas in which the flue gas treatment material is brought into contact with an acidic gas and heavy metal-containing flue gas to treat the acidic gas and heavy metal in the flue gas.SELECTED DRAWING: Figure 1

Description

The present invention relates to a flue gas treatment material and a flue gas treatment method.

In a waste incineration plant that incinerates municipal waste and industrial waste, hydrogen chloride (HCl), sulfur oxide (SOx), and nitrogen oxide (SOx) derived from the raw material of waste are generated during the smoke exhaust generated during waste incineration. It contains acidic gas including NOx) and flying ash. Among these, in order to reduce the concentration of acid gas discharged to the outside air, there is a technology to blow a treatment material containing basic calcium compounds such as _{quicklime (CaO) and slaked lime (Ca (OH) 2) into the flue.} It has been established.
In addition, since the fly ash during smoke exhaust also contains heavy metals derived from dust, typically, after collecting the fly ash in a dust collection facility, the amount of heavy metals eluted is less than the landfill judgment standard. Heavy metals are insolubilized so that they become the same, and then transferred to the final disposal site for disposal.

In order to treat the acid gas and flying ash described above, Patent Documents 1 to 3 disclose a treatment agent to which a phosphoric acid compound having an ability to insolubilize heavy metals such as lead is added to a calcium compound. ..

Japanese Unexamined Patent Publication No. 10-1090114 Japanese Unexamined Patent Publication No. 2000-061252 Japanese Unexamined Patent Publication No. 2009-131726

Generally, since waste is accumulated in the field at the final disposal site, rainwater permeates the waste layer. Therefore, management is carried out to control various items regulated by the Water Pollution Control Law within the standard values so that such infiltrated water can be collected in one place and discharged into rivers and the like. Such control items include, for example, the pH of the osmotic water, the concentration of heavy metals such as lead in the osmotic water, and the chemical oxygen demand (COD).
Of these, in order to suppress the elution of lead into the environment, for example, as disclosed in the treatment materials described in Patent Documents 1 to 3, a phosphoric acid-based compound can be used. However, in order to sufficiently suppress the elution amount of heavy metals such as lead until it becomes equal to or less than the landfill determination standard value, it is necessary to increase the content of the phosphoric acid compound in the treated material.

On the other hand, when a treated material having an increased content of a phosphoric acid compound is used and the acid gas is treated by, for example, blowing the treated material into a flue, the content of the calcium compound per unit mass is increased. Since it will decrease, it was necessary to use a large amount of the treated material itself.
As described above, the techniques of Patent Documents 1 to 3 have not studied at all about achieving both the suppression of acid gas emission and the suppression of elution of heavy metals with a usage amount equal to or less than the conventional one.

Therefore, an object of the present invention is to provide a flue gas treatment material and a flue gas treatment method capable of achieving both suppression of acid gas emission and suppression of elution of heavy metals with a usage amount equal to or less than the conventional one.

As a result of diligent studies to solve the above problems, the present inventors have obtained calcium dihydrogen phosphate, which has a relatively high solubility among phosphoric acid compounds, in addition to calcium hydroxide, in a specific range of particle size. It has been found that the above-mentioned problems can be solved by controlling and using the above-mentioned problem, and the present invention has been achieved.

That is, the present invention contains a powder of calcium dihydrogen phosphate and a powder of calcium hydroxide, and the volume standard cumulative 50% particle size D _{50 measured by the laser diffraction scattering type particle size distribution measurement method of the calcium dihydrogen phosphate.} Provided is a flue gas treatment material having a size of less than 180 μm.

The present invention also provides a method for treating flue gas in which the flue gas treatment material is brought into contact with flue gas containing acid gas and heavy metals.

Further, the present invention comprises a step of contacting smoke exhaust containing an acid gas and a solid component containing heavy metals with calcium hydroxide powder, and then contacting the solid component with calcium dihydrogen phosphate. ,
The calcium dihydrogen phosphate provides a method for treating flue gas _{in which the volume-based cumulative 50% particle diameter D 50} measured by a laser diffraction / scattering type particle size distribution measurement method is less than 180 μm.

According to the present invention, it is possible to treat flue gas at the same time as the conventional amount or less, while removing acid gas in flue gas and suppressing elution of heavy metals.

FIG. 1 is a schematic diagram showing an outline of a waste treatment plant and a position where a flue gas treatment material is blown. FIG. 2 is a schematic diagram showing another outline of the waste treatment plant and the blowing position of the constituent material of the flue gas treatment material.

Suitable embodiments of the present invention will be described below. The present invention is not limited to the following embodiments. In the following description, when "X to Y [Z]" (X and Y are arbitrary numbers and [Z] is a unit) is described, "X [Z] or more Y [" unless otherwise specified. Z] or less.

The flue gas treatment material of the present invention contains calcium dihydrogen phosphate and calcium hydroxide. The properties of calcium dihydrogen phosphate and calcium hydroxide are independent of each other, preferably in the form of powder, from the viewpoint of improving handleability during transportation and use. Further, from the viewpoint of improving the handleability during transportation and use, the flue gas treatment material of the present invention is preferably a powdery mixture. The powder in the present invention refers to an aggregate of particles.
In the following description, as a preferred embodiment of the flue gas treatment material, an embodiment containing a powder of calcium dihydrogen phosphate and a powder of calcium hydroxide will be described as an example.

The flue gas treatment material contains calcium dihydrogen phosphate. Calcium dihydrogen phosphate is typically produced by adding calcium carbonate or calcium hydroxide to phosphoric acid, and is used as a fertilizer, a livestock feed additive, or a fermentation aid for brewing. As for calcium dihydrogen phosphate, powdery or granular products are used depending on its use. In the present invention, it is used to insolubilize heavy metals such as arsenic, hexavalent chromium, lead, and selenium mainly contained in fly ash during flue gas. The calcium dihydrogen phosphate contained in the flue gas treatment material of the present invention may be anhydrous or hydrated.

The calcium dihydrogen phosphate powder contained in the flue gas treatment material has one of the characteristics in the particle size of the particles constituting the powder. As a result of the study, the present inventor unexpectedly used calcium dihydrogen phosphate in which the particle size was controlled within a predetermined range together with calcium hydroxide to insolubilize heavy metals such as lead in flue gas. It has been found that acid gas can be neutralized to suppress the emission of these into the environment. In addition to this, in the treatment of flue gas, the emission standard value of the landfill judgment standard value and the Air Pollution Control Act should be set at the same level as or less than the amount used when the calcium compound alone or the phosphoric acid compound alone is used. We also found that the flue gas could be treated to meet.

Specifically, the powder of calcium dihydrogen phosphate has a particle size of particles constituting the powder, preferably less than 180 μm, more preferably 3 to 100 μm, and further preferably 3 to 40 μm. By having such a particle size, it is possible to enhance the insolubilizing performance of heavy metals such as lead in flue gas and efficiently insolubilize fly ash in flue gas and flue gas. In particular, it is advantageous in that the insolubilizing performance of heavy metals can be enhanced when the smoke exhaust treatment is performed by a dry method such as directly blowing the smoke exhaust treatment material into a flue or the like. The particle size of calcium dihydrogen phosphate may be appropriately adjusted by performing a pulverization treatment with a pulverizer, a crushing treatment, a sieving treatment, or the like.

The particle size of calcium dihydrogen phosphate can be measured by, for example, the following method. First, the sample to be measured was put into a laser diffraction / scattering type particle size distribution measuring device (MT-3000EXII manufactured by Microtrac Bell Co., Ltd.) in which the inside of the circulation path was filled with ethanol (refraction index 1.36, 25 ° C.). A 40 W ultrasonic wave is irradiated for 3 minutes with an ultrasonic dispersion device built in the device to obtain a dispersion liquid, and the particle size distribution is measured. From the obtained volume-based particle size distribution chart, a volume-based cumulative 50% particle size D ₅₀ is obtained. _{The D 50} thus obtained is used as the particle size of the present invention. In the above-mentioned measuring device, the particle information is set to a refractive index: 1.63 (25 ° C.), a shape: non-spherical, and a transmission / non-transmission distinction: transmission.

The flue gas treatment material contains calcium hydroxide. Calcium hydroxide is an acidic gas containing hydrogen chloride (HCl), sulfur monoxide, sulfur oxides such as sulfur dioxide and sulfur trioxide (SOx), and nitrogen oxides such as nitrogen monoxide and nitrogen dioxide (NOx). Mainly used for neutralization treatment. The calcium hydroxide contained in the flue gas treatment material of the present invention may be anhydrous or hydrated.

The calcium hydroxide powder has a particle size of preferably 1 to 20 μm, more preferably 1 to 10 μm, still more preferably 1 to 8 μm. By having such a particle size, it is possible to improve the contact efficiency with the acid gas and efficiently neutralize the acid gas regardless of the type of the acid gas. The particle size of calcium hydroxide may be appropriately adjusted by performing a pulverization treatment by a pulverizer, a crushing treatment, a sieving or the like, for example.

The particle size of the calcium hydroxide particles can be measured, for example, by the following method. First, the sample to be measured was put into a laser diffraction / scattering type particle size distribution measuring device (MT-3000EXII manufactured by Microtrac Bell Co., Ltd.) in which the inside of the circulation path was filled with ethanol (refraction index 1.36, 25 ° C.). A 40 W ultrasonic wave is irradiated for 3 minutes with an ultrasonic dispersion device built in the device to obtain a dispersion liquid, and the particle size distribution is measured. From the obtained volume-based particle size distribution chart, a volume-based cumulative 50% particle size D ₅₀ is obtained. _{The D 50} thus obtained is used as the particle size of the present invention. In the above-mentioned measuring device, the particle information is set to a refractive index: 1.57 (25 ° C.), a shape: non-spherical, and a transmission / non-transmission distinction: transmission.

Powdered calcium hydroxide, BET specific surface area of the particles constituting the powder is preferably ^{30 m} 2 / g or more, more preferably 30 to 60 m ² / g, more preferably 35~55m ² / g, more preferably It is 40 to 50 m ² / g. By having such a specific surface area, the contact efficiency with the acid gas can be improved, and the acid gas can be efficiently neutralized regardless of the type of the acid gas. The treatment efficiency of acid gas becomes more remarkable by setting the above-mentioned particle size in a suitable range in addition to the BET specific surface area. Further, the use of the calcium hydroxide powder having the above-mentioned BET specific surface area is used to neutralize the acid gas when the smoke exhaust treatment is performed by a dry method such as blowing a smoke exhaust treatment material into a flue or the like. It is advantageous in that efficiency can be increased.
The BET specific surface area can be measured by the BET one-point method, for example, in accordance with JIS Z8830. The calcium hydroxide powder having such a BET specific surface area may be obtained, for example, by using a commercially available product, or by the method described in JP-A-2005-350343 and JP-A-2008-290940. can.

Further, the calcium hydroxide powder preferably has pores in the particles constituting the powder, and more preferably has a specific pore volume. Specifically, the total pore volume of the calcium hydroxide powder in the pore size range of 20-1000 Å is preferably 0.10 to 0.30 mL / g, more preferably 0.15 to 0.25 mL / g, further. It is preferably 0.25 to 0.25 mL / g. Since the calcium hydroxide particles have pores and are within the above-mentioned pore volume range, a large amount of acid gas is adsorbed in the pores, and the acid gas is more efficiently used regardless of the type of acid gas. Can be neutralized. The treatment efficiency of the acid gas becomes more remarkable by setting the above-mentioned particle size and BET specific surface area in the suitable range in addition to the suitable range of the pore volume. Further, it is advantageous to use the calcium hydroxide powder having the above-mentioned pore volume when the smoke exhaust treatment is performed by a dry method such as blowing a smoke exhaust treatment material into a flue or the like.
As the calcium hydroxide powder having such pores and pore volume, for example, a commercially available product may be used, or by the method described in JP-A-2005-350343 and JP-A-2008-290940. Obtainable.

The pore volume in the calcium hydroxide powder can be measured, for example, by the BJH method. The specific procedure is as follows. That is, as a pretreatment, the sample to be measured is subjected to vacuum degassing treatment at a heat treatment temperature of 105 ° C. for 8 hours, and then liquid nitrogen is used using a measuring device (Belsorp-max manufactured by Microtrac Bell Co., Ltd.). A desorption isotherm, which is the relationship between the relative pressure when nitrogen is desorbed from the sample at temperature and the amount of nitrogen adsorbed, is obtained. Then, the total pore volume (mL / g) in the pore diameter range of 20 to 1000 Å is calculated from the desorption isotherm by the BJH method.

Apparent specific gravity in the powder of the calcium hydroxide, in loose specific gravity, preferably 0.20~0.50g / cm ^3, more preferably a 0.25~0.45g / cm ^3. The solidification specific gravity is preferably 0.40 to 0.70 g / cm ³ , and more preferably 0.45 to 0.68 g / cm ³ . By having such a specific gravity, the smoke exhaust treatment can be efficiently performed by a dry method such as blowing a smoke exhaust treatment material into a flue or the like.
The loose specific gravity and the solidified specific gravity in the apparent specific gravity can be measured according to, for example, JIS Z8807 “Method for measuring the density and specific gravity of a solid”. The calcium hydroxide powder having such an apparent specific gravity can be obtained, for example, by the method described in JP-A-2002-255957.

The content ratio of calcium dihydrogen phosphate in the flue gas treatment material is preferably 5% by mass or more and less than 50% by mass, more preferably 15 to 40% by mass, and further preferably 25 to 35% by mass in terms of anhydride. .. With such a content ratio, the insolubilizing performance of heavy metals such as lead in flue gas can be fully exhibited.

The content ratio of calcium hydroxide in the flue gas treatment material is preferably 50% by mass or more and less than 95% by mass, more preferably 60 to 85% by mass, and further preferably 65 to 75% by mass in terms of anhydride. .. With such a content ratio, the treatment performance of the oxidizing gas in the flue gas can be fully exhibited.
In particular, by setting both the content ratio of calcium dihydrogen phosphate and the content ratio of calcium hydroxide in the flue gas treatment material to the above-mentioned range, the insolubilization performance and oxidation of heavy metals such as lead in the flue gas It is advantageous in that the gas processing performance can be exhibited at a high level in a well-balanced manner.

The flue gas treatment material of the present invention may be composed only of calcium hydroxide and calcium dihydrogen phosphate. Alternatively, the flue gas treatment material may further contain an additive as long as the effect of the present invention is exhibited. In the former case, the flue gas treatment material does not contain an additive.

As the additive, for example, at least one of a porous substance such as activated carbon, activated clay, and zeolite, and a metal salt of silicic acid such as orthosilicic acid and metasilicic acid can be used. By further containing an additive such as a porous substance, it is possible to achieve both removal of acid gas and insolubilization of heavy metals, and it is possible to discharge flue gas conforming to environmental standards into the atmosphere. Further, by containing silicate or the like, the insolubilizing performance of heavy metals can be further enhanced.
The properties of the various additives may be independently in the form of powder, or may be in the form of a liquid or slurry dissolved or dispersed in a solvent such as water.
It is preferable to perform a preliminary test and determine the presence or absence of addition of various additives and the mixing amount based on the results.

In the smoke exhaust treatment material of the present invention, for example, at least one of both calcium dihydrogen phosphate and calcium hydroxide powders is subjected to particle size control treatment such as crushing or crushing in advance, if necessary. It can also be produced by mixing calcium dihydrogen phosphate powder and calcium hydroxide powder. As an apparatus for mixing both powders, a mixing apparatus usually used in the art can be used, and for example, a ribbon mixer, a paddle mixer, a nouter mixer and the like can be used.

The flue gas treatment material of the present invention can be used in a method of treating flue gas by bringing the flue gas treatment material into contact with the flue gas. In this method, the flue gas treatment material can be brought into contact with the flue gas containing acid gas and heavy metals to suitably neutralize and insolubilize both the acid gas and heavy metals in the flue gas. Typically, the flue gas is only a gas containing acid gas or the like, or a mixture of the gas and a fine particle solid component such as fly ash. Such flue gas is generated, for example, in an urban waste incinerator, an industrial waste incinerator, a thermal power plant using coal as fuel, or the like. Heavy metals in flue gas are mainly contained in solid components such as fly ash, and are at least one kind of heavy metals such as arsenic, hexavalent chromium, lead and selenium, and preferably contain at least lead as a heavy metal.

The contact method between the flue gas treatment material and the flue gas is, for example, passing the flue gas through a container containing the flue gas treatment material or blowing the flue gas treatment material into the flue flow path (flue). Can be done by. The properties of the flue gas treatment material used for the flue gas treatment may be powder, dispersion liquid or solution. For flue gas treatment from the viewpoint of preventing the volume increase of the residue other than gas after flue gas treatment, improving the recovery efficiency of the used flue gas treatment material, and improving the treatment efficiency of acid gas and heavy metals. The properties of the flue gas treatment material used are preferably powder.

Amount of smoke treatment material per flue gas 1 m ³ is the appropriately modified depending on the type and amount of processing incinerated object in incinerators and thermal power plants, acid gases and heavy metals in the flue gas From the viewpoint of achieving both efficient treatment and reduction of treatment cost, it is preferably 5 to 200 g / m ³ , more preferably 10 to 100 g / m ³ , and further preferably 30 to 90 g / m ³ . be. The volume of flue gas is a value at 0 ° C. and 1 atm.

The mass ratio of calcium dihydrogen phosphate in the flue gas treatment material to the mass of fly ash is preferably 1 to 50% by mass, more preferably 1 to 20% by mass, and further preferably 1 to 10. It is mass%. By adjusting the addition ratio so as to have such a ratio, insolubilization of heavy metals such as lead in fly ash can be achieved more efficiently.

Hereinafter, an example of a flue gas treatment method using the flue gas treatment material of the present invention will be described with reference to FIG. FIG. 1 shows a schematic diagram of the equipment of the waste incinerator. As this method, it is preferable to adopt a dry method in which the powder of the flue gas treatment material is directly blown into the flue gas flow path. In FIG. 1, the arrow indicates the distribution direction of the flue gas, the exhaust gas, and the flue gas treatment material.

As the equipment of the waste incinerator 10, typically, a waste pit 20 and a waste pit 20 for accumulating municipal waste and industrial waste (hereinafter, these are also simply referred to as “garbage”) collected by a collection vehicle. An incinerator 30 that incinerates the waste accumulated in the incinerator 30, a waste heat boiler 40 that recovers heat from high-temperature waste smoke generated by waste incineration in the incinerator 30, a cooling tower 50 for cooling the waste smoke, and cooled. It is provided with a dust collecting facility 60 such as a bag filter for collecting flying ash during smoke exhaust, and a chimney 70 for discharging the exhausted smoke after dust collection into the atmosphere. Between the incinerator 30 and the waste heat boiler 40, between the waste heat boiler 40 and the cooling tower 50, between the cooling tower 50 and the dust collecting equipment 60, and between the dust collecting equipment 60 and the chimney 70, the first It is connected by 1 flow path 11, 2nd flow path 12, 3rd flow path 13 and 4th flow path 14, respectively, and communicates with each other so that smoke exhaust can flow inside them.
In addition to this, the treatment material supply unit 100 is provided so that the smoke exhaust treatment material and the smoke exhaust can come into contact with each other. The treatment material supply unit 100 shown in FIG. 1 communicates with the third flow path 13, and by blowing the smoke exhaust treatment material into the third flow path 13, the smoke exhaust treatment material and the third flow path 13 are used. It is configured so that the flue gas circulating inside can come into contact with each other.

At the waste incinerator 10, first, the waste accumulated in the waste pit 20 is supplied to the incinerator 30 together with air using a transfer facility such as a crane, and the waste is incinerated. In the incinerator 30, the incinerator is incinerated at about 800 to 1000 ° C., and the main ash and high-temperature smoke are generated as the waste is incinerated. The main ash is collected separately and disposed of at the final disposal site or reused as a raw material for other products. In addition, the generated flue gas contains fly ash containing acid gas, heavy metals such as lead, chlorides, silicon compounds, etc. due to the raw material of the waste. The high-temperature smoke exhaust passes through the first flow path 11, the waste heat boiler 40, the second flow path 12, and the cooling tower 50, and is rapidly cooled to about 300 ° C. The flue gas after cooling includes acid gas, which is a gas component, and fly ash, which is scattered together with the gas as a solid component. The smoke exhaust after cooling flows to the third flow path 13 side.

Next, the flue gas treatment material and the flue gas after cooling are brought into contact with each other. The contact method may be a method in which the calcium hydroxide powder is held in advance in the flue gas flow path and the flue gas is passed through the powder, or a method in which the calcium hydroxide powder is blown into the flue gas flow path. You may. Of these, it is preferable to blow the flue gas treatment material of the present invention into the third flow path 13 through which the flue gas is circulated from the treatment material supply unit 100 from the viewpoint of enhancing the convenience of the flue gas treatment.

Since the flue gas treatment material contains calcium hydroxide, by contacting calcium hydroxide with an acid gas containing hydrogen chloride or the like, a neutral calcium salt is formed by a neutralization reaction, and the acid gas in the flue gas is exhausted. To remove. In addition, since the smoke exhaust treatment material contains calcium dihydrogen phosphate, by contacting calcium dihydrogen phosphate with a solid component such as fly ash, an insoluble salt of heavy metals and phosphoric acid is formed and discharged. Insolubilizes heavy metals such as lead contained in fly ash in smoke. The generated neutral calcium salt, the insoluble salt of heavy metals and phosphoric acid, and the unreacted flue gas treatment material flow through the third flow path 13 in the form of a solid such as powder, so that they are collected together with fly ash. The exhaust gas is recovered and removed by the dust facility 60, and the solid component is removed from the flue gas. Solid components such as smoke exhaust treatment material, various salts, and fly ash collected by the dust collector 60 are housed in the fly ash accumulation unit 61. At this time, in the fly ash accumulation unit 61, for the purpose of preventing dust generation of the accumulated powder, water is applied to solid components such as fly ash and the smoke exhaust treatment material after contact with the smoke exhaust. May be added by spraying or the like to bring it into contact with water.
The flue gas treatment material, various salts, and fly ash accumulated in the fly ash accumulation unit 61 after contact with the flue gas are transferred to the final disposal site and disposed of after being cured for a certain period of time, for example, one day or more. Then, the exhaust gas that has passed through the dust collecting equipment 60 may be passed through a harmful substance removing equipment, a denitration equipment, or the like, if necessary, to remove the acid gas and the harmful substances remaining in the exhaust gas. After that, the exhaust gas is discharged from the chimney 70 into the atmosphere via the fourth flow path 14.

The reason why the flue gas treatment material of the present invention containing calcium dihydrogen phosphate can form an insoluble salt of heavy metals and phosphoric acid by contacting with fly ash in a solid state is as follows. I'm guessing.
In general, flying ash during flue gas is produced by the reaction of calcium hydroxide and hydrogen chloride, as well as calcium hydroxide used for removing acidic gas, in addition to heavy metal compounds such as lead chloride and lead oxide. Contains chlorides such as calcium chloride. The reaction between flying ash containing such a component and calcium dihydrogen phosphate produces an insoluble salt such as hydroxyapatite, and at the time of its formation, heavy metals such as lead are incorporated into the crystal structure. Thereby, insolubilization can be achieved. Calcium dihydrogen phosphate has a relatively high solubility in water as compared with other calcium phosphates, and is dissolved in a small amount of water present in the smoke exhaust after cooling or in water sprayed by the flying ash accumulation portion 61. , Phosphate ion derived from calcium dihydrogen phosphate, heavy metal ion such as lead ion derived from heavy metal compound, chloride ion derived from chloride, and calcium ion derived from calcium dihydrogen phosphate and slaked lime. Since it facilitates mutual formation and reaction, it is possible to promote the formation of insoluble salts of heavy metals. As a result, insolubilization of heavy metals such as lead can be efficiently achieved. By controlling the particle size of calcium dihydrogen phosphate to be within a specific range, the solubility in water is improved and the reactivity with heavy metals is further enhanced as compared with the particles having a size of more than 180 μm. It is advantageous in that the insolubilization performance can be exhibited more efficiently in a short time.
From the viewpoint of fully exhibiting such an effect, the flue gas treatment material is brought into contact with the flue gas by contacting the flue gas treatment material with water and then adding water to the flue gas treatment material. It is even more preferable to bring the agent into further contact with water. The amount of water added is preferably 5 to 40% by mass at 25 ° C. with respect to the total mass of the powder accumulated in the fly ash accumulating portion 61 including the flue gas treatment material brought into contact with the flue gas. be able to.

As described above, by using the flue gas treatment material of the present invention, the acid gas in the flue gas can be efficiently removed and the heavy metals in the fly ash can be insolubilized. In addition to this, in the treatment of flue gas, the amount used is equal to or less than the amount used when the calcium compound alone or the phosphoric acid compound is used alone, and various types specified in the landfill criteria and the Air Pollution Control Act, etc. Heavy metals such as acid gas and lead in the flue gas can be treated so as to be below the standard value.

Another embodiment of the flue gas treatment method of the present invention will be described below by taking FIG. 2 as an example. The above-mentioned description of each embodiment is appropriately applied to the points not particularly described in the present embodiment. Further, with respect to the form shown in FIG. 2, a component different from the configuration shown in FIG. 1 will be mainly described, and the same components will be designated by the same reference numerals and description thereof will be omitted.

The treatment method of this embodiment is a method in which calcium hydroxide and calcium dihydrogen phosphate contained in the above-mentioned flue gas treatment material are separately used. By adopting this method, it is possible to efficiently treat the acid gas in the flue gas and insolubilize heavy metals without mixing calcium hydroxide and calcium dihydrogen phosphate in advance.
Even when this method is adopted, the particle size D _{50 of} calcium dihydrogen phosphate can be in the above range.
The ratio of calcium hydroxide used to the total mass of calcium hydroxide and calcium dihydrogen phosphate used is preferably 50% by mass or more and less than 95% by mass, more preferably 60 to 85% by mass, and further preferably 65 to 5% by mass. It is 75% by mass. Similarly, the ratio of calcium dihydrogen phosphate used to the total mass of calcium hydroxide and calcium dihydrogen phosphate used is 5% by mass or more and less than 50% by mass, more preferably 15 to 40% by mass, still more preferably 25. ~ 35% by mass. Within such a range, the treatment performance of the oxidizing gas in the flue gas and the insolubilization performance of heavy metals can be fully exhibited.

The waste incinerator 10 shown in FIG. 2 has a first supply unit 150 for supplying calcium hydroxide and a second supply unit 160 for supplying calcium dihydrogen phosphate in place of the treatment material supply unit 100 shown in FIG. Is prepared separately. The first supply unit 150 shown in FIG. 2 communicates with the third flow path 13, and is configured to allow calcium hydroxide to be blown into the third flow path 13. Further, the second supply unit 160 shown in FIG. 2 communicates with the fly ash accumulation unit 61, and is configured so that calcium dihydrogen phosphate can be added and mixed in the fly ash accumulation unit 61.

In the flue gas treatment method of the present embodiment, first, a step of bringing the flue gas containing an acid gas and a solid component containing heavy metals into contact with the calcium hydroxide powder is performed. This step may be a method in which the calcium hydroxide powder is held in advance in the flue gas flow path and the flue gas is passed through the powder, or a method in which the calcium hydroxide powder is blown into the flue gas flow path. You may. Of these, it is convenient for the treatment efficiency of acid gas to bring the flue gas into contact with the calcium hydroxide powder by blowing the calcium hydroxide powder into the third flow path 13 which is the flue gas flow path. It is suitable from the viewpoint of enhancing.
Further, in the contact between the flue gas and the calcium hydroxide powder, it is preferable to make the calcium dihydrogen phosphate non-containing and bring only the calcium hydroxide powder into contact with the flue gas from the viewpoint of improving the treatment performance of the acid gas. The inclusion of calcium dihydrogen phosphate powder is not prevented. When calcium dihydrogen phosphate is contained, it is contained so as to be within the range of the mass used described above.

In the smoke exhaust after contacting the smoke exhaust and the calcium hydroxide powder, in addition to fly ash, which is a kind of heavy metal-containing solid component, the produced neutral calcium salt and unreacted calcium hydroxide powder are solid components. Included as. These solid components flow through the third flow path 13 and are collected and removed by the dust collector 60. A mixture of various salts of calcium hydroxide powder and solid components such as fly ash collected by the dust collector 60 is housed in the fly ash accumulation unit 61.

Next, a step of contacting the heavy metal-containing solid component with calcium dihydrogen phosphate is performed. In this step, calcium dihydrogen phosphate is supplied from the second supply unit 160 to the fly ash or the solid component containing the fly ash contained in the fly ash accumulation unit 61, and the two are brought into contact with each other. This makes it possible to insolubilize heavy metals such as lead contained in fly ash.

The method of contacting the solid component with calcium dihydrogen phosphate may be carried out in the absence of water or in the presence of water. Containing heavy metals from the viewpoint of further enhancing the reactivity between calcium dihydrogen phosphate and heavy metals by utilizing the high solubility of calcium dihydrogen phosphate in water and efficiently developing insolubilization performance in a short time. It is preferable to bring the solid component and calcium dihydrogen phosphate into contact with each other in the presence of water.

As a method of bringing the two into contact with each other in the presence of water, for example, (a) water is added to a solid component containing flying ash, and then calcium dihydrogen phosphate powder is supplied to the solid component to bring them into contact with each other. A method of contacting a solid component containing flying ash in a dry state or a water-containing state with a liquid in which calcium dihydrogen phosphate powder is dissolved or dispersed, or (c) a method of contacting the flying ash in a dry state. Examples thereof include a method in which water is added in the presence of a solid component containing and calcium dihydrogen phosphate powder to bring the solid component containing flying ash into contact with calcium dihydrogen phosphate.
From the viewpoint of improving convenience when adding calcium dihydrogen phosphate, efficiently exhibiting insolubilization performance of heavy metals, and reducing the increase in waste mass due to the excessive presence of water after insolubilization treatment. The calcium dihydrogen phosphate is preferably added as a powder, and it is more preferable to use the _{calcium dihydrogen phosphate powder having the above-mentioned D 50.} That is, it is preferable to adopt the method (a) or (c) described above.

In the treatment of flue gas, if the flue gas containing fly ash is brought into contact with calcium hydroxide in order to treat the acid gas in the flue gas, the flue gas after the treatment becomes a strongly alkaline atmosphere. Heavy metals in flue gas, especially lead, are amphoteric metal elements and have a high content in fly ash. Therefore, when lead in fly ash is exposed to strong alkaline conditions, the amount of lead dissolved in water increases. It becomes easy to change to. For this reason, typically, the exhaust smoke is passed through a dust collecting facility such as the above-mentioned fly ash collecting unit 61 to collect solid content such as fly ash in the exhausted smoke, and then the dust is collected. An organic chelating material is mixed with the ash-containing powder to insolubilize heavy metals such as lead, and the fly ash after the insolubilization treatment is disposed of as waste at the disposal site.
Specifically, solid waste containing fly ash is landfilled at a controlled final disposal site with a wastewater treatment facility. In a controlled disposal site, water such as rainwater that has permeated waste is collected in the above-mentioned wastewater treatment facility, but water containing heavy metals such as lead and water with high COD must be separately purified. As a result, enormous processing costs are incurred over a long period of time. When the organic chelating material is not used, insolubilization of heavy metals such as lead cannot be achieved, and the wastewater treatment cost generated from the treatment plant cannot be reduced. In addition, when an organic chelating material is used, insolubilization of heavy metals such as lead can be achieved to some extent, but the organic chelating material may decompose at the disposal site and the COD of the leachate from the disposal site may become excessively high. Even in this case, it is difficult to reduce the wastewater treatment cost generated from the treatment plant.
In this regard, by separately using the flue gas treatment material of the present invention composed of an inorganic compound or each constituent material of the flue gas treatment material for flue gas treatment, acid gas in flue gas can be removed. , Smoke emission of heavy metals such as lead can be achieved at the same time without using an organic chelating material separately. In particular, by using the flue gas treatment material of the present invention, it is advantageous in that it is possible to achieve both removal of acid gas in flue gas and suppression of emission of heavy metals such as lead by only one treatment. ..
In addition to this, the fly ash after treatment also has the advantage of reducing the adverse effects on the water quality environment caused by heavy metals and organic substances, and reducing the treatment cost of wastewater generated from the treatment plant. .. In addition, calcium dihydrogen phosphate has a lower cost than other phosphates and has less interaction with calcium hydroxide, so that it is mixed with calcium hydroxide like the smoke exhaust treatment material of the present invention. It is advantageous because the deterioration of each raw material can be reduced even when it is used.

Hereinafter, the present invention will be described in more detail by way of examples. The scope of the invention is not limited to such examples.

[Examples 1 to 5 and Comparative Examples 1 to 3]
Solid commercial calcium dihydrogen phosphate crusher (Jet mill manufactured by Nisshin Engineering Co., Ltd., CJ-10; Nara Machinery Co., Ltd., Nara type free crusher M-5 type; Seishin Enterprise Co., Ltd., Medium It is put into a crusher pin mill DD-2-7.5;), and the particle diameter D ₅₀ is 3 μm (using the jet mill, Examples 1 to 3) and 40 μm (using the free crusher, Example 4). ~ 5) or 180 μm (using a pin mill, Comparative Examples 1 to 3) was pulverized to obtain each powder of calcium dihydrogen phosphate. Then, this powder and calcium hydroxide powder (Calbreed SII, manufactured by Ube Material Industries Ltd.) are mixed at the mass ratios shown in Table 1 below to obtain smoke exhaust treatment materials of Examples or Comparative Examples. rice field. All of these flue gas treatment materials were in the form of powder. The calcium hydroxide powder used has a particle size D ₅₀ of 6.5 μm, a BET specific surface area of 45 m ² / g, a total pore volume of 0.22 mL / g in the pore diameter range of 20 to 1000 Å, and an apparent specific gravity. It was 0.36 g / cm ³ (loose specific surface area) and 0.65 g / cm ³ (consolidated specific surface area).

[Comparative Example 4]
In this comparative example, only calcium hydroxide powder (Calbreed SII manufactured by Ube Material Industries Ltd.) was used. That is, this comparative example is a flue gas treatment material containing no calcium dihydrogen phosphate.

[Evaluation of insolubilization performance of heavy metals]
For lead as a heavy metal, we evaluated the insolubilization performance of lead by the flue gas treatment material. First, a simulated ash containing lead was prepared by mixing a silica source, calcium hydroxide (Calbreed SII), calcium chloride, lead chloride and the like. The lead ion concentration of the simulated ash measured according to the method specified in the verification method for metals, etc. contained in industrial waste (Notification No. 13 of the Environment Agency in February 1973, hereinafter referred to as Notification No. 13 of the Environment Agency) is It was 3.2 mg / L.
Then, this simulated ash, the flue gas treatment material of the example or the comparative example, and water were mixed, and the mixture was cured for one day. Water was added in an amount of 30% by weight based on the total mass of the mixture. Then, for the cured mixture, a lead elution test was carried out according to the method specified in Notification No. 13 of the Environment Agency, and the lead ion concentration (mg / L) was quantified. The pH (25 ° C.) of each mixture after curing was in the range of 10.8 to 12.4.
The evaluation standard value of the lead ion concentration was set to 0.3 mg / L, and if it was equal to or less than the standard value, the lead insolubilization performance was evaluated to be good. The lower the lead ion concentration, the higher the lead insolubilization performance. The results are shown in Table 1 below. The mixed mass ratio of each flue gas treatment material shown in Table 1 is a value calculated in consideration of the content of calcium hydroxide contained in the simulated ash.

[Evaluation of acid gas removal performance]
The acid gas removal performance was evaluated using the flue gas treatment materials of Example 4 and Comparative Example 4. The specific procedure is as follows. First, the flue gas treatment material of Example 4 or Comparative Example 4 was molded into granules having a particle size of about 1 mm, and the molded product was vacuum degassed at room temperature for 24 hours. Then, the molded product is filled in an adsorption column and heated to 180 ° C., and O ₂ : 12% by volume, HCl: 400% by volume, SO ₂ : 40 _{% by volume, H 2} O: 25% by volume, in the system. N ₂ : The simulated exhaust gas used as the balance was flown. Then, the simulated exhaust gas that has passed through the adsorption column is introduced into 25 mL of the collected liquid (composition: 1 w / v% hydrogen peroxide solution), and the collected liquid is exchanged every predetermined time (30 minutes) for 2 hours. Collected.
The HCl and SO ₂ concentrations in each collection liquid are quantified by an ion chromatograph method (Integration manufactured by Thermo Fisher Scientific Co., Ltd.), and the arithmetic average value of _{the HCl and SO 2 concentrations in each collection liquid is calculated.} This was defined as the acid gas concentration (volume ppm). The evaluation standard values for acid gas were 60% by volume ppm for hydrogen chloride and 30% by volume ppm for sulfur dioxide, and if it was equal to or less than the standard values, the acid gas removal performance was evaluated to be good. The results are shown in Table 2 below.

As shown in Tables 1 and 2, the flue gas treatment material of the example has both efficient removal of acid gas and suppression of elution of heavy metals such as lead as compared with the comparative example, and has both. It can be seen that the flue gas can be treated so that the level sufficiently meets the standard value of the emission. Further, it can be seen that the flue gas treatment material of each example can achieve both removal of acid gas and suppression of elution of heavy metals in flue gas at a usage amount equal to or less than that of the conventional one as compared with Comparative Example 4. In particular, by adjusting at least one of the particle size of calcium dihydrogen phosphate and the mixing ratio of calcium dihydrogen phosphate and calcium hydroxide to a suitable range, the acid gas in flue gas is efficiently discharged. It can also be seen that elution of heavy metals such as lead can be further suppressed while achieving removal.

[Evaluation of the relationship between calcium dihydrogen phosphate and acid gas neutralization performance]
In this evaluation, a model experiment was conducted on the relationship between the content of calcium dihydrogen phosphate in the flue gas treatment material and the acid gas treatment performance.
First, the behavior of the treatment performance of hydrogen chloride gas was actually evaluated by the above-mentioned method using the flue gas treatment materials of Example 4 and Comparative Example 4 at the same mass. The flue gas treatment material and the hydrogen chloride gas were brought into contact with each other, and the outlet concentration (volume ppm) of the hydrogen chloride gas at the time points of 30 minutes, 60 minutes, 90 minutes and 120 minutes was measured by the above-mentioned ion chromatograph method, respectively. The obtained data were plotted on a graph in which the vertical axis (y-axis) was the concentration of hydrogen chloride gas (volume ppm) and the horizontal axis (x-axis) was the test time (minutes). Then, linear approximation was performed for each measurement point of the example or the comparative example, and a regression line was obtained. The relational expression of each regression line was as follows.
Regression line of Example 4: y = 0.2075x (R ² = 0.9859)
-Regression line of Comparative Example 4: y = 0.0103x (R ² = 0.7208)

Next, the relationship between the slope of each regression line obtained from Example 4 and Comparative Example 4 and the content of calcium dihydrogen phosphate in the flue gas treatment material is shown, and the vertical axis (y-axis) is the slope of the regression line. The values and the horizontal axis (x-axis) were plotted on a graph with the content of calcium dihydrogen phosphate (mass%), and a linear approximation was performed to obtain a second regression line. The relational expression of the second regression line was as follows.
Second regression line: y = 0.0066x + 0.0103 (R ² = 1)

Then, from the value of the slope obtained by substituting the content of calcium dihydrogen phosphate in the smoke exhaust treatment material into the second regression line, the vertical axis (y-axis) is the outlet concentration (volume ppm) of hydrogen chloride gas, and the horizontal. Virtual line formats were obtained for each graph with the axis (x-axis) as the test time (minutes). The hypothetical linear form based on the content of calcium dihydrogen phosphate was as follows.
-Virtual line format with 10% by mass of calcium dihydrogen phosphate: y = 0.0763x
-Virtual line format with 20% by mass of calcium dihydrogen phosphate: y = 0.1423x
-Virtual line format with 40% by mass of calcium dihydrogen phosphate: y = 0.2743x
-Virtual line format with 50% by mass of calcium dihydrogen phosphate: y = 0.3403x
-Virtual line format with 70% by mass of calcium dihydrogen phosphate: y = 0.4723x
-Virtual line format with 80% by mass of calcium dihydrogen phosphate: y = 0.5383x
As the virtual line format when the content of calcium dihydrogen phosphate in the flue gas treatment material was 30% by mass, the regression line (y = 0.2075x) of Example 4 was used as it was.

Finally, in each of the above-mentioned virtual line formats, an estimated value (value of y) of the outlet concentration (volume ppm) of hydrogen chloride gas was calculated when the test time was 180 minutes (x = 180). This test time corresponds to a general interval for removing fly ash and the like accumulated in dust collecting equipment such as a bug filter. The evaluation reference value of hydrogen chloride gas in this evaluation is 60 volume ppm, and if the estimated value is equal to or less than the reference value, it is presumed that the acid gas removal performance is good. The results are shown in Table 3 below.

As shown in Table 3, if the content of calcium dihydrogen phosphate in the flue gas treatment material is less than 50% by mass, it is presumed that acid gas such as hydrogen chloride gas can be neutralized for a long period of time. ..

Claims (8)

Contains calcium dihydrogen phosphate powder and calcium hydroxide powder,
_{A smoke exhaust treatment material having a volume-based cumulative 50% particle diameter D 50} of less than 180 μm measured by the laser diffraction / scattering type particle size distribution measurement method for calcium dihydrogen phosphate. The content ratio of the calcium dihydrogen phosphate in the flue gas treatment material is 5% by mass or more and less than 50% by mass.
The smoke exhaust treatment material according to claim 1, wherein the content ratio of the calcium hydroxide in the smoke exhaust treatment material is 50% by mass or more and less than 95% by mass. A method for treating flue gas, wherein the flue gas treatment material according to claim 1 or 2 is brought into contact with flue gas containing acid gas and heavy metals. The method for treating smoke exhaust according to claim 3, wherein the powder of the smoke exhaust treatment material is blown into the flow path of the smoke exhaust to bring the smoke exhaust treatment material into contact with the smoke exhaust. The method for treating flue gas according to claim 3 or 4, wherein water is added to the flue gas treatment material brought into contact with the flue gas. A step of contacting the flue gas containing an acid gas and a solid component containing heavy metals with a calcium hydroxide powder, and then bringing the solid component into contact with calcium dihydrogen phosphate is provided.
The calcium dihydrogen phosphate is a method for treating flue gas, wherein _{the volume-based cumulative 50% particle diameter D 50} measured by a laser diffraction / scattering type particle size distribution measurement method is less than 180 μm. The method for treating flue gas according to claim 6, wherein the calcium hydroxide powder is blown into the flue gas flow path to bring the calcium hydroxide into contact with the flue gas. The method for treating flue gas according to claim 6 or 7, wherein the solid component is brought into contact with the calcium dihydrogen phosphate in the presence of water.

Images