JP2023097786A - Flue gas treatment material and flue gas treatment method - Google Patents

Abstract

To provide a flue gas treatment material and a flue gas treatment method where the reduction of the insolubilization performance of heavy metals is suppressed even when stability as a mixed powder is high and heat history in high temperature environment such as in a flue gas is undergone.SOLUTION: A flue gas containing an acidic gas and fly ash is brought into contact with a flue gas treatment material containing calcium hydroxide powders and phosphate powders at a temperature zone of 100°C or higher and 200°C or lower. The phosphate powders contain one or more kinds among ammonium dihydrogen phosphate, diammonium hydrogen phosphate and potassium dihydrogen phosphate. A ratio of the phosphate powders to the total amount of the calcium hydroxide powders and the phosphate powders is 20 mass% or higher and 70 mass% or lower.SELECTED DRAWING: Figure 1

Description

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

At waste incineration plants that incinerate municipal waste and industrial waste, the flue gas generated during waste incineration contains hydrogen chloride (HCl), sulfur oxides (SOx), and nitrogen oxides ( NOx) and other acid gases and fly ash are included. Among these, in order to reduce the concentration of acidic gas emissions into the outside air, there is a technology that blows into the flue a treatment material containing a basic calcium compound such as quicklime (CaO) or slaked lime (Ca(OH) ₂ ). Established.
In addition, fly ash in flue gas also contains heavy metals derived from garbage. Insolubilize the heavy metals so that the

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

JP-A-10-109014 JP-A-2000-061252 JP 2009-131726 A

In the final disposal site, generally, the waste is accumulated outdoors, so rainwater permeates the waste layer. Therefore, in order to collect such permeated water in one place and discharge it into a river or the like, various items regulated by the Water Pollution Control Law are controlled within the standard values. Such control items include, for example, the pH of permeated water, the concentration of heavy metals such as lead in the permeated water, and the chemical oxygen demand (COD).
Among these, in order to suppress the elution of lead into the environment, a phosphoric acid compound can be used as disclosed in the treatment materials described in Patent Documents 1 to 3, for example.

However, in the treatment materials containing slaked lime and phosphoric acid compounds described in Patent Documents 1 to 3, the stability of the mixed powder is low and deterioration occurs during storage. There is a problem that the insolubilization performance of heavy metals is lowered when it is received.

Therefore, an object of the present invention is to provide a flue gas treatment material that has high stability as a mixed powder and suppresses the deterioration of heavy metal insolubilization performance even when subjected to heat history in a high temperature environment such as in flue gas, and an exhaust gas. To provide a smoke disposal method.

As a result of intensive studies aimed at solving the above problems, the present inventors have found that the above problems can be solved by adding a given phosphate powder to calcium hydroxide powder in a given ratio. The inventors have completed the present invention.

That is, the present invention includes calcium hydroxide powder and phosphate powder, and the ratio of the phosphate powder to the total of the calcium hydroxide powder and the phosphate powder is 20% by mass or more and 70% by mass or less. and the phosphate powder contains at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and potassium dihydrogen phosphate.

In addition, the present invention is a flue gas containing acidic gas and fly ash, and a flue gas treatment material containing calcium hydroxide powder and phosphate powder, which are brought into contact in a temperature range of 100 ° C. or higher and 200 ° C. or lower. wherein the phosphate powder contains at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and potassium dihydrogen phosphate, and the calcium hydroxide powder and the phosphate Provided is a method for treating flue gas, wherein the proportion of the phosphate powder with respect to the total with the powder is 20% by mass or more and 70% by mass or less.

According to the present invention, the flue gas treatment material and flue gas that have high stability as a mixed powder and suppress the deterioration of the insolubilization performance of heavy metals even when subjected to heat history in a high temperature environment such as in flue gas. It is possible to provide a processing method for

FIG. 1 is a schematic diagram showing an overview of a waste treatment tank and the blowing position of a flue gas treatment material.

Preferred embodiments of the invention are described below. In addition, this invention is not limited to the following embodiment. In the following description, when described as "X to Y [Z]" (X and Y are arbitrary numbers and [Z] is a unit), unless otherwise specified, "X [Z] or more Y [ Z] means “less than or equal to”.

The flue gas treatment material of the present invention contains calcium hydroxide powder and phosphate powder. Since the flue gas treating material is a powdery mixture of calcium hydroxide powder and phosphate powder, it is possible to improve handling during transportation and use. A powder in the present invention refers to an aggregate of particles.

The flue gas treatment material contains calcium hydroxide. Calcium hydroxide is an acid gas containing hydrogen chloride (HCl), sulfur oxides (SOx) such as sulfur monoxide, sulfur dioxide and sulfur trioxide, and nitrogen oxides (NOx) such as nitrogen monoxide and nitrogen dioxide. can be used for the neutralization treatment of

The calcium hydroxide powder may preferably have an average particle size of 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 enhance the efficiency of contact 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, for example, pulverizing treatment using a pulverizer, pulverizing treatment, or sieving treatment.

The average particle size of calcium hydroxide particles can be measured, for example, by the following method. First, a sample to be measured is put into a laser diffraction scattering type particle size distribution analyzer (MT-3000EXII manufactured by Microtrack Bell Co., Ltd.) whose circulation path is filled with ethanol (refractive index 1.36, 25° C.), Ultrasonic waves of 40 W are applied for 3 minutes using an ultrasonic dispersing device incorporated in the apparatus to obtain a dispersion liquid, and the particle size distribution is measured. From the obtained volume-based particle size distribution chart, the volume-based cumulative 50% particle diameter _D50 is obtained. The _D50 obtained in this way is defined as the average particle size of the present invention. In the measuring apparatus described above, the particle information is set to refractive index: 1.57 (25° C.), shape: non-spherical, and transmission/non-transmission: transmission.

In the calcium hydroxide powder, the BET specific surface area of particles constituting the powder is preferably 30 m ² /g or more, more preferably 30 to 60 m ² /g, still more preferably 35 to 55 m ² /g, still more preferably 40 It may be ˜50 m ² /g. By having such a specific surface area, it is possible to enhance the efficiency of contact with the acid gas and efficiently neutralize the acid gas regardless of the type of the acid gas.

The acid gas treatment efficiency becomes more remarkable by setting the above-described particle size within a suitable range in addition to the BET specific surface area. In addition, the use of calcium hydroxide powder having the above-mentioned BET specific surface area is useful for neutralizing acidic gas when performing flue gas treatment by a dry method such as blowing a flue gas treatment material into a flue or the like. This is advantageous in that efficiency can be improved.

The BET specific surface area can be measured by the BET one-point method, for example, according to JIS Z8830:2013. Calcium hydroxide powder having such a BET specific surface area may be, for example, a commercially available product, or may be obtained by the methods described in JP-A-2005-350343 and JP-A-2008-290940. can.

In the calcium hydroxide powder, particles constituting the powder preferably have pores, and more preferably have a specific pore volume. Specifically, the total pore volume in the pore size range of 20 to 1000 Å of the calcium hydroxide powder is preferably 0.10 to 0.30 mL/g, more preferably 0.15 to 0.25 mL/g, and further Preferably, it may be 0.20-0.25 mL/g. Since the calcium hydroxide particles have pores and the pore volume is within the above range, a large amount of acid gas is adsorbed in the pores, and the acid gas is more efficiently removed regardless of the type of acid gas. can be neutralized to The acid gas treatment efficiency becomes more remarkable by setting the above-mentioned particle size and BET specific surface area to the appropriate ranges in addition to the preferable range of the pore volume. Further, the use of the calcium hydroxide powder having the above-described pore volume is advantageous when performing flue gas treatment by a dry method such as blowing the flue gas treatment material into a flue or the like.

Calcium hydroxide powder having such pores and pore volume may be, for example, a commercially available product, or by the method described in JP-A-2005-350343 or JP-A-2008-290940. Obtainable.

The pore volume in 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 was subjected to vacuum degassing treatment at a heat treatment temperature of 105 ° C. for 8 hours, and then using a measurement device (Microtrac Bell Co., Ltd., Belsorp-max), liquid nitrogen. A desorption isotherm is obtained, which is the relationship between the relative pressure at which nitrogen desorbs from the sample at temperature and the amount of nitrogen adsorbed. Then, by the BJH method, the total pore volume (mL/g) in the pore diameter range of 20 to 1000 Å is calculated from the desorption isotherm.

The apparent specific gravity of the calcium hydroxide powder is preferably 0.20 to 0.50 g/cm ³ , more preferably 0.25 to 0.45 g/cm ³ in loose specific gravity. Further, the compacted specific gravity may be preferably 0.40 to 0.70 g/cm ³ , more preferably 0.45 to 0.68 g/cm ³ . Due to having such a specific gravity, the flue gas treatment can be efficiently performed by a dry method such as blowing the flue gas treatment material into a flue or the like.

The loose specific gravity and hardened specific gravity in the apparent specific gravity can be measured, for example, according to JIS Z8807:2012 "Method for measuring density and specific gravity of solid". Calcium hydroxide powder having such an apparent specific gravity can be obtained, for example, by the methods described in JP-A-2005-350343 and JP-A-2008-290940.

The flue treatment material includes phosphate powder. Phosphate powder is any one of ammonium dihydrogen phosphate ( _{NH4H2PO4 ) ,} diammonium hydrogen _phosphate (( _NH4 ) _2HPO4 ), and _potassium dihydrogen phosphate ( _KH2PO4 ) It preferably contains at least one of ammonium dihydrogen phosphate and potassium dihydrogen phosphate, and more preferably contains ammonium dihydrogen phosphate. Although these phosphates can be used in the form of hydrates, the anhydrous form is preferred from the viewpoint of the content of the active ingredient per weight. By using such a phosphate powder, it is stable as a mixed powder with calcium hydroxide, and even when subjected to heat history, the deterioration of insolubilization performance is small, and sufficient insolubilization performance can be exhibited.

The phosphate powder may preferably have an average particle size of less than 5 mm, more preferably 1 μm to 3 mm, and still more preferably 10 μm to 1 mm. By having such a particle size, it is possible to prevent the segregation of materials as a mixed powder and exhibit stable performance. Phosphate powder having such a particle size may be used, for example, if it is available as a distribution product having a suitable particle size, or a phosphoric acid powder having a coarse particle size A pulverized material obtained by pulverizing salt may be used.

The average particle size of the phosphate powder can be measured, for example, by the following method. First, a sample to be measured is put into a laser diffraction scattering type particle size distribution analyzer (MT-3000EXII manufactured by Microtrack Bell Co., Ltd.) whose circulation path is filled with ethanol (refractive index 1.36, 25° C.), Ultrasonic waves of 40 W are applied for 3 minutes using an ultrasonic dispersing device incorporated in the apparatus to obtain a dispersion liquid, and the particle size distribution is measured. From the obtained volume-based particle size distribution chart, the volume-based cumulative 50% particle diameter _D50 is obtained. The _D50 obtained in this way is defined as the particle size of the present invention. In the measuring apparatus described above, particle information is set to refractive index: 1.81 (25° C.), shape: non-spherical, and transmission/non-transmission: transmission. For the refractive index of the phosphate, the same value was set for each phosphate by adopting the recommended value described in the device manual for the case where the refractive index data of the target substance was not available.

The content of various phosphate powders in the exhaust gas treatment material is 20 to 70% by mass, preferably 26 to 60% by mass, more preferably 30 to 45% by mass in terms of anhydride. With such a content ratio, the performance of insolubilizing heavy metals such as lead in flue gas can be sufficiently exhibited.

The content of calcium hydroxide powder in the exhaust gas treatment material is preferably 30 to less than 80% by mass, more preferably 40 to 74% by mass, and even more preferably 55 to 70% by mass. With such a content ratio, it is possible to sufficiently exhibit the performance of treating the oxidizing gas in the flue gas.

In particular, by setting both the content ratio of various phosphate powders and the content ratio of calcium hydroxide powder in the flue gas treatment material to the ranges described above, the insolubilization performance of heavy metals such as lead in flue gas and This is advantageous in that the oxidizing gas treatment performance can be exhibited at a high level in a well-balanced manner.

The flue gas treatment material of the present invention may further contain additives. Examples of additives that can be used include porous materials such as activated carbon, activated clay, and zeolite, metal salts of silicic acid such as orthosilicic acid and metasilicic acid, and hardening components such as cement powder and calcium aluminate. In addition to the additives described above, impurities derived from raw materials may also be contained within a range that does not impair the effects of the present invention. The total amount of calcium hydroxide powder and phosphate powder in terms of anhydride relative to 100 parts by mass of the flue gas treatment material may be 85 parts by mass or more, preferably 90 parts by mass or more, and 95 parts by mass or more. more preferred. With such a composition, the effects of the present invention can be efficiently exhibited, and the amount of the flue gas treatment material used can be reduced.

It is preferable to conduct a preliminary test and determine the presence or absence of addition of various additives and the amount to be mixed based on the results of the test.

In the exhaust gas treatment material of the present invention, for example, if necessary, at least one of calcium hydroxide and phosphate powders is subjected to particle size control treatment such as pulverization or crushing in advance, It can be produced by mixing calcium hydroxide powder and phosphate powder. As a device for mixing both powders, a mixing device commonly used in the technical field can be used, for example, a ribbon mixer, a paddle mixer, a Nauta mixer, or the like can be used.

The flue gas treating material of the present invention can be used in a method of treating flue gas by contacting the flue gas with the flue gas treating material. In this method, the flue gas containing acid gas and heavy metals is brought into contact with the flue gas treatment material, and both the acid gas and heavy metals in the flue gas can be neutralized and insolubilized. Typically, flue gas is either gas alone, including acid gases, or a mixture of such gases and particulate fly ash. Such smoke is generated, for example, at a municipal waste incineration plant, an industrial waste incineration plant, or a coal-fired thermal power plant. Heavy metals in flue gas are mainly contained in fly ash, which is a solid component in flue gas. Heavy metals are at least one of arsenic, hexavalent chromium, lead and selenium. contains at least lead as

The method of contacting the flue gas treatment material with the flue gas is, for example, by passing the flue gas through a container containing the flue gas treatment material, or by blowing the flue gas treatment material into the flow path (flue) of the flue gas. can be done by

The amount of flue gas treatment material added per 1 ^m3 of flue gas can be changed as appropriate according to the type and amount of incinerators in incinerators and thermal power plants. 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 , still more preferably 30 to 90 g/m ³ . be. The volume of flue gas is the value at 0°C and 1 atm.

Further, when the mass of fly ash is 100% by mass, the mass ratio of the phosphate powder to the fly ash supplied by the flue gas treatment material is preferably 7.5 to 60% by mass, more preferably 13. .5 to 50% by mass, more preferably 15 to 30% by mass. By adjusting the addition ratio to achieve such a ratio, insolubilization of heavy metals such as lead in fly ash can be achieved more efficiently.

An example of a method for treating flue gas using the flue gas treating material of the present invention will be described below with reference to FIG. FIG. 1 shows a schematic diagram of the equipment of a waste incineration plant. This method preferably employs a dry method in which the powder of the flue gas treatment material is directly blown into the flow path of the flue gas. Arrows in FIG. 1 indicate the direction of flow of flue gas, flue gas, and flue gas treating material.

As facilities of the garbage incineration plant 10, typically, a garbage pit 20 for accumulating municipal garbage and industrial waste (hereinafter also simply referred to as "garbage") collected by a collection vehicle, and a garbage pit 20 An incinerator 30 for incinerating the waste accumulated in the incinerator 30, a waste heat boiler 40 for recovering heat from the high temperature flue gas generated by the incineration of the waste in the incinerator 30, a cooling tower 50 for cooling the flue gas, a cooled It is equipped with a dust collection facility 60 such as a bag filter for collecting fly ash in exhausted smoke, 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 collection equipment 60, and between the dust collection equipment 60 and the chimney 70, the second They are connected by a first flow path 11, a second flow path 12, a third flow path 13, and a fourth flow path 14, respectively, and communicate with each other so that exhaust smoke can flow through them.

In addition to this, a processing material supply unit 100 is provided so that the flue gas processing material and the flue gas can come into contact with each other. A processing material supply unit 100 shown in FIG. It is configured so that the flue gas flowing inside can come into contact with each other.

In the refuse incineration plant 10, first, the refuse accumulated in the refuse pit 20 is supplied to the incinerator 30 together with air using transfer equipment such as a crane, and the refuse is incinerated. In the incinerator 30, incineration is performed at a temperature of approximately 800 to 1000° C., and main ash and high-temperature flue gas are generated as the refuse is incinerated. Bottom ash is collected separately and either disposed of at a final disposal site or reused as a raw material for other products. In addition, the generated flue gas contains acid gas, fly ash containing heavy metals such as lead, chlorides, silicon compounds, etc. due to the raw materials of the waste. The high-temperature flue gas passes through the first passage 11, the waste heat boiler 40, the second passage 12 and the cooling tower 50 and is rapidly cooled to about 300.degree. The flue gas after cooling contains acid gas as a gaseous component and fly ash scattered together with the gas as a solid component. After cooling, the flue gas is cooled to 200°C or less, generally 100°C to 200°C, preferably 140°C to 200°C, from the viewpoint of suppressing dioxin resynthesis from components in the flue gas. After cooling, the flue gas flows to the third flow path 13 side. Note that the preferable lower limit of 100° C. is determined from the viewpoint of preventing dew condensation in the third flow path 13 and the like.

Next, the flue gas treating material and the cooled flue gas are brought into contact with each other. The contact method may be a method in which a powdery flue gas treatment material is held in the flue gas channel in advance and the flue gas is allowed to pass through the flue gas treatment material. A method of blowing the treatment material may be used. Among these, it is preferable to blow the flue gas treating material of the present invention from the treating material supply unit 100 into the third flow path 13 through which the flue gas flows, from the viewpoint of enhancing the convenience of the flue gas treatment.

Since the flue gas treatment material contains calcium hydroxide, the calcium hydroxide is brought into contact with an acid gas containing hydrogen chloride or the like to form a neutral calcium salt such as calcium chloride through a neutralization reaction, resulting in flue gas. Remove the acid gas inside. The generated neutral calcium salts and unreacted flue gas treatment materials flow through the third flow path 13 in the form of solids such as powder. Exhaust gas is produced by removing solid components from smoke. Solid components such as flue gas treatment materials, various salts, and fly ash collected by the dust collection equipment 60 are stored in the fly ash accumulation unit 61 as collected ash. At this time, in the fly ash accumulation unit 61, water may be added to the collected ash by spraying or the like for the purpose of preventing the accumulated powder from generating dust, and the collected ash may be brought into contact with the water. The amount of water sprayed is generally 20 to 40% by mass with respect to the total amount of accumulated powder.

The collected ash accumulated in the fly ash accumulation unit 61 is cured for a certain period of time, for example, one day or more, and then transferred to a final disposal site for disposal. Then, the exhaust gas that has passed through the dust collection equipment 60 may be passed through a harmful substance removal equipment, a denitrification equipment, or the like as necessary to remove acid gases and harmful substances remaining in the exhaust gas. After that, the exhaust gas is discharged into the atmosphere from the chimney 70 via the fourth flow path 14 .

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 treated collected ash becomes strongly alkaline. Heavy metals in flue gas, especially lead, are amphoteric metal elements, and the content in fly ash is high, so when lead in fly ash is exposed to strong alkaline conditions, the amount of lead eluted into water increases. easily change to For this reason, conventionally, typically, for example, the flue gas is passed through a dust collection facility such as the above-described fly ash accumulation unit 61 to collect the fly ash in the flue gas, and then the collected fly ash is collected. An organic chelating agent is mixed with the contained powder to insolubilize heavy metals such as lead, and the fly ash after the insolubilization treatment is disposed of as waste at a disposal site.

Specifically, solid waste including 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 the waste is collected in the above-mentioned wastewater treatment facility. This results in enormous processing costs over the long term. If the organic chelating agent is not used, insolubilization of heavy metals such as lead cannot be achieved, and the wastewater treatment cost from the treatment plant cannot be reduced. In the case of using an organic chelating material, heavy metals such as lead can be insolubilized to some extent, but the organic chelating material decomposes at the disposal site, and the COD of the leachate from the disposal site becomes excessively high. However, it is difficult to reduce the cost of treating wastewater generated from treatment plants.

In this regard, by using the flue gas treatment material of the present invention containing an inorganic compound for flue gas treatment, the removal of acidic gases in the flue gas and the suppression of the emission of heavy metals such as lead can be achieved organically. Both can be achieved without using a separate chelating material.

In addition to this, the fly ash after treatment also has the advantage of reducing the adverse effects on the water environment caused by heavy metals and organic substances, and the cost of treating wastewater generated from the treatment plant can also be reduced. . Further, since each phosphate used in the present invention has little interaction with calcium hydroxide, even if it is used in combination with calcium hydroxide, deterioration can be advantageously reduced.

Thus, by using the flue gas treating material of the present invention, it is possible to efficiently remove acidic gases in the flue gas and to insolubilize heavy metals in the fly ash.

EXAMPLES The present invention will be described in more detail below with reference to examples. The scope of the invention is not limited to such examples.

[Stability test]
Exhaust gas treatment materials (examples) and mixed powders (comparative examples) were evaluated for deterioration during storage. 10 g of the flue gas treatment material containing calcium hydroxide: phosphate at a ratio of 7:3 was placed in a deep petri dish and stored in a constant temperature and humidity chamber at 35°C and 70% RH. , 24 hours, and 48 hours later, and the presence or absence of heterophase formation after 48 hours were evaluated. Calcium hydroxide and phosphate used were the same as those described in "Preparation of simulated ash" below.
For the evaluation of heterophase formation, the results of XRD measurement in the range of 2θ=5 to 50° under the following conditions were used. The presence or absence of detection of a hetero-phase peak in the XRD pattern was confirmed as a hetero-phase formed during storage of the detected peaks other than the blended raw material composition.

(XRD measurement conditions)
Apparatus: X-ray diffraction apparatus (NEW D8 ADVANCE manufactured by Bruker AXS)
X-ray source: CuKα (using Ni filter), tube voltage: 40 kV, tube current: 40 mA, detector: one-dimensional semiconductor high-speed detector LynxEye, incident/receiving slit: 0.30 degrees, step width: 0.02 degrees, Counting time: 1 second/step

The test conditions were set assuming continuous exposure to a harsh environment within the assumed storage and distribution environment. As a result, it is possible to confirm the effects of deterioration and the like in a short period of time compared to the case of storing under favorable conditions such as room temperature.

In the mixed powder containing dipotassium hydrogen phosphate of Comparative Example 1, a large weight increase was confirmed after 24 hours. A weight increase was also confirmed in the blended mixed powder. Such samples are likely to cause problems such as increased adhesion due to moisture absorption and caking between particles or between particles and the inner wall of the device, resulting in significant deterioration in handleability. Further, different phases were confirmed in the mixed powders containing dipotassium hydrogen phosphate and monocalcium phosphate of Comparative Examples 1 and 2, respectively. With such a sample, the content of the active ingredient in the flue gas treatment material decreases during storage and distribution, and there is concern that the amount used will increase due to deterioration in performance.

It should be noted that the flue gas treating material containing the phosphate of Examples 1-3, which is the present invention, does not exhibit a significant increase in weight, and no formation of a different phase is observed. By using such a phosphate, it is possible to sufficiently insolubilize heavy metals such as lead, and to stably suppress the emission of the heavy metals.

[Evaluation of insolubilization performance of heavy metals]
(Preparation of simulated ash)
Using lead as a heavy metal, the insolubilization performance of the flue gas treatment material (example) and mixed powder (comparative example) was evaluated. First, assuming collected ash collected from an ash accumulation part such as a garbage incineration facility, silica source, calcium hydroxide, calcium chloride, lead chloride, and phosphate powder used in each formulation are mixed, Simulated ash containing lead was prepared.
(simulated ash)
Silica source: fly ash (5 types of JIS test powder 1)
Calcium hydroxide: manufactured by Ube Materials, Calbreed SII average particle size (D ₅₀ ): 6.5 μm, BET specific surface area: 45 m ² /g, total pore volume in the pore size range of 20 to 1000 Å: 0.22 mL/ g, apparent specific gravity (loose specific gravity): 0.36 g/cm ³ , apparent specific gravity (solid specific gravity) 0.65 g/cm ³
Calcium chloride, lead chloride: commercial products Various phosphates: commercial products As a reproduction of unreacted calcium hydroxide contained in the collected ash when performing acid gas treatment using calcium hydroxide, hydration with simulated ash The content of calcium was set to 40% of unreacted ratio (number of moles of calcium hydroxide/(number of moles of calcium hydroxide+number of moles of calcium chloride)).

[Insolubilization performance evaluation]
After mixing the simulated ash produced by the above procedure with water, it was cured (still at room temperature) for 1 day. Water was 20% by mass with respect to the total amount of simulated ash. After that, the cured simulated ash was heated at 180° C. for 3 hours in a flow of moist air having a moisture content of about 40% by volume at a flow rate of 500 ml/min. The heating conditions assume the environment of the dust collection facility described above. A lead elution test was conducted in accordance with the method stipulated in the test method for metals, etc. contained in industrial waste (Environment Agency Notification No. 13, February 1973, hereinafter, Environment Agency Notification No. 13), and lead ion concentration (mg/L) and pH were measured. In addition, when no phosphate was used in the formulation of simulated ash, the results in the Environment Agency Notification No. 13 test were a lead ion concentration of 10 mg/L and a pH of 12.

The evaluation standard value of the lead ion concentration was set to 0.3 mg/L, and the lead insolubilization performance was evaluated to be good if the standard value was less than the standard value. A lower lead ion concentration indicates higher lead insolubilization performance. The results are shown in Table 2 below. The phosphate ratio of each flue gas treatment material shown in Table 2 is the ratio of the amount of phosphate compounded to the sum of the amount of calcium hydroxide equivalent and the amount of phosphate compounded in the simulated ash.

When comparing the flue gas treatment materials and mixed powders with a phosphate ratio of 28% by weight in Examples 5, 8, 10 and Comparative Examples 7-10, the exhaust gas containing the three phosphates of the present invention Although the target value (0.3 mg/L) was sufficiently satisfied for the smoke treatment material even after heating, the target value was not reached for the mixed powder containing other phosphates, especially in Comparative Examples 9 and 10. The mixed powder containing sodium dihydrogen phosphate and magnesium hydrogen phosphate is significantly inferior in insolubilization performance.

From the relationship between the insolubilization performance and the phosphate ratio of the smoke exhaust treatment material and mixed powder containing ammonium dihydrogen phosphate in Examples 4-7 and Comparative Example 5, the phosphate ratio within the range specified in the present invention: Sufficient insolubilization is achieved. In addition, the flue gas treatment material with a phosphate ratio of 61% by weight of Example 7 has an acidic pH after insolubilization, but lead is not eluted, so it is resistant to pH fluctuations. It can be seen that insolubilization is achieved.

From the above results, by adjusting the blending of calcium hydroxide and phosphate within the range specified in the present invention, the mixed powder is stable, and even when subjected to heat history, stable and high performance can be achieved. It can be confirmed that a smoke-exhaust treatment material that can be exhibited can be obtained.

[Evaluation of acid gas removal performance]
Using calcium hydroxide alone (reference example) and a flue gas treatment material (Example 12) that is a mixed powder of calcium hydroxide and phosphate, acid gas removal performance was evaluated. The specific procedure is as follows. First, 10 g of calcium hydroxide and 10 g of calcium hydroxide and ammonium dihydrogen phosphate (calcium hydroxide: ammonium dihydrogen phosphate = 70:30) were granulated into granules having a particle size of about 1 mm. After molding, the molded product was subjected to vacuum deaeration treatment at room temperature for 24 hours. After that, the molded product is packed in an adsorption column and heated to 180° C., and O ₂ : 10% by volume, HCl: 1000% by volume, SO ₂ : 100% by volume, H ₂ O: 15% by volume, A simulated exhaust gas with CO ₂ : 10% by volume and N ₂ : balance was supplied at SV 50000/h. Then, the simulated exhaust gas that passed through the adsorption column was introduced into a collection liquid (composition: 0.3% hydrogen peroxide solution) and collected for 1 hour.

Each collected liquid was made up to 250 ml, the HCl and _SO2 concentrations in the collected liquid were quantified by ion chromatography, the arithmetic mean of the HCl and SO2 concentrations in the collected liquid was calculated, and the concentration of HCl and _SO2 in the collected liquid was calculated. It was used as the acidic gas concentration in the simulated exhaust gas afterward. Table 3 summarizes the acid gas treatment performance of the flue gas treatment material, with the amount of change in the acid gas concentration in the simulated flue gas before and after passing through the column as the acid gas removal rate with respect to the acid gas concentration in the supplied simulated flue gas. The criteria for evaluating the acid gas removal performance are that it exhibits a removal performance of 70% or more, which is equivalent to calcium hydroxide, with respect to the gas treatment performance of the flue gas treatment material composed only of calcium hydroxide as a reference example. bottom.

The flue gas treatment material of Example 12 containing 30% by mass of ammonium dihydrogen phosphate exhibits acid gas treatment performance higher than that expected from the content of calcium hydroxide compared to the flue gas treatment material of the reference example. bottom.

Claims (4)

comprising calcium hydroxide powder and phosphate powder;
The ratio of the phosphate powder to the total of the calcium hydroxide powder and the phosphate powder is 20% by mass or more and 70% by mass or less,
A smoke exhaust treatment material, wherein the phosphate powder contains at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and potassium dihydrogen phosphate. 2. The flue gas treating material according to claim 1, wherein the total amount of said calcium hydroxide powder and said phosphate powder is 85 parts by mass or more when the total amount of said flue gas treating material is 100 parts by mass. A flue gas treatment method in which a flue gas containing acid gas and fly ash is brought into contact with a flue gas treatment material containing calcium hydroxide powder and phosphate powder in a temperature range of 100° C. or higher and 200° C. or lower,
The phosphate powder contains at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and potassium dihydrogen phosphate,
A method for treating flue gas, wherein the ratio of the phosphate powder to the total of the calcium hydroxide powder and the phosphate powder is 20% by mass or more and 70% by mass or less. The flue gas according to claim 3, wherein 10 parts by mass or more and 40 parts by mass or less of water is added to the mixture of the fly ash collected from the flue gas and the flue gas treatment material with respect to 100 parts by mass of the mixture. How to handle.

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