JP7634154B2 - Method and equipment for desalination of chlorine-containing ash - Google Patents

Description

The present invention relates to a method and desalination equipment for efficiently desalting chlorine-containing ash without using chemical solutions.

Incident ash (bottom ash, fly ash, cinders, soot, etc.) generated by incineration of general waste and industrial waste, incineration ash disposed of in landfills at final disposal sites, and clinker dust generated from cement plants are being reused as cement raw materials. However, since these incineration ashes contain about 10% chlorine, in order to recycle the above-mentioned various incineration ashes and clinker dusts that contain chlorine (these are called chlorine-containing ash), they need to be desalted to a degree appropriate to their intended use.

Regarding the desalting of the chlorine-containing ash, most of the chlorine compounds contained in the chlorine-containing ash are _water -soluble and can be desalted by washing with water, but some of the chlorine compounds form Friedel's salt ( _{3CaO.Al2O3.CaCl2.10H2O} ) which is poorly soluble in water, and therefore cannot be desalted sufficiently by washing with water alone. As a means for removing such poorly _water - _soluble chlorine compounds, a method is known in which an acid is added to the chlorine-containing ash slurry to lower the pH and desalt the slurry (Patent Document 1). However, the method of adding an acid dissolves calcium together with chlorine, so that when calcium is recovered after desalting, a separation and recovery process is required, which increases the workload. Furthermore, the use of acidic chemicals such as hydrochloric acid and sulfuric acid increases the cost of chemicals and requires equipment with sufficient corrosion resistance.

Known desalination methods include a method of washing chlorine-containing ash by adding water containing carbonate (Patent Document 2) and a method of washing chlorine-containing ash by blowing carbon dioxide gas into a water slurry (Patent Document 3). In this method, Friedel's salt is decomposed by carbonate or carbon dioxide gas, so that desalted washed ash can be obtained. However, part of the calcium becomes calcium carbonate (CaCO ₃ , CaMg(CO ₃ ) ₂ , etc.) which is poorly soluble in water, and this is recovered as a solid content together with the washed ash by solid-liquid separation after washing. If this washed ash containing calcium carbonate is used as a cement raw material, a large amount of CO ₂ gas is generated in the cement manufacturing process, which is not in line with the environmental demand for CO ₂ reduction.

Patent No. 5561326 JP 2006-326462 A Patent No. 3924822

The present invention solves the above problems with conventional desalting methods for chlorine-containing ash, and provides a desalting method and desalting equipment that efficiently desalts chlorine-containing ash without using chemicals and easily recovers washing residues that contain calcium.

The present invention provides a method and equipment for desalting chlorine-containing ash that solves the above problems by using the following configurations.
[1] A method for desalting chlorine-containing ash, comprising: a water-washing step of forming chlorine-containing ash (raw ash) into a water slurry and desalting and washing it; a water-washed ash recovery step of performing solid-liquid separation of the washed ash slurry after water washing to recover the washed ash; a hydrothermal treatment step of forming the recovered washed ash into a water slurry and subjecting it to hydrothermal treatment to promote desalting; and a desalted ash recovery step of performing solid-liquid separation of the desalted ash slurry after hydrothermal treatment to recover the desalted ash, wherein the washed ash from which 80% or more of the chlorine in the raw ash has been desalted by the water-washing step is treated in the hydrothermal treatment under high temperatures and pressures of 150°C to 250°C and 0.4 MPa to 4.0 MPa to decompose sparingly soluble chlorine compounds and promote desalting, while calcium remains in the desalted ash and is recovered.
[2] A method for desalting chlorine-containing ash as described in [1] above, in which 99.5% to 99.8% of the chlorine in the raw ash is removed by the water washing step and the hydrothermal treatment step, while 80% to 85% of the calcium in the raw ash is recovered by remaining in the desalted ash.
[3] A desalting system for chlorine-containing ash, comprising: a washing tank for turning chlorine-containing ash (raw ash) into a water slurry, stirring and washing it to desalt 80% or more of the chlorine in the raw ash; a water-washed ash separation means for subjecting the water-washed ash slurry sent from the washing tank to solid-liquid separation and recovering the water-washed ash; a hydrothermal treatment system for adding water to the recovered water-washed ash and treating it under high temperature and high pressure of 150°C or more and 250°C or less and 0.4 MPa to 4.0 MPa ; and a desalted ash separation means for subjecting the desalted ash slurry sent from the hydrothermal treatment system to solid-liquid separation and recovering the desalted ash, wherein the chlorine in the raw ash is desalted by the water washing and hydrothermal treatment, while calcium is left in the desalted ash and recovered.

[Specific explanation]
The desalination method of the present invention will be specifically described. In the following, % regarding concentration and the like is % by mass.
The present invention relates to a method and equipment for desalting chlorine-containing ash, which comprises a water-washing step of forming chlorine-containing ash (raw ash) into a water slurry and desalting and washing it, a water-washed ash recovery step of performing solid-liquid separation of the washed ash slurry after water washing to recover the washed ash, a hydrothermal treatment step of forming the recovered washed ash into a water slurry and subjecting it to hydrothermal treatment to promote desalting, and a desalted ash recovery step of performing solid-liquid separation of the desalted ash slurry after hydrothermal treatment to recover the desalted ash, wherein the washed ash from which 80% or more of the chlorine in the raw ash has been desalted by the water-washing step is treated in the hydrothermal treatment under high temperatures and pressures of 150° C. to 250° C. and 0.4 MPa to 4.0 MPa to decompose sparingly soluble chlorine compounds and advance desalting, while calcium remains in the desalted ash and is recovered.
A schematic process diagram of the present invention is shown in FIG. 1, and an example of the equipment flow is shown in FIG.

Water washing process <br/>Water is added to the chlorine-containing ash (raw ash) to make raw ash slurry, which is then stirred and washed to dissolve chlorine compounds that are easily soluble in water (NaCl, KCl, _CaCl2 , CaClOH, etc.). This water washing washes away most of the chlorine contained in the chlorine-containing ash. By first desalting and washing the chlorine-containing ash with water, the burden on the subsequent hydrothermal treatment can be reduced, and chlorine corrosion of the hydrothermal treatment equipment can be suppressed. In addition, the raw ash can be desalted and washed efficiently by crushing it before washing with water. For example, a vibration mill or a hammer mill can be used as a crushing device. Crushing and washing with water can also be performed simultaneously.

The liquid-solid ratio of the raw ash slurry is preferably 2 to 20 (liquid:solid = 2:1 to 10:1), and more preferably 3 to 10 (liquid:solid = 3:1 to 10:1). If the liquid-solid ratio is less than 2, the amount of liquid is too small, resulting in insufficient washing, and the slurry concentration becomes high, causing severe wear on the pipes, pumps, etc. On the other hand, if the liquid-solid ratio exceeds 20, the amount of wastewater generated increases, increasing the burden on wastewater treatment. If the liquid-solid ratio is around 3 to 10, sufficient washing can be achieved and the desalination effect can be improved.

It is sufficient if approximately 80% or more of the chlorine in the raw ash is desalted by washing with water. For example, by adding 100 mL of pure water to 10 g of raw ash to make a water slurry and stirring for 5 to 30 minutes, approximately 80% of the chlorine in the raw ash can be removed. In addition, in continuous desalting treatment, the electrical conductivity of the water slurry can be measured to grasp the desalting state, and the water washing can be terminated when approximately 80% of the chlorine in the raw ash has been removed.

Washed ash recovery process <br/>After washing with water, the raw ash slurry is subjected to solid-liquid separation to recover washed ash. As a solid-liquid separation means, a filter press, a vacuum belt filter, a centrifugal dehydrator, etc. can be used. The washed ash cake separated into solid and liquid by the filter press can be more fully desalted by passing it through and washing it with washing water. In addition, the water content of the washed ash cake is low at 25 to 40%, and since there is little excess water, the weight is reduced and handling is improved, which is preferable.

The wastewater from the water washing process can be discharged after being properly treated in a drainage facility. In addition, the wastewater generated during the through-washing of the filter press has a low chlorine concentration, so it can be recycled and reused as washing water for the water washing process.

Hydrothermal treatment process <br/> Water is added to the recovered water-washed ash to make a water slurry, which is then heated to 100°C or higher for hydrothermal treatment, or subcritical water of 100°C or higher is added to the water-washed ash for hydrothermal treatment. This hydrothermal treatment decomposes and dissolves poorly water-soluble chlorine compounds. The heating temperature is preferably 100°C to 250°C, more preferably 150°C to 200°C. When an autoclave is used, the inside of the vessel is subjected to high temperatures and high pressures of 0.1 MPa to 4.0 MPa at 100°C to 250°C, and 0.4 MPa to 1.5 MPa at 150°C to 200°C, which promotes the decomposition of poorly water-soluble chlorine compounds. Desalination does not proceed sufficiently below 100°C. If the temperature exceeds 250°C, the inside of the vessel is subjected to high pressures of over 4 MPa, and the equipment costs become high in order to maintain pressure resistance. The hydrothermal treatment time may be about 20 minutes to 2 hours. This hydrothermal treatment makes it possible to remove about 99.5% to about 99.8% of the chlorine contained in the raw ash, making it possible to recover desalted ash with a residual chlorine content of about 0.2% to about 0.5%.

As a hydrothermal treatment device, a batch autoclave or a continuous tube reactor can be used. Desalination can be performed more efficiently by performing hydrothermal treatment while stirring and washing.

Hydrothermal treatment allows for a high degree of desalting without the use of chemicals such as hydrochloric acid, reducing chemical costs. In addition, compared to the method of decomposing and eluting poorly water-soluble chlorine compounds by introducing carbonate ions, the recovered desalted ash contains less carbonate, so when the desalted ash is used as a raw material for cement production, the amount of _CO2 gas generated can be reduced, meeting the demand for low carbonization.

Desalted ash recovery process <br/>The desalted ash slurry after hydrothermal treatment is subjected to solid-liquid separation to recover the desalted ash. As a solid-liquid separation means, a filter press, a vacuum belt filter, a centrifugal dehydrator, etc. can be used. As in the water-washed ash recovery process, the washed ash cake separated into solid and liquid by the filter press can be more fully desalted by passing it through and washing it with washing water. In addition, the water content of the washed ash cake is low at 25 to 40%, and since there is little excess water, the weight is reduced and handling is improved, which is preferable. Since the separated wastewater has a low chlorine concentration, it can be reused as washing water for the water-washing process.

The chlorine in the desalted ash is desalted to a low concentration (for example, about 0.2% to about 0.5%). On the other hand, since about 80% to 85% of the calcium contained in the raw ash is contained in the desalted ash, the recovered desalted ash can be used as a cement raw material.

Desalination Equipment An example of equipment for carrying out the desalination method of the present invention is shown in Figure 2. The desalination equipment shown in the figure includes a vibration mill 10 for crushing chlorine-containing ash, an agitation washing tank 20 for washing the crushed chlorine-containing ash, a filter press (washed ash separation means) 30 for performing solid-liquid separation of the washed ash slurry sent from the agitation washing tank 20, a wastewater treatment equipment 40 for treating the wastewater from the filter press 30, a hydrothermal treatment equipment 50 such as an autoclave or tube reactor for hydrothermally treating the washed ash recovered from the filter press 30, and a filter press (demineralized washed ash separation means) 60 for performing solid-liquid separation of the desalted ash slurry sent from the hydrothermal treatment equipment 50.

The chlorine-containing ash is pulverized together with washing water in a vibration mill 10 to form raw ash slurry. This raw ash slurry is stirred and washed in a stirring and washing tank 20 to form a water-washed ash slurry. This water washing removes most of the water-soluble chlorine compounds. The water-washed ash slurry is then sent to a filter press 30 for solid-liquid separation, and the resulting wastewater is sent to a wastewater treatment facility 40, where it is treated and then discharged outside the system, or returned to the vibration mill 10 as washing water.

On the other hand, the water-washed ash recovered from the filter press 30 is sent to the hydrothermal treatment equipment 50, where washing water is added, and the slurry is heated to 150°C to 250°C, and then hydrothermally treated at high temperature and high pressure of 0.4 MPa to 4.0 MPa in a sealed container such as an autoclave. This hydrothermal treatment causes poorly water-soluble chlorine compounds to decompose and dissolve, forming a desalted ash slurry. This desalted ash slurry is separated into solid and liquid by the filter press 60, and the desalted ash is recovered. This desalted ash has a low chlorine concentration and contains most of the calcium content of the raw ash, so it is sent to a cement facility 70 or the like outside the system. On the other hand, the wastewater separated from the desalted ash is sent to the wastewater treatment equipment 40 and discharged outside the system, or a part of it is returned to the vibration mill 10 as washing water.

In the desalting method of the present invention, the water-washed ash is subjected to hydrothermal treatment to decompose and dissolve chlorine compounds that are poorly soluble in water, so desalting can be promoted without using chemicals such as acids or alkalis, and desalted ash with a low chlorine concentration can be recovered.

The desalination method of the present invention can achieve a high level of desalination without using chemicals, which reduces chemical costs. In addition, compared to methods that use carbonate ions to decompose and elute poorly water-soluble chlorine compounds, the recovered desalted ash contains less carbonates, so when used as a cement raw material, it can meet the demand for low carbonization in the cement manufacturing process.

FIG. 1 is a schematic process diagram showing an example of a desalting method of the present invention. FIG. 2 is an equipment flow diagram showing an example of a desalination equipment of the present invention.

Examples of the present invention will be described below.
The chlorine concentration of the desalted ash was measured by dissolving the desalted ash in acid and measuring the chlorine concentration in the solution by coulometric titration. The Ca concentration was measured by X-ray fluorescence analysis (XRF).

[Example]
Chlorine-containing ash (raw ash: Cl concentration 14.7%, Ca concentration 21.2%) was dried at 105°C, sieved to 1 mm or less, and 10 g of the ash was used. This was placed in a beaker, and 100 mL of water was added to make a raw ash slurry with a liquid-solid ratio of 10. This raw ash slurry was stirred for 15 minutes to wash with water. The washed ash slurry after washing was filtered, and the collected washed ash was placed in an autoclave reaction vessel, to which 100 mL of water was added, and heated at 100°C to 250°C for 20 to 180 minutes to perform hydrothermal treatment. The desalted ash slurry after hydrothermal treatment was filtered, and the desalted ash was collected. The collected desalted ash was dried at 105°C to obtain dry desalted ash, and the Cl concentration and Ca concentration were measured, and the Ca residual rate was calculated by the following formula. The results are shown in Table 1 (sample No. 1 is a reference example, and samples No. 2 to 7 are examples).
Ca residual rate (%) = [Weight of demineralized ash (g) × Ca concentration of demineralized ash (%)] / [Weight of raw ash (g) × Ca concentration of raw ash (%)] × 100

Comparative Example
The same raw ash as in Example 1 was made into a raw ash slurry with a liquid-solid ratio of 10, which was washed once with water, and then dried and demineralized ash was obtained without hydrothermal treatment (Sample No. 8).
The same raw ash as in Example 1 was made into a raw ash slurry with a liquid-solid ratio of 10 and washed once with water, and then instead of hydrothermal treatment, it was washed with room temperature water at 25°C for 60 minutes to recover the desalted ash, which was then dried at 105°C to obtain dry desalted ash (Sample No. 9). Also, dry desalted ash was obtained in the same manner as Sample No. 9, except that the desalted ash was recovered by washing with warm water at 60°C (Sample No. 10). These results are shown in Table 1.

As shown in Table 1, the chlorine concentration of the desalted ash of samples 1 to 7 was 0.5% or less, and 80% or more of the calcium contained in the raw ash remained. On the other hand, the chlorine concentration of the desalted ash of sample 8, which was not subjected to hydrothermal treatment, was 1% or more, and desalting was insufficient. Furthermore, samples 9 and 10, which were produced at temperatures below 100°C, had a chlorine concentration of 0.6% or more in the desalted ash, and the desalting effect was low.

10-vibration mill, 20-agitation washing tank, 30-filter press (washed ash separation means), 40-wastewater treatment equipment, 50-hydrothermal treatment equipment, 60-filter press (demineralized washed ash separation means).

Claims (3)

The method for desalting chlorine-containing ash comprises a water-washing step of forming a water slurry from chlorine-containing ash (raw ash) and washing it to desalt it, a water-washed ash recovery step of performing solid-liquid separation of the washed ash slurry after the water washing to recover the washed ash, a hydrothermal treatment step of forming a water slurry from the recovered washed ash and subjecting it to hydrothermal treatment to promote desalting, and a desalted ash recovery step of performing solid-liquid separation of the desalted ash slurry after the hydrothermal treatment to recover the desalted ash, wherein the washed ash from which 80% or more of the chlorine in the raw ash has been desalted by the water-washing step is treated in the hydrothermal treatment under high temperatures and pressures of 150°C to 250°C and 0.4 MPa to 4.0 MPa to decompose sparingly soluble chlorine compounds to promote desalting , while calcium is left in the desalted ash to be recovered. The method for desalting chlorine-containing ash described in claim 1, in which the water washing process and the hydrothermal treatment process remove 99.5% to 99.8% of the chlorine from the raw ash, while leaving 80% to 85% of the calcium in the raw ash in the desalted ash and recovering it. This chlorine-containing ash desalting system comprises a washing tank which turns chlorine- containing ash (raw ash) into a water slurry, agitates and washes it to desalt 80% or more of the chlorine in the raw ash , a water-washed ash separation means which performs solid-liquid separation of the water-washed ash slurry sent from the washing tank to recover the water-washed ash, a hydrothermal treatment system which adds water to the recovered water-washed ash and treats it under high temperature and high pressure of 150°C or more to 250°C or less and 0.4 MPa to 4.0 MPa, and a desalted ash separation means which performs solid-liquid separation of the desalted ash slurry sent from the hydrothermal treatment system to recover the desalted ash, and is characterized in that the chlorine in the raw ash is desalted by the water washing and hydrothermal treatment, while calcium is left in the desalted ash and recovered.

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