JP7392913B2 - Demineralization cleaning method for chlorine-containing ash - Google Patents

Description

The present invention enables continuous filtration of ash slurry with excellent filterability by controlling the particle size distribution without over-pulverizing the ash in the slurry when turning chlorine-containing ash into a slurry for desalination washing. The present invention relates to a demineralization cleaning method.

Chlorine-containing ash, such as fly ash and chlorine bypass dust, can be desalinated and used as a raw material for cement. Since most chlorine compounds are water-soluble, washing with water is often used as a method for desalting chlorine-containing ash. Specifically, chlorine-containing ash is put into a stirring cleaning tank to make a water slurry, and the slurry, which has been stirred and washed to elute the chlorine content, is filtered and dehydrated to remove the chlorine-containing water. There is.

In the above slurry filtration process, the thinner the solid concentration of the slurry, the lower the filterability, so in conventional desalination systems, a settling tank is installed next to the stirring washing tank, and the slurry after stirring and washing is transferred to the settling tank. The system employs a structure in which the ash in the slurry is allowed to settle, the supernatant water is removed, and the slurry is concentrated before being sent to the filtration process.

However, in the above-mentioned conventional desalting system, the ash in the slurry is over-pulverized because the slurry is continuously stirred in the stirring cleaning tank, and the proportion of fine particles with a particle size of less than 0.045 mm is high. Such fine particles are difficult to drain, and when left standing in a sedimentation tank for a long time, they form a layered sedimentary layer, further reducing filterability.

The following methods are known to improve the filterability of cleaning slurry. (a) A method of pressurizing granulation and then filtering (Patent Document 1), (b) A method of pre-coating the surface of the belt filter with relatively coarse ash slurry and then filtering the fine ash slurry (Patent Document 2) (c) Add a polymer flocculant to the washed slurry to sediment and separate the flocs to form an initial concentrated slurry, and after adding water to the initial concentrated slurry, separate it into a fine slurry and a coarse slurry using a wet cyclone. A method in which a polymer flocculant is added to the fine particle slurry to sediment and separate the fine particle flocs to form a fine particle concentrated slurry, and the fine particle concentrated slurry is dehydrated and washed to desalinate (Patent Document 3) , (d) A method of adjusting the particle size by mixing washed ash and coarse inorganic powder (Patent Document 4), (e) Adding a chemical to suppress the increase in viscosity of the slurry, improving the fluidity and dewatering properties of the slurry. (Patent Document 5). In addition, (f) Since the chlorine contained in incinerated ash is mostly found in fine particles, it is recommended to sieve it into fine particles with a particle size of less than 0.5 mm and coarse particles with a particle size of 0.5 mm or more for desalination treatment. known (Patent Document 6).

JP2017-148720A Patent No. 4095929 Patent No. 5761544 JP2004-358288A Japanese Patent Application Publication No. 2013-91029 Patent No. 5561326

Methods (a) and (b) above require extensive equipment improvements, and the properties of fly ash vary greatly, so sufficient effects may not be obtained. The method (c) above requires large-scale equipment, and the method (d) above adjusts the apparent particle size by mixing inorganic powder, but since fine ash remains, the filtration performance is fundamentally affected. is not resolved. Although the above method (e) improves filtration performance to some extent by adding chemicals, it does not provide a fundamental solution. In addition, the above method (f) hardly improves filtration performance.

The present invention provides a desalination cleaning method that solves the above-mentioned problems in conventional desalination processing, and provides a desalination cleaning method that has excellent filtration performance and high throughput without requiring major improvements in equipment. provide.

The present invention relates to a desalination cleaning method that solves the conventional problems with the following configuration.
[1] A desalination cleaning method in which chlorine-containing ash is made into a water slurry, stirred and washed, the water from which the chlorine content has been eluted is dehydrated, and ash with reduced chlorine is recovered. The slurry is stirred and washed so that the proportion of fine particles with a particle size of less than 0.045 mm in the slurry is 50 wt% or less, and the stirred and washed slurry is sent to a belt filter for dehydration without going through a static settling process. A method for desalinating and cleaning chlorine-containing ash, characterized by:
[2] The method for desalting and cleaning chlorine-containing ash described in [1] above, wherein the stirring and cleaning is performed so that the proportion of fine particles with a particle size of less than 0.045 mm in the slurry is 10 wt% or less.
[3] The method for desalinating and cleaning chlorine-containing ash described in [1] or [2] above, in which 3 to 5 times the amount of water is added to the chlorine-containing ash to form a slurry.

[Specific explanation]
The desalination cleaning method of the present invention is a desalination cleaning method in which chlorine-containing ash is made into a water slurry, stirred and washed, water in which chlorine content has been eluted is dehydrated, and ash with reduced chlorine is recovered, and the slurry is After adding a polymer flocculant to the slurry and stirring and cleaning it so that the proportion of fine particles with a particle size of less than 0.045 mm in the slurry is 50 wt% or less, the stirring and cleaning slurry is stirred and washed without going through a static settling process. This is a desalination cleaning method for chlorine-containing ash, which is characterized by sending it to a belt filter for dehydration.

The above slurry of chlorine-containing ash (hereinafter referred to as chlorine-containing ash slurry) is prepared by dispersing chlorine-containing ash recovered from fly ash or chlorine bypass dust of a cement factory in water and adjusting the pH to around 6 to 10. It is slurry. The chlorine-containing ash slurry of the present invention also includes a slurry to which sulfuric acid is added as a pH adjuster, and a slurry made from desalinated wastewater sludge together with chlorine-containing ash.

In the desalination cleaning method of the present invention, when the chlorine-containing ash slurry is stirred and washed in a stirring tank, the slurry is stirred and washed so that the proportion of fine particles with a particle size of less than 0.045 mm in the slurry is 50 wt% or less. It has been found that when the slurry that has been stirred and washed is filtered and dehydrated, the filtration time until the dehydration is completed varies greatly depending on the proportion of fine particles with a particle size of less than 0.045 mm contained in the slurry.

In the example shown in Fig. 1, for ash A, the filtration time when the proportion of fine particles with a particle size of less than 0.045 mm contained in the slurry is (a) less than 2wt%, (b) 50wt%, and (c) 100wt%. (A) is 13 seconds, (B) is 335 seconds, and (C) is 823 seconds, and the filtration time varies greatly depending on the proportion of fine particles with a particle size of less than 0.045 mm contained in the slurry.

The proportion of fine particles with a particle size of less than 0.045 mm contained in the slurry depends on the stirring time of the slurry. In the example shown in FIG. 2, for ash A, the proportion of fine particles with a particle size of less than 0.045 mm is 12 wt% at a stirring time of 300 minutes, and 6 wt% at a stirring time of 15 minutes. Regarding ash B, the proportion of fine particles with a particle size of less than 0.045 mm is 27 wt% when the stirring time is 300 minutes, and 2 wt% when the stirring time is 15 minutes.

Based on the above findings, the present invention, in stirring and cleaning chlorine-containing ash slurry, controls the stirring time so that the proportion of fine particles with a particle size of less than 0.045 mm in the slurry is 50 wt% or less, preferably 10 wt% or less. . If the stirring time is too long, over-pulverization will occur and the proportion of fine particles less than 0.045 mm will increase. The stirring time, stirring speed, etc. may be determined according to the specifications of the stirring cleaning tank.

As shown in Figure 1, the smaller the proportion of fine particles with a particle size of less than 0.045 mm, the shorter the filtration time, so the proportion of fine particles with a particle size of less than 0.045 mm in the slurry is preferably 50 wt% or less, and 10 wt%. The following are more preferable.

In addition, during agitation cleaning, adding a polymer flocculant tends to cause fine particles to coagulate into particles with a particle size of 0.045 mm or more, so the proportion of fine particles with a particle size of less than 0.045 mm should be suppressed. I can do it.

In the desalting and cleaning method of the present invention, after the above-mentioned stirring and cleaning, the slurry that has been stirred and cleaned is sent to a belt filter for dehydration without going through a stationary sedimentation step. Conventional desalination equipment has a stirring cleaning tank and a settling tank for the chlorine-containing ash slurry, and leads the stirred and washed chlorine-containing ash slurry to the settling tank, and allows the slurry to settle in the settling tank, The supernatant water is removed, and the accumulated slurry sludge is sent to a belt filter, where it is dehydrated while being transported.

When examining the relationship between the standing sedimentation treatment and the filtration treatment, it was found that the filtration time differs depending on the standing time, and that the filtration time becomes longer in proportion to the standing time. As shown in Figure 3, when comparing the case where the slurry was filtered without standing still (0 hours of standing) and the case where it was filtered after standing still for 72 hours, for ash A, the filtration time when not standing was However, the filtration time after standing for 72 hours is 22 seconds. In addition, for ash B, the filtration time is 7 seconds when not left standing, but the filtration time after standing still for 72 hours is 10 seconds, and the filtration time after standing still is 10 seconds for both ash A and ash B. become longer.

If the slurry is filtered without standing still, the ash particles will be filtered while being dispersed in the slurry, so water in the slurry will easily come out. However, if the slurry is left standing for a long time, it will become settled sludge, as shown in Figure 4. A clay-like sedimentary layer is observed to be formed on the upper side. It is thought that the filtration time becomes longer because it becomes difficult for the moisture in the slurry to pass through this deposited layer.

The desalting and cleaning method of the present invention is based on the above-mentioned findings, and after stirring and cleaning the chlorine-containing ash slurry, the slurry is introduced into a belt filter without going through a static sedimentation step, and is filtered and dehydrated while being transferred. By filtering and dehydrating the slurry without passing through a static settling step, the time for filtration and dehydration can be shorter than in the conventional dehydration after sedimentation. In addition, in the desalination cleaning method of the present invention, water is introduced into a belt filter for dehydration without going through a static sedimentation process, so in order to avoid an excessive burden on the dehydration process, the amount of water when preparing the slurry is limited to chlorine. The amount is preferably 3 to 5 times the amount of ash contained.

According to the desalination method of the present invention, the filtration time is short, the desalination treatment of chlorine-containing ash can proceed quickly, and the processing capacity of the desalination equipment can be increased.

1 is a graph of filtration time of ash A showing the results of Example 1. A graph showing the dependence of stirring time and particle size showing the results of Example 2. 3 is a graph showing the dependence of standing time and filtration time showing the results of Example 3. A schematic diagram showing the state of sludge that has been allowed to settle.

Examples of the present invention will be shown below. The proportion of fine particles with a particle size of less than 0.045 mm was calculated from the ratio of the weight of ash under the sieve to the total weight of ash when classified using a sieve with a nominal opening of 45 μm according to the JIS Z8801-1 test sieve standard. .

[Example 1]
Using ash A in which the proportion of fine particles with a particle size of less than 0.045 mm was adjusted to (a) less than 2 wt%, (b) 50 wt%, and (c) 100 wt%, three types of slurry with a solid content concentration of approximately 90 g/L were prepared. was prepared. These slurries were placed in a shaker, shaken for 15 minutes or 300 minutes, and filtered and dehydrated until the water content of the slurry became 50 wt% or less. This filtration time is shown in FIG. As shown in the figure, the filtration time for slurry (a) was 13 seconds, the filtration time for slurry (b) was 335 seconds, and the filtration time for slurry (c) was 823 seconds.

[Example 2]
For ash A and ash B, a slurry with a solid content concentration of approximately 90 g/L was prepared using ash with a particle size of 0.2 to 1.0 mm, and the slurry was stirred for 15 minutes using the same stirring washing tank. The proportion of fine particles with a particle size of less than 0.045 mm after stirring for 1 minute was investigated. The results are shown in FIG. As shown in the figure, for ash A, the proportion of fine particles with a particle size of less than 0.045 mm was 12 wt% at a stirring time of 300 minutes, and 6 wt% at a stirring time of 15 minutes. For ash B, the proportion of fine particles with a particle size of less than 0.045 mm was 27 wt% at a stirring time of 300 minutes, and 2 wt% at a stirring time of 15 minutes.

[Example 3]
The ash A slurry and ash B slurry stirred for 15 minutes as in Example 2 were placed in a container, allowed to stand for 0 hours (no standing) or 72 hours, and filtered until the water content of the slurry became 50 wt% or less. Dehydrated. This filtration time is shown in FIG. As shown in the figure, for ash A, the filtration time without standing was about 12 hours, and the filtration time after standing for 72 hours was 22 seconds. Regarding ash B, the filtration time without standing was 7 seconds, and the filtration time after 72 hours of standing was 10 seconds. Furthermore, regarding ash A, the state of the settled sludge of the sample left undisturbed for 72 hours is shown in FIG. As shown in the figure, a clay-like sediment layer was observed above the settled sludge. In the samples that were not allowed to stand still, no settled sludge was observed, and ash particles were dispersed in the slurry.

Claims (3)

A desalting cleaning method in which chlorine-containing ash is made into a water slurry, stirred and washed, and the water from which the chlorine content has been eluted is dehydrated to recover ash with reduced chlorine, and a polymer flocculant is added to the slurry. The slurry is agitated and washed so that the proportion of fine particles with a particle size of less than 0.045 mm is 50 wt% or less, and the agitated and washed slurry is sent to a belt filter for dehydration without going through a static settling process. Characteristic desalination cleaning method for chlorine-containing ash. 2. The method for desalting and cleaning chlorine-containing ash according to claim 1, wherein the stirring and cleaning is carried out so that the proportion of fine particles with a particle size of less than 0.045 mm in the slurry is 10 wt% or less. The method for desalting and cleaning chlorine-containing ash according to claim 1 or 2, wherein 3 to 5 times the amount of water is added to the chlorine-containing ash to form a slurry.

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