JP6964300B2 - Phosphorus recovery technology using gypsum from waste gypsum board - Google Patents

Description

The present invention relates to a phosphorus recovery technique using gypsum of waste gypsum board, and more specifically, a phosphorus recovery method using hemihydrate gypsum derived from waste gypsum board as a phosphorus recovery material and phosphorus recovery for carrying out the method. It is about the system.

Gypsum board is a building material whose surface is covered with paper using dihydrate gypsum as a core material, and is widely used as an indispensable material for construction because it has excellent fire resistance, sound insulation, and dimensional stability. Has been done. When dismantling a building, the gypsum board is treated as a waste gypsum board that has reached the end of its useful life, and is obliged to be treated at a controlled final disposal site.
Therefore, since there are few installation locations in the managed final disposal site, the disposal cost of waste gypsum board is high. In addition, the remaining years of the existing managed final disposal site are also limited.
Therefore, it has been proposed to process the waste gypsum board into hemihydrate gypsum and reuse it as a soil solidifying material, and it has already been implemented.
However, since the strength after solidification is inferior to other competing products, the reuse rate as a soil solidifying material is currently limited to about 40%.
It is expected that the amount of waste gypsum board discharged in Japan will increase more and more in the future, and from the above situation, a new reuse method is required.

On the other hand, since the phosphate ore required for producing phosphorus fertilizer is not produced in Japan, it relies mostly on imports for procurement. Since the region where phosphate rock is produced is limited even in the world, the price fluctuates greatly depending on the world situation at that time. In addition, it has been pointed out that economically minable phosphorus resources will be exhausted at the end of this century, so there is a need for a means of securing phosphorus resources in a way that does not rely on imports.
As one of them, as described in Patent Documents 1 and 2, phosphorus is extracted from the incinerator ash of sludge generated in a sewage treatment plant under alkaline conditions, and a calcium source such as slaked lime is added and reacted to recover it as calcium phosphate. Technology (ash alkali extraction method) is being studied.

However, at room temperature, it takes several hours or more to complete the reaction, and the operating efficiency of the reaction tank is poor. The reaction time can be shortened by heating the reaction vessel, but the fuel cost for that is added. In addition, since the reaction rate of phosphorus is low, excess phosphorus is used for reaction and excess phosphorus is released as wastewater, so not only precious phosphorus is discarded, but also drainage equipment for discarding is required. There is.
Under the above circumstances, it is not possible to generate sufficient profits just by selling calcium phosphate, and the ash-alkali extraction method has not become widespread.

Furthermore, when a plurality of facilities are combined and systematized in order to implement the phosphorus recovery method, whether or not energy can be recycled also has a great influence on profits.

JP-A-2007-246361 Japanese Unexamined Patent Publication No. 2012-56784

The present invention has been made to solve the above problems, and by using waste gypsum board as a phosphorus recovery material instead of slaked lime, the profitability of phosphorus recovery by the ash-alkali extraction method can be significantly improved. It is an object of the present invention to provide a novel and useful phosphorus recovery method.
Another object of the present invention is to provide a phosphorus recovery system for carrying out the above phosphorus recovery method, which incorporates a heat recycling structure using waste heat as a heat source.

［２］の発明は、［１］に記載したリン回収方法において、反応工程では、下水汚泥焼却灰アルカリ抽出液と石膏粉の配合比（ｍｏｌ比）を、０．６≦Ｐ／Ｃａ≦０．８に設定することを特徴とするリン回収方法である。
［３］の発明は、［２］に記載したリン回収方法において、懸濁時間の経過に対して石膏反応割合が上方に凸な曲線を描くことを利用し、前処理に際して、凸頂部及びその近傍を懸濁時間として設定することを特徴とするリン回収方法である。
［４］の発明は、［３］に記載したリン回収方法において、懸濁時間を２０〜３０分間に設定することを特徴とするリン回収方法である。
［５］の発明は、［１］から［４］のいずれかに記載したリン回収方法において、石膏濃度の上限を０．７５ｍｏｌ／Ｌとすることを特徴とするリン回収方法である。 In order to achieve the above object, the invention of [1] is a gypsum recovery method for recovering phosphorus as calcium phosphate by reacting sewage sludge incinerator ash alkaline extract with gypsum powder derived from waste gypsum board. By using a powder containing semi-hydrated gypsum obtained by dehydrating water of crystallization as the main component and suspending the gypsum powder in water in the pretreatment step, the reaction step is 80% within 30 minutes at room temperature. It is a phosphorus recovery method characterized by reaching the above gypsum reaction ratio.
The gypsum reaction rate is calculated by the following formula.

In the invention of [2], in the phosphorus recovery method described in [1], in the reaction step, the compounding ratio (mol ratio) of the sewage sludge incinerator ash alkaline extract and the gypsum powder was set to 0.6 ≦ P / Ca ≦ 0. It is a phosphorus recovery method characterized by setting to 8.8.
The invention of [3] utilizes the fact that the gypsum reaction ratio draws an upwardly convex curve with respect to the passage of suspension time in the phosphorus recovery method described in [2], and at the time of pretreatment, the convex apex and the convex portion thereof. It is a phosphorus recovery method characterized by setting the vicinity as a suspension time.
The invention of [4] is a phosphorus recovery method according to [3], wherein the suspension time is set to 20 to 30 minutes.
The invention of [5] is a phosphorus recovery method according to any one of [1] to [4], wherein the upper limit of the gypsum concentration is 0.75 mol / L.

The invention of [6] is a phosphorus recovery method according to any one of [1] to [5], wherein the solid matter recovered as calcium phosphate satisfies the official fertilizer standard.

The invention of [7] is a phosphorus-side preparation for preparing a sewage sludge incinerator ash alkaline extract in a phosphorus recovery system provided with equipment for carrying out the step of the phosphorus recovery method according to any one of [1] to [6]. Equipped with equipment and equipment for the dehydration process that dehydrates crystalline water from gypsum powder obtained by crushing waste gypsum board by heating and drying, the waste heat discharged from the equipment for the dehydration process is used as a heat source in the phosphorus side preparation equipment. It is a phosphorus recovery system characterized by
The invention of [8] is a phosphorus recovery system according to [7], wherein the equipment for the dehydration process uses the heat of incinerator of waste as a heat source.

According to the phosphorus recovery method of the present invention, the disposal cost can be profitable by using the gypsum powder derived from the waste gypsum board, and the reactivity of the gypsum powder is enhanced to solve the above-mentioned problems. Calcium phosphate It is possible to significantly improve profits when selling gypsum.
Further, in the phosphorus recovery system of the present invention, the phosphorus recovery method can be constructed in a form in which a heat recycling structure is incorporated.
This makes it possible to improve profitability, which is a drawback of the ash-alkali extraction method.

It is a block diagram of the phosphorus recovery system which concerns on embodiment of this invention. It is a graph which shows the change of the gypsum reaction ratio with respect to the reaction time in Example 1. It is a graph which shows the change of the gypsum reaction ratio with respect to the reaction time in Example 1. It is a graph which shows the powder X-ray analysis result of the solid matter in Example 2. It is a graph which shows the change of the gypsum reaction ratio with respect to the suspension time in Example 3.

The phosphorus recovery method according to the embodiment of the present invention will be described below.
The phosphorus recovery method of the present invention is based on the ash-alkali extraction method, and phosphorus is recovered as calcium phosphate.
The phosphorus source is sewage sludge incinerator ash. The sewage sludge incinerator ash is the incinerator ash of sludge generated at a sewage treatment plant and contains phosphorus (P).
The calcium source is waste gypsum board. Waste gypsum board is obliged to be processed at a controlled final disposal site, and if it cannot be reused, it will be processed at a managed final disposal site.

The main steps of the phosphorus recovery method will be described.
FIG. 1 shows the entire phosphorus recovery system, and the phosphorus recovery method is carried out using this phosphorus recovery system. Hereinafter, the equipment related to the process will be described together as necessary.
<Preparation of sewage sludge incinerator ash alkaline extract>
[Alkaline solution adjustment process]
Adjust the alkaline solution (NaOH, KOH) to an appropriate concentration.
This step is carried out using the alkali adjusting tank 1 having the stirring function of FIG. When the alkaline solution and diluted water (warm water) are supplied, mixing proceeds under stirring. The diluted water (warm water) is warmed by the waste heat generated in another step described later, and is adjusted to the temperature required in the subsequent [phosphorus extraction step].

[Phosphorus extraction process]
The sewage sludge incinerator ash is brought into contact with an alkaline solution at 40 ° C. or higher to extract phosphorus.
Correlation tendency between the type, concentration and heating temperature of alkaline solution, liquid-solidity ratio (volume of alkaline solution / weight of sewage sludge incineration ash), contact time and phosphorus extraction rate is already known and actually brought in. In consideration of the phosphorus content of the sewage sludge incineration ash and the capacity of the implementation equipment, each condition is optimally selected and set except for 40 ° C or higher so that the phosphorus extraction rate can be maximized.
This step is carried out using the phosphorus extraction tank 3 having the stirring function of FIG. When the sewage sludge incineration ash is put into the phosphorus extraction tank 3 filled with the alkaline solution, the extraction of phosphoric acid proceeds under stirring.

[Phosphoric acid separation process]
Since the extraction phase of phosphoric acid is a liquid phase, phosphoric acid is separated from other residues by solid-liquid separation.
This step is carried out using the centrifuge decanter 5 of FIG.
Through this step, the preparation of the sewage sludge incinerator ash alkaline extract is completed.

<Preparation of gypsum powder containing semi-hydrated gypsum with dehydrated water of crystallization as the main component>
[Crushing and crushing process of waste gypsum board]
Crush and crush the waste gypsum board to make gypsum powder under 0.5 mm.
In this process, after roughly crushing to a size of about 50 cm square, for example, a gypsum board separator (“HI Plus Turbo” manufactured by Hosoda Standard Co., Ltd., processing capacity 500 kg / h to 5.0 t / h) is used. , Further finely crushed by a compression roll, and separated into pieces and gypsum powder by a spiral pin roll. Then, the separated gypsum powder is sieved by a powder machine. The powder machine is equipped with a screen, which gives a 0.5mm under. If the particle size is reduced to this level, the treatment proceeds smoothly in the subsequent steps. The gypsum powder at this stage is mainly composed of dihydrate gypsum.

[Gypsum powder dehydration process]
The gypsum powder obtained in the above step is heated and dried to dehydrate the water of crystallization from the main component of dihydrate gypsum and change it into hemihydrate gypsum.
In this step, the rotary kiln 7 shown in FIG. 1 is used, and hot air is blown into the rotary kiln 7 at 250 ° C. for about 20 minutes. It is already known that the crystal phase changes from dihydrate to semi-water to anhydrous by adjusting the heating temperature and time, and if it is treated at 200 ° C for about 20 minutes, it becomes almost 100% semi-hydrated gypsum. Therefore, according to the above conditions, 100% semi-hydrated gypsum is obtained.
The gypsum powder discharged after the treatment of the rotary kiln 7 is the "gypsum powder mainly composed of semi-hydrated gypsum obtained by dehydrating water of crystallization" used in the phosphorus recovery method of the present invention.
The rotary kiln 7 burns waste in a carbonization furnace and uses the heat of incineration as a heat source. If you are an industrial waste treatment company, you can easily procure combustible waste, for example, organic waste, and you have the incinerator equipment as existing equipment. Therefore, you can build this phosphorus recovery system using the existing equipment. It can be operated economically by using waste as fuel.
In many cases, the waste is solidified, but this is for convenience of handling, and the shape is not particularly limited for the purpose of the present invention.

Exhaust gas having heat is emitted from the rotary kiln 7, and the heat of the exhaust gas is exchanged by the heat exchange device 9 of FIG. 1 to generate hot water and reduced pressure steam. The hot water in the above-mentioned <Preparation of sewage sludge incinerator ash alkaline extract> was produced here.

<Recovery of calcium phosphate>
[Pretreatment process]
Gypsum powder containing hemihydrate gypsum as a main component is subjected to pretreatment for suspension in water.
Hemihydrate gypsum is more soluble in water than dihydrate gypsum, but increasing the surface area of gypsum powder makes the reaction with phosphorus more advantageous. However, there is a limit to dry crushing. On the other hand, hemihydrate gypsum shows a phenomenon called underwater disintegration. It is presumed that when this water disintegration property develops, the gypsum powder disintegrates and the surface area increases remarkably, which contributes to increasing the gypsum reaction rate.
There is no index that directly indicates the state and properties of the gypsum powder after the pretreatment, and the results vary depending on the particle size and shape of the gypsum powder before the pretreatment even under the same pretreatment conditions. Therefore, using the reaction state in the subsequent [phosphorus reaction step] as an index, the pretreatment condition is that the gypsum reaction ratio reaches 80% or more within 30 minutes at room temperature after the pretreatment. Preferably, the pretreatment condition is that the gypsum reaction rate reaches 90% or more within 30 minutes at room temperature after the pretreatment.

A technique called suspension in water is used to increase the surface area, and suspension in water also causes a tendency to return hemihydrate gypsum to dihydrate gypsum. Dihydrate gypsum is less reactive than hemihydrate gypsum, and if the time is too long, the rate of returning to dihydrate gypsum increases and the effect on the gypsum reaction rate increases, and the gypsum reaction rate tends to decrease.
For example, it is assumed that when 100% dihydrate gypsum is used as gypsum and reacted at room temperature for 20 minutes, the gypsum reaction ratio becomes 13.1 mol%. In the above pretreatment, in order to continue suspension in water for 20 minutes and make the gypsum reaction rate 90%, the allowable upper limit (X) of the increase rate of dihydrate gypsum due to return is calculated by the following formula. ..

Further, in the [phosphorus reaction step] described later, in order to reduce the excess phosphorus, the compounding ratio (mol ratio) of the sewage sludge incinerator ash alkaline extract and the gypsum powder is set to a theoretical value (P / Ca = 0.6). It is recommended to set it to 0.6 ≦ P / Ca ≦ 0.8, which is closer to the side.
Reducing the phosphorus content reduces the favorable quantitative effect on the reaction, so that the gypsum reaction rate decreases more with respect to the extension of the suspension time, but the convexity of the upwardly convex curve indicating the gypsum reaction rate. By setting the suspension time at the top and its vicinity, the above-mentioned gypsum reaction rate requirement can be satisfied.

Further, even if the gypsum concentration is increased to 0.65 mol / L or more in order to increase the addition amount of gypsum and increase the recovery rate of phosphorus, if it is 0.75 mol / L or less, the above gypsum reaction ratio is related. Can meet the demand.

This step is carried out using the phosphorus reaction tank 11 having the stirring function of FIG. When gypsum powder containing hemihydrate gypsum as the main component and warm water are supplied, suspension proceeds under stirring. Suspension is promoted by using warm water.
When this phosphorus recovery system is used, the standard stirring time is 20 to 30 minutes.

[Phosphorus reaction process]
Sewage sludge incineration ash alkaline extract and gypsum suspension are combined and reacted with phosphoric acid at room temperature to convert to calcium phosphate. The processing time is within 30 minutes.
This treatment is carried out using the phosphorus reaction tank 11 of FIG. When the sewage sludge incinerator ash alkaline extract is fed in the state where the gypsum suspension is accumulated in the phosphorus reaction tank 11 in the above [pretreatment step], the reaction proceeds under stirring.

[Calcium phosphate separation process]
Since calcium phosphate is a solid substance, calcium phosphate is separated from other liquid phases by solid-liquid separation after washing in the washing tank 13 of FIG.
This step is carried out using the centrifuge decanter 15 of FIG.
[Calcium phosphate drying process]
After that, the separated calcium phosphate is dried to make a finished product (product).
This step is carried out using the drum dryer 17 of FIG. As the hot air of the drum dryer 17, the decompressed steam produced by the heat exchange device 9 of FIG. 1 is used.

Through the above steps, phosphorus is recovered as calcium phosphate.
As shown in the phosphorus recovery system of FIG. 1, equipment related to a process not mentioned above, for example, a dust cyclone 21 that passes waste heat from a phosphorus extract storage tank 19 and a rotary kiln 7 to the front stage of a heat exchange device 9 and the like. , The configuration of attaching a heat insulating heater to the phosphorus extraction tank 3 and the phosphorus reaction tank 11 and laying a heat insulating material is also shown, but these are appropriately adopted by those skilled in the art in actual operation.
The recovered calcium phosphate (solid matter) meets the official fertilizer standard (by-product phosphate fertilizer) stipulated by the Fertilizer Control Law, and can be used as fertilizer.

By using a suspension of semi-hydrated gypsum obtained by heat-treating gypsum powder as a calcium raw material, the reaction time between phosphorus and calcium, which used to take several hours at room temperature, is shortened to 30 minutes or less, preferably 20 minutes or less. I was able to. Moreover, the phosphorus recovery efficiency has improved dramatically.
In addition, by using gypsum powder derived from waste gypsum board as a calcium raw material, the disposal cost of waste gypsum board can be expected as a profit. Furthermore, by using the waste heat from the rotary kiln 7 as a heat source, it is expected that the profit from the disposal cost and the fuel cost will be reduced. This makes it possible to improve profitability, which is a drawback of the ash-alkali extraction method.
It should be noted that hemihydrate gypsum has been commercialized, and by purchasing this, it is possible to omit the step of processing from dihydrate gypsum to hemihydrate gypsum.

[Example 1]
Gypsum powder was added to the simulated phosphorus extract, and the relationship between the type of gypsum and the gypsum reaction rate was investigated.
Potassium dihydrogen phosphate was added to a 1 mol / L sodium hydroxide solution so as to be 0.24 mol / L-PO4, and the obtained simulated phosphorus extract was used as a substitute for the sewage sludge incineration ash alkali extract. As for gypsum powder, dihydrate gypsum and hemihydrate gypsum of reagents (under 0.5 mm) are added to distilled water so as to be 0.36 mol / L and 0.74 mol / L, respectively, and the gypsum is stirred for 20 minutes as a pretreatment. It was used after making a suspension. The two were mixed so as to have a mol ratio of P / Ca = 1.1, and then reacted at room temperature with stirring for 5 to 120 minutes. After stirring, solid-liquid separation was performed by suction filtration.
The concentration of sulfate ions remaining in the liquid after the reaction was analyzed by ion chromatography, and the gypsum reaction ratio was calculated. The gypsum reaction ratio indicates how much of the sulfuric acid contained in the gypsum used in the test was released into the liquid as sulfate ions. That is, if the gypsum reaction rate is high, it can be said that the gypsum used in the reaction is also high.

The results are shown in FIGS. 2 and 3.
When the gypsum concentration is as low as 0.36 mol / L, when hemihydrate gypsum is used, if the reaction time (= stirring time) is set to 20 minutes or more, the reaction time is 30 minutes even when dihydrate gypsum is used. From the above, it can be seen that the gypsum reaction rate is 90% or more in each case, but the gypsum concentration has poor phosphorus recovery efficiency and cannot be a realistic set concentration.
When the gypsum concentration was as high as 0.74 mol / L, when dihydrate gypsum was used, the gypsum reaction rate was significantly low when the reaction time was 30 minutes or less, and 13.1% when the reaction time was 20 minutes. In the above [Equation 1], this data is used for the trial calculation. On the other hand, when hemihydrate gypsum was used, a gypsum reaction rate of 90% or more was obtained in a reaction time of 20 minutes or more. From this result, it can be seen that as the amount of dihydrate gypsum in the gypsum turbid liquid increases, the gypsum reaction rate within the normal temperature reaction time of 30 minutes is adversely affected.

[Example 2]
In the test in which the gypsum concentration was set to 0.74 mol / L in Example 1 and the reaction time was 20 minutes using hemihydrate gypsum, the phosphorus-containing solid obtained on the filter paper by suction filtration was X-rayed. Diffraction analysis was performed. As a result of the analysis (Fig. 4), it was found that the main substance constituting the solid substance was hydroxyapatite. Since the mol ratio of phosphorus and calcium constituting hydroxide apatite (Ca5 (PO4) 3 (OH)) is P / Ca = 0.6, phosphorus is about 80% under the conditions of Example 1 ((1. It was suggested that it was 1-0.6) /0.6 × 100) excess.
An excessive amount of phosphorus leads to an excessive procurement of the sewage sludge incinerator ash that contains it, and the procurement cost deteriorates profitability. In addition, since excess phosphorus is contained in wastewater, it also affects the wastewater treatment cost. It can be seen that it is necessary to optimize P / Ca in order to efficiently recycle waste gypsum board with a small amount of sewage sludge incinerator ash and reduce the wastewater treatment cost.

[Example 3]
It was confirmed whether the same reaction proceeded when the amount of phosphorus used was reduced from P / Ca = 1.1. The gypsum suspension and the simulated phosphorus extract were prepared in the same manner as in Example 1. When preparing the gypsum suspension, the pretreatment time (= suspension time) after adding the gypsum to water was changed between 0 and 40 minutes. It was judged that it would be difficult for the reaction to proceed ideally without excess or deficiency, and the mixing ratio of the two was set slightly higher than the theoretical value (P / Ca = 0.6) to be 0.66. After 20 minutes of mixing, the gypsum reaction ratio was calculated from the concentration of sulfate ions in the liquid. The results are shown in FIG.
From FIG. 5, when P / Ca = 1.1, if the suspension time when preparing the gypsum suspension was 20 minutes or more, a gypsum reaction ratio of 90% or more was obtained even if it exceeded 30 minutes. However, in the case of P / Ca = 0.66, it can be seen that the gypsum reaction rate decreases when suspended for more than 30 minutes. That is, even if the amount of phosphorus used is reduced in order to optimize P / Ca, if the gypsum suspension time in the pretreatment is set to 20 minutes or more and 30 minutes or less, the gypsum reaction rate is not reduced. You can see that it's done.

[Example 4]
With reference to the reaction conditions obtained in the experiment, phosphorus was recovered using actual waste gypsum board and sewage sludge incineration ash, and the quality as phosphorus fertilizer was confirmed. The waste gypsum board was crushed and heated in advance to be processed into hemihydrate gypsum, added to water and stirred for 20 minutes to obtain a gypsum suspension. The sewage sludge incinerator ash was treated with a 1 mol / L sodium hydroxide solution at 60 ° C. for 20 minutes to extract phosphorus. The mixture was mixed so that the amount of phosphorus was 140.8 mg (the amount of P / Ca = 0.66 when the processed hemihydrate gypsum was assumed to be a pure substance) with respect to 1 g of gypsum, and the mixture was stirred for 20 minutes. The solid matter remaining in the liquid after stirring was collected by suction filtration, and the soluble phosphoric acid content and heavy metal analysis of the solid matter remaining on the filter paper were performed. The test followed the fertilizer analysis method (Food and Agricultural Products Consumption Safety Technology Center).
As a result of the test, it was confirmed that a fertilizer of sufficient quality was obtained as compared with the official fertilizer standard (by-product phosphate fertilizer) stipulated by the Fertilizer Control Law (Table 1).

It is said that the amount of waste gypsum board discharged will increase further in the future. The remaining years of the managed final disposal site are also limited. In addition, a new method is required for the procurement of phosphorus, which relies mostly on imports. Phosphorus is an essential element for the growth of plants, and considering that it is an indispensable resource for farming, this method that can secure cost benefits has high industrial applicability. It can be said that.

1 ... Alkali adjustment tank 3 ... Centrifugation decanter 5 ... Centrifugal separation decanter 7 ... Rotary kiln 9 ... Heat exchanger 11 ... Phosphorus reaction tank 13 ... Washing tank 15 ... Centrifugal separation decanter 17 ... Drum dryer 19 ... Phosphorus extract storage tank 21 ... Dust cyclone

Claims (4)

In a phosphorus recovery method for recovering phosphorus as calcium phosphate by reacting sewage sludge incineration ash alkaline extract with gypsum powder derived from waste gypsum board.
The main component of the gypsum powder is semi-hydrated gypsum obtained by dehydrating crystalline water. In the pretreatment step, the gypsum powder is added to water, stirred for 20 to 30 minutes, and suspended to form a gypsum suspension. In the subsequent reaction step, the gypsum suspension and the sewage sludge incineration ash alkaline extract were mixed with the upper limit of the gypsum concentration at 0.75 mol / L and in a mol ratio of 0.6 ≦ P / Ca ≦ 0. Mix to 8 and react at room temperature to
The ratio of sulfuric acid contained in the gypsum powder released into the liquid as sulfate ions in the reaction step is defined as the gypsum reaction ratio, and is characterized in that the gypsum reaction ratio reaches 80% or more within 30 minutes at room temperature. Phosphorus recovery method. In the phosphorus recovery method according to claim 1,
A phosphorus recovery method characterized in that the solid matter recovered as calcium phosphate meets the official fertilizer standard. In a phosphorus recovery system provided with equipment for carrying out the steps of the phosphorus recovery method according to claim 1 or 2.
It is equipped with a phosphorus-side preparation facility for preparing an alkaline extract of sewage sludge incineration and a facility for a dehydration process in which water of crystallization is dehydrated by heating and drying from gypsum powder obtained by crushing a waste gypsum board, and is discharged by the facility for the dehydration process. A phosphorus recovery system characterized in that waste heat is used as a heat source in the phosphorus-side preparation facility . In the phosphorus recovery system according to claim 3,
In the equipment for the dehydration process, a phosphorus recovery system is characterized by using the heat of incinerator of waste as a heat source .

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