KR20160108764A - The method of neutralization phospho-gypsum using Fluidized bed boiler Fly ash and use thereof - Google Patents

Abstract

Disclosed is a manufacturing method of a cement setting retarder using fly ash from a fluidized bed boiler. According to the present invention, the manufacturing method of a cement setting retarder comprises the following steps of: preparing phosphogypsum, as a starting material, having pH of 4.0 at most generated in a process of extracting phosphoric acid; and neutralizing the phosphogypsum to have pH of at least 7.0 by mixing the phosphogypsum with fly ash obtained from circulating fluidized bed boiler. According to the present invention, neutralized phosphogypsum applicable as a cement setting retarder can be obtained. Through the present invention, discarded or stowed resources can be usefully used to resolve problems of waste and stowage, and can be reused.

Description

The fluidized-bed boiler Fly ash and use of the method of neutralizing phosphate gypsum using the fluidized-bed boiler fly ash

The present invention relates to a method for neutralizing phosphoric acid gypsum generated in a process for recovering phosphoric acid from phosphorus by utilizing fly ash generated in a fluidized bed boiler and recycling it as a caking retarder for cement. More particularly, Which is reacted with limestone added to the acidic phosphate gypsum to remove sulfur from the circulating fluidized bed boiler, is directly or hydrated and then mixed and aged to stabilize the neutralized and soluble phosphoric acid with insoluble phosphoric acid . The present invention also relates to a method of recycling this stabilized neutralized phosphoric acid gypsum as a cement retarding agent by adding it to a cement clinker and crushing it.

Fluidized bed boiler refers to a boiler that burns coal particles made by appropriately pulverizing coal to the mixed powder layer of the fluidized medium by blowing air at an appropriate rate, and is generally used as a boiler for burning coal. It is widely used for power generation. This method overcomes the problems of coal combustion compared to conventional coal combustion technology due to its unique combustion principle.

The advantage of this boiler is that it can be maintained relatively stable during combustion and can be burned at low temperature, so it is possible to burn coal with low quality and the generation of NOx, which is an environmental pollutant, It is a point.

When coal is burned in a fluidized bed boiler, limestone is injected to control the sulfur oxides (SOx) generated by the combustion of the sulfur components in the coal. The limestone is decomposed into quicklime and carbon dioxide, and the lime is reacted with sulfur oxides to produce gypsum (CaSO ₄ ), which is then desulfurized. The dust generated and scattered in this process is collected in the dust collector, which is a fly ash.

The main component of the fly ash is gypsum, and some of the lime is formed during the process of limestone decomposition. As a result, the fly ash has an alkaline property with a high pH.

The amount of fly ash generated in Korea is about 800,000 tons. It is expected that the amount of fly ash will be steadily increased because the power generation facilities of the fluidized bed boiler type are expected to increase in the future.

On the other hand, as shown in the following reaction formula (1), the gypsum gypsum is generated in a wet process in which sulfuric acid is treated in phosphorus as a raw material by using gypsum which is used in the production of phosphoric acid by using phosphate or sulfuric acid.

(Scheme 1)

Ca ₁₀ (PO ₄ ) ₆ F ₂ (s) + 10 H ₂ SO ₄ + 20 H ₂ O

→ 10CaSO ₄ and _{2H 2 O (s) + 6H} 3 PO 4 + 2HF

In Korea, 1,836,000 tons were generated in 2008, but surplus was generated due to low recycling rate.

Therefore, a new method for utilization of fly ash and phosphate gypsum is needed.

As described above, gypsum can be generally used as a coagulation retarding agent for cement, but it is difficult to use it as a coagulation retardant alone because the amount of gypsum contained in the fly ash is small. Phosphate gypsum produced as a by- Is strongly acidic to about 2.5, so that the strength of the cement is lowered and the condensation is delayed too much by the component such as water-soluble P ₂ O ₅ , so that the cement may not be hardened.

Accordingly, the inventors of the present invention have found that when the fluidized-bed boiler fly ash is mixed with phosphoric acid gypsum alone or hydration-treated to neutralize the strong acid phosphate gypsum and furthermore, by using the alkaline calcium oxide (CaO) component contained in the fly ash, (Ca ₃ (PO ₄ ) ₂ ) to reduce the amount of water soluble phosphoric acid. In addition, it was found that the fluidized bed boiler fly ash and phosphate plaster Can be recycled as a cement retarding agent.

Accordingly, the present invention provides a phosphoric acid neutralization gypsum which is neutralized to stabilize the pH to neutral or higher and to lower the concentration of soluble phosphoric acid by mixing or reacting the fluidized bed boiler fly ash which is not recycled, The purpose is to utilize.

Another object of the present invention is to provide a method for producing cement comprising the above-mentioned coagulation retarding agent.

In order to accomplish the above object, the present invention provides a method for producing a phosphate gypsum, And mixing the phosphate gypsum with a circulating fluidized bed boiler fly ash to neutralize the phosphate gypsum to a pH of 7 or higher.

The present invention may further include hydrating the fly ash.

In the present invention, the fluidized bed boiler fly ash or the hydration product thereof may contain 3 to 40 parts by weight of the internal slurry with respect to 100 parts by weight of the phosphate gypsum.

The present invention also provides a method for producing a cement, characterized in that the cement retarding agent produced by the production method according to claim 1 is blended with a cement clinker.

According to the neutralization method of the present invention, it is possible to obtain a phosphoric acid neutralization gypsum which can be used as a cement retarding agent by mixing, aging and drying phosphoric acid gypsum which is not usable as a fluidized bed boiler fly ash after disposal or as a coagulation retarder after hydration treatment. It is possible to utilize resources that have been disposed of or being disposed of, thereby solving the problem of disposal or repatriation and recycling them as resources.

FIG. 1 is a view schematically showing a method for producing a cement retarder according to an embodiment of the present invention. Referring to FIG.
2 is a view schematically showing a method for producing a cement retarder according to another embodiment of the present invention.
3 is a graph showing the results of XRD analysis of the fluidized bed boiler fly ash.

Hereinafter, the present invention will be described in detail.

The present invention provides a method of neutralizing phosphorus gypsum generated in the process of recovering phosphoric acid from phosphorus by utilizing a circulating fluidized bed boiler fly ash and recycling it as a caking retarder for cement.

More specifically, the present invention relates to an acidic phosphate gypsum produced from a phosphate extraction process from phosphate ore by mixing an alkaline fly ash produced by reacting with limestone to remove sulfur from a circulating fluidized bed boiler, A method of stabilizing neutralized and soluble phosphoric acid with insoluble phosphoric acid is used.

Further, when the stabilized neutralized phosphoric acid gypsum according to the present invention is added to the cement clinker and pulverized, it can be recycled as a cement retarding agent.

1 is a schematic view illustrating a method for producing neutralized phosphoric acid gypsum according to a preferred embodiment of the present invention.

Referring to FIG. 1, the circulating fluidized bed boiler fly ash (S10) and the phosphate gypsum generated in the phosphoric acid extraction process are prepared as starting materials (S20). Here, the pH of the phosphate gypsum is usually 4.0 or less.

The starting materials are then mixed in a suitable manner (SlOO). In the present invention, the mixing step can be carried out by a conventional mixing step, such as a mixing mixer.

Next, the mixed material is aged (S110). In the present invention, the aging step can be carried out by drying for 2 to 3 days under the atmosphere.

Meanwhile, FIG. 2 is a view illustrating a procedure of manufacturing a neutralized phosphoric acid gypsum according to another embodiment of the present invention.

Referring to FIG. 2, the fly ash is characterized in that the fly ash is treated (S12). In the present invention, the hydration treatment can be performed by mixing with water and a fluidized bed boiler fly ash, and filtering and drying. The mixing ratio of water to the fluidized bed boiler fly ash is 1: 1 to 1: 5 by weight and the hydration time is 1 to 6 hours.

In addition, in the present embodiment, the moisture contained in the mixed and aged mixture is allowed to dry naturally, or may be dried by other appropriate methods at the request of the consumer.

Hereinafter, the present invention will be described in more detail.

Table 1 shows the chemical composition, pH, and total organic carbon content of the fly ash produced in the fluidized bed boiler by weight%.

(Unit: wt%) SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO Na ₂ O K ₂ O TiO ₂ SO ₃ P ₂ O ₅ LOI TOC 18.75 9.07 5.37 34.20 5.97 2.80 0.52 0.57 14.25 0.24 4.76 0.18

In case of fly ash from general power plants, CaO content is about 5%, while that of fluidized bed boiler fly ash is 34.20% as shown in Table 1. In addition, it can be assumed that the content of SO ₃ is high and contains a large amount of CaSO ₄ . In Table 1, LOI means ignition loss, which means the amount of weight reduction due to the evaporation of organic materials or combined water at 950 ° C.

The reason for the high CaO content in the fly ash of a fluidized bed boiler is that limestone is added to remove sulfur oxides. CaCO ₃ is decomposed into calcium oxide (CaO) and carbon dioxide (CO ₂ ) at high temperature, and the calcium oxide reacts with sulfur oxides to form gypsum (CaSO ₄ ). On the other hand, CaO unreacted with sulfur oxides is present, which results in alkalinity. Therefore, the unreacted CaO can be utilized as a neutralizing agent.

Some water is needed for neutralization and water-soluble phosphoric acid stabilization by mixing with phosphate gypsum. Even when mixed with the fluidized bed boiler fly ash, the neutralization and water soluble phosphate stabilization reaction occurs due to the water content of the phosphate gypsum itself. However, in order to maximize the effect, it is effective in terms of reaction that water is added to the fluidized bed boiler fly ash and mixed with phosphate gypsum in the presence of water. Therefore, in the present invention, all hydrolysis products obtained by reacting the fluidized bed fly ash directly or with water are used. In hydration treatment, it is possible to remove unburned carbon contained in the fly ash which may affect the quality of cement, which is also helpful in terms of cement quality.

3 is a graph showing the results of XRD analysis of the fluidized bed boiler fly ash.

As can be seen from FIG. 3, it can be seen that calcium oxide (CaO) and gypsum (CaSO ₄ ) are present in the fly ash and that some of the undissolved limestone (CaCO ₃ ) is present.

Table 2 below is a table showing the chemical composition (wt%) and pH of the gypsum obtained by XRF analysis.

(Unit: wt%, excluding pH) SiO ₂ Al ₂ O ₃ Fe ₂ O ₃ CaO MgO SrO Na ₂ O K ₂ O TiO ₂ SO ₃ P ₂ O ₅ receptivity
P ₂ O ₅ pH 2.70 0.21 0.06 31.54 0.06 0.09 0.09 0.03 0.02 44.16 0.33 0.17 2.50

As shown in Table 2, the pH of the gypsum gypsum is strongly acidic to 2.5 and the water-soluble P ₂ O ₅ is 0.17%, which is 50% of the total-P ₂ O ₅ level. For this reason, when the phosphate gypsum is used singly, there is a problem of quality of cement which is slow in condensation due to strong acidity and high water-soluble P ₂ O ₅ content.

Therefore, in the present invention, a fluidized-bed boiler fly ash containing a calcium oxide (CaO) component is added to strong acid phosphate gypsum directly or by hydration to neutralize the mixture to a pH of 7.0 or higher. In addition, calcium lime (CaO) is used to induce a reaction to convert water soluble phosphoric acid into an insoluble calcium phosphate lime (Ca ₃ (PO ₄ ) ₂ ) as shown in the following reaction formula 2. As a result, the amount of water soluble phosphoric acid is reduced and the phosphate gypsum which can not be used as a cement retarding agent can be converted to neutralized phosphate gypsum and used as a cement retarding agent.

(Scheme 2)

3CaO + P ₂ O ₅ (water-soluble) → Ca ₃ (PO ₄ ) ₂ (insoluble)

In the present invention, the mixing ratio of the phosphate gypsum with the fluidized bed boiler fly ash or the hydration product is set to a level at which there is no problem in quality when used as a caking retarder. Preferably, 3 to 40 parts by weight of the fluidized bed boiler fly ash or water-containing treated water is contained in an amount of 3 to 40 parts by weight per 100 parts by weight of the gypsum. If the mixing ratio is less than 3 parts by weight, the neutralization effect is not exhibited. When the mixing ratio is more than 40 parts by weight, the content of SO ₃ is low and it is difficult to exert its role as a coagulation retarding agent. More preferably, it is preferable to mix 5 to 10 parts by weight of the fluidized bed boiler fly ash alone or 100 parts by weight of the phosphate gypsum with water.

According to the present invention, the phosphate gypsum and the fluidized bed boiler fly ash mixed at a proper ratio are aged for reaction and stabilization after mixing, and natural drying is carried out in order to reduce the water content as needed.

Hereinafter, the present invention will be described in more detail by way of examples.

(Example 1)

The pH and soluble phosphate content of the neutralized phosphate gypsum were measured by neutralizing the phosphate gypsum by mixing the fly ash obtained from the fluidized bed boiler with hydrated phosphate and the phosphate gypsum produced by the phosphate fertilizer production process. Here, water and fly ash were mixed with water and fly ash at a ratio of 1: 2, stirred for 2 hours, filtered through a vacuum filter, and dried at 105 ° C for pulverization. The mixture of fly ash water and phosphoric acid gypsum was mixed and the mixture was allowed to stand for 2 days in a natural atmospheric dry condition.

In Table 3, the fly ash mixing ratio is a value indicating the content of fly ash added to the gypsum (hydration treatment).

Fly ash
(Hydration treated water)
Mixing ratio (wt%) Unmixed 5 8 10 15 40 pH 2.50 9.23 10.61 10.94 11.57 12.16 Soluble phosphoric acid
(wt%) 0.17 0.010 0.007 0.005 0.008 0.007

As shown in Table 3, when the fluidized bed boiler fly ash was mixed into the phosphate gypsum, the pH was increased to 7.0 or more. As the pH was increased with the addition amount, the alkaline phosphate gypsum was produced, And it is considered to be quite good.

In addition, it was confirmed that the water soluble phosphoric acid which has the effect of setting the hardening property of cement is converted into 0.17 wt% to 0.007 ~ 0.010 wt% and is converted into insoluble phosphoric acid and stabilized.

(Example 2)

The effects of phosphoric acid gypsum prepared by hydration of fly ash obtained from fluidized bed boiler and phosphoric acid gypsum produced by phosphoric acid fertilizer production process on the quality of cement retarder were investigated. The mixing amount of the fluidized bed boiler fly ash (hydration treatment) was 5 parts by weight, 15 parts by weight and 40 parts by weight based on 100 parts by weight of gypsum phosphate. The mixture was aged at room temperature for 2 days to prepare phosphoric acid neutralized gypsum. The phosphoric acid neutralization gypsum thus prepared was added to the clinker so that the SO _{3 content} in the cement was 2.1 wt%. And the powder was pulverized to have a particle size of 3,200 ± 50 cm ² / g. The mortar compressive strength and coagulation of the cement were confirmed. The results are shown in Table 4.

division Mortar Compressive Strength (MPa) Mortar condensation 1d 3d 7d 28d Fresh
(minute) closing
(Hour: minute) Level 1 Phosphate plaster 7.96 26.89 34.36 47.55 220 5:40 Level 2 Fly ash 5wt% 9.70 29.00 37.03 51.44 190 4:50 Level 3 Fly ash 15wt% 9.31 28.35 36.93 50.12 180 4:40 Level 4 Fly ash 40wt% 8.96 28.42 36.64 49.98 170 4:20

As shown in Table 4 above, when the level 1 using phosphate gypsum alone and the level 2 to 4 using phosphoric acid neutralized gypsum prepared by adding the fluidized bed boiler fly ash water treatment, the compressive strength was increased And the condensation is shortened. It can be said that the mortar strength is stably expressed according to the effect of neutralization by CaO, so that the quality is not influenced, and the problem of slowing of condensation due to the insolubilization of water-soluble phosphoric acid is solved.

 As a result, it can be confirmed that mixing and aging by using fluidized bed boiler fly ash in phosphate gypsum can be recycled as a coagulation retardant for cement production which does not affect the quality of cement.

Claims (4)

Preparing phosphoric acid gypsum as a starting material at a pH of 4.0 or lower which is generated in the phosphoric acid extraction step; And
And mixing the phosphate gypsum with a circulating fluidized bed boiler fly ash to neutralize the phosphate gypsum to a pH of 7 or higher. The method according to claim 1,
Further comprising the step of hydrating the fly ash. ≪ RTI ID = 0.0 > 21. < / RTI > 3. The method according to claim 1 or 2,
Wherein the fluidized bed boiler fly ash comprises 3 to 40 parts by weight of the internal mortar with respect to 100 parts by weight of the phosphate gypsum. A method for producing a cement according to claim 1, wherein the cement retarding agent produced by the production method according to claim 1 is blended with a cement clinker.

Images