KR20090065143A - Method for drying gypsum microwave - Google Patents

Abstract

A method for drying chemical gypsum with microwave is provided to obtain the high quality of cement additive by irradiating microwave to dry the adhesive water of the chemical gypsum. A method for drying chemical gypsum with microwave evaporates the moisture contained in the chemical gypsum including flue-gas desulfurization gypsum and phosphoric acid chemical gypsum. The inside of the chemical gypsum is heated up with the microwave having 2.45GHz frequency and the 700~3000W output of magnetron and the moisture is evaporated.

Description

Drying method of Busan gypsum by microwaves {METHOD FOR DRYING GYPSUM MICROWAVE}

The present invention relates to a method for drying Busan gypsum by microwave, and more particularly, by internally heating Busan gypsum (fuel desulfurization gypsum and phosphate phosphate gypsum) by microwaves without phase transformation of dihydrate gypsum (CaSO ₄ · 2H ₂ O). It is a method for drying Busan gypsum by microwave which can evaporate and dry moisture (attachment water) of Busan gypsum (fume desulfurized gypsum and phosphate phosphate) within a short time.

Gypsum has natural gypsum mined from underground resources and Busan gypsum produced artificially or as a by-product of industry.It is divided into gypsum, hemihydrate gypsum and anhydrous gypsum according to the amount of crystal water in gypsum.

Natural gypsum is produced by precipitation of CaSO ₄ component by evaporation of water after tropical dryer. It is relatively high in quantity and high quality. However, in Korea, natural gypsum is hardly buried, so all of it is imported and used.

Pusan gypsum produced in Korea is produced by the flue gas desulfurization gypsum produced by the flue gas desulfurization in coal-fired power plants for the purpose of pollution prevention (about 1.2 million tons per year, containing about 10% of adsorbed water) and phosphoric acid from chemical fertilizer plants. There are phosphate phosphates (about 1.7 million tons per year, containing about 16% of adsorbed water) generated in the manufacturing process, which are mainly used for cement additives and construction.

Flue gas desulfurization gypsum is used as a flue gas desulphurizer because it uses high quality limestone and contains less impurities, so it is not separated or screened. However, because phosphate gypsum is relatively high in impurities, it is used after removing these impurities through separation / selection.

When these by-product gypsum containing adsorbed water is mixed with cement, the contained water is hydrated with the cement, thereby degrading the quality of the cement. Therefore, most of Busan gypsum is used for various purposes in the construction, civil engineering, and cement fields after drying so that the content of adhered water is 1.0% or less by hot air by direct combustion (external heating method) of liquid fuel.

Figure 1 shows the dehydration characteristics of gypsum and hemihydrate gypsum prepared by various methods. In FIG. 1, (1) shows the dehydration characteristics when the dihydrate gypsum is heated in the air, and (2) shows the dehydration characteristics when heating the saturated gypsum with saturated steam. And (3) and (4) show the dehydration characteristics of α and β hemihydrate gypsum by DTA analysis, respectively.

In general, when the water contained in the gypsum is dried by evaporation in the air, the hydrated gypsum is phase-changed by direct combustion → β-type half-hydrate gypsum → Type III anhydrous gypsum → Type II anhydrous gypsum → Type I anhydrous gypsum. Therefore, the type of gypsum produced and the content of each gypsum are different unless the temperature for heating the gypsum gypsum is controlled precisely below 200 ° C., and the properties of the cement product can be changed very irregularly if they are mixed with cement. . Because as can be seen in Figure 2 each gypsum solubility is very different depending on the temperature because they affect the rate of hydration of the cement can have a significant impact on the properties of the hardened cement.

Drying is the removal of moisture in an object by evaporation with heat. The amount of latent heat that changes the state of water into steam is about 600 kcal / kg, and the water is evaporated and dried by transferring heat to the dry object by any heating means.

Each object to be dried has limitations (requirements) in terms of product quality, and it cannot be said that only efficient supply of latent heat of evaporation should be considered. In other words, there is a need to adopt the most efficient heat transfer method among the constraints such as the drying method suitable for the quality requirements of the dry product, the allowable temperature and the like, and to improve the energy efficiency.

In addition, in the case of continuous processing in large quantities, this should be taken into account because not only the amount of heat required for drying, but also considerable energy is required for the handling of the dry matter.

As means for heating or drying (dehydrating) materials, fire, hot air, steam, infrared radiation by heat transfer, and the like are used. They are called external heating by applying heat from the outside of the object to heat the surface of the object and gradually heating it to the inside by the heat conduction of the object.

Conventionally, drying of agricultural and marine products, cooking and processing of foods have been performed by external heating using heat sources such as coal, petroleum, heat transfer, gas, steam, and infrared rays. In this heating method, heat is given to an object by conduction, convection, and radiation from an external heat source, and heat is transferred from the surface of the object to be heated by conduction to the inside, so that the quality of the object to be heated does not change. Controlling the temperature requires a fairly long heating time for the heat to reach the interior of the object.

On the other hand, dielectric heating using a high frequency electric field and microwave heating using a higher frequency electromagnetic wave are called internal heating because the object to be heated itself becomes a heating element and is heated inside the material. In the case of such internal heating, since there is almost no extra heat scattered from the outside of the object, in principle, it is a very efficient heating method.

Since microwave heating is a heating method using the characteristic that a to-be-heated object generates heat | fever without an external heat source as mentioned above, heating time can be shortened significantly and temperature can be raised comparatively constant. In the case of external heating, the outside temperature is high and the inside temperature is low, but in the microwave heating, the amount of heat generated inside and outside can be equalized. Microwaves are also highly efficient because they absorb only heat and do not heat the surrounding walls (metals) and air. Therefore, microwave heating method is widely applied to factory automation and power generation, work environment improvement, product quality improvement and new product development.

Due to the advantages of the microwave, a technique for drying Busan gypsum using a microwave has recently been proposed.

As a technique of applying a microwave according to the prior art in Busan gypsum, there is a Korean Patent Publication No. 2006-0037166, Korean Patent Publication No. 1998-049275.

The former relates to a method for preparing alpha-type half-hydrated gypsum (α-CaSO ₄ -1 / 2H ₂ O) from flue gas desulfurization gypsum using microwaves. It is characterized by reducing the production time by shortening the production time of gypsum.

The latter relates to an alpha-type hemihydrate gypsum manufacturing method from dihydrate gypsum using microwaves, and to produce alpha-type hemihydrate gypsum by simply exposing moisture-containing flue gas desulfurization gypsum to microwaves without a separate reactor.

According to the results of the present invention, simply exposing microwaves to flue gas desulfurized gypsum resulted in the synthesis of beta-type hemihydrate gypsum with better physical properties than alpha-type hemihydrate gypsum. As a result, the above-mentioned prior arts use microwaves, but are merely technologies for the manufacture of alpha-type hemihydrate gypsum, not for the purpose of drying Busan gypsum.

The present invention is to solve the above problems, by internally heating the adhesion water contained in the phosphate gypsum produced in the phosphate fertilizer manufacturing process and the flue gas desulphurized gypsum generated as a by-product from the flue gas desulfurization process by a microwave as a heat energy source It is an object of the present invention to provide a method for drying Busan gypsum by microwave which can dry only the adsorbed water without the phase change of Busan gypsum.

In the drying method of the Busan gypsum by the microwave according to the present invention for achieving the above object, by heating the Busan gypsum for 1 to 15 minutes by microwave having a frequency of 2.45GHz, the output of the magnetron 700 ~ 3000W It is characterized by evaporating to dryness.

According to the method of drying the Busan gypsum by microwave according to the present invention, by injecting microwaves into the gypsum phosphate gypsum produced in the phosphate fertilizer manufacturing process and the flue gas desulfurization gypsum produced in the wet flue gas desulfurization process by the microwave It is possible to obtain a good product, that is, a cement additive, by drying only the gypsum water.

As a result of the experiment, the time required for evaporation of the water is greatly shortened by increasing the microwave output and irradiation time without being greatly influenced by the amount of the sample and the moisture content.

As a result, when the Busan gypsum is heated by microwave, moisture and gypsum generate heat without any external heat source, which greatly shortens the drying time, and makes the calorific value of inside and outside at a constant temperature. Because of its high thermal efficiency because it does not heat the walls (metals) and air, it is expected to contribute greatly to the automation and performance of the Busan Gypsum drying process, the improvement of the working environment, and the improvement of the quality of the finished gypsum products.

The method for drying Busan gypsum by microwave according to the present invention is to dry the vaporized water of phosphate gypsum and flue gas desulfurized gypsum by drying the adsorbed water in the phosphate gypsum and flue gas desulfurized gypsum. ~ 3000W) for 1 to 15 minutes to evaporate only the adhering water and to maintain the crystal phase of the dihydrate gypsum, and the present invention will be described in more detail below.

The present invention uses microwaves as an energy source for heating in drying phosphate gypsum and flue gas desulfurization gypsum, and is a useful method that does not require any additional equipment other than a raw material supply device, a microwave generator, and a raw material transport device.

However, in order to apply the microwave device to the drying of Busan Gypsum, the cost of the micro device increases depending on the moisture content of Busan Gypsum, and the consumables cost may increase due to the short life of the magnetron, which is a major part of the microwave heating device. In consideration of this point, it is possible to dry the adhering water purely by using only microwave as an energy source, but through the pre-treatment process before the drying process by microwave, the moisture content is maintained up to a certain level with good drying efficiency by microwave by general external heating device. It can also be dried by controlling and evaporating only the remaining moisture with a microwave heating device.

In the present invention, when microwave (2.45 GHz, 700 W to 3000 W) is exposed to phosphate and gypsum desulfurized gypsum for 1 to 15 minutes, the water is evaporated and dried by its own heat (internal heating) of adherent water and gypsum contained therein. This is because when exposed to less than 1 minute, the drying effect is lowered and only the adhering water is evaporated by the latent heat of water. In addition, if the microwaves are exposed for more than 15 minutes after evaporation of the adhering water, the amount of crystallized water of the gypsum gypsum is partially detached due to the heat of the gypsum gypsum by microwaves, and the amount of converted gypsum is converted into hemihydrate gypsum. Because it can.

In the present invention, any of the microwaves that can be used may be used as long as it has a wavelength for evaporating the adsorbed water contained in the gypsum or desorbing the crystallized water, but preferably for industrial heat drying, ISM (Industrial Scientific and Medical Use) It is advisable to use a large magnetron output in consideration of the economical aspects at the frequencies of 915 MHz and 2.45 GHz, which are allocated for in-band microwave heat drying.

Hereinafter, the present invention will be described in more detail with reference to the following examples.

<Example 1>

In this example, the flue gas desulfurization gypsum and phosphate fertilizer produced in the coal-fired power plant and Busan phosphate gypsum produced in Busan gypsum. The chemical components are shown in Table 1 below, the micrographs are as shown in FIGS. 3A and 3B, and the particle size analysis is as shown in FIGS. 4A and 4B.

The average particle diameters of flue gas desulfurization gypsum and phosphate phosphate gypsum were about 34 μm and 113 μm, respectively. Flue gas desulphurized gypsum was fusiform and phosphate phosphate was almost spherical.

The microwave generator used in this embodiment generates microwaves having a wavelength of 2.45 GHz produced by domestic electronics, and the magnetron outputs of 700W, 1700W, 3000W, respectively. In order to examine the dehydration characteristics of Busan gypsum for external heating, the drying characteristics of microwave gypsum and Busan gypsum were compared using an experimental dry oven with a power of 1,000W and a far infrared heater with a power of 250W.

Table 1. Chemical Composition of Busan Gypsum

Comparative Example 1

5A and 5B show the evaporation amount of moisture contained in by-product gypsum when heated at 150 ° C. with an experimental dry oven when the amounts of flue gas desulfurization gypsum and phosphate-based gypsum were 10g, 20g and 40g, respectively. Will be shown.

It can be seen that both the flue gas desulfurization gypsum and the phosphate phosphate gypsum have a large amount of time in order to evaporate and remove all the moisture contained therein. It can be seen that in order to evaporate all the 4g of water contained in 40g, it must be dried for at least 35 minutes. In dry oven and external heating method, the heat required for evaporation of water is applied from the outside to the inside, so the time required for drying becomes longer in proportion to the amount of material to be dried.

Comparative Example 2

Figure 6 shows the evaporation rate of the moisture contained in the flue gas desulphurized gypsum when 10g, 20g, 40g of the flue gas desulfurized gypsum having a water content of 10% is heated by a 250W far infrared lamp.

As the sample amount of the flue gas desulfurization gypsum increases, it can be seen that much time is required to evaporate and remove all the contained moisture. It took 35 minutes to dry 25% of the moisture (4g) contained in 40g, which showed lower drying efficiency than heating by dry oven. This is because the output of the far infrared lamp is lower than that of the dry oven (1000W), so it is expected that the evaporation speed will be increased by using the high-power infrared lamp. However, considering that the output of commercially available far-infrared lamps is about 250W, there is a limit to drying Busan Gypsum by these methods.

<Example 2>

7a and 7b are respectively 10g of the amount of flue gas desulfurization gypsum and phosphate phosphate gypsum containing 10% water. It shows the result of measuring the evaporation amount of the adhered water when it changed to 20g and 40g (thickness: 1.0-3.5cm) and exposed to 2.45GHz and 700W microwave for 30 minutes. At this time, the amount of evaporation of moisture contained in Busan gypsum was calculated by the difference in weight of Busan gypsum before and after microwave treatment. And the mineral phase of the constituents produced when the Busan gypsum is heated is analyzed by X-ray diffractometer and shown in FIGS. 8a and 8b.

As shown in FIGS. 7A and 7B, when the Busan gypsum was exposed to the microwave at 2.45 GHz and 700 W, the moisture contained in the gypsum was evaporated within about 15 minutes without being significantly affected by the amount of the sample. This may be due to the fact that microwaves penetrate the sample well and heat moisture and dihydrate gypsum by internal heating. However, if the microwave is irradiated for 15 minutes or more, as shown in Figs. 8A and 8B, the crystal water is separated from the dihydrate gypsum and converted into semi-hydrated gypsum. Therefore, the irradiation time of the appropriate microwave should be adjusted to prevent the phase transition of the gypsum gypsum. .

<Example 3>

The sample amount of flue gas desulfurization gypsum and phosphate phosphate was fixed at 40 g, and the amount of moisture contained was changed, and the water evaporation amount of Busan gypsum was heated when the output of microwaves having a frequency of 2.45 GHz was 1700 W and 3000 W, respectively. 9b, FIG. 10a, and FIG. 10b.

As can be seen in the drawing, the amount of water evaporated at the beginning of heating is somewhat different depending on the amount of water contained in the sample. However, the time to finally evaporate all moisture attached to Busan Gypsum was found to be about the same. In addition, as the power of microwaves increased, the evaporation rate of moisture contained in Busan Gypsum increased, and all the attached water evaporated within 2.45 GHz and within 5 minutes at 1,700 W and within 3 minutes at 3000 W. At this time, the amount of water evaporation exceeds 100% because the crystal water of the gypsum is desorbed as expected in the experimental results shown in FIGS. 8A and 8B.

As a result, the exposure of Busan gypsum to microwaves was not significantly affected by the amount and moisture content of the sample, and the internal heating by microwaves resulted in the heating of water and dihydrate gypsum crystals to evaporate the water and crystal water contained more easily than the external heating. .

1 is a graph of pyrolysis characteristics according to the type of gypsum.

2 is a solubility graph according to the type of gypsum.

3A and 3B are micrographs of flue gas desulfurization gypsum and phosphate

4a and 4b are particle size analysis graphs of flue gas desulfurization gypsum and phosphate phosphate gypsum, respectively.

5A and 5B are graphs showing the evaporation rate of water according to the amount of flue gas desulfurization gypsum and heating temperature by dry oven, respectively.

Figure 6 is a graph showing the evaporation rate of flue gas desulfurization gypsum during far-infrared radiation.

7A and 7B are graphs showing dehydration rates according to sample amounts of flue gas desulfurized gypsum and phosphate phosphate gypsum having a water content of 10% at 2.45 GHz and 700 W, respectively.

8A and 8B are phase transition diagrams of hydrated gypsum with microwave irradiation time of flue gas desulfurized gypsum and phosphate phosphate gypsum having a water content of 10% under conditions of 2.45 GHz and 700 W, respectively.

9a and 9b are graphs showing the dehydration rate according to the water content of the flue gas desulfurization gypsum and phosphate phosphate gypsum of 40g at 2.45GHz, 1,000W, respectively.

10a and 10b are graphs showing the dehydration rate according to the water content of the flue gas desulfurization gypsum and phosphate gypsum of 40g at 2.45GHz, 1,700W, respectively.

Claims (3)

In the method of evaporating and drying the water contained in the Busan gypsum, including flue gas desulfurization gypsum and phosphate gypsum, A method of drying Busan gypsum by microwave heating, wherein the Busan gypsum is internally heated by a microwave having a frequency of 2.45 GHz and a magnetron having an output of 700 to 3000 W. The method of claim 1, wherein the internal heating by microwaves is heated for 1 to 15 minutes. The method for drying Busan gypsum by microwaves according to claim 1 or 2, wherein the water gypsum is heated by a heater after the moisture content of the gypsum is adjusted to 10% by a heater.

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