JPS6172625A - Production of alpha type hemihydrate - Google Patents

Abstract

PURPOSE:To obtain high-quality alpha type hemihydrate requiring a small amount of an absorbent to be blended, having improved strength and a large bulk density, by oxidizing a specific absorbent solution having scavenged a SO2 gas in an exhaust gas with air, neutralizing it to give gypsum dihydrate, concentrating and heat-treating it. CONSTITUTION:An exhaust gas containing a SO2 gas is brought into contact with an absorbent solution containing at least 10-100mmol/kg magnesium sulfossuccinate, so that the SO2 gas is scavenged, oxidized with air, neutralized with lime or slaked lime, to give gypsum dihydrate slurry having 5-25wt% concentration at 4-8pH at 40-80 deg.C. Then, the slurry is concentrated into 30-60wt%, a small amount of seed crystal of alpha-hemihydrate is added to the slurry, which is heated to 110-140 deg.C (0.5-2.7kg/cm<2>G pressure), heat-treated for 1-3 hours, converted into alpha type hemihydrate, which is subjected to solid- liquid separation, the prepared solution is circulated for scavenging the SO2 gas. On the other hand, the alpha type hemihydrate is optionally washed with hot water, and dried rapidly.

Description

[Detailed Description of the Invention] The present invention converts sulfur dioxide contained in exhaust gas into gypsum dihydrate through a so-called gypsum by-product flue gas desulfurization process, without separating it from the absorption liquid. , relates to a method for producing high-quality α-type hemihydrate gypsum (hereinafter abbreviated as α-gypsum) with a large bulk density by heating.

Conventional ■ Limb blood α-gypsum is used as a building material and other raw materials because a dihydrate gypsum molded product with higher strength can be obtained from it than β-type hemihydrate gypsum, but in reality it is expensive. It is used only for very limited purposes. α-gypsum is usually produced by wet heating dihydrate gypsum at a temperature of 100-odd degrees Celsius, but the raw material, dihydrate gypsum, is produced in large quantities by the so-called gypsum by-product flue gas desulfurization process. Therefore, there is a need for the development of an industrial method for converting dihydrate gypsum produced as a by-product in this flue gas desulfurization process into α-gypsum at low cost.

Given this current situation, α related to the flue gas desulfurization process
- Many studies have been conducted on the production of gypsum. Broadly speaking, these methods can be divided into (i) a method of converting sulfur dioxide gas in exhaust gas into α-gypsum without passing through dihydrate gypsum (Japanese Patent Application Laid-Open No. 49-1999-1);
83695, Japanese Patent Publication No. 57-53292, and Japanese Patent Publication No. 57-49491);
- Method of converting to gypsum (JP-A-53-50092, JP-A-55-113621, JP-A-55-55, +
-162426 and JP-A-56-129611
No.).

Originally, the liquid composition conditions required for the absorption liquid in the flue gas desulfurization process are unrelated to the liquid composition conditions required for the medium for producing α-gypsum. Nevertheless, when the production process of α-gypsum is directly connected to the flue gas desulfurization process, the hemihydrate gypsum solution is basically the same as the absorption fluid of the flue gas desulfurization process, and the pH is slightly higher. Only adjustment and some concentration and dilution of the liquid were allowed, making it difficult to obtain high quality α-gypsum.

High-quality α-gypsum means that the amount of mixed water is small and the two-piece gypsum molded product obtained from it has high strength, but such α-gypsum usually has a small aspect ratio of crystals and a low bulk density of the powder. is known to be large. α like this
- To produce gypsum, succinic acid,
It is essential to coexist with dicarboxylic acid salts or tricarboxylic acid salts such as tartaric acid and citric acid.If such organic modifiers are not coexisting, α-
Only gypsum has been obtained (see JP-A-55-162426). However, if such a carboxylic acid-based organic modifier is present in the flue gas desulfurization absorption liquid, it may be decomposed and consumed during the oxidation reaction, or in some cases, it may inhibit the oxidation reaction.

Due to these circumstances, there are only a few processes in which a liquid containing an organic modifier is recycled as a flue gas desulfurization absorption liquid and a hemihydrate gypsum production process in the flue gas desulfurization process and the α-gypsum production process. No. 57-53292 can be seen. However, this method involves the inclusion of volatile organic acids such as acetic acid, which creates a new problem of volatilization during the flue gas desulfurization process, and also involves directly producing α-gypsum without going through dihydrate gypsum. Therefore, there is an inconvenience that the entire wave of the gypsum reaction must be subjected to heat treatment for α-gypsum conversion. In addition, all methods that do not involve gypsum dihydrate require the gypsum production reaction to be gypsum hemihydrate, so they lack operational stability as a flue gas desulfurization process, and they also produce co-production of α-gypsum and gypsum dihydrate. becomes difficult.

On the other hand, as a method using dihydrate gypsum,
Since the method disclosed in No. 26 does not use organic acids,
Although the above-mentioned disadvantages do not exist, since no carboxylic acid modifier is used, α-gypsum with a small aspect ratio cannot be obtained. In this way, the sulfur dioxide gas in the exhaust gas is first fixed as dihydrate gypsum and then converted into α-gypsum, and the hemihydration medium containing the carboxylic acid modifier is recycled as it is as an absorption liquid. There is no known method yet.

As mentioned above, regarding the conversion of sulfur dioxide gas contained in flue gas into useful α-gypsum, there is no need to directly extract high-quality α-gypsum from the flue gas desulfurization process. No satisfactory method is known yet.This is because the conditions required for the absorption liquid for flue gas desulfurization and the medium for the production of α-gypsum are essentially unrelated, and therefore there is no method that is effective for both. This is because it was difficult to create a liquid composition that acts on
It is an object of the present invention to provide a method that can advantageously convert sulfur dioxide gas contained in exhaust gas into α-gypsum by solving this problem of liquid composition.

The structural feature of the present invention is that the exhaust gas containing sulfur dioxide is
By contacting with an absorption solution containing at least magnesium sulfosuccinate to capture sulfur dioxide gas, oxidizing it in the air and neutralizing it with limestone, dihydrate gypsum produced as a slurry in the absorption solution is absorbed into the absorption solution. The purpose is to heat it together with a liquid to convert it into α-type hemihydrate gypsum, then separate it into solid-liquid, and the resulting separated liquid to be recycled and used to capture sulfur dioxide gas.

The inventor of the present invention discovered that sulfosuccinic acid has an excellent crystallizing ability as a result of searching various crystallizing agents for producing high-quality α-gypsum with a large bulk density. In addition, dihydrate gypsum produced in the presence of sulfosuccinic acid is α-
It has been found that it has a high bulk density, which is convenient as a raw material for gypsum.

The present invention utilizes these findings as well as a flue gas desulfurization process using an absorption liquid containing a sulfosuccinate (Japanese Patent Publication No. 58-25492 and Japanese Patent Application No. 58-2
34841), sulfosuccinates are excellent absorbents for desulfurization;
- This was based on the knowledge that the amount of decomposition in the flue gas desulfurization process is smaller than that of citric acid, succinic acid, etc., which are known as crystallizing agents in the production of gypsum.

In order to directly connect the flue gas desulfurization process and the hemihydrate gypsum process, and to obtain high-quality α-gypsum, the liquid circulating in both processes must be essentially the same, so that the purpose of both processes can be effectively achieved. It must be achieved. In this sense, sulfosuccinic acid is a rare ingredient. That is, sulfosuccinic acid has an effect equal to or higher than that of succinic acid, which is known to have an excellent medicinal effect when converting dihydrate gypsum to α-gypsum, at a low concentration of 115, In addition, succinic acid has an excellent t5 mode crystal effect near neutrality, but has almost no mode effect in the acidic range below pl+4, whereas sulfosuccinic acid has good quality not only in the neutral range but also at pH 3 to 4. It has the property of producing α-gypsum.

On the other hand, a liquid containing sulfosuccinic acid is an absorbent liquid with excellent desulfurization efficiency due to the presence of a small amount of sulfosuccinic acid, not only when this is the main component for absorbing sulfur dioxide gas, but also when limestone is the main component for absorbing sulfur dioxide gas. becomes. The organic acids contained in the absorption liquid are inevitably decomposed during air oxidation, and the amount of decomposition depends on the concentration, but sulfosuccinic acid itself has a moderating effect.
Compared to succinic acid, it has a smaller amount of decomposition and is effective in both flue gas desulfurization and hemihydrate gypsum at low concentrations, so the amount of decomposition is extremely small and it is extremely economical.

Furthermore, adipic acid is known in the United States as an organic acid that can be used for flue gas desulfurization, but sulfosuccinic acid has no medicinal effect and is not suitable for producing α-gypsum (see References below).

In the present invention, the term "absorption liquid containing a small amount of magnesium sulfosuccinate" means a liquid containing approximately lO to room mol/kg of magnesium sulfosuccinate, and magnesium sulfosuccinate is the main component for absorbing sulfur dioxide gas. It also refers to liquids in which the sulfur dioxide gas-absorbing component is mainly composed of other substances, such as limestone.

There is no problem even if substances other than the sulfur dioxide gas-absorbing component coexist in this liquid, and the following substances usually coexist.

That is, as dissolved components, anions include various organic ions, which are decomposition products of sulfosuccinic acid, SO; -1CI-2
11SOi is present, and as cations, M g 2'' is present, mainly Na+ and a small amount of Ca'+. Also, as solids, dihydrate, limestone, and calcium sulfite are present.

Any method of absorbing sulfur dioxide gas in exhaust gas using an absorption liquid, air oxidation method, neutralization method with limestone or slaked lime may be used, and each reaction is performed by a liquid containing magnesium sulfosuccinate. It is sufficient if a slurry of industrial water gypsum is produced. Normally, this slurry has a dihydrate-yf concentration of 5 to 25 M%, a pH of 4 to 8, and a temperature of 40 to 80°C, and with respect to the above-mentioned absorption liquid composition, dissolved components include OSO; solid content This is the composition excluding calcium sulfite and limestone.

The double gypsum slurry obtained as described above is desirably concentrated and heat-treated to obtain α-gypsum.The quality of the obtained α-gypsum is basically determined by the liquid composition and heating temperature. , is determined by heating time, but temperature and reaction time have a complementary relationship, and 110~
Thermal energy consumption within the range of 140'C11 to 3 hours,
This may be done by optimizing from the viewpoint of equipment costs, etc. Regarding the liquid composition, the influence of direct connection with the flue gas desulfurization process will also be explained below.

First, as an anion, sulfosuccinic acid is 10 to 100m
mol/kg, this concentration range is defined in the flue gas desulfurization process. Although the mediocrystal effect of sulfosuccinic acid becomes weaker as it becomes thinner, there is no significant difference in this concentration range, and 1 α-gypsum with a sufficiently high bulk density is provided (see Example 2 below).

Incidentally, since sulfosuccinic acid undergoes oxidative decomposition induced in the flue gas desulfurization process, it contains some organic anions which are decomposition by-products, but the coexistence of these has almost no effect on the bulk density.

SO co- exists in the liquid mainly due to the dissolution of l'1g in limestone. 5oH - The higher the 4 degrees, the more melting C
The a2+ concentration is reduced and is effective in preventing scaling in the flue gas desulfurization process, while too high a concentration reduces the oxidation rate of sulfite.

Therefore, depending on the concept of flue gas desulfurization process design, S
O,? - There is a large difference in the concentration, usually 0.5 to 8 wt%
That's about it. When such a liquid is used as a medium for α-gypsum conversion, the higher the temperature (5oH-1 degree), the lower the temperature of half-water level Since it is easy to use, the upper limit is 8 to 10 wt%.

Therefore, as a commonly used flue gas desulfurization process, S
α-gypsum having a sufficiently high bulk density can be obtained within the range of O4-b1 degrees.

CI- is present as chloride in the water and 11(:l gas in the exhaust gas) concentrated in the absorption liquid.Cl-65 in the absorption liquid
The degree of corrosion is closely related to the corrosion of the abrasive materials that constitute the flue gas desulfurization plant, and is usually controlled to be 1 to 2 wt% or less.

There is no problem in turning into α-gypsum within this range, but if the concentration is too high, anhydrite tends to occur like SO knee, and the upper limit concentration is 6 to 8 wt%. Therefore, there is no contradiction with the liquid composition of the flue gas desulfurization process.

Next, we will discuss cations as a liquid composition.

The cation used in the flue gas desulfurization absorption liquid is usually M g 2
", N8+, and a small amount of Ca equivalent to the amount of gypsum melt"
Including +. The flue gas desulfurization process has a unique process configuration that takes advantage of the physical properties of each ion, but recent flue gas desulfurization processes that use limestone as a neutralizing agent only use M g 2+ or M g 2+ A solution containing mainly Na + is often used. On the other hand, α−
It is most preferable to use only M g 2+ as the medium for gypsum conversion, and highly dense α-gypsum (M) is used. However, a small amount of Na As the concentration of Na+ increases, the bulk density decreases, so the concentration must be as low as possible (see Example 3 below).The reason for this is that in equilibrium, 5CaSO+4Na2SO=・31
This seems to be due to the proximity to the hO production region.

Although some N11 may be contained in the absorbent liquid due to ammonia leaked from the electrostatic precipitator or dry denitrification, this has almost no effect on the bulk density of α-gypsum.

Next, specific embodiments of the present invention will be described based on the accompanying drawings.

In the figure, 1 is the exhaust gas desulfurization main equipment that produces dihydrate gypsum as a by-product, and uses an absorption liquid containing at least magnesium sulfosuccinate to desulfurize the exhaust gas 2 containing sulfur dioxide gas into clean gas 3. Limestone or slaked lime and oxidizing air 5 are supplied to the absorption liquid to produce a dihydrate slurry.

The dihydrate gypsum slurry 6 generated here is taken out and concentrated by the thickener 7. The overflow liquid 8 is returned to the flue gas desulfurization main body 1, and the concentrated dihydrate gypsum slurry 9 is used for the production of α-stone. provided, 1. The purpose of this slurry concentration is to reduce the amount of treated liquid per unit of α-gypsum, and also to reduce the capacity of subsequent equipment and the thermal energy required for heating.

Once upon a time, 'h? It is desirable that the slurry concentration is as high as possible within the range that it can be handled as a fluid, and preferably the slurry concentration is 30 to 50% by weight.

The dihydrate gypsum slurry 9 used for the production of α-gypsum is pumped under increased pressure by a pump 10 and sent to the hemihydrate gypsum reaction tank 11, or at 110 to 140°C for the hemihydrate gypsum reaction.
It is necessary to heat to a pressure of 0.5 to 2.7 kg/cnl G), and the temperature is raised by a heat exchanger 12 and a steam heater 13. Note that this heating is performed by these indirect heat exchangers 12.
13, steam may be directly blown into the reaction tank 11. The hemihydrate gypsum conversion reaction tank II may be either a multi-tank flow type as shown in the figure or a hatch switching type.

As mentioned above, the hemihydrate gypsum conversion reaction in the reaction tank 11 is completed in 1 to 3 hours at a predetermined temperature, but at this time, a small amount of α-
It is effective to add gypsum seed crystals 14 in advance to speed up the hemihydrate gypsum conversion reaction.

The α-gypsum slurry 15 obtained by the hemihydrate gypsum reaction is cooled to below the boiling point at normal pressure and returned to the dense pressure, and then sent to the separator 16. As a cooling method at this time, either an indirect cooling method using the heat exchanger 12 or a direct cooling method using flash evaporation can be used. Can be used for heating.

The α-stone cake obtained by solid-liquid separation in the separator 16 is washed with hot water if necessary. At this time, the slurry and α-gypsum cake were kept at 84°C to avoid turning the α-gypsum into industrial water.
At the same time, adhering moisture is promptly removed using a dryer 17 to obtain α-gypsum 18. The filtrate and cleaning liquid 19 from the separator 16 are returned to the exhaust gas desulfurization main unit 1, and the α-gypsum cleaning liquid also serves as make-up water for the exhaust gas desulfurization system.

EXAMPLES Hereinafter, the present invention and its effects will be specifically explained with reference to Examples.

In addition, the indication of 65 degrees in the present invention is for the entire slurry regarding the solid content, and for the aqueous solution excluding the solid content regarding the dissolved components.

Stolen soil C weight/EI + combustion exhaust gas (SO□a degree 1400ppm)
3000ONM'/hr was desulfurized with an absorption liquid containing 45 mmol/magnesium sulfosuccinate,
This absorbed liquid was neutralized with limestone powder and oxidized in air to obtain a 10-15% by weight dihydrate gypsum slurry,
From the flue gas desulfurization equipment that separates the dihydrate gypsum cake, a portion of the dihydrate slurry was fractionated and used for the production of α-petite stone.

The separated 12% by weight dihydrate gypsum slurry was allowed to stand still for 30 minutes.
% slurry was obtained, and 2.5 kg of it (Kousui stone ffo
.

(including 75 kg) into an autoclave equipped with an IVH
Heat treatment was performed for a certain amount of time. This slurry is heated at 95°
Immediately after hot filtration at C. and subsequent washing with hot water at 95.degree. C., the crystals were dried at 100.degree.

The obtained crystals contained 6.1% by weight of water of crystallization, and were confirmed to be α-stone blue by differential calorimetry and X-ray diffraction. The crystal shape has an aspect ratio of 1 to 3, a length of about 30 to 110μ, and a bulk density of 1.61g/Cn! Met.

The liquid composition of the dihydrate gypsum slurry collected from the flue gas desulfurization equipment was as follows.

Sulho Kohaku @ 45 m mo'l/Jsoy
, -4.6 wt% C1,"' 0.8 wt% Mg"
13040 mg/kgNa” 4
050 B/kg pH 5,8 peak week 1 211 obtained from the flue gas desulfurization equipment used in Example 1
The water stone pre-cake was washed with water and dried, and then the reaction temperature was 118°C ± 1°C and the reaction time was 1.5 hours using hemihydration medium solutions having the following compositions with different sulfosuccinate concentrations as described in Example 1. The results in Table 1 were obtained using the same procedure.

Hemihydrate medium 1.5 kg Gypsum dihydrate 375 g (Bulk density 1.43 g/cn
l) The obtained crystals were all α-gypsum as in Example 1.

The modulating ability of sulfosuccinic acid is sufficient even at a fairly low concentration, and in addition, as an anion other than sulfosuccinic acid, S
It can be seen that high quality α-gypsum can be obtained from a solution containing Oney and C1-.

1 Using the same equipment as in Example 2, the effects of the type and concentration of carboxylic acid were examined. 1.5 kg of hemihydrate medium has the composition shown in Table 2,
375 g of dihydrate gypsum was the same as in Example 2. The same operation as in Example 2 was carried out at a reaction temperature of 128° C.±1° C. and a reaction time of 1.5 hours, and the results shown in Table 2 were obtained.

All the crystals obtained were α-gypsum. This result shows that sulfosuccinic acid has almost the same modulating ability as succinic acid at a concentration five times that of succinic acid.

Also, adipic acid is an organic carboxylic acid that can be used in the exhaust gas tax sulfur process, but it can be said that it is inferior to sulfosuccinic acid in terms of medium crystal ability.

This example illustrates the relationship between the type of cation, its concentration, and pH.

Using the same apparatus as in Example 2 and using the hemihydration medium as shown below, the same operations as in Example 2 were carried out to obtain the results shown in Table 3.

Anion concentration 1.508 equivalents/kgp)I-6,
0 All the crystals obtained were α-gypsum. From this result, it can be seen that the lower the amount of Na, the higher the bulk density of α-gypsum can be obtained.

Moreover, it can be understood that even if ρ11 is lowered, the negative effect is not large.

Comparison ■ This example shows the results of an experiment in which trisodium sulfosuccinate was replaced with trisodium succinate at an equimolar concentration as a comparison of experiment number 311 in Table 3 shown in Example 3.

The obtained α-gypsum had a bulk density of 0.111 g/cwt, an aspect ratio of 7 to 13, and a length of about 50 to 200 μm.

From this result, it can be seen that the moderating ability of succinic acid is considerably weakened at low pHC.

This example by Arashi Tsukido illustrates the relationship between the concentration of gypsum slurry and α-gypsum conversion.

Using the same apparatus as in Example 2, using the hemihydration medium as shown below, the reaction temperature was 122±I'c, the reaction time was 15 hours, and the same operation as in Example 2 was performed to obtain the results shown in Table 4. .

pl+ = 6.0 All the crystals obtained were α-gypsum. Although the bulk density decreases as the slurry concentration increases, the effect is slight. The reason why even such a highly concentrated slurry can be handled as a fluid is that both the raw material dihydrate gypsum and α-gypsum have high bulk densities.

[Brief explanation of the drawing]

The attached drawings are process diagrams illustrating embodiments of the present invention. In the figure, 1--1 flue gas desulfurization equipment 2--exhaust gas 6--2 gypsum slurry 9--concentrated slurry 11---hemihydrate gypsum conversion reaction tank 15---1-- α-Gypsum slurry 18・-・-α-Gypsum procedure amendment October 22, 1982

Claims (4)

[Claims] (1) Exhaust gas containing sulfur dioxide gas is brought into contact with an absorption liquid containing at least magnesium sulfosuccinate to capture sulfur dioxide gas, which is oxidized in the air and neutralized with limestone, thereby creating a slurry in the absorption liquid. An exhaust gas characterized in that gypsum dihydrate produced as gypsum is heated together with the absorption liquid to convert into α-type gypsum hemihydrate, followed by solid-liquid separation, and the resulting separated liquid is recycled and used for capturing sulfur dioxide gas. A method for producing α-type hemihydrate gypsum from sulfur dioxide gas. (2) The concentration of magnesium sulfosuccinate is 10 to 10
The method for producing α-type hemihydrate gypsum according to claim (1), using an absorption liquid having a concentration of 0 mmol/kg. (3) The slurry of dihydrate gypsum used to convert dihydrate gypsum into α-type hemihydrate gypsum is a slurry concentrated to a slurry concentration of 30 to 50% by weight. Method of manufacturing hydrogypsum. (4) The method for producing α-type hemihydrate gypsum according to claim (1), wherein the heating temperature is 110 to 140°C.