JPS6255891B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an economical method for producing α-type hemihydrate gypsum and flue gas desulfurization. Conventionally, as shown in Japanese Patent Publication No. 51-43833, a method for producing α-type hemihydrate gypsum is known in which an α-type hemihydrate gypsum reactor is installed after the oxidation tower of a wet desulfurization equipment. In order to produce α-type hemihydrate gypsum with a good crystalline shape for practical use, it is necessary to add a crystal modifier to the reaction solution. The reaction liquid is returned to the desulfurization equipment and used for circulation.
The added crystal modifier will affect the desulfurization reaction. That is, when a commonly used organic crystal modifier is used in the production of α-type hemihydrate gypsum, organic substances degraded by heat accumulate in the desulfurization system, causing various adverse effects. In the α-type hemihydrate gypsum reactor, the reaction is carried out in a liquid, and from a thermoeconomic perspective, the liquid can be recycled or used for heat exchange, but the composition of the liquid must be strictly controlled. If the composition of the liquid in the flue gas desulfurization equipment and the liquid in the α-type hemihydrate gypsum reactor is different, separate the dihydrate gypsum from the liquid so that each liquid does not inhibit the reaction of the other system. (in the form of a liquid-containing cake) must be sent to an α-type hemihydrate gypsum reactor. Furthermore, equipment for removing harmful substances from the cake liquid may even be required. When an α-type hemihydrate gypsum reactor is incorporated into a flue gas desulfurization equipment, the respective liquids will be mixed. The conventional α-type hemihydrate gypsum production equipment described above uses an organic modifier, so the desulfurization wastewater is
Many problems arise, including increased COD, effects on desulfurization performance, and effects on other reactions. The present invention was made in view of the above points, and includes an α-type hemihydrate gypsum reactor installed downstream of the oxidation tower in a wet flue gas desulfurization equipment using an absorbent mainly containing calcium compounds. In the method of producing α-type hemihydrate gypsum by supplying dihydrate gypsum slurry generated in flue gas desulfurization equipment, a magnesium compound is added in advance to an absorbent mainly composed of calcium compounds, and this absorbent is used to remove flue gas. By introducing the desulfurized slurry containing magnesium sulfate as it is into an α-type hemihydrate gypsum reactor, or by separating the air contained in the dihydrate gypsum slurry containing magnesium sulfate discharged from the oxidation tower. By introducing the dihydrate gypsum slurry into the α-type hemihydrate gypsum reactor after sufficiently increasing the concentration, no side effects will occur even if the liquid from the α-type hemihydrate gypsum reactor is returned to the flue gas desulfurization equipment. The present invention aims to provide a flue gas desulfurization method that involves the by-production of α-type hemihydrate gypsum. Hereinafter, the configuration of the present invention will be explained based on the drawings. First, slaked lime or calcium carbonate (hereinafter referred to as slaked lime), which is a main absorbent, is put into the slurry adjustment tank 1, where it is mixed with the slurry discharged from the oxidation tower 2. Magnesium hydroxide is also charged into the slurry adjustment tank 1 in order to maintain the magnesium concentration in the entire system at a constant value. In the slurry conditioning tank 1, a portion of the slaked lime reacts with magnesium sulfate in the oxidized slurry and is converted to magnesium hydroxide. The slurry in the slurry adjustment tank 1 is sent to an absorption tower 3. The absorption tower slurry is sprayed into the tower and comes into contact with the flue gas, and the
SO ₂ is absorbed by the following reaction. Ca(OH) ₂ +SO ₂ →CaSO ₃ +H ₂ O Mg(OH) ₂ +SO ₂ →MgSO ₃ +H ₂ O Calcium sulfite and magnesium sulfite produced by absorption are partially oxidized by oxygen in the gas in the following reaction. and becomes gypsum and magnesium sulfate. CaSO ₃ +1/2O ₂ →CaSO ₄ (dihydrate) MgSO ₃ +1/2O ₂ →MgSO ₄ (solution) In order to complete this oxidation reaction, the slurry from absorption tower 3 is sent to oxidation tower 2, Air is blown in there. A part of the oxidizing tower slurry discharged from the oxidizing tower 2 is sent to the slurry adjustment tank 1, and the rest is sent to the thickener 4, where it is divided into a concentrated slurry and a supernatant liquid. The supernatant liquid is returned to the absorption tower 3, and the concentrated slurry is preheated in a heat exchanger 5 and then sent to an α-type hemihydrate gypsum reactor 6. In the α-type hemihydrate gypsum reactor 6, the slurry is maintained at a high temperature for a certain period of time by steam injection, and dihydrate gypsum in the slurry is converted to α-type hemihydrate gypsum. α type hemihydrate gypsum reactor 6
The slurry discharged from the tank is flashed and returned to normal pressure, and then immediately applied to the solid-liquid separator 7. The solid content is dried in a short time by the dryer 8 to become a product α-type hemihydrate gypsum. The liquid is transferred to heat exchanger 5.
After being used as a heat source for preheating the concentrated slurry from the thickener 4, it is returned to the absorption tower 3. As explained above, the method of the present invention provides the following effects. (1) Magnesium sulfate in the mother liquor of the desulfurization equipment is originally added to enhance the desulfurization effect, but it can be used as is as a modifier for the α-type hemihydrate gypsum production reaction. . That is, the mother liquor of the α-type hemihydrate gypsum reactor can be used as it is from the desulfurizer, and there is no need to add a crystal modifier. Although it is necessary to control the magnesium sulfate concentration in the reactor to a constant value, it has already been adjusted for the desulfurization reaction in the desulfurization device, so there is no need to readjust it. In this way, the fluid in the flue gas desulfurization equipment and the fluid in the α-type hemihydrous gypsum reactor are shared, and both can be operated without interfering with each other's functions and performance, eliminating the problems of the conventional method mentioned above. It is a simple and reasonable method that does not occur at all. (2) It is possible to omit the dihydrate gypsum dehydration device and conveyance device from the desulfurization device. (3) Once the air contained in the gypsum slurry is sufficiently separated at the oxidation tower outlet and the gypsum slurry concentration is increased, the heat consumption required for heating in the α-type hemihydrate gypsum reactor can be significantly reduced. can do. Next, embodiments of the present invention will be described. Example Heavy oil-fired boiler exhaust gas with a temperature of 150°C and an SOx concentration of 1500 ppm (dry base) was treated according to the flow shown in the drawing. The temperature of the clean gas was 55°C, and the SOx concentration was 200 ppm (dry basis). In addition, the liquid at the outlet of the oxidation tower has a MgSO ₄ concentration of 6wt% and a slurry concentration of 7wt%, and the liquid in the α-type hemihydrate gypsum reactor has a MgSO ₄ concentration of 6wt% and a slurry concentration of 20wt%.
%, pH was 5-7, temperature was 120°C, and residence time was 4 hours. The properties of the obtained α-type hemihydrate gypsum were as shown in the following table.

【table】

[Table] As is clear from the above, good α-type hemihydrate gypsum could be obtained while maintaining sufficient desulfurization performance.

[Brief explanation of the drawing]

The drawing is a flow sheet showing an example of an apparatus for carrying out the flue gas desulfurization method involving the by-production of α-type hemihydrate gypsum of the present invention. 1... Slurry adjustment tank, 2... Oxidation tower, 3...
Absorption tower, 4...Sickener, 5...Heat exchanger, 6
...α-type hemihydrate gypsum reactor, 7... solid-liquid separator,
8...Dryer.

Claims (1)

[Scope of Claims] 1. An α-type hemihydrous gypsum reactor is installed downstream of the oxidation tower in a wet flue gas desulfurization system using an absorbent mainly containing a calcium compound, and this reactor is equipped with a In the method of producing α-type hemihydrate gypsum by supplying dihydrate gypsum slurry, a magnesium compound is added in advance to an absorbent mainly composed of calcium compounds, and this absorbent is used to perform flue gas desulfurization treatment to produce α-type hemihydrate gypsum. A flue gas desulfurization method accompanied by by-product of α-type hemihydrate gypsum, characterized by introducing a slurry containing magnesium sulfate as it is into an α-type hemihydrate gypsum reactor. 2. An α-type hemihydrate gypsum reactor is installed downstream of the oxidation tower in a wet flue gas desulfurization equipment that uses an absorbent mainly composed of calcium compounds, and the dihydrate gypsum slurry produced in the wet flue gas desulfurization equipment is fed to this reactor. In the method of producing α-type hemihydrate gypsum by supplying it, a magnesium compound is added in advance to an absorbent mainly composed of calcium compounds, and the air contained in the dihydrate gypsum slurry containing magnesium sulfate discharged from the oxidation tower is removed. A flue gas desulfurization method accompanied by by-product of α-type hemihydrate gypsum, which is characterized in that the dihydrate gypsum slurry is separated and sufficiently increased in concentration, and then introduced into an α-type hemihydrate gypsum reactor.