RU2277066C1 - Method of obtaining sulfuric acid from flue gases - Google Patents

Abstract

FIELD: method of desulfurization of waste gases; power engineering, chemical industry, ferrous and non-ferrous metallurgy.

SUBSTANCE: proposed method includes heterogeneous-catalytic oxidation of sulfur dioxide contained in flue gases and absorption of sulfuric anhydride formed during this procedure by water. Used as catalyst are ferrospinels prepared on base of manganese-zinc powder in form of thin plates which are constantly crushed directly in zone of oxidation of SO₂ and SO₃ in aqueous medium continuously generating freshly formed catalytically active surfaces. Process is performed under normal conditions: room temperature and atmospheric pressure.

EFFECT: enhanced efficiency.

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Description

The invention relates to methods for desulfurization of exhaust gases and can be used in energy, chemical industry, ferrous and non-ferrous metallurgy, etc.

The currently widespread calcareous and calcareous adsorption desulfurization methods no longer always satisfy constantly growing environmental standards. So, the efficiency of dry adsorption does not exceed 60%, wet - 90%. In addition, the use of these methods is associated with the expansion of limestone production and the formation of dumps CaSO ₃ and CaSO ₄ . Meanwhile, if all SO ₂ emitted into the atmosphere in the CIS could be turned into such a valuable product as sulfuric acid, then its production could be reduced by 60%. Recently, various methods of physical action on sulfur-containing media and catalytic systems, which are used to intensify the process of oxidation of SO ₂ to SO ₃ with the simultaneous absorption of the latter by water and the production of sulfuric acid, are beginning to attract more and more attention.

A known method for the photocatalytic oxidation of SO ₂ in SO ₃ in aqueous solutions in the presence of a CuCl ₂ catalyst and KI cocatalyst (potassium iodide), which results in H ₂ SO ₄ (see SU No. 1092895, C 01 B 17/74, 1985). The disadvantage of this method is the need to use ultraviolet radiation (mercury lamp), and also that the resulting acid is contaminated with soluble salts of the catalysts. These disadvantages do not allow the use of this method in industry.

The known process of the company "Ebara" (Japan), in which accelerated electrons are used to oxidize SO ₂ in SO ₃ . At an irradiation dose of 1.0 Mrad, the degree of purification of gases from SO ₂ reaches 90% (Kawamura K., Shuiv. Radiation Phys. And Chem., 1984, 24, No. 1, pp. 117-127). The method is based on the radiolysis of water vapor present in gases, resulting in the formation of free radicals that oxidize SO ₂ to SO ₃ , followed by binding of the latter. The main disadvantage of this method is the high cost of the electron generator (accelerator). So, the cost of an electron generator with a capacity of 100 kW is about $ 1 million.

The closest chemical process to the claimed one is the method of using ultrasound for cleaning gases from SO ₂ (and NO ₂ ) (RZH "OVHT", No. 21, 1994, 21I410) - the prototype. As a result of acoustic cavitation during the ultrasonic treatment of aqueous SO ₂ solutions, high temperatures and pressures develop, which is accompanied by the decomposition of water molecules into OH ^- and H ⁺ and the creation of conditions for chemical processes in the purification of exhaust gases in liquid scrubbers. Ultimately, sulfuric acid is formed, the pH decreases and the concentration of bisulfite decreases, and the sulfate content increases. The disadvantages of this method are the need for the use of bulky equipment (scrubbers), contamination of the resulting sulfuric acid with bisulfites and sulfates and a significant energy intensity of the process.

The purpose of the proposed proposal is to simplify and intensify the process, reducing energy intensity and improving the quality of the final product - H ₂ SO ₄ .

A feature of the proposed method is that the process of oxidation of SO ₂ in SO _{3 is} carried out in an aqueous medium (without oxygen) with continuous generation of a catalytically active medium in the reaction zone, which are solid thin plates of ferrospinel, which are subjected to crushing due to the active hydrodynamic regime, created in the apparatus of a special design.

The essence of the proposed proposal is as follows. In a water-filled apparatus with a special device that ensures that an active hydrodynamic regime is created inside the apparatus with the stirrer operating (see RU No. 2131294, B 01 F 3/12, 1999), the ferrospin catalyst is loaded in the form of thin rectangular plates with a size of 5 × 2- 3 cm and a thickness of 0.5-1 mm. At the same time, while the apparatus stirrer is operating, SO _{2 is} sucked into it through the lower nozzle (due to the pumping effect). During intensive pumping of water with catalyst plates through the openings of the conical septum, rotor and stator of the apparatus, the plates are crushed, as a result of which freshly formed surfaces are constantly generated. Since crushing of the solid in general and ferrite in particular is accompanied by the breaking of interatomic bonds, intermediate states of matter rich in energy with maximum chemical (catalytic) activity appear on freshly formed surfaces. Upon contact with such surfaces of water molecules, they decompose into OH ^- and H ⁺ ions, of which the former serve as active oxidizing agents of SO ₂ to SO ₃ . The resulting SO _{3 is} readily absorbed by water to form H ₂ SO ₄ . The process is conducted under normal conditions - room temperature and atmospheric pressure. The number of revolutions of the mixer is 2500-3000 rpm.

The method is as follows.

Example 1. 5 l of water is poured into the apparatus and the mixer is turned on. Set the speed of the stirrer - 3000 rpm. Then load 0.5 kg of catalyst (ferrospinel plates with dimensions 5 × 2-3 cm and a thickness of 0.5-1 mm). The lower open nozzle of the apparatus is connected to a cylinder with SO ₂ and gas is sucked into the apparatus in an amount of 100 l for 1 hour. At the end of the apparatus, its contents are poured onto a suction filter and the crushed catalyst is filtered off. Approximately 5 L of sulfuric acid conc. 70 g / l When the number of revolutions of the mixer is below 2500 rpm, there is a spill of water through the lower fitting and the uniformity of the supply of SO ₂ gas to the apparatus is violated. If the speed increases above 3000 rpm, there is a danger of flooding, as well as the uniformity of gas suction.

Example 2. An artificial gas mixture simulating the composition of the flue gases of boiler houses burning sulfur coals (75% N ₂ ; 15% H ₂ O; 8% CO ₂ ; 2% SO ₂ ), is sucked into the apparatus working in a volume of 200 l / h in the same mode as in example 1. The amount of loaded catalyst is 0.2 kg About 5 l of sulfuric acid conc. 3 g / l

Thus, the claimed proposal allows you to get the following advantages compared to the prototype:

- to carry out the process under normal conditions - room temperature and atmospheric pressure instead of high temperatures and pressures - as in the prototype;

- significantly simplify the hardware design of the process - instead of a bulky scrubber, the simplest in design capacitive apparatus with a mixer is used;

- reduce energy consumption by abandoning additional devices for obtaining ultrasound and using only an ordinary electric motor to drive the mixer;

- to receive the final product - sulfuric acid pure, not contaminated with impurities of bisulfites and sulfates.

Claims (1)

A method for producing sulfuric acid from flue gases by heterogeneous catalytic oxidation of sulfur dioxide contained in them and absorption of the resulting sulfuric anhydride with water, characterized in that ferrospinels in the form of thin plates are used as a catalyst, which are constantly crushed directly in the oxidation reaction zone of SO ₂ in SO ₃ in an aqueous medium, continuously generating freshly formed catalytically active surfaces, and the process is conducted under normal conditions.