RU2236893C1 - Method cleaning flue gases from sulfur oxides - Google Patents

Abstract

FIELD: chemical cleaning of waste gases from sulfur oxides; heat-power engineering; utilization of flue gases of thermal power plants; oil and gas refining industry for burning hydrogen sulfides in Klauss furnaces; ferrous and non-ferrous metallurgy; mining and chemical industries.

SUBSTANCE: proposed method includes mixing flue gas with air, neutralization in absorption chamber through contact with liquid absorbent and removal of cleaned gases and acid solution. Acid gases are neutralized by alkali absorbing solution and aqueous solution of sulfate of sulfite salt formed after neutralization is subjected to regeneration by unipolar electrochemical treatment in diaphragm-type electrolyzer at obtaining sulfuric acid in anode zone and alkali absorbing solution in cathode zone; alkali absorbing solution is directed to absorption chamber for neutralization of acid gases. Treatment is performed at specific amount of electricity within 3000-4500 C/l.

EFFECT: high degree of neutralization of toxic emissions; reagentless utilization of sulfur oxides and regeneration of absorbent.

2cl, 1 dwg, 2 tbl

Description

The invention relates to methods for the chemical purification of exhaust gases from sulfur oxides and can be used in the power industry for cleaning and utilizing flue gases from heat power plants, as well as in the oil and gas processing industry when burning hydrogen sulfide in Klaus furnaces, ferrous and non-ferrous metallurgy, coal and chemical industries.

The closest in technical essence and the achieved result is a method of purification of flue gases from sulfur oxides, including mixing with air, neutralizing acid gases in an absorption chamber by contacting with a liquid absorbent, removing purified flue gases and acid solution (RF patent No. 2161528, 01 D 53/34, 1999 - prototype).

This method has the following disadvantages: insufficient technological efficiency of purification, the use of acid condensate as an absorbent with the formation of nitric and sulfuric acid leads to the rapid destruction of technological equipment due to the high corrosiveness of these solutions.

An object of the invention is to increase the economic and technological efficiency of cleaning, ensuring the cyclicality of the process and the reagent-free disposal of acid components of flue gas to produce a product having high economic value, while increasing the reliability and durability of technological equipment.

The problem is solved in that in a method for purifying flue gases from sulfur oxides, including mixing them with air, neutralizing in an absorption chamber by contacting with a liquid absorbent, removing purified flue gases and an acidic solution, according to the invention, acid gases are neutralized with an alkaline absorption solution, and the resulting after neutralization, the aqueous solution of sulfate-sulfite salt is subjected to regeneration by unipolar electrochemical treatment in a diaphragm electrolyzer with obtaining in the anode th zone of sulfuric acid and in the cathode zone - alkali absorption solution, which is sent to the absorber chamber to neutralize acid gases.

The problem is also solved by the fact that the electrochemical treatment is carried out with a specific amount of electricity in the range of 3000-4500 C / l.

The technological process of flue gas purification from sulfur dioxide is carried out in three interrelated, sequential and continuous stages:

- gas-air (partial) oxidation of sulfur dioxide SO ₂ with atmospheric oxygen to sulfur trioxide SO ₃ ;

- neutralization of sulfur oxides with an alkaline sorbent to obtain a sulfate-sulfite salt of an alkali metal;

- regeneration of the absorption solution by unipolar electrochemical treatment to obtain the initial sorbent, alkali metal hydroxide and the conversion of sulfate compounds to sulfuric acid.

The chemistry of the technological process of flue gas purification from sulfur dioxide (oxidation, neutralization of sulfur oxides and regeneration of the absorption solution) is presented as follows:

1. The stage of preliminary gas-phase oxidation of sulfur dioxide by atmospheric oxygen

SO ₂ + 1 / 2O ₂ → SO ₃

2.1. Stage of liquid-phase absorption of sulfur oxides by alkaline absorption solution (for example, sodium hydroxide)

SO ₂ + 2NaOH → Na ₂ SO ₃ + H ₂ O

SO ₃ + 2NaOH → Na ₂ SO ₄ + H ₂ O

3.1. The stage of electrochemical regeneration of the absorption solution and the conversion of sulfur oxides to sulfuric acid

Na ₂ SO ₃ + 2H ₂ O + 1 / 2O ₂ → 2NaOH + H ₂ SO ₄

Na ₂ SO ₄ + 2H ₂ O → 2NaOH + H ₂ SO ₄

The total reaction of the process of purification of flue gases from sulfur dioxide with obtaining sulfuric acid as the final product is expressed by the equation

SO ₂ + 1 / 2O + H ₂ O → H ₂ SO ₄

Thus, in the developed technology for the utilization of sulfur dioxide, the flue gas treatment process is carried out by liquid-phase mixing of flue gases containing sulfur oxides with an alkaline aqueous solution obtained by unipolar electrochemical treatment in the cathode zone of a diaphragm electrolyzer while simultaneously producing sulfuric acid in the anode zone as the final product of the cleaning process.

Therefore, during unipolar electrochemical treatment of an aqueous solution of sulfate-sulfite sodium salt in the cathode zone, the initial sorbent is formed - sodium hydroxide (NaOH), and in the anode zone, the final product of the utilization of sulfur oxides is sulfuric acid (H ₂ SO ₄ ). As a result of these reactions, the electrolyte solution is regenerated, i.e. an absorption solution that is fed back into the cycle to absorb sulfur oxides. The production of alkali metal hydroxides from a sulfate-sulfite solution and its regeneration after neutralization of sulfur oxides is carried out simultaneously in the same apparatus, i.e. electric power. spent on absorbent, equivalently also provides its regeneration, which is a new technical effect of the proposed method.

The method is implemented according to the scheme, which is presented in the drawing.

The source flue gas containing sulfur dioxide and to be processed is fed to a mixer 1, where atmospheric air is supplied simultaneously with a centrifugal fan 2, where they are mixed and an air-gas mixture is formed and, therefore, a partial reaction of sulfur dioxide oxidation with atmospheric oxygen. Then the gas-air mixture enters the absorber 3, where at the same time by the centrifugal pump 4 serves an absorption solution - a sulfur oxide neutralizer, where sulfur oxides are absorbed and neutralized with an alkaline sorbent. The purified flue gas is removed from the upper outlet of the absorber 3 and released into the atmosphere. The spent absorption solution (sulfate-sulfite solution) from the absorber 3 enters the diaphragm electrolyzer 5, where the alkaline absorbent is regenerated in the cathode chamber and the sulfur oxides are converted to sulfuric acid in the anode zone. The regenerated alkaline absorption solution enters the tank 6 and is returned via a centrifugal pump 4 to the cycle to re-neutralize the sulfur oxides in the absorber 3, and the sulfuric acid solution from the anode zone of the diaphragm electrolyzer 5 is sent for further preparation (concentration).

In addition to the complete neutralization of sulfur oxides from the exhaust gas, one of the important issues in the developed technology is maintaining the cyclicality of the entire cleaning process, therefore, during operation, maximum regeneration of the spent sorbents and restoration of the composition of the absorption solution are required.

The advantages of the method of purification of flue gases from sulfur oxides by unipolar electrochemical treatment over the known alkaline cleaning methods are as follows. The alkaline solution spent during the cleaning process is not removed for further preparation, but is subjected to regeneration, i.e. The cleaning process is the basis for creating a waste-free production.

The use of a unipolar electrochemical method to obtain an absorbent (alkali) allows to increase the absorption capacity of the solution in comparison with an alkali solution of the same concentrations, but not obtained by the electrochemical method.

An example of the method

An experimental check of the operability of the technological scheme, as well as the choice of the modes of electrochemical treatment of the absorption solution (electrolyte solution) in the process of cleaning flue gas from sulfur oxides, were carried out using a bench installation.

In the course of experimental studies, measurements were made of the redox potential eh and pH.

The flow rate of the processed air-gas mixture to the absorption solution was established in a volume ratio of 100: 1. The pressure in the system was in the range 1.1-1.2 kgf / cm ² at a temperature of about 25 ° C. The results of the analyzes are given in table 1.

As can be seen from table 1, the degree of neutralization of sulfur oxides depending on the initial concentration of sulfate-sulfite salt was different and increased with increasing salt concentration.

At the same time, studies were conducted to determine the modes of electrochemical treatment of the sulfate-sulfite aqueous solution. The electrolyte solution was subjected to electrochemical treatment in various modes, with an exposure intensity of 300, 600, 1500, 4500, 3000, 9000, 13500 and 15000 C / l.

An increase in the specific amount of electricity is achieved by increasing the time of electrochemical exposure at constant current. The results of the analyzes are given in table.2.

From the data in Table 2, it can be seen that under the electrochemical effect on an absorbing sulfate-sulfite solution with a specific amount of electricity q above 3000 C / l, the pH of catholyte increased almost to a maximum value above 12.5 units, and eh to values below -900 mV.

Under the electrochemical effect on the solution in the anode zone (anolyte) with a specific amount of electricity q above 3000 C / l, the pH of the anolyte changed to minimum values below 1.5 units, and eh to values above 1250 mV.

Therefore, the most economical mode of processing an aqueous solution of sodium sulfate-sulfite is in the region q = 3000-4500 C / l.

Thus, as a result of the electrochemical reactions carried out in the cathode zone, the initial sorbent is formed - sodium hydroxide (NaOH), and in the anode zone, the final product is sulfuric acid (H ₂ SO ₄ ), i.e. at the same time, regeneration of the absorption solution (electrolyte solution) and the utilization of sulfur oxides occur.

The developed technological process for cleaning flue gases from sulfur oxides on the basis of new, unconventional technical solutions, unlike the prototype, has shown its manufacturability, cyclicality and operability, ease of operation and management, reliability from the point of view of safety and environmental requirements.

Claims (2)

1. The method of purification of flue gases from sulfur oxides, including mixing them with air, neutralizing acid gases in an absorption chamber by contacting with a liquid absorbent, removing purified flue gases and an acidic solution, characterized in that the acidic gases neutralize the alkaline absorption solution, and formed after neutralization of an aqueous solution of sulfate sulfite salt is subjected to regeneration by unipolar electrochemical treatment in a diaphragm electrolyzer with obtaining sulfuric acid in the anode zone, and in the cathode zone of an alkaline absorption solution, which is sent to the absorption chamber to neutralize acid gases. 2. The method according to claim 1, characterized in that the electrochemical treatment is carried out with a specific amount of electricity in the range of 3000-4500 Coulomb / l.