BG66880B1 - Combined gas purification method and device for its implementation - Google Patents

Abstract

The invention relates to a method for combined purification of gases and a device for implementing the method, which find application in thermal engineering and in particular in thermal power plants and industrial combustion plants. Their use achieves purification of exhaust gases in one facility, with guaranteed maximum acid gas capture and minimum consumption of reagents. The method comprises a supply of flue gas or a gas mixture to an absorber, as the gases pass through the absorber before entering the chimney of the combustion plant. Hereto, the gas mixture passes through a space divided into zones. In each zone, absorption is carried out by spraying and adsorption of one or more components of the mixture by means of different absorbents and adsorbents. The absorbents are in the form of a solution or suspension and are collected separately without mixing. In this way, a different useful product is obtained from each zone. The device for implementing the method includes a horizontal absorber with an absorption section (1) and an inlet (5) for gases on one side and an outlet (6) for the purified gases, as at the lower end and along the length, the absorption section (1) is made of zones (2.1, 2.2, 2.3, 2.4) for solutions or suspensions. Between the separate zones (2.1, 2.2, 2.3, 2.4) are located barriers (11), and at the end of the absorption section (1) are located next to each other a separation section (3) and adsorption section (4) with outlets (9.1, 9.2, 9.3). The absorption (1), the separation (3) and the adsorption (4) sections are mounted in a common casing (10), and to each zone (2.1, 2.2, 2.3, 2.4) there are inlets (7.1, 7.2, 7.3, 7.4) for supply of absorbent agents to the relevant zone and outlets (8.1, 8.2, 8.3, 8.4) for removal of the products upon absorption. The outlet (6) for purified gases is located behind the adsorption section (4).

Description

Field of technology

The invention relates to a method for combined gas purification and a device for its implementation, which are used in thermal engineering and in particular in thermal and thermal power plants and industrial enterprises with combustion plants.

BACKGROUND OF THE INVENTION

A method of combined purification of gases is known, comprising supplying a flue gas or gas mixture to an absorber, the flue gas or gas mixture passing through a space divided into zones, in each zone being absorbed by spraying with solutions or suspensions of absorbents of different acidity (EP 0249400).

The device for implementing the known method is made of a common casing with a horizontal absorber with an absorption part and a gas inlet on one side and an outlet for purified gases, as separate zones for solutions or suspensions with barriers are formed in the casing. provided inputs for supply of absorbent agents in the respective zone and outlets for removal. The barriers are located in the zones and are mesh and determine the independent existence of each separate zone (EP 0249400).

The use of mesh barriers placed in the zones further increases the hydraulic resistance of the system, which makes its application in thermal power plants difficult to implement due to the need for large geometric dimensions. On the other hand, these barriers create a danger of gradual deposition of suspended undissolved particles, which in the process of operation in the treatment of gases from thermal power plants can lead to an increase in hydraulic resistance in the system.

A common problem of the known solutions is to increase the resistance on the path of the flue gases to the chimney. As a result, it is necessary to increase the power of the smoke fans and increase the operating costs.

Technical essence of the invention

The object of the present invention is to provide a method for combined flue gas cleaning and a device for its implementation, ensuring maximum capture of acid-forming gases at minimum reagent consumption, improving the gas-liquid contact without the risk of deviation of the hydraulic resistance according to the designed geometric dimensions of the system. The task is also to increase the capture rate of certain pollutants in order to increase the concentration of possible useful for further processing solutions obtained to the final product.

The problem is solved by a method for combined purification of gases, in which a flue gas or gas mixture is fed to an absorber, as the flue gas or gas mixture passes through a space divided into zones, and in each zone absorption is carried out by spraying with solutions. or suspensions of absorbents of different acidity. According to the invention, the flow of flue gases or gas mixtures has a pulsating linear velocity during absorption and this flow is also subjected to adsorption of one or more components of the gas mixture with adsorbents. The products obtained from the absorption and adsorption from each zone are collected separately.

According to one embodiment of the method, upon absorption of the acid-forming gases, the pH of the absorbents increases in the direction of movement of the gases from the first to the last zone.

It is also possible that in case of absorption of a gas mixture containing components that increase the pH of the absorbents, the acidity of the absorbents is reduced in the direction of movement of the gases from the first to the last zone.

Alkaline or acidic solutions or suspensions, or other inorganic or organic liquids or solutions selectively binding to some of the components of the gas mixture are used as absorbents.

Descriptions of issued patents for inventions № 06.1 / 17.06.2019

The adsorbents used are activated carbon, zeolites or other solids which selectively bind to some of the components of the gas mixture, or solids impregnated with organic or inorganic liquids or solutions which selectively bind to some of the components of the gas mixture.

The flue gas flow has a pulsating linear velocity. The change in linear velocity is done by maintaining different levels in the individual sections.

The problem is solved with a device for implementing the method, including a common casing with a horizontal absorber with an absorption part and a gas inlet on one side and an outlet for purified gases, as separate zones for solutions or suspensions with barriers are formed in the casing. in each zone there are inlets for supplying absorbent agents in the respective zone and outlets for removal. According to the invention, the zones are formed in an absorption part and along its length, and the barriers are located between the separate zones. At the end of the absorption part, a separation part and an adsorption part with outlets are located next to each other. The outlet for the purified gases is located after the adsorption part.

According to one embodiment of the device, at least two nozzles connected to the respective inputs are mounted to each of the zones.

The separation part is made as a drip trap.

According to another embodiment, free-floating polymer spheres of different diameters forming a wetted surface are placed in the solution or suspension zone.

The advantages of the method and the device use the fact that the different components of the gas mixture have different solubility depending on both their properties and the composition of the absorbent. Thus, by using absorbent agents capturing only one or part of the components of the gas mixture in the various zones, separation of the mixture is obtained.

In the case of absorption of acid-forming gases, the higher the pH of the absorbent, the better their absorption. Therefore, the pH of the absorbents increases in the direction of movement of the gases, they. in the first zone it is the lowest, and in the last zone it is the highest. Thus in the first zone the gas forming the strongest acid dissolves, they. acid with the highest degree of dissociation, and in the latter - with the lowest degree of dissociation.

When the gas mixture contains components that increase the pH of the absorbents, the principle is the same, but their acidity changes in the opposite direction. When we have a mixture in which some of the components lower the pH and others raise it, the principle of operation is the same, but it passes through a zone with neutral or close to neutral pH.

When using different reagents, it is possible to combine some of them in order to obtain different commodity products. Depending on the reagents used, some of them can be regenerated at the expense of obtaining a product by mixing them with other reagents.

Exemplary embodiments and application of the invention

Exemplary embodiments of the device for implementing the method are shown in the attached figures, where:

Figure 1, which is a longitudinal section of the device;

Figure 2 - embodiment of zone 2.3 of Figure 1.

In the combustion of carbonaceous fuels, flue gases consist mainly of acid-forming gases, such as carbon dioxide (CO ₂ ), sulfur dioxide (SO ₂ ) and nitrogen oxides (NO _x ). For this reason, when the flue gas is sprayed, the pH of the solution decreases. This is done by the following mechanism:

1. Acid-forming gases are dissolved in an aqueous solution or suspension

2. Acid-forming gases are associated with water by the equations:

SO + H ₂ O θ H ₂ SO ₃

СО ₂ + Н ₂ О θ Н ₂ СО ₃ , etc.

3. The resulting acids dissociate and the separated hydrogen cation lowers the pH of the aqueous phase.

All the processes described above are equilibrium. This means that lowering the pH of the aqueous phase will reduce the solubility of the acid-forming gases. In the proposed method acidity

Descriptions of issued patents for inventions № 06.1 / 17.06.2019 of the aqueous phases in the different zones is maintained different with the help of different reagents. It decreases in the direction of flue gas movement. In the given scheme of Figure 1, the acidity decreases from Zone 2.1 to Zone 2.4, respectively the pH increases in the same direction.

This method achieves two effects simultaneously:

- Maximum capture of acid-forming gases by maintaining a maximum difference in their concentrations between the gas and liquid phases.

- Minimal consumption of reagents, as it is not necessary for their concentration in the liquid phases to be high in order to achieve a more complete capture of pollutants in the flue gas.

Different gases have different solubilities, different degrees of dissociation of the acids obtained from them and different solubilities when combined with different reagents. Based on these properties and using different substances with different concentrations in the different zones of the absorber, separate capture of polluting gases and production of different products can be achieved.

When using different reagents, it is possible to combine some of them in order to obtain different commodity products.

Depending on the reagents used, some of them can be regenerated at the expense of obtaining a product by mixing them with other reagents.

Example 1.

Cleaning of flue gases from coal-fired power plants

In the first zone, only water is sprayed to absorb sulfur dioxide. Additional air is blown into the aqueous phase for secondary oxidation. After dissolving the sulfur dioxide, the following reaction takes place:

2SO ₂ + 2H ₂ O + O ₂ θ 2H ₂ SO ₄

Here the concentration in the gas phase of carbon dioxide and sulfur dioxide are the highest. However, the solubility of sulfur dioxide is higher than that of carbon dioxide, and although its concentration is lower, it will dissolve with advantage. As it dissolves, the acidity of the solution decreases, which in turn blocks the dissolution of carbon dioxide. The concentration of nitrogen oxides in the gas phase is an order of magnitude lower than that of sulfur and they will practically not dissolve.

Thus, only water produces a partial separation of one of the components of the gas phase and a sulfuric acid product is obtained. The second zone is sprayed with a suspension of limestone, calcium carbonate. This suspension has an alkaline pH and creates conditions for maximum capture of sulfur dioxide. Here, too, oxygen is blown into the aqueous phase for the secondary oxidation of sulfur dioxide. The following reactions occur:

2SO ₂ + 2H ₂ O + O ₂ ^ 2H ₂ SO,

H ₂ SO ₄ + 2H ₂ O + CaCO ₃ - + CaSO ₄ .2H ₂ O; + H ₂ CO ₃

H ₂ CO ₃ H ₂ O + CO ₂

This mechanism does not allow the dissolution of carbon dioxide, and maintaining the pH in the range of 6-7, allows a high degree of capture of sulfur dioxide without dissolving nitrogen oxides.

In this area we have practically complete purification of the flue gas from sulfur dioxide and obtaining the final product calcium sulfate (gypsum).

In the third zone, irrigation is carried out with an aqueous solution of ammonia. The solubility of ammonia in water is extremely high and the pH of the solution can reach 14. Under these conditions, almost all of the carbon dioxide from the flue gas and much of the nitrogen oxides can be captured. The reactions are as follows:

NH ₃ + H ₂ O + CO ₂ - + (NH ₄ ) ₂ CO ₃

3NO ₂ + H ₂ O - + 2HNO ₃ + NO $

NH ₃ + HNO ₃ - + NH ₄ NO ₃

The content of ammonium nitrate in the solution will be extremely low due to its low content in the flue gas.

The ammonium carbonate solution is mixed under appropriate conditions with the calcium sulphate of the second zone. The following reaction will take place:

NH ₄ CO ₃ + CaSO ₄ (NH ₄ ) ₂ SO ₄ + CaCO ₃ ;

The resulting suspension was filtered. The calcium carbonate precipitate is fed to a second zone for

Descriptions of issued patents for inventions № 06.1 / 17.06.2019 capture of sulfur dioxide. The clear ammonium sulphate solution can be used as a liquid fertilizer. The presence of ammonium nitrate impurities is not a problem, as it is also used for fertilization.

To obtain a technically pure ammonium sulphate solution, only part of the carbon dioxide present in the flue gases must be captured. This is due to the large difference in the concentration of the two gases, while sulfur dioxide is usually at most 15,000 - 18,000 mg / nm ³ , carbon dioxide is in the range of 100,000 mg / nm ³ . The capture of carbon dioxide is controlled by feeding the amount of ammonia to the third zone.

After passing flue gases through the absorption part 1, they enter the separation part 3, where they pass through drip traps for sprinkling with water and for capturing the entrained solution containing ammonia from zone 2.3.

The use of an adsorbent is not necessary when cleaning flue gases from coal-fired power plants, as all contaminants are trapped in the absorption part 1.

In this example, gases containing acid-forming contaminants are purified. For this reason, the pH of the solution increases in the direction of gas movement. In the first zone, the water absorption of the solution is pH = 3, in the second zone the pH is 5.5 to 6.0, and in the third zone the pH is above 8.0.

In addition to the listed absorbents, purification can also be achieved with a solution of ammonia in the first zone at pH = 5.5:

2SO ₂ + 2H ₂ O + O ₂ + ΝΗ ₃ θ (NH ₃ ) ₂ SO ₄

The advantage of this absorbent is that a saturated solution of ammonium sulfate can be obtained without the use of additional concentration methods.

In the second zone, calcium hydroxide is often used instead of calcium carbonate again at pH 5.5 to 6.0, during which the following reaction takes place:

2SO ₂ + 2H ₂ O + O ₂ ^ 2H ₂ SO,

H ₂ SO ₄ + Ca (OH) ₂ - + CaSO ₄ .2H ₂ O

The advantage here is that no carbon dioxide is released.

In the second zone, a potassium carbonate solution can be used as an absorbent:

K ₂ CO ₃ + H ₂ O + CO ₂ 2KNSO ₃

Here the pH of the absorbance is about 8.0. The resulting solution of potassium hydrogen carbonate is then heated, during which the reverse reaction takes place:

2KNSO ₃ K ₂ CO ₃ + H ₂ O + CO ₂

The solution thus regenerated is returned to the third zone for further absorption. As a product we get a gas with a high content of carbon dioxide.

It can be seen that in the second combination of absorbents the pH of the solutions increases in the direction of movement of the flue gas. The absorbents used in the example are the alkaline compounds calcium hydroxide and ammonium hydroxide (aqueous ammonia solution) and salts whose solutions or suspensions have an alkaline pH, such as potassium carbonate and calcium carbonate. In addition, solutions of organic compounds, such as mono- and diethanolamine, can be used to capture carbon dioxide.

Example 2.

Cleaning of flue gases from incineration of household waste

When burning solid household waste, there are more pollutants in the flue gases, as the raw material has a more diverse composition. Here, in addition to sulfur dioxide and nitrogen oxides, there is also hydrogen chloride generated from polyvinyl chloride, hydrogen fluoride from Teflon and others. The contaminants cited so far are soluble in water. In addition, there is a group of practically insoluble or slightly soluble. These are carbon monoxide, dioxins, furans and others.

In this type of flue gases, the sequence of capture of water-soluble pollutants depends on their quantity (concentration in the gas), their solubility depending on the pH of the aqueous phase. It depends on the same factors in which direction the acidity of the aqueous phase will change. The number of zones will also vary depending on the waste incinerated and the degree of separation of pollutants sought.

Insoluble and sparingly soluble contaminants are trapped in the adsorption part. Here, too, it can

Descriptions of issued patents for inventions № 06.1 / 17.06.2019 to carry out separate capture of impurities and preparation of final products, using a series of adsorption zones with specific for individual substances adsorbents.

The device for carrying out the method is made of a common casing 10, in which the zoned absorption part 1, the separation part 3, which is a drop catcher for separating the entrainment from the liquid phases and the adsorption part 4 are arranged successively next to each other. 1 is formed an inlet 5 for gases, and at the end of the adsorption part 4 - an outlet 6 for the cleaned gases. At the lower end and along the length, the absorption part 1 is made of zones 2.1, 2.2, 2.3, 2.4 for solutions or suspensions, and between the separate zones 2.1, 2.2, 2.3, 2.4 there are barriers 11 which prevent the mixing of solutions or suspensions. By maintaining different levels between the baffles 11 forming the individual zones, the free section along the absorption part 1 is changed, which leads to a change (pulsations) in the linear velocity and the pressure of the gases.

Improved absorption can be achieved by using a floating filler of polymer spheres 13 with different diameters. They get wet and form a whole wetted surface 14, thus increasing the contact surface at the top of the aqueous phase. In addition, during their movement under the influence of dew and the movement of gases, the spheres 13 continuously renew the surface solution and prevent the formation of deposits.

They can also play a role in self-cleaning of the absorption part 1 in case of deposits on its walls.

To each zone 2.1, 2.2, 2.3, 2.4 of the absorption part 1 are provided inputs 7.1, 7.2, 7.3, 7.4 for supply of absorption agents in the respective zone and outputs 8.1, 8.2, 8.3, 8.4 for removal of the products after absorption. On the other hand, at least two nozzles 12 connected to the respective inputs 7.1, 7.2, 7.3, 7.4 are mounted to each of the zones 2.1, 2.2, 2.3, 2.4 of the absorption part 1.

The flue gases pass through the absorption part 1. There they are sprayed with solutions and suspensions specific to various pollutants.

Adsorption part 4 consists of one or more solid adsorbents for trapping traces of contaminants and / or insoluble in aqueous or other solvents. During their regeneration, the respective products or intermediates are removed from the outlets 9.1, 9.2, 9.3.

In this example, the absorption of combustion pollutants such as sulfur, nitrogen and chlorine oxides, hydrogen chloride, hydrogen fluoride and hydrogen sulfide takes place with strong bases such as potassium or sodium, as the concentration of pollutants is lower than that of sulfur dioxide in the first example. . The absorption of carbon dioxide takes place again in the last zone of the absorption part. Absorbents here are ammonium hydroxide (base), potassium carbonate (salt), monoethanolamine, diethanolamine (organic compounds) and others.

The difference from Example 1 is the presence of dioxins and furans. They do not dissolve in aqueous solutions and therefore require the use of an adsorption part. Activated carbon is used as an adsorbent. Carbon dioxide is also captured by activated carbon. The activity of carbon in terms of carbon dioxide is lower than that of dioxins and furans. For this reason, using two activated carbon zones in the adsorption part, the first will capture dioxins and furans and the second carbon dioxide. Thus, through independent regenerations of each of the zones in the absorption part, we will obtain different products.

Claims (10)

A method of combined purification of gases in which a stream of flue gas or gas mixture is fed to an absorber provided with a space divided into zones, each of which is self-absorbed by spraying with solutions or suspensions of absorbents with pH variable, characterized in that the flow of flue gases or gas mixtures passes through the space divided into zones with a pulsating linear velocity, and the pH of the absorbents in each of the zones increases or decreases from the first to the last zone. selection subsequently adsorption takes place in zones of one or more components of the gases with adsorbents, whereby the products obtained from the absorption and adsorption in each zone are collected separately. Descriptions of issued patents for inventions № 06.1 / 17.06.2019 Process according to Claim 1, characterized in that upon absorption of acid-forming gases the pH of the absorbents increases in the direction of movement of the gases from the first to the last zone. Method according to claim 1, characterized in that upon absorption of the flue gas or gas mixture containing components which increase the pH of the absorbents, the acidity of the absorbents decreases in the direction of movement of the gases from the first to the last zone. Process according to Claim 1, characterized in that the absorbents are alkaline or acidic solutions or suspensions and organic or inorganic liquids or solutions selectively trapping components of the flue gas or gas mixture. Process according to Claim 1, characterized in that the adsorbents are solids which selectively capture components of the flue gas or gas mixture, such as activated carbon and zeolites, or solids impregnated with organic or inorganic liquids or solutions which selectively capture components of the gas mixture. Method according to claim 1, characterized in that the pulsating linear velocity is provided by maintaining different liquid levels in the different zones, which forces the flow of flue gas or gas mixture to move at different linear velocities in the different zones. Apparatus for carrying out the method according to claims 1 to 6, comprising a common housing in which a horizontal absorber with an absorption part is positioned, with a gas inlet at one end and an outlet for purified gases at the opposite end, the horizontal absorber being connected to separate zones formed by barriers, each of which has entrances for the supply of absorbents in the respective zone and outlets for drainage, characterized in that the zones (2.1, 2.2, 2.3 and 2.4) are formed along the absorption part (1), and the barriers (11) are located between the separate zones (2.1, 2.2, 2.3 and 2.4), and at the end of the absorption part (1) are successively provided one after the other, separation part (3) and adsorption part (4). ) provided with zones equipped with outlets (9.1, 9.2 and 9.3), where the outlet for purified gases (6) is located after the adsorption part (4). Device according to Claim 7, characterized in that at least two nozzles (12) are mounted to the inlets (7.1, 7.2, 7.3 and 7.4) of the absorbents in each of the zones (2.1, 2.2, 2.3 and 2.4). Device according to claim 7, characterized in that the separation part (3) is designed as a drip trap. Device according to Claim 7, characterized in that in one, several or all zones (2.1, 2.2, 2.3 and 2.4) of the absorption part (1) there are polymer spheres (13) with different diameters which form a wetted surface. (14) by free floating in solutions or suspensions of absorbents.