WO2016049714A1

WO2016049714A1 - Method for combined cleaning flue gases and apparatus for its implementation

Info

Publication number: WO2016049714A1
Application number: PCT/BG2015/000029
Authority: WO
Inventors: Hristo Atanasov KOVACHKI; Yoncho Georgiev PELOVSKI; Rumen Ivanov KUNEV; Angel Hristov ANGELOV; Zhelyazko Yordanov MITEV
Original assignee: Kovachki Hristo Atanasov
Priority date: 2014-10-02
Filing date: 2015-09-15
Publication date: 2016-04-07
Also published as: BG66880B1; BG111830A

Abstract

This invention relates to a method and an apparatus for cleaning a flue-gas, which are applied in thermal engineering and in particular in thermal power plants and industrial enterprises with combustion installations. The apparatus for cleaning a flue-gas comprises horizontal absorber with absorption section (1) and gas-inlet conduit (5) on its one side, and outlet conduit (6) for cleaned gas, as in the lower end and longitudinal the absorption section (1) is implemented by areas (2.1, 2.2, 2.3, and 2.4) for solutions or suspensions. Between the individual areas (2.1, 2.2, 2.3, and 2.4) are located partitions (11), and at the end of the absorption section (1) separation section (3) and adsorption section (4) with outlet conduits (9.1, 9.2, and 9.3) are located next to each other. Absorption (1), separation (3) and adsorption (4) sections are mounted in a common housing (10), and inlet conduits (7.1, 7.2, 7.3, and 7.4) are provided to each zone (2.1, 2.2, 2.3, and 2.4 ) for supplying the absorbing agents in the relevant area, and outlet conduits (8.1, 8.2, 8.3, and.4) for product discharging after absorption. The outlet conduit (6) for cleaned gases is located after adsorption section (4).

Description

METHOD FOR COMBINED CLEANING FLUE GASES AND APPARATUS FOR ITS

IMPLEMENTATION

TECHNICAL AREA

This invention relates to a method and an apparatus for cleaning a flue-gas, which are applied in thermal engineering and in particular in thermal power plants and industrial enterprises with combustion installations.

TECHNICAL BACKGROUND

A method for combined cleaning a flue-gas is known, consisting in supplying flue-gas or gas mixture to an absorber, as flue-gas or gas mixture flows through a space allocated in areas. An absorption occurs in each area by injecting solutions or suspensions of absorbents with different acidity. (EP0249400)

The apparatus for implementation of the known method comprises common housing with a horizontal absorber with absorption section and gas-inlet conduit on its one side and outlet conduit for cleaned gas. In the housing there are formed separate areas for solutions or suspensions with partitions with inlet conduits provided to each area for supplying absorbing agents in the relevant area and outlet conduits for discharging. Partitions are located in the areas and are mesh-type, and determine the autonomous existence of each area. (EP0249400)

The use of mesh partitions located in the areas increase extra the system hydraulic resistance, which makes it difficult to be applied in TPP due to the need of large geometric sizes. On the other hand, these partitions represent a risk of progressive deposition of suspended undissolved particles, which in the process of operation during treatment of flue gas from TPP may result in increasing the system hydraulic resistance.

General problem of the known solutions is increasing the resistance on the way of flue gas to chimneys. This requires increasing the capacity of the flue fans and increasing the operating costs accordingly.

l TECHNICAL DESCRIPTION OF THE INVENTION

The task of the present invention is to create a method and apparatus for combined cleaning a flue-gas by ensuring maximum absorption of acidic gas at a minimum cost of reagents, thus improving the gas-liquid-contact without the risk of deviation of the hydraulic resistance according to the design geometrical sizes of the system. The task is to increase the absorption rate for certain pollutants in order to increase the concentration of any obtained solutions useful for further processing to a final product.

The task is solved through a method for combined cleaning a flue-gas is known, consisting in supplying flue-gas or gas mixture to an absorber, as flue-gas or gas mixture flows through a space allocated in areas. An absorption occurs in each area by injecting solutions or suspensions of absorbents with different acidity. According to the invention the stream of flue-gas or gas mixtures has pulsating linear velocity during absorption and this stream is also subjected to an adsorption of one or more components of the gas mixture with adsorbents. The products from the absorption and the adsorption from each area are collected separately.

According to one of the options for implementation of the method upon absorption of the acidic gas, the pH level of adsorbents is increased along with the flue-gas stream from the first to the last area.

An option is also possible where upon absorption of a gas mixture containing components which increase the pH level of adsorbents the acidity of adsorbents to decrease along with the flue-gas stream from the first to the last area.

Alkaline or acid solutions or suspensions, or other inorganic or organic liquids or solutions connecting selectively to any of the gas mixture components are used as absorbent.

Activated carbon, zeolite or other hard substances connecting selectively to any of the gas mixture components or solids permeated with organic or inorganic liquids or solutions that connect selectively to any of the gas mixture components are used as adsorbents.

The flue-gas stream has pulsating linear velocity. The linear velocity could be changed by maintaining different levels in the different sections. The task is also to be resolved through an apparatus for cleaning a flue-gas which comprises common housing with a horizontal absorber with absorption section and gas-inlet conduit on its one side and outlet conduit for cleaned gas. In the housing there are formed separate areas for solutions or suspensions with partitions with inlet conduits provided to each area for supplying absorbing agents in the relevant area and outlet conduits for discharging. According to the invention areas are formed in an absorption section and by its length, and partitions are located between the individual areas. At the end of the absorption section separation sections and an adsorption part with outlet conduits are located next to each other. The outlet conduit for cleaned gases is located after the adsorption section.

According to one variant solution for the apparatus at least two nozzles connected to the relevant inlet conduits are mounted to each one of the areas.

The separation section is implemented as a dust separator.

According to another variant solution in the area of solution or suspension free floating polymer spheres are placed with different diameters forming a wet surface.

Advantages of the method and the apparatus use the fact that the various gas mixture components have different solubility depending both on their properties, and the composition of absorbent agent. Thus, by using absorbent agents taking up only one or a part of the components of the gas mixture in the various areas separation of the mixture is achieved.

Upon absorption of the acidic gas the higher the pH level of absorbent agent, the better their absorption. Therefore, the pH level adsorbents is increased along with the flue-gas stream, i.e. in the first area it is the lowest and in the last area - the highest. Thus, in the first area the strongest acid-forming flue-gas is dissolved, i.e. an acid with the highest degree of dissociation, and in the last one - with the lowest.

When the gas mixture contains components increasing the pH level of adsorbents, the principle is the same, but acidity changes reversed. When we have a mixture in which one of the components lower pH level, and others increases it, the principle of operation is the same, however, it passes through an area with a neutral or near neutral pH level. The use different reagents creates the possibility for combining part of them, in order to obtain different commodity products. Depending on the reagents regeneration of some of them can occur for the account of obtaining the product by mixing them with other reagents.

EMAMPLES AND APLLICATION

Examples of the apparatus for cleaning a flue-gas are shown in the figures attached, where:

Figure 1, which represents a longitudinal sectional view of the apparatus.

Figure 2 - variant solution of area 2.3 of Figure 1.

During combustion of carbon fuels flue-gas consist mainly of acidic gases such as carbon dioxide (C0₂), sulphur dioxide (S0₂), and nitrogen oxides (NO_x). For this reason upon injecting a flue-gas the pH level of the solution decreases. This is done as follows:

1. Acidic gas is dissolved in the water solution or suspension.

2. Acidic gas binds with the water under the equations: S0₂ + H₂0 «* H₂S0₃

C0₂ + H₂0 «* H₂C0₃, etc.

3. The resulting acids dissociates and the separated hydrogen cation reduces the pH level of the aqueous phase.

All of the above processes are equibalanced. This means that reducing the pH level of the aqueous phase will reduce the solubility of acidic gas. In the proposed method acidity of the water phases in different areas is maintained different by using different reagents. It reduces along with the flue-gas stream. In the scheme given in Figure 1, acidity reduces from Area 2.1 to Area 2.4, and the pH level increases in the same direction respectively.

This method achieves simultaneously two effects:

Maximum absorption of acidic gas by maintaining the maximum difference in their concentrations between the gas and liquid phases.

Minimum cost of reagents, since their high concentration in liquid phases is not required for achieving a more complete absorption of contaminants in flue-gas. Different gases have different solubility, different degree of dissociation of the resulted acids, and different solubility upon their binding with various reagents. Based on these properties and using different substances with different concentrations in the different areas in the absorber separately absorption of pollutant gases and obtaining various products can be achieved.

The use different reagents creates the possibility for combining part of them, in order to obtain different commodity products.

Depending on the reagents regeneration of some of them can occur for the account of obtaining the product by mixing them with other reagents.

Example 1

Cleaning of Flue Gas from Coal-Fired Power Stations

Only water is sprayed in the first area for the purpose of absorbing sulphur dioxide. Air is further blown in the aqueous phase for secondary oxidation. The following reaction takes place after the dissolution of the sulphur dioxide:

2S0₂ + 2H₂0 + 0₂ «* 2H₂S0₄

In this area, the concentrations of carbon dioxide and sulphur dioxide in the gaseous phase are the highest. The solubility of sulphur dioxide, however, is higher than that of carbon dioxide and, although its concentration is lower, it will be dissolved with priority. The acidity of the solution is thereby reduced, which in turn blocks the dissolution of carbon dioxide. Concentrations of nitrogen oxides in the gaseous phase are of a lower order than that of sulphur dioxide and basically they would not be dissolved.

Thus, using only water, partial separation of one of the components of the gaseous phase is achieved and as a result sulphuric acid is produced. In the second area, gas is sprayed with a suspension of limestone, calcium carbonate. This suspension has an alkaline pH level and creates conditions for maximum absorption of sulphur dioxide. In this area, oxygen is also blown in the aqueous phase for secondary oxidation of sulphur dioxide. The following reactions take place: 2S0₂ + 2H₂0 + 0₂— > 2H₂S0₄

H₂S0₄ + 2H₂0 +CaC0₃ -> Ca S0₄ 2H₂C4 + H₂C0₃

H₂C0₃ -> H₂0 + C0₂

This mechanism prevents the dissolution of carbon dioxide, while maintaining pH level in the range of 6 to 7 allows a high level of sulphur dioxide separation without dissolving nitrogen oxides.

In this area, flue gas is virtually cleaned completely of sulphur dioxide and calcium sulphate (gypsum) is formed as final product.

In the third area, gas is sprayed with aqueous solution of ammonia. The solubility of ammonia in water is extremely high and the pH level of the solution can reach up to 14. These conditions allow the separation of almost all of the carbon dioxide and a large part of the nitrogen oxides in the flue gas. The following reactions take place:

NH₃ + H₂0 + C0₂— > (NH₄)₂C0₃

3NO2 + H₂0 -> 2HN0₃ + NO†

NH₃ + HN0₃ -> NH₄N0₃

Ammonium nitrate content in the solution will be very low due to its low content in the flue gas.

Calcium sulphate formed in the second area is mixed, under appropriate conditions, with solution of ammonium carbonate. As a result, the following reaction takes place:

NH₄C0₃ + CaS0₄— > (NH₄)₂S0 +CaC0₃J<

The resulting suspension is filtered. The precipitate of calcium carbonate is fed into the second area for sulphur dioxide absorption. The clear solution of ammonium sulphate may be used as liquid fertilizer. The presence of ammonium nitrate impurities is not a problem since it is also used as fertilizer.

To obtain a technically pure ammonium sulphate, only part of the carbon dioxide in the flue gas should be absorbed. This is because of the big difference in the concentration of the two gases - sulphur dioxide is usually up to 15,000-18,000 mg/nm³, while carbon dioxide is of the order of 100,000 mg/nm3. Carbon dioxide absorption is controlled by feeding ammonia in the third area.

After passing through absorption section 1, flue gas enters separation section 3, where it passes through dust separators in order to be sprayed with water and for the entrained solution containing ammonia from zone 2.3 to be separated.

Cleaning flue gas from coal-fired power stations does not require the use of adsorbent since all pollutants are separated in absorption section 1.

This example illustrates the cleaning of gases containing acidifying pollutants. Therefore, the pH level of the solution increases in the direction of the gas stream. In the first area, where water is used for absorption, the pH level of the solution is 3, in the second area it is 5.5 to 6.0, while in the third are the pH level exceeds 8.0.

In addition to the above absorbents, cleaning can be accomplished with ammonia in a first area at a pH level of 5.5:

2S0₂ + 2H₂0 + 0₂ + NH₃ «* (NH₃)₂S0₄

The advantage of such an absorbent is that it can produce a saturated ammonium sulphate solution without the use of additional methods for concentration.

Calcium hydroxide is often used in the second area instead of calcium carbonate, again at pH level of 5.5 to 6.0, in which case the following reaction takes place:

2S0₂ + 2H₂0 + 0₂ -> 2H₂S0₄

H₂S0₄ + Ca(OH)₂— > CaS0₄ 2H₂C4 The advantage in this case is that no carbon dioxide is given off. Solution of potassium carbonate may be used as an absorbent in the second area:

K₂C0₃ + H₂0 + C0₂— > 2KHC0₃

Here, the pH level of absorption is about 8.0. The resulting solution of potassium hydrogen carbonate is then heated, wherein the reverse reaction takes place:

2KHCO3— > K₂C0₃+ H₂0 + C0₂

The solution thus regenerated is returned to the third area again for further absorption. The resulting product is gas with a high content of carbon dioxide. It can be seen that in the second combination of absorbents pH levels of the solutions increase in the direction of movement of the flue gas. Absorbents used in this example are the basic compounds calcium hydroxide and ammonium hydroxide (aqueous solution of ammonia) and salts the solutions or suspensions of which have alkaline pH levels, such as potassium carbonate and calcium carbonate. In addition, solutions of organic compounds, such as mono- and diethanolamine, can be used for carbon dioxide separation.

Example 2

Cleaning of Flue Gas from Incineration of Municipal Waste

Flue gas from incineration of municipal solid waste contains more pollutants due to the more varied composition of the raw material. During this process, in addition to sulphur dioxide and nitrogen oxides, hydrogen chloride is also formed from polyvinyl chlorides, hydrogen fluoride contained in Teflon, as well as other materials. The above pollutants are soluble in water. In addition, there are a group of practically insoluble or poorly soluble ones. These are carbon monoxide, dioxins, furans and others.

For this type of flue gas, the order of separation of water-soluble pollutants depends on the amount thereof (concentration in the gas), and their solubility depending on the pH level of the aqueous phase. The direction in which the acidity of the aqueous phase changes will also depend on the same factors. The number of areas will also vary depending on the type of the incinerated waste and the desired degree of separation of pollutants.

Insoluble and poorly soluble pollutants are separated in adsorption section. Separate absorption of impurities and formation of end products can also be done in that section by using a series of adsorption areas with adsorbents specific for the different substances.

The apparatus for implementing the method consists of common housing 10 where area- divided absorption section 1, separation section 3, being a dust separator for separating the fly ash from the liquid phases, and adsorption section 4 are located successively and side by side. Flue gas inlet 5 is located to the front of absorption section 1, and cleaned gas outlet 6 is located at the end of adsorption section 4. At the bottom and lengthwise, absorption section 1 consists of areas 2.1, 2.2, 2.3, and 2.4 for solutions or suspensions, with partitions 11 located between areas 2.1, 2.2, 2.3, and 2.4 in order to prevent the mixing of such solutions or suspensions. By maintaining different levels between partitions 11 forming the individual areas, the clear opening along the length of absorption section 1 changes, which leads to changes (pulsations) in the linear velocity and pressure of the gases.

Absorption can be improved by using a floating filler consisting of polymeric spheres 13 having different diameters. They are wetted to form an entire wetted surface 14, thereby increasing the contact surface in the upper part of the aqueous phase. Furthermore, by moving under the influence of solution spraying and gas circulation, spheres 13 continuously renew the solution on the surface and prevent the formation of deposits.

They can also serve a function for the self-cleaning of the absorption section 1 with respect to deposits on its walls.

Inlets 7.1, 7.2, 7.3, 7.4 and outlets 8.1,8.2, 8.3, 8.4 are planned for each of areas 2.1, 2.2, 2.3, and 2.4 of absorption section 1 for feeding absorption agents to the relevant area and for removal of products after absorption, respectively. To each of areas 2.1, 2.2, 2.3, and 2.4 of absorption section 1, at another side, there are mounted at least two nozzles 12 connected to the respective inlets 7.1, 7.2, 7.3, and 7.4.

Flue gas passes through absorption section 1. There, they are sprayed with solutions and suspensions specific for the various pollutants.

Adsorption portion 4 is composed of one or more solid adsorbents for taking up trace contaminants and/or pollutants insoluble in aqueous or other solvents. Upon their regeneration, the relevant products or intermediates are removed through outlets 9.1, 9.2, and 9.3.

In this example, the absorption of pollutants resulting from the incineration, such as sulphur, nitrogen and chlorine oxides, hydrogen chloride, hydrogen fluoride and hydrogen sulphide, is achieved with strong bases, such as potassium or sodium, as the concentration of the pollutants is lower than that of the sulphur dioxide in the first example. The absorption of carbon dioxide takes place again in the last area of the absorption section. Like in Example 1, absorbents used in this section are ammonium hydroxide (base), potassium carbonate (salt), monoethanolamine, diethanolamine (organic compounds), etc. What is different 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 section. Activated carbon is used as adsorbent. Carbon dioxide is also adsorbed by activated carbon. Carbon activity in respect of carbon dioxide is lower than for dioxins and furans. For this reason, there are two areas with activated carbon used in the adsorption section - the first one for adsorbing dioxins and furans, and the second one - carbon dioxide. So, by independent regeneration in each of the areas, different products will be produced in the absorption section.

Claims

1. A method for combined cleaning of gases wherein flue gas or gas mixture is delivered to an absorber, with the flue gas or gas mixture passing through a space divided into areas in each of which absorption is achieved by spraying solutions or suspensions of absorbents of varying acidity, characterized in that the flow of flue gas or gas mixture has a pulsating linear velocity during the absorption and is subjected to adsorption of one or more components of the gas with adsorbents, with the products formed as a result of the absorption and adsorption in each area collected separately.

2. A method, according to claim 1, characterized in that upon absorption of acidifying gases the pH level of the absorbent increases in the direction of movement of the gases from the first to the last area.

3. A method, according to claim 1, characterized in that upon absorption of a gas mixture comprising components which increase absorbents' pH levels, the acidity of the absorbents reduces in the direction of movement of the gases from the first to the last area.

4. A method, according to claim 1, characterized in that the absorbents used are alkaline or acidic solutions or suspensions, or other organic or inorganic liquids or solutions, combining selectively with some of the components of the gas mixture.

5. A method, according to claim 1, characterized in that the adsorbents used are solids combining selectively with some of the components of the gas mixture, such as activated carbon and zeolites, or solids impregnated with organic or inorganic liquids or solutions combining selectively with some of the components of the gas mixture.

6. A method, according to claim 1, characterized in that the flow of flue gas or gas mixture has a pulsating linear velocity controlled by maintaining different levels in the different areas.

7. An apparatus, for implementation the method according to claim 1, consisting of a common housing with horizontal absorber with absorption section having a flue gas inlet at one side and a cleaned gas outlet at the other, with separate areas for solutions or suspensions formed in the housing by means of partitions, as well as with inlets for delivery of absorption agents in the respective areas and removal outlets planned for each area, characterized in that the areas (2.1, 2.2, 2.3, and 2.4) are formed in the absorption section (1) and along its length, and that the partitions (11) are placed between the individual areas (2.1, 2.2, 2.3, and 2.4), and at the end of the absorption section (1) are located, next to one another, a separation section (3) and a adsorption section (4) with outlets (9.1, 9.2, and 9.3), with the cleaned gas outlet (6) located after the adsorption section (4).

8. An apparatus, according to claim 7, characterized in that to each of the areas (2.1, 2.2, 2.3, and 2.4) there are mounted at least two nozzles (12) connected to the respective inlets (7.1, 7.2, 7.3, and 7.4).

9. An apparatus, according to claim 7, characterized in that the separation section (3) constitutes a dust separator.

10. An apparatus, according to claim 7, characterized in that in one, several or all of the areas (2.1, 2.2, 2.3, and 2.4) of the absorption section (1), freely floating polymeric spheres (13) of different diameters are placed in the solution or suspension, forming a wetted surface (14).