WO2015127518A1

WO2015127518A1 - Method for flue gas cleaning and apparatuses for its implementation

Info

Publication number: WO2015127518A1
Application number: PCT/BG2014/000010
Authority: WO
Inventors: Hristo Atanasov KOVACHKI; Stoycho Mitrev STOEV; Angel Hristov ANGELOV
Original assignee: SOVEX Em EOOD
Priority date: 2014-02-25
Filing date: 2014-02-25
Publication date: 2015-09-03

Abstract

Method for flue gas cleaning by absorption in gas-liquid system, wherein the cleanup is accomplished through physical oscillatory movements and pulse movements, caused simultaneously by the helical motion of the gas flow on its introduction into the system, by wide-frequency range acoustic emission and by pulsations; the flue gas flows are treated in whole or only parts of them. An apparatus for gas cleaning is presented using the method with horizontally arranged absorber and an apparatus with vertically arranged absorber.

Description

METHOD FOR FLUE GAS CLEANING

AND APPARATUSES FOR ITS IMPLEMENTATION

TECHNICAL FIELD

The invention relates to flue gas cleaning from various boiler installations, for achieving acceptable environmental conditions.

BACKGROUND OF THE INVENTION

More than 600 installations in the world currently operate using the wet technology of flue gas cleaning. Practically every book in ecology contains information about them, but basically there is little difference between them in the principle of operation. The main equipment in them is the absorber, which is a vertical, most often cylindrical vessel, wherein in countercurrent flue gases are moving, mostly upwards and the absorbent, suitably dispersed, from top to bottom. On their collisions the components from the two flows enter into chemical reaction, new solid compound are formed which due to their weight overcome the resistance of gases and precipitate. With regard to the fact that in a single pass through the reaction zone not all the absorbent is able to react, recirculation is made, i.e. part of the precipitate is continuously taken out and returned into the spreaders together with fresh absorbent. From the lower zone of the precipitate a certain part is constantly taken out as well, which further goes to waste repository or is prepared as a commercial product. The absorbers with wet technology are installed after the electrical and bag filters, which are intended to capture the solid phase of the gas flow, but a small part of the solid particles is able to pass through them and falls into the absorber. In this case absorption of the reagent on the surface of the particles occurs; as a result of that they fall into the precipitate. For economic, transportation and local ecological considerations the following substances are mainly used: limestone, quicklime, slaked lime, hydrated lime, sodium hydroxide, sodium bicarbonate, magnesium lime and seawater. When using calcium-containing substances as absorbents, gypsum is obtained as a waste product, which is a commercial product. This, together with the high efficiency of the wet technology, has led to its mass application. To obtain a high quality product free of calcium sulfite impurities, the precipitate in the absorber is purged with air; the oxygen oxidizes the sulfite ions to sulfate, whereupon together with water gypsum is formed, analogous to the natural, i.e. calcium sulfate with two molecules of water. In some installations the precipitate is purged with air in a tank outside the absorber.

A disadvantage of this gas cleaning technology is the need of greater exchange absorbers, which makes the installation very expensive. A significant disadvantage is the need of repeated recirculation, i.e. returning part of the precipitate in the spray nozzles on order to ensure a higher degree of utilization of the absorbent, as well as maximum transformation of sulfite ions into sulfate. The recirculation requires complex pump devices

In order to enhance the performance of the wet absorbers with dispersal of the absorbent, the use of vibrations from the acoustic spectrum is proposed. Thus, in international patent application PCT/SE004477 the use of vibrations from the infrared spectrum is suggested of the frequency range 150-20 Hz at acoustic power not less than 120 decibels, preferably at least 140 decibels. The emitter is inserted in the area of mass exchange, for which it must be noted that is acidic in character. Furthermore, in almost all countries the admissible acoustic power /intensity/ is 80 decibels.

In patent application JP 9299744 IN the use of acoustic emission is proposed for intensification of gas cleanup wherein the acoustic emitters, as in the previous patent application, are inserted in the acidic reaction zone. Furthermore, its positive impact on the process is limited because of the necessity to work with low acoustic energy due to the fact that the sound range of the acoustics is an audible frequency range.

In the patent application reflected in publication US2006/0037916 A1 the use of the ultrasonic frequency range of unidirectional beam acoustic emission is suggested for the purification of gases from fine particles.

Patent applications 8773016.9 and AT 393094B propose the ultrasound for capturing gas components present in contaminated gases. The above patent applications suggest the use of limited frequency range only /ultrasonic, sonic and infrasonic/ for acoustic emission. Bearing in mind that the different components of the purified gas, depending on their size and density, have a different resonance frequency and perform most vigorously the specific oscillation, it is evident that such an approach of limited frequency acoustic irradiation can not improve significantly the efficiency of gas cleanup, because the mass transfer is best upon active oscillation of particles, which is fulfilled by part of them only if the emission is limited in frequency.

In the patent application according to patent publication US20006/0204407 A1 it is proposed the gas to be introduced tangentially into a vertical cylindrical vessel in order to create continuous rotation of the gas, helping its cleanup from CO2. Under the condition of continuity of the flow, as a result of the centrifugal force, determined by the mass of the gas ingredients, density gradation will be created from the wall of the absorber to its axis, whereby the chances of contaminants to meet and react are reduced significantly.

The task of this invention is to suggest new physical intensifying the gas cleaning factors and processes.

SUMMARY OF THE INVENTION

The purpose of the invention is the disadvantages of the wet desulphurization technology to be decreased by improving the capturing of sulfur oxides and the volume of the used equipment to be reduced. It aims as well at improving the quality of gypsum and increasing the efficiency of gas cleaning in order maximum reduction of the contamination of the flue gas to be achieved.

For that purpose intensifying the process of gas cleaning factors are used, accelerating the absorption and the adsorption, taking place in the reactor and extending the length of the path of the flue gas therein. This is accomplished according to the invention with a method wherein the flue gas cleaning is implemented through physical oscillatory movements caused simultaneously by helical impulse motion of the gas flow at its introduction into the gas-liquid system, by acoustic emission of wide-frequency spectrum and by pulsations, as the flue gas flows are treated in whole or only parts of them.

According to the invention, the method for flue gas cleaning can be implemented as the absorption in the gas-liquid system takes place at the impact of physical oscillatory movements, caused by acoustic emission of wide-frequency spectrum and pulsations.

Depending on the total amount of gas, the concentration of each gas in the mixture, the nature of the individual gases in this mixture, for example sulfur oxides, nitrogen oxides, carbon oxides and others, the ratio of the volume concentration of each gas in the mixture and the type of the selected technology for desulphurization or for capturing other gases, the number of gas pulsations varies from 60 to 300 pulsations per minute, the sound frequency from 0.5 to 25 kHz (sound vibrations per second) and the sound intensity is in the range 0.5 to 10 w/cm².

Therefore, due to the variety of influencing conditions, the parameters of the pulsations and the acoustic vibrations should be determined experimentally for each specific gas mixture.

In carrying out the method the following physical effects occur:

- Formation in the reactor of acoustic emission of wide-frequency spectrum, creating infrasound, sound and ultrasound, which in a closed space forms both running sound waves and standing sound waves with the respective nodal areas, where particles are accumulated regardless of their size. Therefore, in the nodal areas the contact between the absorbing and the absorbed particles is quarantined and the formation of new material phase /gypsum/ takes place; due to its increased weight and acoustic pressure it leaves the nodes and precipitates, which is helped by the running sound waves. The frequency of the emission is selected according to the geometric dimensions of the reactor so that standing and running waves to be formed and the intensity /power/ is determined by the concentration of impurities in order the acoustic energy to be sufficient for all the particles, without extending beyond the wall of the absorber. - Pulsed feed of the gas flow into the reactor so as to create pulsations, which due to the differences in pressures during pulsations and the time between them generate gas force impacts, generating for the particles with different mass different unidirectional velocity motion vector. That in turn causes the appearance of getting ahead /lighter/ and lagging behind /heavier/ particles, as a result of which the number of hitting collisions increases, thereby the opportunity for greater number of chemical reaction contacts, leading to faster gas cleaning. The gas turbulence arising from the pulsations also contributes to the latter. The turbulence also helps the faster cleansing of the surfaces of droplets and particles, uncovering them for new reaction activities. Besides impulse vortices liquidate dead zones.

- Pulsed feed of the absorbent /reagent/ in the reaction zone, which immediately disperses it in the volume and stirs at the same time; that increases greatly the contacts between the absorbent and the gas contaminants, thus contributing to the intensification of the technology.

- Pulsed supply of the oxidizing agent /air/, which stirs intensively the precipitate and helps the quick transformation of the sulfite to sulfate, thus improving the quality of gypsum. At the same time the improved mixing reduces the viscosity, which helps gypsum particles reach faster the lower zone of the precipitate, wherefrom they are taken out of the absorber.

All pulsators for pulse effects are situated outside the reaction zone of the absorber; therefore they are protected from active corrosion.

- Pulsed tangential input of the gas flow into the reactor, creating helical motion of the flow inside the reactor from the inlet to the outlet. The motion of the gas flow is an interrupted helical trajectory, which increases significantly the path of reactants and the magnitude of the extension depends on the pitch of the winding. This pulsed movement causes mixing which eliminates the density gradation and increases the possibilities for larger number of contacts between absorbing and absorbed particles, hence higher quality gas cleaning. Furthermore, certain force impulse is given to the particles, moving at different speed due to their different masses, which creates tangential efforts, accelerating the purification of the surfaces of droplets and particles and therefore causes rapid new reactions. In the intervals between impulses the generated centrifugal force, by taking gypsum particles to the wall of the reactor, helps them flow into the precipitate and also enhances the collisions between gypsum particles and the precipitate, which makes their capturing in the precipitate easier.

- Carrying out the gas cleaning in horizontal flow instead of the currently used vertical flow. This is especially useful for the existing thermal power plants, because they have no free space or if they have, it is too small for the installation of a conventional wet gas cleaning system with vertical absorber. Instead of the countercurrent movement in the vertical absorber, in the horizontal flow the movement is unidirectional and that greatly facilitates the work of the smoke fan. The above described physical effects can be introduced both in horizontal and in vertical absorber.

The apparatus for gas cleaning by the method according to the invention is characterized in that the absorber of the gas cleaning equipment 8 is positioned horizontally or slightly inclined and there are gas distribution plates 2 at the input for equalizing the gas flow over the entire section. The same is done in the tangential side input 3 for creating helical gas motion. Wide-frequency acoustic generators are installed in the reaction zone and near the input a pulsator is fixed (Fig. 1).

The apparatus for gas cleaning, when the absorption in the gas-liquid system takes place under the influence only of physical oscillatory motions caused by acoustic emission of wide-frequency range and pulsations, is characterized in that the absorber of the gas cleaning equipment 12 is vertical and acoustic generators are mounted in the reaction zone, while at the input of the absorber a pulsator 15 is fixed (Fig. 2).

In the devices according to the invention only wide-frequency generators or pulsators 7 can be mounted.

The spraying the reagent system 13 can be installed inside the chimney or can be installed inside the smoke duct, connected with the chimney. EXEMPLARY EMBODIMENTS

EXAMPLE 1

Fig 1 shows in plan a horizontal reactor. The gas distribution plates 2 at the input are for equalizing the flow throughout the entire section. The same is done at the tangential side input 3 that causes the creation of helical pulsed movement of the gas /shown with dotted line in the Figure/. Through the nozzle spraying system 4, mounted near the input, the absorbent 5 is injected impulse wise, the direction of jets can be against the movement of the gas, in the direction of the movement of the gas or transverse to the flow. In the area of spreading a sound generator is installed /not shown in the drawing/. On the sides of the body of the absorber 8 pumps 6 are installed for implementing circulation of the precipitate and air blowers 7 for pulsed supply of the air, needed for the oxidation processes. The cross section of the absorber can be varied, such as circular, semicircular, square, rectangular, etc. The materials for its manufacture can be: concrete with internal acid and heat-resistant coating to 200°C, nickel steel or another sheet iron, fiberglass, heat-resistant plastics, etc. The spraying the reagent system 4 can be mounted inside the gas duct, transporting the flue gases in the chimney. These gas ducts are horizontal or slightly inclined. In this case the efficiency of gas cleaning is increased due to the better use of the heat of gases and the investments for the construction of the gas cleaning system are significantly reduced because there is no need of installing a separate reactor or heater,

The device works as follows: The flue gases before entry into the absorber pass through a pulsator /the Figure does not show a specific structure/ and distribution plates, distributing the gas evenly throughout the entire section. The incoming gas is immediately sprayed with the absorbent on its way to a certain length of the horizontal absorber 8. In the remainder of the absorber contacts between the molecules of sulfur dioxide and the absorber continue, while the slurry 9 is stirred by the pulse wise circulation of the precipitate, achieved with pumps 6. As seen from the Figure, from the side of the absorber air is supplied, necessary for the oxidation of sulfite ions to sulfate, i.e. to the formation of gypsum. To avoid falling of drops into the base of the chimney 11 , which can be taken out by the stream a splash head is installed in the output before the chimney. The gypsum slurry 9 leaving the absorber, as in the above example, is directed to the following appropriate treatment.

EXAMPLE 2

Fig. 2 shows a device for implementation of the gas cleaning in existing or in newly built chimneys. The latter are usually high /to 200 m and more/, therefore it is not necessary the spraying device to be installed highly in the chimney. The installation at height 10 - 15 m fully provides the time for contact, reaction and precipitation of the newly formed product. The installation of the nozzles at that height does not cause problems. The same applies to the installation of the wide-frequency acoustic sources (emitters/. The greater height of chimneys provides enough time for drops with gypsum particles that have eventually passed above the nozzles to meet, merge and return to the precipitate.

The device works in the following manner. The flue gases enter pulse wise the lower part of the reactor /chimney 12/, above the gypsum slurry; they are directed vertically upwards and are sprinkled with fine droplets of the absorbent, moving pulse wise against them. Upon encountering of gases and droplets a chemical reaction takes place, wherein sulfur dioxide forms calcium sulfite with calcium oxide from the hydrated lime. Since flue gases contain a certain amount of oxygen /about 9 - 10%/, part of the sulfur dioxide is oxidized to sulfur trioxide, which forms with calcium oxide calcium sulfate. The newly formed substances precipitate and undergo further pulsed oxidation processing. Parts of the precipitate circulate by means of pumps 14 in order the absorbent to be used completely and the transformation of the precipitate to take place to calcium sulfate with two molecules of water, i.e. compound equivalent in composition to natural gypsum. The gypsum formed in the precipitate is continuously or periodically taken out from the lower part of the reactor, fed into tank 16 and goes to the next dehydrating treatment to about 10% moisture. If that gypsum is intended for household use and construction, it is dehydrated in furnaces, which aims at obtaining stiffening gypsum. The use of that gypsum in cement production is possible. Then the dehydration of gypsum to calcined gypsum is not necessary. A similar device can be realized in a new or in an existing chimney. In this case the chimney performs two functions, namely the transportation of gases and their absorption processing; that increases the efficiency of gas cleaning as a result of the better use of the heat of flue gases, which elliminates the need of additional heating them before entering the reaction zone. In addition to the improving of the efficiency, the investments and the operating costs are significantly reduced, as the need of separate reactor and heater is excluded.

The composition of purified gases 17 is automatically controlled with analyzer.

Depending on the chemical composition of the harmful gas components, their proportion in the mixture, the temperature of the gas, the absorber structure, the volume of the feed gases, the volume of the oxidizing air and the quantity of the absorber, the improvement of the efficiency of the gas cleaning can be realized with the introduction in operation of all the physical intensifiers mentioned, only some or a single one of them. For example, in small absorbers pulsed feed of the gas can be applied only, because the noise is substantially a gas wide-range acoustic emitter and the acoustic energy emitted by it can be sufficient for intensification due to the small size of the absorber, which prevents the fading of acoustics at small distances.

Also, when fast reactions take place in the absorber, it is possible the setting in impulse progressive motion of the entire flow (gas, reagent, air) or part of it to be sufficient for homogenization of the substances in the reaction zone or in the precipitate, so that a reaction can take place.

Claims

PATENT CLAIMS

1. A method for flue gas cleaning by absorption in gas-liquid system on acoustic irradiation and tangential introduction of the gas, characterized in that the cleaning of flue gases is carried out through physical oscillatory movements and pulse movements, caused simultaneously by the helical motion of the gas flow at its introduction in the gas-liquid system, by acoustic emission of wide-frequency spectrum and by pulsations; gas flows are treated in whole or only parts of them.

2. A method for flue gas cleaning according to claim 1, characterized in that the absorption in the gas-liquid system takes place at the simultaneous impact of physical oscillatory movements caused by emission of wide frequency range and pulsations only.

3. A method, according to claims 1 and 2, characterized in that the frequency of the acoustic emission is from 0.5 to 25 kHz and its intensity is in the range 0.5 - 10 w/cm².

4. A method according to claims 1 , 2 and 3, characterized in that the number of gas pulsations varies from 60 to 300 pulsations per minute.

5. An apparatus for gas cleaning using the method according to claim 1 , characterized in that the absorber of the gas cleaning equipment is horizontal or slightly inclined and the gas distribution plates at the input for equalizing the flow throughout the entire section; the same is done at the tangential side input for creating helical motion of the gas, acoustic generators of wide frequency range are installed in the reaction zone and near the input a pulsator is fixed.

6. An apparatus for gas cleaning using the method according to claim 2, characterized in that the absorber of the gas cleaning equipment is vertical, acoustic generators of wide frequency range are installed in the reaction zone and near the input a pulsator is fixed.

7. An apparatus according to claims 3 and 4, characterized in that only wide range acoustic generator or only pulsator is installed.

8. An apparatus according to claims 5 and 6, characterized in that the spraying the reagent system is installed inside a horizontal reactor.

9. An apparatus according to claims 5 and 6, characterized in that the spraying the reagent system is installed inside the smoke duct, connected with the chimney or in the chimney itself.