FI91364B - Method and device for cleaning of process gases containing gaseous contaminants - Google Patents

Abstract

Method and device for cleaning of a process gas containing gaseous contaminants. According to the method, the process gas, such as a flue gas, is introduced together with water and a reactant simultaneously into a grinding of the reactant, whereby the un-reacted, free material surface on the crossed reactant particles is exposed in connection with the grinding, and a quick and efficient reaction is achieved. The device comprises a grinder into which the process gas such as a flue gas is introduced simultaneously, together with water and reactant, for grinding of the reactant. <IMAGE>

Description

Method and apparatus for purifying process gases containing gaseous impurities

The invention relates to a process for purifying process gases containing gaseous impurities, such as flue gases containing sulfur dioxide, which process comprises contacting the process gas with a reactant in the form of a solid reacting with the gaseous impurities to react the gaseous impurities in the form of a solid, the present reagent is ground in a process gas stream during the reaction to enhance it, and the dusty reaction product formed is removed from the process gases after grinding.

The invention further relates to an apparatus for carrying out the method, the apparatus comprising means for introducing the process gas and the reagent into contact with each other and a refiner in which the reagent is ground simultaneously.

Combustion processes and the process industry produce a variety of gases, which often contain harmful gaseous pollutants such as sulfur dioxide, sulfur trioxide. dia and fluoric and hydrochloric acid, etc. Various methods and equipment have been developed for the removal of these, and in particular for the removal of sulfur in the flue gases of the power industry • · ♦ * · 1: oxides based on the use of lime in different ways.

• · In these, the typical principle is to contact the sulfur oxides with the calcium oxide particles so that they react to form calcium sulfite and sulfate.

··· In a known method, lime is fed • ♦ · · into the boiler furnace as calcium carbonate, where it burns • # into calcium oxide, and then the boiler flue gases are fed to a reactor where water is injected to convert calcium oxide into calcium hydroxide and thus • ♦ • · · • · · • · 2 to effect the reaction. A similar solution is also presented in FI publication 84435, in which a reagent is added to the flue gases and then the flue gases are introduced into the humidification reactor in a corresponding manner. In this solution, the particles separated from the gas are returned to the reactor to provide a sufficient particle density. It is further known to purify such gases by injecting lime or calcium hydroxide as an aqueous solution or slurry into the purification reactor, resulting in a dusty dry reaction product in the flue gases which can be easily separated from the flue gases by means of a filter.

It is also known to purify such gases using wet scrubbing, in which case the gases are passed through a lime slurry or a similar absorption slurry.

15 Known solutions provide reasonably good cleaning results, but the equipment they require is quite complex and expensive. In them, the purification is based on the idea that the absorbent is fed pre-ground or slurried into a gas stream. In this case, the free active reaction area available with the absorbent particles for binding the gas molecules is limited to the outer surface area of the absorbent particles. In addition, a significant portion of the free active reaction surface of the particles disappears in the process after the initial grinding of the reagent prior to the feed to the gas stream, • · • · · *. 1: because the finely divided reagent particles are agglomerated. As a result of the agglomeration, the particle density of the reagent and the slurry droplet density, and consequently also the amount of free active reaction surface area, are not high in the process gas stream relative to the gas molecules to be removed. Thus, the binding of the gas molecules to be removed to the reagent particles requires a relatively long time, which causes the size of the equipment required to be enormous. Furthermore, the cleaning is based on the idea that the gases and the absorbent must have a relatively long reaction time, which means that the size of the equipment required depends entirely on the calculated reaction time. -TA. However, these methods do not provide a sufficiently good cleaning result at a reasonable cost, since a significant improvement in efficiency requires longer residence times from the device and thus correspondingly significantly larger devices.

It is an object of the present invention to provide such a method and apparatus for the purification of process gases containing harmful gaseous impurities, such as flue gases, which can be obtained easily and reliably with a relatively small-sized apparatus.

It is essential to the process of the invention that water be added to the process gas and reagent to enhance the reaction, that the process gas and reagent and water be contacted only during grinding of the reagent for a short time, and that water be fed only such that the reaction results in a dry dusty reaction product.

The apparatus according to the invention is characterized in that the apparatus comprises means for supplying water pro-, · ·. mixed with the process gas and reagent in the refiner as the process gas and reagent are passed through the refiner.

* · ·

The essential idea of the invention is based on the fact that • · · * · *: φ flue gases, reagent and water are momentarily added to the • · · '♦ *! in contact with each other as efficiently as possible, whereby the increase in the reactive surface causes a rapid reaction, which results in a very good cleaning result. This is done in accordance with the essential idea of the invention, so that the gases are passed simultaneously with a reagent, such as sulfur dioxide, and water to a refiner, where they mix and * 35 come into direct contact with each other immediately. • · ♦ · ♦ · 4 When grinding, in the presence of all, the reactions between sulfur and lime and water take place almost immediately. By supplying water according to a preferred embodiment of the invention only to the extent that the excess water in the reaction is now able to evaporate due to the heat of the flue gases, the end result is a flue gas containing substantially dry dusty reaction results from which impurities can be removed by a filter.

The essential idea of the invention is based on the fact that the grinding of the reagent material is most preferably carried out in a flue gas stream, whereby the gas molecules to be removed, the reagent and water react in a fraction of a few seconds up to a few microseconds of grinding. In this case, the free active reaction surface of the reagent is maximally available, because agglomeration does not occur before. This method provides a very high reagent particle density, so that the total reaction time required for a high degree of purification is short.

An advantage of the invention is that when gases, water and a reagent such as lime are mixed in the refiner, the result is that as the reagent is ground smaller, a new active surface is constantly exposed, resulting in a very good reaction efficiency. A further advantage of the invention is that the equipment, i.e. the required refiner, is »· 1 **. 25 relatively small in size compared to various water • · '/ spraying and scrubbing reactors, because the reaction time required by the grinder is • • · ··· a fraction of these known. *: the reaction time and delay time required by the solutions.

»· ·: A further advantage of the invention is that a relatively coarse reagent material can be used in the process, since it is ground smaller in the grinder in any case, as a result of which grinding costs are saved.

»'. The invention will be described in more detail in the accompanying drawings, in which Figure 1 schematically shows the method according to the invention and the apparatus used therefor, and Figure 2 shows the results obtained by the invention in removing sulfur dioxide from a boiler. flue gases.

In Fig. 1, a process gas, such as flue gas, is passed along duct 1 to refiner 2. At the same time, a reagent is fed to the apparatus by means known per se, as exemplified in this case for desulfurizing lime and water through ducts 3 and 4, respectively. . During the purification of sulfur-containing flue gases, the following reactions take place in the process: (1) CaO + H 2 O - Ca (OH) 2 15 (2) Ca (OH) 2 + SO 2 - CaSO 2 + H 2 O (3) CaSO 3 + 0.52 - CaSO 4

Other alkaline-reactive solids 20, such as slaked lime Ca (OH) 2, calcium carbonate CaCO 3, dolomite CaMg (CO 3) 2, calcium-containing fly ash, alumina and oxide hydrate A1 (OH) O 2, etc. and the dusty reaction results »· exit to the outlet duct 5, from where they are led to the dust • • Γ1. 25 to the timer 6. With a dust separator 6, which can be any filter known * 1 »'1 [1, the dust is separated from the flue gases, which are • · · · led out and the separated dust is removed through a duct 7.

". 1: The operation of the invention is described in more detail in the following examples, the results of which are shown as curves 30 in Fig. 2: · # ♦ • · · · *: 1. Example 1: • · · * . Heavy fuel oil containing 1.7% sulfur · Sulfur dioxide flue gas from combustion ··· 1 35 Sun with a temperature between 80 - 220 ° C is led • · • ♦ • ♦ • »♦ · ♦ •» 6 along channel 1 to refiner 2. Calcium oxide is simultaneously fed to refiner using channel 3 using a Ca / S molar ratio of 1.0 to 4.0. Water is also fed to the grinder via channel 4. The amount of water is adjusted on the basis of the amount of lime fed using a minimum H 2 O / CaO molar ratio of 1.0. Using a Ca / S molar ratio of 2.0 and a theoretical amount of water, a degree of sulfur dioxide separation of about 70% is achieved. Increasing the amount of water fed to the refiner to correspond to a 10 H 2 O / CaO molar ratio of 2.0 improves the degree of sulfur dioxide separation to about 85%. Increasing the Ca / S molar ratio to 3.0 improves the sulfur dioxide separation to about 95% with the H 2 O / CaO molar ratio still being 2.0. The flue gases and the dry reaction products generated by the refiner 15 leave the refiner 2 out along the tokan 5 to the dust separator 6, from where they are separated as a dry product through the duct 7.

Example 2: 20 Lime is injected into the flue gases produced during combustion. Lime and sulfur dioxide-containing gases are passed together along flue 1 to a refiner ... 2. Calcium oxide is injected into the flue gases. using a Ca / S molar ratio of 1.0 to 4.0. In addition, water from channel 4 is fed to the 25 ducts. The amount of water is adjusted on the basis of the amount of lime fed • * · using a minimum H 2 O / CaO molar ratio of 1.0. By using a Ca / S molar ratio of 2.0 and a theoretical amount of water of about 70%, a degree of separation of about 70% sulfur dioxide is achieved. Increasing the amount of water fed to the refiner to correspond to a molar ratio of H 2 O / CaO to Γ: 2.0 improves the degree of sulfur dioxide separation to about 85%.

Increasing the Ca / S molar ratio to 3.0 improves the degree of sulfur dioxide separation to about 95% with the H 2 O / CaO-γ molar ratio still being 2.0. The flue gases and dry reaction products generated by the * ♦ 9 9 9 · 7 refiner leave the refiner along the outlet duct 5 to the dust separator 6, from where they are separated as a dry product along the duct 7.

5

As the examples show, the process according to the invention has obtained very good cleaning results using a disintegrator-type refiner as the refiner. A desin-integrator grinder is a simple and reliable embodiment of the invention which has two grinding rings rotating in opposite directions. Powder brewing occurs when the material strikes the impact surfaces located on the circumference of the refiner. As the flue gases pass through the material being ground, the broken calcium sulfite / sulfate particles, when supported by the grinding, expose a new active reagent surface, which reacts rapidly with sulfur in the presence of water.

In the solution according to the method, as the examples show, relatively small amounts of lime 20 can be used compared to the corresponding known methods in use, without substantially affecting the reaction result and thus the cleaning ability. The result is also: ··, a dry product that is simple and easy to handle in a dust separator and does not require sludge or other similar abrasion. 25 cargo of material to be handled. The apparatus does not require a separate wetting / washing reactor, which is not only expensive but also large in size. Thus, the investment costs of the apparatus according to the invention are quite low. The operation of the apparatus is also easy to control, since the rotational speed and thus the delay time is small and final; u The control of the los can be done only by adjusting the amounts of reagent and water: i The apparatus according to the invention can also be easily installed in existing power plants or other chemical processes because of the space required. the operating power it requires is relatively small.

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In the above description and drawing, the invention has been shown by way of example only and is not limited thereto in any way. As the refiner, any suitable refiner can be used to make the reagent particles, such as lime particles and the formed sulfide / sulfate particles, ground smaller and thus reactive. From a practical point of view, a disintegrant grinder is a preferred solution because it easily grinds and mixes simultaneously and makes water, reagent and process gases a very thin layer where the reaction distances are short and thus the reaction can take place quickly.

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Claims (11)

1. Process for the purification of gaseous impurities containing process gases, such as e.g. sulfur dioxide-containing flue gases, in which process the process gas is contacted with a solid reagent which reacts with the gaseous impurities in the process gas, to cause the gaseous impurities to react and form a solid dust-like product, wherein the reagents in solid mold is broken into the process gas stream during the reaction to effect the same, and the formed dust-like reaction product is removed from the process gases after grinding, it is noteworthy that to effect the reaction, water is added to the process gas and the reagents, the process gas and the reagents being added. the water is contacted with each other only for a short time in connection with the milling of the reagents and that water is fed only in such an amount that the reaction results in a dry dust-like reaction product. 20 2. A process according to claim 1, characterized in that as a reagent a metal oxide, preferably calcium oxide, which in the grinding reacts with the input water and forms hydroxide which reacts, can be used. passes on with the gaseous impurities in the process gases. • · .1 3. A process according to claim 1 or 2, characterized in that the reagents in solid form and / the water and the process gas are fed to the grinding along different channels. 30 4. A process according to claim 1 or 2, characterized in that the reagents in solid form are passed to the grinding with the process gases and - in the water, is fed to the grinding along a separate channel. 5. A process according to any one of claims 1-4, characterized in that the reaction is supplied with an amount of water at least equal to the minimum amount calculated according to the chemical reaction and water is supplied to the reaction at most in such an amount. that the process gases are cooled down to the so-called wet-bulb temperature. 5 Process according to any of the preceding claims, characterized in that the process gases are conducted to the grinding at a temperature not exceeding 200 ° C and that the process gases are removed from the grinding at a temperature higher than their water temperature. Apparatus for realizing the process according to claim 1, which comprises means for contacting the process gas and the reagents with one another and a grinding apparatus wherein the reagents are simultaneously milled, characterized in that the apparatus comprises means for supplying water to the process gas and the reagents in the grinder, the process gas and the reagents are passed through the grinder. 8. Apparatus according to claim 7, characterized in that the grinder is a disintegrator type grinder. 9. Device according to claim 7 or 8, characterized in that it comprises a separate water supply channel for supplying water to the grinding apparatus. . ·. apparatus. • · 10. Device according to any of claims 7-9, characterized in that it comprises feed *; **. means for feeding the reagents directly to the grinder. • · · l '/ 11. Device according to any one of claims 7-9, characterized in that it comprises feed means for supplying the reagents to the process gas prior to the grinding apparatus. ··· • · 1 • · «♦ • · • · · • • ♦ ♦ · · · · • m · • ♦ · • ♦»