NL8503082A - PROCESS FOR THE REMOVAL OF GASEOUS SULFUR COMPOUNDS, SUCH AS SULFUR DIOXIDE, FROM THE COMBUSTION GASES OF AN OVEN. - Google Patents

Abstract

In addition to a sulphur-containing fuel (4) and an oxygen-containing gas (5), a pulverous alkali metal or alkaline earth metal oxide or carbonate (6) (particularly calcium or magnesium) is fed into the furnace (1) in an amount in excess in proportion to the sulphur dioxide gas formed in the combustion chamber of the furnace, and water and/or steam (9) is sprayed separately into the calcium oxide-containing and/or magnesium oxide-containing flue gases (8) either in the furnace or after leaving the furnace. Alternatively, or in addition, the pulverous oxide (6') can be fed directly into the flue gases (8) leaving the furnace (1). <IMAGE>

Description

i - 1— “1 Q / T *”.

* «W / -'W *; »—-

Short designation: Choice of method for removing gaseous owavel compounds, such as sulfur dioxide, from the combustion gases of an oven

Your unwinding trembles; relates to a method for just removing gaseous sulfur compounds, such as sulfur dioxide, from the combustion gases of an even sulfur-containing fuel, coal or oil.

It is known to prevent the sulfur dioxide content of the furnace combustion gases by adding calcium oxide, calcium carbonate or other alkaline compound into the furnace combustion furnace. In a furnace with a fluidized bed in which the bed circulates, it is possible to reduce the sulfur dioxide content of the combustion gases by as much as 90% by means of a calcium addition when the furnace is in the temperature range which is optimal for the chemical reactions. 300-1.QQ0 ° C functions. The sulfur dioxide absorbed in this way leaves the oven in the form of gypsum, together with the fly ash.

In other furnaces, where it is necessary to use temperatures higher than those mentioned above and where the retention of the addition is short due to the nature of the combustion, it is expected that the reduction of the sulfur dioxide content of the combustion gases remains considerably lower, about 90% or less, and therefore this method has not been applied on an industrial scale for such furnaces.

On the other hand, it is known that the sulfur dioxide content of combustion gases can be reduced by various absorption processes outside the oven. One such method known in the art is the so-called spray or semi-dry method, in which the combustion gas leaving the oven is fed into a separate reactor, in which an aqueous slurry of calcium hydroxide in the form of small droplets passes through specific nozzles. is sprayed. Typically, the reactor is a fairly large vessel, in which the rate of combustion gases is allowed to decrease and the aqueous slurry is sprayed from the top down, from the top portion of the vessel. The temperature of the reactor is at that time 50 DEG-50 DEG C., and the control of spraying the aqueous slurry of calcium hydroxide is extremely important since droplets too large as liquid will remain at the bottom of the reactor. The viscosity of the aqueous slurry of calcium hydroxide should be maintained at such a level that the heat content of the combustion gases would evaporate the water entering the reactor so that the adsorption product in the form of a dry powder can be recovered. With this method 5 it is possible to remove as much as 90% of the sulfur dioxide. The disadvantages of this method include the tendency of the nozzle to become clogged, an additional preparation and metering device for the aqueous slurry of calcium hydroxide, which increases investment costs and difficulties in controlling the droplet size during spraying.

The object of the present invention is to provide a method for removing gaseous sulfur compounds, such as sulfur dioxide, from the combustion gases of an oven, wherein the gaseous sulfur compounds can be converted into solid sulfur compounds which can be easily separated from the gases and this allows effective removal from the combustion gases of an oven, in a simple and economical manner.

The main features of the invention are given in the accompanying claims.

In the process of the present invention, a substance which reacts with gaseous sulfur compounds, and in particular with sulfur dioxide, and water are separately fed into the process, avoiding the problems of preparing, treating and feeding a slurry. following manner: a) a powdered alkali metal oxide and / or alkaline earth metal oxide and / or a respective compound which is converted into an oxide in the oven, such as carbonate, is introduced into the oven in addition to the sulfurous material to be burned and an oxygen-containing gas either said oxide powder is introduced into the sulfur dioxide-containing combustion gases leaving the furnace, b) water and / or steam are separately sprayed into the furnace and / or into the combustion gases to convert the oxide into a hydroxide which reacts with the sulfur dioxide and finally c) a solid containing the alkali metal and / or alkaline earth metal sulfate, and possibly sulfite, and which is obtained as a reaction product, is separated from the gases

The basic idea of the invention is therefore that the calcium and magnesia oxides which are macfive from the point of view of removal of sulfuric sludge are activated in situ in the combustion gases by means of water and / or steam, where they are converted into the respective sulfarozymes to react with sulfur dioxide to form a solid sulfate / sulfoxide mixture which can then be effectively removed from your combustion gases by physical separation methods.

A powdered oxide and / or carbonate is incinerated in the furnace combustion chamber, according to the sulfur content of the fuel, such that the amount of alkali and / or alkaline earth metals is at least the amount corresponding to the amount of sulfur in the furnace. molecular ratio according to the reaction equation, but preferably greater than the amount required for the reaction. By separately feeding the oxide and / or carbonate in the form of a powder into the combustion chamber, or the oxide directly into the combustion gas pipes, it does not need to be supplied in the form of a slurry through nozzles, whereby blockage of the nozzles and the use of additional preparation and feeding devices for the aqueous slurry were avoided. On the other hand, the supply of water and steam through the nozzles is straightforward and convenient.

The supply of water or steam in the combustion gases is practically carried out at a temperature of 50 DEG-80 DEG C., preferably in the temperature range of 0 DEG-200 DEG C. If desired, the absorption product is produced in the process. to recover the form of a dry powder, water is used only in such an amount that the thermal energy and the reaction of the combustion gases are sufficient to evaporate it, p - 1. , 3 amount of energy from outside the system used in addition to the res-t ~ sT * arm.

hereinafter will be described in more detail with the aid of the accompanying drawing, which schematically depicts a device suitable for stirring them according to the method of the present invention.

In the drawing, the furnace is generally shown to burn just-1 sulfur-containing fuel h, usually preheated, an oxygen-containing gas 5, and calcium and / or magnesium-6 * and / or carbonate 6, at preferably in excess of the amount of sulfur dioxide gas formed in the combustion chamber, * ΐ -U- are fed into the combustion chamber of furnace 1. In this context, the term "in excess" is intended to mean that the amount of calcium, magnesium or calcium and magnesium present in the calcium and / or magnesium and / or carbonate are greater than they would theoretically require according to the reaction equation 5 to react with any sulfur fed into the combustion chamber.

The carbonate fed into the furnace is broken down into oxide and carbon dioxide in the combustion chamber. The oxide, in turn, can react with sulfur dioxide to form, initially, sulfite 10 and then, upon oxidation, sulfate. Due to the short retention time in the oven, only a portion of the oxide has the opportunity to react with the sulfur dioxide at a temperature sufficiently high for the reaction, and for this reason burns off calcium oxide and / or magnesium oxide containing combustion gases 8, containing combustion residue and also unabsorbed sulfur dioxide, the furnace combustion chamber through the flue gas conduit 7. In addition, or optionally, powdered oxide 6 'may be fed directly into the flue gas conduit 7 or into a subsequent reactor 2.

In practice, the temperature of the combustion gases 8 is so low that the reaction between the calcium and / or magnesium oxide and sulfur dioxide is relatively low, the oxides under these conditions can be considered relatively inactive in terms of sulfur removal.

However, the combustion gases 8 can be used in the heat exchanger 12 to heat the air 5 which is introduced into the furnace 1.

The calcium and / or magnesium oxide-bearing and sulfur dioxide-containing combustion gases 8 exiting the combustion chamber of the oven are then fed into a reactor, which is generally indicated by reference number 2. To activate the calcium and / or magnesium water 9 or steam is sprayed into the combustion gases in reactor 2, and this water or steam 30 reacts with the calcium and / or magnesium oxide to form the respective hydroxides. The hydroxide in turn reacts with the residual sulfur dioxide in the combustion gases 8, to form the respective sulfite, which, in the presence of oxygen, at least partially oxidizes further to the respective sulfate.

The amount of water 9 which is fed into the reactor 2 is set at such a low value that the heat of the combustion gases 8 is sufficient to evaporate the water supplied in the reactor 2. pen. You can do that; dry fly ash-like reaction product is removed, in the same manner as the other fly ash, in a conventional fly ash separator 3, from which the combustion gases 11 are fed into the chimney 13, and the separated fly ash 12 and reaction product are passed on for possible further treatment.

The order in which water or steam and the powdered oxide are added is in no way critical. For example, the water or steam can be fed into the furnace and the powdered csyde only 10 in a place following the furnace, either in the flue or in the next reactor. The additional advantages of the method of the present invention also include the fact that the method can be used in an oven equipped with any type of burner. The size of the oven is not a limiting factor, and there is no need to 15.

circulate calcium and / or magnesium oxide in the combustion chamber, avoiding the costly circulating bed possibility with the complicated recirculating devices and at the same time the enormous dust nuisance, which is a drawback of the recirculating bed possibility due to its operating principle as well as the dust separation. In comparison with the known spraying process, the spraying of water or steam in the reactor 2 is furthermore considerably less complicated and more inexpensive to use than using. a slurry that clogs the outlets and is difficult to mix. The additional advantage is that the carbonate can be burned economically in the combustion chamber of the furnace itself.

The invention will be described in more detail below with the help of examples.

Paragon 1

Throats with a sulfur content of 1 are fed at a rate of JQ ten / hour into a peder coal oven with a heat output of 600 MW, 3 ~ "with the oven operating at full capacity. An excess of combustion air is supplied so that the oxygen content of the combustion ash is h%.

Calcium, which may be, for example, calcium carbonate, dolomite or calcium oxide, is added to the oven. For example, calcium carbonate with a 90% calcium carbonate content is added to the furnace at a certain changing ratio to the amount of sulfur entering the furnace in the fuel. The theoretical equivalent amount is approximately V% -6- 3 Λ ton / hour calcium carbonate.

The calcium carbonate decomposes according to (1) CaCO 3 CaO + CC> 2 in the oven at high temperature to calcium oxide and carbon dioxide, which leave the oven together with the combustion gases. Some of the calcium oxide in the oven reacts with the sulfur oxides present in the combustion gases to form calcium sulfate or calcium sulfite.

(2) CaO + S02 + 1/2 02 —CaSO ^ or 10 CaO + S02 -> CaSO ^

CaS03 + 1/2 0g - * CaSO ^

Water and / or steam are sprayed into the combustion gases, either in the oven or in the combustion gas pipe, or in a separate reactor that follows the combustion gas pipe.

In terms of energy economy, it is extremely economical to increase the moisture content of the combustion gases by spraying water into a separate reactor, one point following from all heat recovery surfaces.

The increased moisture content of the combustion gases allows a high reactive calcium hydroxide to form from the unreacted calcium oxide in the oven.

(3) Cao + H20 - »Ca (0H) 2 Ca (0H) 2 + S02 - - => CaS03 + H20 which reacts quickly with the sulfur oxides contained in the combustion gases. The higher the moisture content of the combustion gases at their outflows, the more effectively the sulfur dioxide is removed from the combustion gases. In terms of energy economy, however, it is advantageous to operate in such a way that the heat released in the chemical reactions is sufficient to evaporate the amount of water added. When it is desirable to increase the final temperature of the combustion gases, this is either by using heat from outside. "* Carried out by a part of a large combustion gas stream.

It is not essential that the compound known in the reaction zone, ie calcium carbonate or dolomite, be in the form of the 0x7th.

The results were shown in the date below, which indicates in c tracers how much sulfur dioxide from the combustion gases was X * r-; when varying amounts of calexuncardonate were subjected to oven failure according to the invention, the amounts of calcium carbonate are shown as the molecular ratios of the calcium content of the powdered calcium carbonate to the sulfur content of the equilibrium fuel supplied. The temperatures of the combustion gases were measured at a point immediately before the feed point of the water or steam, except at 800 ° C, at which temperature the water or steam was added directly into the oven.

TABLE 1 3}

Ca / 3 7erbrandingsgas Combustion gas S0_ temperature0 temperature reduction

*** D V

3516 S00 ° C 1 o8 ° c * 25 0.52 50 ° c 65 ° C 50% 1 202 ° C 7 ^ ° c 77.1 „„ 1 <56 90 ° c 68 ° C 825 2.20 200 ° C 72 ° C 875 2j22 12C ° G 62 ° C 96% 2.3 - :: q0c 68 ° c 935 5 =: 90 ° C 66 ° C 975 2c 131 3co ° c 110 ° C 725 120 ° C 68 ° C 985 ~ s · * A) water or steam in the evenly added 3} at a point immediately before the water supply point.

Example 2 Dolomite containing calcium carbonate (CaCCL), i-55 magnesium carbonate, rcCO 2, and 105 impurities was fed into a pulverized coal oven according to Example 1, using the same operating conditions. On the basis of equivalence, the amount of dolomite required V i -S- in relation to the amount of sulfur supplied is about 6.8 tons / hour.

The calcium and magnesium carbonates contained in the dolomite are broken down in the oven to calcium oxide, magnesium oxide and carbon dioxide, which leaves the oven along with the combustion gases. Part of the 5 oxides in the oven react with the sulfur oxides present in the combustion gases to form sulfate or sulfite.

Water and / or steam are sprayed into the combustion gases, either in the furnace or the flue gas pipe or in a separate reactor located at a point following the flue pipe, after which the oxides which have not reacted in the furnace, due to the increased moisture content, may form hydroxides. The hydroxyde in turn reacts with the sulfur oxides present in the combustion gases to form a powdery reaction product.

When dolomite is used, the highly reactive calcium hydroxide reacts before the slower magnesium hydroxide reacts which, when the amount of calcium is sufficient, passes through the reactor in substantially unreacted form. By designing the method to proceed only on the basis of the calcium present in the dolomite, the equivalent amount indicated above is obtained. When the molecular ratio of calcium to sulfur is at least 1, the results of the process are essentially consistent with the corresponding values in Table 1.

Example 3

Calcium oxide containing 10% impurities is introduced into the oven according to Example 1, using the corresponding operating values.

In terms of the reaction, the theoretical equivalent amount of calcium oxide relative to the amount of sulfur entering the furnace in the fuel is about 1.9 tons / hour.

Part of the calcium oxide reacts in the oven with the sulfur oxides contained in the combustion gases to form calcium sulfate or sulfite.

Water and / or steam is sprayed into the combustion gases either in the oven or in the combustion gas pipe, or in a separate reactor located one point after the combustion gas pipe.

As a result of the increase in the amount of moisture, calcium oxide forms highly reactive calcium hydroxide, which reacts quickly with the sulfur cyses still present in the combustion gases. The more negligible the moisture content of the combustion gases it is, the more effective the sulfur dioxide is removed from the combustion gases. In terms of energy economics, however, it is advantageous to operate in such a way that the heat released in the chemical reaction is sufficient to add the added water.

When the imported calcium, in the form of calciuncnyde, is calculated as a molecular ratio to sulfur, the results are in agreement with those indicated in Table 1 of Example 1.

Claims (5)

A method for the removal of gaseous sulfur compounds, such as sulfur dioxide, from the combustion gases of an oven, characterized in that a) a powdered alkali metal oxide and / or alkaline earth metal oxide and / or a respective compound which is converted into an oxide in the oven, such as carbonate (6) is introduced into the furnace in addition to the sulfur-containing material (U) to be burned and an oxygen-containing gas (5), or said oxide powder (6 ') is introduced into the sulfur dioxide-containing combustion gases (8) entering the furnace Leaving, 10 b) water (-9) and / or steam are separately (2) sprayed into the furnace (1) and / or into the combustion gases (8) to convert the oxide into a hydroxide which is mixed with the sulfur dioxide reacts and finally c) a solid (12) containing the alkali metal and / or alkaline earth metal sulfate, and possibly sulfite, which is obtained as a reaction product, is separated (3) from the gases (11). Method according to claim 1, characterized in that said powdery compound (6, 6 ') is supplied in excess relative to the sulfur present in the combustion gases. Method according to claim 1 or 2, characterized in that the spraying of the water (9) and / or steam is carried out while the temperature of the combustion gases (8) is 50-800 ° C, and preferably 90-200 ° C is. } +. Process according to one or more of claims 1 to 3, characterized in that water (9) is sprayed into the combustion gases (8) at the most in an amount as much as through the thermal energy which can be generated by the combustion gases and the reactions. be evaporated. 5. Process according to one or more of claims 1-3, characterized in that a small amount of extra energy is introduced from outside into the reactor before the combustion gases are fed to the solids separation. Process according to one or more of the preceding claims, characterized in that the powdered compound supplied are calcium carbonate, calcium magnesium carbonate and / or the respective oxides.