JPS61287419A - Removal of gaseous sulfur compound from flue gas of furnace - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for removing gaseous sulfur compounds, such as sulfur dioxide gas, from the flue gas of a furnace burning sulfur-containing end fuel, coal or oil. .

PRIOR ART AND PROBLEMS SOLVED BY THE INVENTION Traditionally, the sulfur dioxide content of furnace flue gases has been reduced by injecting calcium oxide, calcium carbonate or other alkaline compounds into the furnace combustion chamber. It is known to do. In fluidized bed furnaces with circulating beds, the addition of calcium can reduce the sulfur dioxide content of the flue gas by as much as 90% when the furnace is operated in the optimum temperature range for chemical reactions, i.e. 800-1000°C. I can do it.

The sulfur dioxide gas absorbed in this way leaves the furnace in the form of gypsum together with the fly ash.

In other types of furnaces, where it is necessary to employ temperatures higher than those specified in ``2 and the nature of the combustion'' - the residence time of the additives is short, the rate of reduction in the sulfur dioxide content of the flue gas is substantially reduced. It is about 50% or less. Therefore, this method has not been applied to such furnaces on an industrial scale.

On the other hand, it is also known that the sulfur dioxide content of the flue gas can be reduced by various absorption methods outside the furnace. One of these methods, which is known per se, is the so-called spray method or semi-dry method.

In this method, the flue gas leaving the furnace is directed into a separate reactor where a slurry of calcium hydroxide is sprayed in the form of droplets through specific nozzles. The reactor is typically a fairly large vessel in which the flue gas velocity is reduced and the aqueous slurry is sprayed from above, ie from the top of the vessel downward. The temperature of the reactor is about 50-80'0 at this time, and spray control of the aqueous slurry of calcium hydroxide is very important because if the water droplets are too large they will remain as liquid at the bottom of the reactor.

The aqueous slurry concentration of calcium hydroxide is maintained such that the free components in the flue gas can evaporate the moisture entering the reactor. As a result, the absorption product is recovered as a dry powder. With this method, as much as 90% of sulfur dioxide gas can be removed. Disadvantages of this method include a tendency to block the nozzle, the need for extra investment in preparation and batching equipment for the aqueous slurry of calcium hydroxide, and problems with droplet size control during spraying. .

It is therefore an object of the present invention to improve furnace smoke by converting gaseous sulfur compounds into solid sulfur compounds that can be easily separated from the gas and efficiently removed from the furnace flue gas in a simple and economical manner. An object of the present invention is to provide a method for removing gaseous sulfur compounds such as sulfur dioxide gas from road gas.

Means for Solving the Problems In the method of the invention, the substance that reacts with gaseous sulfur compounds, particularly sulfurous gases, and water are fed separately. In the present invention, the problems associated with slurry preparation, handling and supply are:
This can be avoided in the following way. That is, (a) the respective compounds that become oxides in the furnace, such as powdered alkali metal oxides and/or alkaline earth metal oxides and/or carbonates, together with the sulfur-containing material and oxygen-containing gas as fuel; (b) water and/or the powdered oxide to the sulfur dioxide-containing flue gas exiting the furnace; or steam is separately atomized in the furnace and/or into the flue gas, and finally (c) the alkali metal and/or
or separating solids containing alkaline earth metal sulfates and optionally their sulfites from the gas.

The basic idea of the invention is that calcium and magnesium oxides, which are inert from the point of view of sulfur dioxide removal, are activated by water and/or steam only in the flue gas and are thereby converted into the respective hydroxides. and react with sulfur dioxide gas to form a solid sulfate/sulfite mixture that can be effectively separated from the flue gas by physical separation methods.

Powdered oxides and/or carbonates are suitable for alkali and/or
Or, depending on the sulfur content in the fuel, the alkaline earth metal content is at least sulfur equivalent in molar proportion according to the reaction equation, preferably in a larger amount than the acid required for the reaction. It is thrown into the combustion chamber. Oxide and/or
or by dosing the carbonate separately in the form of a powder into the combustion chamber, or by dosing the oxide directly into the flue gas duct, thereby eliminating the need for dosing in the form of a slurry through the nozzle, eliminating nozzle clogging and the preparation of an aqueous slurry. and batch equipment can be eliminated. Conversely, the supply of water and steam from the nozzle is simple and easy.

The water or steam supply to the flue gas is usually 50 to 8
It is carried out at a temperature of 00°C, preferably in the temperature range of 90-200°C. If it is desired to recover the absorption product as a substantially dry powder, use enough water to evaporate for one minute with the thermal energy of the flue gas and its heat of reaction. Alternatively, a small amount of energy is introduced from outside the system to supplement the reaction heat.

The invention will now be explained in more detail with reference to the accompanying drawings, which schematically show a suitable apparatus for carrying out the method of the invention.

In the figure, the furnace in general is designated by the symbol l. The normally preheated sulfur-containing fuel for combustion 4, the oxygen-containing gas 5 and the calcium and/or magnesium oxides 6' and/or carbonates 6 are preferably present in amounts proportional to the amount of sulfur dioxide gas produced in the combustion chamber. A larger excess is fed to the combustion chamber of the furnace I. The expression “in excess” here means that the amount of calcium, magnesium, or calcium and magnesium in the calcium and/or magnesium oxides and/or carbonates reacts with the total sulfur supplied to the combustion chamber. However, this means that the amount is greater than the amount theoretically required according to the reaction formula.

The carbonate fed to the furnace is decomposed into oxides and carbon dioxide in the furnace. The oxides can react with sulfur dioxide gas, first forming sulfites and then oxidation to form sulfates. Due to the short residence time in the furnace, only a small portion of the oxide can react with the sulfur dioxide gas even at temperatures sufficient for the reaction. For this purpose, the calcium oxide and/or magnesium oxide containing flue gas 8, including combustion residues and unabsorbed sulphurous acid gas, is discharged from the combustion chamber of the furnace through the flue gas duct 7. In addition to or instead of the above, the pulverulent oxide 6' can also be fed directly to the flue gas duct 7 or to the subsequent reactor 2.

Typically, the temperature of the flue gas 8 is so low that the reaction between calcium and/or magnesium oxides and sulfur dioxide gas is relatively weak, and under these conditions the oxides are relatively inert with respect to desulfurization. be regarded. However, the flue gas 8 can also be used in a heat exchanger 12 to preheat the air 5 fed to the furnace I.

The flue gas 8 containing calcium and/or magnesium oxides and sulfur dioxide gas leaving the combustion chamber of the furnace I is then fed to the reactor. The reactor is indicated schematically at 2. To activate the calcium and/or magnesium, water 9 or steam is sparged into the flue gas in the reactor 2. This water or steam reacts with calcium and/or magnesium oxides,
form the respective hydroxides. The hydroxides react with residual sulfite gas in the flue gas 8 to form the respective sulfites. This sulfite is at least partially further oxidized to the respective sulfate in the presence of oxygen.

The amount of water 9 supplied to the reactor 2 is adjusted to such an extent that the wood supplied to the reactor 2 can be sufficiently evaporated by the heat of the flue gas 8. As a result, the dried fly ash-like reaction product can be removed in the known fly ash separator 3 in the same manner as other fly ash. The flue gas 11 from the fly ash separator 3 may be further fed to the chimney 13 and the separated fly ash and reaction products may be subjected to further processing.

The order of adding water or steam and powdered oxide is not limited in any way. Thus, for example, if water or steam is supplied to the furnace and the powdered oxide is only added after the furnace,
It may thus be fed either to the flue gas duct or to a subsequent reactor. A further advantage of the method of the invention is that it can be applied to furnaces equipped with any type of burner. The size of the furnace is not a limiting factor, and there is no need to circulate calcium and/or magnesium oxides in the combustion chamber. As a result, expensive circulating beds or complex recirculation systems and, at the same time, excess dust and even dust separation, which due to the operating principle are disadvantageous with recirculation system methods, can be avoided. Compared to conventional spraying methods, spraying water or steam into the reactor 2 is less complex and easier to implement than using slurries that clog the nozzles and are difficult to mix. be. Another advantage is that carbonates can be burned economically in the combustion chamber of the furnace head.

(Example) Next, the present invention will be explained in more detail with reference to Examples.

Example 1 Coal with a sulfur content of 1.4% is fed at a rate of 70 t/h to a pulverized coal furnace with a heat output of 600 MW. The furnace operates at maximum power. supplying excess combustion air,
As a result, the oxygen content in the flue gas is 4%. Calcium is introduced into the furnace in the form of calcium carbonate, dolomite or calcium oxide. For example, calcium carbonate having a calcium carbonate content of 90% is charged into the furnace in proportion to the amount of sulfur in the fuel entering the furnace. The theoretical equivalent is approximately 3,4 t/h calcium carbonate.

Calcium carbonate decomposes into calcium oxide and carbon dioxide gas at high temperature in the furnace, and exits from the furnace together with (1) CacO3+Cao+co2 flue gas. Some of the calcium oxide in the furnace reacts with sulfur oxides in the flue gas to form calcium sulfate or calcium sulfite.

(2) CaO+SO2+1/202 +Ca5On or CaO+ S 02 + Ca SO3CasO
3+1/202 +Ca5O4 Water and/or steam are blown into the flue gas in the furnace or flue gas duct or in a separate reactor following the flue gas duct.

In terms of energy economy, it is most economical to reduce the water content in the flue gas by blowing water into the flue gas past the residual heat recovery surface in a separate reactor. be.

By increasing the water content of the flue gas, highly reactive calcium hydroxide can be formed from unreacted calcium oxide in the furnace, and (3) Cao+H20
+Ca (OH)2Ca (OH)2+SO2+Ca5
O3+H20 calcium hydroxide reacts rapidly with sulfur oxides in the flue gas. The higher the moisture content of the flue gas leaving the furnace, the more effectively sulfur dioxide gas is removed from the flue gas. However, from an energy economic point of view,
It is advantageous to proceed in such a way that the heat released by the chemical reaction is sufficient to evaporate the added water.

If it is necessary to increase the final temperature of the flue gas, this can be achieved using external heat or by a warm flue gas stream.

It is essential that the compounds obtained from calcium carbonate or dolomite and reaching the reaction zone are in the form of oxides.

The results are shown in Table 1 below. Table 1 shows that when various amounts of calcium carbonate are charged into the furnace according to the invention,
It shows how much sulfur dioxide gas is removed from the flue gas as a percentage. The amount of calcium carbonate is indicated as the molar ratio of the calcium content of the powdered calcium carbonate to the sulfur content of the fuel fed into the furnace. Flue gas temperature was measured just before the water or steam feed point. However, in the case of 80°C, water or steam was directly supplied into the furnace.

Chapter 1 Table SW 0.52 50℃ 65°056% 1.52202°0 74°077% 1.56 90℃ 68℃82% 2.20200℃ 72°087% 2.22120℃　62℃96% 2.3 110℃ 68℃93% 2.5 90℃ 66℃97% 4.1 800'0110℃72% 4.0 120°0 68°098% A) Water or steam was fed into the furnace.

B) Immediate location of the water feed point Example 2 Dolomite containing 45% cr[calcium oxide (caCO3), 45% magnesium carbonate (MgCO3) and 10% impurities, using similar operating values according to Example 1] and charged into the pulverized coal furnace. Based on the equivalent weight, the amount of dolomite required in proportion to the amount of sulfur supplied is approximately 6.
8t/h.

The calcium and magnesium carbonate contained in the dolomite decomposes in the furnace into calcium oxide, magnesium oxide and carbon dioxide, which exit the furnace together with the flue gas. Some of the oxides in the furnace react with sulfur oxides in the flue gas to form sulfates or sulfites.

Water and/or steam is blown into the flue gas in the furnace or in the flue gas duct or in a separate reactor downstream of the flue gas duct. As a result, oxides that did not react in the furnace form hydroxides due to increased water content. The hydroxide reacts with sulfur oxides in the flue gas to form a powdered reaction product.

When dolomite is used, the highly reactive calcium hydroxide reacts before the slow-reacting magnesium hydroxide reacts. Magnesium hydroxide passes through the reactor mostly unreacted when the amount of calcium is sufficient. If the process of the invention is designed to be based solely on the calcium present in dolomite, the above equivalents are reached. When the molar ratio of calcium to sulfur is at least 1, the results of the process substantially correspond to the corresponding values in Table 1.

Example 3 Calcium oxide containing 10% impurities is charged to a furnace using similar operating values according to Example 1.

Regarding the reaction, the theoretical equivalent of calcium oxide, which is proportional to the amount of sulfur entering the furnace, is approximately 1.9 t/h.

Some of the calcium oxide reacts with sulfur oxides in the flue gas in the furnace to form calcium sulfate or calcium sulfite.

Water and/or steam is blown into the flue gas in the furnace or in the flue gas duct or in a separate reactor located after the flue gas duct.

Due to the increase in moisture, calcium oxide forms highly reactive calcium hydroxide, which quickly reacts with the sulfur oxides remaining in the flue gas. The higher the water content in the flue gas leaving the furnace, the more effectively sulfur dioxide gas is removed from the flue gas. However, from the point of view of energy economy, it is advantageous to operate in such a way that the amount of added water can be sufficiently evaporated by the heat released by the chemical reaction.

When the amount of calcium fed in calcium oxide is calculated as a molar ratio to sulfur, the results are consistent with those shown in Table 1 of Example 1.

(Effects of the Invention) As described above, according to the present invention, a spray method that can efficiently remove sulfur dioxide gas without the need for expensive equipment such as a fluidized bed furnace is adopted, while eliminating the drawbacks of the conventional spray method. Problems such as nozzle clogging due to slurry, control of water droplet size, and use of preparation/batch equipment can be avoided. As described above, the present invention can provide a simple, economical, and highly efficient method for recovering and removing sulfur dioxide gas in flue gas in the form of a solid propagation compound.

[Brief explanation of drawings]

The drawing schematically shows an apparatus suitable for carrying out the method of the invention. 1...Furnace 2...Reactor 3...Fly ash separator 4...Sulfur-containing fuel 5...Oxygen-containing gas 6...Calcium carbonate/magnesium 6'...Calcium oxide/ Magnesium 7... Flue gas duct 8.11... Flue gas

Claims (6)

[Claims] (1) A method for removing gaseous sulfur compounds from a furnace flue gas, comprising: (b) supplying each compound to a furnace together with a sulfur-containing material and an oxygen-containing gas as fuel, or supplying the powdered oxide to a flue gas containing sulfur dioxide discharged from the furnace; Water and/or steam are separately sprayed into the furnace and/or into the flue gas in order to convert the substances into hydroxides which react with sulfur dioxide gas, and finally (c) the alkali obtained as reaction product. metal and/or
or a process for removing gaseous sulfur compounds from the flue gas of a furnace, characterized in that solids containing sulfates of alkaline earth metals and optionally their sulfites are separated from the gas. 2. A method as claimed in claim 1 in which the powdered compound is provided in excess in proportion to the sulfur in the flue gas. (3) The method according to claim 1 or 2, wherein the water and/or steam atomization is carried out when the flue gas temperature is 50 to 800°C. (4) A method according to any one of the preceding paragraphs 1 to 3, wherein water is sprayed into the flue gas in an amount that is evaporated to the maximum extent by the flue gas and the thermal energy generated by the reaction. (5) A method according to any one of claims 1 to 3, wherein a small amount of energy is externally introduced into the reaction before subjecting the flue gas to solid separation. (6) A method according to any of the preceding claims, wherein the powdered compound supplied is calcium carbonate, calcium carbonate-magnesium carbonate, and/or their respective oxides.