JPH0253085B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a method for desulfurizing exhaust gases accompanying the combustion of fuels such as coal and heavy oil, wastes such as municipal garbage, and other combustion, drying, and roasting. [Prior art] Sulfur oxides, nitrogen oxides, etc. contained in the exhaust gas generated from the combustion of coal, heavy oil, etc. not only harm buildings, structures, etc., but are also extremely harmful to animals, plants, and even the human body. It has been found that these substances have a significant impact, and methods for removing the above substances from exhaust gas, namely desulfurization and denitration methods, have been studied and a wide variety of methods have been developed. These desulfurization and denitrification methods are broadly classified into dry methods and wet methods. The dry desulfurization method to which the present invention belongs includes the first
The methods shown in the table are shown.

[Problem that the invention seeks to solve]

The purpose of the present invention is to solve the various problems of the conventional dry desulfurization method described above, and to provide a new desulfurization method using a cured composition obtained by a relatively simple manufacturing method from inexpensive raw materials. . [Means for Solving the Problems] The present invention provides a method for using a substance that can supply calcium oxide and a substance that can supply sulfuric acid compounds, halogen element compounds, silicon dioxide, aluminum oxide, sulfides, and alkali metal hydroxides. This is an exhaust gas desulfurization method characterized in that 0.01 mol or more of nitrogen oxide is added per 1 mol of sulfur dioxide gas in the exhaust gas when desulfurizing the exhaust gas using a curing composition made of one or more selected substances as raw materials. First, the raw materials for the cured composition used in the method of the present invention will be explained. Examples of substances that can supply calcium oxide include by-products such as quicklime, slaked lime, carbonated lime, cement, slag, dolomite plaster (containing lime), and acetylene slag. Substances that can supply sulfuric compounds and halogen element compounds include, for example, substances produced by combining alkaline earth metals such as calcium and magnesium, alkali metals such as sodium and potassium, and sulfuric acid and hydrogen halides. Calcium sulfate, magnesium sulfate, calcium chloride, magnesium chloride, sodium sulfate, potassium sulfate, calcium sulfite, calcium hydrogen sulfate, sodium chloride, strontium chloride, calcium bromide,
Examples include calcium iodide, potassium chloride, sodium thiosulfate, sodium hydrogen carbonate, calcium hydrogen carbonate, and black liquor combustion ash. Substances that can supply silicon dioxide include, for example, silicic acid, hydrous silicic acid, metasilicic acid, aluminum silicate, calcium silicate, cristobalite, tridymite, kaolin, bentonite, talc, perlite, shirasu, diatomaceous earth,
Examples include compounds containing reactive silicon dioxide such as glass. Substances that can supply aluminum oxide include, for example, alumina, aluminum hydroxide, aluminum silicate, sulfuric acid, alum, aluminum sulfide, aluminum sulfate, aluminum chloride, bentonite, kaolin, diatomaceous earth, zeolite, pearlite, and aluminic acid. Examples include compounds containing reactive aluminum such as sodium, cryolite, and bauxite. Examples of substances that can supply sulfide include calcium sulfide, iron sulfide, and zinc sulfide. Examples of substances capable of supplying alkali metal hydroxides include sodium hydroxide and potassium hydroxide. Examples of other substances that can simultaneously supply two or more of the six compounds mentioned above include coal ash, volcanic ash, coal fluidized bed combustion ash (calcium oxide, silicon dioxide, aluminum oxide, calcium sulfate, sodium sulfate, sulfuric acid potassium source), cement and cement clinker (aluminum oxide, calcium sulfate, silicon dioxide, aluminum oxide source), slag and shirasu, andesite chaat,
quartz trachyte, opal, zeolite, feldspar, clay minerals,
Minerals containing reactive silicon dioxide such as ettringite (sodium oxide, silicon dioxide, aluminum oxide, calcium oxide), sodium, aluminum, calcium, etc., chlorides, sulfates, etc., as well as in-furnace desulfurization ash such as fluidized bed combustion ash. and wastes such as waste desulfurization agent after flue desulfurization, sludge incineration ash, municipal garbage incineration ash, cement waste, and acetylene slag. Furthermore, when the required materials described so far are supplied by adding elemental sulfur, for example, a mutual reaction between the materials progresses, resulting in the production of calcium sulfide, calcium sulfate, etc. It also includes water glass produced by the reaction of silicic acid and caustic alkali, and substances produced by adding sulfuric acid, hydrochloric acid, etc. Table 2 shows an example of the chemical composition of the raw materials.

【table】

〔Example〕

Example 1 77 parts by weight of coal ash, 15 parts by weight of calcium hydroxide,
Mix 8 parts by weight of dihydrate gypsum (anhydrous base), add water
After adding 40 parts by weight and kneading, the mixture was steam-cured at 100°C for 24 hours, crushed to have a particle size of 0.5 to 0.71 mm, and heat-treated at 100°C for 1 hour to obtain the desulfurizing agent of the present invention. The analytical values of the coal ash used here are shown in Table 3. The desulfurization test was conducted under the test conditions shown in Table 4 (130℃,
I went with SV10000h ^-1 ). The desulfurization rate was calculated using the integral value for 3 hours after gas passage.

【table】

[Table] NOx was added to the above reference gas at a concentration shown in Table 5, and the desulfurization rate was measured and summarized in the same table.

[Table] More than 77% of the NOx added in the above test was removed within the above concentration range. Therefore, a high desulfurization rate can be obtained by appropriately selecting the NOx/SO ₂ molar ratio within the range of NOx concentration that is allowed to remain in the exhaust gas after treatment. Moreover, according to the table above, even if NOx is reduced to zero after the NOx-containing gas has passed through, the desulfurization rate is much higher than the desulfurization rate when NOx is not included from the beginning, but this is an expression of the residual effect of NOx on the desulfurization agent. Seem. Examples 2 to 12 Commercially available slaked lime, calcium sulfate, silicic acid, aluminum hydroxide, calcium silicate, and aluminum silicate were mixed according to the formulation shown in Table 6, water was added and mixed again, and the mixture was heated at normal pressure 100 Steam curing at 24 °C
The resulting cured product is crushed to a particle size of 0.5~
The particles were sized to 0.7 mm and heat treated at 130° C. for 2 hours to obtain a desulfurization agent used in the desulfurization method of the present invention. in the agent
Table 7 shows CaO, CaSO ₄ , SiO ₂ , Al ₂ O ₃ equivalent weight percentage (hereinafter referred to as base material composition) along with the performance test results. The performance test was conducted under the test conditions shown in Table 4.
A desulfurization test (SO ₂ removal test) was conducted with and without addition of 100 ppm, and the results are shown in Table 7. In addition, the measured values of the specific surface area of the test desulfurization agents are also listed in the same table. To measure the specific surface area, heat the sample to 200℃.
After degassing for 1 hour, the BET method was used.

【table】

[Table] Example 13 A desulfurizing agent used in the present invention was obtained in the same manner as in Example 1, except that coal ash, calcium hydroxide, and dihydrate gypsum were used in the proportions shown in the table below, and the amount of NOx added was
The desulfurization rate was calculated by conducting the same test as in Example 1, except that the temperature was fixed at 240 ppm and the temperature was changed from 30° to 1000°C. The results are shown in Figure 1. According to this, almost no influence of temperature on the desulfurization rate is observed at reaction temperatures of 30° to 900°C.

[Table] * Anhydrous equivalent [Effect of the invention] As described in detail above, in desulfurization using a lime-based curing composition, the desulfurization rate can be improved by adding NOx to the treated gas, and the addition The concentration of NOx also decreases. Therefore, according to the desulfurization method of the present invention, when there is exhaust gas to be denitrified, desulfurization and denitration can be efficiently carried out simultaneously using this gas, which has great industrial value.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between temperature and desulfurization rate in the method of the present invention.

Claims (1)

[Scope of Claims] 1. One or more substances selected from the group of substances capable of supplying calcium oxide and substances capable of supplying sulfuric compounds, halogen element compounds, silicon dioxide, aluminum oxide, sulfides, and alkali metal hydroxides. 1. A method for desulfurizing exhaust gas, which comprises adding 0.01 mol or more of nitrogen oxide per 1 mol of sulfur dioxide gas in the exhaust gas, in the desulfurization of exhaust gas using a hardening composition made from the substance described above. 2. The cured composition according to claim 1, wherein the cured composition is obtained by mixing raw materials with water and then molding, or by curing in a humid air or steam, and then molding, and then heat-treating the composition as it is or at a temperature of 30°C or higher. Desulfurization method. 3. A patent claim in which the cured composition is obtained by mixing raw materials with water, curing in humid air or steam, molding the composition, curing in humid air or steam again, and then heat-treating the composition as it is or at a temperature of 30°C or higher. The desulfurization method according to scope 1. 4. The desulfurization method according to claim 1, wherein nitrogen oxides are added so that the concentration of nitrogen oxides changes intermittently.