JPH0675665B2 - Wet desulfurization method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a wet flue gas desulfurization method, and more particularly to an improvement of the lime gypsum method.

[Problems to be Solved by Conventional Techniques and Inventions]

The lime gypsum method uses CaCO ₃ , Ca for the gas to be purified.
SO ₂ is absorbed and removed by contacting with a slurry containing (OH) ₂ or the like, and the main reaction can be considered as follows.

_{SO 2 + Ca (OH) 2} → CaSO 3 + H 2 O (1) SO 2 + CaCO 3 → CaSO 3 + CO 2 (2) CaSO 3 + 1 / 2O 2 → CaSO 4 · 2H 2 O (3) the actual absorber ( In order to cause the reaction of 3), it is necessary to provide an oxidizing device or suck air into the absorbing device, and it is necessary to strictly adjust the SO ₂ concentration, O ₂ concentration, CaSO ₃ concentration and the like.

An object of the present invention is to solve the drawbacks of the conventional lime gypsum method and provide a wet desulfurization method having a high desulfurization rate with only a single absorption tower without blowing air depending on the exhaust gas composition, and the purity of the gypsum to be recovered is also high. To do.

[Means for Solving the Problems]

The present invention is a desulfurization method in which a gas containing SO ₂ is brought into contact with a slurry containing a Ca compound, wherein the slurry contains a nitrite compound, which is a wet desulfurization method.

The Ca compound of the present invention means, in addition to quick lime, slaked lime, and lime carbonate, which have been conventionally used in the lime gypsum method, “a substance capable of supplying calcium oxide, silicon dioxide, and aluminum oxide, a sulfuric acid compound, a halogen element compound, a sulfide. And one or more substances selected from the group of substances capable of supplying hydroxides of alkali metals, added with hydration treatment, and then Ca
-Si-Al-based cured product "or after using this cured product as a dry exhaust gas treating agent.

Substances that can supply calcium oxide, such as quick lime,
By-products such as slaked lime, lime carbonate, cement, slag, dolomite plaster (containing lime), and acetylene slag.

Examples of substances that can supply silicon dioxide include silicic acid, hydrous silicic acid, metasilicic acid, aluminum silicate, calcium silicate and cristobalite, tridymite, kaolin, bentonite, talc, perlite, shirasu, diatomaceous earth, glass, fir shell. Examples include compounds containing reactive silicon dioxide, such as incineration ash such as ash and wood ash.

The substance capable of supplying aluminum oxide includes, for example, alumina, aluminum hydroxide, aluminum silicate, alum sulfate, alum, aluminum oxide, aluminum sulfate,
Aluminum chloride, calcium aluminate, bentonite, kaolin, diatomaceous earth, zeolite, perlite,
Examples thereof include compounds containing reactive aluminum such as bauxite, sodium aluminate, and cryolite.

A substance capable of supplying a sulfuric acid compound or a halogen element compound is a substance produced by combining an alkaline earth metal such as calcium and magnesium, an alkali metal such as sodium and potassium, and sulfuric acid and hydrogen halide, and calcium sulfate. , Magnesium sulfate, calcium chloride, magnesium chloride, sodium sulfate, calcium sulfite, calcium hydrogen sulfate, sodium chloride, strontium chloride, calcium bromide, calcium iodide,
Examples include potassium chloride, sodium thiosulfate, sodium hydrogen carbonate, calcium hydrogen carbonate and the like.

Examples of substances that can supply sulfide include calcium sulfide,
Examples are iron sulfide and zinc sulfide.

The substance capable of supplying the hydroxide of the alkali metal is sodium hydroxide, potassium hydroxide or the like.

Furthermore, in the case where the required materials described so far are added to elemental sulfur, for example, mutual reaction between the materials proceeds, and as a result, calcium sulfide, calcium sulfide, etc. are produced and supplied, It also includes water glass produced by the reaction of silicic acid and caustic alkali.

Examples of other substances that can simultaneously supply two or more of the above-mentioned at least four compounds include coal ash and volcanic ash, coal fluidized bed combustion ash (calcium oxide, silicon dioxide, aluminum oxide, calcium sulfate, sodium sulfate). , Potassium sulfate source), cement and cement clinker (calcium oxide, silicon dioxide, aluminum oxide source), slag and shirasu, andesite, chert, quartz trachyte, opal, zeolite, feldspar, clay mineral, ettringite (calcium sulfate, dioxide) Silicon, aluminum oxide, calcium oxide) and other reactive silicon dioxide, sodium, aluminum, calcium, etc. and minerals containing chloride, sulfate, etc., as well as in-furnace desulfurized ash such as fluidized bed combustion ash and flue gas desulfurized Used Sulfurizing Agent, Sludge Incineration Ash, Municipal Waste Incineration Ash, Cement Not, acetylene single, such as the spent waste water treatment agent, and the like. Here, the used desulfurizing agent is Ca
_{O, Ca (OH) 2,} CaO , shown in CaCO ₂ such as calcium-based ones and JP spent desulfurizing agent 61-209038 of, Al ₂ O _3, Si
It refers to a used desulfurization agent composed of O ₂ and CaSO ₄ composition.

Table 1 shows examples of these representative raw materials and their chemical compositions.

The Ca-Si-Al-based cured product is a combination of the above materials, at least 1% as CaO, 1% as SiO ₂ , 1% as Al ₂ O ₃ , 1% sulfuric acid compound, halogen element compound, sulfide and / or alkali metal hydroxide. 0.1% as a substance, preferably 1 to 80% as CaO, 5 to 90% as SiO ₂ , 5 to 90% as Al ₂ O ₃ , 0.1 to 70% CaSO ₄ , Na ₂ SO ₄ , CaCl ₂ and NaCl. 0.1-50% NaOH is used so that it becomes 0.1-10%.

The hydration treatment means a treatment necessary for proceeding the hydration reaction between the above-mentioned substances (raw materials), for example, as disclosed in JP-A-64-38130, and for example, normal temperature or high pressure room temperature water. Alternatively, it includes hot water curing, wet air curing, steam curing, etc., and is classified into a hardening hydration treatment and a non-consolidating hydration treatment.

Curable hydration treatment is a small mixing ratio (solid-liquid ratio) of the various raw materials and water at the time of treatment, for example, 1: 0.2 to 1: 0.99 to promote bonding between material particles, A hydration treatment for obtaining a cured product.

Non-consolidating hydration treatment is a treatment that prevents the material particles from binding to each other during the hydration treatment and growing into coarse particles, and the solid-liquid ratio at the start of treatment is increased, for example, 1: 1 to. It is set to 1:20, and in hot water curing, the raw material is dispersed in water at 40 ° C to 180 ° C, and stirring, bubbling, circulation, shaking, etc. are performed for several minutes to several days so that the raw material does not precipitate and harden at the bottom. is there.

In the hydration treatment step, after a sufficient amount of water necessary for the production of the active substance in the treatment agent is given, the important step of active compound formation necessary for exhaust gas purification is completed, and during this time, a part of the water or Most are consumed in the compound formation reaction.

Wet air curing in the curable hydration treatment is performed at a temperature of 10 ℃ to 40 ℃.
Relative humidity of 50% to 100% for several minutes or tens of days is preferable, and steam curing is performed at a temperature of 40 ° C to 180 ° C and a relative humidity of 1%.
At 00%, it is preferably several minutes to several days. The cured product obtained by such a hydration treatment is pulverized by a known method and used as a slurry if necessary.

The finer the particle size of the Ca compound in the slurry, the better, and the concentration in the slurry is 10 mg / to 400 g /.

Examples of the nitrite compound of the present invention include sodium nitrite,
Potassium nitrite, calcium nitrite, aluminum nitrite, ammonium nitrite, tin nitrite, strontium nitrite, iron nitrite, copper nitrite, nickel nitrite, magnesium nitrite, manganese nitrite, etc. In order to include these nitrite compounds in the slurry, it is of course possible to use the above salts themselves, or to use a raw material containing these salts or a combination of materials such as a nitrite compound which is produced by a reaction, for example, nitrification. It is also possible to use metallic copper, nitric acid compounds and alumina.

The concentration of the nitrite compound in the slurry is at least 0.001% or more as NO ₂ , and preferably 0.01% to 10%.

A specific example of the desulfurization method using the slurry having the above composition will be described with reference to FIG.

The exhaust gas E containing SO ₂ is introduced into the absorption tower 2 whose residence time can be adjusted according to the gas properties. In the absorption tower 2, the exhaust gas comes into contact with the slurry injected from the spray by the pump 3, absorbs and removes SO _2, and is sent from the conduit 4 to the chimney 5 and released into the atmosphere. The pH of the slurry is adjusted to pH = 1 to 13 by adjusting the flow rate of the slurry sent from the slurry preparation device 6 to the absorption tower via the pump 7 and the conduit 8. Part of the slurry is a sedimentation type solid-liquid separator from the conduit 9.
Slurry sent to 10 and concentrated, pump 11, conduit 12
And is sent to the solid-liquid separator 13 to separate the gypsum G. The supernatant liquid of the sedimentation type solid-liquid separation device 10 is sent to the slurry preparation device 6 through the conduit 15. In the slurry preparation device 6, the Ca compound C and the nitrite compound N are charged, and water is added if necessary,
A slurry is prepared. A part of the supernatant liquid is discharged as drainage D. The filtrate of the solid-liquid separator 13 is returned to the sedimentation separator 10 through the conduit 18.

The feature of the present invention is that by adding a nitrite compound to the formation of CaSO ₃ , which has been a problem in SO ₂ absorption and removal by a conventional Ca compound slurry, in some cases, high-purity CaSO ₄ without introducing excess air. It's about to be. Further, the desulfurization efficiency can be significantly improved.

That is, it is possible to remarkably reduce the air that has been blown into the absorption tower in a large amount in order to change CaSO ₃ into CaSO _4, and further to reduce SO ₂ by the oxidizing action of the nitrite compound.
The absorption efficiency of can be improved.

Regarding the reaction in the absorption tower of the present invention, there are still many unclear parts, but when calcium hydroxide is used as the Ca compound, it can be roughly estimated as follows.

Hereinafter, the method of the present invention will be described with reference to examples.

〔Example〕

Examples 1 to 6 As a gas containing SO ₂ , a gas having a composition shown in Table 2 was prepared, and 6 slurries of 50 cc each having a different composition as shown in Table 3 were stored at room temperature at a gas flow rate of 60 N. A desulfurization test was performed by bubbling with / H. However, in order to prevent water in the gas from condensing in the slurry, the gas was dehumidified before bubbling.

All the compounds represented by the molecular formulas in Table 3 were first-class commercial reagents. The particle size of 60∪40 in Examples 3 and 6 is about 10
CaO 454 g of less than mm was added to water 2646, and after stirring for 15 minutes, 400 g of the used desulfurization agent in Table 1 was added, and while stirring again with heating, curing was carried out at 98 ° C for 12 hours, and a SO ₂ absorbent in a slurry form was obtained. Then, of these, 0.075 g in terms of solid matter was used as the SO ₂ absorbing slurry.

The used desulfurizing agent has the following production method and usage history.

Coal ash (overseas coal) 51 parts by weight of Al ₂ O ₃ 22%, SiO ₂ 64%, Ca
(OH) ₂ 30 parts by weight, CaSO ₄ 19 parts by weight To a powdery material, 45 parts by weight of water was added and kneaded, and steam-cured at 95 to 100 ° C for 12 hours.
After drying at ℃ for 2 hours and crushing, the gas with the composition shown in Table 2 was added to the cured product (desulfurizing agent) with a particle size of 3 to 10 mm at 130 ℃,
Desulfurizing agent after being treated with SV1000 (h ^-1 ) for 17 hours.

The desulfurization performance was evaluated by analyzing the absorbent and the passing gas every 5 minutes after passing the gas up to 70 minutes, and the test results are shown in Table 4-1.

According to Table 4-1, for example, in Example 1, 10% of SO ₂ is removed for 20 minutes after the start of gas flow, but after 30 minutes, S
The O ₂ concentration was increased and reached 800 ppm after 70 minutes. The pH of the liquid at this time was 6.9 to 6.3 until 40 minutes after passing the gas, and did not change so much, but after 50 minutes, became 2.1 and drastically decreased. At this time, the NOx concentration in the gas after passing through the SO ₂ absorbing solution also rapidly increased, and the NOx concentration in the gas before passing through the SO ₂ absorbing solution (set value
450ppm) to 500ppm. But after 70 minutes the same pH
Even in 2.1, it was 415 ppm. In this development, the contained nitrite compound decomposes to generate NOx. When there is no nitrite to decompose, NOx generation also decreases over time. This tendency is clear when looking at the amount of NOx in the liquid.

If the NO ₂ in the SO ₂ absorbent is reduced, the desulfurization ability will be significantly deteriorated and the amount of sulfite produced will increase.

That is, it is shown that by maintaining the pH of the SO ₂ absorbing solution at 6 or more in the presence of NO _2, the desulfurization rate can be maintained at a high rate and the production of sulfite can be suppressed.

The desulfurization rate was slightly inferior in the case of CaCO ₃ among the three Ca compounds used, and there was almost no difference between the two nitrites.

Comparative Examples 1 to 6 The same desulfurization test as in Example 1 was performed using the SO ₂ absorbing solution shown in Table 3 containing no nitrite temperature and / or Ca compound, and the test results are shown in Table 4-2. It was

Comparative Examples 7 to 8 The same desulfurization test as in Comparative Examples 2 and 8 was conducted, and thereafter, 50 cc of these absorbents were further passed for the same time as each gas passing time and a flow rate of 60
The absorbent was analyzed by bubbling air at N / H at room temperature.

The results obtained are shown in the table below.

Examples 7 to 9 Examples 1, 2 and 3 were repeated with the temperature at absorption changed to 60, 80 and 90 ° C.

The obtained results are shown in the table below, and the lower the temperature during absorption, the better the desulfurization efficiency.

Examples 10 to 12, Comparative Examples 9 to 11 The same tests as in Examples 1, 2 and 3 were carried out for 20 minutes, except that the amount of nitrite used was 0.085 g, and then the same nitrite used to prepare 50 ml of the absorption liquid. The operation of adding a nitrate and a Ca compound in the same weight as in each Example to the absorption liquid and performing an absorption test for 20 minutes was repeated, and this repetition was repeated 20 times (Examples 10, 11, 12).

A similar repeated test was also performed for Comparative Examples 2, 3 and 4.
Repeated (Comparative Examples 9, 10, 11), SO ₂ and NO in the gas after passing through
The measured values of x content concentration (ppm) are shown in the following table.

Repeated use of the absorbing solution is effective in reducing the amount of water used, reducing wastewater, and reducing wastewater treatment costs.

[Effects of the Invention] In the wet desulfurization method containing a Ca compound in the slurry as described in detail above, by including a nitrite compound in the slurry, the desulfurization rate is improved, and combustion using normal excess air is also performed. In the desulfurization of exhaust gas, it is possible to form gypsum in the absorbing liquid without blowing in new air.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a desulfurization system according to the method of the present invention. E …… Exhaust gas 2 …… Absorption tower 3,7,11 …… Pump 4,8,9,12,18 …… Conduit 5 …… Chimney 6 …… Slurry preparation device 10 …… Settling solid-liquid separation device 13 …… Solid-liquid separator G …… Gypsum C …… Ca compound D …… Drainage N …… Nitrite compound

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Kunihiro Mori 461-6 Satozuka, Toyohira-ku, Sapporo, Hokkaido Hokkaido Electric Power Co., Inc. Research Institute (72) Takeshi Murayama 461-6 Satozuka, Toyohira-ku, Sapporo Hokkaido Hokkaido Electric Power Co., Ltd. (72) Inventor Hideki Nakamura 461-6, Satozuka, Toyohira-ku, Sapporo, Hokkaido Inside the Research Institute, Hokkaido Electric Power Co., Inc.

Claims (2)

[Claims] 1. A desulfurization method in which a gas containing SO ₂ is brought into contact with a slurry containing a Ca compound, wherein the slurry contains a nitrite compound. 2. A Ca compound selected from the group of substances capable of supplying a sulfate compound, a halogen element compound, a sulfide, and an alkali metal hydroxide to a substance capable of supplying calcium oxide, silicon dioxide and aluminum oxide. The method according to claim 1, which is a Ca-Si-Al-based cured product obtained by adding the above substances and hydrating the mixture, quick lime, slaked lime and / or lime carbonate.