JPH03123622A - Wet-way desulfurization method - Google Patents

Abstract

PURPOSE:To highen desulfurization efficiency and recover a highly pure gypsum only using a sole adsorption tower by bringing a SO2 -containing gas into contact with a slurry containing a calcium compound and a nitrite compound. CONSTITUTION:A SO2 -containing waste gas E is led to an absorption tower 2 and brought into contact with a slurry containing a Ca compound and a nitrite compound sprayed from a spray by a pump 3 in the tower 2. In this way, SO2 is absorbed and removed and the resulting waste gas is sent to a chimney 5 through a duct 4 and discharged to the air. The pH of the slurry is controlled to be 1-13 by controlling the flowing rate of the slurry sent to the absorption tower 2 from a slurry preparation apparatus 6 through a duct 8 by a pump 7. As the Ca compound to be used, there are quicklime, soaked lime, and calcium carbonate, etc. and as the nitrite compound, there are sodium nitrite, calcium nitrite, aluminum nitrite, etc.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a wet flue gas desulfurization method, and more particularly to an improvement of the lime ceracola method.

[Prior art and problems to be solved by the invention] The lime ceracola method adds CaCO3,
S02 is absorbed and removed by contacting with a slurry containing Ca(Of()z, etc.), and the main reaction can be considered as follows.

Sow + Ca (O) I) @ -CaSO3+
H2O(1)SO2+CaCO5= Ca5Os+CO
i (2) Ca5Os+COi −' CaSO
4'2HzO (3) In order to cause the reaction (3) in an actual absorption device, it is necessary to install an oxidation device or to perform operations such as blowing air into the absorption device, and the SO2 concentration, 02 concentration, C
It was necessary to strictly adjust the a5Os concentration, etc.

The purpose of the present invention is to eliminate the drawbacks of the conventional lime ceracola method, and to provide a wet desulfurization method that, depending on the composition of the exhaust gas, can achieve a high desulfurization rate using only a single absorption tower without blowing air, and the recovered ceracola can have a high purity. It's about doing.

[Means for Solving the Problems] The present invention is a wet desulfurization method characterized in that a nitrite compound is contained in the slurry in a desulfurization method in which a gas containing S02 is brought into contact with a slurry containing a Ca compound.

In addition to the quicklime, slaked lime, and carbonated lime conventionally used in the lime ceracola process, the Ca compounds of the present invention include sulfuric compounds, halogen element compounds, sulfuric acid compounds, and other substances that can supply calcium oxide, silicon dioxide, and aluminum oxide. Ca produced by adding one or more substances selected from the group of substances capable of supplying alkali metal hydroxides and hydrating them.
-3t-Al-based hardened sand or this hardened product may be used as a dry exhaust gas treatment agent.

Substances that can supply calcium oxide include quicklime,
Slaked lime, carbonated lime, cement, slag.

By-products include dolomite plaster (containing lime) and acetylene slag.

Substances that supply silicon dioxide include, for example, silicic acid, hydrous silicic acid, metasilicic acid, aluminum silicate, calcium silicate, cristobalite, tridymite, kaolin, bentonite, talc, perlite, shirasu, diatom, earth, glass, and fir. Compounds containing reactive silicon dioxide, such as incinerated ash such as single shell ash, etc.

Substances that supply aluminum oxide include, for example, alumina, aluminum hydroxide, aluminum silicate, sulfuric acid, alum, aluminum oxide, aluminum sulfate,
Aluminum chloride, calcium aluminate, bentonite, kaolin, diatomaceous earth, zeolite, perlite,
These include compounds containing reactive aluminum such as bauxite, sodium aluminate, and cryolite.

Substances that can supply sulfuric acid compounds and halogen element compounds include, for example, alkaline earth metals such as calcium and magnesium, alkali metals such as sodium and potassium, and sulfuric acid,
Substances produced by combining with hydrogen halides, including calcium sulfate, magnesium sulfate, calcium chloride, magnesium chloride, sodium sulfate, calcium sulfite, calcium hydrogen sulfate, sodium chloride, strontium chloride, calcium bromide, and calcium iodide. , potassium chloride, sodium thiosulfate, sodium bicarbonate,
Calcium hydrogen carbonate, etc.

Substances that can supply sulfide include, for example, calcium sulfide,
These include iron sulfide and zinc sulfide.

Substances that can supply alkali metal hydroxides include sodium hydroxide, potassium hydroxide, and the like.

Furthermore, when the necessary materials described so far are supplied, for example, by adding a single substance, mutual reactions between the materials proceed, and as a result, calcium sulfide, calcium sulfide, etc. are produced and supplied. It also includes filtered water glass, which is produced by the reaction of silicic acid and caustic alkali.

In addition, as examples of other substances that simultaneously supply two or more of the above-mentioned at least four types of compounds, coal ash and volcanic ash 1 coal fluidized bed combustion ash (calcium oxide, silicon dioxide,
aluminum oxide, calcium sulfate, sodium sulfate,
sources of potassium sulfate), cement and cement clinker
(calcium oxide, silicon dioxide, aluminum oxide sources), slag and shirasu, andesite, chert, quartz trachyte, opal, zeolite, feldspar, clay minerals, ettringite (calcium sulfate, silicon dioxide, aluminum oxide,
Reactive silicon dioxide such as calcium oxide, sodium, aluminum, calcium etc. and chlorides.

Minerals containing sulfates, etc., as well as in-furnace desulfurization ash such as fluidized bed combustion ash and spent sulfurizers after flue desulfurization.

Sludge incineration ash, municipal waste incineration ash, cement waste.

Examples include acetylene slag and used wastewater treatment agents. Here, the used desulfurization agent refers to Cab, Ca (OH) x
.

Used calcium-based desulfurization agents such as CaC0□ and Cab, A shown in JP-A No. 61-209038-
1203SI02. Refers to used desulfurization agents made of Ca50m-based compositions.

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

Ca-3i-Al-based hardened sand, a combination of the above materials, containing at least 1% SiO□ as CaO
As 1% Al2O5 1% As sulfuric acid compounds, halogen element compound sulfides and/or alkali metal hydroxides 0.1% Preferably as CaO 1-80% 5iO
z as 5-90% Al2
5-90%CaS as O3
One or more of O4, Na2SO4, CaC1g, NaC1 is 0.1-70%CaS
is 0.1 to 5
It is used so that 0% NaOH becomes 0.1-10%.

The hydration treatment refers to the treatment necessary to advance the hydration reaction between the aforementioned substances (raw materials), for example, as disclosed in JP-A No. 64-38130. Alternatively, it includes hot water curing, humid air curing, steam curing, etc., and is classified into hardening hydration treatment and non-hardening hydration treatment.

Curing hydration treatment is a process in which the mixing ratio (solid-liquid ratio) of the various raw materials and water during treatment is reduced, for example from 1:0.2! +0.99
This refers to a hydration treatment that promotes bonding between material particles and obtains a cured product.

Non-caking hydration treatment refers to treatment that prevents material particles from bonding together and growing into coarse particles during hydration treatment, and the solid-liquid ratio at the start of treatment is increased, for example from 1:1 to 1:20 and
In hot water curing, raw materials are dispersed in water at 40°C to 180°C, and stirring, bubbling, circulation, shaking, etc. are performed for several minutes to several days to prevent the raw materials from settling and hardening at the bottom.

In the hydration treatment process, the important stage of forming active compounds necessary for exhaust gas purification is completed after providing sufficient moisture necessary for the production of active substances in the treatment agent. Most of it is consumed in the compound forming reaction.

Humid air curing in hardening hydration treatment is performed at a temperature of 10°C to 40°C.
℃ and relative humidity of 50% to 100% for several minutes or several tens of days, and steam curing is performed at a temperature of 40℃ to 180℃.
℃ and 100% relative humidity for several minutes to several days.

The cured product obtained by such a hydration treatment is used as a slurry by pulverization by a known method 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/β to 400 g/flood.

The nitrite compound of the present invention includes, for example, sodium nitrite,
These include potassium nitrite, calcium nitrite, aluminum nitrite, ammonium nitrite, tin nitrite, strontium nitrite, iron nitrite, copper nitrite, nickel nitrite, magnesium nitrite, and manganese nitrite. In order to contain these nitrite compounds in the slurry, it is possible to use not only the above-mentioned salts themselves, but also raw materials containing these salts, or combinations of materials that produce nitrite compounds by reaction, such as nitric acid and metal copper.

It is also possible to use nitric acid compounds and alumina.

The concentration of the nitrite compound in the slurry is at least 0.001%, preferably 0.001%. old% ~ lO%
It is.

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

The exhaust gas E containing S02 is introduced into an absorption tower 2 whose residence time can be adjusted depending on the gas properties. In the absorption tower 2, the exhaust gas comes into contact with the slurry sprayed by the pump 3, absorbs and removes SO2, and is sent to the chimney 5 through the conduit 4 and released into the atmosphere. The pH of the slurry is adjusted by pump 7. By adjusting the flow rate of the slurry sent to the absorption tower via the conduit 8, pl=1 to 1.
Adjusted to 3. A part of the slurry is sent to the sedimentation type solid-liquid separator IO from the conduit 9, and the concentrated slurry is sent to the solid-liquid separator 13 via the pump 11 and the conduit 12.
Separate gypsum G. The supernatant liquid of the sedimentation type solid-liquid separator 10 is sent to the slurry preparation device 6 through a conduit 15. In the slurry preparation device 6, Ca compound C and nitrite compound N are introduced, water is added if necessary, and a slurry is prepared. A portion of the supernatant liquid is discharged as a drain. The filtrate from the solid-liquid separator 13 is returned to the settling type separator 10 through a conduit 18.

The feature of the present invention is that SO using the conventional Ca compound slurry
By adding a nitrous acid compound, the production of Ca5Os, which has been a problem in 2 absorption and removal, can be made into highly pure CaSO4 without introducing excess air in some cases. Moreover, the desulfurization efficiency can also be significantly improved.

In other words, it is possible to significantly reduce the amount of air that was previously blown into the absorption tower in order to convert Ca5Os to CaSO4, and the oxidation effect of the nitrite compound can improve the absorption efficiency of SO□. .

There are still many aspects of the reaction in the absorption tower of the present invention that are unclear, but when calcium hydroxide is used as the Ca compound, the general reaction can be estimated as follows.

The method of the present invention will be explained below with reference to Examples.

[Example] Examples 1 to 6 A gas having the composition shown in Table 2 was prepared as a gas containing SO2, and 50 cc of each of six types of slurry having different compositions as shown in Table 3 were heated at room temperature, gas flow ff1601
A desulfurization test was conducted by bubbling with 2N/H. However, to prevent moisture in the gas from condensing into the slurry,
The gas was dehumidified before bubbling.

All of the compounds shown by the molecular formulas in Table 3 were first grade commercially available reagents. 60U 40 in Examples 3 and 6 means that 454 g of Ca with a particle size of about 10 mm or less is added to 264 fl of water, stirred for 15 minutes, and then added to the used desulfurizing agent 400 in Table 1.
of the slurry-form SO□ absorbent obtained by curing at 98° C. for 12 hours while heating and stirring again. Of this slurry, 0.075 g in terms of solid matter was used as SO□ absorption slurry.

In addition, the used desulfurization agent is one with the following manufacturing method and usage history.

Coal ash (overseas coal) (Ah0322%, Si0□
64%) 51 parts by weight, Ca(OH)i 30 parts by weight,
45 parts by weight of water was added to a powder containing 419 parts by weight of CaSO, kneaded, steam-cured at 95 to 100°C for 12 hours, and
After drying at 0°C for 2 hours, the cured product (desulfurizing agent) was crushed to have a particle size of 3 to 10 mm, and a gas having the composition shown in Table 2 was added to the cured product (desulfurizing agent) at 130°C at 5v101)O(h'') for 17 hours. Refers to the desulfurization agent after time treatment.

The desulfurization performance was evaluated by analyzing the absorbed liquid and passing gas every 5 minutes until 70 minutes after passing the gas, and the test results were evaluated in Section 4-1.
Shown in the table.

According to Table 2 Gas Composition Table 4-1, in Example 1, 100% of SO3 is removed for 20 minutes after the start of gas flow, but after 30 minutes, SO□O□ gradually increases. After 70 minutes, 800p
It became pm. The pH of the liquid at this time is 6.9 to 6.3 up to 40 minutes after passing the gas, and does not change much, but after 50 minutes it rapidly drops to 2.1. At this time, the NOx concentration in the gas after passing through the SO2 absorption liquid also increases rapidly, and the NOx concentration in the gas after passing through the SO□ absorption liquid increases.

Concentration (exceeds the set value 45 (lppm) and becomes 500ppm. However, after 70 minutes, the same p) Even at 12.1, it is 415p
It became pm. This phenomenon occurs as follows: (1) The contained nitrite compound decomposes and generates NOX. ■When there is no more nitrite to decompose, the generation of NO will decrease over time. This tendency is clear when looking at the amount of NOx in the liquid.

When the amount of N (h) in the SO8 absorption liquid is reduced, the desulfurization ability deteriorates significantly and the amount of sulfite produced increases.

In other words, it is shown that by maintaining the pH of the SO□O□ solution at 6 or more in the presence of NO□, the desulfurization rate can be maintained at a high rate, and the generation of sulfites can be further suppressed.

Furthermore, among the three types of Ca compounds used, the desulfurization rate was slightly inferior in the case of CaCO3, and there was almost no difference between the two types of nitrites.

Comparative Examples 1 to 6 Desulfurization tests similar to those in Example 1 were conducted using the SO2 absorption liquids shown in Table 3 that did not contain nitrite and/or Ca compounds, and the test results are shown in Table 4-2.

Comparative Examples 7 to 8 A desulfurization test similar to Comparative Examples 2 and 8 was conducted, and then air was bubbled through 50 cc of these absorbents for the same time as each gas passage time, at a flow rate of 604 N/H, at room temperature, and the absorbents were analyzed. I did it.

The results obtained are shown in the table below.

Examples 7 to 9 Example 1 was carried out by changing the absorption temperature to 60, 80, and 90°C.
2.3 was repeated.

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

In addition, the operation of conducting an absorption test for 20 minutes was repeated, and this process was repeated 20 times (Examples 10, 11, 1).
2).

Similar repeated tests were conducted 20 times for Comparative Examples 2.3 and 4 (Comparative Examples 9.10.11), and the measured values of the concentration (ppm) of 802 and NOx in the gas after passing the liquid were shown on the vestibule. Ta.

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

Examples 10-12. Comparative Examples 9 to 11 Example 1 except that the amount of nitrite used was 0.085 g
．． The same tests as 2 and 3 were carried out for 20 minutes and then the same nitrite and Ca
The same weight of the compound as in each example was added to the absorption liquid. [Effects of the Invention] As explained in detail above, in the wet desulfurization method containing a Ca compound in the slurry, by containing a nitrite compound in the slurry, the desulfurization rate can be increased. In addition, in normal desulfurization of combustion exhaust gas using excess air, it is possible to gypsum in the absorption liquid without blowing in new air.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of a desulfurization method according to the method of the present invention. E・・・・・・・・・・・・・・・・・・Exhaust gas 2
・・・・・・・・・・・・・・・・・・Absorption towers 3 and 7
．． 11・・・・・・・・・Pump 4, 8.9.1
2.18...guiding path

Claims (2)

[Claims] (1) A wet desulfurization method in which a gas containing SO_2 is brought into contact with a slurry containing a Ca compound, which is characterized by containing a nitrous acid compound in the slurry. (2) The Ca compound is one or more substances selected from the group of substances capable of supplying sulfuric compounds, halogen element compounds, sulfides, and alkali metal hydroxides to substances capable of supplying calcium oxide, silicon dioxide, and aluminum oxide. 2. The method according to claim 1, which is a Ca-Si-Al based hardened product, quicklime, slaked lime and/or carbonated lime obtained by adding a substance and hydrating the product.