JPS6053806B2 - Treatment method for sulfuric acid sludge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating sulfuric acid sludge discharged from chemical factories and the like.

Generally, in many chemical industries, when organic substances are treated with sulfuric acid, waste sulfuric acid, so-called sulfuric acid sludge, containing a large amount of organic substances is discharged.

For example, in petroleum factories, petroleum fractions are treated with concentrated sulfuric acid to remove various undesirable hydrocarbon fractions, but in this case, free sulfuric acid, undissolved organic substances, dissolved hydrocarbons, and organic sulfonic acids are treated. Sulfuric acid sludge containing a complex composition of

These sulfuric acid sludges are black in color and emit a strong pungent odor, and if left unattended, they will gradually polymerize and solidify, and are extremely corrosive, so they cannot be buried or dumped at sea, and there are important problems in their disposal. Ru. Conventionally, various research and proposals have been made as methods for treating this type of sulfuric acid sludge, and representative methods will be described below. Specifically, there is a method of injecting and burning sulfuric acid sludge in a combustion furnace to thermally decompose the sulfuric acid sludge, decomposing the sulfur compounds it contains into sulfur dioxide, and producing sulfuric acid from this sulfur dioxide. In this method, free sulfuric acid is Since the sulfuric acid sludge contained therein is directly burned at high temperature, the combustion furnace is seriously damaged, and separate sulfuric acid production equipment is required to produce sulfuric acid, so the scale of the process is enormous.

Furthermore, since this combustion gas contains trace amounts of low-molecular organic decomposition products, the produced sulfuric acid is colored, which limits its sales as a product. Therefore, considering the equipment investment, repair costs, and quality deterioration of the sulfuric acid product, it is not economically viable except in a few special cases. Next, a method has been proposed in which the sulfuric acid sludge is diluted with water, the concentration of free sulfuric acid is adjusted to 20-30%, and the organic matter and sulfuric acid content are separated and recovered by heating and hydrolysis. Since the sulfuric acid thus recovered has a low concentration and contains a considerable amount of dissolved organic substances having hydroxyl groups produced by hydrolysis, it not only requires a large amount of expense to purify it, but also
The separated organic substances still contain a considerable amount of acid components,
It has no purpose and causes secondary pollution. Furthermore, the concentration of free sulfuric acid contained in the sulfuric acid sludge was increased from 65 to
After adjusting to 90%, there is a method of heating to 150 to 190°C to polymerize and carbonize the organic substances contained, and recover carbide and sulfuric acid. When using this method, the generated carbide has ion adsorption ability and activated carbon ability, and the recovered sulfuric acid is also relatively good. However, in this method, sulfuric acid acts on organic substances to perform a dehydrogenation reaction. Because it is a thing,
Sulfuric acid is consumed. Therefore, there is a limit to the ratio of organic substances and sulfuric acid contained in sulfuric acid sludge, and when the amount of organic substances is large relative to free sulfuric acid, it is not generally necessary to separately add sulfuric acid. As described above, the methods that have been proposed so far are rarely actually put into operation due to problems such as processing scale, equipment investment, product quality, and economic efficiency, and most of them are not used for processing sulfuric acid sludge. The current situation is that most of the waste remains untreated. The present invention is a general-purpose method for completely harmlessly treating sulfuric acid sludge at the site where it is generated, using inexpensive equipment and costs.
Sulfuric acid sludge is added to magnesium hydroxide slurry diluted to 75%, stirred and mixed to form a neutralized muddy sludge with a pH of 7 or higher, and then fed into a combustion furnace together with a combustion improver to a temperature of 75%.
Combustion is carried out at a temperature of 0 to 900°C, and the combustion gas containing sulfur dioxide gas is guided to a gas absorption tower and brought into gas-liquid contact with magnesium hydroxide suspension.The sulfur dioxide gas is converted to magnesium sulfate and discharged as an aqueous solution, and the combustion residue is removed. The present invention provides a method for treating sulfuric acid sludge that is recycled and reused as a neutralizing agent.

The present invention will be explained below based on the drawings.

The drawing is a flow sheet of an embodiment of the method of the present invention,
A magnesium hydroxide slurry solution diluted with water to 30-70% is supplied to the neutralization tank 3 via conduit 2, and then to the neutralization tank 3 through conduit 1.
The sulfuric acid sludge is supplied to the neutralization tank 3, stirred and mixed, and P
H7 or higher, preferably PH7. ~9 slurry-like sludge neutralized product. At this time, heat is generated due to neutralization heat, but there is usually no need for special cooling. Rather, if the mixture is sufficiently stirred and mixed preferably at a temperature of 75° C. or higher, a neutralized sludge with a pH of 7 or higher and fine particles in the form of mud will be obtained. Next, the neutralized sludge produced in the neutralization tank 3 is supplied to the combustion furnace 5 via the conduit 4. At the same time, combustion improvers such as kerosene and heavy oil supplied from the conduit 6 are burned in the combustion furnace using a burner, etc., and the temperature inside the furnace is lowered to 7.
By maintaining the temperature at 50 to 900°C, the sludge is completely combusted, and the combustion gas containing sulfur dioxide gas is introduced into the absorption tower 8 via the conduit 7, and at the same time, the combustion residue containing magnesium oxide as a main component is passed through the conduit. The residue is discharged to a residue storage tank 10 via a filter 9, and is recycled and reused as a neutralizing agent. Gas absorption tower 8
, the introduced combustion gas containing sulfur dioxide gas is brought into gas-liquid contact with approximately 1.0 to 2.0 Wt% magnesium hydroxide suspended water supplied from the conduit 11, and the harmful sulfur dioxide gas in the combustion gas is absorbed and oxidized. It is converted into harmless magnesium and discharged through the conduit 12 as an aqueous solution. On the other hand, the combustion gas that has been purified by removing sulfur dioxide gas is released into the atmosphere from the gas outlet 13 as a harmless gas. In the present invention, sulfuric acid sludge is neutralized using a magnesium hydroxide slurry liquid diluted with water to 30 to 70% as an alkaline agent. However, if a slurry of magnesium hydroxide with a concentration lower than 30% is used for neutralization, The amount of free water in the neutralized sludge increases, resulting in more fluidity than necessary, which reduces the economic efficiency of combustion.

When the slurry concentration exceeds 70%, the water content is low and magnesium hydroxide reacts with sulfuric acid and simultaneously combines with the water in the neutralized sludge to become a hydrated salt of magnesium sulfate and solidify. If solidified, it is not only difficult to feed it to the combustion furnace, but even if the residence time in the combustion furnace is lengthened, it takes a considerable amount of time to completely burn the inside of the solid, making it uneconomical. Moreover, if the fuel is discharged from the combustion furnace with incomplete combustion, secondary treatment will be required. When neutralizing acidic substances in general industry, calcium hydroxide, caustic soda, etc. are often used as neutralizing agents, but if calcium hydroxide is used to neutralize sulfuric acid sludge, it will not react with sulfuric acid. Calcium sulfate, the reaction product, is poorly soluble in water and tends to form lumps. Therefore, in order to neutralize it, a large amount of water must be added to fluidize it, which is economically disadvantageous during combustion. Combustion is incomplete, and the combustion residue becomes colored, impure calcium sulfate containing carbides, which has no special purpose and causes secondary pollution. In addition, when caustic sorter is used as a neutralizing agent, it is not only more expensive than magnesium hydroxide, but also because the melting temperature of sodium salt is low when burned in a combustion furnace, the furnace wall melts during combustion, causing the furnace wall to melt. It is difficult to use it for a long period of time, and if it is burned at a temperature below the melting temperature to prevent this, it has the disadvantage of incomplete combustion. However, in the present invention, since magnesium hydroxide is used as a neutralizing agent, the sulfuric acid component becomes magnesium sulfate. However, since magnesium sulfate becomes magnesium oxide when heated due to the presence of carbon, this sludge neutralized product is
If burned at ℃, it can be recovered as magnesium oxide in the combustion residue, which has the advantage of being able to be recycled and reused as a neutralizing agent for sulfuric acid sludge by adding water to make a slurry liquid equivalent to 30-70% magnesium hydroxide slurry. be. In the present invention, after feeding the magnesium hydroxide slurry to the neutralization tank, sulfuric acid sludge is then added and mixed with stirring to pH
If it is 7 or more, it is treated as a neutralized sludge (1), so a neutralization tank,
Pipes, combustion furnaces, etc. do not require high-grade materials with particularly excellent corrosion resistance.

As the neutralization tank, a mixing tank with an agitator is usually used, but especially in the case of solidified sulfuric acid sludge, a powerful kneading machine such as a kneader is used as a neutralization tank to create a highly fluid and particle-free mixer. It can be made into a slurry-like neutralized product. In the present invention, the sludge neutralized product is burned at a temperature of 750 to 900°C, and if the temperature inside the furnace is lower than 750°C, the supplied sludge neutralized product will not be completely combusted, and the magnesium sulfate will turn into magnesium oxide. Does not convert completely.

Moreover, if the temperature exceeds 900°C, the amount of combustion improver consumed increases, which is economically disadvantageous. Generally, caustic soda, soda carbonate, calcium hydroxide, calcium carbonate, etc. are used as absorbents for sulfur dioxide gas, but sodas are generally expensive and calciums often cause scaling.

In addition, since it reacts with sulfur dioxide gas and becomes sulfite, the COD is high and it cannot be discharged as it is. In the present invention, since magnesium hydroxide is used as an absorbent, the sulfur dioxide gas contained in the combustion gas is more easily absorbed and oxidized than soda or calcium, and becomes a harmless aqueous magnesium sulfate solution. It has the advantage of being able to be released. In addition, since there is almost no occurrence of nozzle clogging or scaling, any type of absorption tower can be used, such as a spray tower, packed tower, or ventilate scrubber. As described above, the present invention is a complete treatment method for sulfuric acid sludge, in which not only sulfuric acid sludge discharged during operation, but also sulfuric acid sludge that has been left to solidify can be discharged as a harmless aqueous magnesium sulfate solution without any problems and in a simple manner.

In addition, according to the method of the present invention, the equipment does not need to be made of expensive materials with particularly excellent corrosion resistance, and can be manufactured at an extremely low cost. Unlike solidified sludge neutralized material, it is easy to supply to the combustion furnace, and the combustion effect is improved. It can burn well and completely,
Furthermore, the combustion residue is recycled and reused as a neutralizing agent for sulfuric acid sludge, which is an extremely useful method for treating sulfuric acid sludge in terms of pollution prevention without releasing any secondary industrial waste. Next, examples of the method of the present invention will be shown.

Example 1 Magnesium hydroxide (commercial product, purity 90.14%) 40
．． A magnesium hydroxide slurry liquid consisting of 7 kg and 95 k9 of water was supplied to a neutralization tank (with a stirrer, capacity 500 e),
Subsequently, 100 kg of sulfuric acid sludge consisting of 30% organic substances, 62% sulfuric acid, and 8% water was added, and as a result of stirring and mixing, the result was a pH of 8 with 12.7% organic substances and 33% magnesium sulfate.
A slurry-like neutralized sludge 235.7k9 was obtained having a composition of 2.3% water, 53.5% water, and 1.5% other.

Next, the sludge neutralized product was heated in a combustion furnace (rotary hearth type, 12
30m/mφ×700rr! ．． /MH) and burned. The combustion conditions and results are as follows. Heat aid (kerosene) supply amount 13.3e/FIR sludge neutralized product processing amount 60.0k9/HR combustion furnace, internal temperature
800'C furnace outlet, combustion gas amount
320Nd/HR combustion residue amount
7.5kg/HR As a result of analyzing the above combustion gas, SO2
, CO2, O2, N2, etc.
2 concentration was 12000 ppm.

This mixed gas is absorbed into an absorption tower (packed tower, 340TrL/WLφ
×5rr1H) and processed. The packed tower was filled with Pyrex #200 to a height of 2.4Tr1. The processing conditions and results are as follows. Gas superficial velocity 1.07n/Sec
Absorption liquid (PH6) 1.5wt. %Mg(0H)2 suspended water absorption liquid circulating amount 4.0 f/d Gas inlet concentration (SO2) 12000 ppm Gas outlet concentration (SO2) 10 ppm Amount of magnesium sulfate produced 19.0 kg/FIR Example 2 Magnesium hydroxide (commercial product, Purity 90.14%) 40.
A magnesium hydroxide slurry liquid consisting of 7k9 and water 17.4k9 was supplied to the same neutralization tank as in Example 1, and then 100kg of the same sulfuric acid sludge as in Example 1 was added and mixed with stirring. As a result, the organic matter was 19.0% at pH 8. , 158.1 kg of neutralized muddy sludge consisting of 48.1% magnesium sulfate, 30.6% water, and 2.3% others was obtained.

Next, the sludge neutralized product was combusted and the combustion gas was treated using the same combustion furnace and absorption tower as in Example 1.

The conditions and results are shown below. Combustion conditions and results Amount of heating aid (kerosene) supplied: 8.0e/HR Amount of neutralized sludge treated: 40.0k9/HR Combustion furnace, internal temperature: 800℃ Furnace outlet, amount of combustion gas: 320N/HR SO2 concentration in combustion gas
13000ppm combustion residue amount
5.0k9/HR Combustion gas processing conditions and results Gas superficial velocity 1.0TrL/Sec Absorption liquid (PH6) 1.5wt% Mg(0H)2 Suspension water absorption liquid circulation amount 4.0e/Igas inlet concentration (SO2) 13000ppm Gas outlet concentration (SO2) 20ppm Amount of magnesium sulfate produced 19.2k9/8 Furthermore, as a result of analyzing the combustion residue obtained in Examples 1 and 2, the composition was 90% as magnesium oxide, and other inorganic sulfuric acid such as magnesium sulfate. Contains 10% salt.

Water was added to this combustion residue to form a slurry liquid corresponding to a 30-70% magnesium hydroxide slurry liquid, which was repeatedly used as a neutralizer for sulfuric acid sludge without any particular problem.

BRIEF DESCRIPTION OF THE DRAWINGS The drawings are flow sheets of embodiments of the present invention. 3... Neutralization tank, 5... Combustion furnace, 8...
...Gas absorption tower, 10...Residue storage tank.

Claims (1)

[Claims] 1 Add sulfuric acid sludge to magnesium hydroxide slurry diluted to 30 to 70%, stir and mix to obtain a neutralized muddy sludge with a pH of 7 or higher, and then feed it into a combustion furnace together with a combustion improver at a temperature of 750 to 900°C. The combustion gas containing sulfur dioxide gas is led to a gas absorption tower and brought into gas-liquid contact with magnesium hydroxide suspended water, and the sulfur dioxide gas is converted to magnesium sulfate and discharged as an aqueous solution, and the combustion residue is used as a neutralizing agent. A method for treating sulfuric acid sludge characterized by cyclic reuse.