JPH0229610B2 - RYUANNOSEIZOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing ammonium sulfate, and in particular, it is suitable for use in fertilizers from ammonium sulfate powder obtained by shaking off the mother liquor of slurry produced after bringing a sulfuric acid-containing liquid into contact with coke oven gas. The present invention relates to a method for producing ammonium sulfate having a particle size. Ammonium sulfate, which is used as a fertilizer, can be spread evenly during fertilization and is less likely to be blown away by the wind.
In addition, in addition to requirements such as not adhering to leaves or stems, when fertilizing is mixed with phosphate fertilizer or potassium fertilizer, the particle size is approximately the same as the particle size of phosphate fertilizer or potassium fertilizer in order to mix uniformly. It is necessary to align the
For this reason, a particle size distribution of about 6 to 18 meshes is desirable. However, when ammonium sulfate was produced using ammonia contained in coke oven gas as a raw material, it was difficult to obtain ammonium sulfate with large crystals. Therefore, many methods have been considered to solve this problem, such as increasing the amount of pyridine recovered mother liquor treated to eliminate the influence of ferric ions, and installing a crystallization tank separate from the ammonia saturator. It has been proposed to lengthen the residence time and further control the free acid concentration and slurry concentration within predetermined ranges. However, even with this method,
The yield on the 18 mesh sieve is only about 10% by weight,
From an industrial standpoint, improving the yield of products with large particle sizes has become an important issue. In view of this, the inventors of the present invention have conducted intensive research on a method for producing ammonium sulfate that has large particle size, good appearance, and high yield, and as a result, they have developed a method for producing ammonium sulfate in which coke oven gas is brought into contact with a sulfuric acid-containing liquid. After that, the mother liquor of the slurry produced was shaken off to obtain crude ammonium sulfate powder, and this crude ammonium sulfate powder was redissolved in water to adjust the pH to 4 to 7. The obtained ammonium sulfate solution was charged into a crystallizer and stirred. By concentrating, ammonium sulfate crystals are precipitated, and from the lower part of the crystallizer, a lower slurry mainly consisting of ammonium sulfate crystals with a predetermined particle size or more is extracted, and an upper slurry mainly containing ammonium sulfate crystals with a predetermined particle size or less is extracted from the upper part of the crystallizer. The mother liquor in the lower slurry is shaken off to remove the ammonium sulfate crystals, and the mother liquor is returned to the crystallizer, and the upper slurry is heated and mixed with the ammonium sulfate solution to regenerate at least a portion of the fine crystals. By dissolving and circulating the ammonium sulfate solution in the crystallizer and decolorizing either or both of the ammonium sulfate solution and the mother liquor of the lower slurry, the particle size of the ammonium sulfate crystals precipitated in the crystallizer can be improved and coloration can be prevented. This is what we discovered and arrived at the present invention. In the present invention, crude ammonium sulfate powder is produced using a conventionally known method, for example, introducing coke oven gas containing ammonia into an ammonia saturator, and converting the coke oven gas into a sulfuric acid-containing liquid such as an aqueous sulfuric acid solution within the ammonia saturator. It is obtained by contacting coke oven gas to collect ammonia as ammonium sulfate, and then applying the resulting slurry to a centrifuge or the like to shake off the mother liquor. In addition, pyridine mother liquor, desulfurization mother liquor, desulfurization mother liquor, etc. containing ammonium sulfate may also be charged into the ammonia saturator. The free acid concentration in this ammonia saturator is usually 2 to 2 when converted to sulfuric acid.
8% by weight, and the slurry concentration is typically 30-50% by weight. In addition to the saturator, a crystallization tank can also be attached. The crude ammonium sulfate powder obtained by shaking the slurry mother liquor extracted from the saturator or crystallizer is
Generally its particle size is small, usually 85-95% by weight
is about 20 to 100 mesh, and the ammonium sulfate concentration obtained by dissolving this crude ammonium sulfate powder in water is 40% by weight.
The ammonium sulfate solution has a pH of about 2 to 3. The crude ammonium sulfate powder thus obtained is introduced into a dissolution tank and redissolved with water to adjust the pH to 4 to 7, preferably 6 to 7. If the pH is lower than 4, the growth of ammonium sulfate crystals will be insufficient and the product yield will be reduced, and if the pH is higher than 7, ammonia will be liberated and coloration will occur, leading to a decrease in product quality. As the dissolving water for dissolving the crude ammonium sulfate powder, it is advantageous to use the drain from the steam ejector of the crystallizer, the evaporated water from the crystallizer, or the ammonium water used for pH adjustment, which will be described later. be. Further, the conditions for dissolving the crude ammonium sulfate powder are not particularly limited, but it is preferably carried out at as high a temperature as possible while stirring, usually at 40°C or higher, preferably at 50°C or higher. Therefore, it is preferable that each of the above-mentioned dissolving waters is introduced into the dissolving tank in a state where the temperature decrease is small by performing a treatment such as heat insulation. The ammonium sulfate solution obtained in this dissolution tank needs to be an unsaturated solution so that crystals do not precipitate during the transfer process, and the ammonium sulfate concentration is usually 35 to 45% by weight, preferably 38 to 42% by weight. Ammonium sulfate concentration
If it is less than 35% by weight, the load on the crystal can becomes too large, and if it is more than 45% by weight, there is a risk that crystals will precipitate when the temperature drops during the transfer process. Further, the iron ion concentration of this ammonium sulfate solution is usually 100 ppm or less, preferably 10 ppm or less. Next, the ammonium sulfate solution is charged into a crystallizer and concentrated while stirring to precipitate ammonium sulfate crystals. As this crystallizer, a continuous mixing type is used, and in particular,
A draft, a tube, a stirring blade, etc. are built into the crystal can, and there is a stirring area and a standing area separated by a tube, and the crystals precipitated in this standing area are sedimented and separated to a predetermined particle size, and the crystals are separated into a crystal can. A lower slurry consisting mainly of crystals with a predetermined particle size or more is extracted from the lower part of the
It is preferable to use a type in which an upper slurry mainly consisting of crystals of a predetermined particle size or less is extracted from the upper part of the crystal can and circulated back into the crystal can. This crystal can has a slurry residence time of 3 to 10
Time preferably 5 to 8 hours, slurry concentration in the can 25
~50% by weight preferably 35-45% by weight, temperature inside the can 50
It is operated under reduced pressure at temperatures above ℃. In addition, the upper slurry extracted from the upper part of the crystallizer is circulated into the crystallizer again, but the circulation amount of this upper slurry is usually 7 to 25 times the feed amount of the ammonium sulfate solution.
Preferably it is 10 to 20 times. The upper slurry circulated to the crystallizer is heated by a heater installed in its circulation line and mixed with a feed ammonium sulfate solution, which is supplied as an unsaturated solution, so that at least some of the fine crystals, preferably all or Most of it is charged into the crystallizer in a molten state. Further, the temperature inside the crystal can is maintained by heat from a heater provided in the circulation line of the lower slurry, and the pressure inside the crystal can is reduced by, for example, a steam evacuator. In addition, this crystallization can is provided with a slurry outlet in the middle position, and a crystal dissolution tank is installed in the ammonium sulfate solution feed line to ensure that the particle size of ammonium sulfate crystals in the lower slurry extracted from the crystallization can is below the desired particle size. When the slurry reaches a certain point, it is desirable to extract the intermediate slurry mainly composed of ammonium sulfate crystals with a predetermined particle size or less from the slurry extraction port, charge it into a crystal dissolution tank, and redissolve it in the feed ammonium sulfate solution. The lower slurry, which is extracted from the lower part of the crystallizer and mainly consists of ammonium sulfate crystals with a predetermined particle size or more, is separated into solid and liquid by, for example, being centrifuged. It is sieved into various products with a particle size distribution of . Also,
This mother liquor is returned to the crystallizer. The method for returning this mother liquor to the crystallizer is preferably to charge it into the upper slurry circulation line, heat it together with the upper slurry in a heater, mix it with the feed unsaturated ammonium sulfate solution, and charge it into the crystallizer. . A decolorizing tank is installed in the feed line for the ammonium sulfate solution supplied from the dissolving tank and/or the feed back line for returning the mother liquor of the lower slurry to the crystallization tank, and when the pH of the ammonium sulfate solution is adjusted in the dissolving tank, sedimentation occurs. Remove iron etc. continuously or intermittently. This removal effect is excellent when the pH is 4 or higher, preferably 5 to 7. The decolorization tank may be of any type as long as it can separate and remove precipitated iron and the like by filtration or adsorption, but a decolorization tank using activated carbon that adsorbs at the same time as filtration is preferred. By using this decolorization tank, the iron ion concentration in the crystal tank can be reduced to normal.
Maintain below 50ppm. Next, the present invention will be specifically explained based on a flow sheet showing an example of implementation of the present invention. Coke oven gas enters the ammonia saturator 2 through line 1, contacts the sulfuric acid-containing liquid that enters through line 3, collects ammonia, and is discharged through line 4. The ammonium sulfate produced in the ammonia saturator 2 becomes a slurry and is extracted from a line 5, and is fixed and separated in a centrifuge 6 to become crude ammonium sulfate powder. This crude ammonium sulfate powder is charged into the dissolution tank 8 from line 7, redissolved by the dissolution water charged from lines 9 and 10, and further dissolved by the ammonium water charged from line 11. Adjusted to PH4-7. The ammonium sulfate solution whose pH has been adjusted in the dissolution tank 8 passes continuously or intermittently through the decolorization tank 13 provided in the feed line 12, and also passes through the crystal dissolution tank 14 provided in the feed line 12 to dissolve the crystals. It is charged into a can 15. This crystal can 15 has a circulation line 16 for extracting an upper slurry mainly consisting of ammonium sulfate crystals having a particle size below a predetermined size, mixing this upper slurry with an ammonium sulfate solution feed line 12, and circulating the mixture to the crystal can 15 again. A heat exchange type heater 17 provided in the circulation line 16 can heat the upper slurry and supply substantially all of the required amount of heat. Also, crystal can 1
5 is provided with a crystal extraction line 18 for extracting a lower slurry mainly composed of ammonium sulfate crystals having a predetermined particle size or more.
The lower slurry extracted from 8 is sent to centrifuge 1.
The ammonium sulfate crystals are taken out from the line 20, and the mother liquor of this lower slurry is taken out from the line 21.
The water is collected from the liquid into a liquid tank 22. The mother liquor of the lower slurry collected in the liquid tank 22 is extracted from the liquid tank 22 and charged into the circulation line 16 which enters the heater 17 via the feedback line 23. It is designed to be returned to the crystal can 15 together with the slurry. Further, the crystal can 15 is provided with a line 24 in its middle portion for extracting the middle slurry when the particle size of the ammonium sulfate crystals in the lower slurry becomes less than a desired particle size. By extracting the partial slurry, the ammonium sulfate crystals in the lower slurry are adjusted to a predetermined particle size or higher, and the extracted intermediate slurry is charged into the crystal dissolving tank 14 provided in the ammonium sulfate solution feed line 12 to dissolve the crystals and crystallize again. It is adapted to be charged into a can 15. In the figure, reference numeral 25 is a steam ejector for reducing the pressure inside the crystallizer 15 and concentrating the ammonium sulfate solution charged into the crystallizer 15, and a line 26
Steam is introduced through line 27, and its condensate exits through line 27. Further, the water vapor evaporated in the crystal can 15 is extracted to the outside through a line 28, condensed in a condenser 29, and uncondensed steam is introduced into the steam evaporator 25.
It is designed to be combined with the condensed water of 7. The condensed water collected in line 27 is led to line 10 via a line not shown, charged into dissolution tank 8, and used to dissolve crude ammonium sulfate powder.
Furthermore, the line 30 is a line for introducing steam into the heater 17, and the condensed water that is condensed by exchanging heat with the upper slurry flowing through the circulation line 16 in the heater 17 is charged to the melting tank 8 from the line 9. and is used to dissolve crude ammonium sulfate powder. In this flow sheet, the crystal canister 15 is 1
Although only the base is depicted, it is possible to provide two or more ammonium sulfate crystal feed lines 12 or branch them,
It is advantageous to install two or more crystallizers in parallel, and in this case, a temperature difference is created in the internal temperature of each crystallizer, and a water vapor line (reference symbol in the figure) is drawn from the crystallizer on the high temperature side. 28) is preferably introduced into the heater of the circulation line provided in the crystallizer on the low temperature side and used as a heat source. In addition, in this flow sheet, decolorization tank 1
3 is provided in the feed line 12 for the ammonium sulfate solution, but as shown by the dashed line in the figure, instead of this or in addition to this, a feed back line 23 is provided for returning the mother liquor of the lower slurry to the crystallization vessel 15. , ferric iron may be decolorized by absorption or adsorption. According to the present invention, it is possible to efficiently produce ammonium sulfate crystals with large particle size, and also to prevent coloring, thereby improving the product value. In the present invention, it is also possible to coexist a crystal modifier such as malic acid, citric acid, caprolactam, oxime, etc. in the ammonium sulfate solution, and to grow the ammonium sulfate crystal to a larger size due to the modulation effect of these modifiers. In addition, fine powder of ammonium sulfate crystals recovered in the drying process and sieving process of ammonium sulfate crystals obtained by shaking off the mother liquor of the lower slurry is charged again into the dissolution tank and used in the ammonium sulfate crystal manufacturing system. You can also return it. The method of the present invention will be explained below based on examples. Examples Crude ammonium sulfate powder having the particle size distribution shown in the table was obtained from a slurry obtained by contacting coke oven gas with a sulfuric acid-containing liquid in an ammonia saturator. This crude ammonium sulfate powder was redissolved in a dissolution tank, and the pH was adjusted with ammonium water.
6. Charge an ammonium sulfate solution with an ammonium sulfate concentration of 41% by weight into a crystallization can, crystal residence time 5 to 8 hours, slurry concentration in the can 35 to 45% by weight, PH in the can 3 to 4.6, temperature in the can 55 to
Ammonium sulfate crystals were produced by operating this crystallizer under the conditions of 58° C. and a ratio of 14 between the amount of slurry circulation and the amount of ammonium sulfate solution feed. The particle size distribution of the obtained ammonium sulfate crystals was as shown in the table. 【table】

[Brief explanation of drawings]

The figure is a flow sheet showing an example of the method of the present invention.

Claims (1)

[Claims] 1. After bringing a sulfuric acid-containing liquid into contact with coke oven gas, the slurry mother liquor produced is shaken off to obtain crude ammonium sulfate powder, and this crude ammonium sulfate powder is redissolved in water to adjust the pH to 4 to 7. Ammonium sulfate crystals are precipitated by charging the solution into a crystal can and concentrating it while stirring, and a lower slurry mainly composed of ammonium sulfate crystals with a predetermined particle size or more is extracted from the bottom of the crystal can, and a predetermined The upper slurry, which mainly consists of ammonium sulfate crystals with a particle size or smaller, is extracted, and the lower slurry is shaken off to remove the ammonium sulfate crystals, and the mother liquor is returned to the crystallizer.The upper slurry is heated and mixed with the ammonium sulfate solution. By doing so, at least a portion of the fine crystals are redissolved and circulated through the crystallizer, and either one or both of the ammonium sulfate solution and the mother liquor of the lower slurry are decolorized continuously or intermittently. Characteristic manufacturing method of ammonium sulfate.