JPH0448730B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing granular ammonium sulfate.

[Conventional technology]

Conventionally, ammonium sulfate has been produced by contacting ammonia contained in coke gas with an aqueous sulfuric acid solution, but in recent years ammonium sulfate with large crystals has become required for use as fertilizer.

Examples of such technology include, for example, Japanese Patent Application Laid-Open No. 1983-
As shown in Publication No. 78924, a lower slurry mainly consisting of ammonium sulfate crystals with a predetermined particle size or more is extracted from the lower part of the crystal can, and an upper slurry mainly consisting of ammonium sulfate crystals with a predetermined particle size or less is extracted from the upper part of the crystal can. The slurry is made by centrifuging the mother liquor to take out the ammonium sulfate crystals and returning the mother liquor to the crystallizer.The upper slurry is heated and mixed with the above ammonium sulfate solution to redissolve some of the fine crystals and return it to the crystallizer. There is a way to circulate it.

[Problem that the invention seeks to solve]

In the operation of the granulation equipment shown above, the crystals are usually extracted so that the total volume of particles in the crystal can remains constant. The crystal surface area is significantly reduced. For this reason, as the particles reach their peak growth, the concentrated ammonium sulfate cannot be absorbed by the crystals in the can, and supersaturation progresses, generating a large amount of microcrystals.

Furthermore, after a large number of microcrystals have been generated, the number of crystal particles inside the can increases and the total crystal surface area increases rapidly.
The ammonium sulfate used for growth is dispersed, and the growth rate of a single particle is reduced. For this reason, it has become difficult to stably produce ammonium sulfate crystals with a predetermined particle size. The present invention provides a method capable of producing ammonium sulfate having a desired particle size with good yield.

[Means and actions for solving problems]

The structure of the present invention is that in a method for producing granular ammonium sulfate by introducing an ammonium sulfate solution into a crystallizer, fine grain crystals after sieving product ammonium sulfate are added to the crystallizer as seed crystals to promote growth. At the same time, the number of crystallized particles in the can is estimated from the total volume of crystal particles determined from the pressure difference in the depth of the liquid in the can and the average particle diameter of the ammonium sulfate product, and based on this estimated number of particles, the amount of seed crystals added and the product are determined. This is a method for producing granular ammonium sulfate characterized by controlling the amount of ammonium sulfate extracted to obtain a desired particle size.

That is, the ammonium sulfate solution is charged into a crystallizer equipped with a concentrator for vacuum evaporation or the like to precipitate ammonium sulfate crystals.
This crystal can is equipped with an ammonium sulfate particle classification mechanism inside the can, and is operated with a particle residence time of 3 to 10 hours, an internal slurry concentration of 10 to 50%, and an internal temperature of 40°C or higher.
It is operated under conditions such that ammonium sulfate crystals with a predetermined particle size or more are extracted from the lower part.

The particle volume V _si in the crystal can is expressed by the following equation (1).

V _si = V・(ΔP/Δh−ρ)/(ρ _s −ρ)…(1
) Δh: Difference in tank liquid depth, ΔP: Pressure difference between Δhi, V:
Volume between Δhi, ρ: liquid density, ρ _s : particle density On the other hand, the average particle size of the ammonium sulfate product can be easily determined by the following method.

(i) Periodically sample the product and determine the average particle diameter by particle size measurement, etc.

() On a belt conveyor, particles are separated and identified based on differences in brightness using an image processing device, etc., and the average particle diameter is determined.

() Extract a portion of the ammonium sulfate product online and determine the average particle diameter using an image processing device, particle size measuring device, etc. etc.

The average particle size determined in this way can be multiplied in advance by the particle classification coefficient in the can in the liquid depth direction as shown in equation (2) below to estimate the average particle size in the liquid depth direction in the can. I can do it.

dhi=×khi...(2): Product average particle diameter, dhi: Estimated average particle diameter between arbitrary Δhi, khi: Coefficient showing correlation with product particle size at arbitrary Δhi Therefore, crystallized particles in the can The number can be estimated using equation (3) below. The number of particles in the can is the sum N of the number of _particles in the volume _divided for each arbitrary liquid depth Δhi _. Particle volume, dhi: Particle diameter between arbitrary liquid depths Δhi There is an optimal value for the number of particles in the can considering the equipment shape and production volume, so if this is K, the number of particles in the can is controlled under the following conditions. do.

When N-K≧0: It is judged that the number of crystals in the can is too large,
Increase the amount of crystal extraction.

When N-K<0: Adjust the amount of extracted crystals to the average production amount, and supplement the decrease in the number of crystals in the can by adding seed crystals (fine crystals).

In the present invention, the number of particles obtained in this way is
By adding seed crystals and adjusting the amount of extracted crystals, the number of particles in the can can be controlled to an optimum number corresponding to the production volume, as described above, and the particle size can be improved and stabilized.

Incidentally, as the seed crystal for adjusting the number of particles, fine-grained crystals obtained by sieving the product ammonium sulfate crystals are used.

〔Example〕

FIG. 1 shows a system diagram of a production facility for granular ammonium sulfate in an embodiment of the present invention. In FIG. The liquid extracted from the upper part of the crystallizer 1 is continuously sent to the vacuum evaporator 2 by a circulation pump 3. In the vacuum evaporator 2, the circulating liquid is concentrated.
The supersaturated circulating liquid flows down the downcomer pipe 4 provided at the center of the crystal can 1, is sent to the lower part of the crystal can 1, and rises inside the crystal can 1. At this time, this circulating liquid causes the crystal particles in the crystal can 1 to grow, and the circulating liquid itself gradually decreases in concentration and advances to the upper part of the crystal can 1. Then, it is sent to the vacuum evaporator 2 again by the circulation pump 3. The feed liquid necessary for crystal precipitation is adjusted to an appropriate concentration in the dissolution tank 5, and is continuously introduced into the vacuum evaporator 2 together with the circulating liquid. The grown crystal particles settle and are extracted from the bottom of the crystallizer by a pump 6, passed through a dehydrator 7 and a dryer 8, and a part of the product ammonium sulfate is extracted online on a belt conveyor, and the average particle size is determined by an image processing device. The average particle size was measured using a particle size measuring device 9, which was then sieved to a predetermined product particle size using a vibrating sieve 10, and the bottom of the sieve was returned to the crystal can 1 as a seed crystal using a quantitative transport device and added thereto.

In such manufacturing equipment, crude ammonium sulfate powder is obtained from the slurry obtained by contacting coke gas with a sulfuric acid-containing liquid in an ammonia saturator, this crude ammonium sulfate powder is redissolved in dissolution tank 5, and the pH is adjusted with ammonium water. The resulting ammonium sulfate solution with a pH of 6 and an ammonium sulfate concentration of 41 wt% was used for crystal granulation.

The granulation conditions for crystal can 1 are as follows: residence time of crystals is 5 to 8 hours, particle concentration in the can is 20 to 30 vol%, temperature in the can is 45 to 50°C, and free acid content in the can is 3 to 4%. I went there.

The average particle size of the obtained granular ammonium sulfate was measured using a particle size measuring device 9.
At the same time, measure the pressure difference at each arbitrary liquid depth and calculate the particle volume inside the crystal can using equation (1).
The average particle size in the liquid depth direction inside the can was estimated using equation (2), and the number of crystallized particles inside the can was estimated using equation (3). In accordance with the fluctuations in the estimated number of particles, when the number of particles increases, the amount of product extracted is adjusted to increase with the pump 6, and when the number of particles decreases, the product under the sieve of the vibrating sieve 10 is used as a seed crystal to adjust the amount added. The estimated number of particles was controlled. Figure 2 shows the timing of each adjustment.The optimum number of crystals (K) is 6 x ₁₀₉ , the increase in the amount of product extracted is adjusted within 20wt% of the production load, and the amount of seed crystals added is Similarly, the production load is 1~
It was adjusted within a range of 10wt%. Further, the number of particles in the crystal can 1 was controlled within the range of (5 to 7)×10 ₉ .

As shown in Fig. 3, the effect of controlling the number of particles, compared to the comparative example, in this example, the particles were larger and the particle size distribution was stabilized, and the product yield on the 14-mesh vibrating sieve 10 increased by about 15 to 20%. .

〔Effect of the invention〕

As explained in detail above, according to the method of the present invention, the number of crystallized particles in the crystallizer is estimated, and seed crystals are added and controlled based on this estimated number of particles, so that the particle size distribution of the crystals can be controlled. This is an excellent invention that can uniformly produce desired large grains of ammonium sulfate at a high yield.

[Brief explanation of the drawing]

Each figure is an example diagram, and FIG. 1 is a system diagram of manufacturing equipment, FIG. 2 is a relationship diagram between elapsed time and the number of crystals, and FIG. 3 is a relationship diagram between elapsed time and sieve yield. 1... Crystallizer, 2... Vacuum evaporator, 3... Circulation pump, 4... Descending pipe, 5... Dissolution tank, 6... Product extraction pump, 7... Dehydrator, 8... Dryer,
9... Particle size measuring device, 10... Vibrating sieve.

Claims (1)

[Claims] 1. In a method for producing granular ammonium sulfate by introducing an ammonium sulfate solution into a crystallizer, fine grain crystals after sieving the product ammonium sulfate are added as seed crystals into the crystallizer to promote growth and reduce the amount of liquid in the can. The number of crystallized particles in the can is estimated from the total volume of crystal particles determined by the depth pressure difference and the average particle diameter of the product ammonium sulfate, and based on this estimated number of particles, the amount of seed crystals added and the amount of product ammonium sulfate extracted are calculated. A method for producing granular ammonium sulfate characterized by controlling and obtaining a desired particle size.