HU205562B - Method for graining melts or enriched fluids containing solid materials and added salt by the course of centrifuging - Google Patents

Abstract

In the process according to the invention, at least two centrifuges (2, 3) are used and the temperature of the melt and / or liquid is maintained at the same temperature in each centrifuge and the distance between the center of the centrifuges (2,3) is adjusted so that the particle stream of the droplets (5, 6) pass from the apertures of the adjacent centrifuges (3,2) from the upper row openings in one of the centrifuges (2, 3). In the course of granulating the melt and / or liquid containing solids such as salt, a separate mixer (10) is used for each (2.3) centrifuge. Figure 1 EN 205 562 B Scope of the description: 6 pages (including 2 sheets)

Description

FIELD OF THE INVENTION The present invention relates to a process for granulating liquids or enriched liquids containing solids and added salt by centrifugation, wherein the molten or solution is precipitated and dropped into at least one of a plurality of orifices through centrifuges, passed through a granulator and formed into solid particles or particles.

Granulation is used primarily for making fertilizers, but also for granulating other types of materials, such as magnesium chloride.

In the granulation process, the bulk of the cost is the cost of the granulation tower. This is important because the granulation tower must be optimized to achieve the desired granulation performance. The height of the tower is largely determined by the amount of cooling required to achieve solid particles of a given size and the temperature of the cooling air and the amount of heat to be removed from the droplets. The diameter of the tower is determined by both the desired power, the amount of material to be granulated per hour, and the precipitation path of the centrifuge. The precipitation path also depends on the design of the centrifuge, that is, the speed, the diameter of the openings in the centrifuge, the particle size and the amount of material to be granulated per hour. Correspondingly, the performance of the granulation tower is primarily determined by its diameter, since granulation cannot be performed at a rate at which droplets flowing from the centrifuge solidify on the wall of the tower rather than being converted into solid particles or particles.

The cross-section of the tower can be circular, elliptical, square. The process of the invention is not limited by the choice of the design of the tower cross section.

Great efforts have been made to produce an optimally sized granulation tower while increasing performance. For example, studies have been made to determine the exact time needed to adjust the centrifuge speed, the optimum timing of the centrifuge cleaning, or the centrifuge opening clogging. Such a process is described in U.S. Patent No. 142,285. According to the patent, the flow length at the bottom of the tower is measured by means of an infrared camera. Exact control of the cooling air led to the tower has also been attempted, but the results of such measurements were not commensurate with the costs.

It is an object of the present invention to provide a granulation process which, without increasing the cost of construction and operation of the granulation tower, achieves higher performance while maintaining the quality of the material.

Despite some limitations, the granulation technique has been an efficient way of producing solid particles for many years. Therefore, we wanted to use as much of the technology as we could over the years to solve this problem. Therefore, the conditions in the existing granulation tumblers were carefully reviewed in order to increase the performance while still maintaining good product quality, i.e., even with the maximum amount of melt / liquid added to the centrifuge, the shape and distribution of the granules would be appropriate.

We also wanted to make the most of the precipitation time without solidifying the droplets on the tower wall.

With respect to optimization of orifice diameter, centrifuge design, orifice series, and control of conditions such as centrifuge speed and hourly melt / liquid volume, there was little potential for improvement. Examining these conditions, it was found that the cooling air was under-utilized. This meant that the amount of cooling air did not limit the tower's performance increase. Based on this, it seemed possible to increase the amount of droplets to be cooled to the granules. The question was how to solve this, since the power of the centrifuge in question had already been fully utilized and a further increase in the amount of melt / liquid to be transported would have resulted in lower quality.

By observing the aforementioned known granulation towers / centrifuges, it has been found that the distance between the individual droplet streams from the centrifuge is large. The calculations further confirmed that the distance between the particles formed from these currents is relatively large. These observations and calculations have led to the conclusion that the granulation tower can be operated simultaneously with multiple centrifuges without compromising product quality.

For this purpose, various models have been developed to study the likelihood of particle collision both theoretically and practically. These tests showed that few particles collided with each other. The magnitude of collisions in a granulating tower can be considered irrelevant.

Theoretical calculations suggested that symmetrical placement of centrifuges at a distance of 2 meters was advisable.

It was then decided to place more centrifuges, which together have higher performance than the previous one. The distance between the centers of the centrifuges was chosen to be 3 meters.

Upon careful examination of the existing granulation tower, we agreed on conditions that led to a significant increase in the granulation capacity of the tower using at least two centrifuges. This experiment further demonstrated the need for close and regular monitoring of production conditions. For example, it was important to be able to accurately control the temperature of the melt / liquid delivered to the centrifuge. In fact, the melt / liquid contains several components, such as the melt / liquid from the evaporator, residual solid and salt. For example, an NPK fertilizer may contain a melt / liquid (NP melt), a potassium salt such as KCl, and a residue (NPK particles). In order to achieve a proper distribution in the centrifuge, we have found it advantageous to use a separate conveyor and mixer for each centrifuge,

205 in case the mixture needs to be granulated. However, the melt / liquid can be taken from an ordinary evaporator and the potassium salt from an ordinary silo. When evacuating the evaporator, the temperature must be substantially constant for a particular type of NP melt / liquid. The salt temperature should also be kept constant. The amount of potassium salt is determined by the NPK composition to be produced. The temperature of the mixture supplied to the centrifuge is accordingly controlled by varying parameters such as melt / liquid and recirculated particle ratio, residual or recycled material and / or potassium salt.

The critical distance between the centrifuges was 1.5-2.0 m for the granulation tower under investigation. It was further determined that the spacing between the centrifuges should be large enough to allow droplet currents to precipitate from the upper openings in one of the centrifuges below the lower edge of the other. The distance between the centrifuges and the tower must be large enough so that the droplets do not collide with the tower wall. In the case of the present granulation tower, this distance is 10 m.

Centrifuge control was performed in the conventional manner.

Thus, the process of the present invention utilizes at least two centrifuges and maintains the temperature of the melt and / or liquid in each centrifuge and adjusts the distance between the centers of the centrifuges so that the droplet particle flow from the apertures of a top row in a centrifuge is below the lower edge. Separating the solids and / or liquids containing solids, such as salt, by using a separate mixer for each centrifuge.

In the granulation of pure melt / liquids without addition of residual material or salt, such as urea granulation, the material may also be transported from the evaporator to the centrifuge. It is also possible to use a conventional mixer. In some cases, it may be advantageous to deliver different amounts of material to different centrifuges. In this way, the granulation space of the tower can be maximized.

Further details of the invention will be illustrated by way of example in the drawings. In the drawing it is

Figure 1 shows a granulation tower with two centrifuges, conveyors and agitators, and a droplet flow from the two centrifuges,

Figure 2 is a plan view of a granulation tower with two centrifuges, a

Figure 3 is a plan view of a circular cross-sectional granulator tower with three centrifuges, a

Figure 4 is the critical distance between the two centrifuges.

Figure 1 shows the upper part of the granulation tower (1). In the upper part of the granulation tower (1), two centrifuges (2) and (3) are centrally arranged for spraying the melt or the concentrated liquid. The particle streams (5) and (6) schematically show the melt / liquid streams that are precipitated from the respective centrifuge (2) and (3). In the granulation tower (1) shown, both the centrifuges (2) and (3) are supplied with melt / liquid separately. From the evaporator (not shown), the melt / liquid is fed through the conduit (9) to the appropriate mixer (10), to which salt, such as KCl, is added through the conduit (11). The ready-mixed saline solution, such as NPK, then passes through the conduit (12) to the appropriate centrifuges (2) and (3).

In the case of a pure melt, the material is fed from the evaporator through the conduit (9 ') to the centrifuges (2) and (3).

Figures 2 and 3 show a plan view of the circular cross-sectional granulation tower (1) and the arrangement of the centrifuges (2, 3). Figure 2 shows the use of two (2 and 3) centrifuges, and Figure 3 shows the use of three (2, 3 and 4) centrifuges. Figure 4 illustrates how the droplet particle flow crosses each other in centrifuges 2 and 3).

Each of the centrifuges (2, 3) has a series of apertures and in the figure are the particle streams (5 and 6) exiting the upper rows of the centrifuges (2 and 3) and the particle streams (7 and 8) exiting the corresponding lower rows. As shown in the figure, the distance between the centrifuges (2 and 3) is exactly so large that in one centrifuge the droplets from the top row pass through the lower edge of the adjacent centrifuge. Accordingly, the droplets that precipitate do not collide or collide with the centrifuge wall.

Example 1

The example shows the results of granulation tests of a concentrated nitrophosphate solution in an evaporator. A centrifuge was used.

A series of tests was performed on a centrifuge in which 53 m ^{3 of} nitrophosphate melt was added every hour. The centrifuge was located in the center of the granulation tower. The droplets / particles did not collide with each other or with the tower wall. The quality of the material was tested. Samples were taken from both the tower and the filtered material, which had a particle diameter of 2-4 mm. In both cases, the amount of "unacceptable" particles, other than spherical, was 10%. Typically, unacceptable particles are formed when particles collide or when particles collide with the tower wall.

Example 2

NP centrifugation was performed using two centrifuges. A number of tests were performed in the granulation tower used in Example 1. The two centrifuges were positioned as shown in Figure 2. The distance between the centrifuges was determined essentially on the basis of model studies and then the distance shown in Figure 4 was applied.

An average of 71 m ^{3 of} NP melt per hour was added to the two centrifuges, but this amount was 83 m ³

HU 205562 Β can also be stepped up. The granulation temperature was maintained at the same temperature in both centrifuges. Both the tower and the filtered product were sampled and the amount of unacceptable particles, which again was about 10% for both products, was measured.

Although the particle flows from the two centrifuges intersect (see Figure 4), the amount of unacceptable particle particles did not increase with the use of two centrifuges. This confirms that there was hardly any collision between the particles in the intersecting particle streams. However, no solid particles were deposited on the tower wall. Accordingly, it was possible to increase the granulation tower capacity by about 35% by using two centrifuges. It was also found that we obtained the same product quality as a centrifuge.

Example 3

This example illustrates the NPK granulation in the granulation tower used in Examples 1 and 2 using a centrifuge. A concentrated NP melt and solid KCl salt were added to the mixer and thence to the centrifuge.

26 m ^{3 of} NP melt and 35 tons of KCl per hour were added to the mixer, totaling 70 tons of material per hour

Product quality was measured as in Examples 1 and 2 and the amount of unacceptable particles in both product categories was 8%.

Example 4

In this example, NPK granulation with two centrifuges is shown. Each centrifuge was connected to a separate mixer and the sodium phosphate melt and salt were added separately. During the tests, it was possible to provide a high degree of flexibility in the amount of melt and solid and to maintain the temperature of the feed in the mixers.

The distance between the centrifuges was determined as in Example 2.

A series of tests were performed and an average of 10 tons of material was added to the two centrifuges per hour. The mixing temperature was substantially the same in both mixers

As in the previous examples, the quality of the product was measured. The amount of unacceptable particles was between 6 and 9%.

Studies have shown that using two centrifuges, it is also possible to achieve higher performance in the granulation of salt / liquid containing salt without degrading product quality. In the tests we achieved a 43% increase in performance.

With simple modifications and little investment, the process of the present invention can achieve a substantial increase in the capacity of the granulation tower by using more than one centrifuge.

Furthermore, the invention provides greater flexibility and continuity by allowing one centrifuge to be switched off while granulation can be continued with the remaining centrifuge (s). In some cases, the granulation space of the tower can be better utilized by unevenly adding material to various centrifuges.

Claims (2)

PATENT CLAIMS A process for granulating liquids or enriched liquids containing solids and added salt by centrifugation, wherein the melt or solution is precipitated and drops through at least one of a plurality of orifices of the centrifuges, passed through a granulating tower and formed into solid particles or granules. at least two centrifuges are used and the temperature of the melt and / or liquid in each centrifuge is maintained at the same temperature and the distance between the centers of the centrifuges is adjusted so that the droplet particle flow from the openings in the top row of one centrifuge is below the bottom edge of the adjacent centrifuge (s). Process according to claim 1, characterized in that the melt and / or liquid containing the solids, such as salt, is granulated with a separate mixer for each centrifuge.