METHOD FOR INCREASING THE MECHANICAL STABILITY OF POTASSIUM CHLORIDE COMPACTED MATERIAL

Abstract

A method can increase the mechanical stability of compacted potassium chloride granules. The method can include applying water in an amount of 0.1 to 0.4 wt. %, based on the mass of the freshly produced compacted potassium chloride granules, onto the surface of the freshly produced compacted potassium chloride granules while they are still hot.

Claims

1: A method for increasing mechanical stability of compacted potassium chloride granules, the method comprising: applying water in an amount of 0.1 to 0.4 wt %, based on the mass of the compacted potassium chloride granules when they are freshly produced, wherein the water is applied to the surface of the compacted potassium chloride granules while they are freshly produced and still hot.

2: The method as claimed in claim 1, wherein at least 80 wt % of the compacted potassium chloride granules, prior to the application of the water and when they are freshly produced, have grain sizes of at least 5 mm, determined by sieve analysis according to DIN 66165:2016-08.

3: The method as claimed in claim 1, wherein the coarse compacted potassium chloride granules, prior to the application of the water and when they are freshly produced, have a temperature of at least 70 C.

4: The method as claimed in claim 1, wherein the coarse compacted potassium chloride granules when they are freshly produced contain less than 10 ppm of organic carbon (TOC value), determined according to DIN EN 15936:2012 and calculated as elemental carbon.

5: The method as claimed in claim 1, wherein the compacted potassium chloride granules, prior to the application of the water and when they are freshly produced, have a water content of 0.01 to 0.3 wt %, determined by way of loss on drying at 105 C.

6: The method as claimed in claim 1, wherein the compacted potassium chloride granules when they are freshly produced have a KCl content of at least 98 wt %, based on nonaqueous constituents of the compacted potassium chloride granules.

7: The method as claimed in claim 1, wherein production of the compacted potassium chloride granules comprises pressure agglomeration of fine potassium chloride with a roll press at elevated temperature.

8: The method as claimed in claim 7, wherein the pressure agglomeration produces resultant slugs, and wherein the pressure agglomeration is followed by comminution of the resultant slugs.

9: The method as claimed in claim 1, wherein organic strengtheners or dust binders are not added to the compacted potassium chloride granules during production, nor are organic strengtheners or dust binders added to the compacted potassium chloride granules before or after application of the water.

10: The method as claimed in claim 1, wherein the water is applied in atomized form to the compacted potassium chloride granules while they are moving.

11: The method as claimed in claim 1, wherein the compacted potassium chloride granules contain less than 27.8 wt % of particles having a size of below 5 mm, after the water is applied and after treatment according to DIN 51717.

12: The method as claimed in claim 1, wherein the compacted potassium chloride granules contain 18.4 wt % or less of particles having a size of below 5 mm, after the water is applied and after treatment according to DIN 51717.

13: The method as claimed in claim 1, wherein the method does not comprise a drying step after the water is applied.

14: The method as claimed in claim 1, wherein a content of alkaline earth metal compounds in the compacted potassium chloride granules, when they are freshly produced, is not more than 2000 ppm, calculated as oxides and based on nonaqueous constituents of the compacted potassium chloride granules.

15: The method as claimed in claim 1, wherein a content of a conventional binder or binders in the compacted potassium chloride granules is below 0.1 wt %, based on nonaqueous constituents of the compacted potassium chloride granules.

Description

EXAMPLES

[0038] The experiments below used potassium chloride raw material having the following specification: KCl content of 99 wt % (=62.5% K.sub.2O), total Ca+Mg content around 0.01 wt %. The residual moisture content of the (moist) potassium chloride raw material is generally 5.7-6.2 wt %.

[0039] Grain size distribution:

TABLE-US-00001 1.1 wt % <0.09 mm 6.3 wt % 0.09 to <0.16 mm 10.1 wt % 0.16 to <0.212 mm 8.8 wt % 0.212 to <0.25 mm 68.5 wt % 0.25 to <0.5 mm 5.2 wt % >0.5 mm

[0040] For the production of compacted potassium chloride granules, the moist potassium chloride raw material was sent to drying at around 135 C. After that, the raw material, together where appropriate with the press reject material in the comminution/fractionation, was fed to the presses. The quantities processed amount to around 40 t/h of potassium chloride raw material.

[0041] For the pressure agglomeration in production, a roll press with reject-material circulation was used. The construction of the roll press is as follows: two rolls rotating counter to one another have waffle profiling on the roll surface (typical roll diameter 1150 mm, typical working width 1000 mm, gap width typically around 15 mm). The press was operated with a linear force of around 70 kN/cm and a roll speed of 0.7 m/s. The potassium chloride raw material was supplied generally by means of a central chain conveyor and the stuffing screws arranged above the presses.

[0042] The slugs produced in the roll press were comminuted by means of a roll crusher. The material was then classified with a conventional sieving apparatus, the fraction with grain size >5 mm (product) was separated off, and the fraction with grain size <5 mm was recycled to the feed. The respective fractions were discharged from the sieving apparatus with a conveyor belt.

[0043] Immediately after discharge from the sieving apparatus, the compacted granules had a temperature of 90 to 110 C. and a loss on drying of less than 0.1 wt %.

[0044] Immediately after leaving the sieving apparatus, the compacted granules thus produced, on the conveyor belt, were sprayed with water, using a flat jet nozzle. The water was mains water with a hardness of 13.8 dH [German hardness]. The nozzle was set so as to generate a flat spray cone with an opening angle of 120. The conveyor belt speed and the amount of water applied were adjusted such that the quantity applied was about 0.3 wt %, based on the compacted granules guided through the spray cone. Over a prolonged period, a total of 22 samples, each of 10-15 kg, were withdrawn, via a sampling hatch, from the resultant compacted potassium chloride granules. 2-3 kg of each of the samples were divided off and, for determining the grain size distribution, were sieved for 5 min. on a sieving machine (EML 450 digital plus from Haver & Boecker).

[0045] The grain size distribution of the resultant compacted potassium chloride granules was as follows (average over 22 samples):

TABLE-US-00002 7.6 wt % <5 mm (4.8 wt % <2 mm, 2.8 wt % 2 to <5 mm) 4.6 wt % 5 to 6.3 mm 13.1 wt % >6.3 to 8 mm 14.4 wt % >8 to 10 mm 15.5 wt % >10 to 12.5 mm 15.3 wt % >12.5 to 16 mm 14.2 wt % >16 to 20 mm 8.6 wt % >20 to 25 mm 6.7 wt % >25 mm.

[0046] The resulting compacted granules were subsequently placed in storage as a heap in a storehouse, via the conveyor belt. After seven days of storage, the material was withdrawn using a digger. A successive 21 samples, each of 10-15 kg, were again taken from the material withdrawn from storage. 2-3 kg of each of the samples were divided off, and the fraction of particles having sizes >2 mm and >5 mm in these sub-samples was determined by sieve analysis in the manner described above. Table 1 below compiles the corresponding values.

[0047] For purposes of comparison, compacted potassium chloride granules were produced in the manner and under the conditions described above, with the sole difference that the compacted granules were not sprayed with water.

TABLE-US-00003 TABLE 1 Grain destruction of compacted potassium chloride granules before placement in storage and after withdrawal from storage. Comparative example, no Example with 0.3 wt % applied amount of water applied water Pre-storage grain <5 mm 10.3 wt % <5 mm 7.6 wt % destruction* <2 mm 7.1 wt % <2 mm 4.8 wt % Grain destruction <5 mm 30.3 wt % <5 mm 18.5 wt % on withdrawal <2 mm 17.4 wt % <2 mm 9.4 wt % from storage** *immediately after production, average over 22 samples **after seven days of storage and withdrawal, average over 21 samples

[0048] The advantageous mechanical stability is also retained on transportation. Accordingly, the compacted granules withdrawn from storage were first loaded onto a truck, then transshipped to a transport ship, and subsequently unloaded. During these procedures it was found that the treated compacted granules in comparison to the untreated compacted granules had a more than 2.5 times smaller fraction of particles having grain sizes of below 5 mm.

[0049] The grain stability may also be determined via the abrasion of the compacted granules by means of a drum test, which is based on the procedures described in DIN 51717 or ISO 3271. In this test, particles having grain sizes of below 5 mm are formed as a result of the mechanical load on the compacted granules. The smaller the fraction of particles having grain sizes of below 5 mm or below 2 mm, respectively, the greater the mechanical stability of the compacted granules.

[0050] For this purpose, in each case 2.00.5 kg of the above-described compacted potassium chloride granules, from the fractions having grain sizes in the 10-20 mm range, were placed into a cylindrical drum with horizontal rotatable mounting, the drum having an internal diameter of 500 mm, a width (cylinder height) of 500 mm, and two lifting bars with a height of 80 mm, mounted at an offset of 180 internally on the lateral surface of the cylinder. To subject the compacted granules to mechanical stress, the drum was rotated at 25 rpm for eight minutes (a total of 200 revolutions). The contents of the drum were then sieved in a sieving machine (EML 450 digital plus from Haver & Boecker) for five minutes, onto a sieve having a mesh size of 5 mm, beneath which was a sieve having a mesh size of 2 mm.

[0051] After treatment in the drum, the compacted potassium chloride granules produced in the manner described above and treated with 0.3 wt % of water contained 18.4 wt % of particles having a size of below 5 mm. The compacted potassium chloride granules produced without water treatment, for purposes of comparison, contained 27.8 wt % of particles having a size of below 5 mm, after treatment in the drum.