LV13349B - Method for production of nitrate-containing products from undercooling melts - Google Patents

Abstract

The invention concerns a method for the production of nitrate containing products (fertilizers, technical products) from undercooling melts, wherein a XN - water solution is evaporated up to a content of 50-99.8 weight % XN, where X is one or more selected from Ca, Mg, NH4, Na and K, and N means nitrate. The preferred range of XN is 70-99.5 weight %. The melt is cooled down to and kept at a temperature at or below the crystallisation point and finely divided solid XN powder consisting of the equilibrium phases is added to the melt. Melt drops are then formed and allowed to cool and solidify during up to 70 seconds. It is preferred to use a cooling belt for solidification of the particles. The belt is cooled by air, water, oil or another medium.

Description

LV13349 “Method for production of nitrate-containing products from undercooling melts” 5 The invention concems production of nitrate-containing products (fertilizers, technical products) from undercooling melts. Pūre CN (Ca(N03>2 ) melts at 560°C and this very high temperature is inconvenient for particulation. Ih order to use devices like centrifūgai or nozzle prilling equipment or pan/ 10 drum granulators, the CN melt has to have compositions that contain 5-8 weight % ammonium nitrate (AN). Today, ali prilled or granulated CN contains this amount of AN in addition to 14-16 weight % water (crystal water). If the ammonium nitrate content is removed from the melt, the composition undercooles to such an extent that prilling/ granulation is not possible. 15

There is stili a need for QN vvithout AN and it is desirable to find methods to producē CN-water solid easily, in large quantities.

From British Patent No. 392 531 it is known a process for production of distributable and 20 non-caking fertilizers containing calcium nitrate. According to this patent, a calcium nitrate/water solution is evaporated to a sandy-pasty consistency in which it contains about 90-95 weight % calcium nitrate (calculated as anhydrous calcium nitrate). Thereafter the concentrated product is converted vvithout any substantial further concentration, into granular form by mechanical disaggregation in bulk at a temperature 25 of 50-100°C. This method gives salt deposits on equipment and a flaked, dusty product. The method is therefore considered not well suited for large-scale production of CN.

From a CN -water solution CN* 4H2O crystals can be obtained in crystallizadon processes well described in the literature. Such crystals are available in the marķēts. Such 30 crystals contain 69-70 weight % CN, but normally they have a high caking tendency and over time they become hard and difficult to handle. Thus, it is not desirable to make a crystalline material. 2

By mapping the phase diagram (from Gmelin) of the system CN-AN -Water, it has been possible to find a rather narrow melt composition region that can be particulated with ordinary plant equipment and today granulated or prilled CN contains 77-80 weight % CN, 5-8 weight % AN and 15-17 weight % water.

By studying the phase diagram of CN -water (Fig. 1) it can be seen that the following solid compounds can be fonned in the system:

Ca(N03)*4H20

Ca(N03)*3H20

Ca(N03)*2H20

Ca(N03>2

Further, it can be realized that according to the CN- water system, ali CN concentrations above 70 weight % should solidify, meaning that ali liquid should have disappeared at equilibrium if temperature is below 40-43°C. Further, it can be seen that by cooling a CN-water solution with CN less than 70 weight %, CN *4H20 crystals will be fonned. llļfMižjeet of the invention is to obtain a method to producē high quality solid CN-water pārticies easily, in large quantities. Another object is to obtain a production method that could be applied generally for nitrate containing salts that very often tend to form super cooling melts.

These and other objects of the invention are obtained with the method as described below, and the invention is further defined and characterised by the accompanying patent claims.

The invention thus concems a method for the production of nitrate containing products (fertilizers, technical products) from undercooling melts, wherein a XN - water solution is evaporated up to a content of 50-99.8 weight % XN, where X is one or more selected from Ca, Mg, NH4, Na and K, and N means nitrate. The preferred range of XN is 70-99.5 weight %. The melt is cooled down to and ķept at a temperature at or below the crysta!lisation point and finely divided solid XN powder consisting of the equilibrium 3 LV13349 is added to the melt. Melt drops are then formed and allowed to cool and so during up to70 seconds, preferably 20-70 seconds. It is preferred to use a cooling belt for solidification of the pārticies. The belt is cooled by air, water, oil or another medīum. 5 The melt temperatūra is preferably ķept 0-10 °C belo w the crystallization point o f the melt. When calcium nitrate pārticies are produced, CN*2HzO and CN *3H2Ū are used as seed pārticies. The pārticies formed have a particle size between 0,2 and 0,8 mm, preferably between 0,4 and 0,6 mm. Pārticies could be made from a melt consisting of 74 weight % calcium nitrate, 14 weight % potassium nitrate and 12 weight % water. Solid 10 pārticies can also be produced consisting of a homogenous mixture of nitrates, chlorides and crystal water. An example of this is pārticies made from a melt consisting essentially of 50 weight % calcium nitrate, 4 weight % ammonium nitrate, 26.5 weight % calcium chloride and 18-20 weight % water. 15 Several experiments were carried out in order to try to make pārticies of the melts. Examnle 1 -Granules (For comnarison) CN-water Solutions were evaporated to above 70,75 and 78 weight % CN.

The various melts were sprayed onto a rotating laboratory pan granulator containing 20 solid NH-CN (calcium nitrate from Norsk Hydro ASA) in various ratios and at various temperatūras.

None of the trials succeeded as the liquid/melt did not solidify. The whole matrix (solid CN+melt) tumed into a sticky slurry that could not be processed with liquid/solid ratios 25 within acceptable limits.

Examnle 2 - Prills (For comnarison)

Melts with Ihe CN concentrations mentioned above, were ķept at temperatūras close to the 30 crystallization point given by the literatūra. Finely crushed NH-CN were mixed into the melt subsequent to pumping the melt at high pressure to nozzles where drops were formed and allowed to cool down to 20 °C for 5-10 seconds. 4

As cooling raedium oil and air were tried. Solid pārticies did not form due to under -cooling. 5 Example 3 - Making pastilles Trial 1 (For comparison):

Droplets of CN-melts with CN concentrations above 70, 75 and 78 weiģht % pure CN where allowed to cool on a chilled mētai plate down to 10°C for several minūtes. 10 The melt-drops tumed into viscous, sticky liquid, solid pārticies did not form.

Trial 2 (For comparison):

Same procedure as above but now finely divided solid CN powder was added to the melt 15 before setting the droplets on the plate. Solīds of NH-CN and crushed CNMH2O crystals were applied.

The melt-droplets tumed into slurries with no particle strength as they cooled down. 20 Trial 3 (according to the invention): CN melt having 23 weight % water and 77 weight % CN were allowed to cool on a plate for 48 hours at 20°C. A white solid material was formed during this time

Now clearly the melt had tumed into a strong solid material over these 25 hours and X-ray analysis showed that the material consisted of CN*2H20 and CN 3*Η2<λ

However, the solidifying time was too long for a convenient particulation process.

Trial 4a (according to the invention): 30 Same procedure as in trial 1, but now a CN-melt consisting of 23 weiģht % water and 77 weight % CN was cooled down to 50-55°C and 2 vveiģht % crushed material from trial 3 was thoroughly mixed into the melt. 5 LV13349

As the drops cooled, crystals were formed and during 30-70 second hard pastiiles were fonned with particle strength above 1 kg. As tirae passed, particle strength became substantially higher. Pārticies did forra with this procedure and the crucial part of this procedure was obviously to add finely divided solid material consisting of the equilibrium phases of the system at room temperature. (CN*2H20 and CN *3H20)

Trial 4b (according to the invention):

Same procedure as trial 4a but now melt composition was 25 weight %/ 75 weight % and 21.5 weight %/ 78,5 weight % (H20/CaN).

Trial 5 (according to the invention):.

Same procedure as in Trial 4, after reducing the temperature of the melt (23% weight % H20/77% weiģht % CN) to approximately 45°C the finely divided solid material was mixed in as seeding pārticies. As crystals started to form in the beaker, drops were allowed to fall on the cooling plate and simultaneously pure melt (23 weight %/ 77 weight %) with temperature below 50°C was added to the beaker, while stirring.

In this way drops containing solid crystals with the rigjht composition were continuously formed and solidified on the mētai plate just by adding one portion of solid material to make the crystallization stari.

However, 40-70 seconds are too long time for using a granulation or prilling technique with an acceptable recycling ratio.

To use procedure 5 for produdng large quantities of pārticies, a way of obtaining 40-70 second crystallization time was looked for. 6

Example 4 - Makine CN pastilles in industrial scale faccordine to the inventiori)

Experiments were carried out on a moving Steel cooling belt (as described in US patent 5 No. 5326541) that is ķept at a low temperature by using water as cooling aģent. On this belt a rotating drum with nozzles, supply drops that can solidify on the belt. A plant tēst was carried out with CN melt (23 weight %/ 77 weight %).

By using procedure described in “Trial 5”, several hundred kg of CN pārticies (pastilles ) 10 were produced on the cooling belt

Example 5 - Making MeN pastilles (accordine to the inventionl Trial 5 in Example 3 was repeated by replacing CN melt with 1: MgN-water melt having 15 composition 67 weight % MgN and 33 weiģht % H2O (boiling point 180 °C) and 2: MģN-water melt with composition 58 weight % MgN and 42 weight %(boiling point 155°C). Both melt 1 and 2 were cooled down to 30 °C by procedure mentioned in trial 5 (Example 3). Letting composition 1 and 2 solidify in an exsiccator for 3 days, and then crush the solids formed into a fine powder made seeding material. 20

With melt 1 and 2 and the procedure described we obtained MgN*4H20 and MgN *6H20 respectively. MgN*6H20 was made also without seeding material as the MgN*6H20 melt very easily solidified. 25 Example 6- Making pastilles of MeN-AN and CN (accordine to the inventiori) A melt consisting of 67 weigjit % CN, 4.0 weight % AN, 10 weight % MgN and 20 weight % water was held at 110°C. The melt was cooled down to 65°C and seeding material thoroughly mixed in as drops were allowed to fall on a cold mētai plate.

During 60 seconds on the plate hard pastilles were formed . Letting the melt composition crystallize in an exsiccator for 2-3 days and then grinding to a fine powder made seeding material. 30 7 LV13349

Example 7- Mixture of CN. AN and CaCl? (accordine to the inventiori) A melt consisting of 50 vveight % CN, 4 weight % AN, 26.5 vveight % CaCh and 18-20 weight % water was made by melting a mixture of NH-CN and CaCl2*2H20 (130-140°C). 5 By using procedure described in 4 b (seeding material added at 120 °C) nice pārticies were formed within 30 seconds on a cold Steel plate. The pārticies consisted of homogenously solidified CaN-AN CaC^ pārticies. 10 Example 8 - Mixture of CN and KN (accordine to the invention) A melt consisting of 74 weiģht % CN, 14 vveight % KN and 12 vveight % water was made by evaporating vvater from a CN -KN -H2O solution. The melt temperature was reduced to 86°C, app. 5-6 °C above crystaHization point. 3 vveight % finely grained seed material was thoroughly mixed in and droplets allovved falling on to a cold mētai plate 15 (23°C).

During 50-60 seconds hard pastilles/particles formed on the plate.

The right seeding material was made by letting the melt composition crystallise in an 20 exsiccator over 2-3 days and then grind to powder the solid formed.

Thus, by applying: -correct melt or CN-water composition 25 -correct temperature of the melt (at or below cryst. point) -correct seeding material (consits of equilibrium phases of the solidifying material) - a cooling belt or a similar system that allovvs 20-70 seconds or more for crystallization, it has been possible to find a procedure for producing solid CN pārticies (CN+crystal 30 vvater) vvithout AN. The procedure can be applied for making solids of several nitrate systems containing Ca, Mg, K, Na, NH4 or mixtures of these nitrates or mixtures of nitrates and chlorides. 8 LV13349

Patent claims 5 1. Method for the production of nitrate containing products (fertilizers, technical products) from undercooling melts, vvherein a XN - water solution is evaporated up to a content of 50-99.8 vveight % XN, where X is one or more selected from Ca, Mg, NH4, Na and K, N is nitrate, the melt is cooled down to and ķept at a temperature at or below the crystaIlisation point, finely divided solid XN powder consisting of the 10 equilibrium phases is added to the melt, vvhere after melt drops are fonned and allowed to cool and solidify during up to 70 seconds. 2. Method according to claim 1, vvherein the content of XN is 70-99.5 weight %. 15 3. Method according to claim 1, wherein a cooling belt is used for solidificahon of the pārticies. 4. Method according to claim 3, vvherein the belt is cooled by air, water oil or another medium. 20 5. Method according to claim 1, wherein the melt drops are cooled and solidified during 20-70 seconds.

6. Method according to claim 1, wherein the temperature is ķept preferably 0-10°C 25 below starting crystallization point of the melt. 7. Method according to claim 1, wherein calcium nitrate is produced and CN*2H20 and CN *3H20 are used as seed pārticies. 30 8. Method according to claim 1, vvherein pārticies are formed with particle size between 0.2 and 0.8 mm, preferably between 0.4 and 0.6 mm. 9 9. Method according to claim 1, wherein pārticies are made from a melt consisting of 74 weight % calcium nitrate, 14 weight % potassium nitrate and 12 weight % water. - 5 10. Method according to claim 1, wherein solid pārticies consisting of a homogenous

Chemical mixture of nitrates, chlorides and crystal water were produced. 11. Method according to claim 10, wherein solid pārticies are made from a melt consisting essentially of 50 weight % calcium nitrate, 4 weight % ammonium 10 nitrate, 26.5 weight % calcium chloride and 18-20 weight % water. 15 20 25 30 35 LV13349 1/1

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The System Ca(N03)2 - H20

rH &J0

Claims (11)

A process for the preparation of nitrate-containing products (fertilizers, technical products) from refrigeration melts, characterized in that the XN-aqueous solution is evaporated to a content of 5099.8% by weight XN, wherein X is one or more cations selected from Ca, Mg, NH4, Na and Κ, N are nitrate, the melt is cooled and maintained at a temperature corresponding to or below the crystallization temperature, the melt is added with a fine crystalline solid XN powder consisting of droplets, which melt after melting, cooled and hardened in '70 seconds. 2. A process according to claim 1, wherein the XN content is 70-99.5% (w / w). 3. A process according to claim 1, characterized in that a cooling strip is used to solidify the particles. 4. The method of claim 3, wherein the bar (jacket) is cooled with air, water, oil or other media. 5. The method of claim 1, wherein the molten droplets are cooled and solidified within 20-70 seconds. 6. A process according to claim 1, wherein the temperature is maintained, preferably between 0 and 10 ° C, below the temperature at which crystallization begins. 7. A process according to claim 1, wherein the calcium nitrate is obtained and the CN * 2H 2 O and CN * 3H 2 O are used as crystallization centers. 8. A process according to claim 1, characterized in that particles having a particle size of 0.2-0.8 mm, preferably 0.4-0.6 mm, are formed. 9. A process according to claim 1, wherein the particles are obtained from an alloy consisting of 74% by weight of calcium nitrate, 14% by weight of potassium nitrate and 12% by weight of water. 10; Process according to claim 1, characterized in that solid particles consisting of a homogeneous chemical mixture of nitrates, chlorides and crystalline water are obtained. 11. A process according to claim 10, wherein the solid particles are obtained from an alloy consisting essentially of 50% by weight of calcium nitrate, 4% by weight of ammonium nitrate, 26.5% (w / w) calcium chloride and 18-20% (w / w) water.