A method of obtaining a granulated urea

 

(57) Abstract:

The invention relates to a method for producing granulated urea, which solves the problem of removing moisture in the method column of the granulation and the problem of concentration of dilute formaldehyde by granulation method using a fluidized bed or a fluidized bed spouted bed when urea granularit in the presence of formaldehyde, i.e., this invention provides a method of obtaining a granulated urea from the drops of liquid or sprayed droplets of the urea solution in which the urea solution is divided into two parts: solution a and solution B, and use the urea solution obtained by mixing an aqueous solution of formaldehyde with urea solution A, the concentration of the specified mixed solution and then mixing it with a solution of urea B. the Molar ratio of urea to formaldehyde is from 0.5 or more, and mixing and concentration is carried out at pH 5 or more. The resulting product has a crushing strength of 25 to 35 N - 2.7 mm and contains 0.2 wt.% water. 2 C.p. f-crystals, 1 Il.

The invention relates to a method for producing granular urea from liquid droplets or atomized is oznachaet General term related to molten urea and water solution of urea.

There are various ways to obtain granulated urea. Commonly used method column granulation and method using a fluidized bed, resulting in a strong stream, and flowing fluidized bed.

In the method column granulating an aqueous solution of urea containing from 0.1 to 0.3% moisture, makes you fall from the top of column granulation in the form of liquid droplets, and the falling liquid droplets are cooled and hardened by contact with an ascending stream of air coming from the bottom of the column granulation, resulting in the formation of particles of urea, which are called granules.

The urea granules obtained in this way have a relatively small size (from 0.5 to 2.5 mm) and have low mechanical strength.

The method using the jetting fluidized bed is used to obtain pellets, which is larger than the pellet obtained by way of column granulation, and has high mechanical strength, and this method is specifically described in U.S. patent 4219589 the fir liquid drops are served in the fluidized bed, in which dissipate the flowing layer containing the seed granules of urea for the buildup of urea solution on the seed particles of urea, followed by drying and solidification, resulting in a gain of urea granules of large size.

As described in the U.S. patents 3067177 and 3112343 and JP-B-50-34536, it is well known that these methods of obtaining granulated urea using fluid spouted bed in the urea solution contribute additive to improve the mechanical strength and resistance to coagulation of the product granules of urea to the large size and efficiency of the granulation, i.e., to reduce the proportion of loss of part of the urea solution in the form of very fine dust without use for the formation of granules during granulation. This additive is an aqueous solution of formaldehyde or a reaction product of the urea/formaldehyde (commercially available under the trade name of, for example, Formurea 80).

In the process of obtaining granulated urea way speaker granulation, it is essential to remove the moisture in the stages. Mechanical strength and resistance to coagulation of the formed granules of urea can be improved by adding from 0.3 to 0t to add a large amount of water in the urea together with him, since the content of formaldehyde in an aqueous solution of formaldehyde is usually from 30 to 37 wt.%, and it contains a large amount of water. This increases the moisture content in the formed granules of urea and in turn improves their quality. Therefore, an aqueous solution of formaldehyde cannot be used in method column granulation, where moisture cannot be removed at all stages of the process.

On the other hand, in the method of producing urea granules large size using fluid spouted bed has the ability to some extent to evaporate the moisture in the granulating apparatus. However, when the moisture contained in excess evaporative capacity of the staff of the granulation, for example when a more dilute aqueous solution of formaldehyde than that assumed in the design, cannot be used, the water content in the mixture of urea and formaldehyde can be reduced to the specified level or below before inserting it in the granulating device.

As described above, the aqueous formaldehyde solution usually contains from 30 to 37 wt. % formaldehyde and, therefore, contains large quantities of the t to the deterioration of the stability of an aqueous solution of formaldehyde and the deposition of polymer of formaldehyde, that, in turn, impedes the flow of formaldehyde in a pre-calculated amount.

Meanwhile, in the methods of granulation, are not capable of drying in the granulating apparatus, such as a method of granulating canovaro type and method of granulating drum, you should avoid water contact. In such ways granulating an aqueous solution of formaldehyde cannot be used as it is in the method column granulation.

The object of this invention is the provision of means for solving the problem of removing moisture in the method column granulation and problems concentrating dilute aqueous solution of formaldehyde by granulation by means of a method using a fluidized bed spouted bed when urea granularit in the presence of formaldehyde.

That is, this invention relates to a method for producing a granulated urea from the drops of liquid or sprayed droplets of the urea solution in which the urea solution is divided into two parts: the urea solution And another solution of urea B, and use the urea solution obtained by mixing an aqueous solution of formaldehyde with rest is B; the method of production of granulated urea, as described above, in which the number specified urea solution A is controlled to 0.5 or more, based on the amount of formaldehyde added to the urea solution from the point of view molar ratio of urea/formaldehyde; and the method of production of granulated urea, as described above, in which the pH was adjusted to 6.5 or more, when the above urea solution A is mixed with an aqueous solution of formaldehyde and mixing the solution concentrate.

In other words, the invention provides a method of obtaining a granulated urea from the drops of liquid or sprayed droplets of the urea solution, which includes a stage of separation of the urea solution into two parts A and B, mixing parts A c aqueous solution of formaldehyde, the concentration of the mixture and mixing the concentrated solution A with part B and then granulating the mixture of A and B.

Preferably the part A is mixed with an aqueous solution of formaldehyde at a molar ratio of urea parts A to formaldehyde in the range from 0.5 or more.

Preferably the mixing part A with an aqueous solution of formaldehyde and concentration is carried out at a pH value of 6.5 or more.

The urea solution prior to feeding into the granulating device 5 is divided into a solution of urea and A urea solution B, and, as will be described below, the urea solution B is mixed with A solution of urea, which return again, and injected into the granulating device through the line 11.

The urea solution A is loaded into the mixer 1 through the line 12. In the mixer 1 is injected aqueous solution of formaldehyde on line 13 and ammonia on line 14, respectively. In the mixer 1, the urea solution is homogeneous mixed with formaldehyde and, if necessary, urea interacts with formaldehyde. The conditions of this reaction will be described below. The resulting mixture ransversal on line 11, mixed with the urea solution B and sent to the granulating device 5.

The quantity of urea solution A is determined so that the added amount of formaldehyde ranged from 0.3 to 0.6 wt.%, based on the amount of urea submitted to the granulating device 5, and the ratio of the urea contained in the mixer 1, the above quantity of formaldehyde was 0.5 or more from the viewpoint of the molar ratio of urea/formaldehyde. That is, the mass ratio A/T quantity of urea solution A to the total amount of urea T is yingfa y-n.2af, where f represents the mass ratio of the quantity of formaldehyde/total number of urea", and represents the molar ratio of the quantity of a solution of A urea/formaldehyde".

The molar ratio is less than 0.5 leads to the increase of the molar ratio of formaldehyde to urea and the formation of polymer of urea and formaldehyde.

If the molar ratio increases more than necessary, for example to 5.0 or more, the number of heated urea increases more than necessary, when the mixture of urea and formaldehyde heated and used in the form of the product of the interaction of urea and formal situations, the amount of the urea solution A is very small compared with the total amount of urea.

The solution of A urea and formaldehyde in a sufficiently improves the mechanical strength and resistance to coagulation of the product granules of urea is large in size, only mixing and concentration (divided the urea solutions can be heated and they can interact at a time when they are reunited and enter the granulating device 5). However, as will be described later, they are more preferably communicate in advance to such an extent that the polymerization does not proceed (hereinafter referred to as a mixed solution of A urea and formaldehyde, and the reaction solution is called the mixed solutions).

In the reaction of urea with formaldehyde at lower values of pH of the mixed solution and at higher temperatures the polymer of urea and formaldehyde is formed more easily. To prevent the formation of this polymer preferably pH is maintained at 6.5 or above by supplying gaseous ammonia or aqueous ammonia. pH less than 6.5 leads to the formation of a polymer of urea and formaldehyde and increases the rate of polymerization even if the reaction temperature is kept low. Accordingly, the polymer is formed before kontsentrirovanie the reaction and increases the amount of formaldehyde, which does not react with urea. In addition, when heated at the stage of concentration of formaldehyde in the evaporation proceeds in the gas phase, and consumed more formaldehyde to provide the amount of formaldehyde, based on pre-calculated amount of urea. Moreover, there are problems lie in the fact that the consumed amount of ammonia is increased more than necessary, and the smell of ammonia is harmful for the health, so the pH must be limited to a value less than 9.5.

The reaction of urea, formaldehyde and ammonia is an exothermic reaction, and the temperature of the mixed fluid rises due to the heat of reaction. Accordingly, the heat must be dissipated via the cooling water. This removal of heat to maintain the right temperature is important to prevent polymer formation. That is, the temperature of the reaction support is preferably in the range of from 40 to 100oC at a pH of 6.5 or higher. Temperature below 40oC reduces the reaction rate and the temperature exceeding 100oC leads to the formation of polymer in some cases, before the concentration.

Shmesani removal of the water from the mixed solution of the evaporator 2 is fed by warm, required for evaporation, by means of steam. The operating pressure is preferably controlled to a vacuum of this magnitude, so that the solution temperature did not rise in the heating process. The vacuum produced by the vacuum pump 4, which is located below the vacuum of the condenser 3. Water vapor evaporated from the evaporator 2, served in a vacuum condenser 3 through the line 17 to cool the condensing water and discharged from the system.

On the other hand, the mixed solution, concentrated to a predetermined concentration, and return again in the urea solution in line 11 through line 16 and is mixed with the urea solution B. Then it is served in a device for granulating to obtain granulated urea.

The present invention before it is entered into the device granulating part of the urea solution is given in the form of urea solution A and mixed with an aqueous solution of formaldehyde. Then the mixed solution is concentrated and used again to obtain granulated urea together with the remaining urea solution B. Accordingly granulated urea can be obtained without increasing the amount of moisture contained in the product. The urea solution A, allotted illegal, and, therefore, the polymerization caused by the heating and concentration, controlled. As the solution of A urea interacts with formaldehyde at a pH of 6.5 or above, polymerization is suppressed.

In this invention a portion of the urea solution is given in the form of urea solution before a granulating device. It adds formaldehyde, and the resulting mixture is concentrated and mixed again with the remaining urea solution B to obtain a granulated urea. Accordingly, as the source of formaldehyde can be used diluted aqueous solution of formaldehyde.

The urea solution A, which is diverted from the urea solution is controlled to obtain a molar ratio of urea/formaldehyde at 0.5 or more, and therefore, the polymerization in the process of heating and concentrating unlikely.

The urea solution A communicates with formaldehyde at a pH of 6.5 or higher, and, consequently, the operation of concentration is possible, while the polymerization of urea with formaldehyde prevented.

In addition, urea, subjected to heat, can be controlled to a very small number compared to all the MSA in the product, can be neglected.

Example 1. In the device for producing urea capacity 41,667 kg/HR of urea solution with A speed of 417 kg/h away from the urea solution coming in the granulating device 5 (device granulation with fluid flowing layer described in JP-B-4-63729), and fed into the mixer 1 through line 12. In addition, the mixer 1 through line 13 with the speed 694 kg/hour serves aqueous solution of formaldehyde (formalin), containing 30 wt. % formaldehyde, so that the ratio of urea to formaldehyde is 1. Ammonia at a rate of 10 kg/h is available on line 14 so that the pH in the mixer 1 is approximately 8, and urea interacts with formaldehyde. The heat released in the mixer 1, removed with cooling water to maintain the temperature of the mixed solution in the range from 70 to 75oC.

The mixed solution fed into the evaporator 2 and concentrated to 75% at an operating pressure - absolute pressure of 150 mm Hg and at a temperature of 80oC. Concentration carried out by heating the steam, and the number of required pair is approximately 310 kg/h Water is separated from the mixed solution in the form of steam with the speed of 264 kg/hour, Oh Maldegem, thus obtained, served in the granulating device 5 via line 16, after mixing with the remaining urea solution B. the resulting urea solution containing about 0.5 wt.% formaldehyde, used for the preparation of granulated urea in the granulating device 5.

Thus obtained granulated urea is dried in addition, granulating device 5, the result is granulated urea containing up to 0.2 wt.% water. This product is characterized by high mechanical strength and less damage during transportation. For example, product strength crush strength is 25 to 35 N/a 2.7 mm

Comparative example. The mixer 1 is as in example 1, except that the feed rate of ammonia, mixed with the urea solution A, change from 10 kg/h to 2 kg/hour. Initially, the pH is 8, but is reduced to 6 at the exit of the mixer, and the formed polymer, which makes further work impossible.

Example 2. The procedure described in example 1 is repeated, but change the operating conditions of the evaporator 2: working pressure is the absolute pressure of 120 mm Hg for the concentration of the mixed R the treatment of granulated urea is well known manner, and get granular urea with a water content of 0.3 wt.%. This product has resistance to crushing from 10 to 15 N/a 1.7 mm

1. A method of obtaining a granulated urea big sizes, in which the seed particles of urea diffuse in a fluidized bed or a fluidized bed with flowing layer and the urea solution with the addition of serves in the form of liquid drops or sputtered drops sticking to the bare particles of urea, characterized in that the urea solution is divided into two parts A and B, then part a is mixed with an aqueous solution of formaldehyde, after which the part A is mixed with an aqueous solution of formaldehyde concentrate, followed by mixing the concentrated part A with part B, then the resulting mixture was fed in the form of liquid drops or sputtered drops sticking to the bare particles of urea dispersed in a fluidized bed or a fluidized bed with flowing layer.

2. The method according to p. 1, in which part a is mixed with an aqueous solution of formaldehyde at a molar ratio of urea to formaldehyde of 0.5 or more.

3. The method according to p. 1, in which the mixing part A with an aqueous solution of formaldehyde and the concentration of spending the Sabbath.

 

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FIELD: production of granulated chemical products, such as granulated trotyl preferably extracted from utilizable ammunitions, may be used in chemical, food-processing and other branches of industry.

SUBSTANCE: granulator has disperser, crystallizer including two rotating cooled drums, and granule collector, said parts of granulator being mounted on single frame. Disperser is made in the form of heatable vessel with openings in its bottom part for accommodation of needles. Disperser needles are fixed on cross-members kinematically connected for reciprocation with cam disks arranged in drum end parts. Drums are kinematically engaged with one another through teeth and mounted on inner shafts so as to define cavity for heat-carrier. Granule collector has two feeding vessels mounted on movable platform below drums.

EFFECT: increased efficiency in manufacture of trotyl granules of high strength and friability.

3 cl, 4 dwg

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