CS202154B1 - Process for continuous manufacturing liquid np-fertilizers - Google Patents

Description

The present invention provides a process for the continuous production of liquid NP-fertilizers.

Liquid orthophosphate-type NP fertilizers are aqueous solutions of a mixture of ammonium dihydrogen phosphate and dibasic sodium phosphate. They are prepared by neutralizing thermal or extraction trihydrophosphoric acid with gaseous or liquid ammonia, or with an aqueous solution of ammonia. ammonia water. Ammoniacalization of the extractive trihydrophosphoric acid precipitates acid impurities such as Al, Fe, Mg, SiFl in the form of hardly filterable precipitates. The amount of these precipitates and their structure is dependent on the pH and temperature of the reaction mixture, i.e. the way in which the neutralization reaction is conducted. Accordingly, the currently known methods for preparing base NP solutions can be divided into two main groups.

The first group comprises processes in which precipitated impurities are separated to obtain a clear NP solution and the separated precipitate is used as a so-called " sludge fertilizer, or incorporated into solid fertilizers. For this purpose, the neutralization process is conducted so as to obtain a precipitate of the highest filtration rate or sedimentation rate. A two-step process for neutralizing trihydrophosphoric acid with ammonia gas is known (U.S. Pat. No. 3,264,087, Chemical Engineering Progress, Vol. 58, No. 9, September 1962, 89-93), wherein the first stage neutralization is carried out at 103 ° C. to pH 4.2, in the second step at 102 ° C the reaction mixture is neutralized to a final product of pH 6.0-6.6. Continuous sedimentation yields 70% by volume of clear fertilizer and 30% of sludge fertilizer.

The second group comprises processes in which the precipitated impurities do not separate, so that in the true sense of the term an NP-suspension is obtained. In these processes, a product is obtained in which the sedimentation of the precipitate particles is slow and the resulting particles are so fine that they do not impair the fluidity of the product and do not clog the spray nozzles of the applicators. Thus, a two-stage neutralization process is known, in which in the first step the neutralization is carried out to a pH of 7 or higher, in the second step the acid is equalized to a pH of 6.7 whilst adding 1-2% hydrophilic clay with swelling properties. Growth of magnesium ammonium phosphate crystals can be prevented by rapid cooling to normal temperature (Agricultural and Food Chemistry, September-October 1961, 343-348).

Further, processes are known in which various stabilizing additives such as attapulgite, bentonite, lignosulfonates, kaolins are added to the finished NP solution (U.S. Pat. No. 3,179,496, U.S. Pat. No. 3,160,495).

The production method and apparatus for preparing liquid orthophosphate fertilizers are also described in U.S. Pat. 2 969.280. Ammonia water, H3PO4 and process water are fed into the reactor from where the burner solution is pumped off and is fed in two streams to a cooling shower tower cooled by circulating cold water.

A process for producing NP-liquid fertilizer using a tubular reactor is the subject of U.S. Pat. 3 130.033. The reactor consists of two zones, H3PQ4 being added to the first zone and ammonia water to the second. An apparatus and method of cooling is disclosed in which 50-75% of the cooled circulating product is mixed with fresh product. According to U.S. Pat. No. 2,917,380, a liquid fertilizer having a predetermined N - Ρ ₂ Ο ₅ - H ₂ O ratio can be prepared by adding liquid ammonia, phosphoric acid and a mixture of water to a mixing vessel located in the reaction vessel itself; circulating chilled product. The temperature of the reaction mixture is maintained up to a maximum of 71 ° C and at pH 6.85 a liquid fertilizer of 8-24-0 is obtained.

The production methods of this second group, although they allow the preparation of pumpable and storable NP-fertilizers, are relatively demanding in terms of technological equipment, whether it is multi-stage neutralization or stabilizer additive preparation and in some processes a relatively complex system of neutralizing heat removal.

It has now been found that the drawbacks of some of the processes described can be largely eliminated by the continuous production of liquid NP-fertilizers according to the invention.

According to this method of neutralizing ammonia trihydrophosphoric acid, the acid and ammonia are fed into the reaction medium of the mixture and the feedstocks, which are circulated at a rate at least 10 times higher and at most 500 times higher than the H3PO4 feed rate.

It is particularly advantageous to introduce ammonia first into the circulating reaction medium and then H3PO4, thereby achieving a desired pH-value adjustment from a slightly basic region, which has a particularly favorable effect on the sludge-precipitated impurities which are introduced into the reaction medium by extraction trihydrophosphorus. acid.

Under these conditions, using considerably contaminated H 3 PO 4 extraction, a fine, homodisperse, gel-like precipitate is formed which does not impair the rheological properties and pumpability of the NP solution.

The NP solution thus obtained has a long shelf life and the sediment resulting from the slow settling of fine particles of the precipitate of impurities can be easily suspended by mixing it in the reservoir, preferably by means of compressed air. The product thus produced contains at least 8% N and 24% of the total P2O5, of which at least 96-98% of P2O5 is in the horizontal form, its pH is in the range of 6-7.

The production process according to the invention is preferably carried out on a production plant, one of which is shown in FIG. 1. Equipment. it consists of a heat exchanger 1, a product container 2, a circulation pump 3, an ammonia supply 4, a trihydrophosphoric acid supply 5, and a water supply 6.

In the manufacture of orthophosphate-type NP solutions, the reaction mixture is circulated from the reservoir 2 via the circulation pump 3 through the heat exchanger 1 back to the reservoir 2. The suction line of the circulation pump 3 is fed with ammonia in the required amount. respectively. gaseous or as aqueous ammonia solution in the form of so-called. ammonia water. At another point in the circulation pipe, a stream 5 is fed in the desired amount of H 3 PO 4. It has proven to be advantageous to supply trihydrophosphoric acid to the suction line downstream of the ammonia feed point in the flow direction of the NP solution. The neutralization reaction itself takes place in the suction part of the pipeline and further in the circulation pump 3, where it is perfectly homogenized. It is advantageous to use a centrifugal pump for circulation in which a high degree of homogenization is achieved. The process water required to obtain the aqueous NP-solution of the desired concentration can be fed to or into the storage tank 2 or also into the circulation pipe. The amount of feedstocks is regulated according to the pH value and specific gravity of the product.

The following examples illustrate but do not limit the invention in any way.

Example 1

The NP-solution is pumped into the 1501 storage boiler in such a quantity that after the circulation pump is started the piping and condenser are flooded and at the same time the NP-solution level is at the side outlet for the liquid capped product corresponding to a 130 liter volume. NP-solution is circulated by the circulation pump at a rate of 1501 ^min-1 through a heat exchanger cooling the flat 1,5 ^m2. Ammonia water with a concentration of 21.88% NH ₃ , process water and extraction acid H3PO4 with a concentration of 47.42% of the total are metered into the suction part of the pipeline in which the reaction mixture circulates. P ₂ O ₅ and an alkalimetric concentration of 69.55% H 3 PO 4.

Extraction trihydrophosphoric acid was dosed at a rate of 1.5 kg min ^-1 , while ammonia water and process water were dosed so that the pH of the continuously flowing product was in the range of 6-7 and its specific gravity was in the range of 1270 - 1350 kg m ^-3 . During an 8-hour continuous experiment, 1390 kg of liquid N-Fertilizer was prepared containing 8.46% total nitrogen and 24.80% total P2O5, with 97% of the total P2O5 content in water-soluble form. The average pH of the final product was 6.8, the average specific gravity at 20 ° C was 1289 kg m ^<1. . During the experiment, the rate of circulation of the reaction mixture was 127 times greater than the rate of trihydrophic acid dosing.

Example 2

The reaction mixture was circulated from a reservoir volume of 150 1 through a heat exchanger with the cooling area of 1.5 m ² in the tray at a rate of 250 kg ^min-1. To the circulating reaction mixture was fed in a rate of 1 kg min ^-1 extraction of H3PO4 containing 52.87% P2O _5, and according to the pH and specific gravity of the product was adjusted dosing of ammonia gas and process water. During a 6-hour experiment, 770 kg of a base NP-solution containing 8.12% nitrogen and 24.35% total P2O5 were obtained.

Example 3

A pre-prepared NP solution was fed into the volume reservoir 31 and circulated through a condenser with a exchange area of 0.3 m ² . The circulation rate of the reaction mixture was 300 kg h ^-1 . To this circulating reaction mixture, extraction was fed H3PO4 containing 52.08% of P2O5, and corresponding to an amount of ammonia water containing 25% _NH3 and process water. Phosphoric acid was dosed at a rate of 10 kg h ^-1 , so that the rate of the circulating reaction mixture was 30 times greater. After two hours of continuous operation, 41.5 kg of a base NP solution containing 8.4% nitrogen and 24.54% P2O5 were obtained.

Claims (1)

OBJECT OF THE INVENTION Process for the continuous production of liquid NP-fertilizers by neutralizing trihydrogenphosphoric acid with ammonia gas, liquid or in the form of an aqueous solution, characterized in that trihydrogenphosphoric acid and ammonia are fed into a reaction medium consisting of a mixture of product and starting materials circulating at 10 to 500 times higher than the rate of trihydrogenphosphoric acid. ¹