NO123565B - - Google Patents

Description

Process for granulating lime nitrogen.

According to the working method that has been used up to now, it is necessary to subject lime nitrogen to a pre-treatment before the actual granulation process and then extensive hydration, as only in this way can a grain with sufficient durability be produced. This hydration is usually carried out in such a way that the required amount of water is appropriately added in several stages, as the moistened material is given the opportunity to react within the individual stages. A certain amount of ammonia evolution cannot be avoided during the hydration. Calculated for nitrogen, this is on the order of 1 per cent and above.

The actual granulation or dry process joins the pre-treatment of the lime nitrogen. The lime nitrogen is moistened in a mixing apparatus with water, lime-nitre-lye, etc. and granulated in a known manner. The amount of moisture required for this is approx. 20 per cent. The produced granules are sieved in a known manner and dried. Use of heating material for drying is approx. 1,000,000 Kcal. per tons of nitrogen. The ammonia evolution that occurs during the drying process amounts, calculated on nitrogen, to l percent and more.

It was now found that by adding urea or urea salts, such as nitrate, phosphate, sulphate, etc., a pre-treatment of the lime nitrogen substance can be omitted, and it can be granulated with significantly smaller amounts of water. Moreover, a considerable simplification of the method is obtained in addition to remarkable economic advantages.

Already 2 percent urea-N, added in solid

form to the untreated lime nitrogen, causes a lowering of the water requirement at graT

zeroing of 25 per cent; at 6 percent urea-N even to only half the amount of water that is normally used. A further lowering of the water requirement is achieved by the simultaneous addition of lime nitrate. Thus, the water demand falls, e.g. at 4% urea-N and 2% nitrate-N to y3 to <1>4 of

the normal value, while at the same time a good shelf life is achieved for the grain.

The addition of urea salts to untreated lime nitrogen has the same effect

proved good. Here the conditions — especially urea nitrate — are even somewhat more favorable than with combinations of urea and

lime nitrate with the same nitrogen concentrations. This additional improvement can be explained by a dissociation of the urea salt, whereby the acid formed neutralizes the free lime and the water thus formed participates in the hydration.

The simultaneous presence of nitrate nitrogen also has a beneficial effect with regard to the fertilizing effect.

According to the new method, the all-so hydration, which is carried out in several steps and is associated with nitrogen loss, can be dispensed with, and the granulation process, which is normally associated with sieve and division aggregates, can take place in a significantly simpler apparatus. The new method does not require more than 20 per cent water, but with the same granulation requirement only 5 to 6 per cent. The dried granules dry strongly already after being in the mixing apparatus. Although an additional drying cannot be completely omitted, the result is a significantly smaller Jørke apparatus. Thereby, the amount of heating material is also greatly reduced. Ammonia release is negligible, as is dicyandiamide formation.

Example 1: 43 parts by weight of lime slaked soda are mixed in a suitable mixing device with 7 parts by weight of urea (equivalent to 6 percent urea-N, calculated on the total weight). After 1 to 2 minutes, sprinkle with 5 parts by weight of water (9 per cent of the total weight), and within 20 to 30 minutes a fine-grained granule forms.

Example 2:

36.5 parts by weight of lime nitrogen are mixed in a suitable mixing device with 5.0 parts by weight of urea (equivalent to 4 per cent of urea-N, calculated on the total weight) and 8.5 parts by weight of lime nitrate (equivalent to 2 per cent of nitrate-N, calculated on the total weight). After 1 to 2 minutes, 3.8 parts by weight of water (7 per cent of the total weight) are injected and within 15-20 minutes a fine-grained granule with the following grain composition is formed:

Example 3: I

50 parts by weight of lime nitrogen are mixed in a suitable mixing device with 11.5 parts by weight of urea nitrate (equivalent to 6 percent urea nitrate-N, calculated on the total weight). After 1 to 2 minutes, inject 3.2 parts by weight of water (5 per cent of the total weight) and in

after 5-10 minutes, a fine-grained granule forms with the same grain composition as in example 2.

Instead of dry urea salts, the moist salts obtained in the centrifuge can also be used, as their water content must be calculated on the total amount of water.

It is already known to mix lime nitrogen with urea nitrate (German patent 304,282) and treat with urea solutions (Swiss patent no. 92,144). In none of these cases does the urea or the urea salt here have the task of replacing the hydration of the lime nitrogen before granulation, as none of these cases involve the production of granulated lime nitrogen. It is in each case surprising that the hydration in the production of granulated lime nitrogen can be omitted by using urea or urea salt. The use of urea or urea salt for dusting the lime nitrogen gives no reason for conclusions which could lead to the hydration in the production of granulated lime nitrogen being replaced by the presence of urea or urea salt.

Claims (1)

Process for granulating lime nitrogen by spraying with water, characterized in that almost hydrate-free lime nitrogen is mixed with urea or urea salts or mixtures containing urea or urea salts and the mixture obtained is then granulated with 2 to 10 percent water, after which the obtained granules possibly dried.