PROCEEDINGS
OF THE TOMSK POLYTECHNIC INSTITUTE
named after S. M. Kirov, holder of the Order of the October Revolution and the Order of the Red Banner of Labor

Vol. 197 1975

RESULTS OF PILOT-INDUSTRIAL STUDIES ON IMPROVING THE PARTICLE SIZE DISTRIBUTION OF AMMONIUM SULFATE

V. M. VITOGIN, N. P. NOZDRINA, A. V. KUZEVANOVA

(Submitted by the scientific seminar of the Department of General Chemical Technology)

In 1965–1966, at the Department of General Chemical Technology, laboratory studies were carried out to examine the effect of microadditives (salts of Mg, Cr, Al, etc.) on the sieve composition of crystalline ammonium sulfate, and a favorable effect of magnesium salts on crystal growth was established.

On the basis of the results of these studies, a technological regime was proposed for obtaining coarse-crystalline ammonium sulfate as applied to the conditions of the sulfate departments of coke-chemical plants.

In order to test this technology under production conditions, in December 1966 tests were carried out at the Kemerovo Coke-Chemical Plant on the crystallization of ammonium sulfate in the presence of an additive—magnesium salt (MgCl$_2$).

The addition of magnesium chloride, calculated as 0.05% (as Mg ion) of solid ammonium sulfate, was fed into all three operating saturators through the circulating-liquor tanks in the form of a solution every hour over a period of 5 h. Samples of crystalline ammonium sulfate were taken from the conveyor belt of the finished product before feeding the additive into the cycle and every 30 min from the moment the first portion of additive was charged (Fig. 1). The sample taken was averaged, dried at a temperature of 102°C, and screened on a +0.25 mm sieve.

The operating regime of the saturators during the tests was kept constant: acidity 5–7%, $t = 60$–62°C.

Fig. 1. Technological scheme of the saturator cycle: 1—saturator, 2—circulating tank, 3—circulating-liquor tank, 4—crystallizer, 5—centrifuge, 6—conveyor; A—place of additive feed, B—sampling point

As a result of the tests it was established:

1. The particle size distribution of ammonium sulfate improves when the microadditive is introduced in the form of MgCl$_2$. Before introduction of the additive, in a sample of solid ammonium sulfate from the conveyor belt, the +0.25 mm fraction amounted to 62.1%; after introduction of the additive, 78.6% (average value).

2. The effect of the microimpurity on crystal growth appears no earlier than 30 min after introduction of the additive.

Table 1

Results of pilot-industrial tests

1. The best results for the particle-size distribution were obtained 30 min after the introduction of the next additive; subsequently the results deteriorate somewhat, probably because a significant portion of the magnesium salt is removed from the cycle with the solid ammonium sulfate and with the brine entering other process lines of the shop.

2. Accumulation of magnesium salt in the mother liquor with an increase in the number of additions evidently does not occur, since the results for the particle-size distribution of ammonium sulfate, on average, remain constant.

3. One and a half hours after the last addition, the effect of $\mathrm{MgCl_2}$ is still reflected in the sieve composition of the ammonium sulfate.

4. Longer tests are necessary to refine the technology for coarsening ammonium sulfate.