Discussion on the high-tower biuret problem

Analysis of the causes of biuret formation 1 Overview Biuret is a by-product in the urea production process. Melting urea slowly releases NH at high temperatures, resulting in the condensation to form various compounds, the most important of which is dicyandiamide (NH CONHCONH2). Biuret reduces the quality of urea and can burn the leaves and young shoots of plants. 2 Analysis of factors affecting the formation of biuret Urea undergoes a condensation reaction at high temperatures; two molecules of urea reacting with each other yield biuret, while three molecules of urea reacting together produce triuret or cyanuric acid. The reaction equations are as follows: 2CO(NH2)2 → NH2CONHCONH2 + NH3. 2.1 Influence of temperature and urea concentration Figure 1 shows the relationship between the rate of biuret formation in urea solutions and temperature as well as urea concentration. When the urea concentration is constant, the higher the temperature, the greater the formation rate of biuret ； At a constant temperature, the urea biuret formation rate increases as the urea concentration rises. From Figure 1, we can also see that the effect of temperature is much greater than that of concentration. The relationship between the yield of biuret formed and temperature when dry urea is heated at a certain temperature for 1 hour is shown in Figure 2. 2.2 Effect of ammonia partial pressure: From the synthesis reaction equation for biuret, 2CO(NH2): NHCON—HHCONH + NH3, it can be seen that increasing the ammonia content in the urea solution can reduce and inhibit the formation of urea condensates ； Conversely, a decrease in the ammonia partial pressure in the urea solution or urea melt facilitates the formation of biuret. Figure 3 shows the relationship between the biuret formation rate and ammonia partial pressure. As can be seen from Figure 3, the lower the ammonia partial pressure in the solution, the higher the formation rate of biuret ； Conversely, the higher the ammonia partial pressure in the solution, the lower the formation rate of biuret. 2.3 Effect of residence time

It is crucial to properly control the insulation steam for the pipeline leading to the tower, as well as to regulate the liquid level at the inlet of the melting pump.