Questions regarding urea granulation – please ask industry experts for answers
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Our factory has two urea production systems using the carbon dioxide stripping method, each with an annual capacity of 150,000 tons; together they have an annual capacity of 300,000 tons, although the actual production capacity is 400,000 tons. The two systems share one upper tower pipeline. Recently, some strange problems have arisen in the evaporation section. During normal production, the vacuum level and temperature are within normal ranges, as are the moisture content and biuret levels of the finished product. However, during the granulation process, small clumps of particles form (several particles sticking together). The temperature of these particles ranges from 40 to 60 degrees Celsius. The ventilation in the top of the granulation tower is normal (the tower was just cleaned after being shut down); it uses fixed louvers. The ventilation at the bottom of the tower is also normal (our bottom vents consist of two layers – the upper layer has two door-style vents that can be opened and closed freely, while the lower layer uses fixed louvers). The nozzles operate at atmospheric pressure, with the frequency control set around 10.0 Hz. When particle clumping occurs, we often adjust the frequency to around 12 Hz for 10 minutes before returning it to 10.0 Hz, which helps improve the situation; or we reduce the frequency from 10.0 Hz to 9.5 Hz or even lower, which also helps. But the problem reoccurs after about 2 hours. The same issue occurs when a single system is in operation. Our granulation tower is 96 meters high and 19 meters in diameter, and it is located in Jiangsu Province. What could be the cause of this problem? We hope experts can help us figure it out!@
The sticking of urea particles is mainly caused by a change in the trajectory of the urea solution after it leaves the nozzle, as well as by droplet collisions. It’s likely that the nozzle is dirty; it is recommended to clean the nozzle when possible and check whether its holes are smooth.
May I ask the original poster: when your nozzles use variable frequency speed control, what is the rotation rate in revolutions per minute at 1 hertz? The frequency conversion is around 10.0 Hz, which seems a bit low. However, to understand the reason, it is necessary to know the following details; please provide further clarification, OP: 1. How long has this been going on? Did it appear recently? Will it stay like this forever? 2. Is your granulation tower naturally ventilated? Or forced ventilation?
The nozzle is blocked by impurities or crystals; this phenomenon occurs frequently in our factory as well. Cleaning the nozzle will solve the problem.
First, check whether the nozzle speed is stable and whether there are fluctuations in the frequency converter Next, check if the nozzle is dirty Recheck whether the dynamic balance has been lost (the rotor is bent)? All of these can cause the particles to deviate from the designed parabola, leading to collisions and sticking together
Loss of dynamic balance (the rotor is bent); this is something we haven’t paid attention to all along
Our granulation tower is naturally ventilated. The second-phase system was successfully put into operation in December 2007, and after the two systems were combined, the quality of the particles remained excellent, with high-quality products being produced in almost every batch. Last November, during maintenance work on the second-phase system, we also modified the U-tubes in both stages; we increased their height and thickness. Since then, the operation of the second-phase system has not been as stable as before the modifications, and the quality of the particles has been inconsistent. It’s a real headache...
Zhouhang20, Haiyou: From what you described on the 9th floor, it seems that the \"modification of the U-shaped tubes in sections 1 and 2\" during your major repairs has nothing to do with \"several particles sticking together\", right? Let’s ask zhouhang20 from Haiyou about one more thing: Is the material flow in the evaporation system steady? If the material feed is unstable, it may result in variable amounts of molten urea reaching the granulation nozzles; when the amount is high, it is possible for several particles to stick together.
Production has taken place in a CO2 stripping urine unit with a capacity of 1,740 tons per day; the tower’s net height is 53 meters and its diameter is 20 meters. At that time, the load was usually high, the temperature was high, ventilation was poor, and the speed of the nozzles was low, which led to the formation of sticky particles – three or four particles sticking together. It is recommended that you check the speed of the nozzles, remove them and use a tachometer to measure their actual speed, so as to adjust the frequency converter accordingly. The ventilation volume also needs to be checked. If the nozzles are blocked, it is most likely due to an excess of powder and fine particles. Are you from Zhangjiagang in the urea industry?
In terms of the height and diameter of the granulation tower, they are more than sufficient to meet the requirements for granulation. It is likely that there is blockage in the nozzles; moreover, since a variable speed system is being used, it is important to ensure that it is compatible with the nozzles!!