Actual amount of ammonia reflux at the top of the absorber (full circulation of aqueous solution)

In practice, the reading on the flow meter serves mainly as a reference; what’s important is to adjust the amount of ammonia returning to the top in order to maintain an appropriate thermal balance within the absorption tower. It isn’t crucial whether the flow meter’s reading matches the actual consumption. Of course, this must be ensured: when the control valve is opened wider, the flow meter reading must also increase accordingly ； Conversely, as the control valve is closed, the flow meter reading must decrease accordingly. As long as this condition is met, the needs of actual production can be satisfied. If the temperature in the refining section is high, the amount of ammonia returned to the top will be increased appropriately; this will certainly increase the load on the ammonia condenser, but it is an inevitable measure. Therefore, in actual production, it is necessary to strengthen the control at the front-end components such as the suction cooler, and try to prevent the load from shifting backward; otherwise, it will be more difficult to carry out control.

In the current urea production process, an external cooler has been added to the first-stage absorption section; the temperature of this absorption tower is easy to control. The amount of ammonia used for reflux has decreased significantly, which reduces the load on the ammonia cooler. Occasional fluctuations in the system occur, and increasing the amount of ammonia used for reflux helps to control the temperature at the top of the first-stage absorption tower. A slight increase in the load on the ammonia cooler does not have any impact on production.

““The temperature in the refining section is too high; the ammonia returning back will evaporate into gaseous ammonia, thereby increasing the load on the ammonia condenser.” – Yes, it’s similar to the bottom of a distillation tower; the higher the temperature at the bottom of the tower, the greater the amount of ammonia that needs to be returned from the top of the tower, which in turn increases the load on the tower and raises energy consumption.

It is not important whether the flow rate of ammonia returning to the top of the absorption tower, as indicated by the flow meter, matches the actual amount used; what matters is how to keep the temperature in the purification section within the specified range. If the temperature in this section is too high, the ammonia returning will vaporize into gaseous ammonia, thereby increasing the load on the ammonia condenser. If the high temperature in the polishing section is caused by the temperature in the bubbling section, the amount of ammonia used in the pipeline of the ammonia reflux flow meter at the tower top is not sufficient; it is necessary to increase the flow of ammonia through the bypass line for bottom reflux. The reflux ammonia will evaporate into gaseous ammonia, causing the pressure inside the absorption tower to rise. Sometimes, the reflux ammonia and ammonia solution fail to enter and instead flow back, which can more seriously block the pipes for these substances.