How to handle a trip of the molten urea pump?

1. Pour material into the pipeline leading to the tower to prevent blockage of that pipeline. 2. Evaporation breaks the vacuum; the urine from the circulation system goes directly into the urine tank, without entering the evaporation system anymore. 3. Dilute the steam condensate entering the evaporation system to prevent pipe blockages. 4. Start the standby melting pump. For any shortcomings, please ask other members to add more.

First: The control system quickly breaks the vacuum to prevent excessive evaporation and crystallization. Second: Supply to the evaporation system is stopped to prevent the separator from filling up and causing liquid to flow into the evaporation condenser. Third: The control system switches the granulation pipeline to circulation mode, promptly notifies the maintenance staff to go to the site to close the outlet valve of the emergency pump, and adds water through the secondary port for displacement, ensuring complete displacement before shutting down the system. Fourth: Start the backup pump to initiate circulation; the urine pump will decide whether to switch to using water based on the temperature of the urine (this can be done simultaneously with step three, but it is necessary to close the outlet valve of the emergency pump first). Fifth: Raise the temperature, create a vacuum, and send the mixture to the granulation unit

The question to ask is: how to prevent reversal?

Reply to 4# cthlj2007: Yes, let’s discuss whether it’s possible to prevent reversal

The pump suddenly stopped functioning properly. Due to the several dozen meters of head in the outlet pipe, the material flowed back into the inlet pipeline and the inlet container. As the material passed through the impeller, it caused the impeller to rotate in the opposite direction, similar to what happens in a hydro turbine. This phenomenon seems inevitable; after rotating in the reverse direction for a while, it appears that the pump can tolerate it without any damage. If there is a backup pump, simply close the outlet valve of the main pump and start the backup pump. If no such backup is available, opening the discharge valve at the pump outlet can also prevent reverse rotation. Of course, it is also necessary to break the vacuum, flush out the liquid to avoid blockages, and then inspect and repair the pump.

Previously, the impeller would reverse rotation after the pump stopped operating, resulting in damage to the pump when it was tried to restart; now it is stipulated that the pump must not be restarted after it stops operating, which causes inconvenience in operation. I would like to ask everyone: based on actual production experience, is it permissible to start this pump immediately after it shuts down? Does this kind of operation increase the likelihood of damaging the pump?

Why has the melt pump in our system never reversed when it shuts down? I have a question: was the position of the second vaporization stage set too low during the design? Does this cause an excessive height difference between the granulation tower and it, resulting in reversal? To be honest, I’ve really never seen a melt pump reverse its direction after tripping. And also. Don’t your motors have overload protection? After all our pumps trip, we must contact an electrician to reset them before they can be restarted. Furthermore, when dealing with the shutdown of the melt pump, the circulation hardly operates at all. The standby pump is started to deliver fluid; steam is then used to displace the faulty pump, after which the faulty pump is shut off. Finally, the condensate is used for cleaning, and the task is handed over to the mechanical technicians and electricians. (In our small unit, the operational requirements aren’t strict.) Although this will affect the particles, the amount is very small, so there’s no need to worry. ）

Reply to 8# fang1st: The pump is on the 1st floor, with a flow rate of 50~60 m3/h. Given that the outlet pressure of the molten urea pump in the urea plant is relatively high and there is no check valve at the outlet, it can be said that the pump will reverse direction whenever the system shuts down. It’s just that due to the different pressures and flow rates of urine in the pipes, the degree of reversal varies. In small and medium-sized urea plants, the amount of urine in the pipes is low, and the reversal time after a shutdown is short, so it may be difficult to detect. Regarding motor protection, if the machine stops operating due to a protection action, it certainly cannot be used again ； In the past, the train would be started immediately in case of a power fluctuation causing it to derail, but that is no longer allowed either.

That’s more or less the same; our pump has a capacity of 48 m3/H. The granulation height of the granulation tower should be around 80 M, while the outlet height of the pump is 0.7 M. I once watched it jump off with my own eyes, and I also stopped it once because the mechanical seal caught fire. It simply didn’t reverse. Does the pump have a unique design to prevent reverse rotation?

Reply 1# htcfkq: The melt pump can be reversed! ! During design, in the event of an emergency with the melting pump (such as power loss or pump failure), the material in the pipeline leading to the upper tower is directed back to the second stage of evaporation, which helps to prevent blockages in that pipeline over long distances. If the melt pump fails and a backup pump is available, it will not have a significant impact on production. Handling principle: No discharge, prevent blockage. If neither pump can operate, then there is no choice but to shut down the system! ! The evaporation process is also simple: water is added (which is a safer approach), and the material must be thoroughly diluted through evaporation before it can be discharged directly; otherwise, blockages are likely to occur.