Reasons for large venting in low-pressure systems
Thread Content
For a CO2 stripping urea plant with a capacity of 1,620 tons per day, in the absence of any equipment or instrument failures, what are the reasons for high vent volume in the low-pressure system during normal operation? This design value for the vent volume is very low, and we have never reached it.
The main reasons for the issue raised by the poster are: 1. The stripping efficiency of the high-pressure column is low, resulting in a heavy load on the low-pressure system. 2. The heat exchange area of the low-pressure ammonium methanate condenser is relatively small, given the condensation load. 3. The system is operating under overload, and the low-pressure ammonium methoxide condenser has limited condensation capacity. 4. Scaling in the low-pressure water system reduces heat exchange efficiency. For other reasons, please have experts add them.
Reply to 2# lxq700918: I would like to ask: Is it a decrease in stripping efficiency and an increase in the load on the low-pressure system that lead to an increase in the amount of water returning to the high-pressure system, thereby raising the water-to-carbon ratio in that system?； Or are other factors responsible for the increase in the water-to-carbon ratio, thereby affecting the stripping efficiency?
Additional information: The system load is around 100%, the components of the high-pressure system are normal, the stripping efficiency is 81%. The flow rate of water used for temperature regulation in the low-pressure ammonium methoxide condenser is 950 m3/h, with a temperature difference of 9°C. The exit temperature of the circulating cooler in the low-pressure absorber is 58°C, giving a temperature difference of 20°C between the inlet and outlet temperatures. There are no other faults with the equipment. The speed of the high-pressure ammonium pump is 68–70 rpm, so the water volume in the system should not be large.
The main issue is the poor stripping efficiency; although the system is operating at 100% load, there may be design defects. Additionally, the poor heat exchange performance of the ammonium methylate condenser is also a key factor.
May I ask what temperature difference can typically be achieved with low-pressure temperature control water? Can the vent rate of the low-pressure system be reduced to 23 kg/h as designed? It seems that the low-pressure vent volume of the CO2 stripping unit is on the high side.
Based on the questions raised by the original poster regarding floors 1, 4, and 6, I have the following points for reference: 1. If I remember correctly, according to the original design, the flow rate of the water used for cooling should be around 1200. 2. Also, if my memory is accurate, in the original design the return flow rate of the methamine pump under a load of 100 is 32; however, due to the influence of the system’s water volume (the control value is definitely higher than the designed value), this value is usually around 34. Under such conditions, the pump’s rotational speed should be around 93–95 revolutions per minute. 3. As can be seen from the original poster’s data, the issue of temperature requires further consideration. In fact, the question raised by the original poster seems simple on the surface, but it actually has a deep meaning. Really. In the 13 sets of 1620-ton processes, it is said that several units manage the recycled stream effectively within the high-pressure system, resulting in a lower load on the low-pressure system; this is reflected in aspects such as the pressure in the low-pressure system, the heat load on the low-temperature cooler, the control temperature of the low-pressure water, and the rotation speed of the methamine pump. These are precisely the areas that we need to study and learn about. Due to the nature of my work, I have not had the opportunity to conduct on-site studies to see firsthand the actual operation data of these systems. I would be extremely grateful if the post owner and other experts could help me obtain 24-hour data reports (records from the control room) I also hope the original poster and other users can offer help. Another point concerns the amount of water in the system. I recall that there was a dedicated thread in the past discussing the impact of this water volume on the system. Everyone is aware of this issue, but its effects are not very obvious. Therefore, it is recommended that the original poster refer to points 1.2 above and increase the flow rate of the low-pressure water appropriately (in my setup, it’s 1300). It’s also advisable to increase the amount of water absorbed at low pressure (currently, the return water flow at medium pressure in my setup is around 6, while that at high pressure is around 10; the speed of the methamine pump is around 95–98 revolutions per minute, with the flow rate indicated by the instruments being around 34). There are also links to the two previous posts that focused on water volume issues; I hope they will be helpful to Wang Lihaiyou and the original poster: Hai Na Chuan River: Determining a high water-carbon ratio, http://bbs.hcbbs.com/thread-604726-1-1.html Ruoyan: The impact of water-carbon ratio on the temperature of synthesis towers, http://bbs.hcbbs.com/thread-597438-1-2.html Note: I didn’t specify the units for the data mentioned above while editing; I believe my friends will understand! Please forgive me!