Vertical one pass (VOP) heat exchangers are commonly applied in urea plants. As the residence time in these heat exchangers is small, unwanted side reactions like biuret formation and hydrolysis of urea are limited. However, some phenomena can limit or reduce the performance of these heat exchangers e.g. bad distribution of the the inlet liquid/gas mixture over the tubes.
Technical discussions on urea plant issues and operating problems, sharing experiences, providing advice and solutions. This compilation series covers Problem No. 1 to Problem No. 50.
Most urea plants operate a two-stage evaporator section. Both stages operate under vacuum pressure conditions and both pressures and temperatures are critical to achieve the right urea product quality. It is not always easy to determine the exact cause of non-optimum values for certain process parameters like, for example, low vacuum pressure in the second stage evaporator. Many factors can influence this vacuum pressure as discussed below.
The CO2 compressor of the urea plant is an expensive piece of critical rotating equipment installed without any spare position. Its reliability is therefore of prime importance. Sometimes reverse rotation occurs which can damage the internals of the compressor. What are the causes and what are the remedies to avoid reverse rotation of the CO2 compressor? There is a lot of misunderstanding around this subject. Here we share the experiences of various end users.
There is a lot of misunderstanding about the purpose and functioning of the seal systems (stuffing box) of the high pressure (HP) ammonia and HP carbamate reciprocating pumps. Some believe that lubrication is the main purpose, while others feel it is all about sealing. Both views are partly true. This article features experiences from various end users.
This discussion is about the risks of active corrosion or failure of passivation during a blocking-in situation of the high pressure synthesis section of the urea plant. It touches on many aspects searching for a possible cause of active corrosion during such a situation. The final outcome is of significant importance for all urea plants worldwide.
A discussion about CO2 coolers in the inter stages of CO2 compressors and the problems that can occur after the third stage when cooling water is on the shell side and the CO2 is on the tubes side.
In the case of a failure in a urea plant, when the problem is expected to be solved within a short period, the high pressure synthesis section is typically blocked in (referred to in this article as reactor hold up). All input and output streams are closed and the synthesis section remains partly filled with a solution consisting of ammonia, CO2, water, ammonium carbamate and of course urea. Several risks can occur during this blocked in situation.
A discussion about the high-pressure CO2 stripper and how to solve the problem of a high temperature in the bottom of the stripper.
Dust formation in the granulator can adversely affect stream time. There are several reasons for increased dust in the fluid bed granulator. No formaldehyde or less formaldehyde injection, lower bed level in the granulator, lower concentration of urea melt to the granulator, a higher pressure in atomisation (sprayer) air and a higher pressure in the urea melt header are all factors which can play a role. This article discusses increased dust level and its causes.