Market Insight
Market Insight courtesy of Argus Media
Tag: Urea
Problem No. 57: Higher moisture content in urea melt due to vacuum pressure issues
A discussion on the effect of vacuum pressure issues on the moisture content of urea prills. As the absolute pressure increases (lower vacuum) the urea melt concentration decreases in concentration (water content % increases). However there are also other causes of high moisture content in the urea melt as mentioned in this discussion.
Problem No. 56: Oil fouling from ammonia plant
One of the most important control parameters in urea plant operation is the synthesis pressure and a sharp increase of this pressure is very dangerous for the urea plant. One cause for an increase of the synthesis pressure is oil contamination in the urea process which causes many abnormal variations in many sections of the plant. This problem can be recognised by taking a sample from the ammonia feed and observing the colour change of the urea product. These samples and observations can prevent much confusion in determining the cause of the problem.
Problem No. 55 How to clean heaters
Heat exchanger tubes in heaters in a urea plant such as the high pressure stripper and medium pressure and low pressure recirculation heaters typically suffer from process-side fouling. This discussion looks at best ways to clean these heaters.
Problem No. 54: High efficiency trays for the urea reactor
The main reasons for the installation of high efficiency trays (HET) in a urea reactor are: 1) to improve the redistribution of unreacted carbon dioxide inside the liquid phase rich in free ammonia, 2) to reduce the back mixing phenomena due to the density increase of carbamate and urea solution from the bottom to the top of the reactor and 3) to reduce channelling which has a negative effect on the solution residence time.
Problem No. 53: Restriction orifices in VOP exchangers and their influence on biuret formation
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.
Problem No. 52: High nickel content in high pressure urea synthesis
This discussion focuses on nickel content as an indicator of local active corrosion in a urea plant. In order to have an indication of what is going on in the urea plant it is important to look at trends.
Problem No. 51: Restriction orifices in VOP exchangers
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.
Problem No. 50: Low vacuum pressure in the second-stage evaporator
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.
Problem No. 49: Reverse rotation of CO₂ compressor
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.