The following case study describes a serious incident and the consequences of erroneously mixing nitric acid with hydrochloric acid. In Part 1 we report on the incident and the causes that led up to the event. In part 2 the impact, recommendations and lessons learned will be discussed.
Reverse rotation of an inline four-stage centrifugal CO2 compressor is an unwanted phenomenon which sometimes occurs in urea plants. Reverse rotation can lead to damage to the internals of the CO2 compressor and an expected outage. This discussion shares experiences and provides suggestion on how to avoid reverse rotation of the CO2 compressor.
Green urea is urea based on green ammonia produced from renewable power via electrolysers and bio-based carbon dioxide and its colour is the same as normal urea. But in this round table discussion we discuss the possible causes for urea turning a green colour as found by the initiator of this discussion. We will learn that the colour of urea can be reddish or brownish in certain conditions where corrosion rates are high and/or oil fouling is high. But what can cause urea to turn green? n
In part 5 of this series on stripper efficiency issues we conclude the discussion with a focus on fouling inside stripper tubes.
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.
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.
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.
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.
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.
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.