Any stripping urea plant needs a protection system against overpressure to avoid operating pressures to rise higher than the design pressure of the High Pressure equipment and piping systems. Overpressure can for example occur in the situation that cooling capacity fails while the High Pressure stripper continues to produce strip gasses. All world standards require in such situations a safeguard by means of pressure safety valves.
Although these pressure safety valves are essential for protecting the High Pressure synthesis section against too high pressures, these also have some limitations and cause some troubles. In synthesis sections of a urea plant typically full lift safety valves are applied because of the large blow off volumes. In most situations the safety valves do not close properly anymore after opening. Furthermore SKW has experienced that sometimes a safety valve already fully opens before reaching the set pressure.
Excellent teamwork between SKW, its service partner Räcklebe & Totz, the safety valve manufacturer LESER and with the support of the licensor Stamicarbon, has resulted in an Innovative Safety Solution for Overpressure Protection in the Urea Synthesis section: Safety Valves with Supplementary Loading Systems (SLS) or also defined as Controlled Safety Pressure Relief Systems (CSPRS) according to ISO 4126-5. Pre-conditions are the use of the material SAFUREX® and special proprietary design and construction details.
The paper describes the step by step development and implementation of the Innovative Safety Solution for Overpressure Protection in the Urea Synthesis of SKW Piesteritz in Germany. The following benefits have been achieved: Increased safety & reliability, operating pressure closer to the set pressure of the synthesis safety valve leading to higher conversion figures in the reactor; for the design of new urea plants, the design pressure of the High Pressure equipment items can be reduced leading to lower investment and longer inspection intervals.
This paper has been presented during the Asian Nitrogen & Syngas Conference 2013 in Singapore.