The urea reactor is one of the critical high pressure equipment in a urea plants; Different types of liners are used in urea reactors according to process conditions such as pressure temperature, N/C ratio and passivation. 2RE69 (25/22/2) is now used in urea reactors in stripping processes. The duplex stainless steel is also used in Stamicarbon plant and has great achievements. Duplex stainless steel is an excellent alternative to existing urea grades such as 316L (Urea grade) and Sandvik 2RE69 (25/22/2). Urea reactor is a plug flow type reactor with high conversion. During normal operation of Urea Reactors common overall corrosion can be found on the internals as well as on the corrosion resistant liner on the reactor wall. While corrosion of the internals is not critical to safety. After many years of operations the liner thickness gradually will become less than needed to form an adequate barrier against the corrosive ammonium carbamate. The life time of the reactor of course strongly depends on the material construction materials used for this protective layer. The design of the vessel, construction materials used, as well as the layout of the leak detection system, is to be considered before a re-lining job is undertaken when liner to be changed after 25-30 years of service.
There are generally three main types of urea reactor vessels which are built as follows: solid wall, multi-layer, or multi-wall. Urea synthesis processes have been carried out at relatively high temperatures (160–270 °C) and high pressures (120–250 bar). This paper intends how to increase life of the urea reactor liner and energy saving with low passivation air and high N/C ratios. Ammonia is the noncorrosive and the ammonia to CO2 Ratio is an important parameter for process optimization occurring less losses and less explosion probability in urea reactor because it affects the amount of produced urea and corrosion to the material in the reactor.
Corrosion or erosion is particularly caused in urea reactors by contact with solutions of ammonium carbamate at the high temperatures and pressures necessary for the synthesis of urea. There are numerous metals and alloys capable of withstanding for sufficiently long periods, the potentially corrosive conditions arising inside a synthesis reactor of urea. In recent years, considerable progress has been made in research of urea reactor liner and there is an increase in the production of urea by reducing the liner leakage and fewer shut downs have been observed throughout the world. Generally we are using urea reactor liner 316L (urea grade) now adopted 2RE69 for large capacity plant (world largest) and Duplex stainless steel.