To produce urea from ammonia (NH3) and carbon dioxide (CO2) using the Stamicarbon CO2 stripping urea technology. Urea finds its application for 90% as fertilizer; further urea is used as base material for the production of resins melamine, as cattle feed, and as a NOx reducing agent “Ad Blue.”
Large urea plants require large high-pressure (HP) equipment that is difficult and costly to manufacture. To reduce costs, Stamicarbon has developed a Mega plant concept for single-line urea plants producing 5,000 metric tpd of urea.
In the Stamicarbon Mega plant concept, a portion of the liquid effluent from the urea reactor is diverted to a medium-pressure (MP) recycling section, thereby reducing the size of the HP vessels needed. Thanks to the Mega plant concept, the size of the required HP equipment and lines will not exceed the size of equipment needed for a 3,500 metric tpd pool condenser type CO2-stripping urea plant. A Mega plant can be built with both the Stamicarbon AVANCORE or the Stamicarbon Urea 2000Plus technology.
About 70% of the urea solution leaving the urea reactor flows to the HP CO2 stripper. The remainder is fed into a MP recirculation section. The reduced liquid feed to the stripper, in turn, reduces not only the size of the stripper, but also the heat exchange area of the pool condenser. The degree of stripping efficiency is adjusted to ensure that as much low-pressure (LP) steam is produced by the carbamate reaction in the pool condenser as is needed in the downstream sections of the plant. bout 30% of the urea solution that leaves the reactor is expanded and enters a gas/liquid separator in a recirculation stage operating at a reduced pressure. After expansion, the urea solution is heated by MP steam. By heating the urea solution, the unconverted carbamate is dissociated into NH3 and CO2.
Stamicarbon’s Mega plant concept does not need the NH3 recycle section or the NH3 hold-up steps that are commonly seen in competitors, total recycle urea plants. This is because the low NH3:CO2 molar ratio in the separated gases allows for easy condensation as carbamate only. The operating pressure in this MP recirculation stage is about 20 bars. After the urea solution leaves the MP dissociation separator, it flows into an adiabatic CO2 stripper, which uses CO2 to strip the solution. As a result of this process, the NH3:CO2 molar ratio in the liquid leaving the MP recirculation section is reduced, thus facilitating the condensation of carbamate gases in the next step. Vapors leaving the MP dissociation separator together with the gases leaving the adiabatic CO2 stripper are condensed on the shell side of the evaporator. The carbamate formed in the LP recirculation stage is also added to the shell side of this evaporator. The heat released by condensation is used to concentrate the urea solution. Further concentration of the urea solution is achieved using LP steam produced in the pool condenser.
The remaining uncondensed NH3 and CO2 leaving the shell side of the evaporator are sent to a MP carbamate condenser. The heat released by condensation in this condenser is dissipated into a tempered cooling water system. This process forms MP carbamate that contains only 20 wt%–22 wt% water. The carbamate is transferred via a HP carbamate pump to the HP scrubber in the urea synthesis section. The urea solution leaving the adiabatic CO2 stripper and the HP stripper are expanded together in the LP recirculation section.
Licensor: Stamicarbon B.V.
