New design for improved heat transfer and steam generation
High-pressure (HP) carbamate condensers are vulnerable to chloride stress corrosion, which typically takes place in the tubes in the top tube sheet of the heat exchanger. Traces of chlorides contained in the steam condensate are deposited typically in the capillary gaps between the tube and tube sheet. These chloride stress corrosion cracks can lead to leakages, which will affect the structural integrity of the HP condenser and significantly reduce its lifetime.
The application of Safurex®, a family of corrosion-resistant super duplex stainless steels, eliminates the problem of chloride stress corrosion in HP carbamate condensers.
While carbamate condensers manufactured from traditional austenitic stainless steel materials typically have a lifetime of 20 years, Safurex® allows extending the vessel’s lifetime to about 30 years without plugging.
Advantages of the HP Carbamate Condenser
The main goal of the HP condenser is to condense the vapor from the HP stripper while recovering heat in the form of steam that can be reused in the urea process. Stamicarbon’s design of the HP carbamate condenser is optimized for the highest energy efficiency.
With Safurex® HP carbamate condenser, the following benefits can be achieved:
- Lower operating costs
- Higher reliability and longer equipment lifetime
Improved heat transfer due to thinner walls of Safurex® tubes leads to improved condensation of gaseous ammonia and CO2 on the process side and improved steam generation on the shell side. The resistance of Safurex® material to the chlorides present in the water/steam flow allows lowering the requirements for water treatment.
Stamicarbon’s material and inspection capabilities offer various advantages for HP equipment. Stamicarbon is fully involved in the manufacturing process, including qualification of welders and regular inspections to eliminate possible defects and ensure overall quality above industry standard.
About HP Carbamate Condenser
The HP carbamate condenser is a vertical shell-and-tube type heat exchanger which condenses the ammonia and carbon dioxide vapors stripped out from the urea solution in the HP stripper to form ammonium carbamate.
The carbon dioxide (CO2) feed stream, together with ammonia and CO2 formed by the decomposition of ammonium carbamate in the HP stripper, are sent to the carbamate condenser, where both fresh and recycled ammonia and CO2 continue to react to form ammonium carbamate.
HP Carbamate Condenser for Non-Stamicarbon Plants
The ammonia stripping process uses a kettle-type carbamate condenser in which stripper off-gas and liquid carbamate are mixed. The high-pressure side is within the U-tubes of the vessel. Inside the kettle/shell side, steam condensate is evaporated to control the condensation rate.
The U-tubes were initially produced using 316L-UG stainless steel. Nowadays, 25-22-2 material is used to produce the U-tubes, which is an improvement as it extends the lifetime of the equipment to approximately 20 years (with or without rotating the in- and outlet side during the lifetime of the vessel). The highest corrosion rates of these condensers are found within the gas/liquid inlet side of the tubes due to condensation corrosion.
In 2021 Stamicarbon delivered the first kettle-type condenser manufactured from Safurex® duplex steel with more than 2000 U-tubes. The client can expect a longer lifetime of the equipment due to the Safurex® material, which is resistant to the main types of corrosion found in HP equipment, including condensation corrosion.
Replacement of any HP vessel in urea synthesis is an opportunity to debottleneck the process in a step-wise manner.
Stamicarbon offers process plant assessment before the replacement of the HP equipment to assess what modifications should be addressed in the design of the new vessel.
As a urea technology licensor, Stamicarbon is also able to calculate possible process improvements based on the new configuration of the condenser design and those can be contractually agreed upon as process guarantees.
Most of the vertical HP carbamate condensers are implemented in the plants with the Stamicarbon CO2 stripping process. This means that Stamicarbon can calculate the heat and mass balances of such plants based on an as-is situation and offer a broader set of options for the step-by-step debottlenecking.
Contact us to learn more about the Safurex® HP carbamate condenser or process plant assessments.