For maximum lifetime and optimal performance

The high-pressure (HP) stripper is a vertical two-phase falling-film heat exchanger and is the key piece of equipment in Stamicarbon’s urea stripping process. From the reactor, urea solution is sent to the stripper, where carbamate from the urea solution is broken down into ammonia and carbon dioxide (CO₂), increasing urea concentration. 

The urea solution flows by gravity to the bottom of the stripper via heat exchanger tubes and comes in contact with CO₂ flowing counter-currently, while high-pressure steam is supplied on the shell side of the tubes. After the CO₂ stripping process, the resulting urea solution continues to the downstream sections of the plant while the off-gases are recycled back into the synthesis. 

The challenge 

The lifetime of the HP equipment is determined by the corrosion rate specific to the process conditions in each vessel. But corrosion caused by the ammonium carbamate solution is the most severe in the HP stripper, particularly in heat exchanger tubes. 

HP stripper is a vessel critical to urea synthesis and carbamate stripping, and its customized design and fabrication are even more critical when replacing equipment in an older plant.

To achieve optimal performance and maximum lifetime of equipment, Stamicarbon offers Safurex^® strippers made of a range of specialty materials developed for use in the urea process (Infinity^∞, Degree°, Star*). 

Our solution: Safurex^®

Safurex^® is a family of duplex stainless steels developed by Stamicarbon and Alleima to address the challenging environments of the urea process and eliminate active corrosion in HP equipment and parts. 

Striving for continuous process optimization, Stamicarbon found that various parts of the HP stripper require different and dedicated materials to ensure its optimal performance. 

Using different grades of Safurex^® allows to achieve maximum corrosion resistance in each part of the stripper:

• Liquid Dividers are made of Safurex® Degree° to improve corrosion resistance.
• Safurex^® Star* used for heat exchanger tubes improves corrosion resistance at the extreme process conditions prevailing in heat exchanger tubes.
• Safurex^® Infinity∞ is used to fabricate lining, gas risers, overlay welded surfaces, and other standard elements of strippers.

Safurex^® Star*

Safurex^® Star* is specifically designed for heat exchanger tubes in the HP stripper to extend the lifetime and contribute to the safety of a urea plant.

It offers the following advantages when used in heat exchanger tubes:

• Optimized performance and longer lifetime of equipment (estimated 25 years).
• Lower weight of the stripper due to the smaller wall thickness of Safurex® Star* tubes.
• Increased heat exchanger surface area without increasing the number of tubes due to small wall thickness.
• Cost savings due to reduced weight.
• Lower need for maintenance and less frequent eddy current inspections.
• Forgiving to process upset conditions such as flooding, dry tubes, loss of passivation air, etc.

To date, after more than 20 years since the first Safurex^® stripper went into operation, never a tube rupture occurred with an installed base of more than 100 strippers. 

Our design and engineering competence combined with in-depth knowledge of the materials and fabrication process results in a highly durable product integral to optimal performance and maximum lifespan within urea production.