^{Achieve maximum productivity of the high-pressure stripper}

The Challenge

The high-pressure (HP) stripper in Stamicarbon CO₂ stripping plants is a vertical falling film evaporator wherein a urea synthesis stream is brought in contact with a counter-current stream of CO₂ gas flowing upwards in the heat exchanger tubes.

The liquid film is created by installing ferrules on top of all vertical heat exchanger tubes, consisting of a liquid divider and a gas tube. They ensure the equal distribution of the urea/carbamate solution over all tubes after the liquid enters the top of the stripper. 

_{^{Liquid dividers create a uniform falling liquid film down to the heat exchanger tubes.}}

This film is created by three equally spaced liquid holes with a specific hole diameter. The CO₂ gas introduced at the bottom of the heat exchanger tubes together with the stripped gas (CO₂ and NH₃ mixture) is expelled via the gas tubes.  

The HP stripper is designed to remain in operation for years, but cross-cut end attack, the type of corrosion common for duplex stainless steels, presents a challenge for liquid dividers.

It increases the hole size thus increasing the liquid load in each heat exchanger tube, which over time could impair the HP stripper efficiency, as a result preventing the stripper, and subsequently the plant, from achieving maximum productivity.

Then, how to increase the effective lifetime of these liquid dividers? 

Our Solution: E.H-type Material

To address the issue of cross-cut end attack in liquid dividers, we developed E.H-type stainless steel. This material is fabricated via the Hot Isostatic Pressing (HIP) method, which results in an isotropic and fine-grained microstructure, improving corrosion resistance and besides that enhancing the material’s mechanical properties at low temperatures. 

We also observed that E.H-type material outperforms the “standard” E.I-type in tests in oxygen-free ammonium carbamate solution.

_{^{The first liquid dividers made of E.H-type material installed in an HP stripper showed hardly any cross-cut end attack corrosion in the liquid divider holes after more than seven years on-stream time.}} 

The following advantages of using E.H-type steel for liquid dividers are evident and include:

• Extended lifetime of liquid dividers to 20 years
• Improved resistance to corrosion, especially cross-cut end attack 

E.H-type material can be used for the manufacturing of other parts that require either extreme corrosion resistance and/or low MDMT (minimum design metal temperature) requirements, which sometimes are specified for high-pressure accessories, such as HP E-type ejectors, E-type control valves, E-type check valves and E-type safety valves. 

Our E-type liquid dividers are based on years of experience and design studies. This piece of equipment will be customized based on your process conditions.

For more information and tailor-made solutions, contact our experts.