2 replies to this topic

[Ather Iqbal (Process Lead)]

We are Operating two ammonia urea plants with old one having a WH boiler at frontend. Due to leakage in the Synthesis loop BFW [boiler feed
water] preheater, [d/s of Ammonia converter higher ammonia content [max 14 ppm] in the steam from boiler steam drum & high pH of boiler
water [max 10.68] was experienced.

We could manage the plant operation for few days however, owing to risk of caustic corrosion on pH hikes we recently shutdown the plant and found a leaking tube in upper heat exchanger A (BFW preheater is configured as two exchanger in series A on the top of B; 4 pass gas side starting from exchanger A while 2 pass shell side). BFW pressure (shell side) is 120 bar while synthesis gas (tube side) is at 240 bar pressure & at a temperature of 375 deg C.

While we have successfully detected the leakage, cause of leakage is still not known with a question mark on the exchanger integrity. The leakage point is at the inner side of U-tube (in middle of tube row) and could not be seen throughout the tube length through boroscopy suggesting that leakage is essentially at the tube bend. Tube & tube sheet material is supperior w.r.t. hydrogen attack.

I would request users to share their experiences in this respect.

[Zauberberg]

What is the temperature at which BFW enters the exchanger and can you provide composition of the Synthesis gas?

[magdyharby]

Dear Ather
based on my experience with this type of WHB I believe it is tube sheet welding problem came from the post weld heat treatment that done at the manufacturer work shop, please refer to the attached file that can give you better description to the problem, and please notify if you need more data or comments.
Best regards.
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