Different Types of Carbon Steel Enhanced Tubes in Ammonia Flooded Evaporator

Abstract

This short paper deals with a real-world case study of a large capacity industrial ammonia-flooded evaporator. Ethylene glycol brine was the process fluid to be cooled. Several options were analyzed (e.g., different versions of shell-and-tube and plate-and-frame heat exchangers). Because of mechanical integrity, control issues, and maintenance requirements, the option of choice was a flooded shell-and-tube. A conventional flooded shell-and-tube with plain surface carbon steel tubes would have been too big, resulting in a large space requirement and greater refrigerant charge. Almost every local code requires the careful audit of ammonia inventory in an industrial plant. The goal of the designers, engineers, contractors, and the end users is to reduce the refrigerant charge to a minimum. In view of design and operational constraints, an evaporator was designed, fabricated, and installed that included a tube bundle with various kinds of tubes. Three different types of tubes were used along the height of the tube bundle. Highly efficient, nucleate boiling characteristics doubly-enhanced tubes were used in the lower section, and inside-only enhanced tubes were used in the top section to minimize the adverse effects of vapor blanketing. Tubes in the midsection were doubly-enhanced with a different outside structure than the tubes in the lower section. This resulted in a very efficient evaporator at a minimum refrigerant charge.