Efficiency Improvement of CDHDS Reboiler Heater (H-60)

Furnace Improvements (FIS) was employed by a Texan refinery to develop an efficiency improvement scheme for CDHDS reboiler heater (H-60).


The CDHDS reboiler heater is a natural draft vertical cylindrical heater, built in 2002. The CDHDS reboiler heater (H-60) was designed for a process duty of 72 MMBtu/hr, with a design efficiency of 81%. The heater was operating at an efficiency of 79%, with the flue gas stack temperature of 780°F.

FIS developed several options to improve the efficiency. After a careful review, the client selected following scheme:

  • Adding six rows of steam generation coil in the convection section consisting of 16 finned tubes per row, arranged in 4 passes

  • 71,000 lb/hr of 450 # steam condensate is flashed to 150 # 2 phase, vapor-liquid stream.

  • Flashing is completed before the steam enters the convection section.

  • The two-phase feed enters the convection section with inlet vaporization of 11.9%.

  • The generated steam leaves the convection section from the top row and the steam generation is co-current to the flue gas flow. At the outlet, vaporization is 28.8%.

  • Adding a new stack transition cone to extend the stack height by 25 ft, to account for additional flue gas pressure drop created by adding extra rows in the convection section

Salient features of the revamped design are as follows:

  • The efficiency of the heater increased by 11.2%

  • The flue gas temperature is alleviated by 368 °F

  • Increased efficiency led the client to save $681,225 on fuel per year

  • The estimated payback period was 1 year & 9 months.

This project was successfully commissioned in October 2007.