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

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

FIS reviewed the design and proposed the following changes to improve the efficiency:

• Adding six rows of steam generation coil in convection section
• New stack transition cone
• 25 ft of stack extension

In this scheme, 71,000 lb/hr of 450 # steam condensate is flashed to 150 # 2 phase, vapor-liquid stream. Flashing is completed before it enters the convection section.

The total heat duty of the heater was increased to 82 MMBtu/hr. The extra 10 MMBtu/hr is absorbed in steam generation coil. Flue gas temperature leaving the stack was reduced at 400°F. The efficiency of the heater was increased to 90%, which brought energy savings of approximately USD $ 590,550 per year. The payback period is 1 year 3 months.

This project has been successfully commissioned in October 2007.