Performance Improvement of Vacuum Heater


FIS was approached by a refinery in Illinois for Vacuum Heater performance improvement study. Client also wanted to revamp the heater to handle Canadian Crude and reduce NOx emissions.

The Vacuum heater was a natural draft horizontal cabin heater with horizontal convection section and a top mounted stack. FIS reviewed the design and operations of the heater and discovered following major issues:

  • The heater was facing coking problem

  • Average temperature drop was 40°F in the transfer line from vacuum heater to vacuum distillation tower, which is very high

  • Flow distribution through each pass was not uniform

On FIS recommendation client decided to build a new Vacuum heater using existing heater foundation. The new heater is 4 ft wider. This vacuum heater is horizontal tube box with a convection section. It is designed for a heat duty of 42.8 MMBtu/hr and an efficiency of 90%.

Salient features of the new heater are as follows:

  • The convection section of the heater has steam generation coils and boiler feed water coils along with the process coils.

  • The heater is designed as a gas firing unit.

  • The flue gas temperature leaving the economizer is alleviated by 72°F to 400°F.

  • The heater is designed for the overall fuel efficiency of 90% (LHV).

Heater was successfully commissioned in March 2009. The heater was delivered within the span of 7 months. A few months after the startup of heater, FIS received the following feedback from the client.

“.. we talked about the performance of the VF4 H28 heater since start up. It has been fantastic! The stack temperature is 370-380°F and the fuel gas usage has dropped about 40% from the old heater. This is one of the most efficient heaters in the refinery. The NOx stack testing came back 0.026 lb NOx/MMBtu, which is also outstanding. They are even trying to reduce the O2 even lower, from 4% to 3%. It’s a lot different when you have a tight firebox. Great job!!!”
— Client