NHT and Platformer Heater Capacity Improvement Project
Furnace Improvements was employed by a refinery in Southeast Texas to increase the capacity of the Platformer Heaters and NHT Heaters. The Platformer Heater (H-20/21/22) and Naphtha Hydrotreater Heater (H-18/19/23) were built in 1977.
The Platformer heater is a three-cell (H-20/21/22) hoop coil heater. There are three vertical cylindrical NHT heaters along with the Platformer heater, which share a common convection section and a stack. They are the Hydrotreater Charge Heater (H-18), Hydrotreater Stripper Reboiler (H-19) and Depropanizer Reboiler (H-23). They are all radiant heaters. Flue gases from these heaters flow together to the common convection section on the Platformer heater.
The Platformer heater was originally designed for 12,000 BPD operation and rated for 119.7 MMBtu/hr heat duty. The design thermal efficiency of the heater was 88% but it was operating only at 81% efficiency. Additionally, radiant tubes and convection section were in bad state, tube fins had burnt out /fouled and stack temperature was 250 °F higher than the design case.
The heaters were running at 13,000 to 15,000 BPD charge rate. Client wished to revamp the heaters to 18,000 BPD capacity. Furnace Improvements (FIS) was employed to develop the best capacity improvement scheme for a #2 Platformer Heater and NHT Heaters.
The conventional revamp option was to extend the existing radiant cells. The other option was to install a new heater for the extra duty required. Both options required a large amount of space and high cost.
FIS’ recommendation was to increase the capacity of the heater based on FIS patented Split Flow Technology. The heaters were revamped for 18,000 BPD capacity and a design heat duty of 149.64 MMBtu/hr. The revamp cost was one-fourth that of the alternate design. The heater firing was limited to the design firing rate.
New Radiant Coils:
Radiant coils were replaced with new coils. Radiant area was increased by 11% in each cell.
New Convection Section:
The convection section was originally provided with heat transfer surface for BFW, steam generation and SSH coils. New convection section was used for heating split streams for all NHT heaters, Platformer heater (cell- H-20 / H-21) and for steam generation. The stack temperature was reduced to 390°F.
Each cell of Platformer heater was provided with 10 number of natural draft, round flame, low NOx burners. The burners in cell H-20 and H-21 were oversized and so replaced with 10 number of ultra-low NOx flat flame burners. The estimated NOx emission was 0.02 lb/MMBtu. The burners in cell H-22 were relocated and moved away from the tubes, closer to the wall.
FIS revamp scheme had following advantages:
The thermal efficiency of the heaters was increased by 9%.
Process duty of the heater was increased by 25%.
Stack flue gas temperature was alleviated by 271°F.