Fired Heater Basics

FIRED HEATERS

Chemical reactions and processes take place at high temperatures and hence heat sources are required.

Various sources of heat Direct fired heaters

Steam heaters Thermal fluid heaters, e.g., Dowtherm Electrical heaters

DIRECT FIRED HEATER

Fluid In Typical examples are Crude heaters, vacuum heaters, Platformer Rx charge heaters etc.

Fluid Out

Steam to various users including turbines, charge heaters, Reboilers etc.

Condensate return to boilers

Typical examples can be seen in almost all plants

THERMAL FLUID HEATER

Fluid In Typical example in LAB plant in PG and polyester plants in HZ & PG Thermal fluid used is Dowtherm A

Fluid Out to heat exchangers

Fluid Out Electrical Power IN

Typical examples are Air heaters, Lube oil heaters, vaporizers

Fluid In

STACK

Radiation Zone is the section where there is a naked flame and about 2/3rd of the heat transfer is by radiation mode

DAMPER

CONVECTION ZONE 800 – 900 C

Convection zone is the section where about 2/3rd of the heat transfer is by convection mode

RADIATION ZONE

1300–1600 C

AIR FUEL GAS STEAM

FUEL OIL

CLASSIFICATION OF HEATERS BASED ON AIR FLOW FOR COMBUSTION

STACK

NATURAL DRAFT FIRED HEATER

DAMPER

P R E S S

CONVECTION ZONE

D I F F

RADIATION ZONE

AIR

BURNERS

STACK

DAMPER

CONVECTION ZONE

FORCED DRAFT FIRED HEATER RADIATION ZONE AIR FROM ATMOS.

PLENUM CHAMBER

FD FAN

BURNERS

STACK

DAMPER

CONVECTION ZONE

BALANCED DRAFT FIRED HEATER

RADIATION ZONE

PLENUM CHAMBER ID FAN

FD FAN

BURNERS

STACK

DAMPER

CONVECTION ZONE

AIR PREHEATER

RADIATION ZONE

STEAM APH

PLENUM CHAMBER

ID FAN

FD FAN

BURNERS

CLASSIFICATION OF HEATERS BASED ON BURNER LOCATION

BOTTOM OR UPFIRED

SIDE OR END FIRED

TOP OR DOWNFIRED

CLASSFICATION BASED ON TYPE OF RADIANT COIL

Radiant tubes are always bare

CYLINDRICAL HEATER WITH VERTICAL COIL Example: Crude, vacuum heaters, xylene col. reboiler

OUT

IN


SECTION

CLASSFICATION BASED ON TYPE OF RADIANT COIL Example : Isomar charge heater at JG, LAB charge heater at PG

Arbor type

Inlet header

Outlet header


Example : Platformer heaters

U tube


HORIZONTAL RADIANT COILS

Example : Coker heaters

FINNED TUBES - CONVECTION

STUDDED TUBES - CONVECTION

Maximize heat transfer by increasing area.

Convection tubes are always horizontal

Bare tubes

BURNER ASSEMBLY

Burner tile

Burner floor refractory

Air register

Pilot burner

Atomizing steam + Fuel Oil OR fuel gas

BURNER ASSEMBLY

Burner tile

Burner floor refractory

Air register

Pilot burner

Fuel gas Atomizing steam

Fuel oil

HEAT SHIELD

350 - 450 C

800 - 900 C

150mm TO 200mm thick castable refractory CERAWOOL LINING CAN BE APPLIED INSTEAD OF REFRACTORY

1300 - 1600 C

Bottom floor 200mm thick castable refractory with one layer of brick lining

DETAIL OF CERAWOOL LINING

SS304 foil 0.2mm thick for corrosion resistance

Heater steel external shell

25mm thick cerawool pads laid one after another. Cerawool blankets hold down bolts

Bitumastic paint coating

Cerawool is not used in furnaces with oil fired burners.

Cost is high

METALLURGY OF TUBES Depends on the fluid inside and the temperature to which the fluid is to be heated Tube metallurgy Max. temp (C) Carbon steel 540 1.25% Cr - 0.5%Mo 595 2.25% Cr - 1%Mo 650 5%Cr-1%Mo 650 9%Cr-0.5%Mo 705 SS304,SS316,SS321,SS347815 HK40(25Cr-20Ni) 1010

For any selected metallurgy of tubes the minimum design life shall be minimum 100 000 hours

Metallurgy of tube supports

Tube metallurgy Max. temp (C) Carbon steel 427 C 2.25%Cr-1%Mo 649 19%Cr-9%Ni 816 25%Cr-12%Ni (Plate) 871 25%Cr-12%Ni (cast) 982 25%Cr-20%Ni(Plate) 871 25%Cr-20%Ni(Cast) 1093 50%Cr-50%Ni 982

If the fuel oil has more than 100ppm vanadium then the supports shall be 50%Cr-50%Ni or refractory lined for corrosion resistance purposes.

IMPORTANT DOCUMENTS TO BE REFERRED Process licensor datasheet Vendor datasheet Equipment drawings for individual heater for more details API 560 - Fired heaters for general refinery services API 530 - Calculation of heater tube thickness

END

STACK

DAMPER

CONVECTION ZONE

AIR PREHEATER

RADIATION ZONE

PLENUM CHAMBER ID FAN

FD FAN

FUEL GAS STEAM

FUEL OIL

Fired Heater Basics

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