Fired Heaters - Introduction

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Mar 2014

FIRED HEATERS

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INTRODUCTION

DEDICATED TO:

Lynn Evans and Bill Handel, Foster Wheeler, UK Robert D Reed, John Zink, USA Today we are able to see further and farther standing on the shoulders of such giants

Acknowledgment

API RP 530/ 535 Std 560 Project Standards/ Specifications Pictures from: many sources, suppliers, internet

Fired Heaters Training 1 - 3 days Introduction (100 slides) Design (40 slides) Operations (45 slides)

Plant energy flow; Fired heaters - Source of high temperature heat Vertical Cylindrical, Box, Cabin, Multi-cell

Fired Reactors

Ethylene Cracker; Steam Hydrocarbon Reformer; EDC Cracker; Visbreaker; Delayed Coker

Other Types

All Convection; Water Bath Firing

Single or double sided; Floor up-fired, End or Side wall fired; Multilevel fired and Roof or Down-fired

Burners

Gas or Oil or Combination; Low NOx Draft

Natural, Forced, Induced and Balanced Components

Tube & Tube Supports; Soot blowers, Stack, Refractory Waste Heat Recovery:

38

- 6 ~ 8 hours - 3 hours + 4 hours in Worksheet - 2 ~ 4 hours

Introduction Process Fired Heaters

Since 1976

Steam Generation; BFW Heating, Air Pre-heater, Gas Turbine Exhaust WHRU

Design Firebox Heat Transfer – A Primer Radiant Section Sizing Convection Section Sizing Coil Design Stack Burners Refractory System Operations Safety Alerts Firebox Explosion Excess Air Control Draft Control Fuel & Firing Control Heater Control Coking & Hot Spots

Topics

Furnaces: Direct or indirect heat transfer to solids or fluids - with physical / chemical changes • Smelters, Ovens, Incinerators, Thermal Oxidizers • Rotary Kilns - Cement, Coke Calcination • Process Fired Heaters, Boilers

Process Fired Heaters Plant energy flow; Heaters - Source of high temperature heat Vertical Cylindrical, Box, Cabin, Multi-cell

Fired Reactors Ethylene Cracker; Steam Hydrocarbon Reformer; EDC Cracker;

Visbreaker; Coker

Other Types All Convection; Water Bath Firing Single or double sided; Floor up-fired, End or Side wall fired;

Multi-level fired and Roof or Down-fired

Topics Burners Gas or Oil or Combination; Low NOx

Draft Natural, Forced, Induced and Balanced

Components

Tubes &Tube Supports Soot blowers Stack Refractory

Waste Heat Recovery Steam Generation; BFW Heating Air Pre-heater Gas Turbine Exhaust WHRU

PROCESS FIRED HEATERS

Process Unit Energy Flow All energy inflows end up in atmosphere Cooling

Product #1

Product #2 Heating

Process Units

Feed Feed at ambient temperature

Product #9

Process at elevated temperature

Product #n Products at ambient temperature

Energy Inflow

Energy Outflow

Electricity

Steam

Fuel

Products

Process Units

Flue Gas Cooling Medium

Crude Distillation Unit CW

110°C (24%)

40°C

Product

30°C

Crude Oil

Top Reflux

125°C (4%) 80°C

Circulating Reflux

CW

Product

CW

Product

CW

Product

180°C (6.5%)

Crude Heater

Crude Column 220°C (12%) 150°C

Circulating Reflux

250°C (7.5%)

350°C

260°C (7%)

HX Train 325°C (39%) 250°C

Long Residue to Downstream Units

Crude Distillation Unit The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Crude Column

Crude Heater

HX Train

Heat Exchangers Save Energy Energy Inflow

Energy Outflow

Electricity

Products

Steam

Flue Gas Cooling Medium

Fuel

Process Units

Recycled Heat, thru Heat Exchangers

Fired heaters are large fuel consumers and major sources of emission

Heat Exchanges

recycle heat; save energy Fired Heaters, Boilers and Motors provide energy Heaters provide high temperature energy, where steam is NOT economical or viable

Development

Open Pan - See one in Digboi Refinery The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Bridge Wall

Similar to boilers 1850s: Batch mode; Open pan retorts and pot still. 36-hour runs + 24-

hour to scrape tar, coke and foreign matter. Deposits caused overheating, leak and fire Continuous, each shell at a higher temperature than its predecessor Milton James Trumble (1879-1931).. 70 patents credited with developing continuous run process heater

Temperature: 300 to 1,100°C. Duty: 0.5 to 150 MW Direct radiant heat was considered bad… 1910 A ’bridge wall’ between firebox and all convection coil Low inside tube velocity, salt deposits and radiant heat from hot flue

gas overheated the tubes coke deposit + ruptured tubes Removal of overheated tubes, overloaded the rest, aggravating the situation. Vicious cycle

• Once designers realized how to distribute radiation from hot flue gas over a large surface and maintain good coil tube velocity, modern design evolved • Heat absorption by tubes reduces gas temperature to convection section and keeps firebox cool

Features Heat transfer coil: CS, C-Mo, Cr-Mo, Cr-Ni

Stack Damper In

250-700°C

Convection Section

Rectangular box on top / side of firebox Convection Transfer (major) + Radiant (minor) Shock or Shield Rows of Tubes 700-900°C

Out

Flue gas recirculation in firebox heats backside of tubes and refractory

Vertical cylinder or rectangular box

Radiant Section/ Firebox Steel casing with refractory Burner

Firebox/ Radiant Section Heat transfer: • Direct flame radiation (minor) + • CO2 /H2O in flue gas radiation (major) + • Refractory re-radiation (minor) + • Convection between N2/O2 and CO2/H2O (major) • Convection from flue gas to tubes/refractory (minor)

Components The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Stack/ Duct

Convection Section

In Convection Tubes

Radiation Section

Shield Tubes

Peep Hole

Access Door

Radiant section/ Firebox 70-80% absorbed duty or

Tube Support

Radiant Tubes Hearth Platform

Out

Preheats feed 20-30% duty Recovers heat from hot

flue gas Plain + Extended surface

Breeching

Refractory Wall

Convection section

55-60% fired duty Houses burners

Based on Service: • Continuous/ Intermittent / Start-up Based on Configuration: • All Radiant; Radiant & Convection; All Convection Based on Structure or Firebox: • Vertical Cylindrical, Box, Cabin, Multi-cell

HEATER TYPES

Vertical Cylindrical – All Radiant


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No Convection Section The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Coil Support

All radiant, no convection < 2.5 MW duty Low efficiency, ≈ 60%. Start-up heaters Coil - Vertical hair pin or Helical Helical - good for free draining in molten salt service Coil removal by removing stack Old designs may have baffle plate on radiant top

Vertical Cylindrical – Return bends on top and bottom form hairpins in a circle

Radiant/ Convection The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.



Stack


Horizontal Convection Section

Radiant Section

3 - 30 MW duty. General service. Common type. Good

efficiency. Beyond 30 MW firebox is too tall 18m (>60’) Vertical hairpin coil in firebox; horizontal tubes in convection.

More coil passes. Symmetrical & uniform heat absorption Burners in a circle on floor. Vertically up fired Smaller foundation/ plot area / cost


Prefabricated

Vertical Cylindrical Tubes pulled up by stack davit

No separate tube pulling plot area required Access platforms at hearth , arch & damper; Ladder to arch The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.


Tube pulling davit



Duct

Ladder

Flue gas ducting to / from grade mounted air pre-heater

Isolation Damper

Box - Arbor Good for low pressure drop vapour service -

Reactor (Catalyst Reformer) feed heaters Arbour or wicket coils avoid return bends

(source of high pressure drop) and provide many parallel flow paths (low pressure drop) The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.



Box heaters have flat arch; Cabin heaters have sloped arch

Box General service. Vacuum heater Square or rectangular cross section Tubes along side wall Burners on floor, side or end wall Minimum return bends. Bends housed

inside firebox or in external header box Extra tube pulling space in plot area

“Boxes” stacked during construction



Internal View The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

External View

End Access Door


Tube Support Burner Holes



Sloped arch

Cabin Peep Holes


End Tube Sheet - return bends End Access Door

Hip or Arch

Large duty, 60 MW This image cannot currently be display ed.

Single cell Crude Heater Box heaters have flat arch.

Usually square cross-section Cabin heaters have sloped arch. Usually rectangular cross section

Box – Twin Cell


For large duty, 30-75 MW, such as Crude Heaters The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Bridge wall fired for Delayed

Coker and Visbreaker Zoned firing allows controlled

cracking and soaking

Flat Flame Burner The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Bridge Wall fired-upon

Double fired twin cells for fired

reactors, such as EDC Cracker Tubes in center and burners on

either side


Box – Multi Cell For very large duty heaters One large hi-intensity burner or multiple

burners/ cell


3 x 2 multicell vertical tubes 4 burners/ cell Center tubes may be double-fired

Convection Section On single service - same as that of radiant Different from radiant In multi-service - radiant fluid pre-heat, air preheat,

BFW (Boiler Feed Water) heating, Steam Generation, Steam Superheating Common convection ~ for a few heaters Convection coils may come in pre-fabricated bundles

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Feed Steam


Convection Section The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Top or side mounted May have additional firing Bottom 2 rows (“shock tubes”) are bare -

receive firebox radiation Low flue gas side heat transfer coefficient - extended surface tubes above shock tubes Finned for gas and light oil firing Studded with oil firing


Extended surface attain heat flux as high

as radiant at low cost

Studs

Fins

Process Heat Duty Equilibrium Flash Vaporization Chart

Heat liquid/ vapor/ gas/ 2 phase Vaporize feed Preheat in convection + soaking / mild

cracking in radiant

Preheat in convection + reaction Ethylene Cracker, EDC Cracker and

Hydrogen Reformer

Pressure

Delayed Coker and Visbreaker 0% Vaporized

60% Vaporized

Temperature

Refinery Heaters Heater

Crude

Vacuum

Visbreaker

Coker

FCC Charge

270-380

350-400

350-400-500

350-500

270-370

P out (∆P), bar

3-4 (10-12)

50-100 mmHg (6-8)

18-20 (20-25)

5 (30-35)

3 (3)

Vapor in/out, %

30-50

20-30

30-80

50-80

-

40 (12,000)

25 (8,000)

25 (8,000)

32 (10,000)

32 (10,000)

60 (200)

40 (130)

44 (150)

40 (140)

32 (110)

Box / Cabin

Box / Cabin

Twin Cell

Twin Cell

VC

2-4 x 6”

2-4 x 4”/6”/8”

2-4 x 4”/6”

2-4 x 4”

2-4 x 6”

T in/ out, °C

Flux, kW/m² (Btu/h.ft²) Duty, MW/tpa (MMBtu/100 kpbd) Type Coil

Design Tip: Higher the flux, lower is radiant section and heater cost. Flux is decided by coking, product discoloration that can lower its value and decomposition

Refinery Heaters Vacuum: Dry (no steam) or wet (with steam) Vacuum, Visbreaker and Coker: Steam injection in radiant coil return bends

Vaporizing heaters: high fluid temperature may occur

a few tubes ahead of outlet Other refinery heaters:

Charge, H2 Reformer, Bitumen Heater H2S off gas Incinerator, Bitumen Incinerator, CO Boiler, Coke

Calcination Kiln

Crude heater may dispose of off-gases

Plot Size

Plot Area 30

Shell DO/ Tube Length, m

25

Box Cabin

20

15

Vertical Cylindrical 10

5

0 0.0

10.0

20.0

30.0

40.0

Heat Fired, MW

50.0

60.0

70.0

FIRED REACTORS

Fired Reactors Visbreaker: Mild cracking of heavy ends Delayed Coker: Severe cracking of heavy ends EDC Cracker: Severe cracking Gas / Naphtha cracker: Severe cracking Hydrogen Reformer: Catalytic conversion of HC and steam to produce H2, CO2, CO High heat density (flux) - kW/m² (Btu/h.ft²) Usually double fired uniform heat transfer

minimum metal temperature / stress/ oxidation minimum coking / carburization

Many small burners fire on a wall, to keep it red hot – pure and

uniform refractory radiation Multi-level burners to match firing rates to changing reaction demands

Ethylene Cracker Feed Dilution Steam

TLE: Quickly quenches effluents, avoid coking and secondary reaction

TLE – Transfer Line Exchangers

Steam Generation

Out

In

In

Out

Multiple inlet small coils for high heat transfer

W Coil Furnace

4 tubes / pass 4 passes / firebox

Large diameter outlet to minimize coking

Cracks gas and liquid HC with steam. High coil outlet temperature

(COT). Heavier components converted into lighter C2=, C3= Steam: A diluent and refractory material High heat density (flux) and short residence time


Ethylene Cracker High alloy cast tubes

Uniform heat distribution with double-sided and multi-level firing Carburizing reaction; mirror free inner surface free of boring/ honing The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.


ID Fan

ID Fan Steam Drum

Steam Drum

Feed Dilution Steam TLE

TLE

Cross Over

Double sided firing with many small burners keeps both side walls red hot, to assure uniform heat transfer to tubes The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

TLE

Tubes Inlet Manifold


Hydrogen Reformer Natural gas or naphtha + steam heated in a catalyst

packed tube to high temperature ~ 800°-980°C (1500°-1800°F), to convert HC into H2, CO, CO2 High heat density (flux) Hi temp: Tubes of 800/800H; HK40, HP The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Double sided top firing with large burners. Flue gas exits via bottom tunnel The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Top fired

Convection Air Preheater Section

Side fired

Convection Section

Hydrogen Reformer

Flexible pigtails connect tubes to inlet manifold. Pigtails help accommodate tubes thermal growth



Flue Gas

Side Wall Burner Tubes


Catalyst inside tubes The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Tubes

Hydrogen Reformer Uniform heat distribution with double-sided and multi-level firing The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Red hot refractory


Inclined red hot side walls


Flat Flame Burner The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

EDC Cracker The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Double-sided multi-level firing Flat flames firing on walls avoid

tube impingement Red hot refractory Uniform heat distribution + Zoned heating Radiant coils installed / removed via arch Natural or forced draft

FIRED HEATERS – OTHER TYPES

All Convection – Flue Gas Recirculation The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

150-250°C The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Heater Coil Heater Coil 650-800°C

Flue gas re-circulated to reduce flame and flue gas temperature to 650-

800°C, eliminating radiant heat. Controlled film temperature Hi flue gas flow; hi convection heat transfer in finned all convection bank To 500°C. To 15 MW. Compact Easy to maintain absorption rates by adjusting recirculation Service: regeneration gas for absorption, pipeline oil, crude oil, water/oil

emulsions, LPG, and other sensitive stocks


Uniflux or Radiant – Convection Heater 3 Parts (1) Fuel Reactor or Combustion chamber. Short

flame. No impingement (2) Heat Exchanger - radiation + convection (3) 26 gauge 430 SS liner on fibre insulation on CS casing. Minimal stored heat. Avoids coking. Positive pressure 80% eff. With economizer 95% Convection transfer - more uniform heat flux Less chances of hot spots Low stored energy; Fast response to changing heat load; less chances of coking after a trip Forced draft - high velocity prevents flashback Compact


1100°F

1000°F 2000°F 900°F

Uniflux Heater Applications. 0.3 to 20 MW (1 to 70 MM Btu/h Heat Transfer Fluid Regeneration Gas Water; Glycol-water Air Steam Superheaters Crude Oil; Emulsions Vaporizers




Water Bath Heater Indirectly heats oil & gas well fluids, oil-

water emulsion Flue gas in fire tubes in lower part heats water; hot water heats HC in upper part Avoids direct contact - flue gas and HC coil Max water temperature fixed by water side pressure. Good for sensitive fluids

Glycol reboilers to 12 MW; gas pipeline, well

fluid heaters 2 MW In high pressure reduction service where

hydrates may form,

Gas first preheated and pressure let down in an external choke and then post-heated

Internal finning/ turbulators in exit firetube improve efficiency

Caution: Do NOT use to heat oilwater emulsion; external salt deposit - overheated / burst firetube Note: Instead of water LP steam to heat to 70 to 105°C; hot oil to heat regen gas to 315°C and molten salt heater to heat to 200 to 425°C

FIRING

Firing

Floor fired: Floor 2 to 2.7m above grade to allow passage. End fired: Floor raised marginally - air circulation to keep foundation cool. Floor below and around heater paved and curbed to avoid oil accumulation. The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.


Sidewall Floor


Floor End

Floor fired: Vertically up. Many burners enhance uniform heat distribution Side wall fired: Usually against a fire wall in firebox center End wall fired: Minimum burners with long flames. Eliminates elevated

floor; reduces costs. Low average flux. Flux mal-distribution high

Firing Burners in a lane in a rectangular box and in a circle in a

cylindrical box Top firing - Forced draft. If FD fan fails, flame may lift up and lick tubes The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Radiant Tubes – Bottom Guided – Top Outlet

Top Fired The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Burners in a circle


Firing

Side double sided 1 or 2 levels

Double sided T0p and side wall-fired as in reactor heaters

Wall fired May fire on central wall (bridge wall) for

uniform heat in delayed coker / visbreaker Bridge wall fired

Side double sided Multi level The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Top double sided The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

BURNERS

Burners

Purpose: To produce and direct flame and hot gases in a preferred manner in firebox

Type: Oil, Gas, Oil & Gas Combination Natural draft (80% of refinery heaters); Forced draft

Burner throw and flame shape to match firebox to avoid

flame and hot gas impingement To provide symmetrical heat distribution Duty 30 MW (100 MM Btu/h) High Intensity 0.5-5 MW; (1-15 MM Btu/h)

Secondary Air

Concentric doors

Natural draft: 5-15 mm WC

(0.15-0.6”WC) Forced draft: 100-150 mm WC (4-6”) WC

Pilot Gas Fuel Gas Atomizing Steam

Gas Manifold Primary Air

Fuel Oil Removable Oil Gun

Tramp air warning: Fully closed concentric cylinder type air doors leak up to 50% air

Combination Oil & Gas – Natural Draft

Burners Fuel Pressure @ Turn Down OR allowable turndown Consider burner tip as an orifice and calculate

With or without preheated air Noise 100 to 110 dBA. Noise attenuation plenums and mufflers for 85 or 90

dBA “A”-weighting ~ human ear response of Sound Power Level SPL

Fuel gas/oil gun - distributes fuel in air Refractory tile Shapes and stabilizes flame Air orifice, controlling air flow

Viewing Ports: To observe pilot and main flame;

to light pilot and main flame

Burner changes to improve flame shape and firing may be justified; but not for improving fuel efficiency, unless FD burners are selected

Oil Gun

The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Ver

Gas Tip(s)


Primary Tile Secondary Tile

Burners Pilot

Plenum / Windbox for air

distribution and control

Oil Gun

Muffler Plenum (Windbox)

Primary/secondary air doors Plenum or muffler - noise reduction Common or individual burner plenum 2 concentric slotted cylinders that slide over each other single slotted cylinder with damper blades single / louvered damper at burner plenum/ windbox Adjust to get equal air Dampers to be lockable to avoid inadvertent

Air Damper


Louvered Air Damper

closure or on vibration Opposed blades good

Individual burner damper control is expensive if > 4 burners Easy to adjust total flow in FD, with fan inlet guide vanes

Burners - Pilot

Kitchen LPG burner = 6,000 to 8,000 Btu/h, 10 times smaller than a single pilot

Constant burning gas burner 22 kW (75,000 Btu/h) To ignite main burner over full operating range

Not to provide “stability” to main burners Lighted by electric igniter; portable igniter, gas torch

and kerosene soaked rag Usually gas fueled. Smaller tip holes. Filter (#80 mesh or 25% min hole size). Basket type superior to Y-strainer

Should be stable even when main fuel is lost Usually kept always lit If no overheat under no-flow or in intermittent service;

to keep refractory dry; to avoid nuisance trips If fuel is ethane and heavy gas When fuel gas mol weight change causes swing in regulated pressure


Burners – Flame Deduction Flame Deduction Rods & Scanners Rod: Flame, an ionized reaction zone. Low voltage

applied to rod results in a current thru the flame and grounded burner assembly UV Scanners - for main and pilot flame. 1 per/burner; 2 if fuel gas is not processed UV: Site at first 1/3 of flame Self-checking, 6 seconds Good response in 200-400 nm spectrum The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.



Gas Burner –

Gas Tip

Raw Gas or Nozzle Mix Most refinery burners Air flow independent of fuel flow;

Air

decided by draft

Air Damper Concentric Cylinders

Can handle 100-250% variation in HHV/

LHV based on supply pressure Quieter. No flash-back risk Large turndowns; lower gas pressure

Gas Tip


Pilot Burner Tile Air Inlet

Pilot

Low heating values HV ≈300 Btu/ft³

Min 50 Btu/ft³ with CO or H2 Separate guns for wide changes in heating value and/or pressure

Prone to coking and tip blockage

Plenum (Windbox)

Air Damper

while firing unsaturates or with liquid carry over

Turndown 1:5 if supplied 1.75-2.5 barg (25-35 psig). Low 0.35 brag (5 psig). Min 0.07 barg (1 psig)

Gas Burner –

Gas Tip The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Pre-Mix Pre-mix/ Inspirating burners

Secondary Air

Fuel flow via venturi pulls in primary

air ≈ 30-100%; balance secondary Short dense flames not affected by wind gusts Xs air unaffected by draft. Good for ND

Primary Air

Gas Spud

Pilot Look: Gas nozzle acting as an injector, as in a Bunsen Burner

Mol Wt + HHV variation: 10-50%;

Fuel gas pressure affects air-pull Flash-back: if fuel velocity < flame speed e.g. Lab Bunsen Burner

Gas Tip or Spider This image cannot currently be display ed.

Secondary Air

High H2. Turndown limited Pre-Mix not recommended if H2 > 70% Caution: Preheated air flash back Turndown 1:3 if supplied at 1.75-2.5 barg (25-35 psig). Good to have 5 barg (75 psig). Min 0.2 barg (3 psig)

Pilot

Primary Air


Gas Burner Gas burning: Smaller flame Good for radiant wall burners

Flame spreads across burner tile and wall refractory. No forward projection into firebox

Hydrogen is an efficient fuel - but has

no visible flame



Flat Flame Burners - for firing on wall Gas Burner – with tiles Gas – Forced Draft The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.


Oil Burner

Pressure and air atomization good for light oils. Air expensive ~ compressor. Steam for atomization: 15-50% oil flow. Inside mix takes less steam. Dry/ superheated steam. High velocity Steam shears oil; foams/ emulsifies oil

Usually Oil & Gas combination burners Bigger flames. Burns after vaporization or

atomization to 10-50µ Mechanical spray or air atomization for light oil; Steam atomization for heavy oil Small tip passages - heavy oils difficult to atomize Superheated steam to 7-10 barg (100-150 psig); 20-27 barg (300-400 psig) for resids

Unburnt light oil (naphtha) may evaporate dense vapor cloud and explosion. Safety interlock required to shut-off fuel to remove gun.

Secondary Air

Steam may vaporize light oils like naphtha

vapor lock Pilot Gas Temp to get 20 - 25 CS viscosity at burner Fuel Gas Different oils ~ different viscosity index Atomizing Steam

Line loss may lead to high viscosity at burner. Insulate and heat trace

Gas Manifold Primary Air

Fuel Oil Removable Oil Gun

Turndown 1:3 if supplied at 5-8 brag (75-120 psig). P= 3-5 barg for steam atomization. Steam at a dP of 1.5-2.0 bar (20-30 psi) at 15-30% oil flow. Pmin = 5-7 barg (80-100) for pressure. For 1:3 turndown, P = 45-60 (700-900 psig)


Steam Ports

Oil Burner

Tip Ports

Steam Oil Oil Orifice

Steam Atomization Vs Steam Assist

Steam atomization - oil at lower pressure; dp of of 1.5-2.0 bar

(20-30 psi); more steam. 15-30% of oil flow. Large fuel orifice; less prone to plugging The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Oil Orifice

Light oil (naphtha)

may require separate Oil oil and steam tubes Steam to avoid vapor lock. Steam Orifice

Steam assist - oil at higher pressure - steam kept at 7-10 barg

(100-150 psig). Less steam. 10-20% of oil flow. High dP at part load increase steam rate. Smaller oil orifice; prone to plugging. Good for high release burners

Foot traffic on yard piping can damage insulation and lead to wet steam –water hammer; wire draw of valves and slug flow to burner and soot blower. Foot traffic can similarly affect fuel oil viscosity to burners

Oil Burning Issues 100% recirculation to maintain back-pressure – good during

turndown; minimize heat loss

Dead-end piping chilled oil, poor atomization/ combustion Flushing connection for residual oil

High asphaltenes or CCR >10% oil prone to tip coking and

plugging; soot and particulate emission Some cracked oils may not blend well with light cutter stock asphaltene precipitation and polymer formation; may crack in oil

gun; tip fouling and plugging Premature vaporization of low boilers pulsating flames. Have separate oil and steam tubes

Added cost - heating, pumping, atomizing steam; studded

tubes; higher Xs air; large flames - large fireboxes Easy to switch from oil to gas; difficult to go from oil to gas. Plan at design stage. Better ask for combination

A yellow-white oil flame is better than a dazzling white flame too much Xs air. Puffing in firebox is dangerous, wind disturbance or blockage of burner tip.

Oil Burning Issues Heat to pumping temp only in storage tanks to avoid polymers. Return oil to pump suction and not to tank

Special Oils

Asphalt: High temp loosens mill scales; plugs burner ports & filters High aromatics: Increase atomizing steam Water in oil or steam: Fire flies; sparky flame and smoke at stack Cat Cracker Oil: Fine abrasive cat solids; erodes atomizers & filters High metal - Vanadium/ sodium: High ash load + tube supports corrosion; Eutectic attack on refractory High Sulfur: Cold end corrosion. V2O5 is a catalyst promoting SO3 Solids: Coke, scale, cat fines; polymers damage oil ports Sludge from storage: flame out and explosion Oil from different sources: Changing viscosity at burner Pyrolysis and polymer oils: Unburnt and particulate emission

Eutectic? V2O5 + SiO2/Al2O3 low melting compounds that damage refractory rapidly

LOW NOX BURNERS

NOx

NOx

Low NOx Burners

Excess Air, %

3 sources 1.

2.

3.

Thermal NOx >1,100°C (2,000°F) Exponentially with temperature Depends on O2/ N2 concentration and residence time in flame Prompt NOx when fuel rich. Thermally disassociated ‘N’ attaches to HC instead of ‘O’ HCN, usually when fuel is staged and Fuel NOx - fuels with ‘N’ e.g. NH3. N2 in gas fuel does not contribute to NOx

NOx

More, 95-98% NO; balance NO2, NOx NO NO2 after stack discharge Regulations define limits in terms of NO2

Flue Gas Temperature Fuel Rich Air Rich

NOx

From: API RP 535

Air: Fuel Ratio

NOx

Nitrogen oxides form during combustion

Air Temperature

Fuel H2, vol %

unsatuates Fuel oil produces 3 times more NOx than gas; generally not used in low NOx projects

NOx

H2 ↑ flame temp and NOx. So also C4+

Liquid Fuel N2, wt % NOx ↑ with Xs air in raw gas burner. Peaks at 7-8% O2 and then declines. NOx ↓ with Xs air in pre-mix burner

Low NOx Burners – 60% Reduction Air or fuel is staged (lean or rich mix) to reduce flame

temperature. 0.05 Vs 0.13 lb NOx /MMBtu

Staged air - Early approach: 40% air into 100% fuel. Balance in

2nd stage. Cooler and O2 starved flame less NOx Staged fuel - now: 30% fuel into 100% air; Balance in 2nd stage. Only with gas fuel. Not with oils since ports get too small The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.




Tertiary Air

Secondary Fuel

Secondary Air

Oil & Steam

Gas Primary Air

Air Primary Fuel

Low NOx Burners Internal flue gas recirculation burners:


Cooler and O2 starved flame less NOx Ultra low NOx Burners: 80-95% reduction. 10-20 ppm Fuel staging + Internal flue gas recirculation

Steam injection into air or fuel. Expensive

Burner

NOx Level

Conventional – Raw Gas

60-100

Staged Air/Fuel

20-60

Staged + Internal Flue Gas Recirculation

10-20

#2 Oil Conventional (Staged Air)

300 (200-250)

#6 Oil Conventional (Staged Air)

120-150 (95-110)


From: “Successfully design fired heaters using ultra-low-NOx burners”, Ahamad S and Vallavanatt R, HP, 6 Jan 2013

Low NOx Burners Special Issues

Longer flames with staging; Firebox dimensions to suit

Smaller burner ports mill scale plugging. Ffilter-coalesecer (0.3

0.6µ) + Superheater + SS piping after KOD Bigger burner tile diameter + bigger flame = bigger firebox In retrofits, longer flames may lick tubes Flames from adjacent burners may merge and get longer Extra 150 mm (6”) clearance to tubes. More burner to burner clearance for effective flue gas recirculation, min 250 mm (10”) VC: Avoid inner circle burners; may not get cool flue gas more NOx Unstable during turndown Flue gas recirculation unstable flame when Xs air is low, specially when floor temperature < 550°C (1000°F). Recirculation reduced under turndown as fuel pressure gets low CFD model: Burner to tube; burner to burner; heat flux; TMT

BWT may go up by 30°C, increasing convection section load From: “Successfully design fired heaters using ultra-low-NOx burners”, Ahamad S and Vallavanatt R, HP, 6 Jan 2013

Noise Not talked about!! Or even asked !!!!

Typical noise

30 to 10,000 cps range “A” scale 1,000 - 5,000 cps 90 in car at 100 kmph 103 Inside Jet flight Natural Draft Burners 107 ~ no muffling 93 ~ with primary muffling 84 ~ with primary + secondary

Each 3dB = doubling Plenum chambers for ND;

Good ducting for FD burners

Burner Noise Combustion: 30-300 cps; air:

fuel mixing at hi frequency Fan operation: Hi frequency Hi frequency – most damaging Firing Direction: Horizontal, Vertical up and Vertical Down Upfire floor reverberation +10 db

Many small burners ↓noise Hi AIT fuels; Hi Intensity

burners ↑ noise High H2% .. 50% H2 ↑ by 10 db

Fuel Piping Gas: Insulate and heat trace, if required Filter-coalescer + Superheater + SS piping to avoid mill

scale plugging after KOD

All fuel/ steam tappings from top of headers Individual burner valves location to allow operation while observing flames Branch-off a ring header around firebox at peep hole

height

DRAFT

Draft Control ∆P - Air side - Burner air door + tile Natural Draft

Met by Firebox stack effect


FD/ID/Balanced: + Inlet stack, duct, air preheater

Met by FD fans Damper

∆P - Flue Gas side - Convn bank, damper and Stack Natural Draft + FD: Met by Stack ID/Balanced: + duct, air preheater:- Met by ID fans

∆P flue

High Draft

Arch

Tramp air + Misleading Xs air + Potential explosion

Low Draft

Air Inlet Stack

Hot gas + acid gas damage to casing

Wind action impacts draft reading- higher/lower by ±5mm (0.2”WC) and air flow. Flue gas velocity impacts draft reading – use multi-hole piezometric head. Probe to be 90° to flue gas flow.

∆P air


Floor

How flue gas flows

10,255

from “vacuum” to “atmospheric” pressure

How flue gases flow from firebox at

“vacuum” to stack tip at “atmospheric” pressure ?? Bernoulli’s law invalid? Buoyancy Beats

Bernoulli??

30m Pressure Profile Air

250°C Damper 10,290

Because “atmospheric” pressure at stack

tip is less than pressure in firebox

66m

Less than pressure at grade

525°C 16m Arch 10,309

“Atmospheric” pressure @ Firebox floor = 101.3 kpaa= 10,333 mm WC

66 m of air = 66*ρair = 78 mm WC Stack Tip = 10,333 – 78 = 10,255 mm WC With salaams to Shang Zhenhua and Abhishek Jha

20m 800°C

10,333 Floor

How flue gas flows

10,255

from “vacuum” to “atmospheric” pressure Location

Draft ∆P, mm P, mm Gain, WC WC mm WC

Stack Tip

10,255

10,255

0

Exit = 3

10,258

10,255

+3

Friction =2

10,281

10,290

9

Head = 1

10,282

Friction = 15

10,304

10,309

5

10,311

10,333

22

Stack Tip Above Damper

30*ρgas = 21

Below Damper Conan Bank

16*ρgas =7

Firebox Floor

20*ρgas =7

Air P, Draft, mm WC mm WC Pressure Profile Flue Gas & Air

Damper 8

10,290

10,282

10,290

8 Damper open Damper Pinched

Note: P below = P above + ∆h + ∆P At high altitude, atmospheric pressure is low, gas density is low reducing draft marginally. Air volume to burners goes up

Pinch Stack Damper to reduce arch draft to 1-2 mm

5

22

Arch 10,309

10,304

10,311 - ive +ive

22

10,333 Floor

Natural Draft Firebox chimney effect

Sucks air thru burners

Stack

Stack friction + ∆P of convection bank and damper

Arch kept (-)1-2 mm (-0.05-0.01”) WC

Damper

Leak in casing allows cool air thru insulation and not hot flue gas out, damaging insulation and casing

Easy to operate and maintain Control Xs air by adjusting each burner air register Operating stack damper alone as an easy way out will have +ive pressure at arch bringing roof down Wide open damper = Tramp Air ~ hi convection ∆P Wide open burner register = high Xs air and high arch pressure. Hot gas leak; damages refractory/ casing

Arch

- ive +ive

Floor

Forced Draft Inside heater: Same as in ND FD fan: air ∆P in ducts, pre-heater and burner Air flow controlled by fan inlet guide vanes; may be linked to O2 or CO analyser Fan Head = 150-200 mm (6-8”) WC FD trip: flexibility to switch to natural draft

Damper

Drop out doors in air ducts + ND burners

advantages of FD and ND burners lost! Drop-out door locations to ensure air

distribution; avoid exposure to hot air Note: Doors are known to fail to open on demand

Arch Air Inlet Stack


Air inlet should be elevated above grade, to avoid sucking in any hydrocarbon leak, that can cause firebox explosion

- ive +ive

Floor

Induced Draft Inside heater: Same as in ND Usually in high efficiency heaters with


cooler flue gas/ low chimney effect and high flue gas ∆P ID fan: flue gas ∆P in convection, damper, ducts, pre-heater and stack Flow controlled by fan inlet guide vanes; may be linked to arch draft Fan Head = 50-75 mm (2-3”) WC ID trip: flexibility to switch to natural draft, opening stack damper

Damper

Arch

- ive +ive

Floor

Balanced Draft


A combination of FD and ID Fans – usually with

air pre-heater Inside heater: Same as in ND A welded casing boiler – with water wall may operate under positive pressure All process heaters operate under -ive pressure If firebox operates under positive pressure, arch refractory is first to crack/ damage and fall Tell-tale signs: Rusted black spot on casing On opening peep door, hot blast of flue gas


Wind Effect on Stack Draft In plains, wind action at stack tip creates

small draft

Felt in cold firebox; good to light first burner Gradual heating to establish draft; Otherwise

furnace will puff

If stack tip is high above surrounding

structures or 600m (2,000’) away from hill/ higher structure, wind aids draft If stack is in a valley or higher structures are nearby, down draft may occur – wind tending to blow in


Conical down draft diverter may help

2D

¾D


Stack Rain Hat / Sleeve Rain Hat - for standby/ Start-up heater External corrosion with S bearing fuels Inhibits dispersion/ Increases GLC

Rain Sleeve - Preferred


Routes rain drop in the annular space,

external to stack

4-5D

FIRED HEATER COMPONENTS

Tubes

Horizontal tubes require tube removal space; Vertical tubes can be pulled-up

Arranged for easy removal; all free to expand Radiant tubes - vertical or horizontal hairpins, along firebox wall

In a central lane in reactors. Convection - horizontal

Usually 4” to 6”. Smaller in steam / water service. Bigger in vacuum Material CS,C - Mo, Cr - Ni, SS, 25 Cr - 20Ni

CS to 425°C(800°F) to avoid spheroidization and graphitization Cr-Mo to 700°C (1300°F); SS above 700°C (1300°F)

Material selection based on:

Internal /external corrosion and oxidation Max TMT that decides creep-rupture life

• Chromium increases resistance to corrosion from H2S, free S, organic S compounds; increases resistance to external oxidation; low improvement on rupture strength • Molybdenum improves resistance to creep • Nickel does not contribute to corrosion or oxidation or creep. Without Nickel, high Chromium alloys become brittle


IN

Tubes 4 Passes

Tubes grouped in passes or parallel flow paths to meet ∆P Note: In heat exchangers, number of

passes reduce “parallel flow paths” and add to frictional length and ∆P


Coil made bigger internally – vaporising and vacuum service

Corbel reduces flue gas bypassing or channelling

Convection coils are in a bank in rectangular or square or triangular pitch

OUT 4 pass means, flow in each pass and frictional lengths are ¼ of total compared to single pass. Hence ∆P will be ≈ 1/64 of single pass. Square Pitch

Corbel Triangular Pitch


Tube End Fittings Same material as tubes Usually 180° bends. Welded between two adjacent tubes. Can

be housed in firebox; adds to heat transfer surface In severe coking services, “mule ear” plug headers

Plugs removed for mechanical “turbining” - cleaning tube inside

surface with air operated tool Cast plug headers: Rolled or welded. Rolled headers may leak small fires With C4 and lighter, preferable to seal weld rolled headers Plug headers are housed in an external header box Headers are located on top in vertical and on one end in horizontal tubes The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.


Manifolds


When there is more than 1 pass, to ensure


equal flow to all passes Flanges: RF or RTJ. In high pressure service, terminals are welded

Flexible pigtails connect reformer tubes to manifold. Pigtails help accommodate thermal growth of tubes The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Which outlet is better?

RF and RTJ Flange Joints The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.


Radiant Tube Support - Vertical Wall


Top Guides The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.


Outlet side supported (“anchored”) to minimize forces to external piping Vertical radiant tubes: top guided and bottom supported, if outlet is at bottom; otherwise, bottom guided Bottom U clamp support, buried in floor refractory - less expensive Top outlets and top support preferred to go straight into column/ reactor Intermediate guides @ 70D (10-12) m for taller tubes Bottom Support


Pipe in Pipe

Bottom Guide

U Clamp in Refractory

Radiant Tube Support - Horizontal Intermediate along length, at 35D


(5-6m); end tube sheets End Tube sheets: Castable lined CS Intermediate supports: SS 304H to 815°C 25Cr-12Ni / 25Cr-20Ni to 870°C 50Cr-50Ni for high vanadium +

sodium fuel oil - fuel ash corrosion The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.



End Tube Sheet

Support with Locking Bar. Tubes may bend and jump out of support

Convection Tube Support The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Intermediate along length, at 35D

(5 -6 m); end tube sheets End Tube sheets: Castable lined CS Intermediate supports

Intermediate Tube Sheet The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

CS to 425°C; Cr-Mo to 650°C SS 304H to 815°C 25Cr-12Ni, 25Cr-20Ni to 870°C 50Cr-50Ni with high vanadium + sodium fuel oil - fuel ash corrosion The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.


Breeching – Space between convection and stack to smoothen flow profile and ensure uniform draft

Convection Tube Support

Tramp Air Paths This image cannot currently be display ed.

End tube sheets arrangement

Detail showing – stud/ fins The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.


End Tube Sheet with return bends The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Soot Blowers Soot blowers (steam lances). MP Steam at sonic velocity

blows away external deposits on extended surface tubes Normally steam; but air and acoustic types available Control: automatic and sequential. One at a time. Multiple blowers can be sequenced for grade or control room operation

Soot Blowers

Extended Surface

Bare Surface

This image cannot currently be display ed. This image cannot currently be display ed.

Soot Blowers Fixed with multi-nozzles - for clean fuel Retractable blower with 2 opposing nozzles for dirty service.

Steam flow per nozzle high. Cleaning range high Retractable: Coverage 1.2 m (4 ft) or 4-5 rows. Tube supports limit to coverage. Bare shield tubes not covered. Erosion protection for convection-section walls: castable refractory with a min density of 2 000 kg/m3 (125 lb/ft3) Steam lancing doors - for clean gas fuel firing Fuel chemical additives - running cost

Caution: You must drain steam feed lines FIRST to avoid high velocity condensate hit and damage extended surface fins/ studs and refractory parts

Stack & Dampers Stack - top of heater/ on grade. Usually self-supporting Height decided by draft; Mostly by GLC of SO2/ SO3/ NOx Mostly lined to keep flue gas hot/ maintain draft; internally

coated

Dampers The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Manually opened and closed, winch at grade; can be made

automatic with air cylinders Multiple bladed louver damper better than single bladed butterfly damper for control Strakes or wind spoilers on stack top

Multi-blade stack damper


Grade mounted winch This image cannot currently be display ed.

Stack sections The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.


IFB behind FB

Refractory Insulation Protects external steel casing from hot gases Help in re-radiation to the back of the tubes; YYYYY

Fire bricks - exposed and “fired” walls Insulating fire brick for “covered” walls A layer of loose fire bricks on floor

V & Y Hooks for cement

VVVVV

“No-flux surface” Bricks


VC - looking up; Looking down


Castable (insulating cement) for non-fired wall Firebox, convection, tube sheets and stack

Ceramic fibre for non-fired wall Aluminium foil vapour barrier prevents acid

migration and condensation/ corrosion with H2S bearing fuel Refractory system: Suitably anchored and supported by high alloy and CS members welded to casing


CF Blanket Radiant Side Wall




Miscellaneous Tube removal door Peep Hole, with internal refractory protection The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Peep holes: All around + floor to

inspect all radiant and shock tubes Tube removal door on arch for vertical tubes Explosion door: to relieve excess firebox pressure and avoid damage to heater structure. On roof facing up or on vertical walls facing away from control room etc. Piping not to block tube removal or explosion door Access: At firebox and top of Stair access to Hearth Platform convection Stairs to hearth level platform + ladder access to others

Explosion door The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Peep Hole


Access Door

Hearth Platform

• • •

Good insulation for casing Good combustion with proper burners with regular cleaning of burner guns Regular check on excess air and adjustment

ENERGY CONSERVATION – WASTE HEAT & AIR PREHEATER

Waste Heat Recovery

370°C

Feed preheat reduces heater

duty; saves energy Hotter feed hot stack gas; reduces heater efficiency Every 25°C = 1% fuel Heat recovery by: Generation and Superheating

On turndown, secondary

services may not get enough heat Additional firing in ducts/ convection base

100 90 80

Xs Air, % 0 10 30 50

70 60

Efficiency, %

Boiler Feed Water heating, Steam

270°C

300°C 200°C

50 40 30 20 10 0 0

200

400

600

Flue Gas Temp,°C

800

1,000


Waste Heat Recovery

Common Convection Section

Waste Heat Recovery - BFW heating,

Steam Generation - recovers energy. Fuel not reduced Pre-heating combustion air with flue gas reduces fuel fired




Air Pre-heater Part of convection or on grade Requires FD and ID fans Viable: High stack gas temperature,

high duty and expensive fuel Better flame control High radiant split

In retrofits: High radiant flux, firebox/ tube & tube

support temperature Reduced convection duty/ flue gas velocity; Independent convection services may not get enough heat Fans: High maintenance Cold end corrosion + acid mist plume Low stack exit velocity/ dispersion

Air – from APH Safe Area



FD Fan

ID Fan


Air Pre-heater Requires large surface (gas and air heat

transfer coeffts low) Tubes, plates, extended surfaces or light metal elements in high density baskets; heat pipes Glass tubes, to cool flue gas below acid dew point, to with stand acid corrosion. Avoided in process heaters

Regenerative Air pre-heater heat absorbing elements housed in a rotating wheel alternatively heated by flue gas and cooled by air . The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.


Heat Pipes - sealed pipes with heat transfer fluids that vaporizes on flue gas side and condenses on air side


Cast Air pre-heater with inside and outside fins


Air Pre-heater Air The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.


Rotary Basket The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Flue Gas

Plate

Tubular

Rotary Ducts

Air Pre-heater Switch-over to natural draft requires auto-drop out doors in air ducts

Extensive duct work for

air and flue gas

Plot limitations



FD and ID Fans

Rotary equipment trip/ failure

Optional switch-over to

part load natural draft operation

Use of natural draft burners limits gains

FD burners with high

air pressure drop

Good flame and air distribution but unable to revert to natural draft operation

Air Pre-heater The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

ID Fan Expansion Vessel HT Medium

Air – from Safe Area The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

APH

FD Fan

Heating Medium

Air – from Safe Area The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

APH

FD Fan

May employ water or heat transfer fluid in a circulating loop

Minimizes duct runs; but 2 equally rated heat exchangers required

Process fluid may be used to heat air and then get heated Low temperature waste streams like excess LP steam may heat air

Ideal to temper cold combustion air to avoid “cold end” corrosion

Air Pre-heater H2S and Sulphur in fuel: convert to SO2 (94-98%) and SO3

(balance) sulphurous acids that corrode cold end Cold End Metal Temperature > acid dew point at all operating conditions to avoid corrosion of tubes, ducts and fans; acid-mist Flue Gas Temperature may fall During part load operation, changes in excess air or fuel composition or low air temperature, Cold air bypass in air pre-heater Preheat cold air with LP steam

External sulfate deposits on tubes is harmless during operations. During shutdown the deposits cool down, absorb moisture from the air to produce sulphuric acid, that corrodes the tubes

Min Cold End Metal Temp, °C (°F)

Maintain Cold End Temperature by The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Mass % Sulfur in Fuel

Summary – Impact Analysis Add Convection Section

Add Steam Generation

Add Air pre heater

1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Stack temperature ……………… … Reduced…………… Reduced………… Reduced Furnace Firing…..…………………… Reduced ………….. No Change……… Reduced Firebox Temperature………………. No Change ……….. No Change…….…Increased Radiant Heat Flux ………………….. Reduced …………… No Change……….Increased Flue gas pressure drop ………….... in the convection section is increased. Draft ..………………………………… Decreased……….… Decreased…….….Decreased Tube side pressure drop ………….. Increased …………..No Change……….No Change NOx ……………………………………. Reduced …………… No Change……… No Change Burner ……………………………….... No Change………… No Change………. Changed More weight …………………………. from added convection tubes/…….... air pre-heater.

1.

Structure and foundation to be checked to see if added weight can be supported. If not, design adjacent structure to house convection tubes and support stack Check impact on steam superheater on account of reduced heater load Air pre-heating requires, extensive ducting, additional plot area, FD/ID Fans, check on tube supports/ refractory due to increased temperature, additional instruments. If fuel is to be changed, some existing convection tubes may have to be removed to accommodate soot blowers

2. 3.

Gas Turbine WHRU Gas Turbines: Run large compressors and generators 300 – 400% Xs air to limit combustion chamber metal

temperature

WHRU

Exhaust at 500°C with 16-18% O2: A rich source of waste heat

– either as hot combustion air or for waste heat recovery Combustion Air: Requires ducting and load co-ordination

between GT and fired heater



Combustion air

Air

Fuel

Common WHRU for 2 Turbines

GT WHRU




Bypass

Bypass

Bypass WHRU

WHRU

Heat hot oil, generate and superheat steam Finned tubes, similar to heater convection section Balance heat load: GT exhaust cooler on part load

GT WHRU Supplementary Firing The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Additional firing to boost exhaust temperature

/ available waste heat, specially during GT part load High exhaust velocity (30m/s) and proper distribution As exhaust has 16-18% O2, fuel (oil or gas or both ) can be directly fired in the duct FD fans: To continue steam generation etc. when GT is down




Duct Burners: Many small burners across duct cross section The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.



The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location. The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Heater Decoking

Decoking Pig Intelligent Pig

Decoking Regular decoking will avoid hot spots and premature tube failure.

Remove coke deposited inside tubes by Gas oil circulation to soften and remove deposits. Not for heavy coking Chemical cleaning – circulating inhibited acid or chemical + water wash for salt deposits Hydroblasting – high pressure water jet; abrasive grit.. Shot/sand Steam: air decoking: In-situ combustion with steam and air While tubes in 1 pass are decoked, tubes in other passes kept cool with steam Cooling steam is 5-15% of decoking steam flow Decoking air 5-15% of decoking steam flow

Pigging – abrasive pigs. Less damage than decoking or acid wash Mechanical turbine thru Mule Ear Plugs

Multi-pass (arbor) radiant inlet/ outlet header

Process Piping


Symmetrical inlets and outlets in multi-pass vaporizing

service, to ensure equal flow and avoid coking

Split or join in stages - 2 passes or streams at a time One large header to split/ combine in all liquid or vapor service

Transfer lines from heater to column: Elevated above

column nozzle and slope towards the column

Radiant Outlet

Pipe Rack Convection Inlet Convection Inlet

Radiant Outlet

Control Valves @ Grade

15 m

Radiant Outlet

Convection Inlet

Convection Inlet

Pipe Rack

Header Box

Header Box

Header Box

Platform

Header Box

Platform

15 m

Control Valves @ Grade

Tube Removal Area

Tube Removal Area

Check List While buying

While running

Duty and margin Type – VC, Box, Multi-cell;

Caution board near heater

single or double fired Efficiency and Xs air Flux and max metal temp Vaporization - Temp profile Plot limitations Inlet/ Outlet locations Extended surface Soot blowing Damper operation location Sky walk to adjacent heaters

on purging O2 reading and Xs air Draft at arch Casing hot spots or rust marks Flame lick / hot spots Wind induced combustion pulsation Drain steam supply piping before soot blowing Clean oil guns / tips

Safety More on Safety in the Operations Part

Heater location: Upwind or side wind to avoid any hydrocarbon ingression 15 m from other equipment or road; edge of unit for easy fire

fighting

FD fans air intake from , ‘safe location’, 5-15m above grade Floor fired: Floor 1.75 m above paved grade Coil purging valve: 10-15 m away. Steam or purge gas. Firebox snuffing steam valve: 10-15 m away. FD Fan or

steam ejectors are acceptable alternatives Fuel gas isolation valve 10-15 m away; FD fan should be stoppable 10-15 m away/ remotely.

Recommended Reading The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

Furnace Operations, R D Reed Petroleum Refinery Engg, W L Nelson, Chapter The link ed image cannot be display ed. The file may hav e been mov ed, renamed, or deleted. Verify that the link points to the correct file and location.

18 Engineering Data Book, GPSA, Section 8 API Publications


Spec 12K Specification for Indirect Type Oilfield Heaters Std 530/ISO 13704:2007 Calculation of HeaterTube Thickness in Petroleum Refineries RP 535 Burners for Fired Heaters in General Refinery Services RP 556 Instrumentation, Control, and Protective Systems for Gas Fired Heaters Std 560/ISO 13705:2006 Fired Heaters for General Refinery Services RP 573 Inspection of Fired Boilers and Heaters

Stay Safe. The best for many years of safe and sustained operations

THANK YOU

Fired Heaters - Introduction

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