102108587 furnace-construction-operations
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FURNANCE CONSTRUCTION AND OPERATIONS
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102108587 furnace-construction-operations
- 1. Furnace Construction & Operations Prepared by GULFAM KHALID SHIFT ENGINEER Ammonia Agritech Limited Pakistan 1
- 2. 2 What is Furnace? Converts Chemical/Electrical Energy to Thermal Energy Examples Household Furnace Metallurgical Furnace Industrial Process Furnace Non Reactive e.g. start-up furnace Reactive e.g. primary reformer in ammonia plant
- 3. 3 Types Draft Natural Draft Forced Draft Induced Draft Balanced Draft Construction Fuel Process Type Vertical Coal Fired Continuous Horizontal Gas Fired Batch Oil Fired Electric Current Burner Heating Arrangement Method Top Fired Direct Bottom Fired Indirect Side-wall Fired Terrace-wall Fired Tubes Arrangement Horizontal Inline Horizontal Staggered Vertical Inline Vertical Staggered
- 5. 5 Types: Draft The slight pressure difference between firebox and the atmospheric pressure that produces the flow of gases dueto temperature difference Forced Mechanical Induced Draft Natural Balanced
- 7. 7 Natural Draft Furnace Air Registers Controls the air flow partially Damper Controls the furnace pressure by manipulating the resistance in flow of the flue gas Excessive opening leads to a significant decrease in furnace pressure Excessive closing leads to pressure building in furnace Reduced furnace pressure: Burner Lifting Increasein draft Flame-out Refractory Damage Incomplete combustion of fuel Increased furnace pressure: Burner backfire Flue gases leak from peep door Explosion Rise in radiation zone temp. Drop of heat duty in convection coil Radiation zone temperature decreases
- 9. 9 Zones: Radiation Fire Box Area around the burners where gas combustion occurs to produce heat and radiation Burners Devices used to inject, mix and burn the fuel Refractory Wall lining / insulation that accumulates, insulates and radiates heat back to the tubes and increases the heat transfer
- 10. 10 Zones: Radiation Radiant Tubes High Pressure and high flow rate process pipelines loaded with catalyst receiving heat via radiation from burners and refractory Shock Tubes Tubes which receive heat via radiation and convection both Types ofTubes: Bare Finned Studded
- 11. 11 Zones: Convection Also called Heat Recovery Section Arch section Space between the convection section and radiant section, where flue gases are mixed to offer uniform heat transfer in convection zone Convection Coils Coils carrying some fluid which recovers heat from the flue gases Breeching Area between the convection section and stack
- 12. 12 Zones: Convection Arch Section Convection Coil Breeching Section
- 13. 13 Zones: Convection Vent Stack The chimney that exhausts theflue gases from breeching to atmosphere Exhaust Damper Draft regulator which works similar to a butter fly valve to control the air and heat flow
- 14. 14 Burners Raw Gas Burners Air and gas is mixed and burnt at spider or burner ring Air inlet is controlled via back and forth movement of air doors Stableoperating range is determined by the fuel gas pressure at the burner inlet
- 15. 15 Burners Pre Mix Burners Uses a jet of gas to draw the air into aspirator Turbulence is maintained throughout the length of the burner tube due to shape of the aspirator and the velocit
- 16. 16 Burners Combination Burner Primary Air: Drawn intro aspirator by force of the gas jet. Mixed with gas before it reaches burner spider Secondary Air: Drawn into thimble and meets the mixture at spider.
- 17. 17 Burners Oil Burner / Gun Uses steam to atomize oil into a fine mist Stable operating range is determined by fuel oil pressure at the burner inlet and the atomizing steam pressure at the burner inlet Combination Burner Operated on oil or gas or both Startup is done via gas supply
- 18. 18 Refractories Heat resistant materials which insulate and protect equipment structure due to their excellent resistance to heat, chemical attack and mechanicaldamage in high temperatures and/or corrosive environment Low iron-low silica content refractories: Insulating castable Insulating brick Ceramic fiber Ceramic module
- 19. 19 Metallurgy In-service degradation mechanisms: Thermal degradation (creep) The primary damage mechanism for high- temperature service Metal dusting Metal dusting is a high-temperature corrosion mechanism that occurs in gaseous environments where the carbon activity exceeds one and the metal temperatures are in the range of 450 to 700 ยฐC Stress relaxation cracking Cracking of a metal because of stress relaxation that occurs during post weld heat treatment (PWHT) or during service at elevated temperature
- 21. 21 Impingement Burner Flame touching a tube in the firebox Causes: Increased gas header pressure Low furnace pressure High draft across furnace Mechanical defect / damage of tubes Problems: Hotspot on tube Uneven expansion of the tube Tube rupture Remedy: Installation Peep doors for monitoring Regular inspection
- 22. 22 Flame Color Blue Flame: Complete combustion Desired heating value Yellow Flame: Oxygen deficient / starving Carbon monoxide rich Less thermal energy Increased fuel consumption
- 23. 23 Post Burning Causes Excess / false air Tube leakage Fuel gas preheat coil leakage Un-burnt fuel carry over Reaction Combustion of un-burnt fuel Oxidation of carbon monoxide Consequences Loss of energy Explosion
- 24. 24 Heat Recovery May be used in forced draft furnaces Recuperative Limited heat recovery Regenerative Blowing + heating / cooling of air supply / flue gases
- 25. 25 Instrumentation Skin Couples/TMT Check tube wall metal temperatures Draft Gauges Measures draft inside the furnace Flue Gas Analyzers Analyzes for excess oxygen supply Damper Regulates air flow outward
- 26. 26 Startup: Checkup Remove Check Open Close โขFlammable materials โขTools and other sources of danger โขBurner โขPilot Burner Valves โขStack Damper โขStack Damper โขSecondary air registers on furnace โขPeep Holes โขFuel Valves
- 27. 27 Startup: Purging Creates a draft and remove all flammable vapors or gas from furnace Purging time should be long enough to ensure all flammable vapors have been removed Purging ensures elements of combustion (fuel, air and heat) are under controlled before we light the burners Natural draft furnace uses steam; Steam not only purges the furnace but also preheats it and creates an initial draft Mechanical draft furnace uses air
- 28. 28 Startup: Lighting the Burners Purging is immediately followed by lighting the burners via pilot / torch To-Do Introduce torch via secondary air inlet Crack the burner gas valve Steady the burner flame pattern by air registers adjustment If fuel doesnโt ignite, purge again. Ensure Satisfactory gas header pressure Safety precautions
- 29. 29 Shutdown Reduce fuel / Reduce Shutdown all heat charge flow burners Close Gas header valve Open Bleeder valves Shut off Gas pilot Open air doorsand stack damper Reduce steam Install blinds in fuel lines
- 30. 30 Thank you Prepared by Gulfam Khalid Shift Engineer Ammonia Plant gulfamkhalid88@gmail.com