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Steven J. O’ConnorAnthony J. Fennell
TOPICS CONSIDEREDRegenerative FurnacesScale Free HeatingOxygen Sensors
REGENERATIVE FURNACES Bao Steel No. 1 Furnace 3 Bao Steel No. 3 Meishan Bao Steel No. 1 Furnace 1 Dual Regenerative Burners for Blast Furnace Gas
BAO STEEL 2050 RETROFIT SHANGHAI, CHINA Eight zone walking beam furnace 350 MTPH capacity Hot strip mill Mixed gas (2050-2450 Kcal/NM3) Bottom heat1 and heat2 zones converted to regenerative
SOAK
58.74 METERS EFFECTIVE LENGTH
HEAT 2 HEAT 1PREHEAT(NOT USED)
FURNACE AS DESIGNED
58.74 METERS EFFECTIVE LENGTH
FURNACE AS MODIFIED
9.6-18.8% fuel savings 47ppm NOx at 11% O2 140 C exhaust gas temperature 500 C air preheat temperature
BAO STEEL 2050 RETROFIT SHANGHAI, CHINA
BAO STEEL #3 HSM SHANGHAI, CHINA
Eight zone walking beam furnace 250 MTPH capacity Hot strip mill Mixed gas (2050-2450 Kcal/NM3) All zones regenerative except top soak Top soak hot air through recuperator
42.5 METERS EFFECTIVE LENGTH
BAO STEEL #3 HSM, SHANGHAI, CHINA
MEISHAN STEEL, MEISHAN CHINA
Eight zone walking beam furnace 250 MTPH capacity Hot strip mill Mixed gas (2050-2450 Kcal/NM3) All zones regenerative except top soak Top soak hot air through recuperator
42.5 METERS EFFECTIVE LENGTH
MEISHAN STEEL MEISHAN, CHINA
MEISHAN STEEL, MEISHAN, CHINA• 262 Kcal/Kg fuel rate• 0.33-0.54% scale loss• 30-55ppm NOx at 11% O2
• <20 C head to tail differential
BAO STEEL 2050, #1 FCE SHANGHAI, CHINA Eight zone walking beam furnace 350 MTPH capacity Hot strip mill Mixed gas (2050-2450 Kcal/NM3) All zones regenerative except top soak Top soak hot air through recuperator
50 METERS EFFECTIVE LENGTH
BAO STEEL 2050, #1 FCE SHANGHAI, CHINA
• 243 Kcal/Kg fuel rate• 30-55ppm NOx at 11% O2
• <20 C head to tail differential
BAO STEEL 2050, #1 FCE SHANGHAI, CHINA
DUAL REGENERATIVE BURNER
The dual regenerative burner makes BFG in a high temperature application possible, reducing customer dependency on higher cost fuel and saving money.
Bloom Engineered Burner• Burner is custom-designed for application using CFD
modeling and laboratory testing• Burner is designed with two stage combustion using air
staging with air passages through a refractory baffle to control mixing, heat release and emissions
• 90% pullback is expected using these burners
Burner Conceptual Design
BLOOM DUAL REGENERATIVE BURNER
BLOOM DUAL REGENERATIVE BURNER
Control of sub-stoichiometric combustion of natural gas to produce a neutral atmosphere within the furnace. Air/fuel ratio to produce a neutral atmosphere may be as low as 5:1. The ratio varies with steel surface temperature.
Implementation requires integration of a heat recovery system.
SCALE FREE HEATING
Scale Free Process Requirements
Scale Formation for Carbon Steel
Reduction of scale formation during heatingSignificant production and maintenance
cost advantagesImprovement in product surface qualityReduction of scale disposal costs
Environmental considerations
Possible Reduction in energy use
Benefits
PROCESS BACKROUND
•Basic process has been known for 40 plus years
•A few operating forging installations have been built
•Current DOE modernization project
•3 Active applications
CONTINUOUS REHEAT FURNACE Soak zone at 50% air – Low Efficiency Air preheated to 1000-1200F or Oxygen boost Stoichiometric Combustion to Steel Surface Temperature
of 1700 F Ratio proportional to 50% air in remaining zones Stiochiometric zones more often than not use secondary
combustion through air nozzles
Scale Free Atmosphere Generation
Use of highly preheated air (~ 10000 F) for combustion of natural gas.
Requires high temperature recuperator, hot air piping and hot air burners.
This option is attractive for new installations
Use of oxygen or oxygen enriched air for combustion.
This requires constant source – cost of oxygen supply.
This option is more attractive for retrofit applications
Use of combination for existing installations with lower degree ((say ~ 6000 F to 8000 F) of preheat and use of oxygen to boost oxygen in combustion air
Active Applications
Rotary Steel Reheat Furnace
Pusher Billet Reheat Furnace
Batch Forging Operation
Rotary Steel Reheat Furnace
100,000 TPY Current cold air operationObjectives: Improve fuel economy
Minimize scale lossImprove die lifeProduct quality improvementEnvironmental neutral
Pusher Billet Reheat Furnace
???? TPY, rebarNew, recuperated furnaceObjectives: Minimize scale loss
Environmental neutral????
Batch Forging Operation
Ring rolling operation, 20 in dia x 2.1 Tn billetsOnly last (soak) part of heating cycle is scale freeFurnaces to operate connected in pairs
One furnace on soak - scale free – exhaust to otherOther furnace on heat – stiochiometric
Objectives: Improve fuel economyMinimize scale loss
OXYGEN SENSORSBloom has an agreement with Marathon Sensors to be their representative, integrator and partner for the steel and aluminum industries. We will market the sensors, private labeled under the ‘Enviro-Helper’ trade name. Our long term objective is to engineer and market leading edge systems based on this technology.
Oxygen Analysis Can directly reflect state of combustion Can compensate for changes in fuel characteristics Can compensate for controls aberrations Prevent overly-oxidizing/reducing environment Can reduce NOx and CO formation Key is accurate, real-time measurement
Benefits of Measuring O2• Safety• Maintain better fuel/air ratios• Maximize fuel savings• Reduce Nox and CO
Oxygen Analysis What is the ideal oxygen sensor? Simple and inexpensive Little or no maintenance Not affected by mass flow variations Temperature compensated Installed in area of complete combustion without
bias from air infiltration Able to withstand high temperatures Accurate measurement from PPM to 21%*
Zirconia–based SensorsTwo categories Extractive (“dry”) sampling In-situ (“wet”) sensors Heated Non-heated
Non-Heated In-situ Sensors• Wet measurement• Located directly in process gas stream• Sample flows directly over cell• Unheated cell• Heat from process utilized• Temperature compensated
High-Temp Oxygen Sensor
High-Temp In-situ Sensors• Advantages
– Wet Measurement– Oxygen measurement based on actual process gas
temperature– True real time measurement– Range of 1200°F - 3000°F– No sampling, cooling, filters, heaters, etc.– Located in or near the combustion zone– Very fast response time to changes– Minimal maintenance– No calibration required but calibration check available
High-Temp In-situ Sensors• Disadvantages
– Thermal shock: long insertion and removal process*
– Ineffective below 1100°F
* New Temperature Resistant Sensor in Beta Test at AK, Middletown
High-Temp In-situ Sensors;Considerations• Location
– “Zoning” of furnaces allows information to be extracted relative to certain zones or even individual burner banks
• Control vs. Monitoring– Control makes O2 a high Return-on-Investment technology– Monitoring offers no pay-back
• Furnace Pressure– Low pressure allows high air infiltration during door opening
which gives false high reading on O2
High-Temp In-situ Sensors;Considerations• Reference Air
– Must be clean and dry. Moisture destroys sensors while dirt shortens life as impurities diffuse into zirconia
• Sheath Materials– Hexalloy (SiC) most rugged but prone to Fe attack if mounted horizontally
in line of gas flow– Alumina least costly but must be handled carefully*
• Probe Length– Dormant (Coanda) gas along furnace walls requires 6” insertion past hot
face for accurate readings• Particulates
– Sacrificial “boot” needed when particulates could accelerate electrode wear
Control Systems
Mass Flow Pressure Balance
Mass Flow Control
Air
Gas
∆ P
∆ P
Controller
Flow transmitter
Flow transmitter
Gas valve
Air valve
Oxygen Control
Pressure Balance Control
Gas
Air
Pressure balanceratio regulator
Impulse line
Motor drivenbleed valve
Air Valve
Oxygen Control
Applications
Reheat FurnacesAL Melters Forge FurnacesBatch Anneal FurnacesAlternative Fuels Compensation
Installations
AK Steel, OH – Strip Mill Reheat FurnacesMacSteel, Monroe – Pusher Billet FurnaceNucor, AK – Tunnel FurnaceNucor, UT – Pusher Billet FurnaceUSS Lorain – Rotary Pipe Furnace
