Energy Efficient Process Heating
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Transcript of Energy Efficient Process Heating
Energy Efficient Process Heating
Energy Balance on Furnace
Energy Saving Opportunities From Energy Balance
Reduce opening losses: radiation and air exchange Reduce cooling losses Reduce conveyance losses Reduce storage losses Reduce wall losses Reduce flue losses
– Improve internal heat transfer– Reduce air leakage into furnace– Control combustion air / oxygen
Reclaim heat – Pre-heat combustion air– Pre-heat load– Cascade heat to lower temperature processes
Reduce Opening Losses
Reduce Radiation Losses: ‘Room’ for Improvement
Reduce Radiation Losses: ‘Better’
Cover Charge Wells
2 ft x 4 ft open charge well radiates and convects heat
Cover charge well with mineral fiber insulation 75% of time
Savings = $1,500 /yr
Preheating Ladles: Too Much Space
Preheating Ladles: Nice Tight Fit
Reducing Air Exchange in Continuous Ovens
By Modifying Entrance/Exit
Reduce Cooling Losses
Reduce Conveyance Losses
Slow conveyor– Brazing oven at 1,900 F– Conveyor runs at 0.7 ft/min– Conveyor loaded 30% of time– Slow conveyor to 0.3 ft/min
when unloaded– Reduces conveyor losses by
40%
Reduce Conveyance Losses
Lighter conveyance
fixtures reduce energy
carryout losses
Reduce Storage Losses
Larger batch sizes to reduce number of loads in heat treat ovens
Reduce Storage Losses
Reduce bricks
(thermal mass) on transport
cars
Reduce Storage Losses
Increase batch sizes
in arc furnaces
Reduce Wall / Surface Losses
Insulate Hot Surfaces
Insulate four lids at 400 F
Induction furnace efficiency = 51%
Savings = $17,0000 /yr
Insulate Extruder Barrels
Turn Off Heat When Not in UseHeat Loss at Contant Temperature
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Reduce Flue Losses
Flue Losses
Flue losses increase with:– Temperature– Flow
Reduce Flue Losses
Reduce Temperature– Improve internal heat transfer
Reduce Flow– Reduce air leakage into furnace – Combustion air control– Use O2 instead of ambient air for combustion
Counter Flow Heat Transfer Reduces Exhaust Temperature
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Parallel Flow
Counter Flow
Convert Batch Cross Flow Processesto Continuous Counter Flow
Batch crucible melting Counter-flow cupola melting
Replace Reverb (Cross Flow) with Stack (Counter Flow) Furnace and Pre-heat Charge
Reverb Furnace Stack Furnace
Lead Melt Furnace: Place Scrap on Top and Drain Molten Lead From Bottom
Molten Glass Transport:Each Exhaust Port Is A Zone
Relocate Exhaust Portsto Increase Counter-flow Within Zones
Increases convection heat transfer by 83%
Contact length = 2 x (5 + 4 + 3 + 2 + 1) = 30 feet
Contact length = (10 + 9 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1) = 55 feet
Set Exhaust Dampers to Increase Counter Flow in Dry Off Oven
Product In Product Out
100% open 75% open 50% open 25% open 12% open
Set Exhaust Dampers to Increase Counter Flow in Tile Kiln
TileExit Tile
Entrance
Reduce Flue Flow
Heat inFlue
Gases
Air LeaksCombustion AirFuel
Reduce Air Leakage
Negative Pressure
Seal Furnace Openings
Seal opening
around lid with
mineral fiber
blanket
Flue damper
Hydraulicpower unit
Controller
Compensating linePressure tap
(not in line withopposing burner)
Hydraulic cylinder
Counterweight
Use Draft Control to Balance Pressure
Reduce Flue Flow: Control Combustion Air
Combustion with Air
Minimum Combustion Air (Stoichiometric):CH4 + 2 (O2 + 3.8 N2) CO2 + 2 H2O + 7.6 N2
Excess Combustion Air:CH4 + 4 (O2 + 3.8 N2) CO2 + 2 H2O + 15.2 N2 + 2 O2
Excess Combustion AirDecreases Flame Temperature and Efficiency
Flue gas temperature)
% Excess Air (% O2) in flue gases
Air Preheat temperature)
% A
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Heat
Reduce Excess Air To 10% or CO Limit
Reduce Flue Flow: Replace Air with Oxygen
Combustion with Oxygen Eliminates Unnecessary Nitrogen
Combustion with Air– CH4 + 2 (O2 + 3.8 N2) > CO2 + 2 H2O + 7.6 N2
– Mair / Mfuel = [ (4 x 16) + (4 x 3.8 x 14) ] / (12 + 4) – Mair / Mfuel = 17.6
Combustion with O2
– CH4 + 2 O2 > CO2 + 2 H2O– Mo2 / Mfuel = (4 x 16) / (12 + 4) – Mo2 / Mfuel = 4.0
Combustion with Oxygen Increases Flame Temperature
Combustion with OxygenIncreases Efficiency
Reclaim Heat
Preheat combustion air Preheat load/charge Cascade to lower temperature process
Preheat Combustion Air with External Recuperator
Preheat Combustion Air with External Recuperator
ex. gas inTh1 = 1,465 F
ex. gas outTh2 = 950 F comb. air
inTc1 = 95 F
comb. air outTc2 = 615 F
Preheat Combustion Airwith External Recuperator
Preheat Combustion Air with Bayonet Recuperator
Preheat Combustion Air with Tube-in-Tube Heat Exchanger
Preheat Combustion Air with Regenerators
Pre-heat Load Using Counter-flow
BurnersStack
Current Design
Recommended Design
Preheat Load Using Counter-flow
Preheat Load Using Preheating Shed
Cascade Heat to Lower-Temperature Process
High Temperature Oven Low Temperature Oven
Cascade Heat to Waste Heat Boiler
VOC Destruction with Thermal and Catalytic Oxidizers
Reduce VOC Stream Pre-heat VOC Stream with Recuperator Pre-heat VOC Stream with Regenerator Use Thermal Oxider Exhaust
Reduce VOC Stream with Carbon Adsorber
Inlet: 50,000 cfm with 50 ppm Outlet: 5,000 cfm with 500 ppm (10x concentration) Outlet (BAC): 50 cfm with 50,000 ppm (1,000x concentration)
Preheat VOC Stream in Thermal Oxidizerwith Regenerator
Preheat VOC Stream in Catalytic Oxidizer with Recuperator
Texhaust stream = 300 F
Burner Catalytic Oxidizer
Tc,1 = 72 F Counter-Flow Heat Exchanger
Tc,2
Tc,3 = 560 F
Th,1 = 625 F
Plant Air
Exhaust AirQcQNG
QHXR
Use Thermal Oxidizer Exhaust: Direct Contact Water Heater
And Don’t Get Covered with Molten Metal !