Energy Efficient Process Heating

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Energy Efficient Process Heating
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Heat Balance on Furnace
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Energy Saving Opportunities From Heat Balance

• Reduce opening losses
• Reduce flue losses
• Reduce cooling/conveyence losses
• Reduce storage losses
• Reduce wall losses
• Reclaim heat from flue to
• Pre-heat combustion air
• Pre-heat load
• Cascade to lower temperature processes

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Reduce Opening Losses
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Reduce Radiation Losses Room for Improvement
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Reduce Radiation Losses Better
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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

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Preheating Ladles Too Much Space
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Preheating Ladles Nice Tight Fit
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Reduce Flue Losses

• Temperature
• Improve internal heat transfer
• Flow
• Reduce air leakage into furnace
• Manual or automatic combustion air control
• Use O2 instead of ambient air for combustion

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Fraction Heat Lost Up Stack
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Improve Internal Heat Transfer

• Better heat transfer reduce Tex
• Reduces heat loss in exhaust air
• Improves efficiency

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Improve Internal Heat Exchange
T
Q
Parallel Flow
x
T
Q
Counter Flow
x
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Batch vs. Continuous(Cross flow vs. Counter flow)

• Batch crucible melting
  Counter-flow cupola melting

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Each Exhaust Port Is A Zone
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Counter-flow Within Zones
2 x (5 4 3 2 1) 30 feet
(10 9 8 7 6 5 4 3 2 1) 55 feet
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Tile Kiln Entrance
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Tile Kiln Heating Section
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Tile Kiln Cooling Section
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Tile Kiln Entrance (Counter flow?)
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Tile Kiln Entrance (Counter flow?)
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Reduce Air Leakage Into Furnace
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Air Flow In Process Heating

• Combustion Air needed to burn fuel
• Ventilation Air used for moisture removal and
  to prevent explosion hazard
• Infiltration Air undesirable can be minimized
  by proper design and maintenance

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Managing Infiltration Vertical Opening

• High inside air
• temperature drives
• buoyancy effect
• with both infiltration
• and exfiltration

Vertical oven opening
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Managing Infiltration Vertical Opening

• Lower Openings
• Decreases buoyancy effects between cool and warm
  air.
• New infiltration velocity from Bernoullis
  Equation.
• Example infiltration decreased from 2,250 cfm to
  2,000 cfm

Oven opening location before and after retrofit
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Managing Infiltration Horizontal Oven

• Move opening to oven floor
• Due to buoyancy effects, negligible infiltration

Horizontal oven opening
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Managing Infiltration Negative Pressure
Heat in Flue Gases
Air Leaks
Combustion Air
Fuel
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Seal Furnace Openings

• Openings
• Usually enable air leakage into furnace
• Always enable radiation loss

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Use Draft Control to Balance Pressure
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Manual or Automatic Combustion Air Control
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Reduce Excess Air To CO Limit (1)
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Natural Gas Combustion with Stoichiometric Air
CH4 2 (O2 3.8 N2) CO2 2 H2O 7.6
N2
HEAT

• Oxygen breaks CH4 into CO2 and H2O
• Nitrogen doesnt react
• Heat absorbed by products CO2, H2O and N2

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Natural Gas Combustion with Oxygen
HEAT
CH4 2 (O2) CO2 2 H2O

• Oxygen doesnt contain N2
• Heat absorbed by less product gasses CO2, H2O
• Increases flame temperature, heat transfer,
  efficiency

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Oxygen Enhancement

• Combustion with Air
• CH4 2 (O2 3.8 N2) gt CO2 2 H2O
• Mair / Mfuel 17.6
• Combustion with O2
• CH4 2 O2 gt CO2 2 H2O
• Mo2 / Mfuel (2 x 2 x 16) / (12 4) 4.0

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Flame Temperature with Oxygen Enhancement
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Available Heat (Combustion Efficiency) with
Oxygen Enhancement
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Oxygen Enhancement
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Reduce Cooling Losses
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Reduce Conveyor Losses

• Slow conveyor
• Brazing oven at 1,900 F
• Stainless steel conveyor at velocity 0.7 ft/min
• Conveyor weighs 5 lbs/ft
• Conveyor only loaded 30 of time
• Conveyor is slowed to 0.3 ft/min when unloaded
• Saves 18,000 Btu/hr, or 40, of conveyor energy

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Reduce Conveyance Losses (Spools)
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Reduce Storage Losses
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Reclaim Heat

• Preheat combustion air
• Preheat load/charge
• Cascade to lower temperature process

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Preheat Combustion Air with Recuperator
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Preheat Combustion Air
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Preheat Combustion Air
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Preheat Combustion Air with Tubein-Tube Heat
Exchanger
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Preheat Combustion Air with Regenerators
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Thermal Oxidizer with Regenerative Heat Reclaim
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Pre-heat Load Using Counter-flow
Stack
Burners
Current Design
Recommended Design
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Preheat Continuous Load with Counter-flow Heat
Exchange
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Preheat Load with Preheating Shed
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Recover Flue Gas Heat with Waste Heat Boiler
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Last Picture