Energy Efficient Process Heating
Energy Balance on Furnace
Energy Saving Opportunities
From Energy Balance
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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 Use
Heat Loss at Contant Temperature
400
350
300
Temp (F)
Heating Savings
250
Heating Energy
400
200
350
150
300
Temp (F)
100
50
0.1
1.1
2.1
3.1
4.1
5.1
6.1
7.1
8.1
9.1
250
Savings
Heating Energy
200
150
Heat Loss With 8-hour Cooldown and 2-hour Reheat
100
400
50
350
1
Temp (F)
300
250
Heating Energy
200
150
100
50
0.1
1.1
2.1
3.1
4.1
5.1
6.1
7.1
8.1
9.1
11
21
31
41
51
61
71
81
91
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
T
Q
Parallel Flow
T
x
Q
Counter Flow
x
Convert Batch Cross Flow Processes
to 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 Ports
to Increase Counter-flow Within Zones
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
Increases convection heat transfer by 83%
Set Exhaust Dampers
to Increase Counter Flow in Dry Off Oven
Product In
100% open
Product Out
75% open
50% open
25% open
12% open
Set Exhaust Dampers
to Increase Counter Flow in Tile Kiln
Tile
Exit
Tile
Entrance
Reduce Flue Flow
Reduce Air Leakage
Heat in
Flue
Gases
Combustion Air
Fuel
Negative Pressure
Air Leaks
Seal Furnace Openings
Seal
opening
around lid
with
mineral
fiber
blanket
Use Draft Control to Balance Pressure
Flue damper
Counterweight
Hydraulic cylinder
Hydraulic
power unit
Controller
Compensating line
Pressure tap
(not in line with
opposing burner)
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
% Available Heat
Excess Combustion Air
Decreases Flame Temperature and Efficiency
Flue gas temperature)
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 Oxygen
Increases 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
comb. air
out
Tc2 = 615 F
ex. gas
out
Th2 = 950
F
comb. air
in
Tc1 = 95 F
ex. gas in
Th1 = 1,465
F
Preheat Combustion Air
with 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
Stack
Current Design
Recommended Design
Burners
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
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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 Oxidizer
with Regenerator
Preheat VOC Stream in Catalytic Oxidizer
with Recuperator
Plant Air
Tc,1 = 72 F
Exhaust Air
Counter-Flow Heat
Exchanger
Burner
QHXR
Qc
QNG
Tc,2
Th,1 = 625 F
Texhaust stream = 300 F
Tc,3 = 560 F
Catalytic
Oxidizer
Use Thermal Oxidizer Exhaust:
Direct Contact Water Heater
And Don’t Get Covered with Molten Metal !