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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Tem

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Heating Energy

Heat Loss With 8-hour Cooldown and 2-hour Reheat

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Heating Savings

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1 11 21 31 41 51 61 71 81 91

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Heating Energy

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

Q

T

T

x

x

Q

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 Air

Fuel

Reduce Air Leakage

Negative Pressure

Seal Furnace Openings

Seal opening

around lid with

mineral fiber

blanket

Flue damper

Hydraulicpower unit

Controller

Compensating line

Pressure tap(not in line with

opposing 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

vaila

ble

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 !