Basics of Stack Melting

Aluminum shaft, or stack furnaces are now widely accepted as a modern operational and sound financial choice because of their higher energy efficiency than of the reverberatory furnace. The stack melter efficiency is improved by better sealing of the furnace and the use of the flue gases to preheat the charge materials. The charge materials slide down the shaft and reach the melting zone where they are melted by the burners, and the molten metal flows down to the holding area. The hot exhaust gases from the melting zone flow through the shaft to preheat the incoming charge, improving the energy efficiency of the stack furnace by 40 to 50%. Melt loss is also dramatically improved from 4-8% in a reverb, down to 1% or less in a well operated stack melter.

Jet Melter® Stack Detail

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Reverb Melting Disadvantages

Reverb Furnace Problems

Poor Thermal Efficiency - Only 25%
Accelerated Dross Formation - 3% to 7%
Large Metal Temperature Variations +/- 50º F
Higher Inclusions Levels
Larger Bath Required To Melt Aluminum
Greater Hydrogen Gas Pick Up

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Reverb Cost Variables

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Technology Comparison Chart

A Clear Green Option, The Real Financial Choice

Comparison Data

Fuel Consumption (Btu/Lb.)
Thermal Efficiency (%)
Metal Loss (%)
Refractory Cleaning
Refractory Life (years)
Charging System
Bath Capacity to hourly melt rate ratio
Molten metal Temp. variation
Noise Level

Jet Melter®

900 - 1000
45 - 55
0.7 - 1.5
Once per day
5 to 8
Semiautomatic or Automatic
2.5 : 1
± 10° F
< 85 dba

Reverb Furnace

1500 – 3000
24 – 32
3 – 7
Once per day
2 to 4
Manual or Semiautomatic
10 : 1
± 50° F
> 90 dba

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Actual Comparison of Melter Performance

(Side by Side Test Results)

Melt Loss
Energy Usage
Molten Metal Temp. Control
Metal Specific Gravity
Metal Cleanliness K-Value

Jet Melter®
0.9%
955 Btu#
± 5° F
2.26
0.0

Reverb
5.5%
1975 Btu#
±32°F
2.10
0.10

Alloys added for chemistry adjustment

Mg
Sr

100#
175g

175#
475g

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Melt Quality Comparison

10:50 AM - S.G. = 2.16   11:50 AM - S.G. = 2.26Modern Jet Melter®
Gas Samples

11:07 AM - S.G. = 2.10   12:12 PM - S.G. = 2.10Reverb Melter Gas
Samples

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Estimated Payback Analysis

Melting Costs ** Typical 2000 #/hr (1 shift operation)

ASSUMPTIONS

UNITS

JET MELTER

REVERB

Melt Loss

percent

1%

4%

Aluminum Cost

$ per pound

$ 1.20

$ 1.20

Energy cost

Average $ per therm

$ .32

$ .32

Energy usage

Btu's per pound melted

1000

2000

Aluminum Usage

Pounds Melted per Month

333,333

333,333

COST TO MELT PER POUND

$0.0032

$0.0064

ENERGY COST PER MONTH:

$1,066

$2,133

MELT LOSS COST PER MONTH:

$4,000

$16,000

TOTAL MELT COST PER MONTH:

$5,066

$18,133

MONTHLY SAVINGS

$13,067

Melting Costs ** Typical 2000 #/hr (1 shift operation)

ASSUMPTIONS

UNITS

JET MELTER

REVERB

Energy Cost

Average $ per therm

$.32

$.32

Energy Usage

Btu's per pound held (assumed)

50

50

Amount Held

Pounds Held

5,000

20,000

Holding Period

Hours held monthly

533

533

COST TO HOLD PER MONTH

$426

$1,706

MONTHLY SAVINGS

$1,280

TOTAL MONTHLY SAVINGS (Melt & Hold)

$14,347
 

 9 Reasons Why:   Stack Melter Technology Beats Traditional Reverb Furnaces

1. Improve safety due to limited exposure to molten metal and pre-heating of the charge material
2. Floor space reduced due to 2.5x holding capacity versus 10x
3. Efficiency of 1,000 Btu per pound versus 2,500 Btu
4. Lowered holding costs caused by 2.5x holding capacity versus 10x in a reverb
5. CO2 emissions lowered (less gas burned = less CO2)
6. Lower melt loss (1% vs.3-8%)
7. Improved process control and resulting metal quality caused by only a +/- 10 degree F holding temperature variation versus large swings each time a cold charge is placed into the hot bath
8. Improved process control and resulting metal quality due to reduced gas levels created by more stable temperatures and reduced burner fluctuation and reduced surface area within the bath
9. Reduced manpower requirements with automated charging systems vs. manual charging exposing operators to metal splash. 

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