7
Eclipse Extern-A-Therm Recuperators, Design Guide 540, 3/9/2009
In addition when using the recuperators on aluminum
melting or holding furnaces, the exhaust temperature
must be diluted to less than 1300°F (704°C). This will
ensure that any aluminum in the exhaust will condense
out before entering the recuperator. Aluminum
condensing on the recuperator tubes will cause damage.
When in doubt consult Eclipse.
Ŷ
Failure to observe these conditions can destroy
the recuperator and will void the warranty.
Determine the Size of Recuperator Required
It is assumed that the net BTU requirement is known. The
table below is an approximate guide for the efficiency with
an Extern-A-Therm recuperator at various furnace
temperatures with 10% excess combustion air. This is
sufficiently accurate to determine the size of recuperator
to use; it should not be used to determine actual gas
usage.
Calculate the gross BTU requirement using this efficiency,
then check the Extern-A-Therm recuperator capacities in
the datasheet to determine the size of recuperator.
Example:
Net required 1.0 mm BTU/hr with furnace temperature of
1700°F. Using the table above, the efficiency = 67%.
Therefore, the gross input = 1.0mm BTU/hr ÷ 0.67 =
1.49mm BTU/hr. From the datasheets, a 1500 MA
Extern-A-Therm with a capacity of 0.4mm BTU/hr to
1.6mm BTU/hr must be used. If a higher preheated air
temperature is required the 2500 MA should be used.
Dilution Air
If the furnace temperature is above 2100°F dilution air
must be introduced to cool the exhaust gases to 2100°F
before they enter the recuperator.
As a guide, the following chart can be used to determine
the amount of dilution air required.
Number of Extern-A-Therm Recuperators
It is recommended that one recuperator be used for each
zone of control. This has the advantage that the
combustion air flow is controlled on the cold side of the
recuperator. All the subsequent instructions and
descriptions are written with this assumption. If it is
required that a single Extern-A-Therm recuperator will
pre-heat the combustion air for multiple zones, consult
Eclipse.
Mounting the Recuperator
The Extern-A-Therm recuperators are designed for
vertical mounting with the recuperator tubes hanging
vertically down. If an alternative mounting arrangement is
required, contact Eclipse.
The recuperator and exhaust housings have sufficient
strength to be self supporting from the mounting flange,
and can support the eductor if fitted. Eclipse recommends
the use of flexible piping at the air inlet/outlet and
entrainment air connections to accommodate expansion
and contraction. See Figure 3.2 for a typical arrangement.
Do not add additional insulation to the outside of the
recuperator, as this will damage the unit.
Mounting the Eductor
The eductor can be mounted directly to the recuperator.
The outlet flange on the recuperator is of sufficient
strength to support the weight of the eductor; no additional
support is required for the eductor.
The standard eductor is designed for vertical mounting, if
horizontal mounting is required, consult Eclipse. No
additional exhaust ducting should be connected directly to
the eductor.
There should be no restrictions at the eductor outlet; this
would affect the eductor performance. See Figure 3.3.
The outside of the eductor should not be insulated.
Furnace Temperature
°F (°C)
Efficiency with
Extern-A-Therm Recuperator
1500 (815)
70%
1600 (817)
68.5%
1700 (926)
67%
1800 (982)
65.7%
1900 (1037)
64.4%
2000 (1093)
63%
2100 (1148)
60.6%
2200 (1204)
59.3%
2300 (1260)
58%
CAUTION
Furnace
Temp
°F (°C)
Burner Capacity BTU/hr (kW)
100,000
(29.3)
200,000
(58.6)
500,000
(146.5)
1,000,000
(293.1)
2,000,000
(586.1)
2200
(1204)
75
(2.1)
150
(4.3)
375
(10.6)
730
(20.7)
1,460
(41.3)
2300
(1260)
150
(4.2)
300
(8.5)
750
(21.2)
1,500
(42.4)
3,000
(84.9)
2400
(1315)
220
(6.2)
440
(12.4)
1,100
(31.1)
2,200
(62.3)
4,400
(124.6)
Table Values for
Volume scfh (m
3
/hr) Cooling Air
