Eclipse Combustion Engineering Guide - Burnerparts

FUME INCERATION – SELECTION & SIZING GUIDELINES
I. Process Information Required
A. Fume stream flow rate, scfm or acfm. (If acfm,
specify temperature at which flow is measured.)
Maximum and minimum flow rates are required.
B. Fume stream temperature at inlet to burner at
maximum and minimum flow rates.
C. Oxygen content of fume stream.
D. Amount of particulates or other non-volatile
matter in fume stream.
E. Incineration temperature required, typically:
600-900°F for catalytic incinerators
1200-1500°F for thermal incinerators.
F. Residence time required in combustion chamber,
typically, 0.3 to 0.7 seconds.
II. Burner Type Selection
Two basic types of burners are used to fire fume incinerators:
raw gas burners, which obtain their combustion
air from the incoming fume stream, and fresh air burners,
which obtain theirs from an external source.
Raw gas burners permit higher fuel efficiency, but they
can’t be used under as wide a variety of operating conditions.
The table below provides some general guidelines
for burner selection.
Fresh Air
Selection Factor Raw Gas Burner Burner
Oxygen content of 18-21% ok ok
fume stream 13-18% maybe–check mfr. ok
below 13% no ok
Fume stream Up to 1100°F Depends on burner– ok
{
{
{
temperature
check mfr.
entering burner Over 1100°F no ok
Particulates or None ok ok
other non-vola- Low probably ok ok
tiles in stream Heavy Depends on burner– ok
check mfr.
III. Calculating Burner Input
A. For raw gas burners, use the chart on the top of page
45.
B. For fresh air burners use the chart on the bottom of
page 45.
These charts give Btu/hr required per scfm of
fume stream. Multiply this figure by the fume
stream flow rate, in scfm, to determine total burner
heat input.
C. If the burner will take part of its combustion air
from the fume stream and the rest from an outside
source, heat input can be closely estimated with
this method:
From page 45, deteremine Btu/hr required with
a raw gas burner. Call this B r .
From page 45, deteremine Btu/hr required with
a 100% fresh air burner. Call this B f .
Btu/hr (partial fresh air) =
Br + % fresh combustion air (Bf–Br)
100
IV. Sizing Profile Plates
If the burner is the type that is placed inside the
fume duct, it has to be surrounded with a profile plate.
Fumes are forced to pass through the gap between the
profile plate and burner, ensuring that they mix completely
with the burner flame.
To size the profile gap, you need to know:
1.Temperature of the fume stream passing over the
burner,
2.Fume stream pressure drop required across the profile
gap (see burner manufacturer’s catalog data).
Refer to the chart on page 17. Locate the required
pressure drop at the bottom of the chart, then read up
to the appropriate temperature curve and left to the
stream velocity. Divide this velocity into the fume
stream flow expressed in acfm:
Profile gap, sq ft = Fume stream flow, acfm
Fume stream velocity, ft/min
For best results, the profile gap must be uniform
width around the perimeter of the burner. Check manufacturer’s
literature for specific recommendations on
design and location of profile plates.
NOTE: The air diffuser openings in some types of
burners are considered part of the profile area. If so,
deduct the area of these openings from the total profile
area. The result will be the area of the gap around
the burner.
V. Sizing Downstream Combustion Chamber
A. Chamber Cross-sectional area (A), Good practice
requires no great than 30 ft/sec velocity in the combustion
chamber, so
A, sq ft =
acfm of heated fume stream
1800
B. Combustion chamber length (L) is dictated by
the required residence time.
L, feet = Stream velocity x residence time.
If, for example, velocity is 30 ft/sec, and residence
time is 0.5 seconds, L is 15 feet.
WARNING! Incineration of fume streams containing
compounds of chlorine, fluorine, or sulfur will produce
combustion products which may be toxic or corrosive, or
both. Consult with environmental authorities before considering
fume incineration.
46