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A review of Supplemental Oxygen Methods for
Glass Melting
Increasing the amount of Oxygen in air from its initial 21% significantly
increases the flame temperature achieved with any fuel. For example,
natural gas burned in air has a flame temperature of 3520 °F
while the flame temperature of natural gas burned in 23% O2
is 3640 °F.
This effect is shown in figure below.
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| Higher flame temperatures in the glass furnace improve
the heat transfer to the batch and glass. This is due to the fact
that all three heat transfer mechanisms, conduction, convection,
and radiation, are flame temperature dependent: |
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| Conduction: |
Q µ (Tf - Tp) |
| Convection |
Q µ (Tf - Tp) |
| Radiation |
Q µ (Tf4- Tp4) |
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| where: |
Tf = Flame Temperature |
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Tp = Product (Lime) Temperature |
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| At glass melting temperatures radiation is the dominant
mode of heat transfer. The heat transfer rates for conduction and
convection are linear with the difference between the glass and
the flame temperature. The heat transfer rate due to radiation is
proportional to the difference between glass and flame temperature,
each raised to the fourth power. Oxygen increases the flame temperature,
which greatly increases radiation, the already dominant mode of
heat transfer. Thus with oxygen enrichment, more heat is absorbed
by the product, less heat is lost in the exiting combustion gas,
and the combustion process becomes more efficient. |
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| Oxygen Enrichment: |
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| With this technique, oxygen is injected into the main
combustion air header well ahead of the delivery point to the furnace.
This pre-mix of oxygen is most common on recuperative furnaces or
unit melters that have many such delivery points (hot or cold air
burners) or on regenerative melters where it is desirable to use
the oxygen to enhance the entire combustion process in a consistent
manner. Experience is needed to deliver the right amount of heat
to the right zones and to ensure safe application of the Oxygen |
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| Oxygen Lancing: |
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| This method has historically been the most cost-effective
way to use oxygen to supplement air-fuel combustion. The strategic
injection of oxygen beside, beneath or through air-fuel flames has
allowed glass melters to reach campaign objectives in terms of pull
rate, fuel efficiency and glass quality. The benefits of oxygen
lancing accrue from having the oxygen mix with fuel where it is
most needed; namely in oxygen-starved areas of the combustion space
or in the under-side (glass surface side) of the air-fuel flames
where flame temperature has the greatest impact on heat transfer
to the melt. Knowing how many lances, where to place them and flow
rates to use, allow us to deliver the most cost effective solution. |
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Oxygen Boosting:
This method of using supplemental oxygen is relatively new to
glass manufacturers and has been enabled by the emergence of superior
oxy-fuel burner offerings developed for the 100% oxy-fuel conversion
of melters. The boosting concept uses oxy-fuel burners positioned
within the air-fuel melter to increase production, quality, efficiency
and furnace stability. Depending on the needs of our customers
we can tailor the operation to deliver the benefit(s) desired.
Oxy-fuel boosting is typically used to increase pull rate on a
furnace that is at capacity or that has been crippled due to a
failure or loss of effectiveness of the air-fuel combustion system.
Payback for the technology is often less than three months. The
advantages of our boost technology are so significant that many
furnaces, which used Air Products' boost at the end of the previous
campaign to address furnace limitations, are rebuilt and come
on-stream using boost.
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| Here, the high temperature flames of oxy-fuel combustion
are placed over the cold batch to create a tremendous amount of
heat transfer. The result is early batch glazing and significantly
enhanced melt run-off; this superior melt rate then allows for an
increase in production or a reduction in over all fuel.Talk to us
to find out which of these, or other, techniques is right for you.
We continue to develop new technologies to improve glassmaking.
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