Two types of air emissions are generated: those
from the combustion of fuel for operating the
glass-melting furnaces, and fine particulates from
the vaporization and recrystallization of materi-
als in the melt. The main emissions are sulfur
oxides (SOx), nitrogen oxides (NOx), and particu-
lates, which can contain heavy metals such as
arsenic and lead. Particulates from lead crystal
manufacture can have a lead content of 20–60%
and an arsenic content of 0.5–2%. Certain spe-
cialty glasses can produce releases of hydrogen
chloride (HCl), hydrogen fluoride (HF), arsenic,
boron, and lead from raw materials. Container,
pressing, and blowing operations produce a pe-
riodic mist when the hot gob comes into contact
with the release agent used on the molds.
Cold-top electric furnaces, in which the melt
surface is covered by raw material feed, release
very little particulate matter, as the blanket acts
as a filter to prevent the release of particulate
matter. Some releases of particulates will take
place in tapping, but furnace releases should be
of the order of 0.1 kilogram per ton (kg/t) when
operated this way.
Lead glass manufacture may result in lead
emissions of about 2–5 kg/t.
In all cases, the concentration of heavy metals
and other pollutants in the raw flue gas mainly
depends on the type of fuel used, the composi-
tion of the feed material, and the portion of re-
cycled glass. High input of sulfates or potassium
nitrate may increase emissions of sulfur dioxide
and nitrogen oxides, respectively. Where nitrate
is used, more than two thirds of the introduced
nitrogen may be emitted as nitrogen oxides. The
use of heavy metals as coloring or decoloring
agents will increase emissions of these metals.
will reduce energy requirements (for an esti-
mated 2% savings for each 10% of cullet used in
the manufacture of melt) and thus air emissions
(up to 10% for 50% cullet in the mix). Typical re-
cycling rates are 10–20% in the flat glass indus-
try and over 50% for the blown and pressed glass
industries.
The amount of heavy metals used as refining
and coloring or decoloring agents, as well as use
of potassium nitrate, should be minimized to the
extent possible.
In the furnace, particulates are formed through
the volatilization of materials, leading to forma-
tion of condensates and of slag that clogs the fur-
nace checkers. Disposal of the slag requires
testing to determine the most suitable disposal
method. It is important to inspect the checkers
regularly to determine whether cleaning is
required.
Particulate matter is also reduced, for example,
by enclosing conveyors, pelletizing raw material,
reducing melt temperatures, and blanketing the
furnace melt with raw material.
Reductions in wastewater volumes are pos-
sible through closed cooling water loops and
improved blowoff techniques.
Target Pollution Loads
Modern plants using good industrial practices
are able to achieve the pollutant loads given here.
Because of the lack of nitrogen in the oxidant,
using oxyfuel-fired furnaces produces four to five
times less flue gas volume than regenerative fur-
naces. As a result nitrogen oxides are reduced by
80%, and particulates are reduced by 20–80%.
For furnaces that operate with a cover of raw
material, a target of 0.1 kg/t for particulates is
realistic. Reductions in sulfur dioxide are
achieved by choosing natural gas over fuel oil
where possible.
Sources
Bounicore, Anthony J., and Wayne T. Davis, eds. 1992.
Air Pollution Engineering Manual. New York: Van
Nostrand Reinhold.
Economopoulos, Alexander P. 1993. Assessment of
Sources of Air, Water, and Land Pollution: A Guide to
Rapid Source Inventory Techniques and Their Use in
Formulating Environmental Control Strategies. Part 1:
Rapid Inventory Techniques in Environmental Pollution.
Geneva, World Health Organization.
Sittig, Marshall. 1975. Pollution Control in the Asbestos,
Cement, Glass, and Allied Mineral Industries. Park
Ridge, N.J.: Noyes Data Corporation.
World Bank. 1996. “Pollution Prevention and Abatement:
Glass Manufacturing Plants.” Draft Technical Back-
ground Document. Environment Department, Wash-
ington, D.C.
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