Glass Melting Technology: A Technical and Economic ... - OSTI

square or rectangular hopper located adjacent to the doghouse, features a discharge feeder to
ensure mass flow of batch and cullet. Heated material is fed out of the bottom and delivered to
the furnace in a continuous flow down through the silo, unlike conventional material handling
equipment that maintains the batch level of the silo in a nearly full condition.
Furnace exhaust gases flow through the batch in horizontal channels, which are formed by rows
of open-bottomed tubes in the silo. Gases from a given row are collected in a plenum at the side
of the hopper and directed up to the next row of tubes. They pass through the silo in a serpentine
path to create a cross/counter current flow with the batch as it moves downward. Because the
tubes are open-bottomed, the batch forms a free surface by its angle of repose at the bottom of
the channel. Since hot, flowing gases are constantly in direct contact with the surface of the fresh
batch material, heat transfer rates are many times greater than those achieved by indirect heat
transfer. Chemically reactive batch constituents (soda ash) react with SOx in the gases. This
forms sodium sulfite and sodium sulfate solid products that remain in the batch, partially
removing SOx from the gas stream and scrubbing the gases. Reactions with HCl and HF are also
possible. However, direct contact causes entrainment of fine batch dust in the flowing gases and
increased loading of particulate in the exiting gases. This requires additional cost for installation
of downstream gas cleanup equipment. This electrostatic mechanism (patent pending), which is
peculiar to the E-Batch technology, precipitates particulate matter from furnace exhaust gases
and deposits it onto the batch surface, where it is delivered to the furnace with the heated batch.
This meets the strictest regulations for particulate emissions.
BOC Gases installed a 14.4tpd E-Batch module in a slip stream of exhaust gases from the four
operating oxy-gas fired furnaces at Gallo Glass (Modesto, CA). Actual glass batch was fed into
the unit, although the preheated batch/cullet was not directly fed into a furnace, to evaluate issues
involving oxy-fuel, particulates, operation with cullet, maintenance and cleaning methods, cold
start-up procedures, and engineering parameters. With no device for air preheating, the inherent
exhaust gas temperature of oxy-fuel furnaces is quite high. Thus the inlet temperature for the E-
Batch, although limited by the sticking temperature of the batch, can be chosen by the designer.
Hot exhaust gases from the furnace are tempered in the flue channel with cooled gases recirculated
from the stack. The amount of re-circulated gases is controlled so that the inlet
temperature to the E-Batch module is about 1148 ˚ F (620 ˚ C), or as high as possible while not
exceeding the sintering temperature of the batch and cullet. Air could also be used for the
tempering, but re-circulated gases, rather than air, are preferable.
Initial advantages of the E-Batch preheater over other types have been suggested, as follows.
• Batch and cullet in any ratio and cullet of any normal size criteria can be handled in norms
considered optimum for the glass melting process.
• The E-Batch module can be adapted to any conventional material handling and furnace
charging equipment.
• All the desired functions can be achieved with one box rather than with a train of devices
through which gas flows in a series.
A proof-of-concept bench-scale unit in the laboratory had initially suggested that:
• velocities for heat transfer are optimum;
76