Natural gas tin float bath roof

A tin float bath with an entirely new heat-insulating bath roof comprising two parts, first, an elongated steel chamber of an inverted U-shape fabrication with sinusoidal-layered ceramic fiber blankets and ceramic fiber boards and, second, side-mounted or top-mounted parallel automatic recuperative natural gas burners. The controlled cooling of the flat glass is accomplished with no problems of contaminating the bath atmosphere, the flat glass or the molten tin.

BACKGROUND OF THE INVENTION 
This invention relates generally to the controlled cooling of the molten 
flat glass ribbon as it passes through the tin float bath at a continuous 
rate. Manufacturing flat glass comprises the delivering of molten glass to 
a bath of molten tin and advancing the glass along the surface of the tin 
under thermal conditions that do not contaminate the internal atmosphere. 
Such contamination is detrimental to both the glass product and the molten 
tin. Glass at approximately 1900 degrees F enters the bath from the 
melting tank and at approximately 1200 degrees F exits the bath to a 
cooling lehr. In prior art installations the temperatures in the bath are 
maintained with electrical resistance heaters suspended from the roof over 
the ribbon of glass. Such electrical heaters do not contaminate the bath 
atmosphere. The metal plate shell of the prior art bath roof is protected 
from the heat with an internal refractory lining, which has little or no 
heat-insulating qualities and isolates the electrical equipment plenum 
above from the heated cavity. This prior art construction has been used 
over the past twenty-five year period. Attempts to burn natural gas over 
the bath by the glass industry failed the industry's contamination 
requirements. 
PRIOR ART 
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Patents 
Number Date Relationship 
______________________________________ 
3,083,551 
04.02.63 Layout of float with molten 
metal 
3,332,763 
07.25.67 Layout of tin float bath utilizing 
electrical heating elements 
3,486,869 
12.30.69 Layout of tin float bath utilizing 
regular and auxiliary electrical 
heating elements 
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Reference Material (To assist in understanding the presentation) 
The Handbook of Glass Manufacture, volume II, 3 rd edition, pages 714-2 
through 714-21 
The Glass Industry Magazine, April 1980 issue, pages 18,20,22, article 
"Float Glass Production: Pilkington vs PPG," by Ronald A. MeCauley, 
Rutgers University. 
A Review Lecture, "The float glass process," by L. A. B. Pilkington, 
delivered Feb. 13, 1949. 
Reference Drawings, sheet 1 with FIGS. 1 and 2 and sheet 2 with FIG. 3 
showing the existing electrical tin float bath. 
Prior art uses electrical heating elements with intricate power supplies, 
conductors, contactors and controls. The present invention's use of a 
natural gas system with automatic recuperative burners surpasses the prior 
art by bring more cost-efficient and more energy-efficient, does not 
contaminate the bath atmosphere, is more easily installed, minimizes 
maintenance and shut-down, all of which promotes increased productivity. 
SUMMARY OF THE INVENTION 
The construction of an entirely new operational roof for the tin float bath 
comprises two parts, the newly designed fabrication of the bath roof and 
the use of automatic recuperative natural gas burners instead of the prior 
art electrical heating elements. Individually, both the new fabrication 
and gas burners contribute to a cost-efficient operation that highly 
excels the prior art operation. 
The fabrication of the new roof housing utilizes a one-half inch steel 
plate furnace shell of a required depth to allow the installation of the 
gas burners in either a horizontal or a vertical position. The interior 
insulation of the new furnace shell consists of a layered ceramic fiber 
lining of blanket modules sold commercially as "Firewall Bonded 22," and 
two one-inch thick boards sold commercially as "Fiberfrax Duraboard," 
type, maintaining a temperature differential from 2200 degrees F. inside 
the shell to an approximately 200 degrees F. outside the shell. No cooling 
chamber is required above the new bath enclosure as is necessary to 
protect the prior art electrical equipment and materials of the prior art 
tin float bath. Such cooling chamber causes a condensation of tin 
oxide/tin sulfide on the suspended internal refractory lining which then 
becomes a contaminate of the glass. 
The use of the new automatic recuperative natural gas burners in the tin 
float bath process will result in the following operational cost 
advantages. The utilization of natural gas is more cost-efficient than 
electricity, approximately a conservative seventy percent savings in this 
case. The new gas burner installation encompasses few moving parts, easy 
insertion of the burners through the mounting flange even during full 
operation, only two piping connections for gas and combustion air, and 
simple HIGH-FIRE, LOW-FIRE, OFF control. Glass production is a twenty-four 
hour daily operation throughout the mechanical life of the bath. Burned 
out or broken electrical heaters periodically cause prior art operational 
adjustments to maintain glass flow until quality is affected and complete 
shut down then becomes necessary. Any shutdown costs are prohibitive, 
thousands of dollars per minute. Prior art shutdowns entail stopping the 
glass flow, cooling the bath, raising the roof, replacing the failed 
electrical heaters with new, making electrical reconnections, lowering the 
roof, reheating the bath and again establishing the glass flow in its 
proper atmosphere. This prior art shutdown encompasses engineering, 
demolition and installation for a ninety day period during which no glass 
is produced. With the new automatic recuperative gas burners no shutdown 
is necessary. Seldom will the gas burners fail. If one does require 
replacement, it can be readily removed and replaced. This replacement will 
take approximately two hours, during which time the glass flows 
continuously with no interruptions. The longevity of the installation is 
increased substantially because, first, the new burners are capable of 
withstanding the corrosive nature of tin oxide/tin sulfide and, also, the 
new layered ceramic fiber lining does not deteriorate.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An explanation of the prior art tin float bath must precede the detailed 
presentation of this invention. In order that this invention may be 
understood more readily, references to the accompanying figures will be 
made. 
FIG. 1 is a plan view of a prior art typical tin float bath chamber with 
electrical heating zones numbered 1' through 32' and with the associated 
zone transformers, numbered 1" through 32". Glass enters the bath from the 
right and exits from the left. 
FIG. 2 is a longitudinal elevation of the prior art bath showing the bath 
roof 33, the bath bottom 34 and the heating transformer locations above. 
FIG. 3 is a transverse section taken on the line 3--3 of FIG. 1, detailing 
the electrical materials internal to the prior art bath roof and 
consisting of copper bus bars 35 terminating in the bus box 36 and 
connectors 37. Cables 38 connect bus bars 35 to the electrical heating 
elements 39 and to the transformers 3" and 8" above. FIG. 3 is typical 
through the length of the bath. Electrical resistance heaters 39 are shown 
extended into the bath atmosphere 40 over the glass ribbon 41 floating on 
the tin 42. The prior art bath roof 33 is suspended separately from the 
bath bottom 34 by a support structure 43. The prior art bath roof 33 with 
all of its associated electrical equipment and materials as shown in FIGS. 
1, 2 and 3 shall be removed in its entirety and replaced with a new bath 
roof 331 as shown in FIG. 6. The prior art support structure 43 will 
remain to support the new bath roof 331. The quantities of electrical 
items eliminated with the prior art roof are listed on FIG. 13. 
FIG. 4 is a plan view of the new elongated tin float bath chamber showing 
the locations of one hundred eighteen natural gas burners 44 in their 
respective heating zones in parallel. Glass enters the bath from the right 
and exits from the left. The new bath roof 331 is shown on FIGS. 5, 6, 7 
and 8. 
FIG. 5 is a longitudinal elevation of the new elongated tin float bath 
chamber showing the locations of the natural gas burners 44 mounted 
through the side walls of the new bath roof 331. 
FIG. 6 is a transverse section taken along the line 6--6 of FIG. 4 showing 
the new bath chamber roof 331 which has depending side walls side-mounted 
natural gas burners 44 are installed horizontally through the depending 
side walls of roof 331. Space 45 is allocated for both natural gas and 
combustion air header pipes. 
FIG. 7 shows the natural gas burners 44 installed parallel to each other 
vertically through the top of the new bath roof 331. Either or both of the 
horizontal or vertical installations can be utilized and the depth of the 
new bath roof 331 will be altered accordingly. 
FIG. 8 shows the construction details of the new bath roof 331. The shell 
80 of the new bath roof is fabricated of one-half inch plate steel and is 
made rigid with an I-beam and angle framework 84. The shell 80 and the 
framework 84 are suspended from the support structure 43. The interior of 
the shell housing is insulated with sinusoidal layers of ceramic fiber 
blanket modules 81 sold commercially as "Firewall Bonded 22," and two 
one-inch thick, rigid, high temperature ceramic fiber boards 82 sold 
commercially as "Fiberfrax Duraboard," type RG, all as manufactured by The 
Carborundum Company. This insulation provides the following advantages: 
lower heat losses, faster heat-up and cool-down cycles, lower installed 
costs, easy repairs, thermal shock resistance, high heat internal 
reflectance, good sound absorption, excellent corrosion resistance and 
longer life of the new bath. Side seal blocks 83 seal the void between the 
new elongated roof 331 and the present elongated bath bottom 34 to form 
the complete tin float bath chamber. Items 47, 49, 50 and 52 of the 
burners 44 are described as part of FIG. 9. 
FIG. 9 is a cutaway view of the automatic recuperative natural gas burner 
similar to that as fabricated from an Fe Cr Al alloy known and sold 
commercially as "Kanthal APM" by Eclipse Combustion of Rockford IL. Each 
burner consists of an ignition and heat-radiating chamber body 46 for 
operation up to 2370 degrees F. which encloses the entire burner and has a 
semi-spherical closed end portion 46a as shown in FIG. 9, a flanged mount 
47 welded to the external chamber roof bath steel shell 48, complete with 
gas inlet 49, air inlet 50, air metering orifice 51, an exhaust outlet 52 
and the internals with a burner nozzle 53 within a sleeve 54 coaxial with 
body 46. This particular burner type is capable of withstanding the 
corrosive nature of the tin oxide/tin sulfide present in the bath 
atmosphere. 
The preceding paragraph refers primarily to the preparation of the new bath 
roof. The remaining equipment, instruments, piping and valves are shown on 
FIG. 10, a typical piping and instrumentation diagram. The explanation of 
FIG. 10 will describe the operation for the installation with the 
horizontal burners. The operation with the vertical burners is similar. A 
four burner zone 7 is shown. Zones with six, seven and eight burners are 
similar, differing only in the quantity of burners. Two blowers, the main 
gas supply with valve train, the control valves and instruments provide 
combustion air and gas to the gas burners on both sides of the bath. 
Natural gas is provided via a four inch gas line 54 to the main gas valve 
train 55, consisting of: two manual shut-off valves, a pressure regulating 
valve, two electrically-operated manually-reset shut-off valves with 
electrical interlocks, a vent valve with an electrical interlock and 
pressure switch with an electrical interlock. All electrical interlocks 78 
are connected to the ignition section of the burner control panel. The 
four inch natural gas line 56 continues from the main gas valve train as 
the main gas supply header running along total bath length in allocated 
space 45, FIG. 6. 
Combustion air is provided by a centrifugal blower 57 via an eight inch 
main air supply header 59. A pressure switch 58 with an electrical 
interlock 79 is utilized to sense correct air header pressure. This eight 
inch main air supply header 59 continues along total bath length in space 
45, FIG. 6. 
The four inch main gas supply header 56 along both sides of the length of 
the bath is tapped at each burner zone location to form a one inch 
secondary gas header 61. Located at the beginning of the one inch 
secondary gas header are two valves. The first is the burner zone 
secondary gas header ON-OFF solenoid valve 62 with an electrical interlock 
79. The second is the burner zone secondary gas header proportionator 
valve 63 with a proportionator impulse line 64 tapped into the secondary 
air supply header 60. This proportionator valve is required to maintain 
the proper natural gas to air ratio required for combustion within the 
automatic recuperative burner 44. The one inch secondary gas header 61 is 
continued from the proportionator valve and is tapped with a one-half inch 
line 65 connected to the zone automatic recuperative burner 44. This line 
is provided with an adjustable valve 66. 
The eight inch main air supply header 59 along both sides of the length of 
the bath is tapped at each burner zone location to provide a four inch 
secondary air supply header 60. Located at the beginning of the four inch 
secondary air supply header is an electrically-operated motor-driven valve 
67, which regulates the combustion air flow. The motor-driven valve 67 is 
provided with a two-position switch 68 which indicates LOW-FIRE or 
HIGH-FIRE conditions. Both the motor-driven valve and the two-position 
switch have electrical interlocks 79. The four inch secondary air supply 
header 60 is continued from the motor-driven valve 67 and is tapped with a 
one inch air line 69 connected to the zone automatic recuperative burner 
44. This line is provided with an adjustable shut-off valve 70. 
In addition, the automatic recuperative burner 44 is provided with a two 
inch exhaust stack 71 to atmosphere. Each automatic recuperative burner is 
furnished with an ignition system. This system comprises an ignition 
transformer 72, ignition plug 73 and an ultraviolet flame detector 74. 
Associated with this system are a timer 75, a relay 76 and an indicating 
light 77 mounted in the ignition section of the burner control panel. Each 
zone burner has its respective interlock 79. All 79 interlocks are part of 
the DCS, Distributive Control System. In each burner 44 combustion air and 
natural gas are ignited and burned within the heat-radiating chamber 46. 
The residue from the burnt gases (by products of combustion of the natural 
gas) is exhausted externally to the bath and has no contact with the 
atmosphere inside the bath. As the burnt gases move through the chamber to 
the exhaust outlet 52, they preheat the incoming gas and air for a more 
efficient operation. 
One burner control panel for the control of both sides of the bath has 
three functional sections: main valve train control, the burner ignition 
control and flame monitoring control. The operational status of all 
burners is indicated at this panel. If one burner fails to ignite, or 
fails to continue operating, the operating personnel knows immediately the 
condition and location of that particular burner and will initiate the 
corrective procedures.