Brian Loncto

1
Refractories in Contact with Glass Melts

• Brian Loncto
• Tony Rodbourn
• School of Engineering
• NYS College of Ceramics
• Alfred University, Alfred, NY

2
Glass Furnace Design

• Tank refractory is in contact with glass
• Superstructure refractory is in contact with
  atmosphere above the melt
• Regenerators refractory is used to store heat
  to save on utilities

3
Refractory Selection
- Silica used mostly in superstructure advanta
ge silica is the main component in glass
melts, contamination is not as important
cheap disadvantage low use temperatures -
Fused-cast AZS used mainly in the
tank advantage good resistance to acid
(glass) attack more wear-resistant than
silica disadvantage high cost
4
Refractory Selection
- Basic Refractories not used except in certain
situations Why? - low resistance to chemical
attack by acidic liquids (siliceous batch)
5
Chrome-Magnesite
Strong push in late 1960s and 1970s to use
chrome-magnesite refractories. - problems arose
in refractories using sea-water magnesite as a
raw material Henthorn, R.S. and Jackson, B.
(1969) - tested refractories and their
resistance to siliceous batch attack - found
that chrome-magnesite refractories warped
significantly
6
Chrome-Magnesite
INSERT PICTURE FROM 1969 HERE!
7
Fused-Cast AZS

• Highly resistant to wear, especially at the
  liquid-solid-vapor line (flux line)
• Busby, T.S. et al (1978) - tested high
  content alumina, fused-cast AZS, and
  aluminosilicate refractories for wear at the
  flux line - general trend noticed that
  increasing silica content increased wear

8
Fused-Cast AZS

• Underwood, W. A. and Thomas, E. A. (1978)
• Tested bonded, sintered and fused cast AZS bodies
  
• Bonded heterogeneous bodies
• Sintered lower porosity and more homogenous
• Bonded AZS (lower zirconia, higher porosity),
  corroded at a higher rate than sintered AZS

9
Fused-Cast AZS

• Underwood, W. A. and Thomas, E. A. (1978)
• - Slightly greater static corrosion rate of
  sintered v. fused cast body
• This despite difference in zirconia content and
  porosity
• Can be contributed to much lower glassy phase of
  the sintered body

10
Glass Furnace Bottom

• Begley, E. R. (1988)
• Discusses Facts, Myths and Trends
• Driving forces for research
• Amount of energy lost out bottom of tank
• Reduction of cost of refractory while maintaining
  high glass quality

11
Glass Furnace Bottom

• Begley, E. R. (1988)
• -Myth 1
• - With careful refractory selection, metal
  drilling can be stopped
• - Metal becomes encapsulated in zircon layer and
  drilling stops
• - Both are wrong
• Begley, Herndon, and Schmidt (1972) state that
  metal drilling is proportional to metal line
  resistance of refractory

12
Glass Furnace Bottom

• Begley, E. R. (1988)
• - Begley, Herndon, and Schmidt (1972) state that
  metal drilling is proportional to metal line
  resistance of refractory
• - Only way to prevent metal drilling is to
  prevent metal from entering furnace

13
Glass Furnace Bottom

• Begley, E. R. (1988)
• - Myth 2
• - Increased temperatures do not make very much
  difference in refractory corrosion
• - Corrosion rates increase exponentially with
  temperature
• - Corrosion rate doubles every 50C

14
Glass Furnace Bottom

• Begley, E. R. (1988)
• - Myth 3
• -Zirconia inversion from the monolithic to
  tetragonal phase causes large joints to open on
  furnace bottom
• - Never seen in industry
• - Can only be produced in carefully controlled
  lab experiments

15
Looking to the Future (2000)

• Glass industry consumes 400,000 tons of
  refractory each year
• Due to collaboration between glass and
  refractories industry, consumption has dropped by
  2 per year for 30 years
• Over this time, refractory cost has increased 50

16
Looking to the Future (2000)

• Benefits of extending furnace life
• Refractories are largest single cost to build
  and repair of glass furnace
• Therefore, extending furnace lives reduces cost
  by reducing amount of refractory needed
• Glass contact area biggest determinant of
  furnace life
• Chrome oxide refractories display superior
  corrosion resistance, amid concerns

17
Looking to the Future (2000)

• Benefits of extending furnace life
• Chrome oxide is traditionally frowned upon due
  to possible contamination of color
• Advances in technology are allowing for its use
• Oxy-fuel firing is attractive to glassmakers due
  to higher efficiency and lower emissions
• Oxy-fuel firing increases refractory wear though
• Companies are working to develop a more resistant
  refractory

18
Current Bottom Design

• Pilkington, North America Laurinburg, NC plant
• - flat bottom design using
• 3 fused-cast AZS
• 12 clay

19
References
1. Henthorn, R.S. et al Refractories for the
Superstructure and Ancillary Parts of
Glass-making Furnaces, British Ceramic Society
Proceedings, No. 14, p. 41, August 1696. 2.
Busby, T.S. et al The solution of some
commercial refractories in soda-lime glass in the
temperature range 1200-1350ºC, Glass Technology,
vol. 19, no. 3, p. 54-56, 1978. 3. Underwood,
W.A. et al How to Avoid Problems When Applying
AZS Refractories, Glass Industry, p. 14-17,
September 1986. 4. Begley, E.R. Glass Furnace
Bottom Construction Trends, Facts, and Myths
A Review, Ceram. Eng. Sci. Proc., vol. 9, no. 3,
p. 306-314, 1988. 5. Evans, G. Glassmaking
Refractories looking to the future, Glass
Tech. vol. 41, no. 4, p. 109-111, 2000.
20
References (2)
6. Roux, J.M. Refined solutions for bottom
superstructure construction, Glass Ind., p.
18-19, March 2001. 7. Dunkl, M. et al Criteria
for the Selection of Refractories for Special
Glass Melting Tanks, Cer. Eng. Sci. Proc., vol.
24, no. 1, p. 197-210, 2003. 8. Varner, J.R.,
Glass-Tank Refractories, CES 414
Refractories, PowerPoint presentation, 2005. 9.
Faulkner, J., Pilkington Furnace Process
Engineer, conversation on April 25, 2005.