The regenerative glass furnace uses a checkerwork of refractory to
Answer: A
The chambers reverse every twenty minutes or so, one heating while the other gives its heat back to the air. Without such recovery the fuel consumption would be far higher than it is. Chamber size is set by the reversal interval.
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Assertion (A): Glass furnaces reverse the direction of firing every twenty minutes or so.
Reason (R): The regenerator chambers must alternate between storing heat and giving it up.
Answer: B
Both are true and the reason gives the mechanism: one chamber is heated by the exhaust while the other preheats incoming air, and the roles must swap before the first is fully charged. The reversal is automatic and continuous.
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State whether the following is true or false.
A glass furnace is normally shut down and cooled for maintenance every few months.
Answer: C
Correct answer: False
A glass furnace runs continuously for eight to twelve years between rebuilds. Cooling it down cracks the refractory lining and costs weeks of lost production, so repairs are made hot wherever possible and the furnace is emptied only at the end of its campaign. That continuous operation is why a glass works cannot follow demand and must find a market for everything it makes.
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Cement manufacture is included among the process industries chiefly because it involves
Answer: D
Correct answer: a high temperature chemical conversion
The kiln converts limestone and clay into new compounds - calcium silicates and aluminates that did not exist in the feed - through calcination and clinkering at around 1,450 degrees. That chemical conversion is what makes cement a process industry rather than a materials-handling one, notwithstanding the very large amount of grinding on either side of it.
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Consider the following statements comparing the cement and glass industries.
1. Both consume large quantities of limestone.
2. Both are energy intensive and use continuous high temperature furnaces.
3. Both produce a crystalline product on cooling.
Answer: A
The first two are correct. The third fails for glass, whose whole value depends on cooling to an amorphous solid rather than crystallising, which would make it opaque and weak. Cement clinker by contrast is deliberately crystalline.
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Devitrification of glass means
Answer: B
Correct answer: unwanted crystallisation on cooling
Glass is a supercooled liquid held in a metastable state, and if it is cooled too slowly through the wrong temperature range, or held there, crystals nucleate and grow. The result is cloudy, weak and prone to cracking because the crystals and the remaining glass have different expansions. Controlling the cooling rate is what prevents it - and the same crystallisation, deliberately induced, is how glass-ceramics are made.
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