Pyroprocessing and Kilns Questions and Answers

Answer: C

The flame runs several hundred degrees hotter, since heat must flow from gas to solid against a temperature difference. Confusing the two figures is a common error when the burning zone is described. Heat must flow down a temperature gradient, so the gas has to be hotter.

Answer: D

Solid-state reaction alone would be far too slow, so the melt provides the medium in which the tricalcium silicate can form. Its quantity is governed by the alumina and iron content, which is one reason those oxides are controlled.

Answer: A

It requires both the high temperature and the liquid phase found only there, which is why the burning zone governs the quality of the clinker. Everything before it prepares the charge and everything after it preserves what has been made.

Answer: B

Slow cooling lets tricalcium silicate decompose back towards the slower-reacting dicalcium silicate and lime. Quenching locks in the phase assembly formed at temperature, which is why cooler performance bears directly on cement strength.

Answer: C

Both are true and the reason gives the purpose: the useful phase is stable at high temperature but not on the way down, so the cooler is there to preserve chemistry as much as to recover heat and protect the conveyors.

Answer: D

Correct answer: blowing air through a bed of clinker on a moving grate

The clinker lies on a grate through which cooling air is forced from below, so it is quenched rapidly and the air is heated in the process. Rapid cooling matters for clinker quality as well as for heat recovery - slow cooling lets the alite decompose and the free lime rise.

Answer: A

Correct answer: True

The air heated in the cooler is drawn straight into the kiln as secondary combustion air, and into the calciner as tertiary air. Recovering that heat is a large part of why a modern plant burns around 3,000 kilojoules per kilogram of clinker rather than the 6,000 a wet process needed.

Answer: B

Multiplying 3,200 by 4,000 gives 12.8 million megajoules a day. Specific heat consumption expressed per tonne of clinker is the standard measure by which kilns are compared. It is quoted alongside electrical consumption in every plant benchmark.

Answer: C

The theoretical minimum for the chemistry is around 1,750, so even a good kiln uses roughly twice what thermodynamics demands. Older wet kilns consumed half as much again as a modern dry one. The gap is almost entirely accounted for by evaporating slurry water.

Answer: D

The chemistry needs roughly 1,750 megajoules a tonne while a good modern kiln uses somewhat over 3,000. Losses through the shell, in the exhaust gas and with the clinker account for the difference. Closing that gap further is the object of most kiln development work.