Pyroprocessing and Kilns Questions and Answers

Answer: C

Correct answer: False

A flame that is too short concentrates the heat in one place, overheating the refractory and burning the clinker too quickly for the reactions to complete evenly. Too long a flame spreads the heat and leaves the burning zone cold. The right flame is a matter of matching the kiln and the feed, not of minimising length.

Answer: D

Correct answer: at the high temperatures of the main flame

Thermal nitrogen oxide forms from nitrogen and oxygen in the combustion air, and the rate rises very steeply with temperature - so nearly all of it is produced in the hottest part of the main flame. The calciner, running some 600 degrees cooler, produces far less, which is one of the arguments for burning more fuel there.

Answer: A

The reagent reacts with the oxides to give nitrogen and water within a fairly narrow temperature window, which the preheater conveniently provides. A catalytic version works at lower temperature but costs considerably more.

Answer: B

The first two are correct. The third names the wrong measure, since dust is controlled by bag filters or electrostatic precipitators rather than by wetting the feed. Wetting the meal would in any case cost fuel to evaporate again.

Answer: C

Correct answer: False

Around 60 per cent of the emissions come from decomposing the limestone, and that carbon dioxide is released whatever the fuel and however efficiently it is burnt. Fuel measures address the smaller share; the process emission requires capture, or a binder that needs less limestone in the first place.

Answer: D

Correct answer: a build-up of material that restricts the bore

Rings are accretions of clinker or dust that build up on the lining at a particular point, narrowing the passage and disturbing both the gas flow and the movement of the charge. They can grow enough to block the kiln, and they are usually attacked with an air cannon or, if that fails, by stopping and cutting them out.

Answer: A

Correct answer: carry the weight of the shell on its support rollers

The tyre is a heavy steel band around the shell that transfers the whole weight of kiln, refractory and charge onto the support rollers. The shell alone could not carry that load without ovalising, so the tyres are what make the arrangement possible - the drive is a separate gear ring.

Answer: B

Correct answer: False

The shell is a comparatively thin steel tube carrying an enormous distributed load, and without tyres it would flex into an oval under its own weight at every revolution. That flexing would destroy the refractory in short order. The tyres spread the load into the rollers and keep the shell round.

Answer: C

Air leaking in dilutes the gas and costs fuel to reheat, while gas leaking out is both a hazard and a loss. Sealing between a rotating shell and a fixed hood is a persistent engineering difficulty. Seal condition is checked routinely because wear is gradual and easily missed.

Answer: D

Correct answer: Both A and R are true, and R is the correct explanation of A

Both are true and the reason gives the mechanism. Air leaking in through a worn seal is heated to whatever temperature it reaches before leaving with the exhaust, and it takes that heat with it. It contributes nothing to combustion, since it enters downstream of the flame, so the fuel that heated it is simply lost.