Pulp and Paper Industry Questions and Answers

Answer: C

The colours name the stages of one closed loop, and following it round is the whole of understanding the recovery island. Green liquor becomes white again in the causticiser. Each colour names one point in the closed loop.

Answer: D

Correct answer: causticising with lime

The smelt dissolved in water is green liquor, containing sodium carbonate. Adding slaked lime converts the carbonate to hydroxide and precipitates calcium carbonate: \[ \mathrm{Na_2CO_3 + Ca(OH)_2 \rightarrow 2NaOH + CaCO_3}. \] The lime mud is filtered off and calcined back to lime in a rotary kiln, so the lime circulates as well, and the restored white liquor returns to the digester.

Answer: A

Refining is a stock preparation operation on the pulp itself, not part of the chemical loop. The other three are the three main stages of recovery. Refining happens far downstream on the pulp itself. The loop closes at the causticiser.

Answer: B

Kraft dominates because it tolerates a wider range of wood species and its recovery is better developed. Sulphite survives in niches where a brighter, more easily bleached pulp is wanted. Kraft also handles resinous species that sulphite cannot.

Answer: C

Correct answer: the residual lignin in a pulp

Kappa number measures how much potassium permanganate a pulp consumes, which is proportional to the lignin remaining after cooking. It is the mill’s daily control figure - it says whether the cook has gone far enough and how much bleaching chemical the pulp will need, and it substitutes for a direct lignin determination that would be far too slow.

Answer: D

Both are true and the reason gives the connection: cooking to a lower kappa costs yield, so the mill trades cooking against bleaching to reach the brightness it needs at least cost. Cooking too hard damages the fibres as well.

Answer: A

The first two are correct and describe elemental chlorine free bleaching. The third is wrong, since bleaching removes further material and always costs a little yield. Brightness is bought at the price of some material.

Answer: B

Correct answer: formed chlorinated organics in the effluent

Elemental chlorine reacting with residual lignin produced chlorinated organic compounds, measured as adsorbable organic halides, including dioxins. That is what drove the shift to chlorine dioxide, which does the same job with far less halogenated by-product, and to the totally chlorine free sequences using oxygen, ozone and peroxide. Chlorine bleached perfectly well; it was the effluent that ended it.

Answer: C

Cooking belongs to pulping and happens long before the stock reaches the paper machine. The other three all prepare the furnish for the headbox. The digester sits at the other end of the mill. Stock preparation ends at the headbox.

Answer: D

Beating raises the surface area available for hydrogen bonding, which is what gives the sheet its strength. Overdoing it shortens the fibres and makes a dense sheet that is slow to drain. Refining energy is a significant operating cost.