Question

In a traditional continuous Kraft (Sulfate) pulping process, consider the following major steps:
Bleaching (BL), Chipping (CH), Debarking (DE), Digestion (DI), and Pulp Washing (WA).
Which one of the following is the CORRECT sequence of steps for this process?

• A. DE → BL → WA → DI → CH
• B. DE → CH → DI → WA → BL
• C. DE → CH → WA → DI → BL
• D. DE → BL → WA → CH → DI

Hint:

Wood must be prepared (debarked, chipped) before it is cooked (digestion), then washed to remove spent liquor, and only then bleached.

Answer 1

The Correct Option is B

Step 1: Understand the overall goal.
The Kraft process converts raw wood logs into chemical wood pulp. Logs arrive with bark, are too large to cook directly, and the resulting pulp is dark with dissolved chemicals, so the process proceeds through a fixed logical sequence.
Step 2: Wood preparation first.
Debarking (DE) removes bark first. The debarked logs are then reduced to Chips (CH) so cooking liquor penetrates evenly. Order so far: DE then CH.
Step 3: Chemical cooking.
Chips are cooked with white liquor in a digester, Digestion (DI), dissolving lignin and releasing cellulose fibres. Order: DE, CH, DI.
Step 4: Washing.
Pulp Washing (WA) separates fibres from spent black liquor right after digestion, before bleaching chemicals would be wasted on residual liquor. Order: DE, CH, DI, WA.
Step 5: Bleaching last.
The washed, unbleached pulp is finally Bleached (BL) to remove residual lignin and increase brightness. \[ \text{DE} \rightarrow \text{CH} \rightarrow \text{DI} \rightarrow \text{WA} \rightarrow \text{BL} \]
Step 6: Eliminate the incorrect options.
Options placing bleaching or washing before cooking are physically impossible since there is nothing to bleach or wash until after the chips are cooked. \[ \boxed{\text{DE} \rightarrow \text{CH} \rightarrow \text{DI} \rightarrow \text{WA} \rightarrow \text{BL} \ \text{(option B)}} \]