Problem 6. In the chemical pulping process, wood chips are mixed with acid in a
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Problem 6. In the chemical pulping process, wood chips are mixed with acid in a digester. The acid dissolves the lignin in the wood chips giving a mixture of wood fibres and "black liquor" (acid watertlignin) at the exit from the digestor, The wood fibres are wanted for the pulp, so stream 3 is filtered to remove most ofthe black liquor, which leaves in stream 4.25%of the black liquor leaves with the wood fibres in 5. In the second part of the process, the fibres are washed with water in a multi-stage washing process which requires 2000 kg/h of wash water. The wet pulp in stream 6 contains all of the wood fibre, and 20% water. The acid and lignin leave in stream 7 with most of the wash water. 90% of the water in stream 7 is recovered and recycled in stream 8. I15 marksl Wood K1 Chips Waste Acid Make-up Digester Water Fiter Wash Tanks Wet Pulp Black LiquorExplanation / Answer
The calculation at stage 3 is done as there materials lost during this step.
It is given that 4.25% of black liquor is coming with wood fibre. So wood fibre should come as it is and 4.25% of rest should reach next stage through step 5 and the balance should be removed through step 4. The values at stage 6 is already given. Stage 7 contains only all the Legin+acid along with water so the quantity of water is calculated accordingly. Out of the total water 90% of the water is recovered in stage 8 and the balance water is added in stage 9 to maintain 2000Kg of water in wash tank so the calculation at stage 8 and stage 9 are done accordingly.
Component 1 2 3 4 5 6 7 8 9 10 11 Wood Fibre 200 200 - 200 200 - - - - Lignin 160 160 153.2 6.8 - 6.8 - - - Water 40 80 120 114.9 5.1 50 2038.1 1834 166 2000 Acid 120 120 114.9 5.1 - 5.1 - - - Total 400 200 600 383 217 250 2050 1834 166 2000Related Questions
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