In chemical pulping, the objective of brownstock washing is to remove the maximum amount of black liquor dissolved solids from the pulp with the use of minimum amounts of water. Removal of black liquor solids is important both for the efficiency and cost of bleaching and papermaking processes and for the efficiency of heat recovery and reduction of the use of make-up chemicals. Optimizing the amount of washing water used is essential and requires careful consideration of the implications of amount of water used on washing efficiency and heat recovery efficiencies. Dilution factor optimization control will lower the amount of water that must be evaporated from weak black liquor. Therefore it will reduce steam consumption in the evaporators. The dilution factor can be optimized by controlling shower water flow on the last washing stage to an optimum level by considering the cost of steam, the cost of bleaching chemicals, the impact on effluent quality, and other process variables (NCASI, 2001. p. 71).
| Development Status | Products |
|---|---|
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Commercial
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Chemical Pulp
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| Parent Process: Chemical Pulping | |
|---|---|
| Energy Savings Potential |
In a US based plant, the measure helped reduce natural gas usage by 327 000 GJ/y and saved 45.6 m3 of water per hour. (Kramer et al., 2009. p.91) |
| CO2 Emission Reduction Potential |
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| Costs |
Corresponding cost savings of $580,000/year were realized (Kramer et al., 2009. p.91) |
This Energy Guide discusses energy efficiency practices and energy-efficient technologies that can be implemented at the component, process, facility, and organizational levels.
This report from National Council For Air And Stream Improvement in the US provides descriptions of technologies for CO2 reduction in pulp and paper mills, and offers calculations on cost and CO2 savings.
