In one US based plant, energy savings are estimated to be 939 000 GJ/year (Kramer, et al., 2009. p.92).
http://www.epa.gov/nsr/ghgdocs/pulpandpaper.pdf
Bleaching
The bleaching process removes color from the pulp (due to residual lignin) by adding chemicals to the pulp in varying combinations, depending on the end use of the product. The same bleaching processes can be used for any of the pulping process categories. The most common bleaching chemicals are chlorine, chlorine dioxide, hydrogen peroxide, oxygen, caustic,and sodium hypochlorite. Concerns over chlorinated compounds such as dioxins, furans, and chloroform have resulted in a shift away from the use of chlorinated compounds in the bleaching process. Bleaching chemicals are added to the pulp in stages in the bleaching towers. Spent bleaching chemicals are removed between each stage in the washers. Washer effluent is collected in the seal tanks and either re-used in other stages as wash water or sent to wastewater treatment (US EPA, 2010. p. 5).
BleachingTechnologies & Measures
| Technology or Measure | Energy Savings Potential | CO2 Emission Reduction Potential Based on Literature | Costs | Development Status |
|---|---|---|---|---|
| Improved Brownstock Washing | Estimated energy savings can be as much as 001 GJ/ton of production. Electricity savings may be around 12 kWh/ton of production (Kramer et al., 2009. p.93). | Commercial | ||
| Heat Recovery from Bleach Plant Effluent |
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In the same US based mill, corresponding annual cost savings are $2.4 million (2003 dollars). At the capital investment of $1.6 million, the payback period is estimated as 0.7 years (Kramer, et al., 2009. p.92). | Commercial | |
| Secondary Heat Use for Chlorine Dioxide (ClO2) Pre-heating |
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For another plant, savings in fuel, electricity, and steam were estimated at $61,000, while capital costs were estimated at $124,000 (2003 dollars) ((Kramer et al., 2009. p.93). |
Commercial |
| Washing Presses | Savings from reduced steam consumption are estimated as 0.38 GJ/t pulp (Martin et al., 2000. p.30). | Operation cost savings from lower chemical use will be approximately $0.53/t pulp. Capital cost with pre- and post-lignification process equipment has been estimated as $6 million for a plant of capacity 900 tpd (Martin et al., 2000. p.30). | Commercial |
Bleaching Publications
Available and Emerging Technologies for Reducing Greenhouse Gas Emissions from the Pulp and Paper Manufacturing Industry
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