Regeneration of pulp liquors

Details Regeneration of pulp liquors Regeneration of pulp liquors

1996-08-05

1998-12-15

Fortuna, Ana

Liquid purification or separation

Processes

Liquid/liquid solvent or colloidal extraction or diffusing...

210651, 210650, 210641, 210805, 210928, 162 29, B01D 6100

Patent

active

058491970

DESCRIPTION:

BRIEF SUMMARY
This invention relates to the manufacture of paper and paperboard and in particular, from recycled paper or paperboard materials.
Conventional paper mill systems are run so that process waters are recycled many times during the production of paper and paperboard. Eventually, however, the concentrations of dissolved inorganic salts and organic materials in the process waters build up to a level where further recycling is impractical without having an adverse effect on the quality of the paper produced. These impurities generally have a high BOD (biological oxygen demand) and a high COD (chemical oxygen demand). Additionally, the dissolved materials promote unacceptable levels of corrosion in process equipment and growth of bacterial slimes, leading to blockage of pipes and sprays. These restrictions necessitate the discharge of large volumes of waste water into conventional waste water treatment plants, located either on the site of the mill itself, or at some remote site, which is often a municipal sewage treatment plant. To make up for this discharge paper mills must also take in large volumes of fresh water for process use. Consequently, paper making which utilises conventional waste water treatment techniques places a heavy demand on often scarce fresh water resources and also on the waste water treatment systems themselves.
The process of papermaking (whether from virgin pulp or wastepaper) involves diluting refined cellulose fibres with massive quantities of water, forming the fibres into a sheet in the forming section of a paper machine, then progressively removing the water until the result is a dry sheet of paper. Vegetable starches are frequently added to the suspension of fibres or to the sheet at an intermediate stage in the drying process to increase the strength of the paper or to reduce the rate at which the paper absorbs water.
In addition to the starch, chemicals are employed in ancillary treatments i.e. acids and caustic soda for water pH control, and flocculants and retention aids to improve the retention of the cellulose fibres and other components in the papermaking process. In many cases the water soluble chemical sodium sulphate is generated as a by-product of the use of aluminium sulphate in the sizing process.
Since not all the cellulose fibre or chemicals are retained in the sheet of paper, the water becomes contaminated by this non-retained material, and eventually reaches a level of contamination where it has to be rejected from the system as effluent.
The nature of this contamination can be categorised into the following forms: dissolved mineral salts)
A proportion of both forms of solids (BOD--Biological oxygen demand and COD--Chemical oxygen demand) require oxidation to convert them to inert and harmless substances.
Paper and paperboard mills in the USA in the period from 1956 to 1966 typically discharged between 3800 and 53000 liters of water per ton of production, the average for the industry being 17680 liters per ton. In 1982 the United States Environmental Protection Authority (EPA) developed guidelines which outlined industry targets to be between 1130 to 41300 liters per ton, the industry average being 17400.
Since the introduction of the EPA development document, 1988/89 industry operations have reduced water discharges to between 530 to 27820 liters per ton with the current average usage being 9530.
Whilst a typical paper mill recycles process water many times in the production of paper and paperboard, eventually the water reaches a level of contamination which precludes its further use and at this stage, the process water, often termed excess water, is discharged from the mill as effluent.
Historically the EPA has regulated these discharges, particularly in terms of BOD.sub.5 (Five Day Biological Oxygen Demand) and TSS (Total Suspended Solids) as outlined below.


______________________________________ Raw Effluent Characteristics EPA Historical Development 1988-89 1956-66 1981 Operations ______________________________________ BOD.sub.5 lbs per ton 10

REFERENCES:
patent: 3873414 (1975-03-01), Rocher et al.
patent: 4155845 (1979-05-01), Ancelle et al.
patent: 4173532 (1979-11-01), Keoteklian
patent: 4990260 (1991-02-01), Pisani
patent: 5290454 (1994-03-01), Dorica et al.
patent: 5385664 (1995-01-01), Oinuma et al.
patent: 5470481 (1995-11-01), Modell et al.
patent: 5558774 (1996-09-01), Tonelli et al.
Japanese Abstract 5-302290, dated Nov. 16, 1993, on "Method for Treating Waste Liquor of Pulp Production,", Mitsubishi Paper Mills Ltd.
Japanese Abstract 5,247868, dated Sep. 24, 1993, on "Treatment of Waste Water in Production of Pulp", Mitsubishi Paper Mills Ltd.
Japanese Abstract 52-35261, dated Mar. 18, 1977, on "Paper Pump Drainage Treatment Method", Daicel K.K.

Affiliated with

Also associated with

Rating

Regeneration of pulp liquors does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Regeneration of pulp liquors, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Regeneration of pulp liquors will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-1454502