Super clean whitewater replaces fresh water - Part II

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Super clean whitewater replaces fresh water - Part II

September 11, 2011 - 20:24
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BRUSSELS, Sept. 12, 2011 (RISI) -In China, many paper mills are working to significantly reduce fresh water use, and possibly return water to the rivers cleaner than it arrived. As Martin Koepenick reports, the PETAXTMfine filtration system from Kadant is one approach that is gaining popularity as a better way to manage water resources. Read Part Ihere.

An Australian leap forward

PETAX has become a preferred solution on an increasing basis throughout Asia. Based upon increasingly tight water supplies, Australia's Encore Tissue looked for the latest technology to reduce water use.

As reported by City West Water, Melbourne, Encore Tissue, decided to employ the fine filtration system in its tissue making process, choosing a system that could handle the high volume of suspended particles, allowing showers to function without build up or potential blockage.

According to Encore Paper's mill manager Hugo Rust, "Petax enabled us to reuse process water in the manufacturing process without compromising our water quality."

Purified whitewater from a Kadant PETAX system can provide for up to a 30% reduction in fresh water, and minimizes wastewater sent back to the effluent plant. Showers don’t plug, because suspended solids bigger than 30 microns (and even smaller) are removed

Repeat successes in Thailand

Thailand's largest packaging producer, Siam Kraft Industry, chose PETAX to recycle whitewater used in the papermaking process via single-stage filtration of liquids containing a high level of suspended solids. The equipment is similar to that supplied to them earlier, as well as a sister kraft packaging plant before that.

Tian adds, "It's important to note that removing almost all of the suspended solids over 30 microns in size in the filtrate, is achieved without the addition of chemical flocculants, fiber sweetener stock, or precoats. Just with the filtered whitewater itself, optimal performance of showers on the wires and felts has been achieved. Our customers are typically seeing up to 30% savings in water consumption."

Water conservation in China
Overall, water resources in China are becoming scarce, and measures need to be taken to prevent water resources from hampering economic and social development.
Water resources per person in China are 2,200 m3/yr, but are projected to decrease by 25%-30% when the population potentially surges up to 1.6 billion. At present in China, there is an annual gap of 36-50 billion m3 in the water supply.
Now, and even more so in the coming years, sustainable use of water resources will play an important role not only to improve the quality of human life but also for development of the economy and society.
Some of China’s leading paper producers are already taking a wide range of measures to reduce water usage, and enhance water during processes and return it to the local river is a sustainably acceptable way.

How are savings achieved?

A specially designed felt-like filter media is applied to each of a series of discs. Process water is evenly distributed into the filter vessel across the surface of each disc. The filter vessel, filled with process water, operates under low pressure (0.1-0.3 bar). The submerged discs slowly rotate, gaining speed as pressure drops. Cleaned filtrate passes through the media to a hollow space in each disc, from which it collects in a central hollow shaft at atmospheric pressure.

Throughout the process, the discs are continuously cleaned in three stages. First, filter cakes are doctored off and pumped away. Then, clean filtrate is pumped back through the media to remove debris, which is pumped away. Next, a submerged, oscillating high-pressure shower also cleans the media.

Mills have been operating the filter media for about six months without replacement. Changing the disc assembly takes only one to two hours.

System benefits
• Reduces fresh water usage and effluent treatment costs.
• Saves energy by reclaiming and reusing process water.
• Minimizes shower nozzle plugging.
• Polishes save-all’s super, clear-leg white water, DAF water, or cooling tower water.
Functional parameters
• Fluid source: disk save-all super, clear-leg white water
• Contaminants: fines and fibers
• Application: white water system; showers on wire and felts

Martin Koepenick has written about the pulp and paper industry for more than 2 years visiting mills around the