The clear message being heard from the Pulp & Paper Industry is that much more emphasis needs to be placed on
the treatment of process water for "safe" re-use.
This need is voiced for many areas; saving fibre, reducing water consumption and consequently effluent flows – but
the one heard time and again is to replace fresh water with clarified water for re-use on showers and many other areas.
Many of the MICROFILTERS delivered recently have been for water saving applications, generally polishing the
clear-water from existing savealls such as Disc-filters and flotation units, producing a "Super-Clear" quality of below 30 ppm – and often lower.
In this paper will be presented these as well as other up and coming treatment areas such as treating Black Liquor
before evaporation. Filtering DIP Sludge to allow separate treatment rather than discharging to effluent and the pre thickening of Bio Sludge generally in the range of from <1-% up to 12%.
WATER CAN NO LONGER BE TAKEN FOR GRANTED!
The legislative net is slowly closing in on the Paper Industry world-wide to use less water and consequently
discharge less and at a far better final quality. Some say that the requirement for Better Water Management is long overdue while others claim it is an increasing pressure on an industry, which is already
overburdened with environmental costs.
This situation is not helped by the fact that generally, any budgeted invest in water treatment is minimal and cut
back further if at all possible.
If we care to look at it closer, in most mills the advantages of better and effective water treatment can far
outweigh, on the basis of return on capital, investments made to increase production.
For example there are still many mills that do not have effective fibre recovery. Yet the saving of fibre does not
just end at saving raw materials but also all the "investment" that has been put into it before it is lost to effluent.
The cost savings in the effluent treatment area are also considerable. By reducing the amount of fibre, one is also
saving chemicals used to filter, float, settle or thicken. Transport needed to remove sludge from mill to the dumpsite has also to be added, plus any dumping tax now imposed by many governments.
Here is a simple formula for you to check your own saving potential (Figure 1):
With the need to treat water more effectively is also coming the search for better methods of treatment. In addition, more positions in the water line are emerging that need treatment.
The Microfilters we are supplying have already been used for many years in the traditional
areas of fibre recovery and water re-use. However, the applications have SLOWLY spread to areas such as effluent treatment as an alternative to large flotation units and sedimentation
basins and polishing after Bio sedimentation, to either guarantee a constant acceptable discharge quality or to enable the clean water to be safely re-used back in the process.
Other benefits include saving space, installation time and flexibility
The areas of application are continuing to grow and perhaps one of those that is being given
high priority, especially by some larger mills, is the polishing of "clean" water from existing savealls. This is to provide a better and cleaner quality of water for safe re-use in place of fresh water.
Remember less water in, the less water to finally discharge.
Microfilters now lead as the concept that is the most effective for a wide range of
applications from river water treatment, fibre recovery, polishing after savealls, primary effluent treatment, and as a safety police unit after Bio sedimentation.
But there are more.
Figure 2. Corrugations do more than just increase surface area
Figure 3. Fibre recovery in a UK mill
Figure 4. Polishing Cloudy to Super Clear
Figure 5. Only Microfilters for Primary Treatment
Figs. 3, 4 and 5 clearly illustrate this with the applications ranging from white water treatment for fibre and water recovery, polishing the cloudy filtrate from a disc filter to less than 20 mg/l and primary effluent treatment, using just Microfilters.
Figure 6. Water Saving in The Mill
Figure 7. Effective waste water treatment
Figures 6 and 7 illustrate some of the treatment areas with application points nos. 5 & 7 quickly growing in importance as more and more companies look to the effective re-use of water both in the mill and after Bio treatment.
The polishing of water after existing savealls provides a extra quantity of a "Super Clear" quality that can be used in traditional re-use areas such as wire showers as well as more demanding places like pump seals and chemical dilution water.
The difference is that Microfilter "Super Clear" is fibre free, which makes it SAFE for re-use.
NEW APPLICATION AREAS
With water becoming an expensive commodity to buy, or abstract and in most cases costing
even more to discharge, new areas for savings of water are being sought.
Figure 8. Recovering water and fibre from a DIP installation. All in one and simple to install
Figure 8 shows a filter installed in a major newsprint mill in Japan, treating the filtrate after screw presses in a De Inking Plant.
The filtrate, straight from the press first passes through a Flotator to remove ink. Then at a
solids level of 5000 ppm it is treated in the Microfilter, recovering the solids and with the filtrate being recycled back as shower water on a Fibre Flow drum pulper. No chemicals are added.
In this case the fibre saved amounts to over 14,000 tonnes every year. As an example, that
means at a raw material cost of US$ 80 per tonne a fibre saving of US$ 1,120,000 every year. To that can be added all other associated savings illustrated in figure 1.
OVERCOMING OLD PROBLEMS
Stickies have been and still are a problem in mills where recycled fibre is partially or
exclusively used as a raw material.
Much has been done in removing this material at source or during the stock preparation
process. However the nature of its form, enables it to pass on to the machine wire and through it into the white water. Where the water is reused, a stickies problem can still remain.
Treatment using for example the DAF process removes some stickies from the water with the
recovered fibre but much, because of its indeterminate specific gravity, neither sinks nor floats and is carried over with the clear water.
Figure 9. Polishing after flotation
Figure 9 shows a Microfilter installed in a mill in Holland, polishing the water from a flotation unit.
Following the trend for mills to further treat the "clear" water from existing savealls in order
to make it suitable and safe for re-use, it has been found that Microfilters installed after DAF units provide a stickies "free" filtrate. Whereas before their installation, a progressive build up
was experienced on forming fabrics and press felts.
SOLVING "NEW" ONES
Figure 10. DIP SLUDGE
The Microfilter treating sludge between 0.7 and 3% provides a clear filtrate of less than 100 mg/l.
In this installation, a following gravity table thickens the recovered solids from the filter at 8
%, then through screw presses, discharging at 60% dry.
The system operates entirely by gravity, without the use of pumps.
BIO SLUDGE THICKENING
So far Microfilters have been used to a very limited degree for thickening Bio sludge.
Although the thickening effect is not so great 1% up to 6 to 8% the resulting thickened sludge is very much easier to mix with primary sludge for de-watering.
It also means the resulting filtrate from the Bio thickening can be passed forward to
settlement, rather than backwards only to be passed through the Bio plant once again.
The benefits look promising and we will be working further with an interested partner through
our company in Germany.
I believe we have generally only just scratched the surface of what can be achieved in the
way of savings from more efficient water management.
The advantages have always been there but as they have not been directly associated with
production, they have to a great extent been passed over.
SAVINGS STILL THERE FOR THE TAKING
- Reducing water into the plant / reducing flow of water out
- Less abstraction costs
- Less power in pumping and chemicals in cleaning the raw water
- Saving energy + power by increasing the temperature of the white water in the
- Save chemicals used, size, colour, optical bleaches, etc.
- Save fibre - and retain the power already used in its pulping, pumping, screening,
cleaning and refining
- Retain added value by making and selling the paper & board made and sold from the
- Reducing solids to waste
- Less equipment
- Less chemicals
- Less solids to discharge
- Less discharge transport costs
- Less discharge tax
SAVINGS FROM ALL THESE AREAS WILL LIE AT THE BOTTOM OF THE BALANCE SHEET AT THE END OF THE YEAR. THEY WILL ALSO, IF GRASPED, HELP IN THE FUTURE, BECAUSE IT
SEEMS WATER WILL BE A BIG FACTOR IN NOT ONLY SUCCESS BUT ALSO SURVIVAL.
POLLUTION PREVENTION PAYS
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