In many operations, within the manufacturing, industrial and commercial sector, the use of water is often an accepted process cost with scant attention paid to reducing it. With water, unlike electricity or gas, the consumer pays for both the supply of water to the plant and its disposal. Pity the process that contaminates this valuable resource, as the cost of treating water effluent is based on many factors including solids, heat, pH and volume. Under the policy of “the polluter pays” the cost of effluent treatment is ever increasing.
The simple fact is, if an organisation can clean up this process water and re-use it just one more time it will effectively reduce its process water costs by a staggering 50%, yet interest in this area of ‘process’ is given little attention. True, the re-use of process water involves the installation of additional filter technology to provide the necessary clean water, however, modern technologies and techniques can provide a significant return on investment.
If a process only uses 10 m3/hr (10,000 litres) and is in 24 hour operation, the water bill for this modest operation could well be in the region of six figures. Having the ability to remove solids of 1.0 micron and less, plus any additional treatments, to enable process water re-use would cost just £30,000 to £40,000 giving a payback within six months. Even with today’s interest rates this is a fantastic return on investment.
Case Study 1
Synseal Extrusions is a long time user of SpinClean, superior filtration technology which meets the quality and efficiency demanded by the extrusion industry. Typically, companies such as Synseal Extrusions, which manufacture UPVC window sections, use 200,000 litres of water for the manufacturing process every hour which is traditionally treated with chemicals and chilled to 12-14 ºC. With such a volume of water being used, a large recirculation tank and larger water chiller (2000 kW is not uncommon) is normally employed.
However, this process generates water contamination due to the amount of dust which is inevitably released in UPVC production. Dust gets into the water system which is such a vital part of the manufacturing process. If particles as small as 20microns - too small to be visible - should then settle in between the molten UPVC as it is being shaped, scratches will result. A damaged section might be 40 metres long and will need to be cut into pieces and then reduced to granules in order to be reprocessed. All of this is costly in terms of time, energy and production efficiency.
In order to try and control this contamination many plants undertake an overflow of 20% of the volume every hour. This means paying for new fresh water at a rate of 40,000 litres every hour and at the same time paying for disposal this water.
Unfortunately, this approach still doesn’t solve the process problems, as the remaining contamination still gives quality and process issues. Installing the correct technology can reduce contamination significantly and reliably and over 90% of the UPVC industry now has better quality products with a near zero loss water system.
In addition, a return on investment can be achieved in less than 6 months because removing the fine particulates reduces surface scratching, eliminating or reducing a company’s scrap rates; reducing chemical use and by doing so producing less organic load; a chillers reliability is maintained as blockages are eliminated by filtration; tool life is extended due to reduced water contamination and the stability of process temperature due to cooling of “clean” water rather than dirty water gives tighter tolerance of product also resulting in less scrap.
Case Study 2
In the commercial sector, in businesses that have large space cooling or heating systems the cost reductions are not based on the cost of the water, so much as the cost of electricity. These systems are often closed loop water heating or cooling systems. Typical areas for quick return on investment in this sector may well be hotels, computer suites, universities, banks, large office complexes, and other public buildings, in fact anywhere where water is used to heat or cool the work environment.
Reducing energy costs
A typical medium sized building with computers may well have installed refrigeration chillers which have 200-300 kw of electrical energy. Larger buildings with high populations of personnel, and, or, computers can be much bigger.
Many public buildings require heating in winter and so use a combined system of chilled water and hot water. Hot water systems would be connected to the hot water boiler, very often driven by oil or gas. On the cooling side there is a cool water circuit, connected to refrigeration chillers to enable cooling to occur. The energy input by the boiler or the chiller is significant whether using gas, oil or electricity to achieve the heating/cooling.
Ask any maintenance engineer what colour the water is in this system and this will range from pale straw (usually found in a new system) to black (found in a typical system). This discoloration is not just ‘yucky’ it is actually having a major negative effect on the system. From our experience, it is not uncommon to see large commercial buildings lose between 15-20% of its total heating energy input just because the water is dirty.
The discoloration is a product of the corrosion which is taking place naturally within the system, and this corrosion reduces the heat transfer from the heat source to the water and then from the water to the heating/cooling outlet. A double energy whammy!
This contamination visually present in the water is a combination of bio-mass and mineral scale, both of which will attach to the inner heat transfer surfaces of the system, including the pipe work, chiller/heater surfaces and all water contact controls.
The initial bio film now acts as an adhesive for all the other contamination present, allowing the layers to build up. This build-up can, and often does, get completely out of control leading to severely reduced pipe work or, in extreme but not unknown cases, blockages.
In addition, if chemicals are used to treat this dirty water, the effectiveness of the chemical treatment will be reduced because of the high solid load within the water. Past examinations of this process have shown that filtration to remove particulates down to 10 micron can improve heat transfer significantly, but our tests on many systems also show that the majority of this contamination is between 1.0 micron and 10 micron.
It is believed that a saving of 15-20% in total energy costs in this process can be readily achieved by cleaning up the heating/cooling water using reliable filtration to less than 1.0 micron connected to both the hot and cold water system. If the water in the system is anything but clear, energy is being wasted. The darker the water the more it is costing a business.
CrossFlow MF1.0 is the latest technology that filters below 1.0 micron - reliably -even achieving down to 0.45 micron to ensure cleaner process water which in turn can reduce the carbon footprint of a business.
Operationally, this technology utilises a unique patented vortex bed stabiliser which maintains flat bed filtration with high surface turbulence. This ensures that no bio-fouling can be seeded whilst holding filtered contamination in suspension above the media bed. This gives lower pressure drops, longer filtration and shorter backwash cycles making direct savings on operational cost.
The high interstitial void volume of the media allows for greater dirt holding capacity and contamination interaction for the Zeta potential of the media to remove the finer particulates.
Compared with conventional media filtration, the inlet configuration allows for high flow rates, these being five times higher than the normal accepted flux rates of conventional filters. Backwash volume used is also significantly lower, especially when the longer operational period is taken into consideration. It is also more effective with backwash times per unit being as low as two minutes.
This new technology has been shown to provide a high efficiency removal rate of over 86% at 1.0 micron in one single pass whereas conventional filters have to undertake multiple passes to get anywhere near such efficiency.
Savings versus technology cost
A typical system using a 100 kw chiller and equivalent heater can use 250,000 kw per annum for a nine hour operation, five days a week. Many systems are running continuously to minimise energy losses so this figure could be as high as 870,000 kw hrs per annum.
Assuming the losses are only 15%, this means a loss of 35,000 kw per hour per annum. If the system is on 24 hours a day this cost increases to over 130,000 kw per hour per annum, all of which could be recovered through investing in proper filtration which could give a return on investment in less than 10 months.
Conclusion
Reducing the use of potable water for non sensitive industrial commercial use would reduce the call on the UK’s overstretched drinking water supplies. By using alternative sources such as bore hole, river or rainwater harvesting, significant savings will be made both on the cost paid for supply and its disposal. The reuse of process water just once can cut water costs by 50%. Making the water clean in heater and chiller systems can save 15-20% of the total energy input and as an added benefit, often reduces health and safety risks.
All of these benefits have proven that water is a true energy source as well as a valuable resource which, on the world stage, is a diminishing resource. By bringing in the use of innovative water saving solutions, everyone and the environment will benefit.