Process water filtration should not be clear as mud

Paul Boughton

If an organisation can clean up its process water and re-use it just one more time it will effectively reduce its process water costs. Steve Cupples reports.

Industry worldwide uses water in many different ways and in different amounts, therefore water saving technology, in many cases, is used in multiple applications.

The commonalities however are that highly efficient water saving techniques are proven to not only reduce an organisations carbon footprint but also to make huge savings on energy bills and improve production and performance.

In many operations within the manufacturing, industrial and commercial sectors the use of water is often an accepted process cost. There is scant attention paid to reducing such a significant service cost with fixing leaking taps often being the extent of energy saving in this area.

With water, unlike with electricity or gas, the consumer pays for both the supply of water to the plant and once used he pays again for its disposal.

Pity the process that contaminates this valuable resource as the cost of treating water effluent is based on many factors, including added solids, heat, pH and volume. And under the policy of ‘the polluter pays’ this 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 and sometime treatment technology to provide the necessary clean water.  However, by installing the right high efficiency filtration technology industry will make a significant return on investment.

If, say, a food processing plant uses 10 m3/hr (10,000 litres) and is a 24 hour operation, the water bill for this operation could well be in the region of six figures. Yet 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 $50,000 (US) to $80,000 (US) giving a payback within 6 months.  This is a fantastic ROI. Industry will also see a reduction in plant down time, increase productivity and reduce wastage without affecting the quality of the finished product.

In the commercial sector, for 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. 

So how can savings be made?

A typical chiller for a medium sized building with computers may well have installed refrigeration chillers which have 200-300kw of electrical energy. Larger buildings with high populations or personnel and or computers can be much bigger.

Many buildings require heating in winter and so use a combined system of chilled water and hot water. On the hot water systems this would be connected to the hot water boiler, very often driven by oil or gas. On the cooling side there is a cool a 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 discolouration 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 discolouration 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!

In addition, if chemicals are used to treat this dirty water, then 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 filtration to remove particulates down to 10 micron can improve heat transfer significantly, but our tests on many systems also shows that the majority of this contamination is between 1.0 micron and 10 micron. We believe that saving of 15-20% in total energy costs in this process can be readily achieved.

The solution is to clean 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 then energy is being wasted. The darker the water the more it is costing a business.

What are the savings against the cost?

A typical system using 100kw 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 870,000kw hrs per annum.

Assuming the losses are only 15%, this means a loss of 35,000kw per hour per annum. If the system is on 24 hours a day this cost increases to over 130,000kw 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. Finding effective water filtration technology that will provide significant savings on water, downtime and energy whilst increasing productivity and efficiency has been a real issue for many years until CrossFlow HEMF was launched onto the market five years ago.

Since then, taking on the task of educating industry on installing this technology has been an up-hill battle because we have had the added task of educating industry to take more notice of their water quality. But industry is now having its ‘Eureka’ moment.

With more and more organisations installing and running this technology the results speak for themselves and this year we received approval by the Drinking Water Inspectorate (DWI) for the application in England and Wales of CrossFlow HEMF by relevant water companies for public water supply purposes.

As a process water user you can save money by the installation of CrossFlow HEMF, and at the same time reduce operating costs. This technology will filter water down to levels below 1.0 micron reliably producing a supply of clean water not only free of solids contamination such as sand, grit and iron, but also reducing bacteria, phages and spores such as cryptosporidium.

Benefits include:

* Filtration of process water down to 0.45 micron with efficiencies up to 99%;

* Filtration up to five times more effective than a conventional filter achieving only 20 micron filtration;

* Longer ‘on line’ filtration time with automatic backwash cleaning;

* Acceptance of solid challenges in access of 200ppm; 

* Short backwash times;

* Achieve more effective chemical treatment with less chemicals;

* Maintain near design heat transfer efficiencies for life of a system;

* Cleaning up older already contaminated systems and improving performance;

* Reducing backwash loss by up to 95%;

* Reducing costs by reducing loss of chiller and or heater kW input during backwash;

* Inlet pressure of only 1.0barg to operate;

* Minimum energy losses for pumping and processing through high flow low pressure;

Steve Cupples is an engineer and the managing director Industrial Purification Systems (IPS), Abertillery, Blaenau Gwent, Wales, UK.