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Wastewater: Getting in the loop

28 June 2018

Tom Grove explains how installing continuous loop water management systems can have a major impact in terms of water conservation, energy use and plant reliability, as well as achieving long-term operational savings. 

Billions of litres of water are discarded every day as a result of industrial processes. In the food industry, for example, seal water injection processes often result in up to six litres of water every minute being injected into pumps and systems to flush and cool mechanical seal faces, which may then have to be treated and discarded at the end of the cycle.

Water waste is often considered to be an unwanted but inevitable by-product of industrial processes. However, solutions do exist which can virtually eliminate unnecessary usage and waste while also delivering energy savings, improved reliability and reduced operational costs.

The key is installing seals and seal support systems with environmental sustainability embedded in their design. Mechanical seals perform a simple but vital role – preventing fluid leaking from the shaft region of process pumps and other rotating equipment. They are a key component of machinery in food and beverage production lines.

In many applications the cool, clean liquid required to flush seal faces is provided from a separate seal support system. A properly configured system or ‘piping plan’ provides lubrication, prevents overheating (caused by dry running) and maximises reliability. There are many ways of configuring a seal support system, and this will influence the amount of liquid used and energy consumed. It can have a serious impact on the reliability of equipment, with cost implications in terms of downtime and repairs as well as leakage and unnecessary waste. Making sure the support system functions to optimum capacity is therefore essential for any company with an eye on waste management as well as the bottom line.

Seal injection processes requiring evaporation, and ‘quench to drain’ configurations which require a constant flow of clean water, are two of the main causes of water waste. But conserving water simply by reducing the amount of liquid being injected into a system is not the answer. Any savings made this way will be offset by a compromise to seal reliability, increasing the risk of leakage and downtime on the food and beverage production line.

Continuous loop
A better solution lies in continuous loop seal support systems which use recycled water as a cost-effective and environmentally sustainable alternative to wasteful once-through piping plans.

These water management systems use an integral vessel to store flushing water for continuous recycling. The barrier fluid is circulated to and from the mechanical seal by thermosiphon, a method of passive heat exchange which circulates the fluid, minimising wastage and providing more efficient cooling.

Closed loop systems come with benefits beyond water conservation. Because they are connected directly to the plant water line, which becomes the system’s fluid and pressure source, the pump’s mechanical seals are protected from harmful products, making them, and therefore the pump itself, more reliable.

Water conservation goes hand in hand with reduced energy consumption, with noticeable reductions in costs, as Netherlands-based Suiker Unie discovered. The company’s sustainability goal is to cut energy consumption by 50% by 2030. Its Dinteloord sugar refinery was using traditional gland packing to seal its juice circulation pumps, lubricating the seal faces with water to maximise the life of the packing. This leaked into the product, and had to be evaporated off. The seals were failing after roughly three campaigns due to leakage – a mean time before failure (MTBF) of little over a year. The packing also caused wear to the pump shaft sleeves, which had to be replaced.

AESSEAL helped solve this problem by replacing the packing with a dual mechanical seal and closed loop water management system on 12 pumps. This remedied the leakage and shaft wear and removed the need to evaporate off seal water from the product.

The system operated without seal failure for eight years and led to the company extending the upgrade to 43 pumps, which had a significant impact on water and energy conservation.

More than 5,944 m3/year of water is being saved, reducing gas usage by 594,432 m3/year – equivalent to an annual saving of approximately £181,000. Suiker Unie also earned tax benefits for achieving an energy saving of between 0.6 and 1.5 Nm³ natural gas equivalent per invested Euro.

Ab Barendregt, senior operator at Suiker Unie Dinteloord, said: “Our target was to cut energy consumption throughout the supply chain by 4% between 2005 and 2014 We invested in a compressor park in Dinteloord. All compressors are now air-cooled instead of water-cooled and this has produced an energy saving of 304,000 kWh.”

“The biggest cost reduction was based on the flush water which went into the process. This water needed to be evaporated. Now we have almost no water entering the process due to the support systems. A smaller cost reduction is based on the energy for the motors. They needed a lot of energy because of the breaking or chucking impact of the packing on to the shaft. A seal hasn’t got any friction.”

Food processors are coming under increasing pressure to be more innovative and to increase product quality against a backdrop of rising costs and narrowing margins. As a result, identifying efficiencies has become a top priority. Continuous loop water management systems have achieved quantifiable savings across many industries and has huge potential to deliver the same results for food and drink processors.

Tom Grove is CEO of AESSEAL Inc.

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