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WATER & WASTE TREATMENT RO SYSTEM RELIES ON SLIDING GATE VALVES


Sliding gate valves from Schubert & Salzer Control Systems are optimising Belgium’s largest facility for RO water purification


filtration process, the local water supplier is now producing drinking water of excellent quality – far above the statutory requirements. At critical points of the process – during reverse osmosis, filtration with activated carbon and remineralisation of the water – sliding gate valves made by Schubert & Salzer Control Systems are responsible for regulating pressure and flow rate. The water supplier, FARYS, produces drinking


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water for the city of Ostend and its surrounding area from the brackish water in the Bruges- Ostend Canal. In the current development stage of the waterworks built by Veolia Water Technologies, up to 1,200 cubic metres of drinking water per hour can be fed directly into the pipe network. The installation can be used flexibly within a variety of canal water qualities and the entire process is carried out with reduced energy costs. Frederik Debaillie, project manager of Veolia


Water Technologies Belgium, described the process: “The canal water is treated in eight stages. First, in coarse, fine and microfiltration, all suspended particles, microbiological substances and pathogenic microorganisms are removed. During the subsequent reverse osmosis, fine-pored, semipermeable membranes filter microcontaminants up to particle sizes of 0.1 nanometre as well as minerals and salts.” Only water molecules remain. This water is sent through activated carbon filters and after injection with carbon dioxide, remineralised with limestone. Finally the water is disinfected with UV light and then chlorinated. The resulting high quality drinking water is fed into the pipe network via buffer storage tanks. “The operator of the waterworks wanted a


facility that works cost-effectively. Maximum energy efficiency was required everywhere – even at the control valves”, explained Tristan Lejeune, International Sales Manager at Schubert & Salzer Control Systems. “Equally, reverse osmosis and the subsequent process stages are demanding applications. There are special requirements here in terms of the control accuracy and reaction speed of the valves used.” “During the reverse osmosis process, precise


and fast pressure regulation is very important”, emphasised Debaillie “The highly sensitive filtration layers are rolled up in pressure pipes.


eolia Water Technologies has built an ultra-modern plant to produce drinking water in Ostend, Belgium. In a multi-stage


In reverse osmosis, micro- contaminants down to particle sizes of 0.1 nanometres are filtered out of the water


Pressure shocks and excessive flow quantities have to be reliably prevented. Even the slightest overshoots in the control process could damage the expensive membranes. That is why we use one DN 125 and one DN50 sliding gate valve in each of the twelve reverse osmosis units. They ensure the exact regulation of the high process pressures that are necessary to compensate for the osmotic pressure of the brackish water and keep the reverse osmosis going.” The decisive factor for the high precision


and extremely short response time of the sliding gate valves is their special design principle. The sliding gate technology controls the flow rate in milliseconds, by two slotted sealing discs. The pneumatic actuator only has to overcome the sliding friction between the two discs. This means that the required actuating force is up to 90 per cent less than on other types of valves. The actuators can be dimensioned considerably smaller and the need for control air can be reduced. Simultaneously, the short strokes of only a few millimetres and the reduced kinetic masses of the throttle element protect the actuator and the spindle seal. The sliding gate valves also offer both size


and weight advantages. The 45 valves in the plant weigh just 1,100 kilograms altogether. Seat valves in comparison would weigh in at around 5 tonnes. This difference is considerable and, due to the savings on resources and CO2, has positive effects over the valve’s entire life cycle – from manufacture to transport through to its operation in the plant. The maintenance and


Copyright: Schubert & Salzer Control Systems


hence the operating costs are also reduced because of the more compact dimensions and low weight. “The long service lives of the sliding gate


valves were also a decisive point. These result, among other things, from the fact that they neutralise the damaging effects of cavitation”, said Lejeune. Berdien Uytterhaegen, the responsible engineer at Schubert & Salzer Control Systems, added: “Due to the special design of the sliding gate valves without flow deflection, the cavitation bubbles implode one to two metres behind the valve in the pipeline. This can easily be designed so that no damaging effect arises from the cavitation. For this purpose, it is sufficient to run the pipe straight for a short distance after the valve.” “The control valves remain more or less


untouched even in case of water shocks,” said Debaillie, illustrating another benefit. “Before the treated water is fed into the region’s pipe network, we use DN150 sliding gate valves during the activated carbon filtration and remineralisation with limestone and CO2,” added Debaillie. Here too, the high-precision Schubert & Salzer positioners, combined with the sliding gate valves, guarantee extremely accurate flow control, such that the eight activated carbon filters and 13 remineralisation tanks are evenly utilised. In this application, a linear flow characteristic curve proves to be particularly suitable for the regulation of the flow quantities to keep the process stable. With an average output of 24,000 cubic


The precise flow control of the sliding gate valves ensures that each of the eight activated carbon filters (pictured here) and 13 remineralisation tanks are evenly utilised


metres per day, the plant provides a reliable and cost-effective supply of drinking water to the Ostend region. Periods of water shortage will also be avoided in the future. For this reason, FARYS is already planning a second similar plant in Nieuwpoort.


Schubert & Salzer Control Systems controlsystems.schubert-salzer.com/en/


SEPTEMBER 2022 | PROCESS & CONTROL 31


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