Monitoring & metering Improving the quality control of
process water F
In this article, Bürkert’s Greg Wainhouse considers ways to improve reverse osmosis monitoring and extend reliability
ood and beverage manufacturers use reverse osmosis to purify process water, which may originally come from either the mains supply or a
borehole. In either case, the objective is to produce a consistently high-quality water supply for the manufacturing process. Sampling and testing of the water is crucial to achieving this, so improving accuracy and consistency has major benefits. Reverse osmosis (RO) uses pressure to force water through a membrane leaving salts and dissolved solids behind. The process delivers consistently high-quality
water, provided the membranes do not become blocked or breached, allowing impurities to pass through.
ConventIonal monItorInG RO on an industrial scale uses banks of membranes connected in parallel to maximise the volume of water being purified. The water quality is monitored using various methods, depending on the needs to the manufacturing process. The most common arrangement is the use of differential pressure sensors on either side of the membranes as well as conductivity measurements being taken on the ‘pure’ water side. The difference between inlet and outlet pressures will change as the filter becomes blocked with impurities. System alarms can be configured to alert maintenance staff that the filter needs to be cleaned. Water that has passed through the RO system, known as the permeate, should have a very low conductivity reading and this can be checked by manually removing samples and testing them in the on-site lab. However, depending on the number of samples being taken each day, this can be a time-consuming exercise. Regular sampling and testing will clearly deliver a
more accurate picture of the water quality and pick up an anomaly more quickly. Better still, an automated process that is capable of sampling multiple lines consistently and providing alarm signals as soon as a membrane breach is detected can be used.
BreWery Improvements As fluid control experts, Bürkert has developed a specialist permeate monitoring system for just this purpose. The advantages are best explained by examining a real-world example. A beer and cider manufacturer that relies on
boreholes for its source of process water was using a conventional RO system with 45m3
of water
required per hour. Most RO systems will have a conductivity sensor on the common outlet, but these can struggle to detect small impurities that may arise from damage to a single membrane. With only a very limited storage capacity, the volume
of production water from the RO system needed to keep up with the manufacturing processes. This meant that downtime had to be kept to an absolute minimum. The brewery had found that certain membranes could foul up quicker than others. Conductivity levels could be seen to slowly increase as one filter became blocked and this was quickly followed by several others causing the conductivity level to increase rapidly. As soon as several filters became blocked, the RO system had to be stopped and repaired as quickly as possible. If this could be achieved while the buffer of stored water is used, then no production capacity was
36 August 2020 Instrumentation Monthly
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