PECM Issue 38 2019 | Page 118

FLUID HANDLING INDUSTRIAL PROCESSES BURKERT MINIMISING COSTS THROUGH PROCESS OPTIMISATION The control of industrial processes can be a complex operation involving multiple valves, sensors and controllers which means there are many considerations when looking for opportunities for process optimisation. Using best practice and ensuring control protocols are updated when process changes are implemented however, ensures the process remains efficient and effective. Greg Wainhouse, UK Water Segment Manager at Bürkert, looks at some examples from different industries, where process optimisation can deliver significant improvements and reduce costs. Process control engineers are constantly aiming for perfection while all the time tackling the challenges that stand in their way. From variable inputs to changing conditions and complex infrastructure, there is always another obstacle to overcome, but by taking advantage of expertise within the industry, it is possible to make significant practical improvements. WASTE WATER PROCESSING One of the major challenges in the water treatment sector involves the sludge dewatering process, which in many cases involves high speed centrifuges that separate the solid and liquid fractions. To assist this process, a polymer is added to the sludge to help bind the solid particles together. The goal is to produce a final product that has the right consistency that makes transport efficient, without moving excess water to the fields, where it is spread as agricultural soil enhancer. The process has a number of variables, including the percentage solids of the raw sludge, the flowrate of the sludge, the amount of polymer being added and the speed of the centrifuge. Of these, the solid content of the sludge is crucial to determine the settings for the rest of the process. There are several ways in which this can be determined, including a process where a sludge sample is placed in a petri dish, and the water is evaporated off to obtain the mass of the solids. This is not a very efficient process and can take 45 minutes to complete. Once the results are available, the centrifuge and polymer settings can be adjusted and an improvement in the consistency of the dewatered sludge should be apparent. 118 PECM Issue 38 Precision control of cleaning processes in hygienic applications can improve productivity. However, changes in the solids content can occur frequently, which makes this process quite ineffective and labour intensive. In addition, it is a reactive process, more often used when the consistency of the dried sludge doesn’t meet expectations. During the time taken to observe the change, complete the test and alter the settings, the centrifuge has continued to discharge a sub- standard end product. By creating a pro-active system that makes adjustments based on data from the inlet, as opposed to a reactive system that observes the results before implementing a change, process engineers will be following best practice. Furthermore, this setup reduces the amount of operator intervention and delivers a more stable output. BREWING PERFECTION In the first instance, assessing the percentage of solids using a turbidity sensor located on the intake to the centrifuge will significantly increase the response time to any changes. These sensors look at refracted light to provide an approximation of the solids loading of the incoming sludge, but they can suffer from fouling problems, and the calibration process can be interpreted differently by various operators. An important part of the brewing process is adding oxygen to the wort to allow the yeast to thrive and create the alcohol and carbon dioxide. After the boiled wort has been chilled to fermentation temperature, oxygen is used to start the fermentation process. If air, which contains 20% oxygen, is added, then the process can only achieve an O2 concentration of eight parts per million (ppm). For higher levels, around 10 ppm, typically used by commercial breweries for higher strength beers, pure oxygen is required. By constantly monitoring the inlet of the process, adjustments can be made quickly and the amount of processed sludge that falls below the required standard is minimised. Further improvements can be made by adding a flowmeter, or better still a device that provides a mass flow measurement. However, the ability of the wort to absorb oxygen is affected by its specific gravity, which is measured on the Plato gravity scale. This measures the concentration of dissolved solids in the wort. Furthermore, each yeast strain has an optimum oxygen level and if this is not achieved precisely, the optimum fermentation rate will not be achieved. DEALING WITH SOLIDS IN SUSPENSION