Process Equipment Update


Can you rely on your last line of defence?


P


ressure relief systems are often the last line


of defence in protecting hazardous process plants against overpressure. However, they are rarely tested in operation, so how can you be sure that they will perform when needed? In order to ensure that


relief systems work correctly both the design and maintenance systems have to be robust. The design must ensure that the worst case relief rate has been identified and that the whole system is designed to handle this rate. Maintenance and inspection systems have to ensure that the relief pipework, in-line items and safety valves are regularly inspected and are functioning properly. Finally any changes and modifications to the system have to be carefully controlled to make sure that they don’t compromise the original design. Many operators find it difficult to guarantee the effectiveness of their relief systems, for the reasons stated above, but one area they feel more confident about is the reliability of relief valves themselves. However recent data from a


study of oil and gas industry relief valves suggests that this confidence may be misplaced.


Nearly 7000 relief valves were tested and some of the key findings were:


n Only 66 per cent lifted within ±10 per cent of their set pressure.


n 4 66 per cent had not lifted at 130 per cent of set pressure. n 49 per cent failed to reseat and hold pressure within 10 per cent of their set pressure. n 30 per cent failed to reseat and hold pressure at all.


Clearly this data is concerning and operators should be vigilant in checking their own safety valve test results and acting on the conclusions. n


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ABB Engineering Services is based Warrington, Cheshire, UK.. www.abb.com/consulting


Peristaltic pumps for biodiesel plant


T


he design consultant for a new biodiesel plant in Argentina faced the challenge of selecting a pump for the metering and transfer of aggressive chemicals and slurries used throughout the ethanol production process. The pump must handle a range of harsh products and provide precise dosing capabilities, ensuring that the set flow is maintained regardless of system pressure fluctuations.


Conventional progressive cavity pumps and diaphragm dosing pumps are often recommended for similar applications but the possibility of a decreasing flow with pump wear meant that flow meters would have to be installed as a safety measure to avoid costly, inaccurate dosing. Given the demanding nature of the application the designer chose the Verderflex peristaltic pump range. This


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particular design of pump not only addressed the specific concerns of the designer but also provided significant savings on auxiliary products.


The seal-less design of the Verderflex peristaltic pump, with no valves or moving parts in the product stream provided an impressive list of cost saving and performance benefits for the end user. Verderflex peristaltic pumps were successfully selected to pump sodium methylate, water and soaps, fatty acids and HCL during the first stage of the production process. n


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Verderflex is based in Hunslet, Leeds, UK. www.verderflex.com


Ultra-compact refrigerated circulator


P


etite Fleur, the baby Tango, is the entry level model for temperature control applications from -40°C to 200°C. Despite its size, just 260mm wide, the Petite Fleur benefits from all the advantages of the Unistat range. The hydraulically sealed system allows fluids to be used safely above flash points without fear of ignition and greasy residue that comes from oil vapours. As fluids are not exposed to the atmosphere while being heated and cooled, they do not degrade dramatically extending their lifetime by years.


The Petite Fleur is suitable for applications where regular vessel changes can result in water being introduced into hoses and reactor jackets, mixing with the heat transfer fluid (HTF) and inhibiting heat transfer. To overcome this, the Petite Fleur features a unique water separation system which removes any water from the thermofluid during heating/cooling cycles without the need to de-gas. In accordance to the “DIN 12876” standard which states that cooling powers are measured at full pump speed, at 20°C the cooling power is 0.48kW. Developments at Huber have shown that reducing the pump speed reduces the heat energy entering the system, which in turn leads to higher cooling powers and lower end temperatures. n


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Peter Huber Kältemaschinenbau GmbH is based in Offenburg, Germany. www.huber-online.com


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