Issue link: https://geospatial.trimble.com/en/resources/i/1415432
Criticality (will the VRU stop or can operation continue for some time?). Delivery time for repair and/or new part. Who will fix it and how long will it take? Furthermore, it is advisable to have a contingency plan for acquiring necessary parts in case of unplanned breakdown (Table 1). Conclusion When keeping things simple, sticking to well-known solutions and having a dependable maintenance scheme, there is every reason to expect a VRU to have an availability of 99%, meaning that it is online 99% of the time it is expected to be online. Planned and unplanned maintenance can take up less than 1% of the time as an average over the lifespan of the VRU. Table 1. Example of spare part contingency plan from pressure-swing based VRU Equipment type Source VRU local stock VRU central/ sister stock VRU supplier stock Part-manufacturer stock Part-manufacturer order Activated carbon 1 × Process pumps – bearings and seals × Process pumps – rotor/ housing/motor/coupling × Instruments 2 × × Valve seals (butterfly) × × Valve actuator repair kits 3 × × Vacuum pumps – bearings and seals × × Vacuum pumps – rotor/ housing/motor/coupling 4 × PLC/power supply/I/O cards 5 × × Notes 1. There is a slow, constant degeneration of activated carbon. The VRU should be designed with additional capacity, ensuring that it will not become an issue for a long time after the VRU is commissioned. In a well-designed system, the carbon has a lifetime of 10 – 12 years and in many cases the emission is still below the limits after 17 years. Under all circumstances, degeneration is a slow process which should be monitored and logged via regular carbon samples analysis – typically starting after 6 – 8 years. 2. Even if it only happens very rarely, instrument failure is likely to be the most frequent reason for unplanned stops in VRUs. The failure is typically sudden, and the control system should be designed to pick it up at once. The VRU supplier will often have the most common spare instruments on stock but it is also advisable to keep spares onsite to ensure minimal downtime. 3. Due to the very high number of cyclic operations, even the best high performance, double eccentric valves will begin to leak at some point, typically after 5 – 10 years. Valve failure is almost never acute but will grow slowly over time. A leak can be seen by studying the trend curves in the system and will be detected in the periodic preventive maintenance which includes a leak test. 4. As an example, Cool Sorption has used the Busch R5 rotary vane pump in the majority of VRUs for around 15 years. In this period, not one breakdown of that pump type has been recorded. The R5 is a relatively slow running (1500 rpm) and quiet pump. A major overhaul is typically done after 10 years. 5. Errors on the PLC itself are extremely rare, but faults on input/output (I/O) cards and power supplies are not uncommon on older VRUs. The VRU supplier should have most spare components on stock. Emission reduction solutions Cool Sorption is dedicated to VOC emission reduction and has an extremely high expertise in vapour processing, vapour treatment, vapour recovery and product recovery. sales@coolsorption.com +45 43 45 47 45 www www.coolsorption.com