FEATURE PUMPS, VALVES & ACTUATORS PROLONGING PERFORMANCE
The task of maximising pump efficiency is more difficult for older equipment where the full specification data is no longer available or has been reappropriated for a new task. Jerry Ruc, field engineer with Sulzer, looks at some causes of poor performance and suggests ways to improve efficiency
A
properly specified pump, matched to the demands of the application, will
operate reliably for decades with only a minimum of repairs needed. It is essential that designers match the conditions that encompass the entire system, typically referred to as the system curve. The pump duty point (design point) is only one point on that system curve. As operating conditions evolve over time, so the pumping application demands also change, this can include a change in flow, media characteristics or duty. However, just because a pump is capable of operating on the outer edges of the system curve does not mean that there will not be consequences in terms of performance or reliability. For this reason, manufacturers establish
the minimum operating flow as well as listing all of the limiting design conditions, such as net positive suction head required (NPSHR), maximum flow and others. It is important to understand the consequences of dialing back pump flows which means measuring the operating conditions and calculating the point at which the pump will be operating on the system curve. This can be illustrated by a recent repair project that was completed by one of Sulzer’s service centers. A multi-stage boiler feed pump was brought in for repair and it was immediately clear that the
pump had suffered some severe damage. An initial inspection showed that the suction-side seal, several impellers, sleeves and stationary components had been destroyed. The evidence indicated that the pump had been operated at or near shutoff flow. When a pump operates in a boiler feed system, iron oxide deposits are often found in the casing. In this case the deposits were absent in the first three stages of the pump but intact on the latter stages. This indicated that the pump had experienced a condition where the input energy from the impellers had turned the water to steam before it had a chance to exit the pump. The creation of steam in a pump is a violent condition which induces considerable vibrations and can lead to surface erosion. The possible causes of the pump failure
in this example were reviewed with the plant owner who was keen to avoid similar cases in the future. A number of issues were highlighted including a
Pump manufacturers and maintenance providers, such as Sulzer, are able to provide detailed
information on existing pumps and make modifications to current systems to deliver maximum performance and reliability
misunderstanding about the required flow rate of the pump which meant the pump was not only operating close to the minimum flow point but its pump operating curve was fairly flat at the lower flow region. To make matters worse, the failed pump
It is important to understand the consequences of dialling back pump flows and the effects on reliability
WIRELESS VALVE MONITORING ENABLES PREDICTIVE MAINTENANCE
Rotork has recently introduced RI Wireless, a wireless valve monitoring and diagnostics concept for the process industry. The field proven solution transmits real-time position indication to the control room and enables predictive maintenance for actuated valves, delivering capital and operating expenditure reduction, increased safety and increased productivity. Designed for new and existing plants in the process industries and utilities, RI Wireless products are
certified as Zone 1 Intrinsically Safe for use in hazardous areas. Predictive maintenance is facilitated through the monitoring of valve opening and closing profiles and the detection of variations from reference profiles.
The system comprises a battery powered Valve Monitoring Device (VMD) that is installed on valve actuators using a NAMUR interface, or on manual valves with an ISO 5211
interface. The VMD collects dynamics-of-state data from the actuator or valve and transmits it as a 64-point packet, providing the information needed for preventative maintenance. A network of Valve Device Routers (VDR) transfer the monitoring data from the VMDs on a
wireless MESH network to the Tunneling VDR (TVDR), which is the ‘last hop’ VDR that transfers the data to the RI Wireless Gateway. The final element in the structure is the RI Wireless Management System (WMS), a software management tool.
Rotork 10 NOVEMBER 2016 | PROCESS & CONTROL
www.rotork.com
discharges into a header, along with other, similar pumps; this creates a parallel pumping system that is designed to increase system flow. The balancing act of a parallel operating system is to ensure that each pump is operating equally in terms of the flow. The key to a successful parallel pumping system is to use pumps with the same shaped characteristic curve and to ensure identical operating environments for each of the pumps. This is best achieved by using the same model pump with identical impeller trims, and both set mechanically to the same OEM standards, including the internal wear parts and design clearances. By using the same suction source for each pump, the suction pressure at the entry point to each pump will be the same. Having addressed the suction side, the
discharge pipe needs to increase to full- line size as soon as possible after the pump and if possible the discharge pipes should be symmetrical from the pumps to the point at which the lines rejoin. Finally, one essential aspect that is often overlooked is the minimum flow line, which should be required for each pump. This ensures that the minimum flow condition is always satisfied, protecting the pump from overheating and subsequent damage. Many industrial processes utilise various
pump designs, often from several different manufacturers, so achieving a comprehensive performance review can be difficult. As an independent specialist, Sulzer engineers have the experience to identify and analyse potential issues in both existing and proposed installations.
Sulzer
www.sulzer.com
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