IMPROVED BOILER FEEDWATER PUMPS
Boiler feedwater pumps are used across industries. Most of these pumps are multi-stage, between bearings pumps (API610 Type BB3, BB4, or BB5). They are also frequently among the biggest pumps in a process facility, consuming large amounts of power. Using Vespel® CR-6100 wear rings, center bushings, throttle bushings, and balance drum bushings in these pumps can improve the reliability, efficiency, and operation of these mission-critical machines.
If you are looking to make your pumps easier to cycle, increase efficiency, improve reliability, or avoid pump seizures in your boiler feed pumps, contact Boulden today.
Boiler feedwater can be a challenging service for many reasons. To start with, hot water has poor tribological properties. When there is contact between the rotating and stationary wear parts in the pump, the hot water does not form a significant boundary against wear, galling, and seizure.
Moreover, flexible rotor designs are generally used for these pumps. This means that the rotor requires the hydraulic forces of the Lomakin Effect for stability in service. At start-up (or during slow-roll if driven by a steam turbine) the rotor will “sag” and contact at internal wear parts is likely. Metal wear parts create high friction contact, potentially leading to galling, seizure, or high wear rates.
The operation of these pumps can also create difficulties. Many plants operate multiple boiler feed pumps in parallel, which can lead to unbalanced loads and start-up issues between the pumps. Due to the size of many boiler feed pumps, they rely upon minimum flow valves to ensure sufficient flow rates. As the power grids have expanded to include more intermittent sources like wind and solar, boiler feed pumps in thermal plants are required to cycle many times per week where the original pump was likely designed for continuous operation. Each cycle of starting the pump offers a fresh challenge to avoid seizure and wear of the internal parts.
Composite Wear Parts
Over the past 20 years, Boulden has helped clients upgrade hundreds of boiler feedwater pumps using composite materials like Vespel® CR-6100. We have optimized the components with our patented PERF-Seal® design to further improve performance and reliability. These upgrades have led to typical efficiency gains in the range of 3-5%, easier operation as pumps can cycle without worry about seizure, and outstanding reliability. Many of these pumps have now been in service for more than 10 years.
Consider Two Case Studies
A few years ago, a rotating equipment symposium published two case studies. In one case study, the customer tried to solve a boiler feed pump problem using metal wear components. In the second case study, the customer upgraded a 50-year-old boiler feed pump using Vespel® CR-6100 wear parts and the Boulden PERF-Seal® design.
Case Study #1: Seizure of Metal Wear Parts
In the first case study, a plant was experiencing pump seizure in their two, new 1.2 MW (1600 hp) boiler feedwater pumps. They thought sand or debris had entered the clearance to cause the seizure. The suction filter was changed to a finer mesh, and clearance at the wear rings, center bushing, and throttle bushing were increased.
The pumps seized again. Repeated start-up attempts against the seized pumps damaged the motors.
Ultimately, the plant found that the minimum flow valve on the pumps was not functioning properly, leading to low flow rates (and associated high radial loads) at start up.
The plant managed to get the pumps running, but only after re-engineering the entire system, installing a new minimum flow valve, overhaul of the pumps with “upgraded” metal parts—running at larger clearance, which required a new rotordynamic analysis.
In the end, the pumps are running, but at what cost? Multiple pump overhauls, motor repairs, engineering costs—it is likely the EPC contractor, OEM, and end user all lost money. The end user continues to lose money today due to lower efficiency from the larger clearances. If they have a local power cost of $0.12/kw-hr, operating costs will be approximately $50,000 per year higher than a pump running with standard clearance.
Case Study #2: Pump Upgraded with Vespel® CR-6100
In a different case study, a plant performed a major overhaul on a 1.1 MW (1475 hp) boiler feedwater pump. The pump was an 8-stage BB5 type design from 1970. Upon disassembly, the pump was found with the metal wear parts worn out to more than double the original design clearance.
Along with repairing and restoring the other obsolete and worn parts in the pump, the case wear rings and balance drum bushing were upgraded to Vespel® CR-6100 and the Boulden PERF-Seal® design. Instead of increasing the running clearance, the pump shop took advantage of the low-friction, non-galling, non-seizing properties of Vespel® CR-6100 and reduced the clearance by 50% compared to the original design values.
50 years after the pump was originally purchased, it was running better than when it was new. The overhaul resulted in a 15% efficiency gain compared to the worn condition of the pump. The pump was also 4% more efficient than the original design. If they have a local power cost of $0.12/kw-hr, their pump costs $45,000/year less to operate than when it was in ‘as new’ condition.
If you have existing boiler feedwater pumps still running with metal wear parts, contact Boulden to discuss an upgrade today. If you are buying new pumps, consider the benefits of adding Vespel® CR-6100 case wear rings, center bushings, and throttle bushings into your specification for the pumps. Boulden has supplied components to nearly all the major pump manufacturers. If you have a boiler feed pump in your shop right now, we have the material you need in stock and can supply raw material or finished parts with very short lead times. Contact us today with your requirements and we will be happy to help.