#boilerfeed

  Power generation plants rely on boiler feed pumps to deliver a reliable and consistent flow of water to the boilers, which create the steam that powers the turbine, which creates electricity. After 45 years in service the boiler feed pumps needed to be replaced and Sulzer managed to achieve an impressive return on investment of just over two years.

Annual running costs at the power plant have dropped dramatically. (Image Source: Shutterstock – Belish) A major UK waste-to-energy plant was experiencing considerable reliability issues with its six boiler feed pumps. Routine maintenance involved a complete refurbishment every two years and the costs for this work were increasing. Sulzer only became involved after one of its turbine specialists was discussing current issues with the maintenance manager. Dale Jarvis, Business Development Engineer with Sulzer, explains: “I had been working with this plant for some time, providing support for the steam turbine, and during one visit the discussion turned to the boiler feed pumps. Knowing that Sulzer has considerable expertise in boiler feed pumps, I invited one of my colleagues to visit the plant and see what we could offer.” The plant has six boiler feed pumps that have been operating since the site was commissioned over 45 years ago. Over the years, the pumps have been regularly maintained, but more recently, they have required major refurbishments to keep them operational. Turnkey solution

Sulzer’s expertise in boiler feed pump design ensured a cost-effective and efficient solution. As a pump manufacturer and independent service provider, Sulzer was well-placed to deliver a turnkey solution that would include the removal of the legacy equipment and the installation and commissioning of new pumps. Having established the specifications of the old pumps, it was possible to source new pumps that would exactly match the original performance characteristics of the old pumps but with improved efficiency. Sulzer’s proposal was to replace two pumps each year, allowing the plant to spread the cost of the project and also appreciate the benefits of the new pumps before committing to the next stage of the installation. The financial benefits were obvious from the outset. The cost of each new pump was only marginally more than the refurbishment costs of the equipment it replaced, giving a return on investment of just over two years.

  The Mojave 280 MW solar plant generates clean electricity to power approximately 90'000 households, preventing the emission of 350'000 tons of CO2 annually. (Photo by Dennis Schroeder) © Dennis Schroeder/Abengoa Solar Sulzer is collaborating with Atlantica, a global player with a strong portfolio in sustainable infrastructure, to install its Blue Box advanced analytics solution on the performance-critical pumps at two solar power plants. Located 100 miles northeast of Los Angeles, US, the Mojave 280 MW solar plant generates clean electricity to power approximately 90'000 households, preventing the emission of 350'000 tons of CO2 annually. KaXu Solar One in South Africa has a capacity of 100 MW and saves emissions to the amount of 315'000 tons annually. The Blue Box advanced analytics solution on the boiler feedwater and heat transfer fluid pumps will strengthen Atlantica's own anomaly detection capabilities and thus increase uptime, improve reliability and eliminate operational risks of their renewable energy plants. After successful completion, Atlantica aims to implement Sulzer's cloud-based technology in all its assets worldwide as a part of their enterprise-level digitalization efforts.

  A boiler feed pump with the largest drive rating worldwide was dispatched by the KSB Group based in Frankenthal in late December 2019. It will be used in the coal-fired power plant Pingshan II that is currently being built in Huaibei, China. The supercritical power station employs a new technology that is said to reach an efficiency of almost 50 percent at a unit output of 1350 megawatts.

  The BB3 pump is one of the most widely used high energy pumps in the world The normal life cycle for a hardworking and crucial asset such as a boiler feed pump is 20 years. However, a Sulzer BB3 pump removed from a refinery in Argentina has been given a new lease of life at 40. The BB3 pump is one of the most widely used high energy pumps in the world, operating throughout the oil & gas industry as well as the hydrocarbon sector. In this case, one example was running as one of a pair of boiler feed pumps in a refinery in Argentina. The pump had to be taken out of service at short notice and refurbished quickly to ensure adequate capacity for the boiler. Minimized downtime The spare pump continued to operate but the failed pump was sent as a critical repair to enable it to return to active duty at the earliest opportunity. This would minimize any downtime and secure the reliable service of the pump for years to come. Sulzer regularly provides maintenance services to the refinery and was one of the first to be invited to submit a quote for the inspection and subsequent repair of the pump. Sulzer’s bid was accepted in the main because of the price and the quality that the company offers, but also because of the speed with which such repairs can be completed. Repair assessment The pump, which had been in service for more than forty years, was removed and shipped to the service center in Buenos Aires. The initial inspection revealed damage to the pump body as well as corrosion of the pump case. The shaft was damaged and all the wear rings would also need to be replaced. The pump shaft was removed and inspected in-house using non-destructive testing (NDT) procedures and found to be damaged beyond repair so it was also replaced. These tests are crucial in detecting structural flaws and in this case, tests were conducted on all of the pump components. Once the full extent of the required repair had been established, the casing walls were rebuilt using a welding process that adds a layer of material that can be machined back to specifications. With the welding complete, this section was again inspected using NDT before the casing was transferred to the machine shop where it could be re-bored. Comprehensive testing In the meantime, the new pump rotor was reassembled and balanced, while the wear rings were replaced when the casing repairs had been finished. The pump was put back together before being hydro tested at 1.5 times working pressure. The test procedure was designed and performed by Sulzer’s engineers to ensure that pump was ready to be reinstalled.

  Boiler feed pumps are essential pieces of equipment for power generation plants. High energy requirements mean they need to be efficient as well as reliable. For one liquified natural gas (LNG) plant in South East Asia, nine boiler feed pumps needed urgent attention and Sulzer was called in to deliver the most effective solution. Having been installed for well over 30 years, the original boiler feed pumps were showing signs of their age. The original design for the installation intended seven pumps to be in service while the remaining two offered reserve capacity that enabled maintenance to be completed without interrupting the boilers. The toll of time Unfortunately, several decades in service had taken their toll and worn seals, increased clearances, and a need to improve efficiency resulted in the engineering manager contacting Sulzer, a company he had worked with before. In fact, the situation had reached such a point that all nine pumps were required to be operating to keep up with demand from the boilers. Once the initial inspection had been completed, the results showed that six of the nine pumps had leakage figures of around 25 m³/hour. Manish Talwar, Head of Retrofits for Pump Services, Asia Pacific, comments: “The original pumps had performed remarkably well, but over the last few years, they have not been running anywhere near peak efficiency. It was clear that we could offer some immediate assistance as well as a plan for the long-term performance of the pumps.” The discussions with the plant engineering manager revealed that the original equipment manufacturer (OEM) had been contacted with a view to repairing or replacing all of the pumps. However, both the proposed costs and the projected lead times for this work were well beyond the expectations of the customer.

Sulzer’s repair and replacement program for the pumps will bring the plant back to original specification but with improved efficiency. Fast fixes The initial contract for Sulzer was to repair and upgrade two of the pumps so that they could operate close to their original performance figures. This involved installing mechanical upgrades to the coupling system, seal improvements and efficiency upgrades through non-metallic wear parts, before returning them to normal service. Given the cost of energy production at the power plant, Sulzer’s engineers were able to calculate the payback period of the overall upgrade project. Having been assessed in the company’s service center in Singapore, it was concluded that the investment in the pump refurbishment would be paid off in less than three years. As a pump OEM, Sulzer has considerable expertise and experience in designing and manufacturing pump components as well as installing upgrades to existing equipment. It was this knowledge, and the ability to deliver the repairs quickly, that convinced the customer to choose Sulzer for the project. Advanced manufacturing

The new pumps will offer a 5 % increase in efficiency and have a lower power requirement delivering on-going cost savings. The new parts were designed and manufactured using state-of-the-art equipment, including 3-dimensional laser scanning technology to create the engineering models that were used with the latest casting techniques to produce the parts. This manufacturing method greatly reduces the lead time compared to traditional pattern making processes. It also simplifies the manufacture of future replacement parts. Manish continues: “By adapting design concepts from Sulzer pumps, our engineers have managed to improve the performance of the existing pump and complete all the design calculations to verify the existing barrel would be safe in operation. A final hydro test was conducted to test the barrel and pipework to confirm its integrity before it was installed.” As well as creating new parts, Sulzer also updated the design of the drive coupling, which was previously a gear coupling. In its place, Sulzer installed a membrane coupling, which offers stable performance, absorbs damping vibration and is easy to maintain. Bespoke replacements At the same time, Sulzer also discussed the repair or replacement of the remaining seven pumps. Considering the age of the original pumps and the improvements that could be delivered by modern replacements, it was decided the most cost-effective solution would be to replace them with custom-made models from Sulzer’s GSG range of boiler feed pumps.

  Technical Paper by Chris Muscavage, Field Technical Service Engineer, at Sulzer. He looks at the importance of pump performance testing and how it can improve plant reliability. Feedwater pumps are the heart of any steam generation process and as such, they are considered critical assets. When viewed from the cardiologic perspective, feedwater pump criticality becomes patently obvious, without a healthy, reliable heart, the process will degrade and eventually cease to function. Just as an electro-cardiogram provides a medical expert with valuable performance data on the human heart during a stress test, field pump performance testing provides the expert with developed head, capacity and efficiency data under normal (or abnormal) operating conditions. Fossil fuels continue to be the primary source fuel for power generation which, according to the U.S. Energy Information Administration in 2017, accounted for 62.7 % of capacity with nuclear capacity accounting for an additional 20%. This equates to nearly 83 % of U.S. power being wholly or partially reliant upon steam generation utilizing feedwater pumps. Deregulation has given rise to an open market where pump “design point” and actual “operating point” may no longer be equivalent and may vary significantly. Such market-driven conditions primarily affect combined-cycle, coal, and biomass-fueled generators during Independent System Operator (ISO) dispatch control. Where is my pump operating? Which pump should take overhaul priority? These are certainly valid questions regarding asset availability, reliability and the associated financial consequences of “abnormal operation”. Where is my pump operating? In the following example, one boiler feedwater pump (BFP) was selected from a group of eight where proactive field performance testing was accomplished. Performance testing was employed to provide the owner/operator with quantifiable pump condition data to aid in prioritizing unit overhaul schedules. This particular generation facility is configured with six separate combined-cycle units employing 12 feed water pumps. The example pump is one of eight axial-split, multi-stage, ring-section pumps. At the time of field performance testing, gross facility generation was limited by ISO dispatch to 60 percent of full generator / heat recovery steam generator (HRSG) load.

Figure 1: Pump actual operating point, flow limited to 58% of design point. Figure 1 shows pump hydraulic performance “as found”. Note how far to the left of best efficiency point (BEP), shown in blue, test results, shown in red, fall on the original equipment manufacturer (OEM) test curve. Critical pump operation is expected to fall within 70-120% of BEP. In this case, although test results fall directly on the test curve indicating satisfactory performance, subject pump hydraulic results show operation at 58% of BEP. This is a surprisingly common situation in the current generation market. In addition, in cases where the pump’s NPSHr curve rises with a reduction in capacity, the NPSHa may be insufficient to overcome the on-set of cavitation. Operation at lower than recommended BEP flows can result in pump inlet flow recirculation leading to increased vibration, wear and reduction in mean-time-between-repairs (MTBR). Which pump should take overhaul priority? Example 2 considers the same group of eight pumps as considered in example one. By prioritizing time-based overhaul scheduling founded on actual unit performance, the owner/operator can maximize unit reliability and availability.

Figure 2: BFP C1 – Hydraulic results indicating increased clearances. Figure 2 shows boiler feedwater pump (BFP) C1 hydraulic performance results which are indicative of degraded or less than optimal internal clearances. Note that results fall below the OEM test curve indicating unsatisfactory performance and that flow capacity is limited to 51% of BEP. Balance line leak-off rate is an excellent and well-documented indicator of internal wear. Figure 3 graphically tabulates leak-off rates of the eight subject pumps and, as expected, the largest flow rate recorded was at BFP C1.