Productivity targets are a key performance measure in any process industry and the refining business is no exception. Increasing output from a large refinery to meet market demand does present its challenges, however, dealing with the pumps does not need to be one of them. Sulzer has proved that a retrofit can provide the most cost-efficient solution, when carried out by a provider with the right design experience and manufacturing expertise.
Matt Kinney, Hydraulic Retrofit Specialist, at Sulzer, discusses a good example of a successful retrofit project.
Due to changes in Government regulations over the past several years, the demand for ultra-low sulfur diesel (ULSD) has increased significantly. As a result, refineries across the country have been forced to adapt and find innovative solutions to meet increasing capacity. A refinery located in Texas found themselves in this situation and reached out to Sulzer’s Odessa Service Center to investigate possible solutions. In a focused effort to address this issue, the two pumps of interest are 6x8x10.5 BB5 10 stage units in diesel charge service. The American Petroleum Institute (API) BB5 is a barrel pump that encloses a multi-stage axial split inner bundle with an opposed impeller configuration (see figure 1). Being that the pressure boundary is radially split, these pumps are typically designed for high-temperature and/or high-pressure applications. With the capability of handling pressures and temperatures up to 6’250 psi (431 bar) and 800 °F (427 °C) respectively, the API BB5 is an excellent pump selection for applications such as water injection, oil export, boiler feed, and charge service.
The subject pumps were originally sold in 2006 at a rated point of 1’110 gpm (252 m3/hr) @ 4’014 ft (1’223 m). However, with the change in ULSD demand the reliability engineers at the refinery were interested in a capacity increase to 1’628 gpm (370 m3/hr) @ 3’450 ft (1’052 m) (see figure 2). The goal for Sulzer was to find the most economical and timely solution to meet the customer’s needs.
When in this situation, there are three possible options:
Purchase a new pump that is designed to deliver the desired capacity Hydraulically modify or “re-rate” the existing pumps Operate their two existing 100% pumps in parallel (depending on customer system curve) Each of these options above have their own advantages and disadvantages. For example, parallel operation would clearly be the least costly to achieve the increase in flow. However, the lack of system redundancy in the event of a failure is risky and can often be very costly in terms of lost production. A new pump selection to fit the application could be advantageous with regards to efficiency but long lead times, the cost to reroute pipework, and baseplate/foundation modifications may make this option less attractive. There is really no downside to re-rating pumps other than the fact that the desired performance may not always be achievable in the given frame size, if feasible, re-rating is often faster and more economical.
Based on the criticality of this service for the overall success of the refinery, the possibility of re-rating was of great interest in this example. To support the customer, Sulzer engineers conducted a thorough feasibility study both hydraulically and mechanically to determine whether the goal was possible. A specific speed (Ns) based search through Sulzer’s vast hydraulic database revealed an existing proven design that would meet the client’s needs – provided the impellers were able to physically fit, and the inner-case volute nozzle areas were able to be increased enough to allow the impeller to meet as-designed performance. A review of the volute development drawings provided confidence that both items could be fulfilled.
The Sulzer approach was to keep it simple:
Select an existing standard Sulzer impeller hydraulic design that is suitable for the desired performance and has been proven by at least two factory tests. Ensure that case modifications can be made to fit the new impeller. Confirm the nozzle area can be increased enough to mimic the reference pump performance.
With a massive array of impeller hydraulic designs available, Sulzer engineers were able to select an existing design that would meet the new desired head and capacity of the application.
A mechanical cutback was done (see figure 3) to achieve both an increase in nozzle area and lip diameter. Based on empirical data, the increase in nozzle area would allow the new impeller selection to runout to the new design point. The increase in volute lip diameter enabled the designers to achieve sufficient lip clearance. This, and the fact that the cutback was ‘angled’, helped with the reduction of vane pass pulsations and overall vibration amplitudes.
The outlet vanes of the impeller were underfiled to increase the outlet area between vanes (OABV) and help flatten the performance curve. This also pushed the best efficiency point (BEP) to achieve higher flows.
The design process highlighted the fact that the new performance level did not require all 10 stages. One stage was removed so that the impeller trim could be near-full diameter. This benefitted both the efficiency and the BEP location for the pump. With the stage reduction, the effect on axial thrust direction and magnitude was analyzed; the internal bushings were resized to ensure the axial load was acceptable for the thrust bearing.
Challenges and drawbacks
With a major re-rate such as this, it can be rather difficult to fit a new, relatively large, high capacity impeller within the existing volute. This is because multi-stage pumps such as this are designed with the shortest possible stage spacing to limit overall pump length. Fortunately, the pumps in this example were originally equipped with a relatively low flow rotor compared to its frame size, which offered more room to work. In order to accommodate the increased impeller outlet width, the volute side walls required widening or “slabbing” to ensure adequate side-room clearance, which is extremely important to centrifugal pumps.
In addition, the inner-case line bore diameter was increased to accommodate the larger impeller eye diameter. The bore was increased to the maximum allowable value while maintaining enough wall thickness between it and the waterways and maintaining structural integrity of the inner bundle.
The increased pump performance required more power than the original 1’250 hp (932 kW) motor could deliver, so a new motor was required to meet this demand. However, no baseplate modifications were required as the frame size for the higher rated motor remained the same.
The Net Positive Suction Head Required (NPSHR) had increased with the new selected suction impeller. However, this was not a problem as the Net Positive Suction Head Available (NPSHA) was adequate.
12 million benefit from ambitious water pumping project
In Brazil, the government has been looking to bring relief to a semi-arid area in the northeast of the country that is home to 12 million people. Sulzer designed and manufactured six of the largest pumps in the project, to transfer water from the São Francisco River to the drought-affected area.
For decades, work has been going on to improve the water supply to the northeast region of Brazil that is equivalent in size to France. Over the past 10 years, the government has brought together designers, engineers and manufacturers to create 600 km of canals, 9 pumping stations, 27 reservoirs and all of the associated infrastructure.
The extraction point for the Northern section would require two of the largest pumps ever manufactured by Sulzer, and some of the pumps would require electric motors rated over 5 MW.
This massive project involved extracting water from two points on the São Francisco River; the first pumping it to the North and the second pumping water to the Northeast. In both cases, the designers had to overcome a number of challenges, especially the variable height of the São Francisco River and the huge distances that the water had to travel.
As one of the world’s leading pump manufacturers, Sulzer was involved in this project from the early stages, offering technical advice on what could be achieved with modern pump designs. This led to Sulzer being awarded the contract in 2007 to design and manufacture six enormous pumps that would help make this concept a reality.
In the North, BKn 1800 vertical pumps were proposed, with a flowrate of 45’000 m3/hour (26’500 cfm), they would weigh almost 100 tonnes (110 tons) each and require an electric motor rated at 5’500 kW (7’300 HP). Each pump would discharge the water using two-meter pipework with a head of 36 meters (118 feet). For two of the pumping stations on the Eastern section, they would be equipped with BK 1870 pumps and BKn 1470 pumps with flowrates of 25’000 m3/hour (14’700 cfm).
All three of the pump models selected for this project had known hydraulic profiles, but they had never been manufactured for such large flows with the associated power requirements. Bruno Antoniassi, Head of Sales, Brazil Energy Business for Sulzer, explains: “It was essential that we create scaled-down models to validate the suction well geometry, the hydraulic performance and the mechanical structure of the pumps.
“Due to the dimensions and the weight of the proposed pump designs, it would not be possible to test them on a commercially available test stand. Fortunately, our designers were able to overcome this and several other challenges that arose during this project. Using computer modelling as well as scaled-down pumps, we resolved all of the issues.”
One of the main complications concerned the river levels, which can vary considerably, depending on the rainfall in the area. The design of the suction layout and the pump itself had to accommodate this variation and still deliver the required flowrate, especially when water levels were low and demand in the arid areas was at a peak. The solution was to create pump designs that could operate at different suction levels, with the flowrates and power demands matching the changing situation.
Of course, with such large power requirements to drive these pumps, efficiency was one of the major challenges for Sulzer. Since the running costs make up 90% of the overall expenditure of each pump, creating a design that delivers optimum efficiency was a major priority for the project. Overall pumping efficiency is calculated from mechanical, hydraulic and volumetric efficiencies, all of which are determined by the engineering design of the pump components. Sulzer refined the design of each pump to ensure it precisely matched its role and provided the customer with a guaranteed efficiency at the rated point.
Having finalized the design and tested the models, manufacturing could begin. With such large castings and a considerable amount of machining to be done, the build time for the six pumps was estimated at 12 to 15 months. All of the work was completed in Sulzer’s Brazilian facilities, which enabled the customer to monitor progress easily.
Completing the grand plan
Bruno Antoniassi continues: “Sulzer was chosen to deliver this contract for a number of reasons, not least our expertise in pump design, but also because of our extensive facilities and labor resources in Brazil and within our global network. These have allowed us to complete the installation and commissioning of six pumps for this project.”
The installation process was a challenge in itself; the size and weight of the components, combined with the remote locations of the pumping stations and the lack of any infrastructure meant the field teams had to be properly equipped to complete the task. The Sulzer engineers completed the commissioning on time and, more than 10 years on, the pumps continue to supply water to the North Eastern region.
Global push for net-zero recovery from COVID-19
In the largest ever UN-backed, CEO-led climate advocacy effort, we join other multinationals in reaffirming science-based commitments to achieving a zero carbon economy and calling on governments to match the ambition.
More than 155 companies — spanning 34 sectors, headquarters in 33 countries and representing a combined total over 5 million employees — have signed a statement urging governments around the world to align their COVID-19 economic aid and recovery efforts with the latest climate science. Grundfos is one of them.
“In spite of its severity, the current health and economic crisis should not lead decision makers across the world to lower their climate ambitions and slow down the green transition. For all of us to truly recover better, we need the very opposite. This means massive investments in energy efficiency, renewable energy production and green electrification,” says Mads Nipper, Group President & CEO, Grundfos.
As debates on recovery packages around the world gather pace, the companies, which are all part of the Science Based Targets initiative, are calling for policies that will build resilience against future shocks by supporting efforts to hold global temperature rise to within 1.5°C above pre-industrial levels, in line with reaching net-zero emissions well before 2050.
“Green investment is not only necessary for reaching the 1.5 degree climate target. It is also a far better way to kickstart the economy during a crisis, as investments in green technologies create more than three times as many new jobs as fossil fuel equivalent investments per million USD invested. Green business is good business. Not just in times of high growth, but especially in tough times like now,” adds Mads Nipper.
By signing the statement, the companies are reaffirming that their own decisions and actions remain grounded in science, while calling on governments to “prioritize a faster and fairer transition from a grey to a green economy.”
New pumps paid off in two years
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.
Reducing the amount of waste that goes into landfill is an important environmental consideration and one that is being supported by waste-to-energy plants, which use the material to create electricity. These plants help to increase sustainable energy production and they are supported by Sulzer, which offers many products and services that can improve efficiency and reliability.
Rising maintenance costs
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.
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.
Dale continues: “Our site services team only needed ten days on site to remove the old pump, modify the pipework slightly and install the new equipment. This ensured that the plant always had sufficient capacity and no downtime was associated with the project. After the first two pumps were installed, the plant manager decided to continue with the project and four pumps have now been replaced. The installation of the remaining two will take place next year.”
Sulzer has so far installed four of its MBN50 high pressure 9-stage pumps, which are primarily designed for power generation applications and provide efficient and reliable service in this demanding environment. The performance of each pump has been tailored to the application to ensure optimum efficiency and reliability.
Dales concludes: “The plant manager has immediately seen the benefits of the new pumps. The annual running costs have dropped dramatically, and the maintenance team is now able to spend more time looking after other important equipment. The whole project has been completed on time without any disruption to the operation of the plant and is on target for completion next year.”
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