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Enhancing pump design

12.01.2011  |  Krueger, S.,  Sulzer Pumps, Winterthur, SwitzerlandCropper, M.,  Sulzer Pumps (US), Portland, OregonParker, J. ,  Sulzer Pumps (US), Brookshire, Texas

How modern tools accentuate pump performance

Keywords:

Only a few decades ago, product development of pumps was performed by the use of drawing boards and simple calculation methods. Most of the development time was spent on 2D CAD drafting, limiting the amount of iterations to a minimum. Together, advances in information technology, computer-aided engineering (CAE), drafting (CAD) and simulation have evolved significantly. A number of step-changes in technology have allowed for an automation of design tools, thereby reducing the development time needed for drafting and allowing for further design iterations. Progress with faster computers, tools for computational fluid dynamics (CFD), structural analysis, standards and databases, releases even more time for pump performance optimization with respect to efficiency and reliability.

Service.

The stringent requirements of the hydrocarbon processing industry demand a guaranteed level of product quality and performance reliability. Today’s social and economic standards also demand that modern pump designs are produced with a focus on safety, reliability, energy optimization, material usage and environmental sustainability. Leaders in pump design technology strive for a continual improvement of their products with a view toward optimizing design for any given application. Improvements in performance-range coverage are the starting point. The addition of further hydraulic performances into an existing product range will certainly increase the probability of finding a performance selection at, or close to, the pump’s best efficiency point.

The creation of compact hydraulic designs has a significant effect on the overall size of the pump casing, thereby allowing a reduction in the overall use of materials while still ensuring the integrity of the pressure boundary and meeting the requirements of pressure vessel design codes. Combining this with a reduction in the pump case suction and discharge nozzle sizes can also allow the piping designer to use smaller connecting piping, valves and piping supports. The overall result is continual improvements to product performance, with optimized use of materials by both the pump manufacturer and the plant designer (Fig. 1).

  Fig. 1. BBS between bearings single-stage
  double-suction pump.  


Modern tools improve the product.

The impeller is the heart of a pump, as it is responsible for hydraulic efficiency and pump head. In addition (as is the case for the BBS pumps), a suction impeller has to achieve a required NPSH3% (Fig 2). Sulzer Pumps developed its own fully parametric, multifunctional impeller design program, and has validated its reliability over decades. More than 80 parameters define meridional contour, blade shape and thickness, ensuring a high flexibility of the impeller geometry. When designing a suction impeller, the developer faces opposing objectives, such as maximizing hydraulic efficiency while minimizing NPSH3% values. This yields different geometry solutions that are all compromised in some manner. For a performance enhancement project, the main impeller dimensions are given (e.g. shaft, impeller eye and outer diameter, as well as impeller length), allowing freedom for a fine tuning of meridional contour and blade shape. The performances and suction capabilities of these designs are usually evaluated by CFD for a wide range of operating points.

  Fig. 2. Cross-sectional view of a BBS impeller.  

This automated process—consisting of impeller design, simulation and result analysis—is implemented into an optimization environment that drives the entire impeller design to achieve overall objectives of efficiency, and head and suction performance. Within this optimization, the simulations are usually done for customer-specified operating points, e.g. duty point, partload and overload operating conditions. Automation allows for impeller design and analysis to continue normal outside working hours. This greatly increases the amount and variety of design information that can be studied when striving towards an optimum solution. Fig. 3 gives an example for such a result analysis within the impeller design. It visualizes the relationship between overall impeller efficiency (a combined value of duty point, partload and overload efficiency), impeller head and cavitation at duty point.

  Fig. 3. Result analysis in modern impeller design.  


The red cross-hatched section shows that four designs can best fulfill the requirements. They are all checked for design and manufacturing constraints and their entire impeller performance curve is simulated and compared against performance impairment and suction behavior. This process allows the selection of the final impeller geometry.

With other in-house tools, the suction and volute casing passageways are generated, and, if necessary, a full transient simulation can be undertaken to check the entire hydraulic and suction performance. Fig. 4 shows the flow field in impeller and volute of a BBS pump. This technique has the great advantage of allowing visualization of flow separation and recirculation zones, based on which the designs can be reiterated and manually optimized.

  Fig. 4. Flow visualization in impeller and volute.  

Based on the selected waterway designs, the pump casing’s mechanical designs are generated and a structural analysis is then performed. The deformations and the stress behavior of pump casing, cover and bolts can be evaluated for different load cases with the use of 3D finite element analysis (FEA).

From the designer’s standpoint, the first design is most likely a light one with a consequential lack of stiffness and higher resulting stresses and deformations than acceptable. In this case, FEA indicates those areas where excessive stress and deformations are beyond target limits. The designer can then decide to modify the casing by selectively increasing wall thickness and using additional stiffening ribs to increase stiffness and to reduce any deformation to acceptable limits. This also allows the designer to optimize the use of raw materials. Use this case as an example: Adding two ribs under the 180° flange is a simple modification that shifts deformation and stresses into the acceptable limits (Fig. 5).

  Fig. 5. Total deformation (same scale and load
  case) for basic design (left) and optimized
  design (right)..  

Product development has changed significantly over recent decades and innovation and concept changes are major keywords. The application of the latest tools, codes and standards are of great help to enhance both efficiency and reliability for new generations of pumps. HP

The authors 

 
  Susanne Krüger is heading the Core Technology and Tools Group within the Sulzer Pumps headquarters in Winterthur, Switzerland. Her responsibilities involve the definition of strategy, the monitoring of the ongoing projects, the research processes, the evaluation of research and the integration into product design processes. Dr Krüger has been working in the turbomachinery business for seven years and joined Sulzer in 2005. She holds an MS degree from the Technical University of Stuttgart, Germany, and a PhD from the Swiss Federal Institute of Technology of Zurich.  

 
  Mick Cropper is heading the Product Development Engineering at Sulzer Pumps (US) Inc. in Portland, Oregon. He is currently responsible for global product development activities, which have included over the last five years, upgrades and additions to Sulzer product lines to conform to the latest industry requirements for applications in refining, oil and gas applications, power generation and water industries. Mr. Cropper graduated from Barnsley College of Technology in England with a higher national certificate in mechanical engineering.  

 
 

John Parker is the Head of Segment for the hydrocarbon processing industry (HPI) located at Sulzer Pumps (US) Inc. in Brookshire, Texas. Mr. Parker is responsible for the global strategic coordination of Sulzer Pumps activities in the HPI. Mr. Parker has been in the pump industry for 38 years. He earned a BS degree in mechanical engineering from Northern Arizona University.  





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PEDRO NEL PEREZ
12.28.2011

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