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Advanced and conventional technologies in power station pumping systems
feature pumping for power stations
Advanced and conventional technologies in power station pumping systems In the third and final paper discussing the use of advanced and conventional technologies in power stations, S G Joshi and R D Kulkarni look at system design and product development technologies employed by pump manufacturers.
System design technology
T
he performance of vertical turbine pumps is largely dependent on the design of intake sumps. Using the most appropriate design of intake sump, a uniform flow to the pump can be achieved and the performance of the pump enhanced. The Hydraulic Institute standards specify general guidelines for the design of sumps. However, site constraints can call for a deviation from the standards making it essential to carry out sump model studies to ensure a smooth flow across the entire flow range of the pumps. The function of the sump is to supply an evenly distributed flow of water entering the suction bell across the entire operating range. An uneven flow distribution in the pump sump can result in surface or submerged vortices forming. If the submergence is low then air entraining vortices are created causing a reduction in capacity, an increase in vibration and additional noise. Furthermore, an uneven flow may lead to an increase or decrease in power consumption. The ideal configuration is a straight channel coming directly to the suction bell as bends and obstructions are detrimental. Due to various constraints, it may not always be possible to construct an ideal sump. Where this happens, it is advisable to examine the sump design early in the project by employing either experimental or computational methods.
Making correct predictions based on theory is always going to be a problem. The actual flow conditions in a prototype sump are complex, so it is advisable to investigate the flow either by experimenting with a sump model or by employing CFD analysis before embarking on the construction of the sump. This will reveal any potentially undesirable flow conditions, which can be eliminated or reduced to a minimum by modifying the sump design. The development of computational tools has helped in resolving some of the issues in sump model studies. Experimental studies are time consuming and may contain inherent limitations as the exact modeling of Reynolds Number, Froude Number and Webers Number is not possible on smaller models that are geometrically similar. However, CFD analysis can be carried out on prototypes. The issues related to inaccurate prediction flows from studies using smaller size experimental models do not come into the picture when CFD tools are used. These tools are well validated but still have inherent limitations at this stage, with surface waves and the air entrainment phenomenon yet to be predicted with
0262 1762/04 © 2004 Elsevier Ltd. All rights reserved
confidence. Research activities in this direction are in progress. Figure.No.1 shows a streak line plot of the sump. In areas that are prone to earthquakes, all equipment supplied should be qualified for mechanical integrity and satisfactory operation and be capable of sustaining seismic loads. The mechanical design of the pump has to accommodate pressure levels, thermal stresses, rotation of the impeller, power transmitted to the impeller, etc. The axial and radial thrusts are taken into account in the bearing selection. The stationary parts of the casing [i.e. the suction and delivery nozzles] have additional loads in terms of forces and moments, as specified in API standards. A mechanical design based on these features is satisfactorily for general-purpose applications, but needs to be crosschecked with additional loads when used in earthquake sensitive areas. Advances in computational techniques have made it possible to check such
Figure 1. A streak line plot of the sump
www.worldpumps.com 25
feature pumping for power stations
mechanical designs even before the pump is manufactured. Should the analysis show some excessive stressing of a particular component, precautionary recommendations can be implemented at the design stage.
variants to minimise the total effect of all causes resulting from variations in manufacturing processes. The dimensional tolerances of the required parameters are determined at the design stage so that the final performance is within the desired limits.
Product development technologies
The availability of experimental data to correlate the size of cavitation bubbles with the life of impellers manufactured, has allowed pump manufacturers to develop techniques for visualizing and measuring the size of cavitation bubbles in rotating pumps. These use transparent materials for the suction passage and stroboscopic light to freeze rotation. As a result, pump manufacturers can identify the bubble-free net positive suction heads required and determine cavitation erosion life.
Rapid Prototyping is widely used by companies involved with accelerated product development. In this process components are designed using the latest computational tools and are manufactured to match the hydraulics to the needs of the design. Solid models of the component are used to generate Stereo-Lithographic (STL) format files, which are directly compatible with machines used to generate rapid prototyped components. Rapid prototyping could be used for covered/uncovered impellers with double curvature blades. The prime objective of any pump design is to meet the functional requirements very efficiently whilst minimising the possibility of performance variation between any two pumps of the same design. However, pure hydraulic design methods alone cannot predict the performance scatter, thereby making it impossible to implement corrective actions at the design stage. Physical experimentation is essential in order to assess the performance scatter after the product is made and then further trials are required to determine the dimensional tolerance limits that give constant hydraulic performance. In recent years, advanced statistical techniques have combined with computational design methods to build robust quality into the product [i.e. to obtain a stable and reliable product at minimum cost]. This approach is termed as Concurrent Design. This technique utilises the nonlinearity of the effects of design
26
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Conventional area technologies The use of pumps as turbines is an issue worth attention and exploration. This is because the application offers the advantages of economics combined with balanced ecological and environmental benefits. Using a pump as a turbine can cost less (almost 50%) than the conventional hydro-turbine of an equivalent size. This is due to the fact that the pumps can be picked from standard ranges whereas turbines are usually tailored to suit the application. Pumps have fewer parts than turbines and experienced pump maintenance personnel can also be used for turbine maintenance duties. Also as the pumps come from standard ranges, spare parts availability is very high. Any pump can be used as a turbine. However, predicting the performance of a pump as a turbine and selecting the right one for the right application is central to the issue. Experience shows that pumps used as turbines offer almost the same, or slightly less,
efficiency than when used in pump mode in the same power range. When used as turbines, pumps are highly suitable for driving a wide range of machinery and can be used as stand alone electricity generation stations for supplying power to remote areas. In turbine mode, pumps are usually checked for the ability of the rotating components to withstand a runaway speed. This is because in the event of a drive mechanism failure or failure of the grid, they can reach a runaway speed very quickly due to their inherent low moments of inertia. Runaway speed operation also leads to pressure surges, so the piping connected to turbines needs to be checked for its integrity in the event of water hammer. In an age when innovation or change is the only constant, time has emerged as the single most important factor for competitive success. Rising customer demands, rapid progress in design and manufacturing technology coupled with fierce global competition are forcing engineering and consumer product companies to continuously seek ways to compress the lead-time from concept to market. In the case of new products, this helps in enhancing one's share of the market and in the case of regular product supply, this helps in strengthening the customer base. A typical engineering or consumer product is realized through a number of steps, which include market research, concept synthesis, detailed design, prototype fabrication, testing, tooling development, production planning, manufacturing, quality assurance, packaging, marketing and product delivery. Successful companies have shown that it is possible to compress the lead-time to market dramatically, often by 50% or more. This is achieved by: • eliminating potential through better design
problems
WORLD PUMPS July 2004
feature pumping for power stations
• performing the tasks concurrently through better communications and project management • removing critical bottle necks through improved technology.
These three objectives are realized through design for manufacture, concurrent engineering and rapid prototyping and tooling technologies. Design for manufacturing involves anticipating potential manufacturing problems at the design stage and carrying out modifications to prevent their occurrence. It is well known that while design activities account for less than 5% of the product cost, they influence more than 70% of the total cost.
Surge analysis While designing pumping station and delivery transmission lines, there is an increasing awareness of the importance of surge or hydraulic transient analysis. Projects like crosscountry water supply schemes, lift irrigation schemes with large pipe sizes with higher discharge, and cooling / make up water systems for power stations all need to be protected from surge and require that analysis is undertaken to provide protection devices in the system. Hydraulic transients or surge phenomena occur in closed conduit or pipe flows associated with rapid changes in the discharge. This causes a pressure wave to form at acoustic speed, which is influenced by the material and wall thickness of the pipe. In a pumping system, a change in the discharge may be due to: • Pump start-up • Pump shutdown • Power failure and single pump failure when multiple pumps are in parallel. When the power fails the shock wave pressure rises and may lead to the design / test pressure being exceeded causing severe damage to the pipe. Therefore, prime importance should be given to the issues of surge when designing a pumping system for any sort of application.
Conclusion The technologies described in this paper have been developed and adopted by pump manufacturers in India. These have helped them to reduce product development times, improve the reliability of pumps and pumping systems, improve pump operating efficiency and develop mechanical design features to make their products cost-competitive. ■ CONTACT Pallavi Kharade Assistant Manager Advertising Department Kirloskar Brothers Limited Udyog Bhavan Tilak Road Pune - 411 029, India Tel: +91-020-24402052
WORLD PUMPS July 2004
www.worldpumps.com 27
Advanced and conventional technologies in power station pumping systems In the third and final paper discussing the use of advanced and conventional technologies in power stations, S G Joshi and R D Kulkarni look at system design and product development technologies employed by pump manufacturers.
System design technology
T
he performance of vertical turbine pumps is largely dependent on the design of intake sumps. Using the most appropriate design of intake sump, a uniform flow to the pump can be achieved and the performance of the pump enhanced. The Hydraulic Institute standards specify general guidelines for the design of sumps. However, site constraints can call for a deviation from the standards making it essential to carry out sump model studies to ensure a smooth flow across the entire flow range of the pumps. The function of the sump is to supply an evenly distributed flow of water entering the suction bell across the entire operating range. An uneven flow distribution in the pump sump can result in surface or submerged vortices forming. If the submergence is low then air entraining vortices are created causing a reduction in capacity, an increase in vibration and additional noise. Furthermore, an uneven flow may lead to an increase or decrease in power consumption. The ideal configuration is a straight channel coming directly to the suction bell as bends and obstructions are detrimental. Due to various constraints, it may not always be possible to construct an ideal sump. Where this happens, it is advisable to examine the sump design early in the project by employing either experimental or computational methods.
Making correct predictions based on theory is always going to be a problem. The actual flow conditions in a prototype sump are complex, so it is advisable to investigate the flow either by experimenting with a sump model or by employing CFD analysis before embarking on the construction of the sump. This will reveal any potentially undesirable flow conditions, which can be eliminated or reduced to a minimum by modifying the sump design. The development of computational tools has helped in resolving some of the issues in sump model studies. Experimental studies are time consuming and may contain inherent limitations as the exact modeling of Reynolds Number, Froude Number and Webers Number is not possible on smaller models that are geometrically similar. However, CFD analysis can be carried out on prototypes. The issues related to inaccurate prediction flows from studies using smaller size experimental models do not come into the picture when CFD tools are used. These tools are well validated but still have inherent limitations at this stage, with surface waves and the air entrainment phenomenon yet to be predicted with
0262 1762/04 © 2004 Elsevier Ltd. All rights reserved
confidence. Research activities in this direction are in progress. Figure.No.1 shows a streak line plot of the sump. In areas that are prone to earthquakes, all equipment supplied should be qualified for mechanical integrity and satisfactory operation and be capable of sustaining seismic loads. The mechanical design of the pump has to accommodate pressure levels, thermal stresses, rotation of the impeller, power transmitted to the impeller, etc. The axial and radial thrusts are taken into account in the bearing selection. The stationary parts of the casing [i.e. the suction and delivery nozzles] have additional loads in terms of forces and moments, as specified in API standards. A mechanical design based on these features is satisfactorily for general-purpose applications, but needs to be crosschecked with additional loads when used in earthquake sensitive areas. Advances in computational techniques have made it possible to check such
Figure 1. A streak line plot of the sump
www.worldpumps.com 25
feature pumping for power stations
mechanical designs even before the pump is manufactured. Should the analysis show some excessive stressing of a particular component, precautionary recommendations can be implemented at the design stage.
variants to minimise the total effect of all causes resulting from variations in manufacturing processes. The dimensional tolerances of the required parameters are determined at the design stage so that the final performance is within the desired limits.
Product development technologies
The availability of experimental data to correlate the size of cavitation bubbles with the life of impellers manufactured, has allowed pump manufacturers to develop techniques for visualizing and measuring the size of cavitation bubbles in rotating pumps. These use transparent materials for the suction passage and stroboscopic light to freeze rotation. As a result, pump manufacturers can identify the bubble-free net positive suction heads required and determine cavitation erosion life.
Rapid Prototyping is widely used by companies involved with accelerated product development. In this process components are designed using the latest computational tools and are manufactured to match the hydraulics to the needs of the design. Solid models of the component are used to generate Stereo-Lithographic (STL) format files, which are directly compatible with machines used to generate rapid prototyped components. Rapid prototyping could be used for covered/uncovered impellers with double curvature blades. The prime objective of any pump design is to meet the functional requirements very efficiently whilst minimising the possibility of performance variation between any two pumps of the same design. However, pure hydraulic design methods alone cannot predict the performance scatter, thereby making it impossible to implement corrective actions at the design stage. Physical experimentation is essential in order to assess the performance scatter after the product is made and then further trials are required to determine the dimensional tolerance limits that give constant hydraulic performance. In recent years, advanced statistical techniques have combined with computational design methods to build robust quality into the product [i.e. to obtain a stable and reliable product at minimum cost]. This approach is termed as Concurrent Design. This technique utilises the nonlinearity of the effects of design
26
www.worldpumps.com
Conventional area technologies The use of pumps as turbines is an issue worth attention and exploration. This is because the application offers the advantages of economics combined with balanced ecological and environmental benefits. Using a pump as a turbine can cost less (almost 50%) than the conventional hydro-turbine of an equivalent size. This is due to the fact that the pumps can be picked from standard ranges whereas turbines are usually tailored to suit the application. Pumps have fewer parts than turbines and experienced pump maintenance personnel can also be used for turbine maintenance duties. Also as the pumps come from standard ranges, spare parts availability is very high. Any pump can be used as a turbine. However, predicting the performance of a pump as a turbine and selecting the right one for the right application is central to the issue. Experience shows that pumps used as turbines offer almost the same, or slightly less,
efficiency than when used in pump mode in the same power range. When used as turbines, pumps are highly suitable for driving a wide range of machinery and can be used as stand alone electricity generation stations for supplying power to remote areas. In turbine mode, pumps are usually checked for the ability of the rotating components to withstand a runaway speed. This is because in the event of a drive mechanism failure or failure of the grid, they can reach a runaway speed very quickly due to their inherent low moments of inertia. Runaway speed operation also leads to pressure surges, so the piping connected to turbines needs to be checked for its integrity in the event of water hammer. In an age when innovation or change is the only constant, time has emerged as the single most important factor for competitive success. Rising customer demands, rapid progress in design and manufacturing technology coupled with fierce global competition are forcing engineering and consumer product companies to continuously seek ways to compress the lead-time from concept to market. In the case of new products, this helps in enhancing one's share of the market and in the case of regular product supply, this helps in strengthening the customer base. A typical engineering or consumer product is realized through a number of steps, which include market research, concept synthesis, detailed design, prototype fabrication, testing, tooling development, production planning, manufacturing, quality assurance, packaging, marketing and product delivery. Successful companies have shown that it is possible to compress the lead-time to market dramatically, often by 50% or more. This is achieved by: • eliminating potential through better design
problems
WORLD PUMPS July 2004
feature pumping for power stations
• performing the tasks concurrently through better communications and project management • removing critical bottle necks through improved technology.
These three objectives are realized through design for manufacture, concurrent engineering and rapid prototyping and tooling technologies. Design for manufacturing involves anticipating potential manufacturing problems at the design stage and carrying out modifications to prevent their occurrence. It is well known that while design activities account for less than 5% of the product cost, they influence more than 70% of the total cost.
Surge analysis While designing pumping station and delivery transmission lines, there is an increasing awareness of the importance of surge or hydraulic transient analysis. Projects like crosscountry water supply schemes, lift irrigation schemes with large pipe sizes with higher discharge, and cooling / make up water systems for power stations all need to be protected from surge and require that analysis is undertaken to provide protection devices in the system. Hydraulic transients or surge phenomena occur in closed conduit or pipe flows associated with rapid changes in the discharge. This causes a pressure wave to form at acoustic speed, which is influenced by the material and wall thickness of the pipe. In a pumping system, a change in the discharge may be due to: • Pump start-up • Pump shutdown • Power failure and single pump failure when multiple pumps are in parallel. When the power fails the shock wave pressure rises and may lead to the design / test pressure being exceeded causing severe damage to the pipe. Therefore, prime importance should be given to the issues of surge when designing a pumping system for any sort of application.
Conclusion The technologies described in this paper have been developed and adopted by pump manufacturers in India. These have helped them to reduce product development times, improve the reliability of pumps and pumping systems, improve pump operating efficiency and develop mechanical design features to make their products cost-competitive. ■ CONTACT Pallavi Kharade Assistant Manager Advertising Department Kirloskar Brothers Limited Udyog Bhavan Tilak Road Pune - 411 029, India Tel: +91-020-24402052
WORLD PUMPS July 2004
www.worldpumps.com 27