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A New Analytical Approach to Predict the Operating Point of a Pumping System Having Groups of Different Types of Radial-Flow Pumps in Parallel and the Resulting Flow Division in the Piping Network

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A New Analytical Approach to Predict the Operating Point of a Pumping System Having Groups of Different Types of Radial-Flow Pumps in Parallel and the Resulting Flow Division in the Piping Network
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           1 3  Journal of The Institution of Engineers (India): Series C Mechanical, Production, Aerospace andMarine Engineering ISSN 2250-0545Volume 93Number 1 J. Inst. Eng. India Ser. C (2012) 93:83-91DOI 10.1007/s40032-011-0013-x  New Analytical Approach to Predict the Operating Point of a Pumping SystemHaving Groups of Different Types of Radial-Flow Pumps in Parallel and theResulting Flow Division in the Piping Network Pranab Kumar Mondal & SanchayanMukherjee           1 3 Your article is protected by copyright and allrights are held exclusively by The Institutionof Engineers (India). This e-offprint is forpersonal use only and shall not be self-archived in electronic repositories. If youwish to self-archive your work, please use theaccepted author’s version for posting to yourown website or your institution’s repository.You may further deposit the accepted author’sversion on a funder’s repository at a funder’srequest, provided it is not made publiclyavailable until 12 months after publication.  CASE STUDY A New Analytical Approach to Predict the Operating Pointof a Pumping System Having Groups of Different Typesof Radial-Flow Pumps in Parallel and the Resulting Flow Divisionin the Piping Network Pranab Kumar Mondal  • Sanchayan Mukherjee Received: 13 April 2011/Accepted: 15 October 2011/Published online: 1 February 2012   The Institution of Engineers (India) 2012 Abstract  For two dissimilar radial-flow pumps runningin parallel mode, selection of the operating point is critical.As the flow is reduced, the pump that builds majority of thehead does the entire job while the other pump or pumps is/ are deadheaded. In this paper, a pumping system havingtwo radial-flow pumps of similar category, running inparallel mode and discharging to the specific area throughpipes, is shown. To meet the extra demand of flow rate asdesired by the process, two other pumps of a differentcategory have been added with the existing system. Theadditional dissimilar pumps are arranged to run in parallelwith the existing system. The delivery pipes of all pumpsare connected in such a way that the total flow rate goes tothe common header. This paper provides an analyticalsolution to predict the desired distribution of the flow ratein a piping network by suitable selection of the operatingpoint of the pumps running parallel in the system. Keywords  Radial flow pump    Parallel operation   Head    Discharge    Piping network  Introduction The radial-flow pumps are widely used in industry wheremoderate flow rate against moderate to high head isrequired. Radial-flow pumps are used for various purposes,i.e., process plant, power plant, steel industry etc. Withincreased rate of productivity, the requirement of waterincreases exponentially. It is sometimes seen that thecapacity of an existing pump is not enough to meet theadditional demand of the plant and very often new pumpsare installed to meet the additional demand of the plant,which may be either with an increased rate of discharge( Q ) for the specific head (  H  ) or vice versa. Often there is aspatial constraint. Also, from the point of view of economicsystem design, the new pumps are preferably arranged tobe installed within the existing system. The situation spe-cific to higher requirement of discharge against the samehead demands for the installation of an additional pump orpumps in parallel with the existing system. To the pumpingsystem designers, installation of a new pump or pumps inparallel with the existing system is not an easy task keepingin mind the selection of the operating point. Moreover, thetask becomes complicated further whenever two dissimilarpumps are required to be connected in parallel. In such apumping station, water is conveyed to one common pres-sure head delivery line (PHDL). The PHDL is used tosupply water in different areas through branch pipes. Thereis a locking set at each pump of a particular pipeline. Thelocking set for the pumping station is a flow control disk type butterfly valve. The water pumping stations, equippedwith long PHDL and several radial-flow pumps, are com-monly connected in parallel to one PHDL. Their opera-tional modes depend on the quantity of the pumping units,their connection schemes, and on the water levels in thedownstream and upstream of the station [1]. High-pressurepumping systems are used in a wide range of industrialprocesses. So careful design of the pumping system isessential for the optimum safety and reliability. Failure toinstall a pump of desired performance and associatedcomponents of the system designed for the task could P. K. Mondal ( & ),  Non-member  Department of Mechanical Engineering, Indian Instituteof Technology Kharagpur, Kharagpur, Indiae-mail: pranab2k3@yahoo.comS. Mukherjee,  Member  Department of Mechanical Engineering, Kalyani GovernmentEngineering College, Kalyani, Nadia, West Bengal, India  1 3 Journal of The Institution of Engineers (India): Series C (January–March 2012) 93(1):83–91DOI 10.1007/s40032-011-0013-x  actually be a potential risk to human life or could result insignificant downtime and loss of productivity of the plant.On the other hand, in the industrial engineering design themost important part is to minimize the total life cycle costof the plant and, thereby, there should be a balance betweenthe safety and the total life cycle cost of the pumpingsystems being designed. Therefore, keeping the abovecriteria in mind, a good designer should always look for theoptimization while designing a system. Selection of pumpsto be connected in parallel is necessary to ensure the safetyand the reliability of the pumping system. Therefore, it isvital to take into account the value and the nature of achange in water flow rate, the duration of the plant oper-ation with one or another flow rate, which, in turn, mini-mizes the number of times the pumping units to beswitched on and off. The number of starting of the largepumping units with a power of more than 2,500 kW islimited to 50–120 times per year [2]. Saving on the totallife cycle cost of a pumping system calls for the optimi-zation, which requires merely maximizing the overallefficiency by optimizing the system design. The optimi-zation of the pumping system design is nothing but the bestpossible economic design and selection of the various partsof the system such as piping, flow control and fluiddynamics [3]. Pressure, friction and flow are the threeimportant characteristics of the pumping system uponwhich optimization depends. Amongst these three impor-tant characteristics, pressure is the driving force responsi-ble for the movement of the fluid. The idea of a parallelpumping is to get higher flow rate or discharge at a requiredhead. Therefore, special attention is given to the frictionalpressure drop in the piping network and the static head.The frictional pressure drop mainly depends on thehydraulic diameter and length of the pipe and the differ-ence of the pipe-end discharge height and the suction tank fluid surface height. The pressure drop due to friction in thepiping network is one of the important determinants of theoverall efficiency of the pumping system. The pressurelosses greatly depends on the configuration of the pipingnetwork, and for a particular configuration of the pipingnetwork, geometric parameters such as hydraulic diameter,fittings and bend geometry play an important role for thedetermination of the overall efficiency of the pumpingsystem [4]. In a pumping system, it is desirable to haveuniform flow distribution over the entire piping network forits optimum operation, while the severity of improperdistribution of the flow, which strongly depends on thegeometric factor, has some bearing on the performanceof the pumping system [5]. For the economic operationof the pumping units, it is recommended to run the unitshaving higher efficiency most of the time. To do that,discharge control of the plant, equipped with the radial-flow pumps operating in parallel on a common pipeline, isaccomplished systematically via starting or turning off thepumping unit. For the organization of the operational modefor different types of pumping units, it is expedient to buildthe curves of the pressure drop for pumping of 1 m 3 of water for each pumping unit (or group of units) [6]. It isclear that the pumping system design is not the selection of pumps only; it is rather an economic as well as a sounddesign of the integrated parts of the system. The applica-tion engineer of various industries always faces the prob-lems related to the optimum design of the pumping systemfor the supply of water starting from the process plant tothe water supply even in multistoried buildings. Sometimesit becomes quite a challenging task to them. The rootcauses behind such problems are the increased productivityrate together with the utilization of the existing system. Inthis study, a practical problem of designing a parallelpumping system associated with the distribution of waterin an iron ore mine of Tata Steel Limited, Noamundi,Jharkhand, India, is cited. The details of the problemassociated with the pumping system along with flow dis-tribution in a piping network have been given in a separatesection of this article. The literatures available in this areaare either based on the flow distribution and pressure dropin the piping network, or on the selection, maintenance andoperation of the pumps. Moreover, the handbooks onpumping system design available to the application engi-neers mainly discuss about the pumping system details inan intuitive way. In the literature, however, no study hasbeen reported so far, providing a complete methodology tosolve this kind of problem. To fulfill the lacuna in this area,an analytical study on the above-mentioned problem ismade in this paper and the impetus of this study is to solvethe problem analytically to get rid of the problem in adifferent and comprehensive way. This is a new approachto solve this kind of problem. System Description In the present study, a pumping system equipped withradial-flow pumps has been considered. Two differentgroups of radial-flow pumps having different characteris-tics have been connected in parallel to supply water intodifferent areas of the process plant. Specification details of the pumps are given in Table 1. All the pumps are con-nected to a common PHDL. The schematic of the pumpingstation along with the necessary fittings is shown in Fig. 1.The pumping station consists of Group-I Pumps, havingthree identical radial-flow pumps and they are connected inparallel with one another to supply the water to the LRPwash plant. Operating only one Group-I pump meets therequirement of water for the LRP wash plant. However, thenewly installed Jig plant demands more than 200 m 3  /h of  84 Journal of The Institution of Engineers (India): Series C (January–March 2012) 93(1):83–91  1 3  water to be supplied from the existing pump house evenafter operating two Group-I pumps at a time. In this situ-ation, running all three pumps together may meet thesystem demand. Nevertheless, the system reliabilityappears to be a matter of concern in doing so. Thecapacities of the existing pumps are, therefore, not ade-quate to cater for the additional requirement of water intoJig plant and, thereby, Group-II Pumps having two iden-tical radial-flow pumps had to be installed in the existingpump house. To make the system even more economic,i.e., to use the existing pump house instead of acquiringseparate pump house as well as to maintain the flexibility,i.e., to have the facility of interchangeability, and finally,for the ease of maintenance, new pumps have beeninstalled in the existing pump house. The line leading to theLRP wash plant as well as to the Jig plant has some but-terfly valves to control the flow. Flow Analysis of the System and Associated Problem The pumps indicated by Group-I, are the existing pumps,used to supply water to LRP wash plant. The requirementsof water for LRP wash plant and Jigging plant are1,200–1,150 m 3  /h, respectively; thus the total requirementof the water to be supplied from pumping station becomes2,350 m 3  /h. Two pumps of Group-I will run in parallel andwill deliver 2,140 m 3  /h of the total demand. The shortfall of the water (210 m 3  /h) as needed by the process has to besupplied by running the Group-II pumps. It is seen from thespecification of Group-II pumps that only one pump canmeet the shortfall, while the Group-II pumps have beenconnectedinparalleltotheexistingpumps.Allthepumpsasshown by Fig. 1, discharge to a common header throughPHDL. From the common header, a separate branch line hasbeen provided to cater for the water in the Jigging head tank  Fig. 1  Schematic diagram of pumping station with pipingnetwork  Table 1  Pump specification detailsPump group No. of pumps Discharge ( Q ), m 3  /h Head (  H  ), mwc Speed, rpm Pump typeGroup-I 3 1,070 37.5 2,900 Radial split casing withend suction top deliveryGroup-II 2 400 40 2,900Journal of The Institution of Engineers (India): Series C (January–March 2012) 93(1):83–91 85  1 3
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