Operation Of Centrifugal Pumps Research Articles

Use of Centrifugal Pumps Operating as Turbines for Energy Recovery in Water Distribution Networks. Two Case Study

The main pipes in water distribution systems have, in many cases, an excess of static pressure. This excess of pressure is usually dissipated by means of intermediate reservoirs, pressure-reducing valves or any other device that produces the required energy loss with the aim to adjust the pressure level to the demand pattern of the system. This hydraulic energy can be used to directly drive a mechanical system or to generate electric power. In this type of recovery energy systems, the available hydraulic power is lower than 100 kW (micro-hydro). In this range, the utilization of conventional hydraulic turbines is not economically viable in short-medium time. In micro-hydropower applications the use of standard centrifugal pumps operated in reverse mode as hydraulic turbines (PAT) can be competitive. In this work, several prediction methods and algorithms suggested by different authors were analyzed and compared. Two case study, in the water system distribution of Murcia and Elche are also presented.

Numerical investigation of a centrifugal pump running in reverse mode

This article reports a work on the three-dimensional flow simulation in a centrifugal pump operating in reverse mode. The simulations were carried out with the commercial code Fluent using unsteady flow calculations together with a sliding mesh technique. Hence, it was possible to account for the effect of blade—tongue interactions on the local flow. The numerical predictions were compared with the experimentally determined performance characteristics and also with the static pressure distribution obtained around the periphery of the impeller. Once validated, the numerical model was used to investigate the global flow. Additionally, the total radial force (steady and unsteady components) on the impeller for a number of flowrates was estimated. It was found that the unsteady radial force (peak to peak) varied between 24 and 54.3 per cent of the steady value within the considered flow interval. The maximum force amplitude was reached when the trailing edge of one blade (pressure side) was located 3° downstream of the tongue tip.

An optimization routine on a prediction and selection model for the turbine operation of centrifugal pumps

The paper presents an experimentally validated optimization routine for the turbine-mode operation of radial flow centrifugal pumps. The optimization routine outlined here is designed to be used with prediction (predicting turbine mode characteristics of a pump) and selection (selecting the most appropriate pump for turbine-mode operation) models. The optimization routine improves upon previous uncertainties in prediction, especially in the low specific speed range. The optimization routine is evaluated experimentally for three pumps with specific speeds of 18.2 rpm, 19.7 rpm and 44.7 rpm, and a significant improvement in the accuracy of the turbine predictions with the errors for all the three pumps falling within the ±4% acceptance bands in the full load operating region is found. It is also shown how the optimization routine validates an approach to selection and prediction based on model experiments and classical principles of applied turbomachinery (specific speed-specific diameter or the Cordier/Balje plots). Such an approach is shown to be the most economic in terms of pump mode input variables. The paper recommends the extensive use of the optimization routine in micro hydro and other energy recovery projects involving pumps as turbines and the creation of a database of accurate field results that can be used to improve the routine further.

Feasibility of hydraulic power recovery from waste energy in bio-gas scrubbing processes

This paper investigates the feasibility of recovering waste energy from typical bio-gas upgrading facilities by means of a hydraulic turbine, and presents analysis of different types of hydraulic power recovery turbines. A selection method and analysis is developed which can be applied to an existing process to determine the effectiveness and energy savings of such a system for its economic viability. A practical testing rig was designed and constructed to verify the reliability and consistency of data for the both selection and optimization techniques. It was found that a centrifugal pump operating in reverse flow, essentially as a turbine, could be a possible option for waste energy recovery.

Influence of Reynolds number on net positive suction head of centrifugal pumps in relation to disc friction losses

Determination of Net Positive Suction Head (NPSH) value in the range of best efficiency is important in order to ensure correct operation of centrifugal pumps in networks. Empirical formulas of NPSH determination include the specific speed, the head and coefficients taking into account the pump impeller type. Using recent formulas on disc frictions and correction factors including the viscosity, a new formula of NPSH correction factor is suggested in this study, taking into account the specific speed, the disc friction losses and the flow velocities at impeller inlet. NPSH evaluated for water by Stepanoff formula is divided in kinetic and disc friction heads. The formulation taking into account disc frictions including viscosity, diameters and velocities enables to determine the NPSH correction factor during the pumping of viscous fluids. Simulations on different centrifugal pump models of specific speeds between 20 and 45 min-1 are conducted. Obtained results show that the NPSH correction factor depends on the specific speed. It is near the unity when Reynolds number is greater than 105. It increases appreciably with Reynolds number values less than 105. It reaches 2.5 for a Reynolds number of 104 and a specific speed of 25 min-1, and 5 for a Reynolds number of 103 and a specific speed of 45 min-1. The established formula is related to those of Stepanoff for water. To validate this formula, a centrifugal pump with a specific speed of 20 min-1 is tested for water and a viscous fluid with a viscosity of 75 cSt. NPSH correction factor is also compared with those obtained by other authors. This comparison enables the validation of this new formula for the examined range of centrifugal pump models. This new formula facilitates manufacturers and users the NPSH prediction of standard centrifugal pumps whatever the viscosity of the fluid.

Operation of centrifugal pumps in off-design conditions

The special features of operation of centrifugal oil pumps in underload conditions are discussed. It is shown that the vibrodynamic characteristics of the pumps are linked with the delivery operation conditions. The cavitation characteristics of screw centrifugal stages are compared. Recommendations are offered for normal pump operation in startup and off-design conditions.

Approaches to stable operation of shaftless centrifugal pump

The shaft-less impeller of the centrifugal pump, which is driven by the magnetic induction, was developed. The impeller rotates under the floating condition without any control device. The floating condition of the impeller is realized by utilizing the pressure in pump casing. The pump performance and the rotational behavior of the impeller were investigated experimentally. It has found that the floating position of the impeller become quite unstable in a partial flow rate operation. And the pressure distribution at the casing wall affects the rotational posture of the impeller. This paper presents the effect of the casing treatment on the rotational posture of the impeller and the pressure distribution. The reasonable casing treatment is available for the stable rotational posture of the impeller.

A CFD parametric study of geometrical variations on the pressure pulsations and performance characteristics of a centrifugal pump

Pressure pulsations may be troublesome during the operation and performance of centrifugal pumps. Such pressure pulsations have traditionally been investigated experimentally but numerical analysis techniques allow these effects to be explored. The multi-block, structured grid CFD code TASCflow has been used to investigate the time variation of pressure within a complete double entry, double volute centrifugal pump. This investigation has taken the form of a parametric study covering four geometric parameters, namely the cutwater gap, vane arrangement, snubber gap and the sidewall clearance. Taguchi methods allowed the number of transient analyses to be limited to a total of 27. Three flow rates were investigated and the pulsations were extracted at 15 different locations covering important pump regions. Taguchi post-processing analysis tools were used to rank the relative importance of the four geometric parameters at each location for each flow rate. The cutwater gap and vane arrangement were found to exert the greatest influence across the various monitored locations and the flow range. A rationalisation process aimed at increased component life and reduced noise/vibration through reductions in pressure pulsations has produced geometric recommendations, which should be useful to designers.

Influence of Viscosity on ESP Performance

This article, written by Technology Editor Dennis Denney, contains highlights of paper SPE 110661, "On the Influence of Viscosity on ESP Performance," by Gilmar Amaral and Valdir Estevam, Petroleo Brasileiro S.A, and Fernando A. Franca, SPE, State University of Campinas, prepared for the 2007 SPE Annual Technical Conference and Exhibition, Anaheim, California, 11–14 November. The paper has not been peer reviewed. Experimental data and a preliminary analysis of the operation of centrifugal pumps with viscous liquids are presented. Two centrifugal pumps, a conventional radial and a semiaxial electrical submersible pump (ESP), were instrumented and tested with water and clear glycerin. The glycerin viscosity was varied from 67 to 1,020 cp by changing the temperature, encompassing the viscosity range of light-to-heavy oils. The main purpose of these tests, besides measuring the influence of viscosity on the pump overall performance, was to supply detailed information on the energy-transfer processes taking place in the pumps' internal components. Introduction ESPs have been used increasingly as an artificial-lift method to produce medium-to-heavy oils in deep offshore fields. The pump may be inside the well or, depending on technical requirements, above the seabed to reduce intervention costs, as is the case in Jubarte field in Campos basin, Brazil. When the oil viscosity is too high to allow efficient pump operation, the oil viscosity can be reduced by injecting light oil (usually referred to as a downgrading technique) or solvents upstream of the pump suction or by raising the mixture temperature. When installed on the seabed, series- or parallel-arranged pump systems can be used to reduce the power required by each pump. Thus, new operation strategies and different equipment allocation and arrangements have been used to exploit heavy oils in these harsh environments. In Jubarte field, an ESP was installed in the production riser, just above the tree, to lift the raw mixture to the platform. When the ESP is on the seabed, the fluid temperature may be lower than the reservoir temperature. The heat generated in the ESP, which reduces the fluid viscosity and increases pump performance, is partially lost to the surrounding cold water. As the pumped mixture cools and attains a higher viscosity, pump performance is affected. Additionally, a pump at seabed level operates at a reduced inlet pressure compared with an in-well pump and may increase the free-gas content, additionally reducing pump performance. Therefore, fluid viscosity is a key technical issue when selecting an ESP to lift medium-to-heavy oil in offshore fields. The performance of pumps operating with liquids of various viscosities is obtained by either empirical or deterministic methods. Empirical methods usually try to adjust the pump performance starting with the published pump-characteristic curves for water. Nondimensional parameters and correcting coefficients for hydrostatic head and efficiency for a given flow rate and fluid viscosity are used to estimate the actual characteristics on the basis of those for water. However, the database is limited in terms of pump characteristics and operational conditions.

Investigation into pressure pulsations in a centrifugal pump using numerical methods supported by industrial tests

The operation of centrifugal pumps can generate instabilities and pressure pulsations that may be detrimental to the integrity and performance of the pump. In the present study a numerical investigation of the time variation of pressure within a complete centrifugal pump was undertaken. A range of parameters and three flow rates were investigated and the pulsations were extracted at 15 different locations covering important pump regions. The transient flow results compared reasonably with experimental data obtained in a limited experimental survey and clearly indicated the pump locations experiencing the largest pulsation levels. It was also noted that monitoring pulsations at the top dead centre of the pump volute casing would provide a better indication of internal pump pulsations than monitoring at the discharge.

Variable speed pumping: myths and legends

Variable speed drives offer many advantages in the operation of centrifugal pumps but, in spite of this, many barriers remain to implementing the technology to its full potential. In this article from the USA, Mike Pemberton of ITT Goulds Pumps seeks to dispel the myths and legends surrounding variable frequency technology and its application, arguing that it has now developed to the point that these barriers are, for the most part, perceived rather than actual.

How Many Ways Can We Kill a Pump?

This month's question asks about operation and maintenance of centrifugal and chemical pumps, specifically whether they can be damaged and how. The answer consists of 10 ways to “snuff” a pump.

Optimizing centrifugal pump operation

Centrifugal pump operation is more than switching the pump on and directing the discharge flow to the required delivery point. This holds true even when a control valve is installed in the discharge line for the purpose of flow or level control. A few very essential operating guidelines must be adhered to if early bearing or seal failure, premature erosion of internal wetted surfaces, or metal-to-metal contact of internal rotating and stationary surfaces, is to be avoided. In this article, Stan Shiels addresses the fundamentals of proper centrifugal pump operation, and the most common areas of improper centrifugal pump operation. It is assumed that the pump has been successfully commissioned.

Operation and repair of submersible electric centrifugal pumps at the joint-stock company Tatneft'

Operation and repair of submersible electric centrifugal pumps at the joint-stock company Tatneft'

Monitored centrifugal pump operation: Experience, problems, and prospects

Monitored centrifugal pump operation: Experience, problems, and prospects

Pulsate regimes of the centrifugal pump operation for assisted circulation.

This paper focuses on the evaluation of dynamic pumps as an element of the assist unit from the standpoint of its capacity to pass and change the left ventricle's pulsations. Analyses of the dynamic equations of the pipelines and pump have been performed. The pump intensification capacity of the disc and blade pumps was computed. Theoretically it was determined and experimentally confirmed that the pump intensification capacity was defined by the performance of the pump head. It was also determined that the existing pumps (e.g., The BioMedicus Biopump and the Moscow Aviation Institute, OK) pass and attenuate the left ventricle pressure pulsations.

Characteristics and Flow Patterns of a Small Screw-Type Centrifugal Pump Operating in Air-Water Two-Phase Flow.

Characteristics and Flow Patterns of a Small Screw-Type Centrifugal Pump Operating in Air-Water Two-Phase Flow.

Etude expérimentale de l'écoulement instationnaire dans le diffuseur aubé d'une turbomachine centrifuge

The unsteady effects caused by the interaction of the rotor wakes with the flow within the vaned diffuser of a centrifugal turbomachine stage have been experimentally investigated. The experiment has been carried out on the simplified model of a centrifugal pump operating in air at the nominal point. The diffuser flow has been surveyed by means of a two-colour four-beam laser Doppler velocimeter on a blade-to-blade surface at midspan and over two cylindrical measuring surfaces located just upstream of the diffuser vanes leading edges and in proximity of the inlet throat of the diffuser. Instantaneous data taken in phase with the shaft rotation have been averaged and used to construct images of the flow field for different relative positions of impeller blades and diffuser vanes. The sequences are detailed enough to show the evolution of the rotor wakes within the forward part of the diffuser. The rotor blade wakes entering the diffuser are chopped by the vanes leading edges into individual segments which are convected through the diffuser passages where they mix out rapidly.

Slurry transport using centrifugal pumps

A laboratory-scale closed-circuit pipeline facility was modified to experimentally investigate the effects of pumping slurries of wheat straw and corn stover particles on the performance characteristics of a centrifugal slurry pumps. The effects of particle size and slurry solid mass content (concentration) on head, efficiency, and power consumption of a centrifugal slurry pumps were studied. In a clear contrast to the general performance of centrifugal slurry pumps in conventional solid–liquid systems, the total head height increased with an increase in slurry solid mass content due to several reasons including unique friction loss behavior (i.e., drag reducing feature) of fibrous particles slurries in pipelines. In addition, small size fibrous particles increased the pump efficiency more than the efficiency of the same pump handling pure water only. A correlation was finally proposed to predict the reduction in head while centrifugally pumping fibrous agricultural residue biomass (wheat straw, corn stover) slurries, compared to the head produced while handling pure water only. The results could be used in the design and operation of centrifugal slurry pumps to transport fibrous agricultural residue biomass materials. However, the effects of other parameters like air in the system and anaerobic problems should be taken into account too.

Prediction of the range of operation of centrifugal pumps according to the cavitation criterion

Prediction of the range of operation of centrifugal pumps according to the cavitation criterion