CHAPTER 1 1 INTRODUCTION

Transcription

1 1 CHAPTER 1 1 INTRODUCTION This chapter describes the overall structure of this thesis work and importance of mixed flow submersible pump in the irrigation sector. 1.1 OVERALL STRUCTURE OF THE THESIS Figure 1.1 Structure of Thesis

2 2 1.2 INTRODUCTION TO SUBMERSIBLE PUMPS Armais Arutun off invented the submersible borewell pumpset at the age of 18 in Ukraine in the year A US patent was obtained in He started the first factory to manufacture them in the name of REDA (Russian Electrical Dynamo of Arutunoff) in 1928 at Bartlesville, Oklahoma, USA. These submerible pumps were used in oil wells to pump crude oil. Oil filled motors were used in these pumpsets. Meanwhile, in Europe, the same design concept was evolved in water filled wet type winding motor, fitted with vertical multistage centrifugal turbine pumps suitable for water pumping from borewells. In Germany, in 1926 Pluger started to manufacture these water borewell pumpsets followed by KSB, Hubner, Odessaa Pumpen, Aturia in Italy and Hayward Taylor in England. Now KSB, Pluger and other companies are still manufacturing these pumpsets throughout the world. Another pioneer manufacturer is Byron Jackson in America. Now both Pluger and Byron Jackson are under Flowserve Corporation. Other water borewell pump manufacturers worldwide are Franklin Electric and Pump Systems, Sta Rite, Goulds in USA and Grundfos who started manufacturing stainless steel pumps in Denmark from KSB came to India in 1969 by establishing its subsidiary company at Pune. Pluger gave its technical know-how to Calama, Ahmedabad in 1960s.These two brands started manufacturing these submersible borewell pumps in India from then on. Following this development, many Indian companies had adopted their design and manufacturing technologies and started manufacturing them. At present the major manufacturers in India are M/s Aquasub Engineering who makes "Texmo" brand submersible pumps, CRI, Taro, Deccan, Mahendra, Suguna, et.al. in Coimbatore, KSB in Pune, Varuna, Pluga, Waterman, Lubi in Ahmedabad, Falcon in Rajkot, Sakthi in

3 3 Madhya Pradesh, Oswal in Haryana, WPIL in Kolkatta, Crompton Greaves in Mumbai et.al. The submersible pumpsets market has grown more than the surface monoblock centrifugal pumpsets. The ground water level throughout India is depleting every year. So, more tubewells and borewells are drilled in large numbers. Now, the lift irrigation for agriculture mainly depends on borewells only. Out of estimated 60 million wells in India, the borewell population is nearly 30 million as per Ministry of Agriculture, India survey. Among all the countries in the world, India was the first country to formulate standards on submersible pumpsets and to specify minimum level of pump efficiencies for various duty points, that is, for various heads and discharge rates. An Indian standardis 8034:2002 (Submersible Pumpsets - Specification (Second Revision) November 2002) was first published in 1976 by the Pumps Sectional Committee of Mechanical Engineering Division of Bureau of Indian Standards (BIS) formerly known as Indian Standards Institution(ISI). In 1994, a standard for submersible borewell motors was formulated by the Electro Technical Department of BIS as IS 9283 (Specification of Submersible motors). following changes. In the year 1989 the standard IS8034 was revised with the 1. Nomenclature for radial flow and mixed flow pumps 2. A graph for overall minimum efficiency for submersible pumpsetswith2-pole motor was added so as to promote energy conservation.

4 4 In the second revision in 2002,alarge number of data relating to submersible pump efficiencies were collected and after analysing the data, minimum pump efficiency has been increased by five percent over the existing pump efficiency values. At present the BIS is once again considering for upward revision of efficiency values on the standard to promote further energy conservation. In USA, Hydraulic Institute (HI) had released charts of "Optimum generally attainable efficiency" in 1994 for different types of pumps. One of them is the Vertical Turbine Bowl Assembly type pump. Apart from this, the HI had also issued two charts, one for "Specific Speed - Efficiency Correction" and another for "Deviation from Generally Attainable Efficiency". The deviation from generally attainable efficiency for a specific speed occurs due to various factors like Casting Surface Quality, Machining Accuracy, etc. Recently in 2012, Hydraulic Institute, USA and Euro Pump, the apex body of associations of pump manufacturers in countries of European Union have initiated a new guideline for energy conservation in pumps and the MEI (Minimum Efficiency Index) concept was introduced. They have released thumb nail efficiency graphs with MEI > 0.1, 0.4 and 0.7 with time limits up to 2013, 2015 and from 2017 onwards respectively.

5 5 1.3 MIXED FLOW SUBMERSIBLE BOREWELL PUMPS The mixed flow submersible pumps are used to pump water from higher depths of the ground. These pumps are erected in the tubewells dug in the alluvial soil mainly in the delta regions of the rivers. The number of pumps utilised for this purpose is increasing in the last two decades all over the world andindia. More and more borewells are drilled for tapping the ground water sources. The sizes of borewells range from diameters 100mm, 150mm, 200mm, 250mm and upto 350mm. 100mm and 150mm borewell sizes are widely used. The present study is about the pumpused in the 150mm diameter borewells Construction and working of Submersible Pumpset These pumpsets are used in borewells and tubewells for pumping water from deeper depths of earth. Since river lift irrigation and shallow well irrigation are not feasible in all parts of India, these pumpsets are used as the back bone of irrigation in the field. With these pumpsets, the agricultural production in India is touching higher levels in the last two decades. The submersible pumpset consists of the following: 1. Pump Assembly and 2. Motor Assembly Submersible Pump The Multistage centrifugal pumps are submersible type and are coupled directly with wet winding submersible induction motors. The submersible pump of mixed flow type is shown in Figure 1.2. The inlet

6 6 bracket (1) is used to guide the water entry into the first stage mixed flow impeller(2). The rotating blade system in the impeller imparts energy to the water and water comes out with high velocity in a conical spiral pattern. The diffuser (3) blade passage collects the water, diffuses its velocity and directs the water to the next stage impeller. The velocity of the water at the second stage is kept same as that of the first stage, but the pressure energy is higher which is gained at the first impeller. This process repeats in all the subsequent stages and the energy is added in all the stages by the work done at the impeller passages. The discharge casing (4) is at the end of the stages. It collects the water and directs it to the column pipe (5) which is transferring the water to the ground level. Also column pipe is supporting the entire pumpset i.e pump coupled with the motor(6) and the axial down thrust caused by the pump impellers during running Submersible Motor It consists of a stator and rotor sub-assemblies. The silicon steel stampings (7) are used in the stator and rotor. The PVC or PP covered copper wires are used in the stator winding (8). The shaft (9) is made up of magnetic stainless steel grade AISI 410, 431. A thrust bearing (10) is used in the bottom of the motor to take care of the down thrust produced in the pump assembly while running. Two journal bearings (11) are used to align the shaft. The thrust bearing is made up of mechanical carbon disk vs. stainless steel pad combination which results in lowest friction. The journal bearings are made of bronze or mechanical carbon for better support.

7 7 Column Pipe P U M P M O T O R Inlet bracket 2.Impeller 3.Diffuser 4.Discharge casing 5.Column pipe 6.Motor 7.Stampings 8.Windings 9.Shaft 10.Thrust bearing 11.Journal bearing Figure 1.2 Submersible Pumpset

8 Impeller This is the main component of pump where the energy is imparted to the fluid by the vane system. The power is received from the pump shaft which is assembled with number of impellers at regular intervals.the torque is transmitted to the central hub portion of the impeller through a key and key way arrangement. There are two types of impellers namely, closed impeller and semi open impeller used in these multistage vertical pump system. In the present case, the impeller is of closed type as shown in Figure A The two sides of the vane system are covered by front shroud or shroud portion and back shroud or hub portion. So the name "closed impeller" is used in vogue. The front shroud portion is having suction boss or clearance seal portion to effectively seal the high pressure side of impeller outlet and the low pressure side of impeller inlet or suction area. The blade system for this specific speed, N S is of mixed flow type where the fluid outlet is slanted to impeller axis with an obtuse angle, more than 90 0 of a typical radial flow outlet. Since the Outlet to Inlet diameter ratio is less than 1.5 times, the double curvature blade surface is required to increase the vane area and impart sufficient blade loading. The manufacturing is complex in comparison with radial flow impeller where the blades are cast 90 to the shroud and hub walls which is easy for manufacturing with single core. For the mixed flow twisted wall blades, special or loose core system is required Diffuser This is the stationary part which collects the water from the rotating impeller outlet passages. It collects and diffuses the high velocity water along its passages. The kinetic energy of the water is converted into pressure energy in the diffuser. The water velocity is reduced to suction eye velocity level at diffuser vane outlet. The multistage mixedflow diffuser

9 9 passage is made into a zig-zag shape in the meridional view and the water is redirected to the next stage impeller eye. Due to this typical shape, the diffuser looks like a bowl as shown in Figure 5.1. The diffuser vanes are arranged symmetrically around the impeller outlet. So, there is no resultant radial force acting on the impeller assembly. A bronze or rubber wear ring is provided in all the diffusers to reduce the leakage of water from high pressure impeller outlet side to low pressure suction inlet side. The purpose of the wear ring is to maintain optimum clearance gap to typically 0.125mm per side to reduce the backflow leakage for maintaining a higher volumetric efficiency. Also, when it comes for service purpose after wear and tear damage due to operation in the field, the wear ring can be easily replaced with a new one quickly and with lesser cost. Otherwise, the diffuser itself has to be changed to maintain the close clearance gap. The diffuser has twisted blade shapes which are difficult to cast. The complex passages are to be cast exactly as per the design model surface file and critical core manufacturing techniques are employed to cast the diffuser. Smooth surface finish is essential in all the diffuser passages. Coating of the core surface results in smooth internal cast surface of the diffuser. Bronze or rubber bearing bush is fitted in each diffuser to support the shaft and impeller assembly. The bearing bush has straight or spiral grooves for better lubrication during running.