Pump Operating System It is important to note that a pump station and pumping system have many important design considerations with a view to focus on aspects that directly contribute to its energy efficiency and life cycle costing. While on this, station loss in a pump system is considered to be a very important key factor in computing pump parameters for selecting suitable pump(s) for the system. It is experienced that in many cases, Engineers as an act of conservativeness consider safety factors while designing pumping Station resulting adverse impact to the operating system. 1. Safety Factor: Unnecessary safety factor drastically change the pattern of system curve affects selection of pumps which are to operated away from BEP resulting loss of energy in the system. This aspect triggers dispute amongst the buyer and seller where buyer wrongly interpret pump parameters to the seller and install over or undersized pumps in the system. The Hazen-Williams equation is assumed to be relatively accurate for piping systems with Reynolds Numbers above 105 (turbulent flow). 1 ft (foot) = 0.3048 m 1 in (inch) = 25.4 mm 1 gal (US)/min =6.30888x10-5 m3/s = 0.227 m3/h = 0.0631 dm3(liter)/s = 2.228x10-3 ft3/s = 0.1337 ft3/min = 0.8327 Imperial gal (UK)/min 2. Selection of Pump: It must be noted that the pattern of pump power curve has rising trend with the flow capacity in case of Radial Type Centrifugal pumps with low specific speed range. Therefore, wrong selection of oversized pumps will not only attract higher power but will limit the range of operation that not fulfill the requirement of operation covering minimum and maximum water level of the system where may reach the cut off point of operating condition because of NPSH factor.
Transcript
Pump Operating SystemIt is important to note that a pump station and pumping system have many important design considerations with a view to focus on aspects that directly contribute to its energy efficiency and life cycle costing. While on this, station loss in a pump system is considered to be a very important key factor in computing pump parameters for selecting suitable pump(s) for the system.
It is experienced that in many cases, Engineers as an act of conservativeness consider safety factors while designing pumping Station resulting adverse impact to the operating system.
1. Safety Factor: Unnecessary safety factor drastically change the pattern of system curve affects selection of pumps which are to operated away from BEP resulting loss of energy in the system. This aspect triggers dispute amongst the buyer and seller where buyer wrongly interpret pump parameters to the seller and install over or undersized pumps in the system.
The Hazen-Williams equation is assumed to be relatively accurate for piping systems with Reynolds Numbers above 105 (turbulent flow).1 ft (foot) = 0.3048 m1 in (inch) = 25.4 mm1 gal (US)/min =6.30888x10-5 m3/s = 0.227 m3/h = 0.0631 dm3(liter)/s = 2.228x10-3 ft3/s = 0.1337 ft3/min = 0.8327 Imperial gal (UK)/min
2. Selection of Pump: It must be noted that the pattern of pump power curve has rising trend with the flow capacity in case of Radial Type Centrifugal pumps with low specific speed range. Therefore, wrong selection of oversized pumps will not only attract higher power but will limit the range of operation that not fulfill the requirement of operation covering minimum and maximum water level of the system where may reach the cut off point of operating condition because of NPSH factor.
3. Site Condition: Site demography is of key importance to draw up actual piping layout for the system where in many cases it has been noticed that there are significant difference between the design layout and physical installation that adversely impact pumping system operating condition. Let us realize that pump sizing and dimensions are the key factors in designing the pump house layout while its of importance for Design Team consisting of Civil, Electro-Mechanical Engineers to consult amongst themselves in arriving at the correct design parameters for attaining desired plant efficiency.
4. Type of Pump Station: Pumping stations are designed according to the application and site condition such as pumping water from a Water Source such as River, Canal, Lake, Reservoir etc. Where Horizontal Centrifugal or Vertical Turbine or Mixed Flow Pump stations are designed with Intake Forebay or Channel for water intake into the pumping station taking into account various design conditions such as intake water flow velocity, spacing of pumps inside or pump house considering multiple pumps for parallel operation in order to maintain flexibility according to the ongoing demand and provision for future demand as well.Channel mounted Inclined pumps are also installed at the river bed in some installation those are generally driven by Diesel or Electric drive through angular gear drive and necessary through bearing keeping axial thrust component in mind.Horizontal Centrifugal Pumps of Radial type of axially split types are also installed in the said application with suction pipes drawing water from the water source where NPSH condition is of prime importance in order to ensure that pump does not suffer due to cavitation at the minimum water level conditions. In some extreme cases Vacuum pump sets are put in thesystem prior to starting of the main intake pumps certainly at an extra cost to the project because of certain site constraints. The river flow varies during the year but the hydro installation is designed to take a constant flow. If the channel overflows there will be serious damage to the surroundings. Weir is put in the system at the upstream of the forebay in order to ensure correct flow to the pumping channel regardless of river is in low or in high flow. The intake structure is designed to regulate the flow to within reasonable limits when the river is in high flow. Further regulation of the channel flow is provided by the spillways. A Sump Model Study at the design stage is of
significant importance prior to finalization of design in order to ensure efficient operating system.De-silting is a regular process which at times are neglected affecting pumping system from smooth pumping operation and damage to pumps due to unforeseen variation water flow to the system with sand particle those are prone to cause abrasion damage to the pumps.According to the experience it is noticed that pumps attain longer life with material combination such as 2 TO 2.5% Nickel Cast Iron Casing with SS to CA15 Impeller, SS410/416 Shaft with SS304 Sleeves where CA15 Material has an unique quality to withstand both corrosive and application.
5. Variable Frequency Drive: VFD has its significance in the pumping system in order to ensure Head-Flow Characteristic through speed variation according to the demand of the system without disturbing or wasting energy due to throttling method in varying the system head characteristics.
6. Surge Analysis: Surges in pipelines carrying liquids are usually caused by opening, closing or regulating valves or pumps starting and stopping. These surges, also called hydraulic transients may range in importance from a slight pressure or velocity change to sufficiently high pressure or vacuum to rupture the piping system, to damage pumping equipment and cause extensive shutdown time. Water hammer, a result of hydraulic transients, will occur when the total surge pressure exceeds approximately twice the value of the static pressure in the system when the fluid is at rest. Surge protection analysis will be performed on critical sections of the piping system to verify design and surge control equipment selection. If excess transient pressures are predicted by the analysis, design and mechanical equipment application will be modified. Hydraulic surge control is a specialized field. If a detailed surge protection study is required, it should be provided by engineers or consulting engineering firms specialized in this field. Detailed pipeline surge analysis by an expert should be considered.
7. Starting Characteristics of Pumps: In normal cases pumps are recommended to start from crack open condition expect for high specific speed pumps where break away torque of drive motors have 20% of FLT in order for smooth starting of pumps without stalling. In the event of extreme conditions of discharge valve failure of pump in parallel operation with corresponding Non Reverse Ratchet failure in case of Vertical Pumps, pump is required to start from reverse flow condition where the drive motors are required to start from such extreme condition. In such cases Double Cage Squirrel type or slip ring motors are recommended with higher starting torque characteristics that can attain to the full load speed within the desired time without stalling and overheating.
8. Pump Motor Control System: When it comes to build an energy efficient pumping system, the choice of the appropriate motor control system and Instrumentation Panel is crucial in order to measure and control Hydraulic, Thermal and Electrical Parameters for smooth and uninterrupted operation of the system. However, it is also recommended according to experience that control system is designed with a pragmatic view so that the system is not prone to unnecessary tripping due insignificant conditions that affects the continued running of the pumping system.
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