- Situation A Pumping Station Supplies An Elevated Reservoir From A Lake The Water Intake And The Conveyance Pipe Are Bui 1 (143.43 KiB) Viewed 33 times
- Situation A Pumping Station Supplies An Elevated Reservoir From A Lake The Water Intake And The Conveyance Pipe Are Bui 2 (189.8 KiB) Viewed 33 times
- Situation A Pumping Station Supplies An Elevated Reservoir From A Lake The Water Intake And The Conveyance Pipe Are Bui 3 (184.97 KiB) Viewed 33 times
Situation A pumping station supplies an elevated reservoir from a lake. The water intake and the conveyance pipe are built and their characteristics are known. The water intake is 6 m below the minimum level of the lake which is at an altitude of 25 m. The conveyance pipe is 100m long and has a diameter of 400mm. The reservoir in height is at a constant level and the surface of the water is maintained there at an altitude of 50 m. Any excess water is discharged to the lake via an auxiliary pipe. The pumping station is equipped with several pumps (including one backup). You will have to choose from the pumps of the models and rotational speeds shown in figure 1. Each pump has its suction pipe which draws water from the wet well and transports it to the pump by a 60 m pipe equipped with a 90° elbow and a gate valve. At the outlet of the pump, a short individual delivery pipe 3 m long equipped with a tap valve and a flapper transfers the water into the main delivery pipe 140 m long which has a bend at 90°. The coefficients of friction of all pipes (adduction, suction, discharge) is equal to 0.02. The system is designed to pump a constant flow rate of 300 L/s continuously (365 days per year). Mandate You must size the pipes (choose their diameter), determine the number, the model(s) and their speed(s) of rotation (which determines the motor for each pump) in order to have a solution feasible that minimizes the total cost (construction, replacement and operation) discounted. Tables 1 and 2 respectively give the costs of the pipes and those of the pumps and electric motors that will operate them. These are costs in the current year (year 0). The economic analysis is in constant $ and the discount rate, i, is 0.05. The service life of the pumps and motors is set at 15 years and their residual value at 15 years is assumed to be nil. The service life of the pipes is assumed to be 30 years, as is the period of the economic analysis of this
pumping station. Wet well construction costs will be estimated in the preliminary design by a unit cost of $200/m3. This cost includes concrete, reinforcement, formwork, labor and equipment. You will assume the bottom slab of the wet well to be 35 cm thick, the top of the wet well to be 24 cm, and the walls of the wet well to be 24 cm. It would be fair to minimize the number of pumps to be installed in the pumping station. The energy cost is $0.04/kWh in constant dollars. Table 1 Cost of pipes and equipment ($) Equipment Diameter (cm)/ cost 20 120 180 210 30 35 40 45 50 240 270 300 35 45 55 65 75 15 60 120 150 180 210 240 80 130 155 185 220 250 Driving (10m) 90° elbow faucet valve valve Table 2 Cost of pumps and motors ($) Pumps Cost ($) I II III IV 1500 1800 2000 2300 Engine (HP) 60 95 180 250 Costs ($) 450 600 750 850 You also need to size the wet well. Assume that each pump is installed in a self-contained well. Decide on the altitude at which to place the pump ensuring that there will be no danger of cavitation in the pump. Whichever pump speed you choose, use the NPSH curverequired corresponding to the speed of 4350 revolutions per minute (rpm). Also determine the elevation of the wet well floor at the entrance and below the suction bell and give the clearances between the suction line, the floor and the walls of the wet well. Report You must submit a technical report which must recall the mandate, explain the approach followed, present the characteristics of the networks and justify your conclusions and recommendations. Do not hesitate to provide tables (Excel or other) summarizing the information produced. This technical report should be short. It should include a dimensioned drawing of the pumping station and the components of the hydraulic system for which you find it useful to provide a drawing. In the appendix, you will submit your calculation note which can be handwritten. It should be kept short, while providing the information needed to assess the accuracy of the results. The calculation note must indicate the purpose of the calculation and provide the working hypotheses;
Economic Analysis Definitions and Equations P: present value (at year 0) Fr: future value at year j HASO-k: annuity (annual constant cost) from year 0 to year k I: annual discount rate (in decimals) Pump Head (m) Pump Head (m) 70 60 50 40 30 20 10 0 70 60 50 20 10 0 10 NPSH required @ 4350 rpm 20 4350 rpm 20 3250 rpm 43% 3250 rpm Figure 1 Characteristic curves, efficiency and NPSH of candidate pumps Pump, I 40 43% 54% 30 Flow (L/sec) 40% 3550 rpm 3250 rpm NPSH required @ 4350 rpm 3850 rpm 40 54% 4350 rpm 4050 rpm P= 3250 rpm L 60 Flow (L/sec) Pump, II 3550 rpm 50 4050 rpm 3850 rpm 40% /4050 грм 3850 rpm 3550 rpm 80 Fi (1+1)' 4350 rpm 350 rpm 4050 rpm 3850 rpm 3550 rpm 100 420 69 46 23 4 2 0 92 69 46 23 NPSH (m) Horsepower input NPSH (m) ; Horsepower input Pump Head (m) P= Pump Head (m) 70 60 50 40 30 20 10 0 70 60 8 50 40 30 20 10 (1+1 (1+1) KI 0 Pump, III NPSH required @ 4350 rpm 40 60% 3250 rpm 3250 rpm 80 HASO-K 60% 4350 rpm 50 100 60% 62% 120 Flow (L/sec) Pump, IV 55% 3550 rpm 3250 rpm 4350 rpm 4050 rpm 3850 rpm Figure 5.24 Characteristic curves for several pump models NPSH required @ 4350 rpm 4350 rpm 4050 rpm 3850 rpm 3550 rpm 160 62% 200 4350 rpm 4050 rpm 3850 rpm 3550 rpm 4050 rpm 3850 rpm 3250 rpm 3550 rpm I 1 150 200 250 Flow (L/sec) 0 184 138 92 46 10 228 171 114 57 NPSH (m) Horsepower input NPSH (m) Horsepower input