energy audit_pumps jherrera
TRANSCRIPT
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Energy Audit Methodology
JOSEPH L. HERRERA
Fuels and Energy DivisionITDI-DOST
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Safety margins were added to the original calculations. Several peopleare involved in the fan/ pump buying decision and each of them is afraidof recommending a fan/ pump that proves to be too small for the job.
It w as anticipated that a larger fan/ pump w ould be needed in the
future, so it was purchased now to save buying the larger fan/ pumplater on.
It w as the only fan/ pump the dealer had in stock and you needed onebadly. He might have offered you a "special deal" to take the larger size.
You took the fan/ pump out of your spare parts inventory. Capitalequipment money is scarce so the larger fan/ pump appeared to be youronly choice.
You purchased the same size fan/ pump as the one that came out of theapplication and that one was over sized also.
Oversized Pumps & Fans?
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Just think
19% of industrial motor electricity use is for pumpsTo lift 1 cubic meter (1,000 liters) of water to a height of 1meter in 1 second requires 9.81 kW of energy
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Energy Balance for a Typical Pumping System
ELECTRICITY
100%
12% LOSS
2% LOSS
24% LOSS
9% LOSS
11% LOSS
MOTOR
COUPLING
PUMPS
VALVES
PIPES
WORK DONE ON WATER42%
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Pump System Components
Pumps
Prime Movers
Piping
Valves End-Use Equipment (Heat Exchanger, Tanks and Hydraulic
Equipment)
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Centrifugal Pumps
These are dynamic devices that impart kinetic energy or
energy of motion to a liquid to the spinning motion of animpeller.
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Types of Centrifugal Pumps
Radial Flow Axial Flow
Mixed Flow
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Axial FlowRadial Flow
Mixed Flow
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Pertinent Data: Pumps/ Motors
Nameplate/settings:
Brand, model and ratedparameters of installedpumps
Pump settings
Static water levels
Motor data & efficiencies
Pipeline material and
lengths
Measurements
Flow rates (m3/hr) Discharge pressures (psi or
bars)
Flow velocities (m/s)
Pipe sizes
Shaft speed (rpm)
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Major Measuring Equipment Used in EnergyAudits
Flow meters measure flowrates (in li/s or m3/hr) aswell as velocities of flow
Power analyzers measureV, A, kW, KVA, KVAR, PF,frequency
Pressure gages measure
pressure in psi or bars Tachometers/Stroboscope
measure motor shaft speedsin rpm
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Pump Operating Point
Determined from the measured flow and the calculated
head Ideally, the operating point is the intersection of the
system curve and the pump curve at BEP
Significant deviations of the actual OP from the requiredOP indicate pump performance problems
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System and Pump Curves
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Formulas/Conversions
Pressure to Head
Psi = (head (ft) x s.g.)/2.31 Bar = (head (m) x s.g.)/10.2
Velocity Head = v2/2g
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Power Requirement & Efficiency
Hydraulic Power (Ph):
Q (m 3/ s) x Total head, hd hs (m) x (kg/m 3) x g (m/ s2)Ph = ---------------------------------------------------------------------
1000
Pump Shaft Power = Hydraulic Power/Pump Efficiency
Electrical Power Input = Pump Shaft Power/Motor Efficiency
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Location of Test Points (Pressure)
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Pump Affinity Laws
Flow:Flow:Q1 / Q2 = N1 / N2
Example:100 / Q2 = 1750/3500Q2 = 200 m3/hr
Head:Head:H1/ H2 = (N12) / (N22)
Example:100 /H2 = 1750 2/ 3500 2
H2 = 400 m
Kilowatts (kW):Kilowatts (kW):kW1 / kW2 = (N13) / (N23)
Example:
5/kW2 = 17503
/ 35003
kW2 = 40
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Particulars Design Operating
Flow, m3/h 800 576
Head, m WC 55 24 (after control valve)
Power, kW 160 124
Speed, rpm 1485 1485
SampleProblem
In a large paper plant, the following are the designed andmeasured parameters for a clear water pump.The pump deliveryhas been throttled to about 30% (closed) manually to get therequired flow rate. Normal required water flow rate is 500m3/h to700m3/h. Calculate the present operating efficiency and in youropinion what should be the optimum solution to get the requiredflow rate variation? And what would be the savings if the pump isdelivering the flow rate of 550m3/h. (Consider efficiency of motoras 93% and pump efficiency as 60%).
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Computations
Q x H x g 576 x 24 x 9.81
Present pump output = -------------------- = -------------------- = 67.51 kW3600 x p x m 3600 x 0.558
Pump input power = 124 kW
pump operating efficiency = (67.51/ 124) x 100 = 54.44%
The pump operating at a poor efficiency of 54.44% due to throttling of the flow.
Since the pump discharge requirement varies from 500m3/h to 700m3/h, the idealoption would be to operate with a VSD. According to affinity laws:
Q1/Q2 = N1/N2; H1/H2 = (N1/N2)2; P1/P2 = (N1/N2)3
For a flow rate 550m3/h, the reduced speed of pump would be:
= 550/800 = N1/1485; N1 = 1021 rpmWith the reduction in speed the reduction in terms of head would be:
= (1021/1485)2 x 5.5 = 2.6kg/cm2
The reduction in power would be:
= (1021/1485)3 x 124 = 40.3 kWthe reduction in power = 124 40.3 = 83.7kW
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Energy Efficiency Options
Give efficiency of the pump due consideration while
selecting a pump. Select pumps to match head flow requirements.
Select a motor to match the load with highest efficiency.
Optimize the piping design. Monitor all important system parameters like: motor kW,
pump head, flow temperature.
Use pumps in series and parallel so that mismatch insystem design or variations in operating conditions can behandled properly.
Use variable speed drives for variations of flow due toprocess requirement.
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Energy Efficiency Options
In general savings through speed control would be substantial
in the following cases: Pumps supplying a system with large change in flow.
Pumps which work with a bypass. These pumps are
normally operated to deliver the maximum discharge andhence consume maximum power.
Parallel pumps which discharge into a common pipe
system. In such cases, each pump is generally switchedon or off depending on the flow required. Here, it issufficient to regulate the speed of only one of these
pumps while the other pumps are operated an on/offmode.
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Energy Efficiency Options
If the head flow is higher than needed by 5 to 15%, (i)
The existing impeller should be trimmed to a smallerdiameter, (ii) or a new impeller with a smaller diameter isto be put. Replacing the impeller by a smaller one of the
same series: Manufacturers usually supply more than oneimpeller for the same casing, thus allowing a change inhead or flow. Depending on the specific job, this can alloweither an increase or a decrease in flow or head, typically
by 10 to 25%.
In multistage pumps, add or remove stages to the existingpump, allowing an increase / decrease in delivered head
of flow, if required.
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Analysis has revealed that except for the small scale sector,pump efficiencies have increased by 5-10% in recent years.
SOME PROJECTIONS:
Savings of 5 - 10% are also generally possible by derating orreplacing oversized pumps.
Much larger saving of 15 - 20% are available on average byminimizing piping-friction loss with typical paybacks for system
retrofit of less than three years.
High efficiency pump often cost the same as less efficient
pumps, and if there is a cost premium, it is modest (of theorder of 5 - 10%).
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PUMP OPTIMIZATION PROJECTIONS: Consider buying pumps based on efficiency and notpurchase price
Portion of a pumps total cost over its life 3% for purchase cost
74% for energy cost
A more efficient pump also has lower maintenance anddowntime cost
TYPICAL ENERGY SAVINGS:
Proper matching of pump size to load 10 to 30%
Variable Speed Drives 5 to 50%
Knowing the system needs not pumping more flow undermore pressure than needed 5 to 20%