ICEOC50_SML Juned IEEE format

8/7/2019 ICEOC50_SML Juned IEEE format

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Energy Savings in Pumping System using

Thermodynamic MethodJuned Ansari

NBI-Water, Mechanical Engineer, Energy Auditor

Secure Meters Limited, Flat 11, Second Floor, Nazim Estate, City Chowk, Aurangabad, India-431001

[email protected]

[email protected]

AbstractToday, energy is one of the necessities of life and wecannot think of life without it. However, we are not able to meet

the rising demand and the gap between demand & supply is

widening. With an increasing population, changing lifestyles and

need for growth, the requirement of energy is at all time high.

This demands a proper check on the energy consuming machines

for better energy efficiency.

Studies show that the power generation efficiency is only between

38-45% [2]. This figure is even lower when you account for

transmission and distribution efficiencies. The overall losses from

the point of generation to the point of use amount to 50%. In

simple terms, for 2 units of energy production, you need to burn5 units of fuel; and only a single unit is delivered at the point of

use.

India is the sixth largest emitter of green house gases (GHGs),

contributing about 1,228 MMTCO2 i.e. 2% of global emissions,

equivalent to 1.3 tonnes per capita emissions. The largest share,

61%, is contributed by the energy sector [1]. Pumps are found in

abundance in every industry and they run with varying degree of

efficiency. It is important to keep a record of the efficiency of the

pumps to help save energy and the resulting carbon emissions.

This paper discusses the thermodynamic way of accessing the

machine performance. Unlike conventional method, it does not

need a flow meter for efficiency evaluation and hence is more

accurate.

KeywordsEnergy Efficiency, Thermodynamic Method, PumpTesting, Efficiency Evaluation, Secure Meters Limited

I. OVERVIEWAlmost 70% of the worlds electricity is consumed by the

industry horses more commonly known as Motors. Out of this,

70% is used to drive rotodynamic machines, which are

primarily pumps, blower, fans and compressors. These

machines operate with varying degrees of efficiency between

20 and 90%. The greater the inefficiency of the machine, the

greater is the energy wasted. It therefore, becomes important

to test, evaluate and monitor the energy consumption of these

machines and their system in a plant.

To fulfil this need, two methods have been commonly used in

industries. The first and the most common is the conventional

method (which measures the output and input energy). The

second one; a more practical approach, is the thermodynamicmethod (which accesses the losses). This paper talks about the

performance monitoring of pumps using thermodynamic

method. It is important to note that the same method can be

applied effectively for monitoring of blowers, compressors &

hydro turbines with ease.

II. INTRODUCTIONCentrifugal pumps are found operating at varying degrees

of efficiency, leading to performance shortfall. Over the life ofthe pump, energy consumption is the biggest contributor (90-

95%) to the total Life Cycle Cost of the machine. Even if a

pump is operating at 70% efficiency, 30% of the energy fed to

it is wasted in the form of heat, noise & vibration. For a

100kW machine, 30 kW is simply unavailable for any useful

work. On many occasions, over the life cycle of the pump, the

value of the energy loss is more than the cost of the machineitself.

Obviously, only a certain part of the wasted energy (as no

machine can be 100% efficient) can be saved by testing,

monitoring and timely corrective action on the pumps. Pump

performance testing and monitoring reveals the asset

condition and helps in averting catastrophic failures. A

number of pumps when simultaneously monitored (Multi

Pump Monitoring), will give an insight as to how the station is

being operated and reveals any operating malpractices.

Besides reducing energy consumption and implementing

energy efficiency, a production plant is equally concerned

about minimizing the downtime, to minimise the direct impact

on the total plant specific energy consumption.

III.THERMODYNAMIC METHODUnlike conventional method involving flow measurement

for efficiency evaluation, the thermodynamic method

measures the inefficiency of the machine by accessing the

losses across the machine, making the readings more reliable.

This makes the method ideal and suitable for even smaller

machines. The method is based on the first law of

thermodynamics and requires differential pressure &

temperature measurement across the machine to evaluate the

efficiency. When this is combined with power measurement,

flow can be accurately back calculated. The basic equations

are as shown below:

Where,

+

=

Hg

TCpp

1

1Hg

PQ pmi

=


2/3

Cp= Specific Heat of the fluid (KJ/Kg-K)

T= Differential temperature across the pump in mK (milli

Kelvin)

H= Pump Head in meters (m)

Pi= Input Power to the Motor in kW

p= Pump efficiency (%)

Q= Pump Flow Rate in m3/s

This method has been widely used on more than 12,000

pumps across the world and the results are overwhelming, asdiscussed in the next section.

IV.CASE STUDYCase studies are the success stories for any organization. Inthis section, we will discuss a few case studies as testimonials

for this method of testing pumps and blowers. There are

various reasons associated with underperformance of a

machine. These directly affect the operating efficiency of the

machine and the system as a whole. Some of these reasons are

listed as under:

a. Wear and tear of the pump due to ageingb. Wear and tear of the pump due to improper

operational practices

c. A bigger pump being run under throttled condition toachieve the desired flowd. Poor suction conditionse. Blockages, leakages, air entrapmentf. Improper pump selectiong. Cavitation

A. Case Study 1This case study deals with a pump in an Indian chemical

industry. This reveals how operational malpractices lead the

pump to operate off BEP (Best Efficiency Point). Besides

poor efficiency, high vibrations were observed in these pumps.

There were four such pumps arranged in parallel. The pumps

were taking suction from the cooling tower sump. The water

returned to the cooling tower top after going through the process. The table below shows the design and measured

parameters for this particular pump.

It was observed that the pump is running exceptionally to the

right of the duty point and was prone to high flow cavitation.

Moreover, it was observed that the flow was not reaching the

cooling tower top when the pump was running in solo due to

the very reason that the pump was not generating enough head

to cope up with the system resistance. Moreover, at the

operating point, NPSH available (7.5 m) was less than the

NPSH required (8.2 m) which caused the pump to cavitate.

This was also the reason for high vibration. These brand new

pumps; if run under these conditions for long, would

definitely have caused damaged to the impeller.

The plant manager was instructed to check the flange jointsand the suction pipe line for any air ingress; as it causes the

pumps capacity to deteriorate. It was also recommended to run

more pumps in parallel to achieve the desired flow through the

system. This improved the individual pump efficiency to 82%.

Design

ParametersValues

Measured

ParametersValues

Flow (m3/h) 1,035 Flow (m3/h) 1,378

Head (m) 42 Head (m) 20.5

BEP (%) 87 Efficiency (%) 51.3

Fluid Water Fluid Water

Rated Power (kW) 160 Input Power (kW) 156.2

Rated Speed (RPM) 1487 Speed (RPM) 1487

NPSH available (m) 7.5 NPSH required (m) 8.2

Table. 1 Design and Measured Parameters

B. Case Study 2This case study deals with a pump in an Indian chemical

company. It shows how design stage miscalculations can spell

big troubles when plant begins actual operation. The pump

that was tested was not giving the desired flow through the

system. The table below shows the design and measured

parameters.

The significant difference between the two clearly indicates a

problem. This pump was taking suction from an open sump

with flooded suction. The fluid was then being sent to the

cooling tower top (approx 16m high) through eight equi-

spaced nozzles in the cooling tower. The cooled liquid after

passing through electrolysis cells returns to the same sump. Itwas observed that the pressure of the fluid just before the

nozzle was only 0.65 bar instead of the required pressure of

1.65 bar. The pump was selected without considering thepresence of nozzles; hence it failed to provide the desired flow.

It was recommended to install a bigger impeller in the existing

pump to achieve the desired performance. This measure also

reduced the specific power consumption of the pump as

shown in figure below. The pump has been running efficiently

for last 09 months without any problems.

Design

ParametersValues

Measured

ParametersValues

Flow (m3/h) 569 Flow (m3/h) 269

Head (m) 25 Head (m) 27.8

BEP (%) 83 Efficiency (%) 44

Fluid SG1.3 Fluid SG1.3

Rated Power (kW) 90 Input Power (kW) 61

Rated Speed (RPM) 1475 Speed (RPM) 1475

Pressure at Nozzle 1.65bar Pressure at Nozzle 0.65bar

Table. 2 Design and Measured Parameters

Pre

Replacement

Performance

Post

Replacement

Performance

Relative

%age

Change

Flow Rate (l/s) 74.6 151.2 102.7

Pump Head (m) 27.8 34.0 22.3

Power (kW) 60.6 98.6 62.7

Efficiency (%) 43.9 67.4 53.9

Pumping Cost(kWh/Ml)

225.4 181.2 -19.6

Saving for SameFlow (Rs.)

- 458,571 -

Table. 3 Comparison Table


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C. Case Study 3At a thermal power plant in India, a vertical turbine type

circulating water pump was tested. There were 13 such pumps

in the system, each fitted with a fixed speed motor running at

490 RPM. The design duty conditions were 15,000 m3/h at

32m head.

Upon testing, it was found that the pump tested was delivering

16,661m3/h at 24.4m head & 74% efficiency consuming 1,560

kW, while 8 other pumps were also running in parallel. This

operating point was to the right of the design duty point and isan area prone to high flow cavitation. The recommendation

was to cut in one more pump; it was no surprise that the pump

was now delivering 16,347m3 /h at 26.1m head & 79.3%

efficiency consuming 1,533 kW, with 9 other pumps running in

parallel.

Therefore, the recommendation was to run more pumps in

parallel to shift the operating point closer to the duty point.

This action, besides saving energy, would also ensure asset

integrity and increase the working life of the pumps.

V. CONCLUSIONA thorough pump & system testing and analysis can reveal

the operating malpractices and asset condition. Many

problems are not just a result of machine malfunction butcould be because of the system as a whole. Efficiency

improvements and energy savings can be achieved by simple

rescheduling prior to any remedial work. The thermodynamic

method for pump testing delivers accuracy better than 1%

which has been verified by the Fluid Control Research

Institute (FCRI), India. Many problems get rectified by merely

a rational approach.

Efficiency improvement is directly related with the reduction

in the energy used and resulting carbon footprint. Though per

capita carbon emissions are quite low for India, but with

increasing speed of development, this is bound to get worse.We recommend getting your pumps, blowers and compressors

tested to attain energy efficiency in real sense.

We do not want to be blamed by the future generations for notallowing them the use of these scarce resources? Let us

conserve energy, water & environment!!!

ACKNOWLEDGEMENT

I wish to acknowledge the ICEOC organising committee

for giving me a chance to present this paper in this esteemed

conference.

REFERENCES

[1] G Subramanyam: CDM & Energy Efficiency Issues-Opportunities inIndia, Electrical India, May10 issue, Chary Publications Pvt Ltd.[2] Bureau of Energy Efficiency: Energy Efficiency in Electrical Utilities-Book 3 for Energy Auditors.

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ICEOC50_SML Juned IEEE format