9-eee - ijeeer - hydro power - r krishna kumar
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HYDRO POWER GENERATION FROM DOMESTIC WATER SUPPLY
SYSTEM AND DEVELOPMENT OF DYNAMIC FLOW MODELLING 1R. KRISHNA KUMAR & 2S. IAN DAVID
1Asst.Professor(Sr.Grade), Dept. of EEE, PSG College of Technology,Coimbatore , TamilNadu , India
2Department of EEE, PSG College of Technology,Coimbatore, TamilNadu , India
ABSTRACT
Pico hydro is a term used for hydroelectric power installations that typically produce up to 5 kW
of electricity. It was regarded as an alternative generation source in recent past. Traditionally
hydroelectric power was generated from flowing and run off water in mountain streams and big
reservoirs. Pico hydro power plant is installed where, only low heads are available (less than 15 m) but
the flow rate must be greater to compensate for the lower water pressure. This paper deals with a
comprehensive renewable energy system, where untapped decentralized water potential such as drinking
water tanks which has sustainable supply of water will be utilized to produce electricity. It describes
hydro graph, supply pattern, plumbing method practiced in typical drinking water tower and the turbine
design that would suit Pico hydro power generation from drinking water reservoirs. It also discusses the
effect of pressure in the terminal outlets in the existing systems. The field studies carried out at the
secondary reservoir at Singanallur, Coimbatore and secondary storage tank at Peelamedu, Coimbatore
are presented. Results from the field study emphasize that the proposed system is feasible enough for
electricity generation and indicate the prospect of further improvement and future research.
KEYWORDS : Archimedes Screw Turbine, Domestic Drinking Water, Pico-Hydro Electricity, PM
Generators, Renewable Energy.
INTRODUCTION
The electricity, not only a vital element for community development but has become one of the
basic need for human life. Hence there is an increasing need to generate electricity from all available
resources. Among various other renewable resources hydro electricity is more reliable and robust. Pico
hydro is a term used for hydroelectric power installations that typically produce less than 5 kW of
electricity, usually using run-off water from streams and lakes in rural areas. But water distributed to
residential area from secondary reservoirs also has the potential for generation of electricity.
In this paper newly designed hydro power system suited for domestic drinking water pipeline
based on field data collected at secondary storage reservoirs at, Coimbatore is proposed.
International Journal of Electrical and Electronics Engineering Research (IJEEER) ISSN 2250-155X Vol.2, Issue 3 Sep 2012 94-105 © TJPRC Pvt. Ltd.,
95 Hydro Power Generation from Domestic Water Supply System and Development of Dynamic Flow Modelling
WATER DISTRIBUTION
Drinking water to Coimbatore city residents is supplied from Pillur –Aathikadavu plant. The
water passes through various purification processes. From the purification plant purified water is sent to
primary reservoirs .Water from primary reservoirs is taken through a complex series of pipes for
delivery to homes and businesses. As a result of this there is continuous inflow of water to the reservoirs
throughout the day for the whole year. It is estimated that an average person consumes about 135 liters of
water per day. The cyclic rotation pattern with duration of 8 hours per street is followed for water
distribution. Hence there is a continuous outflow in the common discharge tube from the reservoir.
Fig:1 Water Distribution Methodology
HYDRO ELECTRICITY
Hydro electricity is generation of electricity from moving water sources by harnessing the
potential and kinetic energy using available head and flow. Hydro power plants are usually found in rural
and hilly areas. Also drinking water distributed to residential areas from the secondary reservoirs also
has excess pressure head and drinking water being basic need, there will be continous flow all round the
year.Hence the secondary storage reservoirs can provide potential sites for Pico-hydro power plants.
PROPOSED METHODOLOGY
In this hydro power system the excess pressure from the flow of water will be harnessedr
without disturbing the distribution flow parameters.When the water passes through the turbine(smooth
turbine surface) the velocity of flow nor flo rate is affected,only the Reynolds number Re (a
dimensionless number that gives a measure of the ratio of inertial forces to viscous forces) changes i.e
the flow changes to turbulent flow. This makes it feasible to be placed in the existing drinking water
supply system.
R. Krishna Kumar & S. Ian David 96
Fig:2 Proposed Methodology
POSITION OF TURBINE
The turbine will be placed at the bottom of the common discharge tube before the bifurcation of
the outflow pipe for distribution to various streets. The turbine is placed in an optimum position to
harness the excessive pressure and the available flow rate .The excess water pressure and flow required
according to standards are the major parameters that determine the position of turbines.
Fig:3 Position of Turbine
Turbine
Common Discharge Tube
97 Hydro Power Generation from Domestic Water Supply System and Development of Dynamic Flow Modelling
TURBINE SELECTION
The availability of head is less than 15 meters and flow rate is around (50-300)
L/sThe key design parameters for a turbine are head (H), volume flow, or discharge (Q) and rotational
speed (N).
From these three parameters, a “dimensionless shape number” or “specific speed” can be determined.
This number gives an indication of the geometry of the turbine and it is the starting point for detailed
design.
For this design procedure we use the following equation:
Specific speed (Ns) = (N√P)/ H5/4
Where P is Power in kW, N is in rpm, Q in m3/s and H in m. The two primary classification of water
turbines impulse turbine or reaction turbines .In addition to these two there is a new type of turbine called
Archimedes Screw turbines.
Type of
Turbine
High
Head
Medium
Head Low Head
Impulse
Turbine
Pelton
Turgo
Cross flow
Multi jet
Pelton Turgo
Crossflow
Reaction
Turbine -- Francis
Kaplan
Archimedes
Screw
The Archimedes screw turbine is closer to the reaction turbine in that the weight of falling water
turns the screw to generate power. The water enters the screw at the top and the weight of the water
pushes on the helical flights, allowing the water to fall to the lower level and causing the screw to rotate.
This rotational energy can then be extracted by an electrical generator connected to the main shaft of the
screw.
R. Krishna Kumar & S. Ian David 98
Fig :4 Archimedes Screw
Archimedes Screw type turbines are especially suited to sites with high flows (200 litres/sec to
6000 litres/second) and work economically with head levels from 1 to 10 meters. The smallest screws are
just .75 meter diameter and can pass 250 liters / second, then they increase in 250 mm steps all of the
way up to 5 meters in diameter with a maximum flow rate of around 14.5 m3/s
Archimedean screws typically rotate at around 26 rpm, so the top of the screw connects to a
gearbox to increase the rotational speed to between 750 and 1500 rpm to make it compatible with
standard generators. Even tough they rotate relatively slowly Archimedean screws can splash water
around, though this is reduced significantly by the use of a splash guard
Archimedean screws are normally set at an angle of 22 degrees from horizontal, which is the
optimum for the most cost-effective installations.
Fig:5 Efficiency(Mechanical) Vs % Flow rate
They are technically very simple with significantly lower installed costs than comparable low
head Kaplan turbines.
99 Hydro Power Generation from Domestic Water Supply System and Development of Dynamic Flow Modelling
A very flat efficiency curve which means that even dramatic changes in flow levels or head levels do not
significantly impact the efficiency of the system (and without the mechanically adjustable blades of a
Kaplan turbine).
Ruggedness – Because the design and construction is so simple, because the design is so
tolerant of trash, etc. Archimedes screw type systems are extremely robust and can be expected to last
40 years or more with a minimum of maintenance.
PERMANENT MAGNET GENERATOR
The generators used in major hydro power generating stations employs electromagnetic field
systems. But the generator used here is of permanent magnet type. The generator has two magnetic
components: the rotating magnetic field constructed using permanent magnets; and the stationary
armature constructed using electrical windings located in a slotted iron core. Fig.6 shows the
construction of a typical PM generator in a cross sectional view.
Fig :6 Permanent Magnet Rotor
The PM’s are made using high-energy rare earth materials such as Neodymium Iron Boron or
Samarium Cobalt. Retention of the PM”S on the shaft is provided by high strength metallic or composite
containment ring. The stationary iron core is made of laminated electrical grade steel. Electrical windings
are made from high purity copper conductors insulated from one another and from the iron core. The
entire armature assembly is impregnated using high temperature resin or epoxy.
The voltage output from the generator is unregulated AC. This voltage varies as a function of
the speed of generator.
MODELLING OF WATER COLUMN
The turbine is to be placed in the drinking water discharge tube at secondary reservoirs(water
towers or water tanks).
Modelling is done by assuming water to be an incompressible fluid and the discharge
tube(Penstock) is a rigid conduit
From the laws of momontum,the rate of change of flow in the discharge tube is
R. Krishna Kumar & S. Ian David 100
(p0-p-pf) ...(1)
Where
Q= Flow rate at turbine
Tw=Characteristic constant of Water Discharge tube called Water Time constant or Water starting time.
p0=Static pressure of the water column
p=pressure at turbine
pf=Pressure loss due to friction in Water Discharge tube
The friction pressure loss is calculated as flow squared.
Pf=fpQ2 ...(2)
MODELLING OF TURBINE
The turbine characteristics depend on Gate position
Q=Gp …(3)
Wher G-function of Gate position.
MODELLING OF THE DISCHARGE TUBE(CONDUIT)
The flow dynamics in the common discharge tube is given by(4),
Twc = p0c - pc - fc Q2 ...(4)
Where,
Twc=Water time constant of common discharge tube
fc=friction coefficient of common discharge tube
pc = pressure at the Turbine between the common tunnel and the individual penstocks.
P0c = static pressure of the water column at the turbine
The flow dynamics in the discharge tube in ith street without the turbine is given by(5),
Twi ( p0i - poc )-( pi - pc )- fpi Q2 ...(5)
Where,
Twi=Water time constant of common discharge tube in ith street
fpi=friction coefficient of discharge tubein ith street
Qi = flow in discharge tube in ith street
101 Hydro Power Generation from Domestic Water Supply System and Development of Dynamic Flow Modelling
poi = static pressure at the discharge tubein
ith street
pi = pressure at the tube in ith street
The flow dynamics in the common discharge tube after the turbine is placed is given by(6),
Twi ( p0i - pi )-Twc - fpi Qi 2- fc Q2-Pturbine
…(6)
Qc = flow in the common conduit (forced to be equal to the sum of the flows in the individual penstocks,
by the continuity equation)
Pturbine = pressure loss due to turbine
Thus eqn(6) explains the loss of flow due to placement of turbine in the discharge tube.
PLUMBING
Steel Pipes are extensively used for water supply. They are best suitable for long distance
domestic water distribution. Mostly grid type of plumbing method is used to interconnect the adjacent
streets.The pipes are kept vertically at 90 degrees but for Archimedean screws are normally set at an
angle of 22 degrees from horizontal, which is the optimum for the most cost-effective installations.
Hence the pipes should be inclined at least 22 degrees.
HYDRO POWER(Ep)
Hydro power is that power derived from the force or energy of moving water,which may be
harnessed for useful purposes such as generating Electricity. It is given as
Ep=mgH ….. (7)
Where
Ep=Potential Energy Of Water(J)
m=Mass of water(kg)
g=Accaleration due to gravity(m/s2)
H=Gross water head(m)
MECHANICAL POWER (P)
The mechanical power output of turbine is
P=gρQH ……. (8)
R. Krishna Kumar & S. Ian David 102
Where
P=Hydro power output(W)
ρ=Density of water (1,000 kg/m3)
Q=Flow rate(m3/s)
ENERGY OUTPUT
The Energy output of the generator is given by
W=P*η*t ...(9)
= gρQH* η*t
=9.81 *1000*QH* η*t
=9.81*QH* η*t kWh
Where
t=Operation duration(time)(8,760h/year)
η=Overall Efficiency (50-90%)
The equation to calculate flow rate of water is.,
Q=Av ...(10)
Q=Flow rate(m3/s)
A=Average Cross-sectional area of discharge tube (m2)
v=surface velocity(m/s)
CASE STUDY I
Fig:7 Secondary reservoir at Singanallur, Coimbatore.
The secondary reservoir at Singanallur has a capacity of 10 Lakh litres. The height of the tank
is 14 meters. There is continuous inflow and outflow occurring all throughout the day. The outflow rate
103 Hydro Power Generation from Domestic Water Supply System and Development of Dynamic Flow Modelling
is 69.44 L/s. The water flow from the reservoir varies from time to time for a given day. The graph below
shows variation of flow rate as a proportion of maximum flow rate (69.44 L/s). The water is distributed
to the household by the force of gravity only.Hence there is an average flow rate of 55.552 L/s
throughout the day.
Fig:8 Variation Of Flow rate in a Day
The reservoir in the tower should have a minimum height of approximately 6 meters (20 ft) and
a minimum of 4 m (13 ft) in diameter to supply water to the household. The water pressure available at
the household terminals is more than the required standards for household domestic water supply.There
has also been some instances of having excessive water pressure which has lead to water main breaks
and leaks. Excess pressure release valves have been installed to reduce pressure.
From the field data ,
With available head of 12.5meters
Average flow rate of 55.552 litres/s
The Net hydro power available is
Ep = 9.8*1000*12.5
=122500 (watts)
With a conversion efficiency of 50% ,
The Electric power output(estimated value),
P=9.8*1000*12.5*55.552*0.5(efficiency)
=3402.56 (watts)
R. Krishna Kumar & S. Ian David 104
CASE STUDY II (PEELAMEDU, COIMBATORE)
The secondary reservoir at Peelamedu has a capacity of 15 Lakh liters. The height of the tank is
15 meters. There is continuous inflow and outflow simultaneously throughout the day. The average
outflow rate is 283.33 L/s. The water flow from the reservoir varies from time to time for a given day.
The graph below shows variation of flow rate as a proportion of maximum flow rate (294.16 L/s). The
water is distributed to the household by the force of gravity only.Hence there is an average flow rate of
283.33 L/s throughout the day.
Fig:9 Variation Of Flow rate in a Day
From the field data ,
With available head of 15 meters
Average flow rate of 283.33 litres/s
The Net hydro power available is
Ep = 9.8*1000*15
=147 kW
With a conversion efficiency of 50% ,
The Electric power output(estimated value),
P=9.8*1000*15*283.33*0.5(eff)/1000
=20.825kW
CONCLUSIONS
Hence there is huge potential for implementation of hydro power system at the secondary
reservoirs for drinking water. The excess pressure of the main pipeline water supply, that representing
the head (falling water), and the water supply flow rate are the main determining factors for this hydro
105 Hydro Power Generation from Domestic Water Supply System and Development of Dynamic Flow Modelling
electric system. The conversion efficiency can be improved by using Permanent Magnet AC generator
and other circuitry.
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