I.C. SUBHAS (08103EN 053)AAYUSH AGRAWAL (08103EN 029)NAVEET HANSDA (08103EN 056)VIVEK KUMAR SINGH (08103EN 027)SHASHANK GANESH (08103EN 009)PARAS VAID (08103EN 028)ABHISHEK JAIN (08103EN 025)JAYANT KAR (08103EN 017)MOHIT KUMAR (08103EN 036)

Proposal for

Project on

‘Hydraulic Design of Water Conveyance Structures of a Small Hydro Power Project’

February 24, 2012

Under esteemed guidance of: Presented by:

Dr. K.K. PANDEY

Asst. Professor, Hydraulic and Water Resources Department of Civil EngineeringInstitute of Technology,Banaras Hindu University

ACKNOWLEDGEMENT

We would like to sincerely express our thanks and gratitude Mr. K. K. Pandey, Assistant Professor, Hydraulic Engineering, Department of Civil Engineering, Institute of Technology, Banaras Hindu University for giving us an opportunity for completing this project. It is also due to his efforts to have guided us and encouraged throughout the compilation and data collection that has helped us get desired results.

CONTENTS

INTRODUCTION:

GENERALHydropower is a prime example of sustainable energy utilization. It can be described as a “beneficiary” of the processes which are necessary to support all life on earth: the heat of the sun evaporates the water in rivers, lakes and oceans and makes it rise into the atmosphere, where it is condensed above cooler regions and returns to earth as rain, hail or snow. Water that is not collected in the oceans or seeps into the ground is collected in lakes, river and streams. The power of water can be captured during its journey to the ocean. This is possible by capitalizing on difference in height, which can be used for power generation in hydropower stations.

Hydropower plays an important role in supporting the world economy. Providing nineteenpercent of the world’s energy, hydropower is the fourth largest source of energy production, placed behind fossil fuels such as coal, oil and gas. This percentage could, however, be significantly higher, because the “theoretical” potential of hydropower is significantly higher than its current output; estimate suggest that it is approximately five times more than that. Thus, the world’s entire power requirements could be met exclusively by hydro power.

In addition to hydro power being a renewable source of generating power, unlike wood, coal, oil and natural gas during the combustion of which carbon dioxide, sulphur dioxide and methane gases are released into the atmosphere – and consequently contributes to the greenhouse effect – the prudent utilization of hydropower leaves the ecosystem largely untouched. Among the sources of alternative renewable energies, such as wind, solar, geothermal and biomass, hydropower is attractive as other renewable sources like wind and solar are available intermittently. Additionally, this technology has now acquired a very high degree of maturity; the high efficiencies of hydro turbines can, at best, be improved further only in the decimals behind the point. Currently, many hydro turbines operate at over 90 percent efficiency. These are all factors which makes the controlled utilization of hydropower unique.

BackgroundHarnessed energy has become a symbol of growth and instrument for development. Hydroelectric power is among the cleanest end use energy input for economic activity, domestic and civic conveniences, climate control, communication and technology. Power generation in India began more than a

century ago in 1897 when the first small hydro power unit of 130 kW was set up in Darjeeling, followed by first stream driven power plant rated 1000 kW two years later at Calcutta in 1899. In 1947, when India attained freedom, the country had an installed capacity of 1362 MW in the utility sector. The installed generation capacity as at end of 2007 was 127673 MW. The overall growth rate has been to the tune of about 8%. However, it is to be noted that to keep the country’s economy on strong footing in the coming years, the country needs to achieve in 10 years what it had achieved in last more than 50 years (in power generation sector).Advantages of Hydro PowerHydro power is a renewable, economic, non-polluting and environmentally benign sourceof energy. Hydro power stations have the inherent ability for instantaneous starting, stopping, load variations etc. and help in improving reliability of power system. There is no fuel cost during the life of the station as hydro power generation is a non-consumptive use of water. The benefit of hydro power as clean, environment friendly and economically attractive sources of energy has now been sufficiently recognized. The need for its accelerated development also comes from its capability of enhanced system reliability and economics of utilization of resources.

Need for Hydro Power GenerationAt the time of Independence, the share of hydro in the total installed capacity was around37%, this continued to rise, crossing 50% in the year 1963. Thereafter, its share started declining. Until the late seventies, the share of hydro remained above 40%, considered to be the ideal hydro- thermal mix for meeting the demand in an efficient manner. However, ever since the eighties, the share of hydro has started declining sharply and at present, the share of hydro constitutes only about 26.1% of the overall installed capacity of the country.Considering the advantages, the reduction in hydro share means increase in pollution andincrease in overall long-term power tariff, it is essential to increase the hydro share.

Initiatives by GovernmentTo encourage greater participation by Indian and foreign private entrepreneurs in hydroelectric power generation, a number of measures have been taken by the central as well as state Governments for increasing the hydro capacity.

To accelerate capacity addition in the Power sector, a policy to encourage greater participation by private entrepreneurs in India and abroad in electric power generation has been announced. Central Government issued notifications for hydro power projects incorporating several incentives to private developers which broadly cover incentives for better availability of machines, for generation of extra energy, compensation for hydrological risk, etc. In India, water resources development is state subject.

EXECUTIVE SUMMARY

The consistent power shortage despite capacity additions is due to the growth of electricity consumption in the country. Hydroelectric power is among the cleanest end use energy. Small Hydro Power (SHP) Projects harnessing small perennial streams can be useful for meeting the growing electricity demand.

The current topic is chosen to study, understand, explain and make easier the design procedure of necessary elements of a Small Hydro Power Project. The various hydraulic parts of a SHP are as follows:

1. Diversion Weir and Intake 2. Feeder Channel3. Desilting Tank4. Power Channel 5. Head Race Tunnel 6. Surge Tank 7. Penstock8. Surface Power House9. Tail Race Channel 10.Approach Roads

The components which will be undertaken for the project are design of Surge Tank and Desilting Tank. The design will be carried out with the help of theories given in textbooks, established research papers and related Indian Standard Codes. The other components shall be taken up depending upon the remaining time before end semester exams.

OBJECTIVE: Hydraulic design of Desilting Tank & Surge Tank of water conveyance structures of a small hydro power (SHP) project manually.

SOURCE OF DATA: The necessary data for computational requirements during the design process shall be taken for a SHP Project (2X3500kW) which is being constructed on a perennial stream Holi, a tributary of river Ravi, in Chamba, Himachal Pradesh. The data for the purpose of study shall be

provided by OM Energy Generation Pvt. Ltd. which is carrying out the aforesaid project.

DESILTING TANK (SETTLING BASIN)

Various types of tanks like Holding Tanks, Desilting Tanks, Weir Tanks, Baffle Tanks and Frac Tanks are used for various groundwater control and construction dewatering projects. Out of which Desilting tank is a very important component of a dam, also known as settling basin.

Desilting tank acts as a basin to remove the silt from the water entering the power channel. R.C.C. rectangular basin open at top and is rectangular in shape with transitions both at the entrance and exit points. Water from feeder channel enters the tank through a transition. The splinter walls are provided to regulate the flow of water through the transition. Desilting tank is divided in to suitable number of parts. Each part is made in the form of a hopper. Arrangement is made to flush out the silt fromthe bottom of the hopper base through a pipe. Desanders and desilters are used for the operation.

Desanders:

Desanders and Desilters are drilling rig equipment with a set of hydrocyclones that separates sand and silt from the drilling fluid. Desander is installed after shakers and degasser but before Desilter. Desander removes those abrasive solids from the drilling mud which cannot be removed by shakers. Desilting is employed in dams and lakes.

A centrifugal pump is used to pump drilling fluid through the set of hydrocyclones.

Desanders have no moving parts. The larger the internal diameter of the Desander is, the greater the amount of drilling fluids it is able to process and the larger the size of the solids removed. Desander (10 inches (250 mm) cone) are able to remove 50% of solids within the 40-50 μm (micrometer) range at a flow rate of 500 US gallons per minute (32 L/s), while Desilter (4 inches (100 mm) Cone) are able to remove 50% of solids within the 15-20 μm range at a flow rate of 60 US gallons per minute (3.8 L/s). Micro fine separators are able to remove 50% of solids within the 10-15 μm range at a flow rate of 15 US gallons per minute (0.95 L/s). Desander is typically positioned next-to-last in the arrangement of solids control equipment, with decanter centrifuge as the

subsequent processing unit. Desanders are preceded by gas busters, gumbo removal equipment (if utilized), shale shaker, mud cleaner (if utilized) and vacuum degasser. Desander is widely used in oilfield drilling.

Partially constructed Desilting tank

General Arrangement: Desilting tank acts as a settling basin to remove the silt from the water entering the power channel. It is a R.C.C. rectangular basin open at top and is rectangular in shape with transitions both at the entrance and exit points. Water from feeder channel enters the tank through a transition. The splinter walls are provided (see fig. 11) to regulate the flow of water through the transition. Floor. Desilting tank is divided in to suitable no. of parts. Each part is made in the form of a hopper (figs. 12 & 13). Arrangement is made to flush out the silt from the bottom of the hopper base through a pipe. This arrangement is operated from outside the tank.Design PhilosophyDesilting tank, being a water retaining structure will be designed on no crack basis. The walls are designed for earth as well as water pressures, while base slab should also consider uplift.

Desilting Tank – General Arrangement

Details of floor of Desilting Tank

Typical Details of Desilting Tank

Design Steps of Settling Tank

Time required for settling of silt:Assuming the opening at the base of hopper be 250 mm.Assuming the slope of the hopper is to be 1:1, depth of hopper = 3m.

Volume of water = A.V = Volt

Change in Volume =

=Now equating both quantities,

, where

Integrating both sides, we get,

Velocity of flow,

Time required for opening of the gate = Total Depth/v

SURGE TANK

A surge tank (or surge drum) is a standpipe or storage reservoir at the downstream end of a closed aqueduct or feeder pipe to absorb sudden rises of pressure as well as to quickly provide extra water during a brief drop in pressure. An open tank to which the top of a surge pipe is connected so as to avoid loss of water during a pressure surge.

In mining technology, ore pulp pumps use a relatively small surge tank to maintain a steady loading on the pump.

For hydroelectric power uses, a surge tank is an additional storage space or reservoir fitted between the main storage reservoir and the power house (as close to the power house as possible). Surge tanks are usually provided in high or medium-head plants when there is a considerable distance between the water source and the power unit, necessitating a long penstock. The main functions of the surge tank are:

1. When the load decreases, the water moves backwards and gets stored in it.

2. When the load increases, additional supply of water will be provided by surge tank.

In short, the surge tank mitigates pressure variations due to rapid changes in velocity of water.

Operations

Consider a pipe containing a flowing fluid. When a valve is either fully or partially closed at some point downstream, the fluid will continue to flow at the original velocity. In order to counteract the momentum of the fluid the pressure will rise significantly (pressure surge) just upstream of the control valve and may result in damage to the pipe system. If a surge chamber is connected to the pipeline just upstream of the valve, on valve closure the fluid instead of being stopped suddenly by the valve will flow upwards into the chamber hence reducing the surge pressures experienced in the pipeline.

Upon closure of the valve, the fluid continues to flow, passing into the surge tank causing the water level in the tank to rise. The level in the tank will continue to rise until the additional head due to the height of fluid in the tank balances the surge pressure in the pipeline. At this point the flow in the tank and pipeline will reverse causing the level in the tank to drop. This oscillation in tank height and flow will continue for some time but its magnitude will dissipate slowly due to the effects of friction.

Schematic diagram of Surge tank

Picture of Surge tank of a dam in Blue ridge mountains

Applications

1. Offshore and land operations2. Drillstem testing3. Well cleanups4. Production/well testing5. Early-production facilities

A small scale Surge tank

Features, Advantages and Benefits

1. Back-pressure control on the gas outlet enables the vessel to be used as a second-stage, two-phase separator for enhanced operational flexibility.

2. Pressure, temperature, and sampling ports located on vessel to maximize phase measurement and sampling.

3. Full-bore bypass manifold with isolation valves enables routing of inlet effluent to gas and oil outlets.

4. Separate vessel drain outlet with isolation valve.5. Configuration and flexibility of vessel’s internal components allow use

of a standard manway.

6. Pressure safety valve on vessel with relief line to edge of skid, diagonally opposed grounding points on baseskid, and explosion-proof lighting at the front and rear of the unit enhance operational safety.

7. Calibrated sight glasses for oil and water measurement.8. Flanged nozzle provision on vessel to allow optional level controller and

Hi-Lo pressure alarm and shutdown sensors.9. CSC certified, ISO rated frame and skid enable stacking of units for

increased durability and mobility.10.Integral forklift pockets provide added flexibility to handling and

movement.

A simple Surge Tank is sluggish and requires great volume therefore, a differential type surge tank i.e. Orifice type Surge Tank is considered. Restricted Orifice type surge tank takes care of water hammer pressure in water conductor system of the power house during hydraulic transient condition.

a) Diameter of Surge Tank:

To ensure stability of the tank, area is governed by Thoma Criteria. Considering a station in isolation, the Thoma criteria is

WhereAth = Thoma Area of Surge TankL = Length of tunnelAt = Area of HRTVt =Velocity in HRTβ = Coefficient of hydraulic losses (say Head losses, hf)Ho = Net Head of Turbine

For a restricted orifice, a factor of safety equal to 1.6 is applied as per IS 7396 (Part-I) – 1985.

Diameter of Surge Tank, D = b) Diameter of Orifice

The resistance (hor) offered by the orifice area (Ao) shall be calculated from the following

Formulas:

The values of discharge coefficient (Cd) usually vary between 0.6 and 0.9 depending on the shape, size and number of orifices. The area of the orifice is so chosen as to satisfy the condition given by Calame and Gaden for maximum flow which is as follows;

Where Z* is surge height corresponding to change in discharge neglecting friction and orifice losses, given by

Z* =

Therefore

So, Diameter of orifice =

c) Maximum and Minimum Surge Levels

The maximum and minimum surge levels can be calculated by an approximate method given by Parmakian (1960) as follow;

(i) Maximum up Surge Level

The maximum up surge height (Zmax) above steady state level in surge tank for total rejection of load is given by as;

Where

&

(ii) Minimum down surge level

The lowest down surge (Zmin) is given by the following equation

Where

&

DESIGN STEPS

1. Desilting tank

Assumptions:1. Design discharge of power house = 2.5 cumec2. Type of turbine used = Pelton type turbine3. Net head on turbine (H0) = 300 m4. Settling velocity = 2.5 cm/sec = 0.025 m/sec

Design Steps:Design discharge of power house is 2.5 cumec. Considering 15% flushing discharge and 10% overloading of the plant, the design discharge =

cumecs

Particle size to be removed = 0.20 mm

Flow velocity in the tank =

Where a = 0.44 for 1.0mm < d < 0.1mm

= m/sec

Let the width of tank is 6.0 m

Depth required= = m = 2.8 m (say)

Moderated settling velocity, v’ = =

= cm/sec = 0.023 m/sec

Settling length of Tank = =

m = 24 m (say)

Provide a Desilting Tank of 6.0 m width, 2.8 m depth and 24.0 m length with one row of hoppers of 6.0 x 6.0 x 2.8 m depth.

Assuming the inlet width = 1.5 m And outlet width = 1.4 m

Length of U/s transition = = 14 m (say)

Length of D/s transition = = 9 m (say)Total length of desilting tank including transitions = 14 + 24 + 9 = 47 m

The flushing shall be carried out by 250 mm φ flushing pipes which will take off from bottom of hoppers and outlet in a nearby drain which leads to the river source. The level of flushing pipes at their outlets shall be kept at least 1.0 m above the maximum water level in the drain/nallah.

Time required for settling of silt:Assuming the opening at the base of hopper be 250 mm.Assuming the slope of the hopper is to be 1:1, depth of hopper = 3m.

Volume of water = A.V = Volt

Change in Volume =

=

Now equating both quantities,

, where

Integrating both sides, we get,

s,Take t=150 s.

Velocity of flow, = 1.22 m/s

Time required for opening of the gate = 5800/v5800/25

= 232 sec ≈ 4 minutes (say)

2. Surge Tank

Assumptions:

1. Design discharge (Qt) = 2.5 cumec2. Area of HRT (At) = 2.5 m23. Length of tunnel (L) = 1000 m.4. Turbine Specs. = Pelton Turbine.5. Net head on turbine (Ho) = 300.00 m6. The minimum head losses in HRT = 0.7 m7. The maximum head losses in HRT = 0.85 m8. Velocity in HRT = 1.0 m/s.

(a) Diameter of Surge Tank:To ensure the hydraulic stability of surge tank, its area is governed by Thoma criteria.

Ath = = 0.606 m2

For a restricted orifice, a factor of safety equal to 1.6 is applied as per IS 7396 (Part-I) – 1985.Thus the area of a restricted orifice type surge tank:= 1.6 x 0.606 = 0.97m2

The diameter of surge tank = =√ 0.97×4π = 1.11 m

A minimum diameter equal to diameter of HRT shall be provided for the surge tank.

The diameter of HRT =√ 2.5×4π

= 1.78 m ≈ 2.0 m, say

The area of surge tank (As) = 3.14 m2.

(b) Diameter of Orifice

The resistance (hor) offered by the orifice area (Ao),

hor= 2.5×2.5

0.7× A×2 x 9.81

Where, A = A0

Z* = = 1.0√ 1000×2.5

9.81×3.14 = 9.0 m

=>

= 6.6 m

So,

or,

Diameter of orifice = m

So provide the diameter of orifice as 1.0 m

Provided area of orifice (Ao) = 0.785 m2.

(c) Maximum and Minimum Surge Levels

(i) Maximum up Surge LevelThe maximum up surge height (Zmax) above steady state level in surge tank for total rejectionof load is given by as;

Where

m &

,

Therefore, m

(ii)Minimum down surge levelThe lowest down surge (Zmin) is given by the following equation

Where,

m &

Therefore, m

Results:

1. Desilting Tank

(a) Size of tank : Length 25.0 m, width 6.0 m & depth 2.8 m(b) Transition length (upstream) : 14 m(c) Transition length (downstream) : 12 m(d) Material : R.C.C.(e) Particle size to be removed : 0.2 mm(f) Silt disposal outlet : 250 mm dia pipes(g) Design discharge : 3.24 cumecs(h) Free board : 0.30 m

2. Surge Tank

(a) Type : Restricted orifice type(b) Diameter : 2.0 m(c) Orifice dia : 1.0 m

References:

1. Standards/ Manuals/ Guidelines for Small Hydro Development, Ministry of New and Renewable Energy, Government of India, April 2008

2. Holi – II Small Hydro Power Project District: Chamba (H.P.), Alternate Hydro Energy Cenre, Indian Institute of Technology, Roorkee, June 2010

3. IS 7396 (Part-I) – 1985