power plant Assignment

7/30/2019 power plant Assignment

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ASSIGNMENT

ON

POWER PLANT

ENGINEERING


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POWER PLANT ENGINEERING

SUBMITTED TO: - SUBMITTED BY:-

PROF. ARUN KUMAR DINESH KUMAR

(MECH. DEPARTMENT) MECH. (8th SEM)

11090963, B1

CONTENTS: - PAGE NO.

1. HYDROLOGY 2

2. RAIN FALL AND ITS MEASUREMENT 2-6

3. RUN OFF AND ITS MEASUREMENT 7-9

4. HYDRO GRAPHS 10-125. FLOW DURATION CURVE 13

6. MASS DURATION CURVE 13

7. SITE SELECTION FOR HYDRO-POWER PLANT 14-15

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HYDROLOGY

Hydrology is the study of water in the environment. Hydrology has evolved as a science

to try and understand the complex water systems of the Earth, to study and predict how

water will behave under different circumstances as it moves through the land phase of the

water cycle. Water is one of the most important natural resources and although plentiful,

is not always in the right place at the right time or of the right quality. An overall aim of

hydrologists is to apply scientific knowledge and mathematical principles to mitigate

water-related problems in society and environmental protection. This may mean working

out the best use of water supplies for cities or for irrigation, controlling river flooding or

soil erosion, protecting or cleaning up pollution, planning long-term water storage

reservoirs, flood risk assessment and flood/drought warning Domains of hydrology

include Hydrometeorology, hydrology, hydrogeology, drainage basin management and

water quality, where water plays the central role. Oceanography and meteorology are not

included because water is only one of many important aspects within those fields.

Hydrological research can inform environmental engineering, policy and planning.

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.

Fig.1 Hydrological cycle

Rainfall

It is defined as the total condensation of moisture from the atmosphere that reaches the

earth, including all forms of rains, ice and snow. Rain is liquid water in the form

of droplets that have condensed from atmosphericwater vaporand then precipitated that

is, become heavy enough to fall under gravity. The major cause of rain production is

moisture moving along three-dimensional zones of temperature and moisture contrasts

known as weather fronts. If enough moisture and upward motion is present, precipitation

falls from convective clouds (those with strong upward vertical motion) such

as cumulonimbus (thunder clouds) which can organize into narrow rain band. In

mountainous areas, heavy precipitation is possible where upslope flow is maximized

within windward sides of the terrain at elevation which forces moist air to condense and

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fall out as rainfall along the sides of mountains. On the leeward side of mountains, desert

climates can exist due to the dry air caused by down slope flow which causes heating and

drying of the air mass.

Fig.2 Rainfall cycle process

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Fig.3 Average Annual Rainfall in India

RAINFALL MEASUREMENTRain is measured using a rain gauge (also known as a udometer or a pluviometer which

gathers and measures the amount of liquid precipitation over a set period of time.

All rain gauges have their limitation .Attempting to collect rain data in high wind

(hurricane conditions) can be nearly impossible and unreliable due to wind extremes

preventing rain from entering the gauge .Rain gauges only indicate rainfall in a localized

area. For virtually all gauges, drops will stick to the sides of the collecting device,

resulting in slightly underestimated measurements .When the temperature is close to or

below freezing, rain may fall on the funnel and freeze or snow may collect in the gauge

and not permit any subsequent rain to pass through.

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Types of Rain GaugeTypes of rain gauges include graduated cylinders, weighing gauges, tipping bucket

gauges, optical, and simple buried pit collectors. Each type has its advantages and

disadvantages for collecting rain data.

Fig.4 Rain Gauge

Standard (Graduated Cylinder) Rain Gauge

The standard rain gauge consists of a funnel attached to a graduated cylinder that fits into

a larger container. If the water overflows from graduated cylinder the outside container

will catch it. So when it is measured, the cylinder will be measured and then the excess

will be put in another cylinder and measured. In most cases the cylinder is marked in mm.

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Tipping Bucket Rain GaugeThe tipping bucket gauge consists of a funnel that collects and channels the precipitation.

The precipitation falls onto one of two small buckets or levers which are balanced in

same manner as a balance scale. When the bucket fills sufficiently to "tip" the balance an

electrical signal is sent to the recorder. Modern tipping rain gauges consist of a plastic

collector balanced over a pivot. When it tips, it actuates a switch (such as a reed switch)

which is then electronically recorded or transmitted to a remote collection station.

The tipping bucket rain gauge is not as accurate as the standard rain gauge because the

rainfall may stop before the lever has tipped. When the next period of rain begins it may

take no more than one or two drops to tip the lever. Tipping buckets also tend to

underestimate the amount of rainfall, particularly in snowfall and heavy rainfall events.

Tipping buckets can be subject to vibration if not surely mounted causing the balance totip resulting in an over estimation of the rain measurement. The advantage of the tipping

bucket rain gauge is that the rain rate (light, medium or heavy) may be easily obtained.

Rainfall rate is decided by the total amount of rain that has fallen in a set period (usually

1 hour) and by counting the number of 'clicks' in a 10 minute period the observer can

decide the character of the rain. Tipping gauges can also incorporate weighing gauges. In

these gauges, a strain gauge is fixed to the collection bucket so that the exact rainfall can

be read at any moment. Each time the collector tips, the strain gauge (weight sensor) is

re-zeroed to null out any drift. Weighing Precipitation Gauge. A weighing-type

precipitation gauge consists of a storage container, which is weighed to record the mass.

Certain models measure the mass using a pen on a rotating drum, or by using a vibrating

wire attached to a data logger. The advantages of this type of gauge over tipping buckets

are that it does not underestimate intense rain, and it can measure other forms of

precipitation, including rain, hail and snow. These gauges are, however, more expensive

and require more maintenance than tipping bucket gauges.

Optical Rain GaugeThese have a row of collection funnels. In an enclosed space below each funnel are

a laser diode and a phototransistor detector. When enough water has been collected to

form a single drop it drips from the bottom of the funnel, falling into the laser beam's

path. The detector is set at right angles to the path of the laser beam so that light scattered

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by the drop of water breaking the laser beam is detected as a sudden flash of light. The

flashes from these photo detectors are then read and transmitted or recorded.

RUNOFF

Runoff is generated by rainstorms and its occurrence and quantity are dependent on the

characteristics of the rainfall event, i.e. intensity, duration and distribution. There are, in

addition, other important factors which influence the runoff generating process.

R= P LWhere R= runoff,

P= precipitation,

& L= All losses.Run-off = Total precipitation Total evaporation

Part of the precipitation is absorbed by the soil and seeps or percolates into ground and

will ultimately reach the catchment area through the underground channels. Thus.

Total run-off = Direct run off over the land surface T Run-off through seepage.

The unit of run-off is m3/s or day-second meter.

Day-second meter = Discharge collected in the catchment area at the rate of 1 in 3/S for

one day

= 1 24 3600 = 86400 m3/day.The flow of run-off can also be expressed in cm. of water on the drainage area feeding

the river site for a stated period, or km, cm of water per unit of time. Surface

Runoffoccurs when theintensity of precipitationexceeds the soil'sinfiltration rate.

THE SURFACE RUNOFF PROCESS

As the rain continues, water reaching the ground surface infiltrates into the soil until it

reaches a stage where the rate of rainfall (intensity) exceeds the infiltration capacity ofthe soil. Thereafter, surface puddles, ditches, and other depressions are filled (depression

storage), after which runoff is generated. The infiltration capacity of the soil depends on

its texture and structure, as well as on the antecedent soil moisture content (previous

rainfall or dry season). The initial capacity (of a dry soil) is high but, as the storm

continues, it decreases until it reaches a steady value termed as final infiltration rate.

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The process of runoff generation continues as long as the rainfall intensity exceeds the

actual infiltration capacity of the soil but it stops as soon as the rate of rainfall drops

below the actual rate of infiltration.

FACTORSAFFECTING RUN-OFFApart from rainfall characteristics such as intensity, duration and distribution, there are a

number of site (or catchment) specific factors which have a direct bearing on the

occurrence And Volume Of runoff.

1. Nature of Precipitation.

Short, hard showers may produce relatively little run-off. Rains lasting a longer time

results in larger run-off. The soil tends to become saturated and the rate of seepage

decreases. Also, the humid atmosphere lowers evaporation, resulting in increased run-off.

2. Topography of Catchments Area.

Steep, impervious areas will produce large percentage of total run-off. The water will

flow quickly and absorption and evaporation losses will be small.

3. Geology of Area.

The run-off is very much affected by the types of surface soil and sub-soil, type of rocks

etc. Rocky areas will give more run-offs while pervious soil and sub-soil and soft and

sandy area will give lesser run-off.

4. Meteorology.

Evaporation varies with temperature, wind velocity and relative humidity. Runoff

increases with low temperature, low wind velocity and high relative humidity and vice

versa.

5. Vegetation.

Evaporation and seepage are increased by cultivation. Cultivation opens and roughens

the hard, smooth surface and promotes seepage. Thick vegetation like forests consumes

A portion of the rain fall and also acts as obstruction for run-off.

6. Size and Shape of Area.

Large areas will give more run-offs. A wide area like a fan will give greater run-off,

whereas, a narrow area likes a leaf will give lesser run-off. In an area whose length is

more than its width, the flow along its width will give more run-off than if the flow is

along its length, since in the former case, seepage and evaporation will be less.

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MEASUREMENT OF RUNOFF

Runoff can be measured by delineating a certain area of a field and collecting and

measuring the volume of water passing the down slope border of that area. In view of the

dynamic character of the process, the runoff rate willgive the most useful information.

From Rain-Fall Records

The run-off can be estimated from rain-fall records by multiplying

The rain fall with run-off coefficient for the drainage area. The run-off coefficient takes

into account the various losses and will depend upon the nature of the catchment area, asgiven below: in Table 1.1

Table 1.1

Drainage Area Run-off-Coefficient

Commercial and industrial 0.90

Asphalt or concrete pavement 0.85

Forests 0.05 to 0.30

Parks, farmland and pastures 0.05 to 0.30

Then, Run-off = Rain fall run-off co-efficient

This is not an accurate method of measuring run-off since the estimation of run-off co-

efficientCan not be very accurate.

2. Empirical Formulas.

Empirical relations to determine the stream flow relate only to a particular site and

cannot be relied upon for general use.

3. Actual Measurement. Direct measurement by stream gauging at a given site for a

long period is the only precise method of evaluation of stream flow. The flow is

measured by selecting a channel of fixed cross-section and measuring the water velocity

at regular intervals, at enough points in the cross-section for different water levels. The

velocity of flow can

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Fig.5 Stream gauging records

Be measured with the help of current meter or float method. By integrating the velocities

over the cross-section for each stage, the total flow for each stage can be calculated.

HYDROGRAPH

A hydrograph is a graph showing the rate of flow (discharge) versus time past a specific

point in a river, or other channel or conduit carrying flow. The rate of flow is typically

expressed in cubic meters or cubic feet per second (cams or cuffs).

It can also refer to a graph showing the volume of water reaching a particular outfall, or

location in a sewerage network, graphs are commonly used in the design ofsewerage,

more specifically, the design ofsurface watersewerage systems and combined sewers.

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Fig.6 Hydrograph

Types of hydrograph can include:

1. Storm hydrographs

2. Flood hydrographs3. Annual hydrographs aka regimes

4. Direct Runoff Hydrograph

5. Effective Runoff Hydrograph6. Raster Hydrograph

7. Storage opportunities in the drainage network (e.g., lakes, reservoirs, wetlands, channel

and bank storage capacity)

UNIT HYDROGRAPHAunit hydrograph(UH) is the hypothetical unit response of a watershed (in terms of

runoff volume and timing) to a unit input of rainfall. It can be defined as the direct runoff

hydrograph(DRH) resulting from one unit (e.g., one cm or one inch) ofeffective

rainfalloccurring uniformly over that watershed at a uniform rate over a unit period of

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time. As a UH is applicable only to the direct runoff component of a hydrograph (i.e.,

surface runoff), a separate determination of the base flow component is required.

A UH is specific to particular watershed, and specific to a particular length of time

corresponding to the duration of the effective rainfall. That is, the UH is specified as

being the 1-hour, 6-hour, or 24-hour UH, or any other length of time up to thetime of

concentrationof direct runoff at the watershed outlet. Thus, for a given watershed, there

can be many unit hydrographs, each one corresponding to a different duration of effective

rainfall.

The UH technique provides a practical and relatively easy-to-apply tool for quantifying

the effect of a unit of rainfall on the corresponding runoff from a particular drainage

basin. UH theory assumes that a watershed's runoff response is linear and time-invariant,

and that the effective rainfall occurs uniformly over the watershed. In the real world,

none of these assumptions are strictly true. Nevertheless, application of UH methods

typically yields a reasonable approximation of the flood response of natural watersheds.

The linear assumptions underlying UH theory allows for the variation in storm intensity

over time (i.e., the stormhyetograph) to be simulated by applying the principles of

superposition and proportionality to separate storm components to determine the resulting

cumulative hydrograph. This allows for a relatively straightforward calculation of the

hydrograph response to any arbitrary rain event.

Aninstantaneous unit hydrographis a further refinement of the concept; for an IUH, the

input rainfall is assumed to all take place at a discrete point in time (obviously, this isn't

the case for actual rainstorms). Making this assumption can greatly simplify the analysis

involved in constructing a unit hydrograph, and it is necessary for the creation of

a geomorphologic instantaneous unit hydrograph.

The creation of a GIUH is possible given nothing more than topologic data for a

particular drainage basin. In fact, only the number of streams of a given order, the mean

length of streams of a given order, and the mean land area draining directly to streams of

a given order are absolutely required (and can be estimated rather than explicitly

calculated if necessary). It is therefore possible to calculate a GIUH for a basin without

any data about stream height or flow, which may not always be available.

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FLOW DURATION CURVE

a flow duration curve shows the relation between flows and lengths of time during which

they are available. The flows are plotted as the ordinates and lengths of time as abscissas.

The flow duration curve can be plotted from a hydrograph.

MASS-CURVE

The use of the mass curve is to compute the capacity of the reservoir for a hydro site. The

mass curve indicates the total volume of run-off in second meter-months or other

convenient units, during a given period. The mass curve is obtained by plotting

cumulative volume of flow as ordinate and time (days, weeks by months) as abscissa. A

mass curve for a typical river for which flow data is given in Table 1.2.

The monthly flow is only the mean flow and is correct only at the beginning and end of

the months. The variation of flow during each month is not considered. Cumulative daily

flows, instead of monthly flows, will give a more accurate mass curve, but this involves

an excessive amount of work. The slope of the curve at any point gives the flow rate in

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second-meter. Let us join two pointsXand Yon the curve. The slope of this line gives the

average rate of flow during the period betweenXand Y. This will be = (Flow at Y-Flow at

X)/Time Span.

SITE SELECTION FOR HYDRO-POWER PLANT

While selecting a suitable site, if a good system of natural storage lakes at high altitudes

and with large catchment areas can be located, the plant will be comparatively

economical. Anyhow the essential characteristics of a good site are: large catchment

areas, high average rainfall and a favorable place for constructing the storage or reservoir.

For this purpose, the geological, geographical and meteorological conditions of a site

need careful investigation. The following factors should be given careful consideration

while selecting a site for a hydro-electric power plant.

1. Water Available.

To know the available energy from a given stream or river, the discharge flowing and its

variation with time over a number of years must be known. Preferably, the estimates of

the average quantity of water available should be prepared on the basis of actual

measurements of stream or river flow. The recorded observation should be taken over a

number of years to know within reasonable, limits the maximum and minimum variations

from the average discharge. The river flow data should be based on daily, weekly,

monthly and yearly flow ever a number of years. Then the curves or graphs can be

plotted between tile river flow and time. These are known as hygrographs and flow

duration curves. The plant capacity and the estimated output as well as the need for

storage will be governed by the average flow. The primary or dependable power which is

available at all times when energy is needed will depend upon the minimum flow. Such

conditions may also fix the capacity of the standby plant. The, maximum of flood flow

governs the size of the headwords and dam to be built with adequate spillway.

2. Water-Storage.

As already discussed, the output of a hydropower plant is not uniform due to wide

variations of rain fall. To have a uniform power output, water storage is needed so that

excess flow at certain times may be stored to make it available at the times of low flow.

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To select the site of the dam ; careful study should be made of the geology and

topography of the catchment area to see if the natural foundations could be found and put

to the best use.

3. Head of Water.

The level of water in the reservoir for a proposed plant should always be within limits

throughout the year.

4. Distance from Load Center.

Most of the time the electric power generated in a hydro-electric power plant has to be

used some considerable distance from the site of plant. For this reason, to be economical

on transmission of electric power, the routes and the distances should be carefully

considered since the cost of erection of transmission lines and their maintenance will

depend upon the route selected.

5. Access to Site.

It is always a desirable factor to have a good access to the site of the plant. This factor is

very important if the electric power generated is to be utilized at or near the plant site.

The transport facilities must also be given due consideration.

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