Power Stations:
An electric power
station is a factory in which energy is converted from one form or another in
to electrical energy. In a conventional thermal station, the energy is first in
the form of heat in the fuel, which may be coal, gas, or oil. This heat is liberated
by combustion in the boiler furnace and is then used to convert water into
steam. The energy in the steam is converted to mechanical energy of a rotating
shaft by some form of steam engine, either reciprocating or turbine and this
energy is converted into electrical energy by means of generator.
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| Power Station |
In a nuclear or atomic station, the energy
from the splitting of the atomic fuel is released in the form of heat in the in
the reactor and the heat is used to convert water into steam. A nuclear station
is similar to any other thermal station except that it is equipped with a
reactor instead of a boiler.
With gas or oil as the initial source of
energy, an alternative means of conversion is provided by the use of internal
combustion engine. In a hydro-electric
station, the potential energy of water stored at a height is converted into
mechanical energy by the use of water turbine and a generator connected to the
water turbine converts the energy into electrical energy.
Source of Energy: The
various source of energy are as follows.
1.Fuels.
The fuels are broadly classified as follows. (i)
Solid fuels. Various solid fuels used are wood, coal including bituminous coal,
anthracite, lignite, pear etc.(ii) Liquid fuels. Liquid fuels include petroleum
and its derivatives. (iii) Gaseous fuel. Gaseous fuels consist of natural gas,
producer gas, blast furnace gas, coal gas etc.
2.Energy
stored in water: The potential energy of water at a higher level is utilized
for generation of electrical energy. The capital cost of hydroelectric power
plants is higher as compared to other types of power plants but the operating
costs are quite low.
3.Nuclear
Energy: Controlled fission of heavier unstable atoms such as U235, Th232 and
artificial elements pu239 liberate large amount of heat energy. The energy
released by the complete fission of one kilogram of U235 is equal to the heat
energy obtained by burning 4500 tones of high grade coal. But difficulties are
high capital cost, limited availability of raw materials, difficulties
associated with disposal of radioactive wastes, and dearth of well trained
personnel to handle the nuclear power plants.
4.Wind
power: wind power can be made use of
where suitable wind velocity is available. Wind power is capable of generating
small amount of electrical energy. Wind turbines prove to be costly if designed
to run at all wind speeds.
5.Solar
energy: The heat energy contained in the rays of sun is utilized to boil water
and generate steam which can be used to drive prime mover to generate
electrical energy.
6.Tidal
power: Ocean waves and tides contain large amount of energy. Such tides rise
and fall and water can be stored during rise period and it can be discharged
during fall. Due to low head of water available low head hydroelectric plants
can work successfully.
7.Geothermal
energy: The steam vents and hot springs come out of earth’s surface. The steam
from such natural steam wells is used for generation of power.
Water treatment
plant: Natural waters usually contain dissolved salts and gases and some
organic and inorganic materials in suspension. They are rarely neutral in
reaction. The salts are chiefly the carbonates, sulphates, chlorides of calcium, sodium and aluminium or silica salts.
Oxygen and carbondioxide are the gases. The
suspended matter is usually alumina and silica in the form of mud and silt or
if organic, sewage and industrial wastes. When the impurities feed their way
into the water of a boiler, they remain until;
1.They
are neutralized by some intentionally produced internal chemical reaction.
2. They are removed by boiler water blow down. Or
3. They produce operating difficulties which if
continued unabated., may finally lead to disuse of the boiler or to explosion.
The troubles caused by the feeding of
water of undesirable quality are scaling,corrosion.foaming.priming and embrittlement.
When outreacted feed water produces enough scale on the boiler surfaces
to interfere with heat transfer, or when it contains elements which either
corrode or alter the strength of the boiler metal. The higher the rate of heat
transfer, the more important it becomes to keep that surface scale free because
the scale can both reduce the steaming capacity and cause over heating of the
tubes. That is why feed water treatment is necessary in the water treatment
plant.
IMPLEMENTATION OF POWER PLANT PROJECT
(From planning to the commercial operation)
1.
Planning:
Electricity is the key to modern civilization
and essential for socio-economic development
of a country,
particularly for a developing country like Bangladesh. At present, there is
huge
shortage of
generation capacity in the country resulting in large amount of load shedding.
As such
the development
activities in industrial, commercial, agricultural & social sectors are
being affected
severely.
Electricity supply is in the Government’s
priority list and the Government’s vision is to
provide access to
electricity for all by 2021. Adequate generating capacity is, therefore,
necessary
to be added to the
system at an accelerated pace.
In any power system, the demand is not
constant and varies throughout the day. The
peak demand occurs
during a certain period of the day. In Bangladesh power demand increases
sharply during the
evening peak hours due to the increase of domestic & commercial load.
The power system in
Bangladesh therefore requires an optimum mix of base load plants and peak
load plants to
provide electricity at least cost.
With a view to reduce “Demand-Generation” gap,
Government has initiated steps to
implement a number
of power plants under ‘Rental’/ IPPs /
Public sector utilities based on heavy
fuel / diesel oil,
which are spread over different parts of the country. Infrastructure facilities
to
import,
transportation, storage and environmental safeguard measures to be adopted for
huge
quantity of liquid
fuel oil required for power generation is yet to be developed, which is a
matter
involving
considerable effort relating to physical and financing arrangement. In
consideration of all
issues, dependable
power generation to meet enormous demand of the country is yet to be
achieved.
The power system
master plan study generally identifies least cost base load and
peak load plants.
Installation of power plant project depends on the view points of
Feasibility
Study of the suitability of
following main issues:
•Availability of land,
•Proximity to major
load centre,
•Selection of type of
power plant,
•Availability of
nature of fuel supply facilities,
•Availability of power
transmission system,
•Availability of
source of water
•Environmental
safeguard measures
•Infra-structure
facilities (Road, Railway, River) to carry heavy equipment / machinery to
the plant site etc.
Thorough study of the above having favorable
results with regard to ‘Benefit
to cost ratio’ (BCR),
‘Internal rate of return’ (IRR), the Development Project Proposal (DPP)
containing all
information / data of a specific project is forwarded to the Government /
competent
authority for
approval. It is the objective of a power plant project to enhance the
generation
capacity in the
country, in view of:
•improving the supply
– demand balance,
•Reduction of
transmission loss
•Improvement in the
fuel economy
• Improve the
stability of the power system.
2.
Preparation of Tender document:
Preparation of Tender document of a specific
project is generally based on the out come
of feasibility study
regarding technical requirements of the power plant project. Tender document is
generally consists of
the following volume of books:
•Volume-1: General
conditions, Particular conditions, Evaluation criteria, Performance Guarantee
&
warranty conditions, etc.
•Volume-2: Scope of
work / Supply: Technical requirements, Technical specification of
equipment / machinery, Drawings / Diagram,
Site investigation report / layout, etc.
•Volume-3: Technical
specification data sheet of equipment / machinery to be offered by the bidders.
Bill of quantity & price schedules, other
Formats & Schedules, etc.
3.
Invitation of Tender:
Tender is invited to select an Engineering,
Procurement & Construction (EPC)
contractor under
competitive bidding method.
4.
Evaluation of Tender proposals of the Bidders:
Tender proposals of the Bidders are evaluated
as per Evaluation criteria described in
the tender document.
Responsive and evaluated lowest bid proposal of a bidder is selected as
an EPC contractor out
of all bid proposals.
5.
Signing of contract with the successful Bidder:
Contract to implement the power plant project
is signed with the responsive and
evaluated lowest bid
Bidder after successful pre-contract discussion held with the bidder
& client. The
contract document of the power plant project contains all issues of the
tender document /
proposal as clarified / amended during the tendering process.
6.
Turn-key implementation of the Project:
The EPC contractor commences the turn-key
implementation of the Project according to
the following
activities:
•Survey, soil testing
and other necessary tests,
•Conceptual design
•Detailed design
•Procurement of
materials
•Land development
•Piling &
Foundations
•Civil & Building
work / erection
•Mechanical /
Electrical / I&C erection work
•Testing &
Commissioning
•Reliability test run
•Performance guarantee
test
•Commercial operation
•Warranty period
operation for 24 months
•Final takeover
