Wednesday, May 25, 2016

Study of Power Station





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.
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

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