Generation of Electricity from Coal

In this PresentationBasic of Power GenerationBasic information on Coal/Fuel OilCombustion ProcessPower Plant CycleFactors affecting EfficiencyBoilers and TurbinesTransmission of Power and Switching

How Generated electricity reached customer

Simplified Diagram

Coal to Electricity .. Basics

Major EnergySources of India

Why Coal?Share of Coal in Power GenerationAdvantages of Coal FuelAbundantly available in IndiaLow costTechnology for Power Generation well developed.Easy to handle, transport, store and use

Shortcomings of CoalLow Calorific ValueLarge quantity to be HandledProduces pollutants, ashDisposal of ash is ProblematicReserves depleting fast

Indias Coal Reserves are estimated to be 206 billion tonnes. Present consumption is about 450 million tonnes.Cost of coal for producing 1 unit of electricity (Cost of coal Rs 1000/MT)is Rs 0.75.Cost of Gas for producing 1 unit of electricity (Cost of Gas Rs 6/SMC)is Rs 1.20.

Knowing more about CoalCoal TransportationRailTruckConveyorShip

Boiler/ steam generatorSteam generating device for a specific purpose.

Capable to meet variation in load demand

Capable of generating steam in a range of operating pressure and temperature

For utility purpose, it should generate steam uninterruptedly at operating pressure and temperature for running steam turbines.

Boiler/ steam generatorRaw materials for design of boilersCoal from mines

Ambient air

Water from natural resources (river, ponds)

Generating heat energy

Air for combustion

Working fluid for steam generation, possessing heat energyA 500MW steam generator consumes about 8000 tonnes of coal every dayIt will be considered good, if it requires about 200 cubic meter of DM water in a dayIt will produce about 9500 tonnes of Carbon di Oxide every day

Types of BoilersFire-Tube Boilers Fire-tube boilers rely on hot gases circulating through the boiler inside tubes that are submerged in water. These gases usually make several passes through the tubes, thereby transferring their heat through the tube walls and causing the water to boil on the other side. Fire-tube boilers are generally available in the range of 20 through 800 boiler horsepower (bhp) and in pressures up to 150 psi.

Types of BoilersElectric Boilers Electric boilers are very efficient sources of hot water or steam, which are available in ratings from 5 to over 50,000 kW. They can provide sufficient heat for any HVAC requirement in applications ranging from humidification to primary heat sources.

Types of BoilersWater Tube Boiler: Here the heat source is outside the tubes and the water to be heated is inside. Most high-pressure and large boilers are of this type. In the water-tube boiler, gases flow over water-filled tubes. These water-filled tubes are in turn connected to large containers called drums.

Steaming CapacityLarge boiler capacities are often given in Tonnes of steam evaporated per hour under specified steam conditions

Coal analysisTypical composition (Proximate analysis)1. Fixed carbon2. Fuel ash3. Volatile material4. Total Moisture5. SulfurHigh calorific value/ Lower calorific value (Kcal/kg)Hardgrove Index (HGI)

Combustion of coalCarbon, hydrogen, sulfur are sources of heat on combustion

Surface moisture removed on heating during pulverization.

Inherent moisture and volatiles are released at higher temperature, making coal porous and leading to char/ coke formation. (Thermal preparation stage)

Flame Inside Furnace

Fuel OilThree liquid fuels used in power plants1. Heavy Fuel Oil (HFO)2. LSHS (Low Sulfur Heavy stock)3. High speed Diesel (HSD)

Oil firing is preceded byLowering viscosity and increasing flowability on heating for better combustion in given turn down ratio.(125oC)Droplet formation on atomization (by steam/ compressed air/ mechanical pressurization) Combustion initiation by High energy spark ignition

Combustion of reactantsReaction rate depends on concentration of one of the reactants

Concentration varies on partial pressure of the reactants.

Partial pressure is a function of gas temperature.

Therefore, reaction rate depends on temperature and substance that enter the reaction.

Combustion Reactions (Carbon)Main reactions 2C+ O2= 2CO + 3950 BTU/lb (Deficit air)C+ O2= CO2 +14093 BTU/lb Secondary reactions2CO+ O2= 2CO2 + 4347BTU/lbC+ CO2= 2CO -7.25MJ/kg

Combustion Reactions (Carbon)Carbon reaction 2C+O2=2CO[Eco =60kJ/mol]C+ O2=CO2[Eco2=140kJ/mol]reaction at 1200oC4C+3O2=2CO + 2CO2 (Ratio 1:1)Reaction at 1700oC3C + 2O2= 2CO +CO2(Ratio 2:1)

It is desirable to supply combustion air at lower temperature regime in furnace

Combustion Reaction (H2, S)Hydrogen reaction2H2+O2= 2H2O +61095 BTU/lb

Sulfur reactionS+O2= SO2+ 3980 BTU/lb (undesirable)

Coal for combustionAnthraciteSemi-anthraciteBituminousSemi-BituminousLignitePeatHigh CV, low VMHigh CV, low VMMedium CV, medium VMMedium CV, medium VMLow CV, high VM, high TMVery low CV, high VM & TM

Basic Power Plant Cycle

Factors Affecting Thermal Cycle EfficiencyInitial steam PressureInitial Steam TemperatureWhether reheat is used or not, and if used reheat pressure and temperatureCondenser pressure Regenerative feed water heating

Benchmark for 500 MW Plant Implementation

PROJECT EXECUTION

2004

ARRANGEMENT OF MAIN BOILER (STEAM GENERATOR) A STEAM GENERATOR IS A COMPLEX INTEGRATION OF THE FOLLOWING ACCESSORIES:

* ECONOMISER * LTSH

* BOILER DRUM * DIV PANEL

* DOWN COMERS * PLATEN SH

* CCW PUMPS * REHEATER

* BOTTOM RING HEADER * BURNERS

* WATER WALLS * APHs

Tangential Firing System

Steam Flows from Boiler to turbineBypassTurbine

to >1300MWto >1300MWfF

Turbo Generator

Enthalpy drop in steam TurbineProcess 5-6 takes place in turbine and the work produced is the difference between point 5 and point 6.

Impulse and reaction Turbine

Turbine are multistage The steam turbine is a form of heat engine that derives much of its improvement in thermodynamic efficiency from the use of multiple stages in the expansion of the steam

Generator Transformer

Electrical Systems in Power Plant

Switchyard One line DiagramTransfer Bus 400 KVMain Bus IIMain Bus ICBCBCBGT20.5/400KVGen BayFeeder BayBusIsolator Transfer Bus Bay

400 KV Switchyard

SF6 CB

SF-6 Breaker

800 KV GIS

Power Supply Systems

Power Generation, Transmission and Distribution

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