Power Plant Classifications

Classification of Power Plants by Energy Source

• Conventional power plants include steam power plants, internal combustion engine plants, gas turbine plants, hydroelectric plants, and nuclear power plants
• Non-conventional power plants include wind power plants, ocean thermal energy conversion (OTEC) plants, geothermal power plants, biogas plants, tidal power plants, solar power plants and Magnetohydrodynamics (MHD) system plants

Classification of Power Plants by Load

• Peak load plants supply extra power during high demand periods
• Base load plants supply continuous power to meet the minimum demand
• Stand-by plants provide emergency backup during outages or failures

Steam Power Plant

• Converts the chemical energy of fossil fuels (coal, oil, gas) into mechanical/electrical energy
• Functions as a base load plant

Classification of Steam Power Plants

• Central stations: Electrical energy intended for general sale to customers
• Industrial power stations/Captive power stations: Run by a manufacturing company for own use, output not available for resale

Layout of a Modern Steam Power Plant

• Coal and ash circuit: Coal arrives at the storage yard, ash is removed to the ash storage yard through ash handling equipment
• Air and gas circuit: Supplies oxygen for combustion, removes flue gases through draft systems, recovers heat via air preheaters
• Feedwater and steam flow circuit:delivers water to boiler, then drives electricity-generating turbine. Steam is condensed back into water and recirculated through feedwater heaters
• Cooling water circuit: Removes waste heat from condenser by transferring it to a cooling medium (water), prevents plant overheating

Components of a Modern Steam Power Plant

• Boiler including superheater, economizer, reheater, and air-heater units
• Steam turbine
• Condenser
• Generator
• Cooling towers
• Circulating water pump
• Boiler feed pump
• Wagon Trippler
• Coal mill
• Ash precipitators
• Forced draught fans
• Water treatment plant
• Control room
• Switch Yard
• Crusher House
• Induced draught fans
• Boiler chimneys

Essential Requirements of Steam Power Plant Design

• Minimum O&M cost
• Low cost of energy supplied to the consumers
• Minimum capital cost
• Minimum losses of energy in transmission
• Reliability

Diesel Engine Power Plant

• Suitable when coal and water aren't sufficiently available or for standby sets where power is to be generated in small quantities
• This is a peak load plant

Subsystems of a Diesel Engine

• Main Engine: Converts fuel chemical energy into mechanical energy to drive the generator
• Starting: Uses electric motors or compressed air to start the engine
• Lubrication: Reduces friction and wear by circulating lubricating oil
• Fuel: Stores, filters, and supplies diesel fuel for combustion
• Air Intake & Exhaust: Provides clean air for combustion and removes exhaust gases
• Cooling: Uses water or air to prevent overheating

Applications of Diesel Power Plant

• Mobile power plants
• Emergency plants
• Nursery stations
• Starting stations
• Central stations (5-10 MW range)
• Stand-by Units

Gas Turbine Power Plant

• Utilizes a turbine as the primary mover with a permanent gas as the working medium, functions as peak load and standby plants

Components of Gas Turbine

• Turbine
• Compressor
• Combustor
• Auxiliaries containing starting devices, lubrication pump, fuel system, oil system, duct system

Gas Turbine Applications

• Mechanical drive for auxiliaries
• Driving generators and supplying peak loads in steam, diesel, or hydro plants
• Combination plants with conventional steam boilers

Hydroelectric Power Plant (HEPP)

• Water moves hydraulic turbines, which then run electric generators
• The energy of water used is kinetic or potential
• This is a base load plant

Elements of Hydroelectric Power Plant

• Catchment area
• Prime movers
• Draft tubes
• Powerhouse and equipment
• Reservoir
• Dam
• Spillways
• Conduits
• Surge Tanks
• A powerhouse should be such that adequate space is provided around the subdivided in substructure, intermediate and superstructure
• The draft tubes allows the turbineto be set above tail-water level to improve access
• Prime movers in Hydroelectric power plant converts the energy of water into mechanical energy and then electrical energy

Conduits in HEPPs – Types

• Open conduits: These are open waterways excavated in natural ground, have slight gradient with height loss, including Canals and Flumes
• Closed Conduits: These are closed channels excavated through natural ground, including Tunnels, Pipelines (flow line, laid on hydraulic gradient), and Penstock (water under pressure to turbine)

Classification of HEPP by Quantity of Water

• Run-of-river plant without pondage
• Run-of-river plant with pondage
• Storage type plants
• Pump storage plants
• Mini and micro hydro plants

Hydraulic Turbines - Classification by Head and Quantity of Water

• Impulse Turbine: Requires high head and small quantity of flow
• Reaction Turbine: Requires low head and high rate of flow

Hydraulic Turbines - Classification by Originator

• Kaplan Turbine: Reaction turbine for low heads and large quantities of flow
• Francis Turbine: Reaction turbine for medium high to medium low heads and medium small to medium large quantities of water
• Pelton Turbine: Impulse turbine used for high head and low discharge

Hydraulic Turbines - Classification by Speed

• Turbines with low specific speeds work under high head and low discharge conditions
• High specific speed turbines operate under low head and high discharge conditions

Classification of HEPP by Head

• High Head Power Plants: 100 m and above, usually stores water for lakes in high mountains, Pelton Wheels are common prime movers
• Medium Head Power Plants: 30 to 100 meters, commonly use Francis turbines, forebay serves as water reservoir and surge tank, channels are the main carries for water from the main reservoir to the forebay
• Low Head Power Plants: 25 to 80 m, utilize a dam across a river, sideway stream is used, uses vertical shaft Francis or Kaplan turbines

Nuclear Power Plant

• Generates energy by nuclear fission, where atoms (uranium-235 or plutonium-239) split, releasing heat
• Functions as a base load plant

Nuclear Reactions Types

• Nuclear Fusion: Combining lighter nuclei into a heavier nuclide, releases energy
• Nuclear Fission: A neutron strikes the nucleus of heavy atoms, causing the original nucleus to split into fragments which carry off most of the energy of fission as kinetic energy

Main Components of Nuclear Power Plant

• Nuclear reactor
• Heat exchanger
• Steam turbine
• Condenser
• Electric Generator

Essential Components of a Nuclear Reactor

• Reactor core: Fission chain reaction occurs, fission energy is liberated as heat
• Reflector: Around the core, to reflect back neutrons
• Control mechanism: Starts the reactor, maintains power at a steady state, shuts down the reactor
• Moderator to slow/absorb neutrons
• Coolants: Removes the intense heat from the reactor
• Measuring instruments: Measures the neutron flow which determines power developed
• Shielding: Protects reactor walls from radiation damage and personnel from radiation exposure

Wind Power Plant

• Electricity is generated using using wind turbines, which convert the kinetic energy of wind into mechanical energy to spin a generator
• They are typically used as supplementary or variable renewable energy sources, contributing to the grid whenever wind conditions are favorable

Wind - Electric Power Plants

• The wind turbine may be located either upwind or downwind of the power.
• In the unwind location the wind encounters the turbine before reaching the tower and are generally preferred especially for large aerogenerators

Types of Wind Machine

• Horizontal Axis Wind Machines:. Common design, complex to produce electric power economically
• Vertical Axis Wind Machine: Doesn't need change wih wind direction, called panemones

Advantages of Wind Power Plant

• Renewable energy source
• Non-polluting
• No adverse effect on the environment
• Economically competitive
• Ideal for rural and remote areas

Disadvantages of Wind Power Plant

• Fluctuating nature
• Present systems are neither maintenance free, nor practically reliable.
• Favourable winds are available only in a few geographical locations, away from cities, forests
• Wind turbine design, manufacture and installation have proved to be most complex due to several variables and extreme stresses.
• Only in kW and a few MW range; it does not meet the energy needs of large cities and industry.

Tidal Power Plants

• Generates electricity by harnessing ocean tides
• Tidal turbines or barrages (dams) capture the movement of water caused by rising and falling tides, then drive a turbine connected to a generator
• Tidal energy is a more reliable renewable source compared to wind or solar power

components of Tidal power plant

• Dam/Dyke that forms barier between the sea and the basin
• Sluice ways which allows the basins to fill the empty according to operational requirments
• Power House with turbines, electric generators and other equipment

Classifications of Tidal Power Plants

• Single Basin: Power is generated intermittently, with a basin separated from the sea by a dam or dyke, flow between them is through sluice ways
• Double Basin: Continuous or on-demand power, more extensive civil works, a dam must be between each basin/sea as well as each basin

Advantages of Tidal Power Plant

• Independent of rain and uncertainty
• Inexhaustible
• Small area are Required
• Pollution free

Limitations of Tidal Power Plant

• Output is not Uniform due to variation of tide
• Plant efficiency is affected by operation over a wide range
• Prone to machinery corrosion due to corrosive sea water
• Sedimentation of basins
• High power transmission costs

Ocean Thermal Energy Conversion (OTEC)

• Generates electricity by using the temperature difference between warm surface seawater and cold deep seawater to run a heat engine
• Typically uses a Rankine cycle, where warm water evaporates a working fluid to drive a turbine, then cold water condenses it back into liquid

Ocean Thermal Energy Conversion Schematic

• Oceans cover 70% of the global surface
• Cold water circulates at the ocean bottom from the poles to the tropics
• In tropical regions, water temperature is ~5°C at 1000m depth and ~25°C at surface

Merits of OTEC Plant

• Clean energy conversion
• Does not occupy land areas
• No payment for its energy required
• Steady source of energy as temperatures are steady

Limitations of OTEC Plant

• 30% of power is used to pump the water
• System must withstand sea water, hurricanes, debris, and fish
• Materials must withstand corrosion
• Floating plants are dfifficult to construct
• Plant size is about 100 MW due to large components

Solar Power Plant

• Generates electricity by converting sunlight using either photovoltaic (PV) panels or solar thermal systems (CSP)
• PV panels convert sunlight into electricity, CSP uses mirrors to concentrate heat, produce steam, and drive a turbine

Photovoltaic Cell

• Solar energy converts into electrical energy via the photovoltaic effect: electromotive force results from absorption of ionizing radiation
• Sensitive element is a semiconductor which generates voltage in proportion to light or radiant energy
• Most commonly used cells are barrier layer type, use iron-selenium cells or Cu-CuO2 cells

Concentrated Solar Power Plant

• Circular/rectangular parabolic mirror collects radiation, focuses it on a small area, and mechanism moves collector to follow the sun

Geothermal Power Plant

• Energy from the earth’s interior is classified as renewable because the earth’s interior is and will continue in the process of cooling for the indefinite future
• Sources are actively sought and economically tapped, resulting a plant that operates as base load

Geothermal Sources (Hydrothermal Convective Systems)

• Vapor dominated or dry stream fields
• Liquid-Dominated system or Wet steam fields
• Hot Water Fields

Dry-Steam Open System.

• The plant directly use pure stream from the geothermal reservior to spin a turbine
• This system type is simple, efficient, and requires rare dry steam reserviors

Flash Steam Open Type System

• The plant extracts high-pressure hot brine, flashes it into steam bylowering pressure, and uses the steam to drive the turbiner is used.
• This approach is the is most commone and efficient but requires handling mineralized brine.

Hot Water Closed (Binary) System

• This plant Uses moderate-temperature geothermal water to heat a secondary working fluid (e.g., isobutane) and that vaporizes
• Has lesser effciency than flash steam but can work with lower temperatures
• Requires a condensor

Advantages of Geothermal Power Plant

• Cost-effective: Geothermal energy is cheaper
• Least polluting
• Produces greater net energy compared to alternative systems
• Inexhaustible
• It is amenable for multiple uses from a single resource.

Disadvantages of Geothermal Power Plant

• Lower Power production efficiency (15% vs 35 to 40%)
• Noisy drilling
• Large areas needed
• Can cause surface subsidence

Biomass Plants - Biogas

• Considered a renewable source of energy because organic matter is generated every day
• Fossil fuel, petroleum oil, and natural gas are not in the category
• A form of solar energy indirectly grows plants by photosynthesis’

Biomass Resources

• Concentrated Wastes(Municipal solid, Industrial waste, Sewage wood, Manure at large lots products)
• Dispersed Waste Residue (Crop residue, Logging residue, Disposed manure)
• Harvested Biomass (Standing biomass, Biomass energy plantations)

Biomass Conversion Process Types

• Direct Combustion (heat generated by burning the dried biomass, used to produce low-calorie value gas by pyrolysis)
• Thermochemical Conversion(biomass decomposed in thermochemical processes, gasification, liquefaction)
• Biochemical Conversion (Anaerobic digestion, Fermentation)

Magnetohydrodynamics (MHD) System

• Concerned with the flow of a conducting fluid in the presence of magnetic and electric fields
• The generator converts heat energy of a fuel directly into electrical energy
• The fluid may be gas at elevated temperature or liquid like sodium or potassium

Power plant cost/lifespan/return table

• (Steam/Oil/Gas) 30-45 years
• (Hydro/Nuclear) 40-60 years
• (Wind/Solar) 20/30 years

Fuel dependency table

• (Fuel dependent)-Coal/oil/turbine/biomass
• (non-fuel)-Solar/wind/hydro/geothermal/tidal

Environmental impact table

• (High Emission)-Coal/oil/diesel
• (Low Emission)-Gas turbine/biomass
• (Zero emission)-Solar/wind/hydro/nuclear

By Startup time

• (Slow)-Coal/Nuclear/OTEC/Biomass
• (Moderate)-Gas Turbine/Geothermal/ CSP
• (Fast)-Diesel/Hydro/Wind/Solar PV