Thermal power station

A A thermal power stationthermal power station is a power plant in which  is a power plant in which

the prime mover is the prime mover is steam drivensteam driven. Water is heated, turns . Water is heated, turns

into steam and spins a steam turbine which drives into steam and spins a steam turbine which drives

an electrical generator. After it passes through the turbine, an electrical generator. After it passes through the turbine,

the steam is condensed in a condenser and recycled to the steam is condensed in a condenser and recycled to

where it was heated; this is known as a Rankine cycle. where it was heated; this is known as a Rankine cycle.

The greatest variation in the design of thermal power The greatest variation in the design of thermal power

stations is due to the different fuel sources.stations is due to the different fuel sources.

Some prefer to use the term Some prefer to use the term energy centerenergy center because such  because such

facilities convert forms of heat energy into electricity.facilities convert forms of heat energy into electricity.

Some thermal power plants also deliver heat energy for Some thermal power plants also deliver heat energy for

industrial purposes, for district heating, or industrial purposes, for district heating, or

for desalination of water as well as delivering electrical for desalination of water as well as delivering electrical

power. A large part of human COpower. A large part of human CO22 emissions comes from  emissions comes from

fossil fueled thermal power plants; efforts to reduce these fossil fueled thermal power plants; efforts to reduce these

outputs are various and widespread.outputs are various and widespread.

Thermal power Thermal power is is generally classified into three generally classified into three

categories based on the type of fuelcategories based on the type of fuel, known as , known as liquefied liquefied

natural gas (LNG),natural gas (LNG), petroleumpetroleum and and coalcoal. While petroleum . While petroleum

used to be used as fuel in most situations, the utilization used to be used as fuel in most situations, the utilization

ratios of LNG and coal have increased since the first oil ratios of LNG and coal have increased since the first oil

crisis of 1973 as petroleum use has decreased over the crisis of 1973 as petroleum use has decreased over the

years.years.

Coal Fired Thermal Power Plants Coal Fired Thermal Power Plants

A coal fired power plant converts heat to electrical

energy in much the same way that it's done in a gas fired

power plant, a nuclear power plant, or even a solar

thermoelectric power plant. The only thing that differs

among these different types of power plants is the way

that the heat is generated.

Coal power plants and gas or oil fired power plants

burn a fuel to generate heat.

A nuclear power plant carries out a controlled

nuclear reaction that generates heat and a solar

thermoelectric power plant uses solar radiation to heat a

fluid. In all of these thermoelectric power plants, the heat

is used to heat water and generate steam that is then

passed through a steam turbine, making it rotate and drive

an electrical generator.

Thus a thermoelectric power plant converts the energy in

coal, gas, oil, nuclear fuel, or the sun’s rays into electrical

energy.

Coal Coal

Mining is the process of removing coal from

the ground. There are two types of mining:

underground mining and surface mining. When the

coal seam is fewer than 125 feet under the surface,

it is mined by surface mining. Coal that is deeper

than 125 feet is removed from the ground by

underground mining.

SURFACE SURFACE MININGMINING

Surface mining is

used when a coal

seam is located close

to the surface. Heavy

equipment is used to

clear the land of trees,

shrubs and topsoil.

Holes are drilled into the rock and explosives are placed in these holes. The explosion breaks up the dirt and rock called overburden.

Large earth-moving

machines move the

overburden to expose

the coal seam. When

the coal is uncovered,

bulldozers and

shovels scoop up the

coal and load it into

large trucks.

UNDERGROUND UNDERGROUND MININGMINING

 

Underground mining is

used when the coal seam

lies deep in the earth. In an

underground mine only

some of the coal is

removed. The coal that

remains helps support the

mine roof.

 

Underground mines look

like a system of tunnels.

The tunnels are used for

traveling throughout the

mine, moving coal from

place to place and

allowing air to circulate

in the mine.

The coal that is mined

is put on conveyor

belts. The conveyor

belts take the coal to

the surface.

A A drift mine drift mine is built when the coal seam lies in the is built when the coal seam lies in the

side of a hill or mountain. Drift mines may also be side of a hill or mountain. Drift mines may also be

built in a surface mine that has become too deep.built in a surface mine that has become too deep.

There are three types of underground mines: slope,

drift, and shaft. When the coal seam is close to the

surface but too deep to use surface mining, a slope

mine can be built. In a slope mine a tunnel slants

down from the surface to the coal seam.

Shaft mine. These

mines may be 125 to

1,000 feet deep. A

large hole, or shaft, is

drilled down into the

ground until it reaches

the coal seam.

Calaca Coal Power PlantCalaca Coal Power Plant

Plant Name:                 Calaca Coal ICalaca Coal IICommissioning Year:     19841995No. and Unit Size

(MW): 2 x 300Location:                      Calaca, BatangasPolitical Region:          IV

Fuel ConsumptionFuel ConsumptionFor 2008, the power plant is expected

to consume half of an estimated purchase of 1.67 million tonnes of coal intended for Calaca and Masinloc coal power plants. [2] The Calaca power plant is fired by pulverized coal, with two generating units of 300 MW each. The plant includes an offshore coal unloading jetty and unloading facilities. Half of the electricity produced from Calaca at peak load is partly covered by transitional supply contracts. [3]

Stage 1 

How Coal Power Plants How Coal Power Plants Produce ElectricityProduce Electricity

The first conversion of energy takes place in the boiler. Coal is burnt in the boiler furnace to produce heat. Carbon in the coal and Oxygen in the air combine to produce Carbon Dioxide and heat.

Coal for Power PlantsCoal for Power PlantsThe coal input to the boiler of the power

plant passes through three different phases before combustion in the boiler.◦Receiving, storing, and transporting the coal

to the boiler. This is bulk storage and bulk handling.

◦Preparing the coal for firing or pulverizing. This is what is special in a coal fired power plant, especially large thermal power plants.

◦Burning the coal in the combustion process to release the energy in the fuel.

 

Coal PulverizingCoal PulverizingThe basic requirement of coal

combustion is that all the carbon particles in coal should get sufficient air to burn and release the heat.

Coal normally is available to power plants in large lumps ranging from 2 mm to 50 mm size. Coal is commercially available in different sizes known as “Run of Mine,” “stoker,” “slack,” etc. depending on their size.

GrindabilityGrindability

-Important characteristic of coal that decides the type, size, and power required for pulverizing.

-denoted by the Hardgrove Grindability Index (or HGI).

Grindability in general is a function of the grade of coal.◦Sub-bituminous coal from the Indian sub-

continent has an index near fifty. A higher number indicates the coal is soft and easy to grind.

◦Anthracitic coals, higher grade coals, have higher hardness and consequentially a lower Grindability Index in the range of forty or less.

◦Lignite, the lower grade of coal, on other hand is very soft and easy to pulverize and can have an index of a hundred and greater.

Stage 2Stage 2 1. The heat from combustion of the coal boils

water in the boiler to produce steam. In modern power plant, boilers produce steam at a high pressure and temperature. 

2. The steam is then piped to a turbine. 3. The high pressure steam impinges and

expands across a number of sets of blades in the turbine.  

4. The impulse and the thrust created rotates the turbine. 

5. The steam is then condensed and pumped back into the boiler to repeat the cycle

Stage 3Stage 3

In the third stage, rotation of the turbine rotates the generator rotor to produce electricity based of Faraday’s Principle of electromagnetic induction.

Diagram of a typical coal-Diagram of a typical coal-fired thermal power stationfired thermal power station

Key1. Cooling tower 10. Steam governor valve 19.

Superheater

2. Cooling water pump 11. High pressure turbine 20. Forced draught fan

3. Transmission line (3-phase) 12. Deaerator 21. Reheater

4. Unit transformer (3-phase) 13. Feed heater 22. Air intake

5. Electric generator (3-phase 14. Coal conveyor 23. Economiser

6. Low pressure turbine 15. Coal hopper 24. Air preheater

7. Boiler feed pump 16. Pulverised fuel mill 25. Precipitator

8. Condensor 17. Boiler drum 26. Induced draught fan

9. Intermediate pressure turbine 18. Ash hopper 27. Chimney Stack

 

1. Coal is conveyed (14) from an external stack and ground to a very fine powder by large metal spheres in the pulverized fuel mill (16).

 2. There it is mixed with preheated air

(24) driven by the forced draught fan (20).

 3. The hot air-fuel mixture is forced at

high pressure into the boiler where it rapidly ignites.

4. Water of a high purity flows vertically up the tube-lined walls of the boiler, where it turns into steam, and is passed to the boiler drum, where steam is separated from any remaining water.

5. The steam passes through a manifold in the roof of the drum into the pendant superheater (19) where its temperature and pressure increase rapidly to around 200 bar and 570°C, sufficient to make the tube walls glow a dull red.

6. The steam is piped to the high-pressure turbine (11), the first of a three-stage turbine process.

7. A steam governor valve (10) allows for both manual control of the turbine and automatic set point following.

 8. The steam is exhausted from the high-pressure

turbine, and reduced in both pressure and temperature, is returned to the boiler reheater (21).

 9. The reheated steam is then passed to the

intermediate pressure turbine (9), and from there passed directly to the low pressure turbine set

(6).

10. The exiting steam, now a little above its boiling point, is brought into thermal contact with cold water (pumped in from the cooling tower) in the condensor (8), where it condenses rapidly back into water, creating near vacuum-like conditions inside the condensor chest. 

11. The condensed water is then passed by a feed pump (7) through a deaerator (12), and prewarmed,

first in a feed heater (13) powered by steam drawn from the high pressure set, and then in the economiser (23), before being returned to the boiler drum. 

12. The cooling water from the condensor is sprayed inside a cooling tower (1), creating a highly visible plume of water vapor, before being pumped back to the condensor (8) in cooling water cycle.

13. The three turbine sets are coupled on the same shaft as the three-phase electrical generator (5) which generates an intermediate level voltage (typically 20-25 kV).

 14. This is stepped up by the unit transformer (4) to a voltage more suitable for transmission (typically 250-500 kV) and is sent out onto the three-phase transmission system (3). 

15. Exhaust gas from the boiler is drawn by the induced draft fan (26) through an electrostatic precipitator (25) and is then vented through the chimney stack (27).

Advantages and Advantages and Disadvantages of Coal for Disadvantages of Coal for Power PlantsPower Plants

Advantages of Coal as Power Advantages of Coal as Power Plant FuelPlant Fuel

Reliability. Affordability. Abundance. Known technologies. Safety. 

ReliabilityReliability

Coal’s ability to supply power during peak power demand either as base power or as off-peak power is greatly valued as a power plant fuel

AffordabilityAffordabilityEnergy produced from coal fired

plants is cheaper and more affordable than other energy sources.

AbundanceAbundanceThere are approximately over

300 years of economic coal deposits still accessible.

Known technologies. Known technologies. The production and use of coal as

a fuel are well understood, and the technology required in producing it is constantly advancing.

SafetySafetyA coal power plant's failure is

certainly not likely to cause catastrophic events such as a nuclear meltdown would. Additionally, the welfare and productivity of coal industry employees has greatly improved over the years

Disadvantages of Coal-Fired Disadvantages of Coal-Fired Power PlantsPower Plants  

Greenhouse gas emissions.Mining destruction.Generation of millions of tons of

waste. Emission of harmful substances. 

Greenhouse gas Greenhouse gas emissionsemissionsIt cannot be denied that coal

leaves behind harmful byproducts upon combustion

Mining destructionMining destructionMining of coal not only results in

the destruction of habitat and scenery, but it also displaces humans as well.

Generation of millions of Generation of millions of tons of wastetons of wasteMillions of tons of waste products

which can no longer be reused are generated from coal fired plants. Aside from the fact that these waste products contribute to waste disposal problems, these also contain harmful substances.

Emission of harmful Emission of harmful substances. substances. Thermal plants like coal fired

plants emit harmful substances to the environment. These include mercury, sulfur dioxide, carbon monoxide, mercury, selenium, and arsenic

WORLD BANK GROUPWORLD BANK GROUP

Effective July 1998-428 PROJECT GUIDELINES: INDUSTRY SECTOR

GUIDELINES elsewhere, to mitigate the impact of these emissions and will also agree on the associated emissions requirements.

Any rehabilitation that involves a shift in fuel type—i.e., from coal or oil to gas, as distinguished from a change from one grade or quality of coal or oil to another—will be subject to the same basic emissions guidelines as would apply to a new plant burning the same fuel.

Environmental AuditEnvironmental Audit

• Review the actual operating and environmental performance of the plant in relation to its original design parameters.

• Examine the reasons for poor performance to identify measures that should be taken to address specific problems or to provide a basis for more appropriate assumptions about operating conditions in the future—for example, with respect to average fuel characteristics.

• Assess the scope for making improvements in maintenance and housekeeping inside and around the plant

• Evaluate the readiness and capacity of the plant’s emergency management systems to cope with incidents varying from small spills to major accidents (check storage of flammables, safe boiler and air pollution control system operation, and so on).

• Examine the plant’s record with respect to worker safety and occupational health.

Environmental AssessmentEnvironmental Assessment

An environmental assessment of the proposed rehabilitation should be carried out early in the process of preparing the project in order to allow an opportunity to evaluate alternative rehabilitation options before key design decisions are finalized.

Assessment points:Assessment points:• Ambient environmental quality in the air shed or water basin

affected by the plant, together with approximate estimates of the contribution of the plant to total emissions loads of the main pollutants of concern

• The impact of the plant, under existing operating conditions and under alternative scenarios for rehabilitation, on ambient air and water quality affecting neighbouring populations and sensitive ecosystems

• The likely costs of achieving alternative emissions standards or other environmental targets for the plant as a whole or for specific aspects of its operations

• Recommendations concerning a range of cost effective measures for improving the environmental performance of the plant within the Thermal Power: Rehabilitation of Existing Plants 429 framework of the rehabilitation project and any associated emissions standards or other requirements implied by the adoption of specific measures.

Emissions GuidelinesEmissions Guidelines• Normally, the energy conversion efficiency of the

plant should be increased by at least 25% of its current level.

• Baseline emissions levels for particulate matter, nitrogen oxides, and sulfur oxides should be computed.

• An analysis of the feasibility (including benefits) of switching to a cleaner fuel should be conducted. Gas is preferred where its supply can be assured at or below world average prices. Coal with high heat content and low sulfur content is preferred over coal with high heat content and high sulfur content, which in turn is preferred over coal with low heat content and high sulfur content.

• Washed coal should be used, if feasible.• Low-NOx burners should be used, where feasible.• Either the emissions levels recommended for new

plants, or at least a 25% reduction in baseline level, should be achieved for the pollutant being addressed by the rehabilitation project.

• The maximum emissions level for PM is 100 milligrams per normal cubic meter (mg/Nm3 ), but the target should be 50 mg/Nm3 . In rare cases, an emissions level of up to 150 mg/Nm3 may be acceptable.

• SO2 emissions levels should meet regional load targets. Cleaner fuels should be used, to avoid short-term exposure to sulfur dioxide.

Monitoring and ReportingMonitoring and Reporting

Monitoring and reporting requirements for a thermal power plant that has been rehabilitated should be the same as those for a new thermal power plant of similar size and fuel type.