Power plants - engineering

Superheater

A greater quantity of steam can be generated from a given quantity of water by superheating it. As the fire is burning at a much higher temperature than the saturated steam it produces, far more heat can be transferred to the once-formed steam by superheating it and turning the water droplets suspended therein into more steam and greatly reducing water consumption.

Bottom ash collection and disposal

At the bottom of the furnace, there is a hopper for collection of bottom ash. This hopper is kept filled with water to quench the ash and clinkers falling down from the furnace. Arrangements are included to crush the clinkers and convey the crushed clinkers and bottom ash to on-site ash ponds, or off-site to landfills. Ash extractors are used to discharge ash from municipal solid waste-fired boilers.

Efficiency of a combined cycle plant

By combining both gas and steam cycles, high input temperatures and low output temperatures can be achieved. The efficiency of the cycles add, because they are powered by the same fuel source. So, a combined cycle plant has a thermodynamic cycle that operates between the gas-turbine's high firing temperature and the waste heat temperature from the condensers of the steam cycle. This large range means that the Carnot efficiency of the cycle is high. The actual efficiency, while lower than the Carnot efficiency, is still higher than that of either plant on its own.

Co2 emissions equation

CO2 emissions = capacity x capacity factor x heat rate x emission intensity x time

Coal

Coal is delivered by highway truck, rail, barge, collier ship or coal slurry pipeline. Generating stations adjacent to a mine may receive coal by conveyor belt or massive diesel-electric-drive trucks. Coal is usually prepared for use by crushing the rough coal to pieces less than 2 inches (5 cm) in size

Coal term

Coal is the most abundant fossil fuel on the planet, and widely used as the source of energy in thermal power stations and is a relatively cheap fuel. Coal is an impure fuel and produces more greenhouse gas and pollution than an equivalent amount of petroleum or natural gas

Different fuels

Coal, Natural gas, and Oil

Water treatment

Feed water for boilers needs to be as pure as possible with a minimum of suspended solids and dissolved impurities which cause corrosion, foaming and water carryover. The most common options for demineralization of boiler feedwater are reverse osmosis (RO) and ion exchange

Fly ash

Fly ash is captured and removed from the flue gas by electrostatic precipitators or fabric bag filters (or sometimes both) located at the outlet of the furnace and before the induced draft fan. The fly ash is periodically removed from the collection hoppers below the precipitators or bag filters. Generally, the fly ash is pneumatically transported to storage silos and stored on site in ash ponds, or transported by trucks or railroad cars to landfills,

waste water

Fossil-fuel power stations, particularly coal-fired plants, are a major source of industrial wastewater. Wastewater streams include flue-gas desulfurization, fly ash, bottom ash and flue gas mercury control. Plants with air pollution controls such as wet scrubbers typically transfer the captured pollutants to the wastewater stream.

Managing low-grade fuels in turbines

Gas turbines burn mainly natural gas and light oil. Crude oil, residual, and some distillates contain corrosive components and as such require fuel treatment equipment. In addition, ash deposits from these fuels result in gas turbine deratings of up to 15%. They may still be economically attractive fuels however, particularly in combined-cycle plants.

Advantages of hydroelectricity

Hydroelectricity is very powerful and safe, and produces no waste. An important advantage of hydroelectric dams is their ability to be used as a peaking power plant. When the electricity demand declines, the dam simply stores more water. Water that has been stored in a reservoir can be released (let go) when needed, so the energy can be made quickly.

1st law of thermodynamics

In a closed system (i.e. there is no transfer of matter into or out of the system), the first law states that the change in internal energy of the system (ΔUsystem) is equal to the difference between the heat supplied to the system (Q) and the work (W) done by the system on its surroundings

More design principles

In a thermal power station, water is the working medium. High pressure steam requires strong, bulky components. High temperatures require expensive alloys made from nickel or cobalt, rather than inexpensive steel. These alloys limit practical steam temperatures to 655 °C while the lower temperature of a steam plant is fixed by the temperature of the cooling water. With these limits, a steam plant has a fixed upper efficiency of 35-42%.

Dual pressure boiler

In order to remove the maximum amount of heat from the gasses exiting the high temperature cycle, a dual pressure boiler is often employed.[4] It has two water/steam drums. The low-pressure drum is connected to the low-pressure economizer or evaporator. The low-pressure steam is generated in the low temperature zone of the turbine exhaust gasses. The low-pressure steam is supplied to the low-temperature turbine. A super heater can be provided in the low-pressure circuit.

Boiler operations

Plants designed for lignite (brown coal) are used in locations as varied as Germany, Victoria, Australia, and North Dakota. Lignite is a much younger form of coal than black coal. It has a lower energy density than black coal and requires a much larger furnace for equivalent heat output. Such coals may contain up to 70% water and ash, yielding lower furnace temperatures and requiring larger induced-draft fans. The firing systems also differ from black coal and typically draw hot gas from the furnace-exit level and mix it with the incoming coal in fan-type mills that inject the pulverized coal and hot gas mixture into the boiler.

coal fired plant efficiency

The 4 main types of coal-fired power stations in increasing order of efficiency are subcritical, supercritical, ultra-supercritical, and cogeneration (also called combined heat and power or CHP).[44] Subcritical is the least efficient type, however recent innovations have allowed retrofits to older subcritical plants to meet or even exceed the efficiency of supercritical plants.[

Rankine cycle

The Rankine cycle is an idealized thermodynamic cycle describing the process by which certain heat engines, such as steam turbines or reciprocating steam engines, allow mechanical work to be extracted from a fluid as it moves between a heat source and heat sink.

Ash disposal

The ash is often stored in ash ponds. Although the use of ash ponds in combination with air pollution controls (such as wet scrubbers) decreases the amount of airborne pollutants, the structures pose serious health risks for the surrounding environment.[13] Power utility companies have often built the ponds without liners, especially in the United States, and therefore chemicals in the ash can leach into groundwater and surface waters.

Disadvantages of hydroelectricity

The building of large dams to hold water can damage the environment. In 1983, the Australian government stopped the Tasmanian state government from building a dam on the Gordon River in Tasmania after a huge public protest.[2] The dam would have flooded the Franklin River. The Three Gorges Dam in China is the world's largest hydroelectricity project, and the world's largest power plant of any kind. The dam has flooded a huge area, meaning that 1.2 million people had to be moved. Scientists are concerned about many problems with the dam, such as pollution, silt, and the danger of the dam wall breaking.[3]

Energy transfers in coal power plants

The coal is usually pulverized and then burned in a pulverized coal-fired boiler. The furnace heat converts boiler water to steam, which is then used to spin turbines that turn generators. Thus chemical energy stored in coal is converted successively into thermal energy, mechanical energy and, finally, electrical energy.

Design Principles

The efficiency of a heat engine, the fraction of input heat energy that can be converted to useful work, is limited by the temperature difference between the heat entering the engine and the exhaust heat leaving the engine.

how to keep 60 cycle AC

The grid provides energy if any power plants trip and the other power plants take up the load

heat into mechanical energy

The second law of thermodynamics states that any closed-loop cycle can only convert a fraction of the heat produced during combustion into mechanical work. The rest of the heat, called waste heat, must be released into a cooler environment during the return portion of the cycle

Surface condenser shell

The shell is the condenser's outermost body and contains the heat exchanger tubes. The shell is fabricated from carbon steel plates and is stiffened as needed to provide rigidity for the shell. When required by the selected design, intermediate plates are installed to serve as baffle plates that provide the desired flow path of the condensing steam. The plates also provide support that help prevent sagging of long tube lengths.

Steam generator components

The steam generator or steam boiler is an integral component of a steam engine when considered as a prime mover. However it needs to be treated separately, as to some extent a variety of generator types can be combined with a variety of engine units. A boiler incorporates a firebox or furnace in order to burn the fuel and generate heat. The generated heat is transferred to water to make steam, the process of boiling. This produces saturated steam at a rate which can vary according to the pressure above the boiling water. The higher the furnace temperature, the faster the steam production. The saturated steam thus produced can then either be used immediately to produce power via a turbine and alternator, or else may be further superheated to a higher temperature; this notably reduces suspended water content making a given volume of steam produce more work and creates a greater temperature gradient, which helps reduce the potential to form condensation. Any remaining heat in the combustion gases can then either be evacuated or made to pass through an economizer, the role of which is to warm the feed water before it reaches the boiler.

Basic combined cycle

The thermodynamic cycle of the basic combined cycle consists of two power plant cycles. One is the Joule or Brayton cycle which is a gas turbine cycle and the other is Rankine cycle which is a steam turbine cycle.[4] The cycle 1-2-3-4-1 which is the gas turbine power plant cycle is the topping cycle. It depicts the heat and work transfer process taking place in high temperature region.

A boiler or steam generator

a device used to create steam by applying heat energy to water. Although the definitions are somewhat flexible, it can be said that older steam generators were commonly termed boilers and worked at low to medium pressure (7-2,000 kPa or 1-290 psi) but, at pressures above this, it is more usual to speak of a steam generator.

fossil fuel power station

a thermal power station which burns a fossil fuel, such as coal or natural gas, to produce electricity

coal-fired power station or coal power plant

a thermal power station which burns coal to generate electricity. Coal-fired power stations generate over a third of the world's electricity but cause hundreds of thousands of early deaths each year, mainly from air pollution.

Brayton Cycle

a thermodynamic cycle named after George Brayton that describes the workings of a constant-pressure heat engine. The original Brayton engines used a piston compressor and piston expander, but more modern gas turbine engines and airbreathing jet engines also follow the Brayton cycle.

combined cycle power plant

an assembly of heat engines that work in tandem from the same source of heat, converting it into mechanical energy. On land, when used to make electricity the most common type is called a combined cycle gas turbine (CCGT) plant.

Hydroelectricity

electricity made by generators that are pushed by the movement of water. It is usually made with dams that block a river to make a reservoir or collect water that is pumped there.

steam turbine power plant

fuel is burned in a furnace and the hot gasses flow through a boiler. Water is converted to steam in the boiler; additional heating stages may be included to superheat the steam

Nuclear power plant process

he coolant may be water or gas, or even liquid metal, depending on the type of reactor. The reactor coolant then goes to a steam generator and heats water to produce steam. The pressurized steam is then usually fed to a multi-stage steam turbine. After the steam turbine has expanded and partially condensed the steam, the remaining vapor is condensed in a condenser. The condenser is a heat exchanger which is connected to a secondary side such as a river or a cooling tower. The water is then pumped back into the steam generator and the cycle begins again. The water-steam cycle corresponds to the Rankine cycle.

2nd law of thermodynamics

indicates the irreversibility of natural processes, and, in many cases, the tendency of natural processes to lead towards spatial homogeneity of matter and energy, and especially of temperature. It can be formulated in a variety of interesting and important ways. One of the simplest is the Clausius statement, that heat does not spontaneously pass from a colder to a hotter body.

Heat sink

is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, thereby allowing regulation of the device's temperature

air compressor

is a pneumatic device that converts power (using an electric motor, diesel or gasoline engine, etc.) into potential energy stored in pressurized air (i.e., compressed air). By one of several methods, an air compressor forces more and more air into a storage tank, increasing the pressure. When the tank's pressure reaches its engineered upper limit, the air compressor shuts off. The compressed air, then, is held in the tank until called into use.

nuclear power plant

is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power stations, heat is used to generate steam that drives a steam turbine connected to a generator that produces electricity.

gas turbine

it combines the Brayton cycle of the gas turbine with the Rankine cycle of the HRSG. The turbines are fueled either with natural gas or fuel oil.

Nuclear decommissioning

the dismantling of a nuclear power station and decontamination of the site to a state no longer requiring protection from radiation for the general public. The main difference from the dismantling of other power stations in the presence of radioactive material that requires special precautions to remove and safely relocate to a waste repository.