Power plants

Power plants

What is a power plant?

Energy plays a unique role in economic growth, social welfare, and improving a society’s quality of life and security. Global studies show a direct relationship between the development of a country and the amount of energy it consumes. Therefore, the access of developing countries to new energy sources is of particular importance to progress and improve their economic situation. Meanwhile, electrical energy is one of the main and fundamental factors in the growth and prosperity of the industrial, economic, and social sectors, so it can be said that one of the indicators of the evaluation and progress of countries is the index of increasing the capacity of electrical energy production and distribution. Various power plants and technologies are used to produce electricity.

A power plant is a set of industrial facilities in which other energies are used to produce electrical energy. Power plants use generators to convert energy from other forms, such as fossil fuel, chemical energy, renewable energy, nuclear energy, gravitational potential energy, etc., into electrical power (in fact, these rotating energy machines convert mechanical energy into electrical energy).

Hydropower

One of the most common power plants is hydroelectric power, which converts water’s kinetic energy and gravitational potential into electrical energy by building dams along the river. In hydroelectric energy production, water collected or stored at higher altitudes is directed to lower altitudes through large pipes or tunnels. The height difference in the water path is called “head.” The water flow at the end of the course causes the turbines to rotate. This issue has been studied simply under the title of work and energy theorem in physics.

Hydroelectric-generating-station1

The turbines, in turn, drive the generators that convert the mechanical energy of the turbines into electricity. Then the transformers raise the generated voltage level to a standard deck for transmission to the place of consumption. The area where the turbines, generators, pipes, and tunnels connected to them are located is called a power plant.

Hydroelectric power plants are usually built next to dams, where water from rivers is collected. For this reason, the water level behind the dam has risen and raised the head as much as possible. The potential energy that can be extracted from a given volume of water is directly proportional to the head or height of the water. Simply put, a dam with a higher head produces more electricity in an equal volume of water than a dam with a lower head.

Steam power plant

If steam power is used to rotate the generator, the power plant is known as a steam power plant. A simple steam power plant produces energy based on the Rankine cycle.

In the first stage, water is injected into the “boiler” using high-pressure water pumps. The high-pressure water in the boiler absorbs heat and becomes “superheat steam” with high pressure. The steam, which has a lot of energy, flows along the “turbine” (a mechanical device that converts the flow of fluid energy into mechanical energy) and rotates it.

To make full use of steam energy, three stages of “low-pressure turbine,” “intermediate pressure turbine,” and “high-pressure turbine” have been considered. The “shaft” of the turbine is connected to the generator shaft, So when the turbine shaft moves, the generator rotates, and electrical energy is produced.

During this process, the steam loses its energy. Then the saturated low-pressure vapor passes through the “condenser” and turns into a liquid. After that, the water is directed to the pumps of the first stage, and the cycle is complete. Therefore, this cycle is constantly repeated to produce energy.

Schematic steam power plant

Gas plant

A gas power plant is a power plant in which the working fluid is air and works based on the Brayton cycle. This power plant has a gas turbine and has three main components: compressor, combustion chamber, and gas turbine. The rotors work in these power plants because the incoming fluid enters the compressor, and after compression and a little heating, it enters the combustion chamber. The fuel burns it, and then the resulting hot air does the work of the same hot steam in the steam turbine. It enters the gas turbine and turns the generator. The compressor used in the gas power plant is like a turbine. Gas turbines used in power plants and industries have many advantages. The size of the gas turbine power plant is smaller than the steam power plant, and its initial cost to produce each unit of power is lower than the cost of the steam power plant.

In recent years, a kind of awareness and attention to the excessive increase in energy consumption and the fact that fossil fuels are perishable has caused comprehensive studies at the global level to reduce the amount of energy consumption and also reducing the costs of energy production, without causing damage to the development process of countries. Accept These studies have led to the emergence of programs and strategies called “energy management.”

The traditional model of electricity production is based on operating a limited number of large-scale central power plants and then transmitting and distributing the energy to consumers who may be thousands of kilometers away from the production site.

CFD analysis in power plants

Types of fluid flow and heat transfer have a very colorful presence in power plants. Mirror, thermal, wind, water, and tidal, solar power plants each generate electricity in some way using fluid flow. The physical phenomena governing almost all power plants (except the simple solar power plant) are related to the movement of working fluids (such as water, steam, gas, and air) and reactive currents in boilers. Depending on the type of power plant, the issues involved with computational fluid dynamics are different. Still, in all power plants, CFD, as the primary fluid analysis tool, plays the primary role in analyzing and improving the design of equipment and power plant space.

Thermal power plants

The most significant difference in the type of thermal power plants is their fuel consumption. All power plants that use coal, liquid fuels such as diesel, gas, nuclear fuels, and Heliostat solar power plants are considered thermal power plants. The working fluid in most thermal power plants (except gas) is steam. In general, in this type of power plant, there are different regimes of water and steam flow types. First, the water enters the boiler through the pumps, after heating and turning into superheated steam (Super-Heated Steam) in the boiler, it goes to the steam turbine which is connected to a generator, and by turning the turbine and reducing its energy, it becomes a two-phase flow consisting of steam. Water is converted into water, and finally, it turns into the water in the condenser. But in gas-fired power plants, the driving factor of the turbine is the exhaust gases caused by the combustion of gas in the combustion chamber. Combined cycle power plants, as their name suggests, use steam and gas turbines using both water vapor fluid and combustion exhaust gases.

Since the application of CFD is intended, the details of the operation of these types of power plants are omitted, and only the cases of CFD application in them are satisfied. Boilers, chimneys, turbines – including steam turbines, gas turbines (for gas power plants), or a combination of steam and gas turbines (for combined cycle power plants) -, condensers, and cooling towers are the most important parts of thermal power plants in which the use of CFD can be beneficial.

Gas steam combined cycle power plant

Now we discuss several cases of CFD application in different components of power plants

CFD analysis in boilers

– Simulating, studying, and checking the high-pressure flow of water entering the boilers and evaluating the performance of the relevant equipment

– Simulating the flow in the water wall and checking its performance as well as optimizing it

Combustion simulation and study and review of multiple modes for parametric evaluation of combustion equipment and conditions

– Simulating the absorption of heat caused by combustion by water and turning it into steam

– Simulation of separating water from water vapor in a Steam Drum

– Solving the flow field, checking heat transfer in superheaters, and checking their performance and optimization

-Simulation of reheating of steam passing through high-pressure turbines and re-entry of heated steam into medium-pressure turbines

It is necessary to explain that the simultaneous simulation of all the above phenomena is possible with all the equipment and available space, and the only problem is the hardware limitation of the processors.

CFD analysis of chimneys

– Simulating and checking the behavior of the water injection system and checking the performance of related equipment

– Simulating, studying, and checking the performance of the dry injection desulfurization system (Dry Injection Desulfurization: DID)

– Solving the flow field passing through different types of Bags, Electrostatic Precipitators, or Dual Action filters and evaluating their performance, simulating and studying the flow behavior of the Recirculation Zone in the Cavity

– Calculation and prediction of temperature, speed, pressure, and change of the type of hot gases exiting from the boilers to the exit from the chimneys

CFD analysis of steam or gas turbines

– Study, behavior, and optimization of the turbine rotor and stator blade sections

– Simulation and optimization of blades of rotors and compressors as well as turbine stages

– Thermal analysis and cooling simulation in turbine blades, especially gas turbines

– Simulation and investigation of flow behavior and reduction of kinetic energy loss, pressure, and temperature in low-pressure turbines, intermediate-pressure turbines, and high-pressure turbines separately or together

– Calculation and optimization of the degree of reaction (Degree Of Reaction: D.O.R) in turbines

– Simulating the flow in Flow Governing and checking its performance to keep the rotational speed of different high-pressure, medium-pressure, and low-pressure turbines constant.

– Simulation of two-phase flow (water and Steam) in turbines using multi-phase models based on Wet Steam to minimize water vapor droplets.

CFD analysis in condensers and cooling towers

– Simulating, studying, and checking the output of hot water from the condenser and its entry into the spray nozzles in the cooling towers and evaluating the performance of the equipment used.

– Simulation of heat transfer with free movement in the cooling tower with the phase change of hot water to water vapor

– Flow simulation in drift eliminators and cooling fills and their performance evaluation and optimization

– Simulating the flow of cool water from the excellent water pool to the condensers

– Simulating the heat transfer between the cold water entering from the cooler and the hot water steam exiting from the turbine in the condensers and checking the performance of the heat exchangers of the condensers.

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