Industrial production is inseparable from coal-fired boilers. Do you understand the working principles and types of coal-fired boilers? This guide provides you with comprehensive information about coal-fired boilers.
What is a Coal Fired Boiler?
A coal-fired boiler is a type of boiler that uses coal as its fuel source. Coal is a fossil fuel that is made up of the remains of plants that have been compressed over millions of years. When coal is burned, it releases heat energy that can be used to generate steam. This steam can then be used to drive a turbine to generate electricity or to heat water for industrial or residential purposes.
Types of Coal Fired Boilers
• Layer-fired boiler: A layer-fired boiler is a boiler that spreads coal particles evenly on a fixed or moving grate, and then controls the supply and distribution of air to cause the coal particles to undergo oxidation-reduction reactions of varying degrees in different areas.
Advantages: simple structure, stable operation, suitable for coal of various qualities.
Disadvantages: lower efficiency, more dust and nitrogen oxide emissions.
• Fluidized bed boiler: Fluidized bed boiler is a kind of boiler that mixes coal particles with inert media (such as sand) to form a liquid-like fluidized state under the action of high-speed airflow, and then performs high-efficiency and low-pollution boiling in this state. Burning boiler.
Advantage: It can adapt to various types and qualities of coal, achieve low-temperature and efficient combustion, and reduce the generation of emissions.
Disadvantages: complex structure, high operating costs, and high operational requirements.
• Circulating fluidized bed boiler: A circulating fluidized bed boiler is a boiler that is based on a fluidized bed boiler and is equipped with a cyclone separator and a return device to circulate some incompletely burned solid particles into the boiler for re-combustion. .
Advantages: Can further improve efficiency and reduce emissions, while expanding boiler capacity and adaptability.
Disadvantages: The structure is more complex, the operation is more difficult, and the requirements for equipment and materials are higher.
• Vertical tube boiler: A vertical tube boiler is a boiler in which water-cooled wall tubes are installed in a vertical direction and perform forced convection circulation within the tubes.
Advantages: Small footprint, compact structure, quick start and stop.
Disadvantages: Water-cooled wall tubes are easily corroded by high-temperature steam and ash, making maintenance difficult. They are suitable for small and medium-sized boilers.
• Horizontal tube boiler: A horizontal tube boiler is a boiler in which water-cooled wall tubes are installed in the horizontal direction and perform natural convection circulation within the tubes.
Advantages: The water cooling wall tube is less eroded and easier to repair. It is suitable for large and extra-large boilers.
Disadvantages: large floor space, complex structure, slow start and stop.
How do Coal Fired Boilers Work?
The working principle of a coal-fired boiler is as follows: coal is fed into the furnace in the boiler and ignited by an igniter to produce high-temperature flames and flue gases. The flame and flue gas flow inside the boiler and transfer heat with the water-cooled tube wall, causing the water temperature to rise. When the water temperature reaches a certain level, steam or hot water will be formed and transported through pipes to where it is needed. Steam or hot water can be used to drive steam turbines or other equipment, producing mechanical or electrical energy. At the same time, the generated waste gas is discharged into the atmosphere after being treated by environmental protection facilities such as dust removal, desulfurization, and denitrification.
The Structure of Coal Fired boiler
Main body
· Spirally corrugated tube
· Arched tube plate
· smoke separation room
· Independent self support and New arch
· Large-sized down pipe
· Front and rear furnace door for watching fire
· Grating type Steam and water separation device
· Two-wing Flue
Advantages and Disadvantages of Coal Fired Boilers
Advantages
Low Cost: Coal is a relatively cheap source of fuel. This makes coal-fired boilers an economical choice for large-scale applications such as power generation and industrial heating.
Reliability: Coal-fired boilers are generally reliable and have a long service life. This makes them a good choice for applications that require a reliable source of energy.
Widely available: Coal is a widely available fuel source. This makes coal-fired boilers ideal for use around the world.
Disadvantages
Air pollution: Coal combustion produces air pollutants such as sulfur dioxide, nitrogen oxides and particulate matter. These pollutants can cause respiratory problems, acid rain and climate change. To reduce air pollution, coal-fired boilers are often equipped with pollution control equipment.
Water pollution: Coal ash, a byproduct of coal combustion, can pollute waterways. Coal ash is often stored in ash storage sites, but if these sites leak, they could contaminate nearby water supplies.
Land Use: Coal mining damages the environment. Coal mines often require large tracts of land, which can have an impact on wildlife and ecosystems.
Coal Fired Boiler Application
Coal-fired boiler is an industrial boiler that uses coal as fuel and is widely used in power generation, heating, chemical industry, metallurgy, papermaking and other industries. Providing heat and steam to industrial production machines.
Introduction to Three-Pass Flue Gas From Coal Fired Boilers
The three-pass flue gas of coal-fired boilers refers to the three-cycle heat transfer process of flue gas generated in coal-fired boilers during the combustion process. This process helps improve the thermal efficiency of the boiler and reduce energy waste.
The first pass --furnace
Boiler operation is automated, the fuel is transported to the chain grate through the grate reducer running, and burned on the chain grate, so the furnace forms the first process
The second pass - two-wing flue duct
The high-temperature flue gas generated by combustion is transferred to the two-wing flue above the furnace through the rear smoke box, that is, the second return flue formed by the bottom of the water pipe and the furnace
The third pass - fire tube
It enters the threaded smoke pipe through the front smoke box, and enters the chimney through the economizer and dust collector, and is discharged to the atmosphere.
Coal Fired Boiler System
The boiler system consists of combustion system, steam and water system, and control system.
Coal-fired boiler combustion system: The coal-fired steam boiler combustion system is equipped with combustion system equipment based on the fuel characteristics and steam capacity of the boiler, which can realize automatic combustion and automatic slag removal functions. The combustion system equipment consists of coal feeder, chain grate, air distribution equipment, coal hopper in front of the furnace, grate reducer and slag removal equipment, etc.
The soda and water system consists of a water supply part and a steam part.
Feed water part: Feed water refers to the water provided to the boiler for steam conversion. Feedwater introduces water into the boiler and controls it automatically to meet steam demand.
Steam Section: The steam section is the part of the boiler that collects and regulates the steam produced by the boiler. Valve and pressure gauge controllers are used to monitor and regulate steam pressure.
Coal-fired steam boiler control system
The boiler control system is a collection of boiler electrical control components. It is the center for collecting and processing boiler operating signals, and is also an operating platform that sends execution instructions to each execution unit of the boiler.
Coal-fired boilers are widely used in all industries, including food, dairy, beverages, breweries, paper mills, textiles, clothing, edible oil factories, chemical plants, packaging plants, central heating, hotels, and more.
Coal-fired chain grate boiler
Steam capacity: 1-75t/h
Rated pressure: 1-2.5MPa
Thermal efficiency: 82%
Type: DZL, SZL, DHL, SHL
Fuel: Bituminous coal, anthracite, lean coal, and more
Coal enters the chain grate through the coal hopper and starts to burn in the furnace as the chain grate moves. The burned coal slag is discharged into the slag well at the end of the chain grate as the chain grate moves. Coal-fired chain grate boilers have certain requirements for the quality of coal.
Fuel: Bituminous coal, anthracite, lean coal, and more
Coal fuel falls onto the grate from the coal hopper and burns. The high-temperature flue gas is reflected forward by the rear arch and enters the furnace. After heat exchange in the radiation heating area, it enters the convection heating area, then into the waste heat boiler, then into the air preheater, and finally into the dust collector. After the dust collector is sucked by the induced draft fan, the flue gas is finally discharged into the atmosphere through the chimney.
The coal-fired circulating fluidized bed boiler adopts a large furnace and low flow rate design to reduce erosion and wear, extend the residence time of coal particles in the furnace, and ensure complete combustion of fuel. To prevent fly ash from entering the economizer, all parts prone to ash accumulation are equipped with soot blowing interfaces, and various soot blowers are available. The serpentine tube economizer and air preheater increase the heating area, absorb the flue gas temperature, and improve the thermal efficiency of the boiler.
Coal-Fired Power Plant
A coal-fired power plant is a thermal power plant that generates electricity by burning coal to produce steam. The steam produced by the combustion of coal in the boiler is used to drive a steam turbine connected to a generator to generate electricity. Coal is a widely distributed fossil fuel, making it a popular choice for power generation.
The power generation process in a coal-fired power plant can be divided into several stages:
1. Fuel Preparation: Coal is pulverized into fine powder and then mixed with air to improve combustion efficiency. The pulverized coal is then stored in coal silos.
2. Combustion: The pulverized coal is fed into the boiler and burned at high temperatures. During the combustion process, thermal energy is released, which is used to convert water into steam.
3. Steam Generation: The heat generated during the combustion process is transferred to the water pipes surrounding the boiler, converting the water into steam. The steam produced is at high pressure and temperature.
4. Steam Turbine: High-pressure steam from the boiler is directed onto the blades of the steam turbine. As the steam flows over the turbine blades, it causes them to spin.
5. Generator: The rotating turbine shaft is connected to a generator, which converts the mechanical energy produced by the turbine into electrical energy.
6. Cooling System: The steam from the turbine leaves the turbine at lower pressure and temperature. It then goes to the condenser, where it is cooled and converted back into water.
7. Water Treatment: After purification, the condensed water is returned to the boiler and converted into steam again, and the cycle continues.
Coal-fired power plants have been widely used for decades due to their reliability and cost-effectiveness. However, they also have some environmental drawbacks. The combustion of coal releases various pollutants into the atmosphere, including sulfur dioxide (SO2), nitrogen oxides (NOx), and carbon dioxide (CO2), which contribute to air pollution and climate change. To mitigate these environmental impacts, modern coal-fired power plants employ advanced technologies such as flue gas desulfurization systems to remove sulfur dioxide and selective catalytic reduction systems to reduce nitrogen oxide emissions. In summary, coal-fired power plants are thermal power plants that use coal as a fuel source to generate electricity. While it is a reliable and cost-effective option for power generation, efforts are being made to minimize its environmental impact through the use of advanced emission control technologies.
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