Air Pollution in The Use of Coal-fired Boilers Among the air pollution problems, the main pollution problems existing in the operation of coal-fired boilers can be divided into two aspects: gas and solid impurities. It focuses on the analysis of these two aspects and coal fired boiler types.
Gas From the point of view of the constituent elements of coal, it is a kind of mineral resource formed by the long-term evolution of underground ore. It is mainly composed of carbon, oxygen and sulfur. Cost is relatively low, mining difficulty is not high. At the same time, coal has a low flash point and is easy to burn, making it a common resource for industrial production in cities and for heating rural residents. Based on the structural characteristics of coal itself, in the actual combustion process, will generate carbon dioxide, sulfur dioxide and other gases. Sulfur dioxide is the main gas that produces acid rain and causes climate warming. Therefore, at present, technicians are mainly studying how to remove sulfur from coal.
Impurities Coal is also divided into many types, different types of quality is not the same, consumption. The economic cost of fee also has certain diversity. This makes many areas in the use of coal to provide heat for the boiler, out of consideration of economic benefits, often choose some cheap coal. This kind of coal is prone to soot particles when burned, which not only pollutes the environment, but also has great harm to human health. Based on this, the relevant technicians should not only solve the problem of high sulfur content in coal, but also focus on how to remove impurities and eliminate soot particles.
Topics
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1.Countermeasures for Flue Gas Pollution of Coal-fired Boilers
Dust Removal Technology
Flue Gas Desulphurization Technology
Wet Desulphurization and Precipitator
Flue Gas Denitrification and Low Carbon Combustion
Smoke Pollution Clearance and Coal Control
Efficient Desulphurization System
Coal-fired Boiler for Industrial
Coal-fired Boiler Power Plant
Advantages of Coal Combustion
Disadvantages of Coal Combustion
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1. Countermeasures for Flue Gas Pollution of Coal-fired Boilers
About the two major air pollution problems mentioned above, they are respectively discussed below and more appropriate solutions are proposed.
1.1 Dust Removal Technology of Flue Gas from Coal-fired Boiler
Mechanical Dust Remover
The basic principle of mechanical dust removal is to design a kind of machine according to the different quality and volume of dust particles to achieve the purpose of dust removal. Among them, cyclone dust collector is the most widely used dust removal machinery. Among all dust removal machinery, its advantages are relatively high cost performance, simple operation, low environmental requirements, good corrosion resistance, high dust removal efficiency. The disadvantage is that it can only act on large particle dust, but not on small particle dust. Therefore, the use of cyclone dust remover still has certain limitations.
The Filter Type Dust Remover
Another kind of commonly used dust remover is the filter type dust remover, its principle is to use the filter net to prevent the dust in the flue gas from entering the atmosphere, so as to achieve the purpose of dust removal. According to the pollution situation, the filter dust can be selected including air filter, bag dust and particle layer dust three methods. Among them, the highest dust removal efficiency is bag dust collector. Although bag-type dust collector belongs to traditional dust collector, with the development of new technology and new technology, its structure type has been innovated, the filter material and the way of ash removal have been constantly improved, the dust removal performance has been improved, the scope of application has been expanded, and the role it plays has been more and more important.
Electric Dust Remover
When dealing with a large amount of flue gas, electric dust removal method is generally used. The relatively high efficiency of electric dust removal is based on the principle of using dust particles with their own electrostatic power to achieve the purpose of dust removal. Because it directly acts on dust particles, the air flow resistance is relatively small, so the efficiency is higher. The advantage of electric dust removal is that it is not afraid of special environments such as high temperature and high pressure, strong acid and alkali; The disadvantage is that the equipment is expensive and large, that is, it takes up a lot of money and occupies a lot of space, so effective technical improvements are needed in this regard.
Wet Dust Remover
Wet dedusting is also a more common dedusting method. The principle is that water and dust particles in the smoke gas combine to form large dust particles with a diameter of more than 10μm, and these large dust particles are removed. Under normal circumstances, wet dust removal can also be used to remove sulfur dioxide. Therefore, wet dust removal is the most efficient method at present. Its advantages include low cost, simple operation, easy maintenance, and wide application environment. The disadvantage is that it will produce a large amount of sewage, and the wet dust collector is easily corroded and needs to be modified into the pipeline material. There are two common wet dust remover that deal with smoke and dust in large quantities. They are Wenqiuli dust remover and granite water film dust remover. According to specific needs, the best dust remover are selected or the two wet dust remover are combined to use. Give full play to the advantages of each type of dust remover. In order to improve the dust removal efficiency, it can also solve the problem of pipe corrosion. The self-excited spray dust collector is suitable for dust removal in small boilers.
1.2 Flue Gas Desulphurization Technology for Coal-fired Boilers
Dry Desulphurization
Dry desulfurization is also called direct desulfurization. Traditional dry desulfurization is to use absorbent or adsorbent material that can be recycled to absorb sulfur dioxide in the flue gas, and then use catalyst to catalyze sulfur dioxide to produce new non-polluting compounds, thus achieving the purpose of desulfurization. With the development of the times, dry desulphurization technology has also made some progress and made considerable progress.
Wet Desulphurization
Wet method is direct desulfurization with salt or alkaline solution that reacts with sulfur dioxide in the flue gas. When the flue gas is passed into the reaction tank containing salt or alkaline solution, the gas sulfur dioxide reacts in the reaction tank at a fast rate and a high desulfurization efficiency. Under the existing technical conditions, when limestone is selected as a desulfurization agent, the desulfurization rate can reach more than 90 % under the conditions of similar calcium and sulfur content. Generally, large coal-fired power stations use this method for flue gas desulfurization. However, whether it is wet desulfurization, a large amount of industrial wastewater is generated, and there is a problem of wastewater treatment. Therefore, an industrial wastewater treatment device should also be installed. This increases the cost of equipment input and the latter is equivalent to the operation of two sets of equipment. The operating cost is also extremely high. In recent years, zero emission requirements have been put forward in industry, which brings new challenges to wet desulphurization technology, and the technology of wet desulphurization technology needs to be improved urgently.
Semi-dry Method
The water is first removed by evaporation, the remaining sulfur-containing material becomes dry powder, and then the dust is removed using a bag-type dust collector. The sulfur-containing material is removed in the form of dry powder particles to achieve effective desulfurization purpose. The traditional dust removal technology is to spray calcium in the furnace. After the technical improvement, the calcium injection in the furnace can be sprayed with some humidifying activators to form an activation reactor, and it can also directly spray water to increase moisture, which is conducive to improving the dust removal efficiency. At the same time, Some desulfurization reactions can also be promoted to achieve the purpose of flue gas desulfurization. Semi-dry and semi-wet desulphurization technology is actually a combination of wet and dry desulphurization technology, retaining the dry and wet methods. The desulphurization agent used is the same as lime or gypsum. When desulphurization is carried out, a desulphurization ash and alkaline matter must be added. When the flue gas enters the flue gas, the flue gas and desulphurization ash are combined with the desulphurization and alkaline substances to achieve effective desulphurization purpose.
2.Technology of Environmental Pollution Control
In recent years, smog has become a global environmental governance problem. Many countries attach great importance to the flue gas problem of coal-fired boilers. China has also developed integrated and coordinated technical means. In general, the smoke treatment of coal-fired boilers is roughly divided into two phases: First, for a single pollutant, different equipment coordination work to achieve the purpose of governance; The second is to use a comprehensive environmental protection equipment to treat different pollutants at the same time. At present, China is in the first stage, the first stage mainly has the following technical characteristics.
2.1 Collaborative Treatment of Wet Desulphurization and Precipitator
Wet desulphurization is a popular desulphurization method used in boilers of coal-fired power plants in China. Its working principle is to mix a large amount of water with limestone powder or raw stone ash powder to form limestone or cooked lime alkaline emulsion and spray it from the upper part of the desulphurization tower. Under the action of a fan, acid flue gas containing a large amount of sulfur dioxide flows upward from the bottom, meets with limestone or cooked lime in alkaline droplets, produces gypsum and other sulfates, falls with the droplets to the bottom of the desulfurization tower, and collects and removes. The joint treatment of wet desulfurization and scrubber can make the flue gas treatment more convenient, thus improving the application effect of desulfurization equipment and increasing the dust removal rate. In addition, the staff can be deployed according to the specific process of wet desulphurization, and through the system management of wet desulphurization and precipitator, the smoke treatment can be truly coordinated.
2.2 Collaborative Treatment of Flue Gas Denitrification and Low Carbon Combustion
The flue gas denitrification technology generally refers to denitrification of exhaust gas from combustion emissions, IE, denitrification of the rear end, mainly by selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), and oxidation denitrification. With the improvement of environmental protection standards in our country, some traditional flue gas denitrification processes are difficult to meet the strict emission reduction requirements. Ozone oxidation denitrification technology has become a better choice. Advanced ozone oxidation technology not only has a good removal effect on nitrogen oxides, but also can remove other harmful pollutants in the flue gas, such as heavy metal Mercury. It has been proved that ozone oxygenation and denitrification technology can meet the new flue gas emission standards, and the localization of large-scale ozone equipment has greatly reduced the initial investment currently. The denitrification technology has been applied in many thermal power plants in China. It has achieved excellent denitrification effect and will gradually become one of the denitrification technologies of thermal power plants. Cooperative treatment of multi-pollutant in sintered tobacco gas means that through the combination of one technology or several technical groups, the unit link or unit environmental protection equipment is linked and matched to achieve the purpose of comprehensive removal of multiple pollutants. Different coal combustion produces different pollutants, people should pay close attention to the combustion efficiency of different coal combustion. In general, people should give priority to the use of low-carbon combustion coal combustion, reduce the emission of pollutants from the root causes, and use flue gas denitrification to further optimize the overall design of combustion, and finally achieve coordinated management of coal-fired flue gas.
2.3 Coordinated Management of Smoke Pollution Clearance and Coal Control
The amount of flue gas in the sintering process is large, there are many kinds of pollutants, the content fluctuates greatly, and the flue gas temperature is low. In the process of flue gas treatment, if we want to achieve the harmonization of pollution removal and coal control, the relevant staff must analyze the data and obtain the relationship between the cost of controlling the amount of coal combustion and the price of environmental protection equipment and the operating cost of the public company. In this way, the quantity of coal combustion can be effectively controlled so as to achieve the purpose of collaborative governance. People should choose a technological route that is technically reliable, coordinated between economic and environmental benefits, and reduce the burden on enterprises.
2.4 Efficient Desulphurization System Is Adopted
According to the current desulfurization technology, the method of universal application is mainly sodium calcium dialkali method wet desulfurization. For sodium calcium dialkali desulfurization system, it mainly includes flue gas desulfurization system, desulfurization liquid ring system and desulfurization agent preparation system. In the process of actual operation, the boiler flue gas needs to be purified by a cloth bag dust collector, and then through the boiler fan, the flue gas is entered into the rotating plate tower in the pipeline. In the cyclone tower, a variety of desulphurization dusts need to be combined. At this time, after the sodium base absorbed and the flue gas come into contact, a chemical reaction will occur to effectively remove the flue gas in the boiler. When the smoke gas is processed, it needs to be discharged through the chimney. For the desulfurization liquid, the main way through the closed loop is mainly divided into two ways: the main cycle and the regeneration cycle. In addition, in the tower, mainly according to the main cycle pump, gradually the self-circulation of the desulfide liquid in the tower is gradually circulated, and then the overflow part of the bottom of the tower is separated and then circulated through the circular pump. Finally, the desulphurization products are guaranteed to be removed, piled and delivered in the sedimentation tank. In addition, for lime powder, it is necessary to use a feeder to add a Humanized ash, make it into a lime slurry, and then flow into the regeneration poor.
3.Coal-fired Boiler Recommendation
3.1 Coal-fired Boiler for Industrial
Coal-fired boilers are widely used for all industries, such as foods, dairy, beverage, brewery, paper plant, textile, garments, edible oil factory, chemical industry, packaging industry, central heating, hotel, etc.
Steam capacity: 1-75t/h
Rated pressure: 1-1.25MPa
Thermal efficiency: 82%
Type: DZL、SZL、DHL、SHL
Fuel: Bituminous coal, anthracite, lean coal, etc.
Coal enters the chain grate through the hopper, and enters the furnace to start its combustion process as the chain grate moves, and the burnt coal slag is discharged to the slag discharge well at the tail of the chain grate as the chain grate moves. Coal-fired chain grate boilers have certain requirements on the quality of coal.
Thermal power: 0.7-29.2MW
Rated pressure: 0.8-1MPa
Thermal efficiency: 80%
Type: YLW
Fuel: Bituminous coal, anthracite, lean coal, etc.
The coal fuel drops onto the grate from the hopper and fires. The high temperature flue gas is reflected to the front by the rear arch and goes into the furnace, after heat exchange by radiation heating area it goes into the convection heating area, and after heat exchange here, it goes into waste heat boiler, then into air pre-heater, and then goes into dust collector. After the dust collector and drawn by the ID fan, the flue gas is finally emitted into the atmosphere through the chimney.
Steam capacity: 1-75t/h
Rated pressure: 1.25-5.3MPa
Thermal efficiency: 89%
Type: SHX, DHX
Fuel: Coal, gangue, biomass, sludge
The coal-fired circulating fluidized bed boiler adopts a large furnace and low flow rate design to reduce erosion and wear, prolong the residence time of coal particles in the furnace, and ensure full combustion of fuel to prevent fly ash from entering the economizer, and all parts prone to ash accumulation are equipped with soot blower interfaces, and a variety of soot blowers are available. And the serpentine tube economizer and air preheater increase the heating area, absorb the flue gas temperature, and improve the boiler's thermal efficiency.
3.2 Coal-fired Boiler Power Plant
A coal-fired boiler 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 an abundant and widely distributed fossil fuel, making it a popular choice for power generation.
The power generation process of a coal-fired boiler power plant can be divided into several stages:
(1) Fuel preparation: coal is crushed into fine powder and then mixed with air to improve combustion efficiency. The pulverized coal is then stored in coal bunkers.
(2) Combustion: Pulverized coal is fed into the boiler and burned at high temperatures. The combustion process releases thermal energy, 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 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 boiler power plants have been widely used for decades because of their reliability and cost-effectiveness. However, they also have some environmental drawbacks. Coal combustion 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. To sum up, coal-fired boiler power stations are thermal power plants that use coal as a fuel source to generate electricity. While it is a reliable and economical power generation option, efforts are being made to minimize its environmental impact through the use of advanced emission control technologies.
4.Advantages and Disadvantages of Coal Combustion
4.1 Advantages of Coal Combustion
Abundant Supply
Easy Storage
Low Capital Investment
Safe to Use
Simple Burning Process
4.2 Disadvantages of Coal Combustion
Non-renewable source of energy
High Carbon Emission
Harms Natural Habitats
Coal is potentially radioactive
Hazardous to the environment by increasing pollution
5.Conclusion
Environmental issues are a topic of common concern to people all over the world, and the atmosphere is more closely related to people's lives. It is urgent to solve the flue gas pollution of coal-fired boilers. Therefore, the flue gas emitted from coal-fired boilers must be strictly controlled, especially the dust content and sulfur dioxide content. Ensure that the dust and sulfur dioxide content in the exhaust gas meet standards. Through the improvement of effective dust removal and desulfurization technology, the effect of flue gas treatment of coal-fired boilers can be achieved to improve the operating efficiency of coal-fired boilers, ensure that the discharged flue gas does not cause air pollution, and realize the concept of green, environmentally friendly, and low-carbon new industries.
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