The erroneous zone of dust collection design in cement plant process
Date：2019-08-28 15:52 Source：cementepcViews:
However, although many cement factories have set up dust collectors in the production process, but the location of dust collection point is not correct, dust collection air volume and dust gas volume do not match, dust collection air pipe layout is not reasonable, exhaust fan pumping force is not enough, resulting in the production of dust collection effect is not ideal, the emission concentration exceeds the standard;Even some cement factories have set up dust collectors in places without dust spots, resulting in increased investment and operating costs.The root cause of these problems is the mistake of process design.
Myth 1: the concept of dusty gas is ambiguous
Dust refers to the fine particles of solid substances brought out by air flow due to the action of mechanical force, the location of generating dust is called dust point, and the gas containing fine particles is called dust gas.The concentration of gas dust is also known as the dust degree of the material, which is related to the material density, water content and fine particles in the material.In China, the gas with dust concentration higher than 30 mg/Nm3 is called dust gas, dust gas must be purified, the amount of dust gas is related to the size of mechanical force and material drop.According to the material type of cement plant and gas dust concentration to determine whether dust collection is needed, and then according to the amount of gas generated by the dust point to determine the dust collector specifications.If the concept of dust-containing gas is vaguely understood in the process of material processing, transportation and storage, setting up dust collector and dust collector specifications according to your own feeling will lead to poor dust collection effect and increase of factory construction cost regardless of dust concentration and gas volume.
mistake 2: don't pay attention to dust pipe design
Dust collection pipeline includes dust collector, air duct and exhaust cylinder, etc.The dust collector shall be set close to the dust source so that the cover mouth is facing the direction of dust emission.For powdery materials, the wind speed of the suction port section of dust collector is about 1m/s;For bulk materials, the wind speed of the suction port section of dust collector should not be more than 3m/s.The circular section should be adopted for the duct, and the elbow should be reduced as much as possible. The radius of curvature of the elbow should be set as R=(1.5 ~ 3)D(D is air pipe diameter or equivalent diameter);The same air pipe may be inclined, horizontal and vertical. In order to prevent dust settling in the pipe, it is suggested to set the wind speed in the pipe at 18 ~ 22m/s.Exhaust cylinder outlet diameter should be determined according to the gas outlet velocity, gas outlet velocity can be 10 ~ 16m/s.Optimization of dust collecting pipeline can reduce the resistance of dust collecting system, improve dust collecting efficiency and reduce the power of exhaust fan.If the dust collecting pipe design problems such as incorrect location of air extraction port, unreasonable wind speed of air pipe, too long air pipe arrangement or too many elbows occur, the dust containing gas generated cannot be fully inhaled into the dust collector, dust settling in the air pipe or increased resistance in the pipe, and the exhaust fan's suction force is not enough, affecting the dust collecting effect.
Myth 3: the higher the concentration of dust in the gas, the greater the amount of dust in the gas
The amount of dust gas is due to the amount of gas discharged from the dust point by the material under the action of external mechanical forces, and its size is determined by the type, specification, running speed and process layout of the mechanical equipment.Dust concentration of gas is related to such factors as the material type, density, moisture content, such as using the same specifications of the conveyor belt conveyor clinker and gypsum, argue that the dust caused by transmission of clinker gas quantity is big, small amount of dust produced by the gas conveying gypsum, which will directly led to the incorrect selection of the bag dust collector, actually dust gas quantity of the same, just different from gas dust concentration.
mistake 4: process design and dust collection design has little correlation
The process design is closely related to the dust collecting design. In the process design, the dust collecting effect of the bag dust collector can be improved by reducing the running speed of the equipment, reducing the material drop, adding buffer device on the discharge chute, etc., which can effectively reduce the amount of dust gas.However, in cement production, once the dust collection effect of a dust spot is poor, the cause is found from the dust collection design, not from the process design, resulting in the treatment of dust collection effect is not obvious.
Myth 5: material characteristics do not affect dust collection design
Material characteristics determine whether dust will be generated and the concentration of gas dust. If the concentration of gas dust exceeds the emission concentration stipulated by the state, a dust collector needs to be set. Therefore, material characteristics are the prerequisite for determining whether to set a dust collector.Particle size, moisture content and density of materials all affect dust collection design. If the density of materials is high or the moisture content of materials is high and the concentration of gas dust is lower than the emission concentration stipulated by the state, dust collection is not required.Measures can also be taken to reduce the concentration of gas dust in the production process, such as appropriately increasing the particle size of the grinding material to reduce the amount of fine powder or spraying water on the material to increase the water content of the material.Before the process design, it is necessary to understand in detail the characteristics of various materials used in the cement plant, and then determine the dust collection design scheme, so as to ensure the standard discharge after production.
Myth 6: air distribution can be guaranteed by setting a regulating valve on a branch duct
When a bag dust collector collects dust from multiple dust points, the resistance balance of each branch air pipe must be calculated. On this basis, a regulating valve is added to make up for the error of air volume estimation in the design.If you do not carry out resistance balance calculation, even if the valve on the air tube of the regulation branch, may not be able to ensure the dust requirements of the air volume, which is also a number of cement plant dust dust effect is not ideal.
Myth 7: ignoring the tightness of an airtight cover (or container)
In all stages of design, installation and operation management, the airtight cover (or airtight container) must be completely sealed. If the airtight cover (or airtight container) leaks and causes short-circuit, negative pressure cannot be formed, and the dust gas generated by the dust point cannot be inhaled into the dust collector, which is the main reason for the poor dust collection effect.
8. To summarize
Cement plant need to collect dust from the design, installation, grab every link of production, the optimization of process design, do have dust are equipped with dust collector, reasonably determine the dust collector, exhaust fan, and the specifications of the dust collecting duct, prevent airtight cover (or airtight container) air leakage, unified understanding of dust collecting involved personnel, to ensure the cement plant emissions standards.If you have any more questions about cement plants, please contact us. We will reply to you as soon as possible.