Abstract: The treatment of exhaust gas from dryers is a difficult point in dust removal technology. This article introduces several dust removal technologies for exhaust gas from dryers.
The exhaust gas volume of the dryer is large, with high dust concentration, high moisture content, high dew point, easy condensation, high emission point, and wide pollution range, which are the difficulties of dust removal technology. The exhaust gas from the tail of the dryer is related to the process conditions of various factories. Some enterprises use it for drying multiple materials, with large production changes, frequent start-up and shutdown, and a large fluctuation range. In addition, coal is used as a drying heat source, and the sulfur oxides in the exhaust gas have a corrosive effect on metal structural components, which brings certain difficulties to the selection of dust collectors.
Cyclone dust removal technology
The cyclone dust removal technology has the characteristics of low equipment cost, ability to handle high-temperature gases, easy operation, and suitability for gases with high dust concentration. The working principle is that under the action of the fan, the dusty airflow enters the volute of the dust collector at a high speed along the tangent direction from the inlet, and rotates in a spiral shape from top to bottom. Under the action of centrifugal force, the dust particles are thrown towards the outer wall and rotate downwards along the wall surface. With the contraction of the cone, they turn to the axis and return due to lower resistance. They rotate in a spiral shape from bottom to top along the axis and are discharged through the core tube. The dust particles on the outer wall are driven by gravity and downward airflow, and fall into the ash hopper along the wall surface to achieve the purpose of dust removal. Due to the fact that the cyclone dust collector relies on the inertia separation of dust particles, the dust removal efficiency is directly proportional to the particle size, and the larger the particle size, the better the dust removal effect; Small particle size, poor dust removal effect, generally handling dust of 20 microns or more, with a dust removal efficiency of 70% to 90%.
Bag dust removal technology
The bag filter is widely recognized for its stability, efficiency, simple maintenance, and reliable operation. It can effectively remove dust from gas particles with a dust content of 0.1 microns, with a dust removal efficiency of up to 99%. When selecting a bag filter for dust removal of dryer exhaust gas, there is no need to consider the issue of excessive emission concentration. The anti condensation fiberglass bag dust collector of the dryer is currently an ideal dust removal and purification equipment. The equipment is controlled by a microcomputer, with chamber backwashing, timed ash cleaning, and equipped with temperature detection display and over temperature alarm device. It uses CW300-FcA anti condensation fiberglass filter bags, which can effectively prevent the filter bags from condensation and will not burn out the filter bags. Hebei Taihang Group Company's slag dryer with a diameter of 3 × 24 meters has changed its two-stage dust removal process to a first stage LFEF7 × 358-HSY/H anti condensation bag dust collector. According to the environmental protection department's measurement, the exhaust gas volume is 42621 standard cubic meters per hour, the import dust concentration is 69620 milligrams per standard cubic meter, and the export dust concentration is 147 milligrams per standard cubic meter, meeting the national emission standards. Not only did it increase production, but it also recycled dry materials, with an annual economic benefit of over 700000 yuan, while also receiving significant social benefits. However, bag filters have the disadvantages of large footprint and high investment. With the development of filter bag covering technology, this disadvantage will be overcome and their use will become more widespread.
High voltage electrostatic dust removal technology
High voltage electrostatic dust removal technology is the process of converting 50 Hz, 220 V AC electricity into DC electricity of over 100 kW and applying it to the corona electrode (cathode) to form an uneven high voltage electric field. This ionizes the gas and generates a large number of negative ions and electrons, which charge the gas dust entering the electric field. Under the action of the electric field force, the charged dust tends to the opposite electrode. The anode is generally the dust collector, and it is discharged from the ash hopper through vibration, completing the purification and dust removal process. High voltage electrostatic precipitators with high efficiency and low resistance can be widely used in dust pollution situations in industries such as building materials, metallurgy, and chemical industry. It deals with high dust concentration and has a more obvious dust removal effect on fine or high specific resistance dust with a diameter of 0.01 micrometers. The series of products meet the requirements of drying equipment with different air volumes, with flexible matching and suitable for dust treatment of dryer exhaust gas characteristics.
Wet dust removal technology
Wet dust removal technology is a process in which dust containing gas is sent into the lower part of the dust removal tower by an induced draft fan through an air duct. As the cross-section increases, the flow rate decreases, and coarse dust particles first settle in the airflow. Fine dust particles rise with the airflow, and the water droplets sprayed down move in the opposite direction of the dust airflow. The dust is wetted and its self weight continuously increases. Under the action of gravity, it overcomes the lifting force of the airflow and descends into mud water, which enters the sedimentation tank through the lower pipeline to achieve the purpose of dust removal. Mud water generally undergoes 2-3 stages of circulating sedimentation to become clear water, which is pumped into a dust removal tower for recycling without causing secondary pollution. The positive pressure operation of this dust removal technology is generally used for drying clay, drying various materials (raw materials), and the recycled materials are easily mixed and cannot be used, and it also causes significant wear and tear on the fan blades. Suzhou Cement Plant uses wet dust removal technology on a 2.2 × 12 meter diameter clay dryer, with an emission concentration of 132 milligrams per standard cubic meter, meeting national emission standards. The sedimentation tank is cleaned once a year, and the wet soil is dried and stored as production raw materials. The dust removal system has high dust collection efficiency, low resistance, no secondary pollution, flexible process, reliable operation, low power consumption, low investment, no condensation, strong adaptability, and good economic and social benefits.
Gravity settling+high-voltage electrostatic dust removal technology
The dust removal process consists of a settling chamber and high-voltage electrostatic precipitator. Dust containing waste gas is sent into the settling chamber at high speed through an induced draft fan through an air duct, collides with the wall, and the airflow direction changes, causing a rapid decrease in wind speed. The particle dust settles and is discharged by the conveying equipment. Fine dust enters the high-voltage electrostatic precipitator electric field with the airflow, is charged by continuous ion bombardment, flies towards the dust collection electrode, and is collected and discharged. The purified gas is discharged into the atmosphere through the air duct. Two stage dust removal process, the primary settling chamber collects large particles of dust larger than 40 microns, reducing the concentration of dust in the gas, which is conducive to improving the dust removal efficiency of high-voltage electrostatic precipitators. The wind speed can be higher, and the equipment can be smaller, effectively reducing investment. The dust removal process of a clay dryer with a diameter of 2.2 × 12 meters in Lanxi Cement Plant, Zhejiang Province. Dust containing waste gas is sent from the tail cover of the dryer to a square settling chamber made of steel plates through an induced draft fan through an air duct. After settling, the waste gas enters a high-pressure electrostatic precipitator and is purified before being discharged into the atmosphere. The induced draft fan and settling chamber are installed indoors, and the electrostatic precipitator is installed outdoors. The dust removal system operates normally and has been used for many years without condensation. According to the environmental protection department's measurement, the emission concentration is 48 milligrams per standard cubic meter, which is lower than the national emission standard.
Cyclone+High Voltage Electrostatic Dust Removal Technology
This dust removal technology involves the dust containing exhaust gas from the dryer entering the front stage high-efficiency cyclone dust collector through the air duct for pre dust removal. The dust is discharged from the ash hopper through the ash discharge equipment, reducing the dust concentration in the airflow, and then entering the secondary dust removal of the high-pressure electrostatic precipitator. The purified gas is discharged into the atmosphere through the fan, improving the dust removal efficiency, making the process flexible, safe and reliable.
The application of exhaust gas dust removal technology in dryers not only protects the environment and reduces labor intensity, but also increases the hourly output and reduces the expenditure on pollution discharge fees. The recovered dust is a good raw material for cement production and has significant economic, social, and environmental benefits.
