Overview of the application of dust removal technology for dryer exhaust gas
Abstract: Drying machine exhaust gas treatment is a difficult point in dust removal technology. Here are several drying machine exhaust gas dust removal technologies introduced.
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 at the tail of the dryer is related to the process conditions of various factories. Some enterprises use it for drying multiple materials, which results in large production changes, frequent on-off cycles, and large fluctuation ranges. In addition, using coal as the drying heat source can cause corrosion of metal structural components by sulfur oxides in the exhaust gas, which poses certain difficulties in the selection of dust collectors.
Cyclone dust removal technology
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. Its 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 tangential direction from the inlet, and rotates in a spiral shape from top to bottom. The dust particles are thrown towards the outer wall under the action of centrifugal force, and then rotate downwards along the wall. With the contraction of the cone, they turn to the axis and return under the resistance of the lower part. 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 to fall along the wall into the ash hopper, achieving the purpose of dust removal. Due to the fact that the cyclone dust collector relies on the inertial separation of dust particles, the dust removal efficiency is proportional to the particle size, and larger particle sizes have better dust removal effects; Small particle size, poor dust removal effect, generally handling dust larger than 20 microns, with a dust removal efficiency of 70% to 90%.
Bag dust removal technology
The bag filter is widely recognized for its stability, high efficiency, simple maintenance, and reliable operation. It can achieve a dust removal efficiency of up to 99% for dust containing gases with particles of 0.1 microns. 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 the ideal dust removal and purification equipment. This equipment is controlled by a microcomputer, with separate chambers for back blowing, timed dust cleaning, and equipped with temperature detection display and over temperature alarm device. It uses CW300-FcA anti condensation fiberglass filter bag, which can effectively prevent the filter bag from condensing and will not burn out the filter bag. 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 environmental protection department measurements, the exhaust gas volume is 42621 standard cubic meters per hour, the inlet dust concentration is 69620 milligrams per standard cubic meter, and the outlet dust concentration is 147 milligrams per standard cubic meter, meeting national emission standards. Not only did it increase production, but it also recycled dry materials, resulting in 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 coating technology, this disadvantage will be overcome and their use will become more widespread.
High voltage electrostatic precipitator technology
High voltage electrostatic precipitator technology converts 50 Hz and 220 V AC electricity into DC electricity of over 100 kW and applies it to the corona electrode (cathode) to form an uneven high-voltage electric field, which ionizes the gas and produces a large number of negative ions and electrons. The gas dust entering the electric field is charged, and under the action of the electric field force, the charged dust tends to the opposite electrode. Generally, the anode is the dust collector, which falls into the ash hopper by vibration and is discharged to complete the purification and dust removal process. High voltage electrostatic precipitators with high efficiency and low resistance can be widely used in industries such as building materials, metallurgy, and chemical engineering where dust pollution occurs. It deals with high dust concentration and has a more obvious dust removal effect on 0.01 micron fine or high specific resistance dust. The series of products meet the requirements of drying equipment with different air volumes and are flexible to match, suitable for dust control of dryer exhaust gas characteristics.
Wet dust removal technology
Wet dust removal technology is a process in which dust containing gas is introduced into the lower part of a dust removal tower through an induced draft fan and an air duct. Due to the increased cross-sectional area, the flow velocity decreases, and coarse dust particles first settle in the airflow. Fine dust particles rise with the airflow and are sprayed down to form water droplets that move in the opposite direction of the dust airflow. The dust is wetted and its own weight increases continuously. Under the action of gravity, it overcomes the lift of the airflow and descends into slurry water, which enters the sedimentation tank through the lower pipeline to achieve the purpose of dust removal. Mud water is generally circulated and precipitated in 2-3 stages to become clean water, which is pumped into the 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 recycling materials are easily mixed and cannot be utilized, and it also causes significant wear on the fan blades. Suzhou Cement Plant uses wet dust removal technology on a clay dryer with a diameter of 2.2 × 12 meters, with an emission concentration of 132 milligrams per standard cubic meter, meeting the national emission standards. The sedimentation tank is cleaned once a year, and the wet soil is dried and stored as raw material for production. This 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 precipitator technology
The dust removal process consists of a settling chamber and high-voltage electrostatic precipitator. The dusty exhaust gas is sent into the settling chamber at high speed by a induced draft fan through an air duct, collides with the wall, and changes the direction of the airflow, causing the wind speed to rapidly decrease. The particulate dust settles and is discharged through the conveying equipment. The fine dust enters the high-voltage electrostatic precipitator electric field with the airflow, is charged by continuous ion bombardment, and flies towards the dust collection electrode for collection before being discharged. The purified gas is discharged into the atmosphere through the air duct. The two-stage dust removal process involves the primary settling chamber collecting dust particles larger than 40 microns, reducing the dust concentration in the gas and improving the dust removal efficiency of the high-voltage electrostatic precipitator. The wind speed can be increased and the equipment can be reduced, effectively reducing investment. The dust removal process of the 2.2 × 12 meter diameter clay dryer at Zhejiang Lanxi Cement Plant involves sending dusty exhaust gas from the tail cover of the dryer through an induced draft fan and an air duct into a square settling chamber made of steel plates. After settling, the exhaust 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, while the electrostatic precipitator is installed outdoors. The dust removal system operates normally and has been used for many years without condensation. According to environmental protection department measurements, 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 of 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 dust removal technology for dryer exhaust gas not only protects the environment and reduces labor intensity, but also increases the hourly output and reduces the expenditure of sewage fees. The recovered dust is a good raw material for cement production, with significant economic, social, and environmental benefits.
