Smoke-Dust Treatment Technical Solution

In recent years, the state has paid more and more attention to environmental protection, gradually improved laws and regulations on pollution prevention, and issued various environmental protection standards one after another, aiming at further strengthening corporate responsibility for pollution prevention and increasing legal sanctions against environmental violations. The new Environmental Protection Law has enhanced the enforceability and operability of the law and put forward higher requirements for environmental protection management of enterprises. As a high energy consumption and high pollution industry, it is imperative to save energy and reduce emissions according to laws and regulations.

Fig. 1: Flue gas from hot forging process


The temperature of hot forging is generally higher than 400℃. In order to prolong the service life of dies, hot forging lubricants must be used to protect the dies from corrosion. Hot forging lubricants are usually composed of three parts: the main lubricating matrix, carrier solvents and additives to improve the comprehensive performance of lubricants, such as extreme pressure agents, tackifiers and antioxidants. Graphite, molybdenum disulfide and composite stearate are typical solid lubricant matrix. Graphite emulsion is widely used in hot forming because of its good lubricity, high temperature stability and adhesion characteristics at high temperature. At present, water-based graphite emulsion is widely used as hot forging lubricant.


The smoke - gas produced from lubricant has complex components, which coexist in three phases: solid, liquid and gas. It contains hydrocarbon decomposition products such as polycyclic aromatic hydrocarbons, graphite, coke, and harmful gases such as CO and NO2, and has great adhesion and pungent smell. The particle size of this kind of smoke-gas is mostly less than 2.5μm, which is easy to be inhaled by workshop workers, endangering their health, causing poor visibility in the workshop, slippery ground, and potential safety and fire hazards. Therefore, it is necessary to adopt appropriate treatment technology to collect and purify the hot forging smoke-gas. 

Fig. 2: Concentration and particle size distribution of hot forging smoke-gas in a precision forging site 


At present, the available purification technologies on the market include wet dust collector, bag filter, filter cartridge dust collector and electrostatic dust collector, etc. For filter cartridges and bag filters, firstly, they are not suitable for treating high-temperature flue gas; secondly, due to the high viscosity of hot forging smoke-gas, the filter bag will be blocked soon, resulting in a sharp decline in efficiency; For wet dust collector, although it can treat high temperature smoke-gas, its purification efficiency is low, especially for graphite dust with extremely small particle size; For dry electrostatic dust remover, its purification efficiency for high-temperature smoke-gas will be reduced, and its efficiency is greatly affected by the physical properties of smoke-gas, and its treatment effect for high specific resistance, fine dust and sticky dust is poor. In addition, it lacks the function of fire prevention and explosion prevention, and graphite dust and grease deposited on the dust collecting plate are easy to be led by sparks generated by spark discharge, and there is a risk of fire.


In comparison, the wet electrostatic dust remover can use water mist to collide with dust in corona area, reduce the specific resistance of dust, make it easy to charge and improve the purification efficiency; It can form a uniform water film on the surface of the polar plate, weaken the adhesion of sticky dust and keep the equipment running at high efficiency; It can also cool high-temperature gas and absorb harmful substances in the gas, and is suitable for treating hydrophilic graphite dust with extremely small particle size.


Therefore, because of its high purification efficiency and low pressure loss, the wet electrostatic dust remover owns an ideal trapping function for fine and sticky dust, and can deal with high temperature, high humidity, flammable and explosive gases, and absorb harmful gases, thus becoming the best choice for treating hot forging smoke.

Fig. 3: Before and after comparison of the application of Venturi Dust Remover and Tubular Wet Electrostatic Purifier in a Precision Forging Site 


The above picture shows a comparison photo before and after the Venturi wet dust remover and the tubular wet electrostatic purifier are used in a precision forging site. There are two 2500-ton forging presses on the site for forging auto parts. The processing tempo is fast, the injection amount of release agent is large each time, and a large amount of oil fume is emitted from the gap of the forging press.


It is obviously that the purification efficiency of Venturi wet dust remover is low, and a large amount of oil fume is discharged from the outlet of the dust remover, and its efficiency is lower than 30% in field test. After replacing the tubular wet electrostatic purifier of Dalian Megaunity, the workshop environment has improved a lot, and no smoke dust can be seen. The third-party detection of the outlet concentration is 1.5mg/m3, which fully meets the requirements of “Emission Standard for Air Pollutantsfor Steel SmeltIndustry”. Moreover, after testing, its wet electrical equipment not only has a purification efficiency of more than 97% for oil mist and dust, but also has a certain removal effect for odor, VOCs and non-methane total hydrocarbons.


The refined structural design is adopted for the tubular wet electrostatic purifier of Dalian Megaunity: The honeycomb hexagonal tubular structure is adopted for the dust collector, which has larger dust collecting area than traditional plate electrostatic equipment. Under the same processing capacity, the equipment is small in size, less in material consumption and low in investment cost; The numerical simulation technology is adopted for the corona electrode, which can determine the electrode structure according to the comparison of electric field intensity and its distribution uniformity. The current is uniform, the average field is strong, and the purification efficiency is high; The combination of numerical simulation and physical test are adopted for air distributor to develop a large-scale air flow uniform distribution technology. Through the on-line adjustable device of air flow uniform distribution, the flow deviation of each honeycomb tube is controlled to ensure the uniformity of flue gas flow; A spraying device is designed between the airflow distribution plate and the electric field, and the sprayed water mist has uniform particle size and high dispersity, which can fully contact with dust-containing gas to improve the charging property of dust, and improve the efficiency by using the inertial collision condensation of the two; A spray device is designed on the upper part of the electric field, and the sprayed water can cover the polar plate completely, forming a water film with a certain thickness on the polar plate, and efficiently removing the dust collected on the dust collecting plate; A high-voltage power supply system with automatic load tracking and spark suppression is designed, which can reduce power consumption under the premise of constant purification efficiency, achieve the effect of energy saving and emission reduction, and can automatically suppress spark development to ensure efficient and stable operation of the purifier.


The wet electrostatic purification equipment is the best choice for treating hot forging smoke, considering many factors such as process adaptability, operation stability, purification efficiency, cost benefit and social benefit.


We hope that environmentalists can make joint efforts to continuously carry out R&D and innovation of environmentally-friendly products and technologies, help forging enterprises realize the transformation and upgrading of green forging, and build sustainable modern forging enterprises. Let’s create a fresh world together, build a beautiful China, and make unremitting efforts to return the blue sky and white clouds for our future generations!

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