Publish Time: 2021-12-08 Origin: Site
There are many types of chemical gases in the laboratory, and activated carbon filters have good adsorption capacity for most chemicals. This is mainly due to the large internal surface area of activated carbon. The internal surface area of one kilogram of activated carbon can reach one square kilometer! Such a large internal surface area forms many tiny holes inside the activated carbon, which can absorb chemicals equivalent to its own weight at most.
According to different manufacturing processes, there are two main types of activated carbon filters: granular activated carbon filters and bonded activated carbon filters. The granular activated carbon filter directly encapsulates the carbon particles in a box. The manufacturing process of this filter is simple, but there are inherent potential penetration problems and carbon leakage problems. Although these problems have been partially improved by adopting a partition structure and an additional safety filter, the reduction in adsorption efficiency caused by carbon leakage and the lack of safety performance caused by penetration are still fundamentally solved.
The bonded activated carbon filter connects the dispersed carbon particles as a whole through strong chemical bonds, completely solving the problems of penetration and carbon leakage, and is currently the most reliable activated carbon filter on the market. However, the manufacturing process of the bonded structure is complicated. Xunling is one of the few manufacturers in the world that mastered this technology.
When choosing an activated carbon filter, there is another problem that needs special attention. Although activated carbon has a good adsorption effect on most chemicals, it is not effective for some chemicals, such as compounds with smaller molecular weights, inorganic acid gases, ammonia and amine compounds, and mercury vapor. For this type of compound, a special type of activated carbon filter that has been chemically impregnated should be used. At present, all major ductless fume hood manufacturers can provide related products.
In addition to chemical gases, many applications also need to isolate gas-soluble particles. In this case, a filter specially designed for adsorbing particles needs to be selected. According to the size of the particles to be processed, a high-efficiency HEPA filter for 0.3μm particles and an ultra-high-efficiency ULPA filter for 0.1μm particles can be selected. According to the standards of the United States and China, the adsorption efficiency of HEPA filter and ULPA filter should not be less than 99.97%. In fact, the adsorption efficiency of the filter in commercial ductless ventilation products is higher. If you need to process chemical gases and gas-soluble particulates at the same time, you can also use activated carbon filters and HEPA/ULPA filters in a stack (if the filter compartment space of the ductless fume hood allows).
Finally, mention a special particulate filter, which is the primary pre-filter installed at the forefront of various filtration systems. The purpose of the pre-filter is to filter out the larger particles in the air, improve the filtration performance of the filtration system and protect the life of the main filter. The filtration efficiency of the pre-filter for dust with a particle size of 0.5μm or more can reach more than 95%. The electrostatic pre-filter can also firmly grasp the blocked dust on the pre-filter through the action of static electricity, so as to avoid the formation of "dust rain" falling when the machine is turned on again.
Regardless of the filter, after a period of use, the filtering performance will decrease. When the filter is close to the saturation limit, the safety performance of the ductless ventilation system will be difficult to guarantee. In this case, a new filter should be replaced in time to avoid safety problems. For the activated carbon filter in use, it is monitored in real time by the gas sensor installed behind the filter. If the content of harmful components in the filtered gas is monitored to reach the preset concentration, it will flash the alarm light and sound the alarm in time At the same time, the alarm is issued. This provides a reliable guarantee for the safe use of ductless fume hoods.
In order to ensure better physical impact resistance and chemical corrosion resistance, the structural materials of ductless fume hoods are mostly made of polypropylene (PP) with excellent strength and corrosion resistance, and the windows and transparent enclosures are made of strength, transparency and Polycarbonate (PC) material with excellent chemical properties. Metal parts with poor corrosion resistance are rarely used in the parts that can be exposed to the gas before treatment.
In terms of structural design, the entire cabinet adopts an integrated design of hot-melt forming. There are no dead corners that are not easy to clean. If necessary, you can also use a strong corrosive cleaning agent to clean the inner and outer surfaces.
All circuit systems of the ductless fume hood are enclosed in an airtight space to avoid exposure to potential chemical gases. The lighting adopts high-spec steam-proof fluorescent lamps or LED lamps, and all electronic components meet or exceed the requirements of relevant standards. These all ensure the safety of the circuit system of the ductless fume hood.