The fundamental principles of filtration focus on the optimal filter media design and the selection of appropriate media for specific filtration applications. Two primary types of filtration exist depth filtration and surface filtration. Depth filtration involves capturing particles within the media, while surface filtration entails trapping particles on the filter surface, forming waste materials.
Surface filtration primarily functions as a coarse filtration mechanism, separating particles larger than the filter medium's size on the filter surface to prevent their entry or passage through the pores. As particles accumulate, waste materials form, increasing in thickness as more particles flow into the filter media.
Depth filtration is primarily employed for separating micron-sized particles, such as safeguarding equipment from clogging and corrosion, protecting catalysts from poisoning, and purifying products. Particles enter the medium and are captured by its multilayer structure. This structure prevents premature clogging and enhances the media's capacity to hold dirt. As particles are trapped in the deeper layers of the media, offline cleaning becomes necessary. Offline cleaning methods may involve solvents, ultrasonic vibration, pyrolysis, steam cleaning, or cleaning with circulating water. Pleated media can be utilized to minimize space requirements and cost.
Understanding a filter's efficiency in removing particles from a gas stream is crucial for successful filter design and operation. For fluids carrying small granular impurities, capturing particles through internal porous media is key to achieving efficient particle removal. The structure of sintered metal offers a tortuous path where particles can be trapped, forming solid waste materials on the media's surface. The newly captured particles accumulate on top of the previously deposited ones. The filter's lifespan depends on its dirt-holding capacity and the resulting pressure drop. In cases where fluids are laden with many particles, the current filtration equipment employs solid filtration. The accumulated filter solid surpasses the filter element, creating an additional filter layer and increasing the pressure drop. Pressure drop rises with particle loading. Once the filtration cycle reaches the final pressure, the filter undergoes backflushing or flushing with clean gas to remove the filtered solid.
The filtration ratio is influenced by factors such as feed particle concentration, viscosity, and temperature. Filter operation modes can be set as constant pressure, constant flow rate, or increasing pressure with decreasing flow rate during filtration. If particles clog the system rapidly, reaching the pressure limit, or the solid filter becomes full, the filtration cycle terminates even if the limit pressure has not been reached. The filter type, fluid temperature, and solids loading affect permeability, expressed as the flow rate relative to pressure drop.
