Cyclonic separators, aerosol collection

The collection of the pyrolysis oils is difficult due to their tendency to form aerosols and also due to the volatile nature of many of the oil constituents. As the aerosols agglomerate into larger droplets, they can be removed by cyclonic separators. However, the submicron aerosols cannot be efficiently collected by cyclonic or inertial techniques, and collection by impact of the aerosols due to their Brownian or random motion must be utilized. A coalescing filter is relatively porous, but it contains a large surface area for the aerosol particles to impact by Brownian motion as they are swept through by the pyrolysis gases. Once the aerosol droplets impact the filter fibers, they are captured and coalesce into large drops that can flow down the fibers and be collected. 

The experimental determination of the feed consumed, the char yield, and the noncondensible gas yields are relatively straightforward. However, the primary vapor and water yields have proven difficult to measure directly due to the formation of aerosols. These aerosols escape high-pressure sprays, cyclonic separators, and impingement or inertial collection techniques. The use of condensible steam as the carrier gas makes the water yield very... 

As a simple and efficient particle separation device, cyclone collectors can be used for anything from dust removal in a fluid stream to material collection in the fluid conveying system. However, the cyclone is not suitable or economical for the separation of extremely small particles (say, less than 1 /xm), which frequently occur in industrial processes. It is recommended that the size of particles to be separated in an industrial ventilation cyclone be in the region of around 10 to 100 p.m. However, for the purpose of aerosol sampling, the size of particles to be separated may be much less than 10 jxm. 

Aerosol for chemical analysis was sampled in the air monitoring trailer through a 1.3 cm ID stainless steel pipe. The air inlet was about 1 m above the roof of the trailer, a total of 4 m above the ground. Loss of 0.1 pm diameter particles to the walls due to turbulent diffusion was calculated to be less than 1% using the method of Friedlander (11). A cyclone preseparator (12) was used to separate the coarse (D > 2 pm) aerosol from the airstream so that only the fine (D <2 pm) aerosol would be collected for analysis. The cyclone was operated at 26-30 liters per minute (1pm) and was cleaned every 8-10 weeks. 

Aerosol can be separated by size using devices such as cyclones, classical impactors, virtual impactors, and filters before detection. These same components can also be used for aerosol concentration and collection as described below. Other methods involving electrostatic and ultrasonic effects are being investigated for aerosol concentration and separation, but these methods are less developed and are not available for near-term deployment. 

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