Packed-bed scrubbers

Packed-bed scrubbers m be construc ted for either vertical or horizontal gas flow. Vertical-flow units (packed towers) commonly use countercurrent flow of gas and liquid, although cocurrent flow is sometimes used. Packed scrubbers using horizontal gas flow usually employ cross-flow of liquid. 

Other Considerations In situations where waste gas contains both particulates and gases to be controlled, venturi scrubbers are sometimes used as a pretreatment device, removing PM to prevent clogging of a downstream device, such as a packed bed scrubber, which is designed to collect primarily gaseous pollutants. 

The suitability of gas absorption as a pollution control method is generally dependent on the following factors 1) availability of suitable solvent 2) required removal efficiency 3) pollutant concentration in the inlet vapor 4) capacity required for handling waste gas and, 5) recovery value of the pollutant(s) or the disposal cost of the unrecoverable solvent. Packed-bed scrubbers are typically used in the chemical, aluminum, coke and ferro-alloy, food and agriculture, and chromium electroplating industries. 

PM Control - In packed-bed scrubbers, the gas stream is forced to follow a circuitous path through the packing material, on which much of the PM impacts. The liquid on the packing material collects the PM and flows down the chamber... 

The attraction of periodic flow interruption for scrubbing is that the pressure drop is low relative to continuous, packed-bed scrubbers and a commercially useful acid can be produced. The catalyst is cheap, but that... 

Fached-Bed Scrubbers Packed-bed scrubbers using gas-absorption-type tower packing may also be used for collecting soluble solids, but are not irrigated intensively enough to avoid plugging by deposits of... 

Based on observations from the RMA cleanup project, downtime and reduced production may be experienced during initial periods of operation due to plugging of packed-bed scrubbers by precipitates from inorganic salts generated from the waste material. 

The latter consists of 2 cyclones in series (5), 2 shell and tube heat exchangers (6), a packed bed scrubber (7), and a mist eliminator (8). 

Packed-bed towers can achieve removal efficiencies of over 99% and have relatively lower water consumption requirements. They also offer design and retrofit flexibility. Disadvantages include high system pressure drops, relatively high clogging and fouling potential, potentially high maintenance costs, and waste water disposal requirements. Packed-bed scrubbers are also more expensive to install and operate than spray towers. 

Packed-bed scrubbers cause impaction of the aerosol droplets or particles on liquid-coated packing materials of various kinds, such as porous plates or mesh screens. The gas stream is usually made to flow upwards through the packed bed and the scrubbing liquid is usually a solvent liquid that is made to flow downwards, countercurrent to the rising gas stream. 

Venturi and packed bed scrubber with alkali circulation for acidic gas removal ... 

The most common types of wet scrubbers are spray towers, venturi scrubbers, packed bed scrubbers and impingement scrubbers. Spray towers are the simplest, least expensive, however not very efficient, tar separation devices [23]. 

Figure 11.2 Wet packed bed scrubber. fSource Reproduced from Ref. [17])...

Bhave, A.G., Vyas, D.K. and Patel, J.B. (2008) A wet packed bed scrubber-based producer gas cooling-cleaning system. Renew Energy, 33, 1716-1720. 

The packed-bed scrubber (PBS), a major type of wet scrubber applied as the APC in waste combustion systems, is not considered a PM control device, especially for submicrometer particulates. The major problems in using packed-bed scrubbers for particulate removal are plugging of the packing and the maintenance problems subsequently incurred. A general rule of thumb is to allow a maximum of 0.2 g/ft of dust to enter a packed tower. 

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