Description

 

Adsorption equipment is used to bind or adhere molecules or particles to a surface in a process stream. This equipment is used for industrial applications such as odor control, the recovery of volatile solvents such as benzene, ethanol, and trichloroethylene, and the drying of process gas streams. They also are incorporated into environmental systems for reclamation or remediation of contaminated water or air streams.

 

Adsorption

 

Adsorption involves the adherence of molecules or particles to an adsorbing media. It can take place through either physical or chemical means. Physical adsorption involves a weak bonding of molecules (typically gases) to the adsorbing solid. Physical adsorption can be reversed by the application of heat or pressure, otherwise known as regeneration.

Chemical adsorption, or chemisorption, involves actual chemical bonding by reaction of the adsorbate with the adsorbing solid. The oxidation of SO2 to SO3 by activated carbon is an example of chemisorption. Except in specialized applications, this process cannot be reversed and the adsorbed material cannot be recovered.

 

Types of Adsorption Equipment

 

Adsorption systems can be referred to as packed beds since the adsorbing material is packed together to filter fluid streams. The two different design implementations are fixed bed adsorbers and fluidized-bed adsorbers.

 

Fixed-bed adsorbers utilize a stationary adsorbent to filter streams. These systems are used in applications ranging from large industrial operations to remove harmful VOCs (volatile organic carbons) to small consumer uses as filters and gas masks. Important properties including pressure drop and life expectancy of the adsorbent are very predictable in these types of systems.

 

Fluidized-bed adsorbers utilize a more complex moving (fluidized) adsorbent to filter streams. This is achieved by inducing a stream velocity high enough to suspend the adsorbent particles. Fluidization allows for continuous regeneration and a uniform temperature gradient, giving these systems the advantage of running continuously. However, energy costs to maintain suspension velocity and deal with large pressure drops are considerably more than in fixed-bed systems. Also, the behavior of fluidized-beds is much harder to predict since much is still unknown. Fluidized-beds require a larger chamber and are usually only implemented in high-volume industrial applications.

 

Adsorption Media

 

Common media used in adsorption equipment include activated carbon, activated alumina, silica gel, and molecular sieves.

 

Activated alumina is an adsorbent made of aluminum oxide (Al2O3). It is used as a desiccant for drying gases and air and as a fluoride filter for drinking water. It has specific use as a silica gel replacement in certain environments due to its thermal shock resistance and physical constancy when immersed in water. It also commonly used as an alternative to activated carbon for VOC removal.

Activated carbon is roasted organic material (coconut shell, bone, wood) that forms porous granules. It is a versatile and inexpensive adsorbent that comes in many sizes and has a range of applications from gas, water, and metal purification to air filtration. It is the most commonly used industrial adsorbent.

Molecular sieves or zeolites are naturally occurring adsorbents with uniform pore size that can be tuned to be highly selective. They are used as dehumidifiers and air purifiers due to their high retention and adsorption capacities even at high temperatures. Zeolites are often combined with activated carbon for combined effectiveness.

Silica gel or silicon dioxide is a common desiccant used in food preservation, humidity control, and various medical devices. It has a higher water adsorption capacity than clay silicates (40% of its weight in moisture), it is very inert, and it can be regenerated through heating.

Selection Considerations

 

When selecting adsorption equipment, the primary considerations are selectivity, capacity, and regeneration.

Selectivity is the amount of specificity an adsorbent has in the materials that it can capture. A very unselective adsorbent will readily capture many different particles, ideal for streams with many pollutants. Highly selective adsorbents will only capture certain types of particles, making them suited for filtering out specific contaminants from a product stream.

Capacity is the amount of contaminant adsorption equipment can capture before the adsorbent is saturated and requires renewal. This is a crucial factor in fixed-bed systems where the material must eventually be replaced or regenerated.

Regeneration is the ability of the adsorbent in the system to be reused. This is important for systems with large-volume or high-cost materials where iterative replacements would be expensive.

Another factor that affects system design is the equipment’s pressure drop gradient or required operating power.

 

Additional Services

 

In addition to manufacturing adsorption equipment, many suppliers offer a number of related services to help maintain purchased equipment.  These include media reactivation and dual vessel system assembly.  In media reactivation, the supplier collects saturated adsorbent and regenerates it for future use.  This can help cut down on both cost and waste generated by adsorption equipment.  Suppliers that engage in dual vessel system assembly make sure that the adsorption equipment is both the proper fit for the user, and help to incorporate the equipment into an existing process line or remediation system.

 

 


Related Products & Services

  • Air Cleaners

    Air cleaners re-circulate, filter and purify air for process and environmental applications.

  • Air Filters (industrial)

    Industrial air filters reduce the number of particles in the air that passes through them. 

  • Air Scrubbers, Wet Scrubbers, and Gas Scrubbers

    Air scrubbers, wet scrubbers, and gas scrubbers are air pollution control devices that use a high-energy liquid spray to remove aerosol and gaseous pollutants from an air stream. The gases are removed either by absorption or chemical reaction.

  • Compressed Air Filters

    Compressed air filters are used to remove water, oil, oil vapor, dirt, and other contaminants from a compressed air supply.

  • Dust Collectors

    Dust collectors are used in many processes to either recover valuable granular solid or powder from process streams or to remove granular solid pollutants from exhaust gases prior to venting to the atmosphere.

  • Mist Collectors and Fume Collectors

    Mist collectors and fume collectors reduce the amount of mist, aerosols and fumes in the workplace atmosphere.

  • Selective Catalytic Reduction (SCR) Systems

    Selective catalytic reduction (SCR) systems inject ammonia into boiler flue gas and pass it through a catalyst bed where the nitrogen oxide gas (NOx) and ammonia react to form nitrogen and water vapor.

  • Thermal Oxidizers and Catalytic Oxidizers

    Thermal oxidizers and catalytic oxidizers are used to destroy volatile organic compounds (VOC) in process gases.