Modern industry is increasingly in need of reliable and high-quality air and gas cleaning systems, and this inevitably leads to the modernization of technologies for capturing and neutralizing harmful and unwanted substances.

Wet-type absorption columns, along with water scrubbers, adsorbers and electrostatic filters, represent one of the largest groups of gas cleaning equipment.

^{Tower-type industrial gas absorber (produced at PZGO LLC, Russia)}

Despite the fact that approaches to the capture of pollutants are often significantly different, the principle of wet sorption, technically, is the basis of almost all gas cleaning procedures.

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What is absorption?

Absorption is the molecular fusion of a substance being captured (absorbate) with an absorbent. A feature of this process is always an increase in the volume of the absorbent.

At the microscopic level, Van der Waals forces are responsible for this mechanism (as well as for the aggregate states of substances). Absorption accompanies all spheres of human life without exception, from swelling of seeds to trapping hydrochloric acid from flue gases.

^{Video: operation of an absorber}

Packing for absorption columns: from the 19th century to the present day

Immediately after the industrial-scale adoption of the sorption purification technology, the researchers came to the conclusion that the maximum capture efficiency is achieved at the maximum contact of the absorbate with the absorbent.

This marked the beginning of development in the production of geometric bodies having a high surface per unit volume and low airdraulic friction.

^{Today’s market offers wide variety of packing bodies for industrial air scrubbers and absorption columns. The material, like the topology / shape, can vary: stainless steel, ceramics, porous polymers impregnated with metals, polypropylene, etc}

One of the pioneers in this field was Fritz Raschig (1863-1928), a German scientist from Berlin, who made many discoveries concerning the treatment of gas phases. It was he who revealed that the tubes, whose diameter coincides with the length, show high efficiency as packing bodies for absorption towers. Later, these tubes were called Raschig rings.

The inventions of the 19th century were so simple, elegant and effective that Raschig rings (and their modifications), Levin’s spirals and Pall rings are among the main absorber packings to this day.

The principle of operation of packed absorbers and fixed-bed scrubbers

Before proceeding to the description of the principles of operation, it should be noted that the operation of wet absorbers and fixed-bed scrubbers has the nearly same model. In some cases, there is no difference at all.

Thus, one of the main functors of the absorbers is the packing, which can be piled up randomly or laid in a certain (structure) order. Regardless of type, size and orientation, the key to successful operation of the absorber is to ensure a sufficient contact area of the absorbent and contaminated media.

^{The process water is being sprayed over a packed bed consisting of stainless steel Pall rings}

Since liquids are good pollutant acceptors, the principle of operation of the devices involves the spraying of water or a chemical reagent over the packing bodies. The liquid forms a micro-film of a huge surface on which the pollutant is deposited. The number and parameters of spraying units may vary from model to model.

The continuity of spraying allows keeping the surface reactivity of the fixed bed, and the contaminated absorbent is discharged into the sludge receiving section.

The efficiency of wet-type absorption is so great that ordinary process water can be used as an atomizing agent. However, to neutralize air streams containing strong chemicals, alkaline, acidic, manganese, lime, bromine and other aqueous solutions are often used.

Packing materials and chemisorption

All that was said above refers to the so-called physical absorption, the main driver of which is the diffusion mechanism, that is, the penetration of one substance into another.

But in manufacturing practice often there is a need not only to effectively neutralize a dangerous or undesirable substance, but also to obtain valuable sludge adaptable for further processing.

In this case, as a reagent, a solution with certain chemical properties is charged into the device. Technically, it is more correct to call such devices chemisorbers.

^{Horizontally-oriented chemisorber (delivery stage)}

A feature of chemical absorption towers is that in the working compartment there is not only a diffusion reaction, but also associations or dissociation reactions. The environments in the working chamber are quite aggressive, moreover, chemisorption, as a rule, is accompanied by the release of heat.

In addition, in chemisorbers, the packing bodies’ materials may also have certain reactivity. As a rule, these are copper (for DeSOx), nickel (for HNO₃), chromium, monel, magnesium and lithium alloys, and also metal-impregnated polymers / plastics.

In the manufacture of high-inert packings, casings and piping for treating acidic, alkaline, ester, alcohol and ketone fumes the following materials are commonly used: PP, RPP, PVC, CPVC, ceramics, stainless steel, titanium, fluoroplastic.

Scope of supply

Typically, the absorption tower consists of the following functional units. Of course, the unit’s design may vary depending on the requirements of the Customer and the specifics of gas filtration procedures.

• The casing / tower or a horizontal frame made of PP, stainless steel, titanium or fluoroplastic (the choice of material largely depends on the thermal conditions and the aggressiveness of the media);
• inlet socket for supplying contaminated air- or gas flow;
• quenching chamber (optional: despite the fact that all wet-type gas cleaning machines are capable of processing high-temperature gas streams, in some cases it is required to include a quenching chamber in the design);
• absorbent tank;
• support reticulate grid / tray for restraining packing material;
• an array of mass transfer bodies made of metal, ceramics, alloy or plastic / polymer (Raschig rings, Intallox saddles, Levin’s bodies, Pall rings, etc.);
• one or more spray sections;
• drip trap;
• pumping station and a set of valves / pipes (made of chemically resistant materials).

Each industrial absorber is also equipped with a control board, as well as power cables, pressure sensors, a pH meter, a flow meter and pit level sensors.

Orifice / Froth / Foam-type absorbers

Another type of chemical gas cleaning apparatuses is self-induced foaming absorber. In basic principles, the design is similar to devices with a stationary bed, with the difference that the mass transfer section is replaced by one or more perforated trays (one above the other), on top of which the liquid reagent is being foamed.

Contaminated flow is fed through the inlet socket and, passing through perforated plates irrigated by atomizing cones, forms a layer of unstable froth having extreme sorption capacity.

^{Foaming absorber (production / assembly process)}

Foam-type gas treaters / cleaners are widely used in the electroplating, printing, chemical and petrochemical industries, as well as in the ferrous and nonferrous metallurgy.

Obvious advantages of absorption-type gas cleaners / air purificators over other types of equipment

The obvious advantages of this type of equipment are:

• purification rate: up to 99.99%;
• compact design (also adaptable for marine vessels);
• low power consumption;
• the ability to handle gas and air environments of high temperature (fumes and vapors after burning organic and inorganic matter / fuel);
• simplicity, durability, low OPEX and CAPEX, technical unpretentiousness and full automation of the device operation (optionally, an automatic conveyor-scraper type sludge remover may be installed within the system).

Perhaps the only drawback of chemical absorbers is the high undesirability of the presence of dust inclusions in the stream being cleaned / processed.

To preserve and maintain the device’s nominal efficiency when processing particulate-containing gaseous media, it is highly recommended to install a Venturi dust collectoror a fluidized bed scrubber upstream the absorber unit.

Design, manufacture, delivery and commissioning of equipment in Europe and Asia

For answers to any questions relating to the individual development, design and manufacture of absorption towers, please contact us by email or fill out the Customer’s questionnaire.

We are also ready to quickly deliver equipment to any point in Europe or Asia and, if necessary, to carry out seamless commissioning of gas cleaning, ventilation and aspiration systems.

PZGO LLC guarantees price affordability (even for medium- and small-scale manufacturing / processing enterprises), reliability and durability.

PZGO LLC – breathe with ease!