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PZGO LLC > Articles > Removal of acid gases and alkaline / caustic fumes, vapors and aerosols in modern industry

Removal of acid gases and alkaline / caustic fumes, vapors and aerosols in modern industry

chemistry

Modern industry, despite the high productivity and variety of products, is often the emitter of a huge amount of acid and alkaline compounds of gaseous, fume, vapor and aerosol / sol nature.

In some cases, caustic vapors and acid gases are catalysts for chemical and physical matter transformations, while in other cases they are a “true” by-product.

The release of the above components into the atmosphere is categorically unacceptable, since acids and alkalis exhibit extremely high potency in binding within biological organisms.

But, one way or another, modern technological cycles cannot show sufficient efficiency without the use of highly reactive chemical compounds. This obliges industrial enterprises to take a serious approach to setting up advanced air- and gas filtration systems.

PZGO LLC has been engaged in the developing and manufacture of dry adsorption towers, acid scrubbers and caustic absorbers for over 30 years. Our gas treatment plants daily confirm their effectiveness and faultlessness at more than 200 industrial organizations in Russia and abroad.

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Scope of alkaline (caustic) and acid scrubbers and absorbers

To date, wet scrubbers of reagent-type are used in almost all areas of the economy and industry. For clarity, the industries needing to remove acid gases are presented in the table below.

TABLE: Branches of industries and corresponding scopes of acid scrubbers and caustic absorbers

Industry Scope of alkaline / acid scrubbers and absorbers
Chemical sector manufacture of artificial fibers, production of plastics, rubbers and polymers
Pharmaceutical sector medicines, ointments, serums, suspensions, emulsions
Textile, light and clothing industry coloring of fabrics and fibers, production of glues, lacquers, enamels
Agro-industrial complex fertilizers, herbicides, insecticides
Water treatment facilities neutralization of acidic / alkaline aerosols and vapors after sewage treatment operations
Ferrous and nonferrous metallurgy deactivation of acid gases after procedures of surface cleaning from scale and oxide films, metals reduction
Extraction and processing of hydrocarbons dehydration / sweetening of gases, production of gasoline, kerosene, diesel, tar, bitumen
Mining & quarrying acid treatment of ores to increase net yield of metals, including rare earth metals

In fact, both absorption columns and scrubbers implement the principle of absorption in their work. The difference between these types of equipment lies in their suitability for treating gas phases contaminated with mechanical impurities. Scrubbers are more related to dust removal equipment, while absorption towers are predominantly chemical apparatuses.

Contrary to popular belief, many acids can exist in a solid / crystallized state of aggregation (for example, tungsten WO3·H2O, boric H3BO3 , orthophosphoric H3PO4 , metaphosphoric HPO3, and also citric acid ((HOOCCH2)2C(OH)COOH), known to all cookery experts.

However, due to the electron-chemical similarity of these substances with other acids, the acid-base neutralization method can also be used (and being used) to deactivate them.

acid scrubber

PP-bodied absorption column for neutralizing acidic and / or alkaline fumes and vapors (produced at PZGO LLC)

Theoretical principle of neutralizing acids

The gradation of all substances into acids, bases and salts has been known since ancient times. To date, there are several theories of acid-base interaction, which have some differences, but are harmonious in one postulate – the interaction between acids and bases (alkalis) occurs through the quantum mechanism of physical attraction between the negatively charged hydroxyl ion OH and the positively charged hydrogen ion H+.

This chemical and physical paradigm, along with the dry adsorption of gases, marked the beginning of one of the most rational way of industrial air purification from acid gases, vapors and aerosols.

absorber-based gas treating plant

Column-absorber-based gas filtering plant

Design and principles of operation of wet-type acid gas treaters

All scrubber systems and absorber units, regardless of purpose, size and spatial orientation, are wet-type gas cleaning devices.

The flexibility of gas treatment procedures in these machines is provided by the possibility of loading reagents with desired chemical properties into the atomizing section. For neutralizing the acidic components of the gas phase, ceteris paribus, alkaline solutions are best suited since their ability to bind with an acidic medium is very strong.

Interesting fact: the strongest acid known to date is fluoroantimonic acid (H2FSbF6). This substance is 20000000000000000000 times stronger (and, thus, more dangerous), than concentrated sulfuric acid!

However, besides alkalis, some other compounds exhibiting basic properties, for example, water solutions of basic salts (also called hydroxyl / alkali salts – halides, borates, carbonates, sulfates and sulfites), can effectively bind / react with acids.

venturi dust arrester

Despite the fact that the Venturi scrubber is more focused on dust collection, it also shows high efficiency in the capture of acid components, (especially in the composition of flue gases)

Among other things, the selection of the proper reagent (at the design stage) allows gas treaters to produce valuable liquid sludge, which can later be dehydrated, processed, and returned to the technological cycle (or profitably disposed of).

When ordering the manufacture of compact, reliable and affordable gas scrubbers in PZGO LLC, you can be sure that we will create the most efficient design and select a reagent that is guaranteed to provide the necessary level of treatment / purification. Please contact us.

Types and design features of chemical scrubbers and absorbers

More than a century and a half has passed since the creation of the first gas scrubber. Over the years, the design has been modified, improved, modernized, and as a result, several main types of scrubber systems have emerged, which today are widely used in all branches of modern industry.

nitrogen dioxide

It is the acidic oxides of nitrogen and sulfur compounds that are responsible for coloring some fumes / smokes in red

The PZGO scrubber systems compare favorably with others in that they show a high efficiency of neutralizing harmful and undesirable substances even when using process water as a reagent.

Depending on the nature of emissions of a production, one of the following types of equipment can show maximum efficiency. Please note that everything described below applies equally to caustic scrubbers.

Type of filtering apparatus Peculiarities and characteristics
Packed / Fixed-bed absorbers
packed column
the working chamber is filled with bodies of a specific topology (Pall rings, Raschig rings, Levin’s bodies), on top of which there is atomization of a liquid (neutral, acid or alkaline) reagent. The main functor of such devices is a thin liquid microfilm, in the interphase layer of which the acid components are being captured. The orientation of the devices can be both tower and horizontal
Fluid / floating bed scrubbers
fbs
the working chamber is filled with hollow polypropylene balls (chemically inert). The balls are located in the equilibrium zone of opposing forces (contaminated flow / liquid layer), which gives them a state of pseudoliquid. In devices of this type, the area of interaction of undesirable substances with a liquid barrier is maximum. FBS are the ideal solution for acidic gases contaminated with a particulate matter. In addition, the working chambers of these devices are self-cleaning
Bubble scrubbers / orifice absorbers
foam absorber
the working chamber contains one or more perforated trays, one above the other. The reagent is fed onto the plates, and the contaminated stream passing through the perforations foams the reagent, creating a self-sustaining layer of unstable froth. Foam absorbers are widely used in chemical, printing and electroplating industries
Venturi scrubbers venturi scrubber the active zone is a so-called Venturi Cone, where the polluted flow accelerates to hundreds of meters per second. At the junction of the confuser and the diffuser are nozzles that spray the liquid reagent. Liquid, under the influence of a stream of high kinetic energy, dissipates into micro fog, which effectively captures pollutants on the surface of microscopic droplets. Read more about Venturi scrubbers on the corresponding page of our site

Dry adsorption columns for acid gases retention

Dry industrial adsorbers show ≈ 100% efficiency in the removal of acid gases (including sulphur dioxide). However, unlike scrubbers and absorbers, their proper operation is directly dependent on several important factors.

  • The flow must be dry. In the case of high humidity of the stream being processed, a gas desiccant must be installed upstream of the absorber.
  • It is not rational to use an adsorption column for streams with significant pressure drops.
  • The composition of the gas phase should be precisely known, constant and unchanged over time.
  • Periodic regeneration and replacing of the adsorbent (silica gel, activated carbon, or porous polymer) is necessary.

adsorption tower

Adsorption tower produced at PZGO LLC

Read more about dry industrial adsorbers.

Particulate removal and gas sweetening in power- and oil-and-gas industry

One of the largest sources of gas emissions into the atmosphere is the fuel and energy complex. A special feature of the waste gases of petrochemical factories, CHP and boiler houses processing the hydrocarbon feedstock is the high pollution of the exhaust flows with mechanical particulate (ash and soot). Sulfur dioxide SO2 is one of the most dangerous acid gases produced when combusting the fossil fuels.

The term “gas sweetening” largely refers to the neutralization of sulfur oxide, but this definition can also be found in the scientific texts, related to the neutralization / removal of acid gases in general (carbon dioxide, carbon monoxide, hydrogen sulfide and others).

Special requirements are placed on equipment capable of simultaneously neutralizing a wide range of gas and mechanical phases. These requirements are fully met by floating / fluidized bed scrubbers.

Specially created demo stand of fluidized bed scrubber working chamber vividly depicts the chaotic movement of hollow PP-balls inside the absorbent

Please familiarize yourself in more detail with the technical characteristics of the apparatuses that use the pseudoliquid layer as the main functor.

Caustic scrubbers and industrial alkaline absorbers

In addition to acids, many industrial enterprises generate alkaline vapor and caustic aerosol waste: caustic soda, caustic potash, hydrated lime, lithium-, potassium-, rubidium-, and thallium hydroxides. Alkalis are often even more dangerous for biological organisms than acids, so their deactivation is no less important industrial task.

packed bed scrubber

Stationary-bed scrubber column with gas handling capacity of 1000 cubic meters of medium per hour

The most aggressive alkali is cesium hydroxide. This substance is 10 times more chemically active than caustic soda or caustic potash. Cesium hydroxide is used as an additive for battery electrolytes.

The main emitters of alkaline aerosols and caustic fumes are:

  • Electroplating shops (galvanizing, nickel plating, chrome plating);
  • Agricultural fertilizer producers;
  • Oil and gas sector (high-sulfur oil production);
  • Dairy and meat farms;
  • Detergent manufacturers;
  • Food industry;
  • Producers of building mixtures, cement, gypsum, alabaster;
  • Pharmacological enterprises.

As for caustic scrubbers and alkaline absorption towers, they work exactly the same way as acid scrubbers. The main reaction occurring in the interfacial layer (liquid-gas) is the acid-base neutralization reaction. Thus, in order to neutralize alkaline vapors, weak acid solutions are used as a reagent.

Since alkalis, in the overwhelming majority of cases, are solid crystalline substances, dry adsorption towers are usually not used for the treatment of alkaline vapors (due to the wet nature of alkaline aerosols and vapors).

Composite chemical resistance rating of structural materials

Material Chemical resistance
Steel lined with acid-resistant paint low, limited lining life
Polypropylene medium, the best option for processing gases and aerosols of normal and near-normal temperature
Fiber glass and fluoroplastic high, increased chemical resistance, the ability of equipment to work with high pressure flows
Stainless steel high, high chemical resistance, the ability to handle gas-air flows of high temperature
Titanium extreme, the ability of equipment to work with chemical compounds of extreme temperature and reactivity
Making an order at PZGO LLC, you can be sure that we will select such structural material(s) that will be necessary and sufficient to perform your specific gas filtering / cleaning or air purification tasks.

Equipment engineering, manufacture, delivery and commissioning in Europe and Asia

For any questions related to the design, manufacture and acquisition of chemical scrubbers, absorbers and adsorption towers, please fill out the Customer’s questionnaire or send us an email.

As a manufacturer of a full cycle, we also offer to purchase modern, compact and inexpensive systems for neutralizing acidic and alkaline / caustic sludges resulting from the operation of chemical gas cleaning equipment.

We are ready to quickly deliver gas cleaning devices and plants / facilities to any point in Europe and Asia and, if necessary, to commission equipment and train personnel.

manufacture of acid scrubbers

PZGO LLC – breathe with ease!