Air Technology Glossary

Abrasion is the method of scuffing, scratching, wearing down, marring or rubbing away. It is often intentionally imposed during a controlled process using an abrasive. Abrasion can also be an undesirable effect of exposure to normal use or exposure to the elements.

The abrasion number is the measurement of the structural strength of granular activated carbon and it is the ability of the particle to stand up to shear forces caused by particles rubbing together or particles rubbing against another surface like a column wall or supporting screen. It is measured by shaking granules with steel balls during a container under certain conditions and expressed as a percentage reduction in Mean Particle Diameter.

Activated carbon, also called activated charcoal, is a form of carbon processed to possess small, low volume pores which increase the surface area available for adsorption of the gaseous molecule. Activated is at times substituted with active. Due to its high degree of micro porosity, one gram of activated carbon has a surface area in excess of 3,000 m² as determined by gas adsorption. An activation level sufficient for useful application could also be obtained solely from high surface area. Further chemical treatment often enhances adsorption properties. Activated carbon is typically derived from charcoal. When derived from coal it is referred to as activated coal. Activated coke is obtained from coke.

Activated carbons are manufactured carbonaceous non-hazardous products having a porous structure and a huge internal surface area. The chemical structure of activated carbon can be defined as a crude form of graphite with a random or amorphous structure, which is very porous over a broad range of pore sizes, from visible cracks and crevices to cracks and crevices of molecular dimensions.

The apparent density of activated carbon is extremely less (typically 400 to 550 kg/m3 ) because there is air space in between particles of an activated carbon sample. Better quality activated carbon has higher density which provides greater volume activity. To determine the apparent density of activated carbon, ASTM D 2854 -09 (2014) is used. The solid or skeletal density of activated carbon typically ranges from 2000 to 2100 kg/m³ (125–130 lbs./cubic foot).

The precursor is first treated with a chemical activation agent, mostly phosphoric acid, and then heated to a temperature of 450 – 700 °C in an activation kiln. The char is then washed with water to get rid of the acid from the carbon. The filtrate is passed on to a chemical recovery unit for recycling. The carbon is dried, and the product is usually screened to get a specific particle size range.

The process by which molecular species get accumulated over the surface by physical forces is known as adsorption and this phenomenon creates a film of adsorbate on the surface of adsorbent.

The process by which molecular species are taken up by bulk phase liquid or solid material and distributed throughout the surface.

Force of attractions occurs on the surface of the material is responsible for adsorption. On the basis of this force of attractions adsorption is classified as physical adsorption and chemical adsorption. The adsorption process where the adsorbent and adsorbate is held physically with London dispersion force which is like weak van der waals force of attraction, it is termed as physical adsorption where as if the adsorption is taking place with chemical bonding then it is known as chemical adsorption, hence it is more stronger.

Adsorption kinetics is the measure of adsorption with respect to time at constant pressure or concentration and this is to measure the diffusion of adsorbate in the pores.

Alkalinity is the ability of water to resist changes in the pH, which would increase the acidity of water.

Rocks are the main sources of natural alkalinity and it contains carbonate, bicarbonate, and hydroxide compounds. Borates, silicates, and phosphates could also contribute to alkalinity. In case of activated carbons, when they are placed into service they can show Ph and alkalinity spikes of significant duration.

Activated carbon is helpful in the application of air purification. It can help to eliminate unpleasant odours as well as pollutants by passing through it. While passing through the carbon, pollutants in the air will get trapped in the pores of carbon leading to the purification of air. For air purification, the action of the activated carbon can be improved by impregnating activated carbon with chemical.

It is a gum resin which has strong smell and obtained from the stems of the N Asian umbelliferous plant Dorema ammoniacum and it is mainly used as an expectorant, stimulant, perfumes and also in the porcelain cement.

Anthracites are those which are considered as hard coal with submetallic luster and it has a high source of carbon with less impurities and it contains highest energy density.

It is basically bulk density of the powder which determines a property of powders or any other particulate matter. It is also known as volumetric density. Apparent density defines the relation between mass and volume of the material. It is denoted as (⍴b). The apparent density of activated carbon is very less (typically 400 to 500 kg/m3 ) because there will be air space in between particles of an activated carbon sample. Better quality activated carbon has higher density which provides greater volumetric activity. To determine the apparent density of activated carbon, ASTM D 2854 -09 (2014) is used.

Ash is the product that is obtained after something is burned. Basically, it is the solid remains of fire. At a specific high temperature, when combustion of products takes place, the inorganic residue will remain and this is termed as ash content.

It is the process of removing residual chlorine present in disinfected water before releasing it into the outside environment. Sulfur dioxide is used mostly for de-chlorination. The alternate methods of de-chlorination are filtration through activated carbon, or ammonia or hydrogen peroxide.

Molasses number is the measure of de-colorization capacity of an activated carbon. To determine the number, some amount of pulverized carbon is mixed and heated with standard molasses solution for a defined time.

Densification, also known as agglomeration, is a process of transferring loose and fluffy biomass into reasonably uniform (in size, shape, and density), smooth materials that flow evenly and well in standard storage and conveyance equipment.

H2S is a toxic, harmful, and odorous compound present in the biogas. It must be eliminated as it is very harmful for human health. Desulphurization of biogas can be done in different ways such as:

• Chemical absorption method: This method includes amine method, carbonate method, ammonia methods to remove H2S from biogas.
• Physical absorption method: Includes naphthoquinone absorption method and ammonia method.
• Wet oxidation method: Oxidizes H2S in the gas by neutral or weak basic solution.

The size of the activated carbons is usually expressed in sieve size, in millimeters (mm) or US mesh. The process of measuring involves shaking the activated carbon through a defined series of sieves. Effective size of activated carbon is the size, expressed in mm for which 10% by weight of granules are smaller. This value indicates the pressure drop and filtration performance of carbon beds.

Activated carbon provides a lot of products and filters for domestic as well as industrial air purification system which are vital for emission control.

• Removal of VOC and hydrocarbons
• Odour control
• Cabin air purification

Steam activation process: Oxidation, carbonization and activation.

Oxidation and carbonization are done at temperatures up to 500C and is a highly exothermic process. Internal surface is created during the steam activation at temperature over 1000 degree C.

Capable of being extracted by specific methods.

Activated carbon are produced in different shapes by extrusion process. Extruded shape includes pellets and cylindrical shapes. It is extruded at high-pressure into a cylindrical shaped form. Sometime activated catalysts are mixed to obtain a specific pore structure.

Fluidized bed reactors (FBR) are chambers that allow for the mixing of liquid or gas substrates with powdered catalysts so that the catalyst starts to act like a fluid, maximizing mixing and interaction. The basic configuration is detailed to the right where a substrate gets passed upward into a chamber under pressure through a plate which can support the catalyst. FBRs are essential to produce many materials and chemicals and could be an effective tool for several basic capabilities of the GVCS. Fluidized-bed reactors (FBR) are the best reactor configurations used for reactions involving solid reactants.

The Freundlich equation is an empirical relation between concentration of the solute on the surface of an adsorbent to the concentration of the solute in liquid with which it is in direct contact. It is also called as Freundlich adsorption isotherm.

The Freundlich adsorption isotherm is usually expressed as.

Gas applications: Industrial gases are used for plenty of industries like oil and gas, petrochemicals, chemicals, power, mining, steelmaking, metals, environmental protection, medicine, pharmaceuticals, biotechnology, food, water, fertilizers, nuclear power, electronics and aerospace. In the commercial and residential sectors, gas is mainly used for space heating and cooling, water heating, and cooking. Power plants can use gas to generate electricity.

Gases get purified for the purpose of further using the gases themselves again or the impurities contained in them. Industrial gases discharged into the atmosphere is purified to prevent pollution of the air by noxious substances. Mechanical and electrical purification is used for recovering solid and liquid impurities from gases, and physicochemical methods are used for removing gaseous impurities.

Graphite is the crystalline form of carbon with atoms arranged in a hexagonal shape. It naturally originates in this form and is the most stable form of carbon under standard conditions. Under high pressures and temperatures, it gets converted into diamond.

Granular Activated Carbon (GAC) has irregularly shaped particles with sizes ranging within 0.2 to 5mm. Granular activated carbons are produced by activating the base material directly or soon after an agglomeration step. Granular sizes from 0.2 up to 2 mm are extensively used in liquid phase applications as adsorption kinetics are more paramount than pressure drop. Granular sizes from 2 to 5 mm are used for gas phase applications where the pressure drop more critical as compared to adsorption kinetics.

Hydrogen sulphide is a colourless, flammable, and severely harmful gas that possess a “rotten egg” smell. Hydrogen sulphide gets produced by the bacterial breakdown of organic materials and animal wastes (e.g., sewage). Hydrogen sulphide is simultaneously a chemical asphyxiant and irritant with adverse effects on both oxygen utilization and the central nervous system.

The most widely used method for H2S removal is adsorption. The adsorbents that can be used in dry adsorption desulfurization processes include natural or synthetic zeolites, activated carbons, and metal oxides. Biological treatment or Liquid-based and membrane techniques can also be used to remove H2S.

The number on a calibrated scale that indicates the relative hardness as determined by a particular system of testing, e.g., Knoop, Mohs, Rockwell, Vickers hardness tests. A steel ball or diamond point is applied with a known variable load for a determined period to produce an indent whose depth or diameter is to be measured.

A hazard is a source of potentially grave danger, or adverse health effects on someone.

When hydrogen chloride gets exposed to air, dense, white-coloured corrosive vapours are formed. For purification, filters are used which were filled with high grade, extremely pure activated carbon products to obtain a good purification efficiency and avoid secondary contamination. The free chlorine gets reduced to below the detection limit and the chloropyramines were strongly reduced to a manageable level.

The main threats from heavy metals are associated with exposures to arsenic (As), lead (Pb), cadmium (Cd), and mercury (Hg). Possible methods to control the metal toxicities in humans include, divalent cation therapy, gastric lavage, ascorbic acid intake, etc. The use of chelating agents in the acute toxicity phase has also been found to be useful. Protective legislation against the use of metal alloy cooking utensils is a potential long-term control strategy.

Heavy metals are naturally occurring elements that have a high relative atomic mass and a density at least 5 times greater than that of water. These metallic elements are systemic toxicants that can cause multiple organ damage, even at lower levels of exposure.