filtration of gases, solids and aerosols
the CRUMA filtration system
Filtration of gases
The basic principal on which the filtration of gaseous molecules is based is the adsorption concept. The two processes based on adsorption are physisorption and chemisorption. The physical adsorption of produced gaseous molecules, takes place by diffusion (Brownian diffusion) or adsorption /condensation by Van der Waals Forces. The gaseous molecules move into the empty spaces among activated carbon particles and diffuse into the internal pores. Attracted and captured by Van der Waals Forces, the molecules penetrate the pores, strike the walls and are finally trapped. The number of active pores in the carbon is huge and the total contact surface is therefore very high. The specific surface measures the surface per mass unit, in m2/g. There are carbons reaching up to 2000 m2/g. The physical process of adsorption is followed by chemical adsorption (chemisorption). It consists of a chemical reaction between the gas and the activated carbon whose reaction product is linked to the active material by chemical bond. The chemical impregnation of activated carbons increases the number of gases that can be removed through this advanced air flow system.
| Produced gases | G GasesVapours | GS Gases Vapours Solids Aerosols |
| Organics | A | AD |
| Inorganic acids | BE | BED |
| Formaldehyde | F | FD |
| NH3 &amines | K | KD |
| Hg (mercury) | MD | |
| Organics/ inorganics/ NH3/amines | ABEK | ABEKD |
G-type hoods are those with a single activated carbon filter (impregnated or not) for filtering fumes.
GS-type hoods are equipped with a double HEPA carbon filter for filtering fumes and particles (solids and aerosols).
The Cruma activated carbon filters
All the activated carbon filters of CRUMA fume hoods have been impregnated, manufactured and tested according to the requirements of the CEN-141 standard.
Type A: adsorption of vapours and organic solvents (ketones, ethers, alcohols, cyclics…). Activated carbon without impregnation.
Type BE: inorganic gases like Cl2, HCl, HNO3,… and volatile sulphur compounds (H2S, H2SO4, SOx…). Activated carbon with impregnations of metallic compounds and neutralizing salts.
Type K: specific for N H3 vapours and amines. Activated carbon impregnated with metallic complexes.
Type F: specific for formaldehyde and derivatives. Impregnated with Cu.
Type ABEK: mixed type among filter A, BE and K. It's able to retain molecules belonging to all these 3 groups. It's impregnated with inorganic neutralizing salts, metallic salts, complexes and Cu.
Specific types: there are special filters available for Hg (type MD).
The designation D indicates that a HEPA absolute filter class H14 (UNE-EN-1822 standard) is fitted as a pre-filter below the activated carbon filter required for applications that generate solids and/or aerosols.
All CRUMA fume hoods are fitted with a class G4 synthetic biofibreprefilter (UNE-EN-779 standard) for the retention of atmospheric dust.
Hepa filters. Filtration of solids and aerosols
In order to handle or generate small size solid or liquid particles (aerosols), a HEPA filter must be installed to prevent the particles from reaching the filter and to prevent carbon deactivation.
HEPA stands for "High Efficiency Particulate Air". These filters are known as "absolute filters" because
of their high filtration efficiency. They are made of pleated glass microfibre papers. The technique of pleating gives the filter retention efficiency.
The HEPA filters used by CRUMA are class H-14, according to the EN-1822 standard, providing a minimum efficiency of 99.995% for 0.3 µm particles, according to test DOP. The highest HEPA category is H-14.
The next most efficient filter, U-15, belongs to the ULPA (Ultraefficiency) filter category, which is used in very specific applications. All CRUMA GS Fume Hoods are equipped with HEPA filters.
Gases, acids, vapours or solvents. There is a filter for each type of toxic compound. For further information, contact our Customer Service Department on + 34 902 370 700
