Gas scrubbing is the technology by which cleans a gaseous emission of the contaminants it contains. Typically, the air pollutant molecules are separated from the gaseous stream upon contact with a liquid, which may be water, a chemical reagent or a combination of these. The gaseous flow, once washed, is free of contaminants and can be emitted into the atmosphere. Contact of the contaminant with the liquid depends on the type of washer, which may be by wet packing, bubbling or aerosol, for example.
Generally, gas scrubbing is used to remove air pollutants such as smells, vapors and toxic gases. Therefore, in most cases, the pollutants present in the gases are susceptible to being oxidized or absorbed in an acid or alkaline medium. Thus, species derived from nitrogen can be absorbed in an acid environment, while species derived from sulfur are sensitive to absorption in an alkaline or oxidizing medium. In some cases, the contaminants are very soluble in water, so no chemical reagent is needed.
Condorchem Envitech offers a wide range of possibilities, with the most common scrubbers being the following types:
Whatever the type of column that best suits the particular conditions of each customer to ensure the success of the scrubbing system, the extensive experience of the Condorchem Envitech technical team has demonstrated that a particularly critical parameter is the effective design of the contaminated air collection systems, so that the entire gas stream to be treated is efficiently conducted to the gas scrubber. The efficiency of the collection and conduction system is equal in importance to the degradation efficiency of the wash column contaminants.
The most effective designs are:
The column is partially filled with a support with a high specific surface area (e.g. Raschig rings, Pall rings and Berl saddles) and the liquid that will absorb or react with the contaminant. The carrier particles encourage the gas entering through the bottom of the column to be move upwardly between the interstitial spaces left by the carrier particles, enhancing the absorption efficiency of the liquid. These columns have a high contact efficiency.
In these types of columns, the liquid descends from plate to plate while the gas rises and passes through holes in the plates, thus ensuring effective contact between the two phases. These columns are particularly useful when liquid and gas loads are very variable, or a large diameter column is required, or fouling is likely to occur (plate columns are easier to clean than packed) or thermal or mechanical stresses occur that may damage the fill.
In this type of tower, a liquid is injected in the form of an aerosol into the gaseous stream and used when high flow rates are to be treated, usually to remove some pollutant from the flue gases. Their use is preferred when a low-pressure loss is required and if there are particles in the gaseous stream to be treated.
The technique is applicable to a wide variety of industrial emissions, of which the following are the most common:
There are numerous industrial processes in which pollutant gases are produced that must be treated before being emitted into the atmosphere. An effective technique consists of subjecting the gases to a gas-liquid absorption process. The gases to be treated enter through the bottom of one or more absorption or scrubber towers, partially filled with a liquid (e.g. water, acid solution, alkaline solution, sodium hypochlorite or potassium permanganate) or a combination of liquids, which absorb the pollutants present in the gas. The gas leaves the scrubber without the pollutants being present and may be emitted into the atmosphere. Pollutants that are satisfactorily eliminated through a gas-liquid absorption process are SO2 and the NOX of the combustion gases, the hydrogen sulphide from wastewater treatment plant, COV, carbon monoxide, etc.
For the decontamination of the gas to be exhaustive, the system must be designed such as to maximize the transfer of material from the gas phase to the liquid phase: