1. Advanced Air Pollution Engineering
Control of Smoke and odors
Learning Outcome
Analyze the effect of process change in air pollution control

2. Odour Control
Following are the methods which may be employed alone or in various combination to eliminate odours:
Modification of the process
Dilution by ventilation or dispersal
Absorption
Adsorption
Combustion or Oxidation
Odour masking
Odour counteraction or neutralization
injection of a reactive substance
Irradiation

3. Odour Control Modification of the process
Changing process either by way of change in the compostion of process amterial Or
Removal of impurities may help in odour control. Methods include :
Substitution of low-odour solvents for highly odours one
Adjustment of odours variable like Temperature, Residence time.
Such alteration if technically and economically feasible then it merits first consideration.

4. Odour Control
Dilution by ventilation or dispersal Since the odour intensity is function to the odourant concentration, then Well designed ventilation is the most common method for removal of odouras from enclosed spaces. Sometimes used for odour abatement outdoors to release odorous gases from tall stacks. It results in normal dispersion in the atmospere and consequent decrease in ground level concentrations below the threshold value. Dispersal by stacks requires careful consideration of the location and meteorological parameters.

5. Odour Control
Absorption Is applicable when the odorous gasses are soluble or emulsifiable in a liquid, or react chemically in solution. Liquid scrubbing of the gasses in a suitable absorption unit is an important method of odour control .

6. Odour Control
Adsorption Adsorption, particularly on activated carbon because its highly porous and has great adsorptive power due to very large surface area. Highly porous structures permits the carbon to remove and hold the organic vapours , hydrogen sulphide and any other oudours producing substances. The retained material can desorbed easily, and the carbom reactivated and used again. If the concentration of odours material is high. The method may not be economical.

7. Odour Control
Combustion or Oxidation (direct incineration) In this process, the odour generating gases are made to pass through a combustion chamber at a temperature of oC in the presence of excess oxygen. The main demerit of this method is the cost of the fuel to produce the required temperature. Heat exchangers may be employed to recover the heat from hot incinerated gases. Since the various gas constituents to be burnt are react at different rates. The residence time should not be less than 0.3 seconds.

8. Odour Control
Combustion or Oxidation (Catalytic Incineration) Cost of heating the gas stream to 650 oC is very high, catalytic combustion may be the choice. In this method oxidation takes place at a much lower temperature than necessary for direct incineration. Process gases pass through specially designed units containing catalyst elements, on the surface of which oxidation occurs. During the catalytic oxidation, the constituents in the gas stream such as hydrocarbons and other organics react with oxygen to form carbon dioxide and water vapour. 260 oC

9. Odour Control
Combustion or Oxidation (Catalytic Incineration) The important properties for a commercial catalyst unit are, high specific surface, low resistance to the flow gases and arrangement in a manner as to provide turbulent mixing of process gases. This unit are being used for odour control of effluent gases from chemical plants, varnish manufacture, paint and enamel-baking ovens, refuse incinerators, refineries burning waste cracking gases, and coffee roasters. The gas stream should be free from fumes,merury,lead and zinc, that might impair catalyst activity by coating the catalyst or deactivating its active centers.

10. Odour Control
Odour masking Is based on the principle that, when two odours are mixed, the stronger one will cover or mask the weak unpleasant odour. Following are the methods for odour masking: 1- Spraying, vaporizing the odorant chosen into air-gas streams in stacks. 2- Adding directly to process wherever possible. 3- Adding to scrubbing liquors. In cases where the masking odourants are directly added to the process, care must be taken to see that they will not effect the quality of the products.

11. Odour Control
Odour masking Outdoor masking can be used to control odours in outdoor places like refuse dumps or waste lagoons. Here, masking compound must vaporize rapidly enough to overcome the unpleasant odour. The selection of the suitable odorant and its quantity should be left to the specialists in the field.

12. Odour Control
Odour counteraction or neutralization Certain pairs of odours in appropriate relative concentrations are antagonistic. Therefore, when they are mixed together, the intensity of each odour is diminished. This effect called counteraction or neutralization. Musk and bitter almond, rubber and cedar wood

13. Odour Control
injection of a reactive substance Odours can be controlled by injecting controlled quantities of chlorine or ozone into the process-gas stream. Ozone converts organic matter by oxidative degradation usually to acetones and acids. Ozone also destroys or prevents the growth of odour producing micro organisms such as fungi and bacteria. chlorine either as a gas or in solution form, used for odour control. Both bacterial and chemical actions are involved. Chlorine is used in the oxidation of effluents from paper manufacturing plant.

14. Odour Control
Irradiation Ultra – violet irradiation can be used for control of odours. The action is probably due to ozone or bacterial effect.

15. Odour Control
Nuisance Regulations Generally , most municipal authorities resort to nuisance prevention law to abate odurs. The most effective method of overcoming the problem is to have regulations which can be directed towards specific emissions from specific industries. For example, regulation of pulp mill odours which limits emission of mercaptans Mercaptans are a group of sulfur-containing organic chemical substances. They smell like rotting cabbage, and are, for the most part, what make pulp mills smell