5. source correction methods
- 1. 15-08-2020 1 FUNDAMENTALS OF AIR POLLUTION CONTROL Air pollution control methods & equipment – The industrial growth had made our life more comfortable – The world has became smaller because of rapid transportation – The growth of industries has another side of coin i.e. pollution – We have to use same control methods to minimize the pollution Dilution • Accomplished by the use of tall stack • It’s Short term control & may cause highly considerable effects. • For effective dilution H = 74 Q0.27 H = Stack height Q = Particulate emission rate • HSO2 = 14 Q1/3 H = Stack height, m Q = SO2 rate, kg/hr
- 2. 15-08-2020 2 Gravity settling Absorption • Natural Absorption process – Particulate or Gaseous • Below cloud level • Falling rain drops absorbs pollutants called as Washout or scavenging • Does not remove particles less than 1µm in size. • Gaseous pollutants removed in dissolved state with moisture with or without chemical changes. Rain
- 3. 15-08-2020 3 Adsorption • Prevention is Better than cure….. • Try to minimize the WASTE at SOURCE • It can be done by – Investigation of various approaches at early stage of process design & Development – Selection of method which do not contribute pollution – This methods are called as source correction methods…. – Application of this methods are difficult in the existing plant, but still could be applied without severely upsetting the economy of the operation Control of pollution at SOURCE • Raw material changes • Operational changes • Modification or replacement of process equipment • By more effective operation of existing equipment
- 4. 15-08-2020 4 Raw material changes • If raw material is responsible for causing air pollution – Use of a purer grade of raw material • Reduce undesirable impurities & by-product • Eliminate treatment of effluent gas – Use of low sulfur fuel in place of higher ones • Limited availability of low sulfur fuel for wholesale use • Fuel desufurisation is an attractive alternative – Ore handling operation usually result in emission of large quantities of dust into atmosphere. • In steel industries replacement of raw ore with pelleted ore has gradually reduced dust emission Process change • It involves new or modified techniques to lowering atmospheric pollutant emissions • Radical changes in chemical & petroleum refining had minimized the material emission to atmosphere. – The volatile substance are recovered by condensation & the non-condensable gases are recycled for additional reaction
- 5. 15-08-2020 5 • Rotary kiln are major source of dust generation in cement plant. • Some dust is controlled by adjusting operating conditions such as – reduction of gas velocities – modification of the rate – location of feed introduction • Smelting & paper industries are major source of emission of sulphourous material • It can be reduced by major process changes such as – hydro-metallurgical separation of ore – Avoiding use of sulphide in paper making • Formation of nitric oxide in combustion chamber reduce by low excess air combustion by flue gas recirculation & water injection • The fly ash emission from coal pulverization reduce by washing of coal before pulverization
- 6. 15-08-2020 6 Equipment modification or replacement • In petroleum industries hydrocarbon vapors are released into atmosphere from storage tanks due to temperature changes, direct evaporation and displacement during filling. • These can be minimized by designing tank with floating roof covers or by pressurizing the tanks. • Replacement of open hearth furnace with oxygen furnace in steel industries • Use of alternative power source for automobiles in place of internal combustion Engine. • In addition to above three methods, air pollutant emission can be reduced by – proper equipment maintenance – housekeeping – changes in the design of local exhaust hood & proper installation • Chemical plants have excessive leakage around ducts, piping, valves & pumps. Checking the seals routinely can prevent such leaks • Floor, storage bins, loading areas & material transmitter conveyors must be kept clean to reduce dust pollution.