Download Combustion and Environment: Lecture 39 - Emission and Its Control and more Study notes Sustainability Management in PDF only on Docsity! Objectives_template file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture39/39_1.htm[10/5/2012 4:47:38 PM] Module 7: Combustion and Environment Lecture 39: Emission and Its Control The Lecture Contains: SOx Emission and Its Control Forced Oxidation Limestone Wet Scrubber Zeldovich Mechanism Fenimore (Prompt) Mechanism Fuel (N2O – Intermediate) Mechanism Objectives_template file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture39/39_2.htm[10/5/2012 4:47:39 PM] Module 7: Combustion and Environment Lecture 39: Emission and Its Control SOx Emission and Its Control Gasification method Sulphur dioxide emission due to burning of coal or fuel oil can be minimized by gasifying them. During gasification, coal undergoes partial oxidation resulting in CO and . Sometimes, and other gases can also be produced during gasification of coal. In this case, sulphur content gets converted into hydrogen sulphide , which can be removed by absorption or adsorption method.. In absorption method, gases are scrubbed with alkaline reagent such as sodium carbonate or ethylamine. Subsequently elemental sulphur is produced. In adsorption method, ferric oxide is used to adsorb hydrogen sulphide using fluidized bed around 400°C. Objectives_template file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture39/39_5.htm[10/5/2012 4:47:39 PM] Module 7: Combustion and Environment Lecture 39: Emission and Its Control Zeldovich Mechanism From the above table it is clear that emission can be reduced by decreasing the temperature. (Figure 39.2) Thermal are formed by simple heating of oxygen and nitrogen. The radical ‘N' can react with to form NO. Thermal NO contribution is low till 1300 K and beyond which it increases rapidly. The thermal mechanism consists of the following two chain reactions. --------(1) --------(2) --------(3) Objectives_template file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture39/39_6.htm[10/5/2012 4:47:39 PM] --------(6) --------(8) --------(7) --------(9) Module 7: Combustion and Environment Lecture 39: Emission and Its Control Fenimore (Prompt) Mechanism Prompt mechanism refers to the which are formed very quickly by interaction of active hydrocarbon species derived from fuel with nitrogen and oxygen. They are generally not observed in flames of non-hydrocarbon flames. They cannot be formed by just heating nitrogen with oxygen. During initial phase of combustion, the radials with carbon atom react with to produce N. --------(4) This reaction is the main path which dictates the rate at which radical ‘N' is formed. The radical ‘N' can also be formed by the following reaction. --------(5) When the equivalence ratio is less than 1.2, HCN can be converted to NO as follows, Objectives_template file:///D|/Web%20Course/Dr.%20D.P.%20Mishra/Local%20Server/FOC/lecture39/39_7.htm[10/5/2012 4:47:39 PM] Module 7: Combustion and Environment Lecture 39: Emission and Its Control Fuel (N2O – Intermediate) Mechanism Thermal NO is quite small below 1300oC Thermal NO rises sharply with temperature Both fuel NO & prompt NO do not vary with temperature But prompt NO increases marginally with temperature. N2O intermediate mechanism plays a very important role for NO control in lean premixed combustion. Three steps of N2O intermediate mechanism are given below; (Figure 39.3) Several techniques are devised to control in combustion as described in next section.
