Mr. Education

Combustion It is defined as, " in which fuel is oxidized and a large quantity of energy is released " . Fuel  ↣   " Any material that can be burned to release thermal energy " . Mostly hydrocarbons. Proportion of Air: Air contains 21 % Oxygen, 79 % Nitrogen by volume. The molar ratio of N 2 /O 2 = 79/21 = 3.76 . So,  Combustion Process Reactants + O 2    ↣   combustion   ↣   Products Simplest combustion process  ↣  known as Stoichiometric Combustion (all carbon from CO 2 , hydrogen from H 2 O). Equivalence Ratio or Excess Air Ratio It is defined as, " ratio of actual fuel-air ratio to the theoretical fuel-air ratio for complete combustion " . Theoretical air (or Stoichiometric Air)   ↣  refers to the minimum amount of air that is required for providing sufficient oxygen for complete combustion of fuel (C, H 2 , S). If equivalence ratio < 1   ↣  Lean Mixture . If equivalence ratio > 1   ...

Boiler Feed Water Natural water usually contains solid, liquid and gaseous impurities. It cannot be used for Power Generation. Makeup Water is needed  ↠  to replace the losses due to Blow Down and Leakages in the cycle. Salt of Calcium and Magnesium is harmful because when heated, it precipitates as solid residue. If 1 litre water is added in boiler  ↠  1 - 2 % of water waste as evaporation losses. Classification of Impurities in Water Impurities in water are classified into the following types: A. Visible Impurity Microbiological Growth  ↠  presence of micro-organisms which produce clogging. Turbidity and Sediments  ↠  Turbidity (suspended insoluble matter) and sediments (coarse particles which settle down in stationary water). B. Dissolved Gases Carbon dioxide Oxygen Nitrogen Methane  Hydrogen Sulphide  C. Mineral and Salts Iron and Magnesium Sodium and Potassium Salts Flourides Silica D. Mineral Acids  Presence of undesirable (re...

Fluidized Bed Combustion Technology Fluidized bed combustion (FBC)  is defined as, " a combustion technology used to burn solid or low grade fuels " . Fuel particles are suspended in a hot bed of particulate materials (like ash, sand, limestone). Since this allows coal plants to burn at cooler temperatures, less NO x  is also emitted. We have large coal reservoirs but it has high Sulphur content  ↣  to deal with this issue, we have Fluidized Bed Combustion Technology.  This technology is used because: Sulphur emission decreases by Lime. NOx emission decreases by decrease in temperature. Circulating Type Fluidized Bed Boiler  It is defined as, " a boiler which works on the fluidized bed combustion technology for producing heat " . There are two  types of Circulating Type Fluidized Bed (CFB) Boiler: Circulating Type   ↣  Particle velocity ranges between 5 - 10 m/s. Bubbling Type  ↣  Particle velocity ranges between 1 - 3 m/s. Con...

Boiler Hydro Test Boiler hydro test is used to ensure all the welding joints, pipe bents and all headers are water leak proof. It is done at pressure of 1.5 times of design pressure. E.g.: If design pressure of boiler is 50 bar, then the hydraulic test pressure will be 75 bar. Pre-Checklist Hydro Test Following are the pre-checklist for the hydro test of Boiler: All erection work should be completed. Confirm that no foreign material left in the boiler. Confirm the drum manhole is closed with proper gasket. Confirm all the drain system ready for operation. All safety valve should be gagged. The range of the pressure should be 2 times of the maximum test pressure but not less than test pressure. The pressure gage should be pre-calibrated before test. The test pump should have capacity of more than test pressure. Minimum quantity of demineralized water should be available equivalent to the boiler capacity. Ensure condensate and Feedwater chemistry parameters to strictly adhere to the requ...

Water Tube Boiler It is defined as, " Boiler in which water flows into the tubes and are surrounded by flue gases (or flames) " . High pressure Boiler Fast Steam Production (due to small ratio of steam and water content) Combustion efficiency is higher Require good water treatment (if sediments present can cause choking) Working Pulverized Coal (powdered form) burned in Combustion chamber  ↣  water is preheated in economizer   ↣  gas temperature decreased which from green house gas emissions   ↣  water from down-comer pass to the water wall (heated by gases)  ↣  heat transferred from flue gases to water (in Counterflow manner )  ↣  saturated steam is produced which is converted into superheated steam ( 600 - 750℃ ) by superheater . Drum   ↣  used to separate moisture content from steam (coming from water wall). Boiler Accessories  It is defined as, " Fittings and equipments required to increase the boiler efficiency " ...

Steam Generator or Boiler It is defined as, " a closed vessel in which steam is produced from water by the combustion of fuel " . Fuel may be solid (wood, coal), Liquid (diesel, petrol), Gas (pulverized coal). Complex integration of furnace, superheaters, evaporators, economizer, burners, fans, duct, collector. Application of Boilers Generation of Electric Power Process requirement in Pharmaceutical for mixing liquid (because steam is good heating medium) For heating biuldings in cold weather for hot water supply Sterilization of surgical equipment's in hospitals Ineffectiveness of Early Design of Boiler Since, heat transfer area is very small, so it is ineffective. Initially water is closed. Primary Requirements of a Boiler Large heating surface to absorb maximum amount of heat. Water must be contained safely. Steam must be of required pressure, temperature, quality, flow rate. Factors while Selecting a Boiler (keep balance between Initial cost and Maintenance cost) Qua...

Steam Turbine It is defined as, " A power unit which produce power from a continuous supply of steam being delivered to the turbine at high pressure and exhausted to the condenser at low pressure " . Motive power is due to the rate of change in momentum. Turbine operates at very high speed up to 40,000 rpm and 40% efficiency . Hero's Turbine ⇔  in which exhaust causes sphere to spin. Applications: Power Generation Petrochemical refineries Paper mills Sugar Industry Classification of Steam Turbine: 1. According to the Direction of Steam Flow Axial Turbine   ⇔  in which steam flows in the direction parallel to the axis of turbine. Radial Turbine   ⇔  in which steam flows in a direction perpendicular to the axis of turbine. 2. According to the Action of Steam on Blades Impulse   Reaction Combination of Impulse and Reaction Ques: How can we distinguish between Impulse and Reaction Turbine? Ans: Degree of Freedom ( DOR ) define it is a reaction of impulse tu...

Steam Nozzle It is defined as, " a passage through which heat energy of steam is converted to kinetic energy by producing a high velocity jet of steam which is used to drive a steam turbine " . Nozzle  ↣  Increase velocity at the expense of pressure drop. Throat  ↣  Produce steam jet with high velocity to drive steam turbine. Types of Nozzles: Convergent Nozzle   ↣  Cross-section decreases continuously from entrance to exit. Divergent Nozzle   ↣  Cross-section increases continuously from entrance to exit. Convergent-Divergent Nozzle   ↣  Cross-section first decreases from entrance to throat, then increase from its throat to exit. Stagnation State For a high speed flows (in jet engines), P.e. is negligible but K.e. is not. It is convenient t combine enthalpy and K.e. of the fluid into a single term called Stagnation or Total Enthalpy . h o = h + 0.5 V^ 2 Total or Stagnation State   ↣  state in which flow is brought to rest...