View Factor Orientation (or View factor or shape factor) plays an important role in radiation heat transfer. View factor is defined as, "fraction of radiation leaving surface 'i' and strike 'j' ". Summation Rule (View Factor) If there is are similar surfaces 'i' and 'j' , then: Blackbody Radiation Exchange Radiation Exchange between Opaque, Diffuse, Gray surfaces in an Enclosure 1. Opaque 2. Surfaces 3. Two surface enclosure Radiation Shield It is used to protect surfaces from radiation act like a reflective surface. References: Material from Class Lectures + Book named Fundamentals of Heat and Mass Transfer by Theodore L. Bergman + My knowledge. Photoshoped pics are developed. Some pics and GIF from Google. Videos from YouTube ( Engineering Sights ).
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Steam Generator & Water Tube Boiler
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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".
It is a type of Straight water tube boiler with Longitudinal Drum.
Not used in Power Generation.
Number of tubes depends on the diameter of drum.
Baffles plates ↣ which guides flue gases and ensure proper heating of water tubes.
It creates hindrance which convert flow to turbulent which enhances heat transfer.
Anti-Priming Pipe ↣ used to separate water from steam.
It contains perforation sheets ↣ moisture content settle down ↣ steam enters to superheated tube heated by flue gases ↣ flows to steam stop valve.
Ash Pit ↣ Ash collected produced by combustion and removed.
Damper (or Valve) ↣ installed before chimney to regulate the air supply to fire box.
Steel Girders ↣ On which boiler assembly is suspended which allow contraction or expansion during boiler operation.
Mud Box ↣ where sediments or mud from water settle down.
b. Straight Water Tube Boiler with Cross Drum
Number of tubes can be installed depends on the length of Drum.
More number of tubes ↣ more steam generation.
c. Four Drum Bent Water Tube Boiler OR Stirling Boiler
It is defined as, "Bent tube, externally fired, water tube boiler, stationary, with natural circulation boiler".
Pressure Range ↣ maximum 60 Bar.
Steam Production Rate ↣ 50 Ton/hr = 50,000 Kg/hr.
Efficiency ↣ (60 - 80) %
Boiler Operation ↣ Diameter up to 2m and length (5 - 8) m.
Construction & Working
3 Horizontal steam drum arranged upper part of boiler settings.
Mud Drum arranged in Lower part.
Drums are connected with each other by Equalizing (maintains steam level) and Circulating tubes (maintains water level).
Water is feed into Drum 3 ↣ moves to mud drum (separate mud and removed from blow off valve) ↣ pure water pass to 1 and 2 drum. Pulverized Coal is burned on Grate (fire box) releasing hot flue gases ↣ deflected by Brick arch and baffles plates. Water in bent tubes connected into steam collected over the water level in drum ↣ steam is collected and pass to super heated tubes and collected from Steam stop valve.
Advantages
High steam production rate due to number of steam drum.
High pressure operation and less pressure drop.
Bent tubes allow free expansion and contraction (undue thermal stress).
Permits great flexibility in Design.
Disadvantages
More difficult to clean and inspect the bent tubes.
Larger in size.
Super heated temperature is limited.
d. Lamont Boiler OR Pump Assistance Circulating Unit
It is defined as, "a forced circulation, internally fired and water tube boiler".
Works on Sub-critical pressure and temperature.
Working
Combustion chamber is vertical where fuel burns.
Water enters feed pump to provide water to economizer (preheat water) ↣ goes to drum ↣ water circulating pump ↣ increases pressure greater than boiler pressure ↣ Distributor header (distribute water to pump) ↣ Radiant evaporator (tubes) ↣ Convective evaporator ↣ goes to steam drum (where moisture content separated by baffles) ↣ pure steam goes to superheater ↣ temperature increases ↣ sent to turbine (primover).
e. Benson Boiler OR Once Through Water Tube Boiler
It is defined as, "a high pressure, drumless, forced circulation, internally fired water tube boiler".
If boiler is operated above supercritical point ↣ no need of drum.
Require extremely clean water about 0.1 ppm/tds.
Operating at 250 bar.
Capacity is 135 ton/hr of steam
Light in weight (because of absence of drum).
Thermal efficiency is around 90%.
Same as Lamont Boiler ↣ but no circulating pump and boiler drum.
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