Boiler Calculations Lecture Notes

Introduction

• Addressing slight problems with the presentation setup
• Topic: Boilers and Boiler Calculations
• Learning Outcomes:
  • Calculate boiler efficiency
  • Calculate equivalent evaporation of a boiler

What is a Boiler?

• Device used to heat water until it changes into steam
• Types of Boilers:
  • Fire Tube Boiler:
    • Fire runs through tubes, water surrounds tubes
    • Steam produced as water exits
  • Water Tube Boiler:
    • Water flows through tubes, fire surrounds them
    • Steam produced as water exits

Boiler Calculations Overview

• Water inlet and steam outlet
• Key parameters:
  • h1: Enthalpy of feed water
  • h2: Enthalpy of steam leaving the boiler
• Important:
  • h1 is always the enthalpy of fluid (hf)
  • Use steam tables to find hf based on water temperature
  • Steam can be:
    • Dry Saturated
    • Wet (requires dryness fraction)
    • Superheated (temperature given)

Dryness Fraction

• Quality of Steam Calculation:
  • If x = 1: Dry
  • If x < 1: Wet
  • If x > 1: Superheated
  • Dryness fraction determines the state of steam

Boiler Efficiency Calculation

• Efficiency formula:
  • ( Efficiency = \frac{Output}{Input} )
  • Output = steam energy (ms * (h2 - h1))
  • Input = fuel energy (mf * heat value)
• Heat energy equation:
  • ( q_{boiler} = \frac{ms}{mf} * (h2 - h1) )*_

Equivalent Evaporation

• Formula for equivalent evaporation:
  • ( ee (100°C) = \frac{ms * (h2 - h1)}{mf * 2257} )
  • Where 2257 kJ/kg is the latent heat at 100°C

Example Calculation

• Given Data:
  • Mass of Steam (ms): 6600 kg/hr
  • Mass of Coal (mf): 600 kg/hr
  • Boiler Pressure: 2000 kPa
  • Feed Water Temperature: 95.2°C
  • Calorific Value: 32 MJ/kg
  • Thermal Efficiency: 80%
• Steps:
  • Draw a diagram of the boiler setup
  • Calculate h1 and h2 using steam tables

Calculation Steps:

1. Calculate h1:
   • Check hf at 95.2°C (should be 399 kJ/kg)
   • If not in tables, use ( hf = T * cp )
2. Calculate h2:
   • Use efficiency equation to solve for h2
3. Dryness Fraction:
   • Use formula ( h2 = hf + x * hfg )
   • Check pressure to find hf and hfg
4. Heat Quantity Absorbed:
   • Use ( q_{evaporator} = \frac{ms}{mf} * (h2 - h1) )*_

Further Information on Economizers

• Economizers preheat feed water before it enters the boiler
• Changes heat transfer and efficiency calculations
• Example Data for Economizers:
  • Feedwater enters at 32.9°C and exits at 90°C
  • Mass of steam used: 5000 kg/hr
  • Mass of fuel: 650 kg/hr
  • Calorific value: 33 MJ/kg
  • Dryness fraction: 0.95

Efficiency and Equivalent Evaporation:

1. Efficiency Calculation:
   • Use new values for heat absorbed
2. Equivalent Evaporation Calculation:
   • Apply the same formulas with new data

Conclusion

• Importance of understanding boiler operation and efficiency
• Need to refer back to steam tables for precise calculations
• Encourage further study and group discussions for clarity

Questions

• Open floor for any questions regarding calculations or concepts