Energy Balance Procedures

1
Energy Balance Procedures

• Draw and completely label a flow diagram
• include temperature, pressure, and phase (solid,
  liquid or gas)
• Perform (if possible) all material balances
• Write the appropriate form of the energy balance
  (closed or open), and eliminate terms that are
  negligible (with proper justification)
• Determine the specific enthalpies of each stream
  component
• look up information in the steam tables
• Other components ? calculate them (Chapters 8 9
  of FR)
• 5. Solve the problem!

2
Example

• Saturated steam at 1 atm is discharged from a
  turbine at a rate of 1150 kg/h. Superheated
  steam at 300?C and 1 atm is needed as a feed to a
  heat exchanger to produce it, the turbine
  discharge stream is mixed with superheated steam
  available from a second source at 400?C and 1
  atm. The mixing unit operates adiabatically.
  Calculate the amount of superheated steam at
  300?C produced and the required volumetric flow
  rate of the 400?C steam.

3
Problem 7.26 FR

• Liquid water is fed to a boiler at 24?C at 10 bar
  and is converted at constant pressure to
  saturated steam. Use the steam tables to
  calculate for this process,
  and then calculate the heat input required to
  produce 15,000 m3/h of steam at the exiting
  conditions. Assume that the kinetic energy of
  the entering liquid is negligible and that the
  steam is discharged through a 15 cm ID (inner
  diameter) pipe.