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Old Jul 29th 2010, 07:40 AM   #1
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Join Date: Jul 2010
Location: Michigan
Posts: 1
Designing coal feeders for a powerplant.

I was given this problem as an excercise in thermodynamics and to better understand powerplant systems. I am having difficulties because as a civil engineering student I haven't taken alot of thermodynamics. The one course I did take was several semesters ago and wasn't that advanced.

Problem:

We are building a 600 MegaWatt (gross) peaking unit coal plant.
The plant burns weatern coal assumed to have 8200 BTU/lb


Turbine Conditions
  • Turbine has High pressure, Intermediate pressure and 2 Double Flow low pressure turbines.
  • Main Steam at 2400 psig, 1000 degress F
  • Reheat Steam at 1050 degrees F
  • Exhaust Condenser at 2.0 in Hga
  • No extractions for feedwater heaters
Boiler Data
  • Western coal is assumed to have 5% ash
  • 50 psig drop through the reheater
  • 75 psig drop through the econmmizer, waterwalls, drum, and superheater.
  • Stoichiometry in combustion zone is 0.97
  • Furnace exit gas temp is 600 F
Boiler Losses, in % of full load
  • 4.4% dry flue gas
  • 3.3% as fired fuel moisture
  • 4.4% H2 moisture
  • 0.7% Unburned carbon
  • 0.2% radiation and convection
  • 0.1% moisture in air
  • 0.5% unaccounted for losses
Turbine Data
  • HP exhaust pressure of 600 psig
  • HP effeciency of 0.88
  • IP/LP efficiency of 0.88
Use motor driven boiler feed pump


Do not consider the following:
  • Bearing and generator mechanical losses
  • Shaft seal leakages
  • Radiation and convective turbine losses
  • Station power loads
  • Atemperating sprays
The unit can reach full load with 5 coal mills. Design the neccesary coal feeders (Tons/Hr) to supply these mills to sustain the powerplant.



Here is a crude drawing I made of the problem with some of the relevant information.

My current plan of attack is to find the enthalpy drop across the HP and the enthalpy drop across the IP and LPs. Using the equation below and knowing the efficiencies of the turbines are .88 and the power plant produces 600 MW I could find the mass flow and go from there.



How do I get the enthalpy after the hp turbine or after the lp turbines. Am I supposed to be working from somewhere else in the system?

My other idea is maybe tabulating the solutions to the system at different massflows until I find a value where everything jives, but I still don't think I have all of the neccesary values.

I know this is a ton of information to have thrown at you at once. Any suggestions or advice would be appreciated. Thanks
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