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Cogeneration

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					     Cogeneration.
Is the simultaneous production
of electrical and thermal energy
    from a single fuel source
Typical Cogeneration Fuels
 Natural Gas
 Coal
 Diesel oil
 Bio mass [e.g. methane, from digesters or
  municipal landfills]
Example
Example
   Overall Thermodynamic Efficiency
       Often called Utilization Factor
          E  T 30  34
 co                   64%
            F    100
   Conventional Efficiency
    Power Plant   33%
    Boiler   85%
      E T    30  34
 c                   51%
        F    85.7  40
                      64  51
 Improvement                 25%
                        51
   Fuel Savings if conventional System
    Output is 50 MW

   34
T     50M  56.7 MW  3.4 MMBtu / hr  193.4 MMBtu
                              MW                hr
   30
        E  50 MW  3.4 MMBtu / hr  170 .7 MMBtu
                          MW                 hr
                       193.4  170.7
   Fuel cogen                       569 MMBtu
                                            hr
                           0.64

                       193.4  170.7
   Fuel conven                      714 MMBtu
                                            0.51
                           0.51


   Fuel Savings  145 MMBtu
                        hr
Economics
   Plant operates 68% of time or
    6000 hrs/year (conservative estimate).

Fuel Savings  6000   hr
                      yr    145   MMBtu
                                    hr      870 ,000   MMBtu
                                                         yr


  If we use natural gas, $8/MMBtu, the
  monetary savings ~$7,000,000/year.
 How much could you invest economically?
 How much CO2 reductions per year?
Operating cycles
   Topping Cycle      Bottoming Cycle
Gas Turbine Topping Cycle
Installed at Rice University
Prime movers
   Reciprocating engines
        efficient
       compact
       easy to install
       suitable for small applications
   Gas Turbines
       Intermediate power applications
       Relatively compact
       Reliable
       Easy to install
       “combined cycles”, but only for large industrial
        applications
Prime Movers (cont.)
   Steam Turbines
       Good efficiency only for units larger that
        10mW
       Can use a variety of fuels including solid waste
        and biomass
       “extraction” turbines; a portion of the steam
        flow removed during the expansion process
       “back pressure” entire steam flow used after
        last stage of expansion
Characteristics Of Prime Movers
Typical Cogeneration Performance
Parameters
Economic Criteria
   Payback Period
       Is the length of time required for the
        cumulative net savings to equal the initial
        installed capital cost. Divide the initial
        investment by the annual net savings.
   Discounted Cash-Flow Method
       Analyses the cash-flows over the full life of the
        project and accounts for the time value of
        money, including interest rate and rate of
        inflation.

				
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posted:8/12/2011
language:English
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