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

Conventional EfficiencyPower Plant Boiler

Improvement

%64100

3430

F

TEco

%33%85

%51407.85

3430

F

TEc

%2551

5164

Fuel Savings if conventional System Output is 50 MW

Fuel cogen

Fuel conven

Fuel Savings

hrMMBtu

MWhrMMBtuMWMT 4.1934.37.5650

30

34 /

hrMMBtu

MWhrMMBtuMWE 7.1704.350 /

51.071451.0

7.1704.193 MMBtu

hrMMBtu569

64.0

7.1704.193

hrMMBtu145

Economics Plant operates 68% of time or

6000 hrs/year (conservative estimate).

Fuel Savings

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?

yrMMBtu

hrMMBtu

yrhr 000,8701456000

Operating cycles Topping Cycle Bottoming Cycle

Gas Turbine Topping CycleInstalled 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.