Energy, Climate, and Society – Lecture 9 Fossil Technologies

Sample analytic questions

How much coal can be saved/emissions can be mitigated if China’s average coal power efficiency increased by 1 percentage point?
Why combined heat and power saves energy?

Thermodynamics

Thermodynamic efficiency
Comparing different technologies
Thermodynamics provides physic limits

Heat engine

Heat -> Mechanical energy (work)

Laws of thermodynamics

Zeroth law
“If two systems are each in thermal equilibrium with a third, they are also in thermal equilibrium with each other.”
First law
“In a process without transfer of matter, the change in internal energy, \(\Delta U\), of a thermodynamic system is equal to the energy gained as heat, \(Q\), less the thermodynamic work, \(W\), done by the system on its surroundings.”
Second law
“Heat does not spontaneously flow from a colder body to a hotter body.”
Third law
“As the temperature of a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.”

Three efficiencies

1st law: actual, thermal efficiency;
\(\eta_1 =\frac{W_{net}}{Q_{in}}=\frac{Q_{high}-Q_{low}}{Q_{high}}=1-\frac{Q_{low}}{Q_{high}}\)
Carnot: maximum possible efficiency;
\(\eta_c =\frac{W_{net}}{Q_{high}}=\frac{T_{high}-T_{low}}{T_{high}}=1-\frac{T_{low}}{T_{high}}\) (Kelvin)
2nd law: comparing 1st and Carnot;
\(\eta_2 =\frac{\eta_1}{\eta_c}\)

A gas turbine engine

A steam coal plant

Brayton cycle vs. Rankine cycle

Jet engine, gas turbine

Steam engine, steam turbine

Brayton cycle vs. Rankine cycle

Brayton Cycle	Rankine Cycle
Jet, Gas turbine	Steam turbine
Open	Open/closed circuits
Working fluid in gaseous phase	Working fluid phase change

Largest coal plant in the U.S.

Georgia Power plant Scherer (3,720 MW)

Can you identify the components

Coal storage
Generating unit
Cooling stack
Bottom ash landfill
Sub-station
Transimission lines
Waste/pollution management

Combined cycle

CCGT Diagram

Defining a Rosenfeld Plant

500 MW
c.f.: 70%
T&D losss: 7%

Results:

3 TWh/year
3 MtCO2/year
NYC electricity use: ~4 TWh/year

References

Koomey, Jonathan, Hashem Akbari, Carl Blumstein, Marilyn Brown, Richard Brown, Chris Calwell, Sheryl Carter, et al. 2010. “Defining a Standard Metric for Electricity Savings.” Environmental Research Letters 5 (1): 014017. https://iopscience.iop.org/article/10.1088/1748-9326/5/1/014017.