LECTURE 5 ELECTRIC POWER INDUSTRY. ECE 371 Sustainable Energy Systems

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1 LECTURE 5 ELECTRIC POWER INDUSTRY ECE 371 Sustainable Energy Systems 1

2 INDUSTRY STATISTICS 70% of the U.S. electricity is generated in power plants that burn fossil fuels - coal, natural gas, and oil 2

3 INDUSTRY STATISTICS 3

4 INDUSTRY STATISTICS About 20% of U.S. electricity comes from nuclear power plants The remaining 10% comes from renewable energy systems (no carbon emissions) Mostly hydroelectric facilities (6%) Wind and solar plants in 2010 accounted for about 2.5% of the U.S. electricity generation 4

5 INDUSTRY STATISTICS About one-third of the energy content of fuels used to generate electricity ends up being delivered to end-use customers 5

6 INDUSTRY STATISTICS 3/4 of U.S. electricity that makes it to customers is used in residential and commercial buildings The remaining one-fourth powers industrial facilities 6

7 INDUSTRY STATISTICS The impact of lighting and air conditioning on California power demand on a hot summer day is shown below 7

8 INDUSTRY STATISTICS The peakiness of electricity demand caused by daytime-building-energy use is one of the reasons the price of electricity delivered to residential and commercial customers is typically about 40-50% higher than that for industrial facilities 8

9 ELECTRIC POWER GENERATION Power plants come in a wide range of sizes Most electricity today is generated in large central stations Power capacities in 100s or even 1000s of MW A large nuclear plant generates about 1000 MW The total generation capacity of the U.S. is about 1000 such power plants (1000 GW or 1 TW) 9

10 ELECTRIC POWER GENERATION Steam power plants (90% of power generation in U.S.) use any of the following resources for heat Fossil fuels Nuclear fission Concentrated sunlight onto a boiler 10

11 ELECTRIC POWER GENERATION 11

12 ELECTRIC POWER GENERATION 12

13 Videos mn9e _lurk

14 ELECTRIC POWER GENERATION Utility-scale thermal power plants are based on Rankine cycle Working fluid (water) is vaporized and condensed Brayton cycle Working fluid remains a gas throughout 14

15 ELECTRIC POWER GENERATION Base load power plants are Rankine cycle plants Peaking power plants are Brayton cycle plants The newest generation of thermal power plants use both cycles and are called combined-cycle plants (more efficient) 15

16 BASIC STEAM POWER PLANTS A fossil fuel steam plant is shown below 16

17 BASIC STEAM POWER PLANTS Since cooling water is drawn from a lake (not shown in the previous figure), heated in the condenser, and returned to the lake, it is called a once-through cooling Efficiency of the turbine is about 90% Efficiency of the synchronous generator is over 90% at full load 17

18 BASIC STEAM POWER PLANTS The Carnot maximum efficiency of this power plant is Carnot TC efficiency = 1 = 1 = 0.65 = T H Carnot efficiency = W Q H = Q H Q Q H C QC = 1 = 65 0 Q H 0 However, the average efficiency of U.S. power plants is only about half of this value, since they are not perfect heat engines 18

19 COAL-FIRED POWER PLANTS Coal-fired, Rankine cycle, power plants were Responsible for 3/4 of SO x and NO x Significant portion (1/3) of CO 2 Significant portion (1/4) of particulate matter (ash) and mercury Because of this, up until 1960s, these plants were notoriously dirty 19

20 Question? What does it mean to be on the wrong side of the tracks. 20

21 COAL-FIRED POWER PLANTS 21

22 COAL-FIRED POWER PLANTS kv DC 22

23 COAL-FIRED POWER PLANTS Flue gas from boiler is sent to an electrostatic precipitator (ESP) Adds charge to the particulates in gas stream Attracts particulates to electrodes that collect them 23

24 COAL-FIRED POWER PLANTS Next, a flue gas desulfurization (FGD or scrubber) system sprays a limestone slurry over the flue gas Precipitating the sulfur Sulfur is removed in a sludge of calcium sulfite (CCCCCCCC 3 ) or calcium sulfate (CCCCCCCC 4 ) As of 2010, less than ½ of U.S. plants had FGD 24

25 COAL-FIRED POWER PLANTS Emission controls for NO x is not shown in the figure Sources of NO x N 2 in the air and a high temperature environment Nitrogen in the fuel Exhaust gases before exiting the stack go through Selective Catalytic Reduction (SCR) and NO x is converted into nitrogen and water (urea). Also used in the automotive industry for meeting new Diesel standards. 25

26 COAL-FIRED POWER PLANTS Now the picture has changed, and 40% of the cost of building a new power plant is spent on pollution controls Not only the cost of pollution controls is high, it also uses up to 5% of the power generated The overall plant efficiency is reduced even more 26

27 COAL-FIRED POWER PLANTS New plants use more expensive designs with cooling towers that transfers heat directly into the atmosphere Advantages are Requires less water Avoids thermal pollution of warming up the lake 27

28 COAL-FIRED POWER PLANTS 28

29 COAL-FIRED POWER PLANTS Thermal efficiency of a power plant is expressed as Heat Rate It is the thermal input (BTU or kj) required to deliver 1 kwh of electrical output 1 BTU/kWh = kj/kwh The smaller the heat rate, the higher the efficiency In U.S. heat rate is expressed in BTU/kWh 29

30 COAL-FIRED POWER PLANTS Inverse of heat rate is the efficiency of the power plant 30

31 COAL-FIRED POWER PLANTS Electrical Engineers (kwh) Mechanical Engineers (BTU) 31

32 COAL-FIRED POWER PLANTS Edison s first power plant had a heat rate of 70,000 BTU/kWh with an efficiency of 5% (MathCAD) A pulverized coal steam power plant has a heat rate of 10,000 BTU/kWh with an efficiency of 33% The best power plants have an efficiency of 40-45% 32

33 MathCAD Heat Rate Example 33

34 Book Example 1.1 MathCAD 34