Chapter 4 Fossil Fuel Energies

1. Chapter 4 Fossil Fuel Energies • Boosting Power Plant Efficient (提昇發電效率) • Low Emission Boiler Systems—LEBS (低排放鍋爐系統) • Pressurized Fluidized Bed Combustion—PFBC (高壓流體化床燃燒技術) • Integrated Gasification Combined Cycle—IGCC (氣化複循環發電技術) • Indirectly Fired Cycle—IFC (間接燃燒循環發電技術) • Advanced Turbine Systems—ATS (先進渦輪機系統)

2. 4-1 Boosting Power Plant Efficient • Less fuel will be consumed to generate the same amount of electricity. ↓ sharply reduce emissions of CO2

3. 4-1 Boosting Power Plant Efficient • Coal-Fired Power Plants • Efficiency ~ 33-38 % • Retrieve waste heat • Simple cycle:heat from the burning coal boils water to create steam which spins a steam turbine-generator ↓ combined two or more power generation cycles

4. 4-1 Boosting Power Plant Efficient

5. 4-1 Boosting Power Plant Efficient • Low Emission Boiler System— “supercritical steam cycle” a conventional power plant boiler releases steam at p~2400 psi (160 bar) & T~1050 oF (570 oC) ↓ p~3400-5500 psi (230-370 bar) & T~1100 oF (590 oC)

6. 4-1 Boosting Power Plant Efficient • Conventional combined cycle— burn natural gas or petroleum products, using the hot combustion gases to power a combustion gas turbine-generator, then channelling the waste heat to drive a steam turbine-generator. ↓ Pressurized Fluidized Bed Combustion & Integrated Gasification Combined Cycle (DOE for “combined cycle” operation to coal-burning power plants)

7. 4-1 Boosting Power Plant Efficient • Pressurized Fluidized Bed Combustion system— coal is burned at elevated pressures (6-16 bars) to produce a high-p exhaust gas stream. →spin a gas turbine-generator. Simultaneously, the boiler also heats water to produce steam (steam cycle)

8. 4-1 Boosting Power Plant Efficient • Integrated Gasification Combined Cycle system— coal is converted into a combustible gas (typically a mixture of CO and H2) ↓ The gas is burned in the combustor for a gas turbine-generator. Simultaneously, exhaust gases from the gas turbine heats water to produce steam (steam cycle)

9. 4-1 Boosting Power Plant Efficient • Integrated Gasification Combined Cycle system— In the future, may combine with high-T fuel cell ↓ A hybrid system combining coal gasification, high-T fuel cells, and high efficiency gas turbine cycles→ efficiency up to 60% & CO2 release cut to half of conventional one.

10. 4-1 Boosting Power Plant Efficient • Integrated Gasification Combined Cycle system— Gasification-based power system produce a concentrated CO2 gas stream→ carbon sequestration ↓ cf. conventional coal-burning tech. release CO2 in a diluted, high-volume mixture with nitrogen (from the combustion

11. 4-1 Boosting Power Plant Efficient • Natural Gas Power Plants • Worldwide, 16% of fuel consumed for electricity generation in 1995→23% in 2015 • Emits only ½ CO2 than coal for the same energy produced.

12. 4-1 Boosting Power Plant Efficient • Natural Gas Power Plants

13. 4-1 Boosting Power Plant Efficient • Natural Gas Turbines 40 years ago, η~20% for a simple cycle system. Today, η~30% for a simple cycle system & η~mid-50% for a combined cycle system . • Thermal efficiency of a gas turbine depends on T of the gas entering the turbine blades.~2300 oF (1260 oC) for modern turbines (temperature barrier) ↓ Reaching the limits of current materials → new materials or better ways to cool the blades • DOE is developing new tech. to push Tinlet to 2600 oF (1430 oC) → η~60% for a combined cycle system

14. 4-1 Boosting Power Plant Efficient • Fuel Cell Power Plants—another way to use natural gas, η> 50% • Using an electrochemical reaction of H2 (fuel) and O2 (from air) to produce electricity, water and heat. • Generate the least amount of CO2 in the fuel processing stage.

15. 4-1 Boosting Power Plant Efficient • 「一度電」的定義就是1kWh也就是一千瓦小時 • 「一度電」就是1000(W)瓦耗電的用電器具，使用一小時所消耗的 電量 • 例如你點亮一個100瓦的燈泡10小時，也就是1000Whr，也就耗掉「一度電」了 • 一度電 = 一千瓦 x3600秒= 3,600,000焦耳

16. 4-1 Boosting Power Plant Efficient • BTU (British thermal unit):a unit of energy used in the United States. In most other areas, it has been replaced by the SI unit of energy, the joule (J). • In the United States, the term "BTU" is used to describe the heat value (energy content) of fuels, and also to describe the power of heating and cooling systems, such as furnaces, stoves, barbecue grills and air conditioners. • When used as a unit of power, BTU per hour is understood, though this is often confusingly abbreviated to just "BTU".

17. 4-1 Boosting Power Plant Efficient • 1 BTU ≡ the amount of heat required to raise T of one pound of water by one degree Fahrenheit. • One BTU is approximately: 1.054-1.060 kilojoule 252–253 cal (calories, small) 0.252–0.253 kcal (kilocalories) 778–782 ft·lbf (foot-pounds-force)

18. 4-1 Boosting Power Plant Efficient • 1 watt is approximately 3.41 BTU/h • 1000 BTU/h is approximately 293 W • 1 horsepower is approximately 2540 BTU/h • 1 "ton of cooling", a common unit in North American refrigeration and air conditioning applications, is 12,000 BTU/h (~3.5kW). It is the amount of power needed to melt one short ton of ice in 24 hours. • 1 therm is defined in the United States and European Union as 100,000 BTU – but the U.S. uses the BTU59 °F whilst the EU uses the BTUIT. • 1 quad (short for quadrillion BTU) is defined as 1015 BTU, which is about one exajoule (1.055×1018 J). Quads are occasionally used in the United States for representing the annual energy consumption of large economies: for example, the U.S. economy used about 94.2 quads/year in 1997.

19. 4-2 Low Emission Boiler System • B&W’s Advanced Coal-Fired Low Emission Boiler System

20. 4-2 Low Emission Boiler System • 1. Rankine cycle. Simple Steam Rankine Cycle

21. 4-2 Low Emission Boiler System • 1. Rankine cycle—coal, oil, and natural gas. Simple Steam Rankine Cycle

22. 4-2 Low Emission Boiler System • 1. Rankine cycle—coal, oil, and natural gas. Simple Steam Rankine Cycle

23. 4-2 Low Emission Boiler System • 1. Rankine cycle—coal, oil, and natural gas. Simple Steam Rankine Cycle

24. 4-2 Low Emission Boiler System • 2. Bryton Cycle—oil or natural gas. Basic Bryton Cycle

25. 4-2 Low Emission Boiler System • 2. Bryton Cycle—oil or natural gas. Basic Bryton Cycle

26. 4-2 Low Emission Boiler System • 3. Combined Cycle

27. 4-3 Pressurized Fluidized Bed Combustion • Fluidized bed combustion (FBC) is a combustion technology used in power plants. FBC plants are more flexible than conventional plants in that they can be fired on coal, biomass, among other fuels. These boilers operate at atmospheric pressure • Fluidized beds suspend solid fuels on upward-blowing jets of air during the combustion process. The result is a turbulent mixing of gas and solids. The tumbling action, much like a bubbling fluid, provides more effective chemical reactions and heat transfer.

28. 4-3 Pressurized Fluidized Bed Combustion

29. 4-3 Pressurized Fluidized Bed Combustion • FBC reduces the amount of sulfur emitted in the form of SOx emissions. • Limestone is used to precipitate out sulfate during combustion, which also allows more efficient heat transfer from the boiler to the apparatus used to capture the heat energy (usually water pipes). The heated precipitate coming in direct contact with the pipes (heating by conduction) increases the efficiency. Since this allows coal plants to burn at cooler temperatures, less NOx is also emitted. • However, burning at low temperatures also causes increased carbon dioxide, nitrous oxide, and polycyclic aromatic hydrocarbon emissions. FBC boilers can burn fuels other than coal, and the lower temperatures of combustion (800 °C) have other added benefits as well.

30. 4-3 Pressurized Fluidized Bed Combustion • FBC evolved from efforts to find a combustion process able to control pollutant emissions without external emission controls (such as scrubbers). • The technology burns fuel at temperatures of 1,400 to 1,700 °F (760 to 930 °C), well below the threshold where nitrogen oxides form (at approximately 2,500 °F (1370 °C)). • The mixing action of the fluidized bed results brings the flue gases into contact with a sulfur-absorbing chemical, such as limestone or dolomite. (> 95% of the sulfur pollutants in coal can be captured inside the boiler by the sorbent) • Commercial FBC units operate at competitive efficiencies, cost less than today's units, and have NOx and SO2 emissions below levels mandated by Federal standards.

31. 4-3 Pressurized Fluidized Bed Combustion(r2001_03_109.pdf,) • The first-generation PFBC system also uses a sorbent and jets of air to suspend the mixture of sorbent and burning coal during combustion. However, these systems operate at elevated pressures and produce a high-pressure gas stream at temperatures that can drive a gas turbine. Steam generated from the heat in the fluidized bed is sent to a steam turbine, creating a highly efficient combined cycle system. • A 1-1/2 generation PFBC system increases the gas turbine firing temperature by using natural gas in addition to the vitiated air from the PFB combustor. This mixture is burned in a topping combustor to provide higher inlet temperatures for greater combined cycle efficiency. However, this uses natural gas, usually a higher priced fuel than coal.

32. 4-3 Pressurized Fluidized Bed Combustion

33. 4-3 Pressurized Fluidized Bed Combustion(2_1a6.pdf)

34. 4-3 Pressurized Fluidized Bed Combustion(2_1a6.pdf)

35. 4-4 Integrated Gasification Combined Cycle Technology • This power plant configuration relies on a coal gasifier rather than a boiler.   • Combustible gases produced by the gasifier can be cleaned to high purity levels (more than 99 percent sulfur removal) before being burned in a gas turbine.   • Exhaust heat can be used to drive a steam turbine.   • 1st-generation systems now being readied for construction can achieve efficiencies up to 42%. 2nd-generation systems could reach efficiencies of 45 % by the end of this decade, and more advanced systems envisioned are expected to exceed 50 % efficiency levels.   • Sulfur dioxide and nitrogen oxides emissions are less than one-tenth of the New Source Performance Standards.

36. 4-4 Integrated Gasification Combined Cycle Technology

37. 4-4 Integrated Gasification Combined Cycle Technology

38. 4-4 Integrated Gasification Combined Cycle Technology

39. 4-4 Integrated Gasification Combined Cycle Technology • IGCC Advantage • A Clean Environment—99% SO2 removed before combustion, NOx reduced by over 90%, CO2 is cut by 35%. • High Efficiency—42 – 52% • Low-Cost Electricity. • Low-Capital Costs • Repowering of Existing Plants—components of IGCC can be integrated into an existing system in modular form • Modularity—allowed for staged additions in blocks ranging in size from 100-450 MW.

40. 4-4 Integrated Gasification Combined Cycle Technology • IGCC Advantage • Fuel Flexibility—most gasifier systems can be easily adapted to different • Phased Construction—1st-phase include only a gas turbine, operating as a simple natural-gas-fired cycle.(2/3 ultimate capacity) →2nd phase, a steam turbine create a combined cycle with full capacity. →3rd phase, integrate the gasifier and gas cleanup systems. • Low Water Use. ~50-70 % that of a PC plant with a flue gas desulfurization system • Low CO2 Emissions. ∵ high efficiency. More reduction when combined with fuel cell systems in the future. 11. Continuous Product Improvement

41. 4-4 Integrated Gasification Combined Cycle Technology • IGCC Advantage • Reusable Sorbents • Marketable By-Products—Waste disposal is minimal: sulfuric acid, element sulfur, Ash and any trace elements are melted and when cooled become an environmentally safe, glass-like slag that can be used in the construction or cement industries. • Co-Products—fuels in the form of methanol or gasoline, urea (尿素) for fertilizer, hot metal for steal making and chemicals. • Demonstrated Success • Public Acceptability

42. 4-4 Integrated Gasification Combined Cycle Technology • Improving Key Components • Advanced Gasifier Systems • Hot Gas Desulfurization • Hot Gas Particulate Removal • Advanced Turbine Systems (ATS)

43. 4-5 Indirectly Fired Cycle Systems • The combustion gases created by burning coal in this high performance power system are prevented from contacting a gas turbine.  Instead, they transfer heat to an impurity free gas, eg. air, that powers the turbine.   • Currently, in the conceptual design phase, indirectly fired cycle systems could offer a coal-based technology with efficiencies approaching 50 %, with sulfur dioxide, nitrogen oxides, and particulates reduced to 1/4 of the New Source Performance Standards.

44. 4-5 Indirectly Fired Cycle Systems

45. 4-5 Indirectly Fired Cycle Systems

46. 4-5 Indirectly Fired Cycle Systems • Ceramic Heat Exchanger Development (Key component) • Survive high operating temperature • Resist corrosion • Withstand pressure differentials • Avoid seal leakage • Avoid catastrophic failure

47. 4-6 Advanced Turbine Systems • What is a Gas Turbine? (also called a combustion turbine) • A rotary engine that extracts energy from a flow of combustion gas. It has an upstream compressor coupled to a downstream turbine, and a combustion chamber in-between. • Energy is released when air is mixed with fuel and ignited in the combustor. The resulting gasses are directed over the turbine's blades, spinning the turbine and powering the compressor, and finally is passed through a nozzle, generating additional thrust by accelerating the hot exhaust gases by expansion back to atmospheric pressure. • Energy is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power aircraft, trains, ships, generators, and even tanks

48. 4-6 Advanced Turbine Systems • What is a Gas Turbine? This machine has a single-stage radial compressor and turbine, a recuperator, and foil bearings.

49. 4-6 Advanced Turbine Systems • What is a Gas Turbine? • The power turbines in the largest industrial gas turbines operate at 3,000 or 3,600 rpm to match the ACpower grid frequency and to avoid the need for a reduction gearbox. Such engines require a dedicated building. • They can be particularly efficient — up to 60% — when waste heat from the gas turbine is recovered by a conventional steam turbine in a combined cycle configuration.

50. 4-6 Advanced Turbine Systems • What is a Gas Turbine? • They can also be run in a cogeneration configuration: the exhaust is used for space or water heating, or drives an absorption chiller for cooling or refrigeration; cogeneration can be over 90% efficient. • Simple cycle gas turbines in the power industry require smaller capital investment than combined cycle gas, coal or nuclear plants and can be designed to generate small or large amounts of power. • Also, the actual construction process can take as little as several weeks to a few months, compared to years for baseload plants. Their other main advantage is the ability to be turned on and off within minutes, supplying power during peak demand. Large simple cycle gas turbines may produce several hundred megawatts of power and approach 40% thermal efficiency.