• Author / Uploaded
• arham

• Categories
• Central eléctrica
• Turbina de gas
• Tecnología energética
• Producción de energía
• Conversión de energía

Citation preview

COMBINED CYCLE POWER PLANT Steam electric power plants which utilize boilers to combust a fossil fuel average 33 percent efficiency. Simple cycle gas turbine (GTs) plants average just under 30 percent efficiency on natural gas, and around 25 percent on fuel oil. Much of this wasted energy ends up as thermal energy in the hot exhaust gases from the combustion process. To increase the overall efficiency of electric power plants, multiple processes can be combined to recover and utilize the residual heat energy in hot exhaust gases. In combined cycle mode, power plants can achieve electrical efficiencies up to 60 percent. The term “combined cycle” refers to the combining of multiple thermodynamic cycles to generate power.

INNER WORKINGS OF A COMBINED-CYCLE POWER PLANT Combined cycle operation employs a heat recovery steam generator (HRSG).A combined-cycle power plant uses both a gas and a steam turbine together to produce up to 50 percent more electricity from the same fuel than a traditional simple-cycle plant. The waste heat from the gas turbine is routed to the nearby steam turbine, which generates extra power.

HOW A COMBINED-CYCLE POWER PLANT PRODUCES ELECTRICITY This is how a combined-cycle plant works to produce electricity and captures waste heat from the gas turbine to increase efficiency and electrical output. 1. Gas turbine burns fuel. 

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The gas turbine compresses air and mixes it with fuel that is heated to a very high temperature. The hot air-fuel mixture moves through the gas turbine blades, making them spin. The fast-spinning turbine drives a generator that converts a portion of the spinning energy into electricity.

2. Heat recovery system captures exhaust. A Heat Recovery Steam Generator (HRSG) captures exhaust heat from the gas turbine that would otherwise escape through the exhaust stack. The HRSG creates steam from the gas turbine exhaust heat and delivers it to the steam turbine.

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3. Steam turbine delivers additional electricity. The steam turbine sends its energy to the generator drive shaft, where it is converted into additional electricity.

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Ques / Ans Q1)

Wound up spring

Batteries connected to motors

Rotating flywheel

Stretched rubber bands

a) State which of the above change shape when their stored energy is transferred? Ans. Wound up spring b) Describe how the energy from a rotating flywheel can be transferred to moving parts of a child’s toy? Ans. Q2) the diagram below shows a pendulum which was released from position A.

A

B

C

a) What forms of energy did the pendulum have at: 1. A? Potential energy

2. B? Gravitational energy + potential energy 3. C? Gravitational energy + potential energy b) Eventually the pendulum would stop moving. Explain what has happened to the initial energy of the pendulum? Ans. The P.E changed to thermal energy. Q3) A type of toy catapult consists of a movable plunger which has a spring attached as shown above. The handle was pulled to fully compress the spring and on release the metal ball of mass 0.1 kg (1N) was projected 0.75 m vertically. a) 1. What type of energy is stored in a compressed spring? Ans. Elastic potential energy. 2. what happens to this stored energy when the handle of this plunger is released? Ans. Changed into K.E and P.E. b) Calculate the maximum P.E acquired by the metal ball. Write down Formula and show working. Data: Mass=0.1 kg G=10 N h=0.75 m Solution: P.E= mgh = 0.1 x 10 x 0.75 = 0.75 J Q6) A crate of mass 300 kg is raised by an electric motor through a height of 60 m in 45 s. Calculate: a) The weight of the crate. Data: Mass= 300 kg G= 10 N W=mg

Solution: W= 300 x 10 = 3000 N b) The work done by the motor. Data: F= 3000N d=60 m W= Fd Solution: W= 3000 x 60 = 180,000 J c) The useful power of the motor. Data: F= 3000 N V= d/T P=F x V Solution: Useful power output=3000 x 60/45 =180000/45 =4000 W Q10) a) Complete the table for other fuels. Fuel

Renewable

Must be burnt to release energy

Found in the earth’s crust

Coal Wood Uranium

No Yes No

Yes Yes No

Yes No Yes

b) 1. Explain how fossil fuels are produced? Ans. They are formed from the remains of animals and plants which lived millions of years ago.

2. State two reasons why we should use less fossil fuels.  The main disadvantage of using fossil fuels, of course, is the pollution that they cause.  They are non renewable.