Fuel Cell Power Plants
Steam Turbine Plants
Steam turbine plants can be divided into three general categories: fossil fueled, nuclear, and renewable. Most of electricity produced in the United States, for example, comes from fossil fuel steam turbine plants, about 70%. The dominant fossil fuels are coal, petroleum and natural gas; others include petroleum coke, coke oven gas, and liquefied petroleum gas. Steam turbine plants operate by burning fuel, which heats water in a boiler; the water boils and produce steam, which is channeled to a turbine and turns it. The turbine is connected to a generator shaft which turns and produces power. All steam turbine plants function the same way.
Of the many fuels used in steam turbine plants, coal is the most common. Coal is inexpensive and readily available since the US has large deposits. Annually electric utilities purchase over 900 million short tons (короткая\малая тонна = 907,2 кг) of coal for electric generation.
Answer the following questions:
1. What three categories can steam turbine plants be divided into?
2. What are the dominant fossil fuels?
3. How do steam turbine plants operate?
4. What are the pros and cons of building steam turbine plants?
Fuel cells are electrochemical devices which directly convert hydrogen, or hydrogen-rich fuels into electricity without combustion. This process is much more efficient than traditional thermal power plants, converting up to J80% of the chemical energy in the fuel (compared to a maximum of 40% for conventional power plants). Although their structure is somewhat like that of battery, fuel cells never need recharging or replacing and can produce electricity as long as they are supplied with hydrogen and oxygen. Fossil flues (coal, oil and natural gas), biomass (plant material), or pure hydrogen can be used as the source of fuel. If pure hydrogen is used, the emissions from a fuel cell are only electricity and water. Fuel cells are small and modular in nature and therefore fuel cell power plants can be used to provide electricity in many different applications, from electric vehicles to large, grid-connected utility power plants. First used in the U.S. space program, fuel cells are a developing technology with a few commercial uses, but may emerge as a significant source of electricity in the near future.
The fuel cell power section contains "stacks" (хранилища) of one or more fuel cells. Most individual fuel cells are small in size and produce between 0.5 and 0.9 volts of electricity. Therefore, any power plants must have a large number of individual fuel cells. This modular nature of fuel cells is one of their advantages. A fuel cell power plant can be built to a certain size and then have its power output quickly and easily increased by adding more stacks of fuel cells when and if demand for electricity increases. Air, (for its oxygen) and hydrogen rich fuel are added to the stacks of the fuel cells, and the output is water, heat and direct current (DC). The power conditioner section of a fuel cell power plant most often consists of an inverter which converts the electricity to alternating current (AC).
(Fuel cell - 1.топливный элемент; 2. топливный бак)
Answer the following questions:
1. Is the process of converting hydrogen, or hydrogen-rich fuels into electricity without combustion efficient? Why?
2. What is emitted from a fuel cell if pure hydrogen is used?
3. Who was the first to produce fuel cells?
4. How much electricity do fuel cells produce?
5. What advantages do fuel cells have?
6. How do fuel cells operate?