|
|

楼主 |
发表于 2004-7-25 17:00:56
|
显示全部楼层
我准备的其中一们课,各位指导一下,看行不
Power plants generate electrical power by using fuels like coal, oil or natural
gas. A simple power plant consists of a boiler, turbine, condenser and a pump.
Fuel, burned in the boiler and superheater, heats the water to generate steam.
The steam is then heated to a superheated state in the superheater. This steam
is used to rotate the turbine which powers the generator. Electrical energy is
generated when the generator windings rotate in a strong magnetic field. After
the steam leaves the turbine it is cooled to its liquid state in the condenser.
The liquid is pressurized by the pump prior to going back to the boiler A simple
power plant is described by a Rankine Cycle.
RANKINE CYCLE(画图解释)
Saturated or superheated steam enters the turbine at state 1, where it expands
isentropically to the exit pressure at state 2. The steam is then condensed at
constant pressure and temperature to a saturated liquid, state 3. The heat
removed from the steam in the condenser is typically transferred to the cooling
water. The saturated liquid then flows through the pump which increases the
pressure to the boiler pressure (state 4), where the water is first heated to
the saturation temperature, boiled and typically superheated to state 1. Then
the whole cycle is repeated.
TYPICAL MODIFICATIONS
REHEAT
When steam leaves the turbine, it is typically wet. The presense of water causes
erosion of the turbine blades. To prevent this, steam is extracted from high
pressure turbine (state 2), and then it is reheated in the boiler (state 2') and
sent back to the low pressure turbine.
REGENERATION
Regeneration helps improve the Rankine cycle efficiency by preheating the
feedwater into the boiler. Regeneration can be achieved by open feedwater
heaters or closed feedwater heaters. In open feedwater heaters, a fraction of
the steam exiting a high pressure turbine is mixed with the feedwater at the
same pressure. In closed system, the steam bled from the turbine is not directly
mixed with the feedwater, and therefore, the two streams can be at different
pressures. |
|