report_dec_22010_0 - INTRODUCTION For this assignment we...

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3 INTRODUCTION For this assignment we were given the steam power plant shown below which operated on a reheat–regenerative Rankine cycle with one re-heater and two feed water heaters, one open and one closed. Figure 1 The problem was that Steam enters the high-pressure turbine at 15 MPa and 600°C and the low- pressure turbine at 1 MPa and 500°C. The condenser pressure is 5 kPa. Steam is extracted from the turbine at 0.6 MPa for the closed feedwater heater and at 0.2 MPa for the open feedwater heater. In the closed feedwater heater, the feedwater is heated to the condensation temperature of the extracted steam. The extracted steam leaves the closed feedwater heater as a saturated liquid, which is subsequently throttled to the open feedwater heater. Consider a mass flow rate of 42 kg/s through the boiler.
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4 THEORY The theory we used in this problem is REHEAT-REGENERATIVE RANKINE CYCLE . Let’s look at the theory behind it. First let’s look at why the Rankine cycle is needed. We studied Carnot cycle s before. There were 3 main things why Carnot cycle is not suitable for power cycle. In Carnot cycle we have to limiting the heat transfer processes to two-phase systems, however, this severely limits the maximum temperature that can be used in the cycle. Limiting the maximum temperature in the cycle also limits the thermal efficiency. Any attempt to raise the maximum temperature in the cycle involves heat transfer to the working fluid in a single phase, which is not easy to accomplish isothermally. The isentropic expansion process can be approximated closely by a well-designed turbine. However, the quality of the steam decreases during this process, as shown on the T-s diagram in Fig.2. Thus the turbine has to handle steam with low quality, that is, steam with a high moisture content. The impingement of liquid droplets on the turbine blades causes erosion and is a major source of wear. Thus steam with qualities less than about 90 percent cannot be tolerated in the operation of power plants. And last thing is that The isentropic compression process in Carnot cycle involves the
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This note was uploaded on 01/18/2012 for the course DEP 235 taught by Professor Eeer during the Spring '11 term at Assoc. of Chartered Certified Accountants.

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report_dec_22010_0 - INTRODUCTION For this assignment we...

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