preview

Pm3110 Unit 6 Lab Report

Better Essays

This chapter discusses the procedure followed and the assumptions made while setting up the design point and part load simulation. The NPSS solver uses a set of independent and dependent variables that is declared by the elements and the user. The independents are varied with each solver iteration until the dependent variables satisfy their specified condition [22].
The heat rise element, i.e. nuclear reactor is modeled in such a way that the temperature of helium exiting the reactor and entering the helium turbine is maintained at 1173 K (900 0C). During part load operation of the Brayton cycle, the mass flow rate is reduced. By reducing the reactor power output, the temperature of helium can be maintained at the design point value. Load following …show more content…

The Brayton cycle is sized based on the quality of the steam that enters the steam turbine. When the heat source is changed from burning coal to the helium turbine exhaust, we must ensure that the turbine exhaust has sufficient thermal energy to generate the required steam.
For the 300 MW steam plant currently under analysis, steam is required at 723 K (450 0C), 10.34 MPa and a mass flow rate of 330 kg/s. The steam turbine extracts 312.5 MW of power at 84 percent adiabatic efficiency. With the generator loss at 4 percent, the electrical output is 300 MWe. A mechanical pump is used to pump the water into the heat exchanger where it absorbs the heat from the helium turbine exhaust before entering the steam turbine. Design point specifications are given in Table 4-1.
Table 4 1 Steam Cycle Design Point …show more content…

In order to maintain synchronous speeds with the gas turbine while still reducing or increasing power output, the engine must be properly controlled [27]. “The control of the engine depends on where in the part-load curve the engine is operating” [27].
The reduction in mass flow rate causes the compressor pressure ratio and efficiency to drop [27]. As the mass flow rate is reduced, the turbine exhaust gas temperature increases to maintain energy balance [27]. The mass flow rate of helium can be decreased to a limit until either material restrictions at the turbine exit or heat exchanger inlet prohibit the higher temperatures [27] or the efficiency of the turbomachinery falls below an acceptable level.
There is a coupling effect between the two systems when the Brayton cycle is operated at part load. The coupling occurs due to two constraints; helium must be cooled to its design point temperature after passing through the heat exchanger and the temperature of steam entering the turbine must be maintained at its design point temperature. The solver calculates the new mass flow rate of water required to cool the helium. The change in mass flow rate of steam due to the reduction of Brayton cycle mass flow rate causes a change in the Rankine cycle power output.
4.3 Rankine Part Load

Get Access