Presentation of the exercise

The objective of the exercise is to model a 300 MW steam power plant in Thermoptim in order to assess its main characteristics.

This exercise is comprised of three parts:

(Session realized on 06/16/11 by Renaud Gicquel)

Steam power plants

Steam power plants

Steam power plant exercise

Thermoptim

Thermoptim

Thermoptim

Thermoptim

Thermoptim

Thermoptim

Thermoptim

Thermoptim

Setting the model parameters

When the simulator elements are created, Thermoptim initializes all points at a pressure of 1 bar and a temperature of 300 K, which must subsequently be modified depending on the data of the problem being studied.

The two next activities will show you how to set the parameters of the points and the processes, and the third one will remind you of the values which should be entered in Thermoptim.

Setting points

Setting processes

Setting the parameters of points and processes

Set now the parameters of the various points one by one, checking that you enter the values of the temperatures known (T1, T3), as well as those of the pressures, as Thermoptim does not set them automatically. In order to do that, follow these steps:

Set then the process’s parameters, for which default options are valid : the compression and the expansion are adiabatic, calculated with the isentropic reference, and their isentropic efficiencies are known. In order to do that, follow these steps:

  • open process “pump”, whose isentropic efficiency is by default equal to 1, then click on “Calculate”, which sets the temperature of point 2 (29.37 °C)
  • open processes “economiser”, “evaporator” and “superheater”, and click on “Calculate”. The temperatures of their inlet and outlet points being known, their enthalpies can be calculated
  • open process “turbine”, and enter an isentropic efficiency of 0.85, then click on “Calculate”, which shows that point 4 is at the saturation temperature (29 °C), is quality being equal to 0.836
  • open process “condenser”, which can now be calculated, points 4 and 1 being known
  • The calculation of the overall balance requires to understand the notion of energy type, explained in the next activity.

    Energy type choice

    Balance and synoptic

    Cycle on (T,s) chart

    Setting an entropy chart (T,s)

    Cycle on (T,s) chart

    Cycle on (T,s) chart

    Refined cycle on (T,s) chart

    Cycle on (h,P) chart

    Cycle on Mollier (h,s) chart

    Summary

    This exercise has allowed you to study a simple steam cycle and to learn how to model it in Thermoptim. This is but a simplification (cycle without reheat nor extraction) of a 300 MW power plant.

    What is interesting in using such a software package is that the substance properties are calculated with a high degree of accuracy and without any difficulty. Once the model built, you can the change the parameters very easily, which enables you to quickly make sensitivity studies on the influence of the various parameters.

    This working manner involves however a risk: that you cannot criticize the values provided by the software package, which can lead you to grant a disproportionate confidence to the results it provides.

    It can happen that the model is not well built, and that its results are not right, and it is necessary to know to diagnose this type of errors. To do this, you should be able to check by yourself its results, at least in an approximate way.

    It is in particular recommended to check the energy balances well. In order to do that, train to recompute them roughly, by summing on a bit of paper all the useful energies like all purchased energies, and by dividing them to obtain the cycle efficiency.

    The layout of the cycle on a chart appears also a very good means of checking the relevance of a model, since the general shape of the cycles is generally well known. An error of entry on the pressure or the temperature often appears obviously.

    You will find below a link towards a note entitled “Methodology of model construction and checking” intended to provide to the users of Thermoptim a certain number of recommendations based on past experience.