Computer aided analysis and optimisation of steam power cycles

Abstract

The design of thermodynamic cycles for steam power plants is a two-stage process. The first stage consists in the analysis of several variants of a basic plant configuration suggested by previous experience, and ends up with selection of one of these variants, that which is considered to be the best by some criteria. Most designs in the past terminated thus. However, increasing energy costs and the economic impact that even a minute improvement in plant efficiency can have made it desirable to follow this stage by a second one where some kind of systematic optimisation is performed. The complexity of the cycles involved, difficulties with the complicated thermodynamic functions required for the analysis and increasing labour costs force the optimisation to be computer aided. This paper describes a method to perform computer aided analysis and design of thermodynamic cycles for steam power plants. Most of what is to be said is, however, easily generalised for other kind of cycles. The paper begins with the definition of a data structure necessary to represent plant configurations in the computer. This data structure was inspired by similar ones related to finite element and electrical network problems. The analysis of thermodynamic cycles is based, as is well known, in the balance of mass and energy laws which lead, under some common simplifying assumptions, to the set up of a linear system of equations. The solution of this system allows the computation of all the variable of interest required in order to generate a balance of mass and energy report. Then an optimisation program is described. This program performs a search for the best cycle, according to the criteria selected by the user, starting from some basic design and given constraints. Some examples representative of the program capabilities are presented.