Analysis of an integrated energy system under variable loads through the symbolic exergoeconomics. 1

This paper is used to analyze an energy recovery and cogenerative plant made up of a turboexpander of natural gas and two cogenerative engines. By means of a mathematical symbolic computer program, the Symbolic Exergoeconomic methodology obtains the algebraic formulae for the total plant efficiency and any other thermodynamic variable as a function of the exergetic efficiencies of the subsystems, the exergy bifurcation ratios and either the system's input or output flows. The exergy flows of the plant, obtained by the thermodynamic simulator, can be used to calculate the numerical values of the exergetic efficiencies and of the exergy bifurcation ratios. By substituting these values in the symbolic formulae it is possible to numerically evaluate the apportionment of the input resources, throughout the plant structure an its components, on the products of the plant. This is useful to determine the true utilization coefficients of each fuel and to quantify how it affects the total efficiency of the plant. Since the behavior of the plant is much different depending on the value of the gas flow rate at the inlet, the annual gas flow rate duration curve has been discretized into five steps, corresponding to four operating configurations in which different depending on the value of the gas flow rate at the inlet, the annual gas flow rate duration curve has been discretized into five steps, corresponding to four operating configurations in which different sets of components are working; the mentioned procedure has been applied to each operating configuration