This article presented a simplified method for quick estimating exergy destruction and irreversibility distribution ratio (phi) in a complex Heat Exchanger Network (HEN) of a large natural gas refinery in South Pars Gas Field located in the Persian Gulf. By the presented method, the designing of the HEN isn't required and the only necessary data are the temperatures and thermo-physical properties of the fluids at the inlets and outlets of the HEN. The equation of exergy destruction for the HEN was developed and the model was adapted to estimate the contributions of heat transfer and pressure drops due to fluid friction, as the two major causes of irreversibility in the HEN. The irreversibility factors were compared with the results obtained by conventional irreversibility analysis, i.e. considering irreversibility analysis of all individual heat exchangers running in the HEN. By comparison of the results of the two methods, it was shown that the values and trends of the irreversibility factors estimated by the two methods were approximately the same. By this procedure, it is possible to estimate the irreversibility distribution ratio in any HEN very quickly, especially in early stages of the thermal system designs, without solving very complex mathematical relations. (C) 2017 Elsevier Ltd. All rights reserved.