Proceedings of the 2nd Annual Gas Processing Symposium Farid Benyahia and Fadwa T. Eljack (Editors) © 2010 Elsevier B.V. All rights reserved. Studying Influence of Changing Fuel on the Operation and Total Annual Cost of the Total Site Using R-curve Shervin Karimkashi, a Majid Amidpour a a Department of Energy system Engineering, Mechanical Engineering Faculty, K.N. Toosi University of Technology, No. 15, Pardis St. Mollahsadra Ave., Tehran, Iran Abstract In large processing sites the cost of fuel and power can be very significant and better management of the utility system can lead to significant cost savings. The R-curve is an analysis tool that provides guidelines for the cogeneration efficiency for a given site power-to-heat ratio demand of an ideal utility system. In this paper, considering a total site as the case study, by changing the operating fuel, different actual R-curves have been constructed and then compared. In all of cases, the gas turbine exists and obviously its fuel is natural gas and does not change. In fact in each case, by changing the fuel injected to the boilers of the site, a different actual R- curve is constructed and then another curve of ‘R-ratio vs. Total Annual Cost’ is sketched to demonstrate the cost of each point of the R-curve. After comparing these curves for different operating fuels, some useful conclusion has been obtained. Keywords: operating fuel, total annual cost, total site, R-curve, cogeneration. 1. Introduction Utility systems are an important part of most processing sites. Cogeneration is usually an important feature of such systems, particularly from steam turbines, gas turbines or a combination of both. In these sites the kind of operating fuel, used in boilers, has a big influence on the operation and total annual cost of the site (Varbanov et al., 2004). In fact, choosing a better fuel for the site being studied, will lead to fewer costs. The R-curve [2,(Kimura and Zhu, 2000)] is an analysis tool that provides guidelines for the cogeneration efficiency for a given site power-to-heat ratio demand of an idealized utility system. Developing the R-curve concept, it is possible to estimate total annual cost of an idealized utility system. This total annual cost is directly dependent on the fuel price and thus the kind of operating fuel. R-curve was first introduced by kenney (Kenney, 1984), who studied different configurations within utility systems, producing plots of cogeneration efficiency vs. site power-to-heat ratio. This plot was referred to as a ‘fuel utilization curve’ or R-curve, Fig. 1. The terms ‘unfired boiler’, ‘supplementary fired boiler’ and ‘fully fired boiler’ in 409