Book excerpt: The economic performance of power plants have received significant notice in today’s modern world. An important parameter that remain as the key performance indicator of power plants of modern times is the plant availability. The out-dated layouts ,components and fuel systems designed of olden times built during plant establishment periods are subject to modifications in terms of configurations ,plant size ,retrofit , renovations and fuel systems with the objective of enhanced economic performance and improved plant availability .In today’s world of depleting energy resources, the importance for energy conservation policies and frame works are high and the outlook towards economic performance of plants and their reliability and availability after process system modifications is highly specific . This book presents the impact of the modifications done in De-Super heater and Flame Burner System of a Boiler during conversion from Oil fired to LNG fired system on the process system value of 7MW Captive power plant of a fertilizer process industry .It also examines the criticality of LNG price variation on the modified processes.First Law Efficiency analysis and Second law efficiency anaylsis are also done on major components of the captive power plant and results are analyzed before and after modifications.