Natural gas pressure decreases in City Gate Stations (CGS) for industrial and residential use. The moisture present in natural gas may result in hydrate formation in the pipelines. Water bath heat exchanger is used to prevent hydrate formation by increasing the temperature of natural gas. Energy consumption in heaters of CGS is considerable and high quality refined gas is used for combustion in these heaters. Because of great amount of air or fuel entered into combustion chamber of the heaters as well as high temperature of stack effluent, these heaters usually work inefficiently and there is room for improving performance. The aim of the present thesis was to save fuel consumption in heaters. Computation fluid dynamic was used to analyse the heater making use of commercial software Fluent 15. Heat recovery from combustion exhausts by installing an economizer was studied. Four economizers with two helical coils with a diameter of 25.4 mm and 50.8 mm and pitch 1.5 and 1.8 and four economizer with a single helical coil with a diameter of 50.8 mm and 101.6 mm and pitch 1.5 and 1.8 were examined. The results showed that installing economizer with two helical coils with a diameter of 50.8 mm and pitch 1.5 made the greatest saving in fuel consumption by10%. Heat recovery from combustion exhausts by installing a recuperator was also studied. Installing recuperator reduces fuel consumption by 11%. Improved performance of the heat exchanger with different finned tubes were also investigated with corrugated fins with height to tube diameter ratio of 0.05, 0.075 and 0.1 and the ratio of blade pitch to height of 4, 10 and 20. Finned tube with the ratio of height to tube diameter of 0.1 and the ratio of pitch to the height of 4 showed the best performance by reducing fuel consumption by 3.3%. Fluid in the tank transfers energy from fire tubes to coils via natural convection. Addition Al 2 O 3 nano particles to the fluid, increased the transfer rate. Addition of 1% (vol) Alumina to the fluid reduced the fuel consumption by 3%. It is proposed that both nano fluid addition and installing economizer or recuperator will be used to achieve the best performance. Keywords : City Gate Station, Helical Coiled Heat Exchanger, Finned Tube, Nano Fluid, Natural Convection Heat Transfer, Subcooled Boiling
