Natural gas is transferred in high pressure by piping system from refiners to city gate stations. For public consumption the gas pressure is reduced in gas pressure reducing stations. The pressure is reduced in regulators and leads to a sudden drop of temperature and consequently the formation of gas hydrates. Preventing hydrate formation, natural gas is heated by passing through water bath gas heaters. In this study, the thermodynamic efficiencies of water bath gas heaters were conducted. The effect of air-fuel ratio and the flow rate of the fuel on the efficiency of this instrument were studied. Also, the variations of efficiencies versus flame temperature have been considered and the optimum points in each state were obtained. From these comparisons, it can be concluded that, first law efficiency is suitable meanwhile second law efficiency is very low. The main reason of low second law efficiency is that high availability generation by fuel causes low enhancement in the availability of natural gas, passed through heaters. Also, one dimensional simulation has been employed to compute temperature distribution numerically in whole of a gas pressure reducing station with water bath gas heaters and with shell and tube heaters (inline heaters). Comparison between these two stations show that the gas pressure reducing station with inline heaters is more appropriate than the one with water bath gas heaters. Finally, water bath gas heaters and inline heaters have been studied economically by utilizing energy flow optimization model, EFOM. It is shown that the inline heaters have less cost of heat generation and they are more economical.

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