Study of Preheating Natural Gas in Gas Pressure Reduction Station by the Flue Gas of Indirect Water Bath Heater

Abstract

In most gas pressure reduction stations, natural gas pressure is reduced through the throttle valve. In regulators due to the Joule-Thompson effect, pressure drop causes temperature reduction. To refuse obstruction of pipelines, indirect water bath heaters warm flow natural gas before passing through regulator. In this paper Mahshahr CGS elected as a case study and thermal efficiency of heater installed in this station computed briefly. Results illustrate that heat losses from stack is the main factor in low efficient heater. To use the thermal energy of flue gases, a shell and tube heat exchanger is proposed to preheat inlet natural gas to heater. The specification of heater is calculated by considering some assumptions at first. Then the effect of using heat exchanger on fuel consumption in atmospheric burner of heater is studied. Results shows that using a heat exchanger can reduce total thermal needed energy from hater 1.3MJ in a year. This means that more than 141000 m 3 fuel is saved and it causes a significant economic saving and environmental pollution decreasing. Payback period of this proposal is 1.2 years and net present value with interest rate of 14% is positive after 2 years. Therefore by using a simple heat exchanger the efficiency of indirect water bath heater improves 11%.