Performance assessment of a natural gas expansion plant integrated with a vertical ground-coupled heat pump

In the present paper, a vertical ground-coupled heat pump system is proposed for energy saving in a natural gas expansion plant. Such plant is a modern type of conventional natural gas pressure drop station. Unlike the conventional type, which waste the natural gas pressure exergy in throttling process, the modern one uses the pressure exergy of the natural gas for producing electrical power. A remarkable feature of the proposed system is the type of energy resource used for preheating aim. In previous studies, natural gas was used for the preheating process, however; the proposed system employs geothermal energy as a renewable energy resource for providing part of heating demand. Initially, the vertical ground-coupled heat pump system preheats the natural gas stream up to medium temperatures, then, gas stream passes through station heater and reaches the desired temperature. For studying the economic and thermal performance of the proposed system, first of all, a system with a high net present value is selected, and then the performance of the selected system is studied in detail. The analysis revealed that the fuel saving potential of the system is 45.80% annually. Economically, the discounted payback period was also calculated about 6 years.