A new design for natural gas pressure reduction points by employing aturbo expander and a solar heating set

Natural gas pressure reduction station (CGS) is one of the most important pieces in natural gas transmission system. In a CGS, the high inlet natural gas (NG) pressure has to be reduced down to a much lower value. Pressure reduction is usually implemented by utilizing throttling valves. Due to the positive Joule-Thompson coefficient of NG, this pressure drop causes significant temperature fall and consequently hydrate forming in the NG stream. The hydrates may prevent stable NG flow through the pipeline. To prevent hydrate forming, the NG should be preheated by some heaters which burn huge amount of fuel. In this work, firstly, adding a solar heating system aiming to reduce the heater fuel consumption and secondly, replacing the throttling valve by a turbo expander in order to utilize the NG stream exergy are proposed. The proposed configuration is simulated for Birjand CGS as a case study. For the simulation, the locally available solar irradiation is estimated by employing solar engineering formulations and the NG availability is calculated by thermodynamics correlations. Net present value (NPV) method is also employed to analyze the proposed system effectiveness economically, resulting to only 3.5 years of pay back ratio.