Reducing Energy Consumption in Natural Gas Pressure Drop Stations by Employing Solar Heat

Abstract

In Iran (and probably in most countries) natural gas is transported through transmission pipeline at high pressures (5-7 Mpa) from production locations to consuming points. At consumption points, or when crossing into a lower pressure pipeline, the pressure of the gas must be reduced. This pressure reduction takes place in CGSs. At CGSs, the pressure is reduced from (5-7 Mpa) to (1.5-2.0 Mpa) (typically 1.7 Mpa) in highpressure intrastate pipelines. Currently, gas pressure reduction is accomplished by using throttle-valves in all of Iran‘s CGSs, where the constant-enthalpy expansion takes place and a considerable amount of energy is wasted. The gas must be heated before it enters throttle valves to ensure that it remains above the hydrate-formation zone and dew point, so that no liquid or solid phase condenses at the station exit. The heaters are consuming a considerable amount of natural gas flowing though the CGS as fuel to provide the required heat for preheating the natural gas stream. As the low temperature heat is required for preheating the natural gas in a CGS, this makes a CGS as perfect place to utilize solar energy and to meet low temperature heat demand. As the low temperature heat is required for preheating the natural gas in a CGS, A solar collector array is proposed to be utilized in the CGS in order to displace heating duty of the heater and to reduce amount of fuel consumption. The proposition includes a modified design of an in-use CGS to take advantage of freely available solar heat. The proposed system has been applied to study the thermal behaviour of a CGS within Iran. The results show that the cost effectiveness of the proposed method with an array of 450 collector modules is resulted in fuel saving with variation between 0 to 20 USD/hr. The annual fuel saving is about 10678 USD and as the capital cost is about 76500 USD, the payback ratio is calculated to be around 9 years. The number of collector modules has been determined based on cost analysis.