Abstract
During the natural gas pipeline transportation process, gas stream pressure is reduced at natural gas regulation stations (GRS). Natural gas pressure reduction is accompanied by energy dissipation which results in irreversible exergy losses in the gas stream. Energy loss depends on the thermodynamic parameters of the natural gas stream on inlet and outlet gas pressure regulation and metering stations. Recovered energy can be used for electricity generation when the pressure regulator is replaced with an expander to drive electric energy generation. To ensure the correct operation of the system, the natural gas stream should be heated, on inlet to expander. This temperature should be higher than the gas stream during choking in the pressure regulator. The purpose of this research was to investigate GRS operational parameters which influence the efficiency of the gas expansion process and to determine selection criteria for a cost-effective application of turboexpanders at selected GRS, instead of pressure regulators. The main novelty presented in this paper shows investigation on discounted payback period (DPP) equation which depends on the annual average natural gas flow rate through the analyzed GRS, average annual level of gas expansion, average annual natural gas purchase price, average annual produced electrical energy sale price and CAPEX.
Highlights
Natural gas is usually transported over long distances through pipelines at high pressures.In order to distribute the gas locally at points along the pipeline, the pressure must be significantly reduced before it is supplied to local distribution systems [1,2]
Except gas regulation stations (GRS) #5 in the range of 3800–5200 h, heat demand for natural gas heating before expansion is higher than the amount of generated electricity
This may seem unreasonable because more energy is lost than produced. This is because natural gas, which we burn for natural gas heating, is a primary energy carrier and costs four times less than generated electricity [26]
Summary
Natural gas is usually transported over long distances through pipelines at high pressures. In order to distribute the gas locally at points along the pipeline, the pressure must be significantly reduced before it is supplied to local distribution systems [1,2]. Most pressure-reducing stations use expansion valves to reduce pressure [3,4]. When there is no heat transfer to or from the environment and if no work is done, the process of choked flow of the natural gas stream, regardless of its type, is an isenthalpic process [5]. In choked flow at constant enthalpy, the gas temperature changes. This change in gas temperature, once the pressure has been reduced, is associated with the so-called
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