Abstract
To investigate the influence of CO2 partial pressure on efficiency of CH4-CO2 swap from natural gas hydrates (NGHs), the replacement of CH4 from natural gas hydrate (NGH) is carried out with simulated Integrated Gasification Combined Cycle (IGCC) syngas under different pressures, and the gas chromatography (GC), in-situ Raman, and powder X-ray diffraction (PXRD) are employed to analyze the hydrate compositions and hydrate structures. The results show that with the P-T (pressure and temperature) condition shifting from that above the hydrate equilibrium curve of IGCC syngas to that below the hydrate equilibrium curve of IGCC syngas, the rate of CH4 recovery drastically rises from 32% to 71%. The presence of water can be clearly observed when P-T condition is above the hydrate equilibrium curve of IGCC syngas; however the presence of water only occurs at the interface between gas phase and hydrate phase. No H2 is found to present in the final hydrate phase at the end of process of CH4-CO2 swap with IGCC syngas.
Highlights
Natural gas hydrates (NGHs) are ice-like compounds formed by water molecules and gas molecules under low temperature or/and high pressure
85% were obtained with CO2 and CO2 /N2, respectively, and the results showed that the structure II (sII) hydrate was transformed into structure I (sI) when sII hydrates were exposed to CO2 and CO2 /N2
The simulated Integrated Gasification Combined Cycle (IGCC) syngas of 39.9% CO2 and 60.1% H2 gas mixture is injected into the reactor from bottom of reactor, and the CH4 gas above the hydrate is discharged at the same time under the stable pressure of 4.5 MPa
Summary
Natural gas hydrates (NGHs) are ice-like compounds formed by water molecules and gas molecules under low temperature or/and high pressure. Most NGH deposits are sI gas hydrates [2,3] which are composed of six 512 62 cages and two 512 cages [1]. Many studies have been carried out to exploit CH4 from NGHs deposits and several field trails have been conducted in last 40 years. The exploitation methods mainly include thermal stimulation, depressurization and chemical inhibitor injection, but the disadvantages such as enormous energy consumption, risks of the probably catastrophic landslide and serious environmental pollution are the main issues we are facing [10]. Effective and environmental friendly production technologies are expected, including CH4 -CO2 swap, in-situ combustion and in-situ catalytic oxidation, etc
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