Gas hydrates are snow-like materials made of water molecules trapping gas molecules under high-pressure and low-temperature conditions such as that at chokes and valves installed on natural gas wellheads and pipelines. Electricity was found generated from flowing methane-, ethane-, propane-, and CO2-hydrates along PVC tubes in laboratories. The rate of building electric charges and the level of the built voltage were found to depend on pressure drop/volume expansion when the hydrate was released to the PVC tube. Sparks/light were emitted when the static voltage reached a level of about 300 mV in the system investigated. An explanation of the observed sparks/light is the generation of static electricity when gas-hydrate passed through the PVC tube at a high velocity (flow electrification), or triboelectricity. The charge level is higher for poorly conductive gas-hydrate flowing through the PVC tube. In addition, the large amounts of gas bubbles flowing through the tube should amplify the static electricity. However, in this investigation, it was noticed that no spark/light was observed and no voltage pulse was detected during the active flow of hydrates. Instead, sparks/light were observed and voltage pulses were detected after the choking valve was switched on. The positive voltage probe was connected to the choking valve and the negative voltage probe was connected to the PVC tube. The voltage meter measured positive pulses of voltage difference between the two probes when the choking valve was off. This indicates current flow from the choking valve to the PVC tube, or electron charge flow from the PVC tube to the choking valve. Our hypothesis to explain these phenomena is that the flowing hydrates captured electrons from the low-conductive PVC tube and transported them in the flow stream, resulting in a “Positive charged” PVC tube in the entry portion. When the flow was terminated by valve closing, the electrons in the down-stream of the PVC tube flew back to the entry portion to minimize the charge unbalance, causing sparks/light and current flow from the choking valve to the PVC tube. This hypothesis needs to be proven in future investigations. Further studies are recommended in this area and more investigations are required for flowing methane-, ethane-, propane-hydrates. Potential applications of the hydrate-triboelectricity include harvesting electricity in the downstream of surface chokes installed on the natural gas wellheads where there exist flowing gas hydrates.
Keywords CO2, gas, hydrate, triboelectricity, experiment