| In the 21st century,theoil supply has become an important issue since the worldwide production can't meet the rocket growing demand.Developing alternative energy technologies seems to be more important due to the gradual exhaustion of the crude oil resource and serious environment pollution.Compared with oil resource,Natural gas burns much cleaner and has greater reverses,which has strong prospects for exploitation and utilization.As the high transportation costs,more and more natural gas resource has been considered to be converted into value-added chemicals,such as alcohol,ethylene,acetylene.But the traditional catalytic conversion of methane requires high temperature and pressure working situation,with a lot of drawbacks,such ashigh capital costs,large equipment size,complex process,exhaust emission.According to their flexible,efficient,easy to operate,rapid start-up and shutdown,plasma technologies have been widely applied in Ozone generation,surface modification,waste gas treatment and other industry sectors.The massive genetic electrons and other reactive species generated by non-thermal plasmas are considered to be very promising for methane convention at room temperature and atmospheric pressure.In this work,two novel non-thermal plasma systems driven by pulse power were developed to overcome the problems that are existed in AC or DC driven plasma systems.The contents and conclusions of this thesis are listed as below.?1?Characterization of the physical and chemical characteristics of the pulsed dielectric barrier discharge?DBD?plasma,a oscilloscope,gas chromatograph,optical emission spectroscopy and digital camera were employed to investigated the V-I characteristics,gas products distribution,intermediate species distribution,and spectroscopic property of pulsed DBD plasma.The results showed that the main productions are H2,C2H6.The conversion of methane and the yield of hydrogen increased with the rising pulsed repetition rates,declined with the increase of CH4 flow rates.At the same pulsed repetition rates and CH4 flow rates,higher CH4 conversion rate and hydrogen yield rate could be reached with microsecond pulsed DBD,while nanosecond pulsed DBD was surpassed to microsecond pulsed DBD on energy efficiency.In the high pulsed repetition rates and low CH4 flow rates conditions,coking and liquid hydrocarbons would formed on the inner electrode and quartz tube respectively,leading to the decline of C&H balance.Contrary to the nanosecond pulsed DBD,the selectivity of H2 and C2H6 raised with rise of input power.?2?Characterization of the physical and chemical characteristics of the pulsed spark discharge plasma.Same diagnostic system were employed to investigated the V-I characteristics,gas products distribution,intermediate species distribution,morphology of coke deposits and spectroscopic property of pulsed spark discharge plasma.Differing from the DBD plasma system,the main gas products are H2,C2H2,with a little C2H6 and C2H4.Driven by nanosecond-pulse power,the discharge mode changed from streamer discharge to spark discharge with the increase of discharge gap.At the same pulsed repetition rates and CH4 flow rates,higher CH4 and H2 yield rate could be reached with microsecond pulsed spark discharge,higher C2H2 and H2 selectivity could also be achieved.According to different discharge mode,the different reactive species distribution lead to diversified reaction paths and varied gas distribution.Microscopy characterization of carbon depositions showed that there were some carbon nanoparticles generated on ground electrode,the mechanism of carbon nanoparticles formation during CH4 conversion require further investigation. |
PDF Full Text Request