A High-Efficiency Reactor for the Pulsed Plasma.pdf
《A High-Efficiency Reactor for the Pulsed Plasma.pdf》由会员分享,可在线阅读,更多相关《A High-Efficiency Reactor for the Pulsed Plasma.pdf(13页珍藏版)》请在沃文网上搜索。
1、Plasma Chemistry and Plasma Processing,Vol.22,No.2,June 2002(2002)A High-Efficiency Reactor for the Pulsed PlasmaConversion of MethaneS.L.Yao1,2E.Suzuki,1N.Meng,1andA.Nakayama1Receied December 12,2000;accepted August 10,2001The authors recently deeloped a high-frequency pulsed plasma process for met
2、haneconersion to acetylene and hydrogen using a co-axial cylindrical(CAC)type ofreactor.The energy efficiency represented by methane conersion rate per unit inputenergy has been improed so that such a pulsed plasma has potential for commercialacetylene production.A pulsed plasma consists of a pulsed
3、 corona discharge and apulsed spark discharge.Most of energy is injected oer the duration of the pulsedspark discharge.Methane conersion using this kind of pulsed plasma is a kind ofpyrolysis enhanced by the pulsed spark discharge.In this study,a point-to-point(PTP)type of reactor that can produce a
4、 discharge channel oer the duration ofa pulse discharge was used for the pulsed plasma conersion of methane.The energyefficiency and carbon formation on electrodes hae been improed.The influencesof pulse frequency and pulse oltage on methane conersion rate and product selec-tiity were inestigated.Th
5、e features of methane conersion using PTP and CACreactors were discussed.KEY WORDS:Pulsed plasma;methane;acetylene;point-to-point reactor;energy efficiency.1.INTRODUCTIONCatalytic methane conversion directly to more valuable chemicals andliquid fuels has attracted much more attention for several yea
6、rs as theinvestment and operation cost can be possibly reduced at an estimate incomparison with a conventional methanol production.(16)This type ofstudy has some challenges since the product methanol is oxidized more read-ily than methane over a catalyst,even one of the most inert materials SiO2.(7)
7、Plasma conversion of methane has been studied as an emerging method to1Contribution from Catalysis Science Laboratory,Research Institute of Innovative Technologyfor the Earth,Kyoto 6190292,Japan.2To whom all correspondence should be addressed.2250272-4324?02?0600-0225?0 2002 Plenum Publishing Corpor
8、ationYao,Suzuki,Meng,and Nakayama226convert methane to acetylene,ethylene,hydrogen,methanol,and otherliquid products.(821)It has been found that a non-thermal pulsed plasma of a high frequency(8kHz)can be used to convert methane to acetylene and hydrogen,at ahigh acetylene selectivity of 92%and a hi
9、gh methane conversion rate of0.93B106molJ1at room temperature and atmospheric pressure using aco-axial cylindrical(CAC)type of reactor,indicating that this process ispotentially competitive with commercial acetylene production processes.(22)The highly endothermic reaction of methane to acetylene req
10、uires tempera-tures above 1500K.(8)The commercial processes include:(1)an arc dis-charge process developed by Huels,in which the reaction energy is supplieddirectly by an arc discharge;(8)(2)a partial combustion process developedby BASF,in which the reaction energy is supplied directly by incomplete
11、combustion of methane;(11)(3)the high-temperature hydrocarbon pyrolysisdeveloped by Wulff,in which the reaction energy is supplied using a cyclicregenerative technique of supplying fuel combustion heat to a refractorymass in one step and in a second step releasing the heat for pyrolysis ofhydrocarbo
12、ns to acetylene,(12)and(4)the calcium carbide process using areaction of calcium carbide with water.(23)A pulsed plasma consists of a pulsed corona discharge and a pulsedspark discharge.Ionization of the background gas(the gas in the wholeplasma space)occurs in the pulsed corona discharge,which yiel
13、ds a dis-charge channel of positive ions.(24)The pulsed spark discharge occurs afterions reach the electrode(s)due to the force exerted by the electric field.Mostof the energy is injected over the duration of the pulsed spark discharge andis used to heat the methane in the discharge channels to temp
14、eratures(25)atwhich methane pyrolysis occurs.(26,27)In the case of the CAC reactor used,the gas temperature downstreamof the plasma space of the reactor was estimated to be higher than thatupstream due to the energy injection.This temperature gradient in theplasma space indicated that the discharge
15、was also not uniform,since thedischarge at a higher temperature occurred more easily than that at a lowertemperature,the discharge tended to occur more frequently in the down-stream region of the reactor.These findings also implied that the space ofthe CAC reactor cannot be used effectively.Furtherm
16、ore,discharges in theplasma space with high background gas temperatures caused carbon forma-tion on the surfaces of the electrodes and finally the discharge cannot beoperated regularly.In this study,a point-to-point(PTP)type of reactor was used to giveonly a single discharge channel with a high reac
17、tion temperature.The influ-ences of pulse frequency and voltage on methane conversion were investi-gated,in comparison with those using the CAC reactor.A High-Efficiency Reactor for the Pulsed Plasma Conversion of Methane2272.EXPERIMENTAL PROCEDURESFigure 1 shows a pulse power generator(DP-15K35,Pul
18、se ElectronicEngineering)and the PTP reactor.The pulse voltage was generated withtwo plasma-forming capacitors(C1(2B1010F)and C2(1B1010F)with ahydrogen thyraton used as a switch S2.The plasma forming capacitors werenegatively charged with a charging system consisting of a capacitor C0(8.5B103F),a gr
19、oup of FET switches S1and their drivers,a coil L0(1.4B106H),a booster transformer T(1:45),and four diodes D.A dcpower supply was used to charge the capacitor C0.Values of other parts L1,L2,R0,R1,R2,and R3were 1B104H,2B104H,200,1300,110,and 100,respectively.The voltages of capacitors C1and C2and the
20、dis-charge voltage were measured using two voltage probes V-1 and V-2(EP-50K,PulseElectronicEngineering),respectively.Dischargecurrentsthrough the anode and cathode were measured using two current trans-formers CTaand CTc(CTa:mode 21.0,CTc:mode 0.51.0,StrangenesIndustries),respectively.The signals f
21、rom the voltage probes and currenttransformers were recorded with a digital oscilloscope(TDS754D,Tek-tronix)having an analog bandwidth of 500MHz.The PTP reactor consisted mainly of a Pyrextube(1.5B102(o.d.)B1.2B102(i.d.)B0.8(length)m3),a quartz tube(1.2B102(o.d.)B8.0B102(i.d.)B0.4(length)mm3),andtwo
22、stainlesssteelwireelectrodes(1.5B103B0.18(length)m2)with sharp-pointed discharge terminals.Thegap distance between the two electrodes was 5.0B103m.Figure 2 shows the configuration of the CAC reactor,which its meth-ane conversion property was partly given for comparison with the PTP reac-tor.The CAC
23、reactor was comprised mainly of a Pyrextube(1.5B102Fig.1.A plasma system for methane conversion.Yao,Suzuki,Meng,and Nakayama228Fig.2.Configuration of a co-axial cylindrical(CAC)reactor for methane conversion.(o.d.)B1.2B102(i.d.)B0.8(length)m3),two quartz tubes(1.2B102(o.d.)B1.0B102(i.d.)B5.0B102(len
24、gth)m3),a stainless steel tube(1.2B102(o.d.)B1.0B102(i.d.)B0.15(length)m3),and a stainless steelwire(5B103B0.8(length)m2).A quartz tube and two acrylic resin hold-ers were used to keep the wire straight and on the axial of the Pyrextube.As has been described elsewhere,(22)methane conversion rate and
25、 acetyleneselectivity could be obviously improved using a pulse frequency higher than2kHz.Since the discharge using the CAC reactor occurred between the centralwire and the inside surface of the stainless steel tube,this type of dischargeA High-Efficiency Reactor for the Pulsed Plasma Conversion of
- 1.请仔细阅读文档,确保文档完整性,对于不预览、不比对内容而直接下载带来的问题本站不予受理。
- 2.下载的文档,不会出现我们的网址水印。
- 3、该文档所得收入(下载+内容+预览)归上传者、原创作者;如果您是本文档原作者,请点此认领!既往收益都归您。
下载文档到电脑,查找使用更方便
30 积分
下载 | 加入VIP,下载更划算! |
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- High-Efficiency Reactor for the Pulsed Plasma High Efficiency