1. 介质阻挡放电生成微等离子体随时间的变化

2. 等离子体在甲烷重整制 H2 方面的应用

Temporal evolution of dielectric barrier discharge microplasma

Marius Blajan and Kazuo Shimizu

Analysis of dielectric barrier discharge microplasma at atmospheric pressure was carried out using emission spectroscopy and imaging techniques.

平行电极间纳秒脉冲产生的放电动力学现象是通过成像技术观察的。放电现象可以通过观察它的空间和时间分布来分析。发射光谱是通过增强电荷耦合装置和分光仪来测量的。

放电间隙的长度计算是通过比较放电间隙的影像和厚度为 50µm 的铜金属片来实现的。

The evaluation of discharge gap length was carried out comparing the images of the discharge gap and of a copper plate with 50 µm thickness.

The highest intensity of light emission occurred at the peak of the discharge current.The evolution of the discharge showed streamer reaching cathode, cathode layer formation,cathode layer enhancement, and cathode layer decay.

Thus,an exact correlation of the peak intensity and peak current was not achieved . This occurred due to the fact that the surface of electrodes analyzed using microscope was not entirely smooth and also the discharge gap was not exactly 100 µm throughout the entire discharge gap.

Still it could be considered that at the highest intensity of the light emission,corresponding to the cathode layer enhancement stage,the current peak was recorded.

Emission spectra were obtained at 1.1kV . The reason for increasing the discharge voltage to 100V comparing with the experiment carried out with the high-speed ICCD camera was that at 1kV,the light intensity especially at 10ns was relatively weak.

This occurred due to the fact that fiber optic diameter was only 100 µm,and by increasing the discharge voltage,we could obtain a higher intensity

and furthermore have less error in measurements.

Still we consider that the 100V difference between these two types of measurements did not changed the phenomena.

Microtechnology and microscale fuel processing:an overview of hydrogen fuel

reforming techniquesYen-Ven Lu and Bindumadhav Sabnavis

The plasma-reforming process is similar to the most conventional reforming processes , with the exception that the energy and free radicals used for reforming process are provided by plasma, which is typically generated with electricity or heat.

The plasma-reforming process can overcome many limitations:

size and weight requirements;

cost and degradation of the catalysts;

slow response;

limited fuel selections from heavy hydrocarbons ;

highly sulfur tolerant.

等离子体重整主要分为两类：热等离子体重整和非热等离子体重整。

热等离子体重整比非热等离子体重整的能量效

率低。

对于热等离子体，大量的能量用于电子和中性物种升温（ 5000—10000K ）。为了防止金属蒸发，需要更多的能量用来冷却电极。然而在非热等离子体中，虽然电子温度较高，但气体温度没有那么高。

热等离子体重整过程的积碳现象很严重，大大限制了能量效率，并且处理比较麻烦。在非热等离子体中预测到能够形成积碳的高温峰只出现短短的几毫秒。因为快速的淬火过程，积碳形成被大大限制。

 

Analysis of reactivity and energy efficiency of methane conversion through

nonthermal plasmasStefanoRavasio,CarloCavallotti

利用微等离子体进行天然气的非氧化转化，生产高价值的产品，例如 H2 和 C2 化合物。具有很好的前景，而且该方法能耗低。

为了研究不同反应器中各种过程参数对乙炔、乙烯、乙烷的能量效率、转化率和活性的影响，采用了两种不同的模型。

The first consists of a detailed kinetic model

and a simplified reactor description , based on

the assumption that the plasma volume is

homogeneous and adiabatic;

The second is a time dependent microdischarge

model based on similar assumptions that is suitable

to study pulsed discharges.

Most studies focused on the correlation between operating parameters of the plasma discharge and process performances . It was thus found that the product distribution is strongly affected by the type of discharge used to sustain the plasma.

能量效率

ηplasma= [F﹛ outHout(Tin) － FinHin(Tin) ] /Qplasma ×100﹜

不包括放电能量转化效率

很多研究发现系统中出现的活性物种主要是CH3 、 CH2 、 CH 和 H ，主要的产物是H2 、 C2Hx 和炭黑 , 浓度依赖于放电特性。研究还发现相当一部分能量浪费在气体加热上。

反应的第一步是电子影响下自由基的形成，许多研究的第一步都类似：

CH4+e→CH3+H+e

H+ CH4→CH3+H2

2CH3→C2H6

室温下用上面式子计算的该反应的最大能量效率为 15 ％。

It was found that in order to obtain high energy efficiencies it is necessary to reach local gas phase temperatures that are sufficiently high to initiate the thermal decomposition of ethane and methane.

研究发现，高的能量效率与等离子体吸收的高比能量有关，而且，同一等离子体体系的多次放电也对能量利用有益。因此，甲烷转化的最高能效出现在脉冲电晕放电中。

提高能效的几个建议： -increase the energy delivered to the discharge,for

example , in the case of a pulsed corona plasma, increasing the maximum Voltage of the power generator,the duration of the pulse,or the discharge frequency;

-try to localize the discharge in a well defined plasma volume;

-decrease the surface/volume ratio,as this will decrease the extent of carbon deposition;

-pre-heat the gases,for example using a heat exchanger to recover the exhaust thermal energy

Innovative Methane Conversion Technology Using Atmospheric Pressure Non-thermal

Plasma Tomohiro NOZAKI and Ken OKAZAKI

Non-thermal plasma uniquely generates reactive species independently of reaction temperature, and these species are used to initiate chemical reactions at unexpectedly lower temperatures than normal thermochemical reactions .

Non-thermal plasma thus broadens the operation window of existing chemical conversion processes ,and ultimately allows modification of the process parameters to minimize energy and material consumption.

Two contrasting approaches of DBD-oriented plasma catalysis of methane are introduced:

(1) Low temperature (300-500 ) methane steam ℃reforming using a plasma-catalyst hybrid reactor.

Combination of reforming catalysts minimizes the

discharge power required for low temperature

methane steam reforming , but methane conversion

as well as product distribution are dominated by the

chemical equilibrium under given conditions.

单独使用 DBD 转化率最低；使用混合反应器转化率最

高

In contrast, methane partial oxidation by radical

injection at room temperature is the key to achieve

high methanol yields where the product distribution is

highly non-equilibrium. In addition to radical injection,

efficient heat removal using a microreactor

configuration is crucial.

(2) Room temperature direct methane conversion

to methanol using a microplasma reactor.

Direct methane to methanol conversion using

DBD has a relatively long research history , but

adequate yield has not been achieved yet . The

combination of DBD and a microreactor enables

excellent control over heat and mass transport in the

discharge field, enabling direct methanol synthesis at

high yield.

重整中使用的等离子体源：

1. 低温非热等离子体 DBD 放电、电晕放电、火花放电 特点：气体温度低，气体部分电离、电极装置

简单、能量来源便宜、原料气为气态原料或者经汽化的液态原料。

2.弧光等离子体 特点：需要高温热量来分解碳，包括将复杂的

原料分解为基本的构成部分如氢和一氧化碳。

3. warm discharge （热放电） 滑动弧光放电 特点：较新，在温度较高的气体介质中生成冷

等离子体，结合了冷等离子体产生自由基和热能提高化学转化效率的特点。

DBD 放电优点： 1.起源于臭氧合成，有很长的应用史，我们

对它的基本物理化学特性以及工业安装需要比较了解。

2. 电极和反应器结构有很大的灵活性： DBD和功能多孔材料的结合使用。

3. 由于介质层的存在， DBD 很少转化为不稳定的火光或弧光等离子体，能够提供稳定的非热等离子体。

Two major conclusions were derived:

First, only non-thermal plasmas might be an inefficient way of converting methane due to the large activation energy required for the electron impact process.

Second , appropriate combinations of thermal

energy (including heat removal) and radical species produced by non-thermal plasma can establish efficient fuel reforming.

Even if the energy efficiency of a plasma

reactor is not as excellent as existing technology, the overall energy and material conversion efficiency of the system could be enhanced .

Because the plasma can broaden the operation window of the system , and enables chemical reaction under unconventional situations.

Further development of plasma fuel reforming has excellent potential to eventually provide viable solutions for future energy and material use.

谢谢