Patent Application
20080131333
The present invention relates to a device for waste gas treatment; more particularly, relates to obtaining a nonthermal plasma through a high voltage discharging device for processing waste gas.
A nonthermal plasma (NTP) device used for processing waste gas is obtained first by high temperature free electrons through high-voltage discharging in a gas, and then the electrons collides with other gas molecules to form free radicals, like excited atom and molecules of N, O, OH and O3, for oxidizing or reducing waste gas into harm less gas rapidly. In the whole process, the energy used is mainly added on the electrons while the gas molecule itself has little increase in energy; so, the temperature of the electrons is much higher than that of the gas molecule, which is thus called NTP. By using this method, a great amount of low-concentration polluted waste gas can be processed with saved energy yet high efficiency.
A design of a high-voltage plasma reactor is closely related to its target. There are two types of plasma reactors, a pipe plasma reactor and a flat plasma reactor, used in processing waste gas. The flat plasma reactor has a smooth gas flow, but discharging uniformity is weakened owing to increase in the flat area; and so its efficiency and flow amount is reduced. Hence, it is rarely used to process a great amount of waste gas. The pipe plasma reactor further has two types of reactors, a pulse-corona plasma reactor and a dielectric barrier discharging (DBD) plasma reactor. The pulse-corona one has no insulating material to separate discharging electrodes. So, to keep from arcing, a high voltage short pulse, which is shorter than 1 microsecond, is used. This method has a high efficiency on processing waste gas, which is used in U.S. Pat. No. 4,695,358 in 1985. Yet, especially in processing a great amount of waste gas, owing to the too high cost to produce the high voltage short pulse with increased high power, it is not economically competitive on applying this method. And on considering the dielectric barrier discharging reactor, one or two insulating material are used to separate discharging electrodes so that a general high voltage alternating current power source can be used to reduce cost in installing the power source. This DBD method is originated from W. Siemens in 1857 for producing ozone and is used till now without great changes. In the other hand, the pipe DBD plasma reactor may be packed with insulating pellets having high dielectric permittivity, which is used in U.S. Pat. No. 5,236,672 in 1993 and U.S. Pat. No. 5,440,876 in 1995.
The general pipe plasma reactor has a straight flow design; that is, the axle of the flow has the same direction as that of the reactor. When enlarging a pipe's diameter to process a great amount of waste gas, the applied high voltage may be increased to an undesirable degree, not to mention the high operation cost in maintenance and safety assurance owing to the severe insulation protection. Therefore, a few reactors connected in a serial and parallel way are usually used in processing a great amount of waste gas Yet, the uniformity of discharging in each reactor has to be put into consideration; the inside flow has to be smooth and evenly distributed; and, load for every reactor has to be consistent. Moreover, any possible connection between the high-voltage electrodes has to be prevented and the insulation design should not affect distribution of the gas flow. However, settlement of the high-voltage wires, distribution of the gas flow and related maintenance considerations are all critical as well, so that complexity of the whole system increases which follows with heightened difficulties. Hence, the prior arts do not fulfill users' requests on actual use.
The main purpose of the present invention is to obtain a nonthermal plasma through a high voltage discharging device for processing a great amount of waste gas.
To achieve the above purpose, the present invention is a lateral-flow nonthermal plasma waste gas treatment device, comprising a plurality of lateral-flow DBD reactor units in a serial and parallel connection; and a plurality of airflow stoppers between lateral-flow DBD reactor units, where the lateral-flow DBD reactor unit comprises a perforated outer electrode, a center electrode, an insulating layer and a high voltage power source; the perforated outer electrode is a grounding cathode whose surface has a plurality of through holes; the center electrode is an anode inside the outer electrode; the insulating layer is located between the perforated outer electrode and the center electrode; the high voltage power source is coup led with the perforated outer electrode and the center electrode; and a required NTP is provided through a breakdown voltage discharging between the perforated outer electrode and the center electrode by using lateral-flow reactor units which is serial and parallel arranged to process a great amount of waste gas with an easy assembly and a low cost. Accordingly, a novel lateral-flow waste gas treatment device using nonthermal plasma DBD reactor units is obtained.
The present invention will be better understood from the following detailed description of the preferred embodiment according to the present invention, taken in conjunction with the accompanying drawings, in which
The following description of the preferred embodiment is provided to understand the features and the structures of the present invention.
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The perforated outer electrode 1 is a grounding cathode and has a plurality of through holes 11 and a fixing flange 12. The perforated outer electrode is a cylinder tube made of a metal conductive material, which is an alloy of stainless steel, copper, iron or aluminum, etc. On fabricating the perforated outer electrode 1, a thin metal plate is made into a cylinder tube with a plurality of through holes 11 on outer surface and a fixing flange 12 is assembled together to obtain a whole one. The fixing flange 12 is made of a metal conductive material with four to six holes for fixation and connection. Total area of the through holes 11 occupies 40 percents (%) to 60% of the outer surface of the cylinder tube; and the cylinder tube thus obtains uniform discharging. The metal plate of the perforated outer electrode 1 has a thickness between 0.8 and 3 millimeters (mm), a length of tube between 60 and 150 centimeters (cm), and a tube diameter between 8 cm and 10 cm; and the through hole has a diameter between 0.5 cm and 1 cm.
The center electrode 2 is located inside the outer electrode 1 to be an a node. The center electrode 2 is a tube made of a metal conductive material, which is stainless steel or copper, etc. A diameter of the center electrode 2 is between 0.5 cm and 3 cm according to an actual requirement.
The insulating layer 3 is located between the outer electrode 1 and the center electrode 2, covered on the center electrode 2. The insulating layer 3 is a tube made of an insulating material, which is polytetrafluoro-ethylene (PTFE), polyethylene (PE), ceramics, glass or quartz, etc. The insulating layer 3 has a thickness and discharge gap which values depend on actual operational consideration, where usually the thickness is set between 0.3 cm and 1.5 cm and the discharge gap has a width range between 1.5 cm and 5 cm.
The high voltage power supply source 4 is electrically coup led with the perforated outer electrode 1 and the center electrode 2 to supply a high voltage for gas breakdown. The high voltage power source 4 can be a high voltage alternating current (HVAC) 60/50 Hz frequency power source or a high frequency HVAC power source, which has an operating voltage between 10 kilo-volt (kV) and 60 kV according to the discharge gap, and an operating frequency between 50 and 10 kHz. Thus, a novel lateral-flow waste gas treatment device using nonthermal plasma reactor units is obtained.
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Moreover, a most beneficial device can be designed by a serial and parallel connection of the lateral-flow reacting units for future needs. In the other hand, owing to the modular design of the present invention, costs on fabrication and maintenance can be greatly reduced.
To sum up, the present invention is a lateral-flow waste gas treatment device using nonthermal plasma reactor units, where plasma is obtained by high voltage gas breakdown for processing waste gas and a plurality of the present inventions can be arranged in a serial and/or parallel way to increase processing time and staying duration of time of the waste gas, to achieve high removal efficiency.
The preferred embodiment herein disclosed is not intended to unnecessarily limit the scope of the invention. Therefore, simple modifications or variations belonging to the equivalent of the scope of the claims and the instructions disclosed herein for a patent are all within the scope of the present invention.
