Power plants – Internal combustion engine with treatment or handling of... – By electrolysis – electrical discharge – electrical field – or...
Reexamination Certificate
2002-06-19
2004-08-10
Tran, Binh (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By electrolysis, electrical discharge, electrical field, or...
C060S274000, C060S295000, C060S297000, C060S303000, C060S311000, C422S186010, C422S186300, C422S186160
Reexamination Certificate
active
06772584
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for removing soot and nitrogen oxide (NO
x
) in the exhaust gas of diesel engines. Particularly, the inventive apparatus is equipped with a plasma/catalyst system comprising a diesel particulate filter, plasma reactor and catalytic reactor for efficiently removing the harmful pollutants in the exhaust gas.
2. Description of the Prior Art
Generally, the diesel engine has an advantage in that it exhausts less pollutant, such as CO and CO
2
gases and hydrocarbons, which have been shown to be the cause of global warming. The environment is therefore more protected by the use of the diesel engine, owing to its higher heat efficiency and durability in comparison to the gasoline engine.
However, nitrogen oxide (NO
x
) in the exhaust gas of the diesel engine causes to generate the photochemical smog, acid rain and ozone (O
3
). In addition, because the soot particulates in the air are more capable of absorbing light than any other particulates, the soot causes poor visibility and also respiratory disease if such particulates are inhaled in any great amount.
There are various filtering technologies for the exhaust gas of the diesel engine. One method physically filters the soot-particles through a filter. Another method is that NO in the exhaust gas oxidizes to NO
2
by using non-thermal plasma, then the soot and NO
x
are simultaneously eliminated. Further, another method is that hydrocarbon is oxidized or NO
x
is deoxidized by catalyst. A combination or modification of the various methods is also used.
European Pat. EP0937870 to the Delphi Co. discloses an apparatus for the removal of hydrocarbon, CO and NO
x
by using a plasma/catalyst system. According to the Delphi's apparatus, the exhaust gas passes through a primary catalytic layer and plasma reactor and then a secondary catalytic layer sequentially. Through the process, a portion of the hydrocarbon and CO gases is removed by being oxidized in the primary catalytic layer, and NO is converted to NO
2
in the plasma reactor. Sequentially, the residual hydrocarbon and CO gases are removed in the secondary catalytic layer by oxidizing with NO
2
, which is produced in the plasma reactor, and catalyst.
PCT numbers W098/00221 and U.S. Pat. Nos. 5,746,984 and 6,156,162 to Hoard disclose the apparatuses, comprised of a filter and plasma reactor for the treatment of the exhaust from a diesel engine. The particulates collected in the filter are removed by oxidizing with NO
2
, produced in the plasma reactor, and disposed of in front of the filter. The filter is made of ceramic, zeolite or perovskite coated with copper oxides or barium oxides. The time for reacting the plasma and replacing the filter is determined depending on the increasing the backpressure of the filter (or decreasing the engine output) by a sensor mounted at the outlet of the apparatus as mentioned above. In addition, it discloses the other various plasma reactors.
U.S. Pat. Nos. 5,711,147; 6,038,853 and 6,038,854 to Penetrante et al. disclose a system for removing NO
x
and particulates by a two-step process. In the first step, NO is oxidized to NO
2
during which time the plasma is generated under the presence of O
2
and hydrocarbon, and the produced NO
2
reacts with soot particles for converting to N
2
or CO
2
. In the second step, the residual NO
2
passes through a catalytic layer under the presence of hydrocarbons for deoxidizing to N
2
. Especially, U.S. Pat. No. 6,038,854 discloses an implementable example of the plasma/filter/catalyst system.
U.S. Pat. Nos. 4,902,487 and 5,943,857 and PCT WO 00/21646 to Johnson Matthey Co. disclose a system for treating the exhaust gas comprised of a catalyst and a diesel particulate filter. The particulate substances are collected through the filter and oxidized by NO
2
, which is produced in the catalytic layer installed in the front end of the filter at the normal temperature for removal. It is possible to use a plasma reactor instead of the catalyst. In this case, ozone (O
3
) is also produced to oxidize with soot.
PCT numbers WO 00/43645 and WO 00/43102 to AEA Technology disclose a method for the removal of particulates and NO
x
by using a plasma reactor and catalyst. When plasma is generated by adding hydrocarbons, NO is transformed to NO
2
, then the generated NO
2
oxidizes the soot to remove. The residual NO
x
is removed by catalyst. A dielectric barrier is disposed between the electrodes without installing a filter.
PCT number WO 00/29727 to Engelhard Co. discloses a system for removing NO
x
(excluding the soot) by using a plasma reactor and catalyst. This system produces NO
2
by plasma under the highly concentrated hydrocarbon to deoxidize with catalyst. It discloses that when a molar ratio of carbon atom to NO
x
is 5:1 in the exhaust gases, approximately 50% of NO
x
is transformed to N
2
.
Ford Co. also reported that when a molar ratio of NO
x
to carbon atom is about 1:5 in the exhaust gas (the same ratio as the Engelhard Co.) by using plasma and catalyst, which is developed by itself, the transforming rate of NO
x
to N
2
and hydrocarbon to water and CO
2
is 50% and 30%, respectively.
In the International Symposium on High Pressure, Low Temperature Plasma Chemistry held at Greifswald, Germany (Sep. 10~13, 2000), Institute of Nonthermal Plasma Physics and Th. J. Heimbach GmbH disclosed an apparatus for removing soot as shown in
FIG. 1
in which a porous element
11
for collecting the soot is used as an electrode. The other electrode
12
a
coated with dielectric barrier is inserted into the center of the filter cell to generate plasma. Thus, the filter cell itself is used as a plasma reactor for removing the collected soot on the filter (HAKONE VII).
For the detailed descriptions referring to
FIG. 1
, the soot in the exhausted gas is filtered through the porous element
11
used as an electrode. The NO in the exhaust gas is transformed to NO
2
by the plasma generated between the porous element
11
and electrode
12
, coated with a dielectric barrier, present at the center of each filter cell. When the produced NO
2
passes through the porous element
11
electrode, the collected soot on the filter is oxidized and thereby removed.
According to the conventional systems for simultaneously removing soot and NO
x
, NO in the exhaust, gas is transformed to NO
2
through the reaction as represented in the following reaction formula 1, and then the soot and NO
2
are simultaneously removed by the reaction as represented in the following reaction formula 2. The residual NO
2
is reduced to N
2
by the catalyst.
Reaction Formula 1:
NO+½ O
2
→NO
2
Reaction Formula 2:
C(soot)+NO
2
→CO+NO or CO
2
+½N
2
Because the reaction for removing the soot and NO
x
occurs while the exhaust gas containing NO
2
is passing through the layer of soot collected on the filter, the reacting time is very short. Therefore, the soot in the exhaust gas is incompletely treated.
SUMMARY OF THE INVENTION
In order to overcome the problems as described above, the present invention provides a plasma system for completely removing the soot and NO
x
in the exhaust gas of a diesel engine.
An objective of the present invention is to provide an apparatus for removing soot and nitrogen oxide in the exhaust gas of diesel engines by a diesel particulate filter adopting a honeycomb type porous element and having at least one pair of electrodes. A plasma reactor for generating a predetermined amount of plasma is mounted downward on the diesel particulate filter. A catalytic reactor is filled with a catalyst selected from
1
B metal group and mounted downward on the plasma reactor. A means of supplying hydrocarbon is connected to a proper position upward on the plasma reactor.
The electrodes in the diesel particulate filter are comprised of a rod-type electrode able to be inserted into the center of the passage section, and a pipe-type electrode mounted to the outside of the passage section. The elec
Chun Bae Hyeock
Chun Kwang Min
Hwang Jung Ho
Jeong Dong Hoon
Lee Dae Won
GWiPS
Tran Binh
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