JP2009108764A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of efficiently purifying hazardous constituents in an exhaust gas containing water vapor without incurring deterioration in catalytic activity. <P>SOLUTION: A countercurrent heat exchanger 3 is arranged in an exhaust gas flow path 2 of an engine 1. In the heat exchanger 3, a partitioning wall 3c separates high-and low-temperature-side flow paths 3a, 3b. Heat exchange is performed between the high-and low-temperature-side flow paths 3a, 3b. Fluid passing the high-temperature-side flow path 3a is cooled while fluid passing the low-temperature-side flow path 3b is reheated. Further, a condensed water removal device 4 is arranged in the exhaust gas flow path 2 of the engine 1, and a silver alumina catalyst 8 acting as an NO<SB>x</SB>selective reduction catalyst is arranged at the downstream side of the condensed water removal device 4. The upstream side of the condensed water removal device 4 and the high-temperature-side flow path 3a of the heat exchanger 3 communicate with each other while the downstream side of the condensed water removal device 4 and the upstream side of the catalyst 8 communicate with each other via the low-temperature-side flow path 3b of the heat exchanger 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device that purifies harmful components in combustion exhaust gas discharged from an internal combustion engine or the like.

Exhaust gas from gasoline lean burn engines and diesel engines contains a large amount of oxygen. For example, a copper ion exchange zeolite catalyst is used as a selective reduction catalyst that selectively reduces and purifies nitrogen oxides (NO _x ) in the exhaust gas. Is used. Since this catalyst has a reduction and purification capability due to a slight amount of water, there is a device for reducing NO _x in the engine exhaust gas, equipped with a water removal device on the upstream side, and calcium chloride as a water removal agent for the water removal device. Is used. In this NO _x reducing device, since passing the catalyst after removing the moisture of the exhaust gas NO _x in efficiently exhaust gas can be converted to N ₂ (e.g., see Patent Document 1).
Further, the exhaust gas introduction pipe from the combustion engine is provided with a soot removing portion provided with a cooling means for cooling and condensing water vapor in the exhaust gas to form water droplets and a separating means for separating the water droplets from the exhaust gas, There are nitrogen oxide, HC removal and noise reduction devices. In the soot removal section, the exhaust gas introduction pipe is cooled from the outside, the exhaust gas passing through the exhaust gas introduction pipe is cooled, the water vapor in the exhaust gas is condensed into water droplets, and these water droplets are collected together with the soot in the water receiving tank. And separated from the exhaust gas (see, for example, Patent Document 2).
In addition, a heat exchanger and an adsorbent are disposed in an exhaust passage through which exhaust gas of the internal combustion engine passes, and a catalyst is disposed downstream of the adsorbent, and the heat exchanger is disposed upstream of the adsorbent, and the adsorbent. There is an exhaust gas purification device that can exchange heat with the upstream side of the catalyst and the upstream side of the catalyst. In this exhaust gas purification device, immediately after the engine is started, exhaust gas containing harmful components discharged from the engine passes through the heat exchanger and flows out at a low temperature, and the harmful components are easily adsorbed by the adsorbent. Become. The exhaust gas from which harmful components have been removed by the adsorbent is heated to a high temperature by a heat exchanger and introduced into the catalyst, and the temperature of the catalyst is quickly raised to the activation temperature. As a result, when the exhaust gas temperature rises immediately after starting the engine, the adsorbent can once adsorb the harmful component until the catalyst reaches an activation temperature at which the harmful component in the exhaust gas can be purified. Can be prevented from being released into the atmosphere (see, for example, Patent Document 3).

JP 7-102952 A (first page) JP-A-8-093443 (first page) Japanese Patent Laid-Open No. 2001-295543 (first page)

In NO _x reducing device of Patent Document 1, because of the use of adsorbent which adsorbs moisture in the moisture removing agent, it is necessary reproducing operation of releasing the adsorbed moisture can not be removed continuously water There was a problem.
In the soot removal unit in the soot, NO _x , HC removal and noise reduction device of Patent Document 2, the exhaust gas is cooled, the water vapor is condensed and water is removed, so that the exhaust gas is reduced to 100 ° C. or less, and the catalyst Thus, there is a problem that the catalyst cannot purify NO _x , CO, and HC without applying energy by a heater or the like.
In the exhaust gas purification device of Patent Document 3, when the engine is started, water vapor in the exhaust gas cooled and output by the heat exchanger can also be temporarily adsorbed and removed by the adsorbent. However, the adsorbent of the exhaust gas purification device is for temporarily adsorbing harmful components until the catalyst reaches an activation temperature that can purify the harmful components in the exhaust gas when the temperature of the exhaust gas rises immediately after the engine starts. As the time elapses after the engine is started, the adsorbent becomes almost the same temperature as the heat exchanger, and there is a problem that moisture is not adsorbed. Further, in the exhaust gas purifying apparatus of Patent Document 3, if the catalyst reaches an activation temperature at which harmful components in the exhaust gas can be purified, the adsorbent is not necessary, so that the adsorbent is not required between the heat exchanger and the catalyst. There is no necessity to provide a function of cooling the exhaust gas.

  The present invention has been made to solve such a problem, and provides an exhaust gas purification apparatus capable of efficiently purifying harmful components in exhaust gas containing water vapor without causing a decrease in catalytic activity. For the purpose.

  An exhaust gas purification apparatus according to the present invention includes a condensate water remover provided in an exhaust gas flow path of an engine, a catalyst provided downstream of the condensate water remover in the exhaust gas flow path, and the exhaust gas flow A high temperature side channel provided upstream of the condensed water remover in the passage, and a low temperature side channel provided downstream of the condensed water remover and upstream of the catalyst in the exhaust gas channel. A heat exchanger separated by a partition is provided.

  The engine exhaust gas is lowered in temperature by the heat exchanger, and the water vapor in the lowered exhaust gas is cooled, condensed, and removed by the condensed water remover. Thereafter, the exhaust gas from which the moisture has been removed is reheated by the heat exchanger to increase the temperature, reach the activation temperature of the catalyst, and is led to the catalyst. Thereby, it is possible to purify harmful components in the exhaust gas stably for a long period of time.

Embodiment 1 FIG.
Exhaust gas emitted from automobile engines contains nitrogen oxides (NO _x ), carbon monoxide (CO), and hydrocarbons (HC) as harmful components, and is contained in exhaust gases from gasoline lean burn engines and diesel engines. Contains a large amount of oxygen, and NO _x purification is particularly problematic. A catalyst that selectively reduces and purifies NO _x in the exhaust gas of a gasoline lean burn engine or diesel engine (NO _x selective reduction catalyst) is carbon monoxide (CO) or carbonization present in the exhaust gas on the catalyst. when reducing purify NO _x hydrogen (HC) as a reducing agent, removing performance of nitrogen oxides Kitaichi a change in crystal structure is reduced by the presence of slight moisture.

FIG. 1 is a configuration diagram of an exhaust gas purifying apparatus according to Embodiment 1 of the present invention. FIG. 2 is a schematic diagram showing the temperature history of the exhaust gas in the exhaust gas purification device, showing the temperature of the exhaust gas at each point in the exhaust gas purification device in FIG. 1, the vertical axis is the temperature, and the horizontal axis is the exhaust gas. Each point in the gas purifier is shown.
As shown in FIG. 1, in the exhaust gas purification apparatus according to Embodiment 1 of the present invention, a counter flow type heat exchanger 3 is disposed in the exhaust gas flow path 2 of the engine 1, and the heat exchanger 3 is on the high temperature side. The flow path 3a and the low temperature side flow path 3b are separated by a partition wall 3c, heat exchange is performed between the high temperature side flow path 3a and the low temperature side flow path 3b, the fluid passing through the high temperature side flow path 3a is cooled, and the low temperature side flow The fluid passing through the path 3b is reheated.
Further, a condensed water remover 4 and a catalyst 8 are disposed downstream of the condensed water remover 4 in the exhaust gas flow path 2 of the engine 1, and the upstream side of the condensed water remover 4 and the heat exchanger 3. The high temperature side flow path 3a flows, and the downstream side of the condensed water remover 4 and the upstream side of the catalyst 8 flow through the low temperature side flow path 3b of the heat exchanger 3. In the present embodiment, a silver alumina catalyst that is a NO _x selective reduction catalyst is used as the catalyst 8.
The condensed water remover 4 cools the exhaust gas flow path 2 from the outside with a fan 5 or the like and cools it to 100 ° C. or lower to condense and separate water vapor in the exhaust gas, and discharges the condensed water 7 from the drain pipe 6. To remove.

As shown in FIG. 1 and FIG. 2, the exhaust gas at about 500 ° C. discharged from the engine 1 is led to the high temperature side channel 3a of the heat exchanger 3 through the exhaust gas channel 2, and the heat exchanger 3 between the inlet 3d and the outlet 3e of the high temperature side flow path 3a, heat is exchanged through the partition wall 3c with the exhaust gas having a low temperature by the condensed water remover 4, and is cooled to about 150 ° C. The cooled exhaust gas is guided to the condensed water remover 4 and cooled to condense and remove water vapor in the exhaust gas. The exhaust gas from which the moisture has been removed is guided to the low temperature side flow path 3b of the heat exchanger 3, and between the inlet 3f and the outlet 3g of the low temperature side flow path 3b, It exchanges heat with the exhaust gas and is reheated to about 400 ° C. Water is removed, and re-heated exhaust gas is introduced into _the NO _x selective reduction catalyst 8, NO _x in the exhaust gas is selectively reduced and purified.

Table 1 shows the relationship between the water vapor concentration in the exhaust gas and the NO _x reduction purification efficiency when a silver alumina catalyst is used as the NO _x selective reduction catalyst 8 in the present embodiment. Generally, the engine exhaust gas contains 10% or more of water vapor. As shown in Table 1, in this embodiment, the water vapor concentration was decreased to 4% from 14%, thereby the _the NO _x reduction purification efficiency higher than 20% can purify NO _x with 70% efficiency. Note that the NO _x reduction purification efficiency is a value represented by the following equation.
NO _x reduction purification efficiency = (catalyst inlet NO _x concentration−catalyst outlet NO _x concentration) / catalyst inlet NO _x concentration

Figure 3 is a characteristic diagram showing the relationship between the temperature and _the NO _x reduction purification efficiency of the silver-alumina catalyst 8 according to this embodiment.
As shown in FIG. 3, in the relationship between the temperature of the silver alumina catalyst 8 and the NO _x reduction purification efficiency, there is a catalyst temperature at which the NO _x reduction purification efficiency is highest, and the silver alumina catalyst has the highest at about 400 ° C. NO _x reduction purification efficiency is obtained.

From the above, according to the exhaust gas purification apparatus of the present embodiment, moisture is removed from the engine exhaust gas containing a large amount of moisture, and NO _{x is} selected to a temperature at which the highest NO _x reduction purification rate is obtained. Since the silver-alumina catalyst, which is a reduction catalyst, can be maintained, it is possible to efficiently reduce and purify NO _x in the exhaust gas efficiently, so it is also effective in purifying exhaust gas from gasoline lean burn engines and diesel engines. Preferably used.

Further, in the present embodiment, the case where a silver alumina catalyst is used as the NO _x selective reduction catalyst 8 is shown, but the same effect can be obtained even if a zeolite catalyst is used as the NO _x selective reduction catalyst. Furthermore, when the catalyst 8 is applied not only to the NO _x selective reduction catalyst but also to other catalysts whose catalytic ability is reduced due to the presence of moisture, the reduction of the catalytic ability is prevented.
Moreover, in this Embodiment, although the condensed water removal device 4 performed cooling by air cooling, it can also perform by water cooling.
In the present embodiment, a counter flow type heat exchanger is used as the heat exchanger 3. However, a rotary Jungstrom heat exchanger used for desiccant air conditioning or dehumidification is used. However, the same effect can be obtained.

Furthermore, in Embodiment 1 of the present invention, an oxidation catalyst for purifying CO and HC may be installed on the downstream side of the NO _x selective reduction catalyst 8. In this case, since the temperature of the exhaust gas from the NO _x selective reduction catalyst 8 is as high as about 400 ° C., a general oxidation catalyst can be used in a highly active state, and sufficient purification can be obtained.

It is a block diagram of the exhaust gas purification apparatus of Embodiment 1 of this invention. It is a schematic diagram which shows the temperature history of the exhaust gas in the exhaust-gas purification apparatus of Embodiment 1 of this invention. The relationship between the temperature and _the NO _x reduction purification efficiency of the NO _x selective reduction catalyst according to the first embodiment of the present invention is a characteristic diagram showing.

Explanation of symbols

  1 engine, 2 exhaust gas flow path, 3 heat exchanger, 3a high temperature side flow path, 3b low temperature side flow path, 3c partition, 4 condensed water remover, 8 catalyst.

Claims (4)

  A condensed water remover provided in the exhaust gas flow path of the engine, a catalyst provided downstream of the condensed water remover in the exhaust gas flow path, and an upstream side of the condensed water remover in the exhaust gas flow path A heat exchanger in which a high temperature side flow path provided in the exhaust gas flow path and a low temperature side flow path provided on the downstream side of the condensed water remover and on the upstream side of the catalyst are separated by a partition wall. An exhaust gas purification device comprising the exhaust gas purification device. Catalyst, an exhaust gas purifying apparatus according to claim 1, characterized in that the _the NO _x selective reduction catalyst. The exhaust gas purification device according to claim 2, wherein the NO _x selective reduction catalyst is a silver alumina catalyst or a zeolite catalyst. The exhaust gas purification apparatus according to claim 2, wherein an oxidation catalyst is provided downstream of the NO _x selective reduction catalyst in the exhaust gas flow path.

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