JP4757076B2 - Liquid storage tank and engine exhaust purification system - Google Patents

Description

  The present invention relates to a liquid storage tank and an exhaust emission control device for an engine, and more specifically, prevents the liquid component contained in the outflowed gas from being released to the outside when the gas flows out from the liquid storage tank via a breather pipe. Related to technology.

As a technique for purifying nitrogen oxide (hereinafter referred to as “NOx”) discharged from a diesel engine by post-processing, a technique based on the urea SCR method is known. In the urea SCR method, ammonia is added to exhaust gas, and NOx is reduced and purified by using ammonia as a reducing agent, and a reduction catalyst is installed in the exhaust passage to promote reduction of NOx. In consideration of storage convenience, urea, which is a precursor of ammonia, is stored in an aqueous solution in a tank. In actual operation, urea water is supplied from this tank and injected into the exhaust passage upstream of the reduction catalyst. (Patent Document 1). In recent years, the technology by the urea SCR method has been applied to exhaust purification in a diesel engine mounted on a large vehicle such as a truck and put into practical use.
JP 2000-027627 A (paragraph number 0013)

In the urea SCR method, urea is used and stored in the state of an aqueous solution in consideration of practical advantages such as handling and storage of urea water, but for storing urea water. Since it is necessary to employ a tank that can have durability against urea water (for example, a thin tank formed of stainless steel), there is the following problem.
In other words, when the tank vibrates due to vibration transmission from the engine or road surface irregularities, and when a large shake occurs in the stored urea water, resonance occurs in the outer shell of the tank depending on the frequency of this vibration, This is to generate pressure pulsation in the vicinity of the opening of the breather pipe provided in the tank for depressurization. When pulsation occurs in the vicinity of the opening of the breather pipe, intermittent gas flows in and out through the breather pipe due to the pulsation. If urea water is attached to the breather pipe due to the shaking generated in the urea water, the attached urea water flows out of the tank by the gas flow generated by the pulsation and is discharged to the outside. It may be possible to prevent the urea water from adhering to the breather pipe by attaching a cover with vents near the opening of the breather pipe, but if the urea water actually adheres to the breather pipe, The outflow cannot be stopped.

  It is an object of the present invention to reliably prevent the release of liquid components contained in the outflowed gas regardless of the liquid adhering to the breather pipe against the outflow of gas through the breather pipe in the liquid storage tank. .

The present invention provides a liquid storage tank and an exhaust purification device for an engine including the same.
The liquid storage tank according to the present invention includes a tank body that forms a liquid storage chamber, a breather pipe that is provided in the tank body and communicates with the outside of the tank body, and is connected to the breather pipe outside the tank body. And a gas-liquid separator that forms a gas flow passage following the breather pipe and into which the gas flowing out of the storage chamber is introduced via the breather pipe. The gas-liquid separator has a connection portion, a separation portion, and a blowout portion, and is connected to the breather pipe at the connection portion. The separation part communicates with the gas inlet formed by the connection part, and separates the liquid component contained therein from the gas flowing in through the inlet, and in a cross section including the central axis of the inlet, It has a circumferential inner surface centered on a point offset upward in the vertical direction with respect to the central axis. The blow-out portion is provided substantially at the center of the separation portion in the cross section including the central axis, and communicates the inside and outside of the separation portion. The connecting portion forms an inlet port toward the lowest point of the separating portion, and the liquid component separated from the gas flowing in the separating portion is discharged from the gas-liquid separator via the inlet port.

  The exhaust emission control device for an engine according to the present invention includes such a liquid storage tank, and adds an aqueous solution of ammonia or a precursor thereof stored in the liquid storage tank to the exhaust upstream of the reduction catalyst provided in the exhaust passage. To do.

According to the present invention, a gas-liquid separator is provided in the liquid storage tank, and the inner surface is formed in a circumferential shape in the separation part of the gas-liquid separator, and the center of the inner surface is formed of the gas formed by the connection part. By offsetting from the central axis of the inlet, the gas flowing out from the storage chamber of the tank body can be swirled in the separation section, and the liquid component contained in this gas can be separated by centrifugal force. . For this reason, the liquid component is prevented from being released by the outflow of gas from the liquid storage tank, and the liquid component is separated by the gas-liquid separator outside the tank body, so that it is ensured regardless of the liquid adhering to the breather pipe. This can be prevented. Further, Rutotomoni is offset upward in the vertical direction center of the inner surface of the separation portion to the central axis of the inlet, by forming with its inlet at the lowest point of the separation unit, it was flowed in the separation unit The liquid component separated from the gas can be discharged from the gas-liquid separator through the inlet and returned to the storage chamber of the tank body. The gas from which the liquid component has been separated is discharged to the outside through the blowout part.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows the configuration of an exhaust emission control device for an engine according to an embodiment of the present invention. The engine 1 according to the present embodiment is a diesel engine and constitutes a drive source for a vehicle (here, a large vehicle such as a truck). This exhaust purification device includes a liquid storage tank 251 according to the present embodiment, and stores therein a reducing agent to be added to exhaust. In the present embodiment, ammonia is used as the NOx reducing agent, but urea water is stored in the liquid storage tank 251 in consideration of easy storage on the vehicle. This urea water is an aqueous solution of urea, which is a precursor of ammonia.

  A reduction catalyst 102 is installed in the exhaust passage 101 of the engine 1 downstream of the manifold portion. NOx in the exhaust is reduced on the reduction catalyst 102 and purified, and then released into the atmosphere. A urea water injection device (corresponding to an “adding device” according to this embodiment) 201 is installed upstream of the reduction catalyst 102, and when the engine 1 is operated, the urea water is discharged from the exhaust passage 101 by the injection device 201. Is injected into the inside. Urea in the injected urea water is hydrolyzed by exhaust heat and generates ammonia as a reducing agent. The generated ammonia efficiently reduces NOx on the reduction catalyst 102 and converts it into harmless gas.

  The urea water is stored in the liquid storage tank 251, and is pressurized from the liquid storage tank 251 by the feed pump 261 and supplied to the injection device 201 during actual operation. The liquid storage tank 251 includes a tank main body 252 to which a breather pipe 253 (FIG. 3) for pressure release is attached, and a gas-liquid separator 254 described later, and is fixed to a vehicle frame F by brackets 256 and 256. Yes. The tank body 252 forms a box-shaped storage chamber 252a, and urea water is stored in the storage chamber 252a. In the present embodiment, the tank body 252 and the breather pipe 253 are formed of a stainless material in consideration of durability against urea water.

  The injection device 201 is connected to the liquid storage tank 251 via the urea water supply pipe 271, and includes a main body 211 of the injection device that mixes the urea water supplied from the liquid storage tank 251 with assisting air, An injection nozzle 212 attached to the main body 211 on the end side and inserted into the exhaust passage 101 on the front end side is provided. The tip 212 a of the injection nozzle 212 is arranged toward the upstream end surface 102 a of the reduction catalyst 102. The injection device 211 is connected to the liquid storage tank 251 through the return pipe 272 in addition to the supply pipe 271, and urea water supplied to the injection device 201 is injected into the exhaust by the injection nozzle 212. Excess urea water other than is returned to the liquid storage tank 251 through the return pipe 272. In the injection device 201, assist air is supplied from an air tank (not shown) to the main body 211 via the introduction pipe 213.

FIG. 2 shows the configuration of the gas-liquid separator 254 according to the present embodiment in a partially broken state.
With reference to FIG. 2, the structure of the gas-liquid separator 254 is demonstrated.
A pressure release breather pipe 253 (FIG. 3) is attached to the tank body 252 of the liquid storage tank 251, and the gas-liquid separator 254 is connected to the breather pipe 253 outside the tank body 252. The breather pipe 253 and the gas-liquid separator 254 are connected by a rubber breather tube 255.

  The gas-liquid separator 254 forms a gas flow path from the outside of the tank main body 252 to the storage chamber 252a during normal operation together with the breather pipe 253. However, due to vibration of the liquid storage tank 251, the breather pipe 253 is formed. When the gas flows out from the storage chamber 252a through the gas, the outflowed gas is introduced into the gas-liquid separator 254, and urea water that is a liquid component is separated from the gas. Thereby, discharge | release of urea water to air | atmosphere is prevented. The gas-liquid separator 254 includes a connection part 254a that forms a gas inlet, a separation part 254b that separates urea water from the introduced gas, and a blowout part 254c that discharges the separated gas from the separation part 254b. Consists of. The connecting portion 254a is provided so as to protrude outward from the side surface of the separating portion 254b, and one end of the breather tube 255 is connected thereto. The separation part 254b is cylindrical as a whole, and causes the swirl along the circumferential inner surface of the introduced gas. Since the center axis AX2 of the separation part 254b is set to be offset with respect to the center axis AX1 of the introduction port formed by the connection part 254a, the introduced gas swirls around the axis AX2 in the separation part 254b. And centrifugal force acts on urea water. The blowing part 254c is provided on the axis AX2 of the separating part 254b, and communicates the inside of the separating part 254b with the outside. In the present embodiment, the axis AX2 is offset upward in the vertical direction with respect to the axis AX1, so that the separated urea water can be smoothly returned to the liquid storage tank 251.

FIG. 3 shows an overall configuration of the liquid storage tank 251 according to the present embodiment in a longitudinal section.
With reference to FIG. 3, the operation of the liquid storage tank 251, particularly the gas-liquid separator 254 according to this embodiment will be described.
A breather pipe 253 is attached to the tank body 252, and one end of a breather tube 255 is connected thereto. A gas-liquid separator 254 is connected to the other end of the breather tube 255 via a connection portion 254a, thereby forming a liquid storage tank 251. The gas-liquid separator 254 is supported above the tank body 252 in the vertical direction by a holder (not shown). The breather pipe 253 is attached so as to penetrate the lid portion of the tank body 252 and communicates the upper portion of the storage chamber 252a with the outside of the tank body 252. A supply pipe 271 vertically penetrates the lid of the tank body 252. The supply pipe 271 extends from the lid to the vicinity of the bottom of the storage chamber 252a. The return pipe 272 also penetrates the lid of the tank body 252 and opens in the storage chamber 252a.

  When the urea water is sucked up by the feed pump 261 through the supply pipe 271 during the operation of the engine 1, outside air is introduced through the breather pipe 253 by the action of the negative pressure generated in the storage chamber 252 a. The introduction of the outside air is performed through the gas-liquid separator 254, the breather tube 255, and the breather pipe 253, whereby the inside of the storage chamber 252a is maintained at a constant pressure, and a smooth supply of urea water is ensured. Deformation of the tank body 252 is prevented. When the vehicle travels, vibration is generated in the tank body 252 using vibration transmitted from the engine 1 or vibration of the vehicle body due to road surface unevenness as an excitation input. Depending on the frequency of vibration, resonance occurs in the tank body 252, causing a pressure fluctuation in the gas in the storage chamber 252 a, and causing a pressure pulsation near the opening of the breather pipe 253. When urea water is transmitted along the inner wall of the tank body 252 or jumps and adheres to the breather pipe 253 due to large vibration caused by vibration from the road surface or the like (the movement of the urea water U due to this vibration is indicated by arrows F1 and F2). ), The adhering urea water flows out of the storage chamber 252a due to the intermittent gas flow F3 generated through the breather pipe 253 due to pressure pulsation. The gas containing urea water is introduced into the gas-liquid separator 254 via the breather pipe 253 and the breather tube 255, and the swirl F4 along the circumferential inner surface is generated in the separation unit 254b. By the action of the centrifugal force accompanying this turning, urea water is separated from the gas as indicated by the arrow F5, and only the gas component is released from the blowing part 254c (the gas flow is indicated by the arrow F6). On the other hand, the separated urea water travels along the inner surface of the separating portion 254b and the breather tube 255 as indicated by an arrow F7, and returns to the storage chamber 252a.

According to this embodiment, the following effects can be obtained.
A gas-liquid separator 254 is provided in the liquid storage tank 251, and urea water is separated from the gas by the action of centrifugal force in the separation unit 254 b. For this reason, it is possible to prevent the urea water from being released into the atmosphere with a simple configuration that does not require power. Further, according to the present embodiment, urea water is separated outside the tank body 252, so that it is possible to reliably prevent the urea water from being released regardless of the urea water adhering to the breather pipe 253.

Further, according to the present embodiment, since the center axis AX2 of the separation part 254b is set to be offset in the vertical direction above the center axis AX1 of the inlet formed by the connection part 254a, the separated urea water is separated from the separation part 254b. It can flow smoothly along the inner surface of 254b and return to the storage chamber 252a.
In the present embodiment, in the gas-liquid separator 254, the separation portion 254b is formed in a hollow cylindrical shape, and the “circumferential inner surface” is formed by the inner surface of this cylinder. However, the present invention is not limited to this, and the separation portion is formed in an annular shape or an S shape (or a meandering shape), and a “circumferential inner surface” is formed by the radially inward inner surface of the annular shape or the S shape. Can also be formed.

Configuration of an engine exhaust purification system according to an embodiment of the present invention Configuration of gas-liquid separator according to the embodiment Operation explanation of gas-liquid separator

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Engine, 101 ... Exhaust passage, 102 ... Reduction catalyst, 201 ... Injection device, 211 ... Main body of injection device, 212 ... Injection nozzle, 251 ... Liquid storage tank, 252 ... Tank main body, 252a ... Storage chamber, 253 ... Breather Pipe, 254 ... Gas-liquid separator, 254a ... Connection part, 254b ... Separation part, 254c ... Outlet part, 255 ... Breather tube.

Claims (5)

A tank body forming a liquid storage chamber;
A breather pipe that is provided in the tank body and communicates the storage chamber with the outside of the tank body;
A gas-liquid separator that is connected to the breather pipe outside the tank main body and forms a gas flow passage following the breather pipe, while a gas flowing out of the storage chamber is introduced through the breather pipe; Comprising and including
The gas-liquid separator is
A connection part connected to the breather pipe and forming an inlet for gas flowing out of the storage chamber;
A separation unit that communicates with the introduction port and separates a liquid component contained in the gas flowing in through the introduction port, and is perpendicular to the central axis in a cross section including the central axis of the introduction port A separation portion having a circumferential inner surface centered on a point offset upward in the direction;
A blow-off portion that is provided at substantially the center of the separation portion in the cross section and communicates the inside and outside of the separation portion;
The connection part forms the introduction port toward the lowest point of the separation part,
A liquid storage tank in which a liquid component separated from the inflowing gas in the separation unit is discharged from the gas-liquid separator through the introduction port.   The liquid storage tank according to claim 1, wherein urea liquid is stored as the liquid.   The liquid storage tank according to claim 1 or 2 mounted on a vehicle. A reduction catalyst provided in the exhaust passage of the engine;
The liquid storage tank according to claim 1, which stores an aqueous solution of ammonia or a precursor thereof as the liquid.
An engine exhaust purification device comprising: an addition device connected to the liquid storage tank and adding the liquid stored in the tank to the exhaust gas upstream of the reduction catalyst.   The engine exhaust purification device according to claim 4, wherein the engine is a diesel engine.

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