JP5581790B2 - Ammonia supply system to SCR equipment - Google Patents

Description

  The present invention relates to an ammonia supply system to an SCR device that denitrates NOx contained in diesel engine exhaust gas by reducing with ammonia.

  A conventional urea selective reduction catalyst (urea SCR) system is a mechanism that injects urea water at the inlet of an SCR device and reduces NOx in the SCR device using ammonia gas generated by hydrolysis of urea as a reducing agent.

  This urea SCR system will be described with reference to FIG.

  In FIG. 2, an SCR device 2 is connected to an exhaust pipe 1 connected to an exhaust manifold 8 of a diesel engine 7, an injection nozzle 6 is provided on the upstream side of the SCR device 2, and urea water 4 from a urea tank 3. Is injected from the injection nozzle 6 via the pump 5, and the urea SCR system is configured.

  Exhaust gas containing NOx from the diesel engine 7 passes through the exhaust pipe 1 from the exhaust manifold 8 and hydrolyzes the urea water injected from the injection nozzle 6 and flows into the SCR device 2, where the ammonia gas is hydrolyzed. NOx is reduced and denitrated.

JP 2008-267321 A Special table 2001-518047 gazette

  However, the following problems remain in the above-described conventional urea SCR system.

  a) Since urea water is supplied to the inlet of the SCR device, the urea water is not completely hydrolyzed when the exhaust gas temperature is lower than 160 ° C., and the efficiency of supplying ammonia particularly at low temperatures is poor.

  b) White crystals such as cyanuric acid are generated during urea hydrolysis and are deposited in the SCR device, causing a decrease in SCR function.

  c) Since the water contained in a large amount in the urea water does not completely evaporate and directly enters the SCR device, the deterioration of the zeolite SCR having poor hydrothermal durability is likely to proceed.

  Therefore, an object of the present invention is to provide an ammonia supply system to an SCR device that solves the above-described problems and can efficiently supply ammonia and prevent deterioration of the SCR as compared with the conventional urea SCR system. There is.

In order to achieve the above object, according to the first aspect of the present invention, when an SCR device is connected to an exhaust pipe of a diesel engine and ammonia gas is supplied to the SCR device, an ammonia source aqueous solution is heated with a heater to generate ammonia gas. And an ammonia supply system to the SCR device that separates the water vapor from the ammonia gas through the ammonia gas generated in the cooler maintained at normal pressure, and supplies the ammonia gas separated from the water vapor to the SCR device by a compressor. is there.

  The invention according to claim 2 is the ammonia supply system to the SCR device according to claim 1, wherein the heater heats the aqueous ammonia source solution to 160 ° C. or higher and 180 ° C. or lower.

  A third aspect of the present invention is the ammonia supply system to the SCR device according to the first or second aspect, wherein the temperature of the cooler is 50 ° C. or higher and 80 ° C. or lower.

  According to the present invention, ammonia can be supplied more efficiently than the conventional urea SCR system, and deterioration of the SCR can be prevented.

It is a figure explaining the ammonia supply system to the SCR device of the present invention. It is a figure explaining the conventional urea SCR system.

  A preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 shows an ammonia supply system to an SCR device according to the present embodiment. In FIG. 1, an SCR device 2 is connected to an exhaust pipe 1 connected to an exhaust manifold 8 of a diesel engine 7, and an injection nozzle 15 is provided on the upstream side of the SCR device 2. The injection nozzle 15 is supplied with an ammonia source. The tank 16 is connected via the pipe 11. A heater 12, a cooler 13, and a compressor 14 are sequentially connected to the pipe 11 from the ammonia source supply tank 16 side, and the aqueous ammonia source solution from the ammonia source supply tank 16 is heated by the heater 12 connected to the pipe 11. The generated ammonia gas passes through the cooler 13 and is jetted from the jet nozzle 15 via the compressor 14 to constitute an ammonia supply system to the SCR device.

  The ammonia source supply tank 16 stores an aqueous solution (ammonia source aqueous solution) of a substance that generates ammonia by thermal decomposition, for example, an aqueous solution of urea, ammonium bicarbonate, or ammonium carbonate.

  The heater 12 heats at a temperature suitable for generating ammonia gas from the ammonia source aqueous solution supplied from the ammonia source supply tank 16. When the ammonia source aqueous solution is a urea aqueous solution having a concentration of 32.5%, the heater 12 is set so as to heat the urea aqueous solution to 160 ° C. or higher and 180 ° C. or lower. If the set temperature is lower than 160 ° C., the urea water is not completely hydrolyzed, and the ammonia supply efficiency deteriorates.

  The cooler 13 includes a cooling pipe 13a for condensing water vapor from ammonia and a recovery tank 13b for separating and recovering the condensed water. As the cooling pipe 13a, for example, a helical pipe used for a Jimroth cooler is used. The water condensed in the cooling pipe 13a is dropped by its own weight and collected in the collection tank 13b. The cooler 13 may be water-cooled or air-cooled.

  The cooler 13 is provided at a position close to the exhaust pipe 1 or the SCR device 2 and is held at a relatively high temperature (50 to 80 ° C.). If the temperature of the cooler 13 (cooling pipe 13a) is less than 50 ° C., the amount of ammonia dissolved in the condensed water increases. On the other hand, if it exceeds 80 ° C., the amount of water vapor that can be condensed in the cooling pipe 13a decreases. The temperature of the vessel 13 (cooling pipe 13a) is preferably maintained at 50 ° C. or higher and 80 ° C. or lower.

  The compressor 14 that boosts the ammonia gas is set so as to send out the ammonia gas at a pressure higher than the exhaust gas pressure in the exhaust pipe 1.

  Next, the operation of the present embodiment will be described.

  In the ammonia supply system according to the present invention, the ammonia source aqueous solution supplied from the ammonia source supply tank 16 is thermally decomposed using the heater 12 to generate ammonia gas, and then the ammonia gas from which water vapor has been separated through the cooler 13 is converted into SCR. The pressure is supplied to the apparatus 2 by a compressor 14 and supplied. In this way, ammonia gas is generated in advance and supplied to the SCR device 2, so that the exhaust pipe is compared with the case of injecting urea water at the inlet of the SCR device 2 to generate ammonia gas as in the conventional urea SCR system. Even if the exhaust gas temperature of 1 is low, ammonia gas can be supplied efficiently. Further, since ammonia is directly supplied to the SCR device 2 in the state of gas, the SCR device 2 can prevent deposition of crystal residues such as cyanuric acid.

  Furthermore, since moisture is removed from the ammonia gas supplied to the SCR device 2, it is possible to prevent deterioration of the zeolite-based SCR having particularly poor hydrothermal resistance.

  Further, after the engine is stopped, residual ammonia in the pipe 11 is dissolved in the trapped water (in the recovery tank 13b), thereby preventing ammonia from being released into the atmosphere.

  As described above, according to the present invention, an aqueous solution of a substance that generates ammonia by thermal decomposition, for example, an aqueous solution of ammonium bicarbonate, ammonium carbonate, or urea is decomposed at an appropriate temperature using a heater to generate ammonia.

  There is also a method (Patent Document 1) in which the above compound is directly pyrolyzed as a solid reducing agent to generate ammonia. However, in this case, when exposed to high temperatures such as under the sun, there is a risk of leakage of ammonia gas to the atmosphere or explosion. Is higher than in the case of a solution, and the solution state is more advantageous in terms of ease of handling during replenishment.

  Since the gas generated by the thermal decomposition of the aqueous solution contains a large amount of water vapor, the present invention condenses and traps water in the generated gas using a cooler. The cooler is attached at a position close to the exhaust pipe or the SCR device, and kept at a relatively high temperature (50 to 80 ° C.). The removal of water in the present invention is not under pressure as in Patent Document 2, but uses a cooler that is maintained at a normal pressure and a relatively high temperature, so that dissolution of ammonia gas in condensed water can be suppressed. .

  In the above manner, the present invention supplies ammonia gas from which water has been removed to the SCR device. When ammonia gas is supplied, it is possible to efficiently supply ammonia gas by increasing the pressure using a compressor and sending the ammonia gas at a pressure higher than the exhaust gas pressure.

1 Exhaust pipe 2 SCR device 12 Heater 13 Cooler 14 Compressor

Claims (3)

When connecting an SCR device to the exhaust pipe of a diesel engine and supplying ammonia gas to the SCR device,
The ammonia source aqueous solution is heated with a heater to generate ammonia gas, and water vapor is separated from the ammonia gas through the ammonia gas generated in a cooler maintained at normal pressure, and the ammonia gas separated from the water vapor is compressed with a compressor. A system for supplying ammonia to an SCR device, wherein the system is supplied to the SCR device.   The ammonia supply system to the SCR apparatus according to claim 1, wherein the heater heats the aqueous ammonia source solution to 160 ° C. or higher and 180 ° C. or lower.   The ammonia supply system to the SCR device according to claim 1 or 2, wherein the temperature of the cooler is 50 ° C or higher and 80 ° C or lower.

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