JP2011144765A - Marine exhaust gas denitration device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the clogging of a urea water injection nozzle or an exhaust pipe. <P>SOLUTION: This marine exhaust gas denitration device 1 includes a reactor 2 for producing ammonia from urea water, the urea water injection nozzle 32 for supplying the urea water into the reactor 2, and a SCR catalyst part 4 provided in an exhaust gas passage on the downstream side of an exhaust turbocharger 5 to be driven by exhaust gas from a diesel engine 3 for performing exhaust gas denitration using the ammonia supplied from the reactor 2. To the reactor 2, the exhaust gas is guided which is extracted part of the exhaust gas to be supplied from the diesel engine 3 to the exhaust turbocharger 5. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a marine exhaust gas denitration apparatus that can be used for a diesel engine having a low exhaust gas temperature, including a marine two-cycle diesel engine equipped with an exhaust turbocharger.

In order to remove nitrogen oxides (NOx) in exhaust gas discharged from internal combustion engines such as diesel engines, denitration equipment using selective catalytic reduction (SCR) is used in automobiles and onshore power generation facilities. It is used a lot. As a reducing agent for such a denitration apparatus, ammonia gas, ammonia water or urea water is used. However, ammonia has an irritating odor and is treated as a deleterious substance with the exception of ammonia water with a content of 10% or less, so when using ammonia water with a content of 25-30% circulating in the city as a reducing agent, leakage detection Special equipment such as sensors, double piping, and ventilation equipment may be required. On the other hand, urea water does not have an irritating odor like ammonia and is not handled as a deleterious substance, and is therefore easier to handle than ammonia in that no additional equipment is required. In a situation where international direction is set, in which nitrogen oxides emitted from marine diesel engines are strictly regulated in some sea areas, from the standpoint of placing the highest priority on the health and safety of crew, A denitration apparatus using a 32.5% content aqueous urea solution that has been commercialized as a reducing agent for a denitration apparatus is highly desired.
The following Patent Documents 1 to 4 disclose techniques using urea water as a reducing agent for a denitration device of an automobile diesel engine.

JP 2002-371831 A JP 2007-218146 A JP 2004-44405 A JP-A-5-285343

  In patent documents 1 and 2, a diesel engine for automobiles is targeted. The diesel engine for automobiles has four cycles, and since the exhaust temperature is generally as high as about 450 ° C., reforming from urea water to ammonia can be sufficiently expected. Therefore, Patent Documents 1 and 2 adopt a configuration in which urea water is injected into the exhaust pipe before the metal-based denitration catalyst such as zeolite.

However, a marine diesel engine equipped with an exhaust turbocharger is frequently used as a main engine for marine propulsion (marine main engine).
Unlike an automobile diesel engine, a marine main engine having such a configuration, for example, in the case of a two-cycle diesel engine, has excellent single-body thermal efficiency, so the exhaust gas temperature after passing through an exhaust turbocharger is about 250 ° C. at the maximum. There is a tendency to become low to the extent. The denitration catalyst employs a titanium / vanadium system exhibiting high activity in a temperature range of 250 to 420 ° C., preferably 320 to 400 ° C., but requires time and a running distance for reforming from urea water to ammonia. The water injection nozzle is arranged as far away as possible upstream of the catalyst exhaust.
When the exhaust gas temperature is low, various solid by-products such as biuret, cyanuric acid and the like are generated in the reforming process from urea water to ammonia. These solid by-products are considered to be generated within the range of the temperature level at which urea begins to decompose (about 133 ° C.) to the temperature level at which cyanuric acid begins to decompose (320 to 360 ° C.).
According to Patent Document 3, the phenomenon when urea water is directly sprayed onto the exhaust pipe with respect to the denitration catalyst is described as follows. “The urea water dropped from the nozzle is evaporated by the heat of the exhaust gas flowing through the pipe when dropped, and ammonia gas is generated in the pipe. Then, nitrogen oxides are reduced by the ammonia and denitrated. Nitrogen oxide is denitrated in the device, and urea water can be sufficiently evaporated and diffused inside the pipe if the flow rate of exhaust gas and the temperature in the pipe are moderate. In a state where the combustion of the device is weakened, the flow rate of the exhaust gas is small and the temperature drops, so the urea water does not evaporate properly, and the urea water drops from the nozzle. ”“ When urea water drops from the nozzle In addition, urea water was solidified at the tip of the nozzle and the nozzle was blocked, and urea produced a by-product such as cyanuric acid by a polymerization reaction when the temperature in the pipe decreased. If produced and attached to the inner peripheral wall of the pipe, the amount of ammonia that is a reducing agent for nitrogen oxides is reduced, and the denitration performance of the denitration device on the downstream side is reduced. In many cases, when urea water accumulates in the downstream (bottom wall) of the pipe, the peripheral wall of the pipe is in contact with the outside air, so there is a temperature difference from the inside of the pipe, and the urea water dripped onto the bottom wall of the pipe The inner peripheral surface of the pipe is cooled to produce cyanuric acid. "
It is difficult to always maintain the ideal exhaust gas temperature and catalyst temperature in a ship that operates under frequent load fluctuations. Direct injection of urea water into the exhaust pipe inevitably generates solid by-products, and it is difficult to open and maintain the exhaust pipe every time the ship is anchored. It is a problem to avoid the accumulation of water. Further, if these solid by-products are left unattended due to incomplete maintenance, the solid by-products grow with time and the exhaust pipe may be blocked.

On the other hand, the titanium / vanadium denitration catalyst required for exhaust gas denitration shows high activity in the exhaust gas temperature range of 320 to 400 ° C. as described above, but when the exhaust gas temperature is less than 320 ° C., sulfur oxidation in the exhaust gas is performed. The denitration catalyst is poisoned by ammonium bisulfate (acidic ammonium sulfate) generated from the product (SOx) and ammonia, and the performance of the denitration device is significantly deteriorated at the 250 ° C. level.
In order to avoid this problem, it is conceivable to arrange a denitration device upstream of a turbocharger that can expect an exhaust gas temperature of 400 ° C. even in a marine two-cycle diesel engine. The responsiveness of the aircraft is reduced, and the exhaust turbocharger does not follow when starting and stopping or when the load fluctuates, causing hunting in the scavenging and exhausting system, significantly affecting engine performance, and hindering safe navigation of the ship There is. In addition, the exhaust gas temperature at the 400 ° C level is generally the upper limit for the operating temperature range of the titanium / vanadium denitration catalyst, and if it is used in a temperature range higher than this, it will be lost due to sintering (sintering) of the catalyst. And the life of the catalyst may be reduced. For these reasons, a system in which a denitration device is disposed upstream of the supercharger has not been put into practical use.
In Patent Document 4, if a denitration catalyst that is disposed downstream of an exhaust turbocharger of a diesel engine, particularly a marine two-cycle diesel engine and uses ammonia as a reducing agent, has been used at a low temperature for a short period of time, the temperature is raised again. In order to put into practical use as a denitration device, the denitration device body in which the activity of the denitration catalyst has been reduced to the original active state due to acidic ammonium sulfate can be put into practical use. In addition, a damper is provided at the inlet of each flow path, and a high temperature gas injection nozzle for heating and regeneration is provided upstream of the catalyst inside each flow path inlet damper. It is proposed to extract and use from the exhaust pipe on the upstream side. However, as described above, since the marine exhaust gas denitration apparatus using ammonia as a reducing agent is not required in terms of safety, the proposal of Patent Document 4 is insufficient.

In a situation where the international direction in which nitrogen oxides emitted from marine diesel engines are strictly regulated in some sea areas is determined, the remaining fuel used is the conventional residual oil with a sulfur content of 4.5% or less. Instead of the regulation of distillate oil with a sulfur content of 0.1% or less, the NOx regulation value has been reduced by 80% from the current regulation.
In order to provide a marine exhaust gas denitration device that can also be used for diesel engines with low exhaust gas temperature, a denitration device is placed downstream of the exhaust turbocharger, and even if the exhaust gas temperature is as low as about 250 ° C, the denitration catalyst by acid ammonium sulfate is used. There is an urgent need to solve two problems: the problem of avoiding poisoning and the problem of using urea water with a content of 32.5% as a reducing agent. The former problem can be solved by using a distillate having a sulfur content of 0.1% or less, but the latter problem remains.

  The present invention has been made in view of such circumstances, and when urea water is used as a denitration reducing agent, the urea water injection nozzle and the exhaust pipe can be prevented from being blocked, safety, An object of the present invention is to provide a marine exhaust gas denitration device for marine diesel engines that emphasizes maintainability.

In order to solve the above problems, the marine exhaust gas denitration apparatus of the present invention employs the following means.
A marine exhaust gas denitration apparatus according to the present invention includes a reactor that generates ammonia from urea water, a urea water injection nozzle that supplies urea water into the reactor, and an exhaust turbocharger that is driven by exhaust gas from a marine diesel engine. A marine exhaust gas denitration apparatus provided with a denitration catalyst unit that is provided in a side exhaust gas passage and performs exhaust gas denitration using ammonia supplied from the reactor, the reactor including the marine diesel engine to the exhaust turbo The exhaust gas extracted from a part of the exhaust gas supplied to the supercharger is guided.

Since the exhaust gas extracted from a part of the exhaust gas supplied from the marine diesel engine to the exhaust turbocharger is guided to the reactor, the reaction temperature in the reactor can be raised. As a result, it is possible to suppress the generation of solid by-products generated during the reforming process from urea water to ammonia, to prevent the urea water injection nozzle from being blocked, and to bring solid by-products into the exhaust pipe. Since it has no structure, the exhaust pipe can be prevented from being blocked.
Further, by extracting a part of the exhaust gas supplied to the exhaust turbocharger, the amount of exhaust gas passing through the exhaust turbocharger is reduced, so that the turbine work of the exhaust turbocharger is reduced and supplied to the engine. Since the amount of air to be reduced decreases, the exhaust gas temperature can be further increased. Thereby, the production | generation of a solid by-product can be suppressed further.

According to the present invention, the exhaust gas extracted from a part of the exhaust gas supplied from the marine diesel engine to the exhaust turbocharger is guided to the reactor and the reaction temperature in the reactor is increased. Generation of solid by-products generated in the reforming process can be suppressed, and blockage of the urea water injection nozzle and the exhaust pipe can be prevented.
Even if a solid by-product is generated in the reactor, the solid by-product is not accumulated in the exhaust pipe which is difficult to open, so it is safe for ship operation, and the solid by-product is accumulated in the lower part of the reactor. In the event of a ship berthing. In addition, the solid by-product gradually melts during the heat regeneration of the catalyst and contributes to exhaust gas denitration. Compared with the method of directly injecting urea water into the exhaust pipe, it is excellent in maintainability.

1 is a schematic configuration diagram showing an embodiment of a marine exhaust gas denitration apparatus of the present invention.

Hereinafter, an embodiment of a marine exhaust gas denitration apparatus according to the present invention will be described with reference to FIG.
FIG. 1 shows a schematic configuration around a diesel engine 3 provided with a marine exhaust gas denitration apparatus 1 according to the present embodiment.
In the ship, a diesel engine 3 that is a main engine for ship propulsion, a denitration device 1 for denitrating exhaust gas from the diesel engine 3, an exhaust turbocharger 5 that is driven by the exhaust gas of the diesel engine 3, The exhaust gas economizer 11 that generates steam by the exhaust gas of the diesel engine 3 is provided.

The diesel engine 3 is a marine two-cycle engine, and a uniflow type that is scavenged in one direction so as to supply air from below and exhaust upward is adopted. The output from the diesel engine 3 is directly or indirectly connected to the screw propeller via a propeller shaft (not shown).
An exhaust port of a cylinder portion 13 (only one cylinder is shown in FIG. 1) of each cylinder of the diesel engine 3 is connected to an exhaust manifold 15 as an exhaust gas collecting pipe. The exhaust manifold 15 is connected to the inlet side of the turbine section 5a of the exhaust turbocharger 5 via the first exhaust path L1. In FIG. 1, reference numeral 8 is an exhaust valve, and reference numeral 9 is a piston.

  On the other hand, the scavenging port of each cylinder part 13 is connected to a scavenging trunk (not shown), and the scavenging trunk is connected to the compressor part 5b of the exhaust turbocharger 5 via a scavenging path K1. An air cooler (intercooler) 19 is installed in the scavenging path K1.

The exhaust turbocharger 5 includes a turbine unit 5a and a compressor unit 5b. The turbine part 5a and the compressor part 5b are coaxially connected by the rotating shaft 5c. The turbine part 5a is driven by the exhaust gas from the diesel engine 3, and the turbine work obtained in the turbine part 5a is transmitted to the compressor part 5b via the rotating shaft 5c. The compressor unit 5b sucks outside air (air) and raises the pressure to a predetermined scavenging pressure.
The exhaust gas after the turbine work is given by the turbine part 5a flows out to the second exhaust path L2. The second exhaust path L2 is branched at the branch point 20 into the third exhaust path L3 and the fourth exhaust path L4. Switching of the exhaust gas path at the branch point 20 is performed by an exhaust gas economizer side opening / closing valve 22 provided in the third exhaust path L3 and a denitration side opening / closing valve 24 provided in the fourth exhaust path L4. These on-off valves 22 and 24 are alternatively selected to be opened and closed. In other words, when exhaust gas denitration is required, such as when navigating a sea area where NOx regulations for exhaust gas are strict, the denitration side open / close valve 24 is opened and the exhaust gas economizer side open / close valve 22 is closed. On the other hand, when exhaust gas denitration is not performed, such as when navigating in a sea area where the NOx regulation of exhaust gas is relatively gentle, the denitration side on-off valve 24 is closed and the exhaust gas economizer side on-off valve 22 is opened.
The on-off valves 22 and 24 can be replaced with one three-way valve.

The exhaust gas economizer 11 is connected to the downstream side of the exhaust gas economizer side on-off valve 22 and generates heat by exchanging heat between the exhaust gas discharged from the diesel engine 3 and the water supplied by the water supply pipe 23. The generated steam is used in various places on the ship.
On the downstream side of the NOx removal side opening / closing valve 24 in the fourth exhaust path L4, an ammonia supply unit 6 that supplies ammonia gas generated by the reactor 2 described later to the exhaust gas, and a selective catalytic reduction method (SCR; Selective Catalytic Reduction) SCR catalyst section (denitration catalyst section) 4 used in the above-mentioned order is connected in this order.

  The marine exhaust gas denitration apparatus 1 includes the SCR catalyst unit 4 and the ammonia supply unit 6 described above, and a reactor 2 that generates ammonia gas from urea water.

  In the SCR catalyst unit 4, NOx in the exhaust gas is selectively reduced by the catalyst and decomposed into harmless nitrogen and water vapor. The exhaust gas denitrated by the SCR catalyst unit 4 joins the downstream side of the exhaust gas economizer 11 at a downstream junction 29 and is discharged to the outside from a chimney (not shown). A shutoff valve 25 is provided downstream of the SCR catalyst unit 4 with the junction 29, and the exhaust valve is closed when the NOx regulation of the exhaust gas is relatively gentle, so that the exhaust gas having a high sulfur content is closed. Prevents the catalyst from being partially exposed to the denitration catalyst side.

  The ammonia supply unit 6 includes a mixing container 27 and an ammonia gas ejection nozzle 26 provided in the mixing container 27 and having a large number of ejection holes. After the ammonia gas ejected from the ammonia gas ejection nozzle 26 and the exhaust gas introduced into the mixing container 27 are mixed, they are guided to the SCR catalyst unit 4.

The reactor 2 includes a reactor vessel 30 and a urea water injection nozzle 32 in which a large number of injection holes are formed. The urea water stored in the urea water tank 34 is supplied to the urea water injection nozzle 32 by the urea water pump P1. Further, the compressed air supplied from the compressed air supply source 36 is merged with the urea water supply path M1 or the urea water injection nozzle 32 on the downstream side of the urea water pump P1.
Between the reactor 2 and the exhaust manifold 15, an exhaust gas bypass path B1 for extracting a part of the exhaust gas is provided. The exhaust gas bypass path B1 is provided with a bypass control valve 40 that is controlled by a control unit (not shown) so that the flow rate can be adjusted. The flow rate adjusted by the bypass control valve 40 is 5 to 20%, preferably 10 to 15%, of the exhaust gas from the diesel engine 3.

Next, an operation method of the marine exhaust gas denitration apparatus 1 having the above configuration will be described.
The exhaust gas discharged from the diesel engine 3 is guided from the exhaust manifold 15 to the turbine portion 5a of the exhaust turbocharger 5 through the first exhaust path L1. The turbine unit 5a is rotated by obtaining exhaust gas energy, and rotates the compressor 5b. In the compressor unit 5 b, the sucked air (outside air) is compressed and sent to the scavenging trunk of the diesel engine 3 via the air cooler 19.

When navigating in a sea area where the exhaust gas NOx regulations are relatively gentle, exhaust gas denitration is not performed. In this case, the exhaust gas economizer side opening / closing valve 22 is opened, and the denitration side opening / closing valve 24 and the bypass control valve 40 are closed.
The exhaust gas discharged from the turbine section 5a of the exhaust turbocharger 5 passes through the branch point 20 from the second exhaust path L2, passes through the third exhaust path L3, and passes through the exhaust gas economizer-side on-off valve 22 to the exhaust gas economizer. 11 leads to. In the exhaust gas economizer 11, water supplied from the water supply pipe 23 is heated by the exhaust gas to generate steam. The generated steam is used in various places on the ship. The exhaust gas discharged from the exhaust gas economizer 11 is discharged from a chimney (not shown) to the outside.

  On the other hand, when navigating a sea area where exhaust gas NOx regulations are strict, exhaust gas denitration is performed. In this case, the exhaust gas economizer side opening / closing valve 22 is closed, and the denitration side opening / closing valve 24, the bypass control valve 40, and the cutoff valve 25 are opened.

The opening degree of the bypass control valve 40 is appropriately adjusted according to a command from the control unit. After the flow rate is adjusted by the bypass control valve 40, the exhaust gas is guided to the reactor 2 via the exhaust gas bypass path B1.
In the reactor 2, urea water guided from the urea water tank 34 is injected into the exhaust gas from the urea water injection nozzle 32 together with the compressed air supplied from the compressed air supply source 36. Then, the injected urea water in the reactor 2 is reformed, and ammonia gas is generated. In this reforming reaction, since it is heated by the sensible heat of the exhaust gas, the production of solid by-products is suppressed. The ammonia gas thus generated is guided to the ammonia supply unit 6 and injected from the ammonia gas injection nozzle 26 toward the exhaust gas.

  The exhaust gas discharged from the turbine section 5a of the exhaust turbocharger 5 passes through the branch point 20 from the second exhaust path L2, passes through the fourth exhaust path L4, and is guided to the ammonia supply section 6. The exhaust gas mixed with ammonia gas in the ammonia supply unit 6 is guided to the SCR catalyst unit 4 and denitrated in the SCR catalyst unit 4. The exhaust gas after denitration passes through the junction 29 and is discharged to the outside from a chimney (not shown).

As described above, according to the present embodiment, the following operational effects are obtained.
Since the exhaust gas extracted from a part of the exhaust gas supplied to the exhaust turbocharger 5 from the two-cycle diesel engine 3 is guided to the reactor 2, the reaction temperature in the reactor 2 can be raised. . As a result, generation of solid by-products generated during the reforming process from urea water to ammonia can be suppressed, so that the urea water injection nozzle 32 and the exhaust pipe located downstream from the reactor 2 are prevented from being blocked. can do.
Further, since the amount of exhaust gas passing through the exhaust turbocharger 5 is reduced by extracting a part of the exhaust gas supplied to the exhaust turbocharger 5, the turbine work of the exhaust turbocharger 5 is reduced and diesel Since the amount of air supplied to the engine 3 decreases, the exhaust gas temperature can be further increased. Thereby, the production | generation of a solid by-product can further be suppressed.

1 Marine exhaust gas denitration equipment 2 Reactor 3 Diesel engine (Marine 2-cycle diesel engine)
4 SCR catalyst part (denitration catalyst part)
5 Exhaust turbocharger 32 Urea water injection nozzle 34 Urea water tank 40 Bypass control valve B1 Exhaust gas bypass path

Claims (1)

A reactor for producing ammonia from urea water;
A urea water injection nozzle for supplying urea water into the reactor;
A denitration catalyst unit that is provided in an exhaust gas passage downstream of an exhaust turbocharger driven by exhaust gas from a marine diesel engine, and that performs exhaust gas denitration using ammonia supplied from the reactor;
A marine exhaust gas denitration device comprising:
The marine exhaust gas denitration apparatus, wherein exhaust gas extracted from a part of exhaust gas supplied from the marine diesel engine to the exhaust turbocharger is guided to the reactor.

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