JP2010513766A - Large turbocharged diesel engine with SCR reactor - Google Patents

Abstract

The present invention relates to a large turbocharged diesel engine having an exhaust gas driven turbine (6) and a compressor (9) driven by the turbine, and comprising a turbocharger for supplying air to an engine cylinder. Regarding (1). The engine (1) is equipped with an SCR reactor (20) downstream of the turbine (6) for reducing NO _x in the exhaust gas to N ₂ and H ₂ O. The heating unit (19) raises the temperature of the exhaust gas on the high pressure side of the turbocharger turbine (6) so that the temperature of the exhaust gas entering the SCR reactor (20) is at least 330 ° C. A part of the exhaust gas flow is branched upstream of the turbocharger turbine (6) and guided to the power turbine (31). The overall fuel efficiency of the engine is improved over engines where the heating unit (19) and the SCR reactor (20) are located on the low pressure side of the turbocharger turbine (6).
[Selection] Figure 1

Description

The present invention is a large turbocharged diesel engine such as a main engine of a ship, which is equipped with a selective catalytic reduction (SCR) reactor for purifying NO _x from exhaust gas. It relates to a supercharged diesel engine.

  Public awareness of environmental issues is growing rapidly. In the International Maritime Organization (IMO), there are ongoing discussions on emission control in the form of air pollution at sea. Authorities in various parts of the world are taking similar measures. An example is the United States Environmental Protection Agency (EPA) bill under discussion.

NO _x in the exhaust gas can be reduced by a primary reduction method and / or a secondary reduction method. The primary method is a method that directly affects the engine combustion process. The actual degree of reduction depends on the engine type and reduction method, but varies from 10% to over 50%. The secondary method is a means of reducing emissions levels using equipment that is not part of the engine itself without changing engine performance from its fuel optimization settings. The most effective secondary process to date, selective catalytic reduction for removing NO _x; a (Selective Catalytic Reduction SCR) method. This method makes it possible to reduce the NO _x level by more than 95% by adding ammonia or urea to the exhaust gas before entering the catalytic converter.

The SCR reactor has several layers of catalyst. The catalyst volume, and thus the reactor size, depends on the activity of the catalyst, ie the level of NO _x reduction required. The catalyst structure typically has a monolithic structure, that is, a catalyst block structure in which a number of channels having catalytic activity are arranged in parallel on the wall surface.

The temperature of the exhaust gas should be at least 280 ° C to 350 ° C, depending on the sulfur content of the fuel. In order to effectively convert NO _x to N ₂ and H ₂ O, a high temperature is required at the inlet of the SCR reactor when the sulfur content is high, and a temperature when the sulfur content is low. May be low.

  Typically, the exhaust gas on the high pressure side of the turbocharger turbine has a temperature of about 350 ° C. to 450 ° C., while the exhaust gas on the low pressure side of the turbocharger turbine is about 250 to It has a temperature of 300 ° C.

  For this reason, in known large two-cycle diesel engines operating with HFO, an SCR reactor is equipped on the high pressure side of the turbocharger turbine. However, because these reactors are required to withstand a pressure of about 4 bar and contain very large pipes and vessels that must be exposed to temperature changes between about 20 ° C. and 400 ° C. The structure of the SCR reactor on the high pressure side of the turbine is quite complex. Thermal expansion and heat setting presents significant design issues.

  In order to avoid these problems, there is a proposal to move the SCR reactor to the low pressure side of the turbocharger turbine.

A state-of-the-art engine system with combined cycle operation and high overall fuel efficiency, the so-called “hot” engine, has an exhaust gas temperature on the low pressure side of the turbocharger turbine that is 250 ° C. of conventional engines. In contrast, it is about 290 ° C to 300 ° C. The increase in exhaust gas temperature in a “hot” engine has been obtained by changing the timing of opening the exhaust valve and the consistency of the turbocharger. This change reduces the efficiency of the engine itself from about 50% to about 48.7%. In order to compensate for a decrease in engine efficiency, an exhaust gas heated steam boiler is used to drive a steam turbine provided downstream of the turbocharger turbine or downstream of the SCR reactor, and a part of the energy in the exhaust gas. It is known to try to recover. The amount of energy produced by the steam generator driven by the steam provided by the exhaust gas boiler is about 7.7% of the engine output at the crankshaft. Furthermore, the turbocharger turbine receives significantly more energy as the exhaust gas is further heated. However, turbochargers do not require additional energy. The additional energy of the exhaust gas on the high pressure side is within the “hot” engine concept and is also utilized. This can be achieved by connecting the turbocharger shaft to the generator via a transmission, or branching off some of the exhaust gas on the high pressure side of the turbocharger turbine and It is realized by driving a power turbine (gas turbine) that is used and connected to a generator. The amount of energy produced by the generator driven by the power turbine is about 4.4% of the engine output at the crankshaft. Therefore, the overall fuel efficiency of a “hot” engine is
48.7 + ((7.7 + 4.4) * 0.487) = 54.6%
It becomes.

However, even with “hot” engines, the temperature of the exhaust gas is insufficient to place the SCR reactor on the low pressure side of the turbine. In order to be able to place the SCR reactor on the low pressure side of the turbocharger turbine, the temperature of the exhaust gas leaving the turbine must be increased from 290 ° C to 300 ° C to about 330 ° C. This can be achieved by a heating unit such as a burner. However, increasing the temperature by 40 ° C. with the burner increases the overall fuel consumption of the engine by 4.6% (the increased 4.6% fuel is burned in the heating unit). Some of this additional energy can be recovered with an efficiency of about 25% in the exhaust gas heated boiler and steam turbine downstream of the SCR reactor. As the exhaust gas temperature rises on the low pressure side of the turbocharger turbine, the output of the steam turbine increases from 7.7% to 10.8% of the engine output (the efficiency of the steam turbine is 27.9%). The overall efficiency of a system with a downstream SCR reactor is
(48.7 + ((10.8 + 4.4) * 0.487)) / 1.046 = 53.6%
It becomes.

  The overall fuel efficiency is therefore reduced from 54.6% to 53.5% compared to the SCR reactor on the high pressure side of the turbocharger turbine. Such a decrease in fuel efficiency is highly undesirable and negates most of the fuel efficiency advances in recent years.

Accordingly, it is an object of the present invention to provide a large two-cycle diesel engine with high fuel efficiency and having an SCR reactor on the low pressure side of a turbocharger turbine. The object is to provide a large two-cycle diesel engine according to claim 1, i.e. a turbocharger for supplying supply air to a cylinder, an exhaust gas driven turbine (6) and a compressor driven by said turbine ( A turbocharger comprising 9); a first exhaust pipe (5) for guiding exhaust gas from the cylinder to the inlet of the turbine (6); and if the inflowing exhaust gas is above a predetermined temperature, the exhaust gas the NO _x in the SCR converter or SCR reactor efficiently reduced to N ₂ and H ₂ O (20); the inlet to the exhaust gas in the SCR converter from the outlet of the turbine (6) (20) A large two-cycle turbocharged diesel equipped with: a second exhaust pipe (7) for guiding; and a third exhaust pipe (22) for guiding exhaust gas from the outlet of the SCR converter (20) to the atmosphere. Engine (1), said SC A heating unit (19) for heating the exhaust gas upstream of the turbine (6) so as to bring the exhaust gas to at least the predetermined temperature at the inlet of the converter (20), and further downstream of the heating unit (19) However, the power turbine (31) driven by the exhaust gas branched from the first exhaust pipe (5) at a point upstream of the turbine (6) or the shaft (8 of the turbocharger) This is achieved by a large turbocharged diesel engine characterized in that it comprises a mechanical power take-off device.

  When a heating unit is placed on the high pressure side of the turbocharger turbine, a 5.9% increase in fuel consumption is required to achieve the required exhaust gas temperature at the SCR reactor inlet, If a heating unit is arranged on the low pressure side of the turbocharger turbine, the increase in fuel consumption required is only 4.6%. However, the inventor improves overall fuel efficiency by placing a heating unit upstream of the turbine, rather than a downstream location that is intuitively logically correct, close to the inlet of the SCR converter. Reached the insight that it was possible. This is to increase the temperature of the exhaust gas in a power turbine driven by the exhaust gas branched from the exhaust pipe on the high pressure side of the turbine, even if the amount of fuel required by the heating unit increases. From the insight that the energy used can be recovered with 100% efficiency.

  Preferably, an exhaust gas boiler is disposed in the exhaust pipe downstream of the SCR reactor, and the engine may further comprise a steam turbine driven by steam generated by the exhaust gas boiler, thereby Fuel efficiency is further increased.

  Preferably, a power turbine or mechanical power take off device is used to drive the generator.

  The engine may further comprise a generator driven by a power turbine or by a power take off device from a turbocharger shaft.

  The heating unit can be a burner.

  About 20% of the potential expansion energy of the exhaust gas on the high pressure side of the turbine is converted or derived from the turbine.

  Preferably, the operation and / or strength of the burner is controlled by the controller in response to a temperature sensor at the inlet of the SCR reactor or a temperature sensor upstream from the inlet.

  Further objects, features, advantages, and characteristics of the large turbocharged diesel engine will become apparent from the detailed description.

In the following detailed portion of the description, the invention will be described in more detail with reference to the illustrated exemplary embodiments.
1 shows a diagram of an intake system and an exhaust system of an internal combustion engine according to a first embodiment of the present invention. FIG. 4 shows a diagram of an intake system and an exhaust system of an internal combustion engine according to a second embodiment of the present invention.

Detailed description

  In the following detailed description, the present invention will be described by means of preferred embodiments. FIG. 1 shows a crosshead type large turbocharged two-cycle diesel engine 1 comprising an intake system and an exhaust system. The engine 1 has an air supply receiver 2 and an exhaust gas receiver 3. The exhaust valve belonging to the combustion chamber is indicated by 4. The engine 1 can be used, for example, as a main engine for ocean-going ships or as a stationary engine for driving a power plant generator. The total output of the engine is, for example, in the range of 5,000 kW to 110,000 kW, but the present invention can also be used in, for example, a 4-cycle diesel engine having an output of 1,000 kW.

  The supply air is guided from the supply receiver 2 to scavenging ports (not shown) of the individual cylinders. When the exhaust valve 4 is opened, the exhaust gas flows into the exhaust receiver 3 through the first exhaust pipe, and further proceeds to flow into the turbine 6 of the turbocharger from the first exhaust pipe 5 and from there. The exhaust gas flows out through the second exhaust pipe 7. By means of the shaft 8, the turbine 6 drives a compressor 9 that is supplied via an inlet 10. The compressor 9 supplies pressurized air to the air supply pipe 11 that communicates with the air supply receiver 2.

  The intake air in the tube 11 passes through the intercooler 12 in order to cool the supply air (supply air leaving the compressor at about 200 ° C.) to a temperature between 30 ° C. and 80 ° C.

  The cooled supply air is guided to the supply air receiver 2 via an auxiliary blower 16 that is driven by an electric motor 17 and pressurizes a supply airflow in a low load state or a partial load state. In higher load conditions, the auxiliary blower 16 is bypassed by the check valve 15 because the turbocharger compressor 9 supplies a sufficiently compressed scavenge.

  A heating unit 19 is disposed in the first exhaust pipe 5 in order to increase the temperature of the exhaust gas in the first exhaust pipe 5. That is, it is arranged upstream of the turbine 6. The heating unit 19 is preferably in the form of a heating unit such as a burner. The exhaust gas in the first exhaust gas pipe 5 must be heated so that the temperature of the exhaust gas leaving the turbocharger turbine 6 is at least 330 ° C.

  In a large two-cycle diesel “hot” engine where the exhaust gas leaving the turbine 6 is about 290 ° C. to 300 ° C., the temperature rise applied to the exhaust gas in the first exhaust pipe 5 is about 50 ° C. In this large two-cycle diesel engine, the amount of additional fuel used by the heating unit 19 for heating the exhaust gas on the high pressure side of the turbocharger turbine is about 5.8% of the fuel consumption of the engine itself.

  In a conventional large two-cycle diesel engine in which the exhaust gas temperature when exiting the turbocharger turbine is about 250 ° C., the temperature rise of the exhaust gas in the first exhaust pipe 5 must be about 100 ° C.

  The pipe 30 is downstream of the heating unit 19 but branches off from the exhaust pipe 5 which is upstream of the turbine 6. The pipe 30 leads a part of the exhaust gas (about 20% in a large two-cycle diesel engine) to an additional power turbine 31. The additional power turbine 31 drives a generator 32. The power turbine 31 has an output approximately equivalent to 7.0% of the output of the large two-cycle diesel engine 1.

  In this way, surplus energy in the exhaust gas flow is converted into electric power, that is, energy having high exergy. The amount of exhaust gas branched into the power turbine 31 can be adjusted by a variable flow rate regulator (not shown) in the pipe 30. The exhaust gas leaving the power turbine 31 is redirected to the main exhaust gas stream on the low pressure side of the turbine 6 upstream of the SCR reactor.

The second exhaust pipe 7 guides exhaust gas from the outlet of the turbine 6 to the inlet of the SCR reactor 20. If the temperature of the exhaust gas at the inlet of the SCR reactor 20 is sufficiently high, ie typically above about 330 ° C., NO _x in the exhaust gas is converted to N ₂ and H ₂ O.

  The third exhaust pipe 22 guides air supply from the outlet of the SCR reactor 20 to the inlet of the boiler 25. The fourth exhaust pipe 27 guides exhaust gas from the outlet of the boiler 25 to the inlet of the silencer 28. The fifth exhaust pipe 29 guides exhaust gas from the outlet of the silencer 28 to the atmosphere.

  The boiler 25 uses heat in the exhaust gas stream to generate steam under pressure (superheated). The pipe 34 guides the steam generated by the boiler 25 to the steam turbine 37. The steam turbine 37 drives the generator 35. The steam turbine has an output power corresponding to about 10.8% of the output of a large two-cycle diesel engine.

  FIG. 2 shows an alternative embodiment of the present invention. This embodiment substantially corresponds to the first embodiment except that the power turbine is replaced with a power take-off device from the turbocharger. Here, the transmission 36 connects the shaft 8 of the turbocharger to the generator 33.

The fuel efficiency of the large two-cycle diesel engine 1 is 48.7%. The overall fuel efficiency in both embodiments is
(48.7 + ((10.8 + 7.0) * 0.487)) / 1.058 = 54.2%
It becomes.

The engine according to the invention comprising a heating unit 19 on the high pressure side of the turbine 6 is clearly higher than the engine described in the background art comprising a heating unit on the low pressure side of the turbine 6 and fuel efficiency of 53.6%. It has a fuel efficiency of 54.2%.
〔Example〕

1. High temperature engine with SCR on the high pressure side (prior art)
2. 2. Install a burner on the low pressure side of the turbocharger turbine. Install a burner on the high pressure side of the turbocharger turbine

  Therefore, the turbocharger is only required to accept a slight reduction in fuel efficiency compared to a “hot” engine, which has many structural problems in its implementation, such as installing an SCR reactor on the high pressure side of the turbocharger turbine. It is possible to enjoy the structural advantage of installing the SCR reactor on the low pressure side of the machine turbine 6.

  In both embodiments of the present invention, the steam generated by the boiler 25 may be used for purposes other than driving the steam turbine, such as heating.

  Each embodiment may be provided with a temperature sensor (not shown) disposed near the inlet of the SCR reactor 20 in order to measure the temperature of the exhaust gas in the second exhaust pipe 7. . The temperature sensor signal is communicated to a controller (not shown). The controller controls the heating unit 19. The controller activates the heating unit 19 when the temperature of the exhaust gas in the second exhaust gas pipe 7 is not sufficiently high, and the temperature of the exhaust gas in the second exhaust gas pipe 7 determines the efficiency of the SCR reactor. If the minimum temperature for typical operation is exceeded, the function of the heating unit 19 is reduced.

Both embodiments can be configured as a so-called humidified air engine (not shown), for example an engine operating with charge / scavenging with a very high absolute moisture (steam) content. In this variant of the invention, the air supply temperature is about 60 ° C. to 90 ° C. (as opposed to 37 ° C. in conventional engines) and the absolute humidity is about 40 g / kg to 80 g / kg, ie “non- About 4 to 8 times the moisture (steam) content of the “humidified air” motor. Humidification can be performed by injecting relatively warm water into a scrubber (not shown). Humidification significantly increases the energy content of the supply / scavenging and thus the energy content of the exhaust gas. The increase in energy during supply is obtained by the following two causes.
• By reducing the amount of energy deducted from the supply / scavenging by the intercooler, ie the amount of “waste” energy generated by the intercooler.
• Injecting water warmed with hot water from the engine's cooling system, that is, by injecting water containing “waste energy”.

  The increased energy in the exhaust gas can be recovered relatively efficiently in the power turbine, thereby obtaining a higher efficiency than the overall fuel efficiency shown in the above embodiments.

  The term “comprising”, used in the claims, does not exclude other elements or steps. The singular terms in the claims do not exclude the plural. Any reference signs used in the claims shall not be construed as limiting the scope.

  While preferred embodiments of the apparatus and method have been described above with reference to the environment in which they were developed, they are not merely illustrative of the principles of the present invention. Other embodiments or configurations may be made without departing from the spirit of the invention and the scope of the appended claims.

Claims (7)

A turbocharger for supplying supply air to a cylinder, comprising an exhaust gas driven turbine (6) and a compressor (9) driven by said turbine;
A first exhaust pipe (5) for guiding exhaust gas from the cylinder to the inlet of the turbine (6);
An SCR converter (20) that efficiently reduces NO _x in the exhaust gas to N ₂ and H ₂ O if the inflowing exhaust gas is equal to or higher than a predetermined temperature;
A second exhaust pipe (7) for guiding exhaust gas from the outlet of the turbine (6) to the inlet of the SCR converter (20);
A third exhaust pipe (22) for guiding exhaust gas from the outlet of the SCR converter (20) further into the atmosphere;
A large two-cycle turbocharged diesel engine (1) with
A heating unit (19) for heating the exhaust gas upstream of the turbine (6) so that the exhaust gas is at least at the predetermined temperature at the inlet of the SCR converter (20);
A power turbine (31) driven by exhaust gas that is downstream of the heating unit (19) but is branched from the first exhaust pipe (5) at a point upstream of the turbine (6), or
A mechanical power take-off device from the turbocharger shaft (8),
An engine comprising:   The engine according to claim 1, further comprising an exhaust gas boiler (25) disposed in the exhaust pipe downstream of the SCR reactor (20).   The engine according to claim 2, further comprising a steam turbine (37) driven by steam generated by the exhaust gas boiler (25).   The engine according to claim 1, further comprising a generator (32) driven by the power turbine (31) or by the power take-off device from the shaft (8) of the turbocharger.   The engine according to claim 1, wherein the heating unit (19) is a burner.   The engine according to claim 1, wherein about 20% of the potential expansion energy of the exhaust gas on the high pressure side of the turbine (6) is converted or derived from the turbine.   Engine according to claim 5, wherein the operation and / or strength of the burner is controlled by a controller in response to a temperature sensor at the inlet of the SCR reactor (20) or upstream from the inlet. .

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