JP4997336B2 - Large two-cycle diesel engine with exhaust gas recirculation system - Google Patents

Description

  The present invention relates to a crosshead large turbocharged two-cycle internal combustion piston engine, and preferably relates to a diesel engine equipped with an exhaust gas purification system, and specifically, a crosshead large two-cycle diesel equipped with an exhaust gas recirculation system. Related to institutions.

  A crosshead large two-cycle engine is typically used as a propulsion system for large ships and as a main engine of a power plant. In these institutions, it is becoming increasingly difficult to meet emission requirements, particularly with respect to nitric oxide (NOx) levels.

  Exhaust gas recirculation (EGR) is a technique known to help reduce NOx emissions in diesel engines. To date, however, there are no commercial large two-cycle diesel engines that use an exhaust gas recirculation system. The reason is that it has become clear that the implementation of an exhaust gas recirculation system in a large two-cycle diesel engine is a serious challenge. One reason that the implementation of exhaust gas recirculation systems in large two-cycle diesel engines has proved to be a major challenge is the fact that these engines typically operate on heavy oils with high sulfur content Is mentioned. For this reason, the sulfur content of the exhaust gas is higher than that of smaller diesel engines operating with fuel oil that has low or no sulfur content. Due to the high concentration of sulfur, the purification methods and devices that can be selected are very limited, and most of these methods and devices are at the sulfur and sulfuric acid levels present in the exhaust gas of large two-stroke diesel engines. I can't stand it.

  One of the exhaust gas purification methods capable of withstanding the high sulfur level of a large two-cycle diesel engine is wet cleaning. In this method, the exhaust gas passes through a so-called wet cleaning device (wet scrubber) that uses water as a cleaning liquid.

However, the exhaust gas recirculation system of a large turbocharged two-cycle diesel engine equipped with a wet exhaust gas scrubber for purifying the recirculated exhaust gas is used for cleaning because evaporated water flows downstream together with the cleaning gas. Consumes a large amount of water. For example, if a MAN B & W type 7S50MC engine is operated to add 20% EGR (ie, 20% of the scavenging gas is made up of recirculated gas from the exhaust), the amount of water will be the amount of scrubbed gas 13% of the mass flow rate of, for example, 2.1 m ³ / h. Although fresh water is valuable for ocean-going vessels, it is clear that a significant amount of fresh water is needed.

  Another challenge is that a huge amount of power is required to direct the recirculated exhaust gas from the exhaust receiver into the scavenging or scavenging gas stream (compressed air for scavenging is recirculated exhaust gas). As used herein, the terms “scavenging” and “scavenging gas” are used interchangeably unless explicitly indicated otherwise, as they may be added to gas components other than gases). In large two-cycle diesel engines, the scavenging pressure is typically about 0.3 bar above the exhaust receiver pressure. Thus, a blower or other means is required to push the recirculated exhaust gas from the exhaust receiver to the scavenging system. For a 12 or 14 cylinder type two-cycle diesel engine with a large bore, such as a MAN B & W 12K98MC-C engine, the power required to drive such a blower can be close to 5 MW. This represents a significant amount of energy used in the exhaust gas purification system. Furthermore, such an electric motor that drives a blower that requires a large amount of electric power is extremely expensive.

  The mass flow rate at the scrubber outlet increases corresponding to the mass flow rate of the evaporated water, and the load on the EGR blower located downstream of the scrubber and upstream of the pressurized scavenging gas cooler increases.

  Document DE 1980618 A1 discloses a large two-cycle diesel engine with an exhaust gas recirculation system. Each cylinder of the engine has three outlets for exhaust gas. Exhaust gas from one of the three outlets is collected and reused for scavenging. In one embodiment of a two-cycle engine, soot particles from the recycled exhaust gas by a dry filter before passing through a cooler and a blower that propels the recycled exhaust gas cooled for reuse to scavenge. Remove.

  Although the two-cycle diesel engine disclosed in the above document reduces the emission of harmful substances, there is still a need for a turbocharged two-cycle diesel engine that can further reduce the emission of harmful substances.

DE1980618A1

  From such a background, an object of the present invention is to provide a large turbocharged two-cycle diesel engine equipped with an exhaust gas recirculation system that is commercially feasible and highly effective.

  This object is achieved by providing a crosshead large two-cycle combustion engine as follows. The engine includes a plurality of cylinders each connected to an exhaust receiver; an exhaust gas recirculation passage for supplying a part of the exhaust gas to the scavenging air; and the exhaust gas recirculation for purifying the recirculated exhaust gas. A wet scrubber provided in a circulation channel, wherein a water-based liquid is used as a cleaning liquid to evaporate water into the recirculation gas and to increase the water content of the recirculation exhaust gas; A cooler disposed downstream of the wet scrubber in the exhaust gas recirculation flow path, wherein the exhaust gas is cooled to a temperature at which at least a part of water vapor in the recirculation exhaust gas is condensed; An apparatus for separating condensed water generated by the recirculation exhaust gas cooler from the exhaust gas recirculation flow path; and a blower disposed in the exhaust gas recirculation flow path, the cooler Disposed downstream of the device for causing leave spare the condensed water blower and; comprises.

  An exhaust gas recirculation flow path including a combination of a wet scrubber, a cooler, a condensate removal device, and a blower provides a unique solution for improving an exhaust gas recycling system. This configuration makes it possible to purify the exhaust gas without losing energy (fuel) consumption.

  Wet scrubbers that apply water-based liquids as cleaning liquids can remove a significant portion of soot particles and harmful gases present in the recycled exhaust gas. However, during the cleaning process of the high-temperature exhaust gas, a part of the water present in the cleaning liquid is unavoidably evaporated in the exhaust gas, which increases the mass flow rate of the gas.

  Therefore, the high-temperature exhaust gas treated by the wet scrubber is guided to a cooler disposed downstream of the wet scrubber and cooled to a temperature at which a substantial part of the evaporated water is condensed. The condensed water is separated from the exhaust gas by a mechanism for separating or branching the condensed water. This reduces the gas mass flow by the mass of the separated condensed water.

  The condensed water may contain additional harmful substances that are not completely removed during the cleaning process, such as soot particles and dissolved gases. These harmful substances are removed together with the condensed water. That is, having a cooling stage with moisture condensation contributes to further purification of the exhaust gas that is reused.

  In addition, removal of harmful substances in the cooler means that elements arranged downstream of the cooler, such as blowers and scavengers, are not exposed to harmful substances, and as a result, special measures against harmful substances are taken in these parts. Provides the advantage of being unnecessary. In general, wet scrubbers and coolers and elements connected to them require highly durable materials or require frequent replacement. Thus, the above advantages provide the benefits of improved life and reduced material costs.

  The purified and cooled recirculated exhaust gas is directed to the blower to be raised to the desired pressure. Since most of the water that evaporates into the exhaust gas during the cleaning process is removed in the subsequent cooler, the blower only needs to rotate at a reduced gas mass flow, thus reducing the energy consumption of the blower. Finally, the exhaust gas that is reused is directed, for example, to a scavenge receiver and reused in the combustion process.

  The present invention thus provides a solution to reduce pollution without compromising the energy efficiency of large two-cycle combustion engines.

  In the chiller, it is possible to use various types of cooling media, such as gas or oil. Nevertheless, the cooler preferably uses a cooling medium selected from water, fresh water, demineralized water, sea water, and a mixture thereof. A water-based cooling medium is effective and inexpensive.

  In order to avoid unnecessary mixing of the exhaust gas and the cooling medium, the cooling medium in the cooler is physically isolated from the exhaust gas flowing through the cooler. This isolation may be due to a metal plate, such as a titanium plate or ceramic, or another physical barrier based on a polymer material. However, these materials must have good thermal conductivity and must be resistant to corrosion.

  In embodiments using commercially available standard equipment, the cooler can be, for example, a small counter-flow heat exchanger unit, preferably having a fin tube for guiding the liquid cooling medium. . This fin increases the heat transfer capacity from the cleaned exhaust gas to the cooler.

  The moisture condensed in the chiller and removed from the exhaust gas may simply be discarded. However, in a place where moisture is a scarce resource, the condensed water removed from the exhaust gas recirculation flow path may be reused as a scrubber liquid. Preferably, the condensed water is purified prior to reuse as a scrubber liquid, for example, harmful substances such as soot particles are removed from the moisture. This provides a cost-effective and environmentally friendly way of using moisture.

  The moisture after condensation in the chiller may be captured and separated by any known means. However, the use of a mist catcher is preferred. The mist catcher captures droplets and finer suspended water particles. The mist catcher can utilize inertial effects, and can be, for example, a centrifuge or an angular flow. This type of device is very effective in collecting condensed water. Naturally, the required valves and / or pumps are provided in the grooves for directing the flow of separated condensed water.

  The mist catcher may be an integral part of the chiller or may be provided as a separate device disposed downstream of the chiller.

  In order to minimize the maintenance costs of the combustion engine according to the invention, the cooler is preferably self-cleaning.

  Before the recirculated exhaust gas reaches the blower, the amount of evaporated water is reduced, thereby reducing the load on the blower and reducing power consumption. The blower can be, for example, a commercially available centrifugal compressor or fan.

  Further, the exhaust gas to be recirculated is increased in density by being cooled, thereby improving the effect of the blower.

  Before the reused exhaust gas is reused as a scavenging gas, the exhaust gas is supplied to the scavenging receiver. The exhaust gas to be recycled is then distributed along the cylinder and introduced into the engine as scavenging.

  The present invention also relates to a method for recirculating exhaust gas from a crosshead large turbocharged two-cycle combustion engine comprising a plurality of cylinders each coupled to an exhaust receiver. The method includes directing at least a portion of the exhaust gas from the exhaust receiver to the scavenge receiver via an exhaust gas recirculation flow path, where the exhaust gas is passed through the next stage. These stages are wet cleaning stages for wet cleaning the exhaust gas, using a water-based liquid as a cleaning liquid for purifying the exhaust gas recirculated in the exhaust gas recirculation flow path, Following the wet cleaning step to increase the moisture content of the exhaust gas; and cooling the exhaust gas to a temperature at which at least a portion of the water vapor in the recycled exhaust gas condenses. Cooling the exhaust gas; separating the condensed water in the recirculated exhaust gas from the exhaust gas in the exhaust gas recirculation flow path; and removing the exhaust gas in the exhaust gas recirculation flow path A blowing stage leading to a blower to increase the pressure of the exhaust gas.

  The method according to the invention provides a highly efficient option with low emissions of harmful substances as an option for operating a two-cycle turbocharged combustion engine.

  This is accomplished by a unique combination of operations performed in the exhaust gas recirculation flow path. The combination of the wash stage, the cooling / condensation stage, the condensate removal, and the blowing stage is more effective than expected, which provides a positive effect on the overall efficiency of the combustion engine. This positive effect is brought about by a reduction in gas mass flow by at least partially condensing the evaporated water.

  In order to reduce the gas mass flow directed to the scavenger and to reduce the load on the blower, the cooling stage is at least 30% of the water evaporated to the exhaust gas during the wet cleaning stage, preferably the wet cleaning stage It is preferred to condense at least 70% of the water evaporated into the exhaust gas. Most preferably, the cooling stage is at least 90% of the water evaporated to the exhaust gas during the wet cleaning stage, even more preferably at least 95% of the water evaporated to the exhaust gas during the wet cleaning stage or the moisture generated by combustion. % Is preferably condensed.

  In order to condense as much water as possible in the exhaust gas, the temperature of the exhaust gas is reduced to a temperature at which the cooling phase is at least 50 ° C., preferably only a few degrees above the temperature of the cooling medium (eg 5 ° C.) It is preferable to make it.

  Normally, it is desirable to keep the scavenging temperature as low as possible. For this reason, in the method according to the invention, the recycled exhaust gas is exposed to one or more further cooling stages before entering the scavenging pan. As a result, the reused exhaust gas contributes to the temperature control of the scavenging gas.

  The recirculated exhaust gas should be able to be introduced into the scavenging gas system, which is accomplished by blowing means that pressurize the recirculated exhaust gas. The pressure in the exhaust gas is preferably increased by at least 1 bar during the blowing stage. More preferably, the pressure in the exhaust gas increases by at least 2 bar during the blowing stage. Then, the pressure of the recirculated exhaust gas should be higher than the total pressure in the scavenging receiver, and a flow of exhaust gas to the scavenging receiver is formed by the pressure.

  Further objects, features, advantages and characteristics of the large two-cycle internal combustion engine according to the present invention will become apparent from the detailed description.

The invention will now be described in more detail with reference to exemplary embodiments shown in the drawings.
1 is a diagram of an engine according to a first embodiment of the present invention. FIG. FIG. 3 shows a diagram of a second embodiment of the present invention.

Detailed Description of the Preferred Embodiment

  DETAILED DESCRIPTION OF THE INVENTION Through the detailed description of a crosshead large turbocharged two-cycle diesel engine according to the present invention and a method of operating a crosshead large turbocharged two-cycle diesel engine, the present invention will be described below using exemplary embodiments. Will be explained.

  The general configuration and operation of a crosshead large turbocharged diesel engine is well known and will not require detailed description here. Details regarding the operation of the exhaust gas system are provided below.

  FIG. 1 shows a first exemplary embodiment of a large two-cycle diesel engine 1 according to the present invention. The engine 1 can be used, for example, as a main engine of an ocean-going ship or as a stationary engine for operating a generator of a power plant. The total power of the engine can be in the range of 5,000 kW to 110,000 kW, for example.

  The engine is provided with a plurality of cylinders 2 arranged in a line. Each cylinder 2 is provided with an exhaust valve 3 in its cylinder cover. The exhaust channel can be opened and closed by an exhaust valve 3. Also shown is the engine crosshead 4 in which the piston rod is connected to the large end of the crankshaft. The exhaust bent portion 5 is connected to the exhaust receiver 6. The exhaust receiver 6 is arranged in parallel with the row of cylinders 2. From the exhaust receiver 6, most of the exhaust gas flow is guided to the turbine side of the turbocharger 7 via the exhaust conduit 8. The remaining small portion of the exhaust gas stream is taken into an exhaust gas recirculation flow path, described in more detail below, to be reused. The exhaust gas is discharged to the atmosphere on the downstream side of the turbine of the turbocharger 7.

  The turbocharger 7 also includes a compressor connected to the air intake. The compressor supplies the compressed scavenging to the scavenging receiver 9 via the scavenging gas cooler 10 and the scavenging gas conduit 11. The scavenging gas is guided from the air supply receiver 9 to the scavenging port 12 of each cylinder 2.

  The exhaust pipe 8 is provided with a branch 14 that guides a part of the exhaust gas to the exhaust gas recirculation path 13. A device can be provided that adjusts the ratio of recirculated exhaust gas to the total flow of scavenging gas, which can be achieved by controlling the operation of the blower. The exhaust gas recirculation path 13 guides part of the exhaust gas to the scavenging airflow. The exhaust gas recirculation path 13 includes a wet scrubber 15 that uses a water-based cleaning liquid to purify the exhaust gas. The cleaning liquid is guided from the cleaning liquid storage unit or the supply source 23 to the scrubber. The scrubber 15 sprays the cleaning liquid to disperse the cleaning liquid as fine droplets inside the scrubber. Spraying the cleaning liquid may be performed in a plurality of stages, and the cleaning liquid is preferably available quality water, such as seawater. The cleaning liquid passes through the nozzle of the nebulizer in an appropriate excess to avoid salt or other impurities etc. being mixed into the gas. In this embodiment, the temperature of the cleaning liquid is controlled according to the temperature of the exhaust gas. The water droplets are mixed with the exhaust gas to be recycled and provide a large surface area suitable for absorbing soot particles contained in the exhaust gas and gases containing sulfur and NOx. The droplets are collected by a water drop collector / mist catcher at the bottom of the scrubber 15 and discarded out or discharged to the regenerator 24. In addition to purifying the exhaust gas that is reused, the scrubber 15 also provides a primary cooling function for the exhaust gas that is reused. During the cleaning process, some of the water present in the cleaning liquid evaporates into the exhaust gas that is reused and is carried away with the exhaust gas that is reused. Also, the fine droplets sprayed on the scrubber 15 can be carried away with the exhaust gas to be reused.

  From the wet scrubber 15, the exhaust gas is guided to the cooler 16 via the conduit 20. The cooler 16 is provided with an integrated built-in mist catcher. The recirculated exhaust gas has a relatively high content of water vapor, which is first generated by combustion and then increased by a wet cleaning process. In the cooler 16, the recirculated exhaust gas is cooled, thereby condensing the water vapor in the recirculated exhaust gas. The flow rate and / or temperature of the cooling medium is controlled by a control unit (not shown) for controlling the condensation rate. Typically, the cooling medium is water and has a temperature in the range of 15 ° C to 35 ° C. The condensed water is collected by a mist catcher and separated from the exhaust gas. The mist catcher can also collect droplets that would possibly be contained because they were carried away from the scrubber 15 by the reused exhaust gas. Liquid collected in the mist catcher is directed to the conduit 18 and discarded or recycled through the conduit 19 to the regenerator 24. Or you may process by another system. In the regenerator 24, the liquid is purified and reintroduced into the scrubber 15 as a cleaning liquid. Further, the regenerator 24 receives the cleaning liquid used for purification from the scrubber 15 so that it can be reused in the scrubber 15. The condensed water and spent cleaning liquid from the mist catcher can include, for example, soot particles, unburned fuel residue, and gases in which NOx and sulfur compounds are dissolved. Therefore, it is desirable to reduce or remove these materials before reuse as cleaning fluid in the scrubber 15.

  The cooling medium in the cooler 16 is usually water. This flows through different compartments in the cooler 16 so that it does not come into physical contact with the exhaust gas. Thus, secondary contamination is avoided.

  A conduit 21 connects the outlet of the cooler 16 to the inlet of the blower 17. Following cooling and condensation, the exhaust gas is directed to the blower 17, which increases the pressure of the exhaust gas that is recycled. The treated exhaust gas is directed from the blower 17 to the scavenging conduit 11, where the exhaust gas is mixed with the scavenging gas stream in the illustrated embodiment before being introduced into the scavenging receiver 9. And further cooled.

  During operation of the diesel engine 1, the temperature of the exhaust gas in the exhaust gas conduit 8 ranges from 200 ° C. to 450 ° C., which is also the temperature of the exhaust gas entering the scrubber 15. In the scrubber 15, primary cooling is performed and the exhaust gas exiting the scrubber 15 via the conduit 20 has a temperature in the range of 60 ° C. to 100 ° C. The exhaust gas is further cooled in the cooler 16, and the temperature of the exhaust gas in the conduit 21 is in the range of 20 ° C to 50 ° C. The temperature of the exhaust gas in the conduit 22 after the blower is preferably about 20 ° C and does not exceed 40 ° C to 60 ° C. The exhaust gas in the conduit 22 is mixed with fresh scavenging in the conduit 11.

  FIG. 2 shows another embodiment. The same reference numbers refer to the same parts in FIG. In an embodiment, the outlet from the blower 17 is connected to a scavenging conduit 11 downstream of the cooler 10, thereby bypassing the cooler 10. Thus, the present embodiment is less rugged and therefore less expensive because the relatively large chiller 10 is not affected by the possibly harmful (mainly corrosive) components of the recirculated exhaust gas. Providing benefits by being able to be made from materials.

  This embodiment is for mainstream exiting the cooler 10 at a temperature that can be more simply adjusted to stabilize the recirculated exhaust gas from the conduit 22 having a temperature in the range of 20 ° C. to 60 ° C. at a desired level. A further option is provided to control the temperature of the scavenging gas in the cylinder 2 to mix with the gas.

  While the teachings of the present application have been described for purposes of illustration, such details are intended solely for that purpose and have been modified by those skilled in the art without departing from the scope of the teachings of the present application. I hope you understand.

  The exhaust gas recirculation path may include more than one scrubber or cooler, and additional blowers may be added to improve engine function. It is also possible to apply further devices such as, for example, filters and heaters.

  It should also be noted that there are many alternative ways of implementing the apparatus of the present teachings.

  The term “comprising”, when used in the claims, does not exclude other elements or steps. The singular terms in the claims do not exclude the plural. A single processor or other unit may fulfill the functions of several means recited in the claims.

Claims (17)

A plurality of cylinders (2) each connected to an exhaust receiver (6);
An exhaust gas recirculation flow path (13) for supplying a part of the exhaust gas to the scavenging airflow;
A cooler (16) provided in the exhaust gas recirculation flow path (13);
A blower (17) provided in the exhaust gas recirculation flow path (13);
A crosshead large turbocharged two-cycle combustion engine (1) comprising:
A wet scrubber (15) provided in the exhaust gas recirculation flow path (13) for purifying the recirculated exhaust gas, and using water-based liquid as a cleaning liquid, Providing a wet scrubber (15) that evaporates inside and increases the water content of the recirculated exhaust gas;
The cooler (16) is disposed downstream of the wet scrubber (15) and is configured to cool the exhaust gas to a temperature at which at least a portion of the water vapor in the recirculated exhaust gas condenses. And
Comprising a device for separating the condensed water produced by the cooler (16) from the exhaust gas recirculation flow path (13);
The blower (17) disposed in the exhaust gas recirculation flow path (13) is disposed downstream of the apparatus for separating the cooler (16) and the condensed water;
A crosshead type large turbocharged two-cycle combustion engine (1) characterized by   The crosshead large turbocharged two-stroke combustion engine according to claim 1, wherein the cooler (16) uses a cooling medium selected from water, fresh water, desalted water, seawater, and a mixture thereof. (1).   The crosshead large turbocharged two-stroke combustion engine (1) according to claim 1, wherein the cooling medium is physically isolated from the recirculated exhaust gas flowing through the cooler (16).   The crosshead large turbocharged two-cycle combustion engine (1) according to claim 1, wherein the cooler (16) is a counter-stream cooler.   The crosshead large turbocharged two-stroke combustion engine (1) according to claim 1, wherein the cooler (16) is a down-stream cooler.   The crosshead large turbocharged two-cycle combustion engine (1) according to claim 1, wherein the cooler (16) has a cooling medium guided by a fin tube.   The crosshead type large turbocharged two-cycle combustion engine (1) according to claim 1, wherein the condensed water separated from the exhaust gas recirculation flow path is reused as a scrubber liquid.   The crosshead large turbocharged two-cycle combustion engine (1) according to claim 7, wherein the condensed water is purified before being reused as scrubber liquid.   The crosshead large turbocharged two-cycle combustion engine (1) according to claim 1, wherein the condensed water is separated by a mist catcher.   The crosshead large turbocharged two-stroke combustion engine (1) according to claim 9, wherein the mist catcher is an integral part of the cooler (16) or is arranged downstream of the cooler. ). A method of recirculating exhaust gas from a crosshead large turbocharged two-cycle combustion engine (1) comprising a plurality of cylinders (2) each connected to an exhaust receiver (6),
Scavenging from the exhaust receiver (6) via an exhaust gas recirculation flow path (13) branched from an exhaust conduit (8) provided between the exhaust receiver (6) and the turbine of the turbocharger (7). Directing at least a portion of the exhaust gas to a receiver (9), wherein the exhaust gas is cooled, and the exhaust gas is guided to a blower (17) in the exhaust gas recirculation flow path to And passing through a blowing step that increases pressure, and the method further comprises:
A wet cleaning step for wet cleaning the exhaust gas, wherein a water-based liquid is used as a cleaning liquid for purifying the exhaust gas recirculated in the exhaust gas recirculation flow path, and the water content of the exhaust gas Having the wet cleaning step increased,
The cooling step is performed subsequent to the wet cleaning step to cool the exhaust gas to a temperature at which at least a portion of the water vapor in the recycled exhaust gas condenses;
Separating the condensed water in the recirculated exhaust gas from the exhaust gas in the exhaust gas recirculation flow path;
Performing the blowing step after the cooling and separating the condensed water;
A method characterized by.   12. A method according to claim 11, wherein the cooling step condenses at least 50% of the water present in the exhaust gas, preferably at least 70% of the water present in the exhaust gas.   12. The method of claim 11, wherein the cooling step condenses at least 80% of the water in the exhaust gas, preferably at least 90% of the water in the exhaust gas.   The method of claim 11, wherein the cooling step reduces the temperature of the cleaned exhaust gas to at least 50 ° C., preferably to a temperature that is only a few degrees above the temperature of the cooling medium. 15. A method according to any of claims 11 to 14 , wherein the exhaust gas passes through one or more further cooling stages before entering the scavenger (9). The method according to any of claims 11 to 15 , wherein the pressure in the exhaust gas is increased by at least 1 bar in the blowing stage. The method according to any of claims 11 to 15 , wherein the pressure in the exhaust gas is increased by at least 2 bar in the blowing stage.

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