Method for carbon dioxide recovery and large two-stroke uniflow scavenged internal combustion engine

Abstract

To provide a large two-stroke turbocharged uniflow scavenged internal combustion engine and an operation method that are able to reduce carbon dioxide emissions.SOLUTION: In a preferable embodiment, a method comprises: supplying carbon-based fuel to combustion chambers; combusting the carbon-based fuel in the combustion chambers, thereby producing an exhaust gas flow containing carbon dioxide; recirculating a first portion of the exhaust gas flow, and exhausting a second portion thereof; cooling the first portion of the recirculated exhaust gas flow using a heat exchange medium flow thereby heating the heat exchange medium flow; chemically absorbing carbon dioxide from the second portion of the exhaust gas flow into a solvent by supplying a carbon dioxide lean solvent flow to an absorber and discharging a carbon dioxide rich solvent flow from the absorber 42 to a desorber 64 and reboiler 62 assembly; and regenerating the carbon rich solvent in the assembly through heating by supplying at least a portion of the heated heat exchange medium flow to the assembly.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The disclosure of this specification relates to large two-stroke internal combustion engines, particularly crosshead-type large two-stroke uniflow scavenging internal combustion engines operated with carbon-based fuels (gaseous or liquid fuels) and configured to reduce carbon dioxide emissions, and also relates to a method of operating such a type of engine. Background

[0002] Crosshead-type large two-stroke uniflow scavenging internal combustion engines are used, for example, as propulsion systems for large ships and as prime movers for power generation plants. The size of this large two-stroke diesel engine is huge. Not only because of its huge size, but this large two-stroke diesel engine has a different structure from other internal combustion engines. For example, the weight of the exhaust valve can reach 400 kg, and the piston diameter can also reach 100 cm. The maximum pressure in the combustion chamber during operation typically reaches several hundred bar. The forces generated from such high pressure levels and piston sizes are enormous.

[0003] DK202170181B1 discloses a large turbocharged multi-cylinder two-stroke uniflow internal combustion engine equipped with an EGR system that conveys the flow of exhaust gas from the exhaust system to the intake system. This EGR system has an EGR blower and an electronically controlled EGR throttle valve. An AC drive motor is used to drive the EGR blower. The AC drive motor is configured to operate at a predetermined constant speed. A sensor provides a signal representing the oxygen concentration in the exhaust receiver, and the signal is received by a controller connected to the electronically controlled EGR throttle valve. The controller is configured to control the flow of exhaust through the EGR system by adjusting the position of the electronically controlled EGR throttle valve as a function of the signal as the main criterion. The engine emits CO2 generated by the combustion process of carbon fuel into the environment. The large two-stroke turbo internal combustion engine is operated with liquid fuel (e.g., fuel oil, marine diesel, heavy oil, ethanol, dimethyl ether (DME)) or gaseous fuel (e.g., methane, natural gas (LNG), petroleum gas (LPG), methanol or ethane).

[0004] An engine operating with gaseous fuel may operate according to the Otto cycle. In the Otto cycle, the gaseous fuel is introduced from a fuel valve arranged near the longitudinal center of the cylinder liner or in the cylinder cover. In this type of engine, the gaseous fuel is introduced into the cylinder during the upward stroke of the piston (from bottom dead center to top dead center), considerably before the exhaust valve closes. The engine compresses a mixture of gaseous fuel and scavenging air in the combustion chamber and ignites the compressed mixture at or near top dead center (TDC) with timing by ignition means (such as liquid fuel injection).

[0005] Engines operating with liquid fuel or engines operating with gaseous fuel of high-pressure injection inject gaseous or liquid fuel when the piston is in a position close to TDC, i.e., when the compression pressure in the combustion chamber is maximum or close to it. That is, these engines operate on the Diesel cycle, i.e., compression ignition.

[0006] Liquid fuels and gas fuels used in known large two-stroke turbocharged uniflow scavenged internal combustion engines generally contain carbon. That is, these are carbon-based fuels, and their combustion generates carbon dioxide. The generated carbon dioxide is discharged into the atmosphere. Carbon dioxide emissions are generally considered to be a cause of climate change and should be minimized or avoided.

[0007] Known carbon capture technologies are usually classified into three types: post-combustion CO2 capture, pre-combustion CO2 capture, and oxy-fuel combustion (also called oxygen combustion). Pre-combustion CO2 capture is to separate and recover carbonaceous components before fuel combustion.

[0008] In pre-combustion carbon dioxide capture, first, the fuel is reacted with oxygen or steam, and then processed in a water-gas shift reactor to produce a mixed gas of H2 and CO2. CO2 is recovered from the high-pressure mixed gas containing 15% to 40% CO2. The advantage of pre-combustion CO2 capture technology is that the amount of gas required for treatment is significantly reduced, and the CO2 concentration in the gas increases. This can reduce the energy consumption and equipment investment of the separation process.

[0009] In oxy-fuel combustion, carbon-based fuels are burned in recycled exhaust gas and pure O2 instead of air. However, due to the high cost of O2 separation, the possibility of commercialization is limited. Oxy-fuel combustion technology consists of an air separation device that separates nitrogen from air. Then, in the recycled exhaust gas and pure oxygen, the carbon-based fuel is burned. The exhaust gas mainly consists of particulate matter, CO2, sulfur oxides from the fuel, and water due to combustion. After being sent to a particulate matter removal device and a sulfur removal device, water is condensed and removed, leaving a compressible CO2 stream. The main advantage is that almost 100% of CO2 can be recovered.

[0010] In the post-combustion CO2 recovery technology, carbon-based fuels are burned in the same way as in conventional power generation, and CO2 is recovered from the exhaust gas. This carbon separation technology is broadly classified into four types: absorption, adsorption, membrane, and cryogenic. To absorb and recover CO2 from the exhaust gas, an amine solvent can be used. Here, CO2 is captured in the solvent, and then the regeneration process of the amine is carried out. The disadvantages are that the scale of the power plant becomes extremely large and a great deal of energy is required for the CO2 recovery process. In particular, an enormous amount of energy is required for the regeneration of the amine solvent. Abstract

[0011] One of the objectives is to provide an engine and a method that solve or at least mitigate the above-mentioned problems.

[0012] The above-mentioned problems and other problems are solved by the features described in the independent claims. More specific implementation forms will become apparent from the dependent claims, the specification, and the drawings.

[0013] According to a first aspect, a crosshead-type large two-stroke turbocharged uniflow scavenging internal combustion engine is provided as follows. This engine At least one combustion chamber defined by a cylinder liner, a piston configured to reciprocate within the cylinder liner, and a cylinder cover; A scavenging port for introducing scavenging gas into the at least one combustion chamber, the scavenging port being arranged in the cylinder liner; A fuel system configured to supply a carbon-based fuel to the at least one combustion chamber; Comprising, the at least one combustion chamber is configured to burn a carbon-based fuel to generate exhaust gas containing carbon dioxide, and the engine further An exhaust outlet arranged on the cylinder cover and controlled by an exhaust valve; Comprising, the at least one combustion chamber is connected to a scavenging receiver through the scavenging port and to an exhaust receiver through the exhaust outlet, and the engine further A turbine driven by an exhaust flow, having a turbine of a turbocharging system in an exhaust system; An air intake system having a compressor of the turbocharging system, the compressor being configured to supply pressurized scavenging air to the scavenging receiver; An exhaust gas recirculation system having a blower for assisting the flow of exhaust gas to the scavenging receiver and configured to recirculate a portion of the exhaust gas discharged from the at least one combustion chamber to the scavenging receiver; An absorber for absorbing carbon dioxide into a solvent, preferably an absorption tower; An assembly of a desorber and a reboiler for desorbing carbon dioxide from the solvent; Comprising; The absorber has a solvent inlet for receiving carbon dioxide-lean solvent from the desorber and a solvent outlet for supplying carbon dioxide-rich solvent to the desorber, The absorber is configured to separate carbon dioxide from the exhaust flow by chemical absorption into the solvent for the exhaust flow passing through the absorber, The assembly has an inlet for receiving carbon dioxide-rich solvent from the absorber and an outlet for supplying carbon dioxide-lean solvent to the absorber, The assembly is configured to heat the solvent to release carbon dioxide from the solvent, The engine further comprises a heat exchange system configured to exchange heat between the recirculated exhaust gas of the exhaust gas recirculation system and the solvent.

[0014] The amount of energy required for solvent regeneration is large and can reach more than 60% of the engine shaft output supplied by a large two-stroke internal combustion engine. Such a penalty on the engine's energy efficiency makes the operation using a carbon dioxide capture system significantly more costly compared to an engine not using a carbon dioxide capture system. However, the inventor of the present application noticed that a large two-stroke diesel engine utilizing exhaust gas recirculation generates a surplus energy flow because the exhaust gas to be recirculated is cooled using a heat exchange medium before being reintroduced into the cylinder. The inventor of the present application also noticed that this heat exchange medium (for example, water or steam) can be heated to a temperature sufficient to be directly used to heat and regenerate the carbon dioxide-rich solvent in the desorber and reboiler assembly.

[0015] In an example of an implementation form of the first understanding, the heat exchange system includes an exhaust gas recirculation heat exchanger configured to exchange heat between the exhaust gas in the exhaust gas recirculation system and the heat exchange medium, thereby cooling the exhaust gas in the exhaust gas recirculation system and heating the heat exchange medium, and the exhaust gas recirculation system has the exhaust gas recirculation heat exchanger, and also has a heat exchanger configured to exchange heat between the solvent and the heat exchange medium to heat the solvent and cool the heat exchange medium.

[0016] In an example of an implementation form of the first understanding, the exhaust gas recirculation system has a scrubber, preferably a wet scrubber, and the scrubber is disposed downstream of the exhaust gas recirculation heat exchanger in the exhaust gas recirculation system.

[0017] In an example of an implementation form of the first understanding, the exhaust gas recirculation system is configured to exchange heat between the recirculated exhaust gas and the solvent in the assembly.

[0018] In an example of an implementation form of the first understanding, the engine includes a control unit configured to adjust the mass ratio of the recirculated exhaust gas in the scavenging gas to at least 40%, preferably 40% to 55%.

[0019] In an example of an implementation form of the first grasping method, the control unit is configured to control the rotational speed of the blower in order to adjust the ratio of the recirculated exhaust gas in the scavenging gas.

[0020] According to a second grasping method, a method for operating a large two-stroke turbocharged uniflow scavenging internal combustion engine having a plurality of combustion chambers is provided. This method includes supplying a carbonaceous fuel to the combustion chamber; burning the carbonaceous fuel in the combustion chamber to generate an exhaust stream containing carbon dioxide; recirculating a first portion of the exhaust stream and exhausting a second portion of the exhaust stream; supplying a pressurized scavenging flow containing recirculated exhaust gas to the combustion chamber; cooling a recirculated exhaust gas stream in the exhaust system using a heat exchange medium stream and heating the heat exchange medium stream; chemically absorbing carbon dioxide from the second portion of the exhaust stream into a solvent by supplying a carbon dioxide-lean solvent stream to an absorber and discharging a carbon dioxide-rich solvent stream from the absorber to an assembly of a desorber and a reboiler; regenerating the carbon-rich solvent in the assembly by heating by supplying at least a portion of the heated heat exchange medium stream to the assembly to heat the solvent; including.

[0021] In an example of an implementation form of the second grasping method, the method includes recirculating at least 40% by mass of the exhaust gas stream. Preferably, at least 40 to 55% by mass of the exhaust gas stream is recirculated.

[0022] In an example of an implementation form of the second grasping method, the method includes controlling the speed of a blower of an exhaust gas recirculation system and adjusting the ratio of the recirculated exhaust gas in the pressurized scavenging gas.

[0023] In an example of an implementation form of the second approach, the method includes supplying a gas stream containing carbon dioxide and steam or vapor generated in the separator to a separator that separates carbon dioxide from steam or vapor.

[0024] The separator is a knockout drum for obtaining a gas stream mainly containing carbon dioxide and a liquid stream mainly containing water.

[0025] In an example of an implementation form of the second approach, the method includes supplying the gas stream mainly containing carbon dioxide to a liquefaction unit and liquefying the gas stream mainly containing carbon dioxide to obtain a stream of liquefied carbon dioxide.

[0026] Preferably, the method includes guiding the liquefied carbon dioxide stream to a liquefied carbon dioxide storage device.

[0027] In an example of an implementation form of the second approach, the method uses the exhaust gas recirculation heat exchanger of the exhaust gas recirculation system to extract heat from the recirculated exhaust gas in the exhaust gas recirculation system, thereby effecting heat exchange between the exhaust gas and the heat exchange medium in the exhaust gas recirculation system, cooling the exhaust gas in the exhaust gas recirculation system, and heating the heat exchange medium;

[0028] effecting heat exchange between the solvent and the heated heat exchange medium to heat the solvent and cool the heat exchange medium; These aspects and other aspects will become further apparent from the embodiments described below.

Brief Description of the Drawings

[0029] Hereinafter, various approaches, embodiments, and implementation examples will be described in detail with reference to the exemplary embodiments shown in the drawings.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

[0030] In the following detailed description, an internal combustion engine is described with reference to an example of a crosshead type large low-speed two-stroke turbocharged internal combustion engine. FIGS. 1-3 depict an example of a turbocharged large low-speed two-stroke diesel engine. This engine has a crankshaft 8 and a crosshead 9. FIGS. 1 and 2 are overview views seen from different angles respectively. FIG. 3 schematically represents the turbocharged large low-speed two-stroke diesel engine of FIGS. 1 and 2 according to an embodiment, together with its intake and exhaust systems. In this example, the engine has six cylinders in series. A turbocharged large low-speed two-stroke internal combustion engine may have from four to fourteen cylinders arranged in series. These cylinders have cylinder liners carried by the engine frame 11. Such an engine can also be used, for example, as a main engine of a ship or as a stationary type engine for driving a generator in a power plant. The total output of the engine can be in the range of, for example, 1,000 to 110,000 kW.

[0031] The engine in this example is a two-stroke uniflow scavenging engine, and a scavenging port 18 is provided in the lower region of the cylinder liner 1. A central exhaust valve 4 is arranged in the cylinder cover 22 at the upper part of the cylinder liner 1. The scavenging gas is led from the scavenging receiver 2 to the scavenging port 18 of each cylinder liner 1 when the piston is below the scavenging port 18.

[0032] When the engine is operated as a premixed engine (an engine based on the Otto principle), a carbon-containing gaseous fuel (e.g., methanol, petroleum gas or LPG, methane, natural gas (LNG), ethane) is introduced from the gas introduction valve 50' under the control of the electronic control unit 100. This is done during the upward stroke of the piston 10 (from BDC to TDC), before the piston passes through the fuel valve (gas introduction valve) 50'. A gaseous or liquid carbon-containing fuel (e.g., fuel oil) is injected into the combustion chamber from the fuel valve 50 at a high pressure (preferably 300 bar or more) when the piston 10 is at or near TDC. The gaseous fuel is supplied by the gas fuel supply system 30' and introduced into the combustion chamber at a relatively low pressure. This pressure is less than 30 bar, preferably 25 bar, more preferably less than 20 bar. The flow containing the fuel for injection through the fuel valve 50 is supplied by the fuel system 30. The high pressure for injection through the fuel valve 50 can be generated by the fuel system 30 (common rail) or the fuel valve 50. The fuel introduction valve 50' is preferably arranged to be distributed at equal intervals on the circumference of the cylinder liner. Also preferably, it is arranged near the longitudinal center of the cylinder liner. The introduction of the gaseous fuel is carried out when the compression pressure is relatively low. That is, it is carried out when it is much lower compared to the compression pressure when the piston reaches TDC, so it is possible to introduce it at a relatively low pressure.

[0033] When the engine is operated as a compression ignition engine (Diesel principle), there is no gas introduction valve 50', and a carbon-containing fuel (gaseous or liquid) is injected at a high pressure through the fuel valve 50 when the piston 10 is at or near TDC.

[0034] The piston 10 within the cylinder liner 1 compresses the mixture of gas fuel and scavenging gas (or scavenging gas only in the case of operation by fuel injection only at TDC). And at or near TDC, ignition is caused by the injection of high-pressure fuel from the fuel valve 50 preferably disposed in the cylinder cover 22. In the case of liquid fuel injection only at or near TDC, ignition is caused by compression. Then combustion occurs, generating exhaust gas containing carbon dioxide.

[0035] When the exhaust valve 4 is opened, the combustion gas (exhaust gas) flows into the combustion gas receiver 3 through the combustion gas duct associated with the cylinder 1 and then flows out into the first exhaust pipe 19. A selective catalytic reactor 33 for reducing nitrous oxide (NOx) in the exhaust gas is provided in the first exhaust pipe 19.

[0036] The turbine 6 drives the compressor 7 via a shaft. The compressor 9 is supplied with outside air through the air intake 12. The compressor 7 feeds the compressed scavenging air into the scavenging pipe 13 connected to the scavenging receiver 2. The scavenging air in the scavenging pipe 13 passes through an intercooler 14 for cooling the scavenging air.

[0037] The exhaust gas recirculation pipe 35 is connected to the scavenging pipe 13 either upstream (shown) or downstream (not shown) of the intercooler 14. The recirculated exhaust gas is mixed with the scavenging air at this position to form the scavenging gas. The scavenging gas flows towards the scavenging receiver 2. As will be described in more detail below, the control unit 100 (electronic control unit) is configured to adjust the ratio of scavenging air to exhaust gas in the scavenging gas.

[0038] The cooled scavenging air or scavenging gas passes through an auxiliary blower 16 driven by an electric motor 17. The auxiliary blower 16 compresses the scavenging air flow when the compressor 7 of the turbocharger 5 cannot provide sufficient pressure for the scavenging receiver 2, i.e., when the engine is at low load or partial load. When the engine load is high, the compressor 7 of the turbocharger can supply sufficiently compressed scavenging air, so the auxiliary blower 16 is bypassed by a check valve 15. The engine can be provided with a plurality of turbochargers 5 forming a turbocharging system.

[0039] The control unit 100 (electronic control unit) may be composed of a plurality of interconnected electronic units including a processor and other hardware for performing the functions of the control unit. The control unit 40 generally controls the operation of the engine, for example, controls gas fuel introduction (quantity and timing), liquid fuel injection (quantity and timing), opening and closing of the exhaust valve 4 (timing and lift amount), recirculated exhaust gas ratio, and also controls the operation of devices such as various coolers and pumps. Here, various signals from sensors informing the operating state of the engine are input to the control unit 100. These signals may include, respectively, engine load, engine speed, blower speed, scavenging temperature, exhaust gas temperature at various locations, signals representing exhaust gas temperature at various locations. Also, signals indicating the pressure in the scavenging system, the pressure in the combustion chamber, the pressure in the exhaust system, and the pressure in the exhaust gas recirculation system may be included. The engine preferably includes a variable timing exhaust valve operating system that enables individual control of the exhaust valve timing for each combustion chamber. The control unit 100 is connected to the fuel valve 50, the liquid fuel introduction valve 50', the exhaust valve actuator, the angular position sensor, and the pressure sensor via signal lines or wireless connections. The angular position sensor detects the angle of the crankshaft and generates a signal representing the position of the crankshaft. The pressure sensor is preferably arranged in the cylinder cover 22, alternatively in the cylinder liner 1, and generates a signal representing the pressure in the combustion chamber.

[0040] Depending on the size of the engine, the cylinder liner 1 is made in various sizes. As typical sizes, the diameter of the cylinder bore is from 250 mm to 1000 mm, and the corresponding overall length is from 1000 mm to 4500 mm.

[0041] The cylinder liner 1 is placed on the cylinder frame 23, and a cylinder cover 22 is installed on the cylinder liner 1. Between the cylinder liner 1 and the cylinder cover 22, gas leakage is prevented. The piston 10 is configured to reciprocate between the bottom dead center (BDC) and the top dead center (TDC). These two dead center positions of the piston 10 are 180 degrees apart in terms of the rotation angle of the crankshaft 8. The cylinder liner 1 is provided with a plurality of cylinder lubrication holes that are distributed circumferentially. These cylinder lubrication holes are connected to a cylinder lubrication line. The cylinder lubrication line supplies cylinder lubricating oil when the piston 10 passes through the cylinder lubrication hole 25. Subsequently, piston rings (not shown) of the piston 10 spread the cylinder lubricating oil over the entire running surface (inner surface) of the cylinder liner. Although not shown, the cylinder liner is provided with a jacket, and jacket cooling water circulates in the space between the jacket and the cylinder liner.

[0042] The cylinder cover 22 is typically provided with a plurality of, preferably three or four, liquid fuel valves 50 per cylinder and is connected to a source of pressurized carbon-containing fuel (not shown). The liquid fuel valves 50 are preferably arranged at equal intervals circumferentially around the exhaust valve 4, particularly around the central outlet (opening) of the cylinder cover 22. The outer shape of the central portion is controlled by the exhaust valve 4. The fuel injection timing and the injection amount are controlled by the control unit 100. The fuel valve 50 is used only for injecting a small amount of ignition liquid (pilot) when the engine is operating in the premixed mode. When the engine is operating in the compression ignition mode, an amount of liquid fuel necessary to operate the engine at the actual engine load being used is injected from the liquid fuel valve 50. The cylinder cover 22 may be provided with a prechamber (not shown). Also, the tip of the liquid fuel valve 50, typically the tip provided with one or more nozzle holes, is arranged such that pilot oil (ignition liquid) is injected into the prechamber and atomized. The prechamber aids in reliable ignition.

[0043] The fuel injection valve 50' is installed in the cylinder liner 1 (or the cylinder cover 22) such that its nozzle is substantially flush with the inner surface of the cylinder liner 1 and the rear end of the fuel valve 50' protrudes from the outer wall of the cylinder liner 1. Typically, one or two, at most three or four fuel valves 50' are provided for each cylinder liner 1. These are arranged in the circumferential region of the cylinder liner 1 (preferably at equal intervals). In this embodiment, the fuel injection valve 50' is disposed at exactly the central portion in the longitudinal direction of the cylinder liner 1. The fuel injection valve 50' is connected to a pressurized supply source 30' of gaseous fuel (e.g., methanol, LPG, LNG, ethane, or ammonia). That is, when supplied to the fuel injection valve 50', the fuel is in the gaseous phase. The gaseous fuel is introduced during the stroke of the piston 10 from BDC to TDC, so the pressure of the gaseous fuel supply source only needs to be higher than the pressure existing in the cylinder liner 1. For the gaseous fuel sent to the fuel injection valve 50', a pressure typically less than 20 bar is sufficient. The fuel injection valve 50' is connected to the control unit 100. The control unit 40 determines the opening / closing timing and the valve opening time of the fuel injection valve 50'.

[0044] Depending on the embodiment, the liquid fuel for ignition is heavy oil, marine diesel oil, heavy fuel oil, ethanol, or dimethyl ether (DME).

[0045] The gas operation mode can be one of several operation modes of the engine. Other modes can include a liquid fuel operation mode in which all of the fuel required for the operation of the engine is supplied in liquid form through the liquid fuel valve 50. In the gas fuel operation mode, the engine is operated mainly with gaseous fuel introduced at a relatively low pressure during the piston stroke from BDC to TDC. That is, the main part of the energy supplied to the engine is supplied by such gaseous fuel. On the other hand, compared to the gaseous fuel, only a small amount of liquid fuel is used and it makes a relatively small contribution to the amount of energy supplied to the engine. The purpose of the liquid fuel is to ignite at a predetermined timing. That is, the liquid fuel functions as an ignition liquid.

[0046] Thus, the engine of this embodiment can be a dual-fuel engine having a mode of operating with only liquid fuel and a mode of operating with substantially only gaseous fuel.

[0047] In this embodiment, the engine is shown as a premixed engine operating according to the Otto principle. However, there are also embodiments where the engine is a compression ignition engine (operating according to the Diesel principle). In that case, the carbon-based fuel (gaseous or liquid) is injected at high pressure when the piston 10 is at or near TDC.

[0048] This engine is operated by supplying a carbon-based fuel (liquid fuel and / or gaseous fuel) to the combustion chamber, burning the carbon-based fuel in the combustion chamber to generate an exhaust stream containing carbon dioxide, separating carbon dioxide from the exhaust gas in a carbon dioxide absorption process, and storing the separated carbon dioxide. Also preferably, this engine operates by recirculating a first portion of the exhaust stream (the first portion of the combustion gas in embodiments where the recirculated gas is taken directly from the combustion chamber) and exhausting another (second) portion of the exhaust stream as exhaust gas, and also by supplying a pressurized scavenging gas containing the exhaust gas to the combustion chamber. Here, the pressurized scavenging gas contains at least 40% by mass, preferably 40 to 55% by mass of recirculated combustion gas.

[0049] Downstream of the turbine 6 of the turbocharger, the exhaust gas enters the second exhaust pipe 28. The exhaust pipe 28 guides the exhaust gas to a boiler 20 (also called an economizer). The boiler 20 is configured to generate steam. This steam is used for various purposes, for example, within the ship in which the engine is installed. Or this steam has a temperature sufficient to be directly supplied to a desorber 66 and a reboiler 62 assembly, which will be described in more detail below, and can be used directly to heat the desorber 66 and the reboiler 62 assembly.

[0050] Downstream of the boiler 20, the second exhaust pipe 28 is connected to a first heat exchanger 40. In this heat exchanger 40, the exhaust gas exchanges heat with a first medium, which will be described in more detail later.

[0051] The second exhaust pipe 28 also continues downstream of the first heat exchanger 40 and is connected to the inlet at the bottom of the absorber 42. The absorber 42 is preferably an absorption tower, for example, a packed absorption tower. The exhaust gas passes through the absorption tower 42 and flows towards the outlet at the upper part of the absorption tower 42.

[0052] The absorber 42 is part of a system that chemically absorbs carbon dioxide using a solvent. An example of a suitable solvent is an amine solution. The amine solution may contain primary, secondary, and / or tertiary amines. Another example of a suitable solution is a NaOH / KOH solution, preferably an aqueous amine NaOH / KOH solution.

[0053] Carbon dioxide is removed from the exhaust gas by the packed absorption tower (absorber) 42. This reaction is exothermic and raises the solvent temperature along the absorption tower 42. As an example, the carbon dioxide concentration in the exhaust gas from the engine is 4 - 5% by volume without exhaust gas recirculation and 9 - 10% by volume with exhaust gas recirculation. The exhaust gas is introduced into the absorption tower 42 as a flow in the opposite direction to the solvent entering the top of the absorption tower 42. This solvent is called a carbon dioxide-lean solvent or a lean carbon dioxide solvent. This carbon dioxide-lean solvent is supplied from the desorber 66 at about 35°C - 55°C and atmospheric pressure. and reboiler 62 assembly At the upper part of the absorption tower 42, there is a water washing section consisting of a packed bed, which removes most of the volatile amine adsorbent that has flowed out into the exhaust gas by condensing and solubilizing it. The total height of the absorption tower 42 can be up to 50 meters. When carbon dioxide is absorbed in the absorption tower 42, the flow of the carbon dioxide-rich solvent (carbon dioxide-rich solvent) from the bottom of the absorption tower 42 is supplied to the cross heat exchanger 60 by the pump 44, heat-exchanged with the flow of the carbon dioxide-lean solvent, and then introduced into the assembly of the desorber 66 and the reboiler 62, where it is heated in the reboiler 62 and carbon dioxide is released from the solvent. The removal (desorption) temperature varies between 120°C and 150°C, and the operating pressure reaches up to 5 bar.

[0054] From the top of the stripping tower 66, a stream of water-saturated carbon dioxide is released. This is cooled in the heat exchanger 68 to condense most of the moisture. The moisture is separated in the knockout drum 69 and returned to the stripping tower 66. The stream of carbon dioxide from the knockout drum 69 is compressed / liquefied in the liquefaction device 70 and temporarily stored in the storage tank 85. Depending on the embodiment, liquefied carbon dioxide can be transported from the temporary storage tank 85, which is an ultra-low temperature storage tank, to the final storage location or a public facility (not shown). When the apparatus is mounted on a ship, the temporary storage tank 85 is arranged inside the ship and emptied when the ship is at a port equipped with a facility for receiving liquefied carbon dioxide.

[0055] In the regeneration process of the amine solution, not all of the carbon dioxide in the solution is removed. The regenerated carbon dioxide-lean solvent is recycled to the absorption tower 42 at a carbon dioxide-lean loading by the action of the pump 64. Before reaching the absorber 42, the carbon dioxide-rich solvent exchanges heat with the carbon dioxide-lean solvent in the cross heat exchanger 60 and the heat exchanger 67.

[0056] The carbon dioxide loading of the solvent after absorbing carbon dioxide through the absorption tower is called the carbon dioxide-rich solvent. The difference between the lean solvent and the rich solvent is the amount of carbon dioxide recovered from the exhaust gas.

[0057] The carbon dioxide concentration in the exhaust gas discharged from the absorber 42 is at most 10 times lower than the carbon dioxide concentration of the exhaust gas flowing into the absorber 42.

[0058] A part of the amine of the solvent may still be present in the exhaust gas exiting the absorber 42. This amine is removed by the amine scrubber 44 arranged in the exhaust pipe 49 downstream of the absorber 42.

[0059] The apparatus generates several surplus energy streams Q1, Q2,... Qn, also called waste heat streams, from various parts of the apparatus. The embodiment in FIG. 3 includes the following. Q1: Primary cooling medium (e.g., water) of the scavenging cooler 14. The cooling water from the scavenging cooler 14 usually has a temperature between about 20 and 240 °C. Q2: Primary medium engine lubricating oil. It is usually at a temperature of 45 - 55 °C. Q3: Primary cooling medium (such as water) of the cylinder jacket cooler. The cooling water from the cylinder jacket usually has a temperature of about 70 - 90 °C. Q4: Primary cooling medium (e.g., water) of the exhaust gas recirculation pipe heat exchanger (cooler) 32. It usually has a temperature of about 50 - 350 °C. Q5: Boiler 20. It usually supplies steam at about 160 - 170 °C. Q6: Primary medium (e.g., water) used in the first heat exchanger 40. It usually has a temperature of 160 - 170 °C. Q7: Primary medium (e.g., water) used in the second heat exchanger 67. It usually has a temperature of 100 - 170 °C. Q8: Primary medium (e.g., water) used in the third heat exchanger 68. It usually has a temperature of 95 - 105 °C. Q9: Primary medium (e.g., water) used to cool the liquefaction device 70. It has a temperature depending on the type of technology used for liquefaction and the type of cooling system used in the liquefaction device 70.

[0060] Note that the list above of the surplus energy flows generated by the engine is not exhaustive and presents merely examples of surplus energy sources.

[0061] At least one of the above surplus energy flows Q1, Q2,... Qn, in particular, those having a temperature lower than the temperature required to heat the desorber 66 and Reboiler 62 the assembly, is supplied to the heat pump 80. (The desorber 66 and Reboiler 62The assembly requires a secondary medium having a temperature of at least 110°C, preferably at least 120°C. The heat pump 80 is configured to generate a flow of energy Qr in the form of a flow of a secondary medium (e.g., water or steam) having a temperature of at least 120°C, preferably at least 130°C. Preferably, the temperature of the secondary medium supplied to the desorber 66 and the reboiler 62 assembly is between 130 and 140°C, most preferably about 136°C.

[0062] Figure 4a shows a first embodiment of the implementation of the heat pump 80. In this embodiment, a plurality of excess energy flows Q1, Q2,... Qn are sent to a single heat pump 80, and the energy flow Qr supplied to the desorber 66 and Reboiler 62 the assembly is generated by the pump 80.

[0063] A second embodiment of the implementation of the pump 80 is shown in Figure 4b. In this embodiment, one of the plurality of excess energy flows Q1, Q2,... Qn is applied to one of the plurality of heat pumps 80, and the energy flow Qr supplied to the desorber 66 is created by the plurality of heat pumps 80. Or preferably, it is combined with one flow of energy Qr to the desorber 66 and Reboiler 62 the assembly.

[0064] One or more heat pumps 80 are used to increase the temperature of the amine solution in the reboiler 62. The heat pump 80 comprises at least an evaporator, a condenser, a compressor, and an expansion valve. Inside the heat pump 80, as shown in FIG. 5, a heat pump (cooling) fluid circulates in a cycle consisting of an evaporator, a condenser, a compressor, and an expansion valve. The heat pump 80 functions by the evaporator receiving heat from the flow of energy Q2. The heat pump liquid evaporates in the evaporator and enters the compressor. The compressor is driven, for example, by an electric motor. The electric power driving the electric motor is supplied, for example, by an alternator or a generator driven by power branched from the crankshaft of the engine. The compressor raises the pressure and temperature of the heat pump fluid. Downstream of the compressor, the heat pump liquid enters the condenser, heat is transferred to the heat sink, and the heat pump liquid condenses. Thereafter, the heat pump liquid expands through the expansion valve before entering the evaporator again, and the cycle is repeated. A secondary medium, such as water or steam, preferably transports heat from the condenser to the reboiler 62 in a cycle driven by a pump, and the secondary medium has a temperature of at least 120° C., preferably at least 130° C. Thus, the reboiler 62 forms the heat sink of the heat pump 80.

[0065] To increase the efficiency of the heat pump 80, in an embodiment, the condenser portion is divided into three heat exchanger (HEX) regions (superheater, condenser, subcooler). The heat extracted in the superheater and condenser regions is sent to the heat sink. The heat extracted in the subcooler is used for preheating the heat pump liquid exiting the evaporator. Such a configuration of the condenser reduces the work of the compressor and improves the system efficiency. Further, a water loop with a steam HEX and an electric coil is applied between the condenser, the superheater, and the reboiler 62. The fluid entering the steam HEX is, in some embodiments, the steam generated in the boiler 20. The steam HEX and the electric coil ensure that the reboiler 62 receives sufficient energy over the full engine load range.

[0066] In FIG. 5, a plurality of energy flows Q1, Q2, ... Qn are utilized. If only one of the applied energy flows Q1, Q2, ... Qn is present, the deaerator downstream of the evaporator can be removed.

[0067] According to an embodiment, the engine comprises an exhaust gas recirculation system having an exhaust gas recirculation pipe 35 that connects a first exhaust pipe 19 to a scavenging pipe 13. Preferably, the exhaust gas recirculation pipe 35 is connected to the first exhaust pipe 19 upstream of a selective catalytic reactor 33. Preferably, the exhaust gas recirculation pipe 35 is connected to the scavenging pipe 13 upstream of a scavenging cooler 14. However, embodiments may exist in which the exhaust gas recirculation pipe 35 is connected to the scavenging pipe 13 downstream of the scavenging cooler 14.

[0068] The exhaust gas recirculation pipe 35 includes a blower 34 for forcibly sending exhaust gas from the exhaust pipe to the scavenging pipe. This is because the pressure in the scavenging pipe 13 during engine operation is typically higher than the pressure in the first exhaust pipe 19. In the illustrated embodiment, the blower 34 is driven by an electric motor. According to an embodiment, the blower may be driven by another rotational power source. In the illustrated embodiment, the blower 34 is disposed between an exhaust gas recirculation heat exchanger 32 that cools the exhaust gas and an exhaust gas recirculation scrubber 36. However, the position of the blower 34 may also be upstream or downstream of other elements of the exhaust gas recirculation path 35.

[0069] The exhaust gas recirculation heat exchanger 32 is disposed upstream of the exhaust gas recirculation scrubber 36. The main purpose of the exhaust gas recirculation scrubber 36 is to remove impurities (soot).

[0070] The control unit 100 is configured to control the speed of the blower 34 of the exhaust gas recirculation system so as to adjust the ratio of the recirculated exhaust gas in the pressurized scavenging gas, preferably to a ratio of at least 35% by mass. This is to increase the carbon dioxide concentration in the exhaust gas and thereby enhance the effectiveness of the carbon dioxide absorption system. The exhaust gas recirculation rate can also be controlled by a valve (not shown) controlled by the control unit 100. Therefore, the control unit 100 is configured to operate the engine with the ratio of the recirculated exhaust gas in the pressurized scavenging gas being 40% or more, 45% or more, 50% or more, etc., according to the operating conditions. Generally, the control unit 100 is configured to operate with the highest possible ratio of recirculated exhaust / combustion gas. "The highest possible" means the highest ratio that does not cause unacceptable harmful effects such as a decrease in the quality of the combustion process, a decrease in the reliability of the combustion process, and an unacceptable increase in the heat load of the engine.

[0071] The medium (such as water or steam) used for heat exchange with the exhaust gas in the exhaust gas recirculation heat exchanger 32 exits the exhaust gas recirculation heat exchanger 32 at a temperature of about 130 - 170°C, so this medium can be used directly in the desorber 66 and Reboiler 62 the assembly without passing through the heat pump 80. The recirculated exhaust gas enters the exhaust gas recirculation heat exchanger 32 at a temperature of about 260 - 400°C. By adjusting the flow rate of the medium passing through the exhaust gas recirculation heat exchanger 32, the medium can be brought to a desired temperature.

[0072] Exhaust gas recirculation increases the carbon dioxide concentration of the exhaust gas supplied to the absorber 42, and as a result, reduces the energy consumption of the desorber 66 and Reboiler 62 the assembly. Also, when the exhaust gas recirculation ratio is increased, the scale of the exhaust gas flow to the absorber 42 decreases, so a smaller-diameter absorption tower can be used when exhaust gas recirculation is used or when the exhaust gas recirculation ratio is increased. Furthermore, the energy extracted by the exhaust gas recirculation heat exchanger 32 is surplus energy (waste heat) supplied to the desorber 66 and Reboiler 62 the assembly, thereby Reboiler 62The amount of energy that needs to be supplied to operate the assembly is significantly reduced.

[0073] The medium supplied from the exhaust gas recirculation heat exchanger 32 is at a high temperature compared to other excess heat flows of the engine. This is because this medium is heated by the exhaust gas that has not passed through the turbine 6 of the turbocharger 5. Therefore, this medium can be used directly in the desorber 66 and Reboiler 62 the assembly.

[0074] Figure 6 shows another embodiment of the engine. In this embodiment, components and features similar to those already described or illustrated are labeled with the same reference numerals as previously used. The engine and its operation in this embodiment are substantially the same as those of the previous embodiment. Therefore, only the differences from the previous embodiment will be described in detail.

[0075] This embodiment includes an optional second scavenging cooler 14a downstream of the scavenging cooler 14. The scavenging cooler 14 can be configured to generate a flow of heat exchange medium having a temperature sufficient for direct use in the desorber 66 and Reboiler 62 the assembly. The second scavenging cooler 14a generates an excess energy flow Q10 in the form of a flow of a first medium (e.g., water). However, the temperature of the excess energy flow Q10 requires the use of a heat pump 80 to generate a flow of a second medium. That is, the use of the heat pump 80 is required before the energy flow can be used in the desorber 66 and Reboiler 62 the assembly. Thus, the energy flow Q10 generated by the second scavenging cooler 14a is sent to the heat pump 80.

[0076] In this embodiment, an additional fourth heat exchanger 41 can be optionally provided downstream of the first heat exchanger 40. This additional fourth heat exchanger 41 can generate another excess energy flow Q11 supplied to the heat pump 80.

[0077] In this embodiment, an additional surplus energy flow Q12 can also be created from the surplus heat from the exhaust gas recirculation scrubber 36 supplied to the heat pump 80.

[0078] Various aspects and implementations of the invention have been described along with several examples. The above embodiments can be combined in various ways. Also, upon examining the specification, drawings, and claims of this application, those skilled in the art will understand and be able to implement that there are many variations in addition to the described examples when implementing the invention described in the claims. The terms "comprising," "having," and "including" as used in the claims do not exclude the existence of elements or steps not described. Even if it is not explicitly stated that the number of elements described in the claims is plural, the existence of a plurality of such elements is not excluded. The functions of several elements described in the claims may be performed by a single processor, controller, or other unit. Even if several matters are described in separate dependent claims, this does not exclude implementing them in combination, and benefits can be obtained by implementing them in combination. The reference signs used in the claims should not be construed as limiting the scope of the invention.

Claims

1. A crosshead type large two-stroke turbocharged uniflow scavenging internal combustion engine, comprising: at least one combustion chamber defined by a cylinder liner, a piston configured to reciprocate within the cylinder liner, and a cylinder cover; a scavenging port for introducing scavenging gas into the at least one combustion chamber, the scavenging port being disposed in the cylinder liner; a fuel system configured to supply carbonaceous fuel to the at least one combustion chamber; wherein the at least one combustion chamber is configured to burn carbonaceous fuel to generate exhaust gas containing carbon dioxide, and the engine further comprises: an exhaust outlet disposed in the cylinder cover and controlled by an exhaust valve; wherein the at least one combustion chamber is connected to a scavenging receiver through the scavenging port and to an exhaust receiver through the exhaust outlet, and the engine further comprises: an exhaust system having a turbine driven by an exhaust flow and having a turbine of a turbocharging system; an air intake system having a compressor of the turbocharging system and configured to supply pressurized scavenging air to the scavenging receiver; an exhaust gas recirculation system having a blower for assisting the flow of exhaust gas to the scavenging receiver and configured to recirculate a part of the exhaust gas discharged from the at least one combustion chamber to the scavenging receiver; and further comprises: an absorber for absorbing carbon dioxide into a solvent; an assembly of a desorber and a reboiler for desorbing carbon dioxide from the solvent; wherein the absorber has a solvent inlet for receiving carbon dioxide-lean solvent from the assembly and a solvent outlet for supplying carbon dioxide-rich solvent to the desorber, the absorber is configured to separate carbon dioxide from the exhaust flow by chemical absorption into the solvent for the exhaust flow passing through the absorber, the assembly has an inlet for receiving carbon dioxide-rich solvent from the absorber and an outlet for supplying carbon dioxide-lean solvent to the absorber, the assembly is configured to heat the solvent to release carbon dioxide from the solvent, and the engine further comprises a heat exchange system having a heat exchange medium, the heat exchange system being configured to exchange heat between the recirculated exhaust gas of the exhaust gas recirculation system and the solvent in the reboiler of the assembly using the heat exchange medium. Engine. ​

2. An exhaust gas recirculation heat exchanger configured to exchange heat between the exhaust gas in the exhaust gas recirculation system and a heat exchange medium, thereby cooling the exhaust gas in the exhaust gas recirculation system and heating the heat exchange medium, is provided in the exhaust gas recirculation system, and a heat exchanger configured to exchange heat between the solvent and the heat exchange medium to heat the solvent and cool the heat exchange medium, The engine according to claim 1.

3. The exhaust gas recirculation system has a scrubber, and the scrubber is disposed downstream of the exhaust gas recirculation heat exchanger in the exhaust gas recirculation system. The engine according to claim 2.

4. The engine according to claim 1, comprising a control unit configured to adjust the mass ratio of the recirculated exhaust gas in the scavenging gas to at least 40% or from 40% to 55%.

5. The control unit is configured to control the rotational speed of the blower to adjust the ratio of the recirculated exhaust gas in the scavenging gas. The engine according to claim 4.

6. The absorber includes an absorption tower, the solvent inlet is located at the top of the absorption tower, and the solvent outlet is located at the bottom of the absorption tower. The engine according to any one of claims 1 to 5.

7. The engine according to claim 6, having a second heat exchanger configured to exchange heat between the carbon dioxide-rich solvent from the solvent outlet and the carbon dioxide-lean solvent supplied to the solvent inlet.

8. The engine according to claim 7, having a third heat exchanger provided between the second heat exchanger and the solvent inlet and configured to recover surplus energy from the carbon dioxide-lean solvent supplied to the solvent inlet.

9. A method of operating a large two-stroke turbocharged uniflow scavenging internal combustion engine having a plurality of combustion chambers, comprising: supplying a carbonaceous fuel to the combustion chamber; burning the carbonaceous fuel in the combustion chamber to generate an exhaust stream containing carbon dioxide; recirculating a first portion of the exhaust stream and exhausting a second portion of the exhaust stream; supplying a pressurized scavenging flow containing recirculated exhaust gas to the combustion chamber; cooling a recirculated exhaust gas flow in the exhaust system using a heat exchange medium flow and heating the heat exchange medium flow; chemically absorbing carbon dioxide from the second portion of the exhaust stream into a solvent by supplying a carbon dioxide-lean solvent flow to an absorber and discharging a carbon dioxide-rich solvent flow from the absorber to an assembly of a desorber and a reboiler. comprising, wherein the absorber has a solvent inlet for receiving a carbon dioxide-lean solvent from the assembly and a solvent outlet for supplying a carbon dioxide-rich solvent to the assembly, the method further comprising: heating the carbon-rich solvent in the reboiler of the assembly by supplying at least a portion of the heated heat exchange medium stream to the assembly to heat the solvent; A method comprising.

10. The method according to claim 9, comprising recycling at least 40% by mass of the exhaust gas stream, or recycling at least 40 to 55% by mass of the exhaust gas stream.

11. The method according to claim 9, comprising controlling the speed of a blower of an exhaust gas recirculation system to adjust the proportion of recycled exhaust gas in the pressurized scavenging gas.

12. The method according to claim 9, comprising supplying a gas stream containing carbon dioxide and steam or vapor generated in the desorber to a separator for separating carbon dioxide and steam or vapor.

13. The method according to claim 12, wherein the separator is a knockout drum for obtaining a gas stream mainly containing carbon dioxide and a liquid stream mainly containing water.

14. The method according to claim 12, comprising supplying a gas stream mainly containing carbon dioxide to a liquefaction unit and liquefying the gas stream mainly containing carbon dioxide to obtain a stream of liquefied carbon dioxide.

15. The method according to claim 14, comprising guiding the liquefied carbon dioxide stream to a liquefied carbon dioxide storage device.

16. The method according to any one of claims 9 to 15, wherein the absorber comprises an absorption tower, the solvent inlet is located at the top of the absorption tower, and the solvent outlet is located at the bottom of the absorption tower.

17. The method according to claim 16, wherein the engine has a second heat exchanger for performing heat exchange between the carbon dioxide-rich solvent from the solvent outlet and the carbon dioxide-lean solvent supplied to the solvent inlet.

18. The method according to claim 17, wherein the engine has a third heat exchanger provided between the second heat exchanger and the solvent inlet for recovering surplus energy from the carbon dioxide-lean solvent supplied to the solvent inlet.

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