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

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 subject matter disclosed herein relates to large two-stroke internal combustion engines, in particular crosshead type large two-stroke uniflow scavenged internal combustion engines configured to run on carbon-based fuels (gaseous or liquid fuels) and to reduce carbon dioxide emissions, and to methods of operating such types of engines.

[0002] Large two-stroke uniflow scavenging internal combustion engines with crosshead are used, for example, in the propulsion systems of large ships and as prime movers in power plants. These large two-stroke diesel engines are huge in size. Not only because of their huge size, they have a different structure than other internal combustion engines. For example, the exhaust valves can weigh up to 400 kg and the pistons can have diameters of up to 100 cm. The maximum pressure in the combustion chamber during operation is typically several hundred bar. The forces resulting from such high pressure levels and piston sizes are enormous.

[0003] DK202170181B1 discloses a large turbocharged multi-cylinder two-stroke uniflow internal combustion engine with an EGR system for conveying the flow of exhaust gas from the exhaust system to the intake system. The 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 representative of the oxygen concentration in the exhaust receiver, which signal is received by a controller connected to the electronically controlled EGR throttle valve. The controller is configured to control the flow of exhaust gas through the EGR system by adjusting the position of the electronically controlled EGR throttle valve as a function of the signal as a primary criterion. The engine releases CO2 produced by the combustion process of carbon fuels into the environment. The large two-stroke turbocharged internal combustion engine is operated on liquid fuels (e.g. fuel oil, marine diesel, heavy fuel oil, ethanol, dimethyl ether (DME)) or gas fuels (e.g. methane or natural gas (LNG), petroleum gas (LPG), methanol or ethane).

[0004] An engine that runs on gaseous fuel may operate according to the Otto cycle, in which gaseous fuel is admitted through a fuel valve located near the longitudinal centre of the cylinder liner or in the cylinder cover. In this type of engine, the gaseous fuel is admitted into the cylinder during the piston's upward stroke (from bottom dead centre to top dead centre), well 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 centre (TDC) by a timed ignition means (such as liquid fuel injection).

[0005] Liquid fuelled engines and high pressure injected gas fuelled engines inject gas or liquid fuel when the piston is close to TDC, i.e. when the compression pressure in the combustion chamber is at or near maximum, i.e. these engines operate on the Diesel cycle, i.e. compression ignition.

[0006] The liquid and gaseous fuels used in known large two-stroke turbocharged uniflow scavenged internal combustion engines generally contain carbon, i.e. they are carbon-based fuels, and their combustion produces carbon dioxide, which is emitted into the atmosphere. Carbon dioxide emissions are generally believed to be a cause of climate change and should be minimized or avoided.

[0007] Known carbon capture technologies are typically categorized into three categories: post-combustion CO2 capture, pre-combustion CO2 capture, and oxy-fuel combustion (also called oxygen combustion). Pre-combustion CO2 capture involves separating and capturing carbonaceous components before the combustion of the fuel.

[0008] In pre-combustion carbon dioxide capture, the fuel is first reacted with oxygen and water steam, and then further processed in a water-gas shift reactor to produce a mixture of H2 and CO2. The CO2 is captured from a pressurized gas mixture that contains 15% to 40% CO2. The advantages of pre-combustion carbon dioxide capture technology are that it significantly reduces the amount of gas required for processing and increases the CO2 concentration in the gas. This reduces the energy consumption and capital investment of the separation process.

[0009] In oxyfuel combustion, carbon-based fuels are burned in recirculated exhaust gas and pure O2 instead of air. However, the high cost of O2 separation limits its commercial viability. Oxyfuel combustion technology consists of an air separation unit that separates nitrogen from the air. The carbon-based fuel is then burned in recirculated exhaust gas and pure oxygen. The exhaust gas, which mainly consists of particulate matter from the combustion, CO2, sulfur oxides from the fuel and water, is sent to a particulate matter removal unit and a sulfur removal unit, where the water is condensed off and a compressible CO2 stream is left. The main advantage is that the CO2 can be captured almost 100%.

[0010] In post-combustion CO2 capture technology, carbon-based fuels are burned in the same way as in conventional energy generation, and CO2 is captured from the flue gas. The carbon separation technologies are broadly divided into four categories: absorption, adsorption, membrane, and low temperature. Amine solvents can be used to absorb and capture CO2 from the flue gas, where it is captured in the solvent, followed by an amine regeneration process. The drawbacks are that the power plant is very large in scale and the carbon dioxide capture process requires a lot of energy, especially the regeneration of the amine solvent requires a huge amount of energy. Abstract

[0011] It is an object to provide an engine and method which overcomes or at least mitigates the above mentioned problems.

[0012] These and other objects are achieved by the features of the independent claims. Further detailed implementations will become apparent from the dependent claims, the description and the drawings.

[0013] According to the first aspect, there is provided a crosshead type large two-stroke turbocharged uniflow scavenging internal combustion engine as follows. This engine has: 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 disposed in the cylinder liner for introducing scavenging gas into the at least one combustion chamber; a fuel system configured to supply a carbon-based fuel to the at least one combustion chamber; wherein the at least one combustion chamber is configured to combust a carbon-based fuel to produce an exhaust gas comprising carbon dioxide, the engine further comprising: an exhaust outlet disposed in the cylinder cover and controlled by an exhaust valve; the at least one combustion chamber is connected to a scavenging air receiver through the scavenging port and to an exhaust air receiver through the exhaust outlet, the engine further comprising: an exhaust system having a turbine driven by the exhaust flow, the turbine being a turbocharging system; an air intake system having a compressor of the turbocharging system configured to supply pressurized scavenging air to the scavenging receiver; an exhaust gas recirculation system configured to recirculate a portion of exhaust gas discharged from the at least one combustion chamber to the scavenge air receiver, the exhaust gas recirculation system having a blower for assisting the flow of exhaust gas to the scavenge air receiver; an absorber, preferably an absorption tower, for absorbing carbon dioxide into a solvent; a desorber and reboiler assembly for desorbing carbon dioxide from the solvent; Equipped with 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 stream by chemical absorption into the solvent for the exhaust stream passing through the absorber; the assembly having 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 includes a heat exchange system configured to exchange heat between the recirculated exhaust gas of the exhaust gas recirculation system and a solvent.

[0014] The amount of energy required to regenerate the solvent is large and can reach 60% or more of the engine shaft power delivered by a large two-stroke internal combustion engine. This penalty to the engine's energy efficiency makes operation with a carbon dioxide capture system significantly more expensive than an engine without a carbon dioxide capture system. However, the inventors have realized that large two-stroke diesel engines utilizing exhaust gas recirculation generate an excess energy stream because the recirculated exhaust gases are cooled using a heat exchange medium before being reintroduced into the cylinders. The inventors have also realized that this heat exchange medium (e.g. water or steam) can be heated to a temperature sufficient to be used directly to heat and regenerate the carbon dioxide rich solvent in the desorber and reboiler assemblies.

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

[0016] In one example of an implementation of the first aspect, the exhaust gas recirculation system includes a scrubber, preferably a wet scrubber, which is disposed in the exhaust gas recirculation system downstream of the exhaust gas recirculation heat exchanger.

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

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

[0019] In one example of an implementation form of the first approach, the control unit is configured to control a rotation speed of the blower to adjust a ratio of recirculated exhaust gas in the scavenging gas.

[0020] According to a second aspect, there is provided a method of operating a large two-stroke turbocharged uniflow scavenged internal combustion engine having multiple combustion chambers, the method comprising: providing a carbon-based fuel to the combustion chamber; combusting a carbon-based fuel in a combustion chamber to produce an exhaust stream comprising carbon dioxide; recirculating a first portion of the exhaust stream and exhausting a second portion of the exhaust stream; supplying a pressurized scavenging air flow comprising recirculated exhaust gas to said combustion chamber; cooling a recirculated exhaust gas stream in an exhaust system using a heat exchange medium stream and heating said heat exchange medium stream; chemically absorbing carbon dioxide from the second portion of the vent 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 a desorber and reboiler assembly; regenerating the carbon-rich solvent in the assembly by supplying at least a portion of the heated heat exchange medium stream to the assembly to heat the solvent; Includes.

[0021] In one implementation of the second aspect, the method includes recirculating at least 40 mass% of the exhaust gas flow. Preferably, at least 40 to 55 mass% of the exhaust gas flow is recirculated.

[0022] In one example implementation of the second aspect, the method includes controlling a speed of a blower of an exhaust gas recirculation system to adjust a proportion of recirculated exhaust gas in the pressurized scavenging gas.

[0023] In one example implementation of the second aspect, the method includes providing a gas flow including carbon dioxide and water vapor or steam generated in the desorber to a separator that separates the carbon dioxide and the water vapor or steam;

[0024] The separator is a knock-out drum to obtain a gas stream comprising primarily carbon dioxide and a liquid stream comprising primarily water.

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

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

[0027] In one example implementation of the second aspect, the method includes: extracting heat from recirculated exhaust gas in the exhaust gas recirculation system using an exhaust gas recirculation heat exchanger of the exhaust gas recirculation system, thereby exchanging heat between the exhaust gas in the exhaust gas recirculation system and a heat exchange medium, cooling the exhaust gas in the exhaust gas recirculation system and heating the heat exchange medium;

[0028] exchanging heat between the solvent and the heated heat exchange medium to heat the solvent and cool the heat exchange medium; These and other aspects will be apparent from and elucidated with reference to the examples described below. [Brief description of the drawings]

[0029] Various aspects, embodiments, and implementations will be described in detail below with reference to exemplary embodiments illustrated in the drawings. [Figure 1] FIG. 1 is a schematic diagram of a large two-stroke diesel engine according to an exemplary embodiment. [Diagram 2] This is an overview of the large two-stroke engine in Figure 1, seen from a different angle. [Diagram 3] 3 is a schematic representation of the large two-stroke engine of FIGS. 1 and 2 according to an embodiment. [Figure 4] FIG. 4a is a schematic representation of a first embodiment of a heat pump for use in the embodiment of FIGS. 1 to 3, and FIG. 4b is a schematic representation of a second embodiment of a heat pump for use in the embodiment of FIGS. 1 to 3. [Diagram 5] FIG. 4 shows a heat pump for use in the embodiment of FIGS. 1 to 4a in more detail. [Figure 6] 3 is a schematic representation of the large two-stroke engine of FIGS. 1 and 2 according to another embodiment. Detailed explanation

[0030] In the following detailed description, the internal combustion engine will be described with reference to an example crosshead type large low speed two-stroke turbocharged internal combustion engine. Figures 1-3 depict an example of a turbocharged large low speed two-stroke diesel engine. The engine has a crankshaft 8 and a crosshead 9. Figures 1 and 2 are schematic views from different angles. Figure 3 is a schematic representation of the turbocharged large low speed two-stroke diesel engine of Figures 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 4 to 14 cylinders arranged in series. The cylinders have cylinder liners carried by an engine frame 11. Such an engine may also be used, for example, as the main engine of a ship or as a stationary engine for driving a generator in a power plant. The total power output of the engine may be, for example, in the range of 1,000 to 110,000 kW.

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

[0032] When the engine is operated as a premixed engine (engine based on the Otto principle), a carbonaceous gaseous fuel (e.g. methanol, petroleum gas or LPG, methane, natural gas (LNG), ethane) is introduced through the gas inlet valve 50' under the control of the electronic control unit 100. This occurs during the upward stroke of the piston 10 (from BDC to TDC) before it passes the fuel valve (gas inlet valve) 50'. A gaseous or liquid carbonaceous fuel (e.g. fuel oil) is injected into the combustion chamber through the fuel valve 50 at high pressure (preferably 300 bar or more) when the piston 10 is at or near TDC. The gaseous fuel is supplied by the gaseous fuel supply system 30' and is 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. A fuel-containing stream 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 in the fuel system 30 (common rail) or in the fuel valve 50. The fuel introduction valves 50' are preferably arranged so as to be equally spaced around the circumference of the cylinder liner. Also, preferably, they are arranged near the center of the cylinder liner in the longitudinal direction. The introduction of gas fuel is performed when the compression pressure is relatively low. In other words, the introduction is performed when the compression pressure is much lower than the compression pressure when the piston reaches TDC, so that it is possible to introduce the gas fuel at a relatively low pressure.

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

[0034] The piston 10 in the cylinder liner 1 compresses a mixture of gaseous fuel and scavenging gas (or scavenging gas in the case of operation with only fuel injection at TDC) and ignition is induced at or near TDC by injection of high pressure fuel from a fuel valve 50, preferably located in the cylinder cover 22. In the case of only liquid fuel injection at or near TDC, ignition is induced by compression and combustion occurs, producing exhaust gases including carbon dioxide.

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

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

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

[0038] The cooled scavenging air or gas passes through an auxiliary blower 16 driven by an electric motor 17. The auxiliary blower 16 compresses the scavenging 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 or partial load. At high engine loads, the turbocharger compressor 7 can provide sufficiently compressed scavenging air and the auxiliary blower 16 is bypassed by a check valve 15. An engine may comprise several turbochargers 5 forming a turbocharging system.

[0039] The control unit 100 (electronic control unit) may be composed of a number of interconnected electronic units, each of which may comprise 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, gaseous fuel introduction (amount and timing), liquid fuel injection (amount and timing), exhaust valve 4 opening and closing (timing and lift amount), exhaust gas recirculation ratio, and also controls the operation of various coolers, pumps, and other equipment. The control unit 100 receives various signals from sensors indicating the operating conditions of the engine. These signals may include signals representing the engine load, engine speed, blower speed, scavenging air temperature, exhaust gas temperature at various locations, and exhaust gas temperature at various locations. They may also include signals representing the pressure of the scavenging system, the pressure in the combustion chamber, the pressure in the exhaust system, and the pressure in the exhaust gas recirculation system. The engine is preferably equipped with a variable timing exhaust valve actuation system that allows individual control of exhaust valve timing for each combustion chamber. The control unit 100 is connected to the fuel valve 50, the liquid fuel inlet 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 representative of the position of the crankshaft. The pressure sensor is preferably located in the cylinder cover 22, or alternatively in the cylinder liner 1, and generates a signal representative of the pressure in the combustion chamber.

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

[0041] The cylinder liner 1 is placed on a cylinder frame 23, and a cylinder cover 22 is installed on the cylinder liner 1. The cylinder liner 1 and the cylinder cover 22 are arranged so that gas does not leak between them. The piston 10 is configured to reciprocate between a bottom dead center (BDC) and a top dead center (TDC). These two dead center positions of the piston 10 are separated by 180 degrees in terms of the rotation angle of the crankshaft 8. The cylinder liner 1 is provided with a plurality of cylinder lubrication holes distributed in the circumferential direction. 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. The piston ring (not shown) of the piston 10 then distributes 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] A plurality of liquid fuel valves 50, preferably three or four per cylinder, are mounted on the cylinder cover 22 and connected to a source of pressurized carbon-containing fuel (not shown). The liquid fuel valves 50 are preferably arranged at equal intervals in the circumferential direction around the exhaust valve 4, in particular around the central outlet (opening) of the cylinder cover 22. The contour of the central portion is controlled by the exhaust valve 4. The injection timing and injection amount of fuel are controlled by the control unit 100. The fuel valve 50 is used only to inject a small amount of ignition liquid (pilot) when the engine is operated in a premixed mode. When the engine is operated in a compression ignition mode, the liquid fuel valve 50 injects an amount of liquid fuel necessary to operate the engine at the engine load actually used. The cylinder cover 22 may be provided with a prechamber (not shown). In addition, the tip of the liquid fuel valve 50, typically provided with a nozzle having one or more nozzle holes, is arranged so that pilot oil (ignition liquid) is injected into the prechamber and atomized. The anteroom aids in reliable ignition.

[0043] The fuel inlet valve 50' is installed in the cylinder liner 1 (or the cylinder cover 22) with its nozzle substantially flush with the inner surface of the cylinder liner 1 and the rear end of the fuel valve 50' protruding from the outer wall of the cylinder liner 1. Typically, one or two, but at most three or four, fuel valves 50' are provided in each cylinder liner 1. They are arranged (preferably equidistantly) in the circumferential area of ​​the cylinder liner 1. In this embodiment, the fuel inlet valve 50' is arranged exactly in the longitudinal center of the cylinder liner 1. The fuel inlet valve 50' is connected to a pressurized supply 30' of gaseous fuel (e.g., methanol, LPG, LNG, ethane or ammonia). That is, the fuel is in gaseous phase when it is supplied to the fuel inlet valve 50'. Since the gaseous fuel is introduced during the stroke from BDC to TDC of the piston 10, the pressure of the gaseous fuel supply source only needs to be higher than the pressure existing in the cylinder liner 1. Typically a pressure of less than 20 bar is sufficient for the gas fuel delivered to the fuel inlet valve 50'. The fuel inlet valve 50' is connected to a control unit 100. The control unit 40 determines the opening and closing timing and the opening time of the fuel inlet valve 50'.

[0044] In some embodiments, the liquid fuel for ignition is heavy fuel oil, marine diesel, heavy fuel oil, ethanol, or dimethyl ether (DME).

[0045] The gas mode of operation may be one of several operating modes of the engine. Other modes may include a liquid fuel mode of operation 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 mode of operation, the engine is primarily fueled by gas fuel, which is introduced at relatively low pressure during the piston stroke from BDC to TDC. That is, the major portion of the energy supplied to the engine is provided by such gas fuel. On the other hand, in comparison to the gas fuel, liquid fuel is used in smaller amounts and contributes relatively little to the amount of energy supplied to the engine. The purpose of the liquid fuel is to ignite at a predetermined time. That is, the liquid fuel acts as an ignition fluid.

[0046] In this manner, the engine of the present embodiment can be a dual fuel engine having a mode in which it operates solely on liquid fuel and a mode in which it operates almost exclusively on gas fuel.

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

[0048] The engine is operated by supplying a carbon-based fuel (liquid and / or gaseous fuel) to a combustion chamber, combusting the carbon-based fuel in the combustion chamber to produce an exhaust stream comprising carbon dioxide, separating the carbon dioxide from the exhaust gas in a carbon dioxide absorption process, and storing the separated carbon dioxide. Preferably, the engine is also operated by recirculating a first portion of the exhaust stream (the first portion of the combustion gas in an embodiment in which the recirculated gas is taken directly from the combustion chamber) and exhausting another (second) portion of the exhaust stream as exhaust gas, and supplying a pressurized scavenging gas comprising the exhaust gas to the combustion chamber, wherein the pressurized scavenging gas comprises at least 40% by mass, preferably 40 to 55% by mass, of the recirculated combustion gas.

[0049] Downstream of the turbocharger turbine 6, the exhaust gases enter a second exhaust pipe 28, which directs the exhaust gases to a boiler 20 (also called an economizer). The boiler 20 is configured to generate steam. This steam can be used for various purposes, for example, within the vessel in which the engine is installed, or it can have a sufficient temperature to be fed directly to the desorber 66 and reboiler 62 assembly, which will be described in more detail below, and can be used directly to heat the desorber 66 and reboiler 62 assemblies.

[0050] Downstream of the boiler 20, the second exhaust pipe 28 leads to a first heat exchanger 40. In this heat exchanger 40, the exhaust gases exchange heat with a first medium which will be described in more detail below.

[0051] The second exhaust pipe 28 continues downstream of the first heat exchanger 40 and connects to an inlet at the bottom of an absorber 42. The absorber 42 is preferably an absorber tower, such as a packed absorber tower. The exhaust gas passes through the absorber tower 42 to an outlet at the top of the absorber tower 42.

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

[0053] Carbon dioxide is removed from the exhaust gas by a packed absorber 42. The reaction is exothermic, increasing the solvent temperature along the absorber 42. By way of example, the carbon dioxide concentration in the exhaust gas from an 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 absorber 42 in a countercurrent flow to the solvent entering the top of the absorber 42. This solvent is called lean CO2 solvent or CO2-lean solvent. This CO2-lean solvent is supplied from a desorber 66 at approximately 35°C to 55°C and atmospheric pressure. The top of the absorber 42 has a water wash section consisting of a packed bed that removes most of the volatile amine sorbent that has escaped into the exhaust gas by condensing and solubilizing it. The absorber 42 can be up to 50 meters in height. Once the carbon dioxide has been absorbed in the absorber 42, the carbon dioxide-rich solvent stream from the bottom of the absorber 42 is fed by the pump 44 to the cross heat exchanger 60, where it is heat exchanged with the carbon dioxide-lean solvent stream before being introduced into the desorber 66 and reboiler 62 assembly, where it is heated to release the carbon dioxide from the solvent. The desorption temperature varies between 120° C. and 150° C., and the operating pressure can reach up to 5 bar.

[0054] A water saturated carbon dioxide stream is discharged from the top of the desorber 66. It is cooled in heat exchanger 68 to condense most of the water. The water is separated in knock out drum 69 and returned to the desorber 66. The carbon dioxide stream from knock out drum 69 is compressed / liquefied in liquefaction unit 70 and temporarily stored in storage tank 85. In some embodiments, storage tank 85 is a cryogenic storage tank from which the liquefied carbon dioxide can be transported to a final storage location or a utility facility (not shown). If the engine is on board a vessel, the temporary storage tank 85 is located on board the vessel and is emptied when the vessel is in port with facilities to receive the liquefied carbon dioxide.

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

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

[0057] The carbon dioxide concentration in the exhaust gas exiting the absorber 42 is up to 10 times lower than the carbon dioxide concentration in the exhaust gas entering the absorber 42 .

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

[0059] The engine generates several surplus energy flows Q1, Q2,...Qn, also called waste heat flows, from various parts of the engine. In the embodiment of Fig. 3 these include: 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. Usually at a temperature of 45~55℃. Q3: Primary cooling medium of cylinder jacket cooler (such as water). The cooling water from the cylinder jacket usually has a temperature of about 70 to 90°C. Q4: Primary cooling medium (e.g. water) of the exhaust gas recirculation pipe heat exchanger (cooler) 32. Usually has a temperature of about 50 to 350°C. Q5: Boiler 20. Normally supplies steam at about 160-170℃. Q6: The primary medium (e.g., water) used in the first heat exchanger 40. It usually has a temperature of 160 to 170°C. Q7: The primary medium (e.g. water) used in the second heat exchanger 67. It usually has a temperature of 100 to 170°C. Q8: The primary medium (e.g. water) used in the third heat exchanger 68. It usually has a temperature of 95-105°C. Q9: The primary medium (e.g. water) used to cool the liquefier 70. It has a temperature that depends on the type of technology used for liquefaction and the type of cooling system used for the liquefier 70.

[0060] It should be noted that the above list of excess energy streams generated by the engine is not exhaustive and merely provides examples of excess energy sources.

[0061] At least one of said surplus energy streams Q1, Q2, ... Qn, in particular those having a temperature lower than that required to heat the desorber 66 and regenerator 62 assembly, is fed to a heat pump 80. (The desorber 66 and regenerator 62 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 stream of energy Qr in the form of a stream of secondary medium (e.g. water or steam) at a temperature of at least 120°C, preferably at least 130°C. Preferably, the temperature of the secondary medium fed to the desorber 66 and reboiler 62 assembly is between 130 and 140°C, most preferably about 136°C.

[0062] 4a shows a first embodiment of the implementation of a heat pump 80. In this embodiment, multiple surplus energy streams Q1, Q2, ... Qn are fed to a single heat pump 80, which generates an energy stream Qr that is fed to the desorber 66 and regenerator 62 assembly.

[0063] A second embodiment of the implementation of the pump 80 is shown in Fig. 4b. In this embodiment, one of the multiple surplus energy flows Q1, Q2, ... Qn is applied to one of the multiple heat pumps 80, and the energy flow Qr fed to the desorber 66 is created by the multiple heat pumps 80 or preferably combined into one flow of energy Qr to the desorber 66 and regenerator 62 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 a throttle valve. In the heat pump 80, a heat pump (cooling) fluid circulates in a cycle consisting of an evaporator, a condenser, a compressor, and a throttle valve, as shown in FIG. 5. The heat pump 80 works by receiving heat from the flow of energy Q2 in the evaporator. The heat pump fluid evaporates in the evaporator and enters the compressor. The compressor is driven, for example, by an electric motor. The power to drive the electric motor is provided, for example, by an alternator or a generator driven by power branched from the engine crankshaft. The compressor increases the pressure and temperature of the heat pump fluid. Downstream of the compressor, the heat pump fluid enters the condenser, where heat is transferred to a heat sink and the heat pump fluid condenses. The heat pump fluid then expands in the throttle valve before re-entering the evaporator, and the cycle is repeated. A secondary medium, such as water or steam, transports heat from the condenser to the reboiler 62, preferably in a cycle driven by a pump, the secondary medium having a temperature of at least 120° C., preferably at least 130° C. Thus, the reboiler 62 forms a heat sink for the heat pump 80.

[0065] To increase the efficiency of the heat pump 80, in an embodiment, the condenser section is divided into three heat exchanger (HEX) areas (superheater, condenser, subcooler). The heat extracted in the superheater and condenser areas is sent to a heat sink. The heat extracted in the subcooler is used to preheat the heat pump fluid leaving the evaporator. This configuration of the condenser reduces the compressor work and increases the system efficiency. Furthermore, 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 steam generated in the boiler 20 in some embodiments. The steam HEX and the electric coil ensure that the reboiler 62 receives sufficient energy in the entire engine load range.

[0066] In Fig. 5, multiple energy flows Q1, Q2, ... Qn are utilized. If only one energy flow Q1, Q2, ... Qn is applied, the degasser downstream of the evaporator can be eliminated.

[0067] In some embodiments, the engine is equipped with an exhaust gas recirculation system having an exhaust gas recirculation pipe 35 connecting the first exhaust pipe 19 to the scavenge air pipe 13. Preferably, the exhaust gas recirculation pipe 35 connects to the first exhaust pipe 19 upstream of the selective catalytic reactor 33. Preferably, the exhaust gas recirculation pipe 35 connects to the scavenge air pipe 13 upstream of the scavenge air cooler 14. However, embodiments may exist in which the exhaust gas recirculation pipe 35 connects to the scavenge air pipe 13 downstream of the scavenge air cooler 14.

[0068] The exhaust gas recirculation pipe 35 includes a blower 34 for forcing exhaust gases from the exhaust pipe to the scavenge pipe, since the pressure in the scavenge 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. In some embodiments, the blower may be driven by other rotary power sources. In the illustrated embodiment, the blower 34 is located between the exhaust gas recirculation heat exchanger 32, which cools the exhaust gases, and the exhaust gas recirculation scrubber 36. However, the location of the blower 34 could be upstream or downstream of other elements of the exhaust gas recirculation path 35.

[0069] The exhaust gas recirculation heat exchanger 32 is located upstream of the exhaust gas recirculation scrubber 36. The primary 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 to adjust the proportion of recirculated exhaust gas in the pressurized scavenging gas, preferably to a proportion of at least 35% by mass, in order to increase the carbon dioxide concentration in the exhaust gas and thereby 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. Thus, the control unit 100 is configured to operate the engine with a proportion of recirculated exhaust gas in the pressurized scavenging gas of 40% or more, 45% or more, 50% or more, etc., depending on the operating conditions. In general, the control unit 100 is configured to operate with the highest possible proportion of recirculated exhaust / combustion gas. "Highest possible" means the highest proportion that does not cause unacceptable detrimental effects, such as a decrease in the quality of the combustion process, a decrease in the reliability of the combustion process, an unacceptable increase in the thermal load of the engine, etc.

[0071] The medium (e.g., water or steam) used to exchange heat with the exhaust gas in the exhaust gas recirculation heat exchanger 32 leaves the exhaust gas recirculation heat exchanger 32 at a temperature of approximately 130-170° C., so that the medium can be used directly in the desorber 66 and regenerator 62 assembly without passing through the heat pump 80. The recirculated exhaust gas enters the exhaust gas recirculation heat exchanger 32 at a temperature of approximately 260-400° C. The flow rate of the medium through the exhaust gas recirculation heat exchanger 32 can be adjusted to bring the medium to the desired temperature.

[0072] Exhaust gas recirculation increases the carbon dioxide concentration of the exhaust gas supplied to the absorber 42, thereby reducing the energy consumption of the desorber 66 and regenerator 62 assembly. Also, a higher exhaust gas recirculation ratio reduces the size of the exhaust gas flow to the absorber 42, allowing a smaller diameter absorber tower to be used when exhaust gas recirculation is used or when the exhaust gas recirculation ratio is increased. Furthermore, the energy extracted in the exhaust gas recirculation heat exchanger 32 is excess energy (waste heat) that is supplied to the desorber 66 and regenerator 62 assembly, thereby significantly reducing the amount of energy that needs to be supplied to operate the desorber 66 and regenerator 62 assembly.

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

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

[0075] This embodiment includes an optional second scavenge air cooler 14a downstream of the scavenge air cooler 14. The scavenge air cooler 14 can be configured to generate a flow of heat exchange medium having a sufficient temperature for direct use in the desorber 66 and regenerator 62 assembly. The second scavenge air cooler 14a generates an excess energy flow Q10 in the form of a flow of the 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 the second medium before the energy flow can be used in the desorber 66 and regenerator 62 assembly. The energy flow Q10 generated in the second scavenge air cooler 14a is then sent to the heat pump 80.

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

[0077] In this embodiment, an additional excess energy stream Q12 can also be produced from excess heat from the exhaust gas recycle scrubber 36 that is supplied to the heat pump 80.

[0078] Various ways of understanding and implementation of the invention have been described with several examples. The above embodiments can be combined in various ways. In addition, by studying the specification, drawings, and claims of this application, a person skilled in the art will understand and be able to embody many variations in addition to the described examples in carrying out the invention described in the claims. The words "comprise", "have", and "include" in the claims do not exclude the presence of elements or steps not described. Even if the number of elements described in the claims is not explicitly stated as being multiple, the presence of the 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 items are described in separate dependent claims, this does not exclude them from being combined and may be advantageously combined. The signs used in the claims should not be interpreted as limiting the scope of the invention.

Claims

1. A crosshead type large two-stroke turbocharged uniflow scavenging internal combustion 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 disposed in the cylinder liner for introducing scavenging gas into the at least one combustion chamber; a fuel system configured to supply a carbon-based fuel to the at least one combustion chamber; the at least one combustion chamber configured to combust a carbon-based fuel to produce exhaust gases comprising carbon dioxide, the engine further comprising: an exhaust outlet disposed in the cylinder cover and controlled by an exhaust valve; The at least one combustion chamber is connected to a scavenging air receiver through the scavenging port and to an exhaust air receiver through the exhaust outlet; The institution further: an exhaust system having a turbine driven by the exhaust flow, the turbine being a turbocharging system; an air intake system having a compressor of the turbocharging system configured to supply pressurized scavenging air to the scavenging receiver; an exhaust gas recirculation system configured to recirculate a portion of exhaust gas discharged from the at least one combustion chamber to the scavenge air receiver, the exhaust gas recirculation system having a blower for assisting the flow of exhaust gas to the scavenge air receiver; With the above in mind, an absorber, preferably an absorption tower, for absorbing carbon dioxide into a solvent; a desorber and reboiler assembly for desorbing carbon dioxide from the solvent; Equipped with 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 stream by chemical absorption into the solvent for the exhaust stream passing through the absorber; the assembly having 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 comprising a heat exchange system configured to exchange heat between recirculated exhaust gas of the exhaust gas recirculation system and the solvent in the assembly. institution.

2. an exhaust gas recirculation heat exchanger in the exhaust gas recirculation system configured to exchange heat between exhaust gas in the exhaust gas recirculation system and a heat exchange medium, thereby cooling exhaust gas in the exhaust gas recirculation system and heating the heat exchange medium; 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 of claim 1.

3. 3. An engine according to claim 2, wherein the exhaust gas recirculation system comprises a scrubber, preferably a wet scrubber, which is disposed in the exhaust gas recirculation system downstream of the exhaust gas recirculation heat exchanger.

4. 4. The method according to claim 1, further comprising: providing a control unit configured to adjust the mass proportion of recirculated exhaust gas in the scavenging gas to at least 40%, preferably between 40% and 55%. An institution listed in any of the above.

5. The engine of claim 4 , wherein the control unit is configured to control a rotation speed of the blower to adjust a proportion of recirculated exhaust gas in the scavenging gas.

6. 1. A method of operating a large two-stroke turbocharged uniflow scavenged internal combustion engine having multiple combustion chambers, comprising the steps of: supplying a carbon-based fuel to the combustion chamber; combusting a carbon-based fuel in a combustion chamber to produce an exhaust stream comprising carbon dioxide; recirculating a first portion of the exhaust stream and exhausting a second portion of the exhaust stream; supplying a pressurized scavenging air flow comprising recirculated exhaust gas to said combustion chamber; cooling a recirculated exhaust gas stream in an exhaust system using a heat exchange medium stream and heating said 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 a desorber and reboiler assembly; regenerating the carbon-rich solvent in 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:

7. 7. The method of claim 6, comprising recirculating at least 40 mass% of the exhaust gas stream, preferably recirculating at least 40 to 55 mass% of the exhaust gas stream.

8. 8. A method according to claim 6 or 7, comprising controlling the speed of a blower in the exhaust gas recirculation system to adjust the proportion of recirculated exhaust gas in the pressurized scavenging gas.

9. providing a gas stream containing carbon dioxide and water vapor or steam generated in the desorber to a separator for separating the carbon dioxide and water vapor or steam; the separator being a knock-out drum for obtaining a gas stream comprising primarily carbon dioxide and a liquid stream comprising primarily water; The method according to claim 6.

10. providing a gas stream comprising primarily carbon dioxide to a liquefaction unit; and liquefying the gas stream comprising primarily carbon dioxide to obtain a liquefied carbon dioxide stream; Preferably comprising directing the liquefied carbon dioxide stream to a liquefied carbon dioxide storage device.

10. The method of claim 9.