CN117988970A

CN117988970A - Large two-stroke turbocharged uniflow scavenged internal combustion engine and method of operating the same

Info

Publication number: CN117988970A
Application number: CN202311459000.3A
Authority: CN
Inventors: 亨里克·克里斯滕森; 尼尔斯·克耶米库普; 斯特凡·迈尔
Original assignee: Mannone Solutions Mannone Solutions Germany Branch
Current assignee: Mannone Solutions Mannone Solutions Germany Branch
Priority date: 2022-11-04
Filing date: 2023-11-02
Publication date: 2024-05-07
Also published as: DK202270534A1; JP2024068162A

Abstract

A large two-stroke turbocharged uniflow scavenged internal combustion engine and method of operating the same by operating the engine in the following manner: supplying a carbon-based fuel to the combustion chamber, combusting the carbon-based fuel in the combustion chamber, thereby producing an exhaust stream comprising carbon dioxide, recirculating a first portion of the exhaust stream, and discharging a second portion of the exhaust stream, cooling the first portion of the recirculated exhaust stream in the exhaust system using a heat exchange medium stream, thereby heating the heat exchange medium stream, chemically absorbing carbon dioxide from the second portion of the exhaust stream into the solvent by supplying a carbon dioxide-lean solvent stream to the absorber (42), and discharging a carbon dioxide-rich solvent stream from the absorber (42) to a desorber (64) and reboiler (62) assembly, and heating the solvent by supplying at least a portion of the heated stream of the heat exchange medium to the desorber and reboiler assembly, thereby regenerating the carbon-rich solvent in the desorber and reboiler assembly by heating.

Description

Large two-stroke turbocharged uniflow scavenged internal combustion engine and method of operating the same

Technical Field

The present invention relates to large two-stroke internal combustion engines, particularly large two-stroke uniflow scavenged internal combustion engines having a crosshead operating on carbon-based fuel (gaseous or liquid fuel), which are configured to reduce carbon dioxide emissions, and to methods of operating such types of engines.

Background

A large two-stroke turbocharged uniflow scavenged internal combustion engine with a crosshead is used for example for propulsion of large ocean going vessels or as a prime mover in a power plant. Not only due to the large size of the internal combustion engines, these two-stroke diesel engines are also configured in a different way than any other internal combustion engine. The exhaust valves of these engines may weigh up to 400kg, the pistons may have a diameter of up to 100cm, and the maximum operating pressure in the combustion chamber is typically hundreds of bars. The forces involved in these high pressure levels and piston sizes are enormous.

DK202170181B1 discloses a uniflow large turbocharged multi-cylinder two-stroke internal combustion engine with an EGR system for delivering the exhaust flow from the exhaust system to the intake system. The EGR system includes an EGR blower and an electronically adjustable EGR throttle. An AC electric drive motor is coupled to the EGR blower to drive the EGR blower. The alternating current drive motor is configured to operate at a predetermined constant speed. The sensor provides a signal indicative of the oxygen concentration in the scavenging gas receiver and the controller receives the signal and is coupled to the electronically adjustable EGR throttle. The controller is configured to regulate the flow of exhaust gas through the EGR system by: the position of the electronically adjustable EGR throttle valve is adjusted based on the first signal as a primary measurement. The engine emits carbon dioxide generated during combustion of the carbon fuel to the atmosphere. Large two-stroke turbocharged internal combustion engines are operated using liquid fuels, such as fuel oil, marine diesel, heavy oil, ethanol, dimethyl ether (DME), or gaseous fuels, such as methane, natural gas (LNG), petroleum gas (LPG), methanol or ethane.

Engines operating with gaseous fuel may operate according to an otto cycle, wherein the gaseous fuel is admitted through a fuel valve arranged centrally along the length of the cylinder liner or in the cylinder head, i.e. the engines admit gaseous fuel during the stroke in which the piston starts to travel upwards (from BDC to TDC) before the exhaust valve closes, and a mixture of gaseous fuel and scavenging air in the combustion chamber is compressed and the compressed mixture is ignited at or near TDC by a timed ignition device, such as a liquid fuel injection device.

Engines operating with liquid fuel and engines operating with gaseous fuel injected at high pressure, when the piston is near or at TDC, i.e. when the compression pressure in the combustion chamber is at or near its maximum, inject gaseous or liquid fuel and thus operate according to the diesel cycle, i.e. by compression ignition.

Liquid and gaseous fuels used in known large two-stroke turbocharged uniflow scavenged internal combustion engines typically contain carbon, i.e. these liquid and gaseous fuels are carbon-based fuels, and combustion of the liquid and gaseous fuels results in the production of carbon dioxide, which is discharged to the atmosphere. Carbon dioxide emissions are generally believed to cause climate change and therefore should be reduced or avoided.

Known carbon capture technologies generally fall into three categories: post-combustion CO ₂ capture, pre-combustion CO ₂ capture, and combustion of oxygen-enriched fuel. Pre-combustion refers to the separation and capture of carbonaceous components prior to combustion of the fuel.

In carbon dioxide capture prior to combustion, the fuel is first reacted with oxygen and/or steam, and then the fuel is further processed in a water gas shift reactor to produce a mixture of hydrogen and carbon dioxide. Carbon dioxide is captured from a high pressure gas mixture containing 15% to 40% carbon dioxide. The advantage of pre-combustion is that the volume of gas required for the process is greatly reduced and the concentration of CO ₂ in the gas is increased. This will reduce the energy consumption and equipment investment of the separation process.

In Oxy-Fuel combustion, carbon-based fuels are burned in recirculated flue gas and pure oxygen (rather than air). This limits the commercial potential of oxyfuel combustion due to the high cost of oxygen separation. The oxycombustion technology includes an air separation unit in which nitrogen is removed from air. The carbon-based fuel is then combusted in the recirculated flue gas and pure oxygen. The flue gas now mainly comprises particulates produced by combustion, carbon dioxide, sulfur oxides in the fuel and water, which is transported to a particulate removal device and a sulfur removal device before water is condensed out, leaving a carbon dioxide stream that can be compressed. The main advantage is that the oxyfuel technology can achieve nearly 100% carbon dioxide capture.

In the post-combustion technology, carbon-based fuel is burned as in conventional energy power generation and carbon dioxide is captured from the exhaust gas. This carbon separation technology is roughly divided into four sub-fractions, namely absorption, adsorption, membrane and cryogenic temperatures. Amine solvents may be used to capture carbon dioxide by absorbing the exhaust gas. Here, carbon dioxide is captured in a solvent, and then an amine regeneration process is performed. The disadvantage is the need for power plants of enlarged volume and large amounts of energy for the carbon dioxide capture process. In particular, a significant amount of energy is required for amine solvent regeneration.

Disclosure of Invention

It is an object of the present invention to provide an engine and method that overcomes or at least reduces the above-mentioned problems.

The above-mentioned and other objects are achieved by the features of the independent claims. Further implementations are evident from the dependent claims, the description and the figures.

According to a first aspect, there is provided a large two-stroke turbocharged uniflow scavenged internal combustion engine having a crosshead, the engine comprising:

at least one combustion chamber bounded by a cylinder liner, a piston configured to reciprocate in the cylinder liner, and a cylinder head,

A scavenging port arranged in the cylinder liner for admitting 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 is configured for combusting a carbon-based fuel, thereby producing an exhaust stream comprising carbon dioxide,

An exhaust outlet arranged in the cylinder head and controlled by an exhaust valve,

The at least one combustion chamber is connected to the scavenging gas receiver via a scavenging port and to the exhaust gas receiver via an exhaust gas outlet,

An exhaust system comprising a turbine of a turbocharger system driven by an exhaust gas flow,

An air intake system including a compressor of a turbocharger system, the compressor configured to supply pressurized scavenging air to a scavenging gas receiver,

An exhaust gas recirculation system configured for recirculating a portion of exhaust gas from the at least one combustion chamber to the scavenging gas receiver, the exhaust gas recirculation system comprising a blower for assisting the flow of exhaust gas towards the scavenging gas receiver,

An absorber for absorbing carbon dioxide into the solvent, preferably the absorber is an absorber tower,

A desorber and reboiler assembly for desorbing carbon dioxide from the solvent,

The absorber has a solvent inlet that receives the lean carbon dioxide solvent from the desorber and a solvent outlet that supplies the carbon dioxide rich solvent to the desorber,

The absorber is arranged for an exhaust gas stream that passes through the absorber to chemically absorb carbon dioxide into the solvent to separate the carbon dioxide from the exhaust gas stream,

The desorber and reboiler assembly has an inlet that receives the carbon dioxide rich solvent from the absorber and an outlet that supplies the carbon dioxide lean solvent to the absorber,

The desorber and reboiler assembly is configured to heat the solvent to release carbon dioxide from the solvent, and

A heat exchange device configured to exchange heat between the recirculated exhaust gas and the solvent in the exhaust gas recirculation system.

The energy required to regenerate the solvent is very high, and can reach more than 60% of the engine shaft power provided by a large two-stroke internal combustion engine. This loss of engine energy efficiency will make operation with a carbon dioxide capture system significantly more expensive than an engine without such a carbon dioxide capture system. However, the inventors have recognized that large two-stroke diesel engines operating with exhaust gas recirculation produce excess energy flow because the recirculated exhaust gas is advantageously cooled using a heat exchange medium before being reintroduced into the cylinders. The inventors have also recognized that the exchange medium (e.g., water or steam) will be heated to a temperature sufficient to allow for direct use of the heat exchange medium for heating and thereby regenerating the carbon dioxide rich solvent in the desorber and reboiler assembly.

In a possible implementation form of the first aspect, the heat exchange device comprises an exhaust gas recirculation heat exchanger (32) located in the exhaust gas recirculation system, the exhaust gas recirculation heat exchanger being configured to exchange heat between exhaust gas in the exhaust gas recirculation system and a heat exchange medium to cool the exhaust gas in the exhaust gas recirculation system and to heat the heat exchange medium, and the heat exchanger being configured to exchange heat between the solvent and the heat exchange medium to heat the solvent and to cool the heat exchange medium.

In a possible implementation form of the first aspect, the exhaust gas recirculation system comprises a scrubber, preferably a wet scrubber, arranged in the exhaust gas recirculation system downstream of the exhaust gas recirculation heat exchanger.

In a possible implementation form of the first aspect, the heat exchange device is configured to exchange heat between the recirculated exhaust gas in the exhaust gas recirculation system and the solvent in the desorber and reboiler assembly.

In a possible implementation form of the first aspect, the engine comprises a controller configured to adjust the mass percentage of the recirculated exhaust gas in the scavenging gas to at least 40%, preferably to between 40% and 55%.

In a possible implementation form of the first aspect, the controller is configured to control the speed of the blower to adjust the percentage of recirculated exhaust gas in the scavenging gas.

According to a second aspect, there is provided a method of operating a large two-stroke turbocharged uniflow scavenged internal combustion engine having a plurality of combustion chambers, the method comprising:

a carbon-based fuel is supplied to the combustion chamber,

Combusting the carbon-based fuel in the combustion chamber, thereby producing an exhaust stream comprising carbon dioxide,

Recirculating a first portion of the exhaust stream, and discharging a second portion of the exhaust stream,

Supplying a pressurized flow of scavenging gas to the combustion chamber, the pressurized flow of scavenging gas comprising recirculated exhaust gas,

Cooling the recirculated exhaust gas flow in the exhaust system using the heat exchange medium flow, thereby heating the heat exchange medium flow,

Chemically absorbing carbon dioxide from the second portion of the exhaust stream into the solvent by feeding the carbon dioxide-lean solvent stream to the absorber, and discharging the carbon dioxide-rich solvent stream from the absorber to the desorber and reboiler assembly, and

The solvent is heated by feeding at least a portion of the heated heat exchange medium stream to a desorber and reboiler assembly, and the carbon-rich solvent is regenerated in the desorber and reboiler assembly by the heating.

In a possible implementation form of the second aspect, the method comprises recirculating at least 40% by mass of the exhaust gas flow, preferably at least 40% to 55% by mass of the exhaust gas flow.

In a possible implementation form of the second aspect, the method comprises controlling a speed of a blower in the exhaust gas recirculation system to adjust a percentage of recirculated exhaust gas in the pressurized scavenging gas.

In one possible implementation form of the second aspect, the method comprises feeding the gas stream containing carbon dioxide and water vapour or steam generated in the desorber 66 to a separator 69 for separating the carbon dioxide from the water vapour or steam, thereby obtaining a gas stream mainly containing carbon dioxide and a liquid stream mainly containing water, the separator preferably being a separation drum.

In one possible implementation form of the second aspect, the method comprises feeding a gas stream mainly comprising carbon dioxide to a liquefaction unit and liquefying the gas stream mainly comprising carbon dioxide to obtain a liquefied carbon dioxide stream, the method preferably comprising: the liquefied carbon dioxide stream is directed to a liquefied carbon dioxide storage unit.

In one possible implementation form of the second aspect, the method comprises extracting heat from the recirculated exhaust gas in the exhaust gas recirculation system using an exhaust gas recirculation heat exchanger in the exhaust gas recirculation system, thereby exchanging 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 exchanging heat between the solvent and the heated heat exchange medium, thereby heating the solvent and cooling the heat exchange medium. These and other aspects will be apparent from the embodiments described below.

Drawings

In the following detailed portion of the disclosure, aspects, embodiments and implementations will be explained in more detail with reference to example embodiments shown in the drawings, in which:

Figure 1 is an elevation view of a large two-stroke diesel engine according to an example embodiment,

Figure 2 is another angular elevation of the large two-stroke engine of figure 1,

Figure 3 is a schematic view of a large two-stroke engine according to the embodiment of figures 1 and 2,

Figure 4a is a schematic diagram of a first embodiment of a heat pump for use in the embodiments of figures 1 to 3,

Fig. 4b is a schematic diagram of a second embodiment of a heat pump used in the embodiments of fig. 1-3, and

FIG. 5 is a more detailed schematic diagram of an embodiment of a heat pump used in the embodiments of FIGS. 1-4 a, and

Fig. 6 is a schematic view of a large two-stroke engine according to fig. 1 and 2 in another embodiment.

Detailed Description

In the following detailed description, an internal combustion engine will be described with reference to a large two-stroke, low-speed turbocharged cross-head internal combustion engine in an exemplary embodiment. Fig. 1,2 and 3 show an embodiment of a large low-speed turbocharged two-stroke diesel engine with a crankshaft 8 and a cross-head (linkage) 9. Fig. 1 and 2 are elevation views from different angles. FIG. 3 is a schematic diagram of an embodiment of the large low speed turbocharged two-stroke diesel engine of FIGS. 1 and 2, wherein the diesel engine has its intake and exhaust systems. In this embodiment, the engine has six in-line cylinders. However, a large low-speed turbocharged two-stroke internal combustion engine may have between four and fourteen in-line cylinders, with the cylinder liners carried by the engine frame 11. The engine may for example be used as a main engine in a ship or as a stationary engine for operating a generator in a power plant. The total output of the engine may be, for example, in the range of 1,000kw to 110,000 kw.

In this exemplary embodiment, the engine is a two-stroke uniflow scavenged engine having scavenge ports 18 located in the lower region of the cylinder liner 1 and a central exhaust valve 4 located in the cylinder head 22 at the top of the cylinder liner 1. When the piston 10 is located below the scavenging port 18, scavenging gas (SCAVENGE GAS) passes from the scavenging gas receiver 2 through the scavenging port 18 of each cylinder liner 1.

In the case of an engine operating as a premix engine (Otto principle (otto principle)), a carbonaceous gaseous fuel (e.g. methanol, petroleum gas or LPG, methane, natural gas LNG or ethane) enters from the gaseous fuel inlet valve 50 'under the control of an electronic controller when the piston 10 is in its upward motion (from BDC to TDC) and before the piston 10 passes the fuel valve 50' (gas inlet valve). When the piston 10 is at or near TDC, a gaseous or liquid carbon-containing fuel (e.g., fuel oil) is injected into the combustion chamber fuel valve 50 at a high pressure (preferably 300 bar or higher). The fuel gas is introduced at a relatively low pressure below 30 bar, preferably below 25 bar, more preferably below 20 bar, and is supplied by the gaseous fuel supply system 30'. An electric current containing fuel for injection through the fuel valve 50 is supplied by the fuel system 30. The high pressure may be generated by the fuel system 30 (common rail) or in the fuel valve 50. The fuel inlet valve 50' is preferably evenly distributed around the outer circumference of the cylinder liner and is placed in a central region of the length of the cylinder liner 1. The entry of gaseous fuel occurs when the compression pressure is relatively low, i.e., much lower than when the piston reaches TDC (top dead center), thus allowing entry at a relatively low pressure.

When the engine is operated as a compression ignition engine (diesel principle), no gas enters the valve 50' and carbonaceous fuel (gaseous or liquid) is injected at high pressure through the fuel valve 50 when the piston 10 is at or near TDC.

The piston 10 in the cylinder liner 1 compresses the charge of gaseous fuel and the scavenging gas (or compresses the scavenging gas in the case of fuel injection only at TDC) and at or near TDC triggers ignition by injecting fuel at high pressure from a fuel valve 50, the fuel valve 50 preferably being arranged in the cylinder head 22 or by compression in the case of liquid fuel injection only at or near TDC. Combustion then occurs and carbon dioxide-containing exhaust gas (exhaustgas) is produced.

When the exhaust valve 4 is open, the combustion gases flow through the combustion gas conduit associated with the cylinder 1 into the combustion/exhaust gas receiver 3 and onward through the first exhaust conduit 19, which first exhaust conduit 19 comprises a selective catalytic reactor 33 for reducing nitrogen oxides (NOx) in the exhaust gases.

The turbine 6 drives the compressor 7 by means of a shaft, the compressor 7 being supplied with fresh air via an air inlet 12. The compressor 7 delivers pressurized scavenging air to a scavenging air conduit 13 leading to the scavenging gas receiver 2. The scavenging air in the conduit 13 is passed through an intercooler 14 for cooling the scavenging air.

An exhaust gas recirculation conduit 35 is connected to the scavenge air conduit 13, either upstream (shown) or downstream (not shown) of the intercooler 14. At this location, the recirculated exhaust gas mixes with the scavenging air to form the scavenging gas flowing towards the scavenging gas receiver 2. The controller 100 (electronic control unit) is configured to adjust a ratio between the scavenging air and the exhaust gas in the scavenging gas, as will be described in more detail below.

When the compressor 7 of the turbocharger 5 does not deliver sufficient pressure for the scavenging gas receiver 2, i.e. at low or partial load of the engine, the cooled scavenging air or gas passes the auxiliary blowers 16 driven by the electric motor 17, the auxiliary blowers 16 pressurize the scavenging flow. At higher engine loads, the turbocharger compressor 7 delivers sufficient compressed scavenging air and then bypasses the auxiliary blowers 16 via the check valves 15. Notably, the test procedure may include more than one turbocharger 5, thereby forming a turbocharger system.

The controller 100 itself may comprise several interconnected electronic units including a processor and other hardware for performing the functions of the controller, the controller 100 typically being under control of the operation of the engine and controlling the following: such as the intake of gaseous fuel (quantity and timing), the injection of liquid fuel (quantity and timing), and the opening and closing of the exhaust valve 4 (timing and lift ranges), the recirculated exhaust gas ratio, and the operation of various coolers, pumps, and other devices. To this end, the controller 100 receives various signals from the sensors, which inform the controller 100 of the following information: the operating conditions of the engine (engine load, engine speed, blower speed, scavenging gas temperature, elevated gas temperature at various locations, exhaust gas temperature at various locations), pressure in the scavenging system, pressure in the combustion chamber, pressure in the exhaust system, and pressure in the exhaust gas recirculation system. Preferably, the engine includes a variable timing exhaust valve actuation system, allowing independent control of exhaust valve timing for each compression chamber. The controller 100 is connected via signal lines or wireless connectors to the fuel valve 50, the liquid fuel inlet valve 50', the exhaust valve actuator, an angular position sensor that detects the angle of the crankshaft and generates a signal representative of the position of the crankshaft, and a pressure sensor, preferably in the cylinder head 22 or alternatively in the cylinder liner 1, to generate a signal representative of the pressure in the combustion chamber.

The cylinder liner 1 can be manufactured in different sizes, depending on the engine size, the cylinder bore typically being in the range of 250mm to 1000mm, with a corresponding typical length in the range of 1000mm to 4500 mm.

The cylinder liners 1 are mounted in a cylinder frame 23, a cylinder head 22 is placed on top of each cylinder liner 1, with an airtight joint between the cylinder head 22 and the cylinder head 22. The piston 10 is arranged to reciprocate between a Bottom Dead Center (BDC) and a Top Dead Center (TDC). These two extreme positions of the piston 10 are separated by a 180 degree revolution of the crankshaft 8. The cylinder liner 1 is provided with a plurality of circumferentially distributed cylinder lubrication holes, which are connected to cylinder lubrication lines that provide a supply of cylinder lubrication oil when the piston 10 passes through the cylinder lubrication holes 25, and then piston rings (not shown) in the piston 10 distribute the cylinder lubrication oil onto the working surface (inner surface) of the cylinder liner 1. The cylinder liner is provided with a jacket (not shown) and jacket cooling water circulates in the space between the jacket and the cylinder liner.

Liquid fuel valves 50 (typically more than one, preferably three or four liquid fuel valves per cylinder) are mounted in the cylinder head 22 and are connected to the carbonaceous pressurized fuel source 30. The liquid fuel valves 50 are preferably arranged around the exhaust valves 4, in particular around the central outlet (opening) of the cylinder head 22, and are evenly distributed in the circumferential direction. The central profile is controlled by the exhaust valve 4. The timing and quantity of the fuel injection is developed to be controlled by the controller 100. The fuel valve 50 is used only to inject a small amount of ignition liquid (pilot) when the engine is operating in a premix mode. If the engine is operating in compression ignition mode, the amount of liquid fuel required to operate the engine at the actual engine load is injected through the liquid fuel valve 50. The cylinder head 22 may be provided with a prechamber (not shown) and the top of the liquid fuel valve 50, typically a top provided with a nozzle having one or more nozzle holes, is arranged such that a pilot oil (ignition liquid) is injected and atomized into the prechamber to trigger ignition. The pre-chamber helps to ensure reliable ignition.

A fuel inlet valve 50 'is mounted within the cylinder liner 1 (or in the cylinder head 22), the nozzle of the fuel inlet valve 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 fuel valves are provided in each cylinder liner 1, but possibly up to three or four fuel valves 50', the fuel valves 50' being circumferentially distributed (preferably evenly circumferentially) around the cylinder liner 1. In one embodiment, the fuel inlet valve 50' is disposed generally midway along the length of the cylinder liner 1. The fuel inlet valve 50' is connected to a pressurized source of gaseous fuel 30' (e.g., methanol, LPG, LNG, ethane, or ammonia), i.e., the fuel is in the gas phase when it is delivered to the fuel inlet valve 50 '. Since the gaseous fuel is introduced during the stroke of the piston 10 from BDC to TDC, the pressure of the gaseous fuel source need only be higher than that present in the cylinder liner 1, and a pressure typically less than 20 bar is sufficient for the gaseous fuel to be delivered to the fuel inlet valve 50'. The fuel inlet valve 50' is connected to the controller 100, and the controller 100 determines the timing of the opening and closing of the fuel inlet valve 50' and the duration of the opening of the fuel inlet valve 50 '.

In one embodiment, the liquid fuel used for ignition is fuel oil, marine diesel, heavy fuel oil, ethanol or dimethyl ether (DME).

The gaseous operating mode may be one of a plurality of operating modes of the engine. Other modes may include a liquid fuel mode of operation in which all fuel required for engine operation is provided in liquid form through liquid fuel valve 50. In the gaseous fuel operating mode, the engine is operated with gaseous fuel, which enters as the primary fuel at a relatively low pressure during the piston stroke from bottom dead center to top dead center, i.e. providing a large part of the energy supplied to the engine, whereas in contrast the liquid fuel constitutes a relatively small amount of fuel, which only contributes relatively little to the energy supplied to the engine, the purpose of the liquid fuel being to time ignition, i.e. the liquid fuel is used as ignition liquid.

Thus, the engine of the present embodiment may be a dual fuel engine, i.e. the engine has a mode of operation solely on liquid fuel and a mode of operation almost solely on gaseous fuel.

In this embodiment, the engine is shown as a premixed engine operating according to the otto principle. However, it should be appreciated that the engine may also be a compression ignition engine (operating according to diesel principles) in which carbon-based fuel (gaseous or liquid) is injected at high pressure when the piston 10 is at or near TDC.

The engine operates by: supplying a carbon-based fuel (liquid and/or gaseous fuel) to the combustion chamber, combusting the carbon-based fuel in the combustion chamber, thereby producing an exhaust gas stream containing carbon dioxide, preferably recirculating a first portion of the exhaust gas stream (or a portion of the combustion gas in embodiments in which the recirculation gas is directly from the combustion chamber), discharging another (second) portion of the exhaust gas stream as exhaust gas, supplying a pressurized scavenging gas containing exhaust gas to the combustion chamber, in one embodiment the pressurized scavenging gas containing at least 40 mass% of the recirculated exhaust gas, preferably 40 to 55 mass% of the recirculated exhaust gas, separating carbon dioxide from the exhaust gas during carbon dioxide absorption, and storing the separated carbon dioxide.

Downstream of the turbocharger turbine 6, the exhaust gas enters a second exhaust conduit 28, which second exhaust conduit 28 directs the exhaust gas to a boiler 20 (also referred to as an economizer (economizer)), the boiler 20 being configured to generate steam. The steam is used, for example, on a vessel in which an engine is installed for various purposes, or the steam may be used directly to heat the desorber 66 and regenerator 62 assembly, as will be described in further detail below, because the steam has a sufficient temperature such that the steam is supplied directly to the regenerator 66 and reboiler 62 assembly.

Downstream of the boiler 20, the second exhaust gas duct 28 continues to the first heat exchanger 40, where the exhaust gas in the first heat exchanger 40 exchanges with the main medium, as will be described in more detail further below.

Downstream of the first heat exchanger 40, the second discharge conduit 28 continues and is connected to an inlet at the bottom of the absorber 42. Absorber 42 is preferably an absorber, such as a packed absorber. The exhaust gas flows through the absorber 42 to an outlet at the top of the absorber 42.

Absorber 42 is part of a system for chemically absorbing carbon dioxide using a solvent. Examples of suitable solvents are amine solutions. The amine solution may comprise primary, secondary and/or tertiary amines. Further examples of suitable solutions are NaOH/KOH solutions, preferably aqueous amine NaOH/KOH solutions.

Carbon dioxide is removed from the exhaust gas by a packed absorber (absorber) 42. The reaction is exothermic and increases the solvent temperature along absorber 42. As an example, the carbon dioxide concentration in the exhaust gas from the engine is between 4% and 5% by volume (no exhaust gas recirculation) and between 9% and 10% by volume (with exhaust gas recirculation) and is introduced into absorber 42 counter-currently to the solvent, which enters at the top of absorber 42 and is referred to as a carbon dioxide lean solvent. The lean carbon dioxide solvent is fed from desorber 66 at about 35 deg.c to 55 deg.c and ambient pressure. At the top of absorber 42, the wash water portion comprising the packed bed removes most of the volatile amine adsorbent by condensing and dissolving the volatile amine adsorbent that has escaped into the exhaust gas. The total height of absorber 42 can be up to 50 meters. As carbon dioxide is absorbed in absorber 42, the carbon dioxide rich solvent stream from the bottom of absorber 42 is pumped by pump 44 into cross heat exchanger (cross heat exchanger) 60 to exchange heat with the lean carbon dioxide solvent stream before being introduced into the desorber 66 and reboiler 62 assembly, the carbon dioxide rich solvent stream being heated in reboiler 62 to release carbon dioxide from the solvent. The stripping (desorption) temperature varies between 120 ℃ and 150 ℃ and the operating pressure is up to 5bar.

The water saturated carbon dioxide stream is released from the top of the desorber 66 and cooled in a heat exchanger 68 such that most of the water content condenses, which is then separated in a separation drum (knockout drum) 69 and returned to the desorber 66. The carbon dioxide stream from separation drum 69 is then compressed/liquefied in liquefaction unit 70 and temporarily stored in storage tank 88, storage tank 88 being an embodiment of a cryogenic storage tank. The liquefied carbon dioxide may be transported from temporary storage tank 85 to a final storage or utility location (not shown). If the engine is installed in a vessel, the temporary storage tank 88 will be arranged in the vessel and the temporary storage tank 88 will be emptied when the vessel is located at a port provided with a facility for receiving liquefied carbon dioxide.

The amine solution regeneration process does not remove all of the carbon dioxide in the solution and the regenerated carbon dioxide lean solvent is recycled to the absorber tower 42 with carbon dioxide lean packing by the action of pump 64. The carbon dioxide rich solvent exchanges heat with the carbon dioxide lean solvent in cross heat exchanger 60 and heat exchanger 67 before reaching absorber 42.

After the solvent has absorbed carbon dioxide through the column, the carbon dioxide charge (carbon dioxide loading) of the solvent is referred to as a carbon dioxide rich solvent. The difference between lean and rich packing is the amount of carbon dioxide captured from the exhaust.

The carbon dioxide concentration in the exhaust gas exiting the absorber 42 is one tenth of the carbon dioxide concentration in the exhaust gas entering the absorber 42.

Some of the amine of the solvent may still be present in the exhaust gas exiting the absorber 42 and is removed by an amine scrubber 44 disposed in an exhaust gas conduit 49 downstream of the absorber 42.

The engine generates a plurality of excess energy flows Q1, Q2, … Qn, also referred to as waste heat flows, from various components of the engine. In the embodiment of fig. 3, these energy flows include:

q1, the primary cooling medium (e.g. water) of the scavenger air cooler 14. The cooling water from the scavenger air cooler 14 will typically have a temperature between about 20 c and 240 c,

Q2, a main medium engine lubricating oil, which lubricating oil generally has a temperature between 45 ℃ and 55 ℃,

The main cooling medium (e.g. water) of the Q3 cylinder jacket cooler. The cooling water from the cylinder jacket typically has a temperature of about 70 c to 90 c,

The primary cooling medium (e.g., water) of the Q4 exhaust gas recirculation conduit heat exchanger (cooler) 32, typically having a temperature between about 50c and 350 c,

Q5 boiler 20, which is normally fed with steam having a temperature between about 160 ℃ and 170 ℃,

Q6 primary medium (e.g., water) used in the first heat exchanger 40, typically having a temperature between 160 c and 170 c,

Q7, a primary medium (e.g. water) for use in the second heat exchanger 67, the primary medium typically having a temperature between 100 ℃ and 170 ℃,

Q8 the primary medium (e.g., water) used in the third heat exchanger 68, which typically has a temperature between 95 c and 105 c,

Q9 is the primary medium (e.g. water) for cooling the liquefaction unit 70, which will have a temperature that depends on the type of technology used for the liquefaction and the type of cooling system used for the liquefaction unit 70.

It should be noted that this list of excess energy flows generated by the engine is not exhaustive and is merely used to provide an example of such sources.

At least one of the above listed surplus energy flows Q1, Q2..qn is supplied to the heat pump 80, in particular the following energy flows are supplied to the heat pump 80: these energy streams have a temperature lower than that required to heat the desorber 66 and regenerator 62 assembly (which requires a secondary medium having a temperature of at least 120 c, preferably at least 110 c). The heat pump 80 is configured to generate an energy flow Qr in the form of a secondary medium (e.g., water or steam) flow having a temperature of at least 120 ℃, preferably at least 130 ℃. Preferably, the temperature of the secondary medium supplied to the desorber 66 and reboiler 62 assembly is between 130 ℃ and 140 ℃, most preferably about 136 ℃.

A first embodiment of an implementation of a heat pump 80 is shown in fig. 4 a. In this embodiment, multiple excess energy streams Q1, Q2..qn are applied to a single heat pump 80, and the energy stream Qr supplied to the desorber 66 and regenerator 62 assembly is generated by the pump 80.

A second embodiment of an implementation of the pump 80 is shown in fig. 4 b. In this embodiment, one of the plurality of excess energy streams Q1, Q2..qn is applied to one of the plurality of heat pumps 80, and the energy stream Qr supplied to the desorber 66 and regenerator 62 assembly is generated by the plurality of heat pumps 80, and preferably combined into one energy stream Qr to lead to the desorber 66 and regenerator 62 assembly.

One or more heat pumps 80 are used to raise the temperature of the amine solution in reboiler 62. The heat pump 80 includes at least an evaporator, a condenser, a compressor, and a throttle valve. Within the heat pump 80, a heat pump (refrigeration) fluid circulates in a cycle including an evaporator, a condenser, a compressor, and a throttle valve, as shown in fig. 5. The heat pump 80 is operated by an evaporator which receives heat from the energy flow Q2. The heat pump fluid evaporates in the evaporator and enters the compressor. The compressor is driven, for example, by an electric motor that receives electric power, such as electric power received from an alternator or generator driven by the starting power from the crankshaft of the engine. The compressor increases the pressure and temperature of the heat pump fluid. Downstream of the compressor, the heat pump fluid enters the condenser, heat is transferred to the radiator and the heat pump fluid condenses. The heat pump fluid is then expanded in a throttle valve before re-entering the evaporator and the cycle is repeated. A secondary medium, such as water or steam, which transfers heat from the condenser to the reboiler 62, preferably the secondary medium transfers heat from the condenser to the reboiler 62 in a pump driven cycle, the secondary medium having a temperature of at least 120 ℃, preferably at least 130 ℃. Thus, reboiler 62 forms a radiator for heat pump 80.

To increase the efficiency of the heat pump 80, in one embodiment, the condenser section is divided into three Heat Exchanger (HEX) areas; superheater, condenser and subcooler. Heat extracted in the superheater and condenser regions is transferred to the radiator. The heat extracted in the subcooler is used to preheat the heat pump fluid exiting the evaporator. By employing such a condenser arrangement, the compressor requires less work and system efficiency increases. In addition, a water circuit with steam HEX and electrical coils is applied between the condenser, superheater and reboiler 62. In one embodiment, the fluid entering steam HEX is steam generated in boiler 20. Steam HEX and electrical coils ensure that reboiler 62 receives sufficient energy throughout the engine load range.

In fig. 5, a plurality of energy flows Q1, Q2..qn are utilized. If only one energy flow Q1, Q2..qn is applied, the deaerator below the evaporator can be removed.

In one embodiment, the engine is provided with an exhaust gas recirculation system comprising an exhaust gas recirculation conduit 35 connecting the first exhaust gas conduit 19 to the scavenging conduit 13. Preferably, the exhaust gas recirculation conduit 35 is connected to the first exhaust gas conduit 19 upstream of the selective catalytic reactor 33. Preferably, the exhaust gas recirculation conduit 35 is connected to the scavenging conduit 13 upstream of the scavenging cooler 14. However, it should be appreciated that the exhaust gas recirculation conduit 35 may also be connected to the scavenging air conduit 13 downstream of the scavenging air cooler 14. The exhaust gas recirculation conduit 35 comprises a blower 34 to force exhaust gas to flow from the exhaust conduit to the scavenging air conduit, as the pressure in the scavenging conduit 13 is typically higher than the pressure in the first exhaust conduit 19 during operation of the engine. In the illustrated embodiment, the blower 34 is driven by an electric motor, but it should be understood that the blower may be powered by any other source of rotational power. In the illustrated embodiment, the blower 34 is disposed between the exhaust gas recirculation heat exchanger 32 that cools the exhaust gas and the exhaust gas recirculation scrubber 36. However, it should be understood that the location of the blower 34 may be upstream or downstream of other elements in the exhaust gas recirculation duct 35. The exhaust gas recirculation heat exchanger 32 is arranged upstream of the exhaust gas recirculation scrubber 36. The primary purpose of the exhaust gas recirculation scrubber 36 is to remove impurities (soot). The controller 100 is configured to control the speed of the blower 34 in the exhaust gas recirculation system to adjust the percentage of recirculated exhaust gas in the pressurized scavenging gas to at least 35 mass percent to increase the concentration of carbon dioxide in the exhaust gas, thereby improving the efficiency of the carbon dioxide absorption system. The exhaust gas recirculation rate may also be controlled by a valve (not shown) controlled by the controller 100. Accordingly, the controller 100 is configured to operate the engine in the following manner depending on the operating conditions: the percentage of the recirculated exhaust gas in the pressurized scavenging gas is made 40% or more, 45% or more, or 50% or more. Generally, the controller 100 is configured to operate at the highest possible percentage of recirculated exhaust gas/combustion gases, as this facilitates removal of the current dioxide from the exhaust gas. "as high as possible" means the highest ratio that does not cause unacceptable detrimental effects such as a reduction in the quality of the combustion process, a reduction in the reliability of the combustion process, an unacceptable increase in the thermal load on the engine, etc. The medium (e.g., water or steam) used for heat exchange of 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 ℃ to 170 ℃, and thus may be used directly in the desorber 66 and regenerator 62 assembly, i.e., without the heat pump 80. The recirculated exhaust gas enters the exhaust gas recirculation heat exchanger 32, the temperature of the recirculated exhaust gas is between about 260 ℃ and 400 ℃, and the desired temperature of the medium may be obtained by: by adjusting the flow of medium through the exhaust gas recirculation heat exchanger 32. The exhaust gas recirculation increases the carbon dioxide concentration of the exhaust gas supplied to absorber 42, resulting in lower energy consumption of the desorber 66 and regenerator 62 assembly. Higher exhaust gas recirculation ratios also reduce the magnitude of the flow of exhaust gas to absorber 42, and therefore absorber towers with smaller diameters may be used when using exhaust gas recirculation or increasing the ratio. In addition, the energy extracted in the exhaust gas recirculation heat exchanger 32, which is the excess energy (waste heat) supplied to the desorber 66 and regenerator 62 assembly, significantly reduces the amount of energy that needs to be supplied for operating the desorber 66 and regenerator 62 assembly. The medium from the exhaust gas recirculation heat exchanger 32 has a high temperature compared to the other excess heat flow of the engine (because the medium is heated by the exhaust gas that has not passed through the turbine 6 of the turbocharger 5), and thus can be used directly in the desorber 66 and regenerator 62 assembly.

Fig. 6 shows another embodiment of an engine. In this embodiment, the same or similar structures and features as those previously described or shown are denoted by the same reference numerals as previously used for the sake of simplicity. In this embodiment, the engine and its operation are largely the same as those of the foregoing embodiment, and therefore only the differences from the foregoing embodiment will be described in detail.

This embodiment comprises an optional second scavenging air cooler 14a located downstream of the scavenging air cooler 14. The scavenger air cooler 14 may be configured to produce a flow of heat exchange medium to the desorber 66 and regenerator 62 assembly that is at a temperature sufficient for use directly in the desorber 66 and regenerator 62 assembly. The second scavenging air cooler 14a generates an excess energy flow Q10 in the form of a main medium (e.g. water) flow, the temperature of which excess energy flow Q10 requires: the heat pump may be used to generate the secondary medium stream prior to using the energy stream in the desorber 66 and regenerator 62 assembly. The energy flow Q10 generated in the second scavenging air cooler 14a is transferred to the heat exchanger 80.

In this embodiment, an additional fourth heat exchanger 41 may optionally be provided downstream of the first heat exchanger 40. This additional fourth heat exchanger 41 allows to generate a further surplus energy flow Q11 which is fed to the heat pump 80.

In this embodiment, an additional excess energy stream Q12 may also be generated from the excess heat from the egr scrubber 36 that is supplied to the heat pump 80.

Various aspects and implementations have been described in connection with various embodiments herein. The embodiments may be combined in various ways. Furthermore, other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed subject matter, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. A single processor, controller or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. The reference signs used in the claims shall not be construed as limiting the scope of the claims.

Claims

1. A large two-stroke turbocharged uniflow scavenged internal combustion engine having a crosshead, the engine comprising:

at least one combustion chamber delimited by a cylinder liner (1), a piston (10) and a cylinder head (22), the piston (10) being configured to reciprocate in the cylinder liner (1),

A scavenging port (18) arranged in the cylinder liner (1) for letting in scavenging gas into at least one of the combustion chambers,

A fuel system (30) configured to supply a carbon-based fuel to at least one of the combustion chambers,

At least one of the combustion chambers is configured for combusting the carbon-based fuel, thereby producing an exhaust stream comprising carbon dioxide,

An exhaust gas outlet arranged in the cylinder head (22) and controlled by an exhaust valve (4),

At least one of the combustion chambers is connected to a scavenging gas receiver (2) via the scavenging port (18) and to an exhaust gas receiver (3) via the exhaust gas outlet,

An exhaust system comprising a turbine (6) of a turbocharger system (5) driven by the exhaust gas flow,

An air intake system comprising a compressor (7) of the turbocharger system (5), the compressor (7) being configured to supply pressurized scavenging air to the scavenging gas receiver (2),

An exhaust gas recirculation system configured to recirculate a portion of exhaust gas from at least one of the combustion chambers to the scavenging gas receiver (2), the exhaust gas recirculation system comprising a blower (34), the blower (34) for assisting the flow of the exhaust gas stream towards the scavenging gas receiver (2),

It is characterized in that the method comprises the steps of,

The engine includes: an absorber (42), said absorber (42) being for absorbing carbon dioxide into a solvent, preferably said absorber (42) being an absorber tower,

A desorber (66) and reboiler (62) assembly, the desorber (66) and reboiler (62) assembly for desorbing carbon dioxide from the solvent,

The absorber (42) having a solvent inlet receiving the lean carbon dioxide solvent from the desorber (66) and a solvent outlet supplying the carbon dioxide rich solvent to the desorber (66),

The absorber (42) is arranged to pass the exhaust stream through the absorber (42) to separate carbon dioxide from the exhaust stream by chemically absorbing carbon dioxide into the solvent,

The desorber (66) and reboiler (62) assembly having an inlet for receiving carbon dioxide rich solvent from the absorber (42) and an outlet for supplying carbon dioxide lean solvent to the absorber (42),

The desorber (66) and reboiler (62) assembly is configured for heating the solvent to release carbon dioxide from the solvent, and

2. The engine of claim 1, wherein the heat exchange device comprises an exhaust gas recirculation heat exchanger (32) in the exhaust gas recirculation system, the exhaust gas recirculation heat exchanger (32) being configured for heat exchange between 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 the heat exchange device comprises a heat exchanger configured for heat exchange between the solvent and the heat exchange medium to heat the solvent and cool the heat exchange medium.

3. An engine according to claim 1 or 2, wherein the exhaust gas recirculation system comprises a scrubber (36), preferably the scrubber (36) is a wet scrubber, which scrubber is arranged in the exhaust gas recirculation system downstream of the exhaust gas recirculation heat exchanger (32).

4. An engine according to claim 1, comprising a controller (100) configured to adjust the mass percentage of the recirculated exhaust gas in the scavenging gas to at least 40%, preferably to between 40% and 55%.

5. The engine of claim 4, wherein the controller (100) is configured to control the speed of the blower (75) to adjust the percentage of recirculated exhaust gas in the scavenging gas.

6. A method of operating a large two-stroke turbocharged uniflow scavenged internal combustion engine having a plurality of combustion chambers, the method comprising:

Supplying a carbon-based fuel to the combustion chamber,

Combusting said carbon-based fuel in said combustion chamber, thereby producing an exhaust stream containing carbon dioxide,

Cooling a recirculated exhaust gas flow located in an exhaust gas system using a heat exchange medium flow, thereby heating the heat exchange medium flow,

Chemically absorbing carbon dioxide from a second portion of the exhaust stream into solvent by feeding the carbon dioxide lean solvent stream to an absorber (42), and discharging a carbon dioxide rich solvent stream from the absorber (42) to a desorber (66) and reboiler (62) assembly, and

The solvent is heated by feeding at least a portion of the heated heat exchange medium stream to the desorber (66) and reboiler (62) assembly, thereby regenerating carbon-rich solvent in the desorber (66) and reboiler (62) assembly by heating.

7. The method according to claim 6, the method comprising: at least 40% by mass of the exhaust gas stream is recirculated, preferably at least 40% to 55% by mass of the exhaust gas stream is recirculated.

8. The method according to claim 6 or 7, the method comprising: the speed of a blower (36) located in the exhaust gas recirculation system is controlled to adjust the percentage of recirculated exhaust gas in the pressurized scavenging gas.

9. The method according to claim 6, the method comprising: the gas stream containing carbon dioxide and water vapour or steam produced in the desorber (66) is fed to a separator (69), preferably a separation drum, to separate the carbon dioxide from water vapour or steam to obtain a gas stream mainly containing carbon dioxide and a liquid stream mainly containing water.

10. The method according to claim 9, the method comprising: feeding a gas stream mainly comprising carbon dioxide to a liquefaction unit (70) and liquefying the gas stream mainly comprising carbon dioxide to obtain a liquefied carbon dioxide stream, preferably the method comprises: the liquefied carbon dioxide stream is directed to a liquefied carbon dioxide storage unit (85).

11. The method according to claim 6, the method comprising: heat is extracted from the recirculated exhaust gas in the exhaust gas recirculation system using an exhaust gas recirculation heat exchanger (32) located in the exhaust gas recirculation system, whereby heat is exchanged between the exhaust gas in the exhaust gas recirculation system and a heat exchange medium, whereby the exhaust gas in the exhaust gas recirculation system is cooled and the heat exchange medium is heated, and whereby heat is exchanged between the solvent and the heated heat exchange medium, whereby the solvent is heated and the heat exchange medium is cooled.