Methane pyrolysis-based gas turbine system and method

Abstract

The power generation system includes a pyrolysis unit, which comprises a pyrolysis reactor adapted to produce hydrogen from the pyrolysis of hydrocarbons, particularly natural gas, and a heat generator adapted to supply heat to the pyrolysis reactor. A gas turbine engine is further provided, which is supplied with hydrogen produced by the pyrolysis unit. A waste heat recovery system recovers waste heat from the flue gas of the gas turbine engine and delivers the recovered waste heat to the pyrolysis unit.

Description

Technical Field

[0001] This specification discloses an internal combustion engine system using a hydrogen-rich fuel, particularly a gas turbine system, and a method of generating electricity using a gas turbine fueled with a hydrogen-rich fuel.

Background Art

[0002] Climate change caused by the power generation process has become a major concern in recent years. Fossil fuels are still widely used to produce mechanical power and electricity through thermodynamic cycles. However, the combustion of fossil fuels generates large amounts of carbon dioxide, a greenhouse gas thought to cause global warming.

[0003] In recent years, in an attempt to reduce greenhouse gas emissions and mitigate climate change caused by human activities, hydrogen has been considered as an alternative fuel to replace fossil fuels because its energy use does not directly result in carbon dioxide emissions.

[0004] Several technologies for producing hydrogen are currently being studied. In particular, the electrolysis and steam reforming of hydrocarbons such as methane are possible options for hydrogen generation. A further technology for hydrogen production with low greenhouse gas emissions is to decompose natural gas, which mainly consists of hydrocarbons, particularly methane (CH4), into carbon and hydrogen according to the following endothermic reaction: C x H y →xC+(y / 2)H2 (The resulting carbon is in a solid state). The decomposition reaction is usually called "pyrolysis". The obtained hydrogen can be used to supply a fuel cell or as a gaseous fuel for an internal combustion engine such as a gas turbine engine or a reciprocating engine. The solid carbon produced by the pyrolysis of hydrocarbons is a valuable by-product that can be used in several industrial fields.

[0005] Hydrogen production is costly and energy-intensive. For example, hydrogen production by pyrolysis requires a considerable amount of thermal energy. Therefore, it is important that hydrogen-using power generation processes are efficient. Consequently, improving the efficiency of power generation systems that use hydrogen as fuel is useful and welcome in this field. [Overview of the Initiative]

[0006] According to a first aspect, a power generation system using an internal combustion engine, such as a gas turbine engine, is disclosed herein. As used herein, the term “internal combustion engine” refers to a machine in which the combustion of fuel inside the machine generates heat, and that heat is partially converted into mechanical power by the engine. Thus, the term internal combustion engine includes not only reciprocating combustion engines but also, in particular, gas turbine engines.

[0007] In embodiments disclosed herein, the system comprises a pyrolysis unit comprising a pyrolysis reactor adapted to produce hydrogen from the pyrolysis of hydrocarbons, particularly natural gas, and a heat generator adapted to supply heat to the pyrolysis reactor. The system further includes an internal combustion engine, particularly a gas turbine engine, adapted to be supplied with hydrogen produced by the pyrolysis unit. A waste heat recovery unit is further provided, which is configured to recover waste heat from the flue gas of the internal combustion engine and deliver the recovered waste heat to the pyrolysis unit. The waste heat recovered from the flue gas of the internal combustion engine reduces the amount of power required for the pyrolysis of hydrocarbon fuels.

[0008] Further features and embodiments of the system described herein are outlined below and are set forth in the attached "Claims".

[0009] In a further embodiment, a method is disclosed herein that includes the step of processing a flow of hydrocarbons in a pyrolysis unit to produce hydrogen and solid carbon therefrom, wherein the pyrolysis unit includes a pyrolysis reactor and a heat generator. The method further includes the step of fueling an internal combustion engine, such as a gas turbine engine, with hydrogen to generate mechanical power. The method further includes the steps of recovering waste heat from the flue gas of the internal combustion engine and supplying the recovered waste heat to a pyrolysis unit.

[0010] Further advantageous features and embodiments of the method disclosed herein are outlined below and described in the attached "Claims". [Brief explanation of the drawing]

[0011] Here, we will briefly refer to the attached diagram. [Figure 1] This is a schematic diagram of the power generation system of the present disclosure in one embodiment. [Figure 2] A schematic diagram of the power generation system of the present disclosure in a further embodiment is shown. [Figure 3] This is also a schematic diagram of the power generation system of the present disclosure in a further embodiment. [Figure 4] This is a flowchart summarizing one embodiment of the method described herein. [Modes for carrying out the invention]

[0012] This specification specifically refers to the use of natural gas and / or methane. However, it should be understood that in other embodiments, the sources of carbon and hydrogen supplied to the pyrolysis reactor may be different hydrocarbons or mixtures of hydrocarbons. The term "hydrocarbon" as used herein may also include mixtures or blends of different hydrocarbons.

[0013] This specification specifically refers to gas turbine engines, but does not exclude systems using other internal combustion engines, such as reciprocating combustion engines.

[0014] To improve the efficiency of the power generation system and reduce its carbon dioxide emissions, the system comprises a gas turbine engine and a hydrocarbon pyrolysis unit. A hydrocarbon feedstock, such as natural gas, is converted at least partially into hydrogen and solid carbon by the pyrolysis unit. The gas turbine engine generates power using hydrogen, or a mixture of hydrogen and unconverted hydrocarbons, as fuel. Waste heat from the gas turbine engine is at least partially utilized in the pyrolysis unit to reduce the amount of heat output required for the pyrolysis process.

[0015] Referring here to the drawings, Figure 1 shows a first embodiment of a power generation system according to the present disclosure. The system as a whole is denoted by reference numeral 1 and includes an upper thermodynamic cycle 2, i.e., a high-temperature thermodynamic cycle, and a lower thermodynamic cycle 4, i.e., a low-temperature thermodynamic cycle. In some embodiments, the lower thermodynamic cycle 4 may be omitted. The terms “high temperature” and “low temperature” are relative terms indicating that the upper thermodynamic cycle operates at a higher temperature than the lower thermodynamic cycle.

[0016] The upper thermodynamic cycle 2 may include a Brayton cycle. In some embodiments, the upper thermodynamic cycle 2 includes a gas turbine engine 3, a pyrolysis unit 5, and a waste heat recovery unit 7.

[0017] The pyrolysis unit 5 may include a pyrolysis reactor 5.1 and a heat generator. In some examples, the heat generator includes a furnace 5.2. The gas turbine engine 3 includes a compressor section 3.1, a combustor 3.2, and a turbine section 3.3. The gas turbine engine 3 further includes an output shaft 3.4 drivably coupled to a load driven by the power generated by the gas turbine engine 3. In the embodiment of Figure 1, the load includes a generator 13 that converts the mechanical power generated by the gas turbine engine 3 into electricity. The generator 13 may be electrically coupled to a power distribution network 15. In Figure 1, the gas turbine engine 3 is schematically shown as a single-shaft turbine. However, it should be understood that different gas turbine engines can be used, such as gas turbine engines having two or more shafts. The gas turbine engine may be, for example, a heavy-duty gas turbine engine or an aerospace-converted gas turbine engine.

[0018] The pyrolysis unit 1 is adapted to convert fossil fuels into hydrogen FF and solid carbon C, at least partially. The hydrogen is used to fuel the gas turbine engine 3, while the solid carbon C is collected in 17 and can be used as a valuable byproduct of the power generation process carried out by the power generation system 1.

[0019] In this specification, the fossil fuel for power generation system 1 refers specifically to natural gas, and more specifically to methane (CH4). However, it should be understood that other hydrocarbons or hydrocarbon blends can be used instead of natural gas, or in combination with it. Natural gas is particularly useful because gas turbine engine 3 can be fueled by a mixture of natural gas and hydrogen produced by the partial pyrolysis of natural gas. Therefore, the decomposition of natural gas in pyrolysis unit 5 may be partial.

[0020] Natural gas is supplied to the pyrolysis reactor 5.1 through a natural gas supply line 19 that extends through the low-temperature side 21.1 of the first heat exchanger 21 of the waste heat recovery device 7. The first heat exchanger 21 is characterized by a first waste heat recovery heat exchanger adapted to recover waste heat from the flue gas of the gas turbine engine 3. The flue gas from the gas turbine engine 3 flows along a flue gas flow path 23 that extends through the high-temperature side 21.2 of the first heat exchanger 21, and the high-temperature waste heat contained in the flue gas is recovered by the first heat exchanger 21 and used to heat the natural gas supplied to the pyrolysis reactor 5.1 through the natural gas supply line 19.

[0021] In some embodiments including the lower thermodynamic cycle 4, a splitter 25 is arranged along the flue gas flow path 23 downstream of the first heat exchanger 21. The flue gas flow is split by the splitter 25 and partially deflected towards the lower thermodynamic cycle 4 to deliver waste heat thereto. Downstream of the splitter 25, the flue gas flow path 23 extends to the furnace 5.2. The flue gas from the gas turbine engine 3 contains residual oxygen O2 that is used as an oxidant in the furnace 5.2. Fuel is supplied to the furnace through a fuel inlet 27. The furnace can use natural gas or another fuel as fuel.

[0022] The combustion gas from the furnace 5.2 contains carbon dioxide CO2 and is processed by a carbon dioxide recovery unit 29 to at least partially remove carbon dioxide from the combustion gas. The CO2-lean combustion gas, i.e., the combustion gas from which CO2 has been completely or partially removed, is discharged into the environment through a chimney 31. The compressed carbon dioxide is sent through a duct 33 to a storage device or pipeline (not shown), etc.

[0023] In the embodiment of FIG. 1, the bottom thermodynamic cycle 4 can include a steam Rankine cycle, an organic Rankine cycle (ORC), etc. In the schematic diagram of FIG. 1, the bottom thermodynamic cycle 4 includes a process fluid heater 41, an expander, such as a steam turbine 43, a condenser 45, and a pump 47. The flue gas bypassed by the splitter 25 and flowing through the bypass line 49 transfers low-temperature waste heat to the process fluid of the bottom thermodynamic cycle 4 in the process fluid heater 41. When the bottom thermodynamic cycle is a steam Rankine cycle, the process fluid is evaporated water, and the steam generated in the heater 41 expands in the steam turbine 43. The turbine shaft 43.1 is drivingly coupled to load the steam turbine 43. In the embodiment of FIG. 1, the load includes a generator 51 electrically connected to the power distribution network 15. In the schematic diagram of FIG. 1, the bottom cycle is represented as a simplified steam Rankine cycle. It should be understood that more complex bottom cycles, including, for example, a regenerative cycle, can be used.

[0024] The flue gas from the heater 41 can be discharged into the atmosphere through the chimney 50. In other embodiments, the flue gas from the heater 41 can be processed through a carbon recovery unit 29 before being released into the environment. This can be advantageous, for example, when the fuel used in the gas turbine engine 3 includes a mixture of hydrogen and hydrocarbons.

[0025] The power generation system 1 described above operates as follows. Natural gas is supplied through the first heat exchanger 21 and preheated by the waste heat from the gas turbine engine 3. The preheated natural gas is delivered to the pyrolysis reactor 5.1. Since the natural gas to be decomposed is preheated, less thermal output is required to activate and assist the decomposition reaction in the pyrolysis reactor 5.1 to produce hydrogen and solid carbon required from the furnace 5.2.

[0026] The hydrogen produced by the decomposition of natural gas (mainly methane) is supplied to the gas turbine engine 3, where it is burned in the combustor 3.2, where the hydrogen is mixed with compressed air and burned. In some embodiments, as described above, the thermal decomposition of natural gas may be incomplete; that is, the entire flow rate of natural gas is not converted into solid carbon and hydrogen. The remaining natural gas is supplied to the gas turbine engine 3 as a mixture with hydrogen.

[0027] The pyrolysis of natural gas removes carbon from the gas supplied as fuel to the gas turbine engine, ensuring that the flue gas from the gas turbine engine 3 does not contain carbon dioxide. Even if only a portion of the natural gas is pyrolyzed, the beneficial effect of reducing the carbon dioxide content in the flue gas is still achieved. In effect, the carbon contained in the natural gas is removed (at least partially) in solid form (in 17) and can be used as a valuable component in other industrial processes, rather than being released into the atmosphere in the form of carbon dioxide after oxidation in the combustor 3.2.

[0028] The thermal energy (in the form of waste heat) contained in the flue gas from the gas turbine engine 3 is used to preheat the natural gas in the natural gas supply line 19, as described above.

[0029] The flue gas exiting the first heat exchanger 21 is still hot enough to provide thermal energy to the lower thermodynamic cycle 4, in which the lower-temperature waste heat is partially converted into additional mechanical power available on the expander or the output shaft 43.1 of the steam turbine 43.

[0030] Flue gas that is not diverted to the lower thermodynamic cycle 4 by splitter 25 introduces thermal energy into furnace 5.2.

[0031] Continuing with reference to Figure 1, Figure 2 shows a further embodiment of the power generation system according to the present disclosure, in which the same reference numerals as in Figure 1 are used to indicate the same or equivalent parts, elements or components of the power generation system, which are again not described in detail.

[0032] The embodiment in Figure 2 differs from the embodiment in Figure 1 mainly in that a splitter 25 is not provided along the flue gas flow path 23 and the flue gas flow path 23 does not extend to the furnace 5.2. Unlike Figure 1, in Figure 2, the entire flue gas flow passes through the high-temperature side of the process fluid heater 41 and is released at the chimney 50 or processed through the carbon dioxide capture unit 29.

[0033] In the embodiment shown in Figure 2, a second heat exchanger 22 is provided along the flue gas flow path 23. The second heat exchanger 22 is a second waste heat recovery heat exchanger adapted to recover waste heat from the flue gas of the gas turbine engine 3. Specifically, the second heat exchanger 22 includes a high-temperature side 22.2 through which the flue gas flows, exchanging heat with the low-temperature side 22.1 of the second heat exchanger 22. The oxidizer flow for the furnace 5.2 flows through the low-temperature side 22.1 and is preheated by the low-temperature waste heat released by the flue gas flowing through the high-temperature side 22.2 of the second heat exchanger 22.

[0034] Therefore, similar to the embodiment in Figure 1, in the embodiment in Figure 2, some of the waste heat contained in the flue gas from the gas turbine engine 3 is delivered to the furnace 5.2, reducing the amount of thermal energy demanded by the furnace 5.2. However, in Figure 1, the residual flue gas flowing into the furnace 5.2 contains waste heat, whereas in the embodiment in Figure 2, the entire flue gas flow passes through the process gas heater 41 to heat or vaporize the process fluid of the lower thermodynamic cycle 4, but before that, some of the thermal energy contained therein is removed in the second heat exchanger 22.

[0035] In the embodiment shown in Figure 2, the first heat exchanger 21 and the second heat exchanger 22 are arranged in series with the second heat exchanger 22 located downstream of the first heat exchanger 21. The reverse arrangement, in which the first heat exchanger 21 is located downstream of the second heat exchanger 22 with respect to the direction of flue gas flow, is also not ruled out.

[0036] Referring again to Figures 1 and 2, Figure 3 shows a further embodiment of the power generation system 1, where the same reference numerals as in Figures 1 and 2 are used to indicate the same or equivalent parts, elements, or components of the power generation system, which are again not described in detail.

[0037] The embodiment in Figure 3 differs from the embodiment in Figure 2 mainly in that the first waste heat recovery heat exchanger 21 and the second waste heat recovery heat exchanger 22 are arranged in parallel rather than in series. Therefore, waste heat is recovered at substantially the same temperature in the first heat exchanger 21 and the second heat exchanger 22 to preheat the natural gas and oxidizer, respectively. The flue gas flow from the gas turbine engine 3 is split in the splitter 54 into a first flow that is led through the first heat exchanger 21 and a second flow that is led through the second heat exchanger 23.

[0038] Figure 4 shows a flowchart summarizing a method for generating electricity using the system described above. The method includes a first step (101) of processing a flow of hydrocarbons in a pyrolysis unit to produce hydrogen and solid carbon therefrom; a second step (102) of fueling a gas turbine engine with the hydrogen to generate mechanical power; a third step (103) of recovering waste heat from the flue gas of the gas turbine engine; and a fourth step (104) of supplying the recovered waste heat to the pyrolysis unit.

[0039] In the embodiment described above, if the thermal decomposition of the hydrocarbon fuel is not complete, the flue gas from the gas turbine engine 3 may contain residual hydrocarbon species, such as residual carbon dioxide produced by the combustion of methane. In such cases, the flue gas can be diverted to a carbon dioxide capture unit 29 to improve carbon capture. This is illustrated by a dashed connecting line 52 that fluidly connects the chimney 50 to the carbon dioxide capture unit 29.

[0040] Exemplary embodiments are disclosed above and shown in the accompanying drawings. Those skilled in the art will understand that various modifications, omissions, and additions may be made to those specifically disclosed herein without departing from the scope of the invention as defined in the following claims.

Claims

1. It is a power generation system, A pyrolysis unit comprising a pyrolysis reactor adapted to produce hydrogen from the pyrolysis of hydrocarbons, particularly natural gas, and a heat generator adapted to supply heat to the pyrolysis reactor, An internal combustion engine adapted to be supplied with hydrogen produced by the pyrolysis unit, A waste heat recovery device adapted to recover waste heat from flue gas discharged by the internal combustion engine and deliver the recovered waste heat to the pyrolysis unit, A power generation system equipped with the following features.

2. The power generation system according to claim 1, wherein the internal combustion engine includes a gas turbine engine.

3. The power generation system according to claim 1 or 2, wherein the waste heat recovery device comprises a first heat exchanger adapted to transfer waste heat from the flue gas to the hydrocarbon flow supplied to the pyrolysis reactor.

4. The power generation system according to any one of claims 1 to 3, wherein the waste heat recovery device is adapted to supply waste heat to the heat generator.

5. The power generation system according to any one of claims 1 to 4, wherein the heat generator comprises a furnace adapted to generate heat for the pyrolysis reactor by combustion of fuel.

6. The generator system according to claim 5, wherein the fuel comprises a hydrocarbon, preferably natural gas.

7. The power generation system according to claim 5 or 6, further comprising a waste heat recovery device and a flue gas supply line adapted to supply oxygen-containing flue gas from the internal combustion engine to the furnace.

8. The aforementioned waste heat recovery device is The power generation system according to any one of claims 5, 6, or 7, further comprising a second heat exchanger adapted to transfer waste heat from the flue gas to the oxidizer flow supplied to the furnace.

9. The power generation system according to claim 8, wherein, if claim 8 is at least dependent on claim 2, the first heat exchanger and the second heat exchanger are arranged in series along a flue gas discharge path.

10. The power generation system according to claim 9, wherein the second heat exchanger is located downstream of the first heat exchanger with respect to the direction of the flow of the flue gas in the flue gas discharge path.

11. The power generation system according to claim 8, wherein the first heat exchanger and the second heat exchanger are arranged in parallel and each is adapted to handle a portion of the total flue gas flow.

12. The power generation system according to any one of claims 8 to 11, wherein the oxidizing agent flow is an oxygen flow.

13. The power generation system according to any one of claims 5 to 12, further comprising a carbon dioxide capture unit adapted to receive exhaust gas from the furnace and capture carbon dioxide therefrom.

14. The power generation system according to any one of claims 1 to 13, comprising a lower thermodynamic cycle adapted to convert waste heat from the flue gas into mechanical power.

15. The power generation system according to claim 13, wherein the lower thermodynamic cycle is adapted to recover waste heat downstream of the waste heat recovery device at a temperature lower than the temperature of the waste heat supplied to the pyrolysis unit.

16. The power generation system according to claim 15, wherein the lower thermodynamic cycle has a process fluid heater adapted to remove waste heat from the flue gas at a temperature lower than the temperature at which the waste heat is delivered to the pyrolysis unit.

17. The power generation system according to claim 16, wherein claim 16 is at least dependent on claim 2, comprising a main flue gas flow path extending from the internal combustion engine to the heat generator, the first heat exchanger being arranged along the flue gas flow path, and downstream of the first heat exchanger, a secondary flue gas flow path being diverted from the main flue gas flow path, the secondary flue gas flow path being adapted to deliver a portion of the flue gas flow to the lower thermodynamic cycle.

18. If claim 16 is at least dependent on claim 7, the power generation system according to claim 16, comprising a flue gas passage extending from the internal combustion engine through the first heat exchanger and the second heat exchanger, wherein downstream of the second heat exchanger, the flue gas passage extends through the process fluid heater to transmit low-temperature waste heat to the lower thermodynamic cycle.

19. A power generation method comprising the steps of processing a flow of hydrocarbons in a pyrolysis unit to produce hydrogen and solid carbon therefrom, wherein the pyrolysis unit comprises a pyrolysis reactor and a heat generator, The steps include supplying the hydrogen fuel to an internal combustion engine to generate mechanical power, The steps include recovering waste heat from flue gas discharged by the internal combustion engine, The steps include supplying the recovered waste heat to the pyrolysis unit, A method of generating electricity, including

20. The power generation method according to claim 19, wherein the internal combustion engine is a gas turbine engine.

21. The power generation method according to claim 19 or 20, wherein the step of supplying the recovered waste heat to the pyrolysis unit includes a step of preheating the hydrocarbon flow supplied to the pyrolysis reactor by heat exchange with the flue gas.

22. The power generation method according to any one of claims 19 to 21, wherein the step of supplying the recovered waste heat to the pyrolysis unit includes the step of supplying the recovered waste heat to the heat generator.

23. The power generation method according to claim 22, wherein the heat generator includes a furnace, and further comprises the step of generating heat by combustion of a fuel and an oxidizer in the furnace.

24. The power generation method according to claim 23, wherein the step of supplying the recovered waste heat to the heat generator includes the step of supplying oxygen-containing flue gas to the furnace as an oxidizing agent.

25. The power generation method according to claim 23, wherein the step of supplying the recovered waste heat to the heat generator includes a step of preheating the oxidizer supplied to the furnace by heat exchange with the flue gas.

26. The power generation method according to claim 25, wherein, if claim 25 is at least dependent on claim 21, the step of preheating the hydrocarbon flow is performed at a flue gas temperature higher than the step of preheating the oxidizer.

27. The power generation method according to any one of claims 23 to 26, further comprising the step of capturing carbon dioxide from the combustion gas of the furnace.

28. The power generation method according to any one of claims 19 to 27, further comprising the step of supplying waste heat from the flue gas to the lower thermodynamic cycle.

29. The power generation method according to claim 28, wherein the waste heat supplied to the lower thermodynamic cycle is at a lower temperature than the temperature of the recovered waste heat supplied to the pyrolysis unit.

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