Thermochemical reactor system

Abstract

An apparatus for carrying out a chemical reaction, which includes a heat source configured to circulating a fluid and a fluidised reactor unit. The reactor unit includes a heat exchanger unit configured to receive the heated fluid to provide heat to the reactor unit, a fluidised bed, and an internally located particle separator.

Description

[0001] THERMOCHEMICAL REACTOR SYSTEM

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a reactor system designed and configured to facilitate thermochemical reactions. More specifically, the reactor facilitates fluidised hydrogen production through the use of renewable energy which provides high temperatures.

[0004] BACKGROUND TO THE INVENTION

[0005] The levelised cost of production of fluidised thermochemical reactions are known to be high, due to the high temperatures involved in the process, one example of a chemical reaction is the production of hydrogen. This particular process increases the cost of production due to the issues discussed below. However, it is appreciated that the invention is applicable to any fluidised thermochemical reaction, not just for the production of hydrogen.

[0006] Hydrogen as an element is highly abundant, however the majority of hydrogen exists as a part of another compound such as water or methane.

[0007] The demand for hydrogen in industry is incredibly high in modern times as it is used in a variety of industrial processes such as metal refining, chemical processes such as ammonia production and methanol products, and food processes such as the manufacture of hydrogenated vegetable oils.

[0008] Furthermore, hydrogen is a clean alternative for powering transportation through the use of hydrogen fuel cells to produce electricity. Hydrogen fuel cells produce electricity through reacting hydrogen with oxygen across an electrochemical cell to produce water, electricity and heat.

[0009] Currently, the production of hydrogen is almost entirely supplied from fossil fuels, with 6% of global natural gas and 2% of global coal going to hydrogen production. As a result, current processes for hydrogen production are responsible for CO2 emissions of around 830 million tonnes of CO2 per year. One of these methods is steam-methane reforming, wherein methane reacts with steam under high pressures and high temperatures (700°C to 1000°C) in the presence of a catalyst to produce hydrogen as well as carbon monoxide and carbon dioxide by-products. This method of production is also highly endothermic. The advantage of this method is that the reaction produces high yields of hydrogen, however the levelized cost of production is high due to the endothermic nature of the reaction.

[0010] ‘Green hydrogen’ is made from using renewable energy sources, as opposed to being produced from fossil fuels. Producing green hydrogen is a method of reducing the impact that hydrogen production currently has on the planet.

[0011] Currently, the most common method of green hydrogen production is the electrolysis of water. This method uses electricity to electrochemically split water into hydrogen and oxygen using an electrolyte and a metal anode and cathode. While this method produces green hydrogen, and zero greenhouse gas emissions, it has a high levelized cost of production due to the use of precious metals and advanced materials, preventing scale up of such a method. In addition to this, electrolysis is also far less efficient than steam-methane reforming.

[0012] Another aspect of hydrogen production which contributes towards the high levelized cost of production is the storage of hydrogen in either a gaseous or liquified state.

[0013] In the gaseous state, hydrogen is commonly compressed under high pressures and stored in tanks. While this is a simple and reliable method for storage, the low energy density by volume means that it requires a large amount of energy to compress and occupies a large volume, making it difficult and expensive to transport while in a gaseous state.

[0014] To store hydrogen under a liquified state, increases the energy density of hydrogen and thus makes it easier to transport. However, storage of liquid hydrogen is complex, as the boiling point of hydrogen is near absolute zero at -253°C, therefore extreme cryogenic conditions are required. The process of achieving such conditions are expensive, highly energy intensive and requires complex insulated storage tanks made from materials that are capable of withstanding such conditions.

[0015] The present invention aims to provide a reactor system which addresses the aforementioned problems by reducing the levelized cost of production for fluidised chemical reactions, such as hydrogen production, through the use of heat from renewable sources.

[0016] STATEMENT OF THE INVENTION

[0017] According to a first aspect of the invention, there is an apparatus for carrying out a chemical reaction, comprising: a heat source configured to circulating a heated fluid; at least one fluidised reactor unit, wherein the reactor unit includes: a heat exchanger unit configured to receive the heated fluid to provide heat to the reactor unit, a fluidised bed, and an internally located particle separator.

[0018] Preferably, the apparatus further comprises a means for recirculating the fluid for reheating.

[0019] Preferably, the heat source further comprises a secondary means of heating a fluid.

[0020] Preferably, the fluidised reactor unit further includes a plurality of baffles housed in an enclosure unit.

[0021] Preferably, the enclosure unit is arranged in a counter-flow heat exchange formation.

[0022] Preferably, the enclosure unit is arranged in a crossflow heat exchange formation.

[0023] Preferably, the baffles are spaced apart and rounded.

[0024] Preferably, the apparatus further comprises a heat recovery system located between the heat source and the reactor unit.

[0025] Preferably, the internal particle separator comprises at least one outlet for the products of a reaction.

[0026] Preferably, the apparatus further comprises a storage means for the products of a reaction. A method of producing hydrogen utilising the apparatus according to any one of the preceding claims, wherein the apparatus facilitates a redox reaction between a fluidised metal and its corresponding fluidised oxide to produce hydrogen, wherein the method comprises the steps of: heating a fluid in the heat source; transferring the heated fluid towards a first reactor unit; reducing the metal oxide with a reducing agent in the first reactor unit to form inter alia the corresponding metal; transferring the reduction product to a second reactor unit; oxidising the metal with an oxidising agent in a second reactor unit to form hydrogen gas and the corresponding metal oxide.

[0027] Preferably, the reducing agent is a mixture of air and hydrogen gas.

[0028] Preferably, the oxidising agent is mixture of steam and air.

[0029] A method of storing and releasing hydrogen gas formed from the method according to claims 11-13, wherein the method comprises the steps of: condensing the hydrogen with air and steam to form liquid water, which can be stored in the product storage means; heating the liquid water to steam; transferring the steam to the second reactor unit to undergo the oxidising step to release hydrogen gas.

[0030] BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Fig. 1 is a diagram illustrating one embodiment of the reactor system in accordance with the invention;

[0032] Fig. 2 is a flow diagram showing the general principles of the reactor system in Figure 1.

[0033] Fig. 3A-D illustrates one embodiment of the thermal energy storage device in accordance with the invention;

[0034] Fig. 4A-D illustrates one embodiment of an individual reactor unit in accordance with the invention;

[0035] Fig. 5 illustrates another embodiment of a thermal storage device in accordance with the invention. Fig. 6 illustrates a further embodiment of the reactor system in accordance with the invention;

[0036] Fig. 7 illustrates the reactor system shown in Fig. 6, showing a detailed depiction of the thermal energy storage device.

[0037] DETAILED DESCRIPTION OF THE INVENTION

[0038] The present invention relates to an apparatus for carrying out fluidised chemical reactions in a reactor unit using a heat source powered by means of renewable energy. Specifically, the apparatus forms a part of a reactor system, which in combination with additional reactor units can be used to carry out chemical reactions on an industrial scale at a reduced levelized cost of production.

[0039] Figures 1 and 2 illustrate an embodiment of the invention wherein concentrated solar power is used to generate high temperatures to carry out a redox reaction between a metal and a metal oxide as a means to produce hydrogen.

[0040] Figure 1 shows a reactor system constructed in accordance with the invention.

[0041] The system comprises a thermal energy storage device 10, capable of heating an incoming fluid 12 from at least one reactor unit 14.

[0042] Fluid 12 enters the device at inlet 16. It is then fluidised with hot solid particles (not shown) in a fluidised bed 18, the fluidised particles are circulated around device 10 until the fluid has reached a desired temperature. The solid particles are then heated in a heat source absorber unit 20, in which thermal energy is sourced from a suitable renewable energy source. The renewable energy source is, for example, but not limited to concentrated solar power or electricity derived from wind or hydropower. Preferably, solid particles used in device 10 have a low heat capacity, such as sand.

[0043] In the event that there are poor weather conditions for renewable energy, a secondary heat exchanger 22 is capable of circulating heated particles between a storage tank 24 and the baffled heat exchanger unit 26, located above fluidised bed 18. Figures 3A-3D illustrates that unit 26 comprises a plurality of channels or baffles 28 housed in an enclosure unit 30. Here, the heated particles are capable of heating fluid 12 up to the desired temperature under pressure in the event of poor weather conditions.

[0044] In a further alternative embodiment (not shown), the thermal energy may be sourced from a suitable clean, non-renewable energy source. Suitable clean, non-renewable energy sources may include, without limitation, nuclear energy.

[0045] In the embodiment shown in the figures, it can be seen that the baffled enclosure unit 30, is arranged in a counter-flow heat exchange formation, wherein, the heated solid particles travel in the opposite direction to fluid 12 to provide a more even temperature gradient and more efficient heat transfer.

[0046] In an alternative embodiment 10B (shown in Figure 5), the baffled enclosure unit 30 is arranged in a crossflow arrangement 30B, wherein the heated solid particles travel perpendicularly to the fluid.

[0047] Fluid 12 is of gaseous nature, preferably air. Alternatively, an inert gas may be used, for example, but not limited to, nitrogen.

[0048] Once the desired temperature has been reached, a particle separator 32 allows for the internal separation of the particles to be recirculated for further use, while the now heated fluid 12 exits the device through outlet 34 into the reactor units 14. Fluid 12 is transferred under pressure to the reactor units 14 through a suitable piping means (not shown, depicted in Figure 1 as a dashed arrow).

[0049] As shown in Figure 3A-3D, channels 28 extend from the base of the heat exchanger 26 to the internal particle separator 32. The channels are generally spaced apart and rounded in nature to aid in flowability and separation of the fluidised particles. The reactor unit 14 generally comprises a fluidised bed 36, a heat exchanger unit 38 which provides heat to the entire unit, and an internal particle separator 40.

[0050] The base of reactor unit 14 is generally polygonal, preferably rectangular or square. In an alternative embodiment (not shown), the base of the reactor unit may be circular.

[0051] Located at the base of the unit 14 is fluidised bed 36, comprising a fluid inlet 42 and a particle inlet 44. The particles become fluidised in the generally heated environment with a reactant fluid (entering through inlet 42), which is gaseous in nature.

[0052] Once fluidised, the particles travel through heat exchanger unit 38, where they undergo the desired reaction under high temperatures. Heat exchanger unit 38 comprises a plurality of channels or baffles 46 housed in an enclosure unit 48.

[0053] As shown in Figure 4A-4D, channels 46 extend from the base of the heat exchanger 38 to the internal particle separator 40. The channels are generally spaced apart and rounded in nature to aid in flowability and separation of the fluidised particles.

[0054] The enclosure unit further comprises an inlet 50 and an outlet 52 and is arranged in a counterflow arrangement (similarly to enclosure unit 26). In an alternative embodiment (not shown), the enclosure unit is arranged in a crossflow arrangement. In a further alternative embodiment (as shown on reactor 14B), the positions of the inlet and outlet (50B and 52B) can be interchanged to accommodate different process requirements.

[0055] The heated fluid 12 enters the enclosure unit via inlet 50, where it transfers heat to the fluidised particles, the used (cold) fluid 12 exits the enclosure unit via outlet 52 wherefrom the fluid can either travel to further reactor units 14 to partake in additional processes or be recirculated back into thermal energy storage device 10 to be reheated to the desired temperature for further reactions. In the embodiment shown in Figure 1, fluid 12 enters a second reactor 14B at inlet 50B for further processing. Fluid 12 then enters device 10 through a suitable pumping means 54, this may be, for example, but not limited to a centrifugal pump. Figure 2 indicates that a heat recovery system 56 (not shown) can be installed between outlet 52 and device 10. The heat recovery system 56 may for example be, but not limited to, an organic Rankine cycle. The electricity produced may be used to power other processes, such as pump 54.

[0056] The reacted fluidised particles are separated within internal particle separator 40. This further comprises a fluid outlet 58 and particle outlet 60, where the reacted particles and the fluids can be transferred respectively to storage or to a further reactor unit 14 for additional processing. As seen in Figure 2, the fluid can be stored in suitable storage means 62.

[0057] It can be appreciated that the transfer of solids and fluids respectively are facilitated through suitable piping means.

[0058] Depending on the nature of the process, more than one reactor unit can be utilised. The embodiment shown in Figures 1 and 2 is a means of producing hydrogen without the need for fossil fuels wherein, two reactor units carry out a redox reaction between a metal and a metal oxide to produce said hydrogen in a circulatory process. The metal and its corresponding oxide may be for example, but not limited to iron and iron(iii) oxide. The process generally proceeds according to the following chemical equations:

[0059] Reduction process : MxOy+ reducing agent -> MxOy.d + ^O2(gas)

[0060] Oxidation process : MxOy.d + cZH2O (gas) -> MxOy+ dH2(gas)

[0061] Wherein, d, is the degree of oxygen defects of the reduced metal oxide (MxOy.d) relative to the oxidised state (MxOy). The oxygen produced in the reduction process may be free oxygen gas or oxygen atoms incorporated in water for example. The reducing agent can for example be, but not limited to hydrogen gas itself.

[0062] Device 10 heats up air 12 to 1500°C using concentrated solar power, which is transferred to reactor unit 14A under 40 mbar pressure. Here a reduction reaction occurs wherein, iron(iii) oxide (Fe2Os) is fluidised in bed 36 with a reactant fluid, comprising of mixture of air and hydrogen gas, to form iron and steam (mixed with air).

[0063] Iron and steam produced from 14A are transferred to reactor unit 14B upon separation at separator 40. As seen in Figure 1 , arrow 64 illustrates the flow of steam / air to fluid inlet 42B, whilst arrow 66 illustrates the transfer of iron to particle inlet 44B. Here an oxidation reaction occurs wherein iron and steam are fluidised within bed 36B with a mixture of steam and air to form iron(iii) oxide and hydrogen gas.

[0064] Air 12 (which is now cooled from the reduction reaction) is also transferred to reactor unit 14B (as depicted by arrow 68), in which it is received by inlet 50B to absorb thermal energy produced from the exothermic oxidation process via heat exchanger unit 38B. Air 12 is recirculated back to device 10 for further heating (as illustrated by arrow 70 in Figure 1) via pump 50.

[0065] Hydrogen gas is separated (via 58B) from the formed iron(iii) oxide which is circulated back to into 14A (via particle outlet 60B, as illustrated by arrow 72 in Figure 1) to restart the production process. The separated hydrogen gas is either directly used for additional processing or transferred to a storage means 62 which comprises a condensing means 74 which condenses hydrogen with waste air and steam to form liquid water.

[0066] Iron and iron(iii) oxide particles can be stored for later use via suitable storage means (not shown).

[0067] When hydrogen gas is required, the desired amount of stored liquid water is converted to steam through a heating means (not shown). Steam along with stored iron particles can then be transferred to reactor unit 14B to undergo the oxidation process to form hydrogen gas and iron(iii) oxide.

[0068] The stored hydrogen can be utilised to start the reduction reaction in reactor unit 14A. Figure 6 refers to another example of a reactor system in accordance with the invention.

[0069] This reactor system comprises a thermal energy storage device 10 and a single reactor unit

[0070] 14. Unit 14 comprises a condenser 74, a water storage means 62 and a steam generating means 76. The steam produced in 76 is transferred to device 10 for use in a fluidised redox reactor located within device 10.

[0071] Figure 7 is the same reactor system shown in Figure 6, showing a more detailed depiction of device 10.

Claims

CLAIMS1. An apparatus for carrying out a chemical reaction, comprising: a heat source configured to circulating a heated fluid; at least one fluidised reactor unit, wherein the reactor unit includes: a heat exchanger unit configured to receive the heated fluid to provide heat to the reactor unit, a fluidised bed, and an internally located particle separator.

2. An apparatus according to claim 1 , wherein the apparatus further comprises a means for recirculating the fluid for reheating.

3. An apparatus according to claim 1 , wherein the heat source further comprises a secondary means of heating a fluid.

4. An apparatus according to claim 1 , wherein the fluidised reactor unit further includes a plurality of baffles housed in an enclosure unit.

5. An apparatus according to claim 4, wherein the enclosure unit is arranged in a counter-flow heat exchange formation.

6. An apparatus according to claim 4, wherein the enclosure unit is arranged in a crossflow heat exchange formation7. An apparatus according to claims 4, 5, or 6, wherein the baffles are spaced apart and rounded.

8. An apparatus according to any of the preceding claims, wherein the apparatus further comprises a heat recovery system located between the heat source and the reactor unit.

9. An apparatus according to any one of the preceding claims, wherein the internal particle separator comprises at least one outlet for the products of a reaction.

10. An apparatus according to any one of the preceding claims, wherein the apparatus further comprises a storage means for the products of a reaction.

11. A method of producing hydrogen utilising the apparatus according to any one of the preceding claims, wherein the apparatus facilitates a redox reaction between a fluidised metal and its corresponding fluidised oxide to produce hydrogen, wherein the method comprises the steps of: heating a fluid in the heat source; transferring the heated fluid towards a first reactor unit; reducing the metal oxide with a reducing agent in the first reactor unit to form inter alia the corresponding metal; transferring the reduction product to a second reactor unit; oxidising the metal with an oxidising agent in a second reactor unit to form hydrogen gas and the corresponding metal oxide.

12. A method of producing hydrogen according to claim 11, wherein the reducing agent is a mixture of air and hydrogen gas.

13. A method of producing hydrogen gas, wherein the oxidising agent is mixture of steam and air.

14. A method of storing and releasing hydrogen gas formed from the method according to claims 11-13, wherein the method comprises the steps of: condensing the hydrogen with air and steam to form liquid water, which can be stored in the product storage means; heating the liquid water to steam; transferring the steam to the second reactor unit to undergo the oxidising step to release hydrogen gas.

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