decarbonisation

Abstract

A system (11) is provided, comprising: a furnace (102); a heat exchanger (104), a gas separator (106) and a first thermochemical reactor (112). The heat exchanger (104) is arranged to receive and cool a flue gas (121 ) comprising carbon dioxide and nitrogen from the furnace (102) thereby producing a cooled flue gas (122). The gas separator (106) is arranged to receive the cooled flue gas (122), and to separate the cooled flue gas (122) into a nitrogen rich gas (124) and a carbon dioxide rich gas (125). The heat exchanger (104) is arranged to heat the nitrogen rich gas (124) and the carbon dioxide rich gas (125). The first thermochemical reactor (112) comprises a thermochemical compound. The first thermochemical reactor (112) is configured to, in a first mode of the system (11), receive the heated carbon dioxide rich gas (126), and to produce carbon monoxide from carbon dioxide in the heated carbon dioxide rich gas (126) by oxidation of the thermochemical compound to form a carbon monoxide rich gas (125).

Description

[0001] DECARBONISATION

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to systems and methods for reducing carbon emission in industrial process, for example in systems that require heat production, or which produce carbon dioxide emissions.

[0004] BACKGROUND

[0005] Many industrial processes produce carbon dioxide, which is a greenhouse gas leading to anthropogenic climate change. In order to address the problem of anthropogenic climate change, it is desirable to reduce the amount of carbon dioxide that is emitted into the atmosphere by industrial processes. Many industrial processes require heat - for example, steel rolling and shaping, forging, heat treatment, and calcination. Heat for such processes is often produced by combustion of hydrocarbons which produces carbon dioxide. The utilisation of combustion to produce heat may be desirable in many circumstances, because existing systems are based on this source of heat. Combustion results in very high heat fluxes coupled into a gas, which can be difficult to achieve with electrical heating. Arc heating, for example, provides heat primarily through radiant flux, and induction heating directly heats a conducting medium by eddy currents. It may be challenging to couple high heat fluxes from an electrical energy source into a gas phase.

[0006] Systems and methods for reducing carbon dioxide emissions from industrial processes are desirable.

[0007] SUMMARY

[0008] According to an aspect of the invention, there is provided a system, comprising: a furnace; a heat exchanger arranged to receive and cool a flue gas comprising carbon dioxide and nitrogen from the furnace thereby producing a cooled flue gas; a gas separator arranged to receive the cooled flue gas, and to separate the cooled flue gas into a nitrogen rich gas and a carbon dioxide rich gas; wherein the heat exchanger is arranged to heat the nitrogen rich gas and the carbon dioxide rich gas; and a first thermochemical reactor comprising a thermochemical compound, the first thermochemical reactor configured to, in a first mode of the system, receive the heated carbon dioxide rich gas, and to produce carbon monoxide from carbon dioxide in the heated carbon dioxide rich gas by oxidation of the thermochemical compound to form a carbon monoxide rich gas.

[0009] The system may further comprise a second thermochemical reactor comprising the thermochemical compound. The second thermochemical reactor may be configured to receive the heated nitrogen rich gas, and to produce oxygen by reduction of the thermochemical compound in the second thermochemical reactor to form an oxygen rich gas.

[0010] The system may be operable in a second mode, in which the first thermochemical reactor is configured to receive the heated nitrogen rich gas, and to produce oxygen by reduction of the thermochemical compound in the first thermochemical reactor to form an oxygen rich gas.

[0011] In the second system mode, the second thermochemical reactor may be configured to receive the heated carbon dioxide rich gas, and to produce carbon monoxide from carbon dioxide in the heated carbon dioxide rich gas by oxidation of the thermochemical compound to form a carbon monoxide rich gas.

[0012] The system may be configured to switch between the first and second mode in order to maintain production of carbon monoxide and oxygen from the first and second thermochemical reactors. Each of the thermochemical reactors may thereby operate a in a reversible cycle of oxidation and reduction, depending on the temperature of the thermochemical reactor.

[0013] The system may be configured to react the oxygen rich gas with the carbon monoxide rich gas to produce heat for the furnace. The reaction between the oxygen rich gas and the carbon monoxide rich gas may take place in a combustor, which may be part of the system. The system comprises may comprise a combustor that is configured to combust the carbon monoxide rich gas to provide heat for the furnace, wherein the combustor is inside the furnace or external to the furnace. The combustor need not use oxygen that is produced from the second thermochemical reactor. Although it is desirable that oxygen produced from the first or second thermochemical reactor (operating in a mode in which the thermochemical compound is reduced) is used for combustion, this is not essential, and atmospheric oxygen may be used instead.

[0014] The system may comprise a further gas separator, configured to produce a purified carbon monoxide gas from the carbon monoxide rich gas. In some embodiments, at least some of the carbon monoxide gas may be captured in a purified form, for example for use in a further industrial process that requires carbon monoxide.

[0015] The system may be arranged to receive the flue gas from a thermal energy plant, for example a waste and / or biomass energy plant.

[0016] The furnace may be a high temperature furnace, arranged to operate at a temperature of at least 800 degrees centigrade; or a medium to low temperature furnace, arranged to operate at a temperature of less than 800 degrees centigrade.

[0017] The thermochemical compound may comprise a metal oxide, perovskite material or a double perovskite material.

[0018] The first thermochemical reactor and optionally the second thermochemical reactor may be configured to receive input electrical energy to heat the thermochemical reactors.

[0019] The system is arranged to receive at least 90% of a net input of energy to the system as electrical energy (e.g. to the first and second thermochemical reactors).

[0020] According to a second aspect, there is provided an industrial method, comprising: cooling a flue gas in a heat exchanger thereby producing a cooled flue gas, the flue gas comprising carbon dioxide and nitrogen; separating the cooled flue gas into a nitrogen rich gas and a carbon dioxide rich gas; heating, with the heat exchanger, the nitrogen rich gas and the carbon dioxide rich gas; producing carbon monoxide from carbon dioxide in the carbon dioxide rich gas by oxidation of a thermochemical compound in a first thermochemical reactor to form a carbon monoxide rich gas.

[0021] The method of the first aspect may be performed using a system according to the first aspect, including any optional features thereof. The method of the first aspect may be performed using any of the embodiments described in the detailed description, including any optional features thereof.

[0022] The method may further comprise producing oxygen by reduction of the thermochemical compound in a second thermochemical reactor to form an oxygen rich gas.

[0023] The method may further comprise producing oxygen in the first thermochemical reactor by reduction of the thermochemical compound in the first thermochemical reactor to form an oxygen rich gas.

[0024] In the second system mode, the second thermochemical reactor may be configured to receive the heated carbon dioxide rich gas, and to produce carbon monoxide from carbon dioxide in the heated carbon dioxide rich gas by oxidation of the thermochemical compound to form a carbon monoxide rich gas.

[0025] The method may comprise alternating between the first and second mode in order to maintain production of carbon monoxide and oxygen from the first and second thermochemical reactors. The method may comprise producing heat for a furnace by reacting the oxygen rich gas with the carbon monoxide rich gas to produce heat for the furnace.

[0026] The method may comprise combusting the carbon monoxide rich gas in a combustor to provide heat for a furnace, wherein the combustor is inside the furnace or external to the furnace.

[0027] The method may further comprise producing a purified carbon monoxide gas from the carbon monoxide rich gas.

[0028] The flue gas may be from a thermal energy plant, such as a waste and / or biomass energy plant.

[0029] The method may comprise providing heat (from combustion of carbon monoxide) to: i) a high temperature furnace, operating at a temperature of at least 800 degrees centigrade; or ii) a medium to low temperature furnace, operating at a temperature of less than 800 degrees centigrade.

[0030] The thermochemical compound may comprise a metal oxide, perovskite material or a double perovskite material.

[0031] The first thermochemical reactor and optionally the second thermochemical reactor may receive renewable input electrical energy to heat the thermochemical reactors.

[0032] The furnace may be used to process (e.g. heat treat) titanium and / or titanium alloys.

[0033] The features of each aspect may be combined, including optional features. Each aspect may further include features taken from any of the example embodiments described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Example embodiments will be described, with reference to the accompanying drawings. These are not intended to be limiting, and are merely exemplary. The scope of the invention should be determined with reference to the accompanying claims.

[0035] Figure 1 is a block diagram of a system for heating a high temperature furnace with reduced carbon dioxide emissions;

[0036] Figure 2 is a block diagram of a system for heating a medium temperature furnace with reduced carbon dioxide emissions; and

[0037] Figure 3 is a block diagram of a system for carbon capture and conversion from a thermal energy plant to reduce carbon dioxide emissions.

[0038] DETAILED DESCRIPTION

[0039] Referring to Figure 1 a system 11 is shown, comprising: furnace 102, heat exchanger 104, gas separator 106, first thermochemical reactor 112 and second thermochemical reactor 114.

[0040] In this example, the furnace 102 may be a high temperature furnace, intended to operate at temperatures in excess of 800 degrees C (e.g. or temperatures of greater than 900 degrees C). The furnace 102 may be employed in any industrial process, for example, metal rolling and shaping (e.g. steel, aluminium, titanium), forging, heat treatment, and calcination etc. The furnace 102 comprises a combustor 103, which receives a carbon monoxide rich gas 128 and an oxygen rich gas 127. The carbon monoxide is burned in with the oxygen rich gas to release heat within the furnace.

[0041] The result of this combustion process is a hot flue gas 121 containing carbon dioxide and a relatively low nitrogen (N2) and carbon monoxide content. Assuming the combustion process is complete, there will be very low amounts of carbon monoxide in the hot flue gas 121 (e.g. less than 400ppm by volume, or less than 100ppm by volume). If the oxygen rich gas 127 is relatively pure oxygen, there may be relatively low amounts of nitrogen gas in the hot flue gas 121 (e.g. less than 50% by volume, or less than 20% by volume). The hot flue gas 121 may comprise at least 50% carbon dioxide, or at least 30% carbon dioxide (by volume). There may be low amounts of hydrogen and water in the hot flue gas (e.g. below 5% or below 1 % by volume or below 0.1 % by volume).

[0042] The heat exchanger 104 receives the hot flue gas 121 and extracts heat therefrom to produce a cooled flue gas 122. The cooled flue gas 122 may be at a temperature of less than 400 degrees C (or less than 250 degrees C), which may make it more straightforward to perform gas separation. The heat exchanger 104 is arranged to provide the heat that is extracted from the hot flue gas 121 to an incoming stream of cool carbon dioxide rich gas 123 and to an incoming stream of cool nitrogen rich gas 124, thereby producing a heated carbon dioxide rich gas 125 and a heated nitrogen rich gas 126.

[0043] In addition to providing cooler gases for the gas separator 106, the heat exchanger 104 re-heats the separated gases 123, 124 that are output from the gas separator 106. This is advantageous for the operation of the first and second thermochemical reactors 112, 114, which will generally require relatively high temperatures (for example, ~700 degrees C or ~800 degrees C, as explained below). The heat exchanger 104 may also be configured as a heat store and / or temperature regulator, so that variations in heat flux received from the hot flue gas 121 and variations in demand for the heated separated gases 123, 124 do not result in variations in the output temperature of the re-heated separated gases. In some embodiments, the heat exchanger 104 may receive electrical energy to provide additional heat to one or both of the gas streams 123, 124.

[0044] The re-heated gases 123, 124 may be at a temperature of approximately 700 degrees C when leaving the heat exchanger 104.

[0045] The gas separator 106 is arranged to receive the cooled flue gas 122, separate the carbon dioxide from the other gases present in the cooled flue gas 122, and output the cool carbon dioxide rich gas 123 (which may comprise at least 90% carbon dioxide with small amounts of nitrogen and carbon monoxide) and the cool nitrogen rich gas 124 (which may comprise at least 90% nitrogen with small amounts of carbon dioxide and carbon monoxide). Any suitable technology may be used for gas separation, for example (but not limited to): sorption, membrane, or chemical acceptor.

[0046] The first thermochemical reactor 112 receives the heated carbon dioxide rich gas 125 and reduces / splits the carbon dioxide to produce a carbon monoxide rich gas 128 by oxidation of a thermochemical compound in the first thermochemical reactor 112. The first thermochemical reactor 112 may be at a temperature of ~800 degrees C. The carbon monoxide rich gas 125 leaving the first thermochemical reactor 112 may be at a temperature of ~ 800 degrees C (e.g. +-25 degrees C)

[0047] A second thermochemical reactor 114 receives the heated nitrogen rich gas 126, and produces oxygen by reduction of the thermochemical compound to produce an oxygen rich gas 127 (comprising oxygen and nitrogen). The second thermochemical reactor may be at a temperature of ~700 degrees C. The nitrogen is provided as an inert carrier / purge gas. In some cases, the heated nitrogen rich gas may comprise trace amounts of hydrogen which may improve the reduction of the thermochemical compound. The oxygen rich gas 127 may comprise at least 20% oxygen by volume, or at least 50% oxygen by volume, with the remaining amount being made up of nitrogen, with trace amounts of hydrogen and carbon monoxide. The oxygen rich gas 127 leaving the second thermochemical reactor 114 may be at a temperature of ~700 degrees C (e.g. +- 25 degrees C).

[0048] The oxygen rich gas 127 and the carbon monoxide rich gas 128 are together combusted in the combustor 103 to produce heat.

[0049] The thermochemical compound in the first and second thermochemical reactor 112 is preferably capable of undergoing a reversible thermochemical cycle. In a first part of the cycle, the thermochemical compound is oxidised and produces carbon monoxide from carbon dioxide, and in a second part of the cycle (at an elevated temperature compared with the first part of the cycle) the thermochemical compound is reduced to produce oxygen gas.

[0050] The system 11 may be configured to cycle the first and second thermochemical reactors between a first and second system mode. In the first system mode, the first thermochemical reactor 112 produces carbon monoxide and the second thermochemical reactor 114 produces oxygen. In the second system mode, the first thermochemical reactor 112 produces oxygen and the second thermochemical reactor 114 produces carbon monoxide.

[0051] The system 11 may comprise electronically operated valves that enable the flow of gases to be re-routed in order to achieve this mode switching and temperature control systems for varying the operating temperature of the thermochemical reactors 112, 114 depending on their mode of operation. For example, the first part of the thermochemical cycle may require temperatures of around 700 degrees C, and the second part of the cycle may require temperatures of 800 degrees C or more.

[0052] The two main classes of materials capable of undergoing a thermochemical cycle to split carbon dioxide into carbon monoxide are simple metal oxides or mixed metal oxides, such as perovskites. Ceria (cerium oxide) is an example of a metal oxide that may be used to split carbon dioxide with good yields; however, it requires high temperatures such as 1400°C for reduction and 900°C for oxidation. Ceria is a non- stoichiometric oxygen carrier meaning that less than one mole of oxygen is released per mole of ceria. Other metal oxides that can be used include the volatile metal oxides and iron oxides. Volatile metal oxides are stoichiometric oxygen carriers and have melting temperatures of the pure metal lower than the reduction temperature of the metal oxide.

[0053] Perovskites are non-stoichiometric mixed metal oxides with an ideal formula of ABOs with A and B being a metallic element. An example perovskite for thermochemical cycles is the La1 -xSrxMnO3 family, which can be reduced at about 1400°C and oxidised at around 900°C with up to ten times higher fuel yields than ceria. Ba2Cao.66Nbi.34-xFex06 (x = 0, 0.34, 0.66 and 1 ) is a double perovskite and can be reduced and made to decompose CO2 at ~800°C making it particularly suitable for undergoing thermochemical cycles to produce carbon monoxide from carbon dioxide.

[0054] Examples of suitable perovskites for carbon dioxide splitting to carbon monoxide in embodiments include those listed below in Table 1 :

[0055] Perovskite Carbon monoxide Reduction / Oxidation yield (pmol / g) temperature

[0056] Lao.6Sro.4Mn03 469 1350 / 1000

[0057] Lao.sCao.sMnOs 525 1400 / 1 100

[0058] Yo.sSro.sMnOs 757 1400 / 900

[0059] Pro.2Sro.8Mn03 637 1400 / 1000

[0060] Smo.sCao.sMnOs 580 1400 / 1 100

[0061] Lao.6Cao.4Mno.8Gao.2O3 515 1350 / 1050

[0062] La0.5Sr0.5Mn0.95Sc0.05O3 545 1400 / 1 100

[0063] Ba2Cao.66Nbo.34Fe06 979 700 / 800

[0064] Table 1: Example perovskites for carbon dioxide splitting

[0065] The thermochemical reaction is reversible, with the thermochemical compound reduced to produce oxygen. In this first example, all of the oxygen produced by the thermochemical reaction is combusted with carbon monoxide to produce heat for the furnace 102.

[0066] Many materials are capable of undergoing a thermochemical cycle, however Ba2Cao.66Nbo.34Fe06 (BCNF1 ) may be used due to its high yields, low reaction temperatures, 100% selectivity towards CO, and a low activation energy of the oxidation reaction. BCNF1 is a double perovskite material. When BCNF1 is reduced at 700°C under nitrogen, oxygen is lost from the crystal structure, forming oxygen vacancies, and releasing oxygen gas where 8 is equal to the degree of non-stoichiometry. The oxidation of BCNF1 occurs at 800°C under carbon dioxide, causing the CO2 to be split to CO, reincorporating the oxygen in the lattice by filling the oxygen vacancies, and reforming the original perovskite.

[0067] Ba2Ca0 66Nb0 34FeO6-s+ SCO2— Ba2Ca0 66Nb0 34FeO6+ SCO (6) oUU c

[0068] This allows the cycle of reduction and oxidation to be repeated, splitting CO2. BCNF1 has been found to convert 10.1 % of CO2 to CO per cycle (mean value over five cycles). Producing 150 m3 / hr of CO would require 5700 kWh of electricity with an 85% efficient electric heater. This plant could produce carbon monoxide at a cost of £0.19 per kg at an electricity price of £0.11 / kWh. At an electricity price of £0.05 (the average US industrial electricity price), carbon monoxide would cost £0.11 per kg.

[0069] Although BCNF1 is particularly promising as a thermochemical compound, any suitable material may be used. The temperatures of the first thermochemical reactor and second thermochemical reactor described herein are relevant to BCNF1 , but different temperatures may be necessary where other thermochemical compounds are used (e.g. as listed in the above table).

[0070] Each of the first and second thermochemical reactors 112, 114 may receive heat from electrical energy 129, which is preferably derived from renewal sources (e.g. wind, solar, pumped-storage, hydro, hydrothermal etc). The electrical energy input to the first and second thermochemical reactors 112, 114 may comprise the majority of the energy provided to the system 11 (e.g. more than 90%).

[0071] The system 11 may be a closed cycle system that essentially converts electrical energy into potential chemical energy in the form of carbon monoxide and then releases the potential chemical energy in the combustor 103 by burning the carbon monoxide for heating of the furnace 102. This releases heat in a manner that is very similar to existing furnace systems that presently rely on fossil fuel. The closed gas cycle means that essentially no carbon dioxide is emitted into the atmosphere, so this approach can be used to eliminate carbon emissions in certain industrial processes that require heating. Figure 1 shows an example in which the furnace 102 is intended to operate at high temperatures, for example over 800 degrees centigrade. In such systems it may be appropriate for combustion to take place within the furnace (and the combustor 103).

[0072] In systems that require lower temperatures within the furnace 102 (for example temperatures below 800 degrees) the high temperature gases produced by combustion may be cooled before they are introduced into the furnace 102, to avoid temperatures in the furnace 102 becoming too high.

[0073] Figure 2 shows an example system 12 which comprises: furnace 102, combustor 103, heat exchanger 104, gas separator 106, first thermochemical reactor 112 and second thermochemical reactor 114. The system 12 works similarly to that shown in Figure 1 , except the combustor 103 is separate from the furnace 102 and exchanges heat arising from combustion of the carbon monoxide with gas streams 130, 131 that are input to the first and second thermochemical reactors 112, 114.

[0074] More specifically, the carbon monoxide rich gas 125 and oxygen rich gas 126 are provided to the combustor 103, which reacts the carbon monoxide with the oxygen to produce hot flue gas 120 comprising carbon dioxide. Some of the heat from the hot flue gas is imparted to the heated carbon dioxide rich gas 125 (from the heat exchanger 104) and to the heated nitrogen rich gas 126 (from the heat exchanger 104) to form further heated carbon dioxide rich gas 130 and further heated nitrogen rich gas 131 respectively. The further heated carbon dioxide rich gas 130 is provided to the first thermochemical reactor 112, and the further heater nitrogen rich gas 131 is provided to the second thermochemical reactor 114.

[0075] The first and second thermochemical reactors 112, 114 produce a carbon monoxide rich gas 128 and oxygen rich gas 127 for combustion in the combustor 103, in the same way as described with reference to the system of Figure 1 . The features relating to the first and second thermochemical reactors 112, 114 described above are equally applicable to this embodiment. The flue gas 121 containing carbon dioxide exiting the furnace 102 is reduced in temperature in this system 12 compared with that in the system 11 , but is still hot enough (e.g. >600 degrees C, or over 400 degrees C) that cooling the flue gas 121 in the heat exchanger 104 enables improved gas separation in the gas separator 106.

[0076] Referring to Figure 3, an example is shown in which a thermal energy plant 101 produces electrical energy 140 by burning fuel to produce a flue gas 121 comprising carbon dioxide. The thermal energy plant 101 may, for example, burn waste or biomass to generate energy, or may bum methane obtained by biodigestion. The energy 140 may be provided to a distribution system (such as a national grid) so that it can be consumed by end-users.

[0077] The system 13 shown in Figure 3 comprises: heat exchanger 104, gas separator 106, first further heat exchanger 104a, second further heat exchanger 104b, first thermochemical reactor 112, second thermochemical reactor 114, further gas separator 106a, and carbon monoxide store 116.

[0078] The flue gas 121 from the thermal energy plant 101 may be at a temperature of 250- 1000 degrees C, and comprises mainly carbon dioxide, water and nitrogen.

[0079] The flue gas 121 is received by a heat exchanger 104, which works in a similar way as described with reference to Figures 1 and 2. The heat exchanger 104 receives the hot flue gas 121 and extracts heat therefrom to produce a cooled flue gas 122. The cooled flue gas 122 may be at a temperature of between 100 and 250 degrees C (e.g. 150 degrees C).

[0080] The gas separator 106 works in a similar way as the gas separator 106 described with reference to Figures 1 and 2. The gas separator 106 receives the cooled flue gas 122 and separates this into cool (<400 degrees C or less than <250 degrees C) streams of carbon dioxide rich gas 123, nitrogen rich gas 124 and water (vapour) 129. The water 129 can be vented to atmosphere. The first and second thermochemical reactors 112, 114 work in a similar same way as described with reference to Figure 2, in that they receive a further heated carbon dioxide rich gas 130 and a further heated nitrogen rich gas 131 respectively. The first and second thermochemical reactors 112, 114 may be cycled between different operating modes to produce carbon monoxide and oxygen, as described above.

[0081] The first further heat exchanger 104a imparts heat from the carbon monoxide rich gas 128 to the heated carbon dioxide rich gas 126.

[0082] The carbon monoxide rich gas 128 that is output from the first thermochemical reactor 112 is cooled by the first further heat exchanger 104a to produce a cool carbon monoxide rich gas 134. The cool carbon monoxide rich gas 134 is received at the further gas separator 106a, which separates any carbon dioxide 135 from the cool carbon monoxide rich gas 134, and provides the separated carbon dioxide 135 back to the first thermochemical reactor 112 (where it will be converted to carbon monoxide).

[0083] The further gas separator 106a thereby produces a stream of purified cool carbon monoxide 136, which is stored in the carbon monoxide store 116. The store 116 may be a gas store, arranged to receive and store the carbon monoxide in gas form. In some embodiments, the carbon monoxide may be stored in liquid form.

[0084] The second further heat exchanger 104b imparts heat from the oxygen rich gas 127 to the heated nitrogen rich gas 125. The oxygen rich gas 127 that is output from the second thermochemical reactor 114 is cooled by the second further heat exchanger 104b to produce a cool oxygen rich gas 133, which can be vented to the atmosphere (or further purified and captured in a store similar to that for the carbon monoxide).

[0085] Each of the heat exchanger 104, first further heat exchanger 104a and second further heat exchanger 104b may be configured as a heat store and / or temperature regulator, so that variations in heat flux and gas flow do not result in variations in the output temperature of the re-heated gases. In some embodiments, at least one (or all) of the heat exchanger 104 and first and second heat exchangers 104a, 104b may receive electrical energy to provide additional heat to gas streams output therefrom.

[0086] Embodiments such as that shown in Figure 3 can be used to reduce carbon dioxide emissions from thermal energy plants 101 by producing carbon monoxide from carbon dioxide. As described with reference to Figures 1 and 2, electrical energy 129 is provided to the first and second thermochemical reactors 112, 114 in order to maintain them at the correct temperature for oxidation and reduction reactions (forming carbon monoxide by oxidation of the thermochemical compound and oxygen by reduction of the thermochemical compound).

[0087] In some embodiments, the furnace may be operable under a range of different conditions (e.g. temperatures). The system may be configured to operate the furnace at temperatures of over 800 degrees C or at temperatures under 800 degrees C (i.e. a multi-furnace may be operable as at least two of: a high temperature furnace, a medium temperature furnace and a low temperature furnace (e.g. in response to a control signal).

[0088] Embodiments of the invention may be particularly useful for processing of titanium alloys, which are prone to hydrogen embrittlement. The use of carbon monoxide as the fuel source for the furnace potentially eliminates hydrogen from the furnace, making titanium processing using a carbon monoxide fuelled furnace potentially advantageous. Similarly, a carbon monoxide fuelled furnace may be attractive for other processes that are sensitive to hydrogen.

[0089] In any of the above examples, the furnace may be operable on a continuous basis (e.g. with a conveyor system). In some embodiments, a batch operated furnace may be used. In batch processing it may be necessary to include thermal storage devices to conserve energy and stabilise the operation of the system.

[0090] In each of the above examples, there may be a need for buffer / storage tanks for any of the gas streams (e.g. carbon monoxide rich gas before entering the combustor). Although specific examples have been described, variations are possible, within the scope of the appended claims.

Claims

CLAIMS1. A system, comprising: a furnace; a heat exchanger arranged to receive and cool a flue gas comprising carbon dioxide and nitrogen from the furnace thereby producing a cooled flue gas; a gas separator arranged to receive the cooled flue gas, and to separate the cooled flue gas into a nitrogen rich gas and a carbon dioxide rich gas; wherein the heat exchanger is arranged to heat the nitrogen rich gas and the carbon dioxide rich gas; and a first thermochemical reactor comprising a thermochemical compound, the first thermochemical reactor configured to, in a first mode of the system, receive the heated carbon dioxide rich gas, and to produce carbon monoxide from carbon dioxide in the heated carbon dioxide rich gas by oxidation of the thermochemical compound to form a carbon monoxide rich gas.

2. The system of claim 1 , further comprising a second thermochemical reactor comprising the thermochemical compound, the second thermochemical reactor configured to receive the heated nitrogen rich gas, and to produce oxygen by reduction of the thermochemical compound in the second thermochemical reactor to form an oxygen rich gas.

3. The system of any preceding claim, wherein the system is operable in a second mode, in which the first thermochemical reactor is configured to receive the heated nitrogen rich gas, and to produce oxygen by reduction of the thermochemical compound in the first thermochemical reactor to form an oxygen rich gas.

4. The system of claim 3, including the subject matter of claim 2, wherein in the second system mode, the second thermochemical reactor is configured to receive the heated carbon dioxide rich gas, and to produce carbon monoxide from carbon dioxide in the heated carbon dioxide rich gas by oxidation of the thermochemical compound to form a carbon monoxide rich gas.

5. The system of claim 3 or 4, wherein the system is configured to switch between the first and second mode in order to maintain production of carbon monoxide and oxygen from the first and second thermochemical reactors.

6. The system of any of claims 2 to 5, wherein the system is configured to react the oxygen rich gas with the carbon monoxide rich gas to produce heat for the furnace.

7. The system of any preceding claim, wherein the system comprises a combustor that is configured to combust the carbon monoxide rich gas to provide heat for the furnace, wherein the combustor is inside the furnace or external to the furnace.

8. The system of any preceding claim, wherein the system comprises a further gas separator, configured to produce a purified carbon monoxide gas from the carbon monoxide rich gas.

9. The system of any preceding claim, wherein the system is arranged to receive the flue gas from a waste and / or biomass energy plant.

10. The system of any of claims 1 to 9, wherein the furnace is a high temperature furnace, arranged to operate at a temperature of at least 800 degrees centigrade; or a medium to low temperature furnace, arranged to operate at a temperature of less than 800 degrees centigrade.

11. The system of any preceding claim, wherein the thermochemical compound comprises a metal oxide, perovskite material or a double perovskite material.

12. The system of any preceding claim, wherein the first thermochemical reactor and optionally the second thermochemical reactor are configured to receive input electrical energy to heat the thermochemical reactors.

13. The system of any preceding claim, wherein the system is arranged to receive at least 90% of a net input of energy to the system as electrical energy.

14. An industrial method, comprising: cooling a flue gas in a heat exchanger thereby producing a cooled flue gas, the flue gas comprising carbon dioxide and nitrogen; separating the cooled flue gas into a nitrogen rich gas and a carbon dioxide rich gas; heating, with the heat exchanger, the nitrogen rich gas and the carbon dioxide rich gas; producing carbon monoxide from carbon dioxide in the carbon dioxide rich gas by oxidation of a thermochemical compound in a first thermochemical reactor to form a carbon monoxide rich gas.

15. The method of claim 14, further comprising producing oxygen by reduction of the thermochemical compound in a second thermochemical reactor to form an oxygen rich gas.

16. The method of claim 14 or 15, further comprising producing oxygen in the first thermochemical reactor by reduction of the thermochemical compound in the first thermochemical reactor to form an oxygen rich gas.

17. The method of claim 16, including the subject matter of claim 2, wherein in the second system mode, the second thermochemical reactor is configured to receive the heated carbon dioxide rich gas, and to produce carbon monoxide from carbon dioxide in the heated carbon dioxide rich gas by oxidation of the thermochemical compound to form a carbon monoxide rich gas.

18. The method of claim 16 or 17, comprising alternating between the first and second mode in order to maintain production of carbon monoxide and oxygen from the first and second thermochemical reactors.

19. The method of any of claims 15 to 18, comprising producing heat for a furnace by reacting the oxygen rich gas with the carbon monoxide rich gas to produce heat for the furnace.

20. The method of any of claims 14 to 19, comprising combusting the carbon monoxide rich gas in a combustor to provide heat for a furnace, wherein the combustor is inside the furnace or external to the furnace.

21. The method of any of claims 14 to 20, further comprising producing a purified carbon monoxide gas from the carbon monoxide rich gas.

22. The method of any of claims 14 to 21 , wherein the flue gas is from a waste and / or biomass energy plant.

23. The method of any of claims 14 to 21 , comprising providing heat to: i) a high temperature furnace, operating at a temperature of at least 800 degrees centigrade; or ii) a medium to low temperature furnace, operating at a temperature of less than 800 degrees centigrade.

24. The method of any of claims 14 to 23, wherein the thermochemical compound comprises a metal oxide, perovskite material or a double perovskite material.

25. The method of any of claims 14 to 24, wherein the first thermochemical reactor and optionally the second thermochemical reactor receive renewable input electrical energy to heat the thermochemical reactors.

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