Processes and systems for the production of methane

Abstract

A process 100 for the production of methane comprises a) providing a biogas process stream 110 comprising a gaseous mixture of at least CH4 and CO2; b) providing a synthetic methane process stream 120

Description

FIELD

[0001] The present disclosure relates to processes and systems for the production of methane, particularly the production of methane from biogas. BACKGROUND

[0002] Biogas is a gaseous mixture produced from raw waste materials including agricultural waste, manure, municipal waste, plant material, wastewater, and food waste. The production of biogas occurs when the raw waste material undergoes anaerobic digestion and the composition of biogas varies according to the raw materials and processing conditions. Typically, the composition of biogas comprises approximately 50 - 75 mol % methane, 25 - 50 mol % carbon dioxide, 2-8 mol % nitrogen, along with traces of hydrogen sulfide, ammonia, hydrogen and other organic compounds depending on the raw waste material.

[0003] Further processing of the biogas is normally required m order to utilize the methane within the biogas in other applications. Methane obtained from biogas can be referred to as biomethane. There are many potential uses of biomethane including as a substitute for natural gas. However, such applications require biomethane streams having a methane content of, typically greater than 95 mol %. Biomethane can be separated from the biogas mixture using established separation processes, such as membrane separation technology, and / or or pressure swing-adsorption, cryogenic separation, or a combination of these technologies to achieve a desired purity and recovery of biomethane.

[0004] Carbon dioxide obtained from biogas is considered to be biogenic carbon dioxide and can be emitted to the atmosphere or sent to permanent storage (for example, carbon capture and storage (CCS)). However, recently there has been interest in utilizing the carbon dioxide in other processes, or within the biomethane production process. For example, it has been shown that converting the carbon dioxide to methane via a synthetic methanation reaction can enhance the production of biomethane from biogas by increasing the overall yield of methane (including biomethane and synthetic methane) from the biogas.

[0005] One such process involves performing methanation directly to a biogas mixture by reacting the biogas mixture with hydrogen in a methanation reaction. The reaction products are then separated resulting in a biomethane process stream which includes the biomethane from the original biogas and the synthetic methane formed in the reaction. However, methanation of biogas directly can require large reactor sizes, and process streams, and often results in rapid exhaustion of the catalysts within the methanation reactor. The process, therefore, requires frequent catalyst regeneration or replacement. The conversion of carbon dioxide to methane is a reverse reaction in the presence of excess methane which means that the direct methanation of biogas is not considered to be an efficient process in converting carbon dioxide to methane because of the high initial content of methane, i.e. the reaction product streams will comprise a relatively large quantity of unreacted carbon dioxide.

[0006] Another example process involves separating the biogas into carbon dioxide and biomethane, and converting the carbon dioxide to methane via a methanation reactor. For example, according to the process described in EP3666880. However, this process still relies on the venting of carbon dioxide from the biomethane production process.

[0007] Whilst developments have been made in the processes for the production of biomethane and improving the yield of methane by utilizing the carbon dioxide from biogas, further improvements are needed to provide, for example, higher yields of methane, process energy efficiencies and a substantially emissions free biomethane production process. SUMMARY

[0008] The present disclosure provides processes and systems for the production of methane from biogas. The processes and systems disclosed herein include separating biogas into a methane process stream, and carbon dioxide process stream, and converting the carbon dioxide into methane. The process may comprise recycling carbon dioxide within the process until the carbon dioxide is fully converted to methane. The process comprises providing a source of hydrogen for the conversion of the carbon dioxide into methane. The process may further comprise recycling the hydrogen within the process until the hydrogen is fully converted to methane. Unreacted carbon dioxide and hydrogen may be separated in a single separation step, and may be recycled within the process m a single process stream.

[0009] The processes and systems of the present disclosure may be considered to be substantially emissions free process in that substantially of the carbon dioxide from the biogas will be converted to methane. In some examples, the process may be considered be a substantially negative emissions process.

[0010] The processes and systems described herein provide a process for improved yields of methane from biogas whilst also cleverly utilizing waste components and energy streams within the wider biomethane production process. Processes and systems according to the present disclosure provide an integrated solution with minimal or no waste streams.

[0011] According to a first aspect of the present disclosure, there is provided a process for the production of methane, the process comprising: a) providing a biogas process stream comprising a gaseous mixture of at least CH4 and CO2; b) providing a synthetic methane process stream comprising a gaseous mixture of at least CH4, CO2 and H2; c) providing a hydrogen process stream; d) supplying the biogas process stream and the synthetic methane process stream to a separator and separating the components of the biogas process stream and the synthetic methane process stream into a methane product process stream and a combined CO2 / H2 waste process stream; and e) supplying the hydrogen process stream and the combined CO2 / H2 waste process stream to a methanation reactor, and producing the synthetic methane process stream.

[0012] The combined CO2 / H2 waste process stream comprises at least carbon dioxide from the biogas process stream, hydrogen and carbon dioxide from the synthetic methane process stream. The provision of a combined CO2 / H2 waste stream from the separator allows for carbon dioxide from biogas, and unreacted reaction products (carbon dioxide and hydrogen) to be provided to the methanation reaction in a single process stream.

[0013] The process may comprise recycling unreacted carbon dioxide and hydrogen within the process via the synthetic methane product stream, the separator and the combined CO2 / H2 waste process stream until fully converted to methane. The process may therefore be considered to be a substantially emissions free process because substantially all, or approximately all of the carbon dioxide from the biogas is utilised in the production of methane via the methanation reactor.

[0014] The methane product process stream comprises methane from the biogas process stream and methane from the synthetic methane process stream. The methane of the methane product process stream may be considered to be biomethane. The process may comprise separating the components of the biogas process stream and the synthetic methane process stream to obtain a methane product process stream having a composition of at least about 90 mol % methane. The methane product process stream may comprise a composition of at least about 95 mol % methane, or at least about 97 mol % methane. The methane product process stream may comprise about 90 mol % to about 100 mol % methane.

[0015] Substantially all of the carbon dioxide being converted to methane may be considered to encompass all carbon dioxide from the biogas stream less any carbon dioxide remaining within the methane product process stream. The loss of carbon dioxide from the process via the methane product process stream may be considered to be minimal, for example, the methane product process stream may comprise less than about 5 mol % carbon dioxide, or less than about 2 mol % carbon dioxide, or less about 1 mol % carbon dioxide. The methane product process stream may comprise from about 0 to about 5 mol % carbon dioxide. The method may comprise separating the components of the biogas process stream and the synthetic methane process stream to remove CO2 from the biogas process stream and the synthetic methane process stream with up to 99.9 % recovery of carbon dioxide.

[0016] The process comprises using a single separator process to separate methane from the other process components thereby forming the methane product process stream and the combined CO2 / H2 waste process stream. The provision of a single separation process, and the resulting methane product process stream and the single combined CO2 / H2 waste process stream allows for a reduction in capital expenditure on process components, operating costs and is more efficient in allowing the conversion of carbon dioxide to methane.

[0017] The process may further comprise a source of biogas. The process step a) may further comprise producing the biogas process stream from the source of biogas. The source of biogas may be at least one of an anaerobic digester, a plurality of anaerobic digesters, an industrial biogas plant.

[0018] The process may comprise producing hydrogen to provide the hydrogen process stream. The hydrogen may be green hydrogen. For example, the process may comprises an electrolyser. The process step c) may comprises producing the hydrogen process stream via electrolysis.

[0019] The process may further comprise providing electrical power to the electrolyser using a renewable energy source. The renewable energy source may comprise at least one of wave, solar, wind, geothermal, hydro electrical power sources. The hydrogen produced in the process may be considered to be green hydrogen.

[0020] The process step e) may comprise producing a waste water process stream from the methanation reactor. The process may comprise utilising the waste water process stream in the electrolyser. The process may comprise supplying the waste water process stream to the electrolyser. This reduces an external water demand for the hydrogen production process which may contribute to reduced operating costs and reduced environmental impact, in terms of water demand for the process.

[0021] The process may comprise supplying the waste water process stream to a water treatment unit. The process may comprise supplying the waste water process stream to a water treatment unit prior to the waste water being supplied to the electrolyser. The water treatment unit may be configured to produce water process stream with a required quality for the electrolyser. The water treatment unit may comprise a biological waste water treatment process. The use of a biological water treatment within the process may allow for biological waste produced within the water treatment unit to be utilised within the source of biogas.

[0022] The process may comprise supplying waste materials from the water treatment unit to the source of biogas. For example, the waste materials from a biological waste water treatment plant may comprise biological waste sludge which may be suitable for anaerobic digestion to form a biogas.

[0023] The electrolysis of water results in the production of the hydrogen process stream and an O2 waste process stream. The process may further comprise supplying the O2 waste process stream from the electrolyser to the water treatment unit for the production of water. This reduces the operating costs and external oxygen demands of the water treatment unit.

[0024] The process may further comprise de-sulphurising the biogas process stream prior to the separating of step d). When the process comprises de-sulphurising the biogas process stream, the process may also comprise utilising the O2 waste process stream from the electrolyser in the desulphurising process. This reduces the external oxygen demands for the de-sulphurising process.

[0025] The separator may comprise at least one of: a membrane separation unit or a pressure swing-adsorption unit. The membrane separation unit may comprise a membrane stage or multiple membrane stages. For example, the membrane separation unit may comprise at least two membrane stages, or at least three membrane stages.. The membrane separation unit may comprise membranes with methane / carbon dioxide selectivity. For example, the membranes may be configured to be permeable to carbon dioxide The membrane separation unit may be configured to be permeable to CO2 and H: The membrane separation unit may comprise at least one polymeric membrane. The membrane separation unit may comprise at least one inorganic membrane.

[0026] The pressure swing-adsorption unit may comprise multiple adsorption beds. For example, the pressure swing adsorption unit may comprise a two bed adsorption unit with a bed for CO2 and a bed for H2 wherein, the resulting CO2 and H2 streams are combined to form the combined CO2 / H2 process stream.

[0027] The process may comprise combining the biogas process stream and the synthetic methane process stream into a combined separation process inlet stream prior to the separating of step d). The process may comprise conditioning the combined separation process inlet stream to conditions desired for the separator. For example, the process may comprise compressing the combined separation process inlet stream to a separator operating pressure.

[0028] The process may comprise operating the methanation reactor at a pressure of about 1 bar to about 80 bar. The process may comprise operating the methanation reactor at a pressure of about 5 bar to about 50 bar. The process may comprise operating the methanation reactor at a pressure of about 1 bar to about 40 bar, or about 5 bar to 30 bar, or about 10 bar to about 50 bar, about 15 bar to about 20 bar. The process may comprise operating the methanation reactor at a pressure of about 15 bar.

[0029] The process may comprise compressing the combined CO2 / H2 waste process stream prior to supplying the combined CO2 / H2 waste process stream to the methanation reactor.

[0030] The process may comprise supplying the hydrogen process stream to the methanation in a quantity which provides a stoichiometric quantity of hydrogen to the methanation reactor. The quantity of hydrogen process stream required may be calculated based on the combined CO2 / H2 process stream. The process may comprise adjusting the operation of the electrolyser to control the output of the hydrogen process stream. The recycling of hydrogen until fully converted to methane via the methanation reactor may reduce the supply demand for the hydrogen process stream. This may allow for efficiencies and cost savings to be made in the operation of the electrolyser to produce the hydrogen process stream. For example, the use of the electrolyser may be reduced compared to processes which do not allow for recycling of the unreacted hydrogen.

[0031] The electrolyser may be configured to be operated at a higher pressure than the methanation reactor. For example, the method may comprise operating the electrolyser at a pressure of greater than about 1 bar to about 80 bar, or about 5 bar to 50 bar, or about 10 bar to about 50 bar, about 15 bar to about 20 bar. The method may comprise operating the electrolyser at a pressure of greater than about 15 bar. This may improve the efficiency of the hydrolysis reaction whilst also permitting energy savings to be made in other process steps.

[0032] The process may comprise expanding the hydrogen process stream prior to supplying the hydrogen process stream to the methanation reactor, and utilising the energy from the expansion step to provide energy for at least one compressor provided within the process. This allows for energy savings to be made within the process.

[0033] The process may comprise expanding an O2 waste process stream from the electrolyser, and utilising the energy from the expansion step to provide energy for at least one compressor provided within the process. This allows for energy savings to be made within the process.

[0034] The process may comprise utilising heat from at least one compressor provided within the process to heat the methanation reactor. This allows for energy savings to be made within the process. The process may comprise operating the methanation reactor at temperatures of between about 100°C to about 1200°C, or about 500°C to about 1200°C.

[0035] A second aspect of the present disclosure relates to methane produced according to any of the process steps of the first aspect.

[0036] According to a third aspect of the present disclosure, there is provided a system configured to perform any of the process steps of the first aspect.

[0037] The system may comprise a biogas process stream, a synthetic methane process stream, a hydrogen process stream, a separator configured to produce a methane produce process stream and a combined CO2 / H2 waste process stream; and a methanation reactor configured to produce the synthetic methane process stream by methanation of the hydrogen process stream and the combined CO2 / H2 process stream. The system may be arranged to provide for substantially complete conversion of hydrogen and carbon dioxide into methane. The system may be arranged such that losses of carbon dioxide and hydrogen from the process are minimised and substantially all of the carbon dioxide and hydrogen within the process are converted to methane.

[0038] The system may further comprise a source of biogas. For example, the source of biogas may comprise at least one of an anaerobic digestor, a plurality of anaerobic digesters, an industrial bio-gas plant.

[0039] The system may further comprise a source of hydrogen. The system may further comprise a source of green hydrogen. For example, the system may comprise an electrolyser. The electrolyser may be configured to be powered by a source of renewal energy. The system may comprise at least one source of renewable energy. The source of renewable energy may comprise at least one of wave, solar, wind, geothermal, hydro electrical power sources. The system may be arranged to supply waste water from the methanation reaction to the electrolyser.

[0040] The separator may comprise at least one of: a membrane separation unit or a pressure swing-adsorption unit. The membrane separation unit may comprise a membrane stage or multiple membrane stages. The membrane separation unit may comprise membranes with methane / carbon dioxide selectivity. For example, the membranes may be configured to be permeable to carbon dioxide The membrane separation unit may be configured to be permeable to CO2 and H2. The membrane separation unit may comprise at least one polymeric membrane. The membrane separation unit may comprise at least one inorganic membrane.

[0041] The pressure swing-adsorption unit may comprise multiple adsorption beds. For example, the pressure swing adsorption unit may comprise a two bed adsorption unit with a bed for CO2 and a bed for H2 wherein, the resulting CO2 and H2 streams are combined to form the combined CO2 / H2 process stream.

[0042] The system may comprise a waste water treatment unit. For example, a biological waste water treatment unit. The waste water treatment unit may be configured to provide water for the electrolyser at required quality. The waste water treatment unit may be arranged to utilise an oxygen waste process stream from the electrolyser, The system may be arranged to utilise waste products from the water treatment unit in the source of biogas.

[0043] The system may comprise a de-sulphurising unit. The de-sulphurising unit may be arranged to remove sulphur from the biogas process stream. The system may be arranged to utilise an oxygen waste process stream from the electrolyser in the de-sulphurising unit.

[0044] The system may comprise at least one compressor arranged to compress at least one of the biogas process stream, the synthetic methane process stream, the methane product process stream, the combined CO2 / H2 waste process stream.

[0045] The system may be arranged such that heat from the at least one compressor is used to provide heat for the methanation reactor.

[0046] The system may comprise at least one expander arranged to expand at least one of the hydrogen process stream, or an oxygen waste stream from the electrolyser. The system may be arranged to utilise energy from the at least one expander during the expansion process in at least one of the compressors provided within the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The above and other characteristics will become clear from the following description of illustrative, non-restnctive examples, with reference to the attached drawings, in which:

[0048] FIG. 1 is a schematic flow diagram of a methane production process according to the present disclosure; and

[0049] Fig 2 is a schematic flow diagram of a methane production process according to the present disclosure. DETAILED DESCRIPTION

[0050] The present disclosure relates to processes and system for the production of methane from biogas, and in particular the upgrading and optimization of the process to increase yields of biomethane from the biogas (by conversion of CO2 to methane via methanation) whilst reducing or eliminating emissions from the process.

[0051] Figure 1 shows a simplified flow chart outlining the steps of a process 100 for the production of methane 140 according to the present disclosure. A biogas process stream 110 is separated into a methane product process stream 140 and a waste process stream 150 comprising CO2 (and other components of the biogas). The separator 130 can be any known separator in the art which is capable of separating methane and carbon dioxide. For example, single or multistage membranes, and / or pressure swing-adsorption beds. The separator 130 is configured to remove CO2 from the biogas process stream 110 with up to 99.9 % recovery. For example, the separator may comprise a three stage membrane separation using polymeric membranes, or a two stage membrane separation using inorganic membranes configured to have a high performance.

[0052] The waste process stream 150 is supplied to a methanation reactor 160 where it is reacted with a hydrogen process stream 170 to form synthetic methane. The waste process stream 150 is smaller in quantity compared to the biogas process stream, and thus a smaller reactor size is required for the methanation reaction, and the catalytic requirement is reduced (for example, compared to methanation of the biogas process stream directly).

[0053] The process 100 may comprise operating the methanation reactor 160 at a pressure of between about 1 to about 80 bar, preferably about 5 bar to about 50 bar. In some examples, the methanation reactor is operated at about 15 bar. The methane produced and any unreacted hydrogen and carbon dioxide is fed back to the separator 130 as a synthetic methane process stream 120.

[0054] Since the quantity of methane within the waste process stream 150 is negligible, the methanation reaction is highly efficient and progresses in a one direction according to the reaction equation: CO2 + 4H2 CH4 + 2H2O

[0055] The synthetic methane process stream 120 is separated by the separator 130. In some examples, the synthetic methane process stream 120 is combined with the biogas process stream 110 prior to the separation. However, two separate feed streams into the separator are also within the scope of the present disclosure. The separator 130 is configured to remove CO2 from the synthetic methane process stream 120 with up to 99.9 % recovery. The separator 130 is configured to also separate other components, including hydrogen from the biogas process stream 110 and the synthetic methane process stream 120. For example, where membrane separation is used, the membrane is permeable to both carbon dioxide and hydrogen, and where pressure swing-adsorption is used, the separation process can adsorb both carbon dioxide and hydrogen via different adsorption beds. The separator 130 is configured to a have single waste stream 150 which is a combined CO2 / H2 waste process stream 150. The provision of a single separation process 130 and a single combined CO2 / H2 waste process stream 150 is advantageous in that it reduces the capital expenditure requirement of the process 100, as well as operating costs.

[0056] According to the process 100 described in Figure 1, carbon dioxide and hydrogen remain within the process 100 and are recycled through the separator 130 and the methanation reactor 160 until converted into methane. The losses of carbon dioxide from the process 100 via the methane product process stream 140 are considered to be negligible. The process 100 is therefore considered to be substantially emissions free and results in an improved yield of methane from biogas.

[0057] Figure 2 shows a schematic flow diagram for a process 200 for the production of methane according to the present disclosure. The process 200 is similar to the process 100 with further optimizations to provide for negative emissions, alongside utilization of all waste materials and energy streams within the process 200.

[0058] A source of biogas 202 is provided. The source of biogas 202 may be any appropriate anaerobic digestion process or facility. The resulting biogas process stream (1) is optionally de sulphurised in a biological de-sulphurisation process 204. The de-sulphurised biogas process stream (2) is then supplied to a separator 206.

[0059] A synthetic methane process stream (9) is mixed with the biogas process stream (2), and the combined separation process inlet stream (3) is compressed 222 to form a compressed combined separation process inlet stream (4) which is fed to the separator 206. The separator 206 can be any known separator in the art which is capable of separating methane and carbon dioxide. For example, single or multi-stage membranes, and / or pressure swing-adsorption beds. The separator 206 is configured to remove CO2from the biogas process stream 110 with up to 99.9 % selectivity. The separator 206 is configured to also separate other components, including hydrogen from the combined separation process inlet stream (4).

[0060] For example, where membrane separation is used, the membrane is permeable to both carbon dioxide and hydrogen, and where pressure swing-adsorption is used, the separation process can adsorb both carbon dioxide and hydrogen via different adsorption beds. The separator 206 is configured to a have single waste stream (5) which is a combined CO2 / H2 waste process stream (5). The provision of a single separation process 206 and a single combined CO2 / H2 waste process stream (5) is advantageous in that it reduces the capital expenditure requirement of the process, as well as operating costs.

[0061] The combined CO2 / H2 waste process stream (5) is compressed 224 and the compressed combined CO2 / H2 waste process stream (6) is supplied to a methanation reactor 208 where it is reacted with a hydrogen process stream (12) to form the synthetic methane process stream (9). The synthetic methane process stream (9) comprises at least methane, unreacted carbon dioxide and unreacted hydrogen.

[0062] The hydrogen process stream (12) is produced via electrolysis in an electrolyser 212. The electrolyser 212 is operated a higher pressure than the methanation reactor 208. For example, where the methanation reactor operates at about 15 bar, the electrolyser is operated at a pressure of greater than about 15 bar. As such, a high pressure hydrogen process stream (11) can be expanded 234 prior to being supplied as the hydrogen process stream (12) to the methanation reactor 208. The energy 260 generated from this expansion is used to provide energy for compression 224 of the combined CO2 / H2 waste process stream (5). The electrolyser 212 can be powered by a source of renewal energy 216. For example, the source of renewable energy 216 may comprise at least one of wave, solar, wind, geothermal, or hydro electrical power sources.

[0063] A methane product process stream (7) is obtained from the separator 206. The methane produce process stream (7) comprises at least about 90 mol % to about 99 mol % methane which can be compressed 226 for export (8).

[0064] The heat generated from the compression of the inlet and outlet streams 222, 224, 226 of the separator 206 is used to heat 250 the methanation reactor 208. The methanation reaction therefore occurs at high temperatures, for example greater than about 100°C to about 1200°C, or about 500°C to about 1200°C. The process 200 may comprise operating the methanation reactor 208 at a pressure of between about 1 to about 80 bar, preferably about 5 bar to about 50 bar. In some examples, the methanation reactor is operated at about 15 bar. The reaction is considered to be efficient because the quantity of methane in the compressed combined CO2 / H2 waste process stream (6) is negligible. The reaction progresses in a one direction according to the reaction equation: CO2 + 4H2 CH4 + 2H2O

[0065] The hydrogen process stream (12) which is supplied to the methanation reactor 208 is controlled such that carbon dioxide is the limiting component in the methanation reaction. Unreacted hydrogen is recycled to the methanation reactor 208 via the separator 206 until the hydrogen is converted to methane. This reduces the need for the supply of newly produced hydrogen. The hydrogen process stream (12) is controlled through selective operation of the electrolyser 212, providing for efficient and cost effective use of the electrolyser 212 to produce hydrogen in the required quantities for the process.

[0066] The methanation of carbon dioxide in the methanation reactor 208 results m a waste water process stream (10) which can be used as a feed stream for the electrolyser 212.

[0067] The electrolysis of water in the electrolyser 212 results in a high pressure oxygen waste process stream (13). The high pressure oxygen waste process stream (13) can be expanded 232 with the energy 260 from the expansion being utilized in the compression 222 of the combined separation process inlet stream (3).

[0068] The expanded oxygen waste stream (14) can be supplied to a biological water treatment system 214 for the production of water which can be combined with the waste water process stream (10) from the methanation reactor 208 to provide a water feed stream (16) for the electrolyser 212.

[0069] The use of a biological waste water treatment system 214 advantageously allows for waste biological material (sludge) (17) from the biological water treatment system 214 to be used as a feedstock for the source of biogas 202.

[0070] When the biogas process stream (1) is being de-sulphurised, some of the expanded oxygen waste stream (15) can be supplied to the de-sulphurisation process 204.

[0071] The process 200 for the production of methane provides a fully integrated process with minimal or no waste stream. The yield of methane from the source of biogas 202 is optimized and emissions of carbon dioxide are minimized by conversion of the carbon dioxide to methane. The process 200 is considered to be substantially emissions free. The process 200 provides options for the integration of other process units or processes to fully utilise waste streams from the methanation reactor 208, the electrolyser 212 and the waste water treatment unit 214. Integration of hydrogen and carbon dioxide separation into a single separation process with a single combined CO2 / H2 waste process stream allows for a reduction in capital expenditure, and operating costs. Furthermore, the recycling of hydrogen within the process 200 until fully converted to methane allows optimized use of the electrolyser 212. The integration of compressors and expanders within the process 200 allows utilisation of expansion / compression energy within the process, reducing the external energy demands of the process. The utilisation of heat from the compressors to provide heating to the methanation reactor 208 also reduces the external heating demands of the process 200.

[0072] It is to be noted that all ranges described herein are exemplary in nature and include any and all values in between. The terms “substantially,” “approximately” and “about” are defined as being largely but not necessarily wholly what is specified (and include wholly what is specified) as understood by one of ordinary skill in the art. In any disclosed embodiment or example, the term “substantially,” “approximately,” or “about” may be substituted with “within [a percentage] of’ what is specified, where the percentage includes 0.1, 1, 5, or 10 percent, typically 10 percent. For a lower limit this represents the lower limit value minus the percentage of the lower limit and for an upper limit this represents the limit value plus the percentage of the lower limit. Measurements that are reasonably close to the stated measurement deviate from the stated measurement by a reasonably small amount as understood and readily ascertained by individuals having ordinary skill in the relevant arts. Such deviations may be attributable to measurement error, differences in measurement and / or manufacturing equipment calibration, human error in reading and / or setting measurements, minor adjustments made to optimize performance and / or structural parameters in view of differences in measurements associated with other components, particular implementation scenarios, imprecise adjustment and / or manipulation of objects by a person or machine. In the event it is determined that individuals having ordinary skill in the relevant arts would not readily ascertain values for such reasonably small differences, the terms “about” and “approximately” can be understood to mean plus or minus 10% of the stated value.

Claims

What is claimed is:

1. A process for the production of methane, the process comprising:a) providing a biogas process stream comprising a gaseous mixture of at least CH4 and CO2;b) providing a synthetic methane process stream comprising a gaseous mixture of at least CH4, CO2 and H2;c) providing a hydrogen process stream;d) supplying the biogas process stream and the synthetic methane process stream to a separator and separating the components of the biogas process stream and the synthetic methane process stream into a methane product process stream and a combined CO2 / H2 waste process stream; ande) supplying the hydrogen process stream and the combined CO2 / H2 waste process stream to a methanation reactor and producing the synthetic methane process stream.

2. The process of claim 1, comprising recycling unreacted hydrogen and carbon dioxide from the methanation reactor via the synthetic methane product stream, the separator and the combined CO2 / H2 waste process stream until conversion to methane is achieved.

3. The process according to claim 1 or 2, comprising using a single separator process to provide the methane product process stream and the combined CO2 / H2 waste process stream.

4. The process of any preceding claim, wherein the process comprises a source of biogas, and a) comprises producing the biogas process stream from the source of biogas.

5. The process of claim 4, wherein the source of biogas is at least one of an anaerobic digestor, a plurality of anaerobic digesters, an industrial bio-gas plant.

6. The process of any preceding claim, wherein the process comprises an electrolyser, and c) comprises producing the hydrogen process stream via electrolysis.

7. The process of claim 6, further comprising providing electrical power to the electrolyser using a renewable energy source.

8. The process of any of claims 6 or 7, wherein e) comprises producing a waste water process stream from the methanation reactor and supplying the waste water process stream to the electrolyser.

9. The process of any of claims 6 to 8, further comprising supplying an O2 waste process stream from the electrolyser to a water treatment unit.

10. The process of claim 9, wherein the water treatment unit is a biological water treatment unit, and the process comprising supplying any biological waste materials from the water treatment unit to the source of biogas.

11. The process of any preceding claim, further comprising de-sulphurising the biogas process stream prior to the separating of step d).

12. The process of claim 11, when dependent upon claims 6 to 10, comprising utilising an O2 waste process stream from the electrolyser in de-sulphurising the biogas process stream.

13. The process of any preceding claim, wherein the separator comprises at least one of: a membrane separation unit or a pressure swing-adsorption unit.

14. The process of any preceding claim, comprising combining the biogas process stream and the synthetic process stream to form a combined separation process inlet stream prior to the separating of step d), and optionally compressing the combined separation process inlet stream to a separator operating pressure.

15. The process of any preceding claim, comprising operating the methanation reactor at a pressure of about 1 bar to about 80 bar, preferably between about 5 to about 50 bar.

16. The process of any preceding claim, comprising compressing the combined CO2 / H2 waste process stream prior to supplying the combined CO2 / H2 waste process stream to the methanation reactor.

17. The process of any of claims 6 to 16, wherein the electrolyser is configured to be operated at a higher pressure than the methanation reactor.

18. The process of claim 17, comprising expanding the hydrogen process stream prior to supplying the hydrogen process stream to the methanation reactor, and utilising the energy from this expansion step to provide energy for at least one compressor provided within the process.19 The process of claim 17 or 18, comprising expanding an O2 waste process stream from the electrolyser, and utilising the energy from this expansion step to provide energy for at least one compressor provided within the process.

20. The process of any of claims 14 to 19, comprising utilising heat from at least one compressor provided within the process to heat the methanation reactor.

21. Methane produced by process according to any of claims 1 to 20.

22. A system configured to perform process according to claims 1 to 20, the system comprising:a biogas process stream, a synthetic methane process stream, a hydrogen process stream;a separator configured to produce a methane product process stream and a combined CO2 / H2 waste process stream; anda methanation reactor configured to produce the synthetic methane process stream by methanation of the hydrogen process stream and the combined CO2 / H2 process stream;wherein the system is arranged to provide for substantially complete conversion of hydrogen and carbon dioxide into methane.