Process For The Production Of Hydrogen With Total Recovery Of Co2 And Recycling Of Unconverted Methane (IFP Energies Nouvelles)

CATEGORY: HYDROGEN
Process For The Production Of Hydrogen With Total Recovery Of Co2 And Recycling Of Unconverted Methane (IFP Energies Nouvelles)
United States Patent Application 20160264417
Bouillon; Pierre Antoine ;   Et Al.   September 15, 2016
Assignee: IFP Energies Nouvelles
Abstract
This invention relates to a process for the production of hydrogen from a hydrocarbon feedstock and steam comprising: A stage for the production of a synthesis gas in a unit for the steam-reforming of the hydrocarbon feedstock, A stage for shift conversion with steam of the synthesis gas that is obtained in the preceding stage producing a hydrogen stream that contains methane and carbon dioxide, A stage for recovering carbon dioxide and methane, present in the stream that is obtained in the shift conversion stage, in the form of hydrates that produce a stream of pure hydrogen, A stage for regeneration of methane, A stage for recycling methane to steam reforming.
Inventors: BOUILLON; Pierre Antoine; (LYON, FR) ; HUYGHE; Raphael; (Saint Andeol Le Chateau, FR) ;
Description
[0001] This invention relates to the field of the production of hydrogen, and more particularly a process for the production of hydrogen with total recovery of CO.sub.2 and recycling of unconverted methane.
[0002] Global warming, observed since the industrial era according to the international scientific community, could dramatically modify the climates and ecosystems of numerous regions of the globe. Emission of greenhouse gas and especially carbon dioxide (CO.sub.2) seems to be responsible for this warming.
[0003] Fossil energy (natural gas, petroleum, carbon) constitutes a large part of the energy that is readily available on the planet. This fossil energy, however, when it is used, produces CO.sub.2 (generally during a combustion stage) and is thus implicated in global warming.
[0004] One of the solutions that is recommended for fighting against the global warming by greenhouse gas emissions is to recover the CO.sub.2 that is produced and then to store it under ground. Several methods are explored, including recovery by precombustion that consists in converting fossil energy into hydrogen with recovery and storage of the CO.sub.2 that is co-produced. Hydrogen, an energy vector, can then be burned freely with no greenhouse gas emissions.
[0005] There are currently several means for producing hydrogen industrially--and thus electricity--starting from fossil energy. The most widely used means is the steam reforming of natural gas that is implemented in a furnace (in English: SMR: Steam Methane Reforming) that offers the advantage of using a feedstock that has a high hydrogen/carbon ratio, taking into account the high methane content in its composition. In a simplified way, the SMR catalytic reaction can be written in the following manner:
CH.sub.4+H.sub.2OCO+3H.sub.2
[0006] This very endothermic reaction is balanced. It is promoted by high temperatures and is carried out in general in a furnace that is heated by a fuel such as natural gas. The SMR unit is conventionally followed by a shift conversion stage (WGS: Water Gas Shift) that makes it possible to maximize the production of hydrogen by the following reaction:
CO+H.sub.2OCO.sub.2+H.sub.2
[0007] When it is necessary to recover CO.sub.2 for the purpose of storing it, it is then possible to use an amine washing unit (activated MDEA, for example) that extracts the CO.sub.2 from the rich hydrogen stream, which is then sent, for example, into a gas turbine for the purpose of producing electricity, while the CO.sub.2 is compressed and sent back under ground.
[0008] One major drawback in this type of process resides in the fact that the SMR reaction is not complete. The hydrogen-rich stream that is produced contains a large quantity of methane that is not converted in the conversion state to vapor and that is not recovered during amine washing. The resultant hydrogen containing methane therefore emits CO.sub.2 when it is burned. The objective of CO.sub.2 recovery is therefore not completely achieved by such a process, and only between 75% and 80% maximum of CO.sub.2 is recovered.
[0009] An improvement to this technique consists in adding a pressure-modulated molecular-sieve adsorption unit (PSA) to improve impurities. At this time, two streams are obtained: a typically 99.99% pure hydrogen stream, and a stream of impurities containing at least 20% hydrogen. This low-pressure stream is sent into the burners of the steam-reforming furnace, which reduces the natural gas that is necessary for the furnace, and therefore the production of CO.sub.2. However, this process offers major drawbacks, and in particular: [0010] The purging of the PSA unit that contains methane is at low pressure and is therefore difficult to recycle economically in the SMR process because its recompression would consume too much energy and would be too expensive. [0011] When the PSA purge stream is used in the burners of the furnace for steam-reforming natural gas, the CO.sub.2 that is generated by the combustion of methane that is present in the PSA purge stream is not recovered. [0012] A significant portion of the hydrogen is lost with the purging of the PSA unit.
[0013] This process therefore makes it possible to obtain pure hydrogen (free of methane), but it does not make it possible to recover the CO.sub.2 that will be emitted during the combustion of the separated methane.
[0014] Another process for the production of hydrogen combined with the process for the production of electricity (called the Hygensys.RTM. process) is also known. This process that is based on the same one as that previously described proposes burning--in a suitable combustion chamber, replacing the PSA unit--the stream of hydrogen that is produced so as to produce electricity without CO.sub.2 emissions. The hot gases that are obtained from the combustion are used via an exchanger reactor (Hygensys.RTM.) to provide the energy that is necessary to the steam-reforming reaction. The Hygerisys.RTM. process implements the reaction for steam-reforming the natural gas in a compact reactor-exchanger that is heated by convection and integrated with a gas turbine. This concept allows a strong thermal integration and leads to the co-production of hydrogen and electricity, while facilitating the recovery of CO.sub.2. This process, however, has the following drawbacks: [0015] A significant proportion of CH.sub.4 remains in the H.sub.2 stream, which entrains a limited CO.sub.2 recovery rate (maximum 80%) over the entire process. [0016] The CO.sub.2 is produced at low pressure (amine), which will require a subsequent compression.
[0017] This process therefore makes possible the production of electricity with recovery of CO.sub.2 at an advantageous yield starting from methane, but shows a recovery rate that is limited by the conversion of the vapor-reforming unit.
[0018] This invention therefore has as its object to remedy one or more of the drawbacks of the prior art by proposing a process for the production of hydrogen that makes it possible to recover CO.sub.2 and methane, and to recycle methane to the steam-reforming stage without a loss of energy.
[0019] For this purpose, this invention proposes a process for the production of hydrogen starting from a hydrocarbon feedstock and steam comprising: [0020] A stage for the production of a synthesis gas in a unit for steam-reforming the hydrocarbon feedstock with a fuel that provides the heat that is necessary to the reaction, [0021] A stage shift conversion of the synthesis gas that is obtained in the preceding stage producing a hydrogen stream that contains methane and carbon dioxide, [0022] A stage for recovery of carbon dioxide and methane, present in the stream that is obtained in the shift conversion stage, in the form of hydrates that produce a pure hydrogen stream, [0023] A stage for regeneration of methane, [0024] A stage for recycling methane to steam reforming.
[0025] According to one embodiment of the invention, the stage for recovery of carbon dioxide and methane in hydrate form is followed by a stage for regeneration of carbon dioxide.
[0026] According to another embodiment of the invention, a stage for regeneration of carbon dioxide is carried out at the same time as the stage for regeneration of methane.
[0027] In one embodiment of the invention, the hydrocarbon feedstock is natural gas.
[0028] In one embodiment of the invention, the stage for recovery of carbon dioxide and methane in hydrate form is carried out in a mixture that comprises water and a non-water-miscible solvent.
[0029] In one embodiment of the invention, this mixture also comprises at least one amphiphilic compound.
[0030] In one embodiment of the invention, the recovery stage in hydrate form is carried out at a temperature of between 0 and 60.degree. C. and a pressure of between 0.2 and 6 MPa.
[0031] In one embodiment of the invention, the stage for regeneration of carbon dioxide is carried out at a temperature of between 0 and 40.degree. C. and a pressure of between 0.2 and 6 MPa.
[0032] In one embodiment of the invention, the stage for regeneration of methane is carried out at a temperature of between 0 and 40.degree. C. and a pressure of between 0.2 and 6 MPa.
[0033] According to one embodiment of the invention, the stage for regeneration of carbon dioxide and methane is carried out at a temperature of between 0 and 40.degree. C. and a pressure of between 0.2 and 6 MPa.
[0034] According to one embodiment of the invention, the methane stream that is obtained by regeneration is recycled at the input of the vapor-reforming stage.
[0035] According to one embodiment of the invention, the process for the production of hydrogen comprises a stage for the production of electricity from the hydrogen stream that is obtained in the stage for recovery of carbon dioxide and methane.
[0036] According to one embodiment of the invention, the production of electricity is carried out by sending the hydrogen stream into a combustion chamber.
[0037] According to one embodiment of the invention, the hot flue gases obtained at the end of the combustion stage are recycled to the vapor-reforming reactor.
Free Full Text Source:  http://appft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=30&f=G&l=50&co1=AND&d=PG01&s1=hydrogen.TTL.&OS=TTL/hydrogen&RS=TTL/hydrogen