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EP-3507239-B1 - SYSTEMS FOR INCREASING A CARBON MONOXIDE CONTENT OF SYNGAS PRODUCED BY A STEAM METHANE REFORMER

EP3507239B1EP 3507239 B1EP3507239 B1EP 3507239B1EP-3507239-B1

Inventors

  • JAHNKE, FRED, C.
  • LAMBRECH, MATTHEW

Dates

Publication Date
20260506
Application Date
20170829

Claims (12)

  1. A system, comprising: a hydrocarbon source configured to provide a hydrocarbon feed that contains methane; a fuel cell unit configured to output anode exhaust gas comprising (H 2 +CO) in an amount in the range of 20 mol% to 40 mol% and CO 2 in an amount in the range of 60 mol% to 80 mol%; and a steam methane reformer configured to receive a first hydrocarbon feed portion from the hydrocarbon source and the anode exhaust gas from the fuel cell unit and to output a syngas having a first H 2 /CO ratio of at most 2:1; wherein the fuel cell unit comprises a direct molten carbonate fuel cell (MCFC) configured to operate at a temperature in the range of 600°C to 700°C; and wherein a cathode of the MCFC is configured to receive CO 2 from at least one of: CO 2 separated from the syngas, CO 2 output by an anode gas oxidizer combustor, or a CO 2 -containing flue gas.
  2. The system according to Claim 1, wherein the hydrocarbon source is a natural gas source.
  3. The system according to Claim 1, wherein the steam methane reformer is configured to operate at a temperature outside of the range of 30°C to 250°C.
  4. The system according to Claim 1, wherein an anode of the fuel cell unit is configured to receive a second hydrocarbon feed portion from the hydrocarbon source.
  5. The system according to Claim 4, wherein the fuel cell unit is further configured to receive a first portion of CO 2 output by the steam methane reformer.
  6. The system according to Claim 5, further comprising an anode gas oxidizer combustor configured to receive a second portion of CO 2 output by the steam methane reformer, wherein a cathode of the fuel cell unit is configured to receive CO 2 output by the anode gas oxidizer combustor.
  7. The system according to Claim 1, further comprising a synthesis reactor configured to convert the syngas to liquid fuel, wherein the liquid fuel comprises at least one of methanol or a Fischer-Tropsch liquid.
  8. The system according to Claim 1, wherein liquid fuel is methanol, wherein the hydrocarbon source is a natural gas source, and wherein the steam methane reformer is configured to receive a natural gas feed from the natural gas source.
  9. The system according to Claim 8, wherein the steam methane reformer is configured to operate at a temperature outside of the range of 30°C to 250°C.
  10. The system according to Claim 1, wherein the anode exhaust gas is added to the first hydrocarbon feed portion such that the steam methane reformer is configured to receive the first hydrocarbon feed portion and the anode exhaust gas as a single stream.
  11. A system, comprising: a hydrocarbon source configured to provide a hydrocarbon feed that contains methane; a fuel cell unit configured to output anode exhaust gas comprising (H 2 +CO) in an amount in the range of 40 mol% to 60 mol% and CO 2 in an amount in the range of 40 mol% to 60 mol%,; and a steam methane reformer configured to receive a first hydrocarbon feed portion from the hydrocarbon source and the anode exhaust gas from the fuel cell unit and to output a syngas having a first H 2 /CO ratio of at most 2:1; wherein the fuel cell unit comprises a solid oxide fuel cell (SOFC) configured to operate at a temperature in the range of 800°C to 1000°C; and wherein the steam methane reformer is further configured to receive recycled CO 2 separated from the syngas.
  12. The system according to Claim 11, further comprising a synthesis reactor configured to convert the syngas to liquid fuel, wherein the liquid fuel comprises at least one of methanol or a Fischer-Tropsch liquid.

Description

CROSS-REFERENCE TO RELATED PATENT APPLICATION This application claims the benefit of and priority to U.S. Provisional Patent Application No. 62/381,375 filed on August 30, 2016. BACKGROUND The present disclosure relates to a steam methane reformer (SMR). In particular, the present disclosure relates to a system and method for increasing a carbon monoxide content of syngas produced by SMRs. Steam methane reformers (SMRs) are generally used as a low-cost option to produce a syngas from a gas feedstock such as natural gas, refinery gas or biogas. The produced syngas can be further processed within the plant to yield various end products, including purified hydrogen, methanol, carbon monoxide and ammonia. Agriculture operations, decomposition refuse within landfills, municipal water treatment plants, and food and beverage processors generate biomass that must be disposed of in an environmentally friendly and economical manner. Anaerobic digesters can reduce the scale of the biomass by a factor of ten, significantly reducing tipping or disposal fees; however, the digestion process and the decay of the biomass generates methane, or biogas, which may be considered to be an undesirable greenhouse gas. The biogas can be flared, but the flaring process generates pollutants such as nitric oxide (NOx), which creates smog and wastes a potential fuel source. Capturing and using biogas as a fuel to generate liquid fuels solves these challenges in a carbon-neutral manner. In the steam methane reforming process, high-temperature steam is used to produce syngas from a methane source, such as natural gas or biogas. See FIGS. 1A and 1B. In an endothermic reforming reaction, methane reacts with steam in the presence of a catalyst to produce hydrogen and carbon monoxide, according to the following formula (1):         CH4 + H2O ↔ CO + 3H2     (1) At the same time, a slightly exothermic water-gas shift reaction takes place in which the carbon monoxide and steam are reacted using a catalyst to produce carbon dioxide and more hydrogen, according to the following formula (2):         CO + H2O ↔ CO2 + H2     (2) The water-gas shift reaction may also be reversed to produce carbon monoxide from carbon dioxide and hydrogen. Syngas, or synthesis gas, is the fuel gas mixture comprised of hydrogen, carbon monoxide, and some carbon dioxide generated from these reactions. An additional step of pressure-swing adsorption (PSA) may take place in which carbon dioxide and other impurities, such as unconverted methane and water, are removed from the gas stream, leaving essentially only hydrogen and carbon monoxide. This hydrogen and carbon monoxide can then be used to produce higher hydrocarbons such as methanol, other alcohols, or liquids from a Fischer-Tropsch (FT) reaction. Steam reforming of gaseous hydrocarbons is seen as a potential way to provide hydrogen fuel for low temperature fuel cells. In this case, a lower temperature shift reactor is located between the reformer and the PSA to convert most of the CO from the reformer to H2 and CO2. Also, the CO is removed from the shifted syngas along with the CO2 and other impurities to produce pure H2. Methanol can be synthesized from syngas according to the following formula (3):         CO + 2 H2 ↔ CH3OH     (3) The reaction of formula (3) may be carried out in the presence of a catalyst, for example, a copper-based catalyst. Carbon monoxide is preferred over carbon dioxide as a reactant for producing methanol. Therefore, it is desirable to produce syngas with a higher carbon monoxide content than is normally produced from the SMR, especially when methane is the feed gas. Also, a very low carbon dioxide content is desired, since CO2 reacts with H2 to produce CO + H2O, and the H2O reduces the reaction rate and yield of desired products. For best results, the theoretically optimal stoichiometric number is 2.0 for converting syngas to methanol and other FT liquid compounds, as seen in formula (4) below: SN=H2−CO2CO+CO2=2.0 In other words, for methanol synthesis, it is desirable to have a 2:1 ratio of hydrogen to carbon monoxide without any CO2. Dimethyl ether (DME) can be synthesized by methanol dehydration according to the following formula (5):         2 CH3OH ↔ CH3OCH3 + H2O     (5) The reaction of formula (5) may be carried out in the presence of a catalyst, for example, a silica-alumina catalyst. The catalyst used in the synthesis of DME is often different from the catalyst used in the synthesis of methanol. The advantage of DME is that it can be used as a direct substitute for diesel fuel in a diesel engine and produces fewer emissions than normal diesel fuel. US 2013/177824 A1 discloses a system comprising a reformer and a MCFC wherein the anode exhaust gas from the MCFC is provided as feed to the reformer. In conventional systems in which natural gas is converted to syngas, which is used to produce liquid fuel (see FIG. 1A), the hydrogen to carbon monoxide ratio will be higher (i.e.