Method and apparatus for producing a stream of synthesis gas containing methane

Abstract

The present invention relates to a method for producing a methane- containing synthesis gas stream, said method comprising the following steps: a) providing a feed gas (101) comprising CO and / or CO2 as a carbon source (103), H2 as a first hydrogen source (105) and optionally H2O as a second hydrogen source (107); b) adjusting the temperature of the feed gas (101) of step a) to a temperature T1 of 150 °C to 300 °C; c) reacting the feed gas (110) of step b) in a methanation reactor (111) to produce heat and a raw synthesis gas (115) comprising methane and CO2, wherein the methanation reactor (111) comprises a catalyst (113) comprising a compound selected from the group consisting of Ni, Co, Fe, Pd, Pt, Ru, Rh and combinations thereof; d) conveying the raw synthesis gas (115) to a separation unit 119 comprising an absorption medium, wherein the separation unit is an amine scrubber 121 and the absorption medium is an amine solution (122); e) separating the raw synthesis gas (115) in the separation unit (119) into a methane-enriched synthesis gas stream (125) and a CO2-saturated absorption medium (129); f) regenerating the CO2-rich absorption medium (129) by increasing the temperature of the CO2-rich absorption medium (129) using the heat produced in the methanation reactor, thereby producing a regenerated CO2-depleted absorption medium (131) and an exhaust stream (127) comprising CO2, wherein the heat from the methanation reactor (111) is transferred to the separation unit (119) by means of a heat transfer device (133) comprising a heat exchanger (137) and water as a heat transfer medium (141, 143, 145, 147).

Description

[0001] The present invention relates to a method and apparatus for producing methane-containing syngas as described in the preambles of claims 1 and 7.

[0002] Methanation is a catalytic reaction of hydrogen (H2) with carbon monoxide (CO) and / or carbon dioxide (CO2) to produce a methane-containing gas. This methane-containing gas, sometimes called syngas, can be used as an alternative to natural gas. In regions where natural gas is scarce, other energy sources (such as coal or petroleum coke) can be partially oxidized during gasification to produce a gas containing hydrogen and CO. This gas containing hydrogen and CO is sometimes called feed gas. The feed gas can then be used to produce syngas (“syngas”) during the methanation process.

[0003] In the presence of a suitable methanation catalyst, the methanation process includes the following reactions:

[0004] (I)CO+3H2->CH4+H2O(-206kJ / mol),

[0005] (II)CO2+4H2->CH4+2H2O(-164kJ / mol).

[0006] Depending on the catalyst, temperature, and concentration present, the water formed during reactions (I) and (II) can subsequently react in situ with CO in the water-gas shift reaction (III):

[0007] (III)CO+H2O->CO2+H2(-41kJ / mol).

[0008] All three reactions (I), (II), and (III) are exothermic.

[0009] Various systems for carrying out the above-mentioned methanation process have been proposed in the prior art.

[0010] WO 2020 / 069974 A1 discloses a fixed-bed arrangement in the form of an insert for a reactor used for the catalytic methanation of a gas mixture containing hydrogen and carbon dioxide.

[0011] GB2018818 discloses a method for preparing methane-rich gas in at least one adiabatic methanation reactor by converting a combination of a preheated syngas stream and a recirculated stream from the methanation reactor. The combined preheated syngas stream and recirculated stream pass directly through a shift catalyst bed before passing through the methanation catalyst.

[0012] US2010 / 0162626 A1 discloses an adiabatic reactor and a method and system for producing methane-rich gas in such an adiabatic reactor. The adiabatic reactor includes a first inlet and a first outlet (defining a first flow path between the first inlet and the first outlet), and a second inlet and a second outlet (defining a second flow path between the second inlet and the second outlet). The first and second flow paths point in opposite directions, are thermally connected via a partition wall, and each includes a catalyst. The described method utilizes the adiabatic reactor to produce a methane-rich product gas from a feed gas containing CO and hydrogen. The described system includes two or more adiabatic reactors connected to each other.

[0013] One problem in the field of methanation reactors is that, in order to maintain constant reaction conditions, excess exothermic reaction energy (heat) must be removed to ensure that the methanation reactor does not overheat (which would damage the catalyst in the reactor).

[0014] Therefore, the problem solved by the present invention is to provide a method and apparatus for producing methane-containing syngas and high-concentration, high-purity CO2 as byproducts in an efficient, energy-saving, and economical manner.

[0015] This problem is solved by the method for producing methane-containing syngas as described in claim 1 and the apparatus for producing methane-containing syngas as described in claim 7. Preferred embodiments are subject to the dependent claims.

[0016] According to the present invention, a method for producing a methane-containing syngas stream is provided, the method comprising the following steps: In a first step a), a feed gas comprising CO and / or CO2 as a carbon source and H2 as a first hydrogen source is provided. In a second step b), the temperature of the feed gas from the first step is adjusted to a temperature T1 of 150°C to 300°C. In a third step c), the feed gas from the second step is reacted in a methanation reactor to generate heat and a crude syngas comprising methane and CO2 (and typically also water). The methanation reactor includes a catalyst comprising a compound selected from the group consisting of Ni, Co, Fe, Pd, Pt, Ru, Rh, and combinations thereof. In a fourth step d), the crude syngas is fed to a separation unit comprising an absorption medium, wherein the separation unit is an amine scrubber, and the absorption medium is an amine solution. In a fifth step e), the crude syngas is separated into a methane-rich syngas stream and a CO2-saturated absorption medium. Finally, in step six f), the CO2-saturated absorbent is regenerated by raising the temperature of the CO2-saturated absorbent using the heat generated in the methanation reactor, thereby producing a regenerated CO2-depleted absorbent and a CO2-containing exhaust stream.

[0017] A key aspect of this invention is the transfer of heat generated in the methanation reactor to the separation unit via a heat transfer device comprising a heat exchanger and water as the heat transfer medium. The benefits of using the heat from the exothermic methanation reaction to regenerate the absorbent medium include stabilizing the methanation reaction, preventing catalyst damage from overheating, enabling efficient production of crude synthesis gas (which is damaged at excessively high temperatures), and reducing production costs because no external energy is required to regenerate the absorbent medium.

[0018] Another advantage comes from using the heat transfer device of the present invention to transfer heat from the methanation reactor to the separation unit, as this allows the two components to be placed separately from each other, unlike the method in which the absorbent medium is transferred through the methanation reactor for regeneration.

[0019] As described above, the heat transfer medium in the method of the present invention is water. However, it will be apparent to those skilled in the art that the heat generated in the methanation reactor can convert the water in the heat transfer medium into steam. Therefore, the use of steam as a heat transfer medium is also possible. However, it is important that the heat transfer medium does not come into direct contact with the reaction. The advantage of using water as a heat transfer medium is that a natural convection system of water / steam can be used, which eliminates the need for pumps to transport water / steam from the methanation reactor to the separation unit.

[0020] Crude synthesis gas typically contains at least 30% by volume methane and up to 70% by volume CO2. Since CO2 is the primary component of crude synthesis gas, exhaust streams containing high-purity CO2 can be used in a variety of applications, such as dry ice production or beverage carbonation.

[0021] In a preferred embodiment of the invention, water is used as a second hydrogen source. Preferably, the water in the feed gas is heated and converted into steam in step b). This steam supply has three main advantages:

[0022] First, it can be used to remove carbon deposits on catalysts via steam reforming according to the following reaction (IV):

[0023] (IV)H2O+C->CO+H2.

[0024] This method regenerates the catalyst and allows it to maintain sufficient catalytic activity for an extended period without any maintenance.

[0025] Secondly, the supply of steam significantly reduces the hydrogen concentration and increases the CO2 concentration in the crude synthesis gas, as CO is converted to CO2 according to the water-gas shift reaction (III) described above. This is advantageous because post-processing of crude synthesis gas with high hydrogen concentration is much more difficult than that with high CO2 concentration. In particular, hydrogen's low boiling point of -252.9°C makes separation by liquefaction impossible, complicating the separation of hydrogen from crude synthesis gas. Furthermore, hydrogen is reactive, making regeneration challenging. Currently, the only reasonable method for separating hydrogen from crude synthesis gas is by means of membrane or pressure swing absorption, which increases separation costs. Therefore, producing crude synthesis gas with minimal hydrogen production is a significant advantage of the method of this invention.

[0026] The third benefit is that steam can be used as an internal cooling system in the methanation reactor because steam has a high capacity to buffer the heat (thermal energy) generated by the exothermic methanation reaction. This is important because excessively high temperature peaks can damage the catalyst.

[0027] Preferably, the heat transfer device includes a first loop connecting the methanation reactor to a heat exchanger and a second loop connecting the separation unit to the heat exchanger. The purity of the water, the heat transfer medium in contact with the methanation reactor, is required to be very high to avoid corrosion of the reactor and heat transfer devices (e.g., pipes). Since highly purified water is expensive, dividing the process into two loops reduces the amount of water in direct contact with the reactor, and thus reduces the amount of highly purified water, which lowers the overall production cost.

[0028] In a preferred embodiment of the invention, the reactor does not contain more than one catalyst. In other words, the reactor contains only a single catalyst, which avoids the need for different treatments or maintenance of multiple catalysts, and thus further reduces the production cost of the syngas.

[0029] In a preferred embodiment of the invention, the catalyst in the methanation reactor comprises Ni and / or Ru. The advantage of using a catalyst comprising Ni and / or Ru is the ability to convert a particularly large amount of CO / CO2 into methane, which allows for a reduction in the size of the reactor and the overall equipment itself.

[0030] Preferably, the superstoichiometric molar ratio of the feed gas is: In the context of this invention, the term superstoichiometric molar ratio is understood to mean In this case, carbon is in excess relative to hydrogen.

[0031] To better understand this, we will explain it using two specific examples:

[0032] For reaction (I)

[0033] (I) CO + 3H₂ → CH₄ + H₂O

[0034] The molar ratio of the stoichiometric concentrations of CO and H2 is calculated using the molar concentrations of the precipitates. Therefore, the superstoichiometric molar ratio of the precipitates in reaction (I) will be less than 3.

[0035] For reaction (II)

[0036] (II) CO2 + 4H2 → CH4 + 2H2O

[0037] The molar ratio of the stoichiometric concentrations of CO2 and H2 is calculated using the molar concentration of the precipitate. Therefore, the superstoichiometric molar ratio of the precipitates in reaction (II) will be less than 4.

[0038] A common problem in this art is that feed gas with a stoichiometric concentration of hydrogen relative to CO and / or CO2 must typically be provided to ensure the methanation reaction is effective. However, "raw" feed gas often contains hydrogen at a superstoichiometric concentration relative to CO and / or CO2 (i.e., containing more carbon than required for the methanation reaction). Therefore, it is usually necessary to reduce the carbon concentration in the feed gas, for example by means of a separation unit, before feeding it into the methanation reactor. Since the method of the present invention allows the production of methane-containing syngas using superstoichiometric feed gas, there is no prior carbon reduction in the feed gas, which reduces the production cost of the syngas. Furthermore, the number of available sources of feed gas for methanation is significantly increased, including gases readily produced via biomass or coal gasification, via electrolysis, via co-electrolysis, or as byproducts of steel blast furnaces. Moreover, it allows the use of feed gases that are typically considered low-value due to their low calorific value, meaning that the method of the present invention can utilize gases that are not preferred for any other application and are therefore inexpensive.

[0039] In a preferred embodiment of the invention, the feed gas from step a) and the crude synthesis gas from step c) are transferred to a heat exchanger, wherein heat from the crude synthesis gas is transferred to the feed gas. In other words, heat is extracted from the crude synthesis gas and used to heat the feed gas. Therefore, it is preferable to lower the temperature of the crude synthesis gas in the heat exchanger to below 150°C. On the other hand, it is preferable to raise the temperature of the feed gas in the heat exchanger to at least 150°C, more preferably at least 200°C.

[0040] Another aspect of the present invention provides a syngas production apparatus. The syngas production apparatus includes a feed gas source that provides a feed gas comprising CO and / or CO2 as a carbon source and H2 as a first hydrogen source. The syngas production apparatus also includes a methanation reactor for producing a crude syngas comprising methane and CO2 from the feed gas, as well as heat as a byproduct. The methanation reactor includes a catalyst comprising a compound selected from the group consisting of Ni, Co, Fe, Pd, Pt, Ru, Rh, and combinations thereof. The syngas production apparatus further includes: a feed gas supply line connecting the feed gas source to the methanation reactor; a separation unit comprising an absorption medium to separate the crude syngas into a methane-rich syngas stream and a CO2-rich exhaust stream; and a crude syngas line connecting the methanation reactor to the separation unit. The separation unit is an amine scrubber, and the absorption medium is an amine solution. According to the present invention, the syngas production apparatus also includes a heat transfer device comprising a heat exchanger and water as a heat transfer medium. The heat transfer device uses the heat generated in the reactor to regenerate the absorption medium.

[0041] Similar to the benefits of the method described above, the apparatus of the present invention allows for the stabilization of the methanation reaction, avoids catalyst damage due to overheating, efficiently produces crude synthesis gas, and reduces production costs because no external energy is required to regenerate the absorbent medium. Another advantage, similar to the method of the present invention, is that the methanation reactor and separation unit can be placed separately from each other due to the presence of the heat transfer device. Furthermore, the aforementioned advantages of using water as the heat transfer medium in the method of the present invention also apply to the apparatus of the present invention. In particular, this allows for the use of a natural convection system of water / steam, which avoids the need to use pumps to transport water / steam from the methanation reactor to the separation unit.

[0042] In a preferred embodiment of the present invention, the feed gas contains H2O as a second hydrogen source. The advantages of the water-containing feed gas described above in conjunction with the method of the present invention are applicable to the apparatus of the present invention with necessary modifications.

[0043] Preferably, the heat transfer device includes a first loop connecting the methanation reactor to the heat exchanger and a second loop connecting the separation unit to the heat exchanger. Considering the purity requirements of the heat transfer medium water, the corrosion risks of the reactor and heat transfer device, and the cost of producing purified water, the advantages of using two loops have been explained above and are applicable to the device of this invention with necessary modifications.

[0044] In a preferred embodiment of the invention, the syngas production apparatus further includes a heat exchanger to transfer heat from the crude syngas to the feed gas. The advantage of this heat exchanger is that the heat from the crude syngas can be used to preheat the feed gas before it is supplied to the methanation reactor. This reduces production costs because no external energy is required to raise the temperature of the feed gas and lower the temperature of the crude syngas.

[0045] Preferably, the reactor does not contain more than one catalyst. The advantages of reactors containing only a single catalyst used in the method of the present invention are applicable to the apparatus of the present invention with the necessary modifications.

[0046] Preferably, the catalyst compound in the methanation reactor comprises Ni and / or Ru. As mentioned above, the advantage of using a catalyst containing Ni and / or Ru is that a particularly large amount of CO / CO2 is converted into methane, which allows for a reduction in reactor size, thereby reducing the overall size of the equipment.

[0047] In a preferred embodiment of the invention, the methanation reactor in the apparatus provides a superstoichiometric molar ratio. The feed gas. For the reasons further described above, this allows the use of inexpensive feed gas sources without requiring a reduction in the carbon concentration in the feed gas, thus significantly reducing the production cost of the syngas. Attached Figure Description

[0048] The invention will now be described by way of example with reference to the accompanying drawings, in which:

[0049] Figure 1 A method and apparatus for producing synthesis gas according to a preferred embodiment of the present invention are shown.

[0050] Figure 1An apparatus 100 is shown, which is provided with a feed gas 101 from a feed gas source (not shown). The feed gas 101 includes CO and CO2 as carbon sources 103, H2 as a first hydrogen source 105, and H2O as a second hydrogen source 107. In the illustrated embodiment, the feed gas 101 is supplied at room temperature and then conveyed to a heat exchanger 109, by means of which the temperature of the feed gas 101 is raised to a temperature of 150°C to 300°C. The thus heated feed gas 110 is then conveyed from the heat exchanger 109 to a methanation reactor 111 containing a catalyst 113. In the methanation reactor 111, the heated feed gas 110 is converted into a crude synthesis gas 115 containing methane (CH4), CO2, and water. The crude synthesis gas 115 exits the methanation reactor 111 at a temperature up to 250°C and is conveyed to the heat exchanger 109. In heat exchanger 109, the temperature of the crude synthesis gas 115 is reduced, and the extracted heat is transferred to the feed gas 101. The cooled crude synthesis gas 117, at approximately 150°C, is then conveyed from heat exchanger 109 to separation unit 119, which includes an amine scrubber 121 and a reboiler 123. The amine scrubber 121 uses an amine solution 122 to separate the cooled crude synthesis gas 117 into a methane-rich synthesis gas stream 125 and a CO2-rich exhaust stream 127. During this process, the amine solution absorbs CO2 from the crude synthesis gas 117 and is conveyed to the reboiler 123 as a CO2-saturated amine solution 129. In the reboiler 123, the CO2-saturated amine solution 129 is regenerated into a CO2-depleted amine solution 131, which is then conveyed back to the amine scrubber 121. This regeneration process utilizes heat provided by the methanation reactor 111. Specifically, the exothermic methanation reaction in the methanation reactor 111 generates heat. The heat is used in heat transfer device 133 to raise the temperature of water used as the heat transfer medium. Heat transfer device 133 includes a first loop 135 connecting heat exchanger 137 to methanation reactor 111 and a second loop 139 connecting heat exchanger 137 to reboiler 123. In the first loop 135, water 141 is supplied from heat exchanger 137 to methanation reactor 111, where it is evaporated by the heat provided by the exothermic methanation reaction, producing flowing steam 143. This steam 143 is then supplied to heat exchanger 137 to raise the temperature of water 145 in the second loop 139. Due to the heat transfer from steam 143 in the first loop 135 to water 145 in the second loop 139, steam 143 condenses back into water 141, while water 145 in the second loop 139 evaporates into flowing steam 147. Steam 147 is supplied to reboiler 123 to regenerate CO2-saturated amine solution 129. Specifically, in the reboiler 123, the heat of the steam 147 is extracted to raise the temperature of the CO2-saturated amine solution 129, which produces a CO2-depleted amine solution 131 and a CO2-rich exhaust stream 127.The CO2-rich exhaust stream 127 is then used for other applications, such as the carbonation of beverages, while the CO2-depleted amine solution 131 is fed back to the amine scrubber 121 from the reboiler 123.

Claims

1. A method for producing a synthesis gas stream containing methane, the method comprising the following steps: a) Provide a feed gas (101) comprising CO and / or CO2 as a carbon source (103) and H2 as a first hydrogen source (105); b) Adjust the temperature of the feed gas (101) in step a) to a temperature T1 of 150°C to 300°C; c) The heated feed gas (110) from step b) is reacted in a methanation reactor (111) to generate heat and a crude synthesis gas (115) containing methane and CO2, wherein the methanation reactor (111) contains a catalyst (113) comprising a compound selected from the group consisting of Ni, Co, Fe, Pd, Pt, Ru, Rh and combinations thereof; d) The crude synthesis gas (115) is fed to a separation unit (119) containing an absorption medium, wherein the separation unit is an amine scrubber (121) and the absorption medium is an amine solution (122); e) In the separation unit (119), the crude synthesis gas (115) is separated into a methane-rich synthesis gas stream (125) and a CO2-saturated absorption medium (129); f) The CO2-saturated absorbent medium (129) is regenerated by increasing the temperature of the CO2-saturated absorbent medium (129) using the heat generated in the methanation reactor, thereby producing a regenerated CO2-depleted absorbent medium (131) and a CO2-containing exhaust stream (127). Heat from the methanation reactor (111) is transferred to the separation unit (119) via a heat transfer device (133), which includes a heat exchanger (137) and water as the heat transfer medium (141, 143, 145, 147). The heat transfer device (133) includes a first loop (135) connecting the methanation reactor (111) to the heat exchanger (137) and a second loop (139) connecting the separation unit (119) to the heat exchanger (137).

2. The method of claim 1, wherein the feed gas (101) comprises H2O as a second hydrogen source (107).

3. The method of claim 1 or 2, wherein the methanation reactor (111) does not contain more than one catalyst (113).

4. The method of claim 1 or 2, wherein the catalyst (113) is Ni and / or Ru.

5. A synthesis gas production apparatus (100), comprising: The feed gas source provides a feed gas (101) comprising CO and / or CO2 as a carbon source (103) and H2 as a first hydrogen source (105). A methanation reactor (111) for generating heat and crude synthesis gas (115) from the feed gas (101), the methanation reactor (111) comprising a catalyst (113) comprising a compound selected from the group consisting of Ni, Co, Fe, Pd, Pt, Ru, Rh and combinations thereof; The feed gas supply line connecting the feed gas source to the methanation reactor (111); A separation unit (119) comprising an absorption medium for separating the crude synthesis gas (115) into a methane-rich synthesis gas stream (125) and a CO2-saturated absorption medium (129), wherein the separation unit is an amine scrubber (121) and the absorption medium is an amine solution (122). The crude synthesis gas pipeline connecting the methanation reactor (111) to the separation unit (119); as well as A heat transfer device (133) comprising a heat exchanger (137) and water as a heat transfer medium (141, 143, 145, 147) to transfer heat generated in the methanation reactor (111) to the separation unit (119) to regenerate the CO2-saturated absorbent medium (129). The heat transfer device (133) includes a first loop (135) connecting the methanation reactor (111) to the heat exchanger (137) and a second loop (139) connecting the separation unit (119) to the heat exchanger (137).

6. The syngas production apparatus of claim 5, wherein the syngas production apparatus further comprises a heat exchanger (109) for transferring heat from the crude syngas (115) to the feed gas (101).

7. The syngas production apparatus of claim 5 or 6, wherein the methanation reactor (111) does not contain more than one catalyst (113).

8. The synthesis gas production apparatus as claimed in claim 5 or 6, wherein the catalyst (113) is Ni and / or Ru.

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