EA041183B1 - CARBON RECYCLING DURING STEAM REFORMING - Google Patents

Description

Technical field

The present invention relates to the field of steam reforming of natural gas feedstocks. In particular, a method is proposed for increasing the efficiency of carbon use in a synthesis gas production unit, as well as a synthesis gas production unit designed to perform this method. To ensure efficient use of the natural gas feedstock, different gas streams can be combined and recycled.

State of the art of the present invention

In a typical synthesis gas plant (synthesis gas here means a mixture containing hydrogen and carbon monoxide), the synthesis gas is purified to H2 and CO by a combination of a CO2 removal unit and a cold block, and sometimes also a PSA. Synthesis gas is usually produced by steam reforming of natural gas.

The catalytic production of synthesis gas by steam reforming of a feed gas stream containing hydrocarbons has been known for several decades. The endothermic steam reforming reaction is usually carried out in a steam reformer (SMR), also called a methane steam reformer. The steam reformer has several tubes filled with catalyst placed in a furnace. The tubes typically have a length of 10 to 14 m and an internal diameter of 7 to 15 cm. Preferably, steam reforming occurs at pressures in the range of 15-30 barg to ensure that pressurized final synthesis gas is obtained directly from the reformer. Heat for the endothermic reaction is provided by burning the fuel in the furnace burners. The temperature of the synthesis gas at the outlet of the steam reformer depends on the use of synthesis gas, but is usually in the range from 650 to 980°C.

It is also known that it is thermodynamically advantageous to have a high concentration of CO2 and a low concentration of water vapor in the feed stream to promote production of syngas with a low H2/CO ratio. However, operation under such conditions may not be feasible due to the possible formation of soot on the catalyst.

An alternative process for producing low H2/CO synthesis gas via steam reforming is the sulfur passivated reforming (SPARG) process, which can be used to produce relatively low H ₂ /CO synthesis gas. This process requires the desulfurization of the produced synthesis gas in order to obtain a synthesis gas free of sulfur.

A more detailed description of the various methods for producing low H2/CO synthesis gas can be found in the article Experience in Industrial Scale Steam Reforming of CO2 Rich Gas, P.M. Mortensen and I. Dybkjaer, Applied Catalysis A: General, 495 (2015), 141-151.

Known methods include those of US 2010074811, US 4732596 and EP 0411506. Compared to EP 0411506, the present technology has the overall advantage that the CO2 stream from the CO2 removal unit and the exhaust gas from the cold unit are at the same pressure. (within 2-3 bar). In contrast, the configuration of EP 0 411 506 requires individually expanding one stream or separately compressing the other stream before mixing them; in general this gives an inefficient process in EP 0 411 506.

Efforts have been made to optimize the production and purification of syngas. The cleaning process itself provides several separate gas streams with different compositions at different temperatures and pressures, and it would be beneficial to use them most efficiently so that waste and/or incineration can be avoided. Use must be carried out in the most economical and energy efficient way.

These difficulties are solved by the present technology. Additional advantages of the technology will become apparent from the following description, examples and claims.

The essence of the invention

It has been found that efficient recycling of the respective gas streams can be used to control the production of CO in a synthesis gas plant. Additional advantages of the present technology are apparent from the following detailed description and embodiments.

In a first aspect, there is provided a method for producing synthesis gas in a syngas production unit, said synthesis gas production unit comprising a reforming section in which the process gas is first reformed in at least one reforming stage to produce a reformed gas stream; and a cooling section in which the reformed gas stream is cooled to obtain a dry reformed stream containing CH ₄ , CO, CO ₂ and H ₂ , said process comprising the following steps:

a) sending the dry reformed stream to a CO2 removal unit to separate it into at least a purified CO2 stream and a CO ₂ flushed stream having a lower CO ₂ content than said purified CO ₂ stream;

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b) directing the CO2 flushed stream from the CO2 removal unit to a cold unit to separate it into at least a cold unit off-gas containing CH ₄ , H2 and CO, an H2 rich stream, and a high purity CO stream;

c) combining at least a portion of the purified CO2 stream from the CO2 removal unit with at least a portion of the cold unit off-gas to produce a combined carbon-rich stream;

d) compressing said combined carbon rich stream;

e) recycling said compressed combined carbon rich stream to the reformer section; And

f) reforming said compressed combined carbon-rich stream in a reformer section, wherein at least a portion of the H2-rich stream from said cold block is used as fuel to heat the reformer section.

Additionally provided is a synthesis gas production unit that includes a reformer configured to reform a process gas in at least one reforming stage to produce a reformed stream containing CH ₄ , CO, CO 2 , H 2 and H 2 O;

a cooling section for cooling the reformed stream and condensing water from said reformed stream to form a dry reformed stream containing CH4, CO, CO2 and H2;

a CO2 removal unit located downstream of said reformer section for receiving said reformed stream and separating it into at least a purified CO2 stream and a CO2 washed stream having a lower CO2 content than said purified CO2 stream;

a cold block located downstream of said CO2 removal unit for receiving said _CO2 flushed stream from said _CO2 removal unit and separating it into at least cold unit off-gas containing _CH4 , _H2 and CO enriched _H2 stream, and high purity CO stream;

a first mixing unit for receiving at least a portion of the purified CO2 stream from the CO2 removal unit and at least a portion of the cold unit off-gas and combining them to form a combined carbon-rich stream;

a compressor for compressing said combined carbon rich stream;

a recirculation loop for supplying said compressed combined carbon-rich stream to the reforming section; and an H ₂ rich stream recycle loop for feeding at least a portion of the H ₂ rich stream from the cold block to the reformer as fuel.

Explanations for the figures

In FIG. 1 is a diagram of one embodiment of a synthesis gas production plant.

In FIG. 2 is a diagram of one embodiment of a synthesis gas production plant including the PSA unit.

In FIG. 3 is a diagram of another embodiment of a synthesis gas plant similar to that shown in FIG. 2, in which the hydrogen-rich stream from the cold block is recycled and used as fuel to heat the reformer section.

Detailed disclosure of the present invention

This technology describes how the carbon balance of synthesis gas can be improved by using the carbon in the off-gas from separation processes. In the following, when the content of a certain component in the gas stream is given as a percentage, this should be understood as mol.%, unless otherwise indicated.

In particular, the concept involves recirculation of carbonaceous gases from a cold block separation process, typically included in CO-producing synthesis gas plants. The technology involves combining the compression of CO ₂ and exhaust gas in one compressor to save costly and energy intensive equipment.

Thus, a method is proposed for increasing the efficiency of carbon use in a synthesis gas production unit. This method includes six main steps, performed in the order described, and optional steps may be included before, after or between these stages.

The synthesis gas production unit includes a reforming section in which the process gas is reformed in at least one reforming stage to obtain a

- 2 041183 reforming a stream containing a mixture of CH ₄ , CO, CO2, H2 and H2O. The process gas is typically natural gas. Steam reforming may, for example, be carried out by a combination of a tubular reformer (also referred to as a steam methane reformer, SMR) and an autothermal reformer (ATR), also known as primary and secondary reformer or two-stage reformer. Alternatively, a stand-alone SMR or a stand-alone ATR can be used to prepare syngas. Alternatively, convective reformers can be used where hot gas (in the form of flue gas or already reformed synthesis gas) is used as heating gas to facilitate the reforming reaction. Alternatively, catalytic partial oxidation can be used. Details of these methods are described in J. Rostrup-Nielsen and L. J. Christiansen Syngas Production Concept, Imperial College Press, published by World Scientific, 2011.

Additional components upstream of the primary reformer may include various pre-reformers and desulfurizers through which the natural gas passes prior to the primary reformer. These standard components are not shown in the accompanying figures.

Typically, the reforming section is connected directly to a cooling section where the hot reformed gas is cooled and the remaining water in the gas is condensed and separated. Thus, a dry reformed stream is provided which contains CH ₄ , CO, CO ₂ and H ₂ .

In the first main process step, the dry reformed stream is sent to a _CO2 removal unit to separate it into at least a purified CO2 stream and a CO2 washed stream.

The term CO ₂ removal unit means a unit that uses a method such as chemical absorption to separate CO 2 from the process gas. In a chemical absorption process, a CO2 containing gas is passed over a solvent which reacts with CO2 and thus binds it. In most cases, chemical solvents are amines classified as primary amines such as monoethanolamine (MEA) and diglycolamine (DGA), secondary amines such as diethanolamine (DEA) and diisopropanolamine (DIPA), or tertiary amines such as triethanolamine (TEA ) and methyldiethanolamine (MDEA), but ammonia and solutions of alkali metal carbonates such as K ₂ CO ₃ and Na ₂ CO ₃ can also be used.

The CO ₂ -washed stream has a lower CO ₂ content than the purified CO ₂ stream obtained in this step and contains H2, CO and CH4 as major components. As a rule, CO2 in the CO2 _- washed stream will be less than 1% and even up to several p.p. ppm, while the CO ₂ in the purified CO ₂ stream will typically be >90%, even >99%.

The purified CO ₂ stream exiting the CO ₂ removal unit typically has a pressure of about 0.5 barg.

In the second main process step, the CO2-flushed stream is sent from the CO2 removal unit to the cold unit. In the cold block, this stream is separated into at least a cold block off-gas containing CH4, H2 and CO, a high purity first H ₂ stream, and a high purity CO stream.

The cold block uses cryogenic separation using the phase change of various substances in the gas to isolate the individual components from the gas mixture by controlling the temperature. Examples of a cold block for CO purification include partial condensation and methane washing as described in R. Pierantozzi's publication Carbon Monoxide in the Kirk-Othmer Encyclopedia of Chemical Technology.

Accordingly, the cold block includes a temperature swing adsorber (TSA) block that is used to collect the remaining CO2 and H2O in the gas, thus providing the TSA off-gas. The TSA block is that component of the cold block through which the CO ₂ flushed stream first passes. Thus, any traces of CO ₂ and water are removed first; otherwise, they may condense or freeze in the lower sections of the cold block. Typically, a small amount (<1%) of the process gas entering the TSA is lost along with the CO ₂ and water trapped in the adsorption unit. The TSA layer can be regenerated by heating with or without an appropriate purge flow. The purge stream may be H ₂ rich gas from the cold block, in which case the small amounts of water and CO ₂ introduced into the TSA will be transferred to the H ₂ rich gas.

In one aspect, at least a portion of the TSA off-gas is fed as fuel to heat the reformer section, optionally in combination with one or more other off-gases.

In another aspect, at least a portion of the cold block off-gas is supplied as fuel to heat the reformer section, optionally in combination with one or more other off-gases.

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An H2-rich stream is one of the desired products of a synthesis gas plant and typically has an H2 content of 97% or more. Depending on requirements, said H2-enriched stream may be used as is, but it may also be further purified to achieve a higher _H2 content, eg 99% or more.

Further purification of the H2-rich stream is usually carried out using pressure swing adsorption. Accordingly, the H2 enriched stream from said cold block can be sent to a pressure swing adsorption (PSA) block to separate it into at least a high purity H2 stream and an off gas PSA.

The high purity H2 stream has a higher H2 content than the H2 rich stream and is typically 99.9%.

PSA off-gas from a PSA unit typically contains H2, CO, CO ₄ and N2. In one aspect, at least a portion of the off-gas PSA is fed as fuel to heat the reformer section. The composition of the PSA off-gas will depend on the desired purity of the high purity H2 stream for the PSA, and typically more H2 is lost to the off-gas of the PSA when the purity of the high purity H2 stream is high.

Preferably, a TSA off-gas part, a PSA off-gas part, or a cold block off-gas part, or a combination thereof, is fed as fuel to heat the reformer section. More preferably, a combination of a portion of the off-gas TSA and a portion of the off-gas PSA is supplied as fuel for heating the reformer section. In addition, natural gas fuel can be sent to the reformer to balance the fuel demand. In some configurations, such as the ATR reformer section, the fuel will be burned in a flame preheater to provide process gas preheating.

A high purity CO stream from a cold block is one of the desired products of a synthesis gas plant and typically has a CO content of 98% or more.

In the third main process step, at least a portion of the purified CO2 stream from the _CO2 removal unit is combined with at least a portion of the cold unit off-gas to produce a combined carbon-rich stream. In one aspect, the entire volume of the purified CO ₂ stream from the CO ₂ removal unit is combined with at least a portion of the cold unit off-gas. In another aspect, the total volume of the purified CO ₂ stream from the CO ₂ removal unit is combined with the total off-gas volume of the cold unit.

The off-gas from the cold unit and the purified CO2 stream from the CO2 removal unit are typically low pressure gas streams and will contain a relatively large proportion of the carbon from the natural gas feedstock. To use this carbon content, they can be recycled to the reformer. In addition, these streams usually have the same pressure. This also makes them relatively easy to handle and easy to mix in the required proportions.

In the fourth main step of the process, the combined carbon-rich stream is compressed, for example, to a pressure higher than the pressure in the reformer, such as a pressure of 5 bar or preferably 2 bar higher than the pressure in the reformer. Because the cold block off-gas and the purified CO ₂ stream are provided at relatively low pressure, it is preferable to compress said combined carbon-rich stream rather than compressing separate streams. Compression of said combined carbon-rich stream suitably takes place in a separate multi-stage compressor. This compressor is an expensive and energy intensive component of the syngas plant and it is therefore more advantageous to use a single compressor for the combined carbon rich stream than to have separate compressors for the cold block off gas and the clean CO2 stream.

In the fifth and sixth main steps of the process, the compressed combined carbon rich stream is recycled to the reformer and reformed in said reformer.

Thus, the present technology involves taking at least a portion of the cold block off-gas (which is rich in methane and potentially also CO), mixing it with at least a portion of the purified CO ₂ stream from the CO ₂ removal unit, and compressing this combined stream. This saves more carbon in the process and increases carbon savings, hence reducing feedstock consumption in the reformer. Combining the CO ₂ stream and the off-gas of the cold block prior to compression allows the use of a single (multi-stage) compressor, meaning that additional recirculation occurs with little additional capital investment, waste reduction and reduced energy consumption. In addition, recirculation of cold block off-gas is quite counterintuitive, since this gas stream contains a certain amount of H ₂ (typically >20%), so the apparent H 2 / CO ratio at the outlet of the reformer section will increase despite the desire to obtain synthesis gas with low H2/CO ratio.

In the general process, the compressed combined carbon-rich stream is recycled to a reformer and reformed in said reformer. This can occur independently of the process gas fed to the reformer section. However, in a preferred aspect, the compressed combined carbon-rich stream is mixed with the process gas prior to being reformed in the reformer section. Thus, only one gas feed stream needs to be supplied to the reformer section.

In one aspect, at least a portion of the H2-enriched stream from said cold block is used as fuel to heat the reformer section. This reduces the supply of fresh hydrocarbon fuel to balance the fuel demand in the reformer section and reduces CO2 emissions to the environment. In another aspect, the full volume of the purified _CO2 stream from the _CO2 removal unit and the total offgas from the cold block are combined, compressed and recycled to the reformer, and the H2 rich gas from the cold block is used as the sole fuel for heating the reformer. Balance gas enriched with H2 from the cold block is used as a product as is or can be further purified in the PSA unit. In this aspect, no additional fresh fuel or carbon-minimum off-gases are required as fuel in the reformer section, and hence CO2 emissions to the environment are greatly minimized.

In another aspect, a synthesis gas production plant is provided that is suitable for carrying out the above method. All details of the various blocks constituting said synthesis gas production plant are the same as described above for the method according to the invention.

The synthesis gas production unit includes a reforming section, such as a steam reforming section with the functions described above. The reformer section is configured to reform the process gas in at least one reforming stage to produce a reformed stream containing CH ₄ , CO, CO2, H2 and H2O.

The cooling section is located downstream immediately after the reforming section for cooling the reformed stream, condensing and separating the main part of the water. Thus, a dry reformed stream containing CH ₄ , CO, CO 2 and H 2 is provided. The cooling section typically includes a combination of waste heat boilers and heat exchangers for temperature control and flash separators for water removal.

The CO2 removal unit is located downstream of said cooling section. The CO2 removal unit has the components and functions described above. It receives the dry reformed stream from the cooling section and separates it into at least a purified CO ₂ stream and a CO ₂ flushed stream having a lower CO ₂ content than said purified CO ₂ stream.

The cold block is located downstream of the CO2 removal block. The structure and function of the cold block are as described above. It receives the CO2-washed stream from the CO2 removal unit and separates it into at least a cold unit off-gas containing CH4, H2 and CO, an H2-rich stream, and a high purity CO stream.

The cold block may include a Temperature Swing Absorber (TSA) block that produces a TSA off-gas containing CO ₂ and H ₂ O.

In cases where a high purity _H2 stream is required, a pressure swing adsorption (PSA) unit is additionally located to receive the H2 rich stream from the cold unit and separate it into at least a high purity H2 stream and off gas PSA.

The synthesis gas generating unit further includes a mixing unit configured to receive at least one portion of the purified CO2 stream from the CO2 removal unit and at least one portion of the off-gas of the cold block and to combine them to form a combined carbon-rich stream. Thus, the mixing unit includes at least two inlets (one for the purified CO ₂ stream from the CO ₂ removal unit and one for the cold unit off-gas) and one outlet (for the combined carbon-rich stream). The mixing block may contain a simple connection between two pipes; one containing the purified CO ₂ stream from the CO ₂ removal unit, and the other containing at least a portion of the cold block off-gas. The mixing unit may contain additional elements, such as, for example, valves for regulating one or more gas flows, and may also contain one or more structural elements (for example, baffles), which contribute to the mixing of gas flows.

A compressor is located downstream of the first mixing unit to compress said combined carbon rich stream. Said compressor is a suitable multi-stage compressor.

The recirculation loop is designed to supply said compressed combined carbon-rich stream to the reformer section. The recirculation loop typically includes gas connections (ie tubes) from the outlet of the first mixing device to the reformer section.

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If it is desired to mix the compressed combined carbon-rich stream with the process gas prior to reforming said combined stream, the synthesis gas generating unit may further comprise a second mixing unit for mixing the compressed combined carbon-rich stream with the process gas and for supplying the resulting mixed streams to the reformer section. .

The plant of the present invention has been described with reference to several separate blocks. Although it is not described in detail, the installation also contains gas connections (eg pipelines, valves) that allow you to have certain gas flows and connections described above.

With respect to the process described above, taking off-gas from the cold block (which is rich in methane and potentially also CO), mixing it (at least in part) with the purified CO2 stream from the CO2 removal unit, and compressing said combined stream saves more carbon in the process and increases carbon savings, hence reducing feedstock consumption in the reformer.

In addition, an H2 rich stream recycle loop may be provided to feed at least a portion of the H2 rich stream from the cold block to the reformer as fuel. Thus, the total fuel consumption can be reduced, resulting in a reduction in the overall production of CO2 in the plant and in the possibility of zero fresh hydrocarbon fuel supply to the plant.

Specific Embodiments.

The concept of the method is shown in Fig. 1 and 2.

In FIG. 1 is a diagram of one embodiment of a syngas production plant 10. Process gas 102 is fed into a reformer section 100 to produce a reformed gas stream 104. The reformed gas stream 104 is cooled and the cooling section 150 condenses and separates water to produce a dry reformed gas. gas 106 containing CH ₄ , CO, CO 2 and H 2 . Said dry reformed gas 106 is sent to a CO2 removal unit 20 where it is separated into at least two gas streams, a purified _CO2 stream 22 and a _CO2 flushed stream 23.

Washed from CO ₂ flow 23 is directed from the block removal of CO ₂ 20 in the cold block. Here, it is separated into at least a cold block off-gas 32 containing CH ₄ , H ₂ and CO, an H ₂ rich stream 36, and a high purity CO stream 38.

At least a portion of the purified CO2 stream 22 from the CO2 removal unit 20 is combined with at least a portion of the off-gas from the cold unit 32 in the first mixing unit 60 to produce a combined carbon-rich stream 52. Said combined carbon-rich stream 52 is compressed in a compressor 50, and the compressed the combined carbon-rich stream 51 is recycled via recirculation loop 70 to reformer 100 where it is reformed. In the illustrated embodiment, the off-gas of the TSA 34 is used as fuel elsewhere in the plant, typically to heat the reformer section 100.

In the illustrated embodiment, the cold block 30 comprises a temperature swing absorber (TSA) block 35, said TSA block 35 producing a TSA 34 off-gas containing CO ₂ and H ₂ O.

In FIG. 2 is a diagram of one embodiment of a synthesis gas production plant that includes a PSA unit. It contains all the elements shown in Fig. 1, plus additional items. The _H2- enriched stream 36 from the cold block 30 is sent to a pressure swing adsorption (PSA) unit 40 to be separated into at least a high purity H2 stream 42 and an off-gas PSA 43.

In the illustrated in FIG. In Embodiment 2, PSA 43 off-gas is combined with TSA 34 off-gas from the cold block and used as fuel elsewhere in the plant, typically to heat reformer section 100.

In FIG. 3 is a diagram of one embodiment of a synthesis gas production plant that includes a recycle loop of H ₂ rich stream 80. FIG. 3 contains all the elements shown in FIG. 1 and 2, plus additional elements. As shown, recycle loop of H ₂ rich stream 80 is configured to feed at least a portion of H ₂ rich stream 36 from cold block 30 to reformer 100 as fuel 45 along with off-gas fuel PSA 43. The combined fuel stream is denoted as 47.

The present technology has been described in terms of several embodiments and figures. A person skilled in the art can combine elements from these embodiments and figures as needed within the scope of the invention as defined in the appended claims. All documents mentioned herein are incorporated by reference.

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Example 1

A steam methane reformer (SMR) was simulated with a lean natural gas (NG) feed and with a CO2 removal unit, a cold unit, and recirculation loops as shown in FIG. 1, but without a separate TSA off-gas, so that the TSA off-gas in the simulation ends up in an H2-rich stream in the cold block. Minor components such as the pre-reformer, desulphurization unit, refrigeration section, and some minor process streams such as compressor loss streams are not shown in the table below. However, these minor components are actually part of the simulation.

A software simulation of the supply of natural gas required to provide a given flow of produced CO was performed with various partial recirculations of the exhaust gas from the cold block.

Energy and mass balance calculations for the chemical process were performed and the results are summarized in the table below.

Options Thread numbers as in figure 1 Units Meaning (where applicable) Off-gas recirculation share 1/1 0 0.25 0.5 Natural gas feedstock stream Nm ³ /h 21114 20206.3 19142.3 Composition of raw materials based on natural gas CH ₄ mol % 97.71 97.71 97.71 С2+ mol % 0.88 0.88 0.88 CO ₂ mol % 0.70 0.70 0.70 n ₂ mol % 0.71 0.71 0.71 S/C ratio mol./mol. 1.5 1.5 1.5 steam flow kg/h 25418 24325 23043 Process gas feed to reformer 100 (raw stream) 102 Nm ³ /h 55230.3 52855.5 50076.4 Composition of the initial process gas n ₂ mol % 7.70 7.70 7.70 CH ₄ mol % 36.31 36.31 36.31 SO mol % 0.04 0.04 0.04 CO ₂ mol % 2.09 2.09 2.09 n ₂ mol % 0.27 0.27 0.27 H ₂ O mol % 53.58 53.58 53.58 Reformed gas from reformer 100 (raw stream) 104 Nm ³ /h 88538.1 87391.7 86174.8 Reformed gas composition n ₂ mol % 53.21 53.71 54.28 CH ₄ mol % 6.1 6.79 7.77 SO mol % 17.88 18.11 18.37

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from ₂ mol % 4.45 4.18 3.84 n ₂ mol % 0.17 0.17 0.16 H ₂ O mol % 18.2 17.04 15.59 Purified CO ₂ from section 20 (dry flow) 22 Nm ³ /h 3962.7 3676 3329.6 CO ₂ purity mol % dry matter 99.11 99.09 99.06 Off-gas from the cold block of section 30 (dry flow) Nm ³ /h 6197.4 6730.6 7487.3 Exhaust gas composition n ₂ mol % dry matter 15.19 13.94 12.49 CH ₄ mol % dry matter 75.72 77.68 79.98 SO mol % dry matter 8.97 8.27 7.44 n ₂ mol % dry matter 0.12 0.11 0.09 Exhaust gas recirculation stream 32 Nm ³ /h 0 1682.7 3743.7 Inlet stream to the recirculation compressor CO ₂ 50 (dry stream) 52 Nm ³ /h 3962.7 5358.7 7073.3 Flow of produced CO from section 30 (as 100% CO) 38 Nm ³ /h 15000 15000 15000 Purity of CO in the resulting CO mol % dry matter 99.06 99.09 99.12 balance flow 36 Nm ³ /h 46139.8 45977 45814.5 obtained H ₂ from section 30 (as 100% H ₂ ) The purity of H ₂ in the resulting H ₂ mol % dry matter 97.99 97.99 97.99

In fact, the calculations show that for a given level of CO produced flow (15,000 Nm ³ /h), natural gas consumption decreases as the recycle fraction of cold block off-gas in the recycle gas increases.

In the table above, S/C means the ratio of steam to carbon, which is the ratio of steam to carbon in the process gas hydrocarbons.

Example 2

A steam methane reformer (SMR) was simulated with a lean natural gas (NG) feed and with a CO ₂ removal unit, a cold block, a PSA block, and recirculation loops as shown in FIG. 3. A portion of the H ₂ -rich stream from the cold block is mixed with PSA off-gas and fed as fuel to the reformer. Minor components such as the pre-reformer, desulphurization unit, refrigeration section, and some minor process streams such as compressor loss streams are not shown in the table below.

However, these minor components are actually part of the simulation.

A software simulation of the natural gas supply required to provide a given flow of CO produced was performed. The table below shows two simulations; the first, in which all of the cold block off-gas and the PSA off-gas are fed as fuel along with the balance fresh hydrocarbon fuel to the reformer section, and the entire H2-enriched stream is processed in the PSA unit to be purified to a high purity _H2 product stream; the second, in which the combined stream of all off-gas of the cold block and the clean CO ₂ stream from the CO2 removal block is recycled to the reformer section as a feedstock, and part of the H _2- rich stream from the cold block, together with the off-gas PSA, is fed as fuel to the reactor section - 8 041183 forming without the need for any fresh fuel.

Energy and mass balance calculations for the chemical process were performed and the results are summarized in the table below.

Options Thread numbers as in figure 3 (where applicable) Units Meaning Share of recycling 1/1 ⁰ 1 waste gas Natural gas feedstock stream Nm ³ /h 21131.9 15899.7 Composition of raw materials based on natural gas CH ₄ mol % 97.71 97.71 С2+ mol % 0.88 0.88 CO ₂ mol % 0.70 0.70 n ₂ mol % 0.71 0.71 S/C ratio mol./mol. 1.5 1.5 steam flow kg/h 25432 19131 Process gas feed to reformer 100 (raw stream) 102 Nm ³ /h 59239.2 55164.1 Composition of the initial process gas n ₂ mol % 7.23 7.52 CH ₄ mol % 33.88 45.17 SO mol % 0.05 1.05 CO ₂ mol % 8.56 5.52 n ₂ mol % 0.25 0.22 H ₂ O mol % 50.02 40.53 Reformed gas from reformer 100 (raw stream) 104 Nm ³ /h 88563.1 83943.7 Reformed gas composition n ₂ mol % 53.22 55.35 CH ₄ mol % 6.11 12.54 SO mol % 17.87 18.85 CO ₂ mol % 4.44 2.6 n ₂ mol % 0.17 0.14 H ₂ O mol % 18.19 10.51

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Purified CO2 from section 20 (dry stream) 22 Nm ³ /h 3961.4 2204.6 CO2 purity mol % dry matter 99.11 98.9 Off-gas from the cold block of section 30 (dry flow) Nm ³ /h 6202.2 11317.3 Exhaust gas composition n ₂ mol % dry matter 15.19 8.21 CH ₄ mol % dry matter 75.73 86.8 SO mol % dry matter 8.96 4.94 n ₂ mol % dry matter 0.12 0.05 Dry recirculating off-gas stream from the cold block 32 Nm ³ /h 0 11317.3 Inlet stream to the recirculation compressor CO ₂ 50 (dry stream) 52 Nm ³ /h 3961.4 13521.8 Flow of produced CO from section 30 (as 100% CO) 38 Nm ³ /h 15000 15000 Purity of CO in the resulting CO mol % dry matter 99.06 99.25 Enriched H ₂ stream (dry) from cold block section 30 36 Nm ³ /h 47107.4 46449.9 The composition of enriched H ₂

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Claims (9)

flow n ₂ mol%. dry matter 97.99 97.99 CH ₄ mol %. dry matter 1.5 1.5 SO mol % dry matter 0.5 0.5 CO ₂ mol %. dry matter 0.01 0.01 Obtained H ₂ (dry) from section 40 42 Nm ³ /h 41587.3 21056.7 The purity of H ₂ in the resulting H ₂ mol%. dry matter 99.9 99.9 Fuel Fuel based on enriched H ₂ stream (dry stream) 45 Nm ³ /h 0 22598 Cold block off-gas fuel (dry flow) Nm ³ /h 6202.2 0 Combined fuel (dry stream) 47 Nm ³ /h 11722.3 25393.2 The composition of the combined fuel n ₂ mol%. dry matter 47.42 96.41 CH ₄ mol %. dry matter 45.74 2.66 SO mol % dry matter 6.75 0.91 CO ₂ mol %. dry substance 0.03 0.02 n ₂ mol % dry matter 0.06 0 Fresh fuel flow Nm3 ^/ h 878.9 0 Net calorific value (LHV) of fresh fuel kcal/ ^Nm3 13322.5 13322.5 Flue gas flow CO ₂ Nm ³ /h 7700 933 CLAIM 1. A method for producing synthesis gas in a synthesis gas production unit (10), wherein said synthesis gas production unit (10) comprises a reforming section (100) in which the process gas (102) is first reformed in at least one stage reforming to produce a reformed gas stream (104); and a cooling section (150) in which the reformed gas stream (104) is cooled to obtain a dry reformed stream (106) containing CH4, CO, CO ₂ and H ₂ , said process comprising the following steps: a) sending the dry reformed stream (106) to a _CO2 removal unit (20) to separate it into at least a purified CO2 stream (22) and a _CO2 washed stream (23) having a lower _CO2 content than the specified stream of purified CO ₂ (22); b) directing the CO2 _- flushed stream (23) from the _CO2 removal unit (20) to the cold unit (30) to separate it into at least the off-gas of the cold unit (32) containing CH4, _H2 and CO, - 11 041183 H2-enriched stream (36) and high purity CO stream (38); c) combining at least a portion of the purified CO2 stream (22) from the CO2 removal unit (20) with at least a portion of the off-gas of the cold unit (32) to obtain a combined carbon-rich stream (52); d) compressing said combined carbon-rich stream (52); e) recycling said compressed combined carbon rich stream (51) to a reformer (100); And f) reforming said compressed combined carbon-rich stream (51) in the reformer section (100), wherein at least a portion of the H2-rich stream (36) from said cold block (30) is used as fuel to heat the reformer section (100). 2. Process according to claim 1, wherein said H ₂ rich stream (36) from said cold block (30) is sent to a pressure swing adsorption (PSA) block (40) to separate it into at least a high H ₂ stream. purity (42), and off-gas PSA (43). 3. The method according to one of the preceding claims, wherein the cold block (30) comprises a temperature swing absorber (TSA) block (35), said TSA block (35) produces a TSA exhaust gas (34) containing CO ₂ and H ₂ O. 4. The method of claim 3, wherein a portion of the TSA off-gas (34), a portion of the PSA off-gas (43), or a portion of the cold block off-gas (32), or a combination thereof, is supplied as fuel to heat the reformer section (100). 5. Process according to one of the preceding claims, wherein the reformer section comprises an autothermal reformer (ATR), a steam methane reformer (SMR), a convective reformer or a catalytic partial oxidation (CATOX) unit, preferably an ATR or SMR unit. 6. Process according to one of the preceding claims, wherein the compressed combined carbon-rich stream (52) is mixed with process gas (102) prior to being reformed in the reformer section (100). 7. A process according to one of the preceding claims, wherein the total volume of the purified CO ₂ stream (22) from the CO ₂ removal unit (20) is combined with the total off-gas volume of the cold unit (32) to obtain said combined carbon-rich stream (52). 8. Installation for producing synthesis gas (10), including a reforming section (100) configured to reform process gas (102) in at least one reforming stage to obtain a reformed stream (104) containing CH ₄ , CO, CO ₂ , H ₂ and H ₂ O; a cooling section (150) for cooling the reformed stream (104) and condensing water from said reformed stream (104) to form a dry reformed stream (106) containing CH ₄ , CO, CO ₂ and H ₂ ; a CO ₂ removal unit (20) located downstream of said reforming section (100) to receive said reformed stream (104) and separate it into at least a purified CO ₂ stream (22) and a CO ₂ washed stream (23) having a lower CO ₂ content than said purified CO 2 stream (22); cold block (30) located downstream of said CO ₂ removal unit (20) for receiving said CO ₂ flushed stream (23) from said CO ₂ removal unit (20) and separating it into at least off-gas a cold block (32) containing CH4, H ₂ and CO, an H ₂ rich stream (36), and a high purity CO stream (38); a first mixing unit (60) for receiving at least a portion of the purified CO ₂ stream (22) from the CO ₂ removal unit (20) and at least a portion of the cold unit off-gas (32) and combining them to form a combined carbon rich flow (52); a compressor (50) for compressing said combined carbon-rich stream (52); a recirculation loop (70) for supplying said compressed combined carbon-rich stream (51) to the reforming section (100); and an H ₂ rich stream recycle loop (80) for feeding at least a portion of the H ₂ rich stream (36) from the cold block (30) to the reformer (100) as fuel. 9. The synthesis gas production unit of claim 8, further comprising a pressure swing adsorption (PSA) unit (40) for receiving _{an H2-} enriched stream (36) from said cold unit (30) and separating it at least , on -