Method for separating off-gas from ferrous metal production plant

Abstract

A method for separating off-gas from a ferrous metal production plant uses a first adsorption unit (4) to separate the off-gas by pressure swing adsorption to produce a gas (5) depleted in carbon monoxide and hydrogen and rich in CO2 relative to the off-gas and a first gas (7) rich in carbon monoxide and hydrogen and depleted in CO2 relative to the off-gas, a unit for partial condensation and / or distillation separation (CC), means for feeding the CO2-rich gas into the unit for partial condensation and / or distillation separation (CC) to produce a CO2-rich fluid (14), a second adsorption unit (6), means for feeding at least a portion of the CO-rich gas to a second adsorption unit (6) for separation by temperature swing adsorption to form, at a first pressure, a CO2-rich gas (23) relative to the first CO-rich gas and a CO and hydrogen-rich second gas (15) relative to the first CO-rich gas, the second gas containing nitrogen; means for feeding, by means of a unit (CB) for partial condensation and / or scrubbing and / or distillation separation, at least a portion of a second gas (15) rich in CO and hydrogen into the separation unit (CB) for separation therein to produce a gas (17) lean in nitrogen and rich in CO relative to the second gas.

Description

[0001] The present invention relates to a method for separating exhaust gas from an iron-based metal production plant.

[0002] The method of producing cast iron in a smelting reactor such as a blast furnace is a method in which at least iron ore, an oxidant, and fuel are introduced into the furnace to melt the ore and obtain cast iron containing at most 5% carbon, where a gas (referred to as "blast furnace gas") is recovered at the reactor outlet, which contains 15 - 45 mol% CO on a dry basis 2 , 15 - 45 mol% CO, and the balance consists essentially of nitrogen, hydrogen, various hydrocarbons, and a small percentage of argon, and then the CO 2 is separated from the remainder of the blast furnace gas, and the latter is sent to a device that uses the gas. Preferably, the blast furnace gas contains 15 - 30 mol% CO and / or CO 2 , each on a dry basis. A blast furnace is an iron-making and steel-making tool for producing cast iron from iron ore and coke raw materials, where the oxidant for combustion is optionally oxygen-rich air. The iron ore is heated, reduced, and melted by the coke, and burning the coke with air provides some of the energy required to heat and melt the iron ore. In addition to coke, coal or another hydrocarbon injected into the blast furnace tuyeres can of course be used. On the other hand, carbon monoxide is produced, which comes from the combustion reaction of coke and / or coal and / or hydrocarbon with air injected into the tuyeres known as the blast, which is rich in oxygen or not rich in oxygen. This carbon monoxide is necessary for reducing the iron ore. The annual production of blast furnace cast iron can reach 100,000 metric tons for the smallest of them and several million metric tons for the most productive ones. One or more blast furnaces can be present in the same plant, up to 10 at most where possible in some places. As a result of the combustion and reactions occurring in the blast furnace, "blast furnace gas" is recovered at the outlet of the furnace, which is generally a mixture of nitrogen (about 35 - 65 vol%) essentially from the air injected into the blast furnace tuyeres, carbon monoxide (about 15 - 30 mol%) obtained from the partial or complete combustion of the coke or generally the injected fuel, and carbon dioxide (also about 15 - 30 mol%). This combustion is also the reason for the presence of water vapor, because the general reaction between the carbon-containing products and oxygen during combustion basically produces CO 2 and H 2 O. Other gases are also found in the blast furnace gas, in smaller total amounts, usually less than 12 vol% in total, and these other gases consist especially of hydrogen, various hydrocarbons, argon from the air, etc. This blast furnace gas is a "poor" gas because it has a low calorific value, usually 2000 - 6000 kJ / Nm 3 , which is contrary to other iron-making and steel-making gases called "rich gases" because they have a much higher calorific value (for example, the gases from cast iron to steel converters or coke ovens usually have calorific values of 6000 - 10,000 kJ / Nm respectively) 3and 12,000 - 20,000 kJ / Nm 3 ). The amount of gas produced by blast furnaces is usually very large, on the order of about 1500 Nm 3 of gas per tonne of cast iron produced. As a result, given the composition of the gas, the amount of carbon dioxide produced per tonne of cast iron is also very large: for example, for blast furnace gas with an average carbon dioxide content of 22% in the dry gas and for a blast furnace producing one million tonnes of cast iron per year, the carbon dioxide emissions in the blast furnace gas are 330 million Nm 3 / year, i.e., about 650,000 tonnes of carbon dioxide are produced in one year. For a blast furnace producing three million tonnes of cast iron per year, the CO 2 emissions are about two million tonnes / year, while for a site producing seven million tonnes of cast iron per year, the CO 2 amount is about 4.5 million tonnes. These amounts are quite large and considering the negative effects of these gases on the atmosphere and the environment, it is not possible to consider discharging them directly into the atmosphere in this way. In addition, discharging the said gas into the atmosphere also requires discharging carbon monoxide into the atmosphere, which is known to be very dangerous and therefore it is necessary to provide a system for recovering this blast furnace gas.

[0003] A typical composition of the waste gas from an iron metal production plant - here blast furnace gas or "top gas" - is as follows:

[0004] ● H 2 : 4 - 5 mol%

[0005] ● CO: 24 - 25%

[0006] ● CO 2 : 23 - 25%

[0007] ● N 2 : 40 - 45%

[0008] ● H 2 O: 3%

[0009] The purpose of extracting CO 2 and N 2 present in the top gas from the blast furnace is to upgrade them: ● as fuel (higher calorific value) for turbines (power generation in integrated steelworks) or other users in the steelworks (such as cowper, mixed with other fuel gases (coke oven gas or natural gas) to preheat high-oxygen air),

[0010] ● as reducing gas for coal in the blast furnace itself.

[0011] It is also known from EP3997235A1 that it is common practice to use blast furnace gas containing more than 20 mol% CO as a raw material for producing biofuels to convert CO into at least one biofuel, such as bioethanol.

[0012] A bioreactor operating, for example, according to WO 08 / 115080 can be used to convert CO into bioethanol therein.

[0013] An object of the present invention is to produce a CO-rich stream from an iron-based metal production plant while capturing the CO generated by the production plant 2 .

[0014] According to one subject of the present invention, there is provided a method for separating exhaust gas from an iron-based metal production plant, wherein:

[0015] i) The exhaust gas contains at least CO, CO 2 , hydrogen and nitrogen and is compressed in a first compressor and then separated by pressure swing adsorption in a first adsorption unit to produce a gas that is lean in carbon monoxide and hydrogen and rich in CO 2 relative to the exhaust gas and a first gas that is rich in carbon monoxide and hydrogen and lean in CO 2 relative to the exhaust gas, which contains no more than 2 mol% of CO 2 , ii) The gas rich in CO 2 is fed into a unit separated by partial condensation and / or distillation and / or solidification to produce a CO-rich 2 fluid containing at least 80 mol% of CO 2 , or even at least 95 mol% of CO 2 ,

[0016] iii) At least a part of the gas rich in CO is separated by temperature swing adsorption in a second adsorption unit to form a gas rich in CO 2 relative to the first gas rich in CO at a first pressure and a second gas rich in CO and hydrogen relative to the first gas rich in CO, wherein the second gas contains nitrogen, and

[0017] iv) At least a part of the second gas rich in CO and hydrogen is compressed and separated by partial condensation and / or washing and / or distillation to produce a third fluid rich in nitrogen and lean in hydrogen and CO relative to the second gas and a fourth gas lean in nitrogen and rich in CO and / or hydrogen relative to the second gas.

[0018] According to other optional aspects:

[0019] ● At least a part of the second and / or fourth gas rich in CO is fed into a method for producing biofuels, such as ethanol, by fermentation.

[0020] ● Compress at least a portion of the second and / or fourth gas rich in CO and hydrogen and separate it by partial condensation and / or washing and / or distillation to produce a third fluid rich in nitrogen and poor in hydrogen and CO relative to the second gas, and a fourth gas poor in nitrogen and rich in CO and / or hydrogen relative to the second gas.

[0021] ● Separate at least a portion of the second gas by partial condensation and / or washing and / or distillation to produce a fourth gas rich in CO and poor in hydrogen and nitrogen relative to the second gas, and a fifth gas poor in nitrogen and CO and rich in hydrogen relative to the second gas.

[0022] ● Feed at least a portion of the fourth gas and / or fifth gas into a process for producing biofuels, such as ethanol, by fermentation.

[0023] ● Feed at least a portion of the third fluid into a process for producing biofuels, such as ethanol, by fermentation.

[0024] ● The gas rich in CO produced by temperature swing adsorption 2 is mixed with the gas rich in CO 2 , optionally upstream of the step of compressing the gas rich in CO 2 .

[0025] ● The exhaust gas contains 15 - 45 mol% CO, preferably greater than 20 mol% CO.

[0026] ● The first gas rich in CO is rich in nitrogen relative to the exhaust gas.

[0027] ● The second gas rich in CO contains at least 60 mol% CO.

[0028] ● Separate at least a portion of the gas containing at least 60 mol% CO by partial condensation and / or washing and / or distillation at a low temperature to reduce its nitrogen content, forming a gas containing at least 80 mol% CO

[0029] and also hydrogen, and a gas rich in nitrogen.

[0030] ● The exhaust gas contains argon and low-temperature separation produces a fluid rich in argon,

[0031] ● Low-temperature separation produces a fluid rich in hydrogen,

[0032] ● The gas poor in CO 2 and rich in CO contains at least 85%, preferably at least 90% of the CO present in the gas mixture fed into the first adsorption unit.

[0033] ● The gas poor in CO 2And the gas rich in CO contains no more than 83%, preferably no more than 80%, of the CO present in the gas mixture fed to the first adsorption unit.

[0034] ● The waste gas is poor in carbon monoxide and hydrogen and rich in CO 2 The gas contains at least 70%,

[0035] preferably at least 80%, or even at least 90% or at least 95%, of the CO present in the gas mixture fed to the first adsorption unit 2 ,

[0036] ● The regeneration gas fed to the second adsorption unit is formed by a part of the gas containing at least 60 mol% CO.

[0037] ● The regeneration gas fed to the second adsorption unit is formed by the gas produced by cryogenic separation,

[0038] ● Separate the gas rich in CO in a separation unit by partial condensation and / or distillation and / or solidification to form at least one gas richer in CO and hydrogen than the gas rich in CO 2 and send the at least one gas richer in CO and hydrogen to the first adsorption unit for separation. ● The gas rich in CO 2 contains water and is dried in a drying unit upstream of the separation unit by partial condensation and / or distillation and / or solidification. The regeneration gas containing CO and / or hydrogen is used to regenerate the drying unit and then sent to the first adsorption unit for separation,

[0039] ● Separate a part of the second gas at a low temperature by partial condensation and / or washing and / or distillation to reduce its nitrogen content, forming a gas containing at least 80 mol% CO and also hydrogen and a gas rich in nitrogen, 2 ● The waste gas contains argon and a fluid rich in argon is produced by separation by partial condensation and / or washing and / or distillation,

[0040] ● Cryogenic separation produces a fluid containing at least 80% hydrogen,

[0041] ● Send at least a part of the gas rich in CO relative to the first gas rich in CO

[0042] and produced by the second adsorption unit to the upstream of the first adsorption unit for separation,

[0043] ● Send at least a part of the gas rich in CO relative to the first gas rich in CO 2 and produced by the second adsorption unit to the upstream of the separation unit by partial condensation and / or distillation and / or solidification for separation,

[0044] ● Send at least a part of the gas rich in CO relative to the first gas rich in CO 2 and produced by the second adsorption unit to the upstream of the separation unit by partial condensation and / or distillation and / or solidification for separation,

[0045] ● Enrich at least a part of the gas rich in CO with respect to the first gas rich in CO 2 And feed the gas produced by the second adsorption unit into an iron-based metal production device, such as a blast furnace.

[0046] Surprisingly, the optimal optimization of this method is that the pressure swing adsorption unit purifies the gas containing at least 20% carbon monoxide from this metal production device and makes the gas rich in CO produced by this adsorption 2 of the gas 2 The operation is aimed at maximizing the yield.

[0047] The present invention will be described in more detail with reference to the accompanying drawings, in which:

[0048] Figure 1 Represents a comparative method.

[0049] Figure 2 Represents a comparative method.

[0050] Figure 3 Represents the method of the present invention.

[0051] Figure 1 Describes a method for separating the top gas generated by the blast furnace HF. The top gas is purified in the pretreatment unit P to remove the dust contained therein, compressed by the compressor C1 and separated by pressure swing adsorption in the separation unit 4 to produce a gas 7 rich in CO and nitrogen and poor in CO with respect to the gas 1 to be separated 2 and a gas 5 poor in CO and nitrogen and rich in CO with respect to the gas to be separated 2 of the gas.

[0052] In the case of the unit 4 for separating by pressure swing adsorption known as PSA - which processes the waste gas compressed to about 8 bar from the iron-based metal device and operates in the "high CO yield" mode - the recovery yield of CO in the gas 7 at high pressure is usually greater than 80% (or even greater than 85%), while the corresponding yield of low-pressure CO 2 extracted in the gas 5 is about 88% and the N 2 yield is about 15%. The aim is to maximize both the recovery yield of CO and the extraction yield of CO 2 / N 2 of the extraction yield.

[0053] The CO-rich stream 7 produced by PSA 4 therefore also contains a large amount of nitrogen (about 85 mol% of the gas stream to be treated), because the CO / N 2 selectivity on the traditional adsorbent is very low. It also contains hydrogen and CO 2 (about 12% of the gas stream to be treated).

[0054] The CO-rich gas produced by the PSA at low pressure 2 also contains unadsorbed CO present in the top gas of the furnace (about 15% of the top gas stream being treated), H 2 , nitrogen, and water.

[0055] Table 1 shows an example of a material balance obtained for PSA 4 operating in the "high CO recovery" mode on off-gas 1 at about 8 bar as shown: Figure 1

[0056] PSA inlet 4 CO-rich gas 7 <![CDATA[Gas 5 rich in CO 2 > Flow rate 100 67 33 <![CDATA[H 2 mol%]]> 5 8 1 CO 25 32 11 <![CDATA[CO 2 > 26 5 68 <![CDATA[N 2 > 43 55 18 <![CDATA[H 2 O]]> 1 0 2

[0057] CO recovery yield = 85.8%

[0058] The practice known from EP1869385 is to separate the CO-rich 2 gas produced by adsorptive separation from the top gas of an iron-based metal plant at low pressure, for example by partial condensation and / or distillation. These two techniques can be integrated by recycling all or part of the CO-lean 2 and CO-containing gas stream, which comes from the separation by partial condensation and / or distillation in separation unit CC upstream or downstream of the compressor for gas C feeding the PSA 4, saving 10% or more of the compression energy of the PSA4.

[0059] Table 2 shows an example of a material balance obtained for PSA 4 operating in the "high CO recovery" mode on off-gas 1 from blast furnace HF at about 8 bar in combination with unit CC for separation by partial condensation and / or distillation and / or freezing:

[0060] Table 2

[0061] PSA inlet 4 CO-rich gas 7 <![CDATA[Gas 5 rich in CO 2 > Flow rate 100 80 20 <![CDATA[H 2 mol%]]> 5 7 0 CO 25 31 0.5 <![CDATA[CO 2 > 26 7 99 N2 43 55 0.5 <![CDATA[H 2 O]]> 1 0 0

[0062] In this case, the CO recovery yield is close to 100%. The recycle gas 11 and / or 13 of the PSA helps to push it closer to 100%.

[0063] The PSA can be operated on the top gas 1 in the "high CO 2 recovery" mode with a reduced CO recovery yield, which can enable an increase in the CO 2 extraction yield. This function can be obtained by modifying the cycle of the PSA and / or by changing the amount of adsorbent and / or by allowing less CO 2 to enter the CO-rich gas.

[0064] Examples of yields obtained by PSA 4 on the top gas at 8 bar:

[0065] Table 3

[0066] PSA 4 Mode High CO recovery in gas 7 <![CDATA[High CO in gas 5 2 generation]]> CO recovery in gas 7 ％ 85 80 <![CDATA[N in Gas 7 2 Yield]]> ％ 86 82 <![CDATA[CO in Gas 7 2 Yield]]> ％ 13 2 <![CDATA[H in Gas 7 2 Yield]]> ％ 94 93

[0067] In the "high CO recovery" operating mode, the PSA 4 is operated to maximize the percentage of CO recovered from the gas 7 fed to the TSA unit. Thus, it can be seen that 85% of the CO present in the gas at the inlet of the PSA 4 is subsequently found in the gas 7 together with 94% hydrogen. However, a significant percentage of CO (13%) is found in the gas 7. 2 (13%).

[0068] Operating in the "high CO 2 production" mode may result in a CO-rich stream HP 7 containing no more than 2 mol% CO. On the other hand, a split of the produced CO (i.e., the CO recovery yield) will be observed to decrease. Surprisingly, in order to optimize the overall process to produce a stream containing sufficiently little CO 2 and allowing the TS unit to remove all the remaining CO 2 it is necessary to adjust the operation of the PSA 4 to reduce the CO 2 content in the produced CO-rich gas 7 as much as possible. 2 content.

[0069] For blast furnace "top gas", if it is desired to simultaneously obtain:

[0070] ● The maximum degree of CO recovery

[0071] ● And / or the maximum degree of recovery of the purified CO-rich 2 stream produced in liquid or gaseous form

[0072] ● And / or a more or less N-lean 2 CO-rich stream

[0073] The invention proposed below can be implemented. It comprises combining a PSA preferably operated in the "high CO 2 production" mode with:

[0074] ● A CO 2 separation unit by partial condensation and / or distillation and / or freezing (and its suitable recycling) to produce purified CO in liquid or gaseous form 2 , and

[0075] ● A CO 2 TSA for the CO-rich stream produced by the PSA to adsorb the residual CO 2 (not exceeding 2%). The required regeneration gas must not contain any CO 2 and can be from:

[0076] ● TSA CO 2 product (see the note below)

[0077] ● N produced by the downstream cold box 2 feed stream or CO feed stream

[0078] ● External feed stream

[0079] The waste gas thus produced can (or may not) be recycled to the PSA inlet and / or to the inlet of the CO separation unit by partial condensation and / or distillation and / or solidification of CO, or recycled to the blast furnace, always with the aim of improving the H / CO and CO molecular recovery yield. 2 2 / CO and CO 2 Molecular recovery rate

[0080] ● Low-temperature unit (with partial condensation and / or washing (e.g., washing with liquid N or liquid CO) and / or distillation steps and a cold box with or without an associated refrigeration cycle) in series with a TSA for the CO-rich feed stream to partially or completely separate the nitrogen present in the CO-rich feed stream. The third waste gas optionally produced in the low-temperature unit can also be recycled upstream of the PSA or upstream of the CO separation unit by partial condensation and / or distillation and / or solidification of CO. 2 or liquid CO washing) and /

[0081] 2 Recycled upstream

[0082] A CO-rich gas compression step may be provided upstream of the low-temperature unit.

[0083] The low-temperature unit can be used to produce at least one more or less H-rich auxiliary feed stream and / or at least one Ar-rich auxiliary feed stream (Ar comes from the air and O introduced into the blast furnace and finally into the top gas). 2 2 )

[0084] The TSA must remove a relatively high CO content upstream of the N / CO cold box, which will require a large amount of heat. Using a part of the decarbonized gas that can be obtained downstream of the TSA is not necessarily ideal for two reasons. On the one hand, if the regenerated gas is sent to the fuel network, it will result in a loss of CO / H yield, or if the gas is recycled upstream of the PSA, it will result in a loss of energy efficiency. On the other hand, the presence of CO / H will limit the regeneration temperature to 150 °C to avoid reactivity problems in the TSA regenerated gas heater. Then it is preferably to use the N feed stream from the CO / N cold box to regenerate the TSA and return the regenerated feed stream to the fuel network. 2 / CO cold box upstream removal of relatively high CO 2 Content will require a large amount of heat. Using a part of the decarbonized gas that can be obtained downstream of the TSA is not necessarily ideal for two reasons. On the one hand, if the regenerated gas is sent to the fuel network, it will result in a loss of CO / H 2 Yield loss, or if the gas is recycled upstream of the PSA, it will result in a loss of energy efficiency. On the other hand, CO / H 2 The presence of will limit the regeneration temperature to 150 °C to avoid reactivity problems in the TSA regenerated gas heater. Then it is preferably to use the N from the CO / N 2 Cold box N 2 Feed stream to regenerate the TSA and return the regenerated feed stream to the fuel network.

[0085] Operating the PSA in the "high CO extraction" mode has the main advantage of facilitating the complete removal of CO downstream 2 ​​​​2 , which is significantly compatible with TSA type technologies and enables the possibility of final N 2 / CO separation. The CO lost in the PSA off-gas will be recovered by a separation unit through partial condensation and / or distillation and / or solidification and recycled to the PSA inlet to improve the production yield.

[0086] The main drawbacks of this solution are the increased recycle gas flow and thus increased equipment, as well as the specific energy of the separation unit through partial condensation and / or distillation and / or solidification increasing due to the CO 2 loss in the PSA off-gas.

[0087] Therefore, overall, pure CO can be produced with a high recovery yield 2 and a very CO-rich stream. The amount of residual nitrogen in the CO-rich stream (i.e., the nitrogen extraction yield) can be suitable for use in the cold box. The purified CO thus produced can be introduced into a biofuel production unit or recycled to the blast furnace (reducing the CO emissions from the blast furnace 2 ).

[0088] The PSA can be sized according to the "maximum CO yield" mode (selecting the adsorbent and the optimal cycle) or according to the "high CO 2 extraction" mode (selecting the optimal adsorbent and / or cycle) or sized to be able to operate in both modes (requiring a suitable adsorbent + modifying the cycle during operation).

[0089] PSA CO 2 in combination with separation by partial condensation and / or distillation and / or solidification has the following objectives:

[0090] ● Both make the PSA off-gas rich in CO 2 to minimize the specific energy of the separation method by partial condensation and / or distillation and / or solidification

[0091] ● And to increase the CO purity of the product that can be fed into a carbon monoxide-consuming process, such as a CO-to-ethanol conversion process using CO.

[0092] For a PSA 4 operating on top gas at about 8 bar in the "high CO 2 yield" mode and combined with a cryogenic CO 2 separation unit CC, TSA 6, and a cryogenic separation of CO and N 2 CB, the material balance example obtained:

[0093] Table 3

[0094] PSA inlet 4 Generated CO 17 <![CDATA[Generated CO 2 14]]> <![CDATA[The generated N 2 19]]> Flow rate 100 31 26 43 <![CDATA[H 2 mol%]]> 5 17.5 0 0 CO 25 80.5 0.5 0.5 <![CDATA[CO 2 > 26 0 99 0 <![CDATA[N 2 > 43 2 0.5 99.5 <![CDATA[H 2 O]]> 1 0 0 0

[0095] CO yield: close to 100%

[0096] It is possible to seek to maximize the CO yield of the PSA 4 to obtain a CO richer off-gas 5 from the PSA 4, thereby reducing the specific energy for separating CC by partial condensation and / or distillation and / or solidification. The main benefit of operating the PSA 4 in the "high CO yield" mode is to increase the CO concentration in the CO-rich gas 5 from the PSA 4, which is the feed stream to the equipment CC for separation by partial condensation and / or distillation and / or solidification. This solution has the advantage of reducing the OPEX of the equipment CC for separation by partial condensation and / or distillation and / or solidification and to a lesser extent reducing its CAPEX. 2 of the off-gas 5, thereby reducing the specific energy for separating CC by partial condensation and / or distillation and / or solidification. The main benefit of operating the PSA 4 in the "high CO yield" mode is to increase the CO in the CO-rich 2 gas 5 from the PSA 4, which is the feed stream to the equipment CC for separation by partial condensation and / or distillation and / or solidification. This solution has the advantage of reducing the OPEX of the equipment CC for separation by partial condensation and / or distillation and / or solidification and to a lesser extent reducing its CAPEX. 2 concentration, which is the feed stream to the equipment CC for separation by partial condensation and / or distillation and / or solidification. This solution has the advantage of reducing the OPEX of the equipment CC for separation by partial condensation and / or distillation and / or solidification and to a lesser extent reducing its CAPEX.

[0097] For a PSA for processing blast furnace top gas, a typical material balance of the CO-rich 2 gas CC system is as follows:

[0098] Table 4

[0099]

[0100] Optimizing the compressor C1 (if any) for the CO-rich 2 gas 5 and the external cold cycle allows for a specific energy consumption of approximately 200 kW per ton of liquid CO produced. 2

[0101] Figure 3 The method of the present invention is illustrated. It includes combining a pressure swing adsorption separation unit PSA 4, a partial condensation and / or distillation and / or solidification separation unit, and a temperature swing adsorption separation unit TSA 6. Examples of the partial condensation and / or distillation separation unit are described in FR2310716 filed on October 6, 2023.

[0102] The gas 1 includes 15 - 45 mol% or even 15 - 30 mol% CO 2 , 15 - 45 mol% or even 15 - 30 mol% CO, with the remainder consisting essentially of nitrogen, hydrogen, various hydrocarbons, water, and a small percentage of argon. The gas is pretreated in the pretreatment unit P to remove solid impurities and then compressed to a pressure of approximately 8 bar in the compressor C.

[0103] The compressed gas 1 is separated by pressure swing adsorption in the unit 4, producing a gas 7 rich in CO and hydrogen relative to the gas 1 entering the unit 4, preferably containing no more than 2% CO. 2 . The unit 4 also produces a gas 5 poor in CO relative to the gas 1 entering the unit 4 and rich in CO 2 .

[0104] The gas 5 can be compressed in the compressor C1. The gas 5 is at a first pressure higher than the second pressure of the gas 7.

[0105] The gas 5 is separated in the unit CC by partial condensation and / or distillation and / or solidification to form a CO-rich 2 fluid (gas or liquid) 14 containing at least 80 mol% CO, 2 or even at least 95 mol% CO. 2 The unit CC also produces a gas 13 rich in carbon monoxide and hydrogen relative to the gas 5, and feeds the gas 13 upstream of the PSA unit 4 or upstream of the compressor C. The gas 13 can be, for example, the gas from the partial condensation step and / or the overhead gas from the distillation column. The unit CC produces a gas 11 rich in carbon monoxide and hydrogen relative to the gas 5. The gas 11 is divided into two parts. One part FG is used as fuel gas and the other part 11 is optionally used to regenerate a dryer (not shown) upstream of the unit CC. The regenerated gas 11 with added water after regeneration is fed upstream of the PSA unit 4 or upstream of the compressor C. Part of the gases 15, 17, 21, 23, 31, 33 can also be used as the regenerated gas.

[0106] The gas 7, G1 is separated in the adsorption unit 6 to form a gas 15 rich in CO and H relative to the gas 7. 2 The gas 15, G2 no longer contains CO, 2 but still contains nitrogen.

[0107] As a variant, only the unit 6 is used to separate the gas 7 and the gas 15 constitutes the product of the process.

[0108] The regeneration gas required for regenerating the unit 6 must not contain CO 2 and can come from:

[0109] ● TSA CO 2 6 products 15, 17, 19

[0110] ● External feed stream

[0111] Thus, the waste gas 23 generated by the TSA 6 unit can (or may not) be recycled to the PSA 4 inlet (stream 29) and / or the unit CC inlet (streams 31, 33) or the HF blast furnace, always for the purpose of improving the H 2 / CO and CO 2 molecule recovery yield.

[0112] Optionally, the gas 15 is compressed in compressor C2 and separated in the cryogenic CB unit. The CB unit includes a thermally insulated chamber containing at least one phase separator and / or at least one scrubbing tower and / or at least one distillation column. The at least one scrubbing tower can be a liquid nitrogen or liquid carbon monoxide scrubbing tower. The CB unit can include at least one refrigeration cycle. The separation performed by the CB unit is a partial or complete separation of the nitrogen present in the CO-rich stream 15. The CB unit produces a fluid 19 that is rich in nitrogen and poor in CO and hydrogen relative to the gas 15. The fluid 19 can contain at least 90 mol% nitrogen. The CB unit produces at least one gas that is rich in hydrogen and / or CO and poor in nitrogen relative to the gas 15. For example, it can produce at least one gas that is rich in hydrogen and poor in nitrogen and CO relative to the gas 15 and / or at least one gas that is rich in CO and poor in nitrogen and hydrogen relative to the gas 15.

[0113] At least a portion of the gas 15 and / or at least a portion of at least one gas that is rich in hydrogen and / or CO and poor in nitrogen relative to the gas 15 from the CB unit are fed to the fermentation unit 13.

[0114] Preferably, at least one gas that is rich in hydrogen and poor in nitrogen and CO relative to the gas 15 and / or at least one gas that is rich in CO and poor in nitrogen and hydrogen relative to the gas 15 are fed to it. Feeding two gases of different purities to the fermentation unit allows the CO and H 2 content in the gas present in the fermentation unit to be changed. A gas 19 rich in nitrogen can also be fed in a variable flow rate to slow down the fermentation reaction.

[0115] Another possibility is to feed at least a portion of the hydrogen-rich gas that is poor in nitrogen and CO relative to the gas 15 and / or at least another portion of the CO-rich gas that is poor in nitrogen and hydrogen relative to the gas 15 to another gas user.

[0116] Any waste gas 21 produced in the cryogenic unit can also be recycled upstream of the PSA 4 (stream 29) or upstream of the unit CC (streams 31, 33).

[0117] The cryogenic CB unit can be used to produce at least one more or less H 2 rich stream, such as a fluid (gas or liquid) containing at least 80 mol% hydrogen and / or a fluid (gas or liquid) containing at least 80 mol% argon (the argon comes from the air and O 2 ) introduced into the blast furnace HF and ultimately into the top gas 1.

[0118] The TSA 6 unit must remove the relatively high CO upstream of the CB unit 2The content will require a large amount of heat. Using a part of the decarbonated gas 15 that can be obtained downstream of this TSA 6 as the regeneration gas is not necessarily ideal for two reasons. On the one hand, if this regeneration gas is fed into the fuel gas network, it will result in a CO / H 2 recovery loss, or if this gas is recycled upstream of this PSA 4, it will result in an energy efficiency loss. On the other hand, the presence of CO / H 2 limits the regeneration temperature to 150 °C to avoid reactivity problems in the heater of this TSA 6 unit. Then, it is preferable to use the N 2 feed stream 19 from the cold box CB to regenerate this TSA 6 and return the regenerated feed stream to the fuel network.

[0119] Operating the PSA 4 unit in the "high CO 2 production" mode has the main advantage of facilitating the complete removal of CO downstream 2 , which is significantly compatible with TSA-type technologies, and enables the possibility of final N 2 / CO separation. The CO lost in the PSA 4 waste gas 5 will be recovered by the separation unit CC through partial condensation and / or distillation and / or solidification and recycled to the PSA inlet to improve the production yield.

[0120] The main disadvantages of this solution are the increase in the recycle gas flow and thus the equipment, and also the specific energy of unit CC increases due to the CO 2 loss in the waste gas 5 from the PSA 4 unit.

[0121] Therefore, overall, pure CO 2 and a very CO-rich feed stream can be produced with a high recovery yield. The amount of residual nitrogen in the CO-rich feed stream (i.e., the nitrogen extraction yield) can be suitable for use in this cold box. The purified CO thus produced can be introduced into a device for producing biofuels, such as ethanol (e.g., using the Lanzatech method), or recycled to the blast furnace (reducing the CO 2 emissions from the blast furnace).

[0122] This PSA 4 can be sized according to the "high CO yield" mode (selecting the adsorbent and the optimal cycle) or according to the "high CO 2 recovery" mode (selecting the adsorbent and the optimal cycle) or sized to be able to operate according to both modes (suitable adsorbent + modifying the cycle during operation).

[0123] The regeneration gas required for the regeneration unit 6 must not contain CO 2 and can come from:

[0124] ● TSA 6 CO 2 product

[0125] ● Nitrogen 19, G3 or CO 17, G4 generated by the downstream CB unit

[0126] ● External material flow

[0127] Since fermentation processes for producing biofuels, such as ethanol, have variable requirements with respect to the feed gas, it is possible to feed in a mixture of at least two gases produced by the process according to the invention, such as at least a portion of two of gases 15, 17, 19, 21 and the hydrogen-rich gas produced by the CB unit.

Claims

1. A method for separating waste gases from a ferrous metal production plant, wherein: i) a waste gas (1) contains at least CO, CO2, hydrogen and nitrogen and is compressed in a first compressor (C) and then separated by pressure swing adsorption in a first adsorption unit (4) to produce a gas (5) which is depleted in carbon monoxide and hydrogen and enriched in CO2 relative to the waste gas and a first gas (7) which is enriched in carbon monoxide and hydrogen and depleted in CO2 relative to the waste gas, wherein the first gas contains no more than 2 mol% of CO2, ii) sending the CO2-rich gas to a unit (CC) for separation by partial condensation and / or distillation and / or condensation to produce a CO2-rich fluid (14) containing at least 80 mol % CO2, or even at least 95 mol % CO2, iii) separating at least a portion of the CO2-enriched gas by temperature swing adsorption in a second adsorption unit (6) to form a gas (23) enriched in CO2 relative to the first CO2-enriched gas and a second gas (15) enriched in CO and hydrogen relative to the first CO2-enriched gas at a first pressure, wherein the second gas contains nitrogen, and iv) compressing (C2) at least a portion of the second gas (15) rich in CO and hydrogen and separating (CB) by partial condensation and / or washing and / or distillation to produce a third fluid (19) rich in nitrogen and poor in hydrogen and CO relative to the second gas and a fourth gas (17) poor in nitrogen and rich in CO and / or hydrogen relative to the second gas.

2. A method according to claim 1, wherein at least a portion of the second and / or fourth CO-rich gas (15, 17) is fed to a process for producing a biofuel, such as ethanol, by fermentation.

3. A method according to claim 1 or 2, wherein at least a portion of the second gas and / or the fourth gas is separated by partial condensation and / or washing and / or distillation to produce a fourth gas (17) rich in CO and poor in hydrogen and nitrogen relative to the second gas and a fifth gas poor in nitrogen and CO and rich in hydrogen relative to the second gas.

4. The method according to claim 3, wherein at least a portion of the fourth gas (17) and / or the fifth gas is fed to a process for producing a biofuel, such as ethanol, by fermentation.

5. The method according to any of the preceding claims, wherein at least a portion of the third fluid (19) is fed to the process for producing a biofuel, such as ethanol, by fermentation.

6. A method according to any of the preceding claims, wherein the CO2-enriched gas (23, 31) produced by temperature swing adsorption is mixed with the CO2-enriched gas (5), optionally upstream of a compression step (C1) of the CO2-enriched gas (5).

7. The method according to claim 1, wherein the first CO-enriched gas (7) is enriched in nitrogen relative to the waste gas (1).

8. The method according to any of the preceding claims, wherein the second CO-rich gas (15) contains at least 60 mol % CO.

9. A process according to claim 8, wherein at least a portion of the second gas (15) is separated by partial condensation and / or washing and / or distillation at cryogenic temperatures to reduce its nitrogen content, forming a gas containing at least 80 mol % CO and also hydrogen and a gas enriched in nitrogen.

10. The method according to claim 1, wherein the offgas (1) contains argon and separation (CB) by partial condensation and / or scrubbing and / or distillation produces an argon-rich stream.

11. The method according to any of the preceding claims, wherein the cryogenic separation produces a stream containing at least 80% hydrogen.

12. The method according to claim 1, wherein the CO2-lean and CO-enriched gas (7) contains at least 85%, preferably at least 90%, of the CO present in the offgas (1) fed to the first adsorption unit (4).

13. The process according to any of the preceding claims 10 to 13, wherein the regeneration gas fed to the second adsorption unit (6) is formed from a portion of the second gas (15) which contains at least 60 mol % CO.

14. The process according to claim 10, wherein the regeneration gas fed to the second adsorption unit (6) is formed from a gas produced by cryogenic separation.

15. A method according to any of the preceding claims, wherein the CO2-rich gas (5) is separated in a separation unit (CC) by partial condensation and / or distillation and / or condensation to form at least one gas (11, 13) that is richer in CO and hydrogen than the CO2-rich gas, and the at least one gas that is richer in CO and hydrogen is sent to a first adsorption unit (4) for separation.

16. A method according to any of the preceding claims, wherein the CO2-rich gas (5) contains water and is dried in a drying unit upstream of a separation unit (CC) by partial condensation and / or distillation and / or condensation, the drying unit being regenerated using a regeneration gas (11, 15, 17, 21, 23, 31, 33) containing CO and / or hydrogen and subsequently sent to a first adsorption unit (4) for separation.

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