Process and apparatus for separating waste gas from a ferrous metal production unit

Abstract

Title: Method and apparatus for separating the waste gas from a ferrous metal production unit An apparatus for separating the waste gas from a ferrous metal production unit comprises a first adsorption unit (4) for separating the waste gas by pressure swing adsorption to produce a gas (5) depleted in carbon monoxide and hydrogen and enriched in CO2 relative to the waste gas and a first gas (7) enriched in carbon monoxide and hydrogen and depleted in CO2 relative to the waste gas, a unit (CC) for separation by partial condensation and / or distillation, means for sending the CO2-enriched gas to the unit (CC) for separation by partial condensation and / or distillation to produce a fluid (14) rich in CO2, a second adsorption unit (6),means for sending at least a portion of the CO-enriched gas to separate by temperature-shift adsorption in the second adsorption unit (6) to form a gas (23) enriched in CO2 relative to the first CO-enriched gas at a first pressure and a second gas (15) enriched in CO and hydrogen relative to the first CO-enriched gas, the second gas containing nitrogen, a separation unit (CB) by partial condensation and / or washing and / or distillation, means for sending at least a portion of the second gas (15) enriched in CO and hydrogen to the separation unit (CB) to be separated there to produce a gas (17) depleted in nitrogen and enriched in CO relative to the second gas. Abstract figure: Figure 3,

Description

Title of the invention: Method and apparatus for separating waste gas from a ferrous metal production unit

[0001] The present invention relates to a method and apparatus for separating waste gas from a ferrous metal production unit.

[0002] A method for manufacturing cast iron in a fusion reactor such as a blast furnace is a method in which at least iron ore, an oxidant and a fuel are introduced therein so as to melt the ore and obtain cast iron comprising at most 5% carbon, in which gases (called "blast furnace gases") are recovered at the outlet of the reactor comprising, on a dry basis, from 15 to 45 mol% CO2, from 15 to 45 mol% CO, the remainder consisting essentially of nitrogen, hydrogen, various hydrocarbons and a small percentage of argon, then the CO2 is separated from the rest of the blast furnace gas, the latter being sent to means for using said gas. Preferably the blast furnace gases comprise from 15 to 30 mol% CO and / or CO2 each on a dry basis.The blast furnace is a steelmaking tool that produces cast iron from a charge of iron ore and coke, the combustion oxidant being air, possibly enriched with oxygen. The iron ore is heated, reduced and melted using coke, the combustion of which with air provides part of the energy needed to heat and melt the iron ore. It is of course possible to use, in addition to coke, coal or another hydrocarbon injected into the blast furnace tuyeres. On the other hand, carbon monoxide is produced, resulting from the combustion reaction of coke and / or coal and / or hydrocarbon with air called the blast, which is injected into said tuyeres, enriched or not with oxygen. This carbon monoxide is necessary for the reduction of iron ore.The annual production of cast iron in a blast furnace can reach a hundred thousand tons for the smallest of them and several million tons for the most productive. In the same factory, there can be one or more blast furnaces, possibly up to ten on certain sites. Due to the combustion and reactions generated in the blast furnace, a so-called blast furnace gas is recovered at its outlet, which is a mixture typically of nitrogen (between 35 and 65 percent approximately by volume) which comes essentially from the air injected into the blast furnace tuyeres, carbon monoxide (between approximately 15 and 30 mol%) and carbon dioxide (also between approximately 15 and 30 mol%) coming from the partial or total combustion of coke or generally from the injected fuel. We also find water vapor due to this combustion since the general reaction between a carbon product and oxygen during the .Combustion produces mainly CO2 and H2O. Blast furnace gas also contains other gases in lower overall quantities, generally less than 12 percent by volume, these other gases being made up in particular of hydrogen, various hydrocarbons, argon from the air, etc. This blast furnace gas is a so-called "lean" gas because it has a low calorific value, typically between 2,000 and 6,000 kJ / Nm3, as opposed to other steelmaking gases which are called "rich" because they have a much higher calorific value (for example, gases from a steel smelting converter or a coke oven, which have calorific values ​​typically between 6,000 and 10,000 kJ / Nm3 and between 12,000 and 20,000 kJ / Nm3, respectively). Generally speaking, the quantity of gas produced by a blast furnace is very significant and in the order of approximately 1,500 Nm3 of gas for one tonne of cast iron produced.It follows that, given the composition of the gas, the amount of carbon dioxide produced per tonne of pig iron is also very significant: for example, for blast furnace gas with an average carbon dioxide content of 22 percent in the dry gas and for a blast furnace producing one million tonnes of pig iron per year, the amount of carbon dioxide emitted in the blast furnace gas is 330 million Nm3 per year, or about 650,000 tonnes of carbon dioxide produced over one year. For a blast furnace producing 3 million tonnes of pig iron per year, the amount of CO2 emitted is about 2 million tonnes per year, while for a site producing 7 million tonnes of pig iron per year, the amount of CO2 is about 4.5 million tonnes.These quantities are quite considerable and, given the negative effect of these gases on the atmosphere and the environment, it is not possible to envisage sending them directly into the atmosphere. Furthermore, releasing these gases into the atmosphere would also mean sending carbon monoxide into the atmosphere, which is known to be very dangerous, and it is therefore necessary to provide systems for recovering this blast furnace gas.

[0003] The typical composition of an example of a waste gas from a ferrous metal production unit, here a blast furnace gas or “top gas”, is as follows: • H2: 4-5 mole % • CO: 24-25% • CO2: 23-25% • N2: 40-45% • H2O: 3%

[0004] The extraction of CO2 and N2 present in the top gases of blast furnaces aims to recover them: • as fuel (higher calorific value) to turbines (generation of electricity for an integrated steel mill) or to other users from the steelworks (such as stovers mixed with other combustible gases (coke oven gas or natural gas) to preheat the enriched air) • as a reducing gas for the coal in the blast furnace itself

[0005] It is also known from EP3997235A1 to use a blast furnace gas containing more than 20 mol% CO as a raw material for the production of biofuels to transform CO into at least one biofuel, for example bioethanol.

[0006] Bioreactors operating for example according to WO08115080, in which CO is converted into bioethanol, can be used.

[0007] It is an object of the present invention to produce a CO-rich stream from a ferrous metal production unit, while simultaneously capturing CO2 produced by the production unit.

[0008] According to an object of the invention, there is provided a method for separating the residual gas from a ferrous metal production unit in which: i. The waste gas contains at least CO, CO2, 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 depleted in carbon monoxide and hydrogen and enriched in CO2 relative to the waste gas and a first gas enriched in carbon monoxide and hydrogen and depleted in CO2 relative to the waste gas, containing at most 2 mol% CO2 ii. The CO2-enriched gas is sent to a partial condensation and / or distillation and / or solidification separation unit which produces a CO2-rich fluid containing at least 80 mol% CO2, or even at least 95 mol% CO2 iii. At least a portion of the CO enriched gas is separated by temperature swing adsorption in a second adsorption unit to form a gas enriched in CO2 relative to the first CO enriched gas at a first pressure and a second gas enriched in CO and hydrogen relative to the first CO enriched gas, the second gas containing nitrogen and iv. at least a portion of the second gas enriched in CO and hydrogen is compressed and separated by partial condensation and / or washing and / or distillation to produce a third fluid enriched in nitrogen and depleted in hydrogen and CO relative to the second gas and a fourth gas depleted in nitrogen and enriched in CO and / or hydrogen relative to the second gas.

[0009] According to other optional aspects: • at least a portion of the second and / or fourth CO-enriched gas is sent to a process for producing biofuel, for example ethanol, by fermentation. • at least part of the second and / or fourth gas enriched in CO and in hydrogen is compressed and separated by partial condensation and / or washing and / or distillation to produce a third fluid enriched in nitrogen and depleted in hydrogen and CO relative to the second gas and a fourth gas depleted in nitrogen and enriched in CO and / or hydrogen relative to the second gas. at least a portion of the second gas is separated by partial condensation and / or washing and / or distillation to produce the fourth gas enriched in CO and depleted in hydrogen and nitrogen relative to the second gas and a fifth gas depleted in nitrogen and CO and enriched in hydrogen relative to the second gas. at least a portion of the fourth gas and / or the fifth gas is sent to a process for producing biofuel, for example ethanol, by fermentation. at least a portion of the third fluid is sent to the process for producing biofuel, for example ethanol, by fermentation. The CO2-enriched gas produced by temperature-shift adsorption is mixed with the CO2-enriched gas, possibly upstream of a compression stage. the waste gas contains between 15 and 45 mol% CO, preferably more than 20 mol% CO. the first CO-enriched gas is enriched in nitrogen compared to the waste gas, the second CO-enriched gas contains at least 60 mol% CO. at least a portion of the gas containing at least 60 mol% CO is separated at cryogenic temperature by partial condensation and / or washing and / or distillation to reduce its nitrogen content forming a gas containing at least 80 mol% CO as well as hydrogen and a nitrogen-enriched gas. The waste gas contains argon and separation at cryogenic temperature produces an argon-enriched fluid. Cryogenic temperature separation produces a hydrogen-enriched fluid. the CO2-depleted and CO-enriched gas contains at least 85%, preferably at least 90% of the CO present in the gas mixture sent to the first adsorption unit. the CO2-depleted and CO-enriched gas contains at most 83%, preferably at most 80% of the CO present in the gas mixture sent to the first adsorption unit. the gas depleted in carbon monoxide and hydrogen and enriched in CO2 compared to the residual gas contains at least 70%, preferably at least 80%, or at least 90% or at least 95% of the CO2 present in the gas mixture sent to the first adsorption unit. • a regeneration gas sent to the second adsorption unit consists of a part of the gas containing at least 60% mol CO. • a regeneration gas sent to the second adsorption unit consists of a gas produced by separation at cryogenic temperature. • the CO2-enriched gas is separated in a separation unit by partial condensation and / or distillation and / or solidification forming at least one gas richer in CO and hydrogen than the CO2-enriched gas and this at least one gas richer in CO and hydrogen is sent to be separated in the first adsorption unit. • the CO2-enriched gas contains water and is dried in a drying unit upstream of the separation unit by partial condensation and / or distillation and / or solidification, a regeneration gas containing CO and / or hydrogen is used to regenerate the drying unit and is then sent to be separated in the first adsorption unit. • part of the second gas is separated at cryogenic temperature by partial condensation and / or washing and / or distillation to reduce its nitrogen content, forming a gas containing at least 80% mol CO as well as hydrogen and a nitrogen-enriched gas. • the residual gas contains argon and separation by partial condensation and / or washing and / or distillation produces a fluid enriched in argon. • separation at cryogenic temperature produces a fluid containing at least 80% hydrogen. • at least a portion of the gas enriched in CO2 compared to the first gas enriched in CO and produced by the second adsorption unit is sent upstream of the first adsorption unit to be separated there. • at least part of the gas enriched in CO2 compared to the first gas enriched in CO and produced by the second adsorption unit is sent upstream of the separation unit by partial condensation and / or distillation and / or solidification to be separated there. • at least a portion of the gas enriched in CO2 compared to the first gas enriched in CO and produced by the second adsorption unit is sent to the ferrous metal production unit, for example a blast furnace.

[0010] According to another object of the invention, there is provided an apparatus for separating the residual gas from a ferrous metal production unit containing at least CO, CO2, hydrogen and nitrogen comprising a first compressor for compressing the residual gas, a first adsorption unit for separating the residual gas compressed in the compressor by pressure swing adsorption to produce a gas depleted in carbon monoxide and hydrogen and enriched in CO2 relative to the residual gas and a first gas enriched in carbon monoxide and hydrogen and depleted in CO2 relative to the residual gas, the first gas containing at most 2 mol% CO2, a unit for separation by partial condensation and / or distillation and / or solidification, means for sending the gas enriched in CO2 to the unit for separation by partial condensation and / or distillation and / or solidification to produce a fluid rich in CO2 containing at least 80 mol% CO2, or even at least 95 mol% CO2, a second adsorption unit,means for sending at least a portion of the CO-enriched gas to separate by temperature-shift adsorption in the second adsorption unit to form a gas enriched in CO2 relative to the first CO-enriched gas at a first pressure and a second gas enriched in CO and hydrogen relative to the first CO-enriched gas, the second gas containing nitrogen, another compressor, a unit for separation by partial condensation and / or washing and / or distillation,means for sending at least a portion of the second gas enriched in CO and hydrogen to the other compressor to be compressed there and means for sending at least a portion of the second gas from the compressor to the separation unit by partial condensation and / or washing and / or distillation to be separated there to produce a third fluid enriched in nitrogen and depleted in hydrogen and CO relative to the second gas and a fourth gas depleted in nitrogen and enriched in CO and / or hydrogen relative to the second gas.

[0011] According to other optional aspects: • the partial condensation and / or washing and / or distillation separation unit is designed to operate at a cryogenic temperature, for example by being thermally insulated • the apparatus comprises means for sending at least a portion of the second and / or fourth CO-enriched gas to a process for producing biofuel, for example ethanol by fermentation. • the apparatus comprises means for separating at least a portion of the second and / or fourth gas enriched in CO and hydrogen by partial condensation and / or washing and / or distillation to produce a third fluid enriched in nitrogen and depleted in hydrogen and CO relative to the second gas and a fourth gas depleted in nitrogen and enriched in CO and / or hydrogen relative to the second gas. • the apparatus comprises means for separating at least part of the second gas by partial condensation and / or washing and / or distillation to produce the fourth gas enriched in CO and depleted in hydrogen and nitrogen relative to the second gas and a fifth gas depleted in nitrogen and CO and enriched in hydrogen compared to the second gas. the apparatus comprises means for sending at least a portion of the fourth gas and / or the fifth gas to a process for producing biofuel, for example ethanol by fermentation. the apparatus comprises means for sending at least a portion of the third fluid to the process for producing biofuel, for example ethanol by fermentation. the apparatus comprises means for mixing the CO2-enriched gas produced by temperature-swing adsorption with the CO2-enriched gas, possibly upstream of a compression step. the waste gas contains between 15 and 45 mol% CO, preferably more than 20 mol% CO. the partial condensation and / or washing and / or distillation unit at cryogenic temperature comprises means for producing a fluid containing at least 80 mol% hydrogen. the partial condensation and / or washing and / or distillation unit at cryogenic temperature comprises means for producing a fluid containing at least 80 mol% of carbon monoxide. the apparatus comprises means for sending a regeneration gas to the second adsorption unit from the cryogenic temperature separation unit. the apparatus comprises means for sending at least one gas richer in CO and hydrogen than the gas enriched in CO2 from the partial condensation and / or distillation and / or solidification separation unit to be separated in the first adsorption unit. the apparatus comprises a drying unit for drying the CO2-enriched gas upstream of the separation unit by partial condensation and / or distillation and / or solidification. the apparatus comprises means for sending a regeneration gas containing CO and / or hydrogen to regenerate the drying unit, the apparatus comprises means for sending the regeneration gas downstream of the drying unit to be separated in the first adsorption unit. the apparatus comprises means for sending at least a portion of the gas enriched in CO2 relative to the first gas enriched in CO and produced by the second adsorption unit is upstream of the first adsorption unit to be separated therein. the apparatus comprises means for sending at least a portion of the gas enriched in CO2 relative to the first gas enriched in CO and produced by the second adsorption unit upstream of the partial condensation and / or distillation and / or solidification separation unit to be separated there. • the apparatus comprises means for sending at least part of the gas enriched in CO2 compared to the first gas enriched in CO and produced by the second adsorption unit into the ferrous metal production unit, for example a blast furnace.

[0012] Surprisingly, the best optimization of the process is that in which a pressure swing adsorption unit purifies a gas from the metal production unit containing at least 20% carbon monoxide and operates with the aim of maximizing the CO2 yield of the CO2-enriched gas produced by this adsorption.

[0013] The invention will be described in more detail with reference to the figures where:

[0014] [Fig-1] represents a comparative method.

[0015] [Fig.2] represents a comparative method.

[0016] [Fig.3] represents a method according to the invention.

[0017] [Fig. 1] illustrates a method for separating a top gas produced by a blast furnace HF which is purified in a pretreatment unit P to remove the dust it contains, compressed by a compressor C1 and separated by pressure swing adsorption in a separation unit 4 to produce a gas enriched in CO and nitrogen and depleted in CO2 7 compared to the gas to be separated 1 and a gas depleted in CO and nitrogen and enriched in CO2 5 compared to the gas to be separated.

[0018] In the case of a pressure swing adsorption separation unit 4, known by the acronym PSA, treating a residual gas from a ferrous metal unit compressed to approximately 8 bars and operated in “high CO yield” mode, the CO recovery efficiency at high pressure in gas 7 is typically greater than 80% (or even greater than 85%) for corresponding CO2 extraction efficiencies at low pressure in gas 5 of around 88% and N2 of 15%. The aim is to maximize both the CO recovery efficiency and the CO2 / N2 extraction efficiencies.

[0019] The CO 7 rich stream generated by the PSA 4 therefore also contains a lot of nitrogen (approximately 85 mol% of the treated gas flow) because the CO / N2 selectivity is very low on conventional adsorbents. It also contains hydrogen and CO2 (approximately 12% of the treated gas flow)

[0020] The CO2-rich gas produced at low pressure by the PSA also contains unadsorbed CO (approximately 15% of the treated top gas flow), H2, nitrogen and water present in the top gas.

[0021] [TAB1] represents an example of material balance obtained for a PSA 4 operating in “high CO efficiency” mode on residual gas at around 8 bars as illustrated in [Fig.l]: PSA Inlet 4 CO enriched gas 7 CO2 enriched gas 5 Flow 100 67 33 H2 mole % 5 8 1 CO 25 32 11 CO2 26 5 68 N2 43 55 18 H2O 1 0 2

[0022] CO recovery efficiency = 85.8%

[0023] It is known from EPI869385 to separate the CO2-enriched gas produced at low pressure by adsorption separation of a top gas from a ferrous metal unit, for example by partial condensation and / or distillation. These two technologies can be integrated by recycling all or part of the CO2-depleted gas stream containing CO from the partial condensation and / or distillation separation in a CC separation unit upstream or downstream of the C gas compressor feeding the PSA 4, allowing savings of 10% or more of the PSA 4 compression energy.

[0024] [TAB.2] shows the example of a material balance obtained for a PSA 4 operating in “High CO efficiency” mode on the residual gas 1 of an HF blast furnace at approximately 8 bars combined with a partial condensation separation unit and / or distillation and / or CC solidification:

[0025] [TAB.2] PSA Inlet 4 CO enriched gas 7 CO2 enriched gas 5 Flow 100 80 20 H2 mole % 5 7 0 CO 25 31 0.5 CO2 26 7 99 N2 43 55 0.5 H2O 1 0 0

[0026] The CO recovery efficiency in this case is close to 100%. Recycling gases 11 and / or 13 to the PSA helps to achieve 100%.

[0027] It is possible to operate the PSA on the top gas 1 in “High CO2 Yield” mode with a degraded CO2 recovery efficiency, which makes it possible to increase the CO2 extraction efficiency. This operation can be obtained by modifying the PSA cycle and / or by adjusting the quality of the adsorbents and / or by leaving less drill CO2 into CO2-rich gas.

[0028] Example of yields which can be obtained by a PSA 4 on top gas at 8 bars:

[0029] [TAB.3] PSA 4 MODE High CO yield in gas 7 High CO2 production in gas 5 CO yield in gas 7% 85 80 N2 yield in gas 7% 86 82 CO2 yield in gas 7% 13 2 H2 yield in gas 7% 94 93

[0030] When operating in “High CO Efficiency” mode, PSA 4 is operated to maximize the percentage of CO recovered in gas 7 sent to the TSA unit. Thus, we see that 85% of the CO present in the gas at the inlet of PSA 4 is then found in gas 7, as well as 94% of the hydrogen. However, a significant percentage of CO2 (13%) is found in gas 7.

[0031] When operating in “High CO2 Production” mode, this may result in a CO-rich HP 7 flow containing at most 2 mole % CO2. On the other hand, a decrease in the partial flow of CO produced (i.e., the CO recovery efficiency) will be observed. Surprisingly, in order to optimize the entire process to produce the flow containing sufficiently little CO2 to allow the TSA unit to remove all the remaining CO2, it is necessary to adjust the operation of the PSA 4 to reduce the CO2 content as much as possible in the CO-enriched gas produced 7.

[0032] On a blast furnace “top gas”, if we wish to obtain both: • a maximum CO recovery rate • and / or a maximum recovery rate of a flow rich in purified CO2 produced in liquid or gaseous form • and / or a CO-rich flow more or less depleted in N2

[0033] The invention proposed below can be implemented. It consists of combining the PSA preferably operating in “High CO2 Production” mode with: a CO2 separation unit by partial condensation and / or distillation and / or solidification (and its appropriate recycling) to produce purified CO2 in liquid or gaseous form and • a CO2 TSA on the CO2-rich stream produced by the PSA to adsorb the residual CO2 (at most 2%). The necessary regeneration gas must not contain CO2 and may come from: • From the TSA CO2 product (see note below) • From the N2 flow or the CO flow produced by the cold box located downstream • An external flow

[0034] The residual gas thus generated may (or may not) be recycled to the inlet of the PSA and / or to the inlet of the CO2 separation unit by partial condensation and / or distillation and / or solidification or in the blast furnace, always with the aim of improving the recovery yields of the H2 / CO and CO2 molecules. • A cryogenic unit (cold box with partial condensation and / or washing steps (for example washing with liquid N2 or liquid CO) and / or distillation with or without associated refrigeration cycle) in series with the TSA on the CO-rich stream for partial or total separation of the nitrogen present in the CO-rich stream. A third residual gas possibly created in the cryogenic unit may also be recycled upstream of the PSA or upstream of the CO2 separation unit by partial condensation and / or distillation and / or solidification.

[0035] The cryogenic unit may be preceded by a step of compression of the CO-rich gas.

[0036] The cryogenic unit can be used to produce at least one additional flow more or less rich in H2 and / or at least one additional flow rich in argon (argon coming from the air and O2 introduced into the blast furnace and ending up in the top gas).

[0037] The relatively high CO2 content that the TSA will have to remove upstream of the N2 / CO cold box will require a significant amount of heat. The use of a portion of the decarbonized gas available downstream of this TSA is not necessarily desirable for two reasons. On the one hand, it would induce a loss in CO / H2 efficiency if this regeneration gas is sent to the fuel network or a loss in energy efficiency if this gas is recycled upstream of the PSA, on the other hand, the presence of CO / H2 would limit the regeneration temperature to 150°C in order to overcome reactivity problems at the level of the TSA regeneration gas heater. It would then be preferable to use the N2 flow coming from the CO / N2 cold box to regenerate the TSA and return the regeneration flow to the fuel network.

[0038] The main interest of operating the PSA in “High CO2 Extraction” mode is to facilitate the complete downstream reduction of CO2, notably compatible with TSA type technology, and opening the possibility of a final N2 / CO separation. The CO lost in the PSA waste gas will be recovered by the separation unit by partial condensation and / or distillation and / or solidification and recycled to the PSA inlet to improve production efficiency.

[0039] The major drawback of this solution is an increase in the flow rate of recycled gas and consequently of the equipment as well as an increase in the specific energy of the separation unit by partial condensation and / or distillation and / or solidification due to the CO2 depletion of the residual gas from the PSA.

[0040] It will thus be possible to produce pure CO2 and a very CO-rich stream with high recovery yields. The quantity of residual nitrogen in the CO-rich stream (i.e. the nitrogen extraction yield) can be adapted in the cold box. The purified CO thus produced can be directed either to biofuel production units or recycled into the blast furnace (reduction of CO2 emitted by the blast furnace).

[0041] The PSA can either be sized in a “Maximum CO yield” mode (choice of adsorbent and optimum cycle), or sized in a “High CO2 extraction” mode (with the choice of adsorbent and / or optimum cycle), or sized so that it can be operated in both modes (requiring an adequate adsorbent + modification of the cycle during operation).

[0042] The coupling of a CO2 PSA with a separation by partial condensation and / or distillation and / or solidification, has the following objectives: • To enrich the PSA waste gas with CO2 in order to minimize the specific energy of separation by partial condensation and / or distillation and / or solidification • To increase the CO purity of the product which can be sent to a carbon monoxide consuming process, for example a CO to ethanol conversion process, using CO

[0043] Example of material balance obtained for a PSA4 operating in “High CO2 efficiency” mode on top gas at approximately 8 bars combined with a low temperature CO2 separation unit CC, a TSA 6 and a cryogenic separation CB of CO and N2:

[0044] [TAB.3] PSA Inlet 4 CO product 17 CO2 product 14 N2 product 19 Flow 100 31 26 43 H2 mole % 5 17.5 0 0 CO 25 80.5 0.5 0.5 CO2 26 0 99 0 N2 43 2 0.5 99.5 H2O 1 0 0 0

[0045] CO efficiency: close to 100%

[0046] Maximizing the CO yield of the PSA 4 can be sought in order to obtain a PSA 4 residual gas 5 richer in CO2, thus reducing the specific energy of the separation by partial condensation and / or distillation and / or CC solidification. The main interest of operating the PSA 4 in “high CO yield” mode is to increase the CO2 concentration in the CO2-enriched gas 5 of the PSA 4, this being the flow rate feeding the partial condensation and / or distillation and / or CC solidification separation apparatus. This scheme has the advantage of reducing the OPEX, and to a lesser extent the CAPEX of the partial condensation and / or distillation and / or CC solidification separation apparatus.

[0047] A typical material balance of the PSA CO2-enriched gas CC system treating a blast furnace top gas is shown below:

[0048] [TAB.4] CO2-enriched gas 5 CO2-rich liquid Gaseous phase(#11) Stripper top (#22) CO2-rich liquid 14 P bara 1.05 65 35 21 21 T °C 40 -52 -52 -53 -20 Flow rate 100 65 35 6 59 H2 mole % 1 0 2.9 0.2 0 CO 11 2.2 29.9 24.6 0 CO2 68 94.1 21.2 33.9 100 N2 18 3.7 46 41.3 0 H2O 2 0 0 0 0 N2 / CO ratio 1.53 1.7

[0049] The optimization of the compressor Cl (if present) of the CO2-enriched gas 5 and the external cold cycles makes it possible to obtain specific energy consumptions of the order of 200 kW / ton liquid CO2 produced.

[0050] [Fig.3] illustrates a method according to the invention. It consists of combining a PSA 4 pressure rocking adsorption separation unit, a separation unit by partial condensation and / or distillation and / or solidification and a TSA 6 temperature swing adsorption separation unit. An example of a partial condensation and / or distillation separation unit is described in FR2310716 filed on October 6, 2023.

[0051] A gas 1 comprising from 15 to 45 mol%, or even from 15 to 30 mol%, of CO2, from 15 to 45 mol%, or even from 15 to 30 mol% of CO, the remainder consisting essentially of nitrogen, hydrogen, various hydrocarbons, water and a small percentage of argon. This gas is treated in a pretreatment unit P to remove solid impurities and then compressed in a compressor C to a pressure of approximately 8 bars.

[0052] The compressed gas 1 is separated by pressure swing adsorption in the unit 4 producing a gas enriched in CO and hydrogen 7 compared to the gas 1 entering the unit 4, preferably containing at most 2% CO2. The unit 4 also produces a gas 5 depleted in CO and enriched in CO2 compared to the gas 1 entering the unit 4.

[0053] The gas 5 can be compressed in a compressor CL. The gas 5 is at a first pressure higher than the second pressure at which the gas 7 is.

[0054] The gas 5 is separated in the unit CC by partial condensation and / or distillation and / or solidification to form a fluid (gas or liquid) 14 rich in CO2 containing at least 80 mol% CO2, or even at least 95 mol% CO2. The unit CC also produces a gas 13 enriched in carbon monoxide and hydrogen relative to the gas 5 which is sent upstream of the PSA unit 4 or upstream of the compressor C. The gas 13 may, for example, be a gas from a partial condensation stage and / or a top gas from a distillation column. The unit CC produces a gas 11, enriched in carbon monoxide and hydrogen relative to the gas 5, which is divided into two, one part FG serving as a fuel gas and another part 11 is optionally used to regenerate dryers (not shown) upstream of the unit CC. The regeneration gas 11 loaded with water after regeneration is sent upstream of the PSA unit 4 or upstream of the compressor C.It is also possible to use part of the gas 15, 17, 21, 23, 31, 33 as regeneration gas.

[0055] Gas 7, G1 is separated by the adsorption unit 6 to form a gas 15 enriched in CO and H2 compared to gas 7. Gas 15, G2 no longer contains CO2 but still contains nitrogen.

[0056] According to a variant, only unit 6 is used to separate gas 7 and gas 15 constitutes the product of the process.

[0057] The regeneration gas required to regenerate unit 6 must not contain CO2 and may come from: • From product 15, 17, 19 of TSA CO2 6 • An external flow

[0058] The residual gas 23 thus generated by the TSA unit 6 may (or may not) be recycled to the inlet of the PSA 4 (flow rate 29) and / or to the inlet of the CC unit (flow rate 31, 33) or in the HF blast furnace, always with the aim of improving the recovery yields of the H2 / CO and CO2 molecules.

[0059] This gas 15 is optionally compressed in the compressor C2 and separated in a cryogenic unit CB. The unit CB comprises a thermally insulated enclosure containing at least one phase separator and / or at least one washing column and / or at least one distillation column. The at least one washing column may be a liquid nitrogen or liquid carbon monoxide washing column. The unit CB may comprise at least one refrigeration cycle. The separation carried out by the unit CB is a partial or total separation of the nitrogen present in the CO-rich stream 15. The unit CB produces a fluid 19 enriched in nitrogen and depleted in CO and hydrogen relative to the gas 15. The fluid 19 may contain at least 90 mol% nitrogen. The unit CB produces at least one gas enriched in hydrogen and / or CO and depleted in nitrogen relative to the gas 15.For example, it can produce at least one gas enriched in hydrogen and depleted in nitrogen and CO relative to gas 15 and / or at least one gas enriched in CO and depleted in nitrogen and hydrogen relative to gas 15.

[0060] The fermentation unit 13 is supplied with at least a portion of the gas 15 and / or at least a portion of at least one gas enriched in hydrogen and / or CO and depleted in nitrogen compared to the gas 15 coming from the unit CB.

[0061] Preferably, it is supplied with at least one gas enriched in hydrogen and depleted in nitrogen and CO relative to the gas 15 and / or at least one gas enriched in CO and depleted in nitrogen and hydrogen relative to the gas 15. Supplying the fermentation unit with two gases of different purity makes it possible to vary the CO and H2 contents in the gas present in the fermentation unit. It is also possible to send a variable flow rate of the nitrogen-enriched gas 19 to slow down the fermentation reaction.

[0062] Another possibility is to send at least a portion of the gas enriched in hydrogen and depleted in nitrogen and CO relative to the gas 15 and / or at least another portion of the gas enriched in CO and depleted in nitrogen and hydrogen relative to the gas 15 to another consumer of the gas.

[0063] A residual gas 21 possibly created in the cryogenic unit may also be recycled upstream of the PSA 4 (flow rate 29) or upstream of the CC unit (flow rate 31, 33).

[0064] The cryogenic unit CB can be used to produce at least one flow more or less rich in H2, for example a fluid (gas or liquid) containing at least 80 mol% of hydrogen and / or a fluid (gas or liquid) containing at least 80 mol% of argon (the argon coming from the air and the O2 introduced into the blast furnace HF and ending up in the top gas 1).

[0065] The relatively high CO2 content that the TSA 6 unit will have to remove upstream of the CB unit will require a significant amount of heat. The use of a portion of the decarbonized gas 15 available downstream of this TSA 6 as regeneration gas is not necessarily desirable for two reasons. On the one hand, it would induce a loss in CO / H2 efficiency if this regeneration gas is sent to the fuel gas network or a loss in energy efficiency if this gas is recycled upstream of the PSA 4, on the other hand, the presence of CO / H2 would limit the regeneration temperature to 150°C in order to overcome reactivity problems at the level of the heater of the TSA 6 unit. It will then be preferable to use the N2 flow 19 coming from the CB cold box to regenerate the TSA 6 and return the regeneration flow to the fuel network.

[0066] The main interest in operating the PSA 4 unit in “High CO2 Production” mode is to facilitate the complete downstream reduction of CO2, in particular compatible with a TSA type technology, and opening the possibility of a final N2 / CO separation. The CO lost in the residual gas 5 of the PSA 4 will be recovered by the CC separation unit by partial condensation and / or distillation and / or solidification and recycled to the PSA inlet to improve the production yield.

[0067] The major drawback of this solution is an increase in the flow rate of recycled gas and consequently of the equipment as well as an increase in the specific energy of the CC unit due to the CO2 depletion of the residual gas 5 from the PSA unit 4.

[0068] It will thus be possible to produce pure CO2 and a very CO-rich stream with high recovery yields. The quantity of residual nitrogen in the CO-rich stream (i.e. the nitrogen extraction yield) can be adapted in the cold box. The purified CO thus produced can be directed either to biofuel production units, for example ethanol (using a Lanzatech process for example), or recycled into the blast furnace (reduction of CO2 emitted by the blast furnace).

[0069] The PSA 4 can either be sized in a “High CO yield” mode (choice of adsorbent and optimum cycle), or sized in a “High CO2 production” mode (choice of adsorbent and optimum cycle), or sized so that it can be operated in both modes (suitable adsorbent + modification of the cycle during operation).

[0070] The regeneration gas required to regenerate unit 6 must not contain CO2 and may come from: • From the product of TSA CO2 6 • Nitrogen 19, G3 or CO 17, G4 produced by the CB unit located downstream • An external flow

[0071] Since a fermentation process producing a biofuel, for example ethanol, has varying feed gas requirements, it is possible to sending a mixture of at least two gases produced by the process according to the invention, for example a part of at least two of the gases 15, 17, 19, 21 and a hydrogen-enriched gas produced by the CB unit.

Claims

1.

2.

3. Claims Process for separating the waste gas from a ferrous metal production unit in which: i. The 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) depleted in carbon monoxide and hydrogen and enriched in CO2 relative to the waste gas and a first gas (7) enriched in carbon monoxide and hydrogen and depleted in CO2 relative to the waste gas, the first gas containing at most 2 mol% CO2 ii. The CO2-enriched gas is sent to a unit (CC) for separation by partial condensation and / or distillation and / or solidification which produces a fluid (14) rich in CO2 containing at least 80 mol% of CO2, or even at least 95 mol% of CO2 iii. At least a portion of the CO-enriched gas is separated by temperature-swing adsorption in a second adsorption unit (6) to form a gas (23) enriched in CO2 relative to the first CO-enriched gas at a first pressure and a second gas (15) enriched in CO and hydrogen relative to the first CO-enriched gas, the second gas containing nitrogen and iv. at least a portion of the second gas (15) enriched in CO and hydrogen is compressed (C2) and separated (CB) by partial condensation and / or washing and / or distillation to produce a third fluid (19) enriched in nitrogen and depleted in hydrogen and CO relative to the second gas and a fourth gas (17) depleted in nitrogen and enriched in CO and / or hydrogen relative to the second gas. Method according to claim 1 in which at least a part of the second and / or fourth gas (15, 17) enriched in CO is sent to a process for producing biofuel, for example ethanol, by fermentation. A method according to claim 1 or 2 wherein at least one part from the second and / or fourth gas is separated by partial condensation and / or washing and / or distillation to produce the fourth gas (17) enriched in CO and depleted in hydrogen and nitrogen compared to the second gas and a fifth gas depleted in nitrogen and CO and enriched in hydrogen compared to the second gas.

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

5. Method according to one of the preceding claims in which at least a part of the third fluid (19) is sent to the process for producing biofuel, for example ethanol, by fermentation.

6. Method according to one of the preceding claims in which the CO2-enriched gas (23, 31) produced by temperature-shift adsorption is mixed with the CO2-enriched gas (5), optionally upstream of a compression step (Cl).

7. Method according to one of the preceding claims in which the first CO-enriched gas (7) is enriched in nitrogen relative to the residual gas (1).

8. Method according to one of the preceding claims in which the second CO-enriched gas (15) contains at least 60 mol% CO.

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

10. Method according to one of the preceding claims in which the waste gas (1) contains argon and the separation (CB) by partial condensation and / or washing and / or distillation produces a fluid enriched in argon.

11. A method according to any preceding claim wherein the separation at cryogenic temperature produces a fluid containing at least 80% hydrogen.

12. Method according to one of the preceding claims in which the gas (7) depleted in CO2 and enriched in CO contains at least 85%, preferably at least 90% of the CO present in the residual gas (1) sent to the first adsorption unit (4).

13. Method according to one of the preceding claims 10 to 13 in which a regeneration gas sent to the second adsorption unit (6) is consisting of a part of the second gas (15) containing at least 60 mol% CO.

14. Method according to one of claims 10 to 13 in which a regeneration gas sent to the second adsorption unit (6) consists of a gas produced by the separation at cryogenic temperature.

15. Method according to one of the preceding claims in which the CO2-enriched gas (5) is separated in a separation unit (CC) by partial condensation and / or distillation and / or solidification forming at least one gas (11, 13) richer in CO and hydrogen than the CO2-enriched gas and this at least one gas richer in CO and hydrogen is sent to be separated in the first adsorption unit (4).

16. Method according to one of the preceding claims in which the CO2-enriched gas (5) contains water and is dried in a drying unit upstream of the unit (CC) for separation by partial condensation and / or distillation and / or solidification, a regeneration gas (11, 15, 17, 21, 23, 31, 33) containing CO and / or hydrogen is used to regenerate the drying unit and is then sent to be separated in the first adsorption unit (4).

17. Apparatus for separating the waste gas from a ferrous metal production unit containing at least CO, CO2, hydrogen and nitrogen comprises a first compressor (C) for compressing the waste gas (1), a first adsorption unit (4) for separating the waste gas compressed in the compressor by pressure swing adsorption to produce a gas (5) depleted in carbon monoxide and hydrogen and enriched in CO2 relative to the waste gas and a first gas (7) enriched in carbon monoxide and hydrogen and depleted in CO2 relative to the waste gas, containing at most 2 mol% CO2, a unit (CC) for separation by partial condensation and / or distillation and / or solidification, means for sending the CO2-enriched gas to the unit (CC) for separation by partial condensation and / or distillation and / or solidification to produce a CO2-rich fluid (14) containing at least 80 mol% CO2, or even at least 95% mol of CO2,a second adsorption unit (6), means for sending at least a portion of the CO-enriched gas to separate by temperature-shift adsorption in the second adsorption unit (6) to form a gas (23) enriched in CO2 relative to the first CO-enriched gas at a first pressure and a second gas (15) enriched in CO and hydrogen relative to the first CO-enriched gas, the second gas, containing nitrogen, another compressor (C2), a separation unit (CB) by partial condensation and / or washing and / or distillation, means for sending at least a portion of the second gas (15) enriched in CO and hydrogen to the other compressor to be compressed there and means for sending at least a portion of the second gas from the compressor to the separation unit (CB) by partial condensation and / or washing and / or distillation to be separated there to produce a third fluid (19) enriched in nitrogen and depleted in hydrogen and CO compared to the second gas and a fourth gas (17) depleted in nitrogen and enriched in CO and / or hydrogen compared to the second gas.

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