Method and apparatus for separating waste gas from a ferrous metal production unit
A multi-step gas separation process optimizes CO2 and CO recovery from ferrous metal production waste gases, addressing inefficiencies in existing methods by enhancing recovery and utilization for biofuel production.
Patent Information
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- LAIR LIQUIDE SA POUR LETUDE & LEXPLOITATION DES PROCEDES GEORGES CLAUDE
- Filing Date
- 2023-11-24
- Publication Date
- 2026-05-22
AI Technical Summary
Existing methods for separating waste gases from ferrous metal production units, such as blast furnaces, are inefficient in recovering carbon monoxide (CO) and carbon dioxide (CO2), leading to significant environmental emissions and safety hazards, while also failing to optimize the recovery of these gases for further utilization.
A multi-step process involving pressure-switching adsorption, partial condensation and/or distillation, and temperature-switching adsorption is employed to separate and enrich CO2 and CO from the waste gases, followed by cryogenic separation to optimize CO2 recovery and produce high-purity CO for biofuel production.
The process achieves high recovery efficiencies for CO2 and CO, enabling their effective utilization in biofuel production and reducing environmental emissions, while minimizing energy consumption and equipment size.
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Abstract
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 the residual gas from a ferrous metal production unit.
[0002] A process for manufacturing pig iron in a melting reactor such as a blast furnace is a process in which at least iron ore, an oxidizer, and a fuel are introduced into the reactor so as to melt the ore and obtain pig iron containing at most 5% carbon. At the reactor outlet, gases (known as "blast furnace gases") are recovered, comprising, on a dry basis, 15 to 45 mol% CO2 and 15 to 45 mol% CO, the remainder consisting essentially of nitrogen, hydrogen, various hydrocarbons, and a small percentage of argon. The CO2 is then separated from the remaining blast furnace gas, the latter being sent to means for utilizing said gas. Preferably, the blast furnace gases comprise 15 to 30 mol% CO and / or CO2 each on a dry basis.The blast furnace is a steelmaking tool that produces pig iron from a charge of iron ore and coke. The oxidant for combustion is air, possibly enriched with oxygen. The iron ore is heated, reduced, and melted by the coke, whose combustion with air provides some of the energy needed to heat and melt the iron ore. In addition to coke, coal or another hydrocarbon can be injected into the blast furnace's tuyeres. Carbon monoxide is also produced, resulting from the combustion reaction of the coke and / or coal and / or hydrocarbon with the air (called the blast) injected into the tuyeres, which may or may not be enriched with oxygen. This carbon monoxide is necessary for the reduction of the iron ore.The annual production of pig iron in a blast furnace can reach hundreds of thousands of tons for the smallest and several million tons for the most productive. A single plant may have one or more blast furnaces, sometimes up to ten at certain sites. Due to the combustion and reactions occurring in the blast furnace, blast furnace gas is released at its outlet. This gas is typically a mixture of nitrogen (between approximately 35 and 65 percent by volume), which comes primarily from the air injected into the blast furnace tuyeres; carbon monoxide (between approximately 15 and 30 percent by volume); and carbon dioxide (also between approximately 15 and 30 percent by volume), resulting from the partial or complete combustion of the coke or, more generally, the injected fuel. Water vapor is also produced as a result of this combustion, since the general reaction between a carbon product and a carbon atom is a chemical reaction. and oxygen during combustion mainly produces CO2 and H2O. Blast furnace gas also contains other gases in smaller overall quantities, generally less than 12 percent by volume, these other gases consisting mainly of hydrogen, various hydrocarbons, argon from the air, etc. This blast furnace gas is a so-called "lean" gas because of its low calorific value, typically between 2,000 and 6,000 kJ / Nm3, as opposed to other steelmaking gases called "rich" because of their much higher calorific value (for example, gases from a pig iron to steel converter or a coke oven, with calorific values typically between 6,000 and 10,000 kJ / Nm3 and between 12,000 and 20,000 kJ / Nm3, respectively). In general, the amount of gas produced by a blast furnace is very significant and on the order of approximately 1,500 Nm3 of gas for one tonne of pig iron produced.Consequently, given the composition of the gas, the amount of carbon dioxide produced per ton 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 tons of pig iron per year, the amount of carbon dioxide emitted in the blast furnace gas is 330 million Nm³ per year, or approximately 650,000 tons of carbon dioxide produced annually. For a blast furnace producing 3 million tons of pig iron per year, the amount of CO₂ emitted is approximately 2 million tons per year, while for a site producing 7 million tons of pig iron per year, the amount of CO₂ is approximately 4.5 million tons.These quantities are quite considerable, and given the negative effect of these gases on the atmosphere and the environment, it is not possible to release them directly into the atmosphere. Furthermore, releasing these gases into the atmosphere would also release carbon monoxide, which is known to be highly dangerous; therefore, it is necessary to implement systems for recovering this blast furnace gas.
[0003] The typical composition of an example of a residual gas from a ferrous metal production unit, here a blast furnace gas or "burst 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 blast furnace flue gases is intended to make use of them: • as fuel (higher calorific value) for turbines (electricity generation for an integrated steel plant) or for other users from the steel mill (such as Cowpers mixed with other combustible gases (coking gas or natural gas) to preheat the enriched air) • as a reducing gas for coal in the blast furnace itself
[0005] It is also known from EP3997235A1 to use blast furnace gas containing more than 20 mol% CO as a feedstock for the production of biofuels to convert CO into at least one biofuel, for example bioethanol.1
[0006] Bioreactors operating for example according to WO08115080, in which CO is converted into bioethanol, can be used.
[0007] An object of the present invention is to produce a CO-rich flow from a ferrous metal production unit, while simultaneously capturing CO2 produced by the production unit.
[0008] According to one object of the invention, a process for separating the waste gas from a ferrous metal production unit is provided, 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-switching 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-toggle 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 part 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 part of the second and / or fourth CO-enriched gas is sent to a biofuel production process, for example ethanol, by fermentation. at least part of the second and / or fourth 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 compared to the second gas and a fourth gas depleted in nitrogen and enriched in CO and / or hydrogen compared to the second gas. at least part 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 compared to the second gas and a fifth gas depleted in nitrogen and CO and enriched in hydrogen compared to the second gas. at least part of the fourth gas and / or fifth gas is sent to a biofuel production process, for example ethanol, by fermentation. at least part of the third fluid is sent to the biofuel production process, for example ethanol, by fermentation. The CO2-enriched gas produced by temperature-switching adsorption is mixed with the CO2-enriched gas, possibly upstream of a compression stage. the residual gas contains between 15 and 45% mol CO, preferably more than 20% mol CO. The first CO-enriched gas is enriched in nitrogen relative to the residual gas. the second CO-enriched gas contains at least 60% mol of 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 residual gas contains argon and separation at cryogenic temperature produces an argon-enriched fluid. Separation at cryogenic temperature 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 relative to the residual gas contains at least 70%, preferably at least 80%, or even 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 portion 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 part of the gas enriched in CO2 relative 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. • at least part of the gas enriched in CO2 relative 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 part of the gas enriched in CO2 relative 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, a device is provided for separating the residual gas from a ferrous metal production unit containing at least CO, from CO2, hydrogen and nitrogen includes a first compressor for compressing the waste gas, a first adsorption unit for separating the waste gas compressed in the compressor by pressure-switching adsorption 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, the first gas containing at most 2% mol CO2, a separation unit by partial condensation and / or distillation and / or solidification, means for sending the CO2-enriched gas to the separation unit by partial condensation and / or distillation and / or solidification to produce a CO2-rich fluid 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-switching 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 separation unit 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 for compression, and means for sending at least a portion of the second gas from the compressor to the partial condensation and / or scrubbing and / or distillation separation unit for separation 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 includes means for sending at least a part of the second and / or fourth CO-enriched gas to a biofuel production process, for example ethanol by fermentation. • The apparatus includes means for separating at least a part 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 includes means for separating at least a portion 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 compared to the second gas and a fifth gas depleted in nitrogen and CO and enriched in hydrogen compared to the second gas. the apparatus includes means for sending at least a part of the fourth gas and / or fifth gas to a biofuel production process, for example ethanol by fermentation. the apparatus includes means for sending at least a portion of the third fluid to the biofuel production process, for example ethanol by fermentation. The apparatus includes means for mixing the CO2-enriched gas produced by temperature-switching adsorption with the CO2-enriched gas, possibly upstream of a compression stage. the residual gas contains between 15 and 45% mol CO, preferably more than 20% mol CO. The partial condensation and / or washing and / or cryogenic temperature separation unit includes means for producing a fluid containing at least 80% mol of hydrogen. The partial condensation and / or washing and / or cryogenic temperature separation unit includes means for producing a fluid containing at least 80 mol% carbon monoxide. The device includes means for sending a regeneration gas to the second adsorption unit from the separation unit at cryogenic temperature. The apparatus includes means for sending at least one gas richer in CO and hydrogen than the CO2-enriched gas from the separation unit by partial condensation and / or distillation and / or solidification to be separated in the first adsorption unit. The device includes a drying unit to dry the CO2-enriched gas upstream of the separation unit by partial condensation and / or distillation and / or solidification. The apparatus includes means for sending a regeneration gas containing CO and / or hydrogen to regenerate the drying unit. The apparatus includes means for sending the regeneration gas downstream of the drying unit to be separated in the first adsorption unit. the apparatus includes means for sending at least a portion of the CO2-enriched gas relative to the first CO-enriched gas and produced by the second adsorption unit upstream of the first adsorption unit to be separated there. • The apparatus includes means for sending at least a portion of the CO2-enriched gas relative to the first CO-enriched gas 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 includes means for sending at least a portion of the CO2-enriched gas relative to the first CO-enriched gas 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-switching 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 process.
[0016] [Fig.3] represents a method according to the invention.
[0017] [Fig. 1] illustrates a process for separating a blast furnace gas produced by a blast furnace HF which is cleaned in a pretreatment unit P to remove the dust it contains, compressed by a compressor Cl and separated by pressure-switching 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, processing a waste gas from a ferrous metal unit compressed to approximately 8 bar and operated in “high CO yield” mode, the high-pressure CO recovery efficiency in the gas 7 is typically greater than 80% (or even greater than 85%) for corresponding low-pressure CO2 extraction efficiencies in the 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 CO₂-rich stream generated by PSA 4 therefore also contains a large amount of nitrogen (approximately 85 mol% of the treated gas flow rate) because the CO / N₂ selectivity is very low with conventional adsorbents. It also contains hydrogen and CO₂ (approximately 12% of the treated gas flow rate).
[0020] The CO2-rich gas produced at low pressure by the PSA also contains non-adsorbed CO (approximately 15% of the treated feed gas flow), H2, nitrogen and water present in the feed gas.
[0021] [TAB1] represents an example of a mass balance obtained for a PSA 4 operating in “high CO efficiency” mode on residual gas at approximately 8 bars as illustrated in [Fig.1]: Inlet PSA 4 CO-enriched gas 7 CO2-enriched gas 5 Flow rate 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 flue 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 for a saving of 10% or more of the compression energy of the PSA 4.
[0024] [TAB.2] shows the example of a material balance obtained for a PSA 4 operating in “High CO₂ Yield” mode on the residual gas 1 of an HF blast furnace at approximately 8 bar combined with a CC partial condensation and / or distillation and / or solidification separation unit:
[0025] [TAB.2] Inlet PSA 4 CO-enriched gas 7 CO2-enriched gas 5 Flow rate 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 is in this case close to 100%. Recycling gases 11 and / or 13 to the PSA helps to approach 100%.
[0027] It is possible to operate the PSA on the feed gas 1 in “High CO2 Efficiency” mode with a degraded CO recovery efficiency, which makes it possible to increase the CO2 extraction efficiency. This operation can be achieved by modifying the PSA cycle and / or by playing on the quality of the adsorbents and / or by allowing less CO2 to penetrate into the CO-rich gas.
[0028] Example of efficiencies that can be obtained by a PSA 4 on a gas feed at 8 bar:
[0029] [TAB.3] PSA 4 MODE High CO efficiency in gas 7 High CO2 production in gas 5 CO efficiency in gas 7% 85 80 N2 efficiency in gas 7% 86 82 CO2 efficiency in gas 7% 13 2 H2 efficiency in gas 7% 94 93
[0030] In operation in "High CO Efficiency" mode, the PSA 4 is operated to maximize the percentage of CO recovered from the gas 7 sent to the TSA unit. Thus, 85% of the CO present in the gas at the PSA 4 inlet is subsequently found in the gas 7, as well as 94% of the hydrogen. However, a significant percentage of CO2 (13%) is found in the gas 7.
[0031] In operation in “High CO2 Production” mode, this can result in a CO-rich flow HP 7 containing at most 2 mole% CO2. Conversely, a decrease in the partial flow rate of CO2 produced (i.e., the CO recovery efficiency) will be observed. Surprisingly, in order to optimize the entire process to produce a flow rate 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 “mouth gas”, if one wishes to obtain both: • a maximum CO2 recovery rate • and / or a maximum recovery rate of a purified CO2-rich stream produced in liquid or gaseous form • or / and a CO-rich flux 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 residual CO2 (maximum 2%). The required regeneration gas must be CO2-free and may come from: • From the product of TSA CO2 (see note below) • Of the N2 or CO2 flow produced by the cold box located downstream • An external flow
[0034] The residual gas thus generated may (or may not) be recycled at the inlet of the PSA and / or at 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 H2 / CO and CO2 molecules. • A cryogenic unit (cold box with partial condensation and / or washing stages (e.g., washing with liquid N2 or liquid CO2) and / or distillation with or without an associated refrigeration cycle) in series with the TSA on the CO2-rich stream for partial or total separation of the nitrogen present in the CO2-rich stream. A third residual gas, possibly created in the cryogenic unit, can 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 compressing the CO-rich gas.
[0036] The cryogenic unit can be used to produce at least one additional stream more or less rich in H2 and / or at least one additional stream rich in argon (argon from the air and from 1'O2 introduced into the blast furnace and found in the blast furnace gas).
[0037] The relatively high CO2 content that the TSA must remove upstream of the N2 / CO cold box will require a significant amount of heat. Using a portion of the decarbonized gas available downstream of this TSA is not necessarily desirable for two reasons. Firstly, it would lead to 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. Secondly, the presence of CO / H2 would limit the regeneration temperature to 150°C in order to avoid reactivity problems in the TSA's regeneration gas heater. It is therefore preferable to use the N2 flow from the CO / N2 cold box to regenerate the TSA and return the regeneration flow to the fuel network.
[0038] The main advantage of operating the PSA in “High CO2 Extraction” mode is to facilitate complete downstream CO2 removal, particularly compatible with TSA-type technology, and enabling final N2 / CO separation. The CO lost in the PSA's residual gas will be recovered by the separation unit through partial condensation and / or distillation and / or solidification and recycled back 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 depletion of CO2 in the residual gas of the PSA.
[0040] This will allow for the overall production of pure CO2 and a very high-CO2 stream with high recovery efficiencies. The amount of residual nitrogen in the high-CO2 stream (i.e., the nitrogen extraction efficiency) can be adjusted in the cold box. The purified CO2 thus produced can be directed either to biofuel production units or recycled back into the blast furnace (reducing CO2 emissions from the blast furnace).
[0041] The PSA can be either sized on a “Maximum CO2 yield” mode (choice of adsorbent and optimum cycle), or sized on a “High CO2 extraction” mode (with choice of optimal adsorbent and / or cycle), or sized so that it can be operated according to both modes (requiring an appropriate adsorbent + modification of the cycle during operation).
[0042] Coupling a CO2 PSA with 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 that can be sent to a carbon monoxide-consuming process, for example a CO-to-ethanol conversion process, which uses CO
[0043] Example of a material balance obtained for a PSA4 operating in “High CO2 Efficiency” mode on a feed gas at approximately 8 bar combined with a low-temperature CO2 separation unit CC, a TSA 6 and a cryogenic separation CB of CO and N2:
[0044] [TAB.3] Inlet PSA 4 CO produced 17 CO2 produced 14 N2 produced 19 Flow rate 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 yield: close to 100%
[0046] Maximizing the CO yield of PSA 4 can be achieved by obtaining a PSA 4 residual gas 5 richer in CO2, thereby reducing the specific energy of the partial condensation and / or distillation and / or solidification CC separation. The main advantage of operating PSA 4 in "high CO yield" mode is to increase the CO2 concentration in the CO2-enriched gas 5 of PSA 4, which is the flow rate feeding the partial condensation and / or distillation and / or solidification CC separation unit. 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 solidification CC separation unit.
[0047] A typical mass balance of the PSA CO2-enriched gas CC system treating blast furnace flue gas is shown below:
[0048] [TAB.4] CO2-enriched gas 5 CO2-rich liquid Gaseous phase e(#ll) 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] Optimizing the compressor Cl (if present) of the CO2-enriched gas 5 and external cooling cycles allows specific energy consumptions to be obtained on the order of 200 kW / tonne of liquid CO2 produced.
[0050] [Fig. 3] illustrates a method according to the invention. It consists of combining a unit of PSA 4 pressure-switching adsorption separation, a partial condensation and / or distillation and / or solidification separation unit and a TSA 6 temperature-switching 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 15 to 45 mol%, or even 15 to 30 mol%, of CO2, 15 to 45 mol%, or even 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 bar.
[0052] The compressed gas 1 is separated by pressure-toggle adsorption in unit 4, producing a gas enriched in CO and hydrogen 7 compared to the gas 1 entering unit 4, preferably containing at most 2% CO2. Unit 4 also produces a gas 5 depleted in CO and enriched in CO2 compared to the gas 1 entering unit 4.
[0053] The gas 5 can be compressed in a compressor CL. The gas 5 is at a first pressure greater than the second pressure at which the gas 7 is located.
[0054] The gas 5 is separated in the CC unit by partial condensation and / or distillation and / or solidification to form a CO2-rich fluid (gas or liquid) 14 containing at least 80 mol% CO2, or even at least 95 mol% CO2. The CC unit 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 overhead gas from a distillation column. The CC unit produces a gas 11, enriched in carbon monoxide and hydrogen relative to the gas 5, which is divided into two parts: one part FG serves as fuel gas, and the other part 11 is optionally used to regenerate dryers (not shown) upstream of the CC unit. The regeneration gas 11, laden with water after regeneration, is sent upstream of the PSA unit 4 or upstream of the compressor C.It is also possible to use a portion of gas 15, 17, 21, 23, 31, 33 as a regeneration gas.
[0055] The gas 7, G1 is separated by the adsorption unit 6 to form a gas 15 enriched in CO and H2 compared to the gas 7. The gas 15, G2 no longer contains CO2 but still contains nitrogen.
[0056] According to one 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 6 unit may (or may not) be recycled at the inlet of the PSA 4 (flow rate 29) and / or at 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 H2 / CO and CO2 molecules.
[0059] This gas 15 is optionally compressed in compressor C2 and separated in a cryogenic unit CB. The CB unit comprises a thermally insulated enclosure containing at least one phase separator and / or at least one scrubbing column and / or at least one distillation column. The at least one scrubbing column may be a liquid nitrogen or liquid carbon monoxide scrubbing column. The CB unit may include at least one refrigeration cycle. The separation performed by the CB unit is a partial or total separation of the nitrogen present in the CO-rich stream 15. The CB unit produces a fluid 19 enriched in nitrogen and depleted in CO and hydrogen with respect to the gas 15. The fluid 19 may contain at least 90 mol% nitrogen. The CB unit produces at least one gas enriched in hydrogen and / or CO and depleted in nitrogen with respect to the gas 15.For example, it can produce at least one gas enriched in hydrogen and depleted in nitrogen and CO compared to gas 15 and / or at least one gas enriched in CO and depleted in nitrogen and hydrogen compared to gas 15.
[0060] The fermentation unit 13 is supplied by at least a part of the gas 15 and / or at least a part of at least one gas enriched in hydrogen and / or CO and depleted in nitrogen compared to the gas 15 from the CB unit.
[0061] Preferably, it is supplied with 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. Supplying the fermentation unit with two gases of different purities allows for varying the CO and H2 concentrations in the gas present in the fermentation unit. It is also possible to supply a variable flow rate of the nitrogen-enriched gas 19 to slow down the fermentation reaction.
[0062] Another possibility is to send at least part of the gas enriched in hydrogen and depleted in nitrogen and CO with respect to gas 15 and / or at least another part of the gas enriched in CO and depleted in nitrogen and hydrogen with respect to gas 15 to another gas consumer.
[0063] A residual gas 21 possibly created in the cryogenic unit can also be recycled upstream of the PSA 4 (flow rate 29) or upstream of the CC unit (flow rate 31, 33).
[0064] The CB cryogenic unit can be used to produce at least one stream more or less rich in H2, for example a fluid (gas or liquid) containing at least 80 mol% hydrogen and / or a fluid (gas or liquid) containing at least 80 mol% of argon (argon from air and 1'O2 introduced into blast furnace HF and found in the blast furnace gas 1).
[0065] The relatively high CO2 content that the TSA 6 unit must remove upstream of the CB unit will require a significant amount of heat. Using a portion of the decarbonized gas 15 available downstream of this TSA 6 as a 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 avoid reactivity issues at the TSA 6 unit's heater. It is therefore preferable to use the N2 19 flow from the CB cold box to regenerate the TSA 6 and return the regeneration flow to the fuel network.
[0066] The main advantage of operating the PSA 4 unit in “High CO2 Production” mode is to facilitate complete downstream CO2 removal, particularly compatible with TSA-type technology, and enabling final N2 / CO separation. The CO lost in the PSA 4 waste gas 5 will be recovered by the CC separation unit through partial condensation and / or distillation and / or solidification and recycled back to the PSA inlet to improve production efficiency.
[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 depletion of CO2 in the residual gas 5 of the PSA unit 4.
[0068] This will allow for the overall production of pure CO2 and a very high-CO2 stream with high recovery efficiencies. The amount of residual nitrogen in the high-CO2 stream (i.e., the nitrogen extraction efficiency) can be adjusted in the cold box. The purified CO2 thus produced can be directed either to biofuel production units, for example for ethanol (using a Lanzatech process, for example), or recycled back into the blast furnace (reducing CO2 emissions from the blast furnace).
[0069] The PSA 4 can be either sized on a “High CO2 yield” mode (choice of adsorbent and optimum cycle), or sized on a “High CO2 production” mode (choice of adsorbent and optimum cycle), or sized so that it can be operated according to 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 downstream CB unit • An external flow
[0071] As a fermentation process producing a biofuel, for example ethanol, has variable requirements in terms of feed gas, it is possible to send to it 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. Demands A process for separating 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-toggle 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 partial condensation and / or distillation and / or solidification separation unit (CC) which produces a CO2-rich fluid (14) 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-toggle 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 part 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 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. A process according to claim 1 in which at least a portion of the second and / or fourth gas (15, 17) enriched in CO is sent to a biofuel production process, for example ethanol, by fermentation. A method according to claim 1 or 2, wherein at least a portion of the second and / or fourth gas is separated by condensation partial 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 process 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. A process according to any one of the preceding claims wherein at least a portion of the third fluid (19) is sent to the process of producing biofuel, for example ethanol, by fermentation.
6. A method according to any one of the preceding claims wherein the CO2-enriched gas (23, 31) produced by temperature-toggle adsorption is mixed with the CO2-enriched gas (5), optionally upstream of a compression step (Cl).
7. A process according to any one of the preceding claims wherein the first CO-enriched gas (7) is nitrogen-enriched relative to the residual gas (1).
8. A process according to any one of the preceding claims wherein the second CO-enriched gas (15) contains at least 60% mol of CO.
9. A process 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. A process according to any one of the preceding claims wherein the residual gas (1) contains argon and the separation (CB) by partial condensation and / or washing and / or distillation produces an argon-enriched fluid.
11. A process according to any one of the preceding claims wherein separation at cryogenic temperature produces a fluid containing at least 80% hydrogen.
12. A process according to any one of the preceding claims wherein the CO2-depleted and CO-enriched gas (7) 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. A method according to any one of the preceding claims 10 to 13, wherein a regeneration gas is sent to the second unit adsorption (6) consists of a part of the second gas (15) containing at least 60% mol CO.
14. A method according to any one of claims 10 to 13 wherein a regeneration gas sent to the second adsorption unit (6) consists of a gas produced by separation at cryogenic temperature.
15. A process according to any one of the preceding claims wherein 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. A process according to any one of the preceding claims wherein the CO2-enriched gas (5) contains water and is dried in a drying unit upstream of the unit (CC) for partial condensation and / or distillation and / or solidification separation, 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).