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

Abstract

Title: Method and apparatus for separating waste gas from a ferrous metal production unit In a method for separating waste gas from a ferrous metal production unit, the waste gas (1) is compressed in a first compressor (C) and then separated by pressure swing adsorption (4) in an adsorption unit to produce a gas (5) depleted in carbon monoxide and enriched in CO2 relative to the waste gas and a first gas (7) enriched in carbon monoxide and depleted in CO2 relative to the waste gas,the CO2-enriched gas is sent to a partial condensation and / or distillation separation unit (CC) which produces a CO2-rich fluid (PL) containing at least 80 mol% CO2 and at least a portion of the first CO-enriched gas (7) is separated by permeation (M) to form a second CO2-enriched gas (21) relative to the first CO-enriched gas at a first pressure and a CO-richer gas (15) than at least a portion of the first CO-enriched 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.

[0003] 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 necessary for heating and melting the iron ore.

[0004] It is of course possible to use, in addition to coke, coal or another hydrocarbon injected into the tuyeres of the blast furnace. On the other hand, carbon monoxide is produced, resulting from the combustion reaction of coke and / or coal and / or hydrocarbon with the 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.

[0005] In the same factory, there may 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 approximately 35 and 65 percent 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 the coke or, in general, from the injected fuel.

[0006] We also find water vapor due to this combustion since the general reaction between a carbon product and oxygen during combustion essentially produces 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, having calorific values ​​typically between 6,000 and 10,000 kJ / Nm3 and between 12,000 and 20,000 kJ / Nm3, respectively).

[0007] Generally speaking, the quantity of gas produced by a blast furnace is very significant and of the order of approximately 1,500 Nm3 of gas for one tonne of cast iron produced.

[0008] It follows that, taking into account the composition of said gas, the quantity of carbon dioxide produced per tonne of cast iron is also very significant: for example, for a blast furnace gas having an average carbon dioxide content of 22 percent in the dry gas and for a blast furnace producing one million tonnes of cast iron per year, the quantity of carbon dioxide emitted in the blast furnace gas is 330 million Nm3 per year, or approximately 650,000 tonnes of carbon dioxide produced over one year. For a blast furnace producing 3 million tonnes of cast iron per year, the quantity of CO2 emitted is approximately 2 million tonnes per year, while for a site producing 7 million tonnes of cast iron per year, the quantity of CO2 is approximately 4.5 million tonnes.

[0009] These quantities are quite considerable and, given the negative effect of these gases on the atmosphere and the environment, it cannot be envisaged to send them directly into the atmosphere. Furthermore, releasing said gases into the atmosphere would also involve 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.

[0010] The typical composition of an example of a waste gas from a ferrous metal production unit (after cooling and extraction of condensed water vapor), 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%

[0011] The extraction of CO2 and N2 present in the top gases of blast furnaces aims to recover the CO-rich product: • as fuel (higher calorific value) to turbines (generation of electricity for an integrated steelworks) or to other users of the steelworks (such as stoves mixed with other fuel gases (coke oven gas, hydrocarbons e.g. natural gas) to preheat enriched air) • as a reducing gas for the coal in the blast furnace itself

[0012] It is also known to use CO-rich gas from blast furnace gas as a raw material for the production of biofuels (for example the Steelanol ® process for transforming CO into at least one biofuel, for example bioethanol.

[0013] According to the invention, there is provided a method for separating the waste 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 an adsorption unit to produce a gas depleted in carbon monoxide and enriched in CO2 relative to the waste gas and a first gas enriched in carbon monoxide and depleted in CO2 relative to the waste gas 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 iii. At least a portion of the first CO enriched gas is permeated to form a second gas enriched in CO2 relative to the first CO enriched gas at a first pressure and a gas richer in CO than the at least a portion of the first CO enriched gas.

[0014] According to other optional features: • at least a portion of the first CO-enriched gas is separated by permeation carried out at room temperature, the CO2-enriched gas relative to the CO-enriched gas being the permeate. • at least a portion of the first CO-enriched gas is separated by permeation carried out at a temperature between 10°C above the outlet temperature of the adsorption unit and 10°C below the outlet temperature of the adsorption unit. • at least part of the first CO-enriched gas is separated by permeation carried out at a temperature below the outlet temperature of the adsorption unit, for example below 0°C and above -52°C, preferably between -10°C and -40°C, the gas enriched in CO2 relative to the gas enriched in CO being the permeate. • at least a portion of the first CO-enriched gas is separated by permeation carried out at a temperature above 50°C and below 100°C, the CO-enriched gas being reheated upstream of the permeation and the CO2-enriched gas relative to the CO-enriched gas being the permeate. • the gas richer in CO than at least a portion of the first gas enriched in CO is sent to a process for producing biofuel, for example ethanol, by fermentation. • the gas sent to the biofuel production process, for example ethanol, contains less than 3% mol of CO2. • the gas sent to the biofuel production process, for example ethanol, contains hydrogen and / or nitrogen and / or carbon monoxide • at least a portion of the second CO2-enriched gas is separated in the separation unit of step ii). • at least a portion of the second CO2-enriched gas is compressed in a compressor with the CO2-enriched gas. • at least part of the first CO-enriched gas is cooled upstream of the permeation by heat exchange with a fluid coming from the separation unit by partial condensation and / or distillation and / or solidification. • the first gas enriched in carbon monoxide and depleted in CO2 compared to the residual gas contains at least 80%, or even at least 85%, of the carbon monoxide present in the residual gas separated in the adsorption unit • at least one gas enriched in hydrogen and / or carbon monoxide relative to the gas depleted in carbon monoxide and enriched in CO2 is produced by the separation unit by partial condensation and / or distillation and / or solidification and is sent to the adsorption unit for separation there.

[0015] According to another object of the invention, there is provided a waste gas separation apparatus connected to a ferrous metal production unit comprising a first compressor connected to compress a waste gas from the production unit containing at least CO, CO2, hydrogen and nitrogen, a pressure swing adsorption unit connected to the outlet of the first compressor to separate the compressed waste gas to produce a gas depleted in carbon monoxide and enriched in CO2 relative to the waste gas and a first gas enriched in carbon monoxide and depleted in CO2 relative to the waste gas, a unit for separation by partial condensation and / or distillation and / or solidification, a pipe connected to the adsorption unit and the partial condensation and / or distillation and / or solidification separation unit for sending the first CO2-enriched gas from the adsorption unit to a partial condensation and / or distillation and / or solidification separation unit, a permeation unit, a pipe for leaving the separation unit a CO2-rich fluid containing at least 80 mol% of CO2 and a pipe for sending at least a portion of the CO-enriched gas from the adsorption unit to the permeation unit to form a second CO2-enriched gas relative to the first CO-enriched gas at a first pressure and a gas richer in CO than the at least a portion of the CO-enriched gas.

[0016] The apparatus may comprise: • means for heating or cooling at least part of the CO-enriched gas upstream of the permeation unit. • a pipe for sending at least a portion of the second CO2-enriched gas to be separated in the separation unit. • a compressor for compressing at least a portion of the second CO2-enriched gas and the CO2-enriched gas.

[0017] The invention will be described in more detail with reference to the figures where:

[0018] [Fig. 1] represents a comparative method.

[0019] [Fig.2] represents a comparative method.

[0020] [Fig.3] represents a method according to the invention.

[0021] [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 C 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.

[0022] In the case of a pressure swing adsorption separation unit, known by the acronym PSA, treating a waste gas from a ferrous metal unit compressed to about 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.

[0023] 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).

[0024] 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.

[0025] [TAB1] represents an example of material balance obtained for a single PSA 4 operating in “high CO efficiency” mode on residual gas 1 at approximately 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

[0026] CO recovery efficiency = 85.8%

[0027] It is known 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 compression energy of the PSA 4 (for the production of a constant partial flow of CO at the outlet of the PSA 4). This integration also makes it possible to increase the CO purity of the HP product of the PSA 4.

[0028] [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: PSA Input CO-enriched gas (product) CO2-enriched gas 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

[0029] The CO recovery efficiency is in this case close to 100%, thanks to the sending of at least one gas enriched in hydrogen and / or carbon monoxide compared to the gas depleted in carbon monoxide and enriched in CO2 from the CC unit to the PSA 4.

[0030] It is possible to operate the PSA on “top gas” 1 in “High CO2 efficiency” 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 allowing less CO2 to penetrate into the CO-rich gas.

[0031] Example of yields that can be obtained by a PSA on top gas at 8 bars:

[0032] [TAB.3] PSA MODE High CO yield High CO2 production CO yield % 85 80 N2 yield % 86 82 CO2 yield % 13 2 H2 yield % 94 93

[0033] When operating in “High CO2 Production” mode, this may result in a CO-rich flow containing less than 2 mole % CO2. On the other hand, there will be a reduction in the partial flow of CO produced and therefore in the CO recovery efficiency.

[0034] The coupling of a CO2 PSA as illustrated in [Fig.2] with a separation by partial condensation and / or CC distillation, has the following objectives: • To enrich the PSA waste gas with CO2 in order to minimize the specific energy of the CO2 separation process by partial condensation and / or distillation and / or solidification. • To increase the CO purity of a PSA product that can be sent to a carbon monoxide-consuming process, for example a CO to ethanol conversion process by fermentation, which uses CO.

[0035] The CO2-enriched gas 5 is sent to a partial condensation and / or distillation and / or solidification unit CC as described in the FR patent application. The CC unit produces a CO2-rich fluid PL containing at least 80 mol% of CO2 and a gas 13 enriched in at least one impurity lighter than CO2, for example carbon monoxide and hydrogen. The gas 13 is recycled upstream of the PSA adsorption unit.

[0036] The gas 5 can be compressed in a compressor C1 upstream of the unit CC.

[0037] The gas 5 can be dried upstream of the CC unit in dryers, for example by temperature swing adsorption. The gas used to regenerate the dryers can then be used as fuel gas FG and / or be recycled upstream of the PSA as IL gas.

[0038] According to a variant of [Fig.2], [Fig.3] illustrates a process in which the CO2-depleted and CO7-enriched gas from the adsorption unit 4 is separated by permeation in the permeation unit M.

[0039] Maximizing the CO yield of the PSA 4 can be sought while trying 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 residual 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 optimization 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.

[0040] Such adjustment of the PSA 4 can be obtained by modifying the PSA cycle and / or by adjusting the quality of the adsorbents and / or by allowing more CO2 to penetrate into the CO-rich gas 7. The CO2 contained in this gas 7 available at 8-9 bar can be largely removed, thanks to the addition of a permeation separation step in a permeation unit M as indicated in [Fig.3]. The membranes used can be of the PI membrane type operated at temperatures below 0°C or PoroGen ® fiber membranes, allowing for example to remove more than 70% of the CO2 while losing only 5% of the CO. The permeate 21 of these membranes M will be a very CO2-rich stream at low pressure, which can be recycled upstream of the separation by partial condensation and / or distillation and / or solidification CC for recovery.

[0041] The membrane unit M installed downstream of the PSA 4 will separate the flow 7 enriched in CO in order to generate two flows:

[0042] 1- a first high pressure flow 15 (residue) rich in CO and N2 and containing a low proportion of CO2. The reduction of CO2 in this stream thus offers the possibility of supplying a customer 17 looking for a product rich in CO, for example to increase the productivity of a fermentation process 17 which consumes the CO in the gas to produce ethanol or other fuel.

[0043] 2-a second low pressure flow 21 (permeate), very rich in CO2, and sent to the separation inlet by partial condensation and / or distillation and / or solidification CC, allowing recovery of the CO and H2 contained in this permeate.

[0044] Four types of membrane separation applications can be considered: 1. Separation at room temperature

[0045] At least a portion of the CO 7 enriched gas produced by the PSA 4 is separated by permeation carried out at room temperature in the membrane unit M, the CO2 21 enriched gas relative to the CO 7 enriched gas being the permeate. This is possible by using membranes that are more selective for CO2 than for CO.

[0046] Examples of a suitable membrane are P-Guard or D-Guard or R-Guard from PoroGen Corporation or PI-1 or PI-2 from Medal Corporation. 1. Separation at a temperature below the operating temperature of adsorption unit 4 (preferable mode)

[0047] At least a portion of the CO 7 enriched gas is separated by permeation M carried out at a temperature below the operating temperature of the adsorption unit 4, for example below 0°C and above -52°C, preferably between -15°C and -35°C, the CO2 enriched gas 21 relative to the CO 7 enriched gas being the permeate. An example of a suitable membrane is PI-1 or PI-2 from the company Medal.

[0048] At least a portion of the CO-enriched gas 7 is cooled upstream of the permeation M by a cold fluid coming from the partial condensation and / or distillation and / or solidification separation unit CC. 1. Separation at a temperature above 50°C and below 100°C

[0049] At least a portion of the CO 7 enriched gas is separated by permeation M carried out at a temperature above 50°C and below 100°C, the CO 7 enriched gas being reheated upstream of the permeation and the CO2 enriched gas 21 relative to the CO enriched gas being the permeate.

[0050] An example of a suitable membrane is G5 or PIX from Medal. 1. Separation at a temperature between 10°C above the outlet temperature of the adsorption unit and 10°C below the outlet temperature of the adsorption unit.

[0051] An example of a suitable membrane is PI 1-P12 from Medal.

[0052] A product 15 of the permeation separation M, according to one of the four types, is depleted in CO2 compared to the gas enriched in CO and is sent to a process for producing ethanol by fermentation 17. The gas 15 preferably contains less than 3 mol% of CO2.

[0053] In this example, no part of the CO 7 enriched gas is returned to the HF blast furnace.

[0054] At least a portion of the second CO2-enriched gas 21 produced by the permeation M is separated in the separation unit CC in order to recover the CO2 it contains. It may optionally be compressed in a compressor with the first gas.

[0055] The HF blast furnace of [Fig.3] can be fueled by air or oxygen.

[0056] At least one gas enriched in hydrogen and / or carbon monoxide relative to the gas depleted in carbon monoxide and enriched in CO2 is produced by the separation unit by partial condensation and / or distillation and / or solidification, for example FG gas. This gas or these gases can be sent to the adsorption unit 4 for separation there

Claims

Claims

1. A method of separating waste gas from a ferrous metal production unit wherein: 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 (4) in an adsorption unit to produce a gas (5) depleted in carbon monoxide and enriched in CO2 relative to the waste gas and a first gas (7) enriched in carbon monoxide and depleted in CO2 relative to the waste gas 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 (PL) containing at least 80 mol% CO2 iii. At least a portion of the first gas (7) enriched in CO is separated by permeation (M) to form a second gas (21) enriched in CO2 relative to the first gas enriched in CO at a first pressure and a gas (15) richer in CO than the at least a portion of the first gas enriched in CO.

2. Method according to claim 1 in which at least a part of the first gas (7) enriched in CO is separated by permeation (M) carried out at ambient temperature, the gas enriched in CO2 relative to the gas enriched in CO being the permeate.

3. Method according to claim 1 or 2 in which at least a part of the first gas (7) enriched in CO is separated by permeation (M) carried out at a temperature between 10°C above the outlet temperature of the adsorption unit (4) and 10°C below the outlet temperature of the adsorption unit.

4. Method according to claim 1 in which at least a part of the first gas (7) enriched in CO is separated by permeation carried out at a temperature below the outlet temperature of the adsorption unit (4), for example below 0°C and above -52°C, preferably between -10°C and -40°C, the gas (21) enriched in CO2 relative to the gas enriched in CO being the permeate.

5. Method according to claim 1 in which at least a part of the first gas (7) enriched in CO is separated by permeation (M) carried out at a temperature above 50°C and below 100°C, the first gas enriched in CO being reheated upstream of the permeation and the gas enriched in CO2 (21) relative to the first gas enriched in CO being the permeate.

6. Method according to one of the preceding claims in which the gas (15) richer in CO than at least a part of the first gas enriched in CO is sent to a process for producing biofuel (17), for example ethanol, by fermentation.

7. A method according to claim 6 wherein the gas (15) sent to the biofuel production process (17), for example ethanol, contains less than 3 mol% CO2.

8. Method according to one of the preceding claims in which at least a part of the second gas (21) enriched in CO2 is separated in the separation unit (CC) of step ii).

9. A method according to claim 8 wherein the at least part of the second CO2-enriched gas (21) is compressed in a compressor with the CO2-enriched gas (5).

10. Method according to claim 3 in which at least a part of the first CO-enriched gas (7) is cooled upstream of the permeation (M) by heat exchange with a fluid coming from the separation unit (CC) by partial condensation and / or distillation and / or solidification.

11. Method according to one of the preceding claims in which at least one gas enriched in hydrogen and / or carbon monoxide (11, 13, FG) relative to the gas depleted in carbon monoxide and enriched in CO2 (5) is produced by the separation unit by partial condensation and / or distillation and / or solidification (CC) and is sent to the adsorption unit (4) to be separated there.

12. A waste gas separation apparatus connected to a ferrous metal (HF) production unit comprising a first compressor (C) connected to compress a waste gas (1) from the production unit containing at least CO, CO2, hydrogen and nitrogen, a pressure swing adsorption unit (4) connected to the outlet of the first compressor to separate the compressed waste gas to produce a gas (5) depleted in carbon monoxide and enriched in CO2 relative to the waste gas and a first gas (7) enriched in carbon monoxide and depleted in CO2 compared to the residual gas, a separation unit (CC) by partial condensation and / or distillation and / or solidification, a pipe connected to the adsorption unit and to the separation unit by partial condensation and / or distillation and / or solidification to send the first gas enriched in CO2 from the adsorption unit to a separation unit by partial condensation and / or distillation and / or solidification, a permeation unit (M), a pipe to output from the separation unit a fluid rich in CO2 (PL) containing at least 80 mol% of CO2 and a pipe to send at least a portion of the gas enriched in CO from the adsorption unit to the permeation unit to form a second gas enriched in CO2 (21) compared to the first gas enriched in CO at a first pressure and a gas (15) richer in CO than the at least a portion of the gas enriched in CO.

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