Method and apparatus for nox treatment of co2 capture

Abstract

In a method for NOx treatment in a CO2 capture plant, in which flue gas (7) from a combustion process (5) is treated in a NOx treatment unit (9) to reduce the NOx content of the flue gas, the flue gas (11) with reduced NOx content is sent to a CO2 capture unit (13), which produces as products a CO2 rich stream (17), and a NOx rich stream (19), and the NOx rich stream is sent upstream of the NOx treatment unit.

Description

[0001] This invention relates to a method and apparatus for NOx treatment in a CO2 capture device.

[0002] It is necessary to reduce NOx present in combustion gases.

[0003] When facilities that include a combustion step (such as steam methane reforming units known as SMR) must comply with local emissions regulations, SCR (Selective Catalytic Reduction) is typically chosen to convert most of the NOx present in the combustion gases into water and nitrogen. These expensive facilities require the injection of urea or NH3 to convert NOx into H2O and N2.

[0004] The SCR is the most efficient in its class, but at the cost of investment costs, it competes with other solutions, including SNCR (Selective Non-Catalytic Reduction), which exhibits low efficiency but low investment costs, hybrid solutions combining the two technologies, catalyst bags, and the use of low-NOx burners.

[0005] When local regulations are stringent, the only viable solution is SCR (or a mixture of SCR and NSCR). The SCR (or SCR / NSCR mixture) allows for a wide range of efficiencies, but higher NOx removal necessitates higher amounts of catalyst and / or NH3 / urea consumption (NH3 conversion efficiency decreases if the excess NH3 is reduced to near stoichiometric values).

[0006] Regardless of the technology used, a NOx escape rate of more than 5% is generally necessary to maintain the SCR as an economical solution.

[0007] If CO2 must be captured from flue gas (e.g., flue gas from a steam methane reforming unit), the amount of NOx present in the flue gas requires special design of the unit, thereby increasing the cost of the unit, and the presence of NOx-rich streams can sometimes cause safety issues.

[0008] Figure 1 An apparatus according to the prior art is shown, in which combustion process 5 is fed by an oxygen-containing stream 1 and fuel 3. The resulting flue gas 7 is treated in unit 9 to remove NOx, and a stream 11 containing less NOx is treated in a collection unit 13 by amine absorption, thereby producing CO2 17 and exhaust gas 15. The presence of NOx in gas 11 degrades the amine (amine reacts with NOx), requiring the amine to be replenished to the process.

[0009] Flue gas from combustion processes (such as steam methane reforming or SMR) has a relatively high CO2 concentration. An alternative capture technique is known, for example, pressure swing adsorption (PSA) assisted by cryogenic separation via partial condensation and / or distillation. The PSA is used to separate N2 from CO2, thereby producing a CO2-rich stream suitable for cryogenic separation. This technique can present capture costs much lower than amines, especially when liquid CO2 is required (in which case the absorption scheme would need to install an additional CO2 liquefaction unit downstream), or when there is not a sufficient amount of recoverable heat in the upstream process.

[0010] In practice, without a specific NOx strategy, the NOx present in the flue gas (mainly in the form of NO) will be converted into nitric acid in the interstage cooler of the flue gas compressor. The residue will then be concentrated in the CO2-rich stream of the PSA (e.g., about 4 times when the flue gas contains 20 mol% CO2), and subsequently converted into NO2 / N2O4 mainly in the high-pressure, low-temperature cryogenic separation section, so that most of it will leave with the generated CO2.

[0011] Conversion of NOx to nitric acid:

[0012] A portion of the NOx can be converted and discharged in the process condensate via nitric acid; the higher the pressure, the higher the conversion rate. Therefore, if drying is present downstream of the main compressor in the cryogenic separation section, NOx can be partially removed in the interstage cooler via the reaction, but at the cost of metallurgical resistance to nitric acid. This situation may lead to the selection of drying upstream of the PSA, resulting in low NOx removal via the nitric acid path. Furthermore, some limitations of the water treatment system may also necessitate the installation of a drying unit at the start of the process. Overall, the amount of NOx that can be removed via the acid pathway is limited and typically requires additional configuration to meet CO2 specifications or environmental regulations.

[0013] Denitrification tower:

[0014] NOx extractors can be installed in cryogenic sections, resulting in a highly concentrated NOx stream (especially when the dryer is installed at low to medium pressures), with CO2 as the primary carrier gas. This stream must be managed intelligently because it presents two main problems: first, the loss of CO2 recovery, as the stream cannot be recycled back to the capture process without any NOx removal treatment; and second, the safety concerns associated with such high concentrations of NOx that are difficult to remove.

[0015] According to one object of the present invention, a method for treating NOx in a CO2 capture device is provided, wherein flue gas from a combustion process is treated in a NOx treatment unit to reduce the NOx content of the flue gas, thereby producing flue gas with reduced NOx content, the flue gas with reduced NOx content being fed to a CO2 capture unit, the CO2 capture unit generating a CO2 enriched stream as a product and a NOx enriched stream, and the NOx enriched stream being fed upstream of the NOx treatment unit and / or to the burner of the combustion process.

[0016] Based on other optional features:

[0017] The NOx treatment unit is a selective catalytic reduction, selective non-catalytic reduction, non-selective catalytic reduction, mixed selective catalytic reduction / non-selective catalytic reduction, or filtration type.

[0018] The CO2 capture unit includes a pressure swing adsorption separation unit, which generates the NOx-enriched stream, the CO2-enriched stream, and the exhaust gas.

[0019] The pressure swing adsorption separation unit separates the CO2-rich stream from the waste gas in contact with an adsorbent selected from X, Y, or A type octahedral zeolite molecular sieves, activated alumina, modified alumina, silica gel, activated carbon, or combinations thereof.

[0020] The exhaust gas includes one or more compounds selected from N2, O2, Ar, CO, CO2, NO, and NO2.

[0021] The pressure swing adsorption separation unit includes at least four adsorbers.

[0022] The pressure swing adsorption separation unit operates in a pressure cycle, which includes an adsorption step at a high cyclic pressure and a desorption step of the CO2-rich stream at a low cyclic pressure, particularly below atmospheric pressure, as well as a countercurrent depressurization step accompanying the discharge of the NOx-rich stream, the countercurrent depressurization step being between the adsorption step and the desorption step.

[0023] The pressure cycle includes a co-current depressurization step, particularly a co-current depressurization and purge gas supply step, followed immediately by a counter-current depressurization step.

[0024] The NOx enriched stream is discharged in the first part of the countercurrent depressurization step, which corresponds to one-quarter of the total pressure change of the adsorber during the countercurrent depressurization step.

[0025] The NOx-enriched stream (especially enriched NO2) is discharged during the countercurrent depressurization step by the desorption of NOx, especially NO2, and by the desorption of a portion of the CO2 adsorbed during the adsorption step.

[0026] The NOx enriched stream is fed into a buffer tank upstream of the NOx treatment unit or before the burner of the combustion process.

[0027] The flue gas from the combustion process contains at least 10% by volume of CO2 on a dry basis, particularly 15 to 50% by volume of CO2 on a dry basis.

[0028] The CO2-rich stream is separated by distillation and / or partial condensation to produce the CO2-enriched stream.

[0029] Alternatively, the CO2-rich stream constitutes the CO2-enriched stream.

[0030] The pressure swing adsorption separation unit is of the PSA unit or VPSA unit type.

[0031] The additional NOx enriched stream is generated by the distillation and / or by the partial condensation, and the additional NOx enriched stream is fed upstream of the NOx treatment unit and / or to the burner of the combustion process.

[0032] The separation via distillation includes a NOx removal column, the bottom liquid of which constitutes the additional NOx enrichment stream.

[0033] The NOx enrichment stream and / or the additional NOx enrichment stream contain NOx concentrations that are 3 times, 10 times, or even 100 times higher than the flue gas produced by combustion.

[0034] The NOx enrichment stream and / or the additional NOx enrichment stream contain at least 50 mol%, or at least 70 mol%, or even at least 90 mol% CO2.

[0035] The NOx enrichment stream and / or the additional NOx enrichment stream contain 50 mol% to 90 mol% CO2.

[0036] The NOx treatment unit is designed to operate without CO2 capture, and the percentage of NOx in the gas being treated increases in CO2 capture mode.

[0037] The NOx-enriched stream is mixed with the oxygen-containing stream sent to the combustion process.

[0038] The NOx enriched stream is mixed with the fuel fed into the combustion process.

[0039] The combustion process is included in steam methane reforming processes, cement plant processes, lime production processes, metallurgical processes, or power, heat, and / or steam production processes.

[0040] According to one object of the present invention, a NOx treatment apparatus for a CO2 capture device is provided, the NOx treatment apparatus comprising a NOx treatment unit, a CO2 capture unit, means for feeding flue gas from a combustion process into the NOx treatment unit to reduce the NOx content of the flue gas, means for feeding flue gas with reduced NOx content from the treatment unit to the CO2 capture unit, the CO2 capture unit generating a CO2 enriched stream as a product and a NOx enriched stream, and means for feeding the NOx enriched stream upstream of the NOx treatment unit or to a burner in the combustion process.

[0041] The invention will be described in more detail with reference to the accompanying drawings:

[0042] Figure 2 The method according to the present invention is shown.

[0043] Figure 3 The method according to the present invention is shown.

[0044] Figure 2A method is illustrated in which a combustion process 5 is fed by an oxygen-containing stream 1 and fuel 3. The combustion process 5 may be a steam methane reforming plant, a cement plant, a lime production process, a metallurgical process, or a power and / or steam and / or heat production center. The resulting flue gas 7 contains at least 10% by volume of CO2 and NOx on a dry basis. The flue gas 7 is treated in unit 9 to remove NOx and produce stream 11. The treated stream 11, containing less NOx, is treated in a capture unit 13 to produce a CO2-enriched stream 17 and exhaust gas 15. Unit 9 is of the selective catalytic reduction (SCR), selective non-catalytic reduction (SNR), non-selective catalytic reduction (NNR), or a hybrid SCR / NNR or filtration type.

[0045] The collection unit 13 first separates the stream 11 into a CO2-rich stream and the exhaust gas 15 via pressure swing adsorption (PSA). This separation occurs upon contact with an adsorbent selected from type X, Y, or A zeolite molecular sieves, activated alumina, modified alumina, silica gel, activated carbon, or combinations thereof. The collection unit 13 generates a stream 19 enriched with NOx relative to the stream 11. A portion of the NOx in the flue gas 7 is converted upon contact with the adsorbent, particularly NO being oxidized to NO2. The pressure swing adsorption separation follows… Figure 4 The pressure cycle is shown in the figure. The pressure swing adsorption separation unit includes one adsorber or multiple adsorbers configured to follow the pressure cycle, with a phase shift between two consecutive adsorbers.

[0046] The capture unit 13 then separates the CO2-rich stream by partial condensation and / or distillation to produce a gaseous or liquid CO2-rich stream 17 as a product. This final step can be omitted, and the CO2-rich stream generated by the PSA subsequently constitutes the CO2-rich stream 17. Separation by distillation may include a NOx removal column, the bottom liquid of which constitutes an additional NOx-rich stream (not shown).

[0047] The stream 19 and the potential additional NOx enrichment stream are fed downstream of the combustion process 5 and upstream of the unit 9, to the unit 9 to remove NOx contained in the stream. In this way, the carbon dioxide present in the stream 19 is not lost.

[0048] The NOx enrichment stream 19 contains a NOx concentration that is 3 times, 10 times, or even 100 times that of the flue gas 7 produced by combustion.

[0049] The NOx enrichment stream 19 contains at least 50 mol%, or at least 70 mol%, or even 90 mol% CO2.

[0050] Figure 3 A method is illustrated in which a combustion process 5 is fed by an oxygen-containing stream 1 and fuel 3. The combustion process 5 may be a steam-cured methane reforming plant, a cement plant, or a power and / or steam and / or heat production center. The resulting flue gas 7 contains at least 10% by volume of CO2 and NOx on a dry basis. The flue gas 7 is treated in unit 9 to remove NOx. A stream 11 containing less NOx is treated in a capture unit 13, thereby producing a CO2-enriched stream 17 and exhaust gas 15. Unit 9 is of the selective catalytic reduction (SCR), selective non-catalytic reduction (SNR), non-selective catalytic reduction (NNR), mixed SCR / NNR, or filtration type.

[0051] The collection unit 13 first separates the stream 11 into a CO2-rich stream, the exhaust gas 15, via pressure swing adsorption (PSA). This separation occurs upon contact with an adsorbent selected from type X, Y, or A zeolite molecular sieves, activated alumina, modified alumina, silica gel, activated carbon, or combinations thereof. The collection unit 13 generates a stream 19 enriched with NOx relative to the stream 11. A portion of the NOx in the flue gas 7 is converted upon contact with the adsorbent, particularly NO being oxidized to NO2. The pressure swing adsorption separation follows… Figure 4 The pressure cycle is shown in the figure. The pressure swing adsorption separation unit includes one adsorber or multiple adsorbers configured to follow the pressure cycle, with a phase shift between two consecutive adsorbers.

[0052] The capture unit 13 then separates the CO2-rich stream by partial condensation and / or distillation to produce a gaseous or liquid CO2-rich stream 17 as a product. This final step can be omitted, and the CO2-rich stream generated by the PSA subsequently constitutes the CO2-rich stream 17. Separation by distillation may include a NOx removal column, the bottom liquid of which constitutes the additional NOx-rich stream (not shown).

[0053] The stream 19 and the potential additional NOx-enriched stream are fed to the burner 5A of the combustion unit because the presence of NOx in the combustion gases will reduce NOx production in the burner (through thermodynamic equilibrium), thereby reducing the total amount of NOx managed by the NOx removal system and minimizing the additional investment and operating costs of the NOx removal system. The stream 19 may be mixed with the stream 1 and / or the fuel 3 fed to the burner 5A. The NOx-enriched stream 19 contains 3 times, 10 times, or even 100 times the NOx produced by the combustion of the flue gas 7.

[0054] The NOx enrichment stream 19 contains at least 50 mol%, or at least 70 mol%, or even 90 mol% CO2.

[0055] To optimize the overall scheme and further reduce investment and / or operating costs, the NOx removal unit 9 can be designed or operated to allow for higher NOx slip as NOx is recycled to the combustion process. This higher NOx slip can be achieved by minimizing the amount of catalyst in the case of SCR (reducing investment costs) or by reducing NH3 slip at the outlet of the NOx treatment or removal unit 9 (reducing NH3 / urea consumption).

[0056] The NOx treatment unit 9 is preferably designed to operate without CO2 capture. When the NOx treatment unit 9 operates in CO2 capture mode, the percentage of NOx in the treated gas increases in CO2 capture mode.

[0057] Figure 4 The pressure cycle is shown, in Figure 2 and Figure 3 In this embodiment, the pressure swing adsorption separation operates in a cyclic manner according to the pressure. The flow 11 is referred to as the "feed gas" in this figure.

[0058] The cycle includes an adsorption step A under high circulating pressure. A portion of the stream 11 is fed downstream into at least one adsorber of the pressure swing adsorption separation unit. CO2 is adsorbed more strongly on the adsorbent than the main component of the exhaust gas 15. For this reason, most of the components of the exhaust gas 15 circulate through the adsorber during the step, while most of the CO2 is retained in the adsorber. The exhaust gas 15 is generated under high circulating pressure. NO is mostly oxidized to NO2 upon contact with the adsorbent, and NO2 is retained in the adsorber. Unconverted residual NO then follows nitrogen and eventually reaches the chimney.

[0059] The cycle includes a co-current depressurization and purge gas supply step E1D+PP. The adsorber is depressurized co-currently to the intermediate cycle pressure. The components of the exhaust gas 15 further move towards the outlet of the adsorber, and the exhaust gas 15 is discharged from the adsorber. A portion of the discharged exhaust gas 15 is used as purge gas, while another portion is used as counter-current repressurization gas.

[0060] The cycle includes a countercurrent depressurization step BD (also known as a blow-down step) accompanying the discharge of the NOx-enriched stream 19. This step is typically achieved by opening a valve to allow a portion of the gas from the bottom of the adsorber to escape. The NOx-enriched stream 19 is discharged in the first part of the countercurrent depressurization step BD, particularly at the beginning of the depressurization, which corresponds to one-quarter of the total pressure change of the adsorber during the countercurrent depressurization step. In practice, most of the NOx is concentrated in the gas discharged during this cycle phase, while the CO2 content of the discharged gas remains lower than that in the subsequent regeneration step. The NOx-enriched stream (particularly enriched NO2) is discharged during the countercurrent depressurization step through the desorption of NOx (particularly NO2) and desorption along with a portion of the CO2 adsorbed during the adsorption step.

[0061] The cycle includes a CO2-rich vacuum desorption step VE, whereby the cycle reaches a low pressure during the vacuum desorption step VE at a pressure below atmospheric pressure, typically achieved by means of a vacuum pump (not shown).

[0062] The cycle includes a purging step P1. The adsorber is countercurrently purged with a purge gas. The purge gas contains compounds that are weakly adsorbed by the adsorbent. Here, the purge gas is provided by step E1D+PP. The partial pressure of CO2 is further reduced in the adsorber, and this reduction in CO2 partial pressure serves as a driving force for the desorption of residual CO2 from the adsorbent. The total pressure in the adsorbent increases again during this step P1.

[0063] It should be noted that the adsorber can be purged with a purge gas during the vacuum desorption step VE—typically in the second part of step VE—and from this point onward, the pressure in the adsorber can also rise from the circulating low pressure (pressure boosting purge), remain approximately constant near the low pressure (constant pressure purge), or continue to decrease to the low pressure (pressure deceleration purge). The pressure change depends on the respective flow rates of the purge gas and the vacuum pump (where applicable).

[0064] The cycle includes a countercurrent repressurization step E1P. The countercurrent repressurization gas provided by step E1D+PP is used in the countercurrent repressurization step E1P.

[0065] The cycle also includes a co-current pressurization step, FEED REP, using another portion of flow 11. The adsorber is thereby further pressurized to the cycle high pressure.

[0066] Given the discontinuous nature of the NOx-enriched stream 19 being discharged only during a portion of the cycle steps, the NOx-enriched stream 19 can be fed into a buffer tank (not shown), and the NOx-enriched stream 19 from the buffer tank can be continuously fed upstream of the NOx treatment unit or to the burner of the combustion process. This allows for compensation for fluctuations that would otherwise be suffered during the treatment of stream 19 by the NOx treatment unit or in the burner of the combustion process.

[0067] "Co-current" and "counter-current" are defined relative to the flow direction of the feed gas and the gas exiting the adsorber of the pressure swing adsorption separation unit during the adsorption step. "Co-current" is the flow direction of the relevant gas, while "counter-current" is the opposite direction.

Claims

1. A method for treating NOx in a CO2 capture device, wherein flue gas (7) from a combustion process (5) is treated in a NOx treatment unit (9) to reduce the NOx content of the flue gas (7) to produce flue gas (11) with reduced NOx content, the flue gas (11) with reduced NOx content being fed to a CO2 capture unit (13), the CO2 capture unit (13) producing a CO2 enriched stream (17) as a product and a NOx enriched stream (19), and the NOx enriched stream being fed upstream of the NOx treatment unit and / or to a burner (5A) of the combustion process, wherein the CO2 capture unit (13) includes a pressure swing adsorption separation unit that produces the NOx enriched stream (19), the CO2 enriched stream, and the exhaust gas (15).

2. The method of claim 1, wherein the NOx treatment unit (9) is a selective catalytic reduction, selective non-catalytic reduction, non-selective catalytic reduction, mixed selective catalytic reduction / non-selective catalytic reduction, or filtration type.

3. The method of any of the preceding claims, wherein the CO2-rich stream is separated by distillation and / or partial condensation to produce the CO2-rich stream (17).

4. The method of any of the preceding claims, wherein the pressure swing adsorption separation unit separates the CO2-rich stream from the waste gas (15) in contact with an adsorbent selected from X, Y or A type octahedral zeolite molecular sieves, activated alumina, modified alumina, silica gel, activated carbon or combinations of these adsorbents.

5. The method of any of the preceding claims, wherein the pressure swing adsorption separation unit operates a pressure cycle comprising an adsorption step (A) at a high cyclic pressure and a desorption step (VE) of the CO2-rich stream at a low cyclic pressure, optionally below atmospheric pressure, and a countercurrent depressurization step (BD) accompanying the discharge of the NOx-rich stream (19), the countercurrent depressurization step (BD) being between the adsorption step (A) and the desorption step (VE).

6. The method of the preceding claim, wherein the pressure cycle includes a co-current depressurization step (E1D+PP), particularly a co-current depressurization and purge gas supply step (E1D+PP), and the counter-current depressurization step (BD) immediately follows the co-current depressurization step (E1D+PP).

7. The method of claim 5 or 6, wherein the NOx enriched stream (19) is discharged in a first portion of the countercurrent depressurization step (BD), the first portion corresponding to one-quarter of the total pressure change of the adsorber during the countercurrent depressurization step (BD).

8. The method of any one of claims 5 to 7, wherein the NOx enriched stream (19) is discharged during the countercurrent depressurization step (BD) by desorption of NOx together with a portion of the CO2 adsorbed during the adsorption step (A).

9. The method as described in any of the preceding claims, wherein the pressure swing adsorption separation unit is a PSA unit or a VPSA unit type.

10. The method of any of the preceding claims, wherein the NOx enrichment stream (19) is fed into a buffer tank upstream of the NOx treatment unit (9) or before being fed to the burner (5A) of the combustion process.

11. The method of any of the preceding claims, wherein the NOx enrichment stream (19) contains a NOx concentration that is 3 times, 10 times, or even 100 times that of the flue gas (7) produced by combustion.

12. The method of any of the preceding claims, wherein the NOx enrichment stream (19) contains at least 50 mol%, or at least 70 mol%, or even at least 90 mol% CO2.

13. The method as claimed in any of the preceding claims, wherein the NOx enriched stream (19) is mixed with the oxygen-containing stream (1) fed to the combustion process (5).

14. The method of any of the preceding claims, wherein the combustion process is included in a steam methane reforming process, a cement plant process, a lime production process, a metallurgical process, or an electricity, heat, and / or steam production process.

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