Method and apparatus for NOx treatment of a CO2 capture device

Abstract

Title of the invention: Method and apparatus for NOx treatment of a CO2 capture device. In a NOx treatment process of a CO2 capture device in which flue gases (7) from a combustion process (5) are treated in a NOx treatment unit (9) to reduce their NOx content, flue gases (11) with reduced NOx content are sent to a CO2 capture unit (13) which produces a CO2-enriched flow (17) as a product as well as a NOx-enriched flow (19), and the NOx-enriched flow is sent upstream of the NOx treatment unit. Abstract figure: Fig. 2

Description

Title of the invention: Method and apparatus for treating NOx from a CO2 capture apparatus

[0001] The present invention relates to a method and apparatus for treating NOx from a CO2 capture apparatus.

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

[0003] When a plant (e.g. a steam methane reformer known as SMR) including a combustion stage must comply with local emission regulations, SCR (selective catalytic reduction) is often chosen to convert most of the NOx present in the flue gases into water and nitrogen. This expensive equipment requires the injection of urea or NH3 to convert the NOx into H2O and N2.

[0004] SCR, which is best in class in terms of efficiency at the expense of investment cost, competes with other solutions including SNCR (Selective Non-Catalytic Reduction), which has low efficiency but low investment cost, hybrid solutions combining both technologies, catalytic bags and the use of low NOx burners.

[0005] When local regulations are strict, the only viable solution is SCR (or hybrid SCR / NSCR (Non Selective Catalytic Reduction). It allows a wide range of efficiency, but the higher the NOx removal, the higher the catalyst quantity and / or the NH3 / urea consumption (if the excess NH3 is reduced to a value close to stoichiometry, its conversion efficiency drops).

[0006] Regardless of the technology used, a NOx slip typically greater than 5% is necessary to maintain SCR as an economical solution.

[0007] If CO2 must be captured from the fumes, for example those of a methane steam reformer, the quantity of NOx present in the fumes requires a particular design of the device, increasing its cost and sometimes posing safety problems due to the presence of flows rich in NOx.

[0008] [Fig-1] shows an apparatus according to the prior art in which a combustion process 5 is fed by a flow 1 containing oxygen and a fuel 3. The fumes produced 7 are treated in a unit 9 to remove the NOx and the flow 11 containing less NOx is treated by absorption with amines in the capture unit 13 producing CO2 17 and a residual gas 15. The presence of NOx in the gas 11 degrades the amines which react with the NOx, requiring the re-feeding of the amine process.

[0009] Flue gas from a combustion process, for example from steam methane reforming or SMR, has a fairly high CO2 concentration. An alternative capture technology such as Pressure Swing Adsorption (PSA) assisted by low-temperature separation by partial condensation and / or distillation is known. PSA is used to separate N2 from CO2, creating a CO2-rich stream suitable for low-temperature separation. This technology can have a much lower capture cost than amines, particularly when CO2 is required in liquid form (in which case the absorption solution would require the installation of an additional CO2 liquefier downstream) or when there is not a sufficient amount of recoverable heat from the upstream process.

[0010] Indeed, without a particular NOx strategy, the NOx present in the fumes, essentially in the form of NO, will be transformed into nitric acid in the intermediate coolers of the fume compressors, then the residual quantity will be concentrated in the CO2-rich flow of the PSA (for example by approximately 4 times when the fumes contain 20 mol% of CO2) and will then be mainly converted into NO2 / N2 O4 in the low-temperature separation part where the pressure is high and the temperature is low, so that the majority will leave with the CO2 produced.

[0011] Conversion of NOx into nitric acid:

[0012] A portion of these NOx can be converted and discharged into the process condensates via nitric acid, the conversion rate being higher the higher the pressure. Thus, if drying is present downstream of the main compressor of the low temperature separation part, the NOx can be partially eliminated by this reaction in the intercoolers but at the expense of dedicated metallurgy to resist nitric acid. This can lead to selecting drying upstream of the PSA, leading to low NOx removal through this nitric acid path. In addition, certain limitations of the water treatment systems can also lead to installing drying at the start of the process.Overall, the amount of NOx that can be removed by this acidic route is limited and often requires additional configuration to meet CO2 specifications or environmental regulations.

[0013] DeNOx column:

[0014] A NOx extractor can be installed in the cryogenic part creating a very concentrated NOx stream (especially when the dryer is installed at low to intermediate pressures), the carrier gas being mainly CO2. This stream must be managed intelligently because it creates two major problems, the first being the loss of CO2 recovery since this stream cannot be recycled into the capture process without any treatment to remove NOx and the second being safety issues related to the presence of such a concentration of NOx which is difficult to evacuate.

[0015] According to an object of the invention, there is provided a method for treating NOx from a CO2 capture apparatus in which fumes from a combustion process are treated in a NOx treatment unit to reduce their NOx content, thereby producing NOx-reduced fumes, the NOx-reduced fumes being sent to a CO2 capture unit which produces a CO2-enriched stream as a product as well as a NOx-enriched stream and the NOx-enriched stream is sent upstream of the NOx treatment unit and / or to burners of the combustion process.

[0016] According to other optional features: • the NOx treatment unit is of the selective catalytic reduction, selective non-catalytic reduction, non-selective catalytic reduction, hybrid selective catalytic reduction / non-selective catalytic reduction or filtering type. • The CO2 capture unit includes a pressure swing adsorption separation unit that produces the NOx-enriched stream, a CO2-rich stream and a tail gas. • the pressure-modulated adsorption separation unit separates the CO2-rich stream from the waste gas in contact with an adsorbent selected from an XY or A type faujasite zeolite, activated alumina, promoted alumina, silica gel, activated carbon or a combination of these adsorbents. • the pressure swing adsorption separation unit comprises at least four adsorbers. • the pressure-modulated adsorption separation unit operates a pressure cycle comprising an adsorption step at a high cycle pressure and a desorption step of the CO2-rich flow at a low cycle pressure, in particular below atmospheric pressure, as well as a countercurrent depressurization step with evacuation of the NOx-enriched flow, said countercurrent depressurization step being between the adsorption step and the desorption step. • the pressure cycle comprises a co-current depressurization step, in particular co-current depressurization and supply of elution gas, the counter-current depressurization step immediately following said co-current depressurization step. • the NOx-enriched flow is evacuated during the first quarter of the countercurrent depressurization stage. • the NOx-enriched flow is fed into a buffer capacity before being sent upstream of the NOx treatment unit or to burners in the combustion process. • the fumes from the combustion process comprise at least 10% by volume of CO2 on a dry basis, in particular between 15 and 50% by volume of CO2 on a dry basis. • the CO2-rich stream is separated by distillation and / or partial condensation to produce the CO2-enriched stream. • alternatively, the CO2-rich flow constitutes the CO2-enriched flow. • the pressure-modulated adsorption separation unit is of the PSA unit type or VPSA. • an additional NOX-enriched flow is produced by distillation and / or partial condensation and the additional NOX-enriched flow is sent upstream of the NOx treatment unit and / or to burners in the combustion process. • separation by distillation includes a NOx elimination column whose tank liquid constitutes the additional flow enriched in NOx. • the NOx-enriched flow and / or the additional NOx-enriched flow contains 3 times, or 10 times, or even 100 times, more NOx in concentration than the fumes produced by combustion. • the NOx-enriched flow and / or the additional NOx-enriched flow contains at least 50 mol% or at least 70 mol%, or even at least 90 mol% of CO2. • the NOx treatment unit is designed to operate without CO2 capture and in which the percentage of NOx in the treated gas increases in CO2 capture mode. • the NOx-enriched flow is mixed with a flow containing oxygen sent to the combustion process. • the NOx-enriched flow is mixed with a fuel sent to the combustion process. • the combustion process is included in a methane steam reforming process, a cement process, a lime production process, a metallurgical process or a process for producing electricity, heat and / or steam.

[0017] According to an object of the invention, there is provided a NOx treatment apparatus of a CO2 capture apparatus comprising a NOx treatment unit, a CO2 capture unit, means for sending fumes from a combustion process into the NOx treatment unit to reduce their NOx content, means for sending fumes with reduced NOx content from the treatment unit to the CO2 capture unit which produces a CO2-enriched stream as product as well as a NOx-enriched stream and means for sending the NOx-enriched stream upstream of the NOx treatment unit or to burners of the combustion process.

[0018] The invention will be described in more detail with reference to the figures:

[0019] [Fig.2] represents a method according to the invention.

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

[0021] [Fig.2] represents a process in which a combustion process 5 is supplied by a flow 1 containing oxygen and a fuel 3. The combustion process 5 may be a steam methane reforming, a cement plant, a lime production process, a metallurgical process or a power plant for the production of energy and / or steam and / or heat. The produced fumes 7 comprise at least 10% by volume of CO2 on a dry basis and NOx. These fumes 7 are treated in a unit 9 to remove the NOx and produce a flow 11. The treated flow 11 containing less NOx is treated in the capture unit 13 producing a CO2-rich flow 17 and a residual gas 15. The unit 9 is of the selective catalytic reduction, selective non-catalytic reduction, non-selective catalytic reduction or hybrid selective catalytic reduction / non-selective catalytic reduction or filtering type.

[0022] The capture unit 13 first separates the flow 11 by pressure swing adsorption (PSA) into a CO2-rich flow and the waste gas 15. This is done in contact with an adsorbent selected from a faujasite zeolite of type X, Y or A, activated alumina, promoted alumina, silica gel, activated carbon or a combination of these adsorbents. The capture unit 13 produces a flow enriched in NOx 19 compared to the flow 11. A portion of the NOx in the flue gases 7 is converted in contact with the adsorbent, in particular the NO is oxidized to NO2. The separation by pressure swing adsorption follows a pressure cycle shown in [Fig.4]. The pressure swing adsorption separation unit comprises one or a plurality of adsorbers configured to follow the pressure cycle with a one-phase shift between two successive adsorbers.

[0023] 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 product. This last step may be omitted and the CO2-rich stream produced by the PSA then constitutes the CO2-rich stream 17. The separation by distillation may include a NOx removal column whose bottom liquid constitutes an additional NOx-enriched stream (not shown).

[0024] The flow 19 and potentially the additional flow enriched in NOx is / are sent downstream of the combustion 5 and upstream of the unit 9, being sent to the unit 9 to remove the NOx that it / they contain. In this way the carbon dioxide present in the flow 19 is not lost.

[0025] The NOX-enriched flow 19 contains 3 times, or 10 times, or even 100 times, more NOx in concentration than the fumes 7 produced by combustion.

[0026] The flow enriched in NOX 19 contains at least 50 mol% or at least 70 mol% or even 90 mol% CO2.

[0027] [Fig.3] represents a process in which a combustion process 5 is supplied by a flow 1 containing oxygen and a fuel 3. The combustion process 5 can be a steam reforming of methane, a cement plant, a power plant and / or water vapor and / or heat production plant. The produced fumes 7 comprise at least 10% by volume of CO2 on a dry basis and NOx. These fumes 7 are treated in a unit 9 to remove the NOx. The flow 11 containing less NOx is treated in the capture unit 13 producing a flow rich in CO2 17 and a residual gas 15. The unit 9 is of the selective catalytic reduction, selective non-catalytic reduction, non-selective catalytic reduction, hybrid selective catalytic reduction / non-selective catalytic reduction or filtering type.

[0028] The capture unit 13 first separates the flow 11 by pressure swing adsorption (PSA) into a CO2-rich flow, the waste gas 15. This is done in contact with an adsorbent selected from a faujasite zeolite of type X, Y or A, activated alumina, promoted alumina, silica gel, activated carbon or a combination of these adsorbents. The capture unit 13 produces a flow enriched in NOX 19 compared to the flow 11. A portion of the NOx in the flue gases 7 is converted in contact with the adsorbent, in particular the NO is oxidized to NO2. The separation by pressure swing adsorption follows the pressure cycle shown in [Fig.4]. The pressure swing adsorption separation unit comprises one or a plurality of adsorbers configured to follow the pressure cycle with a one-phase shift between two successive adsorbers.

[0029] 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 product. This last step may be omitted and the CO2-rich stream produced by the PSA then constitutes the CO2-rich stream 17. The separation by distillation may include a NOx removal column whose bottom liquid constitutes the additional NOx-enriched stream (not shown).

[0030] Flow 19 and potentially the additional NOx-enriched flow is / are sent to the burners 5A of the combustion unit, since the presence of NOx in the flue gases will reduce the creation of NOx in the burners (by thermodynamic equilibrium), reducing the total amount of NOx to be managed by the NOx removal system and minimizing its additional investment and operating costs. Flow 19 may be mixed with flow 1 and / or fuel 3 which are sent to the burners 5A. The NOX-enriched flow 19 contains 3 times, or 10 times, or even 100 times more NOx than the fumes 7 produced by combustion.

[0031] The flow enriched in NOX 19 contains at least 50 mol% or at least 70 mol% or even 90 mol% CO2.

[0032] In order to optimize the overall scheme and further reduce investment and / or operating costs, as NOx is recycled to the combustion process, the NOx removal unit 9 may be designed or operated to allow higher NOx slip. This could be achieved by minimizing the amount of catalyst (reducing investment cost) in case of SCR or by decreasing NH3 slip (reducing NH3 / urea consumption) at the outlet of the NOx treatment or removal unit 9.

[0033] The NOx treatment unit 9 is preferably designed to operate without CO2 capture. The percentage of NOx in the treated gas increases in CO2 capture mode when it operates in CO2 capture mode.

[0034] [Fig.4] shows a pressure cycle according to which the pressure swing adsorption separation operates in the embodiments of Figures 2 and 3. The flow rate 11 is called "feed gas" in this figure.

[0035] The cycle comprises an adsorption step A at the high pressure of the cycle. A portion of the flow 11 is fed co-currently to at least one adsorber of the pressure swing adsorption separation unit. The CO2 is adsorbed more strongly on the adsorbent than the main components of the residual gas 15. For this reason, a major portion of the components of the residual gas 15 circulates through the adsorber during this step, while a major portion of the CO2 is stopped in the adsorber. The residual gas 15 is generated at the high pressure of the cycle. The NO is largely oxidized to NO2 upon contact with the adsorbent and the NO2 is stopped in the adsorber. The unconverted residual NO then follows the nitrogen and ends up at the stack.

[0036] The cycle comprises a step E1D+PP of co-current depressurization and supply of elution gas. The adsorber is depressurized co-currently to an intermediate pressure of the cycle. The components of the residual gas 15 move further towards the outlet of the adsorber and the residual gas 15 is discharged from the adsorber. A portion of this discharged residual gas 15 will be used as elution gas, while another portion will be used as counter-current re-pressurization gas.

[0037] The cycle comprises a countercurrent depressurization step BD with evacuation of the flow enriched in NOx 19 (so-called blowdown step in English), typically by opening a valve causing the evacuation of a portion of the gases from the adsorber from the bottom. The flow enriched in NOx 19 is evacuated during the first quarter of said countercurrent depressurization step. Indeed, most of the NOx is found concentrated in the gases evacuated at this point in the cycle, while the CO2 content of the evacuated gases remains lower than in the following regeneration steps.

[0038] The cycle comprises a VE step of vacuum desorption, i.e. at a pressure lower than atmospheric pressure, of the CO2-rich stream. Said desorption pressure constitutes the low pressure of the cycle and can be reached by means of a vacuum pump (not shown).

[0039] The cycle includes an elution step PI. The adsorber is flushed countercurrently with the elution gas. The elution gas contains compounds that are less strongly adsorbed by the adsorbent. Here, the elution gas is supplied by the E1D+PP step. The CO2 partial pressure decreases further in the adsorber, which acts as a driving force for the desorption of residual CO2 from the adsorbent. The total pressure in the adsorbent increases again during this PL step.

[0040] The cycle comprises a countercurrent repressurization step E1P. The countercurrent repressurization gas supplied by step E1D+PP is used for this.

[0041] The cycle also includes a co-current pressurization FEED REP step, using the other part of the flow 11. The adsorber is thereby further repressurized up to the high pressure of the cycle.

[0042] Given the non-continuous nature of the discharge of the NOx-enriched flow 19 during only part of a cycle step, the NOx-enriched flow 19 may be fed into a buffer capacity (not shown) and the NOx-enriched flow 19 from the buffer capacity may be continuously sent upstream of the NOx treatment unit or to burners of the combustion process. This compensates for fluctuations that would otherwise be experienced during the treatment of the flow 19 by the NOx treatment unit or in the burners of the combustion process.

[0043] “Co-current” and “counter-current” are defined relative to the direction of flow of a feed gas and the gas leaving an adsorber of the pressure swing adsorption separation unit during the adsorption stage. "Co-current" is the direction of flow of the gases in question and "counter-current" is the opposite direction.

Claims

Claims

1. A method of treating NOx of a CO2 capture apparatus in which flue gases (7) from a combustion process (5) are treated in a NOx treatment unit (9) to reduce their NOx content, thereby producing flue gases (11) with reduced NOx content, the flue gases (11) with reduced NOx content being sent to a CO2 capture unit (13) which produces a CO2-enriched stream (17) as a product as well as a NOx-enriched stream (19) and the NOx-enriched stream is sent upstream of the NOx treatment unit and / or to burners (5A) of the combustion process.

2. A method according to claim 1 wherein the NOx treatment unit (9) is of the selective catalytic reduction, selective non-catalytic reduction, non-selective catalytic reduction, hybrid selective catalytic reduction / non-selective catalytic reduction or filtering type.

3. A method according to claim 1 or 2 wherein the CO2 capture unit (13) comprises a pressure swing adsorption separation unit which produces the NOx-enriched stream (19), a CO2-rich stream and a waste gas (15).

4. A method according to the preceding claim, wherein the CO2-rich stream is separated by distillation and / or partial condensation to produce the CO2-enriched stream (17).

5. A method according to either of claims 3 or 4, wherein the pressure-modulated adsorption separation unit separates the CO2-rich stream from the waste gas (15) upon contact with an adsorbent selected from a faujasite zeolite of type X, Y or A, activated alumina, promoted alumina, silica gel, activated carbon or a combination of these adsorbents.

6. Method according to one of claims 3 to 5, in which the pressure-modulated adsorption separation unit operates a pressure cycle comprising a step (A) of adsorption at a high pressure of the cycle and a step (VE) of desorption of the CO2-rich flow at a low pressure of the cycle, possibly lower than atmospheric pressure, as well as a step (BD) of countercurrent depressurization with evacuation of the NOx-enriched flow (19), said step (BD) of countercurrent depressurization being between the step (A) of adsorption and the step (VE) of desorption.

7. Method according to the preceding claim, the pressure cycle comprising a step (E1D+PP) of co-current depressurization, in particular co-current depressurization and supply of elution gas, the step (BD) of counter-current depressurization immediately following said step (E1D+PP) of co-current depressurization.

8. Method according to one of claims 6 or 7, in which the NOx-enriched flow (19) is evacuated during the first quarter of the countercurrent depressurization step (BD).

9. Method according to one of claims 3 to 8, in which the pressure-modulated adsorption separation unit is of the PSA or VPSA unit type.

10. Method according to one of the preceding claims, in which the NOx-enriched flow (19) is fed into a buffer capacity before being sent upstream of the NOx treatment unit (9) or to burners (5A) of the combustion process.

11. Method according to one of the preceding claims in which the NOx-enriched flow (19) contains 3 times, or 10 times, or even 100 times, more NOx in concentration than the fumes (7) produced by the combustion.

12. Method according to one of the preceding claims in which the NOx-enriched flow (19) contains at least 50 mol% or at least 70 mol%, or even at least 90 mol% of CO2.

13. Method according to one of the preceding claims in which the NOx-enriched flow (19) is mixed with an oxygen-containing flow (1) sent to the combustion process (5).

14. A method according to any preceding claim wherein the combustion process is included in a methane steam reforming process, a cement process, a lime production process, a metallurgical process or a process for producing electricity, heat and / or steam.

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