EP3664917A1

EP3664917A1 - Method and facility for purifying a feed gas stream comprising at least 90% co2

Info

Publication number: EP3664917A1
Application number: EP18773788.7A
Authority: EP
Inventors: Guillaume Rodrigues; Philippe Arpentinier; Aurélien FRANCO; Rémi JABES; François LAGOUTTE; Laurent Perru; Etienne Werlen
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2017-08-10
Filing date: 2018-07-13
Publication date: 2020-06-17
Also published as: WO2019030437A1; RU2734348C1; SG11202000945VA; FR3070016A1; CN111065445A; US11400413B2; FR3070016B1; US20200206686A1

Abstract

A method for purifying a feed gas stream comprising at least 90% CO2 on a dry basis, at least 20% relative humidity and at least one impurity chosen from the chlorinated, nitrated, fluorinated or sulfur compounds, comprising the following successive steps: a) a step of subjecting the feed gas stream to a catalytic oxidation in such a way as to produce a gas stream comprising at least one acid impurity chosen from among HCl, NOx, SOx or hydrofluoric acid; b) a step of maintaining the temperature of the gas stream coming from step a) above the highest value between the dew point of water and the dew point of the acid or acids contained in the gas downstream of the catalytic process; c) a step of removing at least a part of the acid impurities by placing the gas stream coming from step b) in contact with at least one corrosion-resistant heat exchanger in such a way as to condense the acid compounds while regulating the temperature of the gas stream exiting below the dew point of water; and d) a step of separating the acid condensates of the gas stream coming from step c) by means of a corrosion-resistant separator in such a way as to produce a CO2 enriched gas stream.

Description

Process and plant for purifying a feed gas stream comprising at least 90% C02

The present invention relates to a method and a plant for purifying a feed gas stream comprising at least 90% CO 2, preferably 95% CO 2.

Carbon dioxide is used in various applications, for example for the food market, which requires that CO2 contain very low levels of impurities. For example, the International Society of Beverage Technologists (ISBT) requires the following composition:

Purity: 99.9% v / v min.

Humidity: 20 ppm v / v max.

Oxygen: 30 ppm v / v max.

Carbon monoxide: 10 ppm v / v max.

Ammonia: 2.5 ppm v / v max.

Nitric Oxide / Nitrogen Dioxide: 2.5 ppm v / v max. (each)

Non-volatile residue: 10 ppm w / w max.

Nonvolatile organic residue: 5 ppm w / w max.

Phosphine: 0.3 ppm v / v max.

Total volatile hydrocarbons: (such as methane) 50 ppm v / v max. with 20 ppm v / v max. for total non-methane hydrocarbons

Acetaldehyde: 0.2 ppm v / v max.

Content in aromatic hydrocarbons: 20 ppm v / v max.

Total sulfur content * (S): (* Total impurities containing sulfur with the exception of sulfur dioxide) 0.1 ppm v / v max.

Sulfur dioxide: 1 ppm v / v max

The CO2-rich feed stream can come from a variety of sources, such as ammonia plants, natural wells, bio-fermentation, syngas production units, and the like. ... containing various traces of impurities, including hydrocarbons, sulfur compounds, nitrous compounds, chlorinated compounds and many other impurities which must be efficiently and economically removed.

Currently, various technologies are used alone or in combination to remove these impurities from the C02 rich feed stream:

- absorption: washing with water, C02 washing (physical absorption) or other types of chemical reaction-based scrubbers (chemical absorption)

adsorption: regenerative systems such as PSA (pressure swing adsorption = adsorption with pressure variation), TSA (temperature swing adsorption = adsorption with temperature variation), or a combination of a PSA and an ASD; or non-regenerable systems such as impregnated activated carbon,

catalytic oxidation (Catox): tolerant to sulfur or not, hydrocarbons and other species in the presence of excess air are completely oxidized at a temperature above 350 ° C thanks to selected catalysts,

Among the absorption technologies, the wet separator is a common solution that can be adapted to high levels of impurities. It consists of passing the feed gas through a medium promoting fluidic contact, for example a structured or random packaging, inside a container. Water is sprayed or dispensed onto the top of the container. If this solution seems effective in removing water-soluble hydrocarbon-containing hydrocarbons such as, for example, ethanol and methanol from feed streams, it is not effective in removing hydrocarbons that are not soluble in water. water, whose solubility in water is very low. Another disadvantage is that water must be introduced into the system. For the food-grade CO2 production area, this water must consume drinking water. Such water may not be available or at a high cost in an industrial plant. Alternatively, the basic anions of the hydroxyl group, carbonate or bicarbonate are introduced in a solid (milled) or liquid form into the feed gas. Basic anions react with acid gases to form salts. The salts are then filtered in a bag filter or separated in a container. The disadvantage of this solution is that it is not referenced for high efficiency removal. Its classic application is the treatment of flue gases, in order to comply with environmental standards. These standards are much less demanding than those applied for food C0 ₂ . As for the water purifier, this solution involves the addition of an external component.

Handling chemical reagent such as sodium hydroxide requires special care and additional equipment (storage, dosing system). For example, the use of sodium bicarbonate entails strong constraints. Indeed, this solution must be used at a temperature between 140 ° C and 300 ° C.

Adsorption beds may be based on physical adsorption. The low adsorption force implies easy regeneration, but also fairly low or moderate adsorption capacities. Thus, on the one hand, it allows a regenerative process, having a long life, on the other hand, it may require high amounts of adsorbents detrimental to the cost or very fast cycle times (time including adsorption then the regeneration steps) implying that large amounts of regeneration gas are available.

For the management of impurities considered, physical adsorption is often associated with chemical adsorption. It consists in using "dead" charges of impregnated adsorbents which react chemically with impurities. As the regeneration of these adsorbents is often not economical on the site, when the bed is saturated with impurities, the load is replaced by a new one. By way of example, sulfur compounds containing CO 2 can be brought into contact with a support material (activated carbon, alumina, etc.) impregnated with metal oxides (FeO, ZnO, CuO, etc.). Then the metal oxides react with sulfur compounds and create metal sulphides and water vapor.

From this, a problem is to provide an improved and economical method of purifying a feed gas stream comprising at least 90% CO 2.

A solution of the present invention is a process for purifying a feed gas stream comprising at least 90% CO2, preferably at least 95% CO 2, at least 20% relative humidity and at least one impurity selected from chlorinated, sulfur-containing, nitrated or fluorinated compounds comprising the following successive steps:

a) a step of subjecting the feed gas stream to catalytic oxidation so as to produce a gas stream comprising at least one acidic impurity selected from HCl, HNO ₃ , NOx, SOx, H ₂ SO 4, HF; b) a step of maintaining the temperature of the gas stream from step a) above the highest value between the dew point of the water and the dew point of the acid (s) contained in the gas downstream of the catalytic process; (we will talk about critical dew point)

c) a step of removing at least a portion of the acid impurities by contacting the gas stream from step b) in contact with at least one corrosion-resistant heat exchanger so as to condense the acidic compounds while regulating the temperature of the gas stream leaving under the dew point of the water; and

d) a step of separating the acidic compounds of the gas stream from step c) by means of a corrosion-resistant separator so as to produce a gas stream enriched with CO2.

Step b) avoids any creation of acidic liquid which corrodes the piping and other standard materials. It will be ensured never to pass below the critical dew point via suitable operating conditions but also thanks to a thermal insulation or even an external temperature maintenance system (electric or steam) preventing the creation of cold spots (temperature locally below the critical dew point) on the equipment.

In step c), if the composition of the feed gas of the catalytic process varies, it will be possible to regulate the outlet temperature of the indirect contact condenser of the plate or tube / calender type via the liquid / gas flow of cooling the supply or via the temperature of it.

Depending on the case, the method according to the invention may have one or more of the following characteristics:

said process comprises, after step d), the following successive steps:

e) a liquefaction step of the gas stream enriched with CO 2,

f) a step of drying the liquefied flow, and

g) a step of sending the dried stream to a cryogenic unit.

The drying is generally carried out via a reversible adsorption unit making it possible to reach water contents compatible with the cryogenic temperature in question (<10 ppmv and preferably <1 ppmv).

- The heat exchanger and the separator are made of materials selected from austenitic steel, glass or a composite resistant to nitric acid, sulfuric or hydrochloric acid. the catalytic oxidation is carried out by means of a catalytic oxidation unit whose catalyst is tolerant of sulfur and chlorine.

the feed gas stream subjected to the catalytic oxidation is at a temperature of at least 300 ° C., preferably at least 425 ° C.

the feed gas stream subjected to catalytic oxidation is at a pressure greater than 1 bar absolute

the feed gas stream can come from various sources such as the monoethylene glycol production units or bio-fermentors

in step c) water or a water / glycol mixture is preferably used as a refrigerant within the heat exchanger.

In order to improve the exchange surface while remaining on standard exchanger sizes or in order to carry out condensation at 2 temperature levels, it will be possible to use several exchangers in parallel or in series respectively with downstream a common separator pot or a separator pot associated with each of the exchangers.

Preferably, the water heated in the heat exchanger by the gas stream is in a closed circuit and is cooled in a second ammonia / water heat exchanger.

The present invention also relates to an installation for purifying a feed gas stream comprising at least 95% CO 2, at least 20% relative humidity and at least one impurity selected from chlorinated compounds, sulfur, nitrated or fluorinated, comprising in the flow direction of the gaseous flow:

a) a catalytic oxidation unit for subjecting the gas stream to catalytic oxidation so as to produce a gas stream comprising at least one acidic impurity selected from HCl, NOx and SOx;

b) a means of maintaining the temperature of the gas stream leaving the catalytic oxidation unit above the acidic dew point;

c) a corrosion resistant heat exchanger for condensing the acidic compounds of the gas stream;

d) a corrosion resistant separator for separating the acidic compounds from the gas stream so as to produce a gas stream enriched with CO2. Preferably in step d) a corrosion resistant drum separator will be used. Preferably in step d), the separator is equipped with an automatic draining system.

Depending on the case, the installation according to the invention may have one or more of the following characteristics:

- said plant comprises downstream of the separator and in the direction of flow of the gas stream enriched in CO2:

e) a liquefier for liquefying the gas stream enriched with CO2;

f) a dryer for drying liquefied gas; and

g) a cryogenic unit.

- The heat exchanger and the separator are made of materials selected from austenitic steel, glass or a composite resistant to nitric acid, sulfuric or hydrochloric acid. By way of example, mention may be made of 254SMO and 904L steels, nickel-based alloys or titanium. Preferably, when chlorinated compounds are present in the feed stream, the heat exchanger is made of 254 SMO stainless steel for the parts in contact with the process gas, the rest being SS 316L steel, specially designed for strong corrosion created by the Hcl.

the catalytic oxidation is carried out by means of a sulfur and chlorine-resistant catalytic oxidation unit.

Example: purification of a stream containing chlorinated molecules

Flux from a monoethylene glycol production unit containing 1 ppmv of chlorinated compounds:

The stream is contacted with a catalyst bed containing a first layer of platinum catalyst and a second layer of palladium catalyst, making it possible to convert most of the hydrocarbons into water and carbon dioxide. At the outlet of the catalytic reactor, the gaseous flow at a temperature above 300 ° C. and containing HCl is cooled to a temperature above the dew point of the water (43 ° C.), in order to prevent condensation.

In practical terms, a minimum temperature of 55 ° C, ie 12 ° C above the theoretical temperature, will be maintained, thus avoiding measuring inaccuracies and equipment insulation faults. skid entrance

Name

molar flow N m3 / h 4819

mass flow kg / h 8999

Temperature ° C 55

Pressure bar at 1.19

Steam fraction 1

molar fraction of CO2 0.910992

molar fraction of Oxygen 0.011299

molar fraction of AcetAldehyde 0.000000

molar fraction of Methane 0.000036

molar fraction of H20 0.077672

molar fraction of Ethane 0.000000

molar fraction of i-Butane 0.000000

molar fraction of Benzene 0.000000

molar fraction of Ethylene 0.000001

molar fraction of C20xide 0.000000

molar fraction of CIC2 0.000000

molar fraction of HCl 0.000001

The fluid, at a temperature of 55 ° C., will then be fed into a skid comprising a heat exchanger made of a material resistant to chloridic acid, such as steel grade 254SMO. The cold will be brought into the exchanger through a coolant such as water, at a temperature below 43 ° C, preferably below 10 ° C to minimize the size of the exchanger. Cooling water supplying the exchanger

Name

molar flow N m3 / h 9953

mass flow kg / h 8000

Temperature ° C 7

Pressure bar at 3.95

fraction of steam 0

In this example, the only condensation of the water combined with a consequent exchange surface, will ensure the removal of HCl contained in the gas phase due to the very high solubility of HCl in water (720g / L at 20 ° C)

The separation of the liquid droplets containing the acid molecules will be ensured by a separator pot (installed directly downstream of the exchanger) in a material resistant to corrosion by chlorine such as steel grade 254 SMO or more simply by a material made of polymer resin.

The process gas leaving the separator pot and the condensed liquid, purged at the bottom of the separator pot will have the following compositions:

Outlet gas pot Outlet liquid pot

Separator separator name

molar flux Nm3 / h 4688 131

mass flow kg / h 8893 106

Temperature ° C 35 35

Pressure bar at 1.14 1.14

Vapor fraction 1 0

molar fraction of CO2 0.936535 0.000055

Molar fraction of Oxygen 0.011615 0.000000 Molar fraction of

AcetAldehyde) 0.000000 0.000000

Molar Fraction of Methane 0.000037 0.000000

Molar fraction of H20 0.051811 0.999942

Fracc (Ethane) 0.000000 0.000000

Molar fraction of i-Butane) 0.000000 0.000000

Molar fraction of Benzene 0.000000 0.000000

Molar fraction of Ethylene) 0.000001 0.000000

Molar fraction of C20xide 0.000000 0.000000

Molar fraction of CIC2 0.000000 0.000000

Molar fraction of HCI 0.000000 0.000003

Claims

claims

1. A method for purifying a feed gas stream comprising at least 90% of dry base CO 2, at least 20% relative humidity and at least one chosen impurity chlorinated compounds, sulfur, nitro or fluorinated comprising the steps following successive

a) a step of subjecting the feed gas stream to catalytic oxidation so as to produce a gas stream comprising at least one acidic impurity selected from HCl, NOx, SOx or hydrofluoric acid;

b) a step of maintaining the temperature of the gas stream from step a) above the highest value between the dew point of the water and the dew point of the acid (s) contained in the gas downstream of the catalytic process;

d) a step of separating the acid condensates from the gas stream from step c) by means of a corrosion-resistant separator so as to produce a gas stream enriched with CO2.

2. Method according to claim 1, characterized in that said method comprises after step d) the following successive steps:

e) a liquefaction step of the gas stream enriched with CO 2,

f) a step of drying the liquefied flow, and

g) a step of sending the dried stream to a cryogenic unit.

3. Method according to one of claims 1 or 2, characterized in that the heat exchanger and the separator are made of materials selected from austenitic steel, glass or a composite resistant to nitric acid, sulfuric or hydrochloric.

4. Method according to one of claims 1 to 3, characterized in that the catalytic oxidation is carried out by means of a catalytic oxidation unit resistant to sulfur and chlorine.

5. Method according to one of claims 1 to 4, characterized in that the feed gas stream subjected to catalytic oxidation is at a temperature of at least 300 ° C, preferably at least 425 ° C .

6. Method according to one of claims 1 to 5, characterized in that the feed gas stream subjected to catalytic oxidation is at a pressure of at least 1 bar absolute

7. Method according to one of claims 1 to 6, characterized in that the feed gas stream comes from a monoethylene glycol unit, a C0 ₂ washing by absorption, a mono-ethylene synthesis unit. glycol, a biofermentation or any other process generating a flow rich in C0 ₂

8. Method according to one of claims 1 to 7, characterized in that in step c) the water is used as a refrigerant within the heat exchanger.

9. Installation for purifying a feed gas stream comprising at least 95% CO 2, at least 20% relative humidity and at least one impurity chosen from chlorinated compounds, sulfur, nitro or fluorinated including in the sense circulation of the gas flow:

c) a corrosion resistant heat exchanger for condensing the acidic compounds of the gas stream; d) a corrosion resistant separator for separating the acidic compounds from the gas stream so as to produce a gas stream enriched with CO2.

10. Installation according to claim 9, characterized in that said installation comprises downstream of the separator and in the direction of flow of the gas stream enriched in CO2:

e) a liquefier for liquefying the gas stream enriched with CO2;

f) a dryer for drying the liquefied gas; and

g) a cryogenic unit.

11. Installation according to one of claims 9 or 10, characterized in that the heat exchanger and the separator are made of materials selected from austenitic steel, glass or a composite resistant to nitric acid, sulfuric or hydrochloric.

12. Installation according to one of claims 9 to 11, characterized in that the catalytic oxidation is carried out by means of a catalytic oxidation unit resistant to sulfur and chlorine.