EP2178622A2

EP2178622A2 - Method for eliminating mercury from a gas containing co2 and oxygen

Info

Publication number: EP2178622A2
Application number: EP08826487A
Authority: EP
Inventors: Philippe Court; Arthur Darde; Vladimir Hasanov; Christian Monereau; Serge Moreau; Jean-Pierre Tranier
Original assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Current assignee: Air Liquide SA; LAir Liquide SA pour lEtude et lExploitation des Procedes Georges Claude
Priority date: 2007-07-13
Filing date: 2008-07-08
Publication date: 2010-04-28
Also published as: WO2009010692A2; FR2918580B1; WO2009010692A3; AU2008277537B2; US8535416B2; CA2693038A1; CN101842144A; JP2010533064A; US20100212494A1; FR2918580A1; AU2008277537A1

Abstract

The invention relates to a method for the purification of a feed gas stream at a pressure of = 3 bar, containing at least 1 vol.-% oxygen (O2) and at least 75 vol.-% CO2 and mercury. The invention is characterised in that it includes an adsorption purification step comprising the use of at least one fixed adsorbent bed containing a sulphur and/or silver adsorbent, such as to eliminate the mercury at least partially.

Description

Process for removing mercury from a gas containing CO _{2 and} oxygen

The invention relates to a method for purifying a feed gas stream at a pressure of> 3 bars comprising at least 1% by volume of oxygen (O2) and at least 75% by volume of CO2 and mercury. , allowing the elimination of mercury.

It is more specifically to develop a process for treating CO ₂ from an oxy-combustion (combustion with pure oxygen or with a gas that is lower in nitrogen than air).

In fact, fossil fuel and / or biomass or waste incineration gases or gases from glass furnaces mainly contain heavy metals such as mercury, organic pollutants and SOx and NOx type compounds.

The danger of mercury pollution is known. Indeed, mercury is a toxic element. In humans, exposure to mercury can lead to neurological and developmental disorders.

Mercury emissions can remain in the atmosphere for hours to years.

Also, it is essential to provide a mercury extraction process for the treatment of flue gases.

It is known that some metals, for example gold, silver and copper form amalgams with mercury and that this property is used to measure mercury.

However, the extraction of mercury by these metals is not used industrially because of the volume of time to be treated. Another possibility is to wash the coal before combustion. However, these washes only eliminate between 0 and 60% of mercury.

Other solutions such as electrostatic precipitators or filter layer separators have been implemented.

However, no trial is conclusive. Furthermore, the document US Pat. No. 4,094,777 describes a process for capturing mercury in the gas or liquid phase by fixing it on an adsorbent mass comprising copper sulphide, optionally silver sulphide deposited on a support based on silica and / or alumina. The process is in a fixed bed and can be used from -50 ^° C. to 200 ^° C., at pressures up to 200 bars. This process is said to apply to the demercurization of natural gas or electrolytic hydrogen. The example given concerns a natural gas containing methane, hydrocarbons up to C5, CO2 and nitrogen. It is also disclosed that the regeneration can be done with air from a temperature of 200 ⁰ C and that it is necessary to re-sulphurize the material.

US 4,909,926 discloses a method for capturing mercury in a hydrocarbon stream. The materials cited include Ag and CuS, the supports being alumina or SiO ₂ . In the case of the implementation of an alumina support, the regeneration is carried out with an oxygen-containing gas and purging oxygen before returning to service. It is stated in this document that this purge must be done at high temperature to prevent the formation of oxide. Finally, it is specified that the process can be applied in the presence of hydrocarbons, hydrogen, H ₂ S, N ₂ , H ₂ O and CO ₂ . Thus, it would seem that the presence of oxygen in a gas to be treated renders its demercurization inapplicable by adsorption on a product containing copper sulphide and / or silver or silver sulphide. Oxygen is effectively described as a regenerative agent, thus desorption of mercury and at low temperature as oxidant and deactivating agent. From there, a problem arises to provide an improved process for purifying a gas stream containing CO ₂ , at least 1% oxygen and mercury, so as to obtain a depleted mercury gas.

A similar problem arises for gas streams containing NOx and / or SOx. Indeed, these compounds have oxidizing properties, capable of reacting with the adsorbent.

However, unexpectedly the inventors have discovered that a solution of the invention is a process for purifying a flow of feed gas at a pressure of> 3 bar, comprising at least 1% by volume of oxygen (O ₂ ) and at least 75% by volume of CO ₂ and mercury, characterized in that it comprises a purification step by adsorption, carried out at a temperature <120 ^° C., and in which at least one embodiment is used. a fixed bed of adsorbents containing a sulfur and / or silver adsorbent, so as to at least partially remove the mercury.

Depending on the case, the process according to the invention may have one of the following characteristics: the flow of feed gas comprises between 1 and 6% by volume of oxygen;

- The feed gas stream comprises up to 5000ppm NOx and / or SOx volume, preferably less than 1000 ppm, more preferably less than 100 ppm;

the flow of feed gas is not saturated with water;

the flow of feed gas contains less than 1000 ppm of water, preferably less than 100 ppm, more preferably less than 1 ppm;

the flow of feed gas is under a pressure of> 10 bar;

the purification step is carried out at a temperature <100 ^° C., more preferably at a temperature of between 5 ° C. and 80 ^° C.

The sulfur and / or silver adsorbent comprises an organic or inorganic support; the organic support is activated carbon;

the inorganic support is chosen from the group comprising porous glasses and silica, alumina, silica-alumina, silicates, aluminates and silico-aluminates;

said fixed bed of adsorbents comprises:

(a) a dispersant or a solid support selected from the group comprising silica, porous glass, alumina, silica-alumina, silicates, aluminates and silico-aluminates,

(b) copper of which at least 30% is sulphide and the total weight of copper oxide copper sulphide is 2 to 65% of the weight of the adsorbent mass of the fixed bed,

(c) 0 to 5% by weight of silver;

said fixed bed of adsorbents has a specific surface area of between 20 and 1300 m ² / g; - 80% of the copper is in the form of copper sulphide;

said process makes it possible to treat between 4,000 and 20,000 vvh of feed gas flow; with vvh = Volume of feed gas entering the adsorber per volume of adsorber and hour; also the unit is h-1 because the volume of gas is measured by convention under normal conditions (1.013 bar abs and 0 ⁰ C); the flow of feed gas is an oxy-combustion smoke. In some cases, the adsorbent bed comprising a sulfur and / or silver adsorbent is a guard bed.

Porous glass is a chemically inert material, particularly resistant to bases and acids, and has good physical characteristics (crushing, attrition).

It consists essentially of SiO _2, generally> 90% by weight, preferably> 95% and may contain a minor extent B2O3, Na ₂ O, Al2O3, ZrO ₂ and / or other metal oxides.

This porous glass has the particularity as its name indicates to have a significant internal vacuum, generally greater than 25% by volume, in the form of pores of variable dimensions depending on the products, which allows it to develop internal surfaces more than one hundredths of ₁ em 2 per gram.

By way of example, mention may be made of VYCOR Porous Porous Glass 7930 from Corning Incorporated, which has a 28% porous volume, 250 m / g internal surface area, and a mean pore diameter of 40 A (4 nanometers).

Contrary to the teaching that can be drawn from the state of the art, it appears that a mixture containing at least 1% by volume of oxygen and at least 75% by volume of CO ₂ can be demercurized by fixing the mercury on a sulfur and / or silver adsorbent mass. It is possible that the high partial pressure of CO ₂ vis-à-vis that of oxygen limits the reactivity of the latter component and that the possible loss of efficiency can be compensated by a higher contact time (or volume per volume and per hour below).

The effects of total pressure and temperature have not been systematically studied since said process proves to be commercially operational under normal operating conditions, namely a CO ₂ content greater than or equal to 75% by volume, a content in oxygen between 1 and 6% volume, a pressure greater than or equal to 3 bar absolute, a temperature below 250 ⁰ C, preferably below 150 ⁰ C, more preferably between 5 and 80 ⁰ C. NOx and the SOx are acceptable in the gas stream treated by the process according to the invention up to 5000 ppm volume. The support of the active compound based on metal, predominantly Cu and / or Ag but may contain minor other metals such as Fe, Zr, Zn, may be activated carbon, alumina, silica, silica-alumina silicates, aluminates, silico-aluminates. As described in US 4,094,777, mercury removal can be carried out in a single adsorber or for example in two adsorbers in series. The adsorbent charge installed will preferably operate without intervention for a minimum of 6 months. In the case of adsorbers in series, it is possible to renew the charges by half. The new load is then used downstream of the load remaining in service ...

In a variant of the process, the polluted charge of mercury can be regenerated in situ. In the presence of a large quantity of mercury (of the order of one milligram per m of gas for example), it may be advantageous to install two adsorbers in parallel, one in service, the other then being in regeneration. In general, the adsorption purification step may comprise other adsorption purification processes than the mercury alone. It may be the stopping of other heavy metals such as arsenic. In this case, a second adequate bed for this stop will be placed downstream or upstream of the bed for stopping the mercury. It is also conceivable a mixture, homogeneous or not, of different adsorbents, at least one corresponding to the cessation of mercury. One and the same product can also be used for mercury and other heavy metals. The purification step may comprise a drying of the feed gas upstream or downstream of the demercurization.

Claims

claims

A process for purifying a feed gas stream at a pressure of> 3 bar, comprising at least 1% by volume of oxygen (O 2) and at least 75% by volume of CO2 and mercury, characterized in that it comprises a purification step by adsorption, carried out at a temperature <120 ^° C., and in which at least one fixed bed of adsorbents containing a sulfur and / or silver adsorbent is used, so as to eliminate at least partially mercury.

2. Purification process according to claim 1, characterized in that the flow of feed gas comprises between 1 and 6% by volume of oxygen.

3. purification process according to one of claims 1 or 2, characterized in that the feed gas stream comprises up to 5000ppm NOx and / or SOx volume, preferably less than 1000 ppm, more preferably less than 100 ppm.

4. Purification process according to one of claims 1 or 2, characterized in that the feed gas stream is not saturated with water.

5. Method according to one of the preceding claims, characterized in that the flow of feed gas contains less than 1000 ppm of water, preferably less than 100 ppm, more preferably less than 1 ppm.

6. Purification process according to one of the preceding claims, characterized in that the flow of feed gas is under a pressure> 10 bar.

7. Method according to one of the preceding claims, characterized in that the purification step is performed at a temperature <100 ⁰ C, more preferably at a temperature between 5 ° C and 8O ⁰ C.

8. Method according to one of the preceding claims, characterized in that the sulfur and / or silver adsorbent comprises an organic or inorganic support.

9. Process according to claim 8, characterized in that the organic support is activated carbon.

10. The method of claim 8, characterized in that the inorganic support is selected from the group comprising porous glasses and silica, alumina, silica-alumina, silicates, aluminates and silico-aluminates.

11. Method according to one of the preceding claims, characterized in that said fixed bed of adsorbents comprises:

(a) a dispersant or a solid support, selected from the group comprising silica, porous glass, alumina, silica-alumina, silicates, aluminates and silico-aluminates, (b) copper of which at least 30% in the form of sulphide and whose total weight copper oxide - copper sulphide represents 2 to 65% of the weight of the adsorbent mass of the fixed bed, (c) 0 to 5% by weight of silver.

12. Method according to one of the preceding claims, characterized in that said fixed bed of adsorbents has a specific surface area of between 20 and 1300 m ² / g.

13. Process according to claim 8, characterized in that 80% of the copper is in the form of copper sulphide.

14. Method according to one of the preceding claims, characterized in that said method can treat between 4000 and 20 000 v.v.h of feed gas stream.

15. Method according to one of the preceding claims, characterized in that the flow of feed gas is an oxy-combustion smoke.