WO2011124773A1 - Method for eliminating alkali metal halides in gaseous phase - Google Patents

Abstract

The present invention relates to a method of eliminating at least one alkali metal halide consisting of a halogen element and an alkali metal element contained in a gaseous feedstock, comprising at least one step consisting in bringing the gaseous feedstock into contact with a first material, comprising at least one metal oxide, under conditions for capturing the halogen element and at least a portion of the alkali metal element in the form of a solid with a perovskite structure, the other portion of the alkali metal element being found in a gaseous effluent in the form of an alkali metal monoxide.

Description

 PROCESS FOR THE REMOVAL OF ALKALI HALIDES FROM A GAS PHASE

The present invention relates to the field of the elimination of alkaline compounds in the gaseous phase, and more particularly to the alkaline halides in the gas phase, that is to say in combustion fumes, synthesis gases, etc.

There are a number of gasification processes for solid fuels (eg thermal power plants) that produce a mixture of carbon monoxide (CO) and hydrogen (H ₂ ) which forms a synthesis gas. These fuels can be coal, coke, asphalt (obtained by deasphalting heavy oil cuts), biomass, or household waste.

 The hot gases leaving the gasification units are sent to exchangers with a water exchanger to produce steam which will drive a turbine to produce energy.

 These gasification units can also be used to produce hydrogen. In this case, the synthesis gas is sent to a water gas reaction reactor ("water-gas shift" according to the English terminology).

 Another known technique also using a gasifier is the Integrated Gasification Combined Cycle (IGCC) technology.

 Whatever the origin and the use of these gases, they contain at the output of gasification units a certain number of impurities which will pose different problems:

 - at the level of the heat exchangers where they will be deposited and thus reduce heat exchanges,

 at the level of the catalysts used downstream of the gasification units,

 - corrosion of the devices.

These impurities are of various natures and with different contents depending on the load used in the supply of the gasification units. In particular, alkaline compounds may be present in these gases. Among these compounds alkaline, it seems that sodium and potassium are among the most common. These compounds are often in the form of alkaline halides.

One of the most effective ways known to remove the alkaline compounds present in the gases is to cool the gases at the outlet of the gasification unit. The alkaline compounds are deposited (or condense) then on the particles suspended in the gases. If the temperature of the gas cooling column is maintained between 400 ° C and 500 ° C, the concentration of alkaline compounds in the gases decreases to 0.1 ppm (weight) and sometimes less. However, this method can be considered expensive from an energy point of view.

 The same problems arise with the gases resulting from various combustion and calcinations and then used in the same way as the gasification gases.

 The present invention therefore aims to overcome one or more of the disadvantages of the prior art by providing a simple and inexpensive method for removing alkali halides present in the gases and for example synthesis gases or gases from the combustion of solid material, liquid (coal, wood, straw, garbage ...).

 For this purpose, the present invention proposes a process for eliminating at least one alkaline halide consisting of a halogen element and an alkaline element contained in a gaseous feedstock comprising at least one step of contacting the gaseous feedstock with a feedstock. first material comprising at least one metal oxide under conditions permitting the capture of the halogen element and at least a part of the alkaline element in the form of a solid of perovskite structure, the other part of the alkaline element being found in a gaseous effluent in the form of alkaline monoxide.

 According to one embodiment of the invention, the contact temperature of the gaseous feed with the material is greater than or equal to 200 ° C.

According to another embodiment of the invention, the contacting of the gaseous feed with the material is carried out at a pressure of between 0.1 MPa and 20 MPa and a temperature of between 200 ° C. and 1500 ° C. According to one embodiment of the invention, the alkaline halide is of formula CX, C being a group 1 element of the Mendeleev classification, chosen from lithium, sodium, potassium, rubidium, cesium and X a member of group 17 of the Mendeleev classification, selected from fluorine, chlorine, bromine and iodine. According to one embodiment of the invention, the metal oxide is of formula BO, O being oxygen and B a group 2 element of the Mendeleev classification selected from among beryllium, magnesium, calcium, strontium, barium .

 According to one embodiment of the invention, the method comprises a second step of contacting the gaseous effluent from the first step with a second material comprising at least one metal oxide under conditions allowing capture in the form of a solid alkaline monoxide, found in the gaseous effluent.

 According to one embodiment of the invention, the contact temperature of the gaseous effluent with the material of the second step is greater than or equal to 200 ° C.

 According to one embodiment of the invention, the contacting of the gaseous effluent with the material of the second step is carried out at a pressure of between 0.1 MPa and 20 MPa and a temperature of between 200 ° C. and 1500 ° C. ° C.

 According to one embodiment of the invention, the metal oxide of the second material is of formula AxOy, O being oxygen and A is an element belonging to group 13 of the Mendeleev classification chosen from boron, aluminum , gallium, indium, thallium and / or group 14 of the Mendeleev classification selected from carbon, silicon, germanium, tin, lead.

 According to one embodiment of the invention, the charge consists of combustion fumes or gases from a combustion or synthesis gas.

 Other features and advantages of the invention will be better understood and will appear more clearly on reading the description given hereinafter with reference to the appended figures given by way of example:

- Figure 1 is a schematic representation of an embodiment of the invention. - Figure 2 is a schematic representation of another embodiment of the invention.

 The present invention relates to a process for removing alkali compounds in the form of alkali metal halides from a feed containing alkali metal halides.

 Alkali halide or alkali metal halide is any compound of the general formula CX wherein C is a group 1 element of the Mendeleev classification, selected from lithium, sodium, potassium, rubidium, cesium and X is a member of group 17 of the Mendeleev classification, selected from fluorine, chlorine, bromine and iodine. For example and without limitation alkali halides may be sodium chloride (NaCl), potassium chloride (KCl), sodium fluoride (NaF), lithium iodide (Lil) ...

 The process for the elimination of the alkaline compounds according to the invention comprises at least a first step (step 1) during which the filler comprising at least one alkaline halide is brought into contact with a first material comprising at least one metal oxide with temperatures greater than or equal to 200 ° C. The metal oxide of the first step is of formula BO, with O for oxygen and B is a group 2 element of the Mendeleev classification, selected from among beryllium, magnesium, calcium, strontium, barium. The purpose of this first step is to capture all of the halogen and a large portion of the alkaline element in solid form. The uncaptured portion is found in the form of gaseous alkaline monoxide.

 At least a portion of the gaseous stream, containing the halides of alkaline compounds, undergoes the first step.

According to another embodiment of the invention, the entire gas stream, containing the halides of alkaline compounds, undergoes the first step.

The process for removing alkaline compounds according to the invention may comprise a second step (step 2) during which the gaseous effluent from step 1 is then brought into contact with a second material comprising at least one metal oxide. at a temperature greater than or equal to 200 ° C. The metal oxide of the second step has the formula AxOy, in which A is an element belonging to in group 13 of the Mendeleyev classification selected from boron, aluminum, gallium, indium, thallium and / or 14 of the Mendeleyev classification selected from carbon, silicon, germanium, tin, the lead. The purpose of this second step is to capture in solid form the alkaline gas monoxide formed in step 1.

 At least a portion of the gas stream, containing the alkali halides, undergoes both steps.

 According to another embodiment of the invention, the entire gas stream, containing the halides of alkaline compounds, undergoes the two steps.

The method according to the invention thus comprises either the first step (step 1), or the first step and the second step (steps 1 and 2).

 Some of the alkali halides are trapped in the first stage. The second step makes it possible to trap the remaining alkali halides.

 The principle of the invention is based on reactions of phase transformations of the various solids according to the following reactions:

- step 1: a CX (gaseous) + β BO (solid) -> (α-2β) ΟΧ. (β) ΒΧ ₂ (solid) + β C ₂ 0 (gaseous) a and β are stoichiometric coefficients of the reaction . These are positive integers that can take values between 1 and 10. For example with a = 2 and β = 1, C = K and X = Cl and B = Mg the reaction is written then:

3 KCl (gaseous) + MgO (solid) -> KCI.MgCl ₂ (solid) + K ₂ O (gas)

This step 1 makes it possible to trap all of the halogen element X in the form of a solid (α-2β) ΰΧ. (Β) ΒΧ ₂ , a structural solid commonly called "perovskite", and to trap 100% of the element alkaline initially present in the charge.

 at

A portion of the alkaline element, [100%] of the alkaline element contained in the initial charge, leaves step 1 as the gaseous alkaline monoxide to undergo step 2. - 2nd step :

In step 2, the alkaline monoxide is captured and converted by a solid of type A _x O _y , where A is a member belonging to group 13 of the Mendeleev classification selected from boron, aluminum, gallium indium, thallium and / or 14 of the Mendeleyev classification selected from carbon, silicon, germanium, tin, lead, and x and y being integers between 1 and 10, which undergoes a reaction of phase transformation according to one of the following reactions given as an example: β C ₂ 0 + β A _x Oy -> β C ₂ A _x O _{(y +} i ₎ β C ₂ 0 + β n A _x O _y -> β C ₂ AnxO _{(ny + 1)}

If, for example, C is potassium, depending on the AxOy solids used, we obtain:

with A _x O _y = SiO ₂ (A = Si, x = 1 and y = 2)

K ₂ O + 2 SiO ₂ (silica) -> K ₂ Si ₂ O ₅ (potassium silicate)

 - with AxOy (A = silicon and aluminum mixture Si and Al)

K ₂ O + Al ₂ O ₃ .2SiO ₂ (metakaolinite) ~> K ₂ O.Al ₂ O ₃ .2SiO ₂ (kaliophilite)

 Step 2 traps the remainder of the alkaline element contained in the feedstock and processed in step 1.

The initial metal oxides of stage 1, belonging to group 2 of the Mendeleev periodic table, can be in mass form, that is to say in pure form, for example magnesium oxide (MgO). ) in the form of pericalase or calcium oxide (CaO) in the form of quicklime or mixed with each other. Without limitation of the invention, a mixture of initial metal oxides used in the context of step 1 of the invention is a mixture of magnesium oxide MgO and calcium CaO as CaMgO ₂ , Ca ₂ MgO _3l Ca ₃ MgO ₄ , Ca ₄ MgO ₅ , CaMg ₂ O ₃ , CaMg ₃ O ₄ ...

The initial metal oxides used for stage 2, belonging to group 2 of the periodic table of Mendeleev, may be in bulk form, that is to say in pure form, or in a mixture with each other . The proportions of the mixture depend on the enthalpies of reactions related to the selected adsorbent and the operating conditions of the reaction, in general the temperature. As a non As a limitation of the invention, a mixture of initial metal oxides used in the context of the invention is a mixture of Al ₂ O 3 alumina and SiO ₂ silica, such as Kyanite or Sillimanite of the same general formula Al 2 O 3 .SiO 2 or Metakaolinite. of general formula AI ₂ 0 ₃ .2Si0 ₂

The initial metal oxides used for step 1 and 2 may be supported on carrier materials such as silicas, or aluminas, or silica-aluminas, or any other solid support materials well known to those skilled in the art. Solid support materials such as natural or synthetic zeolites can be considered in the present invention. By way of example, mention may be made of faujasites, mordenites, X and Y zeolites. The initial metal oxides used for stage 1 may also be placed on support materials such as natural or synthetic clays. aluminates, silicates, titanates, spinel structures. The metal content of the initial metal oxides supported is between 0.01% by weight and 15% by weight, preferably between 0.01% by weight and 7% by weight, more preferably 0.01% and 5% by weight. .

 The initial metal oxides used for step 1 and 2 may be in a mixing material. The mixing material comprises the support as well as compounds involved in the preparation of the support, such as, for example, binders, additives, diluents, blowing agents. By way of non-limiting example, lubricant additives may be used (stearic acid, graph, etc.), additives (starch, etc.), clay additives (montmorillonite, kaolinite, etc.) or any other known additive of the skilled person. When the initial metal oxide is in a material, the material preferably comprises more than 15% by weight of metal oxide, more preferably more than 50% by weight of metal oxide, and even more preferably more than 90% by weight. of metal oxide.

 The initial metal oxides used for step 1 and 2 may be in solid or liquid form, in the form of powder, beads or extrudates. The invention does not require any particular restriction as to the shape of the metal oxide used.

The material (mixing material, support material or any other material known to those skilled in the art) used for step 1 comprising at least one initial metal oxide with which the charge is placed in contact with the material (material mixture, support material or any other material known to those skilled in the art) used for step 2 comprising at least one initial metal oxide with which the charge is put in contact, can thus comprise between 0.01% by weight and 100% weight of metal oxide.

The feedstock of the process according to the invention contains between 0.0001% by volume and 100% by volume of alkali metal halides in gaseous form, preferably between 0.0001% by volume and 50% by volume of alkaline halides and more preferably between 0.degree. 0001% by volume and 10% by volume of alkali halides.

The feedstock of the process according to the invention may be an effluent from coal gasifier, wood, biomass, household waste, or any gas resulting from combustion or incineration. The feed may be an effluent from a partial hydrocarbon redox unit.

 The table below shows the contents of sodium and potassium present in the gases at the gasifier outlet according to the charge used in the gasifier.

 Sodium and potassium content (dry basis) of different fillers

 (Zevenhoven and Kilpinen, 'Trace elements, alkali metals, Chap 8

 (2001): HTTD: //mvw.hut.fi/~rzevenhoAracalk.Ddf))

The conditions for carrying out the reaction between the metal oxides of step 1 and step 2 and the gaseous feedstock containing the alkaline halides CX are chosen so as to keep the alkali halide of the filler and the alkaline monoxide from step 1 in gaseous form, therefore at temperatures greater than or equal to 200 ° C. In general, the contact between the feed comprising alkaline halides and the metal oxides used in steps 1 and 2 can be carried out under the conditions of availability of the feed, at a pressure of between 0.1 MPa and 20 MPa. preferably between 0.1 MPa and 0.3 MPa and a temperature between 200 ° C and 1500 ° C, preferably between 500 ° C and 1100 ° C. In the case of alkaline halides produced during incineration, the contacting between the feed comprising the alkali metal halides CX and the metal oxides used in steps 1 and 2 can be carried out at a pressure of between 0.1 and 0.3 MPa, and a temperature of between 200 ° C and 1500 ° C, and preferably between 500 ° C and 1100 ° C. The treatment according to the process of the invention of other gaseous feeds such as gaseous gases can be carried out under pressure conditions of between 0.2 MPa and 20 MPa, and temperatures of between 200 ° C. and 1500 ° C. C and preferably between 500 ° C and 1100 ° C.

 The contacting between the metal oxides used in steps 1 and 2 of the process and the feed containing the alkali halides can be carried out in multiple ways.

 This contacting can be carried out in a gas-solid or liquid-solid contacting column well known to those skilled in the art. The solid metal oxides used in steps 1 and 2 may be attached to the column members, for example on the distributor trays or on the packing of the column, or used as such as a packing element of the column.

In one embodiment of the invention illustrated in FIG. 1, the charge comprising the alkaline halide arriving via the charge conduit (2) can be brought into contact with the initial metal oxide of the suspended step 1B. in a liquid solvent contained in a first chamber (5). The halide purified gases and the alkaline oxides formed in step 1 are discharged through the duct.

(4) from the top of the first enclosure (5). The solvent containing the converted metal oxide is removed via the pipe (3) coming from the bottom of the enclosure

(5). The gas, coming from step 1 through line (4) coming from the top of the first chamber (5), is brought into contact, by means of the duct (6) arriving in a second chamber (10), with the initial metal oxide AxOy of step 2, A belonging to group 13 and / or 14 of the Mendeleyev classification, in suspension in a liquid solvent contained in the second chamber (10). The purified gases and possibly a portion of the non-captured alkaline oxides are discharged through the conduit (9) from the top of the second enclosure (10). The solvent containing the converted metal oxide is removed via the conduit (8) coming from the bottom of the second enclosure (10). During the process an addition can be made if necessary by a first booster pipe (1) arriving in the first chamber (5) and a second booster pipe (7) arriving in the second chamber (10).

 In other embodiments of the invention the contacting can be carried out in beds.

 As illustrated in FIG. 2, the contacting can be carried out by scanning the effluent comprising alkaline halides CX arriving via the effluent inlet duct (13) into a first reactor (11) containing the oxide. BO metal disposed in the form of fixed beds (12). The gaseous effluent purified from the halides and containing the alkaline oxides released by the reaction produced in the first step is discharged from the first reactor (11) via the conduit (14) from the first reactor (11). This gas is then sent in the second step via the conduit (17) arriving at a second reactor (15) containing the metal oxide AxOy disposed in the form of fixed beds (16). The alkaline depleted effluent is discharged from the reactor via line (18) from the top of the second reactor (15).

 In another form of implementation of the method, it is possible to use the technique of the moving bed. In this case, the charge comprising the alkaline halides is contacted in a reactor with the initial metal oxide BO in the form of powder or particles. The circulation of the charge makes it possible to drive the particles maintaining a homogeneous and disjoint distribution of the metal oxide particles BO. It is the same for the second stage.

The examples given below make it possible to illustrate the invention but are in no way limiting. Examples:

 Example 1 according to the invention

 A method comprising a step

 This experiment was carried out in a pilot unit in which the impurity in solid form is placed in a cup that can be heated up to 1000 ° C. A mass of 0.3 gram of sodium chloride (NaCl) is placed in this cup. The whole is heated to room temperature at 840 ° C. Nitrogen is injected into the system at a rate of 25 ml / minute. Under the influence of temperature, the NaCl solid melts at about 800 ° C. The nitrogen injected into the system will drive the sodium chloride vapor to an adsorbent downstream in the equipment. The adsorbent consists of a mass of 4.8 g of magnesium oxide (MgO). The cup containing the sodium chloride is maintained at 840 ° C. and the adsorbent at 890 ° C. for 24 hours. After cooling, the remaining mass of sodium chloride is weighed. The difference in weight between the beginning of the experiment and the end of the experiment shows that 0.11 gram of NaCl passed through the adsorbent. The lines after the adsorbent are washed with deionized water. The sodium content of the washing water, determined by atomic spectroscopy, makes it possible to know the quantity of sodium not captured by the adsorbent. The analyzes show that the adsorbent has captured 41.9% of the sodium injected into the system.

Example 2 according to the invention

 Process comprising two steps:

A second experiment was carried out with the same apparatus and under the same conditions as in Example 1. The sodium chloride was heated at 840 ° C. and the adsorbent of step 1 (MgO) at 890 ° C. for 24 hours. A second module was added to the previous experimental setup containing the adsorbent of the second process step. This module contains 8.3 grams of silica S1O ₂ . This silica is heated at 790 ° C for 24 hours. In the same way as before, the cup containing the sodium chloride is weighed before and after experimentation. This difference in weight shows that 0.12 grams of sodium chloride was vaporized and passed through both adsorbents. The lines at the exit of the Second adsorbent are washed with deionized water. The sodium content of the washings, assayed by atomic spectroscopy, makes it possible to know the quantity of sodium not taken up by the adsorbents. The analyzes show that the sequence of the two steps made it possible to capture 99.6% of the sodium injected into the system.

 This second example illustrates the fact that the process according to the invention makes it possible to capture almost all the sodium.

The present invention should not be limited to the details given above and allows embodiments in many other forms without departing from the scope of the invention.

Claims

A process for removing at least one alkali metal halide consisting of a halogen element and an alkaline element contained in a gaseous feedstock comprising at least one step of contacting the gaseous feedstock with a first material, comprising at least one minus a metal oxide, under conditions, a pressure of between 0.1 MPa and 20 MPa and a temperature of between 200 ° C. and 1500 ° C., allowing the capture of the halogen element and at least a part of the element alkaline in the form of a solid of perovskite structure, the other part of the alkaline element being found in a gaseous effluent in the form of alkaline monoxide.  A process for removing at least one alkali metal halide according to claim 1, wherein the alkali metal halide is of the formula CX, C being a Group 1 element of the Mendeleev classification, selected from lithium, sodium, potassium, rubidium, cesium and X a member of group 17 of the Mendeleev classification, selected from fluorine, chlorine, bromine and iodine. 3. Process for removing at least one alkali metal halide according to one of claims 1 to 2, wherein the metal oxide is of formula BO, O being oxygen and B a group 2 element of the Mendeleev classification. selected from among beryllium, magnesium, calcium, strontium, barium.  4. A method of removing at least one alkali metal halide according to one of claims 1 to 3, comprising a second step of contacting the gaseous effluent from the first step with a second material comprising at least one oxide metal under conditions allowing the solid capture of the alkaline monoxide found in the gaseous effluent.  5. Process for removing at least one alkali metal halide according to claim 4, wherein the contact temperature of the gaseous effluent with the material of the second stage is greater than or equal to 200 ° C. 6. A method of removing at least one alkali metal halide according to one of claims 4 to 5, wherein the contacting of the gaseous effluent with the material of the second step is at a pressure of between 0.1 MPa and 20 MPa and a temperature of between 200 ° C and 1500 ° C.  A process for removing at least one alkali metal halide according to one of claims 4 to 6, wherein the metal oxide of the second material is of the formula AxOy, where O is oxygen and A is a member belonging to group 13 of the Mendeleev classification selected from boron, aluminum, gallium, indium, thallium and / or group 14 of the Mendeleev classification selected from carbon, silicon, germanium, tin, lead. Process for removing at least one alkali metal halide according to one of Claims 1 to 7, in which the feedstock consists of combustion fumes or gases from a combustion or a synthesis gas.