KR930000278B1 - Process for the production of metal-oxide aerosols for fuel emission control - Google Patents

Abstract

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Description

Method for preparing metal oxide aerosol for control of combustion emission of fuel

1 is a schematic diagram of the method of the present invention for preparing a metal oxide aerosol and using this metal oxide aerosol to remove emissions from the gaseous air stream,

2 is a graph illustrating the ability to absorb emissions from the process of the present invention using calcium as the sorbent metal and sulfur as the emission material,

3 is a graph illustrating the ability to absorb emissions from the process of the present invention using magnesium as the sorbent metal and sulfur as the emission material.

This application is a CIP application of Application No. 263,896, filed Oct. 28, 1988, which is a divisional application of Application No. 096,643, filed Sept. 11, 1987, filed 096,643. As of January 3, 2011, US Patent No. 4,795,478 was registered. This patent is also a CIP application of application number 014,871, filed February 17, 1987, which was registered as US Patent 4,83 4,775 on May 30, 1989. This patent is also a CIP application of Application No. 875, 450, filed June 17, 1986, which is now registered as US Patent No. 4,801,304 on January 31, 1989. This application is also a CIP application of Application No. 342,148, filed April 24, 1989, which is a CIP application of Application No. 133,323, filed December 16, 1987, and filed No. 133,323. Was registered as US Patent No. 4,824,439 on April 25, 1989. This patent is again a CIP application of Application No. 014,871, filed February 17, 1987, which was registered as US Patent No. 4,834,775 on May 30, 1989.

The present invention relates to a method for producing a metal oxide aerosol and a method of using the prepared metal oxide aerosol as a sorbent of the discharge material. As is well known, acid gas emissions such as SO ₂ , SO ₃ , NO, NO ₂ , H ₂ S and HCl resulting from many chemical reactions are the main air pollutants. Previously, it has been known that it is costly to reduce acid gas emissions in these gaseous streams to environmentally acceptable concentrations.

For example, one of the commercial methods used to control SO ₂ emissions from commercial scale power plants is to inject limestone into the furnace. According to this commercial method, limestone is injected into the furnace, where it reacts with sulfur oxides to form solid calcium sulfate. The solid calcium sulfate particles are then separated from the flue gas by conventional particulate matter control equipment. An important disadvantage of the limestone injection method for capturing SO ₂ in the furnace is the low calcium utilization. The amount of sulfur removed from the combustion products by limestone injection in the furnace was 50%, while the calcium utilization was only 15-25%. As a result, very large amounts of limestone are injected per unit mass of sulfur contained in the fuel. This proved to be very uneconomic.

Naturally, it has become very desirable to provide a mechanism to remove emissions from an economical way from industrial scale combustion air streams. It is therefore an important object of the present invention to provide a process for the preparation of sorbent aerosol materials of discharged materials. It is another object of the present invention to provide a process for the preparation of exhaust material sorbent oxide aerosols which is very effective in removing acid gas emissions from gaseous air streams.

Still other objects and advantages of the present invention are described below.

The above objects and advantages are easily achieved by the present invention. The present invention relates to a process for the production of metal oxide aerosols from the corresponding metals and to the use of the prepared metal oxide aerosols as sorbents of the discharge material. The process of the invention vaporizes the metal of the desired sorbent in a gaseous stream of inert gas, preferably in a gaseous stream of inert gas, under an oxidizing environment, preferably in a first zone of temperature T ₁ and then vaporized metal. It is characterized by passing a gaseous gas stream of from the first zone to the second zone, where the metal vapor stream is brought into contact with an oxidant to oxidize the metal vapor to form an aerosol composed of solid metal oxide particles in the gaseous carrier stream. By controlling various variables in the process, the size of the metal oxide particles can be adjusted to produce optimized metal oxide aerosols. The metal oxide aerosol is then supplied to a gaseous air stream containing an acid gaseous material and contacted at a temperature suitable for the reaction between the metal oxide aerosol and the emission material to be captured to form a solid metal compound of the emission material.

The present invention relates to a method for producing a metal oxide aerosol and a method of using the prepared metal oxide aerosol as a discharge material sorbent. The process of the present invention is particularly useful for removing acid gas effluents such as byproducts of various chemical reactions SO ₂ , SO ₃ , NO, NO ₂ , H ₂ S and HCl from the waste gases of chemical reactions.

Hereinafter, the method of the present invention will be described in detail with reference to FIG. 1 and those schematically shown herein.

The method of the present invention is characterized in that a metal oxide aerosol is formed, and then the discharge material to be captured is formed of a solid metal compound. Although the present invention will be described taking sulfur as the exhaust material in the combustion gas stream, the method of the present invention is useful for capturing all of the acid gas exhaust materials described above, which are by-products of many chemical reactions.

Referring to FIG. 1, the metal oxide aerosol vaporizes the metal of the desired sorbent under vaporization temperature conditions in a vaporization zone, an environment free of oxidants, and then passes the resulting metal vapor through the oxidation zone, Here metal oxide aerosols are prepared by contacting metal vapors with oxidants.

According to the process of the invention, the sorbent metal suitable for use in the process of the invention is a metal selected from the group consisting of metals having a valence equal to or greater than alkali metals, alkaline earth metals, alkaline earth metals and mixtures thereof. In particular, suitable metals are magnesium and calcium, with calcium being more preferred. In the process of the invention, it is preferred to vaporize the desired metal sorbent in the vaporization zone in the gaseous air stream. The gaseous airflow is required to be an inert airflow, and any of gases such as argon, helium, nitrogen, and methane may be used. Preferred gases are argon and nitrogen. Inert gas is required because it must occur in a substantially oxidant free environment to ensure complete vaporization of the metal sorbent in the vaporization step. It is preferable to use an inert gas stream because the inert gas stream increases the amount of metal vapor in the gaseous air stream, i.e., the metal vapor load, which has a positive effect on the particle size of the resulting metal oxide. The flow rate of the gaseous airflow must be adjusted to obtain the aerosol properties required for the proper particle size (less than 0.1 μm) of the metal oxide aerosol. The flow rate of the inert gas required must be adjusted to obtain a metal vapor load of 5-250 g / Nm ³ , preferably 50-150 g / Nm ³ .

The flow rate of the inert gas depends on several factors such as the metal vaporization temperature (T ₁ ), the type of metal to be vaporized, the cooling rate used in the aerosol-forming process, and the primary particle size of the required aerosol. The flow rate of the inert gas used in the process of the present invention is chosen to provide a suitable metal vapor load that can consistently obtain an aerosol primary particle diameter of about 0.05 μm, ideally suited for obtaining high metal utilization in the exhaust material absorption stage. desirable.

According to the invention, the vaporization of the metal in the gaseous air stream carried out in the first zone of the furnace needs to be carried out under controlled temperature conditions T ₁ and pressure P ₁ . The temperature T ₁ is the temperature required to obtain complete metal vaporization, ie the melting point of the metal, and varies depending on the metal sorbent to be vaporized. In addition, to achieve full metal vaporization, the vaporization zone must be substantially free of oxidizing agents. Moreover, the temperature used for vaporization is preferably significantly higher than the melting point of the metal sorbent used. This condition is preferred because an increase in the T ₁ temperature increases the vapor load in the air stream supplied to the oxidation zone, which has a positive effect on the metal oxide particle size, as indicated above. The vaporization temperature should be below 2000 ° C for economic reasons. According to the present invention, the vaporization temperature is about 650 ° -1200 ° C, preferably about 1000 ° -1300 ° C for calcium, and 450 ° -1150 ° C for magnesium, preferably 750 ° -950 ° C under atmospheric pressure. to be.

Once the metal vapor is produced in the vaporization zone, the metal vapor in the gaseous stream is passed from the first zone to the second zone of the furnace with or without an inert gas stream.

Subsequently, the metal vapor in the gaseous gas stream is contacted with an oxidizing agent such as oxygen, air, or CO ₂ in the second zone of the furnace to oxidize the metal vapor, thereby forming an aerosol of the present invention composed of metal oxide particles in the gaseous air stream of the carrier gas. Form. According to the invention, the formation of the aerosol air stream in the second zone must be adjusted to obtain the required particle size. It has been found that metal oxide particles having a particle size of submicron units are preferred because of their effective sorbent utilization and thus good capture of the discharge material. Average particle sizes of less than 0.1 micron are preferred, and particle sizes of less than 0.05 microns are ideal.

As noted above, the aerosol airflow supplied from the second zone is in contact with the gas stream carrying the exhaust material in the third zone under controlled temperature conditions. The temperature at which the metal oxide aerosol is in contact with the gas stream carrying the exhaust material must be within a temperature range suitable for the reaction between the metal oxide aerosol and the emission material to be captured so as to form a solid metal compound of the emission material. For example, in the case where sulfur is to be captured, the process of absorbing the discharged material is carried out under the following conditions: 650 ° C to 1250 ° C, preferably about 950 ° C to 1200 ° C for calcium oxide aerosol, and 350 ° C to 1200 ° C for magnesium It is carried out under temperature conditions of 850 ° C, preferably about 700 ° C to 800 ° C. This temperature range represents a substantial and / or thermodynamic limit for the sulfidation of calcium and magnesium oxides.

According to the method of the present invention, the utilization rate of the sorbent is about 90% and 50% or more for CaO aerosol and MgO aerosol, respectively, in a gas stream containing about 2000 ppm SO ₂ .

The following examples illustrate the features of the method of the present invention but are not intended to be limiting in any way.

Example 1

Referring to FIGS. 1 and 2, 3.5 g of calcium metal was fed to the vaporization zone. Argon gas was fed to the vaporization zone at a temperature of 25 ° C. and 1 atmosphere at a gas flow rate of 16.5 ml / sec. The vaporization zone was heated to 1000 ° C. Under these conditions, the aerosol was determined to be produced constantly at a rate of about 5 mg / min. This aerosol stream was contacted with 54 liters / min of dry air stream heated to 950 ° C. in the oxidation zone to produce a metal oxide aerosol of CaO. This aerosol was injected into a gaseous air stream containing a measurand of SO ₂ and contacted with the aerosol air stream at the emission absorption zone. Five separate tests were performed using five SO ₂ concentrations of 250 ppm, 500 ppm, 7 50 ppm, 2000 ppm and 3500 ppm (by volume) in air. The sampling probe of the electrostatic precipitator was placed at the end of the absorption zone to capture the aerosol sample. An aerosol sample was taken to determine the amount of calcium used for sulfur uptake. The results are shown in FIG. It is to be noted that the residence time used during this experiment (about 0.5 seconds) is good within the short time spent reducing the flue gas from 1200 ° C to 950 ° C in industrial boilers. Thus, the results shown were good in the required industrial time schedule. As can be seen from Figure 2, the calcium utilization is at least 80% at SO ₂ concentrations above 1500 ppm, which is much better than the calcium utilization obtained from the limestone injection method in the furnace. In addition to the above, the temperature at which the exhaust material absorption takes place, 950 ° C for calcium and 800 ° C for magnesium, is much lower than the temperature used for the method of injecting limestone into the furnace, which makes the method of the present invention even more Make it an attractive way. Finally, the average particle diameter of calcium oxide was measured, and the value was 0.015 μm.

Example 2

The process of Example 2 was carried out in a similar manner to Example I, except that magnesium was used instead of calcium. Magnesium oxide aerosol was formed and then fed to an air stream containing SO ₂ at the five concentrations described in Example I above. The temperature of the first zone was adjusted to 850 ° C. to vaporize magnesium. The results are shown in FIG. Aerosols containing magnesium oxide particles were not as effective as aerosols containing calcium oxide particles at low SO ₂ concentrations, but magnesium oxide aerosols were still more effective than conventional limestone injection methods. The particle size of the magnesium oxide particles obtained in the aerosol according to the present invention was 0.020 μm.

The present invention can be embodied in other forms or carried out in other ways without departing from the spirit or essential features of the invention. Accordingly, the embodiments of the present invention are intended to be illustrative in all respects and not to limit, and the scope of the present invention is defined by the appended claims, and all changes made within the equivalent meaning and scope belong to the present invention. do.

Claims (10)

(a) vaporizing the metal under a vaporization temperature condition in a first zone at or above a temperature T ₁ ; (b) passing the metal vapor in a gaseous phase from the first zone to a second zone; And (c) spreading the metal vapor by contacting the metal vapor with an oxidant in the second zone to form an aerosol consisting of solid metal oxide particles in the gaseous air stream. How to prepare. The method of claim 1, wherein the metal is selected from the group consisting of alkali metals, alkaline earth metals, metals having a valence greater than or equal to alkaline earth metals, and mixtures thereof. 3. The method of claim 2, wherein said metal is selected from the group consisting of magnesium and calcium. 2. The method of claim 1, wherein an inert gas stream is supplied to the first zone while vaporizing the metal. The method of claim 4, wherein the amount of metal vapor applied to the gas stream is between 5 g / Nm ³ and 250 g / Nm ³ . The method of claim 1 wherein the temperature T ₁ is the melting point of the metal to be vaporized. The method of claim 1 wherein the metal is magnesium and the vaporization temperature is 450 ° -11 50 ° C. under atmospheric pressure. The method of claim 1 wherein the metal is calcium and the vaporization temperature is 650 ° -1300 ° C. under atmospheric pressure. The method of claim 1 wherein the aerosol is characterized by a metal oxide having a particle size of 0.001-1.0 μm. The method of claim 1, further comprising the step of reacting the metal oxide particles with the exhaust material by contacting the aerosol with a gaseous air stream containing the exhaust material under controlled temperature conditions.

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