Method of applying electric arc furnace dust in chemical looping combustion process

Abstract

The present invention discloses a method of applying electric arc furnace dust in chemical looping combustion process, and particularly a method of applying electric arc furnace dust in chemical looping combustion process without releasing of zinc vapor. The method of applying electric arc furnace dust in chemical looping combustion process comprises following steps: (1) providing an electric arc furnace dust and an inert support (Al.sub.2O.sub.3) and mixing the electric arc furnace dust and the inert support (Al.sub.2O.sub.3) to obtain a mixture of the electric arc furnace dust and the inert support (Al.sub.2O.sub.3); (2) calcining the mixture of the electric arc furnace dust and the inert support (Al.sub.2O.sub.3) with high temperature to obtain another mixture of Fe.sub.2O.sub.3, ZnAl.sub.2O.sub.4, and Al.sub.2O.sub.3; (3) applying the mixture of Fe.sub.2O.sub.3, ZnAl.sub.2O.sub.4, and Al.sub.2O.sub.3 as oxygen carrier and inert support in a chemical looping combustion process.

Claims

1. A method of applying electric arc furnace dust in chemical looping combustion process, comprising: (1) providing an electric arc furnace dust and an aluminum oxide inert support and mixing the electric arc furnace dust and the aluminum oxide inert support to obtain a mixture of the electric arc furnace dust and the aluminum oxide inert support; (2) calcining the mixture of the electric arc furnace dust and the aluminum oxide inert support with high temperature to prepare another mixture of ferric oxide, ZnAl compound oxide, and aluminum oxide; and (3) applying the mixture of ferric oxide, ZnAl compound oxide, and aluminum oxide in a chemical looping combustion process.

2. The method of claim 1, wherein the electric arc furnace dust is mainly comprised of zinc oxide (ZnO) and ZnFe compound oxide (ZnFe.sub.2O.sub.4).

3. The method of claim 1, wherein the aluminum oxide inert support is Al.sub.2O.sub.3.

4. The method of claim 1, wherein in the step (1), the electric arc furnace dust and the aluminum oxide inert support are uniformly mixed with each other by solid phase ball milling method.

5. The method of claim 1, wherein in the step (2), the mixture of the electric arc furnace dust and the aluminum oxide inert support is calcined with high temperature in an aerobic environment for preparing the mixture of ferric oxide, ZnAl compound oxide, and aluminum oxide.

6. The method of claim 1, wherein in the step (2), the calcined temperature is 1100 C.

7. The method of claim 1, wherein in the mixture of ferric oxide, ZnAl compound oxide, and aluminum oxide, the ferric oxide is Fe.sub.2O.sub.3, as the ZnAl compound oxide is ZnAl.sub.2O.sub.4, and as the aluminum oxide is Al.sub.2O.sub.3.

8. The method of claim 1, wherein in the step (3), the ferric oxide is used as an oxygen carrier, and the ZnAl compound oxide and the aluminum oxide are used as inert supports.

9. The method of claim 1, wherein the process temperature of the chemical looping combustion process is lower than 792.7 C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 is a flow chart illustrating a method of applying electric arc furnace dust in chemical looping combustion process according to one embodiment of the present invention.

(3) FIG. 2 is a drawing illustrating a XRD diffraction pattern of untreated electric arc furnace dust.

(4) FIG. 3 is a drawing illustrating the result of TXRF analysis of untreated electric arc furnace dust.

(5) FIG. 4 is a drawing illustrating the reaction mechanism for untreated electric arc furnace dust following increasing of reduction time.

(6) FIG. 5 is a drawing illustrating a XRD diffraction pattern of electric arc furnace dust treated with the method of the present invention.

(7) FIG. 6 is a drawing illustrating the result of non-isothermal reduction test of non-isothermal ZnAl compound oxide (ZnAl.sub.2O.sub.4) in electric arc furnace dust treated with the method of the present invention.

(8) FIG. 7 is a drawing illustrating the twenty times of redox reactions with syngas and air for the treated electric arc furnace dust.

(9) FIG. 8A to FIG. 8D are drawings respectively illustrating SEM pictures of the treated electric arc furnace dust, which is treated with the method of the present invention, at 750 C. after different reduction-oxidization cycles.

(10) FIG. 9 is a drawing illustrating CO.sub.2 conversion obtained by applying the treated the electric arc furnace dust, which is treated with the method of the present invention, to perform reduction (reaction) in a fixed bed reactor.

DETAILED DESCRIPTION OF THE INVENTION

(11) The detailed description of the present invention will be discussed in the following embodiments, which are not intended to limit the scope of the present invention, but can be adapted for other applications. While drawings are illustrated in details, it is appreciated that the quantity of the disclosed components may be greater or less than that disclosed, except expressly restricting the amount of the components. Although specific embodiments have been illustrated and described, it will be appreciated by those skilled in the art that various modifications may be made without departing from the scope of the present invention, which is intended to be limited solely by the appended claims.

(12) Please refer to FIG. 1, it is a flow chart illustrating a method of applying electric arc furnace dust in chemical looping combustion process according to one embodiment of the present invention.

(13) As shown is FIG. 1, the method of the present invention comprises following steps: In step S10, an electric arc furnace dust and an aluminum oxide inert support are provided, and then they are uniformly mixed with each other in order to obtain a mixture of the electric arc furnace dust and the aluminum oxide inert support. In step S12, the mixture of the electric arc furnace dust and the aluminum oxide inert support is calcined for preparing a mixture comprised of ferric oxide, ZnAl compound oxide, and aluminum oxide. In step S14, the mixture of ferric oxide, ZnAl compound oxide, and aluminum oxide is introduced into a reactor and the mixture is used as oxygen carriers for performing a chemical looping combustion process.

(14) The chemical composition of the EAFD was determined by total-reflection X-ray fluorescence spectrometer (TXRF, Bruker S2 Picofox). The crystalline structure of the oxygen carrier was identified using X-ray diffraction (XRD, Bruker D2 Phaser) with a Cu-K radiation source (=1.5405 ) in the 2 scan from 20 to 80. The XRD pattern of this XRD analysis and the result of this TXRF analysis are illustrated in FIG. 2 and FIG. 3 respectively. Referring to FIG. 2 and FIG. 3, according to the XRD pattern of this XRD analysis and the result of this TXRF analysis, it is recognized that the electric arc furnace dust is mainly comprised of zinc oxide (ZnO) and ZnFe compound oxide (ZnFe.sub.2O.sub.4) having a spinel structure. Further, according to the XRD pattern of this XRD analysis and the result of this TXRF analysis, we can speculate that the molar ratio of zinc oxide (ZnO) and ZnFe compound oxide (ZnFe.sub.2O.sub.4) in the electric arc furnace dust is about 0.019 mol 0.233 mol, but it is not limit. All electric arc furnace dust which is mainly comprised of zinc oxide (ZnO) and ZnFe compound oxide (ZnFe.sub.2O.sub.4) having a spinel structure can be utilized in the step S10.

(15) Please refer to FIG. 4, it is a drawing illustrating the reaction mechanism for a untreated electric arc furnace dust, which is not treated by the method of the present invention, following increasing of reduction time. In other words, FIG. 4 is a drawing illustrating reduction-oxidization of the untreated electric arc furnace dust. As shown in FIG. 4, during reduction-oxidization of the untreated electric arc furnace dust, the ZnFe compound oxide (ZnFe.sub.2O.sub.4) in the untreated electric arc furnace dust is decomposed into zinc oxide (ZnO) and ferric oxide (Fe.sub.2O.sub.3) first. Next, the zinc oxide (ZnO) is reduced to form zinc metal which has a low melting point, and then zinc vapor is emitted or released. However, the zinc vapor has a bad influence on the reduction-oxidization of the untreated electric arc furnace dust. Therefore, if the untreated electric arc furnace dust is directly applied in a chemical looping combustion process, it also causes a serious issue of zinc vapor emission or releasing. Accordingly, the untreated electric arc furnace dust can not be directly applied in a chemical looping combustion process until the issue of zinc vapor emission or releasing is improved or resolved.

(16) In the step S10, the aluminum oxide inert support is Al.sub.2O.sub.3, and the electric arc furnace dust and the aluminum oxide inert support are uniformly mixed with each other by solid phase ball milling method for preparing (or obtaining) the mixture of the electric arc furnace dust and the aluminum oxide inert support.

(17) In the step S12, the mixture of the electric arc furnace dust and the aluminum oxide inert support is calcined at 1100 C. in an aerobic environment for about 2 hours. Therefore, the mixture of the electric arc furnace dust and the aluminum oxide inert support is calcined to prepare or obtain a mixture comprising ferric oxide, ZnAl compound oxide, and aluminum oxide. This mixture comprising ferric oxide, ZnAl compound oxide, and aluminum oxide is a treated electric arc furnace dust which is treated by addition of aluminum oxide inert support and calcination under high temperature. the mixture comprising ferric oxide, ZnAl compound oxide, and aluminum oxide (or the treated electric arc furnace dust) was identified using X-ray diffraction, and the XRD pattern of this XRD analysis is illustrated in FIG. 5. Referring to FIG. 5, the mixture comprising ferric oxide, ZnAl compound oxide, and aluminum oxide (or the treated electric arc furnace dust) is mainly comprised of Fe.sub.2O.sub.3, ZnAl.sub.2O.sub.4, and Al.sub.2O.sub.3.

(18) Further, the mixture comprising ferric oxide, ZnAl compound oxide, and aluminum oxide (or the treated electric arc furnace dust provided) was identified using non-isothermal reduction test by a thermogravimetric analyzer. The result of this non-isothermal reduction test is illustrated in FIG. 6. As shown in FIG. 6, the result of this non-isothermal reduction test shows that the ZnAl compound oxide does not have obvious weight loss until the reduction temperature is higher than 792.7 C. It means that there is no zinc vapor emitted or released from the ZnAl compound oxide when the temperature is lower than 792.7 C. Therefore, through the treatment (the step S10 and the step S12), the zinc oxide (ZnO) is transformed into the ZnAl compound oxide (ZnAl.sub.2O.sub.4) which is stable and difficult to produce zinc vapor. It is helpful to stabilize the zinc metal component in the electric arc furnace dust and to suppress emission or releasing of zinc vapor in reduction-oxidation or chemical looping combustion process. Therefore, the zinc vapor emission or releasing issue can be resolved. Besides, the ZnAl compound oxide (ZnAl.sub.2O.sub.4) can be used as an inert support because the ZnAl compound oxide (ZnAl.sub.2O.sub.4) does not emit or release zinc vapor when the temperature is lower than 792.7 C.

(19) In the step S14, the treated electric arc furnace dust (or the above-mentioned mixture comprising ferric oxide, ZnAl compound oxide, and aluminum oxide) is put into a reactor, and a synthesis gas (10% CO+10% H.sub.2) is used as a reduction gas and introduced into the reactor for reduction of oxygen carriers. After, air is used as an oxidation gas and introduced into the reactor for oxidation of oxygen carriers. This chemical looping combustion process (or reduction-oxidation) is performed at the temperature which is lower than 792.7 C., and the temperature which is equal to or lower than 750 C. is preferred. The reduction-oxidation equation (or reaction) of the chemical looping combustion process performed by applying the treated (through the step S10 and the step S12) electric arc furnace dust (or the above-mentioned mixture comprising ferric oxide, ZnAl compound oxide, and aluminum oxide) therein is illustrated as following:

(20) Reduction Equation (or Reaction):

(21) ${\mathrm{Fe}}_2{O}_3+{\mathrm{Al}}_2{O}_3+{\mathrm{ZnAl}}_2{O}_4+\mathrm{CO}+H_2\underset{}{.fwdarw.}2\mathrm{Fe}+{\mathrm{Al}}_2{O}_3+{\mathrm{ZnAl}}_2{O}_4+{\mathrm{CO}}_2+H_{2}O$

(22) Oxidation Equation (or Reaction):

(23) $2\mathrm{Fe}+{\mathrm{Al}}_2{O}_3+{\mathrm{ZnAl}}_2{O}_4+\frac{3}{2}{O}_2\underset{}{.fwdarw.}{\mathrm{Fe}}_2{O}_3+{\mathrm{Al}}_2{O}_3+{\mathrm{ZnAl}}_2{O}_4$

(24) In view of above-mentioned equations (or reactions), it is recognized that the ferric oxide (Fe.sub.2O.sub.3) of the treated (through the step S10 and the step S12) electric arc furnace dust is used as an oxygen carrier in the chemical looping combustion process. After the oxygen carrier (Fe.sub.2O.sub.3) is reduced in CO and H.sub.2, Fe metal is produced. After the Fe metal is oxidized in air, the Fe metal is transformed back to the ferric oxide (or oxygen carrier) (Fe.sub.2O.sub.3). In the chemical looping combustion process, the ZnAl compound oxide (ZnAl.sub.2O.sub.4) and the aluminum oxide (Al.sub.2O.sub.3) are not reactive and thereby both of them are used as inert supports.

(25) Through analyzing the weight loss of metal oxide in the chemical looping combustion process by the thermogravimetric analyzer, we can know reaction characteristics of the metal oxide, such as reduction time and oxidation time of the metal oxide, conversion rate, oxygen content capable of being provide to the reaction (such as oxidation), etc. After the synthesis gas (10% CO+10% H.sub.2) is introduced into the reactor as a reduction gas first and air is introduced into the reactor as an oxidation gas next, the data is introduced into the oxidation rate equation of the reactive oxygen in the metal oxygen carrier for calculating the conversion rate of the (metal) oxygen carrier in repeating reduction-oxidation reactions. In such a way, we can know whether the conversion rate of the (metal) oxygen carrier is changed in these repeating reduction-oxidation reactions. Furthermore we can obtain the reaction activity of the chemical looping combustion process. The oxidation rate equation of the reactive oxygen is shown as following:

(26) $X=1-\frac{W_{\mathrm{ox}}-W}{{\mathrm{aW}}_{\mathrm{ox}}{R}_0}$ X: the oxidation rate (%) of the reactive oxygen; a: weight ratio (WT %) of the metal oxygen carrier in the sample (WT %), if there is any other inert oxides composite with the metal oxygen carrier, it need to be multiplied by this parameter; R.sub.0: weight ratio (WT %) of the reactive oxygen; W.sub.ox: weight (mg) of completely oxidation portion of the metal oxygen carrier, which is also the initial weight of reduction (reaction); W: weight variation (mg) of the metal oxygen carrier in weight following time.

(27) Through above-mentioned method, a test of reaction activity is performed to the method of applying electric arc furnace dust in chemical looping combustion process of the present invention for proving whether the method of the present invention can efficiently improve or resolve the zinc vapor emission (or releasing) issue caused by applying electric arc furnace dust in the chemical looping combustion process. This test is performed by twenty times of redox reactions with syngas and air for the treated electric arc furnace dust. The result of this test is illustrated in FIG. 7. FIG. 7 is a drawing illustrating the twenty times of redox reactions with syngas and air for the treated electric arc furnace dust at 750 C. As shown in FIG. 7, in the twenty times of redox reactions, each patter in FIG. 7, which represents each cycle of the twenty times of redox reactions, has no obvious variation. Therefore, it can prove that the reaction efficiency of the chemical looping combustion process performed with the treated electric arc furnace dust treated by the method of the present invention can be maintain without obvious decline. It can also prove that the treated electric arc furnace dust treated by the method of the present invention has an ability to perform many cycles of the chemical looping combustion process (or many reduction-oxidation cycles). Furthermore, it further proves that there is no zinc vapor produced in the method of applying electric arc furnace dust in chemical looping combustion process of the present invention because the test result of reaction activity of the chemical looping combustion process shown in FIG. 7 has no obvious variation. Therefore, it also proves that the method of the present invention can efficiently improve or resolve the zinc vapor emission (or releasing) issue caused by applying electric arc furnace dust in the chemical looping combustion process.

(28) Please refer to FIG. 8A to FIG. 8D, FIG. 8A to FIG. 8D are drawings respectively illustrating SEM pictures of the treated electric arc furnace dust, which is treated with the method of the present invention, at 750 C. after different reduction-oxidization cycles. The reduction-oxidization cycles illustrated in FIG. 8A, FIG. 8B, FIG. 8C, and FIG. 8D are unreacted (zero reduction-oxidization cycle), five reduction-oxidization cycles, ten reduction-oxidization cycles, and twenty reduction-oxidization cycles respectively. Referring to FIG. 8A to FIG. 8D, it is recognized that there are some slight agglomerations formed on the surface after many reduction-oxidization cycles. However, these agglomerations are not obvious and thereby these agglomerations do not have any influence on the chemical looping combustion process (or reduction-oxidization).

(29) Please refer to FIG. 9, FIG. 9 is a drawing illustrating CO.sub.2 conversion obtained by applying the treated the electric arc furnace dust, which is treated with the method of the present invention, to perform reduction (reaction) in a fixed bed reactor. FIG. 9 is also a drawing illustrating the test result of the reactivity of the method of applying electric arc furnace dust in chemical looping combustion process in a fixed bed reactor and the test result of the ability of conversing CO into CO.sub.2. In these tests, the treated (through the step S10 and the step S12) electric arc furnace dust is put into a fixed bed reactor, and the synthesis gas is introduced into the fixed bed reactor to reduce the oxygen carriers for test. As shown in FIG. 9, it is recognized that the treated (through the step S10 and the step S12) electric arc furnace dust has a good reactivity and it is very suitable for applying in the chemical looping combustion process.

(30) According to foregoing embodiments of the present invention, the present invention teaches how to recycle and treat the electric arc furnace dust, which is the industrial waste, with simple processes, such as mixing with an aluminum oxide inert support, solid phase ball milling, and calcination with high temperature, for preparing oxygen carriers used in the chemical looping combustion process. In the method of the present invention, these oxygen carriers are used in the chemical looping combustion process instead of the oxygen carriers which are prepared with complicated processes and high cost and are used in traditional chemical looping combustion process. Therefore, the cost of preparing the oxygen carriers can be reduced. Furthermore, in the method of the present invention, the zinc vapor emission (or releasing) issue can be improved or resolved by treating the electric arc furnace dust with a simple process. Accordingly, the present invention provides a method of recycling the electric arc furnace dust with simple processes and low cost, and it also develops a method (or technology) of applying industrial waste (such as the electric arc furnace dust) in the chemical looping combustion process.