Abstract:
A method to efficiently reduce lead content of cement without exerting influence upon quality of the cement. The method comprises the steps of: controlling O2 concentration of combustion gas in an inlet end of a cement kiln to 5% or lower and/or CO concentration thereof 1000 ppm or more; extracting a part of combustion gas from the cement kiln and collecting dust contained in the combustion gas; and collecting lead from the dust collected. With this, the area where raw material temperature in the cement kiln is between 800° and 1100° can be turned into reducing atmosphere to sharply increase volatilization rate of lead, and collection of lead from the dust allows lead content of cement to efficiently be reduced without exerting influence upon quality of the cement. Together with the control described above, where the inner diameter of the cement kiln is D and the distance from the inlet end of the cement kiln longitudinally into the kiln is L, supplying fuel and/or raw material including inflammable material to the area where L/D of the cement kiln is 0 or more and 12 or lower causes securely maintaining the reducing atmosphere of the area.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application claims priority to International Application No. PCT/JP2007/070401 which was filed on Oct. 19, 2007 and claims priority to Japanese Patent Application No. 2006-288848 filed on Oct. 24, 2006. 
       STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT 
       [0002]    Not Applicable 
       BACKGROUND OF THE INVENTION 
       [0003]    1. Technical Field of the Invention 
         [0004]    The present invention relates to a method for removing lead from a cement burning furnace, and more particularly to a method for removing lead from a cement burning furnace by collecting lead from dust contained in a part of combustion gas that is extracted from a kiln exhaust gas passage running from the inlet end of the cement kiln to a bottom cyclone. 
         [0005]    2. Description of the Related Art 
         [0006]    It has been considered that since lead (Pb) contained in cement is immobilized, the lead does not elute to soil. However, with increased amounts of recycled resources utilized in a cement manufacturing device in recent years, lead contained in cement has been increasing to the extent that the content sharply exceeds the record in the past. Since there is a possibility that the lead elutes to soil due to the increased concentration, lead content of cement is required to be reduced to the previous record. 
         [0007]    In order to reduce lead content of cement, for example, a method of treating waste is described in the first patent document. The method comprises the processes of: a washing process for washing waste; an alkali-eluting process for solid phase separated; a deleadification process for separating lead from the filtrate through precipitation; a decalciumization process for separating calcium through precipitation from the filtrate from which the lead is removed; and salt collecting process for separating and collecting salt by heating the filtrate through separation, to effectively separate and remove chlorine and lead in waste that is fed to a cement manufacturing process. 
         [0008]    In addition, a method of treating waste is described in the second patent document. The method comprises the steps of: mixing waste with a solution containing calcium ion to produce slurry; solid-liquid separating the slurry to generate solid phase containing zinc and water solution containing lead; adding sulfurization agent to the water solution containing lead; and solid-liquid separating the water solution to produce lead sulfide and solution containing calcium ion, to separated and remove lead and the like from waste such as fly ash. 
         [0009]    Patent document 1: Japanese Patent Publication No. 2003-1218 gazette 
         [0010]    Patent document 2: Japanese Patent Publication No. 2003-201524 gazette 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    Although, in the conventional art described in the above-mentioned patent documents, to reduce lead content, lead contained in the chlorine bypass dust, which is recovered from a part of combustion gas that is extracted from a kiln exhaust gas passage from an inlet end of a cement kiln and a bottom cyclone, is removed the ration of the lead, which is removed from the chlorine bypass dust and is discharged to the outside of the system, to total lead is only approximately 30%, so that even if lead contained in the chlorine bypass dust would completely be removed, remaining approximately 70% of lead would still be taken in clinker that is discharged from the cement kiln, therefore, it is not easy to reduce lead content of cement. Therefore, it is important to increase lead concentration of chlorine bypass dust and the like by accelerating lead volatilization in the cement kiln. 
         [0012]    Chloridization-volatilization method and reduction-volatilization method are known as technology for lead volatilization. However, when generally performed chloridization-volatilization method is applied to a cement burning process, it is necessary to feed by far much amount of chlorine than practical amount in cement manufacturing. On the other hand, applying reduction-volatilization method causes color of the cement produced to be yellow-ish, resulting in a problem in quality of the cement. 
         [0013]    The present invention has been made in consideration of the above-problems in the conventional art, and the object thereof is to provide a method for efficiently reducing lead content of cement by increasing lead concentration to the chlorine bypass dust and others. 
         [0014]    To achieve the above object, a method for removing lead from a cement burning furnace according to the present invention is characterized by comprising the steps of: controlling O 2  concentration of combustion gas in an inlet end of a cement kiln to 5% or lower and/or CO concentration thereof 1000 ppm or more; extracting a part of combustion gas; and collecting lead from the dust collected. 
         [0015]    With the present invention, it becomes possible to sharply increase lead volatilization rate by generating reduction atmosphere in the area where temperature of raw material in a cement kiln is between 800° C. and 1100° C., which is near the inlet end of the cement kiln. As a result, extracting a part of cement kiln combustion gas and collecting lead from dust that is collected from the combustion gas allows lead content of cement to efficiently be reduced. In addition, this method has no effect on the quality of the cement. 
         [0016]    In the method for removing lead from a cement burning furnace described above, while controlling O 2  concentration of the combustion gas in the inlet end of the cement kiln 5% or lower and/or CO concentration thereof 1000 ppm or more, fuel and/or raw material including inflammable material can be fed to an area where L/D of the cement kiln is 0 or more and 12 or less, where an inner diameter of the cement kiln is D and a distance from the inlet end of the cement kiln longitudinally into the kiln is L. With this, it is possible to securely maintain reduction atmosphere in the area where temperature of raw material in a cement kiln is between 800° C. and 1100° C., which allows lead content of cement to further efficiently be reduced. 
         [0017]    In the above method for removing lead from a cement burning furnace, powdery and/or slurry fuel and/or raw material including inflammable material may be injected with a nozzle to the area where L/D of the cement kiln is 0 or more and 12 or less. 
         [0018]    Further, lump fuel and/or raw material including inflammable material can be fed with a long distance thrower to the area where L/D of the cement kiln is 0 or more and 12 or less. 
         [0019]    Still further, it is possible to cylindrical or globular fuel and/or raw material including inflammable material is fed by utilizing an inclined surface of the inlet end of the cement kiln to the area where L/D of the cement kiln is 0 or more and 12 or less, and the cylindrical or globular fuel and/or raw material including inflammable material may be formed from small pieces of fuel and/or raw material including inflammable material. 
         [0020]    The fuel and/or raw material including inflammable material can be fed from a port installed in the area where L/D of the cement kiln is 0 or more and 12 or less. 
         [0021]    As mentioned above, with the method for removing lead from cement burning furnace according to the present invention, it becomes possible to efficiently reduce lead content of cement without effect on the quality of the cement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a diagrammatical view exemplarily showing a device to carry out a method for removing lead from a cement burning furnace according to the present invention; 
           [0023]      FIG. 2  is a flow chart showing overall construction of a chlorine bypass system attached to a cement burning furnace; 
           [0024]      FIG. 3  is a graph showing the relation between gas temperature and lead volatilization rate calculated by chemical equilibrium simulation; 
           [0025]      FIG. 4  is a graph showing the relation between inlet end CO concentration of a cement kiln and lead volatilization rate; and 
           [0026]      FIG. 5  is a is a graph showing the relation between inlet end O 2  concentration of a cement kiln and lead volatilization rate. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0027]    Next, embodiments of the present invention will be explained with reference to figures. 
         [0028]      FIG. 1(   a ) shows an example of a device to carry out a method for removing lead from a cement burning furnace according to the first embodiment of the present invention, this device is provided with nozzle  1 , at an inlet end  10   a  (at the end to which a calciner  11  and a bottom cyclone  12  are installed) of a cement kiln  10 , for injecting raw material including powdery and/or slurry fuel and/or raw material including inflammable material hereinafter referred to as “fuels” according to circumstances) into the cement kiln  10 . 
         [0029]    The nozzle  1  is provided with a feeder not shown for feeding fuels F and an injector for injecting fuels F, which is fed to the nozzle  1 , into the cement kiln  10 . With this, fuels F can deeply be injected into the cement kiln  10 . 
         [0030]    The nozzle  1  is provided with a feeder not shown for feeding fuels F and an injector for injecting fuels F, which is fed to the nozzle  1 , into the cement kiln  10 . With this, the fuels F can deeply be injected into the cement kiln  10 . 
         [0031]    Meanwhile, as illustrated in  FIG. 2 , the cement kiln  10  is provided with a chlorine bypass system, and gas extracted from a kiln exhaust gas passage, which runs from the inlet end of the cement kiln  10  to the bottom cyclone is cooled with cooling air from a cooling fan  22  in a probe  21 , and is introduced to a cyclone  23  so as to be divided into coarse powder dust, and fine powder and gas. The course powder dust is returned to a cement kiln system, and fine powder (chlorine bypass dust) including potassium chloride (KCI) and the like is collected by a dust collector  24 . Meanwhile, gas exhausted from the dust collector  24  is released to the atmosphere via an exhaust fan  25 . 
         [0032]    Next, the method for removing lead from a cement burning furnace according to the present invention with the system described above will be explained. 
         [0033]    In  FIG. 1(   a ), powdery or slurry fuel and/or raw material including inflammable material is injected into the cement kiln  10  with the nozzle  1 . Here, as fuels, besides fine coal and heavy oil, which are generally used as main fuels for the cement kiln  10 , various kinds of material such as waste fuels may be utilized. Further, as for raw material including inflammable material also, kinds of material are not limited, and recycled waste may be used. But, when fuels with much volatile matter are used, even if gas with strong reducing effect was generated, the gas would instantly flow downstream and was replaced with gas with oxidizing effect, so that fuels with much fixed carbon are preferably used. 
         [0034]    With the nozzle  1 , the fuels F are injected to the area where L/D of the cement kiln  10  is 0 or more and 12 or less, where the inner diameter of the cement kiln is D and the distance from the inlet end  10   a  of the cement kiln  10  longitudinally into the kiln  10  is L. 
         [0035]      FIGS. 3(   a ) to ( e ) show the relation between gas temperature and lead volatilization rate by chemical equilibrium simulation, the axis of abscissas shows gas temperature and the axis of ordinates shows lead volatilization rate. Further, in the  FIGS. 3(   a ) to ( e ), (a) shows moist air atmosphere, (b) standard combustion gas atmosphere, (c) no oxygen atmosphere, (d) low CO concentration atmosphere and (e) high CO concentration atmosphere, from (a) to (e), atmosphere gradually changes from oxidizing atmosphere to reducing atmosphere, and (e) shows the strongest reducing atmosphere. 
         [0036]    As clearly shown n  FIG. 3 , under the strong reducing atmosphere (e), lead volatilization rate sharply rises in the area where gas temperature is between 700° C. and 1200° C. in comparison with other cases. The above temperature area corresponds to the area near the inlet end  10   a  of the cement kiln  10 . Therefore, to the area where L/D of the cement kiln  10  is 0 or more and 12 or less, that is, to the area where raw material temperature in the cement kiln  10  is between 800° C. and 1100° C., powdery or slurry fuels F are injected to change this area to reducing atmosphere, which allows lead volatilization rate to considerably be increased. 
         [0037]      FIG. 4  gives examination data showing the relation between CO concentration in the inlet end  10   a  of the cement kiln  10  (hereinafter referred to as “inlet end CO concentration”) and lead volatilization rate. When the inlet end CO concentration becomes 0.1% (1000 ppm) or more, the lead volatilization rate becomes approximately 90% or more, and when the inlet end CO concentration becomes 0.3% (3000 ppm) or more, the lead volatilization rate becomes approximately 95% or more. With this, it is substantiated that under strong reducing atmosphere lead volatilization rate considerably rises in the area near the inlet end  10   a  of the cement kiln  10  shown in  FIG. 1 . 
         [0038]    In addition,  FIG. 5  gives examination data showing the relation between O 2  concentration in the inlet end  10   a  of the cement kiln  10  (hereinafter referred to as “inlet end O 2  concentration”) and lead volatilization rate. When the inlet end O 2  concentration becomes 5% or less, the lead volatilization rate becomes approximately 90% or more, and when the inlet end O 2  concentration becomes 3% or less, the lead volatilization rate becomes approximately 95% or more. With this also, it is substantiated under strong reducing atmosphere lead volatilization rate considerably rises in the area near the inlet end  10   a  of the cement kiln  10  shown in the  FIG. 1 . 
         [0039]    Lead volatized in the cement kiln  10  is, in  FIG. 2 , included in the gas extracted by the probe  21 ; the extracted gas is cooled in the probe  21 ; the extracted gas is introduced to the cyclone  23  and is separated into coarse powder dust, and fine powder and gas; and the fine powder is collected by the dust collector  24 . Since to the fine powder is concentrated much lead in comparison to conventional one as much lead is volatilized in the cement kiln  10 , lead content of the cement manufactured by the cement kiln  10  can be reduced by collecting the lead. 
         [0040]      FIG. 1(   b ) shows an example of a device to carry out a method for removing lead from a cement burning furnace according to the second embodiment of the present invention, this device is provided with a long distance thrower  2 , at the inlet end  10   a  of the cement kiln  10 , for feeding lump fuels F into the cement kiln  10 . The long distance thrower  2  adopts elastic body, air pressure, oil pressure or the like as motive energy, and is constructed in such a manner that the fuels F supplied to the nozzle  1  are deeply fed into the cement kiln  10 . 
         [0041]    With this long distance thrower  2  and so on, the fuels F are fed to the area where L/D of the cement kiln  10  is 0 or more and 12 or less, and like the first embodiment, the area where raw material temperature in the cement kiln  10  is between 800° and 1100° can be turned into reducing atmosphere to considerably increase lead volatilization rate. And, as described above, collecting lead from the chlorine bypass dust to which much lead is concentrated in comparison to conventional one allows lead content of the cement manufactured by the cement kiln  10  to be reduced. 
         [0042]    Meanwhile, in this embodiment, condition of the injection such as dimension of the fuels F and initial velocity can be determined by calculation through fluid simulation or the like in consideration of fluid resistance R=C·A·ρ·u 2 /2, where C: resistance coefficient, A: projected area, ρ: density, u: relative velocity. This prevents the fuels F from returning on the kiln inlet  10   a  side by exhaust gas of the cement kiln  10 , which allows the fuels F to securely be fed to the area where L/D of the cement kiln  10  is 0 or more and 12 or less with the long distance thrower  2 . 
         [0043]    In addition, the position that the long distance thrower  2  is installed also, in order to prevent the returning of the fuels F, is preferably determined on raw material side on rear face of the cement kiln. The exhaust gas of the cement kiln does not uniformly flow in the kiln, but preferentially flows on the other side of raw material with low resistance. Therefore, at the feeding of the fuels F, installing the long distance thrower  2  on raw material side with low resistance prevents the returning of the fuels F. 
         [0044]      FIG. 1(   c ) is for explaining a method for removing lead from a cement burning furnace according to the third embodiment of the present invention. In this embodiment, cylindrical or globular fuels F are fed by utilizing an inclined surface  3  of the inlet end  10   a  of the cement kiln  10 . By utilizing inertia of the cylindrical or globular fuels F rolling on the inclined surface  3 , the fuels F are deeply fed to the cement kiln  10 . 
         [0045]    With the above method also, the fuels F are fed to the area where L/D of the cement kiln  10  is 0 or more and 12 or less, and like the above embodiments, the area where raw material temperature in the cement kiln  10  is between 800° and 1100° can be turned into reducing atmosphere to considerably increase lead volatilization rate, and collecting lead from the chlorine bypass dust to which much lead is concentrated allows lead content of the cement manufactured by the cement kiln  10  to be reduced. 
         [0046]    Meanwhile, as for conditions at the feeding of the cylindrical or globular fuels F also, by estimating the position where the fuels F reach based on a vertical position where the fuels F are fed and time for complete burning of the fuels F in an electric furnace or the like that is measured in advance, it becomes possible to more accurately feed the fuels F to a target position in the cement kiln. And, to manufacture cylindrical or globular fuels F, small pieces of fuels may be formed. 
         [0047]      FIG. 1(   d ) shows an example of a device to carry out a method for removing lead from a cement burning furnace according to the fourth embodiment of the present invention, this device is provided with a feeding port  4  installed in the area where L/D of the cement kiln  10  is 0 or more and 12 or less, and a feeder not shown for feeding the fuels F to the feeding port  4 . The feeding port  4  is constructed such that the feeding port  4  opens when positioning above the cement kiln  10  only, and material seal or the like is conducted to minimize the quantity of cool air that is taken into the cement kiln  10 . 
         [0048]    With the feeding port  4  described above, the fuels F are directly fed to the area where L/D of the cement kiln  10  is 0 or more and 12 or less, and like the above embodiments, the area where raw material temperature in the cement kiln  10  can be between 800 and 1100° is turned into reducing atmosphere to considerably increase lead volatilization rate, and collecting lead from the chlorine bypass dust to which much lead is concentrated allows lead content of the cement manufactured by the cement kiln  10  to be reduced. 
         [0049]    Meanwhile, in the above embodiments, fuels are fed to the area where L/D of the cement kiln  10  is 0 or more and 12 or less to turn the area where raw material temperature in the cement kiln  10  is between 800° and 1100° into reducing atmosphere. However, without feeding fuels, tuning the above-mentioned area into reducing atmosphere allows lead volatilization rate to considerably be increased. In actual operation of the cement kiln  10 , in order to securely maintain reducing atmosphere in the above-mentioned area, it is preferable not only to control O2 concentration of combustion gas in the inlet end of  10   a  of the cement kiln  10  to 5% or lower and/or CO concentration thereof 1000 ppm or more but to feed fuels in the area where L/D of the cement kiln  10  is 0 or more and 12 or less. 
       EXPLANATION OF SIGNALS 
       [0000]    
       
           1  nozzle 
           2  long distance thrower 
           3  inclined surface 
           4  feeding port 
           10  cement kiln 
           10   a  inlet end 
           11  calciner 
           12  bottom cyclone 
           21  probe 
           22  cooling fan 
           23  cyclone 
           24  dust collector 
           25  exhaust fan