JP5823269B2 - Cement kiln exhaust gas treatment system and operation method thereof - Google Patents

Description

  The present invention relates to a cement kiln exhaust gas treatment system and an operation method thereof, and in particular, to reduce the amount of mercury and organic pollutants contained in the cement kiln exhaust gas to reduce the amount of emissions to the outside of the cement manufacturing apparatus. Related to the system of

  The cement kiln exhaust gas contains a very small amount of metallic mercury (Hg). Its origin is not only mercury contained in natural raw materials such as limestone, which is the main raw material of cement, but also mercury contained in a wide variety of recycled resources such as fly ash. In the future, recycling of wastes as cement raw materials and fuels will be promoted, and the concentration of mercury in cement kiln exhaust gas may increase as the amount of waste processing increases.

  Therefore, for example, Patent Document 1 discloses that a cement kiln exhaust gas is used to efficiently remove mercury and the like contained in the exhaust gas discharged from the cement manufacturing process, and to reuse the dust collection dust from which the mercury and the like are removed as a cement raw material. After the dust is removed by a dust collector, the collected dust is guided to a heating furnace, and the mercury in the dust is heated to a volatilization temperature and volatilized, and then adsorbed and removed by an adsorbent. A processing method has been proposed.

  On the other hand, some of the recycled resources such as fly ash, main ash, sludge and slag used as raw material for cement are persistent organic pollutants (POPs) represented by dioxins or their skeletons. There are not a few containing ingredients to obtain. Usually, if cement firing is performed stably, most of these organic pollutants are trapped by kiln exhaust gas dust collector dust, circulate in the cement manufacturing equipment, and are decomposed at high temperatures. The amount of organic pollutants released into the atmosphere is negligible and is naturally below emission regulations.

  However, when some trouble occurs in cement firing and it becomes unstable, POPs may be unintentionally re-synthesized, and there is a risk that the amount of emissions from the kiln exhaust gas to the atmosphere will increase. I can't deny it. Therefore, it is desirable to further reduce the content of these organic pollutants.

  Therefore, for example, Patent Document 2 discloses an organic material that controls the amount of solid carbon that adsorbs organic pollutants in the dust contained in the exhaust gas from the preheater in order to reduce the amount of organic pollutants emitted from the cement manufacturing apparatus. Methods for reducing pollutant emissions have been proposed.

Japanese Patent Laid-Open No. 2002-355531 JP 2008-222477 A

  However, when the invention described in the above-mentioned patent document is actually applied to the treatment of cement kiln exhaust gas, mercury and organic pollutants in the cement kiln exhaust gas will be individually treated, which is not necessarily efficient. There were some aspects I couldn't say.

  Therefore, an object of the present invention is to comprehensively and efficiently reduce the discharge amount of both mercury and organic pollutants from a cement manufacturing apparatus.

In order to solve the above problems, the present invention is a cement kiln exhaust gas treatment system, which includes a gas adsorbent addition device for adding a gas adsorbent to a gas discharged from a preheater of a cement firing device, and an exhaust gas of the preheater. A dust collecting device for collecting the dust collected, a mercury collecting device for collecting mercury contained in the collected dust, a first circulation route for returning the dust collected by the dust collecting device directly to the preheater, A second circulation route for returning the dust collected by the dust collector to the preheater via the mercury recovery device; and a third circulation route for returning the dust collected by the dust collector directly to the kiln bottom of the cement kiln. And a fourth circulation route for returning the dust collected by the dust collector to the kiln bottom of the cement kiln via the mercury recovery device . Here, organic pollutants refer to residual organic pollutants (POPs) such as dioxins (PCDD, PCDF, co-PCB), polychlorinated biphenyls (PCBs), and volatile organic compounds (VOC).

According to the present invention, the gas adsorbent addition device causes the gas adsorbent to adsorb volatilized organic pollutants contained in the exhaust gas discharged from the preheater of the cement firing device, and collects the gas adsorbent with the dust collector. By collecting with dust and collecting mercury contained in the collected dust with a mercury recovery device, it is possible to comprehensively and efficiently reduce both mercury and organic pollutants discharged from cement manufacturing equipment. . In addition, the circulation route of the dust collected by the dust collector can be appropriately selected according to the mercury concentration of exhaust gas from the cement firing device and the organic pollutant concentration. Contaminants can be comprehensively reduced according to the concentration at that time.

  In the cement kiln exhaust gas treatment system, the mercury recovery device heats the dust collected by the dust collector, recovers the mercury volatilized by the heating, or cleans the dust that has been collected by the cleaning. Mercury transferred to the liquid side can be recovered.

  Further, the present invention is an operation method of the cement kiln exhaust gas treatment system, wherein when the mercury concentration and organic pollutant concentration of the gas discharged from the preheater are less than a predetermined value, the gas adsorbent is added. And the dust is returned to the preheater via the first circulation route, the mercury concentration of the gas discharged from the preheater is equal to or higher than a predetermined value, and the organic pollutant concentration of the exhaust gas is lower than the predetermined value. In this case, the addition of the gas adsorbent is stopped, the dust is returned to the preheater via the second circulation route, and the mercury concentration of the gas discharged from the preheater is less than a predetermined value, and the When the organic pollutant concentration in the exhaust gas is a predetermined value or more, the gas adsorbent is added to the exhaust gas, and the dust contained in the exhaust gas is removed from the third circulation loop. When the mercury concentration and organic pollutant concentration of the exhaust gas from the preheater are equal to or higher than a predetermined value, the gas adsorbent is added to the exhaust gas, and the exhaust gas is added to the exhaust gas from the pre-heater. The contained dust is returned to the kiln bottom of the cement kiln via the fourth circulation route.

  And according to this invention, like the said invention, according to the mercury density | concentration of the waste gas from a cement baking apparatus, and the organic pollutant density | concentration, the circulation route of the dust collected with the dust collector can be selected suitably. In addition, mercury and organic pollutants discharged from the cement manufacturing apparatus can be comprehensively reduced according to the concentration at that time.

  In the operation method of the cement kiln exhaust gas treatment system, the content of hydrophobic solid unburnt carbon in the dust collected by the dust collector can be 0.2% by mass or more. According to this, the organic pollutant adsorption efficiency can be improved and the organic pollutant can be effectively recovered.

  As described above, according to the present invention, it is possible to comprehensively and efficiently reduce both mercury and organic pollutants discharged from a cement manufacturing apparatus.

1 is an overall configuration diagram showing an embodiment of a cement kiln exhaust gas treatment system according to the present invention. 2 is a graph showing the relationship between the content of hydrophobic solid unburnt carbon in the dust collection dust of the electric dust collector and the concentration of dioxins (DXNs) at the outlet of the dust collector in the cement kiln exhaust gas treatment system of FIG. .

  Next, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows an embodiment of a cement kiln exhaust gas treatment system according to the present invention. This treatment system 1 is attached to a cement firing apparatus including a cement kiln 2, a preheater 3 and a calcining furnace 5, and is a boiler. A gas adsorbent addition device 7 for adding the gas adsorbent A to the exhaust gas G2 from the preheater 3 that has passed through the gas etc. 6, an electric dust collector 8 for collecting the dust and the gas adsorbent A contained in the exhaust gas G2, and an electric It is comprised with the mercury collection | recovery apparatus 9 which collect | recovers the dust collected by the dust collector 8, and the mercury contained in the gas adsorbent A (henceforth "EP dust D").

  The cement kiln 2, the preheater 3, the calcining furnace 5, and the electrostatic precipitator 8 are generally used in cement manufacturing apparatuses, and detailed descriptions thereof are omitted. The boiler 6 or the like generates a boiler that performs waste heat power generation using the exhaust gas G1, a stabilizer (humidity control tower) that controls the temperature and humidity of the exhaust gas G1, and a cement raw material R that is supplied to the preheater 3. Equipment for raw materials such as dryers and mills.

  In general, the gas adsorbent A added by the gas adsorbent adding device 7 is preferably a porous material effective for gas adsorption. Furthermore, the porous material preferably contains hydrophobic solid unburnt carbon, and examples thereof include commercially available activated carbon, fly ash generated from various industries, bottom ash, oil coke combustion ash, and the like. .

  Here, the hydrophobic solid unburnt carbon refers to porous carbonaceous particles having hydrophobicity in solid carbon. For example, it is collected on the toluene side by liquid-liquid extraction of toluene and water from all unburned carbon contained in fly ash or the like.

Further, in the hydrophobic solid unburnt carbon, the specific surface area by BET method is 30 m ² / g or more (preferably 50 m ² / g or more), and the pore volume of mesopores (2 to 50 nm) by BJH method is 0.03 mL. / G or more (preferably 0.04 mL / g or more, more preferably 0.05 mL / g or more) is suitable.

  Further, the addition position of the gas adsorbent A is preferably immediately before the electrostatic precipitator 8. This is because the exhaust gas G1 passes through the boiler 6 or the like, so that the temperature is lowered to 300 ° C. or less, and some organic pollutants in the exhaust gas G1 are generated and re-synthesized. This is because the organic pollutant can be more effectively adsorbed by the addition.

  In the subsequent stage of the electric dust collector 8, four circulation routes 11 to 14 for circulating the EP dust D are arranged according to the mercury concentration and the organic pollutant concentration of the exhaust gas G1. The first circulation route 11 returns the EP dust D directly to the preheater 3, the second circulation route 12 returns the EP dust D to the preheater 3 via the mercury recovery device 9, and the third circulation route 13 D is directly returned to the kiln bottom 4 of the cement kiln 2, and the fourth circulation route 14 is configured to return the EP dust D to the kiln bottom 4 via the mercury recovery device 9.

  The mercury recovery device 9 is a device provided for recovering mercury contained in the EP dust D collected by the electric dust collector 8, and any device capable of efficiently recovering mercury may be used. For example, the EP dust D collected by the electrostatic precipitator 8 is heated to a temperature at which mercury is volatilized or higher to volatilize the mercury in the EP dust D, and then recovers the volatilized mercury, or EP dust D is washed with water or water in which an oxidizing agent is dissolved, so that mercury contained in EP dust D is transferred to the liquid side, and the mercury transferred to the liquid side is recovered by an adsorbent such as a chelate resin. Can be provided.

  In the mercury recovery apparatus 9, the method of heating the EP dust D can be indirect heating or direct heating. As an apparatus for indirectly heating the EP dust D, for example, an external heating furnace can be used. On the other hand, as an apparatus for directly heating the EP dust D, for example, an internal heat type airflow furnace can be used. Here, the heat source for heating the EP dust D can be, for example, hot air generated by a hot air generator, but the clinker cooler attached to the cement kiln 2 or the exhaust gas from the preheater 3 or the cement kiln 2. The exhaust gas can also be used.

  In the case of indirect heating, the mercury concentration in the gas after heating the EP dust D can be increased by minimizing the amount of ventilation in the external heating furnace. On the other hand, in the case of direct heating, the EP dust can be efficiently heated by introducing the EP dust D into the duct through which hot air for heating the EP dust D flows so as to face the flow of hot air. Therefore, mercury can be efficiently volatilized to the gas side, and a part of organic pollutants (PCB or the like) can be recovered. When the EP dust D is directly heated in the airflow furnace, the heating efficiency is higher than in the case where the EP dust D is indirectly heated in the external heating furnace, and less heat energy is required.

  In the mercury recovery device 9, the method of recovering mercury volatilized by heating the EP dust D can be, for example, a dry method or a wet method. The dry method is adsorption recovery using an adsorbent. Mercury is adsorbed and recovered by passing mercury-containing gas through a tower packed with adsorbent. The adsorbent used is not limited as long as it can recover mercury, and the most well-known adsorbent is activated carbon. Further, as an adsorbent other than activated carbon, a metal that can react with mercury (amalgam-forming metal), an adsorbent carrying an amalgam-forming metal instead of them, or a combination thereof may be used. On the other hand, the wet method can be applied when volatilized mercury takes a water-soluble form. In this case, a gas containing water-soluble mercury can be wet-washed with a scrubber or the like, the mercury can be transferred to the liquid side, and the mercury transferred to the liquid side can be recovered by an adsorbent such as a chelate resin.

  Regarding the recovery of mercury volatilized by heating EP dust D, the above-mentioned before and after heating EP dust D when the wet method is to be applied even if the form of mercury volatilized from EP dust D is insoluble metal mercury. Mercury can be efficiently recovered by adding chlorine or a chlorine compound to exhaust gas and actively converting mercury volatilized from EP dust into water-soluble mercury chloride. If the hot air used to heat EP dust D contains a chlorine compound, the mercury chlorination reaction can be performed efficiently and efficiently by optimally controlling the amount of chlorine or chlorine compound added. Can do.

  Next, the operation of the cement kiln exhaust gas treatment system 1 having the above configuration will be described with reference to FIG.

During the operation of the cement kiln 2, the cement raw material R supplied to the preheater 3 is preheated by the preheater 3, calcined in the calcining furnace 5, and then calcined in the cement kiln 2 to generate cement clinker. On the other hand, the exhaust gas discharged from the cement kiln 2 is discharged from the preheater 3 through the kiln bottom 4 and the calcining furnace 5 of the cement kiln 2, and the exhaust gas G1 from the preheater is collected through a fan or the like (not shown). Introduced into the device 8.
Then, the circulation routes 11 to 14 are selected according to the mercury concentration and the organic pollutant concentration of the exhaust gas G1, and the EP dust D collected by the electric dust collector 8 is circulated in the following manner. Note that the exhaust gas G3 after the EP dust D is collected by the electric dust collector 8 is released to the atmosphere.

  When the mercury concentration and the organic pollutant concentration in the exhaust gas G1 are less than the predetermined values, the EP dust D is returned directly to the preheater 3 via the first circulation route 11. At this time, since the gas adsorbent A in the EP dust D circulates in the cement manufacturing apparatus, it is not necessary to add the gas adsorbent A from the gas adsorbent addition apparatus 7.

  Next, when the mercury concentration of the exhaust gas G1 is equal to or higher than the predetermined value and the organic pollutant concentration is lower than the predetermined value, it is necessary to reduce the mercury concentration, so EP dust D is supplied to the second circulation route 12. The mercury is collected by the mercury collecting device 9 and then returned to the preheater 3. Thereby, the mercury concentration of the exhaust gas G1 from the cement manufacturing apparatus can be reduced. In this case as well, since the organic pollutant concentration is less than the predetermined value, it is not necessary to add the gas adsorbent A as described above.

  Further, when the mercury concentration of the exhaust gas G1 is less than a predetermined value and the organic pollutant concentration is equal to or higher than the predetermined value, it is necessary to reduce the organic pollutant concentration, and therefore EP dust D is passed through the third circulation route 13. The organic pollutants in the EP dust D can be combusted and decomposed by directly returning the cement kiln 2 to the high temperature kiln bottom 4 at 900 to 1100 ° C. Thereby, the organic pollutant density | concentration of the waste gas G1 from a cement manufacturing apparatus can be reduced. Here, since a part of the gas adsorbent A contained in the EP dust D put into the kiln bottom 4 is combusted, the gas adsorbent A is added to the exhaust gas G1 by the gas adsorbent addition device 7.

  When the mercury concentration and the organic pollutant concentration in the exhaust gas G1 are equal to or higher than the predetermined values, it is necessary to reduce both the mercury and organic pollutant concentrations, and therefore EP dust D is supplied to the fourth circulation route 14 and the mercury. After the mercury is recovered by the recovery device 9, it is returned to the kiln bottom 4 of the cement kiln 2. Thereby, the mercury and organic pollutant density | concentration of the waste gas G1 from a cement manufacturing apparatus can be reduced. In this case as well, since part of the gas adsorbent A contained in the EP dust D put into the kiln bottom 4 is burned, the gas adsorbent A is added to the exhaust gas G1 as described above.

  As described above, according to the present embodiment, it is possible to comprehensively reduce both mercury and organic pollutants discharged from the cement manufacturing apparatus according to the mercury concentration and the organic pollutant concentration of the exhaust gas G1. .

  In the above embodiment, the electrostatic precipitator 8 is arranged to collect the dust contained in the exhaust gas G2 of the cement kiln 2, but instead of the electrostatic precipitator 8, a bag filter, a cyclone, a mobile type You may make it arrange | position dust collectors etc., collect the dust contained in waste gas G2 with these dust collectors, and convey them to each circulation route 11-14.

  During the operation of the cement kiln 2, the gas adsorbent A was added to the exhaust gas G1 by the gas adsorbent addition device 7 to adsorb organic pollutants. FIG. 2 shows the relationship between the hydrophobic solid unburned carbon content of EP dust D recovered by the dust collector 8 and the concentration of dioxins (DXNs) in the exhaust gas G3 of the dust collector 8 at that time. It is a graph which shows.

  Hydrophobic solid unburnt carbon content is obtained by liquid-liquid extraction of EP dust D using toluene, separating the solid components collected on the toluene side, treating with hydrochloric acid, and again performing solid-liquid separation. The weight of the dried substance (residue) is weighed to determine the residual rate based on the initial EP dust amount, and the following formula is calculated based on the residual rate and the measured carbon content in the residue: It calculated using.

Hydrophobic solid unburned carbon content (mass%) = measured carbon amount in residue (mass%) × residual fraction (mass%) / 100
As is clear from this graph, the concentration of dioxins in the exhaust gas G3 of the dust collector 8 decreases as the amount of hydrophobic solid unburned carbon in the EP dust D recovered by the dust collector 8 increases. It can be seen that it has a negative correlation. And the inlet duct of the dust collector 8 from the gas adsorbent addition device 7 so that the hydrophobic solid-state unburned carbon content of the dust dust D collected by the dust collector 8 becomes 0.2 mass% or more. The concentration of dioxins in the exhaust gas G3 can be reduced to an environmental standard of 0.1 ng-TEQ / m ³ N or less by introducing the adsorbent A into the gas.

DESCRIPTION OF SYMBOLS 1 Cement kiln exhaust gas processing system 2 Cement kiln 3 Preheater 4 Kiln bottom 5 Calciner 6 Boiler etc. 7 Gas adsorbent addition device 8 Electric dust collector 9 Mercury recovery device 11 First circulation route 12 Second circulation route 13 Third Circulation route 14 Fourth circulation route D EP dust G1-G3 Exhaust gas

Claims (4)

A gas adsorbent addition device for adding a gas adsorbent to the gas discharged from the preheater of the cement firing device;
A dust collector for collecting dust contained in the exhaust gas of the preheater;
A mercury recovery device for recovering mercury contained in the collected dust ;
A first circulation route for returning dust collected by the dust collector directly to the preheater;
A second circulation route for returning dust collected by the dust collector to the preheater via the mercury recovery device;
A third circulation route for returning the dust collected by the dust collector directly to the kiln bottom of the cement kiln;
A cement kiln exhaust gas treatment system comprising: a fourth circulation route for returning dust collected by the dust collector to the kiln bottom of the cement kiln via the mercury recovery device . The mercury collecting device heats the dust collected by the dust collecting device, collects the mercury volatilized by the heating, or cleans the collected dust, and collects the mercury transferred to the liquid side by the washing. The cement kiln exhaust gas treatment system according to claim 1 . An operation method of the cement kiln exhaust gas treatment system according to claim 1 or 2 ,
When the mercury concentration and organic pollutant concentration of the gas discharged from the preheater are less than predetermined values, the addition of the gas adsorbent is stopped and the dust is passed to the preheater via the first circulation route. Return,
When the mercury concentration of the gas discharged from the preheater is equal to or higher than a predetermined value and the organic pollutant concentration of the exhaust gas is lower than the predetermined value, the addition of the gas adsorbent is stopped and the dust is removed from the second heater. Return to the pre-heater via the circulation route,
When the mercury concentration of the gas discharged from the preheater is less than a predetermined value and the organic pollutant concentration of the exhaust gas is not less than a predetermined value, the gas adsorbent is added to the exhaust gas and is contained in the exhaust gas Dust is returned to the kiln bottom of the cement kiln via the third circulation route,
When the mercury concentration and the organic pollutant concentration in the exhaust gas from the preheater are equal to or higher than predetermined values, the gas adsorbent is added to the exhaust gas, and dust contained in the exhaust gas is routed through the fourth circulation route. Returning to the kiln bottom of the cement kiln, a method for operating a cement kiln exhaust gas treatment system. The operation method of the cement kiln exhaust gas treatment system according to claim 3 , wherein the content of the hydrophobic solid unburnt carbon in the dust collected by the dust collector is 0.2% by mass or more.

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