JP2010076973A - Apparatus and method for processing exhaust gas of cement kiln - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for efficiently removing mercury from a combustion exhaust gas exhausted from a cement kiln. <P>SOLUTION: The apparatus 1 for processing the exhaust gas of a cement kiln includes: a dust collecting device 2 collecting dust included in the exhaust gas of a cement kiln; and a mercury recovering device 19 heating the collected dust using the exhaust gas G4 of a chlorine bypass attached to cement firing equipment and recovering volatilized mercury. Upon the volatilization of mercury, a new heat source is not required. The collected dust can be heated with a gas passing through a solid-gas separating device subjecting a dust-containing gas of 300 to 700°C to solid-gas separation, and an injection device 13, injecting gaseous chlorine or hydrogen chloride into the exhaust gas of the chlorine bypass after the heating of the collected dust, may be equipped. By injecting gaseous chlorine or hydrogen chloride, the conversion of metal mercury in the dust into mercury chloride can be promoted together with hydrogen chloride in the exhaust gas of the chlorine bypass. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an apparatus and a method for removing mercury from combustion exhaust gas discharged from a cement kiln constituting a cement firing facility.

  Cement kiln exhaust gas contains a trace 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 recent years, the recycling of wastes as cement raw materials and fuels has been promoted, and as the amount of waste processed increases, the mercury concentration in the cement kiln exhaust gas may increase.

  However, it is extremely difficult to remove the mercury contained in the exhaust gas of cement kiln at a low concentration from a large amount of exhaust gas, and if the mercury in the exhaust gas of cement kiln increases, it may cause air pollution, There is also a risk of hindering the expansion of the use of recycled resources such as fly ash.

  Therefore, for example, Patent Document 1 discloses that a cement kiln is used to efficiently remove mercury and the like contained in exhaust gas discharged from a cement manufacturing process, and to recycle dust collection dust from which mercury and the like are removed as a cement raw material. Cement production that removes exhaust gas with a dust collector, then guides the collected dust to a heating furnace, heats the mercury in the dust to a volatilization temperature and volatilizes it, and then adsorbs it with an adsorbent and removes it. An exhaust gas treatment method has been proposed.

By the way, it is known that when the amount of chlorine (Cl) in exhaust gas from a boiler or the like increases, the proportion of divalent mercury that is soluble in water increases, and mercury is easily collected by a subsequent device. Conventionally, based on such findings, the addition of chlorine compounds such as CaCl ₂ to the fuel supplied to the boiler, the mercury removal system that attempts to improve the mercury removal rate in the desulfurization apparatus, and the like have been proposed (Patent Document 2 And 3).

Japanese Patent Laid-Open No. 2002-355531 JP 2004-313833 A JP 2006-263700 A

  However, in the treatment method described in Patent Document 1, after removing dust from the cement kiln exhaust gas with a dust collector, the collected dust is guided to a heating furnace, and the mercury in the dust is volatilized and removed. In addition to the need for a new heat source, the dust collection dust is indirectly heated by the outer periphery of the heating furnace, so the amount of mercury in the exhaust gas cannot be reduced efficiently.

  Then, this invention is made | formed in view of the problem in the said prior art, Comprising: It aims at efficiently removing mercury from the combustion exhaust gas discharged | emitted from a cement kiln.

  In order to solve the above-mentioned problem, the present invention is a cement kiln exhaust gas treatment device, a dust collector that collects dust contained in the exhaust gas of the cement kiln, and dust collected by the dust collector, A mercury recovery device is provided, which is heated using a chlorine bypass exhaust gas attached to a cement firing facility and recovers mercury volatilized by the heating.

  According to the present invention, the exhaust gas from the chlorine bypass is used, and the dust contained in the exhaust gas from the cement kiln and collected by the dust collector is heated. The cost required for removing mercury can be kept low. In addition, the chlorine bypass exhaust gas contains a small amount of hydrogen chloride, which is used to convert insoluble metal mercury in the dust into water-soluble mercury chloride. Can be simplified.

  The cement kiln exhaust gas treatment apparatus may include a dust supply device for supplying dust collected by the dust collector to the exhaust duct of the chlorine bypass and directly heating the dust. As a result, the dust collected by the dust collector can be directly heated by the exhaust gas from the chlorine bypass, so that the volatilization of mercury is promoted and more mercury can be recovered by the mercury recovery device at the subsequent stage. In the direct heating of the dust collected by the dust collector, the dust is introduced into the duct where the exhaust gas flow of the chlorine bypass becomes an upward flow so as to be opposite to the exhaust gas flow, and the upward air flow It is preferable to mix and heat the dust.

  In the above-described cement kiln exhaust gas treatment apparatus, the chlorine bypass exhaust gas for heating the dust collected by the dust collector passed through a solid-gas separation apparatus for solid-gas separation of dust-containing gas at 300 ° C. or higher and 700 ° C. or lower. It can be gas.

  Chlorine gas injection device for injecting chlorine gas into the chlorine bypass exhaust gas for heating the dust collected by the dust collector, or the chlorine bypass exhaust gas after heating the dust collected by the dust collector, or A hydrogen chloride injection device for injecting hydrogen chloride can be provided. By injecting chlorine gas or hydrogen chloride, conversion of mercury metal in the dust to mercury chloride can be promoted together with hydrogen chloride in the exhaust gas of the chlorine bypass.

  Furthermore, in the above-described cement kiln exhaust gas treatment apparatus, a solid-gas separation device that solid-gas separates dust-containing gas of 200 ° C. or more and 600 ° C. or less from the chlorine bypass after heating the dust collected by the dust collector. Can be provided. Thereby, most of the volatilized mercury from the dust collection dust can be present on the gas phase side. Moreover, the sensible heat of the exhaust gas of a chlorine bypass after heating dust collection dust can be utilized effectively as needed.

  The present invention also relates to a method for treating a cement kiln exhaust gas, which collects dust contained in the exhaust gas of the cement kiln and uses the dust obtained by the dust collection as exhaust gas from a chlorine bypass attached to a cement firing facility. It is characterized by recovering mercury that has been volatilized by the heating. According to the present invention, as in the case of the above-described invention, a new heat source is not required for volatilizing mercury in the dust collection dust, and the cost required for removing mercury can be kept low. A trace amount of hydrogen chloride is contained, and by using this to convert insoluble metal mercury in dust into water-soluble mercury chloride, the configuration of the subsequent mercury recovery apparatus can be simplified.

  Furthermore, the present invention is a method for treating cement kiln exhaust gas, wherein dust contained in the exhaust gas of the cement kiln is collected, and the dust obtained by the dust collection is exhausted from a chlorine bypass attached to a cement firing facility. Mercury volatilized by injecting chlorine gas or hydrogen chloride into the exhaust gas of the chlorine bypass, or by injecting chlorine gas or hydrogen chloride into the exhaust gas of the chlorine bypass after heating the exhaust gas of the chlorine bypass or the dust obtained by the dust collection It is characterized by collect | recovering. According to the present invention, by injecting chlorine gas or hydrogen chloride, conversion of metallic mercury in dust to mercury chloride can be promoted together with hydrogen chloride in the exhaust gas of the chlorine bypass.

  In the above cement kiln exhaust gas treatment method, chlorine gas or hydrogen chloride is injected into the exhaust gas of the chlorine bypass after heating the dust obtained by the dust collection, and upstream and downstream of the chlorine gas or hydrogen chloride injection point The concentration of metallic mercury and mercury chloride contained in the exhaust gas on the gas side is measured to calculate the conversion rate to mercury chloride, and the chlorine gas or chloride contained in the exhaust gas downstream of the chlorine gas or hydrogen chloride injection point is calculated. Measure the concentration of hydrogen, set the target value of the conversion rate to the mercury chloride, the target value of the concentration of the chlorine gas or hydrogen chloride, the conversion rate to the mercury chloride and the concentration of the chlorine gas or hydrogen chloride are The amount of chlorine gas or hydrogen chloride injected can be controlled by performing an optimization operation that approaches each of the target values. Thereby, the conversion rate of metallic mercury to mercury chloride and the concentration of chlorine gas or hydrogen chloride can be maintained optimally, and mercury can be efficiently removed from the combustion exhaust gas discharged from the cement kiln.

  As described above, according to the present invention, mercury can be efficiently removed from combustion exhaust gas discharged from a cement kiln at low cost.

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

  FIG. 1 shows an embodiment of a cement kiln exhaust gas treatment apparatus according to the present invention. This treatment apparatus 1 is roughly classified into an electric dust collector 2 for collecting dust contained in cement kiln exhaust gas, and a cement. From the kiln exhaust gas passage from the kiln bottom of the kiln (not shown) to the lowermost cyclone, the probe 4 for extracting while cooling a part of the combustion gas, and the combustion gas extracted by the probe 4 (extraction gas G1) The cyclone 6 for separating the coarse dust D1 contained in the gas, the solid-gas separator 7 for collecting the fine powder D2 contained in the exhaust gas G2 of the cyclone 6, and the exhaust gas G3 of the solid-gas separator 7 are conveyed downstream. Dust collected by the electrostatic precipitator 2 in an exhaust duct (hereinafter referred to as “duct”) 12 between the fan 9 and the cyclone 15 for the purpose (hereinafter referred to as “EP dust”). , A cyclone 15 that collects exhaust gas containing dust heated by the exhaust gas G4, a solid-gas separator 16 that collects the exhaust gas G5 of the cyclone 15, and a solid-gas separator 16 The heat exchanger 18 that recovers heat from the exhaust gas G6 and the mercury recovery device 19 that recovers mercury from the exhaust gas G7 that has passed through the heat exchanger 18 are configured. In addition, the treatment apparatus 1 includes concentration meters 10 and 14 for measuring concentrations of metallic mercury and mercury chloride in the exhaust gases G4 and G6, and a concentration for measuring the concentration of chlorine gas or hydrogen chloride in the exhaust gas G6. A total 17, an injection device 13 for injecting chlorine gas or hydrogen chloride into the duct 12, and an optimization calculator 20 for controlling the injection amount of chlorine gas or hydrogen chloride from the injection device 13 are provided.

  The electric dust collector 2 is normally used as a dust collector for cement kiln exhaust gas, and the probe 4, the cooling fan 5 and the cyclone 6 have the same configuration as that installed in a general chlorine bypass facility. Therefore, detailed description thereof will be omitted.

  The solid-gas separation device 7 is preferably a high heat-resistant bag filter having a ceramic filter and having heat resistance up to about 900 ° C. Various types of bug filters have been developed, such as those in which a plurality of rod-shaped ceramic tubes formed into honeycomb cells are arranged, and those using a sheet-like ceramic filter. In the present invention, exhaust gas is used. The type of filter is not particularly limited as long as it can collect fine particles contained in G2.

  The dust supply device 11 is provided to supply the EP dust conveyed from the electrostatic precipitator 2 to the duct 12, and includes a rotary feeder, a chute, a dispersion plate, and the like, and the EP dust is dispersed in the duct 12 to thereby provide a duct. The EP dust is efficiently heated by the exhaust gas G4 passing through 12.

  The injection device 13 is provided for injecting chlorine gas or hydrogen chloride into the exhaust gas G3 of chlorine bypass or the exhaust gas G4 containing EP dust heated by the exhaust gas of the fan 9. The injection form of hydrogen chloride may be a gas or an aqueous solution, and even if injected as an aqueous solution, it quickly gasifies in high-temperature exhaust gas.

  The cyclone 15 is provided for collecting the exhaust gas G4 into which chlorine gas or hydrogen chloride has been injected, and is configured in the same manner as the cyclone 6 described above.

  The solid gas separation device 16 is provided for collecting the exhaust gas G5 of the cyclone 15 and has the same configuration as the solid gas separation device 7.

  The concentration meter 17 is provided for measuring the concentration of chlorine gas or hydrogen chloride contained in the exhaust gas G6 of the solid-gas separation device 16, and the type of concentration meter is not particularly limited.

  The heat exchanger 18 is provided to effectively use the sensible heat of the solid-gas separation device 16 as necessary. Since there is volatilized mercury in the exhaust gas G6, in order to avoid recondensation of mercury, it is necessary to use a heat exchanger of a type that does not contact the exhaust gas G6 as the heat exchanger 18. The heat recovered by the heat exchanger 18 can be used as a heat source for a steam boiler or a heat source for air preheating.

  The mercury recovery device 19 is provided to remove mercury (mainly mercury chloride) in the exhaust gas G6. As the mercury recovery device 19, either a dry type or a wet type recovery device can be used. However, since the mercury converted into hydrogen chloride is water-soluble, by using the wet mercury recovery device, Mercury components can be effectively removed from In the case of using a dry adsorption device, particularly activated carbon as an adsorption medium, it is necessary to lower the temperature of the exhaust gas G7 to about 100 ° C. through the heat exchanger 18. On the other hand, when a wet gas absorption device is used as the mercury recovery device 19, the exhaust gas G6 does not necessarily have to pass through the heat exchanger 18, and can be directly introduced into the mercury recovery device 19.

  The optimization computing unit 20 calculates the conversion rate to mercury chloride from the measured values of metallic mercury and mercury chloride by the concentration meters 10 and 14, and measures the target value of the conversion rate set in advance and the concentration meter 17. The concentration of the chlorine gas or hydrogen chloride and the preset concentration are optimized so as to approach the respective target values, and the amount of chlorine gas or hydrogen chloride injected from the injection device 13 is controlled. Provided for.

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

  During the operation of the cement kiln, the cement kiln exhaust gas is collected by the electric dust collector 2, and transferred to the dust supply device 11 to remove mercury contained in the collected EP dust.

  During operation of the cement kiln, part of the combustion gas is extracted by the probe 4 from the kiln exhaust gas flow path from the bottom of the kiln kiln to the lowermost cyclone, and at the same time, the extracted gas is reduced by the cold air from the cooling fan 5. Rapidly cool to below 700 ° C. Next, the extraction gas G1 exhausted from the probe 4 is separated into the coarse powder D1 and the exhaust gas G2 containing the fine powder D2 in the cyclone 6, and the coarse powder D1 is returned to the cement kiln system.

  On the other hand, the exhaust gas G2 from which the coarse powder D1 has been removed is introduced into the solid-gas separation device 7, and the fine powder (chlorine bypass dust) D2 containing potassium chloride and the like of the exhaust gas G2 is recovered. The collected fine powder D2 is stored in the dust tank 8 and then used in a cement pulverization process or washed with water and then used as a cement raw material.

  The exhaust gas G3 from which the fine powder D2 has been removed is introduced into the cyclone 15 via the fan 9 and the duct 12. Here, in the duct 12, the EP dust supplied from the dust supply device 11 is heated by the exhaust gas G3 to volatilize mercury contained in the EP dust.

  Next, chlorine gas or hydrogen chloride is injected into the exhaust gas G4 containing the EP dust heated by the exhaust gas of the fan 9 by the injection device 13, and the metal mercury volatilized from the EP dust is converted into water-soluble mercury chloride. Here, in the optimization computing unit 20, a target value for the conversion rate from metallic mercury to mercury chloride and a target value for the concentration of chlorine gas or hydrogen chloride in the exhaust gas G6 are set in advance. Then, the concentration of metallic mercury and mercury chloride is measured by the concentration meters 10 and 14, and the concentration of chlorine gas or hydrogen chloride is measured by the concentration meter 17, and the measured value is input to the optimization calculator 20 as needed. Then, the conversion rate to mercury chloride is calculated from the measured concentrations of metallic mercury and mercury chloride. It is desirable to maintain the actual measurement value so as to clear the target value. On the other hand, the value of chlorine gas or hydrogen chloride measured by the densitometer 17 is preferably maintained at a level lower than the target value so that excessive chlorine gas or hydrogen chloride is not injected. In this way, an appropriate injection amount is calculated by the optimization calculator 20 based on the input values measured by the densitometers 10, 14, and 17, their fluctuation behaviors, and preset target values. The injection amount of chlorine gas or hydrogen chloride is optimally controlled so as to approach the set target value. The target value of the conversion rate from metallic mercury to mercury chloride is set to an arbitrary value depending on the mercury content in the EP dust, the processing equipment and its operating conditions, but is generally set to 80% or more.

  Next, the exhaust gas G4 containing EP dust and volatilized mercury is introduced into the cyclone 15, and the dust D3 collected by the cyclone 15 is returned to the cement kiln raw material system. On the other hand, the exhaust gas G5 containing 200 to 600 ° C. containing volatilized mercury is introduced into the solid-gas separation device 16, and the dust D4 recovered by the solid-gas separation device 16 can be used as a raw material for cement kiln or dust. It may be supplied to the duct 12 via the supply device 11 and reheated.

  Next, after the exhaust gas G6 of the solid-gas separation device 16 is introduced into the heat exchanger 18 and the sensible heat of the solid-gas separation device 16 is effectively used, the exhaust gas G6 is introduced into the mercury recovery device 19 and is contained in the exhaust gas G6. Of mercury (mainly mercury chloride) is removed. It is also possible to remove mercury by directly introducing it into the mercury recovery device 19 using a gas absorption device without introducing the exhaust gas G6 into the heat exchanger 18. Mercury is removed in the mercury recovery device 19 and the detoxified exhaust gas G8 is released into the atmosphere or returned to the kiln system.

  As described above, according to the present embodiment, since the EP dust collected by the electrostatic precipitator 2 is heated using the chlorine bypass exhaust gas, a new heat source is required for volatilizing mercury in the EP dust. However, the cost required for removing mercury can be kept low. In addition to this, by injecting chlorine gas or hydrogen chloride into the exhaust gas of the chlorine bypass after heating the EP dust, together with hydrogen chloride in the exhaust gas of the chlorine bypass, mercury chloride of metallic mercury in the dust Conversion to (water-soluble) can be promoted, and mercury components can be effectively removed from the exhaust gas by using a wet mercury recovery device.

  In the above embodiment, the electrostatic precipitator 2 is arranged at the subsequent stage of the cement kiln. Instead of the electrostatic precipitator 2, a bag filter, a cyclone, a mobile dust collector, etc. are arranged, and the dust collector is used for cement. Dust contained in the kiln exhaust gas may be collected and conveyed to the duct 12 via the dust supply device 11.

  Further, as the mercury recovery device 19, a gas absorption device using an absorbing solution or a gas adsorption device that adsorbs and removes mercury with an adsorbent can be used. Specifically, a cartridge type stationary phase adsorption device, a continuous cross flow, and the like. A type of bed transfer adsorption device or the like can be used. At this time, as the adsorbent, it is preferable to use sulfur or a metal sulfide, an adsorption medium carrying activated carbon or activated carbon, an adsorption medium carrying a metal that reacts with mercury or mercury, or the like. In this case, an adsorbent is blown into the exhaust gas G7 of the heat exchanger 18 to adsorb and remove the gasified mercury and remove the mercury from the exhaust gas G7. The adsorbent that has adsorbed mercury is collected and subjected to an appropriate final treatment. As a preferable final processing method, for example, consignment processing to a company or an organization that specializes in mercury recycling processing can be mentioned.

  Furthermore, by using an adsorption device using activated carbon, activated coke, or the like for the mercury recovery device 19, in addition to mercury, harmful substances represented by organic chlorine compounds such as trace amounts of dioxin and PCB contained in the extraction gas G1 Can also be removed by adsorption.

  In the above embodiment, after the coarse powder D1 is classified by the cyclone 6, the exhaust gas G2 containing the fine powder D2 is introduced into the solid-gas separation device 7, but the extraction gas extracted by the probe 4 without providing the cyclone 6. The gas G1 may be directly introduced into the solid-gas separation device 7.

It is a flowchart which shows one Embodiment of the processing apparatus of the cement kiln exhaust gas concerning this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cement kiln exhaust gas processing device 2 Electric dust collector 4 Probe 5 Cooling fan 6 Cyclone 7 Solid gas separation device 8 Dust tank 9 Fan 10 (Metal mercury concentration meter and mercury chloride) Concentration meter 11 Dust supply device 12 Duct 13 Injection device 14 (metal mercury concentration meter and mercury chloride) concentration meter 15 cyclone 16 solid-gas separator 17 (chlorine gas or hydrogen chloride) concentration meter 18 heat exchanger 19 mercury recovery device 20 optimization calculator D1 coarse powder D2 fine powder D3, D4 Dust G1 Extraction gas G2 to G8 Exhaust gas

Claims (8)

A dust collector for collecting dust contained in the exhaust gas of the cement kiln;
A cement comprising: a mercury collecting device that heats the dust collected by the dust collecting device using an exhaust gas from a chlorine bypass attached to a cement firing facility and collects the mercury volatilized by the heating. Kiln exhaust gas treatment equipment.   The dust of the cement kiln exhaust gas according to claim 1, further comprising a dust supply device for supplying dust collected by the dust collector to an exhaust duct of the chlorine bypass and directly heating the dust. Processing equipment.   The exhaust gas of the chlorine bypass that heats the dust collected by the dust collector is a gas that has passed through a solid-gas separation device that solid-gas separates a dust-containing gas of 300 ° C or higher and 700 ° C or lower. Item 3. A cement kiln exhaust gas treatment apparatus according to Item 1 or 2.   Chlorine gas injection device for injecting chlorine gas into the chlorine bypass exhaust gas for heating the dust collected by the dust collector, or the chlorine bypass exhaust gas after heating the dust collected by the dust collector, or 4. The cement kiln exhaust gas treatment device according to claim 1, further comprising a hydrogen chloride injection device for injecting hydrogen chloride.   5. A solid-gas separation device that solid-gas separates a dust-containing gas of 200 ° C. or more and 600 ° C. or less from a chlorine bypass after heating the dust collected by the dust collector. The cement kiln exhaust gas treatment apparatus according to any one of the above. Collect dust contained in the exhaust gas of cement kiln,
The dust obtained by the dust collection is directly heated using the exhaust gas from the chlorine bypass attached to the cement firing facility,
A method for treating a cement kiln exhaust gas, comprising collecting mercury volatilized by the heating. Collect dust contained in the exhaust gas of cement kiln,
The dust obtained by the dust collection is directly heated using the exhaust gas from the chlorine bypass attached to the cement firing facility,
And, chlorine gas or hydrogen chloride is injected into the exhaust gas of the chlorine bypass, or the exhaust gas of the chlorine bypass after heating the dust obtained by the dust collection,
A method for treating a cement kiln exhaust gas, comprising recovering mercury volatilized by the heating. Injecting chlorine gas or hydrogen chloride into the exhaust gas of the chlorine bypass after heating the dust obtained by the dust collection,
Measure the concentration of mercury metal and mercury chloride contained in the exhaust gas upstream and downstream of the chlorine gas or hydrogen chloride injection point to calculate the conversion rate to mercury chloride,
Measure the concentration of chlorine gas or hydrogen chloride contained in the exhaust gas downstream of the chlorine gas or hydrogen chloride injection point,
Set the target value of the conversion rate to the mercury chloride, the target value of the concentration of the chlorine gas or hydrogen chloride,
The conversion rate to the mercury chloride and the concentration of the chlorine gas or hydrogen chloride are controlled so as to approach the respective target values to control the injection amount of the chlorine gas or hydrogen chloride. The processing method of the cement kiln exhaust gas of Claim 6 or 7.

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