JP2011105985A - Method for treating exhaust gas in sintering machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for treating exhaust gas in a sintering machine of an exhaust gas circulation system, in which desulfurization and denitrification efficiency is further improved while securing a heat recovery rate while dealing with the increase of the content of moisture in exhaust gas generated from a sintering process accompanying the increase of the using amount of high crystallization water ore. <P>SOLUTION: When the space between the rear part of an ignition furnace 2 and an ore discharge part 3 in a sintering machine 1 is divided into two of a front region A and a rear region B, exhaust gas having a high temperature-high SO<SB>x</SB>concentration from the rear region B (hereinafter referred to as high temperature circulation gas) is circulated onto the pallet 4 of the front region A as it is, and further, exhaust gas 21 having a low temperature-high NOx concentration (hereinafter referred to as low temperature exhaust gas) from the front region A is simultaneously subjected to desulfurization and denitrification by a dry desulfurization-denitrification apparatus 14, and is thereafter exhausted, the divided position between the front region A and the rear region B is adjusted in such a manner that the temperature of the low temperature exhaust gas 21 reaches the acid dew point of the low temperature exhaust gas 21 or more, and also reaches the ignition temperature of the activated carbon in the dry type desulfurization-denitrification apparatus 14 or less. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for treating exhaust gas from an exhaust gas circulation type sintering machine, and more particularly to an exhaust gas treatment method for improving the efficiency of desulfurization / denitration from exhaust gas.

  The raw materials for the sintered ore are fine iron ore as an iron source, dust collection dust, mill scale, limestone as a solvent, dolomite, fine coke as solid fuel, anthracite, and the like. A mixture of these is tumbled and granulated together with water and a binder in a drum mixer, and is used as a sintering raw material composed of particles having an average particle diameter of 3 to 4 mm containing predetermined moisture. This sintering raw material is supplied to a sintering machine and is continuously sintered by a downward suction type sintering machine (DL type sintering machine).

  In recent years, in order to reduce the amount of exhaust gas and NOx total exhausted out of the sintering machine from the viewpoint of environmental conservation, and to improve the heat recovery and productivity of exhaust gas, exhaust gas circulation can be used instead of the conventional air suction method. The method of operation is widely adopted. Here, the sintering operation method by the exhaust gas circulation method is to divide the wind box group of the DL type sintering machine in the longitudinal direction of the sintering machine as appropriate, and circulate a part of the exhaust gas generated by the sintering onto the pallet of the sintering machine. Some of them are operated by sucking instead of the atmosphere.

  However, since the raw material of sintered ore is granulated by adding moisture, the exhaust gas generated from the sintering process contains a large amount of moisture. When the exhaust gas containing a large amount of water is circulated and used in this way, there is a problem that the moisture concentration in the exhaust gas further increases, the acid dew point of the exhaust gas increases, and the risk of corrosion of the device further increases.

  Therefore, various countermeasures have been proposed to solve the above problems.

  For example, Patent Document 1 discloses that the exhaust gas having a high temperature and high SOx concentration in the latter half of the sintering process is cooled and desulfurized and then introduced into the first half of the sintering process, and together with the introduced gas, the first half of the sintering process. A method of denitrating exhaust gas having a low temperature and a low SOx concentration is disclosed.

  According to this method, it is considered that by desulfurizing the exhaust gas having a high SOx concentration before circulation, the SOx concentration in the exhaust gas can be lowered, and the acid dew point can be lowered to prevent the apparatus corrosion.

  However, in this method, since the exhaust gas having a high temperature is cooled and then returned to the sintering process, the sensible heat of the exhaust gas cannot be effectively recovered, and desulfurization and denitration must be performed separately. There are problems such as an increase in equipment cost and complicated control.

  Further, in Patent Document 2, the space from after the ignition furnace of the sintering machine to the discharge portion is divided into a front region, a middle region, and a rear region, and the exhaust gas from the front region is dehumidified, Most of the oxygen is enriched and circulated on the pallet in the front area, and the remaining exhaust gas after dehumidification is denitrated and exhausted, while the exhaust gas from the rear area remains as it is in the middle and rear pallets. A method is disclosed in which the exhaust gas circulated upward and exhausted from the middle region is exhausted without denitration.

  According to this method, after dehumidifying the exhaust gas having a high moisture concentration in the front region, it is circulated in the sintering process or exhausted after denitration, so that the moisture concentration in the exhaust gas can be lowered and the acid dew point is lowered. It is considered that the corrosion of the apparatus can be prevented.

  However, in this method, a condenser for dehumidification is separately required, and when desulfurization is necessary, desulfurization is performed from the exhaust gas from the middle region. As in Patent Document 1, desulfurization and denitration are performed. Are required to be performed by different devices, and there are problems such as an increase in equipment cost and complicated control.

JP 58-170523 A JP 2007-270202 A

  Therefore, the present invention further improves the desulfurization / denitration efficiency while ensuring the heat recovery efficiency while responding to the increase in the amount of moisture in the exhaust gas generated from the sintering process accompanying the increase in the amount of high crystal water ore used. An object of the present invention is to provide an exhaust gas treatment method for an exhaust gas circulation type sintering machine.

  According to the first aspect of the present invention, the space from after the ignition furnace of the downward suction type sintering machine to the discharge portion is divided into a front region and a rear region, and exhaust gas having a high temperature and high SOx concentration from the rear region ( Hereinafter, the high-temperature circulating gas is circulated as it is on the pallet in the front area, and the low-temperature high NOx concentration exhaust gas (hereinafter referred to as “low-temperature exhaust gas”) from the front area is dry desulfurization denitration equipment. When the exhaust gas is exhausted after performing desulfurization and denitration at the same time, the temperature of the low temperature exhaust gas is not less than the acid dew point of the low temperature exhaust gas and not more than the ignition temperature of the activated carbon of the dry desulfurization denitration apparatus. It is the processing method of the exhaust gas of a sintering machine characterized by adjusting the division position of a zone and a rear zone.

In the invention according to claim 2, the ignition temperature of the activated carbon of the dry desulfurization denitration apparatus is 130 ° C., and the acid dew point of the low temperature exhaust gas is calculated by the following formula 1 according to the SO ₃ concentration and the water concentration in the low temperature exhaust gas. It is the processing method of the exhaust gas of a sintering machine of Claim 1 which is set as the value made into.
Formula 1 [acid dew point of low-temperature exhaust gas (° C.)] = 20 × log [SO ₃ concentration in low-temperature exhaust gas (volume%)] + 35.4 × log [water concentration in low-temperature exhaust gas (volume%)] + 80

The invention according to claim 3 adjusts the division positions of the front region and the rear region so as to satisfy the following formula 2 according to the content of crystallization water in the sintering raw material supplied to the sintering machine. It is a processing method of the sintering machine exhaust gas of Claim 2.
Formula 2 13% ≦ [exhaust gas circulation rate (%)] ≦ 30−0.67 × [content of crystal water in sintering raw material (mass% [dry basis])]
Here, exhaust gas circulation rate (%) = [length of rear region] / [total length of front region and rear region] × 100.

  According to the present invention, the high-temperature exhaust gas from the rear region is circulated as it is (without cooling) on the pallet in the front region, so that the sensible heat of the high-temperature circulation gas can be effectively recovered and the front region Since the exhaust gas having a low temperature and high NOx concentration is exhausted after performing desulfurization and denitration simultaneously in a dry desulfurization denitration apparatus, the equipment cost can be reduced and the control can be simplified. Further, only the exhaust gas from the rear region having a low moisture concentration is circulated to suppress an increase in the moisture concentration in the exhaust gas from the front region, and the temperature of the low temperature exhaust gas from the front region is at or above the acid dew point, and Since the dry desulfurization denitration apparatus is kept below the ignition temperature of activated carbon, neither the problem of apparatus corrosion nor the problem of apparatus trouble due to activated carbon combustion occurs.

It is a flowchart which shows schematic structure of the exhaust gas circulation system sintering equipment which concerns on embodiment. It is a graph which shows the relationship between an exhaust gas circulation rate, the temperature of a low-temperature exhaust gas, and a water concentration. It is a graph which shows the relationship between a waste gas circulation rate, the temperature of a low temperature waste gas, and an acid dew point. It is a graph which shows the relationship between the crystallization water content in a sintering raw material, and the suitable range of exhaust gas circulation rate.

  Hereinafter, the present invention will be described in more detail with reference to the drawings.

(Embodiment)
FIG. 1 shows a schematic configuration of an exhaust gas circulation type sintering facility according to an embodiment of the present invention.

  As shown in the figure, the space from after the ignition furnace 2 of the downward suction type sintering machine 1 to the discharge portion 3 is divided into a front region A and a rear region B. The position of the division is such that the temperature of the front area exhaust gas 21 sucked by the wind box group in the front area A, which will be described later, is equal to or higher than the acid dew point of the front area exhaust gas 21, and the dry desulfurization denitration apparatus 14 described later. For example, each distribution of exhaust gas flow rate, moisture concentration, oxygen concentration, etc. in the longitudinal direction of the sintering machine obtained by measurement in each wind box in the past operation is used so that it is below the ignition temperature of the activated carbon used in It may be determined by calculating the material balance.

  Then, the high-temperature exhaust gas 22 sucked by the wind box group in the rear region B is pressurized by the booster blower 13, and the rear region circulation gas 22 ′, which is the exhaust gas after the pressure increase, is not cooled and is directly cooled. It is introduced (circulated) into the front region circulation gas hood 5 installed on the pallet 4 in the region A, and is again sucked into the sintering bed.

  Further, the low-temperature front area exhaust gas 21 sucked in the wind box group in the front area A is gradually dusted by the dust collector 11, and after the SOx and NOx are removed by the dry desulfurization denitration device 14 via the main exhaust fan 12. Released into the atmosphere.

  Here, as the dry desulfurization denitration apparatus 14, a known apparatus for adsorbing or decomposing SOx and NOx using activated carbon as a catalyst can be used.

  In this way, since the high-temperature exhaust gas 22 from the rear region B is introduced (circulated) as it is into the sintering bed in the front region A without being cooled, the sensible heat of the high-temperature circulating gas can be effectively recovered.

  The exhaust gas 22 from the rear region B contains high concentration of SOx, but is introduced (circulated) as it is into the sintering bed of the front region A without being desulfurized. The exhaust gas 21 contains not only NOx at a high concentration but also SOx at a high concentration. The exhaust gas 21 having such a high SOx and high NOx concentration from the front area A is exhausted after being simultaneously desulfurized and denitrated by the dry desulfurization / denitrification apparatus 14, so that the equipment cost can be reduced and the control can be simplified.

  Further, only the exhaust gas 22 from the rear region B having a low moisture concentration is circulated to suppress an increase in the moisture concentration in the exhaust gas 21 from the front region A, and the division positions of the front region A and the rear region B are adjusted. By doing so, the temperature of the low temperature exhaust gas 21 from the front area A is kept above the acid dew point and below the ignition temperature of the activated carbon of the dry desulfurization denitration device 14, so that the problem of device corrosion is also activated carbon. There is no problem of equipment trouble due to combustion.

  The ignition temperature of the activated carbon of the dry desulfurization denitrification apparatus 14 varies depending on the type of activated carbon used, but is preferably set to 130 ° C. for safety.

The acid dew point of the low-temperature exhaust gas 21 varies depending on the SO ₃ concentration and the water concentration in the low-temperature exhaust gas 21. For example, a well-known calculation formula generally referred to as an Otsuka equation (Japanese Patent Laid-Open No. 2003-106796 [ [0007] can be estimated by the following formula 1 obtained by modifying FIG.

Formula 1 [acid dew point of low-temperature exhaust gas (° C.)] = 20 × log [SO ₃ concentration in low-temperature exhaust gas (volume%)] + 35.4 × log [water concentration in low-temperature exhaust gas (volume%)] + 80

  Here, in recent years, with the depletion of high-quality iron ore, the amount of high crystal water ore (pisolite ore) that has not been used so far in the production of sintered ore has increased. As the amount of high crystal water ore used increases, the amount of moisture generated by the crystal water decomposition increases, so the amount of moisture contained in the exhaust gas generated from the sintering process tends to increase.

  Therefore, it is desirable to keep the moisture concentration in the low temperature exhaust gas 21 properly by adjusting the division position of the front region A and the rear region B according to the content of crystal water in the sintered raw material.

  For example, when the content of crystallization water in the sintering raw material increases, the division position of the front area A and the rear area B is moved to the side of the exhausting section 3 to circulate exhaust gas having a lower moisture concentration. What is necessary is just to suppress the raise of the moisture concentration in the low temperature exhaust gas 21.

  However, if the division position of the front area A and the rear area B is brought too close to the exhausting section 3 side, the temperature of the circulating high temperature exhaust gas 22 becomes high, so the temperature of the low temperature exhaust gas 21 also rises, and the dry desulfurization denitration device 14 The risk of exceeding the ignition temperature of activated carbon increases.

  Then, the following analysis was performed in order to determine the division | segmentation position of the front part area A and the rear part area B more accurately according to the crystal water content in a sintering raw material.

  That is, in the sintering machine installed in the applicant's Kakogawa Works, in the sintering raw material based on the distribution data of the exhaust gas temperature and moisture concentration in the longitudinal direction of the sintering machine 1 measured in the past operation. When the content of crystallization water (mass% [dry basis)] is sequentially changed, the change in exhaust gas moisture concentration distribution is calculated by mass balance calculation (even if the content of crystallization water in the sintering raw material changes). It is assumed that the amount of grain moisture does not change.) Based on the prediction calculation result, the division position of the front area A and the rear area B, that is, the exhaust gas circulation rate, the temperature and the moisture concentration of the low temperature exhaust gas 21 And estimated the relationship. In addition, exhaust gas circulation rate (%) = [length of rear region] / [total length of front region and rear region] × 100.

  The result is shown in FIG. As shown in the figure, as the exhaust gas circulation rate increases, the temperature of the low temperature exhaust gas 21 decreases, while the moisture concentration in the low temperature exhaust gas 21 tends to increase. Moreover, the water concentration in the low temperature exhaust gas 21 is increasing with the increase in the content of crystal water in the sintered raw material. The exhaust gas temperature distribution in the longitudinal direction of the sintering machine 1 does not change so much even if the content of crystallization water in the sintering raw material changes, and therefore the temperature of the low temperature exhaust gas 21 is almost determined only by the exhaust gas circulation rate. Only one curve is shown inside.

Next, the SO ₃ concentration in the low temperature exhaust gas 21 is 0.1 volume% (constant) based on the past operation results, and the SO ₃ concentration (= 0.1 volume%) in the low temperature exhaust gas 21 is expressed in the above formula 1. By substituting the water concentration shown in FIG. 2, the water concentration was converted into an acid dew point, and the relationship between the exhaust gas circulation rate, the temperature of the low temperature exhaust gas 21 and the acid dew point was re-plotted in FIG.

  In the same figure, in order to maintain the temperature of the low temperature exhaust gas 21 at 130 ° C. or less of the activated carbon of the dry desulfurization denitrification apparatus 14, the exhaust gas circulation rate is 13% regardless of the crystallization water content in the sintered raw material. It turns out that it is necessary to do it above. On the other hand, in order to maintain the temperature of the low temperature exhaust gas 21 at a temperature equal to or higher than the acid dew point, it is necessary to lower the upper limit of the exhaust gas circulation rate as the crystallization water content in the sintered raw material increases.

  The upper and lower limits of the temperature of the low temperature exhaust gas 21 obtained in FIG. 3 are plotted in FIG. The exhaust gas circulation rate, that is, the front region A and the rear region is satisfied so as to satisfy the following formula 2 in accordance with the content of crystal water in the sintering raw material so as to be within the range shown as the preferred range in the figure. It is recommended to adjust the division position of B.

Formula 2 13% ≦ [exhaust gas circulation rate (%)] ≦ 30−0.67 × [content of crystal water in sintering raw material (mass% [dry basis])]
Here, exhaust gas circulation rate (%) = [length of rear region] / [total length of front region and rear region] × 100.

1: Sintering machine 2: Ignition furnace 3: Exhaust section 4: Pallet 5: Front zone circulating gas hood 11: Dust collector 12: Main exhaust fan 13: Booster blower 14: Dry desulfurization denitration device 21: From the front zone Exhaust gas (low temperature exhaust gas)
22: Exhaust gas from the rear region (high temperature exhaust gas, rear region circulation gas, high temperature circulation gas)
22 ': Rear region circulating gas after pressure increase A: Front region B: Rear region

Claims (3)

  The space from after the igniting furnace of the downward suction type sintering machine to the discharge portion is divided into a front region and a rear region, and exhaust gas having a high temperature and high SOx concentration from the rear region (hereinafter referred to as “high temperature circulation gas”). ) Was circulated on the pallet in the front area as it was, and the low-temperature high NOx concentration exhaust gas (hereinafter referred to as “low-temperature exhaust gas”) from the front area was simultaneously desulfurized and denitrated with a dry desulfurization denitration device. When exhausting later, the division position of the front and rear regions is adjusted so that the temperature of the low-temperature exhaust gas is not less than the acid dew point of the low-temperature exhaust gas and not more than the ignition temperature of the activated carbon of the dry desulfurization denitration device. A method for treating exhaust gas from a sintering machine. The ignition temperature of the activated carbon of the dry desulfurization denitrification apparatus is 130 ° C., and the acid dew point of the low temperature exhaust gas is a value calculated by the following formula 1 according to the SO ₃ concentration and moisture concentration in the low temperature exhaust gas. The processing method of exhaust gas of a sintering machine as described.
Formula 1 [acid dew point of low-temperature exhaust gas (° C.)] = 20 × log [SO ₃ concentration in low-temperature exhaust gas (volume%)] + 35.4 × log [water concentration in low-temperature exhaust gas (volume%)] + 80 3. The sintering machine according to claim 2, wherein the division positions of the front region and the rear region are adjusted so as to satisfy the following formula 2 according to the content of crystal water in the sintering raw material supplied to the sintering machine. Exhaust gas treatment method.
Formula 2 13% ≦ [exhaust gas circulation rate (%)] ≦ 30−0.67 × [content of crystal water in sintering raw material (mass% [dry basis])]
Here, exhaust gas circulation rate (%) = [length of rear region] / [total length of front region and rear region] × 100.

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