JP5540658B2 - Thermal energy recovery method for exhaust gas generated from metallurgical furnace - Google Patents

Description

  The present invention relates to a method for recovering the thermal energy of carbon dioxide-containing exhaust gas generated from metallurgical furnaces such as converters, smelting reduction furnaces, and electric furnaces, and more particularly to the sensible heat of high-temperature exhaust gas. Utilizing it to lead to an efficient reforming reaction between the reducing agent supplied from the outside and carbon dioxide in the exhaust gas, effective in increasing the thermal energy of the recovered exhaust gas and reducing the carbon dioxide emission New technology.

  In recent years, reducing carbon dioxide emissions has become an important issue in order to protect the global environment and prevent global warming. In particular, at steelworks, the success or failure of reducing carbon dioxide emissions has become the most important issue related to the existence of companies. Conventionally, various proposals have been made for this purpose, but a full-fledged carbon dioxide reduction technology has not yet been completed.

  In general, steelworks generate high-temperature exhaust gas containing a large amount of carbon dioxide gas from converters, smelting reduction furnaces, and the like. Since these exhaust gases contain carbon monoxide and hydrogen in addition to carbon dioxide, they are also used as energy sources for operating various facilities in the steelworks. From the viewpoint of utilizing the sensible heat of such high-temperature exhaust gas, it is also common to recover waste heat by supplying low pressure steam to a boiler. However, the utility value of low-pressure steam at steelworks is low, and it is rather desirable to be able to use hot exhaust gases chemically.

  By the way, it is known that various hydrocarbons such as methane and oxygen-containing compounds such as methanol and dimethyl ether react with carbon dioxide gas or steam to be reformed to carbon monoxide or hydrogen. As a waste heat recovery technique using this reaction, Patent Document 1 discloses a gas and / or liquid containing hydrocarbons in a high-temperature exhaust gas containing carbon dioxide and / or steam generated from a refining facility such as a converter. Has been disclosed to increase the carbon monoxide and hydrogen in the exhaust gas, thereby increasing the latent heat of the exhaust gas.

  By the way, in this literature 1, when natural gas is blown into the converter exhaust gas and the reforming reaction of the following formula (1) is performed, the temperature at the position where this reaction is considered to be completed is about 375 ° C. It proposes a method of recovering by lowering to a minimum. However, according to the studies by the inventors, when the completion temperature of the reforming reaction is lower than about 800 ° C., the generation of carbon becomes significant, and the carbon and dust are likely to be deposited in the exhaust gas recovery facility. I found out there was a problem. In addition, when the completion temperature of the reforming reaction is lowered, the reforming reaction efficiency is lowered and the conversion rate of carbon dioxide is also lowered.

CH ₄ + CO ₂ → 2CO + 2H ₂ (1)

  In Patent Document 2, coal is supplied to a position where the temperature of the gas discharged from the converter is 600 ° C. or higher, and the exhaust gas and the coal are brought into opposing contact with each other, whereby the reforming reaction of the following formula (2) is performed. A method of increasing the heat of exhaust gas by generating carbon monoxide by performing the method is disclosed.

CO ₂ + C → 2CO (2)

The method disclosed in Document 2 is excellent in that the reforming reaction is performed using inexpensive coal. However, according to the study by the inventors, the completion temperature of the reforming reaction is lower than 800 ° C. , Instead of the equilibrium reaction according to the above equation (2) during the reforming reaction, the disproportionation reaction (Budard reaction) as in the following equation (3) occurs, and carbon is likely to precipitate, resulting in a decrease in reaction efficiency. I understood that. As a result, not only carbon but also dust (non-combustible components such as SiO ₂ and Al ₂ O ₃ ) are easily deposited in the exhaust gas recovery duct, and the reforming reaction efficiency itself is reduced and carbon dioxide is converted. It was found that the rate also declined.

_{2CO → CO 2 + C (3} )

JP 2000-212615 A Japanese Patent Laid-Open No. 5-117668

  As described above, the conventional technology uses the sensible heat of the carbon dioxide-containing exhaust gas generated from a metallurgical furnace such as a converter to increase the latent heat of the exhaust gas (reaction generation of the endothermic component of formula (1)). It accumulates in the form of combustion heat of things). In the conventional technology for increasing the heat, the generation of carbon becomes remarkable as the reaction temperature decreases, which not only decreases the efficiency of the carbon dioxide reforming reaction, but also causes the precipitation of carbon and decreases the increase in the heat of recovered exhaust gas. And there was a problem that the reduction effect of CO2 emission reduction occurred.

  Accordingly, an object of the present invention is to provide a metallurgical furnace capable of reliably achieving carbon dioxide gas emission reduction with increasing heat of exhaust gas without incurring carbon generation accompanying the lowering of the reforming reaction temperature and lowering of reaction efficiency. The purpose is to propose a thermal energy recovery method for the generated exhaust gas.

In order to overcome the above-mentioned problems of the prior art and simultaneously achieve an increase in exhaust gas heat generation and a reduction in carbon dioxide emission, the present invention adds a reducing agent into the recovery duct of the metallurgical furnace exhaust gas, In the thermal energy recovery method of exhaust gas generated from a metallurgical furnace that leads to reforming of the exhaust gas by introducing a reforming reaction between carbon dioxide gas and a reducing agent contained therein, from a position where the exhaust gas temperature after addition of the reducing agent is 800 ° C. or less A method for recovering the thermal energy of exhaust gas generated from a metallurgical furnace is proposed in which the gas residence time until quenching is 0.01 seconds or more and 5 seconds or less.

The present invention can provide a more preferable solution by adopting the following configuration.
( 1 ) When the gas residence time (t) is an exhaust gas flow rate F (m ² / h) and an exhaust gas duct empty volume V (m ³ ), the following equation (4):
t (sec) = 3600 × V / F (4)
Use the one obtained by.
( 2 ) The metallurgical furnace is a converter.
( 3 ) The reducing agent is added at a position from the upper blowing lance, upper hood, or upper hood to the upstream side of the primary wet dust collector.

(1) According to the present invention, the gas residence time from the position where the exhaust gas temperature after addition of the reducing agent is 800 ° C. or less to the position where the gas is rapidly cooled, preferably the water injection position of the primary wet dust collector, is 5 seconds or less. By managing it, an efficient carbon dioxide reforming reaction can be led without causing generation of carbon or the like and a reduction in reaction efficiency, thereby reliably realizing an increase in exhaust gas heat and a reduction in carbon dioxide emission. be able to.
(2) According to the present invention, as a reducing agent, fossil resource-based compounds such as natural gas and liquefied petroleum gas, and non-fossil resource-based compounds such as vegetable oils such as bioethanol, biodiesel, and palm oil Since an organic compound can be used, thermal energy recovery of high temperature exhaust gas can be realized at low cost.

It is an approximate line figure of converter exhaust gas recovery equipment for explaining the present invention. It is a basic diagram of the simulation test furnace used in the Example.

In the present invention, a reducing agent is added to high-temperature exhaust gas discharged from a metallurgical furnace such as a converter, a smelting reduction furnace, or an electric furnace, and the carbon dioxide (carbon dioxide) contained in the exhaust gas and the reducing agent are used in the above ( 1) In order to recover the thermal energy of the exhaust gas by introducing the reforming reaction shown in the formula, the reducing agent is added from the position where the exhaust gas temperature after addition of the reducing agent is 800 ° C. or less, for example, from the top blowing lance part of the converter. When adding, the position of the second radiant section upstream from the first radiant section downstream, and when adding the reducing agent from the first radiant section upstream, the position of the second radiant section downstream is the exhaust gas temperature. Corresponds to the position where the temperature becomes 800 ° C. or less. From these positions, the gas residence time until the exhaust gas is rapidly cooled is set to 0 . By controlling to a short time of 01 seconds or more and 5 seconds or less, the carbon dioxide reforming reaction is caused without causing the generation of carbon by the Boudal reaction shown in the above formula (3) and the reduction of the reaction efficiency due to this. This is a method for recovering high-temperature exhaust gas thermal energy generated from a metallurgical furnace, which simultaneously achieves heat increase of exhaust gas and reduction of carbon dioxide emission. The position where the exhaust gas is rapidly cooled is preferably the water injection position of the primary wet dust collector.

The reason for managing the gas residence time in the range of 0.01 to 5 seconds is to suppress the formation of carbon, which is considered to be mainly due to the Butard reaction (disproportionation reaction) shown in the above formula (3).

The Budoal reaction is known to proceed at a relatively low temperature in terms of chemical equilibrium, but is characterized by a relatively slow reaction rate. Therefore, the inventors set the gas residence time until the gas is rapidly cooled by a primary wet dust collector or the like to a short time of 5 seconds or less even when the exhaust gas temperature after addition of the reducing agent is 800 ° C. or less. It has been found that the generation of carbon due to the reaction of the formula (3) is suppressed, and as a result, it is possible to suppress a decrease in the efficient thermal energy recovery reaction.

Here, the gas residence time t (sec) is defined as F (m ³ / h) at the position where the exhaust gas temperature after addition of the reducing agent is 800 ° C. or less, and the exhaust gas temperature after addition of the reducing agent is 800 ° C. or less. When the exhaust gas duct empty volume between the position where the exhaust gas is rapidly cooled (preferably the water injection position of the primary wet dust collector) is V (m ³ ), it can be expressed by the following equation (4).
t (sec) = 3600 × V / F (4)

However, if the gas residence time (t) is shorter than 0.01 seconds, only the effect of suppressing carbon generation can be obtained, but the gas flow rate increases, so that the pressure loss increases and the exhaust gas is sucked. Since power becomes large, it is not preferable. Further, when the gas flow rate is increased, the exhaust duct wall wears faster, which is not preferable. On the other hand, if the gas residence time is longer than 5 seconds, carbon generation becomes remarkable, and carbon (soot) deposition on the exhaust gas duct wall is recognized, which is not preferable.

The gas residence time from the position where the exhaust gas temperature after addition of the reducing agent is 800 ° C. or lower until the exhaust gas is rapidly cooled is preferably in the range of 0.01 seconds to 5 seconds. In addition, in the converter shown in FIG. 1, the position where the exhaust gas temperature is lowered to 800 ° C. means that when the reducing agent is added from the side pipe of the top blowing lance, the downstream side of the first radiating unit 5 is upstream of the second radiating unit 6. When the reducing agent is added between the sides or from the upstream side of the first radiating unit 5, the position on the downstream side of the second radiating unit 6 is suitable.

In addition, when the gas residence time is longer than 5 seconds, by increasing the flow rate of oxygen injected from the top blowing lance, or by increasing the flow rate of argon or nitrogen gas blown at the bottom for stirring the molten steel, It can be 5 seconds or less. In this case as well, the residence time can be obtained from the equation (4).

  By the way, it is known that if a reducing agent such as natural gas is added to the exhaust gas generated from the metallurgical furnace, the reforming reaction represented by the formula (1) proceeds. As the reforming reaction, which is an endothermic reaction, proceeds, the exhaust gas temperature decreases. The exhaust gas temperature can also be determined by generating steam with a waste heat boiler that uses a water cooling structure to protect the exhaust gas duct wall, or by using a contact boiler installed in the duct to recover heat. descend.

  In the present invention, the exhaust gas temperature after addition of the reducing agent means not only a temperature decrease due to the reforming reaction but also a temperature including a temperature decrease due to heat recovery as steam in the above-described boiler. Furthermore, even if the added reducing agent remains unreacted at the position where the exhaust gas temperature after addition of the reducing agent is 800 ° C., the effect of the present invention is not affected at all. That is, the unreacted reductant at the position where the exhaust gas temperature after addition of the reductant is 800 ° C. or lower reacts further until the gas is rapidly cooled, for example, up to the water injection position of the primary wet dust collector. This is because the reaction reducing agent remains in the exhaust gas as a reducing agent such as methane after quenching, contributes to increasing the combustion heat of the exhaust gas, and does not reduce the effect of the present invention.

  In the present invention, the reducing agent added to the exhaust gas includes natural gas, liquefied petroleum gas, methane, ethane, light naphtha, raffinate, methanol, ethanol, dimethyl ether, and other fossil resource-based compounds, or bioethanol, biodiesel, or Non-fossil resource-based organic compounds such as vegetable oils such as palm oil can be used. As the reducing agent, those described above may be added alone, or a plurality of compounds may be mixed, or different compounds may be added from different addition positions.

Furthermore, water or steam may be added to the reducing agent so that the steam reforming reaction occurs simultaneously. For example, when methane is selected as the reducing agent, the following reactions mainly proceed.
CH ₄ + CO ₂ → 2CO + 2H ₂ (1)
CH ₄ + H ₂ O → CO + 3H ₂ (5)
CO ₂ + H ₂ → CO + H ₂ O (6)
C + H ₂ O → CO + H ₂ (7)

Equations (5) and (7) are not direct reactions with carbon dioxide gas, but they are endothermic reactions, contributing to substantial heat increase of exhaust gas and consequently contributing to the object of the present invention. It is a reaction to. Further, a large amount of carbon-containing dust is often generated from the metallurgical furnace. In this case, a part of the carbon in the dust can be changed to CO and H ₂ by the equation (7), which is preferable. .

When the steam reforming reaction is caused, it is preferable to add H ₂ O in the form of steam that does not lower the exhaust gas temperature. The amount of H ₂ O added is suitably up to about 35% by mass with respect to the reducing agent. If it exceeds 35% by mass, water falls into the metallurgical furnace to cause a decrease in the temperature of the molten metal, which may increase the energy consumption, which is not preferable.

  In the present invention, particularly favorable results can be expected when the metallurgical furnace is a converter 1 as shown in FIG. This is because the converter 1 is generally provided with an exhaust gas recovery facility called a converter OG facility 8, and it is not necessary to newly install an exhaust gas recovery facility in order to implement the present invention. Moreover, the exhaust gas generated from the converter (usually referred to as “off-gas”) has a high temperature in the vicinity of the furnace port of about 1600 ° C., which is a suitable temperature for causing the reforming reaction. Addition of the reducing agent to the converter exhaust gas is performed by the top blowing lance part of the converter, the position of the upper hood 4 using the side pipe of the top blowing lance, or between the upper hood 4 and the upstream side of the primary wet dust collector 7. It is preferable to carry out at the position. Moreover, it is preferable to carry out at these positions at a plurality of positions in the gas flow direction in the exhaust gas recovery facility or in the circumferential direction of the facility. On the other hand, the skirt 2 and the lower hood 3 are close to the furnace opening, and the added reducing agent may be burned by air entering from the gap between the converter and the skirt, which is not preferable. In addition, although the reducing agent can be added from the sublance not shown, the sublance is used for side temperature and sampling, and the reducing agent can be added only at the timing when the sublance is inserted into the converter. Therefore, it is not preferable.

  In this example, an experiment was conducted using a simulation test furnace comprising an alumina tube 20 having an inner diameter of 12 mm and a length of 5 m. As shown in FIG. 2, in this test furnace, a simulated gas introduction pipe 25 is attached to the upstream side flange F1 of the alumina tube 20, and a reducing agent introduction pipe 21 for blowing a reducing agent and an inlet side thermocouple protection pipe 22 are attached. And is attached. The addition of the reducing agent is performed at a position 1.5 m downstream from the upstream flange F1, and the inlet gas temperature is measured at a position 1 m downstream from the upstream flange F1. On the other hand, an outlet-side thermocouple insertion tube 23 and a water-cooled gas cooling facility 24 are attached to the downstream flange F0, and an integrating gas flow meter and a gas analyzer are attached downstream of the gas cooling facility. ing. The alumina tube 20 is entirely covered with the electric furnace E, but only the heater located at the upstream 1 m position can be energized so that this portion becomes a preheating zone for the converter simulated gas, The heater on the downstream side is not energized and becomes an adiabatic reaction zone. Note that the temperature measurement position of the outlet-side thermocouple insertion tube 23 attached to the downstream flange F0 was the outlet position of the adiabatic reaction zone.

  In this experiment, the pipe diameter and length from the downstream flange F0 to the gas cooling facility 24 are adjusted as appropriate, and the outlet thermocouple insertion tube 23 and the gas cooling facility 24 attached to the outlet position of the adiabatic reaction zone It was decided to control the gas residence time in this way by changing the empty volume. The air volume was changed because the experimental apparatus was small and it was easier to change the pipe diameter and pipe length than to change the simulated gas flow rate.

  As described above, the reducing agent and the like are blown into the position 0.5 m downstream of the preheating zone (1 m), so the actual length of the adiabatic reaction zone is 3.5 m.

A mixed gas of CO ₂ : 20% by volume and N ₂ : 80% by volume was prepared as a converter simulated gas, and hexane was prepared as a reducing agent. The metering pump was adjusted so that the simulated gas flow rate was 1 l / min and the hexane flow rate was 26 ml / min in terms of gas.

  Carbon dioxide conversion and mass balance were calculated from the outlet gas flow rate and gas analysis results. Carbon was generated by visual observation in the piping after each experiment, but it was difficult to quantify because of the small-scale experiment. Therefore, the difference between the C atom mass balance measured value (%) and 100 (%) was adopted as the carbon generation amount.

Experiment numbers 1 to 6 shown in Table 1 are experimental examples in which the temperature of the preheating zone is controlled so that the outlet temperature becomes 800 ° C. Therefore, the gas residence time (hereinafter referred to as t ₁ ) from the position where the exhaust gas temperature after addition of the reducing agent is 800 ° C. or less to the position where the gas is rapidly cooled can be calculated from the equation (4). In these experiments, the gas residence time (hereinafter referred to as “t ₀ ”) in the heat insulation zone was 4 seconds.

On the other hand, Experiment Nos. 7 and 8 are experiments in which the temperature of the preheating zone was controlled so that the outlet temperatures were 700 ° C. and 600 ° C., respectively. In Experiment Nos. 7 and 8, it is unknown where the gas temperature is 800 ° C. in the heat insulation zone. Therefore, in order not to underestimate t ₁ , the value obtained by adding the above t ₀ (= 4 seconds) to the residence time obtained from the empty volume from the outlet position of the adiabatic reaction zone to the gas quenching position is the experiment number 7, Equal to t ₁ at 8.

As is clear from the results of Table 1 below, the gas residence time (t ₁ ) from the position where the exhaust gas temperature after addition of the reducing agent is 800 ° C. or less to the position where the gas is rapidly cooled is 10 seconds or less. For example, the production of carbon is very small, and it is clear that efficient sensible heat recovery and carbon dioxide emission reduction can be achieved.

  The present invention is not only for reforming and recovering converter exhaust gas, but also for metallurgical furnaces such as smelting reduction furnaces and electric furnaces that discharge high-temperature gas containing a large amount of carbon dioxide, and other furnaces used in non-ferrous refining. This is useful as a technology for recovering exhaust gas thermal energy.

DESCRIPTION OF SYMBOLS 1 Converter 2 Skirt 3 Lower hood 4 Upper hood 5 1st radiation part 6 2nd radiation part 7 Primary wet dust collector 8 Converter OG equipment 20 Alumina tube 21 Reducing agent introduction pipe 22 Inlet side thermocouple protection pipe 23 Outlet side thermocouple Insertion pipe 24 Gas cooling facility 25 Simulated gas introduction pipe F0 Downstream flange F1 Upstream flange E Electric furnace

Claims (4)

In the method for recovering thermal energy of exhaust gas generated in a metallurgical furnace, a reducing agent is added to the recovery duct of the metallurgical furnace exhaust gas, and the exhaust gas is reformed by introducing a reforming reaction with carbon dioxide gas and the reducing agent contained in the exhaust gas. A method for recovering heat energy of exhaust gas generated in a metallurgical furnace, characterized in that a gas residence time from the position where the exhaust gas temperature after addition of the reducing agent is 800 ° C. or less to the rapid cooling is 0.01 seconds or more and 5 seconds or less. The gas residence time (t) is the following formula when the exhaust gas flow rate F (m ² / h) and the exhaust gas duct empty volume V (m ³ ):
t (sec) = 3600 × V / F
The thermal energy recovery method for exhaust gas generated from a metallurgical furnace according to claim 1, wherein The method for recovering thermal energy of exhaust gas generated from a metallurgical furnace according to claim 1 or 2 , wherein the metallurgical furnace is a converter. 4. The heat energy of the exhaust gas generated in the metallurgical furnace according to claim 3 , wherein the reducing agent is added at a position from the upper blowing lance, the upper hood, or the upper hood to the upstream side of the primary wet dust collector. Collection method.

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