JP5471154B2 - Method and equipment for reforming exhaust gas containing carbon dioxide - Google Patents

Description

  The present invention relates to a method for reforming a carbon dioxide-containing exhaust gas and a reforming facility employed in carrying out this method. For example, high-temperature carbon dioxide generated from a metallurgical furnace or a sintering furnace such as a converter or a smelting reduction furnace. This is a technique for reforming gas-containing exhaust gas and effectively recovering it as thermal energy. In particular, the present invention provides a technique for effectively reforming exhaust gas by using sensible heat of exhaust gas and using boil-off gas that volatilizes and generates in a liquefied gas storage tank as a reducing agent. suggest.

  In recent years, in order to protect the global environment and prevent global warming, reducing carbon dioxide emissions has become an important issue for industry. In particular, at steelworks, reducing carbon dioxide emissions is the most important issue related to the company's future. Conventionally, various proposals have been made for this purpose, but the actual situation is that a full-scale carbon dioxide reduction technology has not yet been completed.

  By the way, a tank for storing liquefied gas such as liquefied natural gas (LNG) or liquefied petroleum gas (LPG), that is, a liquefied gas storage tank is installed in an ironworks, a power plant, a chemical factory, or a gas company. Yes. In these liquefied gas storage tanks, hydrocarbon-based gas obtained by gasifying the liquefied gas, that is, boil-off gas (low-pressure gas volatilized and generated in the liquefied gas storage tank, hereinafter abbreviated as “BOG”). It is well known that In general, the boil-off gas (BOG) is usually returned to the liquefied gas storage tank after being re-liquefied by pressurization and compression. However, such a process for reliquefaction requires a large amount of compression power. Therefore, recently, a technology has been developed that uses the cold energy of the stored liquefied gas to reduce the energy required for the BOG reliquefaction. Despite its development efforts, the energy for reliquefaction is still large. Therefore, from the viewpoint of reducing carbon dioxide emissions, establishment of a technique that can be used without reliquefying this BOG is desired.

  On the other hand, it is known that a large amount of high-temperature exhaust gas containing carbon dioxide gas is generated in a steelworks through a metallurgical furnace such as a converter or a smelting reduction furnace. 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. Further, from the viewpoint of utilizing the sensible heat of such high-temperature exhaust gas, it is common to recover waste heat by supplying the boiler with low-pressure steam. However, the utility value of low-pressure steam at steelworks is low, and it is rather desirable to make hot exhaust gases chemically usable.

  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. Is supplied to cause a reforming reaction to increase carbon monoxide and hydrogen in the exhaust gas, thereby increasing the latent heat of the exhaust gas to increase the heat.

  In the method disclosed in this document 1, natural gas is blown into the converter exhaust gas to cause the reforming reaction of the following formula (1), but there is no disclosure of using BOG as a gas containing hydrocarbons. . Further, the temperature at the position where this reaction is considered to be completed is lowered to about 375 ° C. However, according to the research by the inventors, when the completion temperature of the reforming reaction is lower than 800 ° C., the generation of carbon becomes remarkable, and there is a problem that carbon and dust are deposited in the exhaust gas recovery facility. I found it. In addition, it was also found that the reforming reaction of the formula (1) causes a reduction in reforming reaction efficiency and a carbon dioxide conversion rate when the reaction completion temperature is 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 this document 2 is excellent in that the reforming reaction is performed using inexpensive coal, but non-combustion components (SiO ₂ , Al ₂ O _3, etc.) contained in the coal accumulate in the flue. Or fall into the converter and cause an increase in the amount of slag.

  Further, in Patent Document 3, methane and water vapor are added to a position where the temperature of the exhaust gas generated from the converter is 1300 ° C. or more to cause the water gas reaction of the following formula (3) to be performed. A method and apparatus for increasing thermal energy by increasing the amounts of carbon oxide and hydrogen are disclosed.

CH ₄ + H ₂ O → CO + 3H ₂ (3)

In the method disclosed in this document 3, the reaction that occurs due to the addition of water vapor only generates CO and H ₂ , and the reforming reaction involving carbon dioxide does not occur, so that it does not contribute to the reduction of CO ₂ at all. There is.

JP 2000-212615 A Japanese Patent Laid-Open No. 5-117668 JP-A-2-11715

  As described above, normally, the boil-off gas (BOG) inevitably volatilizes in the liquefied gas storage tank installed in a steelworks or the like. The generated BOG is usually compressed and reliquefied and then refluxed into the tank. However, in order to reliquefy this BOG, a large compression power (energy) is required.

Further, as described above, a large amount of high-temperature carbon dioxide-containing exhaust gas is generated from a carbon dioxide-containing exhaust gas discharge facility, particularly a metallurgical furnace or a sintering furnace such as a converter or a smelting reduction furnace. Conventionally, the sensible heat of the exhaust gas is used to cause a reforming reaction with a reducing agent, increasing the energy (latent heat) of the exhaust gas (accumulating the endothermic component in the form of the combustion heat of the reaction product) Attempts have been made to increase the heat. However, this conventional technique often causes the accumulation of non-combustion components such as carbon, SiO ₂ , and Al ₂ O ₃ in the exhaust gas pipes and the like, or decreases the carbon dioxide reaction efficiency, thereby increasing the exhaust gas. There was a problem that it was less effective in reducing emissions of heat and carbon dioxide.

  Therefore, an object of the present invention is to use the BOG described above as a carbon dioxide gas reducing agent, thereby eliminating the trouble of re-liquefying the BOG and efficiently increasing the exhaust gas heat and reducing the carbon dioxide gas emission. It is to propose a technique for this purpose. Furthermore, another object of the present invention is to propose a technique for realizing a carbon dioxide reforming reaction that can reduce deposition of carbon, non-combustion components, and the like in an exhaust gas pipe.

  In order to overcome the above-mentioned problems of the prior art and eliminate the need to reliquefy BOG, and at the same time, efficiently and efficiently realize exhaust gas heat increase and carbon dioxide gas emission reduction, the present invention provides the following: A promising solution is proposed. That is, the present invention firstly adds a reducing agent to a high-temperature carbon dioxide-containing exhaust gas, leads a reforming reaction by the carbon dioxide gas and the reducing agent contained in the exhaust gas, and reforms the exhaust gas. A boil-off gas that volatilizes and generates in a liquefied gas storage tank is used as the reducing agent.

In the method for reforming exhaust gas containing carbon dioxide of the present invention,
(1) The boil-off gas is used as it is without being reliquefied.
(2) The addition of the boil-off gas to the exhaust gas is performed when the oxygen concentration in the exhaust gas is 1% by volume or less, and the reforming reaction is completed when the exhaust gas temperature is 800 ° C. or higher.
(3) The liquefied gas is at least one of liquefied natural gas, liquefied petroleum gas, or liquefied dimethyl ether,
(4) The carbon dioxide-containing exhaust gas is exhausted from a metallurgical furnace or a sintering furnace,
Is a more preferable solution.

  Secondly, in the present invention, a boil-off gas storage tank that stores boil-off gas that volatilizes and generates in a liquefied gas storage tank, a high-temperature exhaust gas and boil-off gas, for an exhaust gas discharge device that generates high-temperature exhaust gas containing carbon dioxide gas. A carbon dioxide gas comprising: a reforming reaction apparatus that causes a reforming reaction with carbon dioxide gas in the exhaust gas to contact with each other; and a blowing apparatus for blowing boil-off gas into the reforming reaction apparatus Provide reforming equipment for contained exhaust gas.

In the carbon dioxide containing exhaust gas reforming equipment of the present invention,
(1) Between the boil-off gas storage tank and the blowing device, a boil-off gas boosting device and a flow rate control device are disposed;
(2) The exhaust gas discharge device is a metallurgical furnace or a sintering furnace,
Is a more preferable solution.

(1) According to the present invention configured as described above, for example, for a high-temperature carbon dioxide-containing exhaust gas generated from a carbon dioxide-containing exhaust gas discharge device generated from a metallurgical furnace such as a converter or a sintering furnace, Since Boilhof gas (BOG) such as hydrocarbons and oxygenated compounds generated from the liquefied gas storage tank is added as a reducing agent for carbon dioxide gas, first of all, there is no need to reliquefy BOG and hence liquefy This is advantageous in terms of economy as well as carbon dioxide emission reduction. In addition, according to the present invention, it is possible to establish an effective heat increase technology for exhaust gas, and simultaneously and efficiently achieve reduction of carbon dioxide emission.
(2) Further, according to the present invention, the carbon dioxide-containing exhaust gas discharge device is intended for a device that discharges high-temperature exhaust gas, for example, a metallurgical furnace such as a converter or a smelting reduction furnace, or a sintering furnace. As a result, the sensible heat of the high-temperature exhaust gas can be used effectively, so that high reforming reaction efficiency can be achieved. Further, when introducing the carbon dioxide reforming reaction, it is necessary to use BOG as a reducing agent and to control the addition timing (O ₂ ≦ 1 vol%) and the reforming reaction timing (temperature ≧ 800 ° C.). Thus, non-combustion components such as carbon, SiO ₂ , and Al ₂ O ₃ are not deposited on the inner wall surface of the exhaust system tube furnace, and the maintenance and management of the facilities are facilitated, which is economical.

It is a basic diagram which shows the basic flow of the exhaust gas reforming method which concerns on this invention. It is a basic diagram which shows the flow of the reforming method using the converter exhaust gas which is one Embodiment of this invention method. It is an approximate line figure of converter exhaust gas recovery equipment for explaining the present invention. And outlet temperature of the model gas, amount of carbon (C) and CO ₂ conversion is a graph showing the relationship between the CH ₄ conversion. It is a graph which shows the relationship between the oxygen concentration of a simulation gas, the lower heating value, the CO ₂ conversion rate, and the CH ₄ conversion rate.

  The present invention uses the above-mentioned BOG as a reducing agent for reforming exhaust gas containing carbon dioxide gas, and uses the BOG as it is (gas state) instead of re-liquefying it. There are features. According to such an exhaust gas reforming method using BOG, not only the operation of pressure compression for BOG reliquefaction is unnecessary, but also BOG which is a gas such as hydrocarbon or oxygen-containing compound is used. Heat increase and reduction of carbon dioxide emissions can be realized at the same time. That is, the present invention is preferably carried out in a liquefied gas storage tank in an exhaust gas containing carbon dioxide gas generated from a metallurgical furnace such as a converter or a sintering furnace and having a high temperature of 800 ° C. or higher, preferably 1000 ° C. or higher. This is a method for reforming exhaust gas in which BOG generated by volatilization is added as a reducing agent for carbon dioxide. Hereinafter, although the detail of this reforming method is demonstrated, this is an illustration and is not limited only to the following description.

  In a liquefied gas storage tank that stores liquefied natural gas (LNG) or liquefied petroleum gas (LPG) in a liquefied state, the liquid in the tank when liquefied gas is received, heat input from outside the tank, etc. As a result, a part of the liquefied gas is volatilized and gasified in the tank. The gas volatilized and generated in the tank is usually set to a pressure of about 10 to 30 kPaG in the liquefied gas storage tank. Therefore, it is necessary to prevent the tank internal pressure from exceeding the design pressure. It is necessary to discharge from the top. This released gas is called the boil-off gas (BOG) described above.

The pressure of the BOG usually varies depending on the type of liquefied gas and the design pressure of the tank, and is usually about 4 to 20 kPaG. It is known that the amount of BOG generated varies greatly under the influence of the environment. In particular, it is known that a large amount of BOG is generated when liquefied gas is received. In addition, since this BOG is generated by volatilization, it is one of the features that a specific component in the liquefied gas is concentrated. For example, in the case of LNG, almost pure methane gas (CH ₄ ) is generated as BOG.

  FIG. 1 is a schematic diagram showing a flow of reforming equipment for explaining the exhaust gas reforming method of the present invention. The present invention will be described below with reference to this figure. As described above, since the amount of BOG generated constantly fluctuates, in the present invention, in addition to the liquefied gas storage tank 1, the boil-off gas for absorbing and storing the variation in the amount of BOG generated is stored. A storage tank 2 is provided. The boil-off gas storage tank 2 may be of a sealed type that can withstand the pressure of BOG, and this includes a cylindrical type gas holder such as a water type, an anhydrous type, and a dry type, a spherical gas holder, etc. Can be used.

  In the present invention, the BOG stored in the boil-off gas storage tank 2 is used as a reducing agent for reducing the carbon dioxide in the carbon dioxide-containing exhaust gas. The reforming reaction proceeds. The BOG is transported to the reforming reaction apparatus 6 by a duct, a pipe 8 or the like. However, since this BOG has a low pressure, it is preferable that the BOG booster 3 boosts the BOG. The pressure increase of the BOG varies depending on the diameter and length of the pipe 8, the number of bent portions, the BOG flow rate, etc., but is preferably 10 to 1000 kPaG, more preferably about 50 to 500 kPaG. The reason is that if the pressure of the boosted BOG is 10 kPaG or more, the flow rate and flow rate of BOG required in the reforming reaction apparatus 6 can be secured, and the reforming reaction efficiency is not lowered. On the other hand, if the pressure is set to 1000 kPaG or less, energy loss to be unnecessarily increased is small without affecting the reforming reaction efficiency, and the equipment does not have a high-pressure specification and does not increase costs. As the BOG booster 3, for example, a vortex pump, a reciprocating pump, a rotary pump, or the like can be used.

  The boosted BOG is preferably controlled by the BOG flow control device 4 to a flow rate required for the reforming reaction with the carbon dioxide gas. The flow rate of the BOG to be controlled is preferably changed depending on the type of BOG, the flow rate of carbon dioxide in the carbon dioxide-containing exhaust gas, the target carbon dioxide conversion rate, and the like.

In controlling the flow rate of BOG, for example, when BOG is a pure methane, a hydrocarbon such as butane, or an oxygen-containing compound such as dimethyl ether, the reaction between BOG and carbon dioxide can be performed by the following (4), (5 ) And (6).
CH ₄ + CO ₂ → 2CO + 2H ₂ (4)
C ₄ H ₁₀ + 4CO ₂ → 8CO + 5H ₂ (5)
CH ₃ OCH ₃ + CO ₂ → 3CO + 3H ₂ (6)

Therefore, considering the case where BOG is pure methane (CH ₄ ), if the CO ₂ flow rate in the carbon dioxide-containing exhaust gas is 10,000 Nm ³ / h and the target CO ₂ conversion rate is 50%, From the stoichiometry shown in the reaction formula, it is understood that the flow rate of BOG may be controlled to about 5,000 Nm ³ / h. Further, when the BOG is pure butane (C ₄ H ₁₀ ) and the CO ₂ flow rate and the target CO ₂ conversion rate are equal to the above, the BOG flow rate may be controlled to about 1,250 Nm ³ / h.

  As the flow control device 4, a valve or the like that can control the flammable BOG flow rate can be used. For example, a flow rate control valve linked with various types of mass flow meters such as a needle valve and a variable throttle valve is preferably used.

  As described above, the present invention is only required to promote the heat increase of the exhaust gas and the reduction of carbon dioxide emission by using BOG as the reducing agent of the high temperature exhaust gas containing carbon dioxide to be reformed. There is no limit to the gas conversion rate. However, when the carbon dioxide gas conversion rate is lowered, the significance of blowing BOG is diminished and the blowing effect is reduced. In this sense, from the viewpoint of economy, it is necessary to aim for such a carbon dioxide conversion rate of at least about 1%, preferably 3% or more. Further, this carbon dioxide gas conversion rate is at least 10%, more preferably 20%, in order to achieve the goal of eliminating the BOG reliquefaction operation and simultaneously achieving increased heat of exhaust gas and reduced emission of carbon dioxide gas. The above has a great economic effect. On the other hand, the upper limit of this carbon dioxide conversion rate is better, but if the conversion rate is too high, the capacity of the BOG storage tank 2 becomes excessive and not economical, so it should be 90% or less, more preferably 80% or less. Is recommended.

  In general, the reaction of the BOG proceeds to an equilibrium composition according to the above equations (4) to (6) in the reforming reaction apparatus 6 shown in FIG. 1 in accordance with the carbon dioxide concentration, the exhaust gas temperature, the pressure in the apparatus, and the like. Will do. However, even if this reforming reaction does not reach equilibrium due to changes in the flow rate or composition of the carbon dioxide-containing exhaust gas, only a part of this BOG remains in the reformed gas in a mixed state. Therefore, it will not be a problem.

The carbon dioxide flow rate in the carbon dioxide-containing exhaust gas generated from the exhaust gas exhaust device 7 depends on the type and size of the exhaust gas exhaust device 7. For example, if the exhaust gas discharge device 7 is a converter, the carbon dioxide flow rate is about 5,000 to 50,000 Nm ³ / h. If the exhaust gas discharge device 7 is a sintering furnace of iron ore, the carbon dioxide flow rate Is about 10,000 to 100,000 Nm ³ / h.

  In FIG. 1, a BOG blowing device 5 for blowing BOG into the reforming reaction device 6 is provided downstream of the BOG flow control device 4. The blowing device 5 quickly diffuses the BOG blown into the reforming reaction device 6 and mixes it well with the carbon dioxide-containing exhaust gas so that the BOG concentration distribution in the reforming reaction device 6 becomes as small as possible. It is preferable to use one that can be used. For example, a Laval nozzle used in a supersonic region, a tapered nozzle or a straight tube nozzle used in a subsonic to low flow velocity region, a slit nozzle ejected from a large number of slits, or the like can be used.

As shown in FIG. 2, the BOG blowing device 5 has an exhaust gas discharge device 7 as a converter, and a reforming reaction device 6 includes an upper hood 6a, a first radiation portion 6b, and a second radiation portion 6c. When it is equipment, it is preferable to arrange it at the position from the lower part in the height direction to the vicinity of the center, that is, from the upper hood 6a to the first radiation part 6b. The reason why it is installed on the lower side of the upper part in the height direction is that H ₂ having a small specific gravity is generated by the reforming reaction, and therefore, if it is an upward flow, it is possible to prevent the conversion rate from being lowered due to the reverse diffusion of the generated H _2. Because.

  The jet velocity of BOG from the blowing device 5 is preferably 1 to 100 times the flow rate of the carbon dioxide-containing exhaust gas in the reforming reaction device 6 in the vicinity of the blowing device 5, preferably 3 to 50 times. It is more preferable to adjust so that it may become 2 times or less. The reason is that if the flow rate of the BOG is less than 1 times the flow rate of the carbon dioxide-containing exhaust gas, the injected BOG loses the inertial force of the carbon dioxide-containing exhaust gas flow and is pressed against the inner wall of the reforming reaction apparatus 6. Absent. On the other hand, if the flow rate ratio exceeds 100 times, the inertia force of the blown BOG is too large, and the BOG rises in the vicinity of the center of the reforming reactor 6, which is not preferable. Moreover, if the flow rate is a large flow rate such as more than 100 times, the supply pressure of BOG to the blowing device 5 becomes high, and the BOG temperature after blowing becomes remarkably low due to cooling by adiabatic expansion, which is not preferable. .

  The reforming reaction device 6 is such that BOG and carbon dioxide-containing exhaust gas can join together to ensure a sufficient residence time for performing the above reforming reaction, for example, ensuring the length of the reaction zone It is necessary to have a structure that can be used, and there is no particular limitation on the structure and material. The residence time of the mixed gas of BOG and exhaust gas may be about 0.01 to 50 seconds, and more preferably has a length that can secure the residence time for 0.1 to 20 seconds. The length of the reaction zone described above is mainly determined by the scale (size, length) of the apparatus. The reason for setting the gas residence time to 0.01 seconds or more is to secure a reaction time sufficient for completing the reforming reaction, and it is economical without leakage of unreacted reducing agent. On the other hand, the reason for setting the gas residence time within 50 seconds is that the reaction does not proceed beyond the equilibrium point even if the reforming reactor 6 is of a size such that the gas residence exceeds 50 seconds. Because it is uneconomical.

  For example, as such a reforming reaction apparatus 6, an existing exhaust gas duct can be used as it is. This is because in this case, it is not necessary to construct a new reforming reaction apparatus 6, which is economical. Examples of the existing exhaust gas duct include a converter exhaust gas recovery facility and a flue of a sintering furnace.

  It is known that the reforming reaction in the reforming reaction apparatus 6 is accelerated when a nickel-based catalyst such as metallic nickel or nickel oxide is used, and the reaction is accelerated using these commercially available reforming catalysts. It is effective to make it. By the way, the present inventors have newly found that transition metals such as metallic iron, iron oxide, metallic cobalt and cobalt oxide and their oxides are also effective for the above reforming reaction in addition to the nickel-based catalyst. I know.

  In this regard, in the present invention, high-temperature exhaust gas discharged from the metallurgical furnace or sintering furnace is used. Exhaust gas discharged from a metallurgical furnace or sintering furnace contains not only carbon dioxide, but also contains a large amount of dust mainly composed of transition metals such as Fe and Co that have a catalytic action and their oxides. Therefore, it can be said that it is particularly effective exhaust gas.

  That is, in the present invention, the exhaust gas discharge device 7 is a metallurgical furnace or a sintering furnace (hereinafter referred to as “converter”) such as a converter that discharges exhaust gas containing a large amount of dust such as catalytic iron oxide. It is effective to use In short, the present invention adds the BOG to high-temperature exhaust gas (hereinafter referred to as “off-gas”) discharged from a converter or the like, so that the carbon dioxide contained in the off-gas One of the features is that a reforming reaction using dust as a catalyst is caused between the BOG and the BOG.

In general, the off-gas discharged from the converter contains 10 to 20% by volume of CO ₂ and about 50 to 80% by volume of CO, and has a calorific value of about 1500 to 2000 kcal / Nm ³ at the furnace port during operation. The temperature is about 1200 to 1800 ° C. In the present invention, BOG is added as a reducing agent to the off-gas of the converter, and the reforming reaction of the above formulas (4) to (6) by the BOG and carbon dioxide gas is performed under the intervention of iron oxide. As a result, the off-gas heat increase and the carbon dioxide gas emission reduction can be realized simultaneously. That is, the heated off-gas, that is, the reformed off-gas is used (burned) as, for example, various heat sources in the steelworks, so that carbon dioxide gas is finally discharged, but is used in the steelworks. Auxiliary fuel such as heavy oil can be reduced by an amount corresponding to the heat increase, and carbon dioxide gas can be reduced accordingly.

  FIG. 3 is a schematic diagram showing an example applied to an exhaust gas recovery facility for a converter in order to implement the exhaust gas reforming method according to the present invention. As shown in this figure, the off-gas containing the high-temperature carbon dioxide gas discharged from the converter C is a primary dust collector that is connected downstream of the upper hood 6a and the first and second radiating portions 6b and 6c. (Wet dust collector) 9, while being discharged through the secondary dust collector 10, etc., continuously or semi-continuously with the flow meter 11 and gas analyzer 12 disposed on the outlet side of the secondary dust collector 10, or The off-gas flow rate and off-gas oxygen concentration are measured intermittently. When the oxygen concentration in the off gas is higher than 1% by volume, the control valve 4 for controlling the amount of addition (injection) of the reforming reaction reducing agent (BOG) is closed and at the same time the gas flow path switching valve 13 It is preferable that the off-gas flows toward the flare 14 with a gap therebetween.

  The type of the gas analyzer 12 is not particularly limited, but it is preferable to be able to measure the carbon dioxide concentration (flow rate) and the off-gas flow rate in addition to the oxygen concentration. From the measured value of the gas analyzer 12, the flow rate of the carbon dioxide gas can also be obtained, and as a result, the injection amount of the reducing agent for reforming reaction can be determined.

  In the present invention, it is preferable to use an off-gas that is an object to be treated in which the oxygen concentration contained in the gas is reduced to 1% by volume or less. In the reforming process, the above reforming reaction is completed when the off-gas temperature measured at the position of the thermometer 15 shown in FIG. It is preferable to do. Therefore, while the reforming reaction is in progress, the gas flow path switching valve 13 is opened, the flow rate control valve 4 is opened, and the reforming reaction reducing agent is passed through the side pipes of the upper hood 6a and the oxygen top blowing lance 16. While the addition of (BOG) is performed, the modified off gas is allowed to flow toward the gas holder (not shown). Meanwhile, the thermometer 15 continuously measures the temperature of the off-gas to be treated, and injects the BOG so that the reforming reaction is completed when the temperature of the off-gas increased by the reforming process is 800 ° C. or higher. The amount and / or the addition (injection) position may be controlled.

  As described above, BOG is preferably added to the off-gas when the oxygen concentration in the off-gas becomes 1% by volume or less. The reason for this is that if the oxygen in the off-gas is 1% by volume or less, the amount of water vapor generated by the reaction of the hydrogen gas in the off-gas and the hydrogen atom in the reducing agent with oxygen decreases and the reaction between the water vapor and the reducing agent. Will not occur. As a result, the carbon dioxide gas reduction effect can be increased without reducing the carbon dioxide gas conversion rate. If a reducing agent is added when the oxygen concentration in the offgas is 1% by volume or less, there is no risk of ignition or explosion.

  On the other hand, in order to efficiently perform the carbon dioxide reforming reaction represented by the above formulas (4) to (6), it is preferable that the oxygen concentration in the off-gas is as close to zero as possible, but about 1% by volume. It is because it is an allowable range if it is mixed up to. The converter exhaust gas recovery equipment is designed so that a little air is mixed in, so it takes a long time to reduce the oxygen concentration below the detection limit. If the reducing agent (BOG) cannot be added in the meantime, not only the heat increase effect is reduced, but also the amount of combustion by the flare 9 is increased, resulting in an increase in carbon dioxide emission. Is not preferable. Therefore, in the present invention, the oxygen concentration in the off-gas when starting the injection of the reducing agent is preferably 1% by volume or less.

  In the present invention, the temperature of the low-temperature reformed exhaust gas, that is, the off-gas that has been increased as the latent heat of the reaction product is increased by the above reforming reaction using sensible heat of the exhaust gas. It is preferable to adjust the addition amount and / or the addition position of the reducing agent so that the reforming reaction is completed. Thus, the off-gas temperature at the completion of the reforming reaction is preferably 800 ° C. or higher, and more preferably 850 ° C. or higher. The reason for this is that when the off-gas temperature at the time of completion of the reforming reaction is 800 ° C. or higher, not only the flue deposition due to the generation of carbon such as fly ash does not occur, but also the conversion rate of carbon dioxide gas does not decrease, Both the heat increasing effect and the carbon dioxide gas reducing effect are not lowered.

  That is, one of the features of the idea of the present invention is not to control the reforming reaction by the flow rate of carbon dioxide gas in the offgas, but to control the offgas temperature (preferably 800 ° C. or higher) at the completion of the reforming reaction. Therefore, the off-gas heat increase control is performed. The reason for such control is that converters are generally batch-type furnaces and have the property that the off-gas temperature fluctuates greatly when a blowing abnormality such as an increase in iron oxide occurs in the molten steel. is there. That is, according to such a method, it is advantageous to avoid the influence due to the fluctuation of the off-gas temperature.

  The reforming off gas in the heated state by being accumulated as thermal energy preferably determines the amount and position of addition of the reducing agent so that the reforming reaction is completed when the temperature is 800 ° C. or higher. For example, the amount of reducing agent added can be controlled by adjusting the flow rate of carbon dioxide, the type of reducing agent, the stoichiometry of the carbon dioxide reforming reaction, the off-gas temperature at the addition position, and the gas residence time from the addition position to the position of the thermometer 15. It is necessary to change depending on the situation.

  Here, the above-mentioned “completion of the reforming reaction” means that the reaction between the added BOG (reducing agent) such as methane and carbon dioxide in the exhaust gas has progressed to an approximate equilibrium in the atmosphere. Since it is theoretically necessary to allow the reaction to proceed until it is completely in equilibrium, an infinite residence time is required, so the approximate equilibrium cannot be strictly defined. Therefore, in the present invention, when the hydrogen gas concentration described below increases with respect to the hydrogen gas concentration in the exhaust gas before reforming, it is preferable that the “reforming reaction is completed”.

  For example, in decarburization blowing, the amount of hydrogen gas in the exhaust gas is originally as low as 1% by volume, and the hydrogen gas concentration in the exhaust gas after reforming increases to about 2 to 25 times that before reforming. Is easy. Therefore, in the decarburization blowing, it is preferable that “the reforming reaction is completed” when the hydrogen gas increases more than twice before the reforming.

  On the other hand, in the dephosphorization blowing process where the exhaust gas flow rate is originally low and the exhaust gas recovery rate is low, in recent years, waste plastics and the like are introduced to increase the exhaust gas amount to increase the recovery rate. In this case, because of hydrogen gas generated from the auxiliary raw material such as waste plastics, the hydrogen gas concentration in the exhaust gas before reforming reaches about 10 to 15% by volume. Further, in the bottom blow converter, LPG is supplied as a cooling gas to prevent damage to the tuyere, so that a large amount of hydrogen gas is generated even when LPG is decomposed. When such a large amount of hydrogen gas is generated, the amount of increase in the hydrogen gas concentration in the exhaust gas after reforming is only about 1 to 5% by volume compared with that before the reforming. Accordingly, in the dephosphorization blowing and bottom blowing converter, it is preferable that “reforming reaction is completed” when hydrogen gas is increased by 1 vol% or more than before reforming.

  Since the exhaust gas temperature decreases as the reforming reaction proceeds, it is physically meaningful to complete the reaction when the exhaust gas temperature after the reaction is preferably 800 ° C. or higher. On the other hand, hydrogen atoms derived from the added reducing agent are changed to hydrogen gas by the reforming reaction. It is essential to analyze the composition of exhaust gas if it is a process that collects exhaust gas as an energy source, and monitoring the completion of the reaction based on the hydrogen gas concentration has chemical significance and is also important for operation management. It is.

  Further, the reformed gas produced by reforming off-gas means an increased gas generated by the completion of the reaction between the carbon dioxide gas in the exhaust gas and BOG.

  In the above description, in the stoichiometry of the carbon dioxide gas reforming reaction, as shown in the following general formula (7), (XZ) moles of carbon dioxide gas react with 1 mole of the reducing agent. Means. In general, it is preferable to inject an equivalent amount of a reducing agent. However, when the off-gas temperature at the addition position is not so high as compared to 800 ° C., which is a preferable lower limit temperature for completion of the reaction at the position of the thermometer 15. It is preferable to add less than the equivalent amount. For example, when the carbon dioxide concentration of the converter off-gas is 15% by volume and BOG that is methane is used as the reducing agent, since (X−Z) = 1 is equivalent, the off-gas temperature at the injection position should be 1600 ° C. or higher. For example, carbon dioxide and an equivalent amount of methane may be added. However, if the off-gas temperature at the injection position is 1200 ° C., about 2/3 of the equivalent amount is an appropriate addition amount. Here, the appropriate addition amount means an amount at which the reforming reaction is completed at a position where the temperature of the heated off-gas is 800 ° C. or higher.

  For example, when the carbon dioxide concentration in the converter off-gas is 15% by volume, BOG (methane) is used as the reducing agent, and the off-gas temperature at the addition position is 1600 ° C. or higher, to add methane equivalent to carbon dioxide When the residence time is 0.5 to 5 seconds, the reforming reaction can be completed, and the gas temperature at the completion of the reaction is 800 ° C. or higher.

  The addition position of the reducing agent is determined in consideration of the gas residence time and the off-gas temperature at the addition position. For example, as described above, when the gas residence time is 0.01 to 50 seconds, the addition position of the reducing agent is desirably a position where the off-gas temperature is as high as possible. FIG. 3 shows an example in which the reducing agent is blown from the position of the side pipe of the oxygen top blowing lance 16. In this case, it can be said that the off-gas temperature is the highest and the gas residence time can be sufficiently secured. On the other hand, when the amount of carbon dioxide in the converter off-gas is relatively small, the reaction time may be short, so BOG may be added at the position of the upper hood 6a or the first radiation part 6b. . The addition position is not limited to one location, and may be a plurality of locations. For example, the addition location may be performed at two locations of the side tube of the lance 16 and the upper hood 6a.

Example 1
In this example, a simulated test furnace made of an alumina tube having an inner diameter of 12 mm and a length of 5 m was used, and high-purity methane gas was used as a simulated BOG. In this test furnace, a methane gas introduction pipe and a thermocouple protection pipe with an outer diameter of 3 mm are attached to the upstream flange provided at the upper end of the alumina tube, and the addition of methane gas is located 1.5 m below the upper end (upstream flange). Further, the gas temperature measurement control is performed at a position 1 m from the upstream flange. In addition, a thermocouple insertion port and a water cooling gas cooling facility are attached to the downstream flange of the test furnace, and an integrating gas flow meter and a gas analyzer are attached to the downstream side of the gas cooling facility. . The entire alumina tube is covered with an electric furnace, but only the heater within the range of 1m upstream is energized, and this part is used as the preheating zone for the converter simulated gas, and the heater downstream is not energized. The adiabatic reaction zone. As described above, since methane is added at a position 0.5 m below the preheating zone, the actual length of the adiabatic reaction zone is 3.5 m.

The converter simulant gas, CO: 50 vol%, _CO 2: 15 _{volume%, H} 2: 1 _vol%, N 2: 34 was prepared volume% of the mixed gas. The simulated gas flow rate is fixed at 1 L / min, the methane gas flow rate is fixed at 150 mL / min, which is equivalent to CO _2, and the temperature of the preheating zone is changed to 1800 ° C, 1500 ° C, 1300 ° C, 1100 ° C, 900 ° C. A reforming reaction experiment was conducted. Under these examples, when the outlet temperature of the adiabatic reaction zone was calculated by a thermocouple attached to the downstream flange, the preheating zone temperature was 1800 ° C, 1500 ° C, 1300 ° C, 1100 ° C, 900 ° C in each experiment. The outlet temperatures were 1060 ° C, 840 ° C, 775 ° C, 735 ° C and 705 ° C, respectively. The hydrogen gas concentrations at the outlet were 21% by volume, 20% by volume, 19% by volume, 18% by volume, and 17% by volume, respectively. And the gas residence time in the heat insulation zone was 2 to 6 seconds.

The conversion rate and mass balance were calculated from the flow rate of the reacted outlet gas and the gas analysis results. Carbon generation was performed by visual confirmation in the piping after each experiment, but it was difficult to quantify because of the small-scale experiment. Therefore, the difference between the actual mass balance (%) of C atoms and 100 (%) was defined as the carbon generation amount. In FIG. 4, the horizontal axis shows the outlet temperature of the heat-increasing simulated gas, the left vertical axis shows the CO ₂ conversion rate and CH ₄ conversion rate, and the right vertical axis shows the amount of carbon produced. As shown in this figure, in the experiment where the outlet temperature of the increased heat simulation gas was 1060 ° C. (in the case of the preheating zone temperature of 1800 ° C.), the formation of carbon by visual observation was not observed, but the outlet temperature of the increased heat simulation gas was 800 In the experiment lower than ℃ (in the case of the preheating zone temperature of 1300 to 900 ℃), the formation of carbon was remarkable.

  Further, as is clear from FIG. 4, by controlling the reforming reaction to be completed at a position where the temperature of the off-gas increased by the reforming reaction is 800 ° C. or higher, a high carbon dioxide conversion rate and a high increase are achieved. It has been clarified that the thermal effect can be achieved and the generation of carbon causing the flue blockage can be suppressed.

(Example 2)
A reforming reaction experiment was conducted in the same manner as in Example 1 except that the gas shown in Table 1 was used as the converter simulated gas composition and the preheating zone of the simulated gas was set to 1600 ° C. The exit temperature of the increased heat simulation gas was 800 ° C. or higher in all cases. FIG. 5 shows the oxygen concentration in the simulated gas on the horizontal axis, the CO ₂ conversion rate and the CH ₄ conversion rate on the left vertical axis, and the lower calorific value of the heat increasing simulated gas obtained from the gas composition on the right vertical axis. As shown in FIG. 5, the experiment No. 1 in which the oxygen concentration in the simulated gas exceeds 1% by volume. In 2-4 to 2-6, although the CH ₄ conversion rate was high, both the CO ₂ conversion rate and the lower heating value were greatly reduced. This indicates that the H ₂ O reforming reaction of CH ₄ has progressed as a result of the generation of H ₂ O by oxygen in the simulated gas.

  Further, as apparent from FIG. 5, by controlling the start of addition of the reducing agent so that the oxygen concentration in the off-gas becomes 1% by volume or less, a high carbon dioxide conversion rate and a high heat increase effect can be obtained. Clearly it can be achieved.

  The present invention is not only exhaust gas from converters but also metallurgical furnaces such as smelting reduction furnaces that discharge high-temperature gas containing a large amount of carbon dioxide and various furnaces used in non-ferrous refining, and various sintering furnaces. This is useful as an exhaust gas reforming technology.

DESCRIPTION OF SYMBOLS 1 liquefied gas storage tank 2 boil-off gas storage tank 3 pressure | voltage rise apparatus 4 flow control apparatus 5 blowing apparatus 6 reforming reaction apparatus 6a upper hood 6b 1st radiation part 6c 2nd radiation part 7 exhaust gas discharge apparatus 8 piping 9 primary dust collector 10 Secondary dust collector 11 Flow meter 12 Gas analyzer 13 Gas flow path switching valve 14 Flare 15 Thermometer 16 Oxygen blowing lance C Converter

Claims (8)

A liquefied gas storage tank is used as the reducing agent when a reducing agent is added to a high-temperature carbon dioxide-containing exhaust gas and the exhaust gas is reformed by introducing a reforming reaction between the carbon dioxide gas and the reducing agent contained in the exhaust gas. A method for reforming a carbon dioxide-containing exhaust gas, characterized by using a boil-off gas that volatilizes and forms inside. The method for reforming a carbon dioxide-containing exhaust gas according to claim 1, wherein the boil-off gas is used as it is without being reliquefied. 2. The boil-off gas is added to the exhaust gas when the oxygen concentration in the exhaust gas is 1% by volume or less, and the reforming reaction is completed when the exhaust gas temperature is 800 ° C. or higher. Or the carbon dioxide-containing exhaust gas reforming method according to 2 above. The method for reforming a carbon dioxide-containing exhaust gas according to any one of claims 1 to 3, wherein the liquefied gas is at least one of liquefied natural gas, liquefied petroleum gas, and liquefied dimethyl ether. The method for reforming a carbon dioxide-containing exhaust gas according to any one of claims 1 to 4, wherein the carbon dioxide-containing exhaust gas is discharged from a metallurgical furnace or a sintering furnace. A boil-off gas storage tank that stores boil-off gas that volatilizes and generates in a liquefied gas storage tank, and a high-temperature exhaust gas and boil-off gas are brought into contact with the exhaust gas discharge device that generates high-temperature exhaust gas containing carbon dioxide gas. A reforming equipment for a carbon dioxide-containing exhaust gas, comprising a reforming reaction apparatus for causing a reforming reaction with carbon dioxide gas and a blowing apparatus for blowing boil-off gas into the reforming reaction apparatus. 7. The carbon dioxide-containing exhaust gas reforming facility according to claim 6, wherein a boil-off gas boosting device and a flow rate control device are disposed between the boil-off gas storage tank and the blowing device. The said exhaust gas exhaust apparatus is a metallurgical furnace or a sintering furnace, The reforming equipment of the carbon dioxide containing exhaust gas of Claim 6 or 7 characterized by the above-mentioned.

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