JPS6332842B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for injecting flame-retardant fuel into a blast furnace,
In detail, when injecting powdered fuel such as pulverized coal and coke, which are generally considered to have poor combustibility, as well as tar, heavy oil, etc., from a fuel injection burner into a blast furnace,
The present invention relates to a method that can increase the combustion rate of these flame-retardant fuels.

[Prior Art] The fuel used in blast furnace operation has shifted from injection of heavy oil to all-coke operation, and has also progressed to injection of tar and pulverized coal. However, pulverized fuel such as pulverized coal (hereinafter collectively referred to as pulverized fuel), tar, and heavy oil have poor combustibility compared to ordinary C heavy oil, and pulverized coal contains non-combustible components such as ash. Because of this drawback, it is necessary to take various measures when blowing.

Under these circumstances, the present applicant has been conducting research for some time in order to establish an effective injection method for powdered fuel, and has proposed, for example, the technique disclosed in Japanese Patent Publication No. 53081/1981. In this method, the injection position of the powdered fuel is adjusted upstream of the blowpipe in order to satisfy both of the following two requirements: (1) improving the combustion rate of the powdered fuel and (2) preventing ash from adhering to the inside of the blowpipe. With this method, even if the temperature of the hot air supplied into the blowpipe is increased, the adhesion of ash to the blowpipe wall can be prevented, so the above two requirements can be satisfied at the same time. I was able to do it.

[Problems to be solved by the invention] In other words, in the proposed invention,
As shown in the figure, we believe that using hot air at a high temperature of 1050℃ or higher is a necessary condition for improving the combustion rate, and the combustion rate when using hot air below 1050℃ is extremely low. Therefore, the operating temperature of the hot air stove must be increased, which is disadvantageous from the viewpoint of energy conservation, and also shortens the life of the furnace wall refractories and ducts, which deteriorates the maintainability of the equipment.

The present invention has been made in view of these circumstances, and its purpose is to prevent powdered fuel, tar,
The present invention aims to provide a method for injecting flame-retardant fuel into a blast furnace that can sufficiently increase the combustion rate of flame-retardant fuel such as heavy oil.

[Means for Solving the Problems] The structure of the method of the present invention that has achieved the above-mentioned object is that when injecting flame-retardant fuel such as powdered fuel, tar, and heavy oil into a blast furnace, it is possible to A flammable gas fuel is injected into the outer circumference of the flammable fuel independently of and parallel to the flame-retardant fuel flow, and the amount of gas fuel blown is adjusted to the above-mentioned flame-retardant fuel flow. The gist of this is that the amount of fuel injected should be 2% or more in terms of calorific value.

[Operations and Examples] The configuration and operation effects of the present invention will be explained in detail below along with the progress of experiments. The following explanation will mainly be given to powdered fuel as a representative example of flame-retardant fuel, but it goes without saying that the same applies to tar, heavy oil, and other flame-retardant fuels. Figure 1 is a schematic diagram of the apparatus used in the combustion experiment, which is designed to resemble an actual blast furnace tuyere. Powdered fuel A is conveyed from a ground hopper 1 to a coal bin 3 by a screw conveyor 2. A pulverized fuel quantitative feeder 4 is provided at the bottom of the coal bin 3, and the pulverized fuel A cut out in fixed amounts at this portion is sent to the burner 7 through a transport pipe 6 together with transport air 5.
Although the supply of liquid fuel such as tar or heavy oil is not shown, an appropriate method may be used, such as increasing the pressure of tar or heavy oil stored in a heating tank with a pump and supplying it to the burner 7. Can be done. On the other hand, the hot air obtained from the high-temperature hot air furnace 8 is passed from the blast pipe 9 to the blow pipe 10 and the water-cooled tuyere 11 to the combustion test furnace 12.
sent to. 13 in the figure is a chimney.

Since the fuel injection section of a blast furnace is completely different from a general combustion device and consists of a blow pipe 10 and a water-cooled tuyere 11, this experimental device approximates an actual blast furnace injection section. In addition, this test furnace is equipped with numerous observation windows for observing the combustion and ignition conditions, as well as inspection holes for measuring the temperature inside the furnace, gas composition inside the furnace, dust inside the furnace, amount of flame radiation, etc. , and in the upstream bent part of the blow pipe 10,
A peephole 14 is provided for observing the state of adhesion of ash to the wall surface of the blow pipe 10.

The conditions for the series of experiments described later using this apparatus are as follows.

Experimental conditions Flame-retardant fuel: 1. Pulverized coal (volatile content 35% by weight) 2. Tar fuel injection amount: 75 × 10 ⁴ kcal/hour (constant) Hot air temperature: 1000℃ Flame-retardant fuel injection position: Q point, 200mm upstream from the boundary position of the tuyere and blowpipe First, we tried the method disclosed in the above-mentioned published invention and examined the reason why the combustion rate was not sufficiently improved when the hot air temperature was less than 1050℃, and found the following facts. It became clear. That is, the powdered fuel blown into the blow pipe 10 from the powdered fuel injection burner 7 is
First, volatile components (hydrogen, carbon monoxide, etc.) are volatilized by receiving heat from the hot air flowing through the blow pipe 10, and when these components reach an ignition temperature, combustion is started. However, in the conventional method as described above, if the hot air temperature is too low, a considerable amount of heat will be taken away by the carrier gas that is blown in a mixed phase with the temperature of the powdered fuel itself, and the essential powdered fuel will not be sufficiently heated. As a result, not only is the start of volatilization of the volatile matter delayed, but also the rate of volatilization is slowed, and furthermore, the time for the volatile gas to reach the ignition temperature is delayed, and it takes a considerable amount of time from injection to ignition combustion. become. As a result, ignition of the powdered fuel occurs at the tip of the tuyere or within the raceway, and the combustion time from ignition until exiting the raceway is relatively significantly shortened. Therefore, if the hot air temperature is lower than 1050℃, the powder fuel injection position should be changed to 100℃ as shown in the above-mentioned published invention.
Even if it was moved upstream by about 350 mm, the combustion time within the raceway could not be substantially extended, and the combustion state of the powdered fuel at the end of the raceway was hardly improved. In particular, the time required for powdered fuel to pass through the raceway during blast furnace operation is extremely short compared to the time required for fuel to pass through boilers, kilns, sintering ignition furnaces, etc. (the former is approximately 1/300 to 1/500 of the latter). ), under these conditions, nearly half of the total residence time is consumed in so-called preheating, including volatilization of volatile matter and ignition, and the actual combustion time becomes insufficient to improve the combustion rate. It is considered that it was not obtained.

Therefore, the present inventor has determined that in order to increase the combustion rate of powdered fuel to a satisfactory level even when using relatively low-temperature hot air, the time required for the powdered fuel blown into the blow pipe to ignite is We thought that it would be effective to shorten the time period as much as possible, and conducted further research based on this idea. As a result, when pulverized fuel is injected into the blast furnace, easily flammable gas fuel is injected in parallel, and volatile matter from the pulverized fuel is rapidly evaporated and ignited by the combustion heat of the gas. I came up with the idea that it would be effective to promote this. As a result of further research to realize this idea, we came to the conclusion that the above idea could be realized as a practical technology by injecting gas fuel independently into the outer periphery of powdered fuel. . In this case, the easily flammable gas fuel (hereinafter sometimes simply referred to as gas fuel) is natural gas, city gas, converter gas, petroleum gas, blast furnace gas, and is not particularly limited in type, but may include coke oven gas, etc. is particularly preferred because it has a high combustion rate and is easily available at steel manufacturing sites.

In other words, the main component of coke oven gas is hydrogen (50-60℃ overall), and its combustion rate is that of LPG.
It is seven to eight times more powerful than natural gas, and when it is blown into a blowpipe, it quickly ignites and burns even with relatively low-temperature hot air. The combustion heat exceeding a certain amount promotes the rapid volatilization of the volatile matter in the powdered fuel and its ignition, resulting in a marked reduction in the time required for the ignition of the powdered fuel. The combustion time of the fuel is extended, and the combustion rate can be significantly increased. By the way, the reason why the gas fuel is independently blown into the outer circumference of the powdered fuel is as follows. In other words, when gas fuel is mixed with powdered fuel and supplied into the blow pipe, the increase in temperature and ignition of coke oven gas caused by hot air is suppressed by the mixture of powdered fuel, resulting in the expected combustion promotion effect. can't get it. To explain this point in more detail, when injecting powdered fuel into a blast furnace, it is said that the amount of low-temperature carrier gas should be as small as possible, and the weight ratio of powdered fuel/carrier gas is generally 10. Selected from the range of ~30 (Kg/Kg). Under such injection conditions with a high concentration of powdered fuel, the radiant heat transfer efficiency and optical transparency of the injected solid-gas multiphase flow must be extremely low. Moreover, if a method of supplying gas fuel mixed with powdered fuel is adopted, the gaseous fuel will be diluted with a large amount of powdered fuel. The ignition combustion of the multiphase flow proceeds by receiving heat from the hot air on the outermost side, but at the same time, in order for the gas fuel to rise to the ignition temperature, the powder fuel (which has a lower heat capacity than the gas) Since it is necessary to raise the temperature even to a large temperature, the ignition and combustion of the gas fuel itself is delayed together with the ignition delay due to dilution with the powdered fuel, making it impossible to satisfactorily enhance the combustion promotion effect. In addition, it goes without saying that it is preferable to inject both fuels independently from the standpoint of individually controlling the flow rates of the powdered fuel and the gaseous fuel, as well as ensuring safety.

On the other hand, if a predetermined amount or more of gas fuel is independently supplied to the outer peripheral portion of the powdered fuel, the hot air will first intensively heat and raise the temperature of the gas fuel that is in contact with the hot air. For this reason, the gas fuel instantaneously heats up to the ignition temperature and ignites and burns. As a result, the outer periphery of the powdered fuel flow is enveloped in flames caused by the combustion of the easily combustible gas fuel, so that the outer periphery is heated all at once.
The heat of combustion directs the powdered fuel flow from the outer periphery to the center, heating it and raising its temperature, which promotes the volatilization and ignition of the volatile components in the powdered fuel, leading to the start of combustion of the powdered fuel. The time is significantly reduced. As understood from the above explanation, the amount of gaseous fuel blown into the fuel needs to be such as to generate a sufficient amount of heat to promote the volatilization and ignition of the powdered fuel.

The most preferable burner for performing such combustion has a fuel injection nozzle with a multi-tube structure (double tube in the example shown), as shown in FIG. It is also advantageous to have a method of supplying gas fuel C from the outer tube 7b at the same time as supplying fuel A.

Figure 3 shows an example of the results of an experiment using pulverized coal and tar as representative examples of flame-retardant fuel using the combustion experiment apparatus shown in Figure 1 above. Similar results can be obtained in the case of 1 and 2 in the figure indicate what was done in the next experiment.

(1) A pulverized coal injection burner with a double tube structure shown in FIG. 2 was used, and pulverized coal was blown into the inner tube 7a, and coke oven gas (COG) was blown into the outer tube 7b independently.

(2) Use a burner with a double tube structure (thinner than the burner above) as shown in Figure 2, and separate tar from the inner tube 7a and coke oven gas (COG) from the outer tube 7b. Infused.

The horizontal axis is the amount of coke oven gas (COG) blown in, and shows the ratio of the amount of heat blown into coke oven gas to the total amount of heat blown into pulverized coal or tar. Therefore, the point where the coke oven gas injection amount is zero is when pulverized coal or tar is injected alone. The vertical axis shows the total combustion rate at 0.4 m from the tuyere tip. The amount of pulverized coal or tar injected is 75×
When the coke oven gas injection rate is increased while keeping it at 10 ⁴ kcal/hour (constant), the combustion rate gradually increases, reaching approximately 75% with pulverized coal injection and 100% (complete combustion) with tar injection. Get closer.

The effect of increasing the combustion rate is only 2% compared to the flame-retardant fuel of coke oven gas and pulverized coal or tar.
(Calorie conversion) It can be improved by about 15% just by co-firing.
That is, since the combustion rate within the raceway can be improved, the flow of unburned components to the outside of the raceway is reduced, and a large amount of fuel can be injected. The combustion rate of pulverized coal injection is saturated at about 75% because the remaining 75% depends on the combustion of the coal, which has a low combustion rate. As is clear from Figure 3, in order to promote the volatilization and ignition of the flame-retardant fuel and to exhibit the combustion promoting effect, it is necessary to use at least 2% gas in terms of calorific value based on the amount of injected flame-retardant fuel. Fuel injection is required. In order to achieve a combustion promoting effect by reducing the amount of coke oven gas blown as much as possible, it is preferable that the amount of coke oven gas blown is in the range of 2 to 10%.

The above combustion promotion effect was also confirmed with natural gas, city gas, petroleum gas, converter gas, and blast furnace gas.
Coke oven gas was the best in increasing the combustion rate at a constant gas injection amount.

[Effects of the Invention] The present invention is configured as described above, and its effects can be summarized as follows.

(1) Even when the hot air temperature is low, the combustion rate of flame-retardant fuel can be increased to a satisfactory level, and even when it is difficult to obtain a high-temperature hot air temperature, it is possible to inject a large amount of flame-retardant fuel. It is possible to achieve significant cost reductions.

(2) It is also possible to operate the blast furnace by actively lowering the hot air temperature, increasing energy-saving efficiency. It is also possible to suppress deterioration of refractories including ducts and the like. In addition, the gas fuel in the outer periphery also serves as a cooling gas for the burner, and the temperature of the hot air can also be lowered, so even non-water-cooled burners have a long life.

(3) Since the combustion rate can be sufficiently increased, it becomes possible to increase the usage ratio of inexpensive flame-retardant fuels such as pulverized coal, and it is possible to reduce fuel costs.

(4) Since the combustion rate is stable at a high level, the stability of blast furnace conditions can be improved, and blast furnace operating efficiency can also be improved.

(5) To carry out the present invention, only burners with a multi-layered structure or other gas fuel injection devices are required, so the increase in burden is small.

(6) Coke oven gas and blast furnace gas are generated in the coke manufacturing process and are essential as raw materials for blast furnace charging, and are usually located adjacent to blast furnace equipment and can be obtained at low cost. .

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing the combustion device used in the experiment.
FIG. 2 is a partially cutaway side view illustrating a multi-structure burner used in carrying out the present invention, and FIG. 3 is a graph showing the effects of the present invention. A...Powdered fuel, C...Easily flammable gas fuel, 1...
...Ground hopper, 2...Screw conveyor, 3
. . . Coal bottle, 4 . . . Quantitative feeder, 5 . . . Transport air, 6 . . . Transport pipe, 7 .

Claims (1)

[Claims] 1. When injecting a flame-retardant fuel such as powder fuel, tar, or heavy oil into a blast furnace, the flame-retardant fuel stream is A blast furnace characterized in that an easily flammable gas fuel is injected in parallel with the inflammable gas fuel, and the amount of the inflammable gas fuel injected is 2% or more in terms of calorific value with respect to the amount of inflammable fuel injected. method of injecting flame-retardant fuel.