JPH04301017A - Structure for nozzle for supplying reducing gas - Google Patents

Abstract

PURPOSE:To uiformize blowing into a fluidized bed, to prevent the dropping of ores from a nozzle to ores in the fluidized bed due to the variation in gas pressure according to operational variation and to improve reduction efficiency and the operation in the structure of the nozzle for introducing fluidized bed forming gas into a fluidized bed reduction furnace for ore. CONSTITUTION:In the structure of reducing gas nozzle for fluidized bed furnace, the ratio of the length L to the inside diameter D of plural reducing gas nozzles 10 set at the bottom part of the above-mentioned fluidized bed reduction furnace is made to be L/D>=4, and the blowing of reducing gas into the fluidized bed is uniformized and the dropping of ores is prevented and the reduction efficiency and the operation are improved.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to equipment for reducing iron ore using a fluidized bed reduction furnace.

0002

BACKGROUND OF THE INVENTION The smelting reduction method is attracting attention as an alternative to the conventional method of producing hot metal using a blast furnace. This method has been developed with the aim of producing hot metal at low cost by using fine ore, steam coal, and omitting the coking process. In addition, in order to effectively utilize the reducing power and heat of the exhaust gas generated in the smelting reduction furnace, a method has also been developed in which the raw ore is preheated and pre-reduced by supplying it to the fluidized bed reduction furnace as a fluidized gas.

[0003] As such a fluidized bed reduction device, Japanese Patent Application Laid-Open No. 1982
-269283 and JP-A-1-111807, this type has a fine ore input part on the side and a carrier gas introduction part for forming a fluidized bed near the bottom. A fluidized bed (riser) equipped with a fluidizing gas introduction section with multiple reducing gas nozzles on the entire surface of the bottom plate of the fluidized bed, and a powder circulation fluidization section for circulating powder via a cyclone outside of the riser. There are two types: one has a circulating fluidized bed consisting of a downcomer (downcomer), and the other has a non-circulating fluidized bed in which the powdered iron ore (reduced ore) collected by the cyclone is not returned to the riser.

In either type, the reducing gas is introduced into the fluidized bed through a number of cylindrical nozzles provided in the fluidized bed.

[0005]

[Problem to be solved by the invention] However, due to pressure fluctuations during operation, the amount of reducing gas supplied to the fluidized bed increases or decreases, and when the amount of reducing gas becomes considerably small, it is difficult to blow gas between the nozzles. A quantity bias occurs. At this time, fine ore forming a fluidized bed falls into the nozzle hole. Once the ore enters the nozzle, it is not blown up from the nozzle into the fluidized bed and falls through the nozzle hole into the fluidized bed. If this phenomenon occurs frequently, the amount of fallen ore will increase, resulting in a decrease in reduction efficiency and a significant decrease in productivity.

[0006] As a measure to prevent this uneven flow of the blown reducing gas and achieve uniform dispersion within the fluidized bed, the number of nozzles arranged in the fluidized bed is increased by making the opening surface of each nozzle smaller. Possible countermeasures include providing a baffle plate at the outlet of the hole to increase the pressure loss ratio.

However, when the opening surface of the nozzle is made smaller, troubles due to nozzle clogging are more likely to occur, and the arrangement of baffles etc. complicates the bottom structure and requires more power to increase the pressure loss ratio. New problems such as an increase in the size of the source and an increase in cost will arise, and this cannot be a practical solution.

The problem to be solved by the present invention is that in fluidized bed reduction of powdered iron ore for smelting reduction, reducing gas can be uniformly blown into the powdered ore fluidized bed in a stable state, and The objective is to find conditions for the nozzle configuration to effectively prevent ore falling.

[0009]

[Means for Solving the Problems] The present invention provides a nozzle for supplying reducing gas circulated from a smelting reduction furnace to a fluidized bed reduction furnace, in which the ratio of the length L of the nozzle hole to the inner diameter D is set to L. /D≧4.

0010

[Function] The ratio of the length L of the nozzle hole and the inner diameter D is L/D≧4.
By doing so, a sufficiently long rectifying area is formed for the introduced reducing gas, and the reducing gas flow that blows upward from below applies an upward drag force to the ore that has fallen into the nozzle, slowing down the descending speed of the ore. The particles are accelerated in the upward direction, and the particles are entrained in the reducing gas and blown out of the nozzle. When the L/D ratio is approximately 4, the above phenomenon becomes extreme, and the larger the ratio, the greater this tendency.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a cylindrical nozzle 10 made of a cobalt-based heat-resistant alloy. The length of the nozzle hole from the reducing gas inlet 1 to the discharge port 2 is L, and the inner diameter of the nozzle hole is D. This nozzle 10 was applied to a circulating fluidized bed reduction furnace 20 of the melting reduction furnace shown in FIG. 2(a).

In FIG. 2(a), a circulating fluidized bed reduction furnace 20 includes an external particle circulation device comprising a riser 23 having an ore inlet pipe 21 and a reduced ore discharge pipe 22, a cyclone 24, and a downcomer 25. 26, respectively, the riser 23 and the external particle circulation device 26 are connected by an inlet pipe 27 in the upper part and a connecting pipe 28 in the lower part.
are connected. Reference numeral 29 denotes an inert carrier gas introduction pipe to the riser 23. The carrier gas from the introduction pipe 29 is once introduced into the gas header 30, and from there it is introduced into the riser 23 from the breathable nozzle support plate 31. It is squirted. The reducing gas introduced into the riser 23 through the reducing gas introduction pipe 32 from the melting reduction furnace (not shown) is as follows:
Reducing gas is introduced into the riser 23 from the reducing gas header 34 located below the floor plate 33 through nozzles 10 uniformly arranged on the floor plate 33 surface.

As shown in FIG. 2(b), the nozzle 10 is fixed to a nozzle support plate 31 and a floor bottom plate 33 with mounting brackets 11, and seals are installed to prevent gas leakage from the respective gas headers 30 and 34. It also serves as a retainer.

FIG. 3 shows a circulating fluidized bed reduction furnace 20 in which the ratio of the total nozzle inner hole area to the fluidized bed bed surface is 15%, with the nozzle length kept constant and the nozzle hole length L and diameter D The ratio L/D
The results of investigating the amount of fallen ore by changing various values are shown. The introduced reducing gas is gas from a melting reduction furnace at 1200°C, and the discharge speed is varied to determine the difference between the final particle velocity Ut, which is the lowest gas velocity at which the particles scatter upward, and the nozzle discharge velocity Uo. The amounts of fallen ore are shown when the ratio Ut/Uo is 100, 50, 20, and 5, respectively. In the figure, the amount of fallen ore is the ratio F of the total amount of ore F to the total amount of ore input T introduced from the ore introduction pipe 21 shown in FIG. 2(a).
/T (%).

As shown in the figure, which Ut /Uo
In both cases, the amount of fallen ore decreases rapidly by increasing the L/D ratio, and the inflection point for this decrease is when the L/D ratio is approximately 4.
It can be seen that it exists at the position. In particular, when the L/D ratio exceeds 4 or more, a nozzle discharge speed that is quite close to the particle terminal velocity Ut produces a similar effect.

[0016]

[Effects of the Invention] The present invention provides the following effects.

(1) Trouble caused by falling ore can be eliminated and operational stability of the fluidized bed reduction furnace can be increased.

(2) It becomes easier to control the degree of reduction and the amount of discharge, and the operational efficiency of all equipment including the melting reduction furnace is improved.

(3) Since the blow-by phenomenon in the fluidized bed due to the introduced gas does not occur, the catalytic reaction of solid gas in the dense fluidized region at the bottom of the fluidized bed becomes good, and the reaction efficiency is improved.

(4) Since the pressure loss rate of the nozzle can be lowered,
No extra power costs required.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an aspect of a nozzle according to an embodiment of the present invention.

FIG. 2 is a diagram showing an example of a fluidized bed reduction furnace to which the nozzle of FIG. 1 is applied, and a nozzle mounting structure.

FIG. 3 is an explanatory diagram of the effects of the present invention.

[Explanation of symbols]

1　Reducing gas inlet 2 Discharge port 10 Nozzle 11 Mounting bracket 20 Circulating fluidized bed reduction furnace 21 Ore introduction pipe 22 Reduced ore discharge pipe 23 Riser 24 Cyclone 25 Downcomer 26 External particle circulation device 27 Introductory pipe 28 Connecting pipe 29 Carrier gas introduction pipe 30 Carrier gas gas header 31 Nozzle support plate 32 Reducing gas introduction pipe 33 Floor bottom plate 34 Reducing gas header

Claims (1)

[Claims] 1. In a reducing gas supply nozzle for a fluidized bed reduction furnace, a plurality of reducing gas supply nozzles are arranged at the bottom of the fluidized bed reduction furnace, and the ratio between the length L and the inner diameter D of the nozzle is L.
/D≧4 reducing gas supply nozzle structure.