WO2012086403A1 - Blast furnace slag sensible heat recovery device - Google Patents

Abstract

Provided is a blast furnace slag sensible heat recovery device which atomizes blast furnace slag using compressed air, lets sensible heat of the blast furnace slag be absorbed by the air by heat exchange between the air and the slag particles, and recovers heat, characterized by comprising: a gas atomizer (3) having an injection nozzle which injects gas upwards in an opposite direction to the gravity direction, and in which molten slag is fed towards the gas injected from the injection nozzle; and a first heat exchange tower (4) composed of a tubular body extending upwards from the gas atomizer (3) and inside of which the atomizer gas and atomized slag particles flow upwards.

Description

Blast furnace slag sensible heat recovery system

The present invention relates to a blast furnace slag sensible heat recovery device that can efficiently recover sensible heat of blast furnace slag generated as a by-product in a pig iron manufacturing process of a blast furnace.

In the blast furnace, 3 tons of blast furnace slag of about 1,500 ° C. is generated while 10 tons of hot metal is produced. This blast furnace slag is mainly used as a raw material for cement. In that case, 95% or more of the total blast furnace slag needs to be vitrified.

In order to rapidly cool the blast furnace slag to vitrification (amorphous structure), the cooling rate shown in FIG. 1 is required.

That is, a molten slag of about 1,400 ° C. is 21 ° C./sec or higher from 1,200 ° C., 6.0 ° C./sec or higher from 1,200 ° C. to 1,100 ° C., 1,100 ° C. to 1,000 ° C. It is necessary to cool at a cooling rate of at least 2.5 ° C./sec and from 1,000 ° C. to 850 ° C. at a cooling rate of 0.3 ° C./sec.

In order to obtain the above cooling rate, a water granulation process is generally performed in which water is blown into a blast furnace slag to crush it, and approximately 90% of the blast furnace slag is rapidly crushed into 75 μm to 5 mm particles by this water granulation process. Has been.

In the above-mentioned water granulation treatment, a large amount of low-temperature waste water of 50 to 70 ° C. is generated by heat exchange between the blast furnace slag and the cooling water, but there is a problem that it cannot be used for power generation at this water temperature level.

The efficiency at which the input thermal energy is used for work and power generation does not exceed the Carnot efficiency shown in FIG. That is, it is advantageous to recover heat at a higher temperature.

Therefore, many slag atomizations by air jets have been continuously devised as a method for recovering the energy possessed by blast furnace slag as sensible heat at a high temperature (see, for example, Patent Document 1).

JP 2009-132546 A

However, a heat recovery apparatus that recovers sensible heat of blast furnace slag by atomization of slag by an air jet has not been put into practical use at present.

The reasons for this are as follows: (1) Compared to the heat transfer coefficient of water and blast furnace slag, the heat transfer coefficient of air and slag particles is generally only about 1/10. (2) Since a large amount of cooling air is required to satisfy the cooling rate, the air temperature recovered as hot air from the slag flowing out of the blast furnace at a high temperature of 1,500 ° C. is about 500 The temperature is lowered to 0 ° C., and what is finally obtained as steam for power generation is low-pressure steam of about 200 ° C., and it can be mentioned that power generation cannot be performed with high efficiency from the Carnot efficiency of FIG.

The present invention has been made in consideration of the problems in the conventional heat recovery apparatus as described above, and provides a blast furnace slag sensible heat recovery apparatus that can efficiently recover the sensible heat of blast furnace slag.

In the blast furnace slag sensible heat recovery apparatus that atomizes blast furnace slag using compressed air, further absorbs sensible heat of the blast furnace slag by air exchange by heat exchange between air and slag particles, and performs heat recovery.
A gas atomizer that has an injection nozzle that injects gas upward in the direction opposite to the direction of gravity and that is supplied with molten slag toward the gas injected from the injection nozzle, and a cylindrical shape that extends upward from the gas atomizer A blast furnace slag sensible heat recovery apparatus comprising a body and comprising a heat exchange tower in which atomized gas and atomized slag particles flow upward.

In the present invention, it is preferable that a nozzle for injecting the cooling air upward is disposed on the outer peripheral portion of the injection nozzle.

In the present invention, it is preferable that the heat exchange tower has a radial cross-sectional area that is enlarged from the bottom to the top.

In the present invention, it is possible to provide a separation tower that settles and separates the atomizer gas and the slag particles that flow in the heat exchange tower and are injected in a mixed state from the upper part of the heat exchange tower.

In the present invention, there is provided a position sensor for detecting a deposition height of the slag particles deposited in the separation tower and having a gate valve at the lower part of the separation tower, and the gate valve outputs a signal output from the position sensor. If the slag discharge amount is adjusted by opening and closing based on the slag, slag can be deposited at a constant height at the lower part of the separation tower at all times, so that air leakage can be prevented.

In the present invention, the heat exchange tower is a double cylinder in which an inner cylinder that allows air to permeate and an outer cylinder that does not allow air to permeate are doubled, and an annular space between the inner cylinder and the outer cylinder is in a height direction. Provided with a partition plate for partitioning into a plurality of rooms, a low-pressure air supply passage for supplying low-pressure air to each of the above-mentioned rooms via an on-off valve and a flow meter, and a high-pressure air having an on-off valve for supplying high-pressure air to each of the above-mentioned rooms If the on-off valve of the high pressure air supply path is opened when the flow rate of the low pressure air measured by the flow meter falls below a threshold value, slag particles adhere to the inner wall of the heat exchange tower. Can be prevented.

In the present invention, the high-pressure air supply path preferably further includes an air nozzle that injects high-pressure air toward the annular space.

According to the present invention, vitreous slag particles can be obtained by atomization of slag using an air jet, and sensible heat of blast furnace slag can be efficiently recovered.

It is a graph which shows the cooling rate required for vitrification of the molten slag which concerns on this invention. It is a graph which shows the Carnot efficiency which concerns on this invention. It is a block diagram which shows the structure of the blast furnace slag sensible heat recovery apparatus which concerns on this invention. It is an enlarged view of the atomizer of FIG. 3, and its peripheral part. It is an enlarged view which shows the structure of the acceleration nozzle applied to the atomizer of FIG. It is the photograph which image | photographed the injection state by upward atomization. It is the graph which showed the drag coefficient of the slag particle | grains atomized. It is the graph which showed the air temperature in a primary heat exchange tower, and the particle temperature time history for every particle diameter. It is the graph which showed the particle temperature time history for each particle diameter in a primary heat exchange tower. It is the graph which showed the relationship between the particle temperature for every particle diameter, and a cooling rate. It is the graph which showed the temperature change of the slag accumulated on the belt conveyor and cooling air. It is the schematic which shows the structure of the reverse pressure removal mechanism which concerns on this invention. It is a graph which shows the change of various heat exchange performance at the time of changing slag flow volume. It is the graph which showed the slag particle temperature distribution in the primary heat exchange tower by slag flow rate 1.25 times. It is the graph which showed the heat recovery efficiency and electric power generation amount change at the time of changing slag flow volume, maintaining air slag ratio constant. It is the front view which showed 2nd embodiment of the heat recovery apparatus of this invention.

Hereinafter, the present invention will be described in detail based on the embodiments shown in the drawings.

1 Blast Furnace Slag Sensible Heat Recovery Device 1.1 Overall Configuration and Operation Method of Blast Furnace Slag Sensible Heat Recovery Device FIG. 3 is a block diagram showing the configuration of a blast furnace slag sensible heat recovery device (hereinafter abbreviated as a heat recovery device) 1 It is.

In FIG. 1, a heat recovery apparatus 1 includes a slag tundish 2, a gas atomizer (hereinafter abbreviated as “atomizer”) 3 for injecting gas upward in the direction opposite to the direction of gravity, and an upward extension from the atomizer 3. A primary heat exchange tower (heat exchange tower) 4 made of a cylindrical body in which atomizer gas and atomized slag particles flow upward, and flows in the primary heat exchange tower 4 from above the primary heat exchange tower 4 A slag accumulation tower (separation tower) 5 that separates and separates atomizer gas and slag particles injected in a mixed state, and a secondary heat exchange chamber 6 are provided.

Both the primary heat exchange tower 4 and the secondary heat exchange chamber 6 are intended to cool the slag particles by bringing the slag particles into contact with air (at this time, the air is heated and heat exchanged). The air heated in the heat exchange tower 4 and the air heated in the secondary heat exchange chamber 6 flow independently to the primary system line L1 and the secondary system line L2.

The primary system line L1 is returned to the atmosphere through the primary system cyclone 7 for collecting fine powder, the primary system steam boiler 8 for passing heat to the steam, the dust collector 9 and the diffusion tower 10, and the secondary system line L2 is returned to the atmosphere. The secondary cyclone 11, the secondary steam boiler 12, the blower 13, the dust collector 9, and the diffusion tower 10 are returned to the atmosphere.

The primary heat exchange tower 4 in the present embodiment has a cross-sectional area that is enlarged about 1.5 times from the lower part to the upper part, and is from a tower having a diameter (minimum diameter) of 1.3 m and a height of about 40 m. It is configured.

Comparing the state of steam heated by air in the primary system steam boiler 8 and the secondary system steam boiler 12 in both systems of the primary system line L1 and the secondary system line L2, the primary heat exchange tower system (primary system line L1 ) Is in a high enthalpy state of high temperature and high pressure.

Therefore, energy is recovered as electric power by the generator 14 in the primary system.
On the other hand, in the secondary heat exchange chamber system (secondary system line L2), which has a lower enthalpy state than the primary system, high-pressure atomized air (this atomized air is the primary heat exchange medium air) is added to the primary system atomizer 3. ) Power of the compressor 15 for sending Aa, and a blower 13 for introducing the atmosphere to send the secondary heat exchange medium air to the secondary heat exchange chamber 6 and sending it to the diffusion tower 10 via the dust collector 9 In order to supply the power, the turbine 16 recovers energy as power.

That is, power is sent from one turbine 16 to the primary compressor 15 and the secondary blower 13 via the common rotating shaft 17.

In actual start, operation, and stop, first, power is supplied from outside the system to operate the blower 13 and the compressor 15, and air is sent to the atomizer 3 and the secondary heat exchange chamber 6, respectively.

Next, molten slag is supplied from the blast furnace to the slag tundish 2, and the gate 18 to the slow cooling facility (not shown) located at a position lower than the atomizer 3 is switched from open to closed.

Thereby, molten slag is supplied to the atomizer 3 and atomization is started.

The slag particles of φ5 mm or less atomized by the atomizer 3 rise in the primary heat exchange tower 4 by the upward gas and finally fall in the slag accumulation tower 5.

Next, the slag particles move from the slag accumulation tower 5 through the gate valve 19 into the secondary heat exchange chamber 6, further cooled by the secondary heat exchange medium air, and discharged at a temperature of about atmospheric temperature + 5 ° C. .

Normally, in the operation of a blast furnace, continuous dredging is performed without interruption while switching a plurality of dredging openings about every 3 hours, and by connecting these plural dredging openings to a tundish at one place with a boil It is possible to operate continuously except when the wind is off.

When the output stops due to wind breaks, etc., the slag supply to the atomizer 3 is stopped by opening the gate 18 and sending molten slag to the slow cooling facility.

After the slag supply is stopped, the operation of the atomizer 3 can be ended by stopping the blower 13 and the compressor 15.

1.2 Atomizer FIG. 4 is an enlarged view of the atomizer 3 shown in FIG. 3 and its peripheral portion.

In FIG. 4, the atomizer 3 includes an atomizing gas injection device 3a that is disposed in the center of the primary heat exchange tower 4 and injects the atomized gas upward, and a molten slag nozzle 3b that discharges the molten slag upward, and the atomizing gas injection device 3a. Is provided with a cooling air nozzle 20 for injecting cooling air upward. In addition, S has shown the slag particle which has fallen in the figure.

Atomized air Aa injected toward the molten slag from the atomized gas injection device 3a, and cooling air injected in a cylindrical shape from the vicinity of the inner wall of the primary heat exchange tower 4 at a position away from the discharged molten slag The total amount of Ca is adjusted so as to be approximately the same mass flow rate as the molten slag.

Specifically, the atomizer is first designed and the atomizer air flow rate is determined so that the maximum particle diameter by atomization is 5 mm, and then the nozzle diameter of the cooling air nozzle 20 so that the total mass flow rate matches the slag mass flow rate. And the number of nozzle holes is adjusted.

However, since it is desirable for the atomizer 3 to quickly exchange heat with slag particles and to ensure a sufficient operating margin, a highly efficient atomizer that can atomize molten slag to a maximum particle diameter of 5 mm with as little air flow as possible is adopted. Should.

Therefore, in this heat recovery apparatus, the one-stage type of acceleration nozzle described in Japanese Patent No. 4268193 filed earlier by the present applicant is used as the atomizer.

FIG. 5 is an enlarged longitudinal sectional view showing the configuration of the acceleration nozzle.

In the figure, the atomizing gas injection device 3a is mainly composed of a conical molten slag nozzle 3b having an upward discharge port 3b 'and a ring component 3c disposed adjacent to the upward discharge port 3b' and in the periphery thereof. ing. The injection port 3c ′ formed at the center of the ring component 3c is formed in a circular arc shape so as to expand downward. In the figure, 3d is a gas passage through which the atomized air Aa is introduced.

The atomized air Aa supplied to the gas passage 3d forms a high-speed gas flow by passing through a throat portion T formed between the outer wall of the molten slag nozzle 3b and the injection port 3c 'of the ring component 3c. The molten slag is atomized by the high-pressure gas flow, and the atomized slag particles are injected from the injection port 3c ′.

FIG. 6 is a photograph of the upward spraying state when the operation was performed by simulating molten slag with water, and shows that the atomized particles do not spread immediately but have a high straightness.

The atomizer 3 having the above-described configuration has an advantageous feature that the atomization and particle cooling can be performed at an air flow rate of about 1/3 compared to a conventional perforated nozzle array type atomizer that connects a jet at one point. have.

1.3 Primary Heat Exchange Tower The most unique feature of the heat recovery apparatus 1 of the present invention is the primary heat exchange tower 4 that makes slag particles fly in the direction opposite to the direction of gravity.

The primary heat exchange tower 4 obtains the steam at 550 ° C. whose efficiency is asymptotic to the maximum value as described in FIG. 2 while satisfying the cooling rate described in FIG. It is configured for the purpose of realizing.

Since there is no latent heat in the amorphous state, the cooling rate dT _s / dt at a low Reynolds number is generally described by the equation (1).

　ここで記号の意味は、Ｔ：温度、ｔ：時間、Ｒｅ：レイノルズ数、λ：熱伝導率、Ｄ：粒子径、ρ：密度、Ｃ_ｐ：定圧比熱、ｕ：速度、μ：粘性係数。添え字の意味は、ｇ：ガス（空気）、ｓ：スラグである。

Here, the meanings of the symbols are T: temperature, t: time, Re: Reynolds number, λ: thermal conductivity, D: particle diameter, ρ: density, C _p : constant pressure specific heat, u: velocity, μ: viscosity coefficient. The meaning of the subscript is g: gas (air), s: slag.

It can be seen that the cooling rate is proportional to the relative speed difference | u _g −u _s | of the air and slag particles to the power of 0.6.

Since all other conditions are property values and temperatures, all are basically the same and difficult to change. Therefore, in order to obtain the cooling rate required for vitrification, the relative speed difference between air and slag particles | There is nothing but to increase u _g −u _s |.

Therefore, the equation (2) is obtained by solving the equation of motion for the relative velocity difference | u _g −u _s | between air and slag particles in the equilibrium state.

Here, the meanings of the symbols are g: gravitational acceleration, C _d : drag coefficient of slag particles. The gravitational acceleration g is positive in the same direction as the velocity u. If drag coefficient C _d is if slag particles spherical, if the large particles (Reynolds number greater condition) as φ5mm particles is a value asymptotic to a constant value as Cd = 0.44. More precisely, it is a function of the Reynolds number as shown in FIG.

When the acceleration of gravity g is positive (the velocity and direction of gravity are the same, ie, equivalent to downward gas atomization) and negative (the velocity and direction of gravity are opposite, ie, equivalent to upward gas atomization) Is solved, it becomes like (3) and (4).

As can be seen from a comparison of formula (3) and (4), the particle velocity u _s a downward gas atomization of formula (3) is larger than the air velocity u _g, flight distance of very long particles to achieve the I need it. On the other hand, the upward gas atomization of formula (4), the particle velocity u _s

　に設計することも可能であり、下向きアトマイザーと比較して短い飛行距離で目標達成した装置を実現できる。

It is also possible to design a device that achieves the target at a short flight distance compared to a downward atomizer.

When the relative speed difference | u _g −u _s | is eliminated from Expression (1) and Expression (2), Expression (6) is obtained.

From the formula (6), the cooling rate is finally inversely proportional to the 1.1th power of the particle diameter D _s , so that φ5 mm having the largest diameter among the assumed particles is the smallest here. Therefore, it turns out that vitrification becomes difficult.

Incidentally, atomizer 3, the primary heat exchanger column 4, pressurized including slag accumulation tower 5, the cooling rate in proportion to the 0.3 power of from [rho _g that the formula to increase the air density ρ _g (6) is greater will be designed formula (4) from the air velocity u _g is small (reduced air quantity, more heat can be recovered at a high temperature) it has the advantage that.

This point will be described in a second embodiment applied to blast furnace blowing described later.

In the formula (4), when the design is performed under the condition (u _s = 0) in which the largest 5 mm particle (D _s = 0.005 [m]) is stationary in the primary heat exchange tower 4, the inside of the primary heat exchange tower 4 air velocity u _g in is given by equation (7).

On the other hand, if the cross-sectional area of the primary heat exchange tower 4 is A, the air mass flow rate dot _mg in the primary heat exchange tower 4 is constant at any height in the tower, so Thus, equation (8) is established.

By transforming equation (8), equation (9) is obtained.

The air temperature T _g is not constant in the primary heat exchange tower 4, and when the slag particles are cooled, the air temperature increases. Therefore, the air temperature T _g increases in the height direction in the tower, and the air density ρ _g is Decrease. Air to maintain the particle velocity u _s constant, in order to keep the minimum height of the primary heat exchanger column 4, according to the relation of formula (9), that the cross-sectional area of the primary heat exchanger column 4, decreases it is effective to increase in inverse proportion to the square root of the density [rho _g.

Specifically, in FIG. 3, the atomizer air temperature rises from 180 ° C. to 870 ° C., thereby reducing the air density from 1.17 kg / m ³ to 0.461 kg / m ³ to about 40% of the initial. Therefore, in accordance with Equation (9), a pipe that gradually expands is used so that the cross-sectional area of the primary heat exchange tower 4 is 1.5 times the cross-sectional area of the bottom part from the bottom part to the top part. .

FIG. 8 is a graph showing calculation results of temperature changes of air and particles in the primary heat exchange tower 4 solved by coupling energy equations of particles and air.

From this result, it can be seen that if the height (particle flight distance) of the primary heat exchange tower 4 is about 40 m, any particle diameter of 0.075 to 5.0 mm will reach an equilibrium temperature almost equal to the air temperature. .

FIG. 9 is a graph showing the particle temperature time history for each particle diameter in the primary heat exchange tower 4.

FIG. 10 is a graph showing the relationship between the particle temperature and the cooling rate for each particle diameter, and the relationship between the slag temperature and the required cooling rate processed from FIG.

In FIG. 10, the required cooling condition is not satisfied at a particle diameter of 5 mm (see F1 in the figure), and the particle diameter of 3.375 mm (see F2 in the figure) is the maximum diameter that can satisfy the required condition for the cooling rate. I understand that.

In the particle size distribution targeted at the stage of gas atomization, the ratio of the particle diameter of 2 mm or more is 5%, the particle diameter of 3.375 mm or more is 2%, and the particle diameter of 5 mm or more is 0%. Therefore, a vitrification rate of 98% is expected as the performance of the primary heat exchange tower 4, and a vitrification rate of 95% or more of the cement material specification is expected to be satisfied.

1.4 Slag Accumulation Tower The slag accumulation tower 5 uses gravity to deposit slag particles in the lower part to separate it from the air, and the air passes from the upper part of the slag accumulation tower 5 to the primary steam boiler 8 via the primary cyclone 7. On the other hand, only the slag particles are prepared to be sent out to the second heat exchange chamber 6. There are two points (a) and (b) that must be considered.

(a) Minimizing particles that are rolled up with air Slag particles that accompany air are not sent to the secondary heat exchange chamber 6 but are recovered by the primary cyclone 7, and the slag particles are cooled from 860 ° C. As much sensible heat does not contribute to heat recovery, it must be minimized. Therefore, a perforated plate 5a (see FIG. 3) is installed on the ceiling of the slag accumulation tower 5 to make the flow uniform by providing fluid resistance, and air is sucked uniformly from the entire surface at a speed of 0.85 m / s. Design to do.

At this time, the relationship between the air velocity and the stationary particle size is expressed by Equation (7). Further, the drag coefficient C _d shown in FIG. 7 is approximated by the equation (10) in the section of 1 <Re <10 ⁴ as a function of the Reynolds number.

Since slag particles are highly likely to contain bubbles inside, using a true slag density of 2,600 kg / m ³ as the particle density ρ _s is a dangerous evaluation. Therefore, a safe evaluation is performed using 1,300 kg / m ³ which is a unit volume mass of slag particles filled with voids.

Is simultaneous equations (7) Equation _{(10), u g = 0.85} , in theory as _u s = 0 is the seek particle diameter rests slag accumulation tower 5, Ds = 0.25 mm is obtained .

That is, when the particle diameter is 0.25 mm or less, it is sent to the primary cyclone 7 side together with air. The ratio of the particle diameter of 0.25 mm or less targeted by gas atomization is 5%, and the sensible heat brought out by the 860 ° C. slag particles having a particle diameter of 0.25 mm or less is 1.4 MW.

(b) Minimizing the air leaking from the slag accumulation tower to the secondary heat exchange chamber Whereas the pressure in the slag accumulation tower 5 is 50,000 Pa (G), the pressure in the secondary heat exchange chamber 6 is − Since it is 300 Pa (G), there is a possibility that air leaks from the slag accumulation tower 5 to the secondary heat exchange chamber 6 in the path of the slag particles, thereby reducing the power generation amount in the primary system.

In order to prevent this, slag is always deposited at a certain height in the lower part of the slag accumulation tower 5, and air leakage is prevented by the fluid resistance of the slag particle packed bed P.

First, the opening area of the gate valve 19 for adjusting the flow rate of the slag particles is obtained. Modeling the gate with an orifice and passing the slag particles at a mass flow rate of 28 kg / s, the orifice diameter D ₀ is the Beverloo equation

　より求めると、Ｄ_０＝０．１７１ｍになる。嵩密度１，３００kg/m³のスラグ粒子が嵩速度０．９４m/sでオリフィスを通過していることになる。

More specifically, D ₀ = 0.171 m. Slag particles having a bulk density of 1,300 kg / m ³ are passing through the orifice at a bulk velocity of 0.94 m / s.

Next, the relationship between the filling height and the leakage air flow rate is obtained from the pressure loss of the slag particle packed bed P on the gate valve 19 using the Elgan type. From Ergan's formula (12)

The relationship between the filling height L and the air flow rate dots _{mg, leak} is expressed by equation (13).

　ここで、Δｐ：スラグ集積塔と二次熱交換室の圧力差、ε：充填層空隙率である。

Here, Δp is a pressure difference between the slag accumulation tower and the secondary heat exchange chamber, and ε is a packed bed porosity.

From equation (13), it can be seen that, for example, the leakage air flow rate dot _{mg, leak} at a filling height of 0.5 m is 0.07% of the air flow rate in the slag accumulation tower 5.

Therefore, if slag particles of about 500 mm are always deposited at the bottom of the slag accumulation tower 5, the amount of leaked air can be reduced to a level that can be substantially ignored.

In the heat recovery apparatus 1 of the present embodiment, the upper limit fiber sensor 5b and the lower limit fiber sensor 5c (see FIG. 3) as position sensors are attached to the lower part of the slag accumulation tower 5 in a state of being vertically separated, and the slag filling height is adjusted. An upper limit signal and a lower limit signal are output. If the upper limit is exceeded, the gate valve 19 is opened. If the lower limit is cut, the gate valve 19 is closed, so that the height of the slag particle packed bed P is lower than the lower limit fiber sensor 5c. It controls so that it may be located between the upper limit fiber sensors 5b.

According to the investigation on the adhesion temperature between the amorphous slag particles related to the blast furnace slag, the lower limit of the adhesion temperature between the amorphous slag is 950 ° C. Therefore, in the present heat recovery apparatus 1, the slag is placed below the slag accumulation tower 5. During the deposition of the particles, the 860 ° C. slag particles do not adhere to each other.

1.5 Secondary heat exchange chamber (a) Outline of the apparatus In the secondary heat exchange chamber 6, the slag particles flowing from the primary heat exchange tower 4 as the primary heat exchange chamber at the average temperature of 860 ° C. via the slag accumulation tower 5. The purpose is to further recover the sensible heat to cover mainly the power of the entire heat recovery device 1 (compression power of the atomizer gas and cooling air blowing power in the secondary heat exchange chamber 6).

In the primary heat exchange tower 4, the slag particle temperature is lowered to 1,000 ° C. or less in accordance with the cooling rate shown in the graph of FIG. 1, so that the secondary heat exchange chamber 6 has a cooling rate of at least 0.3 ° C./s. If there is, it will be good.

Therefore, a sufficient cooling rate can be obtained by allowing the secondary cooling air Aa ′ to permeate the deposition layer while being deposited on the belt conveyors 6a to 6d (see FIG. 3) and transported.

As shown in FIG. 3, the belt conveyors 6a to 6d are arranged in multiple stages in the height direction so that the slag particles move from top to bottom, and each belt is composed of a screen that can be ventilated. . Since the secondary cooling air Aa ′ passes from the bottom to the top through the belt and the slag accumulation layer, the gap is filled so that the gap between the side wall of the secondary heat exchange chamber 6 and the belt is minimized.

Specifically, a belt conveyor having a width of 5 m and a length of less than 23 m is assembled in four steps in the vertical direction.

Therefore, the horizontal plane cross section in the secondary heat exchange chamber 6 is about 5 × 23 m, and the cross-sectional area is 115 m ² .

In addition, the total belt length of the belt conveyors 6a to 6d is 92 m, and the residence time from when the slag flows into the secondary heat exchange chamber 6 until it is carried out to the outside is planned to be 250 seconds. The moving speed is 0.368 m / s (22 m / min).

As the belt, a 100-mesh stainless screen (aperture of about 0.15 mm) is used so that slag particles can be held while being porous to allow air to pass through.

The total bulk volume of the slag accumulated on the belts 6a to 6d at each stage is 4.6 m ³ and the total mass is 6.7 kg. The average belt accumulation bulk of the slag at this time is 10 mm.

The porosity ε is about 43% from the unit mass of slag. From the calculation of the cooling process, the air / slag ratio is 1.23. Therefore, the average cooling air ascending speed in the secondary heat exchange chamber 6 is about 0.6 m / s.

Since the slag is carried out of the room while being placed on the belt conveyor, it is necessary to make the inside of the secondary heat exchange chamber 6 negative with respect to the atmospheric pressure to prevent dust generation outside the secondary heat exchange chamber 6. . Therefore, the secondary heat exchange chamber 6 is installed on the suction side of the blower 13.

(b) Heat exchange process calculation For a total of 40 mm thickness of 4 stages x deposition thickness 10 mm, slag particles are from top to bottom, secondary cooling air (fluid) Aa 'is from bottom to top, and the two phases are countercurrent. In moving countercurrent heat exchange, one-dimensional flow in the slag thickness direction and heat transfer were calculated. The empirical formula (14) at low Reynolds number by Seki et al. Was used for heat transfer between slag particles and fluid.

FIG. 11 is a graph showing the temperature distribution in the thickness direction of the slag particles deposited on the belt conveyor and the temperature distribution in the thickness direction of the cooling air.

Since the temperature decreased by 800 ° C. over 250 seconds, an average cooling rate of 3.2 ° C./s was achieved. In this calculation model that assumes a one-dimensional countercurrent heat exchange in which the flow of slag particles and the flow of cooling air on the belt conveyor are opposed, the maximum temperature of the cooling air discharged from the upper stage is 1,044K (771 ° C) is expected. Since the cooling air inlet temperature + 5 ° C. is expected as the discharge temperature on the slag particle side, sensible heat can be recovered almost completely.

(c) Pressure loss of the deposited layer The pressure loss when air passes through the belt of 100 mesh screen at a superficial velocity of 0.6 m / s is about 25 Pa in total even if the belt conveyors 6 a to 6 d are configured in four stages. The pressure loss in the slag particle deposition layer is more dominant.

When a slag particle accumulation layer having a total of 40 mm was calculated in consideration of changes in air density and viscosity with temperature, it was 250 Pa using Elgan's formula (12). Therefore, a combined pressure loss of the belt is expected to be about 300 Pa. This 300 Pa corresponds to the negative pressure in the upper space of the upper belt conveyor 6a. On the other hand, the lower belt conveyor 6d is substantially equal to the atmospheric pressure, and the slag particles that have been cooled can be discharged smoothly.

1.6 Primary Boiler and Generator The primary steam boiler 8 and the generator 14 have almost the same specifications as the Coke Dry Quenching (CDQ) that is actually used in steelworks.

Specifically, the red hot coke (1,050 ° C.) after the dry distillation is cooled by the nitrogen gas sent from the lower part while descending the CDQ chamber.

Nitrogen gas is heated to 980 ° C. and sent to the boiler, where it exchanges heat with steam, and the steam rotates the turbine for the generator.

The CDQ is a non-open circulation system using nitrogen gas. However, in the slag sensible heat recovery facility, the slag sensible heat recovery facility is set to 0 in order to cool the slag particles while keeping the determined cooling rate in the primary heat exchange tower 4. Because relatively low-temperature (200 ° C or lower) air adiabatically compressed with a compressor up to a high pressure of 3MPa is required, it can be used by adiabatic compression by incorporating high-temperature exhaust air in a circulating system. In this case, an air cooler is required. Therefore, an open system is built for economic reasons.

Table 1 shows the comparison from primary steam boiler to power generation in CDQ and heat recovery device 1.

In CDQ, the heat exchange medium temperature is 980 ° C., whereas in the primary steam boiler 8 of the heat recovery apparatus 1 in the present embodiment, it is 870 ° C., which is 100 ° C. lower, but the number of boiler tubes It is possible to increase the performance of the heat exchanger and to match the boiler outlet steam conditions of the steelworks. After the boiler, the existing turbine and generator can be used by joining the steam.

As shown in Table 1, it is considered that 6.7 MW / blast furnace power can be generated by the heat recovery apparatus 1 of the present embodiment. If a boiler / generator that uses coal, which has a large contribution to CO ₂ emissions, as a fuel source is suspended by an amount corresponding to the amount of power generation, the purchase cost of the boiler fuel can be reduced, and CO ₂ emissions can also be reduced. be able to.

1.7 Secondary Steam Boiler and Turbine The secondary steam boiler 12 produces superheated steam at 400 ° C and 4MPa from 700 ° C air, and produces power to rotate the compressor in the turbine at an efficiency of 26%. It has become.

1.8 Compressor Since the compressor 15 has the same pressure range as the blast furnace blast, the same type of axial flow compressor can be used.

1.9 Blower Since the blower 13 requires a pressure of about 1,000 to 5,000 Pa, a turbo fan blower can be used.

2 Measures to prevent slag particles from adhering to the inner wall of the first heat exchange tower The minimum temperature at which blast furnace slag particles can adhere between the particles and the collision plate when the blast furnace slag particles in flight collide with the collision plate The minimum temperature that can be adhered to the surface has already been obtained from experiments. According to this, the lowest temperature at which adhesion between particles occurred was 950 ° C., and the lowest temperature at which adhesion occurred on the impingement plate was 1,050 ° C.

Therefore, also in the heat recovery apparatus of the present embodiment, slag particles of 1,050 ° C. or higher may adhere to the inner wall of the primary heat exchange tower 4 while rising in the primary heat exchange tower 4.

FIG. 7 shows the 1,050 ° C. line by a broken line.

However, the above experiment is the case where the slag particles collide with the collision plate almost perpendicularly. In this device, the contact strength is tangential to the inner wall. It is assumed to be weak.

In order to prevent slag particle adhesion, the atomizer 3 is arranged on the central axis of the primary heat exchange tower 4 having a cylindrical shape, and at the initial stage, the slag particles are kept away from the wall surface of the primary heat exchange tower 4 as much as possible, and the outer periphery of the atomizer Only air that does not contain slag is blown, so that slag particles flow in the center and air that does not contain slag particles flows in the vicinity of the wall surface.

However, if the dispersibility in the particle flight direction is measured, it is expected that slag particles flying over a distance of 40 m will eventually have a substantially uniform distribution in the tower.

In FIG. 8, 50% of the total slag particles (particle diameter of 0.85 mm or less) are less than 1,050 ° C. at a flight distance of less than 10 mm, but particles having a representative diameter of 3.4 mm that are most delayed in ground cooling (ratio 5). %) Requires a flight distance of 25 m (refer to the X axis) before the temperature falls below 1,050 ° C. (1,323 K). Therefore, it is necessary to take measures in substantially all 40 m sections.

Therefore, as a measure to prevent slag particle adhesion in the entire 40m section, the reverse pressure drop-off mechanism used in the bag filter is applied.

2.1 Reverse pressure drop-off mechanism FIG. 12 is a schematic view showing the mechanism.

In the figure, the reverse pressure drop-off mechanism 21 has a primary heat exchange tower 4 having a double structure of an inner cylinder 4a that allows air to permeate and an outer cylinder 4b that does not allow air to permeate. The inner side of the inner cylinder 4a is atomized air, Slag particles and cooling air flow upward. The outside of the outer cylinder 4b corresponds to the slag accumulation tower 5 shown in FIG.

The donut-shaped space sandwiched between the inner cylinder 4a and the outer cylinder 4b is air-tightly partitioned by an annular partition plate 4c so that the height of the tower is 40 m in 40 sections per 1 m.

The inner cylinder 4a uses a stainless steel metal mesh material, and the air supplied to the space S between the outer cylinder 4b and the inner cylinder 4a passes through the mesh material and oozes out into the inner cylinder 4a. Has been.

As a configuration for that purpose, four nozzles 4d for supplying air are arranged at 90 ° intervals on the same ring header 4e in the annular space between the outer cylinder 4b and the inner cylinder 4a.

One ring header 4e provided with four nozzles 4d is installed in a section having a height of 1 m, and a total of 40 ring headers 4e are installed in the primary heat exchange tower 4. In FIG. 12, the number of ring headers 4 e is represented by five for easy understanding of the configuration.

Each ring header 4e is connected to a common low-pressure air header 4f via flow meters FM1 to FM40 and solenoid valves VN1 to VN40, thereby constituting a low-pressure air supply path.

This low-pressure air header 4f is branched from the cooling air and supplied with air. Finally, the low-pressure air header air flow rate, the cooling air flow rate of the outer periphery of the atomizer 3 and the air flow rate of the atomizer 3 are totaled. The flow rate is determined so that the air / slag ratio with the slag flow rate becomes 1.

During operation, the solenoid valves VN1 to VN40 are opened, and air oozes out from the stainless steel mesh to prevent slag particles from adhering to the stainless steel mesh to some extent. At this time, the flow rate supplied to each ring header 4e is measured by the flow meters FM1 to FM40, and if the flow meter indication value in a certain section decreases, slag particles adhere to the stainless mesh in that section and air Is determined to be blocked.

In that case, the solenoid valve VN on the pipe line is closed, and the solenoid valve VE connected to the high-pressure header 4g having a high pressure of 3 MPa is instantaneously opened. As a result, a large flow of air passes through the stainless steel mesh in the section, and a high-speed air current flows intensively from the four nozzles 4d toward the four narrow areas, causing an impact and vibration of the stainless steel mesh. Then, the slag particles adhering to the inner surface of the inner cylinder 4a are removed to the inside.

The piping line including the high-pressure header 4g and the solenoid valve VE functions as a high-pressure air supply path.

2.2 Correspondence to slag flow rate change In the basic design, the air / slag ratio is set to 1, gas atomization is performed within this air flow rate, air is heated to an equilibrium temperature of 870 ° C, and sent to the primary boiler. It has become.

If the particle size to be atomized by gas atomization is also simplified, if the atomized air / slag ratio is maintained, substantially the same particle size can be obtained even if they do not completely match.

In order to raise slag particles having a particle diameter of 5 mm or more in the primary heat exchange tower 4 while ensuring the cooling time of the slag particles in the primary heat exchange tower 4, air combined with cooling air and atomized air is used. The amount must be kept constant.

On the other hand, the slag flow rate during tapping varies.

Therefore, when the slag flow rate fluctuates, the range that can be operated according to the fluctuation will be explained.

FIG. 13 shows changes in various heat exchange performances when the slag flow rate is changed while the air amount in the primary heat exchange tower 4 is kept constant.

The minimum limit of the slag flow rate is 0.75 times the time average value and the maximum limit is 1.25 times the time average value, which corresponds to the expected operating range. That is, the slag flow fluctuation is allowed only in the range of the design value ± 25%. Therefore, a slag flow rate adjustment value is required. In addition, the said time average value means the average time which divided | segmented the amount of the iron tapping from a certain blast furnace tapping port by the tapping time.

The minimum operating range is limited by a drop in the inlet air temperature of the primary steam boiler 8 (primary heat exchange tower outlet air temperature -70 ° C).

When the slag flow rate is 1 time (design value), the inlet air temperature of the primary steam boiler 8 is 800 ° C (1,073K), but when the slag flow rate is increased by 0.75 times, it reaches about 707 ° C (980K). Decrease by 100 ° C.

Therefore, unless the primary steam boiler 8 is designed in a large size with a considerable margin, the influence of the temperature difference from 556 ° C. to about 3/5 from 250 ° C. to 150 ° C. cannot be absorbed.

That is, in order to cope with the slag flow rate of −25%, it is necessary to design the primary steam boiler 8 with an air-steam temperature difference of 150 ° C.

On the other hand, the maximum limit of the operating range is limited by the condition that the slag particle temperature is cooled to 1,050 ° C. or less, which is the wall surface adhesion limit, in the primary heat exchange tower 4.

FIG. 14 is a graph showing the slag particle temperature distribution in the primary heat exchange tower at a slag flow rate of 1.25 times. It can be seen that the temperature reached 1,050 ° C. (1,323 K) at the tower exit with a particle flight distance of 40 m.

FIG. 15 shows the heat recovery efficiency of the primary heat exchange tower 4 and the secondary heat exchange chamber 6 when the air slag ratio is kept constant and the slag flow rate is varied from 0.75 to 1.25 times the time average value. It is the graph which showed the change of the primary system power generation amount.

In the graph, the heat recovery efficiency of the primary system is high at a low slag flow rate (see graph F3), and the heat recovery efficiency of the secondary system tends to be high at a high slag flow rate (see graph F4). As a result, when looking at the power generation amount derived from the primary system steam, the power generation amount does not increase in proportion to the slag flow rate, but the power generation amount increases in proportion to approximately the 1/2 power with respect to the increase in the slag flow rate ( (See graph F5).

3 a second embodiment gas atomizer of the present invention, primary heat exchanger column, pressurized including slag accumulation tower, increasing the air density [rho _g is proportional to the 0.3 power of from [rho _g formula (6) the cooling rate is increased, it is also designed smaller air velocity u _g from equation (4). That is, there is an advantage that the amount of air can be reduced and heat can be recovered at a higher temperature.

FIG. 16 shows a second embodiment of the heat recovery apparatus of the present invention, in which the molten slag is atomized by an upward gas atomizer pressurized to 0.5 MPa, and the atomized air is similarly used in the heat exchange tower. By performing heat exchange between them, high-temperature air of 870 ° C. is obtained, and the air is further heated to 1,200 ° C. and then used as blast furnace air.

In the figure, 30 is a shaft furnace, and the slag discharged from the tap 31 is once stored in the slag tundish 32.

A cylindrical slag descending passage 33 extends downward from the bottom of the slag tundish 32, and the distance from the slag tundish 32 to the lower end of the slag descending passage 33 is set to 20 m.

In addition, the outside of the slag descending passage 33 is surrounded by a cylindrical high-frequency heating device 34, and the temperature drop of the molten slag moving in the slag descending passage 33 is suppressed and maintained at a predetermined temperature.

An atomizer 35 having the same configuration as that of the atomizer shown in FIG.

In order to push the molten slag into the atomizer 35 pressurized to 0.5 MPa, the molten slag needs to be pressurized to 0.5 MPa and sent in the same manner. Therefore, as described above, the slag tundish 32 having a depth of 20 m is installed and pressurized to 0.5 MPa using the hydrostatic pressure of the molten slag.

The atomizer 35 is supplied with atomized air pressurized by a compressor 36, and the compressor 36 is operated by a turbine 38 that is rotated by a steam boiler 37.

In addition, the code | symbol 39 is a cylindrical primary heat exchange tower which has a diameter of 1 m, and upward atomization of molten slag is performed. In addition, the code M.I. S is molten slag; I is a molten iron, 40 is a gas cleaning device, 41 is a hot stove, 42 is a cyclone, and 43 is an outlet for taking out the molten iron.

According to the second embodiment, the energy 24 MW of the primary cooling air in FIG. 3 is used for blast furnace blowing, so that the amount of fuel gas (by-product gas at the ironworks) used in the hot stove currently in operation is reduced. It becomes possible to reduce about 13%.

If this fuel gas is used as boiler fuel at a steel plant power plant and power is generated by a steam turbine, it is 1.3 times the heat recovery device shown in FIG. 3 that performs steam turbine power generation through a CDQ type boiler. Can be obtained.

The heat recovery device of the present invention performs gas atomization of molten slag, supplies high-temperature air obtained by efficient heat exchange with the atomizer gas to a steam boiler, and operates the generator to operate the sensible heat of the blast furnace slag as electric power. In addition, when the high-temperature air is further heated, it can be used as blast in a blast furnace.

1 Heat recovery device (Blast furnace slag sensible heat recovery device)
2 Slag tundish 3 Atomizer (upward gas atomizer)
3a Atomized gas injection device 3b Molten slag nozzle 3b 'Upward discharge port 3c Ring component 3c' Injection port 3d Gas passage 4 Primary heat exchange tower 5 Slag accumulation tower 5b, 5c Position sensor 6 Secondary heat exchange chamber 7 Primary system cyclone 8 Primary system Steam boiler 9 Dust collector 10 Radiation tower 11 Secondary cyclone 12 Secondary steam boiler 13 Blower 14 Generator 15 Compressor 16 Turbine 17 Rotating shaft 18 Gate 19 Gate valve 20 Cooling air nozzle 21 Reverse pressure drop-off mechanism

Claims (11)

In the blast furnace slag sensible heat recovery device that atomizes the blast furnace slag using compressed air, further absorbs the sensible heat of the blast furnace slag by air exchange by heat exchange between air and slag particles, and performs heat recovery,
A gas atomizer that has an injection nozzle that injects gas upward in the direction opposite to the direction of gravity, and that is supplied with molten slag toward the gas injected from the injection nozzle;
A blast furnace slag sensible heat recovery device comprising a cylindrical body extending upward from the gas atomizer, and comprising a heat exchange tower in which the atomizer gas and atomized slag particles flow upward . The blast furnace slag sensible heat recovery device according to claim 1, wherein a nozzle for injecting cooling air upward is disposed on an outer peripheral portion of the injection nozzle. The blast furnace slag sensible heat recovery apparatus according to claim 1 or 2, wherein the radial cross-sectional area of the tower is enlarged from the lower part to the upper part of the heat exchange tower. The blast furnace slag sensible heat recovery according to claim 1 or 2, further comprising a separation tower that flows in the heat exchange tower and settles and separates the atomizer gas and the slag particles injected in a mixed state from the upper part of the heat exchange tower. apparatus. A gate valve at a lower portion of the separation tower and a position sensor for detecting a deposition height of the slag particles deposited in the separation tower, the gate valve being based on a signal output from the position sensor; The blast furnace slag sensible heat recovery apparatus according to claim 4, wherein the slag discharge amount is adjusted by performing an opening / closing operation. A primary system line for recovering heat from the atomizer gas separated by the separation tower is connected to the upper part of the separation tower, a cyclone for recovering fine powder from the atomizer gas to the primary system line, and a gas from which fine powder has been removed The blast furnace slag sensible heat recovery apparatus according to claim 4, wherein a steam boiler that is operated at is provided. A heat exchange chamber is provided at a lower portion of the separation tower, and the heat exchange chamber includes a ventilable belt conveyor for conveying the slag particles discharged from the gate valve, and air is supplied to the slag particles on the belt conveyor. The blast furnace slag sensible heat recovery apparatus according to claim 5, wherein the blast furnace slag sensible heat recovery apparatus is configured to transmit the blast furnace slag. A secondary system line for recovering heat from the high temperature air heated in the heat exchange chamber is connected to the upper part of the heat exchange chamber, and a secondary system cyclone for recovering fine powder from the high temperature air is connected to the secondary system line. A blast furnace slag sensible heat recovery device according to claim 7, wherein a secondary steam boiler operated with the high-temperature air from which fine powder has been removed is provided. The compressor which produces the atomized gas of the said gas atomizer, and the turbine operated with the steam from the said secondary system steam boiler are comprised so that the motive power of the said compressor may be obtained from the said turbine. The blast furnace slag sensible heat recovery device described in 1. The heat exchange tower has a double cylinder in which an inner cylinder that allows air to permeate and an outer cylinder that does not allow air to permeate are doubled, and
A partition plate that partitions the annular space between the inner cylinder and the outer cylinder into a plurality of rooms in the height direction;
A low-pressure air supply path for supplying low-pressure air to each of the rooms via an on-off valve and a flow meter;
A high-pressure air supply passage that has an on-off valve and supplies high-pressure air to the rooms,
The blast furnace slag sensible heat recovery apparatus according to claim 1, wherein the high-pressure air supply path is configured to open the on-off valve when a flow rate of low-pressure air measured by the flow meter falls below a threshold value. The blast furnace slag sensible heat recovery apparatus according to claim 10, wherein the high-pressure air supply path further includes an air nozzle that injects high-pressure air toward the annular space.

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