CN101921884B - Blast furnace slag dry-type sensible heat recovery system and production process - Google Patents

Abstract

The invention provides a blast furnace slag dry sensible heat recovery system and a production process. The whole system and production process include five key parts: slag tundish heat preservation process, spray gun slag extraction process, slag multi-jet granulation heat transfer process, impact mill crushing process and secondary cooling fluidized bed heat recovery process. After the blast furnace slag is saturated with nitrogen blowing in the tundish, it is taken out by the high-speed airflow spray gun, and the slag particles pass through the jet mill and the high-speed airflow slag particles collide with each other to enhance heat transfer. ; The secondary cooling fluidized bed recovers the heat of the slag particles twice, and the heat recovered from the first recovery and the second recovery is converted into heat energy or electric energy through a heat exchanger. Applying the system and production process provided by the present invention, the heat recovery efficiency of blast furnace slag can reach more than 80%; the yield of finished slag is more than 90%, and the particle size is less than 5mm; the whole process of the system does not use cooling water, and the dry treatment saves a lot use water.

Description

Dry-type sensible heat recovery system and production process for blast furnace slag

Technical field:

The invention belongs to the technical field of waste heat and waste energy recovery, and in particular relates to a blast furnace slag dry-type sensible heat recovery system and a production process.

Background technique:

The sensible heat of blast furnace slag is a high-grade waste heat resource with high recovery value. At present, most iron and steel enterprises use water quenching process to treat blast furnace slag, and the sensible heat of slag is basically not recovered. With the increasingly intensified international competition and the continuous shortage of energy, the iron and steel industry is facing many environmental-friendly issues to maintain sustainable development strategies. Among them, efficient and high-grade recovery of sensible heat from blast furnace slag has become an urgent technical problem.

US Patent No. 5,255,900 reports a related design method of a granulator and a fluidized bed for recovery of slag waste heat. The temperature of the slag particles in the fluidized bed can be controlled by adjusting the circulating air volume, generally at 500-800°C. The heat recovery rate of the device is about 64%, but the effective energy utilization rate is low.

The patent 200510047090.0 applied by Anshan Iron and Steel Group discloses a blast furnace slag sensible heat recovery system and production process, which is composed of primary cooling-crushing unit, gas-slag heat exchange unit, and waste heat boiler. The crushing unit adopts two methods, one is composed of a slag distributor, a slag gear, a cooling nozzle and a slag retaining plate; the other is a direct nozzle type, which consists of a slag flow tank, a slag distributor, Composed of cooling nozzle and slag retaining plate. The slag in this unit is cooled to below the freezing point of 1200°C-1300°C and broken into slag particles with a diameter of less than 100mm. The initial cooling-crushing unit is followed by a continuous transport device, and then connected with an air-slag heat exchange unit. This unit can use two types There are different ways, one uses a chain grate machine, and the other uses a slag tank structure. The air in the unit is heated to 700°C-800°C, the slag is cooled to below 150°C, the heated air is sent to the waste heat boiler, the water in the boiler heating tube absorbs the heat of the gas, and the pressure is 0.3-0.4MPa, the temperature It is steam at 260-350°C. The invention realizes the effective recovery of sensible heat of liquid blast furnace slag, the comprehensive energy recovery rate reaches over 70%, reduces the energy consumption of iron and steel production, reduces the consumption of slag cooling water, and the environmental pollution caused thereby. However, due to the relative simplicity of this process, the crushed slag has a relatively coarse particle size, and the resulting finished slag is of poor grade, making it difficult to realize high-value utilization. At the same time, the heat exchange contact area between the coarser slag particles and the air is small, which is not conducive to heat exchange, and the heat exchange efficiency is low.

In the 1980s, Japan developed the blast furnace slag sensible heat recovery technology by wind crushing method. The molten slag discharged from the blast furnace with a temperature above 1400°C is introduced into the granulation section of the wind tunnel, and three equally divided slag streams are used to supply the slag. The molten slag is blown and granulated by the high-speed air jet coming out of the nozzle, and the air flow rate at the nozzle is adjustable. The size of the wind tunnel is 25m in length, 7m in width and 13m in height (processing capacity is 100t/h). There is a dispersing plate in the wind tunnel to make the slag particles at a temperature of about 1050°C hit the plate and fall. During the falling process, the air blown in from the lower part of the wind tunnel is cooled, and the slag particles are discharged out of the wind tunnel at about 800°C. The discharged hot slag particles are stored in the hot slag particle storage bin after being passed through a weighing machine and a vibrating screen (to remove large-diameter particles), and then discharged through a secondary fluidized bed heat exchanger to cool to about 150°C to obtain the finished slag. The quality is guaranteed by the cooling rate in the wind tunnel. The average heat recovery rate achieved in the test is 48%, the wind temperature at the outlet of the wind tunnel reaches 500°C, the particle size of the finished slag is less than 5mm accounts for more than 95%, the overall vitrification rate of the slag particles is greater than 95%, the crushability is good, and the quality is as good as Water quenching slag is equivalent. The slag crushing process developed in Japan can still be called the highest achievement of the wind crushing method until now. The large-scale production test results of the slag processing capacity of 100t/h show that the heat recovery efficiency and the finished slag The quality can meet the requirements of industrialization. However, due to the limitations of factors such as huge equipment system, large floor area, high investment cost and excessive energy loss in the system process, the progress was stopped at that time.

According to the analysis of existing technical data, most of the current processes have problems such as low heat exchange efficiency, large particle size of finished slag, and huge equipment. The present invention proposes a novel blast furnace slag sensible heat recovery system and production process aimed at these problems.

Invention content:

The invention proposes a blast furnace slag dry-type sensible heat recovery system and production process. The liquid blast furnace slag is crushed by high-speed airflow, gas-solid heat transfer is realized by jet impact, high-grade hot air is replaced, and sensible heat is realized by waste heat boiler. Heat recovery, while obtaining uniform fine finished slag.

The technical scheme of the present invention is as follows: the slag tundish technology is used to centrally process the blast furnace slag, which ensures the continuity and high efficiency of the operation process; the spray gun is used to control the carrying out and granulation of the slag, and the gas medium used can be It is easier to crush and granulate the slag by using the excess nitrogen or air in the steel plant; the jet mill has unique advantages in enhancing heat transfer and refining slag particles to strengthen the crushing and rapid cooling of slag particles; The impact mill further promotes the crushing and heat exchange cooling of high-temperature slag particles; the second cooling fluidized bed is used to recover the heat of slag, which improves the overall heat recovery efficiency.

The key to implementing the present invention is to granulate the molten slag in the granulation chamber with a suitable ratio of slag-gas volume and air velocity and cool it rapidly to below 950°C. At this temperature, the slag particles will not adhere to each other and cause re-slag. The phenomenon of coarsening; the granulated slag particles are broken into finer particles under the action of the jet mill (blast furnace slag undergoes ductile fracture when it is greater than 1250°C, and brittle fracture occurs when it is lower than 1250°C), and in the granulated At the same time, the speed of heat exchange between the slag particles and the gas medium is accelerated; finally, under the action of the impact mill, the slag particles are refined again to further enhance the heat transfer effect. In addition, the slag particles in the whole system of the present invention are all at a temperature of <950° C., and the slag particles cannot adhere to the vessel wall (the adhesion temperature is 1050° C.). Therefore, this solution can really obtain high heat recovery efficiency (reduced gas consumption, increased hot air temperature) and high value-added dry slag products (finer particle size, higher degree of vitrification) at the same time.

In view of the characteristics of blast furnace slag, the process system of the present invention includes five key processes: slag tundish heat preservation process, spray gun slag extraction process, slag multi-jet granulation heat transfer process, impact mill crushing process and secondary cooling Fluidized bed heat recovery process.

The slag tundish heat preservation process proposed in the present invention is designed with slag blowing nitrogen saturation measures, which promotes the mixing of slag in the tundish and the uniform distribution of temperature, and ensures that the temperature of slag in the tundish is kept above 1400°C to prevent melting The influence of early solidification of slag and part of solid slag brought out from blast furnace outlet on the whole process system.

The spray gun slag carrying out process proposed by the present invention uses a circular or flat single Laval nozzle spray gun to submerge the molten slag liquid surface, and controls the amount of slag discharge by adjusting the height of the nozzle and the bottom outlet _. The sonic jet will take out the slag and granulate it at the same time.

The slag multi-jet granulation process proposed in the present invention is to completely granulate the slag in a very short time, and rapidly cool it to below 950°C, and the obtained granulation and heat exchange effects are ten times or even several times that of the traditional method. ten times.

The impact mill crushing process proposed in the present invention is to further refine the granulated high-temperature slag particles in the crushing zone to obtain high value-added slag products, and at the same time, the refining process further removes heat and cools the slag particles.

The secondary cooling fluidized bed heat recovery process proposed in the present invention is to perform secondary heat recovery on the 400-600°C slag particles from the crushing area to ensure qualified slag products and improve the overall heat recovery efficiency.

The production technology mentioned in the present invention has the following characteristics:

(1) The slag outlet of the lower tundish is designed as a Laval inner shape: the advantage is that when the upper top lance is blowing directly to the slag mouth, the slag mouth becomes a Laval-shaped extension of the slag nozzle of the top lance, and the surface of the high-pressure air flow is covered by the molten slag. Surrounding, the speed difference between the slag flow and the air flow increases continuously, resulting in a strong shear force that turns the slag flow into fine droplets. Since the air flow is supersonic, there is almost no heat exchange between the two when the air flow accelerates the slag flow. Therefore, the risk of the slag mouth being condensed and adhered by molten slag is greatly reduced.

(2) Jet mill: The granulation heat exchange chamber is inserted into the upper and lower sides of three or more symmetrical annular radially arranged high-speed airflow spray guns to form a jet mill, and the liquid droplets whose speed has been greatly reduced from above are drawn into the swirl flow area, The slag droplets undergo heat exchange during the course of following the cyclone airflow, and are further granulated when they reach the grinding area in the center of the jet mill. This circulating flow prolongs the average residence time of liquid droplets or slag particles in the granulation chamber, and further granulation greatly increases the total heat transfer area, thus enhancing the heat transfer effect.

(3) Impact mill: The slag particles that are completely solidified in the granulation heat exchange chamber and the relatively coarse slag particles that still have a liquid phase in the center are formed by the outlet of the granulation heat exchange chamber through a high-pressure accelerated two-phase flow nozzle with strong kinetic energy. The high-speed jet impacts the impact plate located at the lower part of the crushing chamber to form an impact mill, so that the slag particles are miniaturized again and the heat exchange effect is enhanced again.

These features are incomparable to any other wind crushing air cooling method. Compared with the aforementioned method developed in Japan, the heat transfer efficiency of the device is high, the shear drive of the high-speed airflow, and the high-intensity turbulent oscillation infiltration in the impact area greatly improve the heat transfer efficiency of gas and slag; the volume of the heat exchange chamber is greatly reduced , high space utilization rate; the initial recycling of slag, the particle size and quality of slag products will be finer and better; in addition, the cooling gas medium can also use the surplus nitrogen of the steel plant, and the use of inert gas is expected to improve the final slag particles performance.

Technology mentioned in the present invention will reach following effect:

The heat recovery efficiency of blast furnace slag exceeds 80%, and the hot gas temperature can reach 700-800°C, which can be converted into water vapor or electricity for use; the yield of slag products is more than 90%, and the particle size is less than 5mm, and the vitrification rate is greater than 95%. It is used as cement clinker to achieve high value; no cooling water is used in the whole process, and no related equipment and investment are required; dry treatment saves a lot of water, and the alkaline components in the slag do not cause water pollution, and do not produce harmful gases such as H2S. Air pollution, avoiding a large amount of energy consumption in the slag drying process.

Description of drawings:

The invention will be further described below with reference to the accompanying drawings:

Attached Figure 1 is a schematic diagram of dry sensible heat recovery system for blast furnace slag

In the drawings: 1. Slag tundish; 2. Vent plug; 3. Slag outlet; 4. Slag; 5. Spray gun; 6. Granulation heat exchange chamber; 7. Nozzle; 8. Ring pipe; 9. Jet mill; 10. Grinding area; 11. Crushing chamber; 12. Pneumatic catcher; 13. Nozzle; 14. Impact mill; 15. Impact plate; 16. Cyclone separator; 17. Hot particle discharge port; 18. Second cooling moving bed (fluidized bed); 19, air inlet nozzle; 20, annular pipeline; 21, porous cone; 22, exhaust nozzle; 23, annular pipeline; 24, perforated plate; 25, slag sand outlet; 26, heat exchanger; 27, heat exchanger

Detailed ways:

Example 1: The process shown in Figure 1, the molten slag flows continuously from the slag ditch or the slag ditch connected to the slag ditch above the vent plug 2 in the pit of the tundish 1, and is fed into the _N2 or The air saturates the slag with gas under the condition that the air is close to the emulsified state of the slag. After the gas-saturated slag 4 reaches the specified liquid level, it is sprayed by a spray gun 5 with a flat or oval or round Laval nozzle head. The ejected supersonic airflow carries the molten slag into the granulation heat exchange chamber 6 from the outlet 3. At the expansion part of the molten slag outlet 3, the slag-gas two-phase stream expands and expands downward, and the molten slag is granulated by the airflow while flowing toward the Heat transfer in the gas phase, and form a high-speed downward axial main flow in the upper part of the granulation chamber. The main flow and the jet mill 9 formed by the high-speed air flow from the annular pipe 8 through the nozzle 7 make the slag particles further granulated in the grinding area 10. change. The hot slag particles and hot gas pass through the accelerating nozzle 13 to cause a two-phase mixed jet to impact the impact plate 15 at the lower part of the crushing chamber 11 at high speed to form an impact mill 14 . The slag particles are crushed and refined again, and the heat transfer effect is further enhanced. Using an appropriate slag-gas ratio to ensure that the temperature in the lower part of the granulation chamber is not higher than 900°C is the basic condition for the smooth flow of the process. The pneumatic catcher 12 extending into the upper part of the crushing chamber catches the mixture of slag particles and gas and sends it into the cyclone separator 16 along the tangential direction through the pipeline. The hot air separated from the slag particles is sent into the heat exchanger 26 through the pipeline. The gas cooled by 26 is sent to the circular pipeline for recycling. The hot slag particles are discharged from the hot particle outlet of 16 to the secondary cooling fluidized bed 18. The lower part of 18 is sent into the cold air through the annular pipe 20 and the air inlet nozzle 19, and the cold air is evenly distributed through the porous cone 21 from bottom to top. The air outlet perforated plate 24 divides the flow evenly, and sends it to the heat exchanger 27 through the hot air outlet nozzle 22 and the ring pipe 23 connected to the straight pipe. The gas cooled by 27 returns to the ring pipe 8 for recycling. The slag particles cooled by the secondary cooling fluidized bed are discharged through the slag sand outlet 25 . The secondary cooling fluidized bed may adopt a multi-stage method of 2 to 3 stages of low pressure loss. Whether the heat exchangers 26 and 27 are combined into one depends on the temperature difference of the hot air obtained from the first cooling and the second cooling.

Example 2: In the process shown in Figure 1, under the premise of ensuring high heat exchange efficiency, part of the equipment and content in 18-25 and 27 is directly omitted in the process, and granulated slag particles are directly obtained at 17, and 26 Direct access to waste heat.

Claims (5)

1. A dry-type sensible heat recovery system for blast furnace slag, which is composed of five parts: a slag tundish, a granulation heat exchange chamber, a crushing chamber, a secondary cooling fluidized bed, and a heat exchanger. The airflow takes the high-temperature liquid blast furnace slag out of the tundish, and is hit by a high-speed jet in the granulation heat exchange chamber to realize slag granulation and gas-solid heat exchange enhancement. The slag particles are further impacted and crushed in the crushing chamber and then enter the secondary cooling fluidized bed After the second heat exchange, the hot gas passes through the heat exchanger to recover sensible heat and obtain uniform fine slag. 2. A blast furnace slag dry-type sensible heat recovery system as claimed in claim 1 carries out blast furnace slag dry-type sensible heat recovery process, it is characterized in that, the whole production process includes the slag intermediate containing the slag blowing nitrogen saturation step Including heat preservation process, the spray gun is submerged into the slag liquid surface, _and the amount of slag discharge is controlled by adjusting the height of the nozzle and the bottom outlet. The process of carrying out slag is to insert more than three high-speed airflow spray guns arranged in a symmetrical annular radial pattern into the granulation heat exchange chamber to form a jet mill, and use multiple jets to granulate all the slag, and rapidly cool it to a melting point below 950 °C. The slag multi-jet granulation heat transfer process, the granulated high-temperature slag particles are granulated and heat-exchanged in the crushing zone, and the slag particles in the granulation heat exchange chamber pass through the high-pressure accelerated two-phase flow nozzle from the outlet of the granulation heat exchange chamber The high-speed jet impacts the impact plate located at the lower part of the crushing chamber to form an impact mill crushing process, and the secondary cooling fluidized bed heat recovery process for secondary heat recovery of slag particles at 400-600 ° C from the crushing area. 3. The blast furnace slag dry-type sensible heat recovery system as claimed in claim 2 carries out blast furnace slag dry-type sensible heat recovery process, it is characterized in that the tundish slag outlet in the spray gun slag carrying-out process is Laval shape. 4. The blast furnace slag dry-type sensible heat recovery system as claimed in claim 2 carries out the blast furnace slag dry-type sensible heat recovery process, characterized in that, in the granulation heat transfer process of molten slag multi-stream jet granulation The upper and lower chambers are inserted with more than three high-speed airflow spray guns arranged radially in a symmetrical ring to form a jet mill. 5. The dry-type sensible heat recovery system for blast furnace slag as claimed in claim 2 carries out the dry-type sensible heat recovery process for blast furnace slag, characterized in that, in the impact mill crushing process, the slag particles in the granulation heat exchange chamber are all made of The outlet of the heat exchange chamber passes through the high-pressure accelerated two-phase flow nozzle to form a high-speed jet that impacts the impact plate at the lower part of the crushing chamber to form an impact mill. the

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