Knowledge of blast furnace production

1. Questions and Answers on Blast Furnace Safety

The blast furnace is made of steel plates as the furnace shell, and the shell is lined with refractory bricks. The blast furnace body is divided into five parts from top to bottom: furnace throat, furnace body, furnace waist, furnace belly, and furnace hearth. Due to the advantages of blast furnace ironmaking with good technical and economic indicators, simple process, large production volume, high labor productivity, and low energy consumption, the iron produced by this method accounts for the vast majority of the world's total iron production.

During blast furnace production, iron ore, coke, and slagging flux (limestone) are loaded from the top of the furnace, and preheated air is blown in from the tuyere located at the bottom of the furnace along the furnace circumference. At high temperatures, the carbon in the coke (some blast furnaces also inject auxiliary fuels such as pulverized coal, heavy oil, natural gas, etc.) burns with the oxygen blown into the air to produce carbon monoxide and hydrogen. During the process of rising in the furnace, the carbon monoxide and hydrogen in the iron ore are removed. Oxygen is reduced to iron. The smelted molten iron is released from the iron mouth. The unreduced impurities in the iron ore are combined with fluxes such as limestone to form slag, which is discharged from the slag outlet. The generated gas is discharged from the top of the furnace and, after dust removal, is used as fuel for hot blast furnaces, heating furnaces, coke ovens, boilers, etc. The main product of blast furnace smelting is pig iron, as well as by-products blast furnace slag and blast furnace gas.

2. What are the principles of blast furnace ironmaking production

In the development process of blast furnace ironmaking technology, people have concluded through research the impact of smelting intensity on the coke ratio. The smelting intensity continues to increase the coke ratio. will then increase, and later, the yield will begin to gradually decrease.

This law reflects the complex heat and mass transfer phenomena between the gas and charge streams in the blast furnace. Blast furnace ironmaking workers should grasp this rule and apply it to guide production, that is, according to specific production conditions, determine the smelting intensity value suitable for the lowest coke ratio, so that the blast furnace can run smoothly and stably with high production.

However, the smelting conditions of blast furnaces can be changed. With the advancement of iron-making technology, such as strengthening fine materials, adopting reasonable charge structure, adopting high-pressure operation and comprehensive blast technology, and transforming equipment, high Furnace operating conditions can be greatly improved. Under advanced operating conditions, the appropriate smelting intensity value can be further increased, while the minimum coke ratio is further reduced, and the output is further increased.

This is why countries around the world have been continuously improving smelting conditions for decades to increase smelting intensity, reduce coke ratio, and increase output.

3. Complete knowledge of blast furnace ironmaking

The equipment used for ironmaking is called a blast furnace, also called a blast furnace. It is shaped like a tube. The method of making iron is to add ore, coke and limestone from the top of the furnace, and pass pressurized air into the furnace from the bottom of the furnace. When the coke is burned, the ore, limestone and coke react together to eventually form molten iron and slag.

There are several areas in a blast furnace. The bottom of the furnace is the place where molten iron is loaded, which is called the hearth. The part above the hearth is called the furnace hearth. The section above the furnace hearth is called the furnace body (sometimes also the furnace body). can be subdivided). There is a charging device on the top of the furnace body, from which the charge (that is, ore, coke and limestone) enters the furnace. On the upper part of the furnace hearth, there are dozens to dozens of blast tubes arranged around the furnace. The tubes are connected to the tuyere of the furnace. The preheated air and fuel (such as oil or natural gas) injected into the furnace pass through these tubes. The pipe is injected into the furnace. At this time, the preheated air entering the furnace can reach a temperature of 900 to 1250 degrees Celsius. After such high-temperature gas enters the furnace, it will react violently with the coke, generating gas (carbon monoxide) and rising along the inside of the furnace, reaching 1650 degrees Celsius, causing the charge to change. Into molten iron and slag. The bosh is the hottest part of the blast furnace because it is where the air and coke react violently (that is, burn). In order to protect the furnace with a steel plate shell from being burned, people build refractory materials inside the furnace. There are also cold water circulation systems, water spray devices, etc. embedded in the furnace wall. The molten iron generated from the ore is gathered in the furnace, and the furnace is equipped with a tap hole for discharging molten iron and a slag hole for discharging slag. Because the slag is lighter than the molten iron and floats on the molten iron, the slag outlet is above the taphole. A large blast furnace has more than one tap hole and one slag hole. Take a look at the schematic.

The production of a blast furnace is continuous. Once it is ignited, it will continue to burn unless there are special circumstances (usually the time from opening to shutdown of a blast furnace can be more than ten years). The furnace body will be filled with coke, ore and limestone in layers. The coke is ignited at the bottom of the furnace and then burned violently by hot air, causing the ore to melt and produce molten iron. The ashes of the coke, together with limestone and iron ore residues, form slag.

The hot gas rises from the combustion zone and heats the new charge added to the furnace, and is then directed out of the gas pipe on the top of the furnace. Depending on the size of the blast furnace, the amount and frequency of tapping varies. Generally, 6 to 12 tappings are made every day and night. A large blast furnace has 2 to 5 tapholes, which take turns to tap out iron. The interval between each tapping is 30 to 60 minutes. The released molten iron will flow into the molten iron tank, and then be transported to the steelmaking plant for steelmaking, or pig iron can be cast nearby. When tapping, use an electric drill to open the taphole so that the molten iron can flow into the molten iron tank along the molten iron ditch. After the molten iron is discharged, a machine called a mud cannon is used to drive the blocking mud used to seal the taphole into the taphole to seal the exit. After a while, the slag will start to be discharged. There is a special slag tank to collect the slag, and it is transported away after it is full. Because the blast furnace operates continuously, when the slag is discharged from below, the violent combustion in the furnace is still going on. When the slag is almost finished, the furnace charge that is burning above the slag has also reached the vicinity of the slag discharge port. The scene at this time will be very spectacular—— There is flame ejected from the slag outlet. At this time, the slag outlet must be blocked. Generally, a blast furnace has two slag outlets. Some modern giant blast furnaces have reduced the amount of slag and no longer have a slag outlet. The slag is allowed to flow out of the taphole along with the molten iron, and then the slag is cleaned. The place where the blast furnace taps iron and slag is also called the blast furnace tapping yard, which is the busiest place of the blast furnace. We usually see scenes of workers sweating in front of furnaces in movies and TV shows. In fact, they were all filmed in the blast furnace tapping yard. Hot metal tanks and slag tanks are mostly transported by train, so there are always trains and rails next to the blast furnace.

Before the 18th century, people did not use coke but coal or charcoal to make iron. The blast furnaces at that time were also very small. By the beginning of the 20th century, large blast furnaces in the United States could only produce a few hundred tons of iron per day. In the mid-19th century, people invented a method to blow hot air into the blast furnace instead of blowing cold air. In the early 20th century, the blast furnace blower was innovated, and blast furnace ironmaking developed rapidly. Modern blast furnaces are more than 20 to 30 meters high, with a true diameter of 6 to 14 meters, and can produce 1,000 to 10,000 tons of pig iron per day.

In the past, small blast furnace walls did not have cooling equipment. In the 1860s, blast furnaces began to use water for cooling. There are many cooling methods, and because the temperatures in various areas of the blast furnace are different, the cooling methods adopted are also different. Some places have water tanks, some have water sprays, some have ventilation, etc. The water that removes heat from the blast furnace is cooled and reused.

At this point, we have a general understanding of blast furnaces and ironmaking. In fact, the blast furnace is just a piece of equipment for refining, and there are many auxiliary system facilities related to it. Let’s get to know these devices.

4. What are the safety characteristics of blast furnace ironmaking production

The safety characteristics of blast furnace ironmaking production are: (1) The ironmaking process is a continuous high-temperature process The physical and chemical change process and the entire process are accompanied by high temperature, dust and poisonous gas; the slag and iron tapping processes are closely related to high-temperature melt and blast furnace gas.

(2) A large amount of smoke, dust, harmful gases and noise escape during the operation, polluting the environment and worsening working conditions. (3) During the operation, a lot of electromechanical equipment, overweight transportation equipment, and high-pressure systems such as high-pressure water, high-pressure oxygen, and high-pressure air are required.

(4) There are many and complex auxiliary equipment systems, and the collaboration between various systems requires strict requirements. (5) The labor intensity of the furnace operators is relatively high.

In short, the characteristics of iron-making production are labor-intensive, high labor intensity, high temperature, noise, and dust hazards, many gas areas and flammable and explosive places, vertical and horizontal roads and railways, three-dimensional and cross-cutting operations, and up and down operations. The processes are closely coordinated and the equipment is numerous and complex.

5. Knowledge about blast furnace ironmaking: What is full-wind blocking rate

There are four main assessment indicators for tapping operations:

(1) Iron casting punctuality rate. In order to maintain stable furnace conditions, continuous production blast furnaces must tap iron according to the specified time. The calculation formula is: on-time tapping rate = on-time tapping times/actual tapping times*100%.

(2) Poor iron quantity or iron tapping uniformity. The difference between the actual iron production amount and the theoretical iron production amount is the iron amount difference.

(3) High-pressure full air blocking rate. Blocking the taphole with high pressure and full air volume is not only beneficial to the forward movement, but also helps to protect the mud bag formation at the taphole. The calculation formula is (normal pressure blast furnace only calculates the full-wind blocking rate): high-pressure full-wind blocking rate = high-pressure full-wind taphole blocking times/actual tapping times * 100%.

(4) Qualification rate of taphole depth. In order to ensure the safety of the taphole, each blast furnace has a certain taphole depth range that must be maintained. Those whose actual measured depth meets the regulations each time the taphole is opened are qualified. The calculation formula is: taphole depth qualification rate = depth qualification times / actual tapping times * 100%.

6. Who can tell me some knowledge about the blast furnace reaction of cast iron?

Main reactions: 2Fe2O3 + 3C = high temperature = 4Fe + 3CO2↑ and: CaCO3 = high temperature = CaO+ CO2 CaO+SiO2=CaSiO3 C+CO2=2CO The operating policy of blast furnace ironmaking is based on fine materials.

The influence rate of fine material technology level on blast furnace ironmaking production is about 70%, the influence rate of equipment is about 10%, the influence rate of blast furnace operation technology is about 10%, and the influence rate of comprehensive management level is about 5%, and the influence rate of external factors is about 5%. 1. The connotation of blast furnace concentrate technology. Blast furnace concentrate technology includes: "high, cooked, clean, small, even, stable, less, and good".

"High" means that the iron content of the ore entering the furnace must be high; the drum strength of sintering, pellets, and coke must be high; and the alkalinity of the sinter must be high (generally 1.8~2.0). The core of concentrate technology is that the grade of ore entering the furnace should be high.

For every 1% increase in the grade of ore entering the furnace, the blast furnace fuel ratio will decrease by 1.5%, the blast furnace output will increase by 2.5%, the amount of iron slag per ton will decrease by 30kg, and the blast furnace will be allowed to increase the injection of pulverized coal by 15kg/t. "Cooked" means that the clinker ratio of the raw materials entering the blast furnace is higher.

Clinker refers to sinter and pellets. With the continuous advancement of blast furnace ironmaking production technology, there is no longer much emphasis on a high clinker ratio.

Some companies have put into the furnace about 20% of high-grade natural lump ore. "Net" means that the raw fuel entering the furnace should be smaller. "Small" means that the particle size of the materials entering the furnace should be smaller.

The production practice of blast furnace ironmaking shows that the particle size of the best strength is: 25~40㎜ for sintering, 20~40㎜ for coke, and the particle size of easily reduced hematite and limonite is 8~20 ㎜. The particle size of raw fuel for small and medium-sized blast furnaces is allowed to be smaller.

"Uniform" means that the particle size of the blast furnace charge must be uniform. Grading the charge of different particle sizes into the furnace can reduce the filling of the charge and improve the permeability of the charge, which will save coke and increase output.

"Stable" means that the chemical composition and physical properties of the raw fuel entering the furnace must be stable and the fluctuation range must be small. At present, the unstable performance of raw materials entering blast furnace ironmaking in my country is the main factor affecting the normal production of blast furnaces.

Ensuring a reasonable storage capacity in the raw material yard (to ensure that the ore blending ratio does not change much) and establishing a neutralizing and mixing yard are effective means to improve the stability of the composition of the furnace charge. "Less" refers to iron ore and coke containing less harmful impurities.

In particular, the contents of S and P must be strictly controlled, and attention should also be paid to controlling the contents of En, Pb, Cu, As, K, Na, F, Ti (TiO2) and other elements. "Good" means that the metallurgical properties of iron ore are better.

Metallurgical properties mean that the reduction degree of iron ore should be greater than 60%; the reduction powdering rate of iron ore should be low; the load softening point of the ore should be high, and the range of reflow temperature should be narrow; The dripping property requires high temperature and narrow range. 2. Attach great importance to the impact of coke quality on blast furnace ironmaking. The impact of changes in coke quality on blast furnace ironmaking production indicators is 35%, that is to say, it accounts for half of the impact of the concentrate technology level.

Coke plays the role of the skeleton of the charge in the blast furnace, and is also a reducing agent in the smelting process. It is the main source of heat income from blast furnace ironmaking (accounting for about 60%~80%), and the carbon content of pig iron. of suppliers. Especially under the condition of high coal injection ratio, the coke ratio is significantly reduced, making the effect of coke on the skeleton of the charge more obvious.

At this time, the quality of coke is good, which plays a key role in improving the air permeability of the charge and the permeability of slag iron. Large blast furnaces adopt a large ore batch charging system to thicken the coke layer in the furnace (up to 300~500mm thick), forming good coke window permeability, which plays a good role in smoothing the blast furnace production.

Due to the high material column of large blast furnaces and the high compression rate of the charge, the evaluation of coke quality can no longer only meet the requirements for indicators such as M40, M10, ash content, sulfur content, etc., but should also include the evaluation of coke quality. Requirements for thermal reaction performance indicators, such as post-reaction strength (CSR), reactivity index (CRI) and other indicators. The quality of coke used in large blast furnaces in industrially developed countries is generally better than that in my country, which is one of the important reasons for the improvement of foreign blast furnace indicators.

The M40 of coke used in large foreign blast furnaces is generally greater than 85%, M10 is less than 6.5%, and the ash content is at 3 product levels. Advanced processes, technologies, and equipment are used to achieve high efficiency of the blast furnace. High efficiency of the blast furnace refers to high utilization coefficient and Low energy consumption. Improving the grade of ore entering the furnace is an effective means to achieve a high utilization coefficient.

Achieving a reasonable charge structure can improve the grade of the ore entering the furnace. At present, the proportion of pellets in the charge structure of blast furnace ironmaking in my country is relatively low (the average of key steel companies across the country is 11%).

The iron grade of pellets can be between 60% and 66%, while the sinter grade above 58% is considered a high level. Therefore, our country should strive to improve its pellet production capacity and increase the pellet ratio to more than 20%.

It is recommended to actively use belt roasting machines and grate machines - rotary kiln production equipment to produce pellets. The quality of pellets produced by this equipment is better than that of shaft furnaces.

Author: indu1 2007-12-1 09:47 Reply to this statement-------------------------------- -------------------------------------------------- -2 Theory of Conditions for Blast Furnace Ironmaking Production (Table) It is necessary to vigorously promote the use of bell-less furnace top equipment to achieve reasonable distribution and improve the utilization rate of CO2 in gas (increasing the CO2 content in gas by 0.5% can reduce fuel consumption by 10kg/t) , which in turn can reduce fuel consumption; it can also effectively control the edge development of the gas flow, thereby increasing the life of the blast furnace. Our country has successfully developed various forms of bell-less furnace top equipment and has applied them to large blast furnaces, and the cost is more than 50% lower than the imported ones.

We should vigorously promote domestic equipment and support the development of China's manufacturing industry. Actively promote the blast furnace top gas pressure differential power generation technology (TRT), which can recover 30% of the energy of the blast furnace blower and reduce the energy consumption of the ironmaking process by 11~18kgce/t.

Blast furnaces with top gas pressure greater than 120kpa should be equipped with TRT devices. The power generation varies with the top gas pressure. Generally, each ton of pig iron can generate 20 to 40 kilowatt hours of electricity. Using dry dust removal can increase power generation by about 30%.

For every 10°C increase in gas temperature, the power generation turbine output can increase by 3%. The injection of pulverized coal into the blast furnace is the central link in the structural adjustment of the ironmaking system and is also a major trend in the development of ironmaking technology at home and abroad.

Injection of pulverized coal into blast furnaces may not only save coke and alleviate the shortage of coke in my country, but also reduce environmental pollution caused by the coke production process. It can also save energy (the energy consumption of the coking process is 144.4kgce/t, The energy consumption of the pulverized coal process is 20~35kgce/t) and the cost of ironmaking is reduced (the price of 1 ton of pulverized coal is about 500 yuan lower than the price of 1 ton of coke). The quality of raw fuel for large blast furnaces.

7. Production process of non-blast furnace ironmaking

There are three types of gas-based direct reduction equipment currently in operation.

The first type is the shaft furnace, represented by the MIDREX process. The shaft furnace process accounts for the majority of direct reduction production capacity.

The second type is the reaction tank. The only process using the reaction tank is the HYL method. The reaction tank adopts the backward fixed-bed discontinuous production method and is therefore in the process of being gradually eliminated. However, until 1997, the sponge iron produced by the HYL method still accounted for more than 7% of the total output.

The third type is the fluidized bed. The current only representative is the FIOR method, with a production share of 1% in 1997. Among coal-based direct reductions, only the rotary kiln process has considerable production capacity.

The representative rotary kiln process is the SL-RN method. The rotary furnace process uses carbon-containing pellets, which is still in the development and research stage.

The external heat reaction tank, also known as the stuffy tank, is a process in which mineral powder and reducing agent are put into the reaction tank and then reduced through external heating.

This process is generally used abroad to produce iron powder for powder metallurgy, and the heating is performed in a tunnel kiln.

In recent years, many local and private enterprises in China have used this method for small-scale sponge iron production. Heating often utilizes existing equipment and is not limited to tunnel kilns.

Electric thermal direct reduction consumes a lot of electricity and has been discontinued at present. There are also a few processes with small production capacity whose position is unclear in this classification method, such as the KINGLOR-METOR method.

This method uses gas for heating outside the shaft furnace and coal for reduction inside the shaft furnace. The consumption of natural gas and coal converted into heat is roughly the same.