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I. Introduction
Light burnt dolomite is a mineral material obtained by mixing dolomite ore with a certain fuel and calcined. It can be used as a good auxiliary material for slag discharge in steel making process. Since 1984, Taigang Composite Materials Factory has built 5 Φ2.5 m×12.5 m light-burning dolomite soil shaft kiln, only 3 normal production, and the production of light-burned dolomite is mainly used for Taigang No. 2 Steelmaking Plant. Use slag. In recent years, with the development of Taigang's production and the construction of a new 1.5 million tons of stainless steel projects, the production capacity and product quality of the existing soil shaft kiln cannot meet the demand. In order to change this passive situation, three original soil shaft kiln were demolished and a mechanized shaft kiln was built to guarantee the company's demand and improve economic efficiency.
Second, the original soil shaft kiln production status
(1) Technical indicators of raw materials and products (Tables 1, 2)
Table 1 Raw materials for light burnt dolomite
raw material
Dolomite mine
Anthracite (%)
MgO
(%)
SiO 2
(%)
R 2 O 3 +Mn 3 O 4
(%)
Particle size range
/mm
Fixed charcoal
Ash
Volatile matter
S
index
≥19
≤2.0
≤2.0
20-45
≥76
≤10
≤14
≤1.0
Table 2 Light burnt dolomite product quality indicators
project
MgO (%)
SiO 2 (%)
Burning (%)
Particle size range / mm
index
≥29
≤4.0
≤22
10-40
(2) Production process (Figure 1)
Figure 1 Process of producing dolomite in soil shaft kiln
The raw materials are self-produced dolomite lump ore. The fuel is made of anthracite lump coal. The dolomite lump ore is calcined for 2 hours and then deposited into the finished silo. The main parameters of the shaft kiln are: outer diameter 3.6m, inner diameter 2.65m, effective height 11m, effective volume 58m 3 , annual production capacity of 10,000t/seat.
The useful components in the dolomite ore are MgCO 3 and MgO, and the useful component in the light burned dolomite is MgO. In order to increase the content of MgO, the dolomite ore is calcined at a high temperature of 1050-1200 ° C to thermally decompose MgCO 3 , thereby increasing the content of MgO.
(III) Process evaluation
In addition to the mechanical operation of feeding, cloth, calcination and sieving, the production process of raw materials, batching, discharging, and material selection are all manual operations. Therefore, production is greatly affected by human factors, kiln conditions are unstable, and there are often phenomena such as under-burning and over-burning, resulting in unstable quality. At the same time, the labor intensity of workers is also large. In 2005, the total labor productivity was only 542t/person. .
With the development of Taigang (Group) Co., Ltd. and the completion of the construction of a new 1.5 million t stainless steel project, the amount of light burnt dolomite has increased from 30,000 tons to 59,000 tons per year since 2001, and the final demand is expected to reach about 14 10,000 t / a; at the same time the product quality requirements are also constantly improving, the main component of the MgO content increased from 28% to 29.8%, eventually will require more than 30%. Therefore, the original soil shaft kiln production capacity can not meet the demand in terms of output or quality, and it is urgent to improve.
Third, the new mechanized shaft kiln
(1) The necessity of building a new mechanized shaft kiln
In order to meet the requirements of Taigang (Group) Co., Ltd. for the quality and output of light-burned dolomite, if the original three soil shaft kiln is to be transformed, the annual production capacity is only about 55,000 tons, and the process is backward and the product quality is poor. Far from meeting the needs of the company's development. At the same time, according to the environmental protection standards, the existing soil shaft kiln of Taigang Composite Materials Factory is in the scope of elimination. To this end, it is imperative to build a mechanized vertical kiln production line with advanced construction technology and high environmental quality.
(II) Overview of new mechanized shaft kiln
The newly-built light-burned dolomite 500m 3 mechanized shaft furnace is one of the supporting projects of Taigang (Group) Co., Ltd.'s new 1.5 million t stainless steel renovation project. The shaft furnace is fully mechanized and automatic operation. It is a shaft furnace with advanced level in the same industry in the country. It can produce 13-140,000 tons of light-burned dolomite annually, and the product quality will be greatly improved, which is satisfied in terms of output or quality. The needs of the company.
(III) Technical indicators of raw materials and products (Tables 3 and 4)
Table 3 Raw material indicators for mechanized shaft kiln
raw material
Dolomite mine
anthracite(%)
MgO (%)
SiO 2 (%)
R 2 O 3 +Mn 3 O 4 (%)
Particle size range / mm
Fixed charcoal
Ash
S
index
≥19
≤2.0
≤2.0
30-50
≥85
≤14
≤5.0
Table 4 Mechanized shaft kiln product quality indicators
project
MgO (%)
SiO 2 (%)
Burning (%)
Particle size range / mm
index
≥30
≤4.0
≤22
10-40
(4) Production process (Figure 2)
Figure 2 Mechanized shaft kiln process
The prepared mixed dolomite and coke powder are evenly distributed into the furnace through the distributor. The shaft furnace body can be roughly divided into a pre-tropical zone, a calcining zone and a cooling zone from top to bottom. As the bottom product is discharged, the upper furnace material is slowly moved downward by its own weight. The pre-tropical cold material exchanges heat with the high-temperature exhaust gas from the calcining belt, and the high-temperature exhaust gas can preheat the cold material to about 830-850 ° C; in the calcination zone, MgCO3, CaCO3 absorbs heat, and the coke powder burns to supplement heat, calcination The temperature of the belt is generally controlled at 1050 ~ 1200 ° C, and the temperature is up to 1300 ° C; the high temperature light burned dolomite fired in the cooling zone is exchanged with the cold air blown by the hood at the bottom of the furnace bottom, and the cold air is preheated to about 600- At 700 ° C, the lightly burned dolomite is cooled to 30-70 ° C, and the preheated air acts as a combustion-supporting air for the calcined coke combustion. The exhaust gas generated by the combustion and the CO 2 generated by the decomposition of MgCO 3 and CaCO 3 enter the flue gas dedusting system from the top of the furnace. The calcined dolomite is uniformly removed by the disc unloader at the lower part of the furnace, and alternately operated by the sealed ash type ash valve, intermittently discharged, so that the ash is discharged to the large dip angle tape without stopping the wind, and the large dip angle is obtained. The tape conveyor transports the finished product to the finished product warehouse. The top exhaust gas temperature is 150-200 ° C, and the bottom discharge temperature is 30-70 ° C.
The light burnt dolomite is screened, 5-45mm enters the finished silo, and <5mm is transported by the car to the powder mine bin for recycling. This not only avoids the discharge of solid waste, but also improves the grade of the fine ore.
The system adopts automatic control from mixing, feeding, roasting and unloading, and is equipped with electronic weighing scales to eliminate the influence of human factors, so that the original and fuel are evenly mixed, so that the fabric is reasonable, uniform in heat and stable in quality. The product components are: MgO>30%, Ca0>50%, low residual amount of CO2; raw firing rate + over-burning rate <8%; and less impurity content. The main index parameters of the mechanized shaft kiln are: effective height 27m, effective diameter 5m, annual production capacity up to 140,000t/set.
The technical indicators after the completion of the shaft kiln are shown in Table 5.
Table 5 Technical indicators of new 500m3 mechanized shaft kiln products from August to October in 2006
project
August
September
October
Production (including surface ash) / t
1660
6784
7884
Component (%)
MgO
31.14
32.28
31.14
CaO
45.25
46.29
48.79
SiO 2
3.41
2.00
3.41
Burning down
17.4
16.5
16.7
(5) Process evaluation
Mechanized shaft kiln system is a mature process system at home and abroad. The labor intensity of workers using automatic control is reduced by 80%. At the same time, the influence of human factors is completely eliminated, and the necessary conditions for product quality stability are provided. The annual labor productivity of the whole staff is 2,917 t/person, which is 5.4 times that of the original soil shaft kiln.
Main technical features of mechanized shaft kiln compared with original soil shaft kiln:
-The production process uses a PLC control system with a central control room CRT and several electrical rooms. At the same time, the raw materials, finished products and production processes are controlled. The electronic weighing technology is used to accurately weigh the raw materials and fuel before entering the kiln, and can realize automatic compensation.
- Continuously rotate the fabric with new equipment, so that the ore and coke are evenly distributed on the circumference of the different radii of the vertical kiln along the material surface. The same ring belt has no convex and concave phenomenon, and the material surface of different annular belts is ≤300mm. In the fabric process, large pieces of dolomite can be placed in the center of the kiln, and small pieces are placed around the kiln to mitigate the effects of the surrounding effect of the kiln.
- The pulsed liquid level detector is used to control the height of the material in the kiln, so that the height of the material in the kiln is kept within a certain range, thus stabilizing the thermal system of the kiln and improving the product quality.
-The rotary dolomite is uniformly discharged from the kiln by the disc unloader, and the double-layer hydraulic sluice ashing machine has good sealing effect and reliable operation, and can uniformly discharge without stopping the wind. It is conducive to the smooth movement of materials in the kiln and improve product quality.
- The Roots blower is used to supply air into the kiln. The amount of air blow is not affected by the change of resistance in the kiln, which can ensure the stability of the thermal system in the kiln and help stabilize the quality of dolomite.
- The kiln exhaust gas is highly dust-removed and purified, which reduces the pollution to the environment. Its dust emission concentration is <50 mg/m 3 , which improves the production environment and has greater social benefits.
The use of light-burned dolomite 500m 3 mechanized shaft kiln has achieved good economic benefits. After the project is put into production, it can produce 140,000 tons of high-quality light-burned dolomite (all ash), with an investment profit rate of 60% and a pre-tax rate of 89.70%. The investment recovery period (including the construction period) is 1.67 years after tax and 1.11 years before tax.
November 17, 2021