Design of the compressed air drying system for coal injection in Xiangtan Iron and Steel Co., Ltd. Li Hanming (Xiangtan Iron and Steel Company) 1 cited § With the increase of coal injection volume in the blast furnace, the coal powder transportation is required to be stable and uniform, the material flow is smooth, and the pulsation phenomenon is less. Therefore, in recent years, people have put forward higher requirements for the quality of compressed air of coal powder conveying medium, requiring compressed air to be free from pollution.
There are three types of pollutants in compressed air, namely oil, dust and water. The oil is derived from the compressor lubricating oil, and some of them are often decomposed to form oxides, such as organic acids. The water-soluble substances are highly corrosive, and other liquid oxides form oily and sticky residues. Liquid water may contain ionic soluble gases, such as co2. When water comes into contact with steel, it usually produces iron oxide hydrate. This reddish brown powdery substance is insoluble in water and can also form fouling, causing blockage of certain parts.
2 Two common compressed air drying methods are compared with the commonly used compressed air drying methods in the industry: adsorption and freezing. The adsorption method uses a special desiccant to absorb the moisture in the compressed air by its physical properties, and uses the method of transformation or temperature change to explain the regeneration to achieve the purpose of recycling. The adsorption method is suitable for the production of compressed air with a dew point above 20C. The gas loss is relatively large, generally 15% and 20%, and is suitable for cold regions. The freezing method uses the freezing principle to achieve air drying by reducing the temperature of the compressed air. The freeze dryer is a popular drying equipment developed in the late 1970s and early 1980s. It does not consume any desiccant and does not require regenerative gas. The dew point is stable and the price is low. This method is applicable to the working principle of manufacturing a dew point temperature that is difficult for the water to be cooled. Wet air first enters “0820 Contact: Li Hanming Senior Engineer (1101) Design Institute Pre-cooler of Xiangtan Iron and Steel Co., Ltd., Xiangtan City, Hunan Province, exchanges heat with the exported outlet air – pre-cooling (pre-cooling to 25C); Enter the evaporator and the cold medium (Freon) for heat exchange - cooling, cooling to 23C (pressure dew point corresponds to atmospheric pressure dew point - 23C); the cooled air enters the oil-water separator, removes mechanical water and oil droplets, and then enters the pre- The cooler pre-cools the incoming fresh air and finally enters the pipe network from the air outlet. The functions of the pre-cooler are as follows: (1) pre-cooling the inlet humid air to save energy; 2 heating the outlet cold air to prevent secondary condensation and condensation outside the outer outlet air line and the downstream line, and Increased water capacity of compressed air.
3 Xianggang's compressed air freeze-drying system design Xianggang's coal injection workshop has two series of pulverized coal preparation system and three series of blast furnace coal injection system, and another set of pulverized coal transportation station for three blast furnaces (1000m3X2, 750m3Xl) for coal injection The current total gas consumption is lm3/min. The workshop air compressor station has 40m3/minX3 and 20m3/minX2 piston air compressors. The original system does not have a compressed air drying device, and only a part of the mechanical water can be removed by the gas storage tank. Therefore, the compressed air has a large water content and oil content. In production, especially in the rainy season in spring and summer, equipment failures such as blockage of pipes and blockage of coal seams often occur. In severe cases, the coal mouth is often repaired, and the phenomenon of dripping of coal powder is often found. In the past, the production level of the blast furnace in Xiangtan Iron and Steel Co., Ltd. was low, and the understanding of coal injection coke was insufficient, and there was insufficient investment in the technical transformation of the coal injection system. With the continuous improvement of the technical indicators of the blast furnace, especially the iron production has been greatly improved, the coke supply of the coking plant of the company has become increasingly tight, and the blast furnace coal injection has become an important process of blast furnace production. In order to ensure that the blast furnace can stably and uniformly spray coal, the company modified the compressed air drying system of the coal injection workshop in 1998 to solve the difficulties caused by the excessive oil content of compressed air.
The compressed air drying method of Xiangtan Iron and Steel Co., Ltd. uses a freezer drying method, and the process flow is as shown. The original design parameters are: air treatment capacity 120m3/min, gas tank outlet temperature 5060"C, air oil content environmental parameters: atmospheric temperature 23X: atmospheric pressure 98kPa, atmospheric humidity 80%. User-oil cold air station cold water freezing However, the dryer is separated from the dryer. 2 Xianggang Refrigeration Drying Machine Process Plant recommends the use of 2 or 3 sets of 60mVmin freeze dryers (two-purpose and one standby) in parallel. The design takes into account the differences in pipeline layout systems. It is difficult to balance the intake air volume of two freeze dryers, so a 120m3/min freeze dryer is used to simplify the system. As for the dual-use and one-preparation, not only the investment is increased, but the ear pipeline is long, the valve is many, the system Complex, occupying a lot of land. From the perspective of system operation, there is not much need. Because the manufacturer promises that the freeze dryer can run for many years (similar to household refrigerators), the 46 system deoiler needs to be replaced with a filter. There are no other wearing parts, and the time to replace the filter is extremely short. Therefore, there is no need to increase the investment.
The freeze dryer is divided into normal type and high temperature type according to the inlet air temperature. The air inlet temperature <45C is a normal type, and the <80'C is a high temperature type. Although Xianggang's coal injection air compressor has a rear cooler, the temperature of the compressed air after the cooler is still high, generally 5060C. It is recommended to use a high-temperature freeze dryer, so that the freeze dryer can be eliminated. Cooler. However, the design considers that Xianggang uses a piston air compressor and has been used for many years. The compressed air contains a large amount of oil. If the compressed air cannot be effectively degreased before entering the freeze dryer, the multi-oil gas enters the freeze dryer. When the refrigerant evaporator is used, the low-temperature refrigerant copper tube is easily adhered by the oil, thereby lowering the cooling efficiency.
The piston cylinder of coal-fired air compressor of Xiangtan Iron and Steel Co., Ltd. uses No. 100 lubricating oil. The kinematic viscosity of mechanical lubricating oil is inversely proportional to the temperature. Therefore, it is necessary to effectively de-oil the compressed air when entering the oil-water separator before the freeze dryer. It is necessary to reduce the temperature of the compressed air before the oil-water separator. After the viscosity is increased, the diameter of the oil mist droplets is correspondingly increased, and the oil filtering efficiency of the separator is greatly improved.
The design is provided with a compressed air cooler in front of the oil-water separator in front of the freeze dryer, and the freeze dryer is a water-cooled common type.
The rational selection and use of the oil-water separator is also an important part of whether the freeze-drying system can adapt to the gas used for coal injection. The higher the grade of the separator, the higher the efficiency of oil-water separation, but the greater the gas resistance. The principle of separator setting in the system should be that the level before the freeze dryer is low and the level after it is high. The filter particle size of the oil-water separator in the freeze dryer is generally 3fun. In this design, the filter particle size of the oil-water separator before the freeze dryer is 5fim (or even 10fxm), and the oil-water separator after freeze-drying is eliminated. The reason is: the large oil-water separator has large resistance loss, which will affect the pressure requirement of coal injection gas; the coal injection process does not require excessively "pure" compressed air; the amount of dewatering of the fine separator accounts for the proportion of system dewatering Smaller.
The freeze-drying system is set as close as possible to the air pressure rather than the user (the coal injection station) because the dew point of the air changes as the pressure changes. The compressed air pressure drop from Xianggang Steel Injection Air Compressor Station to Coal Injection Station is about 05 MPa, which does not include the freeze-drying system resistance.
The temperature of the outlet gas of the freeze dryer is low, and there is a heating process (especially in the south) during the pipeline transportation from the freezing system to the coal injection station. The increased temperature of the compressed air increases its water capacity, which reduces the humidity of the gas, which is another benefit of the freeze-drying system close to the air compressor station. Inspired by this, the drying method can be used for drying the compressed air. Whether it can also be used on the reverse side, the heating method is used. In fact, the heating method has been practiced.
4 operating freeze-drying system. The two 80mVmin freeze dryers used in the two blast furnaces of the A plant were put into operation in less than two months. A 60m3/min freeze dryer of plant B also basically failed. The compressed air part passes through the freeze dryer and partially passes the bypass pipe. If the freeze dryer is completely gone, the compressed air resistance is too large to meet the pressure of coal injection. It is required that the freeze dryer is actually in a semi-turn state. Only one 80mVmin freeze dryer of the C plant has been running for half a year, and the effect is better. However, after the compressed air from the system comes out of the freeze dryer, a compressed air heating device is added before the coal injection station (according to the scene, no Before the heater is installed, the freezing and drying system is not easy to use, and the coal is often blocked. The compressed air of these three plants is no longer provided with cooling by the air compressor from the air compressor tank before entering the freeze dryer, and the freeze-drying system is set close to the coal injection station.
The Xianggang Steel Injection Compressed Air Freeze Drying System was operated for 2 months. The effect on the site was very good. The pipe blocking phenomenon has not occurred, and the coal injection is even and stable. The original coal injection volume of No. 1 blast furnace was 7t/h, and now it reaches 10t/h. In the case of no oxygen enrichment, the coal injection amount is above 1kg/t. The chilled-drying system provides high-quality compressed air, which is an important prerequisite. The equipment failure of the gas-using equipment is also greatly reduced, especially in the past, solenoid valves that often have clogging problems, and almost no clogging.
Practice has proved that the design of the freezing and drying system is successful, the process is reasonable, the equipment selection is appropriate; the system is simple. Less investment; the compressed air dehydration effect is good, meets the production requirements, and has reached the expected.
(Responsible editor Hu Huili). Technical Information. “Development and application of single-layer double-sided self-cleaning cantilever screen vibrating screen on 750m3 blast furnace†was identified by “Development and application of single-layer double-sided self-cleaning cantilever screen vibrating screen on 750m3 blast furnace†Item 0 in 199910 On the 27th, it passed the appraisal hosted by Shandong Metallurgical Industry Corporation.
The Laiwu Iron and Steel Group Co., Ltd. Laiwu Iron and Steel Co., Ltd. ironmaking plant, Jinan Zhongran Industrial Development Co., Ltd. assisted the completion of the "single-layer double-sided self-cleaning cantilever screen vibrating screen on the 750m3 blast furnace development and application" project has achieved With good economic and social benefits, Laiwu Steel's two 75m3 blast furnaces can generate economic benefits of more than RMB 10,000 a year. The development and application of single-layer double-sided self-cleaning cantilever screen vibrating screen is the first in China. Because of its reasonable structure and advanced design, it has the characteristics of light weight, strong wear resistance, low energy consumption, long life, high screening efficiency and stability. After applying this technology, Laiwu Steel's 750m3 blast furnace greatly reduced the amount of powder entering the blast furnace. The powder of <5mm in the sinter was controlled at about 3.5%, and also reduced the quantity of qualified products entering the return mine, which qualified in the return mine. The mine is less than 20%, the average screening efficiency is up to 80%, and it can maintain stability for a long time, reducing the workload of cleaning the screen, thereby improving the gas permeability of the column, improving the blast furnace forward, increasing the output and reducing the finished product. The consumption of sinter mine reduces the cost of pig iron.
This technology has obtained national patents. Its development and application not only fundamentally solves the key technical problems existing in the long-term screening of raw materials in the ironmaking industry, but also provides successful experience for other industries to improve the screening quality.
C Wuhan Iron and Steel Design and Research Institute Cheng Jianguo)
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