Type selection and application of iron removal from iron slag mill
Abstract : The characteristics of dusty exhaust gas in slag grinding system, the current status of domestic treatment technologies and new dust removal technologies are introduced. From the determination of process air volume, the determination of the type of bag filter, the selection of the filter speed, the calculation of the filter area, and the dust collector The selection of specifications and other aspects introduced the selection of slag powder bag filter, and the application of PPC slag air bag pulse bag dust collector and LDMC large low resistance bag filter dust in the slag grinding system.
Key words: slag grinding, bag filter, selection, application
1 Introduction
Blast furnace slag is the waste residue discharged from the production process of iron and steel plants. The national iron and steel enterprises generate about 120 million tons of slag each year. The slag is ground into fine powder of slag, which replaces cement by equal amounts. It can change waste into treasure and save cement production. The required mine resources are an important way to develop a recycling economy and realize sustainable development. Slag powder is a new type of high-strength concrete admixture and high-quality cement mixed material. Its raw material is blast furnace slag in the metallurgical industry. It is a new environmental protection product that protects the ecological environment and utilizes industrial waste residue. In the past ten years, many large domestic steel companies have invested The slag grinding production line was built, and the slag powder project was listed as a key point in the development of the non-steel industry.
The terminal equipment for the slag grinding system is a bag filter. The bag filter has the dual function of collecting finished products and environmental protection dust, and plays a vital role in the grinding system. The emission of slag grinding system exhaust gas is implemented in accordance with the new standard “Emission Standard for Air Pollutants in the Cement Industry” (GB4915-2004). The new standard imposes a strict stipulation on the exhaust emission limits: from July 1, 2006 to As of December 31, 2009, the allowable emission concentration of particulate matter in the exhaust pipe of the existing production line was 50 mg/Nm3, and since January 1, 2010, the high allowable emission concentration was 30 mg/Nm3; since 2005 On the 1st of the month, the allowable concentration of particulate matter in the exhaust pipe of the new production line mill is 30mg/Nm3. In order to adapt to the new standard, the selection of a new type of high efficiency bag filter is an inevitable trend in design selection.
2. Characteristics of Dust Exhaust Gas of Slag Grinding System
In order to better play the potential of slag, it is necessary to grind the slag. From the "granulated blast furnace slag powder used in cement and concrete" (GB/T18046-2000) standard, as long as the slag specific surface area is controlled at 420 ~ 450m2/kg, the S95 level requirements in the standard can be met. This not only satisfies the requirement of the cement manufacturer to provide 42.5 to 52.5 slag cement (30% to 50% of slag content), but also meets the requirement of the ready-mixed concrete company to have a configuration larger than C60 concrete. According to the existing equipment, vertical mill, roller press, ball mill, and vibration mill can be used for the final grinding process, or the combined grinding process of vertical mill + ball mill, roller press + ball mill. In recent years, the final grinding process using vertical mills to produce slag fines has become common and has developed rapidly.
Slag grinding system exhaust generally has the following characteristics:
(1) Fine dust particles. Grinding the slag powder to a certain fineness (specific surface area) can fully participate in the hydration reaction and increase the activity, but at the same time, it is also related to the particle composition, and the specific surface area is larger for many fine particles. The specific surface area and particle composition of different mineral micropowders are shown in Table 1. It can be seen from Table 1 that under the standard surface area specified by the standard, particles with a slag size of less than 10 μm account for 58%, more than fly ash and P.0525 cement. It can be seen that the slag powder has a small particle size and has strong levitation in the exhaust gas, which makes it difficult to remove dust.
(2) High dust concentration. Regardless of the ball milling process or the vertical grinding process, due to the cancellation of the secondary dust collection cyclone dust collector, the dust concentration of the dust-containing exhaust gas of the slag grinding system is relatively high, generally 400-1000 g/m3.
(3) Dust has high moisture content. Because the water quenched slag has high water content, sometimes as high as 15% to 20%, it is difficult to remove the moisture before entering the mill. During the milling process, a large amount of heat is generated. The vertical mill is also provided with a hot blast furnace for supplying hot air to the mill. Machine, the finished product powder moisture control in 0.5% ~ 1.2%, with the exhaust gas into the bag filter fine powder can easily cause condensation bag phenomenon.