When silicon metal and ferrosilicon is melting at high temperature, the exhaust gases or dust is called silica fume silica. The main ingredient is SiO2 and the flue gas accounts for about 90% of the total dust, which contains the free state about 10% SiO2. Particle size is very small, the average particle size of about 0.3μm, so it is known as silica fume. It can directly enter the body through the respiratory alveoli and do great harm to human health. China currently has thousands of ferrosilicon and silicon metal furnace blocks. In the production process, silica fume is produced about 250,000 t. Environmental protection equipment has been able to capture about 50,000 tons. The other gas goes directly into the atmosphere, which not only pollutes the environment, but also is a waste of resources. Silica fume has no precise price at present,about 1800 ~ 3800 yuan per ton. If the price is  2000 yuan per ton, about $ 500 million is lost every year because of the annual straight row of micro-silica fume. Therefore, it is imperative to recycle flue gas and capture silica fume . Silica fume capture is not only a problem of environmental and social benefits, but also contains a great economic and scientific and technological value. Here are the application and capture of micro-silica fume:

1. The application of micro-silica fume

Silica fume widely used in construction, chemical, and metallurgical industries is home to high-tech fields and has broad application prospects in the fine material. A great deal of micro-silica is mainly used for cement or concrete admixtures, cement or concrete to improve the performance of the preparation with a high strength, wear resistance, erosion, corrosion resistance, frost penetration, high early strength concrete or composite special cement, water, scraping for large hydropower, port terminals, railway bridges, highways, airport runways, tunnels and urban high-rise buildings and other projects. It can be used in paints, coatings, resins and other polymer filler. Rubber can be used to improve the extension of rubber, tear and tensile strength. It can also be used for the production of refractory and ceramic products and improve product strength and durability.

   In the early 1980s, developed countries successfully used this technology. For example, the United States had the annual production of silica fume up to 30 million tons, making up 1 / 4 of the world's annual production of silicon powder, followed by the former Soviet Union and Norway, the annual production of silica fume were 150,000 tons and 120,000 tons. In Texas, the United States in 1980 commercial buildings were built with silica fume concrete, the strength of 1OOMPa. In recent years, especially the United States has prepared a 250MPa high-strength concrete. In China's major water conservancy construction, bridge, tunnel, heritage restoration and other practical applications, it also fully proved concrete mixed with silica fume in the amount of works can greatly improve the quality of the project.
The following are concrete projects using silica fume to improve the mixing quality of the project.
(1) Micro-silica fume concrete used in water conservancy and hydropower projects, can improve the ability of anti-erosion project.

The traditional anti-abrasion material at home and abroad are more than other polymer materials with epoxy mortar. Anti-abrasion ability of these materials is good, but because it itself is several times larger in the linear expansion coefficient of the base ordinary concrete, and concrete temperature doesn’t fit well with the substrate, in the natural climatic conditions and is likely to crack off. And the construction of complex, toxic, expensive, is not in large scale. According to statistics, China has built 32 large hydropower stations, where there are 22 subjects to erosion damage, especially in several hydropower stations on the Yellow River and southwest of the water conservancy and hydropower project, due to a large content of silt and bed load, high velocity, abrasion problem more prominent, has endangered public safety.

Silica fume as anti-abrasion materials in China began in 1985. Since 1986, Nanjing IWHR in collaboration with a sister unit, the results has been used in the Gezhouba Dam, Dahuofang reservoir, Yingxiu Bay Hydropower Station, and Long amniotic fluid Gorge  After a few floods out over the water test, the effect is very good. It has doubled the capacity of its anti-abrasion about anti-48m / s velocity level abrasion resistant capacity of more than 3 times. Xiaolangdi hydropower projects in micro-silica fume package also show their talents.

(2) Micro-silica fume concrete used in hydraulic engineering, and engineering can improve the resistance of crack.

Hydraulic concrete cracks, have become a widespread concern for the big problem. Cracks due to heat of hydration heat up the material itself, such as the incorporation of fly ash in concrete. Although you can reduce hot water heating,  the early strength is relatively low, then the amount of fly ash is limited. In the Fifth International Conference on the dam, the dam Norwegian Kai-shek in Forrreass mixed with silica fume and produce good results in the situation, causing the participants attention. After the meeting, China's Nanjing IWHR commitment to the "Plan" research project using silica fume modified to improve the crack resistance of concrete research tasks.
   Volute turbine experiments Fan Station in Fujian in 1987 show that incorporation of appropriate micro-silica fume and comparison of non-doped, save 38% cement, 30% lower heat of hydration, the field strength to ensure that more than 98%, unilateral material fee is not increased, compared with the original design of steel fiber reinforced concrete materials to save a cost of 14 yuan.

(3) Micro-silica fume concrete can improve the anti-permeability, salt corrosion properties to protect steel

According to the survey, data show that, underwater engineering, due to chloride ion penetration in concrete, cause rapid corrosion of steel, concrete delamination, short life, destructive serious, Norway in 1971, the micro-silica fume used in concrete, while filling in the cement around the particles, so that slurry is more dense; the other hand, it generated with the cement hydration produce calcium hydroxide combined with calcium silicate hydrate gel (also known as CSH gel), the gel plug in the capillary, make pores smaller and not continuous, greatly increased the density of concrete, effectively improving the resistance to chloride ion penetration damage caused by the electrochemical capacity and greatly enhance its anti-corrosion properties. Nanjing IWHR after three years of research, timber terminals in Lianyungang, Jiangsu Province on the trial, each side to save cement concrete 80 ~ 110kg, and to facilitate the construction, service life extension of 1.2 times.

Underwater concrete pouring commonly used catheter, due to loss of slurry in water, it exists with the primary bond is not good, some contact with water reduces the strength and other issues. Silica fume concrete mixed in the water, it can be significantly improved.

(4) micro-silica fume concrete repairs in traffic on the road surface, is highly wear-resistant properties

Pouring concrete with ordinary road, need 28 days to normal traffic, usually early-strength concrete have three days to the opening of the concrete road surface damage is inevitable. Repair using conventional methods. Often causing traffic disruption, leading to serious economic losses. To solve this problem, according to the advanced experience of foreign countries, 1986 Nanjing Academy of Agricultural Sciences has devised the wear characteristics of early-strength silica fume concrete, the practical application of the results are quite satisfactory.

Associates, Inc. 1988 Yizheng replacement of prefabricated factory center block roads require 12 hours to reach the opening requirements. Nanjing IWHR invited to design a 12-hour 200 # super-early-strength concrete formula micro-Gui Yang, plant in early September in central corridors pouring 100 square. Field sampling results showed that the compressive strength of concrete 12 hours to 25MPa, anti-abrasion increased by 1, 24 / hour compressive strength 37MPa, a long time to open to traffic. Bypass construction period of the car only cost savings of nearly 5 million, but they increase the cost of materials 4,000 yuan on its technical and economic results are quite remarkable.

Require the use of the airport runway more than 80MPa concrete and wear resistance, and shock can show their skills to Yang.

2. Silica fume capture devices do

As the micro-silica fume particle size is too small, mechanical filter, including the settlement of dust, dust and rotary inertia with dust, did not capture it. Film Dust capture it very difficult. But also because of its specific resistance is particularly high, up to 1013Ω • cm, the use of electrostatic precipitator devices are often, will have a back corona phenomenon, but also difficult to capture it. The use of advanced ESP units - Pulse ESP, from a performance perspective, to capture high-resistivity dust, but its investment in equipment is extremely expensive, about 10 times the conventional electrostatic precipitator. Therefore, micro-silica fume capture at home and abroad with a device most of the "big" bag filter, bag filter ahead of the reason why it is the highest in the "big", which is determined as the dust features. If the general trapping dust bag filter is used to capture the direct experience of micro-silica fume, may not achieve the desired results. Currently the United States, former Soviet Union, Norway and other countries are also using a large bag capture micro-silica fume. China is also basically the same.
This method there are some problems:
A. As the industrial silicon or ferrosilicon in the smelting process, the exhaust gas temperature is high, up to 500 ~ 600 ℃, and very unstable, which is entirely due to production status decision. So in front of bag filter unit, cooling unit must be located, it also increased the removal of equipment investment, otherwise it will burn bag.
B. removal equipment failure rate. As the particle size of silica fume is very fine, very viscous, cleaning is not easy to rapping, seriously affect the effect of dust, while increasing system resistance, energy consumption increases. And could easily lead to broken bags, out of bags, this time is bound to stop repair, will affect the normal production, but also increases the maintenance of zero.
C. the high running costs. The essence of the bag filter cloth filter the gas tax with a set of dust.
How to combine the high flue gas temperature and particle size characteristics of fine and sticky city is critical to choose a good tour to do. Even so, the running time is not long, the hole will be blocked cloth, always clean, but also reach the necessary air flow, filter cloth prone to breakage, the high cost for bags. The more serious problem is the filter cloth resistance increases, the required power is also increased. For example, the United States, a Taiwan 30000kVA silicon furnace equipped with a bag filter with the fan power is 1864kw, the average per square kVA power protection required for the 62kw, China's dust bag in addition to health in general is the large number of -..

Company developed the micro-silica fume capture device is the use of new technology line of high-voltage electrostatic trapping method. Completely different from the conventional bag capture method. The electrostatic capture device is not used at home and abroad conventional electrostatic precipitator as hard features pulsating DC power supply, but hard to soft features as stable DC power supply. From body structure, do not use conventional fixed-wire plus sleeping blow plate vibration cleaning means, instead of using the mobile dust scraper cleaning pole plus the way. Proved through practice, this method can capture the micro-silica fume, and the Buddha enough to meet the national emission standards. 1800kVA Jiaozuo Mining Bureau in 1995 and 2000, the Sanmenxia ferrosilicon furnace ferrosilicon furnaces Batou 2200kVA have been confirmed. This device compared with the large bag filter, has the following outstanding features.
A. one-time investment is low. A full set of equipment investment, a large bag filter of 70%;
B. operating costs low. Per square kVA furnace fan power required to 12kw, 20% fairly bag filter;
C. failure rate. It during operation, there is no broken bags, impact bags out of production problems, mechanical deliberately very low, basically in sync with the master device to run. Easy maintenance and management;
D. operability. A full set of equipment and raw materials used in equipment are made, and are ~ general material.
In short, we have the ability to use low-cost, efficient method of trapping silicon ferrosilicon furnaces and industrial process emissions in the production of micro-silica fume pollution in the atmosphere. It can not only solve the environmental pollution, but also turn waste into wealth, the development of modern high-tech fields urgently required resources.