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The whole process of magnesium process can be divided into by-product sulfuric acid and magnesium sulfate heptahydrate as two kinds of light burnt magnesium spheres. The following processes are described separately:
(1) The flue gas temperature of sulphuric acid production from boilers is mostly above 140 C, which contains a large amount of carbon dioxide, dust and sulphur dioxide. Light burning magnesium powder also includes acidic gases such as hydrofluoric acid, hydrochloric acid and sulphur trioxide. The flue gas first enters the dust removal system. More than 99% of the dust is collected by electrostatic precipitator or bag filter and sold to cement plant and other related enterprises as building materials. It can not only increase the profits of enterprises, but also avoid blocking the nozzle because of dust particles and reduce the desulfurization efficiency. After dust removal, the flue gas enters the desulfurization reaction tower from the bottom of the desulfurization tower. A water spray cooling device is installed at the entrance of the flue gas of the desulfurization tower. The temperature of the flue gas is lowered to be more suitable for the chemical reaction of SO2. A swirl plate is installed above the entrance of the flue gas in order to slow down the increase of the reaction time of the flue gas flow and achieve the effect of uniform distribution of the flue gas in the tower. There are three layers of nozzles continuously spraying desulfurizer slurry on the top of the swirl plate, which contacts the flue gas from bottom to top in reverse and reacts adequately. In order to reduce the structural blockage of equipment and reduce the excessive pressure loss in the tower to ensure smooth flue gas flow, there is no support or overhaul frame in the tower. After washing, the humidity of the flue gas is relatively high, so it needs to be dehydrated. Generally, two dehumidifiers are installed above the spray layer in the absorption tower. At the same time, an automatic process water flushing system is installed on the mist eliminator to deal with the ash deposit on the mist eliminator after a period of operation. The flue gas temperature from the desulfurization tower is generally about 55 - 60 C, and there is still a little moisture in the flue gas, which is easy to cause the fan blades and chimneys to be corroded by the fan water. Therefore, in front of the fan, the flue gas temperature is raised by heating and then discharged, so that the corrosion of the fan chimney can be avoided. In order to ensure that the normal operation of the boiler is not affected when the equipment in the desulfurization tower is repaired, a bypass system is added to protect the desulfurization system by controlling the direction of the flue gas through the baffle door, without any adverse effects on the operation of the boiler. For magnesium oxide, it reacts with sulfur dioxide in the absorber and becomes magnesium sulfite, which is partly oxidized by oxygen in the flue gas to magnesium sulfate. Mixed slurry removes surface water and crystalline water from solids through dehydration and drying processes. Magnesium sulfite and magnesium sulfate after drying can be roasted and decomposed in regeneration process. Magnesium oxide can be obtained and sulfur dioxide can be precipitated at the same time. The roasting temperature has a great influence on the properties of magnesium oxide. The roasting temperature suitable for regeneration of magnesium oxide is 660 ~ 870 C. Magnesium oxide can be sintered when the temperature exceeds 1200 C and can no longer be used as desulfurizer. The sulfur dioxide concentration in roaster exhaust is 10-16%. After dust removal, it can be used to produce sulfuric acid. The regenerated magnesium oxide can be recycled for desulfurization.
1. The flue gas system of flue gas system refers to a number of flue gas treatment systems including pre-precipitator, bypass, flue gas heating device and chimney. In this system, the flue gas from the boiler is adjusted to a more suitable reaction condition after dust removal and cooling treatment. At the same time, when the equipment fails or the system is not working properly, the flue gas can pass through the bypass to ensure the normal operation of the whole power plant system. The purpose of the flue gas heating is to reduce the moisture content of the flue gas and facilitate the rapid diffusion of the flue gas from the chimney.
2. If the size of magnesia spheres purchased from slurry preparation system meets the desulfurization requirement, the slurry with a concentration of 15-25% can be made directly into the digestion device without crushing. Then the slurry is pumped into the absorption tower to achieve the desulfurization purpose.
3. The absorption tower of SO2 absorption system is the main place for SO2 absorption. The material is mostly made of ordinary steel structure with anti-corrosion layer. The bottom of the tower is a slurry tank, the middle of the tower is a spray layer, and the top is a mist eliminator. The slurry is continuously circulated in the tower. When the slurry concentration reaches a certain level, it is discharged into the slurry treatment system through the slurry output pump.
4. The slurry of slurry treatment system from absorption tower is mainly magnesium sulfite and magnesium sulfate solution. When regeneration of magnesium oxide is required, the solution should be purified first, then concentrated and dried. After drying, magnesium sulfite is calcined at 850 C in the presence of carbon to regenerate magnesium oxide and sulfur dioxide. The calcined magnesium oxide is returned to absorption system and collected for purification. Higher sulphur dioxide gas is fed into sulphuric acid plant to produce sulphuric acid.