Magnesium sulfite is an intermediate product in the flue gas desulfurization process of the magnesia method. It can be further oxidized to produce magnesium sulfate crystals, and it can also be calcined to recover sulfur dioxide and magnesium oxide. It can also process plant fiber raw materials and produce pulp. In order to optimize the control of the above process, it is necessary to use high-purity magnesium sulfite samples to carry out experimental research. However, because magnesium sulfite is easily oxidized to magnesium sulfate, it may deteriorate during its production process, and there are many factors affecting its oxidation rate, so there are no high-purity samples on the market.
Preparation of magnesium oxysulfide short fiber material
The magnesium sulfite and the magnesium oxide are ground to a particle size of 74 μm, the mass ratio is 4:1, and deionized water is added to the reaction kettle according to the liquid-solid ratio of 4:1, and oxygen is introduced at a stirring speed of 300r/min. , the reaction temperature is controlled to be 120 ° C, the oxygen pressure is 0.2 MPa, the solid-liquid separation is carried out after the hydrothermal reaction for 2 h, and the solid is dried to obtain the magnesium oxysulfide short fiber material. The magnesium oxysulfide short fiber material obtained by the process has an aspect ratio greater than 50, and the filtered liquid can be recycled.
At present, the preparation of known higher-purity magnesium sulfite is to use its insolubility to pass sulfur dioxide gas into an aqueous solution of magnesium oxide to obtain a suspension of magnesium sulfite, and the main component of the obtained filter residue after filtration is sulfite Magnesium Sulfate. However, the actual operation process of this method is complicated, and the obtained magnesium sulfite sample has a high water content, which is not easy to transport and store. In the preparation of large-scale magnesium sulfite, the magnesium oxide flue gas desulfurization process can be used to react the magnesium hydroxide slurry with sulfur dioxide in the flue gas, and then flocculate the formed desulfurization slurry and separate solid-liquid to obtain the Crystals of magnesium sulfate (patent number CN101254932A). In this process, an oxidation inhibitor should be placed in the desulfurization tower at the same time to consume the oxygen in the flue gas, thereby preventing magnesium sulfite from being oxidized into magnesium sulfate. However, due to the complex composition of flue gas, impurities such as fine fly ash and inhibitors are easily mixed into magnesium sulfite for precipitation, and the magnesium sulfite obtained by solid-liquid separation has a high water content, so the magnesium sulfite obtained by this method has a high water content. The purity is not high.
(1) Magnesium sulfite drying: The wet magnesium sulfite with 8-20% water content produced by the desulfurization system is sent to the spin flash dryer through the double helix. Inside the spin flash dryer, the magnesium sulfite rises with the hot air flow, In the process of rising, the drying of the material is realized, and then it enters the two-stage gas-solid separation, and the dried magnesium sulfite is recovered to the intermediate storage silo for calcination, so as to realize the organic connection between the drying and calcining processes and ensure the stable operation of the system. . The heat used for drying is to use the waste heat of the calcination and decomposition section. The drying hot air temperature is 200 to 350 ° C to remove more than 99% of the free water and 10 to 50% of the crystal water in the magnesium sulfite, so as to reduce the heat consumption of the calcination and decomposition section. . The rotary flash dryer can effectively avoid the problem of magnesium sulfite agglomeration and clogging. The dried magnesium sulfite particles are fine and do not need to be broken again.
(2) Magnesium sulfite decomposition: The magnesium sulfite in the intermediate storage bin is sent to the kiln head of the externally heated rotary kiln through the feeder. With the rotation of the rotary kiln, the magnesium sulfite moves to the kiln end and decomposes continuously. It is magnesium oxide and sulfur dioxide. Magnesium sulfite is basically decomposed completely before reaching the end of the kiln, and the magnesium oxide powder with high activity is discharged from the end of the kiln, and the sulfur dioxide gas with a concentration of 20-60% is discharged from the head of the kiln. The fuel can be coal or natural gas, the calcination temperature is controlled at 700～900℃, and the residence time is controlled at 20～60min to meet the requirement of complete decomposition of magnesium sulfite. When the raw coal is directly burned as the heat source of the rotary kiln, the exhaust gas contains a lot of soot, which cannot be directly used for the drying of magnesium sulfite. It is necessary to add a heat exchanger to heat the air and use it in the drying system; when using coal to produce gas Or when natural gas is burned as the heat source of the rotary kiln, the flue gas can be directly used for the drying of magnesium sulfite after adjusting the temperature.