Differences between heavy soda ash steam calcination furnaces and light soda ash steam calcination furnaces

This post was last edited by mkp369 on 2013-3-15 at 11:47. Please refer to the following source: http://bbs.hcbbs.com/thread-81665-1-1.html. The calcination process of heavy soda ash is primarily a dehydration process, and the heat required for dehydrating heavy soda ash is much less than the heat needed for evaporating free water and decomposing sodium bicarbonate during the calcination of light soda ash. The material residence time should also be shorter. Therefore, the length of the furnace body in a steam calcination furnace for heavy soda ash is shorter than that in a steam calcination furnace for light soda ash; it has a higher rotation speed and a larger installation inclination angle. Moreover, a steam saturation pressure of 1.3–1.6 MPa is sufficient, and the heating area per unit of production also needs to be much smaller. Due to the large crystal size and high density of heavy soda ash (sodium carbonate monohydrate), it cannot remain in a suspended state like light soda ash (in powder form) during the heating process as the cylinder rotates; instead, it flows close to the cylinder walls between the finned tubes, creating significant resistance to the rotation of the furnace. As a result, the drive power required for a steam calcination furnace using heavy soda ash is much higher than that for one using light soda ash. During the calcination of light soda ash, sodium bicarbonate decomposes when heated, producing large amounts of carbon dioxide gas, which needs to be recovered and reused in many soda ash plants. The concentration of this gas in the furnace gases is required to be at least 85%, which imposes high demands on the sealing between the furnace interior and the outside environment. The flue gas generated during the calcination of heavy soda ash is mainly water vapor; it is occasionally recovered and reused, with relatively low requirements. As a result, the sealing requirements at the point where the furnace connects to the outside world are not as strict as those for furnaces using light soda ash. Additionally, heavy soda ash produces less dust, so there is no need to install a spiral conveyor for transporting alkali dust at the furnace head. Sodium carbonate hydrate (sodium carbonate monohydrate) coming out of the hydrating machine contains a certain amount of free water; together with the crystalline water, its water content is roughly equivalent to that of the light sodium carbonate produced by the soda filtering machine, ranging between about 18% and 23%. To prevent scorching in the furnace caused by the high moisture content of the strong alkali, a certain amount of calcined finished alkali (return alkali) is mixed with it to reduce the moisture content to an appropriate level of 6%–8%. The back-alkalinity ratio is generally between 1.1 and 1.5, with the specific value depending on the content of free water during production. In steam calciners for light soda ash, since the feed material is mainly sodium bicarbonate and its moisture content exists primarily in the form of free water, the amount of back-soda generated is relatively high, ranging approximately between 2.5 and 3.0.

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