In many enterprises that use evaporative crystallization (commonly known as boiled sugar) to extract products, the steam consumption used incrystallization accounts for a large proportion of the total steam consumption of the enterprise, especially sugar refining enterprises, whose proportion is ashigh as 60-70%.
We all know that evaporation generally uses multiple effects. For most products, because the evaporative crystallization temperature should not be too high, and the boiling point of evaporative crystallization increases greatly,single-effect crystallization is generally used, and double-effect or multi-effect crystallization is rarely used. Therefore, from the perspective of energy saving,the material to be evaporated and crystallized should be concentrated to the highest possible concentration through multiple-effect evaporation. However,since the evaporation concentration will inevitably fluctuate even if the automatic control is adopted, and the material will always cool down during the transportation and storage process, this restricts us to further increase the concentration of the material before crystallization.
In order to reduce the steam consumption in the evaporative crystallization process, when the steam driving temperature difference is sufficient (in most cases it is sufficient), an evaporator is connected in series on the evaporative crystallization feed pipe to pre-concentrate to form a two-effect evaporation system combined with evaporation and crystallization ,can reduce the consumption of crystallization steam by 30 to 40%. Because the evaporative discharge of the combined system hardly stops and directly enters the evaporative crystallization, and the connecting pipe is equipped with electric heat tracing, its concentration can be controlled to be slightly supersaturated (supersaturation degree 1.0-1.05), and there is no need to worry about it crystallization occurs in the pipe.
Due to the fact that the feed in the intermittent evaporation crystallization operation is not uniform and continuous, and the feed in the boiling water process is interrupted in the later stage of crystallization, the combined system can save less than 50% of steam consumption, and a reasonable and effective automatic control system should be equipped. To avoid the situation that the crystallization feed is too concentrated due to individual operation steps, the second is to ensure that the steam used for crystallization will not be affected by the combined use. It can be said that the quality of the automatic control system setting determines whether the combined system can be successful or not.