Anti-scaling innovation solution for FGD effluent evaporation
Anti-scaling and Descaling measure during the operation of evaporation systems
In the high-salt wastewater projects undertaken by Hubei Sanfeng Environmental Protection for treatment, scaling is a common and easily-occurring problem in the evaporation crystallization system.
The scaling phenomenon is mainly manifested in the scaling of the crystallizer (the main equipment) and the heating pipes. It will not only reduce the effective volume of the equipment but also decrease the heat transfer coefficient of the heating pipes, deteriorate the production conditions, and cause a decline in production capacity. Severe scaling will even force production to stop, shorten the effective production time, reduce the service life of the equipment or even damage the equipment, and increase the consumption of raw materials and energy. Therefore, anti-scaling and descaling have always been technical issues that are highly valued in the operation of evaporation crystallization.
Types and Causes of Evaporation Scaling
- Crystallization Scaling: Such as salt solutions like CaCO3, CaSO4. This kind of scaling occurs when crystals precipitate and settle during equipment operation. Specifically, due to the negative solubility of CaSO4-when the temperature exceeds 40℃, its solubility decreases as the temperature rises. Additionally, issues like blockage due to operational resons, abnomal liquid levels, or sudden surges in heating steam can cause material bumping, leading to salt adhesion and scaling on equipment.
- Chemical Reaction Scaling: Evaporators mostly operate under high-temperature conditions. At high temperatures, some organic and inorganic substances react, generating soild precipitates that adhere to heat-exchange surfaces.
- Particulate Scaling: This type of scaling mostly comes from particles suspended in the fluid depositing on heat-exchange surfaces.
- Corrosive Scaling: Formed by reactions between corrosive feed liquid and the material of heat-exchange surface during evaporation operations.
- Biological Scaling: For example, seawater, lake water, or river water containing algae that haven’t undergone disinfection treatment.
- Solidification Scaling: Refers to scaling formed when clean liquids soildify after passing through heat-exchange surfaces.
Application Prospects
Most organic substances are materials with low boiling point rise. Therefore, this technology has broad application prospects in the field of organic substance rectification. At present, the systems successfully applied by Hubei Sanfeng includ methanol rectification, DMF rectification, etc., achieving good energy-saving effects. Meanwhile, for different light-component materials, our company has developed compressors suitable for different physical properties, expanding the application prospects of this technology.
Application Case
Hubei Sanfeng successfully applied this technology in a company in Yingkou that produces methylhydrazine. An MVR compressor was used to replace live steam as the heat source. The system processing capacity is 13t/h, and the concentration of the fed methylhydrazine in the bottom product of the tower is ~47%. The system electricity consumption is about 1100kWh, and the steam saving is about 19t/h. Calculated at an electricity price of 0.5yuan/kWh and a steam price of 180 yuan/t, the operating cost can be saved by 2,870yuan per hour, and the annual operating cost can be saved by 22.96 million yuan (calculated based on an annual operation of 8000 hours). It has obvious energy-saving effects and economic benefits.