Drying Technology
Keywords:activatedsludgewastewatertreatment、sludgedisposal
Due to the high output, high moisture content and huge volume of sludge in the increasingly large-scale sewage treatment plant, it is not only inconvenient in the process of storage, transportation, loading and unloading, but also has high potential environmental safety risks and hidden dangers. The cost of sludge disposal in some developed countries accounts for 40% ~ 60% of the total cost of sewage treatment plants, and some even reach 65%. The average disposal and transportation fee in European countries is about 470 ± 280 euros per ton. In 2016, the average disposal cost of enterprise sludge in China was basically 1500 ~ 6000 yuan per ton (of which the transportation cost accounted for about 5% ~ 15%), and it is still facing price rise. According to the data, the annual output of sludge in China in 2015 was 33.59 million tons (with a moisture content of 80%). In view of the mature sewage biochemical treatment technology, low cost and many other advantages, at present, 90% of the world's sewage treatment plants adopt activated sludge process, and the sludge output is still growing rapidly every year.
The sludge of sewage treatment plant is mainly composed of primary sedimentation tank (grit chamber) and bottom sludge of oil separation tank, scum of air flotation machine, residual activated sludge and chemical sludge of other process units. Sludge is a kind of solid waste. If it has the characteristics of acute toxicity, flammability, reactivity, corrosivity, leaching toxicity and infectious disease, it is a hazardous waste. According to the environmental protection priority clause of the environmental protection law, the solid waste produced by factories and mining enterprises is treated as hazardous waste before being identified, while the sludge of factories and mining enterprises in China basically belongs to hazardous waste because it contains various toxic chemicals or heavy metals
Sludge drying presents a fire and explosion hazard. The sludge drying system is affected by many factors such as sludge type, composition, heat source type and so on when the device starts and stops. The surface temperature of the dry sludge is easy to soar, and the superheated sludge will instantly form a large amount of dust mass, resulting in an explosion, resulting in catastrophic consequences.
According to the final target moisture content, it can be divided into "semi-dried" and "full-drying". The safety of the drying system depends on the target moisture content, which is a prerequisite for the sludge drying process, so the drier the sludge, the more dangerous it is. In order to achieve the dual purpose of water removal and production safety, semi-drying, Technical measures such as low temperature drying, nitrogen protection, temperature and oxygen content instrument chain control are used to improve the safety of the sludge drying device.
