What is the sludge drying? It usually refers to the process making wet sludge to dry mud. The wet sludge firstly will be broken and put into a drying device, then heat with the dry hot circulating air. Now, direct heating method is the main technology adopted in domestic sludge drying process. Such method uses “direct heat sources”, such as, steam, tail gas, electricity etc, to heat the sludge above 100℃. This not only has high energy consumption, but also lead to secondary pollution, and even safety hazards.
But low temperature sludge drying adopts lower temperature. The general temperature of the hot-gas is 60-70 Celsius degrees with 20% humidity is. For this technology, its hot-gas can be recycled. Therefore, this technology has low energy consumption, no secondary pollution, high safety, high automation, and lower sludge drying cost. So recent years, in China, such technology is going to be popular.
At present, most industries use mechanical dewatering machine for sludge dewatering, such as, belt filter press, plate filter press and so on. If dewatering via plate filter press, the moisture content is generally 50-60%; if for belt filter press, the cake moisture will be around 65-80%. After drying, the moisture content can be further reduced to about 30%. Thus the sludge can be incinerated directly after deep treatment, so this can improve its cost performance.