城市污泥的低温热干燥

Urban sludge thermo drying under low temperature

污泥是城市产生的重要废弃物之一,因较高的含水率而体积庞大,因此对其进行脱水和干燥是实现减量化的重要手段。低于100℃的低温热干燥方法因干燥温度较低,具有节能、减少臭气排放等优点,可有效利用工业余热、废热、太阳能,以及热效率很高的热泵干燥工艺。采用薄膜态污泥进行低温干燥,通过实验分析了在温度为50℃和70℃、表面风速为0.3～1.2 m·s-1条件下污泥质量与含水率的变化。结果表明,较低的干燥温度一定程度上延长了干燥时间,但采用薄膜形态可以缓解干燥速度减慢的问题,且可有效解决＂硬壳＂现象而实现等速干燥,对提高能源利用效率具有较大好处。给出了气流温度、流速、泥层厚度对干燥速度的影响,干燥消化污泥所需时间要快于同条件下的未消化污泥。还给出了2种低温干燥工艺流程,为工业应用提供借鉴。

Sludge is an important type of urban waste. In comparison with the other types, sludge contains more water, which increases the volume of the waste. Dewatering and drying are therefore important methods for treating sludge. A lower temperature （ 〈 100℃ ） was found superior in the drying process of sludge for saving heat energy and reducing odor emission. Heat from industrial waste, solar energy, and heat pumps with high thermal efficiency are suitable for drying sludge at lower temperatures. In this study, a thin layer of sludge was dried at low temperatures （50 ℃ and 70 ℃） and at surface air speeds of 0.3 to 1.2 m ·s-1 The changes in the mass and water contents of the wet sludge were tested and analyzed in the experiments. The results showed that the lower temperatures led to an increase in drying time; however, the problem could be alleviated and the speed of evaporation improved by limiting the thickness of the sludge layer （ i. e. , a thinner layer）. In addition, a thinner layer could facilitate the uniform velocity of the drying process and prevent the formation of a sludge crust. In this paper, we present the effects of the air temperature, speed, and the depth of the sludge layer on the drying speed, and we show that digested sludge requires a shorter drying time compared with undigested sludge. In addition, we indicate two techniques for drying sludge at low temperatures for industrial application.