Study on drying characteristics of sludge under different conditions based on the low-temperature sludge heat pump drying model

The study established a model for a closed low-temperature heat pump drying (HPD) system and structured a sludge drying experimental platform to validate it. The effects of incoming air temperatures of the drying cabinet, circulating air volume, and ambient temperature on both drying rate and system performance were investigated. The findings revealed that the drying rate and specific moisture extraction rate (SMER) rise with higher incoming air temperatures of the drying cabinet and circulating air volume, while the coefficient of performance (COP) exhibited a contrasting trend. The sludge dried the fastest with a drying rate of 6.01 kg/h when the incoming air temperatures of the drying cabinet and circulating air volume were set to 65 degrees C and 900m(3)/h, respectively. At the incoming air temperature of the drying cabinet was 65 degrees C and the circulating air volume was set to 850 m(3)/h, the SMER reached the maximum value, 2.782kg/(kW<middle dot>h). In addition, the COP increased as the ambient temperature rose, while the drying rate and SMER both decreased gradually. The drying rate demonstrated an average decline of 0.29 kg/h for every 2 degrees C rise in ambient temperature, while the SMER exhibited an average decrease of 0.148kg/(kW<middle dot>h). These works offer guidance for the practical implementation of the sludge HPD system.