污泥连续水热炭化工程系统研究

水热炭化可以显著改善污泥的脱水性能，促进污泥的无害化、减量化、资源化利用，但目前污泥水热炭化技术的工业化应用鲜有报道。该研究基于工程规模的污泥水热炭化系统开展研究，重点研究了系统工程设计和控制逻辑，开展了系统参数测试，分析了污泥炭、气相和水相的理化性质和组分分布，并在此基础上进行了系统能量平衡分析。结果表明，系统污泥年处理量达1.4×104 t，水热炭化后的三相产物分别为污泥炭28.57%，水相70.00%，气相1.43%，污泥脱水率达75%，综合整个生产系统，系统加热能为454.22 MJ/t，动力耗能为64.80 MJ/t，连续水热炭化工程系统能耗比为83.83%，能量回收率为66.68%，系统具有较高的能耗比。该研究可为生物废弃物连续水热炭化技术的研发和推广应用提供重要的工程依据。

Research of industrial system based on sludge continuous hydrothermal carbonization

The high moisture content of sewage sludge and the difficulty of dewatering are the common technical problems that restrict the utilization of sludge resources. Hydrothermal carbonization technology can change sewage sludge into hydrochar, liquid phase and a small amount of CO2 through a series of hydrothermal reactions under a certain temperature and pressure. The dewatering performance of sewage sludge can be greatly improved after hydrothermal carbonization, which promotes reduction and resource utilization of sludge. At present, there are many achievements have been made in process optimization and product characteristics, but few reports on the industrial scale of sewage sludge hydrothermal carbonization, which promoted the large-scale application of hydrothermal carbonization technology in sludge dewatering. In this paper, the sludge hydrothermal carbonization system based on engineering scale was studied, the technological process and control logic of system were elaborated. In the engineering system, we carried out continuous testing for 4 days, analyzed the physicochemical characterization of sewage sludge and hydrochar, discussed the product distribution of hydrochar, liquid phase and gas phase, and calculated the energy balance of the system. The results showed that the system worked well, and all indexes met the design requirements, the three-phase products after hydrothermal carbonization were 28.57% of hydrochar, 70% of liquid phase, 1.43% of gas phase, and the sludge dewatering rate could reach 75%. Under the hydrothermal reaction conditions of high temperature and high pressure, the water in the sludge was in a subcritical state, with high free ionization constant and low dielectric constant, which made the water have strong solubility and penetration ability as the reaction solvent and broke up the sludge microbial cells in the reaction process, The organic substances (protein, fat and carbohydrate) in the sludge cells were further hydrolyzed into small molecular substances, and the cell bound water was released, which improved the dewatering performance of sludge. Through the analysis of hydrochar, it can be seen that the O/C ratio of hydrochar was 2.58, indicating that the stability of hydrochar was poor. Combined with the ultimate analysis of hydrochar, the low calorific value was 13.17 MJ/kg and ash content was 35.05%, it was concluded that the fuel characteristics of hydrochar were not ideal, and other resource utilization paths need to be explored. The concentrations of nitrogen, potassium and phosphorus in aqueous phase were 2 000-5 000, 100-600 and 10-200 mg/kg respectively. The hydrothermal phase products had a high potential in the preparation of organic fertilizer. However, considering the high COD content and complex composition in aqueous phase, the treatment and resource utilization of aqueous phase products need to be further studied. Considering the whole production system, the heating energy and power consumption of the system were 454.22 and 64.80 MJ/t respectively, the energy consumption ratio of the continuous hydrothermal carbonization system was 83.83%, and the energy recovery ratio was 66.68%, which showed that most of the energy was transferred to the products of each phase, and indicated the hydrothermal carbonization of sludge has a good application prospect. Through the analysis of dewatering rate and energy balance, it can be found that hydrothermal carbonization technology has better technical advantages in the treatment of high water content sludge. This study could provide an important technical reference for the development and application of continuous hydrothermal carbonization of sludge.