干化+焚烧技术已逐渐成为我国大中城市中心城区污泥的重要处置手段,水热炭化预处理可提高污泥脱水性能,进而降低系统能耗,但对水热+干化污泥预处置过程的能耗分析还鲜有报道。研究了200~260℃下水热炭化预处理污泥的三相产物分布及水热液有机组分构成,在此基础上建立了水热+空气干化系统的能量-质量流模型,并分析了水热条件对系统能耗的影响,最后与空气干化系统、厌氧发酵+空气干化系统能耗进行对比。发现釜内压力为8MPa,水热反应温度由200℃上升至240℃时,由于水热液中热值较高的有机组分芳香烃、含氮杂环比例明显下降,水热反应釜能耗由184kJ/kg(以原污泥计)降至161kJ/kg,温度上升至260℃时,由于水蒸气气相分率明显增加及水热液中芳香烃含量回升,能耗上升至278kJ/kg。受水蒸气气相分率影响,240℃下水热反应能耗随压力升高而降低,压力升至4MPa后降低趋势迅速放缓。直接空气干化系统在干化空气温度为110℃时,系统总能耗为1942kJ/kg;厌氧消化+干化系统由于对沼气进行高效热回收利用,消化时间为10d时,系统热耗低至212kJ/kg,总能耗为984kJ/kg;而水热炭化+干化系统由于有效提升了污泥脱水性能,使系统总能耗进一步降低,240℃水热温度下系统总能耗为597kJ/kg。研究结果为污泥独立焚烧或与燃煤电站耦合燃烧前预处理方式的选择和优化提供了基础数据和理论依据。

Drying and incineration technology has gradually become an important disposal method for sludge in the central urban areas oflarge and medium-sized cities in China. Hydrothermal carbonization can improve the dewatering property of sludge, thereby reducing theenergy consumption of the system. However, there are few reports on the energy consumption analysis of hydrothermal and drying sludgepre-disposal process. In this article, the distribution of three-phase products and the organic components of hydrothermal liquid at hydrothermal temperatures from 200 ℃ to 260 ℃ were studied. Based on this, the energy-mass flow model of the hydrothermal and air-dryingsystem was established, and the impact of different hydrothermal conditions on system energy consumption was analyzed. Finally,the energy consumption with air-drying system, and the anaerobic fermentation as well as the air drying system was compared. It is found thatwhen the pressure inside the kettle is 8 MPa, the temperature of hydrothermal reaction is increased from 200 ℃ to 240 ℃ .The energy consumption of the hydrothermal reactor decreases from 184 kJ/ kg (sludge,the same below) to 161 kJ/ kg, mainly due to a significant decrease in the proportions of aromatic hydrocarbons and nitrogen-containing heterocyclic rings in the hydrothermal liquid. When the temperature rises to 260 ℃ , the energy consumption increases to 278 kJ/ kg due to the significant increase in the vapor phase fraction and the recovery of aromatic hydrocarbon mass. It is found that the energy consumption of hydrothermal reaction at 240 ℃ decreases with the increase of pressure due to the influence of the vapor phase fraction. The decreasing trend slows down rapidly after the pressure increases to4 MPa. The total energy consumption of the direct air drying system is 1 942 kJ/ kg when the drying air temperature is 110 ℃ . In the anaerobic digestion and drying system, due to the efficient heat recovery of biogas, the heat consumption is as low as 212 kJ/ kg at 10 days′ digestion time, and the total energy consumption is 984 kJ/ kg. As for the hydrothermal carbonization and drying system, due to the significant enhancement of the dewatering performance, the total energy consumption can be further reduced, and the energy consumption is597 kJ/ kg at a hydrothermal temperature of 240 ℃ . This paper provides basic data and theoretical basis for the selection and optimizationof pretreatment methods before sludge incineration independently or coupled combustion in coal-fired power stations.

0 引言

1 模型建立

   1.1 水热炭化+干化系统

   1.2 厌氧消化+干化系统

   1.3 直接干化系统

2 结果与讨论

   2.1 水热反应特性

   2.2 水热过程能耗分析

   2.3 干化空气温度对直接干化系统能耗的影响

   2.4 厌氧消化时间对厌氧消化+干化系统能耗的影响

   2.5 不同预处理方式的系统能耗比较

3 结论