污泥干燥环形快速加热防粘附机理及MVR热泵耦合运行特性研究

According to the data of the environmental statistics annual report of the Ministry of environmental protection of People's Republic of China, the national sludge production was 30 million 159 thousand tons in 2015. The harmless treatment and disposal of large quantities of sludge has become a major problem in the field of environmental protection. The outstanding characteristics of sewage sludge are high moisture content. The moisture of sewage sludge cake after mechanical dewatering will still be as high as 70～80%. It is difficult to sewage sludge treatment both at technically and economically due to its high moisture content and bulkiness. However, decreasing the moisture content of sludge is the crux of the matter in harmlessness and bulkiness reduction, which is also the premise of resource utilization. .The objective of this project is intended to use annular rapid indirect heating to make the sludge rapidly heated, and form a steam diaphragm between the sludge and heating surface quickly. Meanwhile, the sludge shrinkage rapidly, and the striped sludge falls off under the action of gravity, so as to prevent the indirect heating of the sludge from sticking to the wall. After multilevel annular rapid heating and drying, the moisture of sludge should be dropped from 70～80% to 50%, and successfully passage through the dry sticky zone to solve the technical problems of sludge drying, such as sticking, caking and plasticizing crusts. In superheated steam as convection drying medium, combined drying process of indirect heating and convection direct heating, recycling secondary steam latent heat of sludge water evaporation by the mechanical vapor recompression (MVR) heat pump system, the total energy consumption only appears as mechanical energy consumption, thermal resistance and heat leakage, and energy saving effect is very significant.

根据环保部环境统计年报数据，2015年全国污泥产生量为3015.9万吨，大量污泥无害化处理处置日益成为环保领域一大难题。污泥显著特征是含水率高和粘度大，经机械脱水后的泥饼含水率为70～80%，由于含水率高，体积庞大，为污泥处理处置带来经济和技术上困难。降低污泥含水率是无害化、减量化处理的关键和资源化利用的前提。.项目拟采用环形快速间接加热使污泥急速受热，在污泥与加热面之间迅速形成蒸汽隔膜，同时体积急剧收缩，条状污泥在重力作用下自然脱落，防止污泥间接加热粘壁现象的发生。经过多级环形快速加热干燥，污泥水分由70～80%快速降至50%以下，顺利通过干燥粘滞区，解决污泥干燥普遍存在粘壁、结块与“塑化”结壳等技术难题。以过热蒸汽作为干燥介质，组成间接加热与过热蒸汽对流直接加热联合干燥工艺，采用MVR热泵回收干燥过程水分蒸发产生大量二次蒸汽的潜热，能耗仅为干燥系统机械能耗、热阻与热漏，节能效果显著。

随着我国污水处理量的不断增加，污泥年产量将很快突破6000万吨。机械脱水污泥的含水率仍然高达70～80%，降低含水率是污泥减量化、稳定化、无害化处理的关键与资源化利用的前提。项目在搭建的干燥试验台上，选取直径为50mm厚度为10mm的污泥样品在160℃和200℃下进行过热蒸汽与热风干燥试验,利用图像处理技术分析干燥过程污泥收缩现象及特性。结果表明：污泥在干燥过程中存在明显的收缩现象，前段干燥收缩幅度大，后段干燥收缩幅度小，收缩变化规律与水分变化规律一致。160℃、200℃污泥过热蒸汽与热风干燥终了时刻体积比约为0.3，体积收缩系数为0.7，过热蒸汽干燥和热风干燥对污泥的收缩影响一致。开展了机械脱水污泥的物理特性与粘附特性试验研究，为污泥环形快速加热防粘附干燥单元的设计提供技术支持。研制了污泥环形快速加热防粘附干燥单元，对污泥环形快速加热防粘附干燥单元进行了一维稳态传热分析与干燥单元传动齿轮的受热分析。开展了污泥过热蒸汽耦合MVR热泵干燥系统研究，采用Aspen plus软件对基于单螺杆压缩机的MVR热泵干燥系统性能进行了计算机仿真，得到MVR热泵干燥系统性能指标与各影响参数之间的关系。开展了污泥真空压滤联合高压过热蒸汽高效脱水技术研究，在同一工序上连续完成结饼、真空压滤脱水、蒸汽压滤脱水及过热蒸汽闪蒸干燥4个工艺过程。能将含水率在96%～97%的初沉淀污泥通过真空浓缩、真空压滤与过热蒸汽闪蒸干燥相结合，污泥含水率一次降至40%以下，撬装式成套设备已推广应用。