On site use of sludge dryer

Landfilling, incineration, sea disposal, and land use. The management of sludge treatment in foreign countries is very strict, it must be environmentally safe and cannot produce secondary pollution. So foreign sludge drying technology attaches great importance to tail gas treatment and odor control. Early ESP direct heating systems introduced external air that was heated and then passed into a dryer to evaporate the moisture in the sludge and transport it. For landfilling, according to the European Waste Management and Disposal Policy, since 2000, Europe has imposed a landfill tax on sludge landfilling, requiring a reduction in sludge landfilling. By 2005, landfilling was banned. The first three treatment methods have gradually decreased due to increasing environmental and economic pressures, among which ocean dumping is prohibited by maritime law.

Drying different types of sludge, such as industrial sludge and urban sludge, also requires different equipment requirements. Because the characteristics of urban sludge are very viscous, and there is a special adhesive phase stage during the drying process. In this extremely narrow transition section, the sludge is prone to clumping, with a hard surface that is difficult to crush, while the inside is still thin mud. In order to overcome this difficulty and achieve a drying effect with a solid content greater than 90%, the dry material mixing process has been developed. Controlling the mixing ratio reduces the moisture content of the mixture to 30% to 40%, which allows the sludge to directly pass over the adhesive phase and greatly reduces the adhesion of the sludge in the dryer. During drying, only the surface moisture of the particles needs to be evaporated, making drying easier and reducing energy consumption. This poses great difficulties for further drying and sterilization of sludge. Before feeding into the dryer, a certain proportion of dry sludge particles with a solid content greater than 90% are returned to the mixer (or coating machine) and mixed with wet sludge. During the process, the dry particles act like pearl nuclei, while the wet sludge is only thinly wrapped around the dry particles.

In recent years, people have started using incineration methods for factory sludge and domestic sludge. This method facilitates the effective extraction of heat energy from waste, reduces environmental costs, and does not cause secondary pollution. However, both of the above methods require the sludge to be dried first. In addition, most of the sludge contains odors, and the exhaust gas from drying needs to be deodorized. Hot air drying has a large exhaust volume, while conduction heating has a small exhaust volume. After adopting the latter drying process, the equipment investment and operating costs for exhaust gas treatment are greatly reduced. Most users believe that the hollow blade dryer is the basic form, and after improvement based on the material characteristics and economy of various sludge, it is an ideal sludge drying equipment because this model has a high utilization rate and lower operating costs compared to other drying forms. Moreover, sludge itself is not a high value-added product.