Application of paddle dryer in sludge drying

Paddle sludge drying process can achieve sludge reduction, harmless, stable and resource-based disposal methods, and the wide use of its drying products undoubtedly provides more flexibility and operability for the sludge pipe system. With the development of sludge drying technology, the level of comprehensive utilization of sludge is bound to leap to a new level.

At present, we should vigorously support the construction of national environmental protection and environmental protection facilities. With the improvement of sewage treatment rate, the problem of sewage sludge treatment and disposal is becoming more and more obvious.

There are many methods of sludge treatment and disposal, such as landfill, composting, building materials utilization, etc., but the dewatering and drying of sludge is the key to its subsequent disposal and resource utilization. Sludge drying appeared as early as 1940s. The early drying equipment was mainly used for industrial sludge treatment. After decades of continuous improvement, sludge drying equipment has gradually overcome the technical difficulties of biochemical sludge, which is more unstable than industrial sludge, easy to produce biogas, difficult to evaporate, easy to stick, combustible and explosive in the drying process. With the improvement of equipment performance and the contradiction of other disposal methods, the advantages of high efficiency, flexibility, safety and stability of sludge drying device are gradually recognized.

Project Overview:

Zhejiang printing and dyeing Co., Ltd. is positioned as an environmental protection printing and dyeing company with high-tech industry. To solve the problem of environmental pollution by means of central heating, water supply and centralized treatment of wastewater. The design scale of the company's sewage treatment station is 20000m3 / D, the scale of sludge drying system is 50t / D, the moisture content of inlet sludge is 80% - 85%, and that of outlet sludge is 30%. The drying heat source is steam of 0.4-0.8mpa and 150-200 ℃.

Sludge pretreatment process:

Sludge discharge from sewage treatment system → sludge homogenization tank → Belt Thickening integrated dehydrator → sludge discharge

Sludge characteristics:

The sludge produced in the process of printing and dyeing wastewater treatment can be divided into organic sludge and inorganic sludge. Biological sludge is organic sludge, which is mainly composed of organic matter. Typical organic sludge is excess activated sludge in secondary sedimentation tank and organic sludge removed by primary sedimentation tank and air flotation tank. It usually has high organic content and is easy to decay and stink. Sludge particles are small, often in the state of flocculent, with low relative density; high water content, strong water holding capacity of particles, and not easy to sink and depress Dense, dehydration, good fluidity, convenient for pipeline transportation. Inorganic sludge is mainly composed of inorganic substances, also known as sludge. It is produced by physical and chemical treatment methods, such as coagulation sedimentation or air flotation pollutants, which is usually not easy to decay; the sludge group has large particles and high relative density; low moisture content, poor particle water holding capacity, good stability, easy precipitation, compaction, dehydration, poor fluidity, and difficult to be transported by pipeline. In addition, due to the presence of dyes, size and additives, the composition of dyeing sludge is relatively complex. The structure of dyes has nitro and amino compounds and heavy metal elements such as copper, chromium, zinc, arsenic, etc., which has great biological toxicity and great pollution to the environment

Process flow description of drying system:

The system can continuously dry the wet sludge; the micro negative pressure exhaust system is used to prevent the odor from overflowing and affecting the environment; the discharging hollow screw can cool and discharge the high-temperature materials at the same time; the operation is convenient.

Sludge receiving and conveying system:

The dewatered sludge in the sludge stacking area of the sewage station is used to enter the wet sludge bin through the belt conveyor. One wet mud bin is provided with a drying machine, and the volume of each wet mud bin is 10 m3. It is made of carbon steel and anticorrosion process. Suction outlet is set on the wet sludge bin, and the pipeline is connected with the sludge drying air pipe. It is opened when cleaning regularly to avoid odor leakage. The wet mud silo is equipped with sliding frame, maintenance port, material level meter, gate valve, etc. There are two sludge pumps under the wet sludge bin.

Structure and working principle of hollow paddle dryer:

The hollow paddle sludge dryer is composed of two or four blade shafts, W-shaped shell with jacket, frame, transmission parts and rotary joint. The whole drying process of sludge is carried out in a closed state. The organic gas and odor gas are sent to the tail gas treatment device under closed atmosphere to avoid environmental pollution.

The dryer uses steam, hot water or heat transfer oil as the heating medium, and the shaft end is equipped with a rotary joint for hot medium introduction and export. The heating medium is divided into two channels, which enter into the jacket of the drying shell and the inner cavity of the propeller blade shaft respectively to heat the body and blade shaft at the same time, and heat and dry the sludge in the way of conduction heating. The dried sludge is sent to the feeding port of the dryer quantitatively and continuously by the sludge pump. The sludge enters the back of the dryer, and the sludge is turned and stirred by the rotation of the paddle blade. The heating interface is constantly updated and contacted with the device body and paddle blades. It is fully heated to evaporate the surface water contained in the sludge. At the same time, the sludge is transported to the outlet in a spiral track with the rotation of the blade shaft, and the stirring is continued during the transportation, so that the water seeping from the sludge continues to evaporate. ^After that, the qualified products dried evenly are discharged from the outlet.

Engineering design parameters:

Wet sludge volume after dewatering: 50t / D;

Sludge type: biochemical sludge;

The moisture content of sludge is about 85%;

Moisture content of dry mud: about 30%;

Working system: 24h.

Engineering calculation and selection:

The following calculation and selection are based on the unit of 50t / D / set:

The average wet material handling capacity is about 2.08 tons per hour;

Calculation: 2.08 * (1-85%) = x * (1-30%) then x = 0.446 tons, then the evaporation water per hour is 2.08-0.446 = 1.634 tons

The evaporation capacity of hollow paddle dryer is about 10-15kg / h per square meter, which is calculated as 13kg / h,

The area to be dried is 1634 / 13 = 125 m2;

Therefore, a hollow blade dryer with an effective heat transfer area of 125 M2 is selected.

The actual operation experience shows that the moisture content of wet sludge is less than 30% and the volume reduction is 3 / 4 after drying by hollow paddle dryer, which can ensure the stable operation of the equipment.

Therefore, the application of hollow paddle dryer in sludge drying process is of great significance to the comprehensive utilization of sludge. Paddle sludge drying process can achieve sludge reduction, harmless, stable and resource-based disposal methods, and the wide use of its drying products undoubtedly provides more flexibility and operability for the sludge pipe system. With the development of sludge drying technology, the level of comprehensive utilization of sludge is bound to leap to a new level.