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Industrial Agitated Sludge Thin Film Dryer Slurry Treatment Drying Machine

1) Horizontal thin film drying system has good airtightness, can achieve strict oxygen content control and high safety. It is one of the safest drying processes in the field of sludge drying today.

2) Horizontal thin film drying process sludge drying equipment is the development trend of sludge treatment and disposal, which has obvious advantages in safety, stability, reliability, advanced and other aspects. The application of horizontal thin film drying process in cooperative sludge disposal is a scientific and reasonable choice for sludge treatment and disposal today.

3) The coupling is used to connect the main shaft of the thin film drying machine with the reducer, which makes the thin film drying machine more stable in operation and enhances the stability of the reducer. The expansion coupling sleeve is used to connect the main shaft of the thin film drying machine, which reduces the friction loss between the main shaft and the bearing. The structure is simple and easy to use.

4) In the sludge mixing and firing power generation project, the control of dry sludge form and moisture content is very critical, which will affect the operation of the subsequent incineration system of the drying system. On the one hand, the horizontal thin film drying process can generate granular products with uniform particle size and no dust, and on the other hand, it can quickly realize the adjustment of moisture content by changing the steam pressure and the speed of the two-stage linear drying machine. The good control of the shape and moisture content of the dry sludge can ensure the stable operation of the whole system.

    Project Introduction


    With the rapid development of economy and the continuous improvement of the production value of industrial enterprises, as well as the rapid progress of urbanization, the discharge and treatment volume of industrial wastewater and urban sewage are also increasing day by day. With the all-round popularization of sewage and wastewater treatment facilities, the improvement of sewage and wastewater treatment efficiency and the deepening of sewage and wastewater treatment degree, it also brings a sharp increase in sludge output. Sludge treatment and disposal has become a bottleneck problem restricting the development of sewage treatment industry.

    According to the Technical Guide for sludge treatment and disposal of Urban sewage treatment Plants issued by the state, four disposal methods of sludge are proposed, namely land use, sanitary landfill, building materials utilization and dry incineration. Due to the increasingly prominent constraints and adverse factors of sludge in agriculture, landfill, sea and other aspects, sludge drying incineration treatment and disposal method has been widely used and widely promoted in various countries, there is no doubt that sludge drying incineration will become one of the most important and ideal technical disposal schemes at this stage.

    According to the sludge generated by a company has the technical characteristics of hazardous waste, incineration and disposal of the products after drying, and the need for steam heat source, so it is necessary to comprehensively consider its safety, technical adaptability, economic adaptability, application and promotion, combined with the type of drying process equipment used in sludge drying that has been put into operation, Six sludge drying process equipment types, including fluidized bed type, two-stage type, thin layer type, paddle type, disc type and spray type, were compared and selected. Combined with the technical maturity, system stability, operation safety and disposal environmental protection of the above six drying equipment, the thin film drying process equipment type was finally determined.

    Working principle of thin film dryer

    1. Equipment components of thin film dryer
    In general, a thin film dryer is composed of a cylindrical shell with a heating layer, a rotating rotor in the shell, and a driving device of the rotor. The rotor is equipped with a lot of different shapes and specifications of the paddle, the paddle and the rotor are fixed by bolts, the assembly mode can be flexibly adjusted, in order to adapt to the change of sludge characteristics and treatment capacity; The whole shell of the thin film dryer is combined in sections. According to different disposal requirements, it can be divided into multiple heating areas, and can realize individual control, temperature adjustment, flexible switch and other operating elements.

    2. Description of sludge treatment process and material movement by thin film dryer
    The whole machine of the sludge thin film dryer is arranged and installed horizontally. Both the cylindrical shell with heating layer and the rotating rotor in the shell are horizontal. Different types of blades are installed on the rotor, and the spacing between the blades and the hot wall is 5~10 mm. The arrangement of these blades is embedded in the rotor, and a total of 18 rows of blades are arranged in the radial direction around the circumference of the dryer barrel.

    The spread blades are distributed at the mud inlet end and the mud outlet end of the rotor. Four spread scraper blades are installed on each column of the mud inlet end of the cylinder, which are installed at an Angle of 45° with the column line. The purpose of such installation is to realize that the sludge is immediately attached to the surface of the hot wall after entering the cylinder and has the function of conveying to the discharge end, a total of 72 pieces; Two end cover spread scraper blades are installed on each column of the mud end, and the spread scraper blades at the feed end are installed at an oblique Angle of 45°, so that the purpose of installation is to buffer the inertia force of the product when discharging to achieve the function of free discharging by gravity, a total of 36 pieces.

    The transmission blades are distributed in the middle area of the rotor, and 40 blades are installed on each column, totaling 720 blades.

    The different types of blades comprehensively realize the important functions of sludge distribution, spreading, scraping, stirring, backmixing, self-cleaning and transportation on the hot wall surface from the function. In summary, when the wet sludge enters from one end of the horizontal dryer, it is immediately continuously distributed on the surface of the hot wall by the rotating rotor to form a thin layer of material. While the blades on the rotor continuously roll the thin layer of wet sludge distributed on the surface of the hot wall, the conveying blades with the guide Angle function installed on the rotor rotate with the circular rotation of the rotor. The semi-dry sludge particles generated in the process of sludge thin layer and drying show a horizontal transfer with the axial direction of the rotor at a certain linear speed, and move forward to the sludge outlet at the other end of the thin film dryer. The axial length size of the thin film dryer is not only the horizontal line from the feed end to the discharge end, but also completes the feeding and discharging of the sludge in the whole horizontal cylinder thin film dryer. In this process, the wet sludge is evenly heated by the steam hot wall and the water is evaporated. The residence time of wet sludge in the thin film dryer is 10~15 min, which can realize fast start, stop and emptying, and the process operation and adjustment control of the equipment are very fast.

    3. Exhaust gas collection process of thin film dryer
    The moisture content of the sludge fed by the thin film dryer is 75%~85%(calculated as 80%), and the moisture content of the sludge produced by the thin film dryer is about 35%. The semi-dry sludge presented as granular is transported to the next unit through the next stage conveying equipment. The mixed carrier gas, such as water vapor, escape dust and odor gas, generated in the working process of the thin film dryer, moves inversely with the sludge in the cylinder, and is discharged into the condenser through the pipeline from the exhaust gas tank above the sludge feeding port. In the condenser, the water of the carrier gas is condensed from the steam, and the non-condensing gas is separated by droplets and discharged into the drying system through the exhaust gas induced draft fan. The amount of process exhaust gas of thin film dryer is relatively small, usually only 5%~10% of the evaporation of the system. The exhaust induced draft fan makes the whole drying system in a micro negative pressure state to avoid the overflow of odor gas and dust.


    Equipment selection of thin film drying system

    1. Thin film drying system process flow
    Sludge medium process: wet sludge receiving bin + sludge delivery pump + thin film dryer + semi-dry sludge output equipment + linear dryer + product cooler.
    Exhaust gas medium process: evaporation steam (mixed steam)+ waste gas box + condenser + mist eliminator + induced draft fan + deodorization device.
    The sludge in the sludge receiving bin is directly sent to the thin film dryer by the sludge screw pump for drying treatment. The sludge inlet of the thin film dryer is equipped with a pneumatic knife gate valve, which is interlocked with the logic control parameters of the feeding pump, feeding screw, safety protection of the thin film dryer and other equipment and detection instruments.

    The thin film dryer body model, the net weight of a single machine is 33 000 kg, the net size of the equipment is Φ1 800×15 180, horizontal layout and installation, the sludge entering the thin film dryer is evenly distributed on the hot wall surface of the dryer by the rotor during the rotation process, while the paddle on the rotor repeatedly re-mixing the sludge on the hot wall surface, And forward to the outlet of the sludge, the water in the sludge is evaporated in the process. The semi-dry sludge particles after drying from the thin layer are transported to the linear dryer through the sludge conveyor (activated according to the demand of the moisture content of the sludge product), and then enter the sludge cooler. The sludge product is cooled by the air flowing in the cooler and the cooling water flowing in the shell and rotating shaft. The moisture content is reduced from 80% to 35%(the sludge moisture content of 35% is the process control upper limit of the single equipment of the thin film dryer).

    The carrier gas discharged from the thin film dryer contains a lot of water vapor, dust and a certain amount of volatile gas (mainly H2S and NH3). If directly discharged, it will cause a certain degree of pollution to the environment. Therefore, this project considers the carrier gas collection system and condenser and mist remover to remove the dust and water vapor in the exhaust gas, which is opposite to the direction of sludge movement in the rotating cylinder. The exhaust gas pipe outlet above the sludge enters the condenser, and the water is cooled down from the evaporation exhaust gas. By means of indirect heat exchange, the spray water is removed by plate heat exchanger and cooling tower, so as to save water and reduce sewage discharge. Non-condensible gas (a small amount of steam, N2, air and sludge volatiles) passes through the demister. Finally, the exhaust induced draft fan is discharged from the drying system to the deodorization device. 

    The heat source demand is determined to be steam, which is taken from the thermal coverage pipe network built nearby the project implementation site. The steam supply conditions are steam pressure of 1.0MPa, steam temperature of 180 ℃ and steam supply of 2.5t /h.


    2. Technical parameters of main equipment for thin film drying process
    According to the demand of this project, the sludge treatment capacity of a single set of sludge drying system is determined to be 2.5t /h(according to the moisture content of 80%), and the sludge moisture content is 35%. The daily sludge treatment capacity of a single thin film dryer is 60 t/d(according to the moisture content of 80%), the rated evaporation capacity of a single thin film dryer is 1.731 t/h, the heat exchange area of a single thin film dryer is 50 m2, and the moisture content of sludge inlet is 80%, and the moisture content of sludge outlet is 35%. The heat source of the thin film dryer is saturated steam, and the quality of steam supply is imported parameters: steam temperature is 180 ℃, steam pressure is 1.0 MPa, steam consumption of a single thin film dryer is 2.33t /h, and the number of thin film dryer is 2, one for one use.

    The saturated steam of 180 ℃ is transported to the linear dryer through the pressure pipeline, and it is used as a heat source to indirectly heat the semi-dry sludge. The water in the semi-dry sludge is further evaporated in the linear dryer. According to the actual demand of the sludge product (start and stop), the final sludge can reach 10% moisture content and go to the product cooler.

    The processing capacity of linear dryer is 0.769t /h(moisture content 35%), the rated evaporation is 0.214t /h, the heat exchange area is 50 m2, the moisture content of sludge inlet of linear dryer is 35%, the moisture content of sludge outlet is 10%, the steam quality inlet parameters of linear dryer: The steam temperature is 180 ℃, the steam pressure is 1.0 MPa, the steam consumption of a single linear dryer is 0.253 t/h, and the quantity is equipped with 1 set.

    The equipment type of carrier gas condenser is direct injection hybrid condenser, with an air intake of 3 500 Nm3/h, an inlet gas temperature of 95~110 ℃, an outlet gas temperature of 90~180 Nm3/h, and an outlet gas temperature of 55 ℃.

    The equipment type of carrier gas induced draft fan is high pressure centrifugal fan, the maximum air suction volume is 400 Nm3/h, the air pressure is 4.8 kPa, the physical parameters of the carrier gas medium: the temperature is 45 ℃, the humidity is 80%~100% wet air odor gas mixture, a single set of drying system is equipped with 1 set.

    The processing capacity of the product cooler is 1.8t /h, the sludge inlet temperature is 110 ° C, the sludge outlet temperature is ≤45 ° C, the heat exchange area is 20 m2, and the quantity is 1 unit.


    3. Analysis of economic energy consumption during commissioning of thin film dryer
    After nearly half a month of single commissioning and mud load commissioning of the thin film drying process system, the results are as follows.

    The design configuration processing capacity of a single thin film dryer in this project is 60 t/d. At present, the average wet sludge treatment during the commissioning period is 50 t/d(moisture content is 79%), which has reached 83% of the designed sludge wet base treatment scale and 87.5% of the designed sludge dry base treatment scale.

    The average moisture content of the semi-dry sludge produced by the thin film dryer is 36%, and the moisture content of the semi-dry sludge exported by the linear dryer is 36%, which is basically in line with the target value of the design product (35%).

    Measured by the external saturated steam meter in the sludge drying workshop, the saturated steam consumption is 25 t/d, and the theoretical total daily heat consumption of latent heat of steam vaporization is 25 t×1 000×2 014.8 kJ/kg÷4.184 kJ =1.203 871 9×107 kcal/d. The average daily total evaporation water of the drying system is (50 t ×0.79)-[50 t ×(1-0.79)]÷(1-0.36)×1 000=23 875 kg/d, Then the unit heat consumption of sludge drying system is 1.203 871 9×107÷23 875=504 kcal/kg evaporated water; Because the sludge drying system is subject to the change of wet sludge moisture content, the quality of external steam, and the characteristics of semi-dry sludge product transportation equipment for granularity requirements and other factors, it is necessary to optimize the value of various variables in the future long-term trial operation, so as to summarize the best operating conditions and economic energy consumption index of the system.

    Structure of thin film drying system equipment

    1.Thin film dryer machine
    The equipment structure of the thin film dryer consists of a cylindrical shell with heating layer, a rotating rotor in the shell, and a driving device of the rotor: motor + reducer.


    The shell of the sludge dryer is a container processed and manufactured by the boiler steel. The heat medium heats the sludge layer indirectly through the shell. According to the nature and sand content of the sludge, the inner shell of the dryer adopts the inner shell wear-resistant high strength structural steel (Naxtra -- 700) P265GH high temperature resistant boiler structural steel coating or special high temperature treatment of wear-resistant coating. Other parts in contact with sludge, such as rotor and blade, are made of stainless steel 316 L, and the shell is P265GH high-temperature boiler structural steel.

    The rotor is equipped with blades for coating, mixing and propulsion. The distance between the blades and the inner shell is 5 to 10 mm. The heating surface can be self-cleaned, and the blades can be individually adjusted and removed.

    Drive device: (motor + reducer) frequency conversion or constant speed motor can be selected, belt reducer or gearbox can be selected, direct connection or coupling connection can be used, rotor speed can be controlled at 100 r/min, rotor outer edge linear speed can be controlled at 10 m/S, sludge residence time is 10~15 min.

    2. Linear dryer body
    The linear dryer adopts U-shaped screw conveyor type, and the transmission blade is specially designed and processed to avoid the extrusion and cutting of sludge particles. The shell and rotating shaft of the linear dryer are heating parts, and the shell of the shell can be disassembled. Except for the heating parts, the part in contact with the sludge is made of stainless steel 316 L or equivalent material, and the other parts are made of carbon steel, that is, the linear drying equipment is made of SS304+CS.

    3. Condenser
    The function of the carrier gas condenser is to wash the exhaust gas from the sludge dryer so that the condensible gas in the gas condenses. The structure type of the equipment is direct spray condenser, and the processing material is SS304.

    4.Product coolers
    The function of the product cooler is to reduce the semi-dry sludge of 110 ° C to about 45 ° C, with a heat transfer area of 21 m2 and a power of 4 kW. Its main processing and manufacturing material for SS304+CS.


    Technical characteristics of thin film sludge drying process 
    The thin film sludge drying process has become popular in recent years due to its technical characteristics, making it an efficient and effective sludge treatment method. The process involves using thin film dryer, to quickly and efficiently remove moisture from the sludge, leaving a dry granular product that is easy to handle and transport. Combined with the operation experience of process system equipment of different technologies in the field of sludge drying and incineration, the technical characteristics of sludge thin film drying process are as follows.

    1. The key technical features of the thin film sludge dryer machine is its simplicity integration. This method requires the least auxiliary equipment and is simple to operate and control. The drying process does not require back-mixing, and the sludge directly skips the "plastic stage" (sludge viscosity zone), making the process more efficient and streamlined. In addition, the amount of tail gas generated is relatively small and the tail gas treatment process is simple, making it an economical, efficient and environmentally friendly sludge drying option.

    2.Operating economy is another important aspect of the thin film sludge drying process machine. It is known for its relatively low energy consumption and consistently high evaporation efficiency. Recovery and recycling of the heating medium is also possible, further reducing energy costs. Additionally, the equipment is rugged, has low maintenance costs and requires minimal monitoring, making it a cost-effective solution for sludge drying.

    3.Operational flexibility is also a notable feature of the thin film sludge dryer machine. It is suitable for drying different types of pasty sludge and can produce uniform product sludge particles with any moisture content. This process has low solids load, easy start and stop, and short emptying time, which further enhances its operational flexibility.

    4. The thin film sludge drying process is known for its safety and environmental protection. It adopts multi-faceted inert design such as N2, steam, and self-extinguishing detection. The process operates in a negative pressure closed system with low oxygen, no odor and no dust leakage, reducing the possibility of dust explosion and ensuring the safety and environmental protection of the sludge drying process.

    In summary, the technical characteristics of the thin film sludge drying process make it an efficient, economical and environmentally friendly sludge treatment option. This process has the characteristics of comprehensive simplicity, operating economy, operational flexibility, safety and environmental protection, etc., and is a valuable solution for sludge drying equipment.


    Promotion and prospect of thin film sludge drying technology
    As the intermediate link of the ultimate disposal sludge incineration, sludge drying process is of great significance to improve the operability of incineration disposal and effectively control the investment in the construction of incineration disposal facilities.

    Combined with various sludge disposal projects that have been successfully put into operation, the analysis of the project case operation research results of sludge thin film drying technology shows that using saturated steam as the heat medium and inert saturated steam, there is no overheating, short and fast, less exhaust gas and an open circuit discharge, and the enrichment of hydrocarbon substances in the drying process gas is completely avoided. It has the characteristics of stable and reliable operation, safety and environmental protection; It is not only suitable for the treatment and disposal of hazardous waste sludge in the fields of petroleum and chemical industry, but also has a good reference and promotion significance in the treatment and disposal of municipal sludge. For all kinds of sludge disposal to effectively solve the problem, to achieve the maximum reduction, to reduce the cost of sludge disposal and other engineering beneficial practice, and the realization of mud and water co-treatment theme, also has a high reference significance.