Sludge drying Treatment Solution:
Application status and case analysis of horizontal thin film drying two-stage process in sludge mixed firing power generation field
This article introduces the two-stage process of horizontal thin film sludge drying machine in detail, and analyzes the sludge treatment, disposal expansion project in bamboo Park as an example. Horizontal thin film drying machine has large single processing capacity, high safety, good sealing, less exhaust gas, and friendly workshop environment. Based on the advantages of horizontal thin film drying equipment two-stage process in safety, flexibility, economy and other aspects, this sludge drying process is more and more applied in the field of sludge mixing and firing power generation, and can be used as one of the preferred processes for sludge treatment and disposal projects in power plants.
With the rapid development of the city, the amount of sewage continues to increase, and the progress of upgrading sewage treatment plants continues to accelerate, resulting in a great increase in sludge output. By the end of 2016, China's sewage treatment volume has reached 150 million m/d, and the total amount of sludge is nearly 30 million tons. It is estimated that China's sludge output will exceed 60 million tons by 2020 based on 80% moisture content.
The sludge generated in the collection and treatment process of urban sewage may contain heavy metals, pathogens, viruses, microorganisms and a large number of toxic organic matter. If not properly treated and disposed of, it will cause serious secondary pollution to the environment around the discharge area and threaten human health. The problem of sludge treatment and disposal has become a prominent environmental problem under the current situation.
At present, the main sludge treatment methods include concentration, conditioning, dehydration, drying, etc., mainly concentration, conditioning and dehydration, drying rate is still at a low level. Sludge disposal refers to the final destination of sludge after treatment. At present, the main sludge disposal methods include sanitary landfill, land utilization, building materials utilization after incineration, etc., among which sanitary landfill is the most commonly used method. On the one hand, due to the increasingly strict standards and limited available land resources on the other hand, the treatment and disposal of drying and incineration is becoming more and more common.
Horizontal thin film sludge drying two-stage processSludge drying is a process that uses the heat energy or industrial waste heat and waste heat generated by burning fossil fuels to quickly evaporate the water in sludge through special technology and equipment. Sludge drying removes the water in the sludge, so as to achieve the purpose of drying the sludge, reducing the volume of the sludge, improving the calorvalue of the sludge, and simultaneously realizing the reduction and stabilization of the sludge.
Horizontal thin film sludge drying two-stage process is one of the mainstream processes of large-scale sludge drying projects at present, which is an indirect heating drying process using saturated steam or heat conduction oil as heat medium.
Core equipment
The core equipment of horizontal thin film sludge drying two-stage process is horizontal thin film drying machine. Xinjieyuan Environmental Protection Technology Co., Ltd. 's related environmental equipment products involve petrochemical, pharmaceutical, food, environmental and energy fields. The Xinjieyuan Company has a complete products research and development center and test base. The company is a world leader in thermal separation solutions for refractory mixed materials and thin film evaporation technology, as well as a leader in the development and production of equipment for drying high viscosity materials.
The figure shows the structure diagram of the horizontal thin film drying machine. The horizontal thin film drying machine is mainly composed of three parts: shell, rotor and blade, and driving device. The shell is a pressure vessel, and the shell jacket can be filled with saturated steam or heat conduction oil as the heat medium of sludge drying process. The material is high temperature resistant boiler steel of European standard. The inner wall is the heat transfer part in contact with the sludge, providing the main heat exchange area and the carrier of the thin layer of sludge. Corrosion resistance and wear resistance are better than other materials; The rotor is an integral hollow shaft, and its special processing technology can ensure that the rotor does not produce deflection while being heated and rotating at high speed, and the distance between the outer edge of the blade and the inner wall is always maintained at 5-10mm. Under the rotation of the rotor and the coating of the blade, the sludge entering the dryer will form a dynamic thin layer on the inner wall uniformly, and the thin layer of sludge is constantly updated. It continues to dry as it advances toward the outlet.
Process flow
After decanter centrifuge dewatering, the wet sludge with a moisture content of 80%-85% is transported to the wet sludge silo through vehicle transportation or pipeline. The silo is provided with a slide frame to prevent sludge from erecting Bridges, and the bottom is provided with unloading screw and wet sludge delivery pump.
The wet sludge conveying pump transports the sludge to the entrance of the thin film dryer, and the sludge entering the thin film dryer is coated on the surface of the hot wall by the blade on the rotor. The blade not only repeatedly turns and blends the sludge on the surface of the hot wall, but also pushes it forward to the mud outlet. In this process, the water in the sludge is heated and evaporated into water steam, which moves inversely with the sludge inside the drying machine and enters the exhaust gas condensation system from the exhaust tank above the sludge feeding port.
After the evaporation tail gas generated in the thin film drying machine enters the condensation system through the exhaust box, it first enters the condenser. In the condenser, the waste steam is washed by water, and the water is condensed from the evaporation tail gas. A small amount of non-condensing gas (volatile matter in air and sludge) is discharged from the drying system by the exhaust fan after droplet separation by the demisting device and processed in the deodorization system or incineration system. The amount of exhaust gas discharged by the self-drying system is very small, only 5%-10% of the evaporation water of the system. The exhaust gas fan makes the whole drying system in a negative pressure state to avoid the overflow of odor and dust.
The dried sludge with 30%-40% moisture content produced from the thin film drying machine is further dried in the subsequent linear drying machine, and the minimum moisture content can be dried to 5%. When the dry sludge is temporarily stored, the sludge cooler is set up. The sludge after drying by the linear dryer is cooled first, and the temperature of the sludge is reduced to below 50℃ to improve safety and prevent the sludge from smoldering or spontaneous combustion. Then it is sent to the dry sludge silo for storage through the discharge valve and scraper conveyor in turn. When the subsequent incineration system is connected, the drying system can be directly connected with the incineration system in series through the conveying equipment.
The two-stage horizontal thin film drying process can achieve the requirement of self-inertification in the system through the evaporating water in the sludge. In the case of start-up and emergency, low pressure steam, fresh water or nitrogen gas are used as the inertification medium of the drying system. The oxygen content analyzer is set at the outlet of the exhaust tank, and the safe and stable operation of the sludge drying system can be realized by controlling the oxygen content in the drying system.
Advantages of process
1) Safety: good airtightness of the thin film sludge drying system, always maintain a micro negative pressure of -0.5 to -1kPa, no odor and dust overflow; The system can be self-inert and set a variety of inert means, the oxygen content in municipal projects is controlled below 5%; The drying sludge temperature at the outlet of the dryer can reach 100℃, which can fully play the role of sterilization and meet the EPA503 standard of the sludge disposal code of the US Environmental Protection Agency. There is no safety incident in the application history.
2) Stability: in the sludge and coal cooperative incineration project, when the moisture content of the sludge entering the boiler of the power plant is large, it is easy to have a negative impact on the boiler equipment, which may lead to serious equipment damage. First, the inner wall of the furnace is washed and worn seriously, and the second is easy to lead to the blockage of the conveying system, resulting in the shutdown of the furnace. The two-stage process of thin film sludge drying has low sludge moisture content, and can realize rapid adjustment of sludge moisture content between 20%-33% by adjusting the steam pressure in the drying machine. Compared with other processes, it has obvious advantages and plays a positive role in maintaining the stability of power plant equipment and power grid operation.
3) Simple: the uniformity and granulation of sludge products can enhance the stability of power plant boiler operation. Other processes need to increase crushing or granulation equipment, while the thin film dryer can be self-granulation, the product is uniform granulation sludge, without additional granulation equipment; Small number of auxiliary equipment, small footprint, simple operation and control; No carrier gas circulation, no sludge back mixing; According to the "Pressure Vessel Maintenance Regulations", all kinds of drying machines need to carry out periodic inner wall inspection, thin film drying machine maintenance without other lifting equipment, convenient and efficient maintenance.
4) Flexible: wide range of application, suitable for a variety of types of sludge, can accept into the mud moisture content of 65%-90% wet sludge; The two-stage process can produce any product with uniform solid content. Start, stop and emptying time is short, and no cleaning operation is needed to start again.
5) Economy: high evaporation efficiency. In the sludge co-incineration project, the steam of the power plant can be directly used as the heat medium. The evaporation water per square meter of the thin layer dryer can reach more than 45kg per hour. Municipal projects can be combined with other systems (such as digestive system), can achieve more than 80% high efficiency of heat energy recovery; Low maintenance cost, only one annual inspection of 5-10 days per year; Odor is very small, low treatment cost; Fully automatic control, low monitoring requirements.
Case study of horizontal thin film sludge drying two-stage process in sludge mixed firing power generation field
The service object of the sludge treatment and disposal expansion project of Shanghai Zhuyuan Area is the dewatered sludge generated by the sewage treatment of the first and second Zhuyuan sewage treatment plants upgraded to the effluent standard of Grade A and the 2.2 million m/d sewage treatment after the completion of the new upgrade and supplement project. The construction scale of the project is 223tDS/d, equivalent to the sludge volume of 80% moisture content 1115t/d. The facility configuration considers the maintenance condition of the incineration line of the first phase of the project, and the peak treatment scale of the project is 288.5tDS/d, equivalent to the sludge volume of 80% moisture content 1442.5t/d.
The sludge treatment process route adopts thin layer drying two-stage method + power plant mixing and firing process. The dewatered sludge with 80% moisture content is transported to the sludge treatment plant by dump truck. After the sludge receiving and storage system, the wet sludge is pumped to the thin film sludge drying system, and then the average moisture content is reduced to 30% (adjustable range of 20% ~ 30%) after the drying system treatment. The dry sludge generated is transported by closed trucks to Shanghai Waigaoqiao No. 2 Power Plant or No. 3 Power Plant for co-incineration with coal.
The figure is the sludge drying system diagram of the sludge treatment and disposal expansion project in Zhuyuan area. After the sludge truck is weighted by weighbridge, the wet sludge is dumped to the underground receiving bin, and then transported to the wet sludge storage bin through the plunger pump system. Then the wet sludge is transported to the thin film drying machine through the unloading screw and screw pump.
The wet sludge enters the thin film drying machine for the first stage of drying, and the dried sludge falls into the linear drying machine through the chute. The dried sludge is further dried in the linear drying machine. The moisture content of the sludge can be quickly completed in the range of 20%-33% by adjusting the steam pressure in the drying machine. After the second stage of drying, the sludge enters the cooling screw for cooling, and then is transported to the dry sludge silo for temporary storage through the unloading valve and scraper.
The evaporative tail gas generated by the self-drying machine moves in reverse with the sludge, and the exhaust box above the self-drying machine enters the subsequent tail gas condensation system. The evaporative tail gas is sprayed and condensed in the condenser, and the non-condensing gas enters the subsequent defogger. After droplet separation in the defogger, the final tail gas is discharged from the drying system through the fan and enters the odor treatment system for treatment.
The public engineering conditions used in the horizontal thin film drying system mainly include saturated steam, medium water, instrument air, circulating cooling water and fresh water. The steam used in the drying system comes from the power plant and is distributed to 10 production lines through sub-cylinders. The drying system is equipped with an air pressure system to supply instrument air, the condensate recovery system is used to recover the steam condensate of the drying machine, and the circulating cooling water system provides circulating cooling water for the system.
The waste water produced by the drying system is mainly the spray water after washing the evaporation tail gas with medium water spray, and this part of the sewage will be returned to the sewage treatment plant for treatment. The exhaust gas enters the odor treatment system for centralized treatment. After drying, the sludge is sent to Waigaoqiao Power Plant for co-incineration with coal.
The sludge drying system of the sludge treatment and disposal expansion project of Zhuyuan Area successfully passed the performance assessment in August 2020. The annual running time of the project can reach 8000h, and the annual sludge treatment capacity can reach more than 400,000 tons. The completion and operation of the project will fundamentally solve the problem of sludge outlet in Zhuyuan Area, and help Shanghai's economy to achieve sustainable development. It can provide reference for domestic sludge treatment and disposal projects with power plant co-incineration.
Summary
1) The horizontal thin film drying system has good airtightness, can achieve strict oxygen content control, and has high safety. No safety accident has occurred in the application history of more than 30 years, and it is one of the safest drying processes in the field of sludge drying today.
2) 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 layer drying two-stage 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.
3) Horizontal thin layer drying two-stage sludge drying cooperative disposal is the development trend of municipal sludge treatment and disposal, which has obvious advantages in safety, stability, reliability, advanced and other aspects. The application of horizontal thin film drying two-stage process in cooperative disposal of sludge is a scientific and reasonable choice for municipal sludge treatment and disposal today.
