Biochemical sludge is the solid sediment produced during the biochemical treatment of sewage. When the sewage enters the biochemical treatment unit, such as the aeration tank in the activated sludge method and the biofilter in the biofilm method, the microorganisms carry out metabolism by decomposing the organic pollutants in the sewage, and in this process, the microorganisms themselves proliferate continuously, and at the same time, they will adsorb the suspended solids, colloids and other substances in the sewage. With the treatment process, these microorganisms and their adsorbed substances to form a floc structure, through precipitation, filtration and other ways to separate from the sewage, the formation of biochemical sludge.
If not properly treated, the organic matter and nutrients (e.g., nitrogen, phosphorus, etc.) in biochemical sludge will decompose in the natural environment, leading to eutrophication of water bodies. At the same time, microorganisms and harmful substances (e.g. heavy metals, pathogens, etc.) in the sludge may enter the soil and water bodies, causing pollution to the ecological environment. For example, biochemical sludge containing heavy metals will increase the content of heavy metals in the soil when it enters the soil, affecting the ecological function of the soil and the growth of crops. Due to its high water content, viscosity and complex composition, biochemical sludge is difficult to treat. In the dewatering process, special dewatering equipment and processes are needed to improve the dewatering efficiency. Moreover, biochemical sludge containing pathogens needs to be disinfected to prevent the spread of diseases. In addition, how to effectively resource the organic matter and nutrients in the sludge is also an urgent problem to be solved.
With the increasingly stringent environmental protection requirements, higher standards have been set for the treatment and disposal of biochemical sludge. Traditional sludge treatment may have secondary pollution and other problems, while semi-drying paddle dryer can effectively dry biochemical sludge, reduce the volume and moisture content of sludge, reduce the difficulty and risk of subsequent treatment, so as to make it more in line with environmental protection requirements, and therefore favored by the market. Biochemical sludge semi-drying paddle dryer has the technical advantages of high thermal efficiency, low energy consumption, flexible operation and good drying effect. It adopts indirect heating method, avoiding a large amount of carrying air to take away the heat, with remarkable energy-saving effect; at the same time, its special paddle structure can make the sludge fully contact with the heating surface, realizing uniform drying, and improving the drying efficiency and product quality, which make it stand out from the competition in the market, attracting the attention of many users.
Biochemical sludge semi-drying paddle dryer process flow
(1) Feeding stage: firstly, the biochemical sludge is continuously and quantitatively fed into the feeding port of the paddle dryer through screw conveyor and other conveying equipment. The feeding speed of sludge can be adjusted according to the processing capacity of the dryer and the required drying degree.
(2) Heating and stirring stage: the sludge entering the dryer is constantly turned and stirred under the rotating action of the paddle. At the same time, the heating medium (such as steam, heat-conducting oil or hot water, etc.) is introduced into the cavity of the paddle shaft and the jacket of the shell through the rotary joint, so that the paddle shaft and the machine itself are heated, and the heat is transferred to the sludge through conduction, so that the surface water contained in the sludge is rapidly evaporated. The special structure of the paddle makes the sludge alternately squeezed and relaxed during the drying process, which strengthens the drying effect and prevents the sludge from sticking to the paddle and the wall.
(3) Conveying and deep drying stage: driven by the rotation of the paddle, the sludge is conveyed in a spiral trajectory towards the outlet. In the process of conveying, the sludge continues to be stirred, and the water inside continues to seep out and evaporate, realizing deep drying. At this stage, the residence time of sludge in the dryer can be controlled by adjusting the parameters such as charging speed, stirring shaft speed and material filling degree, generally ranging from a few minutes to a few hours, in order to achieve the expected semi-drying degree.
(4) Discharge stage: the sludge which is dried evenly and meets the semi-drying requirements is finally discharged from the discharge port, and the discharged semi-dried sludge can be further processed for subsequent treatment, such as incineration, landfill, composting, or recycling as resources.
(5) Tail gas treatment stage: In the whole drying process, the water vapor released from the material and a small amount of entrained dust, etc. are discharged from the exhaust pipe at the top of the dryer under the action of the induced draft fan. The discharged exhaust gas is usually treated by dust removal, deodorization and other treatments before being emptied to prevent secondary pollution to the environment.
Biochemical sludge semi-drying paddle dryer performance advantages
(1)Good drying effect
Strengthening drying effect: the paddle has a special structure, the material is squeezed and relaxed alternately during the drying process, which strengthens the drying effect and makes the moisture in the sludge evaporate out more quickly and improves the drying efficiency.
The material is heated evenly: adopting jacketed shell structure, the sludge is heated evenly at all interfaces inside the machine, and the rotation of the shaft body makes the sludge constantly tossing inside the equipment, and the heated surface is constantly updated, which greatly improves the evaporation efficiency of the equipment, ensures that the sludge is dried uniformly, and avoids local overheating or incomplete drying, and reduces the moisture content of the sludge to the ideal level, such as reducing the biochemical sludge with usually high moisture content from 70%~90% or so to below 30%.
(2) High efficiency and energy saving
Indirect heating mode: the heat required for drying equipment relies on indirect heating by heat conduction, and no or only a small amount of gas is required to take away the moisture in the drying process, which greatly reduces the loss of heat taken away by the gas flow and improves the utilization rate of heat, and effectively reduces the energy consumption compared with some other drying equipment that requires a large amount of hot air circulation.
High heat transfer coefficient: Stirring and mixing make the material flip violently, obtaining high heat transfer coefficient, thus accelerating the drying speed and shortening the processing time, which in turn reduces the overall operating cost.
(3)Stable and reliable operation
High process stability: Due to the special compression-expansion-stirring effect of wedge-type paddle, the material particles are fully in contact with the heat transfer surface, and the gradient of temperature, humidity and mixing degree of the material is very small in the axial interval, thus ensuring the stability of the process, and the ability to consistently and stably output dried sludge products to meet the needs of large-scale continuous production.
Strong equipment reliability: the equipment structure is relatively simple, small wear and tear, low maintenance costs, low probability of failure during operation, and the equipment is better closed, which can effectively prevent sludge leakage and odor diffusion, reduce the impact on the surrounding environment, and help to maintain the cleanliness and hygiene of the production environment.
(4)Strong adaptability
Wide range of processing materials: using different heat media, both to deal with heat-sensitive materials, but also to deal with high-temperature treatment of materials, commonly used media such as steam, thermal oil, hot water, cooling water, etc., and can be operated continuously as well as intermittently, can be applied in many fields, can be used for municipal sludge, printing and dyeing sludge, papermaking sludge, electroplating sludge and other areas of the sludge drying.
Good adaptability to material characteristics: it has good adaptability to sludge with different humidity and viscosity, and can deal with various forms of sludge, such as pasty sludge, etc. Even for sludge with high viscosity, good drying effect can be realized through the stirring effect of paddles.
(5)Space and investment saving
Compact structure design: the unit effective volume has a huge heat transfer surface, so that the equipment covers a small area and space, can save the cost of plant infrastructure. And the drying process gas consumption is small, low flow rate, the amount of dust taken away by the gas is small, after drying the gas dust recovery is convenient, the recovery equipment volume is small, can further save equipment investment.
(6) Convenient for automatic control
According to different seasons, ambient temperature and specific characteristics of sludge, it is convenient to adjust the operation parameters accordingly, such as adjusting the charging speed, mixing shaft speed, material fullness and other parameters, in order to achieve the best drying effect of ZUI. And it is easy to be combined with automation control system to realize remote monitoring, fault diagnosis and automation operation of sludge treatment process, optimize the management quality level, improve the production efficiency and management convenience.
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