The process flow of a town sewage treatment plant is divided into four treatment sections according to the hydraulic flow: pretreatment section, biological treatment section, sludge treatment section and deodorization system section. The pretreatment section includes a coarse grid chamber, a lifting pump room, a fine grid and a cyclone grit chamber; The biological treatment section comprises a high-efficiency sedimentation tank, an aerated biological filter and a rotary disc filter; The sludge treatment section comprises a sludge dewatering machine room; The deodorization system part includes a deodorization workshop. The coarse grid room, lifting pump room, fine grid and cyclone grit chamber in the pretreatment section have been widely used in the pretreatment of sewage treatment plants at home and abroad.
Pretreatment part
The function of the coarse grid is to intercept the larger particles in the sewage entering the sewage treatment plant to avoid damaging the impeller of the water pump; The purpose of grit chamber is to remove inorganic sediments and reduce the impact on subsequent biological treatment.
Because of the simple principle of grating and desanding equipment, domestic equipment manufacturers use stainless steel, and the equipment performance and treatment effect are not much different from those imported from abroad. Due to the heavy weight of the equipment, it is necessary to pay high freight and equipment costs for importing from abroad. It is suggested to choose domestic equipment to meet the requirements of coarse grille room, lifting pump room, fine grille and cyclone grit chamber.
biological treatment
High-efficiency sedimentation tank, biological aerated filter and rotary filter are patented design processes of Veolia Water in France.
Its effect and performance of removing pollutants have been widely recognized by sewage treatment plants all over the world, and it has incomparable advantages over similar domestic treatment processes. Although its price is much higher than that of domestic products, the water treatment effect is unmatched by domestic treatment processes, and its technical and economic comparison with domestic treatment processes is as follows:
Investment and operating cost analysis
The investment of foreign filters is higher than that of domestic heavy media filters 10% to 30%, but the requirements for water quality are obvious. From the analysis of operation cost, due to the high energy consumption of backwashing system, the energy consumption of domestic heavy media filters is 20% ~ 30% higher than that of foreign countries.
Life commitment period of filter materials
Foreign countries promise that the service life of filter materials will be more than 15 years, while other heavy filter materials will be completely replaced after 3 to 5 years. Even imported filter materials will be gradually replaced after 10 years, which will bring a lot of maintenance costs and maintenance costs.
Civil engineering investment cost
Due to the large unit area of foreign filters, the civil engineering cost of domestic heavy media filters is high, but the gap is not big.
Equipment grade
All the key equipment of the filter are imported, otherwise the life and performance will be worse. Fans, swirl heads, pneumatic butterfly valves and control instruments must be imported, and water pumps are better. Air compressors can be joint ventures, and electrical appliances and automatic control components should be assembled by internationally renowned brands in China. Through the above technical and economic comparison, it is recommended that the patented equipment provided by Veolia Water in France be used in the biological treatment section.
Sludge treatment section
High-efficiency sedimentation tank adopts dehydrator to treat sludge, and belt dehydrator and centrifugal dehydrator can meet the requirements. The investment of centrifuge is higher than that of belt conveyor. Considering that the centrifugal dehydrator has the characteristics of good dehydration effect, good operating environment and less maintenance workload, this project adopts centrifugal dehydration to treat sludge. Technical and economic comparison between domestic and imported centrifugal dewatering equipment;
material
In the equipment at home and abroad, the main components are all stainless steel, especially the drum and spiral part are all stainless steel.
pattern plan
Only some domestic manufacturers have this technology, mainly from technical cooperation and introduction with foreign companies, and only a few manufacturers are innovative technologies after digesting and absorbing foreign technologies and improving them. But it is different: a few domestic companies have absorbed Alfa Laval's BD baffle technology or other companies' extrusion screw design; Another design is to set the pressure plate with Archimedes spiral shape on the spiral cylinder.
In addition to the above two kinds of foreign centrifuge designs, there is also thin plate technology. Different foreign manufacturers adopt different technologies in centrifuge design and realize them in different ways. The design is mainly realized by changing the structure of drum and screw, but some manufacturers also realize it by feedback control of speed difference.
Drive type
There are great differences between Chinese and foreign driving modes, and there are as many as 5 ~ 6 different driving modes for imported equipment. The driving mode of centrifuges in China is usually simple, and the most commonly used driving mode is double-motor structure, that is, one variable frequency motor directly drives the drum to rotate through the belt, and the other motor drives the screw through the reducer.
Because different driving methods will eventually lead to different speed differences, the lowest speed difference of domestic equipment is generally a few revolutions per minute, and only a few manufacturers can reach 0.5r.p.m, while the lowest speed difference of foreign equipment can reach 0.2r.p.m, a difference of more than ten times, that is, the retention time of sludge can be increased by more than ten times. Velocity difference is the key factor affecting the moisture content of mud cake. Low speed difference can produce drier mud cake, and correspondingly reduce the wear of the screw, thus greatly prolonging the service life of the screw.
Differential machine
The differential structures used in centrifuges at home and abroad are basically the same. Generally, it is a two-stage planetary involute gear differential, such as 2K-H, 3K and K-H-V, or a combination of a planetary cycloid pin wheel and an involute gear differential. Due to the high speed and torque of the differential, the clearance adjustment requirements of all parts in the assembly process are particularly high and the tolerance requirements are very accurate. Too large or too small clearance is not conducive to the operation of differential, and centrifuge manufacturers often need special design and processing.
Many domestic manufacturers have tried to localize the differential, and the machining accuracy and performance of some manufacturers have basically reached the international level. However, there is still a certain gap in general, especially in the assembly accuracy and experience. In addition, improper selection of main parts or limited materials often lead to the failure of the differential to meet the design requirements, low efficiency and short service life. At present, many domestic manufacturers often use imported differential to meet the performance of equipment.
Spiral sealing mode
Screw seal mostly adopts mechanical seal or labyrinth seal, and domestic and imported centrifuges are basically the same.
Wear protection
The centrifuges of major manufacturers at home and abroad all adopt the process of embedding sintered wear-resistant alloy sheets or ceramic sheets on the outer edge of the spiral blades in contact with sludge, which is convenient to replace, but the overall replacement cost is relatively high. Some manufacturers carry out tungsten carbide thermal spraying treatment on the outer edge of spiral blades, and the cost is relatively low.
Automatic control mode
The efficient dehydration performance of centrifuge can only be realized by perfect automatic control system.
At present, the mainstream control mode at home and abroad is PLC control. At present, the control technology of centrifuges in some foreign manufacturers is several years ahead of that in China. In recent years, some manufacturers have begun to use industrial computers or DCS control systems ten years ago, which can achieve more and more powerful control functions than PLC systems.
Through the overall technical comparison, it is not difficult to see that only a few domestic manufacturers can produce small centrifugal dehydrators, and the overall level of domestic centrifuge manufacturing industry is still far behind that of foreign centrifuge manufacturing and new technology research and development, especially in terms of reliability, stability, service life, assembly accuracy, flexibility and humanization of operation, and the application of some new technologies, etc., it is recommended to choose foreign centrifugal dehydrators.
Deodorization system
Two commonly used deodorization methods are analyzed and compared.
Compared with organic biofilter, the main technical advantage of inorganic biofilter is that the construction of centralized odor treatment biofilter occupies less area, only 1/5, which greatly reduces the land acquisition cost. Although the cost of treating unit odor is relatively high, the advantage of reducing land acquisition cost can make up for the relatively high cost. Moreover, there is little difference in annual operating costs and it is not affected by climatic conditions. Inorganic biological filtration deodorization method has been widely used in the world, and the technology is mature and reliable. According to the above comparison, under the condition of paying more and more attention to the environment, it is recommended to use inorganic filter materials imported from abroad to achieve the deodorization effect of sewage treatment plants.
label
Urban sewage treatment plants have different performance requirements for the equipment in each treatment section. It is suggested that domestic equipment should be used in the pretreatment section, and imported equipment should be used in the biological treatment section, sludge treatment section and deodorization system section.
Brief introduction of common equipment for sewage treatment
Sewage treatment equipment can effectively treat domestic sewage and industrial wastewater in urban areas and prevent sewage and pollutants from directly flowing into water areas, which is of great significance for improving ecological environment, upgrading urban quality and promoting economic development. Today, Bian Xiao will show you some sewage treatment equipment!
centrifuge
Centrifuges are mainly used to separate solid particles from suspended liquids; Or separate two immiscible liquids with different densities in the emulsion (such as separating cream from milk); It can also be used to dehumidify liquids in solids, such as washing clothes with a washing machine; The special ultra-high speed tubular separator can also separate gas mixtures with different densities; Some settling centrifuges can also classify solid particles according to their density or particle size, and the settling speed of solid particles with different density or particle size in liquid is different.
sludge dehydrator
The sludge dewatering machine has the characteristics of automatic control operation, continuous production and stepless speed regulation, and is suitable for sludge dewatering in water supply and drainage, paper making, casting, leather, textile, chemical industry, food and other industries.
aeration machine
The aerator directly injects "micro bubbles" into untreated sewage through the diffusion impeller. Under the joint action of coagulant and flocculant, suspended solids undergo physical flocculation and chemical flocculation to form large suspended solid flocs, which float to the liquid surface to form scum under the floating action of bubbles, and are separated from water by a slag scraper; There is no need to clean the nozzle, and no blockage will occur. The equipment has good integrity, convenient installation, saving operation cost and occupying less land.
Drum filter
Microfiltration machine is a drum screen filtration device. The treated wastewater enters the drum along the axial direction and flows out through the screen along the radial direction, and impurities (fine suspended solids, fibers, paper pulp, etc. ) is trapped on the inner surface of the screen on the drum. When the impurities trapped on the filter screen are carried to the upper part by the roller, the pressure washing water is backwashed into the slag discharge tank to flow out. During operation, 2/5 of the drum diameter is exposed out of the water, and the rotating speed is 1-4r/min. The filtration speed of the screen can be 30- 120m/h, the washing water pressure is 0.5- 1.5kg/cm2, and the washing water volume is 0.5- 1.0% of the raw water output. The microfilter occupies a small area, has a large production capacity (250-36000m3/d) and is convenient to operate and manage. It has been successfully applied to water supply and wastewater treatment.
TDAF
Air flotation machine is a kind of equipment to remove suspended matter, grease and colloid from various industrial and urban sewage. The equipment is widely used in the treatment of industrial wastewater and urban sewage such as oil refining, chemical industry, brewing, slaughtering, electroplating, printing and dyeing.
According to the dissolved air way, it can be divided into: inflatable air flotation machine, dissolved air flotation machine and electrolytic air flotation machine. Its principle is to efficiently mix water-insoluble gas or two or more different liquids (the generated microbubbles have a particle size of 20-50 microns). Micro-bubbles are used as carriers to attach to impurity particles in water, and the particles are carried by bubbles to the surface to separate from water, thus achieving the purpose of solid-liquid separation.
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