Some Typical Applications of Vacuum Technology in Wastewater Treatment

Some Typical Applications of Vacuum Vacuum Technology in Wastewater Treatment Cui Cunyan, Zhu Wu, Chen Changqi, Gan Yiyi, Xie Yuan, Wang Xianlu (School of Mechanical and Automotive Engineering, Hefei University of Technology, Hefei 230009, Anhui, China); Shenchi and digester sludge dewatering; vacuum flotation method to accelerate the flotation process by creating negative pressure conditions; there are vacuum mixing, vacuum degassing and so on. These are enough to show that vacuum technology occupies an important place in wastewater treatment and even environmental protection. With the rapid development of modern industry, the global pollution has become increasingly serious. This global issue has attracted the attention of countries in the world. According to estimates of experts, China’s annual loss caused by environmental pollution amounts to 280 billion yuan, of which only about 50 billion yuan is related to water pollution. Environmental pollution has been so serious that it has caused the country’s high attention to environmental protection to be listed in China. One of the basic state policies. The "three rivers and three lakes" project initiated by China and its achievements fully reflect that sewage treatment is an important aspect of environmental protection.

The wastewater treatment process involves more theories, technologies and methods, among which there is no lack of vacuum technology. This article describes several typical applications of vacuum technology in wastewater treatment, including vacuum crystallization vacuum filtration dehydration, vacuum flotation, vacuum Mixing, vacuum degassing and so on. The purpose of publishing this remark is to initiate an elaboration. Our vacuum workers can turn some of their sights to environmental protection. 1 Typical process of wastewater treatment Wastewater treatment essentially uses various means and technologies to separate pollutants from wastewater or convert them into wastewater. It is a harmless substance, so that the sewage is purified to meet the emission standards.

Modern sewage treatment methods include physical treatment methods and biological treatment methods. Due to the high content of pollutants in sewage, large concentrations, and complex forms of various components, it is often necessary to use multiple treatment methods in combination. A combination of multiple treatment units can eliminate pollutants to achieve purification requirements. Treatments (mainly urban domestic wastewater and certain industrial wastewater treatment) can generally be divided into primary and secondary grades. Primary treatment is the removal of solid pollutants in the suspended state. Secondary treatment is to substantially remove colloids from the wastewater and Dissolved organic contaminants (ie, BOD substances) are tertiary treatment to further remove secondary pollutants that have not been depleted. A typical process for urban wastewater treatment. Raw sludge moisture content, pk-a cake moisture content, filtrate dynamic viscosity ,kgs/m2 P-one filtration pressure or degree of vacuum, kg/cm2M-a ratio of immersion liquid, generally takes 0. 3T-a daily working hours 2 Typical application of vacuum technology in sewage treatment The theory and technology of sewage treatment involves Physics, biology, chemistry, electronics, and many other disciplines, vacuum technology also plays a very important role in the sewage treatment process, especially in the transfer of Slime treatment more fully embodies the advantages of vacuum technology.

2.1 Vacuum filtration The mechanical dehydration method of dewatered sludge mainly includes pressure filtration, centrifugation and vacuum filtration. Pressure filter operation is cumbersome, can not be continuous operation, the yield is not high Centrifugal sludge pretreatment requirements are too high A widely used sludge dewatering method is a vacuum filtration method, which is characterized by continuous operation, stable operation With a large amount of treatment and automation of process operation, the solids content of the treated cake can reach the dehydration requirement. This method can be used for sludge dewatering in primary sedimentation tanks and sludge dewatering in digesters.

There are three types of vacuum filter rotary drum roping type. The most widely used is the GP drum vacuum filter, as shown. The main components are the hollow drum and the lower sludge drum. The vacuum drum filter yield is determined by the following formula: 1994-2015cia AemicoumlfElecfrooicPublish Operational cost increase n According to the nature of the sludge, the vacuum level is generally in two directions: If the fan-shaped compartment connecting pipe communicates with the vacuum pipe of the fixed part, it is in the filter cake forming area and the suction drying area, and continues to suck dry water; when the pipe communicates with the compressed air, it enters the back blowing area and the filter cake is inverted. The filter cake blown loose and peeled off is transported away by a belt conveyor for one revolution, followed by filtration cake forming zone, suction drying zone, backflushing zone and dead zone drum vacuum filtration process. The vacuum degree is promoted by vacuum filtration. Force is directly related to filtration yield and operating costs. In general, the higher the vacuum, the greater the filter cake thickness and the lower the moisture content. However, due to the increase of the filter cake's thick filter resistance, it is not conducive to filtration. After the dehydration vacuum is increased to a certain value, the increase of the filtration rate is not obvious, especially for the compressive sludge, and the vacuum degree is too high. The filter cloth is easy. Plugged and damaged, the power consumption and the lower half of the hollow drum are immersed in the sludge storage tank. The surface of the drum is covered with a filter cloth. The drum is divided into many fan-shaped compartments with radial partitions. Each compartment has a separate communication tube. The end is connected with the distribution head. The distribution head is provided with a rotating rotor and a fixed slice: the rotating slice of the rotating drum is connected with each sector-shaped grid through a communication tube. The fixed plate can be communicated with the compressed air pipeline and the vacuum pipeline respectively when the drum rotates, due to the effect of vacuum. The sludge is adsorbed on the filter cloth and the liquid flows through the filter cloth along the vacuum tube to the air-water separation tank. The filter cake adsorbed on the drum is transferred from the sludge surface of the sludge tank to 5.32 to 7.98 kPa. The filter cake formation area is about 5.32~ Table 1 lists the drum vacuum filter to treat various domestic sewage sludges. 7.98kPa, Typical operating data for filtering capacity obtained from 6.679.kPa kPa and industrial sewage sludge 4L Sludge type Source properties Conditioning filter capacity Filter cake Solid content Initial precipitation Sludge Organic living mix Fresh sludge Pro Water Sewage Mixing Digestion Sludge Aerobic Stabilization Sludge Organic Hydrophilic + Inorganic Hydrophobic Brewery Sludge + 10% Sulfonate Fiber Containing Pulp Paper Mill Sawdust and Confetti Fiber 20% + Hydrogen Oxide Inorganic Hydrophobic Steel Plant Lime Removal Sulfonate Fe Converter Gas Wash Coal Wash Coal Washing Polymer 0. 3kg/L Dry Solid Oily Refinery First Stage Precipitated Sludge Prefilter 2.2 Vacuum Crystallizer Crystallizer Yes It is used to separate the solids with crystallization properties in the effluent. It is concentrated by evaporation or cooled to cool the solution so that the solution saturates and the excess solute is crystallized and recycled. There are many types of equipment that can be used for crystallization, such as crystallizer tank evaporative crystallizer vacuum crystallizer, etc. The crystallizing process of the crystallizer tank is not easy to control, the obtained crystal is large, and the purity is low. The evaporative crystallizer has equipment corrosion problems. The vacuum crystallizer can be operated intermittently or continuously. It has the characteristics of simple structure, light weight, easy corrosion control, etc., and does not require foundation, so it can be installed in “overhead” structure. The generation and maintenance of vacuum here is generally accomplished using a steam jet pump. Because the steam jet pump has no mechanical movement and is not constrained by conditions such as friction, lubrication, vibration, etc., it can be made into a pump with a large capacity of exhaust gas and has reliable operation. If the service life is long, if corrosion-resistant materials are used for manufacturing, Can be used for wastewater treatment with corrosive substances 1. Feed inlet 23. Pump 4. Circulation tube 5. Condenser 6. Two-stage steam jet pump 7. Steam jet pump Vacuum crystallizer 2.3 Vacuum aeration, flotation, stirring and Other jet diffusers, also known as jet aerators, vacuum aerators, are pumped into the mixture and form a high-velocity jet at the jet's throat, which is mixed and stirred with the air that is inhaled or pressed in, smashing the bubbles. The oxygen is quickly transferred to the mixture. The configuration of the ejector is as shown.

The jet diffusion principle has certain applications in vacuum aeration, flotation and agitation.

The aeration power consumption occupies the total continuous vacuum crystallizer of the whole plant. The solution is continuously added from the feed inlet. The crystal and part of the mother liquor are continuously discharged from the pump and the solution is forced to circulate along the circulation tube to promote the uniform mixing of the solution to maintain the Favorable crystallization conditions. Evaporated water vapor escapes from the top of the appliance to the condenser where the condensation water is condensed. The function of the two-stage steam injection pump is to keep the crystallizer in a vacuum state. The operating temperature in the vacuum crystallizer is generally low. The solvent vapor cannot condense in the condenser, so it can be equipped with a steam jet pump to compress the solvent vapor to increase the condensing temperature. The continuous vacuum crystallizer can also use multi-stage operation, that is, several crystallizers are connected in series, and different levels are kept different The degree of vacuum and temperature, so as to achieve the purpose of improving the quality and speed of crystallization, is 60%~7 ​​(%) of the power consumption of a sewage treatment plant, which is the key point of energy saving. The advantage of low energy consumption of vacuum aerator is the most user-friendly At the same time, the vacuum aerator also has a series of advantages such as strong oxygen supply capability, uniform mixing, simple structure, low price, stable performance, no noise and other hazards, and strong corrosion resistance. Jet structure is a schematic diagram One of the flotation methods is a method of flotation of air into a wastewater stream using a gas-jet ejector.The high-speed wastewater ejected from the nozzle creates negative pressure in the suction chamber. , And suction air from the suction chamber, in the water and gas mixture into the throat section after the intense energy exchange, the air is crushed into tiny bubbles; then enter the diffuser section (diffusion section), kinetic energy into potential energy, further compressed air bubbles, increase Larger air solubility in water; then into the flotation cell for gas-water separation, that is, flotation process dissolved gas vacuum gas flotation method is the use of highly dispersed micro-bubbles as a carrier to adhere to the pollutants in the wastewater, making it The main characteristic of the process of solid-liquid or liquid-liquid separation is that the apparent density is less than water and floats to the surface of the water. The main feature is that the air flotation tank operates under negative pressure. Therefore, the air is easily supersaturated in water. The amount of air to be separated depends on the amount of dissolved air and the vacuum. The advantage of this method is that the dissolved gas pressure is lower than the pressure dissolved gas method and the energy consumption is smaller.

The water jet agitator consists of a sludge pump and a water jet (also known as a jet pump). The structure of the water jet is similar to that of the pump. The high speed sludge is ejected from the nozzle, and the suction chamber of the water ejector is negatively charged. Pressure, inhale the digested sludge in the digester and mix it with the sludge. After a period of operation, the sludge in the digester can be stirred. The vacuum deaerator can remove the sludge floes discharged from the digester. The bubbles greatly improve the sedimentation performance of the sludge. The vacuum degree of vacuum degassing is 5 kPa. In addition, the application of the vacuum unit vacuum device is also common in the chlorination system sludge discharge and the sludge flotation concentration siphon filter digester.

From the above discussion, it is not difficult to see that crystal dehydration, aeration, flotation and agitation are important steps or methods in the wastewater treatment process, and vacuum technology plays an important and even very critical role in it. It can be seen that the vacuum technology has a broad space for development in the treatment of sewage, vacuum workers can give full play to their own advantages, in the 21st century, Chaoyang industry 11 environmental protection in the grand show

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