真人做人爱试看一

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          Current situation and comparison of European sludge dehydration technology

          Author: Taida machine       Release time:2016-08-24
          Reading guidance:1. Policy preparation on sludge disposal in EU countries 1.1 lawmaking EU has made disposal policy of sludge as early as in 1982. It has two key aspects: Forbidden discharging sludge to surface water s
          1. Policy preparation on sludge disposal in EU countries
           1.1 lawmaking
              EU has made disposal policy of sludge as early as in 1982. It has two key aspects:
             Forbidden discharging sludge to surface water system;
             Encourage sludge to be used for agriculture with strict supervision and track;
            Member states have in accordance with the guiding policy formulate the local laws and regulations. In Italy, for example sludge is as solid waste a (special garbage), in accordance with the provisions of the law, by garbage maker and owner is responsible for proper disposal, namely, sewage treatment plant. The disposal expenses to the provisions of the sewage treatment fee (including the drainage pipe network and sewage treatment plant) form a separate charge.
            Sewage treatment fees in some countries have been higher than the cost of running water, especially in big cities.
            1.2 implementation and supervision of policy
          In 2000 years in the EU in the sewage treatment plant produces about 790 million tons (dry sludge, in Italy, about 92 million tons. Italy's sludge treatment has a strong area and economic characteristics of. Formulation, environmental policy and project approval is equivalent to the provincial government of the district government, the project implementation is a municipality consisting of the economic union.
           1.3 attitude and awareness of citizens
           The EU countries have been on the environmental problem has been paid more attention. Whether industrialist or ordinary citizens, law-abiding consciousness is very important, especially relates to the environmental protection aspects. Under the law, the perpetrators in addition to impose a fine, and investigated the criminal responsibility.
            2. Main characteristics of sludge disposal in Europe
            2.1 dehydration is a necessary process
             From direct application to direct burning, after the drying of the application, to the dry burning, until the recent dry gasification, basically confirmed the importance of drying as a necessary intermediate process:
             Economy, whether it is transportation disposal reduction, or energy consumption reduction, sanitation and agriculture.
            2.2 final disposal methods is decided by condition of a country
             Landfill is certainly not desirable, not only because of the high value of land, mainly from the energy and bio energy resources to consider, the EU requirements to reduce and limit sludge landfill.
            The excess energy of the whole nation, may choose to burn as effective means of disposal. Of the sludge heat to maintain its heat demand. Therefore, it is necessary to add new cheap heat source, such as forest trash or municipal garbage. Disposal of the apart from the fact that the investment is high, and public opinion have certain conflict, although current technology may it can guarantee that the very secure.
          Way for countries in the energy importers or incinerator. To solve the sludge problem is best farm. The main problems of agricultural is the protection of land, avoid excessive heavy metal precipitation in the soil, must have the appropriate means and system guarantee this. At present, there is a considerable accumulation of knowledge of the pollution of heavy metals in the sludge, producer of the recording system has been built up, at least for users still need to time for study and management.
          Still occupies an important share of sludge landfill, because the stem can be greatly reduced, effectively reducing landfill charges and transportation costs, so for this is not the solution dried become a necessary way for cost reduction.
            2.3 Sludge disposal is an industrial operation with economic benefit as the main driving force.
            The final disposal means in itself is a resource, the use of such resources must be paid.
             Removal of water supply system has been completely privatized, the vast most of the sewage treatment factory owner is the city government, in general, sewage treatment plant operation were commissioned by the municipal government joint body and a private, state-owned company operations. Operators do not necessarily have all and necessary treatment. They can only get limited funds, within the range of funds the best management mode.
             3. Characteristics of European sludge dehydration process
            3.1 dehydration technology is a improvement of traditional drying technology
            Since the 1970s, the world has many manufacturers made or tested sludge drying, these companies almost without exception, all from agricultural products, chemical, pharmaceutical, food drying field. The method is in the original technique based on sludge drying experiment, of which there are successful, but more is failure. Failure in many large well-known equipment group or enterprise. Because, not all dry technology suitable for drying sludge of this kind of material.
            3.2 the biggest difficulty of dehydration is security
             In the past twenty years, dry sludge of Europe and North America project has been the size of a large minority of accident cases, from the spontaneous combustion of the dry sludge, to equipment explosion, making some countries even formulate the special mud dry equipment safety guidance, urged managers to carefully consider the various potential risk factors in the process of dry.
            3.3 there exist big difference between theory and practice
            For most people, sludge drying should be very simple, nothing more is to rely on heat water evaporated from the sludge. Evaporation of water requires a certain amount of heat per liter of evaporation requires a minimum of 620 calories, plus certain efficiency losses are not enough? All the dry heat demand equipment processing it all of its nominal system is 800 to 850 calories, you basically all is common. If the sludge drying is so simple, there are some Taiwan, large technology group dozens of sales will have to withdraw from the field. In fact, it is because of the sludge in the theory and practice of drying process existed make some difference, the operation of equipment there are great unpredictability and instability, leading to its "overwhelmed".
            3.4 there exist obvious difference between dehydration efficiency and profit
             Technology and equipment stability is very important for the human resources of expensive European manufacturers, whether it is the user or equipment providers, if the device is inefficient, it means that the high cost of labor.  
            Energy costs for European companies is obviously not as good as developing sensitive, but due to the energy in a dry total system operating cost accounted for more than half, energy saving even if is rarely part of, also have important significance.
            4. Main process types of european dehydration equipment
            4.1 process type
          According to the form of heat supply, it can be divided into two series, each series has several representative processes:
          4.1.1 direct heating method
              Rotary drum
              Conveyor belt dryer
          Pneumatic transport dryer
          Batch as well as solar dryer
          4.1.2 indirect heating method
             Disc dryer
             Paddle dryer
             Thin film dryer
             Fluid bed dryer
             Turbo thin film dryer
            4.2 reason why difference of heat exchange efficiency
             As is known to all, evaporation means that a certain amount of heat energy is transferred to the evaporation in the unit time. Generally, it is required to pass through a medium, either air or steam, or metal, etc.
             Through the wall of a metal heat, water molecules and metal direct heat, the so-called heat conduction; through or not through the heat exchanger to heat transfer to the air, through the heat exchanger to heat to the steam, and air or steam and water molecules for heat exchange, the so-called thermal convection.
             To measure the heat transfer efficiency of a parameter is the thermal conductivity, namely in unit time, unit area can transfer (through) the heat. Thermal conductivity of the metal significantly better in the air or steam, heat the metal surface and the medium of heat transfer, is the highest efficiency of heat transfer. Need medium, heat exchanger of the effective heat transfer area will determine the supplier efficiency of heat supply.
              Similarly, the recipient of heat, the heat capacity is limited. Specific heat is defined as: unit weight of the material, every increase of 1 degree required heat. The material is accepted a certain quantity of heat, there must be enough quality to get it and carry it. Although the heat exchanger through a metallic surface can be in unit time is given enough calories, but in unit time if there is no adequate volume to accept it in vain. Therefore, thermal convection system requires not only large volume for material handling, also need the gas to carry enough temperature of heat.
             In addition, the air vapor movement is the limit of time and space, that is subjected to the heat transfer surface area, pipeline, flow velocity, friction, heat loss and so factors influence. Heating temperature is high, volume is larger, the total heat loss is greater. Air to air heat exchange efficiency of the lowest and other media to air heat exchanger has greater losses.
             Reducing the heat transfer loss method, can only choose the best material (thermal conductivity), increase the heat exchange surface area, reduce the number of heat transfer, heat transfer time, increase the heat preservation and so on.
             Unfortunately, most of the energy were derived from in a fuel burning, burning is a continuous supply of air, has a specific rate, obtained at the rate of heat if not all use must back into the atmosphere. The formation of physical energy loss, that is, the so-called "combustion efficiency", the loss according to the change of fuel type.
             No matter direct and indirect heating methods, there are same combustion efficiency problem.
          Direct heating mode after the fuel is burned directly into the system, flue gas to atmosphere directly to drain nor by heat exchanger. Therefore, it has high thermal efficiency, but this part of the flue gas, together with the whole system of the gas must be washed, and a heat loss. In addition, incomplete combustion is a potential problem. The problem is that, due to air heat transfer property is bad, in the sludge must be dry sludge back mixing, it is necessary to take into account a series of "heat recovery", in order to in the overall energy consumption to remain competitive.
          Indirect heating drying anyway by one and a plurality of heat exchangers, which formed first loss. And purge gas become the second loss. Therefore, we should consider combustion efficiency. Indirect heating method to obtain high thermal efficiency, we must rely on the effective thermal conductivity to obtain high heat exchange efficiency.
          4.3 main problems of dehydration process
          The problems of heat convection and heat conduction in sludge drying are separately listed.
          4.3.1 heat convection system
           Rely on dry sludge back-mixing
           High content of dust
           Much hidden danger
           High heat-exchange efficiency
           Slow dehydration speed
           Much gasification amount; much heat loss
           Many equipment; many key control point
           Large equipment volume
           Need long time to stop the machine
           Complex maintenance especially cleaning work;
           High request of energy
          4.3.2 heat conduction system
             Rely on dry sludge back-mixing
             High content of dust
             Much hidden danger
             High heat-exchange efficiency
             Slow dehydration speed
             Much gasification amount; much heat loss
             Many equipment; many key control point
             Large equipment volume (only for fluid bed)
             Sludge stick on inner wall of equipment which will reduce heat conduction efficiency;
          Complex maintenance especially cleaning work;
          4.4 solutions of main problems and main problems
            Reduce time unit in the logistics, canceled the dry sludge back mixing can reduce equipment units more than half, the control key points to reduce to the lowest degree. Unfortunately, for most of the systems is impossible;
            The safety hidden danger caused by the oxygen content of the steam circuit is adopted, and the scheme can only be applied to the indirect heating mode and can not be used in the direct heating system;
             Increase the gas flow rate (speed), in order to improve the efficiency of drying, so that the results will cause greater heat loss;
          Increase the heat exchange system to reduce heat loss as far as possible; from the point of view of the theory is very good idea, but meaning is limited in practical application. This is mainly because of the low temperature waste heat, recovery ratio is low;
             The more wearable and anti adhesion material and process for manufacturing equipment; no matter what wear resistant material, have a certain life, besides drying condition is complex, affecting the use life of too many factors, if needs some special material too much, will lose the economic feasibility.
             Using waste heat or cheap energy; waste including waste heat steam, gas, such as bio gas, cheap energy including coal, heavy oil and other. Direct heating mode in addition to using a heat exchanger using waste heat steam preheating, still has other energy sources, coal, heavy oil containing sulfur dioxide and energy in high humidity environment may lead to the formation of sulfuric acid will damage the equipment, unless you install expensive dry desulfuration equipment, but it will greatly reduce the system process temperature. Indirect heating can use all the waste heat, or cheap energy.
          4.5 How to solve the limitation of two kinds of heat transfer modes
             Turbine thin layer technology is a special drying technology developed by Italy VOMM company. It adopts heat conduction and heat convection. The effective heat convection accounts for about 40% of the total heat transfer quantity, and the heat conduction accounts for more than 60%.
          This process completely abolished the dry mud back to mix, making the process is simple, the number of equipment is very small, the overall reliability of the increase;
             Process using equivalent to ordinary thermal convection process less than half of the gas, play a role in material handling, and with heat conduction, forming the best evaporation efficiency, dry time is only 2.5 minutes, at the same time, the protective effect of the surface of steam, to avoid overheating of the granular sludge, and reduce the dust problem;
             The vortex formed by the high speed turbine is stirred, so that the material is not attached to the metal wall, on the contrary, there is a strong self cleaning effect.
             Weary metal parts and the scope is very limited, so you can use a good heat treatment technology to improve their life.
             Because the processing time is greatly reduced, there are few materials in the system in the unit time, so the time is short, and the amount of cleaning is very small in the case of emergency shutdown.
          A variety of cheap energy or waste heat can be used to form a competitive solution. In addition, turbo washing process can effectively solve the problem of high desulfurization of coal utilization in.
             Overall, although each process may there are advantages and disadvantages of such, for customers, more need is actually a process to adapt to the specific economic, technical conditions to within the framework of existing conditions, using the cheapest energy, with the lowest cost and safely complete stem of this task.
          5. Thin layer technology of turbine with steam as carrier gas
             On successful turbo thin process based, VOMM developed steam is used as the carrier gas system, and successfully used in the Swiss Neuch "on the Tel program.
             In Switzerland saiod, Colombier area of the the Union itself is a waste incineration plant, accept the province seven sewage treatment plant sludge, the solid content of cake rate ranged from 18% to 30%, the trucks of sludge scene time change is bigger, it is difficult to ensure uniform mixing, so that the wet mud solid containing rate changed greatly. After drying, use is made of cement, thus requiring solid containing rate about 92%.
              This project is characterized in terms of energy, provide only waste steam from the United incinerator.
              Steam circuit was originally designed to meet the requirements of customers in order to achieve the so-called "absolute security" and the development.
             And requires all process temperature, then we must all and not part of the use of waste heat steam for the entire process provides a source of heat. This means 4.5 bar of waste heat steam must be able to meet      our requirements, the drying system is a more severe test. As the direct heating mode is not the introduction of steam to the system, the requirements of process temperature 4-4.5 simply can not from the steam, and indirect heating heat if the temperature is low, only rely on the condensation of steam in the release of heat, but inappropriate heat, surface area (sludge particles to obtain the actual heat transfer surface) will also greatly reduce its efficiency.
              Taking into account the above two major technical problems, vomm design a new process:
              In the whole circuit, the steam is used as the medium to circulate and cancel the washing of the air, thus saving some heat, which is the main reason for the lower energy consumption;
              Only condensation evaporation, reduce the amount of cooling water;
             To provide optimal conditions, in order to improve the unit time of granular sludge heat transfer surface area, enhance the efficiency of heat conduction; because the steam on the surface of particles with good overheating protection function, so you can more full play to the advantages of heat conduction in the conduction of heat rate;
              It is a environment without oxygen, so it is safer.
          This system uses two production lines, per hour total handling capacity for 4200 kg of wet mud, evaporation capacity 3080 liters, sludge processing capacity 88 - 110 tons. Energy consumption per hour less than 700 kcal / evaporation.
          6. Conclusion
             Turbine thin sludge dry process is currently one of the few very successful sludge treatment scheme of, until now, in Europe and has been installed more than 90 sets, all in the production and operation, no safety accident record. The largest municipal sludge project for the day treatment capacity of 600 tons. Mainly installed in France, Spain and Italy and market share are in more than 50%.
             Turbine thin-layer drying process is very few in the energy, temperature, logistics is more relaxed in the scheme of. All kinds of fuel, waste heat, all kinds of sludge, regardless of its nature, can find the best use and ways to deal with.
             In terms of energy consumption, regardless of heat or kinetic energy, are in the lower limit of the European sludge drying, these figures have a convincing process theory and the actual performance can be proved.
           
           
           
           
           
              
           
           

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          真人做人爱试看一

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