Sludge is the product of sewage treatment. The main characteristics of sludge are high water content (up to 99%), high content of organic matter, easy to stink and smelly, which requires sludge drying treatment, the current sludge treatment process In the sludge treatment, the proportion of the proportion of dry treatment is still the first place. Xiaobian today summarized some of the sludge drying technology solutions for your reference. 1, What does the product temperature in the drying process mean? Sludge is a kind of ultra-fine powder with high organic matter content. The purpose of sludge drying is firstly reduction and hygiene. Regardless of the final disposal method, sludge drying itself does not change the nature of the sludge, that is, temperature does not cause degradation or quality problems in the sludge product. In view of this, no matter from the quality of sludge products, or dryer efficiency point of view, the higher the temperature should be better. However, due to safety concerns, most of the drying processes tend to minimize the temperature of the product, ie reduce the ignition energy of so-called dust explosions. However, according to the study, sludge dust ignition energy is very low, when the oxygen, dust concentration reaches a certain amount, about 100 degrees temperature, the ignition energy as low as a few to a dozen millijoules. When the ignition energy reaches 1 joule, 70-80 degrees is enough to form a combustion. When the dust concentration is higher, there may be a risk even in the 20-30 degree environment. Many silos spontaneous combustion and explosion are the case. Drying process in order to ensure a certain efficiency of treatment, the temperature is inevitable, but not very low, the typical value of 105-125 degrees. The safety of the process can only start with reducing the dust concentration and suppressing the burning atmosphere. Simply relying on lower product temperature to ensure safety is not the right idea. 2, why dry sludge composition analysis? According to experience, the sludge composition to do some analysis, to determine the drying process, to obtain the best design parameters, confirm the working conditions are necessary. Drying process associated with wet mud testing include: moisture content, viscosity, fat content, acid-base corrosion, sediment rate and so on. Dried mud tests related to the final sludge disposal include: heavy metal content, organic matter content, calorific value, bacteria content and so on. 3, why sludge drying is the first step in resource utilization? Sludge whether from industry or municipalities, the treatment of a viable goal is to make all the pollutants from the industry as raw materials back to the process. All of the pollutants are in fact the raw materials lost in the intermediate process. As a result, most of the lost media are water, removing water, which will allow a large number of potential pollutants to be re-used. The pollutants contained in sludge generally have very high calorific value, but due to the presence of a large amount of water, this part of calorific value can not be utilized. If you incinerate a sludge with high moisture content, you will not only get no heating value but also need to replenish it with a large amount of fuel to complete the combustion. Burning is possible if the moisture content of the sludge is reduced to a certain extent, and the heat generated by the combustion can meet the needs of partial or even complete drying. The same token, regardless of the manufacture of building materials or the use of illustrations, to reduce water content is the key. Therefore, it can be said that sludge drying or semi-drying is actually the first step in resource utilization of sludge. 4, the cyclone solid recovery rate is how much? In many heat convection systems, sludge drying must collect all or part of the product by means of cyclone separation. Due to the different amounts of air and air pressure in each process, the particle sizes and proportions recovered by this method are different, causing their design Vary widely. In general, the cyclone solids recovery is between 95-98%. The higher the solid content, the smaller the particle size of the product, the more difficult the capture will be. 5, drying which includes the necessary process steps? The purpose of sludge drying is to remove part of the wet mud in the water to meet the different disposal requirements. Drying means that in a unit of time a certain amount of heat will be passed to the moisture contained in the material, the moisture vaporized by the heat, separated from the material, lost moisture material and vaporized moisture were collected, which is Drying process. Describe the process from the equipment perspective, including feeding, drying, gas-solid separation, dust capture, moisture condensation, solid transport and storage. If the properties of the material (viscosity, moisture content, etc.) may cause instability of the drying process (eg sticking, agglomeration, etc.) then it is necessary to use a process where the partially dried product mixes with the wet material (return, Dry mud backmix). At this point, before feeding and after the solid transport should be increased transportation, storage, separation, crushing, screening, upgrading, mixing, feeding and other equipment. 6, Why should distinguish between indirect drying or direct heating method? The division of direct and indirect heating methods is the difference in the form of utilization of heat sources, in particular directly as a medium or indirect heating medium. Drying is done by the heat, the heat is generally generated by energy combustion. The heat generated by combustion is present in the flue gas. There are two types of heat utilization: (1) direct use: the high temperature flue gas directly into the dryer, through the contact of gas and wet materials, convection heat transfer. This practice is characterized by the high efficiency of heat utilization, but also emissions problems if the materials being dried have pollutant properties, since the entry of hot flue gases is continuous and therefore also results in an equal flow rate of Exhaust gases that have been in direct contact with the material must be discharged after special handling. (2) indirect use: the heat of flue gas through the heat exchanger, passed to a medium, these media may be HTF, steam or air. The medium circulates in a closed loop without contact with the material being dried. Flue gas after partial utilization of heat is normally discharged. Indirect use there is a certain heat loss. For the drying process, direct or indirect heating with different thermal efficiency losses, but also have different environmental impacts, is an important part of the project EIA and economic inspection.
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