Multistage Centrifugal Spray Dryer Applicable Forms and Significance of Spray Drying
Spray drying has the special advantages of powdered products which can be directly obtained from the solution or suspension system, and is currently widely used in the chemical, light industry, food and other industries. The chemical industry is most commonly used in the dye industry. Through the efforts of engineers and technicians in recent years, spray drying technology has become more mature, and the determination of tower size has also been successfully calculated. The atomizers used are still three types: pressure type, centrifugal type, and air flow type. However, the application of centrifugal centrifugal spray dryers has been on the rise in recent years. For true solution spray drying, it is worth noting that different hydrophilic solute requires different drying medium temperatures. Such as inorganic salts strong hydrophilic substances, the evaporation of its aqueous solution is mainly carried out in the boiling point of the solution, the gas temperature of the tower is less than 130 °C difficult to operate. Although there is a significant gap between China and foreign countries, the level of manufacturing and operation of spray drying equipment has also been greatly improved.
When multi-stage centrifugal spray dryers are used in single-form dryers to dry materials, they often fail to meet the quality requirements of the final product. Therefore, two or more types of dryers must be combined in series to achieve the final product quality requirements. . Although it is a single form of centrifugal spray dryer, but in the product because of the integration of several types of products, in the finished product than a single improvement in color and taste, such as the series of food industry production of milk powder, coconut powder, Coffee and so on.
The spray drying process is completely dependent on the product of the composition. Some are very easy and others are very difficult to dry. In this regard, it should be pointed out that to ensure the longest possible operating time, it is necessary to stop cleaning the plants before. Centrifugal spray dryer has good uniformity, fluidity and solubility, high product purity and good quality. The production process is simplified and the operation and control are convenient. Although the process is simple, there are also some problems in energy consumption and efficiency in the work process. This has always been an anxious issue for manufacturers. How to reduce energy consumption and reduce costs is particularly important in the industry competition.
The energy consumption in the spray drying process directly affects the economic benefits and development prospects of the company. We know that centrifugal spray dryers have different reactions to different materials, such as 40-60% moisture content (up to 90% for special materials). The liquid can be dried into a powdered product at a time and dried without crushing and screening. However, for products with high moisture content or relatively high fat content, we should first process the materials and then dry them. This will greatly assist the maintenance of the centrifugal spray dryer and the improvement of production results. Reduced excessive energy consumption. At the same time, we can further improve the energy-saving effect of spray drying equipment and reduce costs through the improvement of drying media and thermal cycling.
The pressure spray dryer is operated for a long time or due to improper operation. It always occurs in some equipment and affects normal operation. At this point, it is necessary to stop the work and perform cleaning. For the drying tower cleaning summary cleaning work should open the door, use a long broom to sweep the bottom of the funnel-shaped aggregate, open the valve, rinse the column with tap water. Cyclone dust remover also needs to open the cyclone separator, gather with the broom, and also need to rinse with clean water when necessary. For bag filter cleaning, open the control switch, beat it continuously, clean it again, beat the bag filter, and finally replace the filter bag. For the cleaning of the slurry piping system, the bidirectional filter should open the drain valve, clean the filter filter and piping, then open the material pump, water and raw materials, clean the pump tube, supervise the bag and pipe.
After a period of time, we need to carry out the necessary inspection and maintenance of the granulation centrifugal spray dryer. Feed system, filters should be checked, pipes, valves, nozzles, etc. to see if there is no clogging, regular cleaning, check the nozzle wear conditions in order to replace. The feed pump should check for leaks, normal pressure, normal oil level, etc. The oil should be checked for hot shafts and bearings, presence or absence of vibration, noise, etc. Clean the blades and balance the blades if necessary. For the heater, check whether the heat pipe is normal, if necessary, clean the oil pipe, pump, and three filter chokes. In addition, it should also take the notes of non-heating motors, vibrations, different sounds, etc., and whether the control cabinet's meters and appliances work properly.
For different needs, centrifugal spray dryers also have many classification methods, such as the gas-liquid flow divided by parallel flow (forward flow type), counter-current flow and mixed flow type; according to the atomizer installation method divided into upper spray type , spray under the type; according to the system has an open type, part of the cycle and closed and so on. As we all know, spray-drying mist splitter has a variety of, but according to its atomization basis, the atomizer is divided into centrifugal, pressure and air flow three. Traditionally, people classify centrifugal spray dryers by atomization, that is, by the structure of the atomizer. The spray drying is divided into three types: rotary disk type (centrifugal type), pressure type (mechanical type), and air flow type. The use of a large number of centrifugal spray dryers is a matter of nearly two decades. The earliest industrialization in China should be an air-flow centrifugal spray dryer. However, with the successful development of centrifugal and pressure centrifugal spray dryers, the shortcomings of high energy consumption of the air flow centrifugal spray dryer are revealed (the atomizer consumes 4 to 8 times the energy of the other two).
Centrifugal spray dryers are drying devices that process solutions, suspensions, or slurries. It is a method of spraying, so that the material is dispersed in the hot air droplets, the material and hot air flow in the cocurrent, countercurrent or mixed flow contact each other, so that the rapid evaporation of water, to achieve the purpose of drying. With this drying method, the unit operation such as concentration, filtration, and crushing can be omitted, and a granular product of 30 to 500 μm can be obtained. The drying time is very short, the general drying time is 5 ~ 30s. It is suitable for the drying of materials that are easy to disperse in the process of concentration of highly heat-sensitive materials and liquids. The product has good flowability and fast dissolvability.
The gas-solid two-phase contact surface area in the centrifugal spray dryer is large, but the gas-solid two phases are in dilute phase flow, so the volumetric heat transfer coefficient is small, generally 20 to 100 kcal/m3?h?°C, and the hot air inlet temperature is in the concurrent operation. The time is 260~500°C, and the countercurrent operation is 200~300°C. Industrial-scale centrifugal spray dryers typically have a thermal efficiency of 30 to 50%. In foreign countries, spray drying with waste heat recovery can achieve a thermal efficiency of 70%. However, this equipment has economic significance only when its production capacity is greater than 100kg (water)/h.
The basic flow of spray drying for Changzhou Lima Drying Engineering Co., Ltd. is as follows. The feed liquid passes through the atomizer and is sprayed into droplets and dispersed in the hot air flow. Air is blown into the air heater through a blower and heated, and then enters a centrifugal spray dryer where it contacts the droplets for drying. Part of the product falls into the bottom of the tower, and part of it is sucked by a first-level induced draft fan into a cyclone separator. After separation, the exhaust gas is vented. The products at the bottom of the tower and the products collected by the cyclone separator are extracted from the secondary air extractor and separated by a secondary cyclone separator.
The spray-dried products are fine particles. In order to meet the requirements of environmental protection, the spray drying system only uses a cyclone separator to separate the product and purify the exhaust gas. It is still not enough, and it is usually cleaned by a bag filter. If the dust content in the exhaust gas is less than 50mg/Nm3, or if a wet scrubber is used, the dust content of the exhaust gas can be reduced to 15~35mg/Nm3.
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