How to deal with sticky walls during spray drying

Spray drying is a widely used process in liquid forming and drying industry It is suitable for producing powdery, granular or bulk solid products from solution, emulsion, suspension emulsion and pump paste liquid raw materials Zui Therefore, spray drying is an ideal process when the particle size distribution, residual moisture content, bulk density and new particle size of the finished product must conform to the Jing standard With this drying method, the gas-solid two phase contact surface of the spray dryer is large, and the drying time is short It is generally 5 to 30s, and is suitable for drying heat sensitive materials The dried product has good performance, can obtain 30-50 mm particles, and has good fluidity and instant solubility The disadvantages of the dryer are its large volume, low heat transfer coefficient, low thermal efficiency and large power consumption There are many classifications of spray dryer According to gas liquid flow, they can be divided into parallel flow, counterflow and mixed flow According to the installation of nebulizer, they can be divided into upper and lower ones According to the structure of atomizer, they can be divided into centrifugal type, pressure type and airflow type According to whether the heating gas can circulate, it can be divided into open type, partial circulation type and closed type Sticking phenomenon is a serious problem that hinders the normal operation of spray dryer The spray drying process of solid preparations (especially Chinese Medicine) is particularly obvious Material sticking to the wall is not only not conducive to operation and collection, but also with the extension of time, sensitive sticking materials will deteriorate into unqualified materials From the point of view of technology, the solutions include choosing suitable solvents, adding auxiliary materials and changing process parameters However, there is not much room for these methods to be adjusted Therefore, it is necessary to seek fundamental solutions from the perspective of equipment Researchers have studied the problems of wall sticking and caking in the drying process, and think that the main reason of wall sticking is the wall temperature The spray drying machine adheres the wall generally in three situations: 1 Semi wet material adheres the wall: the reason is that the droplets sprayed out have contacted with the wall before reaching the surface dry, and therefore stick to the wall The position of the sticky wall is generally on the plane of the droplet trajectory on the atomizer, and the structure of the atomizer, the hot wind is related to the movement state of the tower 2 Hot melt wall adhesion of low melting point materials: the reason is that the materials begin to melt at a certain temperature and become sticky and adhere to the wall 3 Surface adhesion of dry powder: the movement of dry powder in a limited space will always touch the wall of the device, which can not be avoided, but such wall adhesion is generally not thick, as long as it can be shaken down by air blowing or gently tapping, Zui's simple solution is to polish the inner wall, which can solve this problem to a certain extent The common methods to prevent wall sticking are as follows: 1 The wall temperature of the tower is kept below 50 ℃ by using the wall drying tower with air cooling; 2 The secondary air is introduced into the wall of the tower through the tangential direction of the rotating air sheet of the tower wall to cool the tower wall; 3 An air broom composed of a row of nozzles is installed near the wall of the tower, and it is rotated slowly along the tower wall 4 Add air hammer to the tower wall, and force the wall sticking materials to separate through the impact of air hammer; 5 Increase the processing accuracy of the equipment, and polish the inner wall of the tower can also reduce the wall sticking