Contacts in the choice of adsorbent adsorption drying
   Select the contact with the adsorbent adsorption drying , you should consider the following aspects
   ( 1 ) Dry the product type and end-use ;
   ( 2 ) the adsorbent material to be dried and the physical and biological affinity ;
   ( 3 ) adsorbent properties ;
   ( 4 ) the commercial availability of the adsorbent and economic considerations ;
   ( 5 ) implementation, the possibility of downstream processes .
    Dry product type and end use is to select one of adsorbent major label push . Contact with an inert adsorbent for adsorption drying , also need to consider whether the product mix trace adsorbent can be received. From another perspective , the product remains in contact adsorbent adsorbent may become dry and additional features, such as the use of natural zeolite , dry cereals for animal feed . With the main features of active adsorbent adsorbent to become an integral part of the final product . Therefore, not only does not affect the product adsorbent purposes. And once able to improve its quality and prolong shelf life or expand its scope of application . For example , some of the dried product ( living house , antibiotics, protein concentrate , etc. ) are used as animal feed additives , it is not only easy to digest animal and to improve the flavor of the final product .
    Adsorbent material to be dried in a physical or biochemical affinity adsorbent is no negative impact on product quality . For example , although a high adsorption capacity of activated carbon , but not for the dehydration of bacterial biomass , as it will kill microorganisms. Does not recommend the use of wheat flour or corn flour , as these adsorbents are lactobacillus and other microbial growth medium .
    Adsorption isotherm characteristics including , adsorption kinetics , adsorption drying efficiency of its contact with the dryer 's choice has a direct impact . Adsorbent to adsorb the moisture from the material generally go through three processes , namely ① adsorbate gas film from the fluid passing through the body to the adsorbent surface ( external diffusion ); ② adsorbate within the pores through the material from the surface to an internal ( internal diffusion ) ; ③ adsorbate is adsorbed to the inner surface. Mass transfer rate depends mainly on internal diffusion and external diffusion , according to the material type and operating conditions, a diffusion of its towel takes control .
    Obviously, for use in the operating humidity range flat adsorption capacity of the adsorbent is the best option , unless other selection criteria are more important. For example , the steam down the process, such as freezing and vacuum drying , the zeolite should be used . Teach or ground wheat rapeseed recommended for spray drying or fluidized bed drying , because of their environmental relative humidity of 80 % to 90 % and has a high adsorption capacity. In the matter subjects - adsorbent system reached equilibrium state, by mass balance can be calculated by removing the wet branch requires a certain quality of the amount of sorbent .
    Commercially, the availability and price of the adsorbent has a practical importance , particularly in the case of high production plant. Contact adsorption drying also need to consider whether the practice, the downstream operations , such as screening, adsorbent sterilization, broken agglomerates , irresolute gas purification , packaging , transportation and storage of the final product . Using active adsorbent , because all the components in the product before or during drying has become the integral . No similar homogenizing and mixing operations. The upstream operations. Such as crushing, screening and sterilization, it is important to keep the adsorbent during the sterilization Physical and Mechanical Characteristics . For example, flour and bran hot air sterilization, spontaneous combustion may occur relative to explode. For most agricultural and food products , direct sterilization with superheated steam is not desirable, because this will change the absorbent structure, reducing the absorption capability. Thus , suitable adsorbent for such direct heating sterilization method , in appropriate cases can also be used cold sterilization or gamma irradiation , and add antibiotics.