Complementary Method Improves Drying Efficiency of Aqueous Paste Material

In the fermentation process of medicines and foods, intermediate products or by-products of various states are often produced. Among them, a considerable part is a paste with a high moisture content. The drying problem of a large number of high-moisture pastes has been plagued with problems. Technical staff. Many pastes are not handled well, the yield is reduced, or they become a pollution hazard to the environment; otherwise the yield can be increased, or it can be recycled to convert it into useful resources.

Existing drying equipment faces many difficulties

The fermentation product generally contains proteins, pectin, sugar, etc., and easily adheres to the steel heating surface of the indirect heating dryer to form a fouling seriously affecting the heat transfer, resulting in the difficulty in maintaining the smooth and stable heat transfer effect of the heated surface for a long period of time in such drying equipment. , It must be stopped and cleaned regularly.

Protein is a heat-sensitive substance. If the drying temperature is too high, the protein will denature. Some ammonia-containing fermentation effluent concen- tration slurries use a curtain belt dryer. The high-temperature hot air blows along the curtain of spray-concentrated slurry. Organic substances are often affected. The hot air is baked and deteriorated, and some of the organics are even heated and carbonized to produce bad odors.

Some high-moisture paste materials can have extremely low efficiency in different types of indirect heating dryers. The drying machine with mechanical stirring and pushing action will push the wet and viscous material out of the drying zone to form a hollow in the mixing and drying zone. In the rake type vacuum dryer, the wet and sticky material will firmly adhere to the rotating shaft to form a rotation. The large wet mass is idling while heating the outer jacket to disengage a certain gap. Both of these extreme conditions almost lose the heat drying effect.

Both drying methods have their own length

Steam heating drying and internal heating fluidized drying are two methods discussed in recent years for paste drying, both of which have advantages and disadvantages.

The fluidized drying granulation technique can dry the Chinese herbal extracts, which have a higher moisture content than the paste, and have higher viscosity and heat sensitivity than the paste, the paste material should be more easily dried. The difference between the two is just how to disperse the specific dried material. The fluidized dry granulation adopts the liquid extract spray dispersion method, and the paste form is from the slurry state, the thin paste state to the semi-solid group, and the slurry or the thin paste can be used to increase the speed of the spirophore to the high speed. The high-center disperser disperses into micro-wet particles, and then it is thrown into the loosely-heated fluidized material together with the pulverized back-mixed dry material. For the semi-solid material, it can be pulverized and back-mixed. The dry material is put into a fluidized material together with a pendulum-type particle machine to make granules.

However, the thermal efficiency of fluidized drying is very low and it is far from being comparable with steam heating (energy saving) dryers (90%). However, the internal heating group is fluidized and dried, the dry material dehydration heat of the wet material is provided by the indirect heating steam of the internal heating group, the fluidization adopts the lowest critical fluidizing air velocity, the fluidization air inlet temperature is equal to the outlet air temperature, and the fluidized air The function is degraded to promote material fluidization, movement and heat transfer. The amount of fluidized air is greatly reduced, which not only saves the power consumption of air pressure, but also reduces the heat loss caused by a large amount of hot air exhaust, and can increase the thermal efficiency to about 75%.

In spite of this, the thermal efficiency of internal heating fluidized drying is still lower than that of indirect steam heating. However, when fluidizing a dry paste, the paste can be continuously and uniformly dispersed into the loose and hot fluidized material containing the back-mixed dry material, and the viscous compound in a steam heating (energy-saving) dryer. Completely different, there will be no batter blobs to stick to the hot surface. It can keep the surface of the inner heating group clean and smooth for a long time, and the stability is in the best state of high-efficiency heat transfer. That is, using the drying method in which the paste is dispersed in the inner heating fluidized bed, the equipment can be operated stably for a long period of time.

There is another significant difference between the two drying methods, namely, the indirect steam heating (energy saving) dryer is basically in the cold condition (at the feed port end) to mix the backmixed dry material with the paste, completely relying on The mixed dry material absorbs and disperses a large amount of moisture in the paste; while in the internal heating fluidized drying bed, besides the need to add the return dry material, the paste is dispersed into fine particles and continuously and evenly added to the already loose and heat. In the fluidized material. The water in the paste-like fine particles is instantly evaporated to remove a part, so this part of the water no longer needs to rely on the back-mixed dry material to absorb and disperse, so the amount of back-mixed dry material can be greatly reduced, and also significantly reduced The amount of material circulating in the fluidized bed in the chamber is very beneficial to improve the equipment efficiency and reduce the equipment size.

The combination of both plays a complementary role

Indirect steam heating dryers have been recognized as having very high thermal efficiency, but the drying pastes of this type of dryers are not adaptable, and a large amount of backmixed dry materials are used to reduce the moisture content and adhesion of feeds, resulting in large dry material turnover. The increase in the amplitude has seriously affected the efficiency of drying equipment. Even with the internal heating type fluidized drying technology, its thermal efficiency is still lower than that of the indirect steam heating dryer, but the fluidized drying method can be used to continuously disperse the paste into small particles into the fluidized material, supplemented with a smaller amount. The backmixed dry material is able to satisfy the moisture content of the paste-like material drying, and completely avoid the unstable operation of the large-scale production equipment such as stoppage of the paste and the like. Thus, the two drying methods are brought together to complement each other's disadvantages and to exert their greatest advantages.

Studies have shown that if you maintain a fluidized material moisture content of 25% (the specific operating moisture content should be determined by testing the specific paste to determine the reasonable moisture content without affecting the fluidized drying and operation of the indirect steam heating dryer), increase the fluidization Drying the amount of dehydration can further reduce the amount of backmixed dry material, and correspondingly reduce the dehydration load of the indirect steam heating dryer. In doing so, it means that the amount of material turnover in the total drying process is reduced, which is conducive to improving the efficiency of the drying equipment. However, due to the reduction in the amount of dehydration by indirect steam heating and drying, this part of the water is transferred from the energy-saving drying equipment to the fluidization with relatively low thermal efficiency. Drying naturally reduces the energy efficiency of the entire process. Therefore, there is much work to be done to choose the best fluidized dry evaporation volume and backmixed dry material volume, involving equipment investment and equipment efficiency.

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