The features and inadequacy of double cone vacuum dryer
Source： | Date:
2010-10-10
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1. Overview
Double cone vacuum dryer (hereinafter referred to as double cone) ------ a vacuum indirect heating dynamic dryer experiences a long history and belongs to the energy-saving drying equipment. It is characterized by 3600 rotation of vacuum cone pushed by the driver to mix the materials in cone and heat the materials by contact with cone heating surface. To mix constantly the materials is good for self-cleaning of heating surface. Vacuum operation helps reducing the evaporation pressure and evaporation temperature to improve the temperature difference between the heating medium and heating materials and also helps cryodrying for many thermal sensitive materials. Double cone’s operation in vacuum without the intervention of other inert gas helps drying by evaporation for various Organic solvents materials. The structural shape of double cone helps the speedy discharging for the finished dried materials. This is a good and unique operation virtue compared with any other dryers.
Double cone is suitable for drying inviscid materials. The vacuum pump equipped with exhaust gas filter in the cone largely reduces the loss of exhaust gas carried product dust and improves the yield of dried materials. The efficiency of double dynamic drying is much higher than various tray drying. However, some shortcomings also exist in double cone drying. First, double cone is only applicable to drying. Some foreign material caused by seal components friction can not be avoided as a result of taking friction mechanical vacuum seal components.
Double cone belongs to jacket hating dryer. The expansion of double cone from small diameter to large diameter, its heating area is far less than capacity expansion. If 5m double cone’s F/V value is half approximately smaller than 0.3m double cone---about 3.6m/m, when double cone’s capacity expands to 10m, its F/V value decreases to 2.5m/m.
Double cone vacuum dryer is used as heating drying which is characterized by heating drying efficiency and the size of heat exchange area. Comparatively speaking, its capacity is secondary.
But at present the specification of double cone is based on the capacity size in almost all the product samples of double cone dryer, which misleads the users to some extent.
Many thermal sensitive products with drying temperature below 100 ℃ still adopt the hot water<100℃ as the heat source to dry the materials. For this reason, some auxiliary facilities such as hot water tank, heat pump and hot water pipe must be equipped. Compared with the steam drying, the hot water heating obviously decreased the temperature difference, which is disadvantageous to heating the thermal sensitive materials.
Many dried materials mix and rotate constantly in double cone, so some crystalloid and minuteness products contained high water content such as riboflavin, acetyl spiramycin, etc. in the process of mixing, easily forms the pellet varied in size. Once pellets are formed, the materials are difficult to achieve full and complete drying. In principle, double cone is not used to dry the materials susceptible to forming the pellets.
It is common knowledge that the thermal resistance of stainless steel is 5 times larger than that of carbon steel. Very thick stainless steel inner tank doesn’t help the cone’s thermal transmission, which reduces the drying efficiency. Heavy drive inner tank is accordingly raised the power of drive motor. So is the outer jacket.
Double cone works several thousand hours/year. Therefore, it is worth our while to deeply research and discuss how to correctly treat the efficiency-improving and the energy-saving of the double cone with long time working. We discuss the double cone without the requirement of GMP below.
2. Expansion of double cone
The expansion of double cone vacuum dryer obviously refers to the expansion of the heat exchange dimension. Fortunately, large space in the cone can be available, so it is the key to how to make use of this space. In consideration of the equipment-cleaning, the surface of the heat exchange component is the more simple the better. The selection of thin inner heating panel meets the requirement of surface-finish and compaction. To take 10m double cone as an example, the thin inner heating panel can be set up in the direction of the materials flow of the very large cone space. In the space for maintenance and cleaning, namely, 110-160mm space between the inner heating panels to be reserved to increase the dimension of inner heating panel 1.5-3 times more than the primary heating dimension in an effort to increase the F, V value to 0.2m.
3. To add the inner heating panel helps stainless steel saving
Still taking 10m as an example, double cone of per square meter needs 111.4 kg stainless steel, but the inner heating panel of per square meter needs 24kg stainless steel, namely the stainless steel consumption for heating dimension of double cone of per square meter is 4.6 times more than the heating panel of same heating dimension.
4. Enhancement of the construction of inner heating panel
Articulated and non-destructive welding enhancing technology is taken on the enhancing construction of new double cone inner panel, the holes will not be drilled on the double-faced platter of inner heating panel, which will avoid some drawback hole-drilling brings and settle some real processing puzzles of inner heating panel based on the double cone expansion.
5. Heat source issue of the low temperature(100℃) of double cone
The traditional double cone is to adopt the hot water as the heating method when the thermal sensitive products are to be dried by double cone. The temperature difference of hot water heating is disadvantaged to drying. But if the saturated water vapor is to be taken as the heat source based on the restrict controlling of the temperature of double cone heating jacket and the timely extraction of water of condensation in the jacket, 0.2 MPa saturated water vapor will be taken as low temperature heat source of double cone.
6. Issue of reducing the wall thickness of large double cone
Contemporarily, energy-saving is taken into account. In terms of large furnace, we should take some measures to reduce consumption, conduct some research on stainless steel saving and the drying efficiency improving and make some contribution in the field of drying technology.
7. Conclusion
Our output value and energy consumption proportion of industrial production is much higher than other developed countries regardless of misunderstanding of price based on equipment’s weight. So double cone vacuum dryer is the typical example probably in this regard.
Next: CHINA-PHARM 2010
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