1. Field of the Invention
The present invention relates to removal of deposits from the interior of a tobacco drying apparatus. More particularly, the present invention relates to the removal of tobacco deposits in a high humidity drying apparatus with the use of recirculating heated air.
2. Discussion of the Prior Art
In the manufacture of cigarettes and like articles, it is the usual practice to reduce tobacco, the term being used herein to include both lamina and stems, to a particle size appropriate for manufacturing cigarettes. The moisture content of the tobacco is generally increased prior to this size reduction processing in order to minimize tobacco breakup and provide a material of uniform particle size. Furthermore, in order to process the treated tobacco in the manufacturing of cigarette rods, it is necessary to reduce the moisture content of the tobacco to a level below that which the tobacco is at after treatment by casings, flavorings and other high moisture containing additives. The actual drying process has a direct impact upon the quality of tobacco utilized during cigarette manufacturing because of the effect the drying process has upon the tobacco material itself.
Additionally, drying of tobacco after the addition of flavorings and casings has a direct impact upon the quality of the tobacco. If, during drying, the tobacco is subjected to rigorous agitation or contact with stationary surfaces, the tobacco material can be damaged by breakup thus decreasing the filling capacity of the tobacco. This unwanted result is also achieved when drying under low humidity conditions. It is therefore desirable to dry the moist tobacco under high humidity drying conditions.
The high humidity pneumatically conveying drying apparatus used to dry cut tobacco typically requires cleaning due to the interior buildup of deposits of flavorings and other materials added to the tobacco as well as portions of the tobacco material itself. The buildup of material in the dryer is most prevalent in areas where the direction of the pneumatically conveyed tobacco is changed. These `corners` or `elbows` usually have the highest incidence of material buildup on their interior surfaces and this buildup can cause hygiene problems as well as reduce the smooth flow of material coming into contact with the built up residue.
Previously, to remove the buildup of material in tobacco dryers, whether they be high humidity dryers or typical in-line dryers, the dryer had to be shut down and cleaned out by flushing with a high volume of hot water or other solution at relatively high pressure. Usually, this cleaning process was performed every 15 to 17 drying operations. Thus, this cleaning had the undesirable effect of lengthy down time for the drying apparatus while the dryer was cleaned. Additionally, if a cleaning solution was used, water had to be flushed through the dryer to remove all traces of the cleaning solution so that subsequently dried tobacco would not be contaminated with the cleaning solution. The excessive cleaning time severely impacts the manufacturing of tobacco products. Moreover, liquid cleaning does not contact all interior drier surfaces.
Prior art attempts to clean interior surfaces and passageways of equipment is shown in U.S. Pat. No. 3,888,302 wherein a heat exchanger for coke ovens and interior passageways therefor require general cleaning on a periodic basis. A reactive material, such as anhydrous hydrochloric acid, is introduced into the passageways to produce reaction products which are volatile when removed in a gas stream and thereby discharged. However, the ability to introduce such reactive material into the present system is extremely restricted due to the necessary requirement of completely removing the reactive material prior to further tobacco processing.