Tobacco – Tobacco treatment – With fluid or fluent material
Patent
1989-11-13
1991-01-15
Millin, V.
Tobacco
Tobacco treatment
With fluid or fluent material
131302, 131303, 34 92, A24B 304
Patent
active
049845870
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a rotary cylinder dryer for drying tobacco under high humidity conditions and in particular relates to a tobacco drying process in which due regard is given to the gain of filling power which is achieved when the tobacco is dried in a steam atmosphere.
The dryer of the present invention is intended for use with all forms of tobacco leaf but more particularly for the separated midrib in the finely cut or rolled and cut form. The latter is known as cut rolled stem (C.R.S.).
2. Statement of Prior Art
A rotary cylinder dryer of the single cylinder type is described in our UK Patent No. 1,209,929 and the double cylinder type (annular dryer) is described in our UK Patent No. 1,345,373. The cylinder of both these types are heated by steam or high pressure hot water. Rotary cylinder dryers are also known which are heated by other means such as a direct flame or a hot gas.
These dryers are of the type where the heated cylindrical shell provides the majority of the heat for drying by conduction or radiation from the shell to the tobacco and the ventilation air through the cylinder removes the moisture. The air flow is limited from 0.3 to 0.6 m/s to avoid making the tobacco airborne and so the air can only contribute a minority of the drying heat, but very often provides none.
Filling power is the specific volume or inverse of bulk density measured under defined conditions. Typically a 50 g sample, which has been brought to a standard moisture content and temperature, is placed in a 60 mm dia vertical cylinder and subjected to a free falling piston load of 3 kg for 30 seconds before measuring the height of the tobacco and calculating the filling power.
The filling power is usually expressed as cc/gm or ml/g. The filling power gain of a process is the percentage increase in the filling value from before to after the process.
It has been established that drying tobacco in a high humidity atmosphere results in a filling power gain. This has been shown for air duct type dryers such as described in UK Patent application No. 2004999A in which the heat for drying is entirely supplied by the air which carries off the vapor. The circulating air has a wet bulb temperature of at least 65 degrees C. and a dry bulb temperature up to 343 degrees C.
The humidity may be further increased until the wet bulb is 100 degrees C. i.e. the saturation temperature for steam at atmospheric pressure, as described in UK Patent application No. 2 149 897A, in which case dry bulb temperatures of 343 degrees C. to 510 degrees C. are used, i.e. the steam is superheated to provide the heat for drying the tobacco.
Similarly it is established practice to raise the humidity of the ventilating air in a rotary dryer in order to increase the filling power of the tobacco, but this has up to now been confined to modest increases in humidity and the retention of air as a ventilating means.
For tobacco to dry, the vapor pressure at the surface of the tobacco must exceed the vapor pressure in the surrounding atmosphere. If the water in the tobacco was `free` water then the water on the tobacco would start to evaporate when its temperature equalled the saturation temperature of the surrounding atmosphere which is related to the humidity. In fact tobacco is hygroscopic and most of the water is `bound` water so evaporation does not start until the tobacco exceeds the saturation temperature. Bound water is described in "Elements of Chemical Engineering" by Badger and McCabe, second edition, published by McGraw-Hill.
There is thus a warm up period at the start of a drying process when the tobacco is being heated and the vapor pressure within the tobacco is increasing without any loss of moisture. In fact if the atmosphere is saturated there will be condensation on the tobacco and an increase in moisture during this period. It appears that the increase in filling power with high humidity drying is due to the enhanced vapor pressure of the moisture within the cellular structure of the tob
REFERENCES:
patent: 3906961 (1975-09-01), Rowell et al.
patent: 4471790 (1984-09-01), Davis et al.
patent: 4615125 (1986-10-01), Wyborn
patent: 4898189 (1990-02-01), Wochnowski
GBE International plc
Millin V.
Wray James C.
LandOfFree
Rotary cylinder dryer and method of drying tobacco products does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Rotary cylinder dryer and method of drying tobacco products, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Rotary cylinder dryer and method of drying tobacco products will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-49444