The present invention relates to a method for treating fibrous material prone to degradation by biological activity, particularly cotton bales, and to a plant for executing the method.
For trade and transport purposes, raw cotton is pressed into bales. Presently, the cotton bales are defined to have 8.5% water content inter alia because their price is fixed by weight. However, being a biological material, and supported by this water content, the cotton is prone to rotting, i.e. biological degradation by bacteria, fungi etc.
U.S. Pat. No. 6,557,267 (Wanger; filed on 27 Apr. 2001) which is hereby incorporated by reference, describes a method for suppressing or at least retarding the rotting process of cotton bales. The bales are repeatedly subjected alternatingly to vacuum and “water gas”, i.e. essentially steam (“Steaming”). Thereby, the steam penetrates deeply into the bales driven by the pressure difference between bale core and the outside of the bale. Usually, the steam has a temperature of about 80° C. (“steaming temperature”) and is applied with a pressure equal to the vapour pressure of water at the steaming temperature which is about 0.5 Bar.
The process is conducted in a manner that even the core of the bales reaches a temperature of about 80° C. At this temperature, most active microbes are destroyed or deactivated. However, e.g. spores of fungi survive, and accordingly, growth of fungi will occur again some time later, e.g. after 1 to 2 months.
Similar rotting or degradation effects are observed with yarns and textile materials consisting at least partly of fibrous material susceptible to such degradation. In particular, yarns are traded with a water content of 8.5%, too, which promotes biological activity.
It is an object of the present invention to propose a method providing an ameliorated protection of fibrous material, particularly of cotton bales, prone to degradation by biological activity, more particularly by the activity of microbes including fungi.
Accordingly, the microbes including their spores are more efficiently and substantially destroyed or inactivated by ozone penetrating the fibrous material, or more precisely by a gas having an effective concentration of ozone. Particularly, the material may be bales of (raw) cotton.
Within the whole specification including the claims, by the word “microbes”, any kind of microscopic organisms are meant, like bacteria and fungi, either in its active form or spores. By spores, the durable forms of bacteria and fungi are meant.
Percentages are given by weight if not otherwise indicated.
Preferably, the treatment by ozone, the so-called ozonisation, is performed after a steam treatment, e.g. according to U.S. Pat. No. 6,557,267.
According to claim 14, a plant for executing the method comprises a vessel for receiving the fibrous material, a venting or vacuum pump, and an ozone generator. Generally, for practical reasons, ozone destroying means and air purging means are needed in order to establish acceptable working conditions by purging the atmosphere in the vessel. The latter means are needed for complying with requirements of working conditions and environmental protection.
As mentioned above, in a preferred embodiment, a plant according to the invention additionally comprises the equipment needed for the steam treatment.
The invention will now be further described by means of an non-limiting exemplary embodiment with reference to the drawing.
Structure
The plant 1 for performing the method is arranged around a vessel 3 which is filled by the material to be treated. The material may be bales of raw cotton, but also uncolored cotton yarn bobbins, cotton textile pieces, webs, felts, fleeces or the like. Instead of pure cotton fibrous materials, other natural fibrous materials like ramie, sisal, jute, flax, wool, silk, either as pure material or in combination with cotton may be considered, too, which are susceptible to biological degradation. As a rule, these materials are of biological origin.
The vessel 3 is connected to an ozone reservoir 5, a purging gas conduit 7, a vacuum pump 9, and a steam generator 11 via respectively an ozone supply valve 14, a purging valve 16, a vacuum valve 18, and a steam valve 20.
The vessel 3 and the ozone reservoir 5 are connected via respective exhaust valves 22, 23 to the exhaust line 25. The exhaust line 25 is provided with a vent ozone destructor (VOD) unit 27 and a sensor 28 for determining the ozone concentration in the exhaust line 25. The vent ozone destructor unit 27 reduces the ozone concentration to a degree that the exhaust gas may be discharged into the environment.
The exhaust valve 23 of the ozone reservoir 5 allows to dispose ozone in case of overpressure or to exchange its contents entirely after a working interruption or for long non-using periods.
The ozone reservoir 5 is supplied with ozone via an ozone generator valve 30 by the ozone generator 32. The ozone generator 32 is of a known type, e.g. one using a dielectric barrier discharge. The ozone generator 32 is supplied with the purging gas as the working gas. The gas is furnished by a gas supply 34.
As an alternative, the ozone generator 32 may have its own gas source, e.g. pure oxygen for producing a gas stream of elevated ozone concentration to the reservoir 5. The purging gas may be air which is purified in order to avoid a secondary contamination with microorganisms of the treated material during the purging step. If the gas source 34 serves the ozone generator 32, the gas needs to comply additionally with the requirements of the latter, i.e. it has to have a dew point of e.g. −60° C. at most and must be free of dust and hydrocarbons. For instance, with pure oxygen, an ozone concentration of up to about 14% can be reached, whereas with air, at most about 4.5% of ozone are feasible with ozone generators of the dielectric barrier discharge type.
In order to keep the ozone reservoir 5 small, it is filled with ozone containing gas under elevated pressure. Hence, the ozone generator is of a type furnishing ozone containing gas of at least 1 Bar overpressure.
Operation
The material to be treated, e.g. cotton bales, is stored in the vessel 3 and the vessel 3 is closed.
In the second phase, one to five cycles of steaming during time 42 are performed. First, the steaming valve 20 is opened for flooding the vessel 3 with steam. After about 2 minutes, the steam valve 20 is closed and the vacuum valve 18 is opened to reduce the pressure again to about 200 mBar within about 2 minutes. During the steaming periods 43, the pressure in the vessel is about 500 mBar, and the temperature is about 80° C. As mentioned above, the pressure is determined by the vapor pressure of water at the selected steaming temperature, e.g. 80° C. Still to be noted that the temperature in the core of the bales of cotton, particularly if compacted as is usually the case, reaches about 80° C. in the last steaming period 43 only.
In other terms, the steaming cycles are repeated as often, and the ratio of steaming duration and withdrawal of steam by vacuum is chosen the way that at least during the last period, the so-called core temperature of the units of treated material (e.g. cotton bales) reaches the steaming temperature.
Still to be observed that the temperature in the vessel decreases to about 60° C. at the end 44 of each underpressure period. This temperature is, however, arbitrary and merely occasioned by the thermal characteristics of the system (insulation, time needed for establishing the reduced pressure, evaporation etc.).
The fifth steaming period is followed by the ozonization phase 45 which takes about 5 minutes and during which the pressure in the vessel attains ambient pressure (1 Bar). The vessel is filled with ozone containing gas from the ozone reservoir 5 by opening the ozone supply valve 14. As ozone generators in reasonable size are not capable of furnishing the needed volumes of ozone in only a few minutes with reasonable efforts, the time between the ozonization phases is used for filling the ozone reservoir 5 using an ozone generator of lower output rate.
As the pressure in the vessel 3 is still about 500 mBar or less, the ozone is drawn into the material. Furthermore, as long as there is free ozone available it remains active in the inner parts of the material and continues to deactivate microorganisms and spores etc., particularly also during the following phases.
After the ozonization phase 45, the vessel 3 is purged by opening the purge valve 16. The purging process, normally with purified air or oxygen furnished by the gas source 34, is maintained until the ozone sensor 28 indicates that the vessel may be opened without danger.
The purge gas valve 16 is closed and the vessel 3 is opened. The material is removed and wrapped in an about microorganism-tight packaging, e.g. a foil. The packaging retains the ozone containing atmosphere in the material. Formerly, the material have already been packed in a sealed package in order to maintain the water content of 8.5%, hence often the conventional packaging step may be sufficient, possibly slightly modified to ameliorate microorganism-tightness.
As the ozone has a sterilizing and anti-microbial effect as well within the material, the long-term danger is merely re-contamination from the environment. However, besides the packaging, the periphery of the material itself has a filtering effect and impedes penetration and secondary contamination by microorganisms and spores. Particularly, the feared rotting in the core of the material (e.g. cotton bales) which is almost invisible from the outside is effectively suppressed.
After the m ozonization cycles, the procedure as described above with reference to
From the above said, further variants are conceivable to the one skilled in the art, like alternatingly steaming and ozonising several times. However, the last step is an ozonization step so that the advantage of the effect of ozone remaining within the wrapped material, e.g. cotton bales is maintained.
Still to mention that the ozone may also have a bleaching effect which may be an additional advantage at least in the case of treating cotton bales.
Another aspect is that ozone even kills higher organisms like insects. Particularly in border-crossing trading, a special and often environmentally critical treatment like fumigation with e.g. methylbromide, cyanic acid or other biocides may be avoided.
From the examples set forth above, the one skilled in the art is able to derive numerous variants and alterations without leaving the scope of protection of the invention which is defined by the claims, for example:
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/CH04/00558 | 9/6/2004 | WO | 3/5/2007 |