Cleaning and liquid contact with solids – Processes – Hollow work – internal surface treatment
Reexamination Certificate
1995-11-16
2001-03-20
Scheiner, Laurie (Department: 1641)
Cleaning and liquid contact with solids
Processes
Hollow work, internal surface treatment
C134S022100, C134S010000, C134S022120
Reexamination Certificate
active
06202654
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for cleaning a container and conduits associated with said container by adding a cleaning solvent to the container and circulating said solvent through said conduits back to said container. The container may be a reaction vessel for chemical processes.
The invention also relates to an apparatus for use in the above method, and a filter unit forming part of such an apparatus.
BACKGROUND TO THE INVENTION
Reactors, i.e. large vessels for chemical processes often performed under elevated temperatures and elevated pressures, have to be cleaned periodically during use or after use to remove any contaminants or other matter disturbing the chemical process carried out in the reactor or influencing the yield. The cleaning is particularly important when the reactor is to be used for another process. Said cleaning is normally made in different steps, such as a first rough cleaning of the reactor by means of high pressure liquid jet cleaning, if necessary complemented by mechanical cleaning, followed by solvent cleaning in which a suitable solvent (chosen in dependence of the contaminants to be removed) is circulated through the vessel and through the conduits and manifolds connected thereto. One typical solvent is for instance ethanol.
In one commonly used method, which for instance may be termed “forced circulation”, the solvent simply is pumped through the system in such a way that the liquid comes into contact with all contaminated parts of the system. After some time the solvent will be contaminated to a degree entailing that a continued circulation of the solvent will just re-contaminate the reactor system and the solvent consequently must be replaced by new, pure solvent.
In another commonly used method the solvent may be added to the reactor and brought to the boiling point, the solvent thus at least partly being vaporized. The vaporized solvent is led to a cooler in which it is condensed, preferably in the cooler normally being associated with the reactor, and the condensed solvent is allowed to flow in a direction which is opposite to the normal direction of flow in the reactor system and the conduits associated therewith in order to dissolve and remove any contaminants. This procedure is sometimes termed “reflux” and will be so called in the discussions below.
Since the contaminants also may be volatile, at least to some extent, the amount of contaminant following the vaporized solvent back into the reactor system, and to some extent re-contaminating the reactor system, will increase in proportion to the increase of the contaminants in the solvent. At a certain point, the cleaning recontamination will reach an equilibrium and the contaminated solvent consequently will have to be drawn off and replaced with new, pure solvent.
These above solvent-cleaning procedures are repeated until the required degree of decontamination has been obtained. The degree of decontamination necessary for pharmaceutical purposes may for instance be ascertained by UV spectral analysis within a specific wave-length range for a specific solvent, by filter tests and by visual control of the cleaning solvent, the amount of contaminants in the circulating solvent indicating the degree of remaining contamination of the reactor system.
These processes are however very time-consuming and very wasteful in regard of the cleaning solvent, since the solvent has to be replaced several times before the solvent has reached a purity level indicating that the rector and the manifold associated therewith has a degree of cleanness which is sufficient for the purposes of the chemical processes to be carried out in the reactor system. It is of course also difficult and expensive to recycle or otherwise take care of such large amounts of contaminated solvent, not least from an environmental view. The additional costs arising as a consequence of the long delay before the reactor system can be used again are high.
DE 3918285-A1 Elastogran Polyurethane GmbH) discloses a process and apparatus for rinsing or cleaning of mixing apparatuses for multi-component plastics, especially polyurethane. The rinsing agent can be fed back into the rinsing agent cycle after it has been cleaned in a filter. The rinsing agent is simply drained off into a collecting vessel, and recycled manually as required.
U.S. Pat. No. 2312091 (Gray/Gray Company, Inc.) discloses an apparatus for cleaning automobile engines. Solvent is circulated internally throughout the engine, where it collects varnish, sludge, gum deposits, carbon dirt and the like. After the engine is stopped again, the dirt-laden solvent is pumped out and gravitationally filters through one or more filter units, which clean the solvent. The cleaned solvent collects in a reservoir, and is again recycled manually as required.
Both of these documents are concerned with cleaning apparatuses in which the solvent is cleaned after the cleaning process has occurred. Thus, if cleaning is to be continued, considerable delay is caused by:
stopping the cleaning process,
draining off the solvent,
filtering it,
feeding it back into the reactor system, and
starting the cleaning process again.
Elsewhere, for example in U.S. Pat. No. 1635115 (Deutsch et aL /Deutsch), cleaning systems have been used in which a cleaning liquid is constantly led through a filter as it is circulated. This has the disadvantage that delay is caused by constantly:
leading the solvent to the filter,
filtering it, and
feeding it back into the reactor system.
In the event of the filter becoming blocked, the cleaning process would stop altogether, as circulation is no longer possible.
DISCLOSURE OF THE INVENTION
We have now found that the above disadvantages may be eliminated by using a method of the kind described above in which the cleaning solvent additionally may be forced intermittently through a filter unit containing a suitable absorbent material and allowed to flow through conduits to a container, said container and conduits thus intermittently being flushed with pure solvent.
Thus, according to the present invention there is provided a method for cleaning a container and conduits associated with said container by adding a cleaning solvent to the container and circulating said solvent through said conduits back to said container, characterized in that the cleaning solvent additionally may be forced intermittently through a filter unit containing a suitable absorbent and allowed to flow through said conduits to said container, said container and conduits thus intermittently being flushed with purified solvent.
Such a method allows both the consumption of cleaning solvent and the time needed for the cleaning to be minimized, and also minimizes the environmental problems associated with large amounts of contaminated solvents.
It is advantageous to have the solvent come into contact with as many of the contaminated surfaces as may reasonably be achieved. This can be done by circulating the solvent by heating the solvent to the boiling point and conducting the resulting vaporized solvent to a cooling unit located above the container and permitting the condensed solvent to flow through the conduits back into the container. This way, all the contaminants are gradually dispersed in the solvent and can be filtered out again.
A pump may be used to ensure that the solvent is circulated in such a way that the solvent comes into contact with all contaminated surfaces.
The passage of solvent through the filter is preferably done in a controlled fashion. This may be achieved by orienting the filter unit in such a way that the direction of flow in use is vertical and upwards.
An absorbent material should be chosen that effectively leaves the solvent in a purified form, though it need not be left entirely free of contaminants. A suitable absorbent material in the filter unit is granulated, active carbon.
The method may be used for cleaning any apparatus in which a container is associated with conduits, such as chemical process equipment. It is ideally suited for cl
Karlsson Patrik
Lindquist Peter
Astra Aktiebolag
Parkin J. S.
Scheiner Laurie
White & Case LLP
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