Liquid purification or separation – Processes – Ion exchange or selective sorption
Reexamination Certificate
1999-09-17
2003-12-02
Cintins, Ivars (Department: 1724)
Liquid purification or separation
Processes
Ion exchange or selective sorption
C204S572000, C210S748080
Reexamination Certificate
active
06656364
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for cleaning liquids containing impurities, in which an addition of adsorbents takes place, together with an apparatus for carrying out said method.
2. Related Art
It is known that in manufacturing processes impurities, for example dyestuffs, phosphatides and solids particles, have to be separated from liquid recyclates. For example, DE 31 23 462 A1 describes an apparatus for the electrostatic cleaning of dielectric liquids, in which the dielectric liquid is exposed to an electric field in a tank with an inflow opening for the contaminated dielectric and an outflow opening for the cleaned dielectric in the upper part of the tank, as well as an outlet opening for the impurities in the lower part above two systems of electrodes disposed therein. The separation of the very small particles which get into the dielectric liquid during electrochemical machining is barely possible with mechanical filters because of the low permeability of the filter cake formed. Electrostatic cleaning is particularly suitable for this.
In particular for the obtaining or processing of animal, vegetable or marine oils it is known; in general from DE 42 10 795 C1 that the liquids, in particular those for the production of foodstuffs, form a mixture together with solids particles. The solids particles and impurities can be inter alia undesirable phosphatides, soap residues and complex colloidal compounds, but also adsorbents added for performing a cleaning such as bleaching earths, activated carbon and silica. The adsorbents are mixed with the liquid for the cleaning. In so doing said adsorbents contact in a so-called bleaching stage inter alia dyestuffs such as carotene and chlorophyll, heavy metals, residues of phosphatides and soaps as well as peroxides. Due to the contact the substances from the oil or fat attach themselves to the adsorbents and can be removed from the liquid together with the latter.
The separation of the adsorbent loaded with the above-mentioned substances from the bleached oil takes place in the known process with the aid of pressure filters which operate according to the principle of precoat filtration. There are known for the filtering e.g. plate-and-frame presses, plate filters and tube filters, as well as crossflow filtration. It is a disadvantage with pressure filtration, however, that the filter cake formed inhibits strongly the flow of the liquid. In keeping with this, a considerable expenditure of energy is required for the pumping through of the liquid. Furthermore, the carrying capacity of the filters is rapidly exhausted, making frequent filter replacement or filter cleaning necessary.
Conversely, there is known from DE 43 44 828 A1 a method and an apparatus for cleaning liquids containing impurities in which the contaminated liquid is exposed to an electric field by means of mutually insulated electrodes, in which simultaneously the viscosity of the liquid to be cleaned is lowered by heating. With this method, although one part of the liquid can be withdrawn cleaned, a not inconsiderable part of the liquid nevertheless remains in the bleeding. It is furthermore disadvantageous that the layout and control of the electrodes are cumbersome.
SUMMARY
The invention is based on the problem of specifying a method and an apparatus for cleaning liquids containing impurities, such as oils and fats, in which method/apparatus the separation takes place with relatively little equipment and low energy requirements.
The problem is solved for the method given in the preamble by the steps:
addition of adsorbents, which adsorb the impurities, to the liquid,
agglomeration of respectively several particles of adsorbent with the impurities adsorbed therein/thereon to form greater particles of adsorbent,
renewed suspension of the now greater particles of adsorbent in the liquid and
filtering of the liquid containing the suspended greater particles of adsorbent.
First of all, in the conventional manner, the relatively fine-grain particles of adsorbent adsorb the impurities that are present in the liquid as solids particles or dyestuff or other and are to be removed. When or while the particles of adsorbent have taken/been taking up the impurities, an agglomeration of the fine-grain particles of adsorbent is then carried out.
Preferably the suspension is first of all exposed to an electric field for a particular time, wherein the loaded particles are moved towards an electrode. There the particles agglomerate, are separated and are suspended in the liquid once again on disconnection of the electric field, wherein the particles of adsorbent exhibit as a result of the agglomeration an enlarged particle structure. In particular the particles have after the agglomeration a porous, loose structure.
The subsequent filtration, which is preferably carried out as a pressure filtration, can be executed more effectively by virtue of the enlarged particle structure, since the enlarged particles bestow a sufficient permeability for the liquid during the formation of the filter cake. Thus it is possible according to the invention to operate the filtration up to a considerably higher loading of the filter area.
If, as known from DE 43 44 828 A1, a fraction of the liquid which is substantially free of adsorbents and hence of solids particles is withdrawn simultaneously during the agglomeration of the solids, for example at an outlet disposed in the upper part of a tank, a part of the liquid to be separated has already been cleaned. There arises in the remaining liquid, on renewed suspension of the solids collected and attached first of all due to the electric field, a strongly concentrated suspension. Because of the porous structure of the agglomerated particles in the liquid to be cleaned during the subsequent pressure filtration the area of the precoat filters for example used can be reduced considerably.
The invention becomes particularly effective if it is used as a part step in a countercurrent bleaching process, such as is described in German patent application 196 20 695.2-41 published at a later date. In counter-current processes uncleaned oils are brought into contact with already partially loaded adsorbent in a stage and then in a second stage the oil partially cleaned in the first stage is brought into contact with fresh adsorbent. The adsorbent used in the second stage then serves as partially loaded adsorbent in the first stage. The end product of the second stage is then highly cleaned oil.
The concentrated suspension now obtained according to the invention, containing the already agglomerated and loaded particles of adsorbent, can now be treated in such a countercurrent process as the “partially loaded adsorbent” and be introduced in the first stage together with the still uncleaned oil. The agglomerated particles of adsorbent can thus be used again with a saving on materials.
The use of bleaching earth as adsorbing agents is preferred for the cleaning of animal, vegetable or marine oils and/or fats, in particular those for the production of foodstuffs. The use of silica gels or activated carbon, for example, is however also possible.
Because the bleaching earth to be fed has a large fine grain content, for example with a grain spectrum of 5 to 10 &mgr;m, the adsorptive power is increased due to the enlarged free surface of the fine-grain bleaching earth. It is no longer necessary, therefore; to use an excessive proportion of bleaching earth. The consumption of bleaching earth therefore falls with advantage. The amount of bleaching earth used can in the case of rape oil, for example, be reduced in absolute terms from the minimum 0.6% conventional to date to 0.3%. Furthermore, the fine grain bleaching earth is more favourable as regards procurement costs than the bleaching earth structured as a result of pretreatment which is used to date. For the grain size distribution has represented to date a compromise between a sufficiently good bleaching effect and a sufficiently good separability by conventional filte
Borner Gunter
Schneider Matthias
Transfeld Peter
Wetzel Rainer
Cintins Ivars
OHMI Forschung und Ingenieurtechnik GmbH
Salter & Michaelson
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