LU82365A1 - WASTEWATER DRAWING PROCESS - Google Patents

Description

2.

! t I C 2034/8004.

"I: i (\! I j METALLURGICAL RESEARCH CENTER -CENTRUM V00R RESEARCH IN DE METALLURGIE,

Non-profit association - vereniging zonder winstoogmerk in BRUXELLES, (Belgium), and THY-MARCINELLE & PROVIDENCE, »Société Anonyme in COUILLET, (Belgium).

Wastewater taring process.

The present invention relates to a method of taring waste water, applicable in particular to coke plant waste water.

During the usual coal coking process, the combustible gases produced by heating carbonaceous materials contain a certain amount of parasitic components, such as for example tars including / // / 2.- "·.

they must be removed before they can be used. The tar removal operation for these gases is usually carried out in two successive phases, firstly during a first stage, by cooling the gas and washing it with water, and then during 'a second stage, by an electrostatic filtration operation.

During the washing of the gas, the water used in turn gradually becomes tar and must then be rid of it, before it can be purified into the dissolved or suspended constituents which it contains, then finally be discharged into the natural environment.

The problem of taring the gas washing water has so far also been resolved in two stages, p- the first consisting of decantation under the effect of weight, and the second by filtration through gravel. It is thus possible to reduce the tar content of the waters as much as possible to values of | around 20 mgr / 1 and their content of suspended matter at values of around 50 mgr / 1. These results can be further improved by then passing the water through tanks

Ide retention and long-term storage (for example 48 hours), before starting the chemical and biological purification of the waters considered.

It is well known that the chemical purification of waste water is most often carried out in so-called "stripping" columns with attack with lime or soda, by means of live steam or any other suitable fluid. This chemical purification is itself followed by biological purification, for example by activated sludge. Other purification methods, in particular by ion exchange resins, adsorbent resins, activated carbon, etc., are also well known.

; K Whatever the chemical and / or * biological purification method used, it turns out that residual tars, / from the previous tar removal operation remain / y

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still in the waters to be purified "in proportions creating many operating difficulties. Among these, one can quote for example: - the fouling of the columns? stripping and associated heat exchangers? " - bacteria inhibition during biological purification, - foaming during stipping and biological purification, s - rapid clogging of re = ines and activated carbon, - fouling of pipes '* iss, storage tanks, sewage tanks, - fouling of measurement and control instruments.

The object of the present invention is a particularly effective method of de-watering, by means of which the above-mentioned drawbacks can be easily avoided.

The process, ol “and of the present invention, is essentially characterized in that the waste water from the taring of the coking plants is subjected to the action of a centrifugal force by any means, by means of which the water separation - tar can be easily produced, almost completely and in a space-saving installation.

Several varieties of this Process can be implemented, all of which have specific advantages.

According to a first variant, the action of the centrifugal force is, in cad "-5 of the usual sequence of taring of waste water" as recalled in the preamble, carried out on chae-es waters (For example 50 to 100 ° C) after decantation under the effect ~ e gravity. Filtration on gravel can follow the action of said force. This variant has the advantage: particular to protect the whole installation downstream and to f · -iser1'extraction of the tarring / in liquid form, for example ^ -le preferably in a centri - // \: <; ; 4.-; s 1ϊ I runaway clarification and separation in 3 phases, namely ij waste water, liquid oily tar materials, | ï suspended solids. The liquid phase “, tar- j * | oil and oil can be advantageously recycled upstream, || in the installation, for example at the static tar decanter.

H ~ ~ ~ i i! 5; According to a second variant, the so-called centrifugal action is carried out on hot water (temperature above 5 ° C. after filtering over gravel and before any subsequent purification of the water. As an additional advantage of this variant, it can be mentioned that given the preliminary taring operation by the gravel filter, water that is more free is obtained; j oily, tarry and solid materials.

| The two above variants can be implemented | ] works during sequences identical to those already indicated, but after having cooled the water to be tared, to a temperature i for example between 20 ° C and 50 ° C, which has the advantage of being able to work for example with a particularly economical 2-phase centrifuge. (Gud dron is extracted at the same time as the solid matter, in the form of a viscous gum).

| According to a third variant of the process of the in- | vent ion, the action of the centrifugal force of water to be tared | is preferably carried out on cold water, after chemical treatment, but before biological treatment or treatment on! activated carbon or resins. As a particular advantage of this | ^ variant, it should be noted the simultaneous elimination of sludge j lime, when during stripping the elimination of fixed ammonia] niac is carried out by means of lime.

Thanks to the process of the present invention and which /; that is to say that chosen among the above-mentioned variants, one / / can obtain the following final contents: /// 5.- - when the centrifugation operates in roughing (1st variant) - tars: less than 10 mgr / 1 - suspended matter: less than 20 mgr / 1.

- when the centrifugation operates in polishing (2nd and 3rd 'variants) - tar: less than 1 mgr / 1 - suspended matter: less than 5 mgr / 1.

According to the invention also, it has been found advantageous to bring the centrifugation to a level such that the centrifugal force reaches at least 1000 g (g = acceleration due to gravity) and preferably between 3000 g and 18000 g, which ensures the elimination of particles with a diameter greater than 1 yUMi.

The process of the invention, as described above can be carried out discontinuously, by providing for example a cleaning circuit of the centrifuge, based on hot water, solvent or detergent, but it is preferred to use in continuous form, using for example an automatic settling apparatus, the extraction zones of which are advantageously heated so as to facilitate the fluidity of the tars and the extraction of the solid materials.

It is also possible to improve the effectiveness of the various variants mentioned above, by introducing into the water to be purified a coagulating and / or flocculating and / or demulsifying material of hydrocarbon materials. In this way, it contributes to increasing the dimensions of the solid and / or tar particles to be removed, which has the consequence either of being able to increase the purification to "g" equal in the centrifuge, or of retaining the same purification, but with a lower "g". This flocculation or coagulation operation is carried out for example by physico-chemical route or by electrical route, in particular by making use of an appropriate '' / specific polyelectrolyte. / a ... * J, 6.- r 'fi ï In addition, it has been found interesting to incorporate in the water to be purified, a surfactant (for example at a rate of 1 mg / 1), Mistletoe can reduce the sticking effect of tars, without however, which is surprising, unexpected and unpredictable, harm the desired coagulation or flocculation effect.

It is worth pointing out here that to facilitate cleaning and maintenance of the centrifuge, i i v uses hot water containing a solvent or i! a detergent, which facilitates the dissolution and therefore the removal of the tarry particles remaining in the centrifuge! # / ·! 1 j \, i.

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Claims (5)

3. Method according to either of claims 1 and 2, characterized in that the centrifugal force is exerted after filtering the water. 4. Method according to any one of claims 1 to 3, characterized in that the centrifugal force is carried out after chemical purification, but before biological purification or treatment with activated carbon or on resins. 5. Method according to one or other of claims 1 to 4, characterized in that the centrifugal force is carried out on water, at a temperature above 50 ° C. 6. Method according to one or other of claims 1 to 5, characterized in that the centrifugal force is obtained by means of a centrifuge. 7. Method according to one or other of claims 1 to 6, characterized in that the centrifugal force reaches at least 1000 g and preferably is between 3000 g and 18000 g. 'eccins: ......... p ^ nc'vs ........ 3 ........ p-: c dent ...... y ... page of psrda .... 6 p / oes cU ...... Ji f -: es ce r venolcadons