Process for cleaning the waste gas from drying processes using h

Details Process for cleaning the waste gas from drying processes using h Process for cleaning the waste gas from drying processes using h

1996-10-21

1998-11-03

Spitzer, Robert

Gas separation: processes

Compressing and indirect cooling of gaseous fluid mixture to...

And liquid contact

95169, 95188, 95204, 95237, B01D 5314, B01D 500, B01D 4706

Patent

active

058302603

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION



FIELD OF THE INVENTION

This invention relates to a process for cleaning the waste gas from drying processes using heated gas for products containing volatile ingredients, more particularly for cleaning the waste gas accumulating in the spray drying of surfactant-containing materials, such as detergent slurries.
More particularly, the invention relates to, but is not confined to, the industrial production of surfactants and detergents by drying of a slurry in spray drying towers. The slurry is sprayed through nozzles into the drying zone and dried with the hot gas stream flowing in co-current or countercurrent. The drying gas used is generally air taken in from the surrounding atmosphere which is mixed with the waste gas of a burner and thus heated. Accordingly, the drying gas contains the water from the ambient air and the water formed during the combustion process.
However, the invention is not confined to a particular type of drying gas. It may consist of air or other gases, for example superheated steam.
The drying of products containing volatile ingredients removes not only water, but also relatively large or relatively small amounts of the volatile components, depending on the drying temperature. In the production of detergents by drying of a water-containing paste, the slurry, the volatile components are mainly organic substances, for example nonionic surfactants in the form of fatty alcohols with low degrees of ethoxylation and unsulfonated fatty alcohols in fatty alcohol sulfates. They are present in gaseous form or in the form of extremely fine condensation aerosols in the waste gas of the installations used for drying, for example spray dryers. The aerosols frequently have concentrations of the order of 100 ppm in the waste gas. On account of their extremely small particle size, they cannot be separated to a satisfactory extent by the textile filters or cyclones normally used to clean waste gases from drying installations and, accordingly, pass to the outside with the waste gas stream. Separation of the aerosols by textile filters, even to a small extent, is actually a disadvantage because the filters become blocked and have to be changed after a relatively short time. The waste gas emission produced by the aerosols, which is brought about above all by the steam volatility of certain components of the slurry, is known as "pluming".


DISCUSSION OF RELATED ART

Numerous solutions have been proposed in the prior art for reducing unwanted pluming. The temperature of the drying gas can be reduced, the final water content of the dried product can be kept high and, in addition, drying can be carried out on the countercurrent principle. However, these variants reduce the efficiency of the drying installation, affect product quality and limit the process control possibilities. Another known method of reducing pluming is to modify the composition of the slurry. The disadvantage of this is that the optimal formulation has to be changed.
It has also been proposed to condense the gaseous organic constituents in a washer-cooler. Unfortunately, washing the waste gas in this way is uneconomical on account of the high throughput of drying air which is in excess of 100,000 m.sup.3 /h. In addition, the environment problem is merely shifted from the waste air to the wastewater.
It is generally not possible to use a countercurrent ionization washer for cleaning waste air in view of the high moisture content.
Another known method of eliminating aerosols is to burn the waste air. However, this involves the additional consumption of energy which can be higher than the energy consumption of the actual drying process.
To summarize, it may be said that the known methods for reducing or eliminating pluming are complicated and expensive.
Accordingly, the problem addressed by the present invention was to provide an effective and economic process of the type mentioned at the beginning for eliminating the aerosols, particularly the organic aerosols, present in the waste gas.


DESCRIPTION OF THE

REFERENCES:
patent: 3651617 (1972-03-01), Hodgson
patent: 4265642 (1981-05-01), Mir et al.
patent: 4772295 (1988-09-01), Kato et al.
patent: 5492626 (1996-02-01), Uenoyama et al.

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