Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Patent
1990-11-30
1992-04-28
Heller, Gregory A.
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
423528, 423529, C01B 1769, C01B 1774
Patent
active
051087316
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a process in producing sulfuric acid in substantially vertical tubes of an acid resistant material, usually glass, while condensing vapours of sulfuric acid. Its purpose is to ensure that droplets of sulfuric acid (acid mist) are caught in a special filter The condensed sulfuric acid flows downwards through the tubes and is collected near their bottom end. The invention also relates to an apparatus for use in the process.
The process is especially suitable for the removal of sulfur dioxide from roasting processes and flue gases from boilers and power plants so as to recover the contents in the gas of sulfur oxides in the form of concentrated sulfuric acid, but it is also suitable for producing sulfuric acid from gases containing up to 10% sulfur oxides.
Plants in principle belonging to the present general type for desulfurizing and simultaneously removing NO.sub.x from flue gases has been described i.a. by P. Schoubye in Dansk Kemi [Danish Chemistry] 11, 1985, 327-330, and P. Schoubye et al in "Processing and utilization of High Sulfur Coals II", Chugh et al (ed.), Elsevier 1987, and in U.S. patent application No. 924,621.
Typically the tubes have an inner diameter of 25-60 mm and an effective cooling length of 120-150 times the inner tube diameter. The number of such tubes depend on the size of the plant in question. In a power plant having an effect of 300 MW the number is of the order of magnitude 60,000.
BACKGROUND OF THE INVENTION
It has been known for a long time that by cooling and condensing sulfuric acid vapours in air and in air containing aqueous vapour (steam) a sulfuric acid mist is formed, i.e. an aerosol of minute droplets of sulfuric acid. In U.S. patent specification No. 2,017,676 it has been proposed to counteract the formation of the acid mist by cooling a gas containing SO.sub.3,H.sub.2 SO.sub.4 vapour and H.sub.2 O in vertical, narrow ceramic tubes surrounded by a layer of sand the purpose of which is to delay the cooling of the gas, and by an outer metal tube; coolant, preferably water, is in contact with the outer surface of the metal tubes. In this manner there can only be obtained sulfuric acid of low concentration and the gas discharged from the top of the tubes contains more acid mist than allowed under present environmental demands.
In DK patent specification No. 145,457 (corresponding to U.S. Pat. No. 4,348,373) there is disclosed a process for preparing concentrated sulfuric acid from gases containing SO.sub.3 and excess of H.sub.2 O. The gas is cooled and the sulfuric acid condensed and concentrated in two steps in an absorption tower containing filler bodies. In the lowermost step the feed gas is passed upwardly countercurrently with the condensed acid, the concentration of which is thereby increased. In the subsequent step the sulfuric acid vapour is absorbed in sulfuric acid recycled through the layer containing filler bodies. The content of sulfuric acid mist is kept down by virtue of a specified regulation of the temperature at which the recycle acid is removed from the tower. According to this patent specification remaining acid mist is removed in an aerosol filter placed after the absorption zone. The filter is a "low velocity" filter operating at a linear velocity below 1 m/s and with a pressure drop above 20-30 mbar.
In DK patent application No. 1361/82 (corresponding to GB patent specification No. 2,117,368) a process is disclosed for preparing sulfuric acid in a sulfuric acid tower described in the specification. The tower is constructed as a tubular heat exchanger having two horizontal tube sheets and a bundle of vertical, acid resistant tubes extending into an inlet compartment below the lower tube sheet.
BRIEF DESCRIPTION OF THE DRAWINGS
This known process is most easily, like the present invention, described with reference to the drawings FIG. 1 of which represents the present state of the art in this technical field.
In the drawings
FIG. 1 schematically shows an apparatus for carrying out the proce
REFERENCES:
patent: 2901061 (1959-08-01), Hartig et al.
patent: 4348373 (1982-09-01), Schoubye
Haldor Topsoe A/S
Heller Gregory A.
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