Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Patent
1995-08-09
1997-07-01
Bhat, Nina
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
423171, 423555, 422173, 422269, 422270, 432 58, 432103, C01B 1750, B01D 1104
Patent
active
056435487
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a process for drying and then separating moist salts, such as magnesium sulfite, coming from a wet sulphur dioxide (SO.sub.2) absorption plant into MgO, SO.sub.2 and water vapor. The moist magnesium sulfite is dried in a dryer and then passed through a solid materials lock to a separating plant which is separated from the dryer thereby. A gaseous component of SO.sub.2 separated from the magnesium sulfite in the separating plant is used to heat combustion air needed to heat the separating plant and another gaseous stream of exhaust gas escaping from the separating plant is used to heat the dryer.
The present invention also relates to an installation for drying and subsequently separating moist salts such as magnesium sulfite coming from a wet SO.sub.2 absorption plant.
In chemical reclamation plants (such as those described in Austrian Patent No. 347,235) and in wet desulfurization plants operating on the basis of MgO, as well as in other salt reclamation plants, a salt such as MgSO.sub.3 or Mg(HSO.sub.3).sub.2 develops in a moist or dissolved state. If this salt is separated for reclamation of the components, acid vapors such as SO.sub.2 -water vapor mixtures develop at high temperatures, and such mixtures are highly corrosive during cooling (condensation of the water vapor) and also operate to thin the acid to be obtained or cause the acid to be combined with the corrosion products. This hinders heat recovery, equipment costs increase and productive power drops. Moreover, the corrosive vapors adversely affect the equipment, so that maintenance expenses or replacement expenses further lower the productive power of the chemical reclamation plant. Thus, the overall presence of SO.sub.2 -water vapor mixtures is very problematic in salt reclamation operations.
Another reference, German Patent Publication No. DE 1 199 74 describes a similar process for obtaining sulphur dioxide by using zinc oxide whereby the main problem is to avoid sulphatizing the zinc in the separation reactor. This problem does not occur in the present invention wherein the main difficulty sought to be overcome is the corrosion of the elements of the separation plant due to the presence of sulphur dioxide-water vapor mixtures and the high heat requirements of the plant.
OBJECTS AND SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a new and improved drying and separating process and installation for moist salts, such as magnesium sulfite, in which the problems described above are avoided.
It is another object of the present invention to provide a new and improved drying and separating process and installation which substantially eliminates the disadvantages mentioned above by separating sulphur dioxide (SO.sub.2) and steam (H.sub.2 O) to prevent the formation of sulphur dioxide-water vapor mixtures. As such, a pure (dry) acid anhydride (SO.sub.2) is formed. In accordance with the invention, it has been found that the components affected by the pure (dry) acid anhydride (SO.sub.2) are less subject to corrosion than if contacted with SO.sub.2 -water vapor mixtures, so that the productive power of the plant is unexpectedly high.
In the process in accordance with the invention, the dryer in which the moist salts (MgSO.sub.3) are situated is heated to a temperature of about 200.degree. C. and preferably more than 200.degree. C. by the circulation of a portion of an exhaust vapor stream of the dryer through a system of conduits. The portion of the exhaust vapor stream of the dryer is heated as a result of heat exchange with an exhaust gas being discharged from the separation plant and directed through a system of conduits, i.e., by passing the streams through separated tubes of a heat exchanger. By means of the heating to a temperatures greater than about 200.degree. C., in addition to the moisture adhering to the salt, the water of crystallization of the salt in particular, is completely eliminated in this drying operation. Thus, in the sepa
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Bammer Josef
Blocher Bernhard
Glaser Wolfgang
Loquenz Heinz
Staufer Walter
Austrian Energy & Environment SGP/Wagner-Biro GmbH
Bhat Nina
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