Gas separation – Means within gas stream for conducting concentrate to collector
Patent
1983-04-14
1985-01-22
Hart, Charles
Gas separation
Means within gas stream for conducting concentrate to collector
55 80, 55 85, 55 89, 55228, B01D 5304, B01D 4705
Patent
active
044949677
DESCRIPTION:
BRIEF SUMMARY
Because of legal requirements and/or economic reasons the solvents, with the exception of water, that are liberated during production and operational processes must be recovered. Such production and operational processes include chemical reactions, e.g. polymerization reactions, precipitation reactions, thermal decomposition reactions and similar reactions; examples of operational processes include the coating, soaking or spraying of arbitrary objects with solutions. If the solvent is removed by evaporation in a warm or hot stream of transferal gas, even the solvent constituents which are nonvolatile or difficult to volatize find their way into the gas stream as impurities. This danger occurs especially during spray-drying of solutions or during spraying of objects with solutions for coating or soaking, e.g. in painting technology.
Such contaminations can involve solid and liquid, especially high-boiling, substances, e.g. polymeric paint- and lacquer-particles, residual monomers derived from polymerides, catalytic substances, pigments, dust particles, products of thermal decomposition, such as tarry or resinous products or combustion products as well as caustic or corrosive substances.
In order that these substances not be drawn into the condensation or absorption part of a solvent recovery mechanism and there lead to fouling or contamination of the recovered solvent or the solvent mixture, the gas stream bearing the solvent vapors as well as the impurities must first be cleaned.
For the removal of impurities in the form of solid or liquid particles in suspension, mechanical mechanisms are known, such as, for example, cyclones or filters, for whose operation a relatively large amount of energy must be expended with respect to the cleaning effect. Similar considerations are true of electrostatic filters.
It is further known that very fine dust which can no longer be picked up in a centrifugal separator due to the small diameter of the particles can be separated if water is injected into the centrifugal separator (compare, for example, Ullman's Enzyklopadie der Technischen Chemie [Encyclopedia of Technical Chemistry], Volume 1 (1951), Page 374). By means of such a washing apparatus the finest dust particles are bound to the washing liquid which is removed from the air stream by baffle cleaners.
The separation of the suspended particles by means of water-washing, however, has the disadvantage for a gas stream bearing solvent vapors that the water absorbs the vapors of solvents which are miscible with water and that the solvents are thereby lost or can only be recovered at great cost, since they generally are contained in the wash water only in a small concentration. Moreover, with solvent mixtures the hydrophobic solvent components are not washed out of the vapor mixture while simultaneously a part of the wash water changes to the vapor state. During the subsequent condensation one finds a two-phase mixture whose hydrophobic component is frequently emulsified in the aqueous phase so that the phase separation is made more difficult. As a result of the washing out of the hydrophilic solvent component the composition of the hydrophobic solvent component no longer corresponds to the original composition and consequently the solvent can no longer be directly reintroduced into the process but rather must be enriched with a fresh, hydrophilic solvent component.
Finally, the washed out particles in suspension involve in many cases reusable substances, e.g. lacquer or paint particles. If these particles are present in an aqueous suspension, a preparation is extremely difficult.
The invention is based on the requirement of eliminating the disadvantages inherent in the known water-washing operations and of providing a method as well as a mechanism for removing the impurities from a gas stream containing solvent vapors for which purpose, on the one hand, the impurities are efficaciously removed and, on the other hand, a solvent or solvent mixture, which can be reused with as little additional cost as possible, is obtaine
REFERENCES:
patent: 3324669 (1967-06-01), Cooper et al.
patent: 3343916 (1967-09-01), Cahn et al.
patent: 3618301 (1971-11-01), Handman
patent: 4227891 (1980-10-01), Maguire et al.
patent: 4265642 (1981-05-01), Mir et al.
patent: 4287138 (1981-09-01), Buckner
Hart Charles
Lohmann GmbH & Co. KG
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