Gas separation: processes – Liquid contacting
Reexamination Certificate
1999-04-14
2001-09-04
Barry, Chester T. (Department: 1724)
Gas separation: processes
Liquid contacting
C095S230000, C095S237000
Reexamination Certificate
active
06284022
ABSTRACT:
The present invention relates to a method for removing gaseous and particulate contaminants (aerosols) from a vapor-saturated gas stream, in which method a gas stream, containing at least one gaseous contaminant and at least one aerosol, is brought into contact with a scrubbing liquid in such a way as to form a vapor phase, the degree of saturation S of which is greater than 1.
In the past, progressive industrialization of the production of foodstuffs and consumer goods has often led to increased pollution of the air, particularly in industrial centers. In recent years, statutory measures have made it possible to reduce emissions from large-scale furnaces, for SO
2
, NO
x
and dust, by approx. 80%.
With a few exceptions (e.g. in the case of fibrous dusts), pollutant limit values for emissions and immissions have often been fixed in the form of mass concentrations, so that in this analysis submicron particles are of minor importance. For example, in Germany, according to the 17th Ordnance relating to the Federal Immission Control Act (17. BImschV, 1990), up to 10 mg/m
3
(STP) of contaminants in dust form are permissible in the off-gas from an incinerator. This results, even for a particle size of 0.1 &mgr;m, in a particle surface area of 0.28 m
2
/m
3
off-gas. From this, it is clear that even submicron particles provide an extremely large surface area on which substances can accumulate, representing a high health hazard potential. Such substances are, for example, heavy metals or numerous highly toxic gaseous and liquid components, including, for example, nuclear fission products.
Engineering processes, e.g. those which lie downstream of incinerators for production residues, often produce solid or liquid aerosols in addition to gaseous substances (e.g. HCl, HF, HBr or heavy metal vapors). The gaseous contaminants are usually scrubbed out in scrubber columns (absorption columns). However, the aerosols formed in the incineration process are generally very fine and often pass through the scrubber columns without any significant reduction in the level of such contaminants.
The combustion of production residues produces, for example, NaCl aerosols in concentrations of up to approximately 250 mg/m
3
. The size distribution of such aerosols clearly lies in the submicron range. For this reason, deep-bed diffusion filters, wet scrubbers (e.g. Venturi scrubbers) or electrostatic filters have to be connected downstream. These standard processes generally entail high investment and/or operating costs.
The separation methods which are known from the prior art are generally unable to carry out all the cleaning functions required at the same time, i.e. they are either only able to ensure sufficient removal of particulate contaminants or are only able to remove gaseous pollutants from the gas stream. For example, the publication “Abscheidung submikroner Partikel aus Gasströmen in Fullkörperschuittungen” [Separation of submicron particles from gas streams in packed beds], by S. Heidenreich, H. Büttner and F. Ebert (Chemie Ingenieur Technik (69), 1997, pp.110 ff) describes a method for removing particulate contaminants from gas streams. In this method, a gas stream in a scrubber column which is filled with packing bodies is exposed to a countercurrent scrubbing liquid. The method described is carried out in two stages, a first stage using hot water for scrubbing and a second stage using cold water for scrubbing. However, the method described does not provide satisfactory simultaneous removal of particulate and gaseous contaminants.
A large number of methods for reducing the amount of gaseous contaminants in a gas stream are known from the prior art. An example which may be mentioned is the monograph “Abgasreinigung” [Off-gas cleaning] by M. Schulte (Springer-Verlag, Berlin, Heidelberg, N.Y., 1996). The monograph cites a considerable number of standard methods which are concerned with reducing the levels of sulfur, nitrogen, carbon and halogen compounds in off-gases and with reducing the hydrocarbon emissions.
However, a drawback of all the methods which are known from the prior art is that they only allow the removal of either gaseous contaminants or particulate aerosols. Therefore, to remove both types of contaminant from an off-gas stream, it is generally necessary to connect two method steps in series. However, in practice this entails high investment costs, since it is necessary to provide two, generally different, types of installation. Furthermore, this procedure increases the operating costs, since each stage generally has a high power and water consumption.
Therefore, there was a need for a method for the simultaneous removal of gaseous and particulate contaminants from gas streams which allows both types of contaminants to be removed from the gas stream in a single method stage.
It is an object of the present invention to provide such a method.
We have found that it is possible to remove both types of contaminants from gas streams if a vapor-saturated gas stream which contains both types of contaminants is fed through a scrubber column which has an internal surface area, produced for example by packing bodies, of at least approximately 100 m
2
/m
3
, and a degree of saturation S which is greater than 1 is used.
In the context of the present text, an “internal surface area” is understood to mean the surface area inside the scrubber column which is available for contact between gas stream and scrubbing liquid. In the text which follows, the internal surface area will also be referred to as the “contact surface”.
Therefore, the present invention relates to a method for removing gaseous contaminants and aerosols from a vapor-saturated gas stream, in which method a gas stream containing
a) at least one gaseous contaminant which is soluble in a scrubbing liquid, with or without salt formation, and
b) at least one aerosol with a particle size from 0.01 to 10 &mgr;m,
having a flow rate of at least 0.5 m/s and a temperature from 30° C. to 100° C. in a scrubber column which has an internal surface area of from 50 to 1000 m
2
/m
3
, is brought into contact, if appropriate following prior saturation with vapor, with a scrubbing liquid which has a feed rate Z to the scrubber column and the temperature of which is lower by at least 2° C. than the temperature of the gas stream, resulting in the formation of a vapor phase, the degree of saturation S of which is greater than 1, and in the removal of the gaseous and particulate contaminants from the gas stream.
Gas streams which are suitable are in principle all gas streams which have a carrier gas which is to be cleaned at the process temperature and which contains both gaseous and particulate contaminants which are to be removed.
Generally, particularly suitable carrier gases are those gases which, under the conditions of the method, do not undergo a reaction with any of the components involved in the method, i.e. with either the scrubbing liquid or a material of the apparatus in which the method according to the invention is carried out. Therefore, in a preferred embodiment of the invention, the carrier gas to be cleaned is a gas or gas mixture which is substantially inert under the reaction conditions and which has a boiling point which lies below at least approximately −50° C. Examples of gases to be cleaned are nitrogen, hydrogen, oxygen, carbon dioxide, helium, neon, argon, krypton or mixtures of two or more of these gases.
In a preferred embodiment of the invention, the carrier gas to be cleaned is a gas mixture formed in the incineration of production residues, for example in refuse incineration.
The gas stream used in the implementation of the method according to the invention is to be vapor-saturated. Preferably, the vapor phase is to be completely saturated with the vapor of the liquid which in the subsequent method is used as the scrubbing liquid.
“Vapor-saturated” is understood to mean the state in which the vapor phase contains its maximum level, as a function of pressure and temperature, of molecules of the co
Sachweh Bernd
Ulbrich Michael-Dieter
Weissker Wolf-Steffen
Barry Chester T.
BASF - Aktiengesellschaft
Keil & Weinkauf
LandOfFree
Method for removing contaminants from a gas stream does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for removing contaminants from a gas stream, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for removing contaminants from a gas stream will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2514398