Gas separation: processes – Liquid contacting – Gaseous fluid mixture discharged against or beneath surface...
Reexamination Certificate
2001-06-21
2003-09-30
Smith, Duane S. (Department: 1724)
Gas separation: processes
Liquid contacting
Gaseous fluid mixture discharged against or beneath surface...
C096S333000, C096S335000, C096S336000, C096S340000, C096S343000
Reexamination Certificate
active
06626983
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a U.S. national phase application of PCT International Application No. PCT/GB99/03930, having an international filing date of Nov. 25, 1999 and claiming priority to Great Britain Application No. 9825812.2 filed Nov. 25, 1998. The above PCT International Application was published in the English language and has International Publication No. WO 00/30734.
This invention relates to a method and apparatus for removing particulates and/or other undesirable components. In particular the invention concerns such a method and apparatus for removing particulates and/or other undesirable components from a gas stream such as an exhaust gas stream.
There are many instances when it is desirable to remove particulates from a particulate-containing gas stream. For example in many industrial processes it is desirable for gases to be cleaned of particulates before undergoing eg. chemical or physical processing.
Another instance where it is desirable to remove particulates is in the field of vacuum cleaners. Although conventional filtration techniques are capable of removing comparatively coarse dust particles from the air flowing through a vacuum cleaner, such techniques are poor at removing fine particulates, which tend to cause various ailments, including respiratory disorders, if allowed to exhaust from a vacuum cleaner into the ambient air of a room.
Another field in which particulate removal is particularly important is that of diesel engine exhausts.
Diesel engines are widely used throughout the world, particularly in heavy vehicles (trucks, buses and trains) and increasingly in automobiles. They are robust, fuel-efficient, long-lasting, and emit relatively low levels of carbon monoxides but they suffer from two major disadvantages which are causing increasing environmental concern. These are: (a) the emission of particulates, and (b) the emission of undesirable components such as oxides of nitrogen, sulphur and/or polynuclear hydrocarbons.
The particulates, which are carbonaceous in nature, are associated with undesirable hydrocarbons, of which the class known as polycyclic aromatic hydrocarbons are of particular concern. One of these compounds, 3-nitrobenzanthrone, has been reported (Suzuki et al, Environment Science and Technology, Volume 3, page 2772, 1997) as being extremely active in causing mutations in the DNA of standard strains of bacteria, as measured by the so-called Ames Test. Other compounds also present in diesel exhaust gases, such as 1,8-dinitropyrene, have also been found to be strongly mutagenic. These observations point to a strong link between diesel exhaust emissions and carcinogens in the atmosphere. It has been estimated that the tiny combustion particles, especially those with dimensions of less than 1 micrometre, are capable of carrying these chemicals into the deep recesses of human lungs. Virtually all diesel particles are in this size range (Michael P. Walsh “Global Trends in Diesel Emission Control—1 1997 Update”, SAE Technical Series Paper 970179). Particulates from diesel exhaust gases may cause 10,000 deaths in Britain and 60,000 deaths in the USA each year. (“Dying from too much dust”, New Scientist, Mar. 12, 1994, page 12). This leads to the conclusion of J. Merefield and I. Stone (New Scientist, Sep. 20, 1997, page 58) that “we could greatly improve our health and the urban air if we had better control over our vehicles' exhausts”.
Oxides of nitrogen (and ozone) are also very undesirable atmospheric pollutants because they generate oxygen radicals, which can damage DNA and attack cell membranes. Nitrogen dioxide, NO
2
, emitted from diesel engines is capable of producing oxygen atoms under the influence of sunlight, i.e.:
sunlight+NO
2
→NO+O.
These oxygen atoms can then combine with oxygen in the atmosphere to form ozone, O
3
, i.e.:
O+O
2
→O
3
.
This explains why ozone pollution is especially serious during warm, sunny days. It should be noted also that ozone is harmful not only to humans in a number of ways (damage to airways linings, inflammatory reactions, and increased likelihood of asthma attacks), but also to vegetation, causing reduced yields from a range of crops including wheat, barley and peas.
Naturally, because of the worldwide concerns for these problems, there has been a great deal of effort directed towards finding a solution. The most obvious of these, designed to remove particulates, makes use of filters or traps. The main problem with these is that they tend to become blocked, which results in numerous inefficiencies in the operation of the engines to which they are attached. This technology has been studied extensively. (See, for example, Y. Teraoka et al., Catal. Today, Volume 27, page 107 (1996). It is possible to regenerate the filters by burning off the trapped soot, and this procedure is rendered more efficient if a catalyst is incorporated into the filter material (as referred to by J. P. A. Neeft et al. in Appl. Catal. B. Environmental, Volume 8, Page 57 (1996)). Naturally this constant need for removal and regeneration is a serious disadvantage. An alternative approach has been advocated by Cooper and Thoss (SAE Technical Paper 890404 (1989)). In this case a platinum-containing catalyst was mounted upstream of a particulate trap in order to oxidise nitrogen to nitrogen dioxide. The resulting NO
2
is a powerful oxidising agent which is capable of removing carbon, viz.,
2NO
2
+C→2NO+CO
2
.
Unfortunately, as this equation shows, the reaction generates nitric oxide. Furthermore, the catalyst is sensitive to poisoning by sulphur, which is present to a greater or lesser extent in diesel fuels throughout the world.
Therefore it is clear that there is a need for a system which is capable of removing particulates efficiently (especially those smaller than 1 &mgr;m) and which is unaffected by the presence of sulphur.
U.S. Pat. No. 5,453,107 and U.S. Pat. No. 3,803,813 disclose apparatus for filtering particulates from exhaust and other gases wherein the gas is first bubbled through a liquid prior to passing through a filter.
U.S. Pat. No. 5,129,926 describes an engine exhaust system comprising a water-filled scrubber tank through which the exhaust gas is released. The system further comprises a moisture trap for returning some of the condensed gas back to the inlet manifold of the engine and a filter to filter the gases once they have passed through the moisture trap.
U.S. Pat. No. 3,957,467 discloses an exhaust gas purifier and silencer in which exhaust gases are first released from a conduit into a liquid to purify the gas and thereafter returned to the same conduit and exhausted.
DETAILED DESCRIPTION OF THE INVENTION
According to a first aspect of the invention, there is provided a method of removing particulates and/or other undesirable components from a gas stream, comprising wetting at least a portion of the gas stream in order that the particulates and/or undesirable components are entrapped and/or dissolved in the liquid thereby cleaning the gas; and further comprising cooling the gas stream and/or cleaned gas to condense desired fractions thereof.
This method is advantageously simple, and inexpensive since it does not require the expensive metals usually needed in particulate removal systems that operate by catalysts. Also, the method of the invention has the capability of removing certain oxides of nitrogen and sulphur.
Desirable the majority or substantially all the gas stream is wetted.
It is to be understood that the term wetting includes both passing said at least a portion of the gas stream through a liquid, or merely blowing the gas stream onto the liquid in order to wet it.
Preferably the liquid is or is predominantly water, and more preferably includes a detergent. In preferred embodiments the detergent constitutes 1 part in 50,000 of the liquid.
The detergent ensures that the liquid wets the fine particulates, and has been found to be particularly effective when the gas stream is diesel exhaust gas.
Howeve
Myers Bigel Sibley & Sajovec P.A.
Smith Duane S.
University Court of the University of Dundee
LandOfFree
Method and apparatus for removing particulates 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 and apparatus for removing particulates, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for removing particulates will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3076395