Gas separation: processes – Liquid contacting – On surface extending mass
Reexamination Certificate
1999-10-13
2001-11-06
Smith, Duane S. (Department: 1724)
Gas separation: processes
Liquid contacting
On surface extending mass
C095S224000
Reexamination Certificate
active
06312503
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of and apparatus for the quenching and scrubbing of gases. More particularly, the present invention relates to a method of and apparatus for the cooling of hot gas and removal of condensables by counter-current liquid contact between a gas and a cooling/scrubbing solution. The model system is the quenching and scrubbing of nitrogen gas using ethylene glycol.
2. Background
The cooling and purification of gases is important because large quantities of inert gases are used in many commercial processes. One particular such use is in the production of polyethylene terephthalate (PET) polymer. Specifically, inert gases are used during the polymerization reaction of PET to develop molecular weight by removing unwanted byproducts and excess reactants from the polymer resin such as ethylene glycol, acetaldehyde, and water. Hence, the presence of pure inert gases facilitates the solid state polymerization reaction. A complete description of this particular gas cleaning application is -found in several references including U.S. Pat. Nos. 5,434,239; 4,263,425; 4,356,299; 4,340,721 and 4,230,819, all herein incorporated by reference.
Moreover, since effective polymerization depends on the ability of the gas to strip contaminants which in turn depends on the purity of the gas, the polymerization reaction chamber requires continual replenishment of clean gas. Once the gas leaves the polymerization chamber, however, it contains the above mentioned contaminants. Before further use in the polymerization reaction therefore, the gas itself must be cleaned of contaminants. Such recycling reduces the cost associated with supplying a continuous stream of virgin gas to the polymerization reaction chamber while maintaining polymer line throughput.
Cleaning usually consists of cooling the gas by direct contact with a cool liquid so as to cool and condense out contaminants. These steps are respectively referred to as quenching and scrubbing. A typical gas stream exiting a polymer production apparatus is extremely hot, approximately 175° C. It therefore initially requires extensive quenching to complete the recycle process. Only then does it undergo a scrubbing/absorption step where the majority of condensation of gas contaminants occurs.
DESCRIPTION OF THE RELATED ART INCLUDING INFORMATION DISCLOSED UNDER 37 CFR 1.97 AND 1.98
U.S. Pat. No. 5,474,597 ('597) issued to Halldin et al., hereby incorporated by reference, teaches that particulates may be removed from gases by means such as cyclones, electrostatic precipitators or filtration devices, and that gaseous pollutants may be removed from gas streams by direct contact techniques such as by condensation or reaction with a liquid surface, or by adsorption on the surface of a solid. These techniques, however, fail to remove in some cases gaseous or particulate contaminants from gases.
The '597 patent also teaches that gas/liquid direct contact systems can roughly be divided into two categories: open towers where the gas encounters only a finely divided liquid, and packed scrubbers (“packed columns” or “packed towers”), where gases pass through solid structures drenched with cooling liquid.
In packed scrubbers, packing serves to increase the gas/liquid interface by providing a surface on which the finely divided liquid forms a film. Liquid is supplied to the packed sections by nozzles above each packed section. It flows downwardly over essentially the entire surface area of the packing as a substantially continuous liquid film, providing enhanced surface area for gas/liquid interaction, which promotes either gas quenching through heat transfer or scrubbing through condensation and mass transfer of impurities. Accordingly, quenching and scrubbing steps are usually carried out respectively in separate columns, thus comprising the conventional twin column system. The first packed column quenches the hot process gas, while the second packed column then scrubs the quenched gas.
However, these systems are plagued by the problem of aerosol mist formation during quenching. As defined herein, aerosol mists consists of small droplets sized at less than or equal to about 10 microns. Their formation occurs as some of the liquid used to quench the gas diffuses into the gas phase and condenses as a mist, further contaminating the gas. Moreover, unlike larger spray mists, these aerosol mists cannot be removed effectively with conventional in-line droplet removal devices, such as commercially available demisters. Aerosol mist removal therefore requires the use of more expensive external droplet removal systems which are used after the quenched gas exits the packed column. Such systems may consist of a fiber bed and are presently used in many industrial line applications. Eliminating their use is a long-felt need in the industry.
Hence, there is room for improvement in the art for quenching and scrubbing hot gases.
SUMMARY OF THE INVENTION
It is therefore, a principle object of the present invention to provide an improved method of and apparatus for scrubbing an inert gas.
It is an additional object of the present invention to provide an improved method of and apparatus for quenching and scrubbing inert gas in a single column or unit.
It is a further object of the present invention to provide a method of eliminating the formation of aerosol mists during the quenching of hot inert gas.
These and other objects are achieved in one aspect of the present invention by a method of cleaning inert gas. The method comprises sequentially passing a substantially dust-free gas through three contact zones all having solid material packing overflowed with cooling liquid. The gas travels countercurrent to the liquid. In the first zone the liquid quenches the gas at a rate controlled to eliminate the formation of aerosol mist. In the second zone, the cooling liquid scrubs and is thus selected to selectively condense gaseous contaminants in the gas. Cool liquid containing no recycled portion of either of the first two portions of cooling liquid passes over the third contact zone to selectively absorb substantially all contaminants remaining in the quenched and partially scrubbed gas. All of these steps preferably are accomplished in a single treatment column from which a cool, clean gas is produced. This achieves improved removal of particulate and gaseous contaminants from an inert gas thereby to provide a consistent stream of high quality recycled gas without the formation of aerosol mists.
These and other objects are achieved in a second aspect of the present invention by an apparatus for cleaning inert gases. The apparatus comprises: a single column with an inlet for hot, contaminated gas, an outlet for cleaned, cooled gas, and a series of contact sections located therebetween. Each contact section is supplied with liquid by a plurality of nozzles. These nozzles spray divided liquid into each contact zone parallel and counter-current to the main flow direction of the gas.
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Bartels Jorg
Fike Lawrence Robert
Freeman Stephen Jonathan
Osornio Miguel Angel
Schmidt Torsten
Arteva North America S.a.r.l.
Smith Duane S.
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