Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture
Reexamination Certificate
1995-09-13
2001-02-06
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
C423S245300, C165S005000, C588S253000, C588S253000, C588S253000
Reexamination Certificate
active
06183707
ABSTRACT:
FIELD OF INVENTION
The present invention is directed to the treatment by incineration of air or gases containing toxic or odorous fumes which include a variable amount of a suspension of condensible vapors in the form of a mist of liquid droplets.
More particularly, the invention is directed to a method of treating air or gas containing volatile toxic or odorous compounds in the form of a mist or a suspension of fine liquid droplets arising from the cooling of vapors of high boiling points upon contact with a cooler gas such a ventilation air, which method permits to achieve a high level of destruction of the pollutants with a high heat recovery factor, and a reduced risk of external pollutioninternal fouling of the incineration system and potential fire hazards.
BACKGROUND OF THE INVENTION
In order to protect health and the environment, it is necessary to eliminate undesirable odors and toxic gases from the ventilation air or waste gases occurring as by-products of many manufacturing processes before their discharge to the environment. A known method for removing odors and other organic impurities contained in air or ventilation gases consists in heating the fouled air or gases in a thermal regenerative incinerator system. Such a system which is disclosed by way of example in U.S. Pat. No. 3,870,474, generally comprises at least two and preferably three heat accumulation chambers or regenerators each containing a suitable packing material such as ceramic spheres or nodules, and a combustion chamber positioned to cooperate with both regenerators to effect oxidation of the impurities.
Such an incinerator system has an operating cycle including a plurality of successive steps. In the first step, the waste gases are caused to flow through one of the regenerators in such a manner as to be heated by contact with the packing that has previously been heated, and then to the combustion chamber where total oxidation of the fumes takes place. The hot combustion products are thereafter directed to a second regenerator wherein their heat content is transferred to the packing material. The gases are finally exhausted to the atmosphere. In a second step, the waste gases are directed in the reverse way through the second regenerator, where they are heated. After combustion, they are cooled by passage through the first regenerator and exhausted. Heat losses are made up by injection of auxiliary fuel in the combustion chamber.
In current practice, the incinerator system usually comprises a third regenerator which is added thereto in order to allow for the purging of the waste gases remaining in a regenerator after the waste gas heating period but prior to the introduction of the purified gases.
Regenerative incinerator systems of the above mentioned type are well known apparatuses that have found application for some years for the treatment of waste air or gas streams containing volatile organic compounds in gaseous form, like those produced during the preparation or application of solvent based paints, varnishes or other coatings.
A number of problems arise however when this process is used for the treatment of waste gas or air streams containing condensible organics in the form of aerosols or suspensions of fine liquid particles, like those produced during the impregnation of roofing felts with asphalt base coatings. When treating such waste gases, the condensed vapors or liquid aerosols are carried into the regenerator bed and deposited as a thin liquid film on the inside surfaces of this regenerator and on the packing material in the entrance zone of the regenerator. Upon reversal of the flow, the soiled surfaces are heated by contact with the hot exhaust gases, causing some of the organic liquid film to evaporate and contaminate the otherwise clean gases. This has the effect of materially reducing the destruction efficiency of the process. In addition, any portion of the liquid deposited which is not evaporated remains on the packing and adds up during subsequent cycles, causing a run-off of excess liquid in the gas plenum of the regenerators. This liquid wets the regenerator and packing surfaces and upon evaporation increases the contamination of the exhaust gases. Further, this excess liquid is slowly distilled in contact with the hot gases, leaving behind deposits of tarry substances on the packing and on the walls of the plenum chambers as well as on the valve chambers and moving parts. These deposits can impair the operation of the process and, if allowed to accumulate, can ignite and cause severe overheating and failure of mechanical parts.
OBJECT OF THE INVENTION
The object of the present invention is to provide a method for treating waste gases or air containing odorous or toxic compounds, especially organic compounds, in the form of saturated vapors, mists, aerosols and suspensions of condensible liquid droplets in equilibrium with their vapor phase, which method derives from the one carried out with the known regenerative incinerator system but is improved over the same so as to achieve virtually complete elimination of the above mentioned compounds while simultaneously achieving a high thermal recovery factor and reducing risks of overheating and damaging the equipment.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a method for treating waste gases containing volatile toxic or odorous compounds as a condensed phase in the form of a mist or a suspension of fine liquid droplets, using a regenerative incinerator system of the type comprising at least three regenerators containing a packing material, each of the regenerators having one end always in open communication with a combustion chamber common to all of the regenerators.
The method according to the invention has a cycle of operation comprising:
a) during a first period of time:
passing the waste gases first through at least one of the regenerators so that the waste gases be pre-heated by contact with the packing material contained therein when this material is hot; then through the combustion chamber to assure complete oxidation of the compounds contained in the waste gases; and finally through at least one other of the regenerators to cool the gases from the combustion chamber by contact with the packing material contained in the at least one other regenerator, such a contact causing the packing material to be heated up, the gases leaving the at least one other regenerator being clean and discharged to the atmosphere; and
simultaneously recycling part of the clean gases as a purging gas through at least one of the remaining regenerators for purging the at least one remaining regenerator of any waste gases or of the compounds remaining therein, the purging gas being fed into the at least one remaining regenerator opposite the one end thereof in communication with the combustion chamber so that the purging gas leaving the at least one remaining regenerator be fed into the combustion chamber to remove any contaminant that would be carried by the purging gas before the purging gas is discharged from the system together with the clean gases;
b) during a second period of times:
reversing the direction of flow through the regenerators so that the waste gases to be treated be fed first through the at least one other regenerator which was, in the first period of time, traversed by the flow of gases coming from the combustion chamber; thus through the combustion chamber and finally through the at least one remaining regenerator which was just being purged; and
simultaneously recycling part of the clean gases as a purging gas into the at least one regenerator which was previously fed first with the waste gases; and
c) during a third period of time:
reversing again the direction of flow of the waste gases, the clean gases and the purging gas through the regenerators in the same manner as above to achieve preheating of the waste gases in the at least one remaining regenerator, heat exchange with the hot packing material in the at least one regenerator now purged, and purge of the other regenerator
Drouin Guy
Gosselin Gerard
Gravel Jean J. O.
Biothermica International Inc.
Greigg Edwin E.
Greigg Ronald E.
Griffin Steven P.
Vanoy Timothy C
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