Chemistry: electrical and wave energy – Processes and products – Processes of treating materials by wave energy
Reexamination Certificate
2002-03-14
2004-08-03
Wong, Edna (Department: 1753)
Chemistry: electrical and wave energy
Processes and products
Processes of treating materials by wave energy
C588S253000
Reexamination Certificate
active
06770174
ABSTRACT:
FIELD OF THE INVENTION
The invention is directed to industrial process emission control for industrial waste gas containing formaldehyde. Specifically, the invention is directed to an adsorption, desorption-photochemical oxidation (ADPO) system for minimizing formaldehyde levels in the gaseous effluent.
BACKGROUND OF THE INVENTION
Formaldehyde is a ubiquitous, hazardous pollutant emitted from a variety of large-scale industrial processes, including wood processing, furniture manufacturing, painting and coating, textile production, and cement manufacturing processes. Industrial processes emitting hazardous materials are regulated subject to reporting and mandated abatement requirements. Formaldehyde is a known carcinogen and subject to U.S. Environmental Protection Agency “Maximum Achievable Control Technology” (MACT) standards. Large-scale plants that emit in excess of 10 tons of formaldehyde annually are classified as major sources under these MACT standards.
Incineration is a high-energy process and often leads to non-benign secondary emissions such as nitrogen oxides (NOx) and unburned hydrocarbons. Photocatalysis systems are relatively capital intensive to install and require high maintenance to avoid degrading efficiencies and treatment reliability. Other techniques lead to secondary wastes and leave the ultimate fate of the pollutants unresolved. A technique is needed that can reliably treat chemical pollutants in a cost-effective manner.
Known methods to reduce formaldehyde emissions include eliminating the sources from raw materials, incineration, activated carbon-bed adsorption, adsorption on zeolite supports, and aerogels and adsorption techniques in conjunction with photocatalytic destruction. Obvious drawbacks of incineration include the cost of fuel and additional treatment of CO and NOx emissions. Costs incurred in the use of activated carbon include disposal and/or recovery costs in handling spent activated carbon. Captured volatile organic compounds (VOC) are not destroyed as they are retained only by a physical adsorption mechanism since chemisorption mechanisms are not provided in the use of activated carbon.
The costs associated with the addition and recovery of exogenous photocatalysts introduced to a waste stream containing VOC are obvious. Avoidance of specially adapted substrates would be desirable especially in industrial processes with very high effluent volume and with relatively low concentrations of VOC. Also, catalytic methods involve exothermic reactions, and are sometimes accompanied by over oxidation from the favored attack of partially oxidized products over the starting VOC.
The current commercial technology for reducing SO
2
and NO
x
emissions from power plants is wet scrubbing. Wet scrubbing generates hazardous slurry wastes. Dry sorbent injection technologies produce dry hazardous wastes. The dry sorbents are injected into a conventional power plant either in the combustion furnace (870-1200° C.), the economizer outlet (300-400° C.), or the air preheater outlet ducts (120-200° C.). Typical sorbents include finely ground limestone, dolomite, hydrated lime, sodium bicarbonate, and sodium sesquicarbonate. Known use of dry sorbents reacted with SO
2
emissions forming solid products, such as CaSO
4
or Na
2
SO
4
, are then removed with the coal ash or with the dust by the particulate matter collection system, e.g., electrostatic precipitator or baghouse, depending on the point of injection.
Photochemical destruction of VOC is known. U.S. Pat. No. 3,977,952 discloses a process for the decomposition of one or more carbon-containing compounds such as in an industrial waste or flue gas containing VOC, oxygen and water vapor. The method is carried out by exposing humidified gas to radiation of a wavelength of about 20 to 600 nanometers.
In some industrial processes, such as pyroprocessing of cement, recovery of the particulate solids to the production produce is of economic importance. A discussion of dry sorption methods is found in U.S. Pat. No. 6,080,281 teaching an emission control process using photocatalytic and nonphotocatalytic aerogels for adsorption, and exposing the photocatalytic aerogel material containing adsorbed VOC to ultraviolet (UV) radiation resulting in their destruction.
U.S. Pat. No. 4,210,503 discloses a direct photolysis method for controlling gaseous emissions, and particularly vinyl chloride, by exposing the emissions to UV light and, thereafter, absorbing such decomposition products in a scrubber which substantially eliminates the vinyl chloride and most other decomposition products from the effluent stream.
U.S. Pat. No. 4,981,650 discloses a method to remove dioxin-contaminated waste by way of extraction in a liquid capable of extracting dioxins. A hydrogen donor is added to the extracting solvent or later on during addition of an activating agent. The dioxin-containing liquid extract is treated in a direct photolysis reactor which contains immersion UV lamps.
U.S. Pat. No. 5,045,88 discloses the removal of halogenated and non-halogenated volatile and non-volatile organic contaminants from a gaseous stream by mixing a gaseous oxygen bearing substance with the contaminated gaseous stream, contacting the mixture with a solid photocatalyst; and exposing the photocatalyst and organic components to UV light having a wavelength up to 600 nanometers. The catalyst is pre-selected to prevent formation of a liquid phase.
U.S. Pat. No. 5,417,825 discloses a thermal photolytic process that utilizes high temperatures in combination with radiation exposure to induce a photochemical reaction to detoxify a wide variety of organic pollutants, for example, chlorinated aromatic hydrocarbons. The hydrocarbons are treated in the gaseous phase by heating to a temperature greater than 200° C., preferably 600-800° C., and exposing the heated gas to radiation at wavelengths of less than 280 nanometers, preferably from 185 nanometers to 280 nanometers, for at least two seconds.
U.S. Pat. No. 5,650,549 teaches a photothermal process for the detoxification of chlorinated aromatic hydrocarbons contained in a gas stream comprising the steps of: heating chlorinated aromatic hydrocarbons to a temperature of greater than 200° C. to form a gas stream or maintaining a pre-existing chlorinated aromatic hydrocarbon containing gas stream produced from a combustion source at a temperature of greater than 200 ° C. and exposing the gas stream to radiation at a wavelength of less than 280 nanometers for at least one second to convert said chlorinated aromatic hydrocarbons nontoxic reaction products, and releasing said gas stream to the atmosphere.
U.S. Pat. No. 5,839,078 discloses a method of direct vitrification of nuclear waste comprising the steps of providing waste in the form of relatively small pieces with vitrifiable material, providing high intensity light source of sufficient power to cause melting and subsequent vitrification of said waste; and, cooling and storing said vitrified material.
U.S. Pat. No. 5,342,582 discloses an apparatus for reprocessing special wastes of photopolymerizable scrap material to produce domestic waste, comprising a housing equipped with a feed hopper, at least one UV emitter arranged in the housing to irradiate and heat the scrap material, and a chopper arranged in the housing to comminute the scrap material. The photocrosslinkable and thermally crosslinkable scrap is composed of, for example, dry resist, solder resist, color proof films, screen printing films, and the like, which form special waste because of their reactive constituents.
U.S. Pat. No. 5,476,975 discloses a method for photodegradation of a solution of organic toxic chemicals recoverable from contaminated wood products by the use of a super-critical fluid, by exposing the extracted solution to UV, in the presence of a photosensitizer.
U.S. Pat. No. 5,935,525 discloses a pre-treatment system and an air treatment system for abatement of contaminated air that includes pollutants such as VOC, NOx, and/or CO. The air stream is treated using UV light under cond
Goshaw David G.
Richards John R.
Air Control Techniques, P.C.
Coats & Bennett PLLC
Wong Edna
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