Gas and liquid contact apparatus – Contact devices – Injector type
Reexamination Certificate
2000-10-02
2001-11-27
Bushey, C. Scott (Department: 1724)
Gas and liquid contact apparatus
Contact devices
Injector type
C261S079200, C261S123000, C095S185000, C095S221000, C095S261000, C096S216000, C096S301000
Reexamination Certificate
active
06322055
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an apparatus and method for dissolving gas in a fluid, and, more particularly, to dissolving a gas into a fluid which may contain other dissolved gases.
BACKGROUND OF THE INVENTION
There are many instances when it is desirable to dissolve a gas, whether soluble or insoluble, into a fluid which may already contain other dissolved gases. For example, the macro and microbial organisms in all rivers, lakes, oceans, and all aerobic wastewater treatment processes are based on the presence of sufficient dissolved oxygen to sustain their life processes. Normally, in undisturbed bodies of water there is a rather low density of macro and micro organisms in the surface water and the limited natural absorption of oxygen from the air into the water is sufficient to maintain sufficient concentrations of dissolved oxygen in the water to sustain the life processes of that body of water. However, with increased population density and industrial activity, the associated organic water pollution causes a high microbial oxygen demand that natural oxygen aeration processes cannot begin to provide sufficient oxygen resources. Thus, artificial aeration mechanisms are required to enhance oxygen absorption.
Some specific examples of oxygenation applications are worthy of discussion. Odors at aerobic wastewater treatment facilities are associated with the inability to maintain sufficient levels of dissolved oxygen (“D.O.”). In the absence of sufficient D.O., nitrates are reduced to N
2
gas. In the absence of both D.O. and nitrates, strongly reducing conditions develop and sulfates are reduced to H
2
S, also known as “rotten egg gas”. This process can occur in any aquatic system where the oxygen demand exceeds the D.O. supply.
The high organic pollution in municipal wastewater of sewer lift stations supports a corresponding high microbial population, which, in turn, requires a high rate of D.O. to meet the demand. If the demand is not met, H
2
S formation readily occurs. Consequently, sewer force mains are a common source of odor nuisance for municipal public works.
Some industries (pharmaceutical, petroleum, and chemical, for example) create significant air pollution problems in the course of aerobically treating their wastewater by the use of conventional aeration systems. The wastewaters contain significant volatile organics/solvents which are readily biodegradable if they can be retained in the aqueous phase for a sufficient time. The use of conventional aeration systems has led to the requirement that the wastewater aeration basins must be covered to capture and incinerate the off gas in order to comply with air emission regulations. The need for a covered basin arises because conventional aeration systems readily strip the organics/solvents from the aqueous phase, not allowing for a sufficient time to biograde in the liquid.
Aerobic activated sludge processes are dependent upon oxygen transfer and sludge settling and recycle in the secondary clarifiers. It is now possible to develop high concentrations of sludge concentrations within the reactors, such as with the use of aerobic fluidized beds and moving bed filters, to the point where oxygen transfer becomes the limiting factor. Specifically, high levels of D.O. are required without subjecting the sludge to high energy dissipation/turbulence conditions which could shear off the biofilms or hinder flocculent sedimentation in the secondary clarifiers.
Fish farming and shrimp production commonly occurs in large ponds. To maximize production, the ponds are operated at the edge of D.O. availability. Since a still pond absorbs very little oxygen, there exists a need for artificial aeration to sustain high levels of fish/shellfish production.
The desire to increase dissolved oxygen levels is also applicable to slow moving rivers (such as the Cuyahoga River flowing through Cleveland, Ohio, and the rivers in Bangkok and Taipei) and canals (such as the waterways of Chicago, Ill. and the canals of Amsterdam). Many industries must curtail production (to considerable economic detriment) due to insufficient D.O. in the rivers, streams, and canals to which they discharge their treated wastewaters. Odor and corrosion problems can also occur in the bottom layer of stratified lakes and reservoirs feeding hydroelectric power dams. The low D.O. levels also result in fish kills.
Systems for dissolving a gas into a fluid are not limited to dissolving oxygen in water. Other gas/fluid combinations include: hydrogenation of vegetable oils, coal liquification, yeast production, Vitamin C production, pharmaceutical and industrial aerobic bioprocesses, and other processes well known in the art.
Therefore, it is desired to provide an apparatus and method of dissolving a gas into a fluid possibly containing other dissolved gases that has application in at least the following situations:
Slow moving rivers and canals
Reservoirs
Fish, shrimp shellfish, and/or mussel ponds
Aerobic wastewater treatment systems
Sewer lift stations
Wastewater industries such as the pharmaceutical, petroleum, and chemical industries
Aerated lagoons
Hydrogenation of vegetable oils
Coal liquification
Yeast Production
Vitamin C product
Pharmaceutical and industrial aerobic bioprocesses
Ozonation of water or other fluids
Dissolving xenon in fluids for injecting into the body
Supersaturating eye-wash liquids with supersaturated D.O.
Conventional aeration systems either bubble air through diffusers in the bottom of the aeration tank or splash the water in contact with the air. These systems typically absorb 1 to 2 lbs. of oxygen per kilowatt hour of energy consumed. Oxygen absorption efficiency is generally not an issue with these systems because air is free. These systems are most efficient when the D.O. in the water is near zero and are progressively inefficient as the water D.O. level approaches saturation, i.e., 9.2 ppm at 20° C. at sea level. Because the oxygen used in the aeration process is from the air and therefore at no cost, the costs of such systems emanates from capital costs and operating costs. The capital cost of a surface aerator capable of dissolving one ton per day of D.O. is about $40,000. The cost of power for the aerator is $70 to $140/ton of D.O. If the capital costs are amortized at 8% for a 10 year life, the total cost is approximately $87 to $157/ton of D.O.
In addition to costs, there are other disadvantages or shortcomings of conventional aeration systems. These shortcomings include: (a) low achievable D.O. concentrations of only 1 to 3 ppm; (b) high off-gas production; (c) high air stripping of volatile organic contaminants; (d) high energy dissipation in the reactor; (e) floc shear; and (f) limited D.O. supply potential.
As an alternative to conventional systems using “free” air to increase D.O. levels, systems now exist which generate or store oxygen on-site and dissolve this generated or stored oxygen into the water. Some of these systems are as economical as conventional aeration systems. Some of these systems address some of the shortcomings of conventional aeration systems. However, these systems have their own shortcomings.
For example, when high purity oxygen is being transferred into water, issues arise as to handling of dissolved nitrogen (“D.N.”) already in the water. D.N. is not utilized in an aqueous environment. Air is primarily comprised of 21% oxygen and 79% nitrogen gas. When water is in contact with air for prolonged periods, the water is saturated with D.N. At 30° C., the saturation concentration of D.N. in water is 16 mg/L. With conventional aeration systems, D.N. levels remain in a steady state. However, when high purity oxygen is introduced into the water, it results in a reduced D.N. partial pressure which strips the D.N. from the dissolved phase into the gas phase where it, in turn, reduces the percentage oxygen composition. The reduction in percentage oxygen composition reduces the partial pressure of oxygen in the gas phase, and the saturation concentration of oxygen, and ultimately the rate of oxygen
Bushey C. Scott
Eco-Oxygen Technologies, LLC
Gridley Doreen J.
Ice Miller
St. Peter Rachel L.
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