Gas separation: processes – Liquid contacting – And degasification of a liquid
Reexamination Certificate
1998-12-11
2001-02-27
Simmons, David A. (Department: 1724)
Gas separation: processes
Liquid contacting
And degasification of a liquid
C095S159000, C095S263000, C095S265000, C055S356000
Reexamination Certificate
active
06193786
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the exchange of a non-combustible gas for a combustible gas in a liquid. More particularly, this invention relates to the reduction of combustible gas content in oil from electrical apparatus.
BACKGROUND OF THE INVENTION
The principal function of transformer oil is to provide electrical insulation and to cool transformer windings by absorbing the heat generated during operation and conducting it to the exterior surfaces. In switch gear and circuit breakers oil also quenches the electric arc. To carry out its functions in the most efficient way, insulating oil must be of good quality and free of contamination. Some electrical and electronic apparatus requires insulating oil of a superior quality in respect to freedom from contamination in order to insure high dielectric strength and extended service life under extreme stresses. Also, cables, extra high voltage transformers, bushings, and capacitors are in this category and require oil of high purity.
The presence of contaminants in the oil can adversely affect the insulating properties of the oil. Contaminants and products of oil deterioration reduce dielectric strength of oil by forming a path of low resistance for electric discharge through the oil. Further, when the contaminants are combustible gases, the potential for explosion exists.
There are many types of contamination, such as water, solid particles of dust, metals, colloidal carbon, products of corrosion, acids, resins, gums, tar, sludge, organic contaminants and solvents, air and gases.
Contamination enters insulating oil in many ways. Some occurs in various phases of oil transfer from the refinery to the point of use. Some contaminants enter through breather vents or during the process of filling or overhaul. Some moisture and contamination can be found even in new transformers as soluble water and air are present in oil. Water in its free phase may be present either dispersed in form of emulsion or settled at the bottom of the reservoir. With synthetic oils, which are heavier than water, water will tend to collect at the surface or near the top of the transformer.
Contaminants can also be introduced through the degradation of the oil under the extreme conditions existing inside the electrical apparatus. This degradation can give rise to combustible gases. Gases which are typically found in transformer oils include ethane, ethylene, acetylene, methane, carbon dioxide, carbon monoxide, hydrogen and oxygen. Protection of electrical apparatus by continuous or frequent purification of insulating oils will eliminate costly breakdowns and assure a safe and dependable operation.
Purification and reconditioning of transformer oil are practiced in the art. As described in the Institute of Electrical and Electronic Engineers Guide for Acceptance and Maintenance of Insulating Oil in Equipment (ANSI/IEEEC57.106-1977), the reconditioning step when contacting the oil with filter media and/or when performing the mechanical separation of oil and water by centrifuging must be accomplished at low temperature to avoid a high level of dissolved water in the oil, since the saturation amount increases rapidly with temperature. The Guide further describes that in reclaiming, the oil is usually treated by contact with Fuller's earth, an adsorbent clay material which is effective in removing the oxidation products and acids.
The above Guide also describes vacuum dehydrators (degasifiers) as an efficient means of reducing water and gas in the oil to a very low value. There is considerable other literature which describes this vacuum treatment step. Typical references to this step are U.S. Pat. No. 3,675,395 (Jul. 11, 1972) by Baranowski and U.S. Pat. No. 3,339,346, (Sep. 5, 1967) by Buchanan, both of which describe an apparatus for heating, filtering/coalescing and vacuum degasifying of transformer oil, and an article by Schenck in January 1983 Transmission and Distribution magazine describing apparatus for heating, filtering and vacuum degasifying of transformer oils. This latter reference discusses use of a cold trap operating at −85° F. to obtain adequate vacuum to sufficiently reduce the water content to meet specifications. This cold trap is refrigerated with a cascade refrigeration unit to attain the very low temperature.
These methods of degasifying transformer oils require costly equipment and the input of energy to heat the oil, to run the vacuum pumps and to maintain the cold trap system to protect the vacuum pumps. As such, these devices are more appropriately considered stationary devices that might reside in a central power generation station or an oil recycling station. For processing oil from transformers which are located in areas remote from such stations, it is extremely useful to have an oil degasifying device which can be easily transported to the transformer location. Of even greater use is a degasifying unit which is of simple design, inexpensive to build and which requires a minimal input of energy to run. The present invention provides such a device and methods for using this device.
SUMMARY OF THE INVENTION
When electrical transformers are located at sites which are remote from central power generating stations and oil recycling/disposal stations, it is necessary to transport contaminated oil to an appropriate station for either recycling or disposal. The transportation of contaminated oil is a hazardous activity because of the combustible gases which are often dissolved in the oil. Previous methods for degasifying oil have relied on devices which use vacuum pumps and the attendant apparatus in conjunction with an absorption column to remove dissolved gases and other impurities from the oil. These systems can be difficult to transport and are expensive to build, to maintain and to operate.
This invention provides methods and devices for removing combustible gases from transformer oil which eliminate the need to heat the oil and the necessity for any vacuum apparatus. Further, an absorption column is not a necessary component. The simple methods and devices of the invention provide for removing an amount of combustible gas from the transformer oil sufficient to render the oil safe for transportation and recycling.
Thus, in a first aspect, the present invention provides a method utilizing a device for reducing combustible gas concentration in an oil, the method comprising:
(a) contacting a first inert gas and the oil in a first gas-oil contact device to form a first inert gas-oil mixture;
(b) passing the first inert gas-oil mixture into a second gas-oil contact device comprising a packed bed wherein said first gas-oil mixture and a second inert gas are contacted in countercurrent flows, thereby forming a combustible gas-inert gas mixture; and
(c) venting the combustible gas-inert gas mixture from said device.
In a second aspect, the present invention provides a device for reducing combustible gas concentration in an oil. The device comprises a column for a packed bed, a gas-oil contact device adapted to combine oil and a first inert gas flow into a first gas-oil mixture and a manifold which provides a means for passing the first gas-oil mixture and a second inert gas through the column in countercurrent flows.
In a third aspect, the present invention provides a transportable device for reducing combustible gas concentration in an oil. The device comprises a column for a packed bed which is pivotally mounted to a trailer bed for pivoting between a first position in which the column is vertical and a second position in which the column is horizontal. The device also has a gas-oil contact device adapted to combine oil and gas flows into gas-oil mixture. The device utilizes a manifold to provide means for passing a gas and the gas-oil mixture through the column in countercurrent flows when the column is in the first position.
Other objects and advantages of the present invention will be apparent from the detailed description and examples that follow.
REFERENCES:
patent: 3013631 (1961-12-01), Johnson
patent: 333
Pacific Gas and Electric Company
Pham Minh-Chau T.
Simmons David A.
Townsend and Townsend / and Crew LLP
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