Hazardous or toxic waste destruction or containment – Destruction or containment of radioactive waste
Reexamination Certificate
1999-06-11
2001-07-17
Joyce, Harold (Department: 3749)
Hazardous or toxic waste destruction or containment
Destruction or containment of radioactive waste
C429S071000
Reexamination Certificate
active
06262328
ABSTRACT:
FIELD OF THE INVENTION
DISCUSSION OF BACKGROUND
Hydrogen accumulation is a major concern in various industrial applications and processes. Hydrogen gas is highly flammable and is often generated or evolved as a by-product or waste emission. A hydrogen explosion can take place if the hydrogen concentration is allowed to exceed four (4%) percent. Furthermore, accumulations of hydrogen gas can present over-pressurization problems in sealed containers along with the attendant hazards of explosion and fire.
For instance, in U.S. Pat. No. 5,660,587 to Baer, which is incorporated herein by reference, a passive ventilation system and method for venting hydrogen from a chamber housing a battery is shown. As described in Baer, battery charging in remote cabinets, office building and electric vehicles has resulted in numerous explosions that destroy the battery and its container and possibly injure people. These explosions are frequently caused by igniting hydrogen gas in insufficiently ventilated battery chambers.
When batteries are overcharged, the current in the cell produces hydrogen. To avoid the accumulation of hydrogen in the battery, battery chambers are typically vented to release the hydrogen to the environment. The invention of Baer is directed to allow ventilation only when there is an increase of hydrogen concentration in the battery chamber. The invention however, does not address the removal of hydrogen from the environment to which it is vented.
As discussed in U.S. Pat. No. 5,624,598 to Shepodd, the operating life of a lamp, either incandescent or pressurized discharge lamps, can be greatly affected by the presence of certain gases in the internal lamp atmosphere. Water vapor is particularly harmful. In an incandescent lamp, for example, the temperature of the tungsten coil is sufficient to decompose water vapor into hydrogen and oxygen. Removal of the hydrogen is key in prolonging the useful life of the lamp. Shepodd seeks to solve this problem by disclosing hydrogen getters which are useful only at elevated temperatures.
In the nuclear industry, there is often a need to store and ship waste consisting of Pu-238 and high activity fraction of Pu-239. However, as a result of radiolysis, hydrogen gas is generated. The evolved gas poses an over-pressurization concern during storage, transportation and the ultimate disposal of the waste. Presently, waste consisting of Pu-238 and high activity fraction of Pu-239 cannot be shipped to long term storage areas, because of the hydrogen gas pressurization concerns of the storage containers. Thus, there remains a need in the industry for a method and container for reducing the concentration of hydrogen gas in a waste container consisting of Pu-238 and high activity fraction of Pu-239.
Various metals and metal alloys can absorb and then desorb large amounts of hydrogen under appropriate temperature and pressure conditions. These materials are referred to as metal hydrides and are well known in the art. They include pure metals such as Mg, Pd, Ti, Pt, U, and alloys such as those based on nickel, lanthanum and aluminum.
U.S. patent application Ser. No. 09/094,293, filed on Jun. 9, 1998 by the Applicant, and incorporated herein by reference, discloses a sol made from tetraethyl orthosiliate, ethanol, water and hydrochloric acid mixed with a hydrogen-absorbing metal alloy and solidified to form a porous glass matrix with the hydrogen absorbing alloy dispersed uniformly throughout the matrix to form a composite useful in the present invention. The composite is aged and subsequently heat treated to obtain a porosity that allows the hydrogen to react with the metal alloy to form a metal hydride, excluding poisonous CO and H
2
S from the metal alloy. The metal alloy encapsulated in the porous matrix is, thus, protected from the hydride poisons present in the environment, e.g. a gaseous stream.
The composition used in the present invention is immune to gaseous poisons and is ideally suited for hydrogen absorption from environments where mixtures of various gases may be present.
SUMMARY OF THE INVENTION
According to its major aspects and broadly stated, this invention is directed to a container and method for reducing the concentration of accumulated hydrogen from the interior of a sealable container. The container comprises a material suitable for the product or method to be accommodated. In a preferred embodiment, the container comprises a hydrogen absorber. Additionally, in an alternative embodiment, the container comprises a vent or exhaust port in communication with the hydrogen absorber so that, while hydrogen gas is removed from the container exhaust, other gases or by-product are released to the environment minus the hydrogen gas. One skilled in the art will appreciate that there are instances when venting the contents of a container is feasible upon removal of the hydrogen gas. In such instances, the hydrogen absorber used in this invention is not affected by the presence of other gases which may poison the hydrogen absorber.
A general method of practicing the invention comprises the steps of providing a container, placing a hydrogen absorber into the container, sealing the container and removing evolved hydrogen gas from the container contents by the hydrogen absorber.
The hydrogen absorption composition preferably used in this present invention is described in U.S. patent application Ser. No. 09/094,293, incorporated herein by reference, and describes a formulation of a glass matrix in which the pore size has a high degree of uniformity. In particular, the pore size permits the free passage of hydrogen gas to occur, while excluding certain other gaseous molecules such as metal hydride poisons H
2
S and CO. The glass matrix is extremely porous and has a very high surface area-to-volume ratio. It is chemically and physically stable and holds the hydride particles securely. Thus, it enables the absorption of large amounts of hydrogen by the hydride over repeated cycles of use while the matrix physically excludes gaseous poisons.
In a first embodiment of the present invention, the described hydrogen absorption composition is contained within a closed container seen as a 55 gallon waste drum. The container contains substances which release hydrogen as a gaseous by-product. Because the container is sealed, there is a need to remove hydrogen in order to preclude a build up of excessive pressure or explosive H
2
concentrations within the container. The hydrogen absorber is able to absorb the hydrogen gas without being affected by other gases which act as poisons.
In a second embodiment of the invention, the hydrogen absorber is placed within sealed battery systems or in areas housing large battery systems. In a closed battery system, there would be a similar need to remove a build up of hydrogen gas which could cause an over-pressurization or accumulation of dangerous H
2
levels within the system. In a room or containment area housing battery systems, there is a need to remove hydrogen gas from the environment in order to avoid fire or explosion hazards. The hydrogen absorber, in either situation, is capable of removing the hydrogen without being adversely affected by other gases that may also be present.
One particular use of the invention is with sealed battery systems related to battery-operated emergency lighting. Such lighting systems are designed to turn on in the event of a power failure to provide lighting in critical areas such as stairwells, exits, and areas of potential hazards. Such systems typically employ a battery-operated power supply which is continuously recharged. The recharging process normally produces small quantities of hydrogen gas. The present composition can be added to the sealed battery compartment to avoid overpressurization and hydrogen gas accumulations.
It is an object of the present invention to provide a method for absorbing hydrogen in a closed environment.
It is another object of the present invention to provide a container for absorbing evolved hydrogen gas emissions.
It is a further object of the pre
Heung Leung K.
Lee Myung W.
Wicks George G.
Dority & Manning PA
Joyce Harold
Westinghouse Savannah River Company
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