Germicidal low pressure mercury vapor discharge lamp with amalgam location permitting high output

A germicidal lamp having amalgam for controlling mercury vapor pressure contained in a location facilitating efficient high output operation. A low pressure mercury vapor discharge lamp has an amalgam container containing an amalgam positioned behind an electrode out of the arc path or space. The amalgam position is retained during high wall loading of the lamp preventing the amalgam from moving out of position. Efficient operation with high current loads and resulting high wall loading and temperatures is possible. The germicidal lamp is particularly suited to being positioned vertically in a waste water treatment system.

FIELD OF THE INVENTION

The present invention relates generally to low pressure mercury vapor discharge germicidal lamps used to disinfect or purify fluids, and more particularly to a germicidal lamp having a structure permitting high output and relatively high temperature operation.

BACKGROUND OF THE INVENTION

Low pressure mercury vapor discharge lamps are commonly used to generate ultraviolet radiation and used to irradiate a fluid to kill potentially harmful organisms contained in the fluid. Often, relatively high doses of ultraviolet radiation are required. The necessary relatively high doses of ultraviolet radiation typically require the use of multiple germicidal lamps. The use of multiple germicidal lamps increases expenses, as well as maintenance. Therefore, it is desirable to use fewer higher output germicidal lamps. However, producing a high output germicidal lamp is not without difficulties. During operation of a low pressure mercury vapor discharge lamp, the vapor pressure of the mercury greatly affects lamp operation. A predetermined vapor pressure is desirable for efficient operation of the lamp. However, under heavy loads used to produce a high output, mercury vapor pressure may increase reducing the efficiency and operation of the lamp. Amalgam has often been used to control the mercury vapor pressure within the lamp, permitting the lamp to operate more efficiently. However, the higher temperatures occurring at high loading of the lamp often cause the amalgam to melt. If the amalgam melts, it will move out of position and could make contact with an electrode and cause possible shorting or ineffective operation of the lamp.

A germicidal lamp using an amalgam is disclosed in Patent Cooperation Treaty international application No. PCT/DE96/00647 having a publication number of WO96/31902 and published Oct. 10, 1996, entitled “Low Pressure Mercury Vapor Discharge Lamp”. Therein disclosed is a low pressure mercury vapor discharge lamp having an amalgam placed along the inner wall between the electrodes. The lamp tube is in mechanical contact with a cooler on the outside of the lamp adjacent the location of the amalgam. While this lamp structure is helpful in keeping the amalgam cool and therefore permitting higher loading of the lamp to improve output, the amalgam could still melt causing the amalgam to move out of position. This is particularly problematic in applications where the lamp is held vertically rather than horizontally, which could result in the amalgam falling downward onto one of the electrodes.

Therefore, there is a need for a low pressure mercury vapor discharge germicidal lamp for producing a high output of ultraviolet radiation that reduces the possibility of an amalgam melting or moving out of a desired location during high loading.

SUMMARY OF THE INVENTION

The present invention relates to a germicidal low pressure mercury vapor discharge lamp for operating under a high load having improved operation and output. An amalgam is positioned out of the arc path during operation of the lamp. An amalgam container is positioned behind the electrode in a relatively cool location or cold spot. The amalgam container is open, permitting the surface of the amalgam to be exposed to the interior space of the lamp, yet restricted to prevent the amalgam from moving out of position from behind the electrode where it is out of the arc path.

One embodiment comprises a germicidal lamp system having a plurality of elongated lamps held vertically within a fluid. The amalgam container holds amalgam in a location behind the electrode preventing the amalgam from moving out of position during high loading of the germicidal lamps. The positioning of the amalgam in a cooler location makes possible the higher loading of the germicidal lamp.

Accordingly, it is an object of the present invention to provide a high output germicidal lamp capable of operating at high wall loads.

It is another object of the present invention to provide a germicidal lamp that is capable of using amalgams that may melt at the internal operating temperature of the germicidal lamp.

It is another object of the present invention to provide a germicidal lamp that can effectively operate over a wide temperature range.

It is an advantage of the present invention that the germicidal lamp can be held vertically during operation.

It is another advantage of the present invention that the amalgam is held in a cooler location outside of the arc path or positive column.

It is a feature of the present invention that the amalgam is held in a position behind an electrode.

It is another feature of the present invention that a container is used to prevent the amalgam from moving out of a desired position.

These and other objects, advantages, and features will become readily apparent in view of the following more detailed description.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1schematically illustrates a germicidal system10of the present invention. A container12holds a fluid14therein. The fluid may be waste water, air, or any other fluid type material that is to be purified or disinfected using ultraviolet radiation. The fluid or waste water14flows in the direction indicated by arrow16. A plurality of germicidal lamps18are vertically placed within the fluid14. Each of the plurality of lamps18may have a variety of different configurations. By way of example, several differently configured germicidal lamps are shown for illustrative purposes. Additionally, each of the germicidal lamps18may be placed in a protective sleeve20. At each end of the lamp, end caps22are placed. The end caps22may be made of a plastic material and sealed against the glass tube of the germicidal lamp. The germicidal lamp may be sealed within the protective sleeve20by rubber seals or any other equivalent or conventional technique. For illustration purposes, a double ended lamp24is shown. The double ended lamp24has electrical connections or pins at either end of the lamp. A single ended lamp26may also be used. The single ended lamp26has two pins on one end for connecting to an electrical power source with a conductive wire extending along the length of the lamp to form an electrical connection with an electrode at the opposite end of the germicidal lamp. Such a single ended lamp26is more fully disclosed in U.S. Pat. No. 4,700,101 entitled “Elongated Tubular Lamp Construction” and issuing to Ellner et al on Oct. 13, 1987, which is herein incorporated by reference. The germicidal lamp may also be a single ended pigtail type lamp28. The single ended pigtail lamp28has a pigtail29attached to the electrical terminals of the electrodes to facilitate an electrical connection. The pigtail29comprises flexible wires electrically attached or coupled to the electrodes and a connector having pins for connecting to a power source. Any conventional or equivalent electrical connection may be made with different types of germicidal lamps, as is well known.

In a germicidal lamp held vertically within a fluid column, it is often desirable to operate the germicidal lamp at high wall loading to improve output. The high wall loading may be greater than 250 milliwatts per centimeter squared. Comparatively, a conventional fluorescent lamp is generally only operated at a wall load of about 100 milliwatts per centimeter squared. During high current operation, with the resulting high wall load, the internal temperature of the lamp may increase to greater than 140° centigrade. At these temperatures, the mercury vapor pressure within the germicidal lamp increases to unacceptable levels. In order to keep the mercury vapor pressure within predetermined limits for effective operation of the lamps, amalgams are used to absorb and release mercury as required to maintain efficient operation. However, at high temperatures, the amalgam may melt, limiting their effectiveness and causing them to move out of position within the germicidal lamp. The present invention positions the amalgam outside of the arc path or outside of the positive column at a location behind the electrode in a cooler spot. The amalgam is positioned at a location where the internal temperature or wall temperature of the germicidal lamp is less than about 140° centigrade, even under high load. The location of the amalgam and containing the amalgam within the location permits efficient operation of the germicidal lamp at higher loading, and resulting higher temperatures. Additionally, by containing the amalgam in a restricted location yet open to the interior of the germicidal lamp, the amalgam may function effectively but be retained in the desired location if the amalgam melts during the high temperature occurring during high wall loads. This is particularly important in a germicidal application where the germicidal lamp is held vertically. Unless the amalgam is held in position according to the present invention, it would fall out of position upon melting and could possibly contact an electrode, greatly shortening the life of the germicidal lamp.

Additionally, different amalgams may be utilized that may melt at the internal operating temperatures therein improving operating efficiencies. The germicidal lamp of the present invention is capable of operating at external wall temperatures ranging from about 40° C. to 140° C. This temperature range is particularly advantageous in a germicidal lamp submerged in a liquid where the temperature of the liquid may vary. Accordingly, the present invention is particularly well suited and solves problems associated with germicidal lamps vertically positioned and operated under high loads.

FIG. 2Aillustrates one end of one of the plurality of germicidal lamps18illustrated inFIG. 1. The opposing end of the germicidal lamp is similar. An end cap, illustrated as22inFIG. 1, typically would cover this end portion of the germicidal lamp. However, for purposes of illustration, the end cap has been removed to better view the structure of the end of the germicidal lamp. A tubular quartz envelope30has a pressed portion32sealing an end thereof. The pressed end32seals the end against ribbon conductors34. Wires36are electrically coupled to the ribbon conductors34. The wires36extend out of the end cap, not illustrated, and are electrically connected to pins for making an electrical connection to the lamp. The electrical connection to the germicidal lamp may be of any conventional electrical connection technique. Electrode supports38extend into the interior of the germicidal lamp and hold a filament electrode42. Placed on one of the electrode supports38may be auxiliary amalgam40. The auxiliary amalgam40preferably is composed of an amalgam with a high melting point to prevent melting during the high temperatures associated with high wall loads. However, this auxiliary amalgam40is generally not sufficient to maintain the desired mercury vapor pressure for efficient operation of the germicidal lamp. Additionally, this auxiliary amalgam40may not be required but may be utilized in some applications.

Formed on the quartz envelope30between the sealed end32and the filament electrode42is an amalgam container46. The amalgam container46may be a quartz or glass tube communicating with the interior of the quartz envelope30. A restricted open end50is formed adjacent the quartz envelope30. Amalgam44is placed within the amalgam container46. The amalgam container46is sealed at sealed end48. During manufacture of the germicidal lamp, the amalgam container46may be used to evacuate the quartz envelope30as well as to introduce other substances, such as an inert gas, prior to the placement of an amalgam44and being sealed at sealed end48. The restricted open end50is sufficiently small to prevent the amalgam44from passing therethrough. However, the amalgam is in communication through the restricted open end50to the interior of the quartz envelope30. Therefore, the mercury vapor pressure within the quartz envelope30may be controlled by the absorption and release of mercury by the amalgam44. The amalgam44may be any conventional amalgam well known for the purpose of controlling the mercury vapor pressure in a low pressure mercury vapor gas discharge lamp. However, because the amalgam44is retained in the amalgam container46, the type of amalgam44selected could be an amalgam that has desirable properties, but would melt at the expected high temperatures resulting from high wall loads and improved output.

FIG. 2Billustrates another view of a portion of the end of the gas discharge lamp illustrated inFIG. 2A. InFIG. 2B, the end of the gas discharge lamp is rotated 90° from the view illustrated inFIG. 2A.

FIGS. 3A and 3Billustrate another embodiment of an amalgam container for retaining the amalgam between the end of the lamp and the electrode. InFIG. 3A, a glass cylindrical or tubular envelope130has a sealing stem132used to seal the end of the tubular envelope130. The sealing stem132has electrode supports138formed therein. One end of the electrode supports138hold a filament electrode142with the other end of the electrode supports138passing through the sealing stem132and are electrically coupled to wires136. Wires136are electrically connected to pins, not illustrated inFIG. 3A, used to power the germicidal lamp. Formed within the sealing stem132is an amalgam container146. The amalgam container146has a sealed end148and a restricted open end150. Also formed adjacent the restricted open end150is a metal hook retainer152. The combination of the restricted open end150and the hook retainer152prevents amalgam144from passing therethrough and into the interior of the glass tubular envelope130. The restricted open end150and the hook retainer152are configured such that a gap formed there between is capable of retaining the amalgam even when in a fluid or liquid state. The amalgam typically being a mercury compound, generally has a property of being viscous yet capable of being retained within an opening having small enough dimensions. Accordingly, the surface of the amalgam144is opened to the interior of the tubular envelope130of the germicidal lamp, but is retained in position behind the filament electrode142and adjacent the end of the germicidal lamp. The amalgam container146may be a small tube that is also used to evacuate the interior of the germicidal lamp as well as introduce other materials, such as an inert gas, during manufacture of the germicidal lamp prior to sealing.

FIG. 3Bis an enlarged view illustrating a portion of the amalgam container146. As more clearly illustrated inFIG. 3B, the restricted open end150is formed by a hole154within the amalgam container146and the hook retainer152. The hook retainer152may be made of a metal material that is imbedded within a side of the glass amalgam container146. The amalgam144is thereby retained in position even when the germicidal lamp is held vertically during operation.

The present invention makes possible a high output mercury vapor gas discharge germicidal lamp that can be heavily loaded without overly heating an amalgam. The position of the amalgam outside of the arc path and in a cooler location behind the electrode prevents the amalgam from being overheated. Overheating of the amalgam compromises the efficient operation of the germicidal lamp. Additionally, the restriction and containing of the amalgam within the desired location makes possible operation of the germicidal lamp in a vertical position while under high load. The present invention also makes possible the efficient operation of a germicidal lamp over a relatively wide range of operating temperatures. This is particularly important when used in waste water treatment due to the range of waste water temperature. Additionally, since a higher load high output germicidal lamp is obtained with the present invention, fewer lamps are needed to achieve a desired germicidal action thereby resulting in the need for fewer lamps and resulting in lower cost. Further, maintenance costs are reduced due to the use of fewer germicidal lamps.

While the present invention has been described with respect to various embodiments, it should be appreciated by those skilled in the arts that various modifications may be made without departing from the spirit and scope of this invention.