Ultraviolet radiation is an important workhorse in the industrial community for promoting chemical reactions, initiating chemical reactions, degrading organic and non-organic molecules, inducing mutations in biological systems, acting as an antiviral and bactericidal agent and the like. Normally the source of the ultraviolet radiation is emitted from an electric discharge lamp having various types of gases which when excited by the electric discharge, emit UV radiation. These lamps are generally categorized as low or medium/high intensity lamps. They may operate at low or high pressures for the gases within the lamps. Normally the lamps are of a quartz material which is transparent to the emitted UV radiation. The lamps may operate at low or high temperatures ranging from approximately 30.degree. C. up to 1100.degree. C. The power input of these lamps may range from less than 40 watts to in excess of 60,000 watts of UV radiation. The lamps may be even customized to the extent that a certain portion of the UV spectrum is omitted or enhanced rather than the entire portion of the UV spectrum.
A driving force for such variety in UV lamps is that each of the above industrial applications requires lamps having different UV intensities, different wavelength of emission, operating pressure and temperatures and power requirements.
Normally the lamps, as employed in reactor systems, particularly reactor systems which contain aqueous media, have a variety of UV transparent protective sheaths within which the lamps are placed so that the lamps do not come in contact with the material being treated by the UV radiation. This technique protects the quartz of the UV lamp and the electrical connections to the lamp electrodes. Also it can facilitate lamp replacement without having to disassemble the reactor. Two examples of this type of water treatment system are disclosed in U.S. Pat. Nos. 3,462,597 and 3,562,520. An annular chamber is defined between the outer cylindrical wall of the water treatment apparatus and the inner sheath of the apparatus which protects the UV radiation emitting lamp from the fluids that are passed through the annular chamber in the fluid treatment apparatus. Both systems are designed so as to enclose the lamp ends as the lamp is positioned centrally of the apparatus and enclosed by the protective sheath. The sheath is of quartz or other UV transparent material. Special sheath cleaning mechanisms are described in these arrangements. The drawbacks of those systems are discussed in detail in applicant's U.S. Pat. Nos. 5,133,945 and 5,266,280.
The systems of these two earlier U.S. patents are adequate for use as an antiviral and bactericidal agent for treating drinking water. Low temperature lamps are used in accordance with standard techniques for exposing water to radiation. The lamps are totally enclosed. As demonstrated in both U.S. patents the lamp ends are completely enclosed and sealed off within the sheath. This allows replacement of air within the annular space defined between the lamp and the protective sheath with inert gases which are not oxidized by the UV radiation. This prevents the formation of ozone which is thought to be very harmful to the components used in the UV treatment systems. Completely enclosed lamps may be acceptable for systems using lamps operating at lower temperatures within the 40.degree. to 150.degree. C. range.
Another general approach for exposing fluids to UV radiation to initiate or expedite a desired chemical reaction within the fluids is to position a plurality of UV lamps around a reaction container having a vessel wall which is transparent to the UV radiation. This permits radiation emitted by the lamps to pass through the vessel walls and be absorbed by the fluids within the reaction container so as to initiate or expedite the desired reaction. Normally, the lamps as they surround the reaction vessel are enclosed. The enclosure may have UV reflective surfaces so as to direct radiation emitted by the lamps in a direction away from the reactor to reflect such radiation back towards the reactor. With the provision of several lamps within the enclosure overheating of the enclosed lamps can become a problem. An example of this type of reactor is discussed in U.S. Pat. No. 4,002,918.
In U.S. Pat. No. 4,897,246 and its divisional application U.S. Pat. No. 4,952,376 a UV treatment system is disclosed for decontaminating various forms of waters and waste waters. The waste waters are introduced at one end of the reactor system and by use of baffles, the waters are directed in a zigzag pattern flow over lamps within the reactor chamber. The reactor chamber is rectangular with a continuous flow of liquids through the reactor chamber. The lamps used in the system are of significantly higher power than the lamps used in the aforementioned water treatment systems of U.S. Pat. Nos. 3,462,597 and 3,562,520. In accordance with standard techniques the UV radiation emitting lamps are isolated from the fluids being treated by suitable protective sheaths. Also in accordance with standard practice the ends of the lamps are sealed off so as to define a sealed annular space between the lamp and the protective sheath. In this arrangement the preferred form of lamp used is a higher pressure mercury lamp, sometimes referred to as a medium pressure lamp. These lamps have been called both medium pressure and high pressure lamps in the literature. The operating characteristics for these lamps can vary a great deal. Lamps which we will refer to as medium pressure lamps are mercury lamps with pressures of 1 to 10 atm, with bulb temperatures greater than 300.degree. C. and input power densities of 40 to 100 watts/cm of bulb length. These lamps operate at considerably higher temperatures than the low pressure UV lamps. Medium pressure lamps operate at temperatures usually in excess of 300.degree. C. One advantage in using the high temperature medium pressure lamps is that they are less susceptible to changes in fluid temperature. On the other hand, with low temperature low pressure UV lamps any significant change in water temperature can appreciably affect the operating temperature of the low pressure lamp and hence, affect its overall performance.
Higher intensity lamps, such as medium pressure mercury lamps are therefore preferred in this respect as discussed in U.S. Pat. No. 4,952,376. However, in view of the lamps being sealed within the protective sheath of the reactor, difficulties can be encountered in overheating of the lamps and possible deterioration as the lamp power increases. Other than cooling of the lamps as provided by fluid flowing over the protective sheaths, the temperature sensitive lamp end portions which include the electrical terminals are not adequately cooled and can from time to time overheat resulting in lamp failure. Such overheating problem with the higher temperature medium pressure lamps has therefore discouraged their use in UV treatment systems. As a result, lamps used in the system of U.S. Pat. No. 4,952,376 operate at the lower end of the temperature scale for medium pressure lamps and hence have less output compared to lamps operating at the higher end of the temperature scale.
Many commercially available systems function with the use of low temperature low pressure mercury lamps which have low power input usually in the range of 40 to 140 watts of UV power for each individual lamp. This power input usually equates to approximately 0.4-0.8 watts/cm of lamp arc length and operating temperatures less than 100.degree. C. A commercial use of low power lamps for killing microorganisms in drinking water is described in U.S. Pat. No. 4,179,616. Conventional G-37-T6 ultra-violet lamps are used which have an operating output in the range of 37 watts with an operating temperature well under 60.degree. C. The primary use of the Coviello et. al. system is to produce optimum quantities of ozone by passing air through the system at a very low flow rate. The produced ozone is then transferred into a treatment tank to further sterilize the drinking water. Coviello et. al. contemplate the passage of air over the lamp ends, such as described with reference to FIGS. 3 and 5. The air is introduced under pressure and circulates at high velocity only over the lamp ends. The system of FIG. 4 of Coviello contemplates passage of air at a low flow rate over the lamp to optimize a generation of ozone, whereas apparently at the lamp end portions, the space is relatively constricted so that a higher flow rate is achieved over the lamp ends to effect cooling thereof. Although, these approaches to lamp end cooling may be suitable for low pressure lamps operating at relatively low temperatures normally less than a 100.degree. C, such cooling systems are totally unsatisfactory for medium and high pressure lamps operating a temperatures in excess of 300.degree. C.
There are several other disadvantages and drawbacks to the above systems for the treatment of contaminated fluids. Low pressure lamps have good efficiency (30%) which refers to the percent output of UV between 200 nm and 300 nm, which is the important UV region for decontaminating fluids. However, low pressure lamps have a major disadvantage since they are of such low input powers (40-120 watts typically) that a very large number of lamps are required for the treatment of fluids at high flow rates. This becomes impractical since many lamps and reactor chambers have to be built and maintained. Conventional medium pressure lamps are of low efficiencies, &lt;20%, such that again too many lamps are required and the electrical consumption is high. There is thus a need for a lamp which operates at high power with good efficiency. There are now lamps available with high power inputs and efficiencies of around 30%. These lamps have higher input per unit length of arc than do the standard medium pressure lamps (100-300 watts/cm compared to &lt;100 watts/cm). The lamps also run hot with bulb temperatures in the range of 600.degree. C.-1000.degree. C. These factors result in much more heat being generated at the quartz surfaces of the sleeve and lead to problems with cooling of the lamps and the surrounding materials of constructions.
In applicant's aforementioned U.S. Pat. Nos. 5,133,945 and 5,266,280, a cooling system is described for the high pressure lamps which operate at temperatures normally in excess of 600.degree. C. Individual cooling fans are provided at each end of the reactor system to direct cooling air onto the ceramic mount for each lamp end. Each cooling fan has a duct for directing the cooling air at the ceramic mount to ensure that the electrodes sealed into the lamp ends do not degrade due to the high temperatures in the quartz of the lamp. Air which is directed at the lower portion of the lamp may enter the annular space between the protective sheath and the quartz lamp surface. Such circulating air is allowed to exit at the top of the reactor to further enhance the cooling of the system. Although this system is adequate for cooling of the high pressure lamps, it has been found that lamp operation is not always consistent and hence has been enhanced by the cooling system described in applicant's aforementioned U.S. patent application Ser. No. 07/836,617 filed Feb. 18, 1992.
The present invention provides an exhaust system for lamp cooling which not only improves lamp cooling but as well improves lamp operation and at the same time continues to provide protection for the surrounding materials supporting the lamp in the reactor.