Patent Application
20110318237
This invention relates to ultraviolet reactors, and more particularly, to baffle configurations for ultraviolet reactors.
Ultraviolet light (UV) light is an effective means for pollutant removal from contaminated waters through either direct UV photolysis or UV radiation-indirectly-induced oxidation of chemical compounds. UV light has also been proven to be effective for water and wastewater disinfection. The efficiency with which a UV reactor is able to degrade the contaminant or inactivate the microorganisms is dependent on several parameters including the hydraulic characteristics of the reactor, the spatial UV fluence rate distribution within the reactor and the degradation or inactivation kinetics of the target compounds or species. The UV fluence rate is attenuated by the distance from the lamp and the transmittance of the media. Generally, the higher the UV fluence rate, the faster the activation of oxidant.
Developing a suitable flow pattern is an important consideration for increasing the efficiency of a UV reactor. It is desirable that the flow pattern result in sufficient radial mixing with a uniform residence time so that the water receives a relatively uniform UV dosage. Turbulent flow is typically used to achieve sufficient radial mixing. However, such flow is achieved by using a relatively high flow rate, which undesirably results in a relatively short residence time. In order to achieve uniform residence time, plug flow is desired. However, this results in relatively poor mixing especially for fluid particles flowing in regions relatively far from the UV lamp, such as near the wall of the UV reactor.
Ultraviolet reactors having an ultraviolet light source for treating a fluid are disclosed. In one embodiment, a reactor is disclosed which includes a vessel having an inlet for receiving fluid and an outlet for discharging fluid. The vessel further includes a plurality of segmented baffles. The baffles further include a partial circumferential edge section that terminates in a vertical edge section to form right and left segmented baffles. The left and right segmented baffles are arranged in an alternating pattern in the vessel to provide plug flow and enhanced radial mixing.
a-4c depict the fluence rate distribution for a UV reactor without a baffle, with a full helical baffle and with a helical baffle having an 80% width, respectively.
a-5e depict a particle flow path for a UV reactor without a helical baffle and for a UV reactor having helical baffles of varying widths.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising,” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms “mounted,” “connected,” “supported,” and “coupled” and variations thereof are used broadly and encompass direct and indirect mountings, connections, supports, and couplings. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings. In the description below, like reference numerals and labels are used to describe the same, similar or corresponding parts in the several views of
Referring to
In order to increase input UV energy, a pair of UV lamps may be utilized although it is understood that other configurations may be used. In the current embodiment, the UV reactor 100 includes first 106 and second 108 UV lamps which extend from first 110 and second 112 ends, respectively, of the vessel 102 into the chamber 104.
The UV reactor 100 further includes spiral or helically shaped first 114 and second 116 baffles which extend around the first 106 and second 108 UV lamps, respectively. In a preferred embodiment, the first 114 and second 116 baffles each include 10 coils or layers. The first 114 and second 116 baffles serve to guide or channel fluid in a helical flow path which corresponds to the shape of the respective baffles 114,116 as fluid flows from the first end 110 to the second end 112 of the vessel 102. The first 114 and second 116 baffles may be fabricated from stainless steel or quartz.
The first 114 and second 116 baffles increase hydraulic retention time and provide enhanced radial mixing.
The UV reactor 100 also includes inlet 118 and outlet 120 ports for receiving and discharging fluid, respectively. The inlet 118 and outlet 120 ports are positioned substantially perpendicular to a longitudinal axis 122 of the vessel 102 and are aligned to cooperate with the first 114 and second 116 baffles.
It has been found that the presence of a baffle fabricated from stainless steel inside the reactor 100 blocks a portion of the UV light emitted by the UV lamps.
a depicts a particle flow path 115 for a UV reactor that does not include a baffle.
Calculations show that the average UV irradiance for a 10 layer, 100% width baffle reactor is approximately 80% of that in a reactor without baffle. In order to decrease the amount of UV energy loss due to the baffle, either a UV reflective or a photo catalytic coating layer may be applied to the stainless steel surface of the baffle. In regard to a baffle having photo catalytic coating, it has been shown that silver ion effectively activates the persulfate ion to generate a sulfate radical. Another coating which may be used to decrease the effect of UV energy loss is a titania coating having a mesoporous nano-structure which can effectively adsorb organics. Further, the band gap of nano-structure titania may be adjusted to absorb the corresponding UV wavelength output for the UV lamp that is being utilized. An atom of a persulfate catalyst (e.g. Ag, etc.) can be immersed into the titania crystal structure to enhance the catalytic effects.
A UV reactor is typically fabricated from stainless steel. In order to enhance UV reflectivity, the interior stainless steel wall of the UV reactor is typically polished. The reflectivity for a polished stainless steel surface is in the range of 30% to 50%. Thus, 50% or more of UV light which falls on the reactor wall is either absorbed by the reactor or converted into heat. In order to enhance reflectivity, a microporous diffuse type reflector may be used to coat the interior wall of the UV reactor. A suitable reflector may be fabricated from GORE™ DRP® Diffuse Reflector Material type light diffusing material, for example. This material is fabricated from highly stable, chemically inert polytetrafluoroethylene (PTFE) and provides the added benefit that no secondary contamination will leach out from the reflector. The reflectivity of a reflector is related to the thickness of the material and wavelength of the UV light that is used. By way of example, a 1 mm thick reflector has a reflectivity of greater than 99.5% at a UV wavelength of 254 nm. In the presence of a UV reflector, the UV light undergoes multiple reflections within the UV reactor and leads to a greater UV intensity and a more homogeneous UV field compared to a system without a reflector.
Experiments regarding the effect of a UV reflector were performed with a UV batch reactor that is used for high purity water treatment. The light path of the UV batch reactor was 4 cm. The average intensity in the UV batch reactor without reflector was simulated to be 31.2 W/m2. Persulfate was used as an oxidant precursor. The transmittance of persulfate solution at a UV wavelength of 254 nm was determined to be 99.3%, which indicates that 97% of UV energy will impinge on the wall of UV reactor.
A UV reflector is suitable for use in several applications including high purity water treatment wherein the transmittance is usually higher than 99% which thus leads to an increased amount of energy reaching the wall of the reactor. In addition, a shorter light path maximizes the efficiency of a reflector. In accordance with the present invention, fewer UV lamps may be needed in a reactor to achieve an equivalent UV intensity if a UV reflector is used. Therefore, the capital cost for a UV chamber and operational costs for items such as energy consumption and UV lamp replacement are significantly decreased.
In another embodiment, the current invention is directed to a UV reactor having a segmented baffle configuration. This configuration also provides enhanced radial mixing and relatively uniform UV dosage as previously described. In addition, the segmented baffle configuration may be fabricated using straightforward manufacturing techniques and may be readily scaled up depending on the application.
Referring to
The segmented baffles 134 may be either left 142 or right 150 segmented baffles. Referring to
The right segmented baffle 150 has a reverse configuration to that of the left segmented baffle 142. In particular, each right segment baffle 150 has a substantially C-shaped configuration which includes a partial circumferential edge section 152 that terminates in a right vertical edge section 154 located on the right side of the baffle 150. Each right segmented baffle 150 also includes through holes 148 for receiving the UV lamps 134. Although the left 142 and right 150 segmented baffles are shown with a left 146 and right 154 vertical edge sections, respectively, it is understood that the edge sections 146,154 may be oriented horizontally or angled between vertical and horizontal in accordance with the present invention. In addition, the left 142 and right 150 segmented baffles may also include a reflector coating as previously described to reduce the effects of any UV light blocking by the segmented baffles 142,150.
Referring to
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While the invention has been described in conjunction with specific embodiments, it is evident that many alternatives, modifications, permutations and variations will become apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended that the present invention embrace all such alternatives, modifications and variations.
