Title of Invention

A TANK AERATOR HAVING MAXIMUM OXYGEN TRANSFER RATE AND AN IMPROVED AERATION PROCESS USING THE SAME

Abstract

A tank aerator comprising a tank, plurality of rotor blades connected to a motor, the said blades being place at equi -distance from each other and positioned at a predetermined place, the said tank being designed following the optical geometric similarity for any dynamic condition, being defined as: - L/D =2.88; H/D =1; b/D =0.24; I/D = 0.3 and L/D = L/H 0.94 wherein L = size of the tank D= diameter of the rotar, H = Fluid depth of the tank & b & 1= dimensions of the blade.

Full Text

The invention relates to water quality management. It is concerned with water treatment plants and wastewater treatment plants. Further this invention is concerned with water and wastewater treatment plants in industries where both or either of aeration and mixing are involved. Precisely this invention related to and concerned with simulation of maximum oxygen transfer rate by using an optimal geometrically similar surface aerator (Design of surface aerators for maximum oxygen transfer). It is well known in the art that aeration is a process of inducting oxygen into a water body (which is oxygen deficient) for its treatment or purification by increasing the dissolved oxygen content. It is achieved mostly by surface aerators. Aeration is an essential process that should be employed in water and wastewater treatment plants. At present the aerators which are available commercially face various shortcomings and disadvantages. The object of the invention is to overcome or surmount the problem associated with prior art methods and system. Manufacturers are supplying surface aerators as a black box to the user to meet specific requirements in the filed. The most commonly available aerators are designed with outdated technology and they are not efficient to meet the present day requirements. Moreover, once such aerators are supplied and installed, they can not be modified to meet the changing environments and needs in the treatment plants. The aerator invented herein overcomes all such difficulties faced by the user, and it has been developed based on years of modern hydraulic research. The primary objective of the invention is to invent a novel surface aerator. It is another objective of the invention is to invent a novel surface aerator, which will enable maximum oxygen transfer. It is another objective of the invention is to invent a novel surface aerator, which has optimal geometric similarity. Other objects of the invention will be clear from the following description. The equipment required are a tank aerator having preferably a square shaped tank, a plurality of rotor blades. The blades being equal distance to each other are positioned at pre determined places, the said blades being fixed to a rotor which is in turn fixed to a motor, the said tank aerator inducts maximum aerator rates due to its optimal geometric similarity and desired level of mixing. This invention thus provides a tank aerator comprising a tank, plurality of rotor blades connected to a rotor which is in turn connected to a motor, the said blades being place^at equi-distance fi-om each other and positioned at a predetermined place, the said tank being designed following the optical geometric similarity for any dynamic condition, being defmed as L/D = 2.88; H/D = 1; b/D = 0.24; I/D = 0.3 and L/D = L/H = 0.94 wherein L = Size of the tank D = Diameter of the rotar H = Fluid depth of the tank b & 1=} dimensions of the blade. Now the invention will be described with reference to drawings accompanying this specification. Fig.l shows the schematic diagram of square tank aerator. Fig.2 shows the simulation of oxygen transfer in square tanks. With reference to the drawing this novel aerator is a square tank aerator. Its cross sectional elevation is shown in Figure 1. It consists of 6 flat blades (n = 6) of dimensions b and I. All the blades are radically at equidistant and at same level on a diameter D, called as rotor diameter. These blades are fixed to a rotor rod and it is then fixed to the shaft of an electrical motor by a flange. The speed of rotation of the rotor (also called as an impeller), N in rpm can be controlled. The size of the tank is L and its bottom is horizontal with sides vertical. It is open to atmosphere. The fluid depth in the tank is H. The blades are submerged in the water such that the distance between the top of the blades to the bottom of the tank is h. The rotor with blades are to be concentric with the tank cross section, and all the blades are at the same level. The kinematic viscosity of the fluid is V. The acceleration due to gravity is g. The aerator including the rotor with blades can be made of steel or of a suitable materials to withstand the forces. Optimal geometric similarity; The following optimal geometric similarity has to be maintained to achieve maximum oxygen transfer coefficient, Is^ao, for any dynamic condition, N of the rotor, L/D = 2.88; H/D = 1; b/D = 0.24; I/D = 0.3; and h/D = h/H = 0.94. (1) The above geometric similarity can be used to design various geometric elements of a given size of tank. Thus the geometric design of the aerator can be accomplished. Simulation of Maximum Oxygen Transfer Coefficient, ki^aTn in any size of a geometrically similar tank: The following equation is developed based on a concept of "power per unit volume", to predict kLa2o, which has been established by conducting numerous experiments in several geometrically similar tanks of different sizes, kLa2o = Oxygen transfer coefficient at standard conditions and at 20° C. Design Example: Design an aeration system to reaerate lOm^ of water in a single square tank. The initial concentration of oxygen, Co is zero ppm and it is required reach 90% of saturation value, C* over a period of aeration of t seconds. Find the times, t required for say four different rotor speeds of N =10, 20, 30 and 40 rpm to achieve the required aeration. Take, the temperature T of the test water is 30 °C and its kinematic viscosity, v = 0.804x10-^ m^/s. Solution: First step of the problem is to determine the various geometric dimensions of the square tank aeration system, as shown in Figure 1, by making use of geometric similarity given in Eq. 1. According to that, as L = 2.88D and H =D hence the volume of water V = L^H = L^D = L^/2.88 =10m2/s, therefore the required linear dimension of the tank, L = (10x2.88)^"^ = 3.0652m., and the diameter of the rotor, D = L/2.88 = 1,0643m. The dimensions of the blade, b = 0.24D = 0.2554m and / = 0.3D = 0.3193m. The number of blades, n = 6. The water depth in the tank is to be maintained at, H = D = 1.0643m and the distance between the top of the blades to the bottom of the tank, h = 0.94D =1.0005m. The second step is to determine kLazo from the simulation Eq. 2 by knowing N, D and v. Accordingly, kLa2o values for the speeds of 10, 20, 30 and 40 rpm are respectively 0.0002594, 0.001717, 0.006319 and 0.01182 per second. The third step is to determine the oxygen transfer rate from Eqs. 3 and 4. Accordingly, as Co = 0 and Ct /C* = 0.9, from Eq. 4, t kLBr = -/n(1-0.9) = 2.3026 and from Eq. 3, t kLaao =2.3026/1.024"^°-2°" = 1.8164. Finally from the previous two steps the respective intervals of time, t the rotor to be rotated at speeds of N=10, 20, 30 and 40rpm to achieve the same required aeration rate are 7002, 1058, 287 and 154 seconds. Any of these speeds can be maintained to achieve the same aeration of Ct /C* = 0.9, however durations of the rotation are to be different. Thus the solution is obtained. In the above example entire volume of water is aerated in a single tank. As a matter of fact the given volume of water can as well be aerated by using two or more tanks of different or same sizes depending on the choice based on the economy of construction and power consumption, and the convenience of maintenance of given sizes of aeration systems. On similar grounds, the speeds of rotation can also be decided. Thus, the design criterion presented above is useful in designing as well as maintenance and operation of square tank aerators. It may be appropriate to mention here that the results presented are developed for pure water without any contamination. However, in reality the water may not be pure and it may contain certain sediments and pollutants, hence for such cases suitable corrections have to be applied to arrive at more appropriate values of oxygen transfer rate. Finding the effects of pollutants on oxygen transfer process is within the scope. It is also within the scope that above results can be extended to other shapes of tanks as well as to continuous flows (instead of in a tank) with suitable and appropriate modifications of the above equations. Special Advantages: This aerator inducts maximum aeration rate due to its optimal geometric similarity. The aerator is easy to fabricate, operate and maintain and skilled persons are not required. It is very economical. It can be operated to achieve desired induction of oxygen transfer rate in the fluid body as well as to achieve desired level of mixing. It is to be noted that the aforesaid description is intended to explain the salient features of the invention and it is not intended to limit the scope of the invention. It is also to be noted that using the simulation equation (2) along with the optimal geometric equation (1), one can design an aerator of any size and for any speed of rotar, wherein the oxygen transfer rate is predicted and can be employed in water treatment plants. It is to be further noted that within the scope of the invention various modifications are permissible. I Claim: 1. A tank aerator having maximum oxygen transfer rate comprising a tank, plurality of rotor blades connected to a rotor which is in turn connected to a motor, the said blades being placed at equi-distance from each other and positioned at a predetermined place, the said tank being designed following the optical geometric similarity for any dynamic condition, being defined as :- L/D = 2.88; H/D = 1; b/D = 0.24; I/D = 0.3 and L/D = L/H = 0.94 wherein L = Size of the tank D = Diameter of the rotar H = Fluid depth of the tank 1 = length b = breadth 2. A tank aerator as claimed in claim 1, wherein the tank used is preferably a square tank. 3. A tank aerator substantially as hereinbefore described and illustrated in the drawings. Dated This 5* Day of February 2000

Documents:

0169-mas-1999 abstract-duplicate.pdf

0169-mas-1999 abstract.pdf

0169-mas-1999 claims-duplicate.pdf

0169-mas-1999 claims.pdf

0169-mas-1999 correspondence-others.pdf

0169-mas-1999 correspondence-po.pdf

0169-mas-1999 description (complete)-duplicate.pdf

0169-mas-1999 description (complete).pdf

0169-mas-1999 description (provisional).pdf

0169-mas-1999 drawings-duplicate.pdf

0169-mas-1999 drawings.pdf

0169-mas-1999 form-1.pdf

0169-mas-1999 form-13.pdf

0169-mas-1999 form-19.pdf

0169-mas-1999 form-26.pdf

0169-mas-1999 form-3.pdf

0169-mas-1999 form-5.pdf

0169-mas-1999 form-62.pdf