Patent Application
20080215248
The present invention concerns a method and device for real-time monitoring of biofilms and other deposits attached to the surfaces of ducts, reservoirs and equipments.
One of the major and more frequent problems in ducts, reservoirs and other equipments is the build up of undesirable biofilms and deposits. Fluids flowing in ducts and other equipment usually carry some type of nutrients that favor the development of microbial colonies which attach to surfaces in the most suitable places.
After this initial attachment, further adhesion of micro-organisms becomes easier, leading to the rapid formation of a biofilm. The development of such microbial layers causes not only an increase in the resistance to flow, but also an increase in the heat transfer resistance to the outside of the surface, resulting in higher energy costs and in an overall reduction of the efficiency of the fluids distribution systems.
Additionally, biofilms are matrices that favor the incorporation and development of pathogenic micro-organisms, and their release to the external fluid which, in the case of drinking water systems, constitutes a risk to public health.
Some micro-organisms can also induce corrosion on the surfaces of ducts, increasing the maintenance costs of such infrastructures.
Such deposits may have different causes, generically classified in three main groups:
The real-time detection of such deposits is crucial to prevent or minimize their development, since it enables the application of appropriate counter-measures in due time. With such purpose in mind, several monitoring methods were developed, some of them being in effective use at the moment, and others seeming to be potentially useful (bibliography [1] to [12]), based on:
The methods based on pressure drop and heat transfer measurements, (a) and (b), are not sensitive enough to the presence of small amounts of deposit, that is, to the initial phase of adhesion. The methods based on heat transfer measurements are particularly appropriate for monitoring heat exchange equipments, although they are subject to well known experimental errors associated to the measurement of small temperature differences in solid surfaces.
The differential turbidimetry (c1), the optical fiber sensor (c2), the infrared sensor (c3) and the image sensor (c4) can be applied only to the deposition on transparent or semi-transparent surfaces (which is rarely the case of ducts and industrial equipment), the same is also true in Quartz Crystal Microbalance devices (d1) and in Photo Acoustic Spectroscopy (d2). The direct contact of the sensing element with the fluid, as well as the fact that the materials of the duct and the sensor surface are different are also disadvantages in many applications. In the case of the quartz crystal microbalance it is also necessary to assure that the flow, if it exists, is laminar. The method (d3) is specifically appropriate for the detection of solid particles.
The techniques described in (e), measurement of electrochemical parameters, has the disadvantage of being only applied to deposits formed on metallic surfaces. Such methods are particularly sensitive to the influence of external electric and magnetic fields.
The technique (f) cannot be applied to ducts neither allows real-time data acquisition.
Finally, method (g) is not automatic and, therefore, has a limited interest.
Transducers based on acoustic waves (d) SAW (Surface Acoustic Wave), TSM (Thin Shear Mode), QCM (Quartz Crystal Microbalance) are composed of a polished substratum of piezoelectric material, usually quartz, and two electrodes, the emitting element and the sensor, respectively, located on the end zones of the substratum. On the central zone, a chemically inert metallic element, typically gold is placed. The wave propagation characteristics of this element vary with the chemical substance that is supposed to detect (SAW). These devices can make use of Rayleigh waves or surface shear waves, called ‘Love Waves’, which are more appropriate for liquids. The frequency used for the excitation lies in the ultrasound range, normally hundreds of MHz. In the QCM, the deposit formed on the quartz surface modifies the mass and consequently affects the resonance frequency of the crystal. These are expensive devices, often used in chemical analysis and quite sensitive to external factors, therefore demanding very carefully operating procedures. However, their main disadvantage for monitoring biofilms and other deposits is the need of direct contact with the sample, which eliminates the possibility of measuring such deposits on the most common surfaces in ducts and other equipments. Additionally, turbulent flow produces significant interferences on the output signal of these devices.
The objective of the present invention is to disclose a simple and economical solution for in-line real-time detection of the deposits formed on the surfaces of ducts, reservoirs or equipments made of different materials.
The solution is based on the fact that the formation and/or removal of the deposit modifies the wave propagation properties of the surface, which can be measured by a suitable sensor.
Thus, the objective of the present invention is to provide a method for monitoring the formation of biofilms and other deposits using vibration, characterized to include the following steps:
Moreover, it is also objective of the present invention to disclose a device for measuring and identification of biofilms and other deposits using vibration, according to the above method, comprising:
Ducts and other equipments in contact with fluids are subjected to the formation of undesirable deposits that can affect negatively the energy performance of industrial units, constitutes a risk to public health and degrades the material on the equipments.
The present invention has substantial advantages over the existing techniques for industrial applications, being: the device can use different surface materials, like metals, polymers and glass; it is not required the sensor element to be in direct contact with the fluid, neither with the deposit formed on the surface under study; it enables to monitor the entire area between its elements; it gives an instantaneous response; it enables a correlation between the output signal and the physical properties of the deposit. The described device is cheap, compact, easy to maintain and operate, can be applied in industrial circulation fluid systems and reservoirs and it can sense small deposit masses (under 100 μg/cm2). The device can be applied in-line or in side stream, with laminar or turbulent flow.
The device disclosed here can detect the presence of deposits, measure them and identify their nature through mathematic analyses of the response of the surfaces to a pre-defined excitation.
The device object of this invention can have different configurations, being generically composed by an element that generates vibration (1), an element that senses vibration (2), a duct, reservoir or equipment (3), an electronic data acquisition unit (4), that generates the vibration signal, acquires and process the signal from the element that senses the vibration (2), as represented in the
Both elements are, for example, of piezoelectric type (ceramic, polymer or quartz) and the device is controlled by an electronic data acquisition unit (4). Alternatively, the element that generates vibration (1) is of piezoelectric type and the vibration sensor (2) is an accelerometer. The element that generates vibration and the element that senses the vibration, can be fixed inside or outside a duct, reservoir or other equipment to be monitored, placed in pairs. They can be connected to a single unit (4) that can make the digital signal processing of several sensors. The electronic data acquisition unit can be connected directly to the element that generates vibration (1), or having a power amplifer in between (5) to increase the power of the vibration induced in the duct (3).
In the same way, the signal of the vibration sensor can be connected directly to the electronic unit (4) or having a signal conditioning interface in between for amplification and filtration (6). The electronic data acquisition unit can be based on a computer with a data acquisition board (for example from National Instruments®), or a DSP board (for example from Texas Instruments®) or also a board based on a microcontroller (for example from Atmel®) able to generate and acquire data. Alternatively, a function generator (for example from Agilent®) can be used for the generation of the vibration and an oscilloscope (for example from Tektronix) for signal acquisition from the element that senses the vibration.
To increase the sensitivity of the monitor device, the signal can have a frequency close to the resonance frequency of the surface, although it can be operated at other frequencies. Normally, the vibration signal is periodic and can be, for example, a sinusoidal or square wave type.
After being acquired by the electronic unit (4), the signal from the vibration sensor must be mathematically processed by using well known tools for digital processing signal (for example, FFT, average, amplitude, phase shift, area below the curve, etc.) or by using techniques of artificial intelligence (like for example, neuronal networks).
The electronic data acquisition unit identifies the characteristic values of the vibration signal: amplitude, frequency, peak values, phase shift, damping, among others, that can be related with the deposits (deposition/removal) and their physical properties.
Namely, it was verified that the amplitude and the frequency are related to the mass of the deposit.
In the following example, the element that generates vibration (1) and the element that senses the vibration (2) are glued to the outside of the PVC surface (9) fixed to the flat surface of a water duct with a semi-circular cross section (3)—
The element that generates vibration (1) and the element that senses vibration (2) are piezoelectric ceramics of the bender type, with the dimensions of 25×7.5×0.4 mm glued with epoxy on the surface of the PVC board (9) and attached to the outer side of the duct. The distance between the element that generates vibration (1) and the element that senses vibration (2) is of 60 mm.
The electronic data acquisition unit (4) is based on a computer equipped with a data acquisition board, ref. PCI 6221 (National Instruments®). The signal generated by this unit is amplified by six times in the power amplifier (5) and then connected to the piezoelectric element that generates the vibration (1),—
By using standard digital signal processing techniques, several characteristics of the output signal are calculated. Among them are the phase shift between the signal generated and acquired, the amplitude of the signal peaks, FFF, damping factor, integral, etc. These parameters can be related with the process of formation/removal of the deposits in ducts and with the deposit structure.
During the experiments, vibration data is periodic acquired and processed (of about one hour interval). The amplitude of the FFr of the measured signal at the resonance frequency can be correlated to the mass of the deposit and, then, to the deposit formation/removal process on surfaces. Notice that this amplitude has an inverse variation with the amount of the deposit. For this reason, and in order to make the text easier to understand, the value corresponding to the monitor clean (starting time—before the deposition starts) is consider as a offset, being all amplitude values subtracted from this. This way, it will be used the variation of the output signal (output processed signal), to observe a direct relation between this parameter and the increase of the deposit in the surface.
In
In this example, the above referred procedure of example 1 was repeated, having been studied the silica deposition in turbulent flow instead of a biofilm.
The main conclusion presented in the example 1 is also valid for the example 2.
The variation of the output signal is directly related with the amount of deposit (wet mass per unit of area) in the duct. However, the output signal is different in both cases.
Silica is a rigid material (less elastic) than a biofilm, so the variation of the output signal is affected by a different damping factor. It can be observed that for identical masses of silica and biofilm, the variation of the output signal is smaller in the first case. Thus, the variation of the damping factor is a parameter that can be used to compare different types of deposits, since larger variations in the damping factor are observed for more elastic deposits (like the case of the biofilm, in comparison to the silica)—
In example 3, it was used as a vibration sensing element, a high sensibility accelerometer—
The above examples are presented as illustrative, and they cannot intend to represent all the range of applications where this invention can be used.
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| Number | Date | Country | Kind |
|---|---|---|---|
| 103344 | Sep 2005 | PT | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB06/52992 | 8/29/2006 | WO | 00 | 3/10/2008 |
