A PROCESS TO REMOVE SALT OR BACTERIA BY ULTRASOUND. DESCRIPTION OF THE INVENTION

OBJECT: The object of the application for this patent is a process to remove salt and/or bacteria by ultrasound which, by means of the control of cavitation, achieves the removal of the salt cristals and also aids in the removal of coliforms and bacteria from the fluid by means of bursting the gas bubbles in such, so that water is obtained which meets different quality criteria, with low impact on the environment, low energy costs and a high rate of processing.

FIELD OF THE INVENTION: The present invention relates to the technical area of removal of salt from water by means of ultrasound, providing a solution to the technical problem of obtaining drinking water.

PRIOR ART: The scarcity of water has become critical. Alternative methods of obtaining such are through use of underground sources (which are becoming more and more contaminated by the use of agro-chemical products) and sea water, which in order to be drinkable must be cleansed and have the salt removed.

There are numerous procedures for removing salt which contain diverse techniques, but which can be divided up into two large groups :

Group 1.- The water changes its state durting the course of treatment :

A) Passing through a gas phase (distillation) : *Process involving gas compression

*Thermal multiple effect process

*"Multiflash" (multiple expansions) thermal process

B) Passing through a solid phase: *Freezing

*Formation of hydrates

Group 2.- The water does not change state during treatment (processes with membranes) :

*electrodyalisis

*inverse osmosis

Inverse osmosis has been the area which has attracted most attention from an innovation point of view (381 patents) , followed by technologies which use solar energy (212), multiflash evaporation (116), ionic interchange (106), multiple effect evaporation (54), steam compression (11) and patents using zeolite (10) .

The countries which have produced most patents in the area of salt removal are the USA, Germany, Japan, China, Great Britain and France; and the countries which have received most patent applications related to salt removal are the USA, Japan, Great Britain, Germany and China. ¹

The process of inverse osmosis to obtan good quality water, takes a long time and uses a lot of energy, which translates into a high cost for each cubic metre of water. The process consists of a single operation in which the whole of the transfer of the mass of water is carried out at the ambient temperature, with no need for regeneration. The rejection of saline ions provoked by the gradient of concentration which exists in the space membrane- solution and its consequent dielectric interactions on the surface of the membrane result in the rejection of the salts so that a flow of water passes through the pores with a rejection of the

Publicity material: Process for removal of salt from water - diverse technologies.-

salt of up to 99%. The organic substances are separated by means of a mechanical filter, in which case the degrees of filtration depend almost exclusively on the size of the particles. -

The type of polymeric structure and the size of the pores allow the membranes in the inverse osmosis process to eliminate bacterias, viruses and colloids which are present in the water to be treated. Before being used the water is processed using ultraviolet light which reassures its purity. The untreated water is pre-treated by means of a filter, the retaining of solid particles is obtained using filters of 5 microns. The water treated by means of these filters is re-pumped and propelled to the modules of Inverse Osmosis.

In this stage the removal of salt from the water is obtained resulting in two currents of water, one pure and one with effluents or particles.

In order to prolong the lifetime of the membranes, the system contains a simple washing process which the operator can use by the simple functioning of valves. As a form of avoiding multiplication of the micro-organisms retained in the membranes, periodical cleaning takes place to remove bacteria using the same system mentioned previously, which process does not take longer than 10 minutes.

The applicant is also aware of the following prior art regarding the procedure for removal of salt and the use of ultrasound to purify water and other liquids or fluids:

Ultrasound Design for sterilising liquids WO9737937, 16/10/1997, also published as DE19614240

Ultrasound equipment to remove gases dissolved in water DE 19652127, 18/06/98

Ultrasound treatment for water and other fluids

Destruction of pathological agents by ultrasound GB2350106, 22/11/2000

Designs and processes for use in treatments using ultrasound WO2005005322, 20/01/2005

However the applicant is not aware of any prior invention which has the characteristics contained in the present description. By way of this invention a technical solution is obtained for the removal of salt from water, so that the water meets diverse quality criteria, has a low environmental impact, low energy costs and a high rate of treatment. All these parameters are achieved by the invention described herein.

DESCRIPTION : The new process consists of two steps: 1.- Decanting of sediment and coliforms and 2.- Removal of salt and bacteria .

The first step - decanting of sediment and coliforms - is carried out in a water treatment unit in which the processes of preparation and injection of chemical products, coaggulation- flocculation, sedimentation, filtration and disinfection take place. The second step - removal of salt and bacteria - is located in the previous system in the part where flocculation and coaggulation are carried out; in this process the decanting of coliforms is carried out using a doseage of aluminum sulphate and the movement of the fluid. At this phase of the process, the ultrasound procedure is added, which, by means of control of cavitation, enables the salt cristals to be decanted and also assists in decanting the coliforms and bacteria by means of bursting the gassed bubbles of such.

Ultrasound is no more than mechanical vibrations which take place in the surrounding area, generated, either naturally or

artificially for scientific or industrial purposes, and they have the particular characteristic that they are not audible to the human ear. This is not strange, since our range of hearing is quite limited, covering approximately 20 hz to 20 Khz. Thus all vibrations over 20khz will be considered as ultrasound. In the human and animal environment these vibrations are found on many occasions. One does not need to refer to the well known cases of bats or dolphins: the simple rattle of keys produces the major part of its noise outside the human range of hearing and the loss of fluid under pressure through the pores of a tube which are almost inaudible can only be detected by ultrasound detectors.

The present section deals with some of the basic physical concepts which are necessary to better understand the concrete applications which can be made of ultrasound.

The parameters of interest in a vibration which is transmitted through any material are the local pressure put on some particles of the material on others and the relative speed of such, and the movement of the particles with respect to the position of rest which they occupied when there are no vibrations .

In the frequencies used in industrial ultrasound, the length of the waves of vibration will always be several times greater than the dimensions of the molecules, so that quantic effects will not have to be taken into account, it being possible to consider the means of propagation as continuous. Starting from very simple considerations it is possible to easily establish the equations for the propagation of mechanical vibrations in gases and in liquids and solids.

1) It is possible to produce mechanical vibrations in any fluid (gas or liquid) or solid, with the form of vibration of the particles and the speed of formation of the waves varying from case to case

2) In fluids the speed of formation is provided by the following equation:

In which Y is the constant adiabatic of the matter, PO is the pressure to which it is submitted and pO is the density at rest .

Obviously it is assumed that the contractions and dilations of the fluid are adiabatic and that the real speed of the particles is sufficiently low to enter into an acoustic state called lineal, that is, when the equation of formation takes the usual form of the equation of waves.

3) In solids the possibilities of formation are more complex, since there are basically two types of vibration, that is longitudinal waves, in which the speed of the particles have a direction of propagation and waves of windshear, in which the movement of the particles is in the same direction as the propagation of the front of the wave. In a real case it is possible for both modes of vibration to exist simultaneously, which situation is not desirable in industrial applications since the division of energy between different modes of vibration contributes to diminishing, appparently, the desired vibration.

As regards the speed of propagation for the case of longitudinal waves this is given by the formula:

Vs long = V

Where λ and μ are the so-called Lame quotient, constant for each material and pO is the density.

For the transversal waves the formula is:

Vs cis = V pO

In which the symbols have the same meaning. It should be noted that the coefficient μ coincides with the module of windshear for an isotrope material and that the module of Young for the material is given by the formula :

YO = μ ( 3+2μ ) λ+μ

4) It is convenient to note that the previous results are valid for a means of infinite propagation. If this is not the case then the relationships indicated above can take on different aspects.

In this way it can be shown that for a long piece of small transverse dimensions with regard to the length of the wave and which is subject to a longitudinal vibration, the speed of propagation in the vibrations is given by the formula:

11

Vs = V po

A very useful concept in acoustics is that of acoustic impedence, by analogy with the electrical impedence of a circuit. This impedence is defined as the quotient between the pressure of the particles at a particular point and their speed, that is:

Z =

V

Both P and V will be complex numbers since it is supposed that that the problem is analysed in a permanently sinusoidal regime. In the case of an undefined flat wave, the acoustic impedence has a real value as follows:

Z = pOVs

In which Vs is the speed of propagation in the matter. By means of analysis of the acoustic impedence of the different matter that an acoustic wave must travel through, one can establish the energy reflected and transmitted in each interphase. The coefficient of reflection of matter 1 to another 2 of acoustic impedence Zl and Z2 respectively is represented by:

R = Z2 - Zl Zl + Z2

Normally it will be a complex number whose module will provide the relationship of the modules with the pressure of the reflected and incidental waves and the phase will provide the difference between both waves.

The square of the module of R provides the relationship of densities of acoustic energy both reflected and incidental.

A phenomenon of great interest in the industrial application of ultrasound is that of so called cavitation, which arises in liquids and solids in a state of fusion.

This phenomenon consists of the formation and subsequent violent explosion of bubbles of liquid in gas form which provoke local pressure waves which are very intense. The phenomenon arises when the maximum pressure of the ultrasound wave which passes through a fluid is greater than the difference between the hydrostatic pressure and the pressure of steam of the fluid at the temperature at which this is found. The prior presence of bubbles favours the start of cavitation. At the same time the existence of pointed corners on pieces immmersed in the liquid makes the phenomenon start at those points.

There appear to be three phases observed in the process of cavitation .

In the first place, on applying ultrasound, gas is removed from the liquid due to the low pressure of steam of the dissolved gases .

This gives rise to the appearance of small gas bubbles in which liquid in a gas state is found. These bubbles interact with the pressure waves from the ultrasound, producing an enlargement in the size of the bubbles by grouping.

On reaching a particular diameter, a phenomenon of resonance is produced and the bubble starts to vibrate with a great length, until eventually it bursts, collapsing on itself and producing an intense pressure wave which extends throughout the fluid. The dimension at which the bubbles resonate varies according to the frequency of the ultrasound applied.

Figure 1 represents the value of the diameter of resonance based on this parameter, it being possible to observe that it decreases as the frequency increases. From this curve it can be deduced that if initially the bubbles present in the liquid are of a size greater than the resonance, then cavitation will not arise, or it willl occur at a very low intensity. This implies that if the gas is not removed from the liquid previously the maximum frequency of ultrasound to be used in order to create cavitation is severely limited. On the other hand, the violence of the bursting of the bubbles depends on the relationship between the maximum diameter that the bubbles achieve on resonating and their initial diameter, so that if the frequency is very high, the relation of diameters will be small and the effect as regards the shock wave produced will be scarce. This limits for practical purposes the frequencies which are useful to those below 1 Mhz. As a consequence in order to achieve an effect equivalent to high frequencies, it is only possible to greatly increase the potency of the ultrasound applied.

Figure 2 shows the density of potency needed to produce cavitation on the basis of the frequency, the great increase necessary as the frequency increases being noteable. For this reason in practice above all in ultrasound washing, it is not usual to use frequencies above 100 Khz, limiting the margen of use to below around 20 Khz, in order that, above all, the phenomenon is not audible for the operators because of the nuisance this would casue.

Figure 2

Density of potency

lMhz lOMhz Frequency

The following scheme describes the process for removing salt and bacteria by ultrasound

1, 2,3, 4 ULTRASOUND AMPLIFIER

5 WIDE BAND PRE-AMPLIFIER

6 POTENCY CONTROLLOR FOR VARYING FREQUENCY

7 DIFFERENTIAL AMPLIFIER

8 OSCILLATOR

9 AMPLIFYING SIGNAL FROM SENSOR

10 OSCILLATOR

11 FREQUENCY MODULATOR

12 OSCILLATOR

13 SMART CARD

The modulator 11 modulates the signal from the oscillator 12 in frequency with the signal of the oscillator 10, which passes through the differential amplifier 7.

This signal is sent to the wide band amplifier 5 which, in turn, amplifies it and sends it to the potency amplifiers; these amplifiers each respond to different frequencies so that the signal will activate one or the other depending on its frequency.

The amplifier of potency will provoke cavitation (the fluid becomes a gas) in the hydraulic mass of the recipient. When this happens, the sensor registers such and sends a signal to the amplifier 9 which activates the oscillator 8 whose signal annuls that of oscillator 10 by reducing such by means of the differential amplifier 7 so that at this moment the only active signal is that generated by oscillator 12.

At the same time the signal from oscillator 8 will activate the smart card 13 which will cause a change in frequency of oscillators 10 and 12, repeating the operaton but activating another of the amplifiers of potency.

The potency controller 6 controls the energy sent to the potency amplifiers which do not contain a regulating force of their own purposely, since with the variation in the energy sent to such it is possible to modulate the width of the signal sent to the transducer.