RU2167692C1 - Method of dehydration of water-and-oil emulsion - Google Patents

Abstract

FIELD: dehydration of oil by treatment of oil in alternating electrical field both at oil fields and at oil refining plants. SUBSTANCE: use is made of alternating electrical field at period T; intensity of electrical field in half-cycle is formed as pulse whose duration if lesser than half-cycle. Duration of leading edge of intensity pulse is formed between 2•10^-5 and 5•10^-4 s at pulse amplitude of 0.5-1 kV/cm. Duration of pulse may be changed depending on oil conductivity so that magnitude of intensity is constant with 0.2-0.4 kV/cm at definite load current. EFFECT: enhanced efficiency without impairing degree of dehydration and throughput. 3 cl, 4 dwg

Description

 The invention relates to the field of separation of liquids, and in particular to methods of dehydration of oil by processing it in an electric field. Currently, there are various ways to dehydrate a water-oil emulsion by treating it in an electric field.

 So from the patent of France N 2697443 M.cl. B 01 D 17/06, publ. 11/05/92 [1] there is a known method of dehydration of an oil-water emulsion by passing it through a helical channel with simultaneous processing of the emulsion in a constant pulsed electric field created between the electrodes. According to the same patent, it is possible to supply an alternating sinusoidal voltage to the electrodes.

 The disadvantage of this method is the high cost of electricity going to ensure the dehydration process.

 There is also a similar method for dehydration of an oil-water emulsion by processing it in an alternating electric field of a sinusoidal shape (see, for example, US patent N 5468385, Mcl B 01 D 17/06, publ. 21.11.95) [2].

This method also has several disadvantages. Studies have shown that when polarized droplets approach each other in an electric field due to the conductivity of the oil, the polarization charges of the drops are neutralized with a time constant of the order of τ = (1-5) • 10 ^-4 s, which is much less than the half-period of the electric field oscillations (0.5T = 0.01 s). This leads to the fact that the electric field provides an effective approach of droplets only to distances of the order of 0.1 radius. With a further approach of the droplets, the redistribution of charges causes a sharp decrease in the force of attraction and the efficiency of the dehydration process decreases sharply. To maintain the effectiveness of this process, the effective value of the tension should lie within (0.5-1) kV / cm, and this, in turn, requires increased energy consumption.

 The closest in technical essence and the achieved result is a method of oil dehydration by processing it in an alternating electric field with a period T, where the electric field in the half-cycle is formed in the form of a pulse of various durations, including those with a duration of less than 0.5T, which allows saving energy consumption in the implementation of the method. This method is described in the application of Germany N 1642867 M.cl. B 01 D 17/06, 05/31/72 [3].

However, this method is also not without a number of significant drawbacks, since it involves an almost instantaneous increase in the electric field from zero to a nominal value, i.e. the duration of the leading edge of the pulse τ _f tension is assumed to be zero, which is practically not feasible. When forming pulses with a front duration approaching zero, the cost of equipment that implements this method is sharply increased.

 The problem to which the present invention is directed, is to increase the efficiency of the oil dehydration process while reducing its energy intensity, taking into account the physical characteristics of the dehydrated oil.

 The technical result that can be obtained by using the present invention is to reduce energy consumption by a factor of several in comparison with currently used methods for dehydrating oil in an electric field. At the same time, the remaining process indicators — the degree of dehydration and productivity — do not deteriorate, and the process itself allows you to select the process parameters of the method taking into account the physical properties of the dehydrated oil.

The problem is solved due to the fact that in the method of oil dehydration by processing it in an alternating electric field with a period T, where the electric field in the half-cycle is formed in the form of a pulse with a duration of less than 0.5 T, the duration of the leading edge of the pulse of intensity τ _{f is} formed within from 2 • 10 ^-5 to 5 • 10 ^-4 s with a pulse amplitude lying in the range of (0.5-1) kV / cm. Here, the upper limit is determined by the time constant τ, typical of oil, of neutralizing the polarization charge of converging droplets, and the lower limit is determined by the fact that when τ _f <2 • 10 ^-5 , the droplet fusion efficiency does not increase, but the equipment needed to implement the method becomes more expensive. In accordance with the following experimental data, it is preferable to change the pulse duration depending on the electrical conductivity of the oil, while the actual value of the voltage when the load changes is set constant within (0.2-0.4) kV / cm at a load current I _n less than or equal to the permissible value I _add = (0.5-0.9) I _max , where I _{max is the} maximum permissible current for the selected source.

In cases where to maintain the current tension within (0.2-0.4) kV / cm, a load current I _n is required that exceeds the permissible value I _add , it is advisable, after two half-periods with electric field strength, to form a section with electric intensity in the form of a pulse field equal to zero, and with a duration equal to an integer number of half-periods.

 The invention is illustrated by four figures, where in FIG. 1 presents a general diagram of the implementation of the method, FIG. 2 and FIG. 3 shows various characteristics of the pulsed field strength, and FIG. 4 shows the characteristic of controlling the load current depending on the effective current value and the allowable load current of the source.

 The specified method can be implemented in an industrial two-electrode electrodehydrator by applying alternating pulsed alternating voltage to the lower and upper electrodes.

The method is as follows. A water-oil emulsion is supplied to the tank 1. Electrodes 2 and 3 are placed inside the container 1, to which a pulse alternating voltage U is applied. As in the method known from [3], the emulsion is processed in an alternating pulse field. However, the duration of the leading edge of the pulse τ _f should be commensurate with τ, i.e. should not exceed 5 • 10 ^-4 s, and the amplitude of the pulse of tension to remain at the level of (0.5-1) kV / cm, as shown in figure 2.

 It was experimentally established that, at the indicated parameters, the effect of the electric field on the process of enlargement of water droplets is enhanced due to the fact that during time τ there is no significant redistribution of the polarization charges of the droplets. In addition, to ensure the same efficiency of the dehydration process as when using a sinusoidal change in the electric field strength, the pulse duration τ can be chosen shorter than the half-period duration of 0.5 T, which can drastically reduce energy consumption for the dehydration process.

Experimental studies have shown that when using a pulsed voltage with τ _f <5 • 10 ^-4 s and an amplitude E = (0.5-1) kV / cm, the optimal effective value of the field strength is in the range (0.2-0.4) kV / cm. The optimal effective value of the field strength can be maintained by varying the pulse duration τ.
Therefore, it is necessary to control the pulse durations τ, so that the effective value of the voltage E _d remains constant when the load changes, at the level of (0.2-0.4) kV / cm, while the actual value of the load current I _n does not reach the value I _extra = (0.5-0.9) I _max , where I _max is the maximum permissible current, determined by the power of the source. With a further increase in the load, the equality I _n = I _add is maintained, as shown in FIG. 3.

 With high oil conductivity and limited power supply, sometimes it is not possible at the maximum permissible load current to provide the pulse amplitude necessary for the process. To overcome this difficulty, it is possible, after two half-cycles with an electric field strength in the form of a pulse, to form a section with zero electric field strength and with a duration equal to an integer number of half-periods, as shown in Fig. 4.

As an example of the method, the use of a dehydrator with a source of power P = 25 kVA can be given. Allowed for this source current I _add is 0.8 I _max and equal to 1.4 amperes. When applying to the electrodes a pulse voltage corresponding to an effective voltage U _acting equal to 4-7 kV, the energy consumption compared with the use of a sinusoidal voltage is reduced by 3 or more times while ensuring the same degree of oil dehydration.

Claims (3)

1. The method of dehydration of oil by processing it in an alternating electric field with a period T, where the electric field in the half-cycle is formed in the form of a pulse with a duration of less than 0.5 T, characterized in that the duration of the leading edge of the voltage pulse is formed within 2 • 10 ^-5 - 5 • 10 ^-4 s with a pulse amplitude lying in the range of (0.5 - 1) kV / cm. 2. The method according to claim 1, characterized in that the pulse duration is changed depending on the electrical conductivity of the oil, so that the effective value of the tension is constant within (0.2 - 0.4) kV / cm at a load current I _n less than or equal to the permissible the value of I _add = (0.5 - 0.9) • I _max , where I _max is the maximum permissible current for the selected source.  3. The method according to claim 1 or 2, characterized in that depending on the electrical conductivity of the oil between two pairs of pulses, a section is formed with an electric field strength of zero, and with a duration equal to an integer number of half-periods.

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