Device For Controlling The Process Of Desalting And Dehydration Of Oil In An Electric Dehydrator

Abstract

A device for controlling the process of desalting and dehydration of oil in an electric dehydrator having two electrodes comprising a current difference detector responding to the currents in the circuits of said electrodes and being connected to an error detector comparing the real value of the currents in the electrode circuits with a specified value, the output of said error detector being connected to the actuating mechanism of a valve controlling the discharge of the salt water and mud sludge from the electric dehydrator; inserted between the current difference detector and the error detector is a unit shaping a signal corresponding to the real value of the currents in the circuits of the electrodes.

Description

The present invention relates to equipment for conducting processes of preparation of oil for processing and, more particularly, the invention relates to devices for controlling the processes of desalting and dehydration of oil in electric dehydrators. The invention can be employed in the oil-recovery and petrochemical industry.

Known in the art is a device for controlling the process of desalting and dehydration of oil in an electric dehydrator having an oil tank accommodating two suspended electrodes connected to a high-voltage transformer.

The crude oil is pumped through a pipeline into the tank into which there are concurrently supplied water and deemulsifier. The salts contained in the crude oil are dissolved in the water. The water-oil emulsion is fed into an electric field created by the electrodes and is divided into oil removed from the electric dehydrator through a pipeline for removing the processed oil and salt water which is collected together with mud sludge in the lower portion of the electric dehydrator. The water and sludge are removed through a pipeline for discharging salt water and mud.

To provide for constant conditions of precipitation of salt water and sludge at variations in the quality of oil, temperature, relation between the consumptions of water and deemulsifier, it is necessary to maintain a constant difference in the currents flowing through the circuit of the upper and lower electrodes by means of a special device.

The known device for controlling the process of desalting and dehydration of oil in an electric dehydrator comprises a current difference detector checking the currents in the circuits of the upper and lower electrodes of the electric dehydrator, an error detector comparing the value of the current difference with a specified value which is connected to the actuating mechanism of a control valve through which water and sludge are removed from the tank of the electric dehydrator.

During variations in values of the current difference in the circuits of the upper and lower electrodes due to change in the quality of the crude oil, its temperature and the water-to-deemulsifier ratio, water and sludge are removed through the control valve so that the value of said difference is kept constant automatically.

However, the known device has insufficient noise stability for example, during a change in water content and dispersity of the water-oil emulsion or at disturbances in its deposit composition, in which cases the control of the current difference in the electrode circuits becomes unstable. Practically, the changes in the above properties of the water-oil emulsion can lead to electric breakdowns between the electrodes of the dehydrator or between the lower electrode and the surface of the separated salt water. These breakdowns interrupt the technological process, results in disconnection of the electrodes and to a failure of the known device.

An object of the invention is to eliminate the above-mentioned disadvantages.

The main object of the invention is to provide a device for controlling the process of dewatering and desalting of oil that ensures high noise stability at changes in physical and chemical properties of the emulsion.

This object is accomplished by providing a device for controlling the process of desalting and dehydration of oil in an electric dehydrator having two electrodes, each being connected to a current transformer and both the electrodes being connected to a current difference detector responding to the currents flowing in the electrode circuits; said detector comprises a current detector for the upper electrode inserted into the circuit of the upper electrode; a current detector for the lower electrode inserted into the circuit of the lower electrode, and a substracter of these currents to which are connected the outputs of both the detectors; the output of the substracter is connected to an error detector comprising the real value of the current difference with a specified value; the output of the error detector is connected to the actuating mechanism of a valve controlling the discharge of salt water and mud sludge from the electric dehydrator; according to the invention, the device comprises a shaping network producing a signal corresponding to the real value of the currents in the circuits of the electrodes and inserted between said current difference detector and said error detector and including a compensator of the direct-current component of the current difference in the electrodes circuit determined by the constructive parameters of the electric dehydrator, one input of said compensator being connected to the output of the substracter and the other input thereof being fed with a d-c compensating voltage, while the output of the compensator is connected to one of the inputs of a commutator; series connected elements: a differentiator connected to the current detector of the lower electrode, a selector of pulses preceding the breakdown in the electric dehydrator, a network for shaping a signal indicating the presence of said pulses and another signal proportional to the current of the lower electrode; a time-delay relay fed with the last signal from the output of said shaping network, while the output of said relay is connected to the other input of said commutator, in which case the second output of the shaping network which sends the first signal and the output of the time-delay relay are connected to the third input of the commutator whose output is connected to the input of said error detector.

Such an arrangement makes it possible to increase the efficiency of controlling the process of desalting and dehydration of oil in an electric dehydrator by the difference in the currents flowing through the electrode circuits.

Other objects and advantages of the invention will be apparent from the following detailed description of an embodiment of the invention with reference to the accompanying drawing which shows a schematic diagram of the electric dehydrator with a block diagram of the device for controlling the process of desalting and dehydration of oil in this dehydrator.

The proposed device for controlling the process of desalting and dehydration of oil in an electric dehydrator comprises an electric dehydrator 1 with a pipeline 2 for feeding a water-oil emulsion, a pipeline 3 for removing the processed oil, and a pipeline 4 for removing the salt water and the mud sludge. The pipeline 4 is provided with a control valve 5 with an actuating mechanism. Suspended inside the electric dehydrator 1 are a lower electrode 6 and an upper electrode 7. The electrodes 6 and 7 are connected to a high-voltage transformer 8 whose primary winding is connected to the power mains. Inserted into the transformer circuit is a current difference detector 9. The detector 9 responds to the difference in the currents in the circuits of the electrodes 6 and 7 and consists of a current detector 10 of the upper electrode 7 and a current detector 11 of the lower electrode 6. The detectors 10 and 11 are connected to a current substracter 12.

The proposed device also comprises a unit 13 for shaping a signal corresponding to the real value of the currents in the circuits of the electrodes 6 and 7 which has a compensator 14 compensating for a direct-current component of the currents in the circuits of the electrodes 6 and 7, one input of the compensator 14 being connected to a current substracter 12 and the other input thereof being fed with a d-c compensating voltage determined by the parameters of the electric dehydrator 1.

The differentiator 15 of the unit 13 is connected to the following series connected elements: a selector 16 of the pulses preceding the breakdown in the electric dehydrator, a network 17 shaping a signal proportional to the current of the lower electrode 6 and another signal indicating of the presence of said pulses. The signal of the presence of these pulses from the first output of the shaping network 17 is fed to a time-delay relay connected to a commutator 19, while the signal proportional to the current of the lower electrode 6 from the second output of the shaping network 17 is fed directly to the other input of the commutator 19. By means of the commutator 19 the output of the compensator 14 and the outputs of the shaping network 17 and the time-delay relay 18 are connected to one of the inputs error detector 20 comparing the real value of the current difference in the circuits of the electrodes 6 and 7 with a specified value. The output of the error detector 20 is connected with the actuating mechanism of the control valve 5.

The device operates as follows.

At any change in the content of water in the crude oil being processed, dispersity of the water-oil emulsion, disturbance in its precipitate, etc. the currents in the circuits of the electrodes 6 and 7 change too. In order to provide for a stable technological process, it is necessary to maintain a predetermined value of the current difference in the circuits of the electrodes 6 and 7. The signals from the current detectors 10 and 11 responding to the currents flowing through the circuits of the upper 7 and lower 6 electrodes are fed to the current substracter 12. The signal corresponding to the difference of these currents from the output of the substracter 12 is fed to one of the inputs of the compensator 14 whose other input is fed with a compensating voltage the value of which is determined by the direct-current component of the said current difference and depends on the construction parameters of the electric dehydrator 1, while the polarity of this voltage is opposite to the polarity of said signal. As a result, at the output of the compensator 14 there is produced a useful component of a control signal which through a commutator 19 is fed to the error detector 20. In the case of misalignment between the actual value of the current difference in the circuits of the electrodes 6 and 7 and the predetermined value, an error signal is produced at the output of the unit 20 which controls the operation of the valve 5 through which the salt water and mud sludge are removed from the tank of the electric dehydrator 1.

Under certain operating conditions, for example at changes in water content in the emulsion, sludge disturbances, variations of the emulsion dispersity, the current in the circuit of the lower electrode 6 can fluctuate within a wide range. In this case the current pulses cause an electric breakdown interrupting the operation of the electric dehydrator 1. To avoid this, special steps should be taken to protect the electric dehydrator. One of such steps consists in intensifying the discharge of the salt water and mud sludge.

In this case the signal from current detector 11 responding to the current flowing through the circuit of the lower electrode 6 of the current difference detector 9 is fed to the differentiator 15 which produces pulses at the moment preceding the breakdown. If the parameters of these pulses exceed a specified value, they pass through the selector 16 to the shaping network 17. At the output of the shaping network 17 there appears a signal proportional to the current difference and a signal of the presence of prior-to-breakdown pulses. The latter signal triggers the time-delay relay 18 which through the commutator 19 disconnects the output of the compensator 14 from one of the inputs of the error detector 20 and connects the output of the shaping network 17 to the input of the error detector 20 for applying to this input a signal for opening the valve 5. Under the action of this signal the actuating mechanism opens the valve 5 for a time interval determined by the time-delay relay 18.

After the time interval limited by the delay of the relay 18, the output of the compensator 14 is connected to the input of the error detector 20.

The electric dehydrators equipped with the proposed device are preferably employed at oil field and oil refining plants for pre-refining preparation of oil having a high content of water, salts and mud. The proposed device for automatically controlling the process of desalting and dehydration of oil provides for a stable and trouble-free operation of the electric dehydrator.

The device provides for stabilization and, therefore, high efficiency of the whole process of desalting and dehydration.

Claims

We claim:

1. A device for controlling the process of desalting and dehydration of oil in an electric dehydrator having two electrodes: upper and lower, comprising in combination: a transformer to which are connected said electrodes; a current difference detector in the circuits of said electrodes having a current detector for said upper electrode inserted into the circuit of said upper electrode, a current detector for said lower electrode inserted into the circuit of said lower electrode and a substracter of said currents whose inputs are connected to the corresponding outputs of said current detectors; a unit shaping a signal corresponding to the real value of said currents in the circuits of said electrodes having a compensator of the direct-current component of said current difference in the circuits of said electrodes determined by the constructive parameters of said electric dehydrator, one input of the compensator being connected to the output of said substracter and the other input thereof being fed with a d-c compensating voltage; a commutator whose one input is connected to the output of said compensator; a differentiator whose input is connected to said current detector for the lower electrode; a pulse selector passing the pulses preceding the breakdown in said electric dehydrator, the input of the pulse selector being connected to the output of said differentiator; a network shaping a signal proportional to the current of said lower electrode and a signal indicating of the presence of said pulses, the input of the shaping network being connected to the output of said selector; a time-delay relay whose input is connected to one output of said shaping network through which is fed said signal indicating of the presence of pulses preceding the breakdown, while the output of said relay is connected to the second input of said commutator whose third input is connected to the other output of said shaping network through which is fed said signal proportional to the current of said lower electrode; an error detector whose input is connected to the output of said commutator; a unit comparing the real value of the current difference in the circuits of said electrodes with a specified value; an actuating mechanism whose input is connected to the output of said error detector; a valve controlling the discharge of salt water and mud sludge from said dehydrator associated with said actuating mechanism.