A coalescer is a device which is performing coalescence. It is primarily used to separate emulsions into their components via various processes. One type of coalescer is the electrostatic coalescer which uses electrical fields to induce droplet coalescence in water-in-crude-oil emulsions to increasing the droplet size. After the coalescence it will then be easier to separate the droplets of water from the oil.
A prior art power supply PS for a coalescer is shown in FIG. 1, together with an electric equivalent of the coalescer denoted as EC. The coalescer EC is here comprising an electric equivalent of the coalescer fluid (or emulsion) denoted as EF, comprising a resistor Remul in parallel with a capacitor Cemul. The coalescer comprises coated electrodes represented by the capacitor Ccoating. Hence, the entire coalescer can be represented as the capacitor Ccoating connected in series with the parallel connection of the resistor Remul and the capacitor Cemul. It should be noted that the present coalescer EC is an AC type of coalescer.
The coated electrodes comprise electrodes made of an electrically conducting material with a surface coating. The coating is typically made of polytetrafluoroethylene (also known as Teflon). The purpose of the coating is to prevent short circuit currents which may otherwise occur between pure metallic electrodes if, for example sea water, is introduced into the coalescer.
The power supply PS comprises a first transformer T1, which is a step-up up transformer, typically supplied with primary voltage of typical 250-500 V (rms) and supplies a secondary voltage of typical 5-10 kV (rms) to the electrodes of the coalescer. Due to fluid variations in the coalescer the voltage between these electrodes may vary. Moreover, as the coalescer is a capacitive load, there is also a need to provide the coalescer with reactive power.
Hence, in order to control the voltage supplied to the primary side of the first transformer T1, the power supply PS further comprises a second transformer T2, a magnetic controllable inductor MCI and a resonant control circuit RCC for resonance control.
The second transformer T2 is connected between a power supply source, such as the mains, a generator etc, typically supplying 230V-690 V AC (rms) and the magnetic controllable inductor MCI. The typical output voltage of the second transformer T2 is 500-900V (rms).
The magnetic controllable inductor MCI is described in US 2005190585 and is a device which inductance can be controlled. Hence, the magnetic controllable inductance provides the possibility to control the reactive power supplied to the first transformer T1 and also to control the output voltage level even if the load (the coalescer) is varying.
As discussed above, the capacitance of the load is varying and the inductance of the magnetic controllable inductor MCI is also varying. It is therefore necessary to provide the power supply PS with the resonant control circuit RCC in order to ensure that potentially damaging resonance between the inductance and the capacitance of the entire circuit in FIG. 1.
The power supply PS also comprises a control system for controlling the magnetic controllable inductor MCI.
Such a power supply PC is today sold and marketed by Magtech AS. The total weight of this power supply is typical about 500-800 kg (nominal voltage of 5 kV). The weight is mostly caused by the amounts of copper and iron used in the magnetic devices (transformers T1 and T2 and the magnetic controllable inductor MCI).
There has been a demand for power supplies being able to supply power to larger coalescers, that is, coalescers with higher surface area of the electrodes, higher nominal power (up to approximately 25 kVA) and/or higher nominal voltage levels (up to approximately 15 kV AC (rms)). This will cause the reactive power consumed by the coalescer to increase, which would provide a considerable increase in the size of the magnetic controllable inductor MCI. However, for some projects there has also been a requirement that the total weight of the power supply is kept below 1000 kg. Also for other projects it is desired to reduce the total weight due to the material costs and production costs. Hence, also for other reasons it is desirable to provide a power supply with reduced weight.
Hence, one object of the invention is to provide a power supply that is able to supply power and voltage control to a coalescer with increased size and higher voltage rating, without increasing the total weight of the power supply considerably.
Moreover, one object of the invention is to provide a power supply with reduced risk of short circuit currents between the electrodes of the coalescer. It is also a purpose to be able to reduce the short circuit current if such short currents still occurs.