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by Anatoly LEPEKHA, Director General, Experimental Plant of Chemical Engineering, Moscow; New Pumping Technologies, Ltd.;
Yelena BORISOVA, expert, OOO FiD (Fokin & Co.)
The pump is the principal gear in oil mining. It pumps out crude and pumps in recirculated water for sustaining the required pressure in an oil- bearing bed.
There is a variety of crude oil pumps. Until recently, in 60 percent of the cases, one preferred to use electrical centrifugal pumps of dynamic action in which the liquid is driven by a centrifugal force generated by the rotation of pump impeller equipped with special blades. Less often one made use of other units pumping oil and water through periodic changes in the working chamber volume (volumetric action pumps).
But gone are the times when we could mine oil shallow, just below the ground surface: today we have to go ever deeper to get it. Hence the amount of extracted oil-making material (the average daily production rate of oil wells) has been going down, with the concentration of suspended matter in it being as much as 500 to 1,000 mg/l. Since the oil occurrence depth has increased considerably, some wells have slanted or crooked holes here and there which should be straightened. Another compounding factor for conventional oil-mining technology! Besides, the intensive escape of associated gas dissolved in the liquid (fluid) interferes with the work of pumping units and causes paraffin (wax) salts to accumulate within.
All these negative factors are responsible for excessive overloads on the operational units, and cut down their service life (under normal conditions the life of their reliable performance is 5 to 6 years). What with the shrinking number of high-performance oil wells worldwide, there is a felt need for a new generation of pumping units-not as awkward, but smaller in size, though less productive in output. And here our oil experts have had their say.
Late in the 1980s we at our enterprise designed an essentially novel type of units - the rotary flow-eddy pump (trademark RVN). Its work is based on an effect we discovered - that of hydromechanical resistivity - which accounts for a high rate of energy transfer to the working (power) fluid and ensures a low level of fluid-flow pressure losses in the How component of the unit. This assembly is composed of rotary flow-eddy stages, or chambers, mounted on the same shaft in number depending on a concrete task (well depth, required discharge head of pump and other factors).
At first sight there is nothing special about this assembly - just two stators and a rotor in between. The rotor, mounted on a shaft key, rotates together with the shaft; but the stators, fixed co-axially with the rotor, are immobile. The supply and removal of the working fluid occurs along the shaft through suction and injection (pressure) ports within the rotor.
All that looks simple enough. But what is the gimmick of the new pumping unit? How does it do the trick (the effect of hydromechanical resistivity and all)?
This is its design. Rather than going into circumstantials, we'd better tell you about essentials. We supplied the lateral surfaces of the rotor (on both sides) and stators (on the inner side) with recesses, or chambers, in the form of a torus cut lengthwise. These, smooth on the rotor, are equipped within the stators with transverse partitions, or blades, tipped at a definite angle. A liquid fed through the suction port gets into two half chambers of the rotor where, driven by centrifugal forces (to a physicist it is but a three-dimensional eddy), it is spilled into the recesses of the stators and is captured by the blades. At this stage the flow rate slows down, whereupon the liquid returns to the rotor's chambers at a significantly lower rate. This process is rerun several times. Thereby part of the kinetic energy of the moving material is transformed into pressure and, once a definite level of this pressure has been attained, the material is forced into the next stage of the pump, and so forth.
That is to say, the RVN unit enables intensive compression to proceed through a repeated drive-and-brake of the liquid, with the head (pressure) generated by one stage being 6 to 10 times higher than that produced by a conventional centrifugal pump of the identical outside diameter. In its type the new pumping unit occupies an intermediate position between pumps of dynamic and volumetric action, and combines the advantages of both.
To make assurance double sure, let us compare some of the characteristics of the rotary flow-eddy (RVN 5-50-1400) and centrifugal (ECN 5-50-1400) pumps. Both can be used for a daily feed of liquid equal to 50 m 3 from a depth of 1,100-2,000 m; both are capable of sustaining a head of 1,400 m. The outside parameters of their stages are the same, and so is the outside diameter - 92 mm. But their identity ends at that. Now look. The RVN pump needs 46 working stages, while the ENC - as many as 273; RVN measures 2.7 m in length, and ENC - only 8.3 m; their weight is 85 and 270 kg, respectively Besides, RVN gives an economy of 15-25 percent in power used for the compression and injection of liquid. These are but only a few comparative characteristics among the many, and all of them are in favor of our brainchild.
Our enterprise had developed a family of pumping units for a variety of purposes. One such innovative unit is URVN, a rodless rotary flow-eddy setup for oil mining. In addition to the pump, it includes a submersible electric motor cum protector, a transformer substation, a control board extension and a range of auxiliary modules put to use if necessary.
We have developed 16 modifications of URVN with a wide range of applications. Some can pump a minimum amount of oil per day, about 10 m 3 , while others can extract a maximum, i.e. 40 m 3 , with a head (pressure) of up to 3,000 m and power consumption of 32 kW.
All these units actually have no alternative in crooked and slanted wells: their pumps are only 1.1 to 3.4 meters long. They are indispensable in low-production wells and also if the formation fluid contains an enhanced concentration of gas and mechanical impurities. There are also other merits to our pumping units, such as low specific power consumption (economy of power is 40 percent compared with conventional gear), low maintenance and repair costs, and high wear resistance - their parts are manufactured from wear-resistant materials.
We have come forward with yet another innovative setup so badly needed in the oil-mining industry. This is a horizontal rotary How-eddy unit ARVNP. We guess a bit of explanation is needed here. Oil in a find is under virgin formation pressure which is high enough to lift the fluid from the pool. But as the pool gives out, the pressure in it falls accordingly; hence it should be sustained at a proper level. Water injection is one of the remedies to keep the pressure up. Hitherto preference was given to collector systems, or group pumping stations. But our setup is of much better performance. Why?
To begin with, ARVNP means considerable economy (as much as 20 percent in specific energy consumption); such setups can operate on several wells (as many as ten), and even on one single well, something that other systems can never do. Besides, the parts of the flow section are made of high chromium- plated cast iron, and the rings for the double-support hangers of rotors as well as the support disks of the pivot are manufactured from sintered silicon carbide. These are wear-resistant materials. Furthermore, the barrels of the shaft radial and axial supports are made of aluminum oxide, a material capable of pumping "noxious" fluids with a concentration of free gas up to 60 percent, and of sand- 1 g/l. Their kinematic viscosity may reach 10-20 mm 2 /s, and temperature - to 90 0 C.
In some cases our setups are just indispensable. Take the group pumping stations we mentioned above. These are designed for a very large scope of work, 180 m 3 /h and more, while what we need is a set of less productive units that could pump from 10 to 120 m 3 /h of liquid. That's what the industry needs. So far we are the only suppliers of such hardware. Its design allows for mobile, transportable modifications, which is of great significance in field conditions. Our oilmen are the world's pioneers in using such units.
Yet another aspect. With the rapid development of small and medium-sized businesses and large-scale suburban construction, there is a soaring demand for drinking and nonaggressive service (process) water underground. To facilitate its recovery, we have developed submersible rotor/flow-eddy pumping units of the RVNV type. They give a 15 to 20 percent saving in energy compared with the centrifugal pumps but produce a head (pressure) of liquid two and three times as high. The mass of like units is down to 30-50 percent. And last but not least, they are not as expensive.
In its turn, the new pumping hardware makes better use of power. The point is that most of our home-made a.c. electric motors "drive" the pump rotor not above 3,000 rev./min. Such electric drives are bulky, costly and leave much to be desired in economy and reliability. So we had to think what could be done about upgrading electric motors for pumping units. In the end we have developed a unified electric drive (PEDPS) and a frequency converter making it possible to up the rotor rate to 9,000 rev./min, and change it smoothly when needed. Since this converter has no transformers and throttles (valves), this device is simple in design and reliable in operation. Its compactness (the volume of its control section not above 150 m 3 and its mass-around 100 g) and excellent efficiency (95 percent!) add to its merits.
The hydromechanical resistivity effect we have discovered opens up broad opportunities for a new generation of turbines, compressors and pneumatic hardware. Thus far our multipurpose rotary flow-eddy pumps developed on the basis of this effect (power, <500 kW) are without peer in this country and elsewhere-in operational characteristics, in service life and in low cost above all. Our pumping hardware merited a bronze medal at the international fair EUREKA held in Brussels, Belgium, in 1993; it was awarded a diploma and a silver medal at the First International Salon of Innovations and Investments in Moscow in 2001; and it got a diploma and a gold medal of the Russian Federation's Chamber of Commerce and Industry. We have received ten patents of the Russian Federation.
Prepared by Arkady MALTSEV
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