ENERGY-SAVING TECHNOLOGY
Practice of introducing variable-frequency electric drives in KazTransOil JSC assets
The Kalamkas oil pumping station with estimated capacity of 8 mln tons per year was designed and built to pump oil from the Kalamkas field. For this the project worked out the pumping scheme using the 1250 c.m. capacity main units with 4 induction closed-circuit ventilation, normal starting moment and overpressure case purge of 1250 kilowatt electric engines and 14 NDSN supporting units with the 2nd series explosion-protected blowing induction motors of 160 kilowatt capacity.
The given oil pumping station was the most distant from the MAEC (Mangishlak atomic energy combine) electric energy generating source in the Buzachi peninsula. The length of the feed air-line from MAEC to the Kalamkas oil-pumping station (OPS) is 210 km. First turn of the Buzachi energy system projected initially under 220-kilowatt voltage was employed under 110-kilowatt voltage and has been employed under this voltage up to date.
As times goes by, the expansion of oil production in the Buzachi peninsula fields gradually entailed increase of energy consumption in the given region and correspondingly, the existing power supply system could no more stand the growth of electric load. In view of this, periodical employment of pumping units in the Kalamkas Head Oil Pumping Station (HOPS) was becoming problematic by already 2001 for the protracted and hard starting moments of asynchronous motors that in turn caused their disconnection by automatic machinery's relay protection facilities.
Besides, change of the oil-pumping modes on the Kalamkas-Karazhanbas site of the Kalamkas-Karajanbas-Aktau pipeline was realized by already outdated methods, viz pressure adjustment by pressure regulator at exit of the pump station and use of different wheel size pump units.
Maintenance of the steady service pressure at the pump station's output entailed one more problem - security of hermiticity and perfect serviceable state of the pump end seal, for the pump casing annuity and the pressure pipeline portion between the pump unit and pressure regulator had steady max serviceable pump pressure of 2.8 megapascals. The work of the pump units in such modes was accompanied by increased noise and vibrations, which in turn reduced the cumulative reliability of the pumps' operation, caused premature wear of the junctures, both the pumps and electric engines and cut the period of the interrepair cycle.
Regulation of the pumping units' work is currently provided due to application of two major kinds of equipment:
1. Hydraulic and electromagnetic clutches for pump shaft rotation frequency variation with permanent rotation frequency of electric drive shaft;
2. Electronic regulators of electric drive shaft rotation frequency and correspondingly, shaft speed.
Analyses of the settlement of analogous problems in other branches of industry in the KazTransOil JSC preferred frequency regulation of pumping units' electric drive shaft rotations, for under the tentative estimations, this solved a whole complex of existing problems to a significant degree at comparatively low expenditures. The variable-frequency electric drive technology was preferred, because the given technology is rather efficient from the economic point of view at employment of oil mains operating in temporary technological oil pumping modes.
The capacity consumed from the networks at control of frequency changer is calculated by the following formula:
Thus, when pump output reduces two folds, electric energy consumption at frequency adjustment reduces almost eight folds!
Open competition on fulfillment of the works on application of variable-frequency electric drive at the Kalamkas OTS was declared in 2002.
The Ukrainian firm MIIC LTD won the open competition and suggested frequency changer produced by the EOS research and production enterprise (Kharkov city) on the basis of self-excited current inverter. The advantage of the given frequency changer was maintenance of electric engine's optimal service due to the economical regulation law, regenerative control opportunity, maintenance of sinusoidal output voltage and actual sinusoidal output current, which left no necessity for installing output guard filters at low harmonics generated in supply main and high malfunction consistency.
The project was fulfilled by the Design Institute of Kazakhstan TyajPromElektroProekt LLC. The realization of the design works targeted at maximum use of the applied frequency changers' principal functions:
- Smooth start and braking of electric engines with rate adjusted;
- Modulating control or maintenance of electric drive features at the planned level;
- Electric pumpback at braking;
- Force cutback in engine winding;
- Current and moment limiting at dynamic operation mode;
- Autoreclosing following short-time voltage loss;
- Malfunction diagnosis;
- Connection through RS-232 and RS-485 interfaces with control and higher visualization systems;
- Process variable autocontrol through the built-in regulator PI control.
The works on introduction of variable-frequency electric drives of tyristor electronic frequency changer series were run in accordance with the acting OTS conditions. The variable-frequency electric drives were implemented in container execution with VAC (ventilation and air-conditioning) system, which provided the needed equipment temperature rate, guarded it from dust as well as saline. The works in the asset created effective creative cooperation between KazTransOil, EOS and MIIK experts.
The effectiveness of the variable-frequency electric drives was assessed following their employment.
The first rather perceptible result was the possibility of smooth start of the electric engine with current less than 0.5 INOM.
At frequency start the danger of pipe hydraulic impact initiation fell significantly, dynamic loads in end seals and pump unit's angular-contract bearings reduced. Application of 2 sets of the variable-frequency electric drives allowed increasing the oil-transfer station's safety due to work reservation, cut of engine, pump and other equipment faults.
The second important feature was energy saving. Oil pressure in the pipeline and productivity at the station output were now regulated by the frequency changer. Energy saving after application of the frequency adjustment was more than 30%. So, at adjustment-free mode of the pump units, electric energy unit discharge for pumping 1 ton of oil makes 1.85 kilowatts per hour, and at the adjustment mode - 0.73 kilowatts per hour.
One more result of the new technology application was drop of vibration noises in the electric engine and pump. Pressure regulator shutter at the station output is now fully open. Usage of variable-frequency electric drive of the tyristor electronic frequency changer series on the basis of self-excited current inverter for control over the standard with 4 induction closed-circuit ventilation electric engine cut down the pressure, heating and noises in the engine in static and dynamic work modes.
Further it is planned to start variable-frequency electric drives to the SCADA system, which will allow realizing full automation and visualization of technological processes at the oil-transfer pump station. The variable-frequency electric drives of tyristor electronic frequency changer series produced by the EOS research-and-production enterprise are capable to operate in process control system industrial information networks.
Two VFD (variable-frequency drives) sets installed in the Kalamkas OTS passed control operation in 2003 for a more detailed study of advantages and shortages of KazTransOil JSC variable-frequency electric drives at various pumping modes. The control operation produced positive results on all the checked features. Moreover, the experimental-industrial tests worked out and are currently using the working mode of the main unit without supporting pump at certain operating pumping practices, which produced positive results. Such operation mode, possible only with VFD, allows additional energy saving and increase of the reliable work of the whole oil-transfer station.
At actual annual transfer via the Kalamkas-Karajanbas oil line 4 192 thousand tons electric energy consumption without pump unit variable-frequency electric drives were to make 13 910.9 thousand kilowatt per hour.
Actual energy consumption after application of frequency changer equaled to 9 459.4 thousand kilowatts per hour. Actual energy saving at the Kalamkas OTS in 2003 equaled to 4 451.5 thousand kilowatts per hour.
Pure energy saving without account of the rest operational charges totaled:
4 451 500 kilowatts per hour x 4.37 tenge (electric energy tariff) = 19 453 thousand tenge / 143.8 (USA dollar rate to tenge for late 2003) = $135.2 thousand US.
Presently the planned tendencies for technique and technology development in the field of variable-frequency drives give us optimistic hopes for that in near future actually all the units of the pipeline transport will be operated with VFD application. Thus we hope that all the advantages of frequency regulation will be effectively used and developed and we will realize with proud that the KazTransOil JSC is one of the first national companies of Kazakhstan Republic to actually apply the given achievement of scientific and technological advance at its production assets.
Authors:
B. Sayakhov,
K. Latifov,
Z. Lukpanov, S. Kostin