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The pros and cons of modernization of electric drive GPA with the use of a VFD

Key equipment in technological processes of gas processing complex – centrifugal compressors. When choosing a supplier of gas compressor units of the enterprise in the first place pay attention to the manufacturer of the experience and resources to design and manufacture unique compressor units according to individual requirements. This article discusses the experience of the manufacturer JSC Kazankompressormash and design Institute CJSC "Naturvetarna them. V. B. Economies" in the implementation of complex projects for the supply of compressor units for one of the largest operators of gas processing complex in Russia – JSC "SIBUR".

Production enterprise JSC Kazankompressormash and research Institute JSC "Naturvetarna them. V. B. Economies" are a major engineering and engineering holding HMS Group and work as a unified scientific-technical complex. Kazankompressormash has 20 years experience in the production of compressors driven by gas turbine units (GTU) with a capacity from 6 to 25 MW, as well as of complete compressor stations. Tight integration with leading Russian developer "Naturvetarna them. V. B. Economies" provides an opportunity to deliver highly efficient and reliable compressor equipment according to the technological characteristics of the customer's facility. An important place in design solutions to issues related to energy saving technologies, reduction of losses of non-renewable energy resources, improvement of environmental situation in the areas of oil and gas production.

In the period from 2008 to 2012 in the framework of the General agreement with OJSC SIBUR about the design, manufacture and supply of equipment Kazankompressormash put OJSC SiburTyumenGaz six compressor units driven by gas turbines: GC-124/14-79 GTU (2 pieces), 66HZ-1162-1,3-38 GTU (3 pieces), GC-375/4-77 STU (1 piece).

Turboplay compressor unit for JSC SiburTyumenGaz
Turbomemory compressor unit for JSC SiburTyumenGaz

Two turboprint compressor unit GC-124/14-79 GTU was supplied to the booster compressor station (BCS) of South balyk GTP. When creating turborider compressor unit were applied progressive technical solutions currently used in the world practice of creating a gas-compressor units.

Compressor units are gas turbine drive with a capacity of 8 MW and performed in hangar design. Centrifugal compressor for compression of associated gas, and further processing performed in a "dry" (oil-free) version, equipped with magnetic bearings company "S2M" (France) and dry gas-dynamic seals, designed and manufactured "Naturvetarna them. V. B. Economies". The case of compression – ten with one intermediate cooling.

the Basic parameters of the compressor GC-124/14-79 GTU:

  • performance, reduced to normal conditions (20 °C 0,101 MPa), nm3/hour (m3/min) – 100000(124,05)
  • initial pressure, nominal, MPa – 1,34
  • the final pressure, nominal, MPa – 7,7

In the compressor unit uses advanced automatic control system, providing functions of control and regulation of all systems of the unit, including a gas turbine engine (based on the controller Yokogawa (Japan) and Allen Bradley (USA). Thus, operation of the unit have been possible without the constant presence of operating personnel.

In the cold season heating cover and block Assembly that allows the unit running in less than 1 hour, even in the harsh conditions of the Siberian climate. Anti-surge compressor system provides automatic regulation and protection of the compressor against surge, and emergency protection (GROOVE) of the compressor protects the equipment against any accidents and human error.

the Development, testing and delivery of aggregates GC-124/14-78 GTU South balyk GTP were carried out in a short time – within 15 months from the date of signing the contract. In 2009, pilot models of units passed the acceptance tests and were accepted for commercial operation. In Assembly GC-124/14-79 GTU was installed gas turbine engine driven aviation type AI-336-2-8 (manufacturer – "Motor Sich", Ukraine). But in response to the need "Siburtumengaz" to increase the flow rate of gas was consistent decision-making on the replacement drive motor for the gas turbine engine NK-ST-10 (manufacturer – JSC "Kuznetsov", Samara) power of 10 MW, which also provided the extension of the control range the performance of the unit compared to the original.

Compressor unit GC-124/14-79 GTU for South balyk GTP, SiburTyumenGaz
Compressor unit GC-124/14-79 GTU for South balyk GTP, SiburTyumenGaz

In 2012, was performed a complex of works on development of design documentation, procurement of equipment, modernization of head Assembly and commissioning tests. Technological features of associated petroleum gas utilization with Mamontov oil Deposit required the creation of a compressor unit high performance 700 million nm3/year.

Compressor unit type 66HZ-1162/1,3-TO on parameters such points was designed and manufactured at JSC Kazankompressormash, installed and successfully operated since 2010 in JSC "Yuzhno-balyk GPK" (Pyt-Yah).

Compressor and is supplied blocks maximum factory readiness. Units low compression and high-pressure lubrication system, sealing system, rack equipment, some gas lines. Engine blocks, mesoamericana engine, fuel and start gas placed in easy-to-assemble building, also included in the scope of delivery of the unit. In the compressor installation used gas turbine engine NK-16ST production of JSC "Kazan production engine-building production Association" (JSC "KMPO").

the Basic parameters of the compressor 66HZ-1162/1,3-TO:

  • performance, reduced to normal conditions (0 °C 0,101 MPa), nm3/hour (m3/min) -83340 (1162)
  • the suction pressure, MPa – 0,13
  • pressure, MPa – 3.7 V
  • the range of variation of the suction pressure, MPa – 0,13–0,17
  • the range of variation of productivity, m3/min – 1162-859
  • In order to comply with environmental requirements and produce products with high value-added Russian oil and gas companies devote considerable attention to the efficiency of associated petroleum gas. In the framework of this task, one of the largest enterprises for processing of hydrocarbon raw materials of LLC "LUKOIL-Permneftegazpererabotka" (LLC "LUKOIL–PNGP") launched the project "Reconstruction of low-temperature condensation and rectification (NEW). The construction of the second line for processing of associated petroleum gas (APG)".

    Supplier of compressor equipment in the framework of the project by the scientific and production complex "CJSC Naturvetarna" OJSC Kazankompressormash (structural engineering holding company OJSC "HMS Group"). During the 2013-2014 enterprises has been successfully implemented complete supply of booster compressor units compressor station. The scope of supply included:

    • turboprint compressor units – 3 PCs.
    • refrigeration centrifugal compressors – 2 PCs.
    • centrifugal compressor – 1 PC.
    • screw – 1 PC.
    • easy-to-assemble building.

    Turboplay compressor unit GC-70/17-62 gas turbine composed of a booster compressor station (photo 1, table. 1) is designed for compression of dry stripped gas from the installation of NEW and feeding it into the main gas pipeline "Gazprom" and the unit of LLC "LUKOIL-Permnefteorgsintez".

    as an actuator applied to a gas turbine unit GTU-PG.

    Photo 1. Booster compressor station "LUKOIL–PNGP" consisting of three turboprint units GC-70/17-62 STU


    table 1. The main parameters of the unit GC-70/17-62 STU

    abstract: From regulation theory it is known that the most effective form of regulation is the regulation of the compressor by changing the frequency of rotation.

    In recent years, the frequency converters (VFD) for motors from a few kW to tens of MW, frequency range 5...50 Hz, with high electrical characteristics. Manufacturers  of the inverter is recommended to use these devices, promising high  performance indicators.

    In the present work the following list of tasks that need to be addressed when installing frequency converters operated in centrifugal compressors without changing the electric drive motor, as well as the results of the analysis of gas-dynamic characteristics of compressors, widely used in industry.

    Key words: centrifugal compressor, elektroprivodnye compressor unit, frequency converters, control performance, aerodynamic characteristics, efficiency

    Consider what tasks you need specialists to solve the operating organization during installing a VFD on a centrifugal compressor designed the motor with a constant speed.

    The first challenge relates to the method used for a frequency that is different from the supply frequency (50 Hz).

    AC power to the rectifier is converted to DC, which is then switched with the required frequency fass and through the filter is fed to the motor (Fig. 1).


    the
    Fig.1. The block diagram of the frequency Converter:
    1-rectifier; 2-switch; 3-filter; 4-electric motor.

    From Fig.2 clearly shows that dial-up AC voltage is much different from the desired sinusoidal voltage and the difference is pure losses that reduce the efficiency of the motor and the inverter.

    Fig.2. The shape of the output voltage of a simple switch (the power supply voltage depending on time)

    To reduce these losses, the creators of the if use a complex, multilayer switches that bring the output voltage of the inverter to a sine wave (Fig.3), but "stepping stones" still remain.

    Fig.3. Output voltage waveform of multilevel switch

    Today's inverters have 24 or more pulse straightening system for IGBT modules with 3-level pulse-width modulation, which allows to have a low level of higher harmonics (and thus low losses). Efficiency modern AC drive is about 98%.

    The second task is limited to the capabilities of the switches on limit voltage, which is units of kilovolts. If the motor is designed to supply a voltage of 10kV, the input of the inverter must supply a step-down transformer that reduces the voltage to an acceptable value of the semiconductor switch and the AC - a step-up transformer for increasing the voltage up to the nameplate data on the motor. In recent semiconductor power devices for higher voltage, but the output transformer, usually installed because it simultaneously serves as a filter, cutting off high-frequency components of the spectrum of the supply voltage at the output of the inverter.

    Thus, the drive inherent losses associated with switching and the use of transformers, which have the efficiency. Moreover, high-voltage transformers have relatively large dimensions.

    The third task when using the if - problem of cooling of electric motor in which the cooling is the fan mounted on the shaft. When reducing the rotational speed by using the inverter, the efficiency of the fan is reduced and the engine may overheat.

    Therefore, the use of frequency converters for electric motors intended for operation in the unregulated mode, you need to contact the manufacturer specific engine with a question about the possibility of using it in a regulated mode.

    The fourth task is to account for the natural frequencies of the rotor system: the rotor of the motor-coupling to the output shaft of the multiplier is the output shaft of the multiplier coupling the rotor of a centrifugal compressor. The number of housings of the compressor can reach three, so the calculation of the dynamics is necessary to consider the coupling and the rotors of these buildings.

    In the presence of the resonant frequencies of the rotor system in the range from 0 to 50 HZ, they will not affect the operation of the compressor, because you will quickly be taken when starting and stopping the motor. At the same time, the application of resonance frequency FC can be in the working range of variation of the rotational speed with the consequential negative factors.
    Therefore, when using the inverter for compressor units, designed with the use of an electric motor with a constant speed, it is necessary to calculate the dynamics of rotor systems to determine critical speeds, and the control system should exclude the work to identify the critical frequencies.

    The fifth challenge - the creators of the inverter, typically offer several options for working with motor: constant torque; maintaining a constant output power or change these parameters according to a certain law, depending on the frequency. The consumer must decide and choose one of the options.

    Sixth task - the most important is the analysis of changes of gas-dynamic characteristics of a centrifugal compressor while changing the rotational speed of the electric motor with the inverter.

    When you create the CC with electric drive with constant speed the task of obtaining the maximum efficiency of the installation and effective maintenance of all modes of technological process available as part of the installation of regulatory bodies (throttle on the suction or inlet guide vanes, and a bypass valve), and the question "What happens to gas-dynamic characteristics of the CC when you change the frequency of rotation?" - before a developer is not put. To answer this question we have performed calculations of the ten characteristics of the Central Committee of the frequency variation of the rotation (table 1). The calculations are estimates and therefore the assumption that the value of the calculation point is adopted, the frequency of rotation of the rotor of the Central Committee after the multiplier at the frequency of rotation of the motor is 3000 rpm (synchronous motor), i.e., given the limits of change of frequency of rotation in the plus direction: +45%; +22%, etc.; are conditional. This assumption made due to the fact that suppliers of electric motors is not going to increase more than 50 Hz mains frequency.

    The analysis of a range of changes in speed from the calculated values, while the lower bound is determined by the border surge, and the upper maximum power consumed by the compressor, which is limited to available capacity of the electric motor. At the same time was determined and the boundaries of flow rates.

    table # 1

    Mark CC
    Frequency of rotation of the rotor of the CC
    in a settlement point
    (rpm)
    Expense of the pelvis in the calculation point (m3/min)
    estimated
    point
    (rpm)

    changes
    %
    estimated
    point
    (rpm)

    changes
    %
    CTC 12,5/35
    13600
    - 1,5.....+4,5
    188
    - 18,1.....+17
    GC-109/18-76
    11406
    - 23,4.....+22
    124
    -16,1....+11,3
    GC-100/5-1 iO
    11318
    - 31......+7,3
    -21.8.....+4,5
    CTC......7/14
    13648
    -2,5.....+1,8
    127
    -25..... +10
    GC 1-200/3,5
    9546
    -5,7.....+10
    210
    -28,6....+23,8
    543 CC-410/35
    9600
    - 0.....+6,25
    446
    -0... +16,1
    College-2,5/3,5
    11200
    - 10,7.....+5,3
    45
    -48,9...+17,7
    VC -100/9
    25010
    0.....+8
    102
    -0... +20
    WC   160/9
    19396
    - 1.....+3
    159
    -5... +17
    GC-75/5.3-115
    18811
    - 4,3.....+3,7
    73
    - 34... +13
    Submersible pump
    Frequency
    rotation
    nominal
    - 20.....+40
    Consumption
    rated
    -50.....+100

    From table 1 it is seen that for the CTC of 12.5/35; CTC 7/14; 543 CC-440/35; VC 100/9; VC-160/9 the ranges of rotational speeds comparable with the accuracy of measurement of frequency of rotation in the operating conditions and the limits of change of flow rate (total) is small, so the use of frequency converters for these compressors is impractical. For the rest of the range of variation of consumption is also small. The widest range of flow control compressors have chlorine HHC-2,5/3,5 and oxygen GZ 1 -200/3,5.

    Although, in accordance with the theoretical framework, the regulation parameters The Central Committee of the change of the rotational speed is the most efficient mode, the considered compressor have a throttle valve and a bypass valve, which allows in a wide range to adjust the parameters of the compressor without changing the frequency of the supply network and are cost effective.

    For comparison, table 1 shows the characteristics of submersible pump, from where you can see obviously the advantage of the inverter installations: if you change the frequency by 60% of the flow is changed to 150%. Therefore, obtaining good results in the implementation of frequency converters for pumps, the creators of the if believe that the same results happen on centrifugal compressors.

    Table 1 shows the data on the Central Committee, which are widely used in many technological process metallurgy, chemistry, oil & gas and have high pressure ratios (stop to start) p=PK/Pn (some authors call this option "the degree of pressure increase"), which is from 3.5 to 35. These compressors usually fairly narrow range high efficiency performance.

    In "Gazprom" operated a large number of electrically driven gas pumping units (EGPA) power of drive motor 4; 6,3; 10 and 12.5 MW. Supercharges those that have low pressure ratios p=l,25 1.5, so is of interest, the nature of the behaviour of gas-dynamic characteristics when installing the inverter.

    table 4

    Mark CC
    Frequency of rotation of the rotor of the CC
    in design point (rpm)
    gas Flow at the design rate
    (m3/min)
    estimated
    point
    (rpm)

    changes
    %
    estimated
    point
    (rpm)

    changes
    %
    Egpu-4/40-1,25
    8200
    -32... +5
    260
    -65....+30
    Egpu-6,3/56-1.44
    8200
    -32...+5
    213
    -60...+20

    Table 2 presents the results of the analysis of gas-dynamic characteristics of the two superchargers: egpu-4/40-1.25 (manufacturer JSC "Nevsky Zavod") operated by LLC "Gazprom transgaz Tomsk" and egpu-6,3/56-1,44, developed in JSC "Naturvetarna them.In.B.Economies" (HMS Group).

    As can be seen from table 2, the range of regulation of speed and flow are wide enough to install the inverter on these egpu will have a positive effect.

    In this article discusses options for using high-frequency motors and FC on frequency over 50 Hz (3000 rpm) until the working frequency of the rotor of the compressor and to eliminate a multiplier. This decision immediately suggests the use of electromagnetic bearings and dry gas seals, i.e. oil-free (dry) compressors – a question that is beyond the scope of the Central themes of the work. It must be reiterated that in centrifugal compressors, the use of frequency converters require special calculations to determine the appropriateness and effectiveness of their application.

    the Authors:
    Ph. D. Gozalbes Y. Z., CJSC "Naturvetarna" (HMS Group),
    Ph. D. Ibragimov, E. R., CJSC "Naturvetarna", JSC Kazankompressormash (HMS Group),
    ing. Livshits, B. M. JSC Kazankompressormash (HMS Group)
    Ph. D. Lunev A. T., JSC "Naturvetarna" (HMS Group)



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