Tuesday, October 31, 2006
State-of-the-art drives for old compressors
As part of a modernisation project, the chemical company Brunner Mond, based in north-west England, is now using variable-speed drives, instead of steam turbines to drive its centrifugal gas compressors. The 50-year old compressors, now fitted with state-of-the-art drive technology, will remain to become an energy-saving, low-maintenance system with a high availability. This has all been made possible by combining special high-speed motors, gearless couplings and medium-voltage drive converters with intelligent HV IGBT (Insulated Gate Bipolar Transistor) power semiconductors.
In addition to supplying the drive system, Siemens carried-out the computer-based vibration analysis, system integration, training of the operating personnel, commissioning and after sales service.
Brunner Mond Group plc.
is one of the leading European producers of alkaline chemicals.
The Company has a total of four plants in Europe and Africa with its head office located in Northwich, in north-west England.
The company produces mainly soda ash, a basic material for use in the glass industry and the production of washing powders, as well as industrial minerals.
Until September 2000 Brunner Mond owned and operated coal, oil and gas -fired boilers in the production facilities at Winnington and Lostock, close to Northwich.
The boilers kept the plants supplied with process steam as well as high-pressure steam for the steam turbines driving the compressors.
Brunner Mond now have all of their steam raising carried out by Powergen Combined Heat and Power via a combination of five new gas boilers.
These central, gas-fired, boilers supply low-pressure steam, to the two facilities at Winnington and Lostock.
This can be used as process steam, but is not suitable for driving the compressors.
Brunner Mond therefore decided to keep the fifty-year old compressors, which were still fully operational, and replace the steam turbines with variable-speed electric drives.
At Lostock, this involved four units.
Compared with steam turbines, electric drives are distinguished by their high reliability and low service requirements.
As deposits continually reduce their efficiency, steam turbines have to be stripped down completely twice a year, cleaned and the seals replaced.
Modern electric drives, however, operate almost maintenance-free with the added advantages of significantly lower noise levels and cooler operation.
The speed of the motor is continually adapted to actual operational requirements, which guarantees accurate process control.
Energy is also saved because the system takes only the amount of power, which it actually requires.
In order to gain the advantages of variable-speed drive technology for the existing Brunner Mond compressors, Siemens selected a system comprising special high-speed motors, gearless couplings and water-cooled medium-voltage Simostart MV drive converters.
The drive converters are equipped with intelligent HV IGBT (Insulated Gate Bipolar Transistor) modules, which are optimally harmonised with each other.
These drives guarantee optimum reliable compressor operation over the complete speed range.
The motors, which have an operating range from 3800 to 6400 RPM, are an individually customised design from the Siemens special drives centre in Berlin.
Induction motors with laminated squirrel-cage rotors are used for the four drives, two machines require 1.5 MW of absorbed power at the coupling and two smaller machines of 1.3 MW, so that the motor dimensions allow the two existing compressors to be used without modification.
The motors have air-to-water heat exchangers, the internal cooling circuit using separately-driven fans with counter current cooling at both ends.
The rotor has a ribbed surface for good cooling characteristics.
In order to eliminate vibration problems from the very beginning, the usual bending and torsion analysis of the rotor was supplemented by investigations into the strength and stiffness of the motor frame, which was optimised by computing the natural frequency.
In order to optimise the dynamic performance of the rotors, Siemens used special tilting-pad bearings.
Four additional balancing planes permit modal balancing and therefore a specific reduction in the bending vibrations in all of the natural forms.
In spite of the wide range of speeds, the application of each of these measures made it possible to locate all of the natural frequencies outside the speed control range.
Full-load system tests were carried out in the Berlin Dynamowerk factory, prior to installation, to ensure that all of the specifications were fulfilled.
For the Brunner Mond application, the motors are coupled to the compressors without using gearboxes.
This configuration has the advantages of a higher overall efficiency, low wear, and increased availability due to the elimination of all problems associated with gearboxes.
In order to guarantee the smooth running properties of the new motors, they were perfectly harmonised with the 50-year old compressors.
Siemens carried-out a torsion and vibration analysis for the complete mechanical transmission using a specially generated three-dimensional finite element model of the old compressor and the new motor.
The moment of inertia for the compressor was determined from documents, which were about 40 years old and using the FEM model, all possible operating situations and mutual interactions were simulated by computer.
From the information gained, optimum smooth running characteristics were obtained for the mechanical transmission up, to a maximum speed of 6400/min.
A Simovert MV medium-voltage converter is used to control the speed.
This unit has an output of 2300 kVA at a motor voltage of 3.3kV and an output frequency of 107 Hertz.
As a result of its unique design, Simovert MV requires little maintenance and has a high availability.
This is particularly due to the fact that it is the first drive converter in the medium-voltage range, which uses HV-IGBT (Insulated Gate Bipolar Transistor) power semiconductors.
In conjunction with a three level voltage DC link, the HV-IGBT modules permit a clearly structured, modular and space-saving design, which is both extremely reliable as well as service-friendly.
This could not be achieved when using other power semiconductors because the HV-IGBT is the only semiconductor element of its class which requires absolutely no snubber circuitry.
Together with the gating system, the IGBT modules form an intelligent switching unit which allows switching, independent of the load, and as a result unnecessary current peaks are eliminated.
In conjunction with the three-level technology and the high-performance transvector control, this guarantees sinusoidal motor currents.
This, in turn, reduces the motor losses and minimises the torque fluctuations, which reduces overstressing of the motor, mechanical transmission and especially the driven load.
Although Simovert MV units can be either water-cooled or air-cooled, it was only possible to use the water-cooled version for the Brunner Mond drives.
The ambient air was far too aggressive for air-cooled converter technology, which is frequently the case in the chemical industry.
In addition to supplying the drive system, Siemens carried-out the computer-based vibration analysis, system integration, training of the operating personnel, commissioning and after sales service.
Brunner Mond Group plc.
is one of the leading European producers of alkaline chemicals.
The Company has a total of four plants in Europe and Africa with its head office located in Northwich, in north-west England.
The company produces mainly soda ash, a basic material for use in the glass industry and the production of washing powders, as well as industrial minerals.
Until September 2000 Brunner Mond owned and operated coal, oil and gas -fired boilers in the production facilities at Winnington and Lostock, close to Northwich.
The boilers kept the plants supplied with process steam as well as high-pressure steam for the steam turbines driving the compressors.
Brunner Mond now have all of their steam raising carried out by Powergen Combined Heat and Power via a combination of five new gas boilers.
These central, gas-fired, boilers supply low-pressure steam, to the two facilities at Winnington and Lostock.
This can be used as process steam, but is not suitable for driving the compressors.
Brunner Mond therefore decided to keep the fifty-year old compressors, which were still fully operational, and replace the steam turbines with variable-speed electric drives.
At Lostock, this involved four units.
Compared with steam turbines, electric drives are distinguished by their high reliability and low service requirements.
As deposits continually reduce their efficiency, steam turbines have to be stripped down completely twice a year, cleaned and the seals replaced.
Modern electric drives, however, operate almost maintenance-free with the added advantages of significantly lower noise levels and cooler operation.
The speed of the motor is continually adapted to actual operational requirements, which guarantees accurate process control.
Energy is also saved because the system takes only the amount of power, which it actually requires.
In order to gain the advantages of variable-speed drive technology for the existing Brunner Mond compressors, Siemens selected a system comprising special high-speed motors, gearless couplings and water-cooled medium-voltage Simostart MV drive converters.
The drive converters are equipped with intelligent HV IGBT (Insulated Gate Bipolar Transistor) modules, which are optimally harmonised with each other.
These drives guarantee optimum reliable compressor operation over the complete speed range.
The motors, which have an operating range from 3800 to 6400 RPM, are an individually customised design from the Siemens special drives centre in Berlin.
Induction motors with laminated squirrel-cage rotors are used for the four drives, two machines require 1.5 MW of absorbed power at the coupling and two smaller machines of 1.3 MW, so that the motor dimensions allow the two existing compressors to be used without modification.
The motors have air-to-water heat exchangers, the internal cooling circuit using separately-driven fans with counter current cooling at both ends.
The rotor has a ribbed surface for good cooling characteristics.
In order to eliminate vibration problems from the very beginning, the usual bending and torsion analysis of the rotor was supplemented by investigations into the strength and stiffness of the motor frame, which was optimised by computing the natural frequency.
In order to optimise the dynamic performance of the rotors, Siemens used special tilting-pad bearings.
Four additional balancing planes permit modal balancing and therefore a specific reduction in the bending vibrations in all of the natural forms.
In spite of the wide range of speeds, the application of each of these measures made it possible to locate all of the natural frequencies outside the speed control range.
Full-load system tests were carried out in the Berlin Dynamowerk factory, prior to installation, to ensure that all of the specifications were fulfilled.
For the Brunner Mond application, the motors are coupled to the compressors without using gearboxes.
This configuration has the advantages of a higher overall efficiency, low wear, and increased availability due to the elimination of all problems associated with gearboxes.
In order to guarantee the smooth running properties of the new motors, they were perfectly harmonised with the 50-year old compressors.
Siemens carried-out a torsion and vibration analysis for the complete mechanical transmission using a specially generated three-dimensional finite element model of the old compressor and the new motor.
The moment of inertia for the compressor was determined from documents, which were about 40 years old and using the FEM model, all possible operating situations and mutual interactions were simulated by computer.
From the information gained, optimum smooth running characteristics were obtained for the mechanical transmission up, to a maximum speed of 6400/min.
A Simovert MV medium-voltage converter is used to control the speed.
This unit has an output of 2300 kVA at a motor voltage of 3.3kV and an output frequency of 107 Hertz.
As a result of its unique design, Simovert MV requires little maintenance and has a high availability.
This is particularly due to the fact that it is the first drive converter in the medium-voltage range, which uses HV-IGBT (Insulated Gate Bipolar Transistor) power semiconductors.
In conjunction with a three level voltage DC link, the HV-IGBT modules permit a clearly structured, modular and space-saving design, which is both extremely reliable as well as service-friendly.
This could not be achieved when using other power semiconductors because the HV-IGBT is the only semiconductor element of its class which requires absolutely no snubber circuitry.
Together with the gating system, the IGBT modules form an intelligent switching unit which allows switching, independent of the load, and as a result unnecessary current peaks are eliminated.
In conjunction with the three-level technology and the high-performance transvector control, this guarantees sinusoidal motor currents.
This, in turn, reduces the motor losses and minimises the torque fluctuations, which reduces overstressing of the motor, mechanical transmission and especially the driven load.
Although Simovert MV units can be either water-cooled or air-cooled, it was only possible to use the water-cooled version for the Brunner Mond drives.
The ambient air was far too aggressive for air-cooled converter technology, which is frequently the case in the chemical industry.
# posted by Medical Information : 1:58 AM
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