May 2012, Vol. 239 No. 5

Features

Systematic Turbine Compressor Controls Employ High Performance Modules

On its long journey from extraction to the consumer, natural gas has to be compressed repeatedly to maintain the required discharge pressure in the pipelines. Russia’s leading supplier of automation equipment for the gas turbine compressors used for this purpose places its trust in the proven “made in Germany” control technology. This ensures reliable long-term operation as well as maximum supply quality and reliability during natural gas transport.

Natural gas pipelines are the equivalent of the veins of civilization, which supply the material that warms us and increasingly also drives our vehicles, mostly from very inhospitable areas. The pipelines often run thousands of kilometers across borders and continents and are subjected to extremely harsh climatic conditions. This makes their operations management a very challenging task, in addition to their construction and maintenance.

For example, the natural gas has to be transported through the pipeline at the appropriate flow rate to ensure that the amount being transported is sufficient. However, the pressure decreases during transport due to the internal friction of the molecules in the gas flow and the external friction of the gas flow against the inner walls of the piping. For this reason, compressor stations are installed every 100-200 km along the pipelines running from northern Siberia to the west, south and east, in which several turbo compressors compensate the pressure drop. The pressure, flow volume and temperature of the natural gas are measured and controlled to the specified values in one or more passes.

Sound Basis For Maximum Reliability
Since failures would result in extremely high costs, in particular at compressor stations far away from civilization, there are one or two reserve turbo compressors in each station. The auxiliary units feature redundant automation and high availability to some extent. Important process parameters are monitored and controlled continuously.

The ZAO Systema-Service, a closed joint-stock company (???????? ??????????? ????????, ???) headquartered in St. Petersburg, is one of the largest suppliers, worldwide, of control and automation systems for gas turbine compressors and power plants. The company, which has been an autonomous entity for 16 years, has its origins in a scientific research institute and has been active in the automation of such stations for more than 30 years (see sidebar). As a service provider, the system vendor also has the scientific and technological knowledge required for reliable long-term operation of highly complex plants that are often subjected to extreme environmental temperatures ranging from -60°C to +50°C.

With Siemens AG, which has held a stake in Systema-Service for several years, the St. Petersburg company has a partner that for its part produces gas turbines of the type required for such compressor stations. It was therefore natural to use the latest Siemens automation technology in the course of the MSKU 5000 innovation round – the current seventh generation of the multiprocessor-based control and operations management system for the stations. At the same time, however, Dr. Simon D. Altshul, general director of Systema-Service, stresses the performance-oriented nature of the close cooperation: “Our systems have to fulfill the highest demands with the maximum possible reliability. That requires not only the most efficient automation technology, but also a sound understanding of the challenges faced.”

The MSKU 5000 is based essentially on integrated automation components that have been tried and proven in the manufacturing and process industries. The heart of the gas turbine controller system is the Simatic S7-400 controller. Fault-tolerant S7-400H controllers are used for some auxiliary units, such as the oil supply and gas cleaning units. These have two autonomous CPUs each coupled using fiber-optic cables that constantly calibrate their data. If one unit fails, the other automatically takes over its part.

Quick And Chronological
The decisive factor for maximum control speed and quality, however, is the high-end application module SIMATIC FM458-1 DP whose computational power exceeds even the fastest SIMATIC CPU by at least 10-fold. The module has extremely rapid inputs/outputs and analog channels with conversion times of 1 µs. This allows extremely rapid control times (for example, 10 ms specified by Systema-Service for closed-loop pressure and flow control) to be ensured even with large quantity structures.

The FM458-1 DP is integrated in the SIMATIC S7-400 rack and reduces the calculation, counting and measuring tasks to be carried out by the main control system. Configuration and programming is carried out using the convenient Continuous Function Chart (CFC) programming language in which functions are interconnected graphically blockwise instead of having to enter text-based commands. For the numerous tasks managed by the MSKU control systems, Systema-Service has created its own function blocks in ANSI C that specifically supplement the rich collection of more than 300 blocks. An integrated diagnostic interface makes even complex control structures transparent and comprehensible.

Whenever the quantity structure of the FM458-1 DP is insufficient, it is easy to extend the framework centrally and inexpensively by means of expansion modules. Thus the Systema-Service uses the EXM438-1 with 16/8 digital and 5/8 analog inputs/outputs for additional rapid I/O channels. Further standards from the automation range of Siemens that are used in the MSKU system are, for example, the SIMATIC ET 200M and ET 200S distributed I/O modules for linking field devices, as well as Industrial Ethernet switches of the Scalance series at the communications level. The fail-safe CPU 300 with Distributed Safety is also used for export systems.

And that is not all: For efficient and transparent operations management, including the detection, conditioning, visualization and archiving of process data, Systema-Service relies on SIMATIC WinCC as a SCADA solution for the Supervisory Control System (SCS) superimposed on the MSKU units. This is configured in a distributed server-client architecture, in some cases with two process servers and an additional archiving server that allow convenient operator control and monitoring in the control room. In perfect interaction with the S7-400, WinCC also ensures reliable alarm logging.

When a turbine stops, up to 50 parameters that were recorded at 10-ms intervals starting 25 minutes before the event until five minutes after the shutdown must be available for analysis. The SIMATIC controller enables this using the ALARM_8 and AR_SEND blocks. The former ensures the chronological flagging (Sequence of Events, SOE) of the alarms. The latter ensures that that analog values are recorded every 10 ms, sent to WinCC and stored there in 30-minute archives. In the long term only those archives that document a turbine stop are then stored.

End-To-End Integration
Let us talk now about end-to-end integration in four tailor-made variants. In addition to the required performance capability, the dominance of SIMATIC has tangible reasons in the engineering field: “The end-to-end integration during planning is most pronounced in the case of Siemens automation technology,” said Dr. Andrey V. Chernikov, lead developer at Systema-Service. “This facilitates handling and integration with systems of other manufacturers, thus saving us valuable time.”

The MSKU 5000 is available in four variants that are installed by Systema-Service, either in large containers for outdoor use, or in conventional cabinets. The four variants offer tailor-made and perfectly synchronized equipment for control and operation of 1) individual compressors/gas turbines; 2) complete compressor stations/halls; 3) individual gas turbine generator units as well as 4) complex gas turbine power plants.

The main task of the compressor/gas turbine control system GCU ACS (gas compressor unit/automation control system) MSKU 5000-01 is to control the pressure and the flow volume of the outgoing gas with a degree of accuracy of ±0.5% at a setpoint of approximately 75 bar. The control cycle of 10 ms previously mentioned requires highly dynamic algorithms and correspondingly high-performance hardware with rapid inputs and outputs, a fact that was ultimately decisive for the use of the FM458-1 DP module. Further important functions of the MSKU 5000-01 are the control of all system components in all operating modes, the fuel supply, the anti-surge control function, safety and protective tasks (emergency off) as well as data exchange with the higher-level SCADA system.

The main task of the CWS ACS (compressor workshop/automation control system) MSKU 5000-02 system, on the other hand, is the control of the extensive auxiliary units, from gas cleaning and cooling (after compression), through processing and preparation of the gas burned in the turbine as fuel, down to the well-balanced automatic distribution of the load among the individual compressors. At the maximum throughput, a gas pipeline requires a compressor output of approximately 80 MW, which is distributed among several 16-MW compressors, for example, depending on the load.

The GTPU ACS (gas turbine power unit/automation control system) MSKU 5000-03 control system is, in turn, conceived for use with individual gas turbine generator blocks. Such blocks often form smaller autonomous stand-alone power plants, so that one of the most important tasks here is the exact frequency control. Systema-Service bundles the complete hardware and software required for control and operations management of more complex gas turbine power plants into the fourth variant, the PS ACS (power station/automation control system) MSKU 5000-04.

Fruitful Cooperation — Also For German Consumers
A benchmark rating carried out at Gazprom, Systema-Service’s largest end customer, finally tipped the scales in favor of Siemens as the supplier of the modular MSKU system as the SIMATIC technology outperformed the rest. The long-term guaranteed availability of spare parts was another factor.

“The gas industry places increasingly high requirements on the performance capability and competitiveness of our systems,” said Kirill A. Vasilyev, head of business development at Systema-Services. “In order to remain one step ahead we require a partner who not only works with us to achieve significant milestones but also provides the right solutions on a small scale.” For example, Siemens increased the number of variables that can be stored in WinCC user archives by more than six-fold, not least at the request of the St. Petersburg company, a factor that markedly increased the flexibility with regard to evaluation, archiving and communication on the control level. With the changeover to the latest Version 7 of the visualization system, the maximum number of alarm and tag logging operations has been increased again. A further example was the development of a SIMATIC ET 200M module designed specifically for the requirements of the Russian market and the country-specific standards (GOST) for the connection of thermo-resistors and thermo-couples.

Unanimous Assessment From The Russian Side
With the proven and reliable high-performance control technology, the MSKU systems for gas compressors and power plants have become significantly more efficient and precise. This allows an even greater contribution to be made to maximum supply quality and reliability at competitive prices – a fact from which natural gas customers in Germany will benefit even more directly in the foreseeable future when Systema-Service automates the planned Baltic pipeline “Nord Stream” with 30-40 MSKU 5000 systems. This pipeline will significantly raise the bar for reliable control of parameters for gas transport. The planned 1,220-km supply vein will run almost completely under water, meaning that controlling interventions during transport will not be possible and that a notably higher gas input pressure of around 250 bar will be required.

From Research To Success

As Russia’s leading automation specialist for gas turbine compressors and power plants, ZAO Systema-Service places great value on its roots as a scientific research institute, which it still cultivates with its 250 permanent employees. The latter is primarily in the form of financial and technological sponsoring of training and education at the St. Petersburg State Polytechnic University. Together with Siemens, the company supports projects that include equipping laboratories with state-of-the-art automation systems as well as training courses for their use. Gas compressors and power plants are much more complex than a modern passenger aircraft – their automation is therefore also correspondingly more demanding. This explains why Gazprom, the largest company in the Russian gas market, requires that operators of these systems be certified by the St. Petersburg company.

Other customers of Systema-Service in the domestic Russian market include most of the machine manufacturers in the gas sector, among them Iskra, Newski, Saturn and Kasan. The company is active in Turkey, Kazakhstan, Turkmenistan, the Ukraine and Belarus. Cooperation is also under way with the Thales Group in France and with Siemens Industrial Turbomachinery AB in Sweden. Around 3,000 automation systems from Systema-Service are in operation worldwide, of which 350 are the latest generation MSKU 5000 – an upward trend.

Author
Michael Rosemeyer is a technical senior consultant for Siemens AG, Industry Sector, Industrial Automation Systems. He has more than 30 years of experience in automation projects. Since 2003 he has been the technical partner for Systema Service in the headquarters in Nuremberg.