ENGINE & TURBINE TECHNOLOGY
minimised OPEX once the system was up and running.
DEFINING KEY COMBUSTION CHARACTERISTICS Before the CATS could be designed, it was important to identify the key combustion characteristics. Tis would involve gathering large quantities of data regarding turbine combustion, NOx generation and existing controls. For over six months, Sulzer collected and analysed tens of thousands of sets of unit operating data, discerning the characteristic values for thresholds that, if exceeded, would affect burn stability and NOx emissions. Tis would help create the control model that the CATS would adhere to. Extensive research was conducted on the turbine itself. As part of this, combustion tuning testing was carried out in varying operational conditions, allowing for parameters to be assessed. Troughout all testing, continuous NOx emissions monitoring was conducted to show how certain parameters affected emissions. Te key was to achieve the emissions standard without reducing the efficiency of the gas turbine. Te results showed that NOx emissions
were being affected by combustion temperature, fuel variability, humidity, ambient temperature and a phenomenon known as humming. Humming refers to pressure oscillations caused by combustion instabilities. To create an automatic control system, all of these factors would need to be measured using sensors. Tis signal data would then require processing and applying to the operational threshold values discovered during research. Ten a control model could be realised for stable combustion, allowing the new emissions standard to be achieved.
TURNING DATA INTO ACTION Based on the findings and analysis, Sulzer developed the modular control system in-house, carrying out control strategy design, control logic configuration and simulation verification. Te system is designed to seamlessly integrate with the control system currently installed on the gas turbine. A custom key data display was also implemented, showing signal data from different parameters including NOx, humming, natural gas heat, humidity and temperature. Functionality available from the bespoke control interface includes dedicated
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modules for auto-fuel adjustment, a combustion stability control, NOx emissions reduction, performance optimisation control, fuel calorific value manual input function, function status display, alert alarm and a historical graph.
A CONTROLLED BURN In operation, the CATS provides closed loop control, using feedback from sensor signal data to keep operational parameters within the desired thresholds. If any signal value exceeds the desired range, automatic dynamic adjustments are made to ensure that key parameters such as emissions, combustion dynamics, power output and efficiency are maintained. Furthermore, using historical data gathered during research and operation, feed forward control is also possible. Using models to make predictions on burn stability in different conditions, the system can also take proactive actions to control the burn. Tis aspect of the system becomes more proficient as data is collected, recalibrating the characteristics of the individual turbine accordingly. All this ensures that NOx emissions are reduced during running, as the gas turbine is prevented from straying into unfavourable operating conditions. Across a range of loads, gas calorific
values, humidity and ambient temperatures, the CATS was able to deliver average emissions below the 30mg/m3
standard.
In fact, since its installation, the highest instantaneous value of NOx emissions from the turbine is lower than 28.5mg/m3
Sulzer offers power plants the gas turbine expertise required to achieve stable combustion performance and reduced emissions
,
with an hourly average of just 27mg/m3
–
25% to 30% lower than the average NOx emission value in 2020.Tis ensures that the turbine now meets the “Stationary Gas Turbine Air Pollutant Emission Standard” coming into effect in Jiangsu Province. Tis breakthrough CATS solution has
provided the power plant with a one- off CAPEX saving of US$1.4 million, while delivering OPEX savings of over US$41,000 per turbine annually. Te system has reduced emissions by 120 tonnes in its first year of operations, unlocking annual carbon tax savings of nearly US$44,000. Furthermore, the CATS is fully applicable to other selective Siemens, General Electric and Mitsubishi heavy duty GT models, ensuring these multiple advantages can be attained by other combined cycle and gas power plants. Sulzer’s industry and solution engineering expertise offers power plants the gas turbine expertise required to achieve stable combustion performance and reduced emissions reliably and cost- effectively. With a proven, bespoke control solution, legacy turbines can be modernised to attain new efficiency standards, while avoiding the long lead times and investment required for replacement equipment. With emissions standards around the world becoming more prescriptive – a trend that is set to continue – operators now have access to a new technical innovation that can breathe new fire into their efforts to reduce emissions and improve efficiency.
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