The objective of this system is to continuously monitor and automatically optimize the performance of the DLN combustion system as it responds to:
- Changes in seasonal ambient conditions
- Degradation of combustion hardware over its maintenance cycle
- Degradation of gas control valve calibrations
- Changes in fuel Wobbe index (composition or temperature) within limits specified in GE’s gas fuel specification (+/-5%)
The specific performance benefits achieved by the auto-tuning system are:
- Limiting wear and mechanical distress of the combustion hardware caused by combustor dynamic pressures
- Preventing lean blow out of the combustor
- Maintaining NOx & CO emissions within design or regulatory compliance limits
Based on the customer’s specific requirements and past operating history, different priority can be given to each of the above three factors. For example, a combined–cycle site which has an SCR and has previously experienced damaged combustion hardware may want to prioritize dynamics reduction over minimizing NOx because excess NOx emissions can be reduced by the SCR. However, simple-cycle peaking units subject to stringent emissions regulations must prioritize keeping NOx below 9 ppm ahead of minimizing dynamics. Prevention of lean blow out is given high priority in all instances.
The auto-tuning system can be installed on units having either lean-PM1 or rich-PM1 operating configurations; it can also be implemented on units that either do or do not use quaternary fuel.
Our field engineers have extensive experience in tuning and troubleshooting more than 80 GE F-class gas turbines. Additionally, we employ engineering staff that were involved in the development of the DLN-2.6 combustion system at GE. Our broad practical experience and in-depth design knowledge of the DLN-2.6 combustion system are incorporated into the auto-tuning system algorithms. This breadth and depth of knowledge are necessary for developing an auto-tuning system that can handle the wide range of combustion system behaviors seen throughout the GE 7FA fleet.
The auto-tuning system is comprised of four main components:
- Auto-Tuning Software Program
- Combustion Dynamic Monitoring System (CDMS)
- Continuous Emissions Monitoring System (CEMS)
- Turbine Controller (Mk V / VI)
Lean blowout and regulatory NOx excursions are common operational problems on DLN-2.6 systems that have been improperly tuned. Our team understands the impact of ambient temperature variation on inducing these problems and establishes tuning criteria to eliminate their future occurrence.
Sometimes a turbine comes out of a scheduled outage with significantly increased NOx, above regulatory limits. We will analyze pre and post-outage turbine performance data to diagnose the cause of the problem and provide short and long term solutions to maintain operation within compliance.
For DLN combustion systems, combustion tuning is required during initial unit start-up and periodically any time after combustion or hot gas path hardware is changed out. Additionally, combustion tuning may be required to help meet your goals for operational flexibility.
The objective of DLN tuning is to ensure that the DLN combustion system operates within its regulatory emissions limits, while also minimizing combustion dynamic pressure levels and providing sufficient lean blow out margin over the low NOx operating range. Based on fuel split testing data at various gas turbine loads, adjustments are made to existing fuel split schedules to achieve an optimal combination of emissions, dynamics and lean blow out margin.
Our combustion engineers can travel to your site or connect remotely to carry out this tuning exercise. The combustion engineer uses site CEMS emissions data and CDMS combustion dynamics data as necessary to assess the condition of the system and to make changes to optimize emissions and combustion dynamics to minimize combustion hardware stress levels.
Where customers do not have permanently installed CDMS system, TTS can rent a portable system for use during the tuning process. TTS also builds portable and permanent systems for sale to customers.
Combustion Dynamics Monitoring Equipment
Dry Low NOx (DLN) Combustors operate at very lean fuel-to-air ratios in order to meet single digit NOx emissions regulations. Operation at fuel/air ratios close to the lean flammability limit make DLN combustors prone to dynamic pressure oscillations that can lead to accelerated wear and mechanical distress, flashback of the flame into the pre-mixer, or lean blow out trips. Regular tuning of these systems is required to ensure compliance with emission regulations and long term component integrity.
TTS' CMS-1000 Combustor Dynamic Monitoring System is specifically tailored for measuring dynamic pressure pulsations in gas turbine DLN applications. Hardware configuration and setup are simple, and the software is user-friendly and provides data in formats that DLN tuners and operators need to easily optimize DLN operation. This system can be provided in two configurations: Portable and Permanent.
DLN-1 High Load Transfer
DLN-1 combustion systems must operate in the Premixed Steady-State (PMSS) combustion mode to achieve low NOx and CO emissions. DLN-1 combustion systems transfer from the Lean-Lean (LL) combustion mode to PMSS mode as the gas turbine load increases above nominally 50% load. The combustion system remains in PMSS mode between 50% and base load.
Momentary system upsets such as gas supply pressure fluctuations, the presence of liquids in the fuel, gas control valve fluctuations, or instrumentation problems can cause the flame to re-ignite in the primary combustion zone. This primary re-ignition (PRI) causes the unintended transfer of the combustor from PMSS to Extended Lean-Lean (LL-EXT) mode. In LL-EXT mode, the gas turbine operates out of emissions compliance, with NOx increasing from single digits to approximately 100 ppm. Additionally, operation in LL-EXT mode results in a life maintenance factor of 10 for the combustor hardware.Click to Read Case Study
We provide training to allow operators to make simple adjustments to correct minor NOx and dynamic variations.