When Turbines Technology Services (TTS) is working on a modernisation project, it involves more than...
Despite fuel resource limitations or fluctuations, increased demand, and the pressures from environmental compliance, confidence needs to be high that the unit will start and operate well.
With that in mind, many utilities will use dual fuel capability as a back-up just in case their primary fuel resource fails in quality or availability.
Some areas of the country face economic and reliability risks due to the weather. Forbes reported that below 20°F, each time the temperature drops one degree another 400MW of electricity is needed.
Its not just about electrical demand, as winter 2014 saw a 20 fold increase in gas prices on isolated, cold days.
Because much of today’s gas supply comes from shale plays, many operators have seen an increase of liquids in the gas, which can cause serious issues for the turbine’s operation (primary re-ignition for example) and the environment. The quality of the supply needs to be monitored closely.
- Switching to dual fuel, however, has its challenges:
- Dual fuel is more complex as indicated by the following schematics
- More complexity equates to increases in maintenance
- Liquid fuel requires careful selection of the fuel filtration system. GE manual calls for a one-micron filter
- Fuel quality from long term storage will naturally undergo chemical degradation due to Oxidation and Polymerization.
- Coking can be an issue. 250°F often cited as threshold for coking, but coking severity is on a temperature / time continuum.
If these challenges didn’t dissuade you, reliable liquid fuel operation relies on the successful operation of numerous control components from multiple systems including: liquid fuel, atomising air, water, liquid, and gas purge and false start drain.
Your operations and maintenance (O&M) programme should incorporate:
- Component inspection
- Device calibration
- Component testing
- System testing
- Robust startup, operating, and shutdown procedures
Some important takeaways:
- Monitor and address fuel quality issues
- Reduce the potential for coking by reducing temperatures in key fuel system components: Water-cooled check valves, 3-way valves/distributor, and post-shut down purging of fuel from system
- Consider upgrading to corrosion-resistant flow dividers
- Inspect and test dual-fuel components and systems, particularly in the late fall
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