COOLflow™ Case Study 113 NRG’s El Segundo Station

The Situation

NRG Energy explored its options for refurbishing and retrofitting Units No. 1 and No. 2 at its El Segundo Station power plant in California to increase energy production and reduce emissions. In the midst of unprecedented power volatility, investments for upgrades to these units had to be minimal if this plant was to remain economical to operate. In addition, the State of California mandated reduced emissions levels for this project. John Zink Company’s TODD Combustion Group recommended its premiere COOLflow modeling technology – a cost-effective solution for optimizing burner performance and achieving outstanding emissions reduction.

The Boiler

Units No. 1 and No. 2 are Babcock & Wilcox (B&W) front wall natural-gas fired boilers, each designed to supply a 175 MW turbine with approximately 1,140,000 lb/hr of superheated steam at 1,990 psig and 1,000°F. The units are each equipped with 16 original B&W register burners and four Over Fire Air (OFA) ports located above each burner column. However, the OFA ports were taken out of service and instead staging was achieved by firing through only 12 burners, with the top row of Burners Out of Service (BOOS). This staging technique was preferred due to airflow problems that caused uncontrollable CO emissions when the OFA ports were used. The use of BOOS instead of OFA was a clear indication that the combustion process within the furnaces had not been optimized.

After assessment of the units, baseline tests and careful analysis, our burner engineers concluded that the combustion performance could be dramatically improved, and emissions significantly reduced, by eliminating the airflow imbalances and placing the OFA ports back into service. To design these cost-effective retrofits for Units No. 1 and No. 2, the engineers employed COOLflow modeling (Fig. 1) to design baffles and turning vanes, which would be installed in the windboxes and ductwork systems to correct airflow distribution. These modifications would coincide with other maintenance work intended to enable greater power production by each unit. Implementing COOLflow to optimize the combustion process would also allow the existing OFA ports to be returned to service, reducing both NOx and CO.

The TODD Result

Several discoveries were made during the modeling process that revealed why the OFA ports were not used for staging. The modeling engineers found that the dampers which supplied air to the OFA ports were undersized, resulting in low velocities and low furnace penetration. The air trajectory through the OFA ports was not straight into the furnace, which would allow for effective mixing. Instead, the air exited the ports at a 45- degree angle upward, leading to this air staying close to the front wall and leaving the furnace without sufficiently completing the combustion process.

As a result of the COOLflow technology retrofit, NOx emissions on both units were reduced by an average of 22%. (See Fig. 2.) The CO levels in the post-retrofit tests were also significantly lower than achieved during the baseline (pre-retrofit) tests, with a 5% reduction on Unit No. 1, and a 65% reduction on Unit No. 2. During the post-retrofit test, it was also demonstrated that the maximum load capability of Unit No. 2 had been increased by 26 MWn (17%). In fact, Unit No. 2 can now run at approximately 172 MWn with the same NOx level as the baseline test, an increase in power output of 21 MWn (14%) without additional emissions.