Dynaswirl-LN™ Case Study 109 Contra Costa Power Station Unit No. 7

The Situation

The Environmental Protection Agency (EPA) continues to lower the allowable NOx emission rates through stringent regulations. These regula-tions are being met by several advanced methods in California. Mirant’s (formerly Southern Energy California) plant in Antioch, CA required a new low NOx burner system to comply with the clean air requirements. The daily average emission rate of the existing utility boiler needed to be reduced to less than 30 ppm.

The Boiler

The Contra Costa Station Unit No. 7 is a 345 MWe power boiler capable of delivering 2,160 kpph steam at 2,475 psig and 1,053°F. The unit has two firing walls with two rows of six burners on each wall. There is a row of six Over Fire Air (OFA) ports – one above each burner column on each firing wall. The burners and OFA ports are all in one common windbox. Flue Gas Recirculation (FGR) is supplied to the air stream via sparger sections. Table 1 shows the boiler data.

Unit No. 7

No. Burners 24 
No. Over Fire Ports 12
Boiler/Turbine Output, MWe 345 
Steam Flow @ MCR, kpph 2,160
Nominal Combustion Air Temp., °F 600

The TODD® Solution

In 1996, a contract was awarded for the turnkey supply and installation of 24 TODD Dynaswirl-LN burners and 12 TODD venturi OFA ports. The Dynaswirl-LN is a low NOx gas/oil burner for multi-burner and utility boilers.

In preparation for the retrofit, COOLflow ™ technology was used to design a physical model of Unit 7. COOLflow modeled the combustion air, FGR and OFA systems; helped correct airflow problems; maximized the FGR mixing device performance; and helped ensure the proper OFA penetration into the rising furnace gases. In conjunction with the COOLflow results, the Stone & Webster Engineering Corporation (SWEC) upgraded the FGR system from 17% to 30%.

The TODD burners and OFA ports were installed during a turnkey outage in March 1997.

The TODD Result

The TODD Dynaswirl-LN burners, OFA ports and COOLflow modeling solutions increased FGR flow and reduced NOx emissions in Unit 7 by over 80% to 26 ppm. The excess O2 and CO levels were lowered. Additionally, the Dynaswirl-LN retrofit improved the boiler turndown and operating flexibility.

In 1997 the sub-30 ppm NOx guarantee for this project was the lowest ever stated and successfully demonstrated for a utility low NOx retrofit project. At the time of this turnkey retrofit, the Contra Costa Unit 7 achieved the lowest NOx in the USA on any utility boiler greater than 200 MWe using only combustion modifications for NOx control.

Refer to the Dynaswirl-LN case study 110, the Cabrillo Power I LLC Encina Station Units No. 4 and No. 5, for more recent NOx innovations.