SNCR, Balanced Draft Conversion & General Maintenance

Client / Owner


Architect / Engineer

Sargent & Lundy, LLC




Graycor Industrial

Project Scope

Graycor Industrial installed Selective Non-Catalytic Reduction (SNCR) technology in conjunction with a furnace balanced draft conversion on San Juan Generating Station’s Units 1 and 4. The project, which was completed to reduce NOx and fugitive dust emissions for the station, converts the boilers to balanced draft to meet current environmental requirements. In addition, Graycor replaced Unit 1’s boiler reheat header, Unit 1 cooling tower electrical upgrades and Units 1 and 4 economizer ash modifications.

Unit 1 consisted primarily of two outages where Graycor removed an abandoned electrostatic precipitator (ESP) by isolating the ESP from the existing flue gas system. This approach had numerous benefits including enhancing the project safety record as well as reducing the primary project outage schedule by one week. The primary outage, performed mid-February 2015 through early April, involved reconfiguring the inlet and outlet ductwork from the ESP bypass duct to the boiler and balanced draft system. The balanced draft portion of the project included the building of foundations for the Variable Frequency Drive Control House (VFD-PDC) followed by installation of a pre-assembled modular power and control house. Also included during this outage was installation of boiler wall boxes along with new gallery steel intended for the mounting of a STEAG SNCR injection system.

Following the spring outage, Graycor constructed the balance-of-plant (BOP) facilities and installed the SNCR equipment. The BOP consists of a central process building, a tank farm and miscellaneous processing and urea handling equipment along with the civil and electrical work necessary to make the system operational.

Unit 4 included installation of SNCR technology in conjunction with furnace balanced draft completed primarily during a fall 2015 outage. This unit required the installation of three new ID booster fans along with the installation of a VFD-PDC. Foundations for the VFD-PDC and the three fans were also included in the scope of the project. This portion of the project required reinforcement of the furnace side, ESP outlet duct, and flue gas recirculation duct. The Unit Auxiliary Transformer (UAT) was also replaced during the fall outage.