John Zink executed a successful conversion for Puerto Rico Electric Power Authority (PREPA), transforming two 410 MWe tangentially fired boilers at the South Coast Generating Station. The conversion involved equipping unit #5 and #6 boilers with advanced gas burners, safety valves, and pressure-regulating skids. This allowed PREPA to flexibly switch between natural gas and fuel oil firing, achieving fuel cost reduction and adherence to regulations. The conversion preserved existing oil-firing capabilities and optimized boiler performance, resulting in substantial operational benefits for PREPA.
Objective
PREPA South Coast Generating Station wanted to convert two 410 MWe tangentially fired (T-fired) boilers (unit #5 & #6) that fired heavy fuel oil only, to fire natural gas and combinations of natural gas and fuel oil. One of the key drivers for the project was to reduce fuel costs. PREPA’s cost for fuel oil had more than tripled between 2004 and 2011. Adding natural gas firing capabilities would allow the station to select gas or oil fuel in any combination to help control costs.
- Unit 5: Six burner elevations per corner (24 burners total)
- Unit 6: Four burner elevations per corner (16 burners total)
Solution
Aware of our successful conversions of more than 20 T-Fired units, PREPA contracted us to supply necessary engineering services, equipment and commissioning for the gas conversion. Several up-front studies were conducted including CFD modeling to optimize air-flow distribution and predict flame patterns in the furnace as well as a thermodynamic study to evaluate the boiler heat absorption impact due to the gas conversion. We utilized proprietary computer models to predict fuel and air flows to all corners and elevation zones. We also performed an audit of the BMS and controls to evaluate compliance with the current Boiler and Combustion Systems Hazards Code (NFPA 85).
Equipment supplied for the conversion included gas burners, local burner safety shut-off valves, boiler header skids, local control panels and a main gas pressure regulating skid. We designed a main gas pressure regulating skid to handle compressed natural gas (CNG) that was supplied from an offshore barge with pressure from 450 to 650 psig (31 — 45 bar) and at temperatures from 0 to 40˚F (—17 to 4˚C).
Results
We successfully converted the two utility boilers to fire gas while preserving the existing oil-firing capability. The new dual-fuel system allows PREPA to select fuel (gas or oil) on a per burner basis, permitting co-firing of oil and gas in any combination between 100% gas and 100% oil.
