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NEC designed and built the Puente Hills Energy Recovery from Gas (PERG) plant, incorporating superior technical and economic design. Work on this fast-track, turnkey project was completed in 19 months, and the project began operating in October 1986. Since then, it has been producing 50MW of electricity for customers throughout the Los Angeles region, and has dramatically reduced methane emissions, a particularly potent greenhouse gas.


Technical Summary


The PERG project utilizes landfill gas (LFG) generated by the bacterial decomposition of organic materials contained in municipal solid wastes of the landfill. The energy content of the gas withdrawn from the landfill is approximately 400 to 500 BTU per cubic foot. The LFG is collected through a piping network embedded in the landfill and transported by compressors applying a vacuum to the collection pipes. The compressed LFG is processed through booster compressors and into two 216,000 lbs/hr steam generators producing steam at 1,350 psig and 1,000 of which is fed to a steam turbine generator producing 50MW of electricity. The steam cycle consists of three high pressure and two low pressure feed water heaters along with a deaerator system. The boiler water is demineralized through an anion, cation, and mixed bed system water treatment system. A cooling tower system handles 32,000 GPM and the entire energy producing facility is situated on 50,000 square feet of land. The plant was interconnected to a local electrical substation and local power transmission lines, which were provided by a regional utility authority.


Construction of the plant was completed in 19 months with 2 months allocated to operational start-up and equipment performance verification for each segment of the system. This resulted in a final acceptance in just 21 months.


NEC engineered and designed the facility with a high efficiency steam cycle as just one of the major unique features of this plant. The plant is also automatically controlled from a central control room location utilizing an advanced distributed control system, configured by NEC. This maximized access to operational data and control while eliminating excessive wiring throughout the facility. Using the advanced control software developed by NEC, the plant can be operated with maximum efficiency and reliability. 


Project Performance   


  • Puente Hills is the largest landfill in the United States, and the PERG plant is the largest landfill to energy center in the world.

  • Since the project began operation in 1986, it has been generating electric power from LFG with greater than 95% availability.

  • The plant emissions are well below the strict emission standards established in Los Angeles, by the South Coast Air Quality Management District.

  • In October 1987, a large 6.0 (Richter scale) earthquake struck Los Angeles, centered in Whittier, California, only 5 miles from the plant. The plant was operating at the time of earthquake and did not sustain any damage, despite wide-spread damage to the surrounding area.

  • NEC's design maximized the overall plant efficiency, producing a heat rate of less than 10,000.



Landfill Gas Power

Puente Hills, California, USA 

Aerial view close up of the power generation facility (PERG) showing cooling tower, boilers, steam turbine generator and control building. To the right of the cooling tower is the gas collection equipment.

Ground level view looking at the cooling tower, boiler and steam turbine generator.




Technical Summary 

NEC designed, engineered, and rebuilt two 225 MW generating units (3 & 4) and implemented state-of-the-art pollution control equipment to revitalize this large scale natural gas fired AES thermal power station.

NEC, as prime contractor working with PMSI, redesigned and replaced two super-critical steam generators and rebuilt two 225-megawatt cross-compound high pressure turbine generator units simultaneously. In addition, all auxiliary equipment and systems were upgraded or replaced with the latest technology. State-of-the-art NOx and CO emission systems were designed and put into place, and the primary control system was replaced by installing a new central distributed control system, including steam turbine generator control systems.

The project required only 16 month, operating 2 shifts per day, employing 735 men at the peak phase with over 270 subcontractors totaling 1,000 men.

The steam generator work consisted of redesigning and replacing all the high-pressure boiler components, associated equipment, and flue gas ducting from the boiler to the stack. This work entailed major structural modifications to the existing boiler and ductwork structures, and included removing and replacing 1,200 tons of boiler pressure parts and 650 tons of flue gas ducting to accommodate a higher-pressure boiler gas path system from the fans to stack breeching. NEC developed an analytical model of the boiler and duct structure to validate reinforcing requirements in order to maintain complete structural integrity. The process included a three dimensional analytical model to identify effects of the boiler structures and was used in removing and replacing new duct sections.

The air pre-heater was rebuilt and replaced, as well as the control dampers and expansion joints, which consisted of 25 tons of material. The steam generator burners were replaced with 24 new low NOx burners for each unit. Four new 1,750 HP boiler fans were put into place with variable frequency drivers.

In addition, the units post combustion controls were re-designed and installed to include both selective catalytic reduction (SCR) and oxidizing catalyst to reduce both emissions levels to be below 5PPM at 3% O2. NEC's design and implementation of the SCR and CO systems established this project as the cleanest burning plant in California to date. The SCR system included structural design and support of all SCR ductwork and support of the SCR housing within a new support structure, including 750 tons of ducting and 400 cubic yards of reinforced concrete foundations and structure steel to support SCR and CO systems. A new process was installed for ammonia production "on-demand".

The two 225 megawatt cross compound steam turbine generators were disassembled, overhauled, and rebuilt. A complete overhaul of the turbine generator rotor and stator, including re-wedging, an inspection/testing program, meggar, polarization index, El Cid, and high potential testing each of the four generators was completed. NEC implemented a new solid-state excitation system and a power stabilizer system consisting of redundant controllers.

The project also included replacing 28,000 tubes in two condensers, repairing four 500 HP vertical mixed flow circulating water pumps with an operation flow of 44,000 GPM, refurbishing 18 feedwater point heaters and eddy current test tubes, and in some cases, re-tubing the heaters.

All auxiliary equipment was overhauled, upgraded, or replaced and tested. This included the deaerator system, equipment related to the turbine-generator block (including boiler feed pumps), seal oil and hydrogen related equipment, condensate pumps, booster pumps, lube oil pumps, steam exhausters, and associated equipment. A new plant instrument air system was designed and put into place, along with new air piping.

NEC also removed, redesigned, fabricated and reinstalled approximately 50,000 lineal feet of pipe ranging from A-106 Grade B standard up to A-335, P-11, and P-22 with up to 3-inch wall thickness, and rebuilt or supplied approximately 1,000 valves. All plant piping was tested on-site through x-ray and heat treating critical systems. The condensate polishing system was also designed and replaced, including new back-washable pleated filters with 1-micron cartridges.

A complete overhaul of the turbine generator rotor and stator was performed, including re-wedging, an inspection/testing program, meggar, polarization index, El Cid, doble and high potential testing each of the four generators. A new solid-state excitation system and a power stabilizer system was also installed.


Project Performance   


  • NEC's design and implementation of the SCR and CO systems established this project as the cleanest thermal generating facility in California to date. In general, this plant has been regarded as the cleanest thermal power plant in the world.

  • All NEC designs and supporting calculations were approved by the State of California energy technical consultants. There were no major injuries and no loss time.

  • The plant emissions are well below the strict emission standards established in Los Angeles by the South Coast Air Quality Management District and the U.S. federal standards set by the Environmental Protection Agency (EPA).



Aerial view of part of the 1200 acre Puente Hills landfill site (largest in the United States) near the top of the photo. Near the bottom of the photo is the power generation facility (PERG). Look closely to see the landfill to see LFG collection pipes

"World's Cleanest Thermal Plant" Huntington Beach, California, USA  

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