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LANDFILL GAS PROJECT


LANDFILL GAS UTILIZATION PROJECT

MOUNTAINGATE LANDFILL, WEST LOS ANGELES

PROJECT BACKGROUND AND SCOPE

Landfill Gas
NST/Engineers, Inc. prepared updated P&ID information and plant safety and operating instructions for the second decade of the MountainGate Landfill Gas Plantís operation. 
 
The Plant and well field system were designed, built, and have been operated for about two decades as a GSF facility. The Plant is owned and operated by the GSF Energy, a wholly owned subsidiary of Montauk Energy Capital, a subsidiary of DQE Financial Corp.  
 
The landfill consists of eight canyons in the Brentwood-Westwood area of West Los Angeles, with the plant located off Sepulveda Boulevard.  
 
The Los Angeles County Sanitation Districts (LACSD) operated the landfill until 1980. LACSD deposited municipal solid waste into the eight canyons. The GSF energy plant recovers its feed gas from five of the canyons covering approximately 375 acres. Four of the canyon surfaces are now supporting 27 holes of championship golf as part of the MountainGate Country Club. 
 
The GSF Facility consists of gas well fields, a gas processing plant, and a gas delivery pipeline to the customer, the University Of California Los Angeles (UCLA). The facility is designed to: 
1) recover the crude methane gas naturally being generated within the landfill,  
2) process the gas to produce "medium Btu" gas (about 500 Btu), and  
3) deliver it 4.5 miles away via a dedicated pipeline to a 40MW cogeneration facility at the UCLA campus. 
UCLA uses this otherwise wasted and polluting LandFill Gas (LFG) to provide a significant portion of their boiler stationís fuel needs. 
 
CRUDE GAS PRODUCTION AND COLLECTION AS PLANT FEED 
 
The MountainGate plant collects about four million standard cubic feet per day of LFG . The gas is drawn from 125 wells ranging between 60 and 100 feet in depth. The wells are connected to a main collection header that carries the gas to the entrance of the canyon and down an 80-ft cliff to the processing plant. The total gas collection system is about 9 miles in length including the main line and laterals. 
 
There are a number of production wells in each canyon wellfield. Each wellhead connects with the near-surface-level lateral system of gas collection piping and delivery pipelines to the plant. Where the wellfields are a mile or so from the plant, a booster blower is used to supplement the vacuum produced by the plant inlet blower. The flowrate and composition of the gas from each well is carefully monitored. Wellfield technicians "tune" the wells (adjust the gas flowrates) to get the maximum flowrates with an acceptable composition. 
 
MIGRATION CONTROL 
 
GSF Energy operates another gas collection system at MountainGate designed to prevent the migration of LFG into neighboring, upscale, residential communities. These are smaller wells drilled at the periphery of producing wellfields. The gas migration control system consists of 125 control wells, 230 monitoring probes, seven miles of pipeline and two flares. 
 
These migration control systems are complete in themselves. They draw an even more crude gas from the wells to the lateral system with blowers. This gas is also collected in piping manifolds, and then disposed of by controlled combustion. 
 
By operating both production and migration control systems at maximum efficiency, GSF Energy is able to meet both the environmental and energy recovery objectives of the project.  
 
CRUDE GAS PROCESSING TO PRODUCE SALES GAS 
 
The processing plant draws the crude methane from the well fields. Numerous vapor-liquid separators are used throughout the gas collection, processing, and pipeline delivery steps to remove contaminating liquid condensate from the gas. The liquid is mostly water and a complex mixture of hydrocarbons. The hydrocarbons, resembling contaminated gasoline or kerosene, are separated from the wastewater and disposed of, or sold. 
 
Further vapor contaminant removal is accomplished by solvent scrubbing. The crude gas is compressed and then cooled and scrubbed by countercurrent solvent flow. 
 
The solvent is regenerated by countercurrent air stripping. The stripper overhead vapor stream is incinerated at 1800 deg.F in a flare, eliminating objectionable emissions.  
 
SALES GAS DELIVERY TO UCLA 
 
The processed gas is analyzed to determine its composition and fuel value. If the gas does not exceed the safe level of oxygen content, it is sent through the pipeline as a boiler fuel to UCLA. 
 
Pipeline gas is analyzed routinely for: methane, carbon dioxide, hydrogen, nitrogen, oxygen, and Btu content. The composition averages about half methane and usually less than 0.1% oxygen, with an energy content of about 500 Btus. 
 
If the oxygen content rises to 0.5%, an alarm is initiated. Should the oxygen content rise to 1.0%, the plant is shut down. Then, LFG draw from the wellfields is tuned to lower the oxygen content. The gas pressure delivered to the sales pipeline is controlled at about 100 psig.  

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