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The engineering and construction scope of Landfill Gas to Energy Projects (LFGE) can be summarized as:

• Gas collection system
• Flare
• Gas Cleanup
• Gas Compression
• Pipeline (if needed)
• Energy Conversion Unit
• Interconnection

Depending on the gas analysis and engineering of individual sites, the arrangement of the gas compression system as well as the gas cleanup equipment and flare may be different. The diagram is intended to illustrate the basic components of a typical LFGE project.

Collection System

To collect the landfill gas, a series of "wells" will be drilled into the landfill mass. The wells will be connected to a main collection header. The main collection header is then piped to the compression and cleanup system. The collection system is typically constructed from HDPE. Ferrous or alloy metal components will be used when conditions warrant. But their high cost compared to plastics, require a judicious approach.

During project execution, design and construction of the gas collection system would be subcontracted to an engineering company that specializes in analysis of landfill gas production, design of systems and their construction.

A key component of determining the viability and performance parameters of any LFGE project is an initial study of the gas production characteristics of a site. To support any performance guarantees, the engine generator or combustion turbine supplier will require a gas analysis.

Gas Compression and Cleanup

Landfills typically produce gas at a positive pressure. The pressure is typically not high enough to be of any use, so it must be boosted to push the gas through the cleanup system and on into the energy conversion system.

Engine generators require an inlet pressure of 10 - 30 psi. For these conditions, a low-pressure blower can achieve such conditions.

Combustion turbines sized around typical landfill gas production rates (1 MWe - 5 MWe) typically require 35-65 psi. Such conditions may require gas compression.

Unprocessed landfill gas is made up of approximately 50% methane, 45% carbon dioxide and 5% other constituents. The gas constituents of landfills are unique to the mass dumped into them and will therefore vary from site to site. Gas cleanup is therefore dependent on the entrained contaminants. Significant amounts of water are generally present and at a minimum, gas treatment will require moisture removal. When halides, chlorides, sulfur, furans or any number of other constituents are present significant gas cleanup may be necessary. The capital cost of this equipment may have a significant impact on the viability of any project. The impact on the O&M costs may also be significant. It is important to treat gas analysis and cleanup as a unique component of each individual project.

The gas analysis is key to understanding the selection of the materials of construction of the cleanup and energy conversion equipment. Failure to address the impact on initial capital cost, O&M cost and equipment availability will lead to unrealistic revenue expectations, underestimated O&M expenses and optimistic payback analysis.

Offsite Pipeline

Depending on the layout of a site and prospects for offsite generation a gas pipeline may be required. It is always preferable to site the energy conversion equipment as close to the collection system as possible, but in the event that this is not possible a gas pipeline may be constructed from the collection system to the energy conversion equipment. If a pipeline is required, gas compression equipment will likely be required. Other than the obvious cost of the pipeline and complications of right of way, additional compression and cleanup may be required. As gas is compressed, various constituents present in the gas tend to condense and therefore may need to be removed prior to the gas being compressed and sent down the pipeline. Gas compression equipment is expensive and may adversely impact the economic viability of any potential project.

Selection of Energy Conversion Equipment

The potential output of a project is, obviously, based on the amount of gas that the landfill is projected to produce. But more importantly the potential project electrical output is based on the amount of gas that is estimated to be recovered by the system of wells.

As important as the amount of gas to be recovered is the production rate. The following chart illustrates a typical landfill gas production rate.

The chart shows the landfill gas production increasing as the landfill ages. What is key, is to match the output of the engine generation sets (or combustion turbines) to the gas generation of the landfill. This is best achieved by adding generation capacity in modular blocks when the amount of gas produced can support the increased generation capacity. For instance, in this scenario, a single engine generator would initially be installed at this site. As the gas production increases, a second engine generator would be installed after 2 or 3 years and the output of the facility would follow the gas production of the landfill. Any additional gas produced by the landfill that cannot be burned by the energy conversion system will be flared.

The energy conversion system can be designed around internal combustion engine, combustion turbine, fuel cell, micro-turbines, etc. In most cases, the internal combustion (IC) engine offers the lowest cost on projects of 5 megawatts or smaller. Each potential site must be evaluated on it's own merits, but the scalability, reliability, lead time and economics of the IC engine make this the preferred energy conversion technology.

To match the gas production of any particular landfill, modularized internal combustion engine generator sets make sense. Each modular unit is containerized and is constructed with all of the attendant auxiliary equipment, controls and switchgear. Each unit will be delivered to the site and installed on a concrete pad. This pre-engineered and shop constructed unit reduces the amount of field exposure to construction risk. Standardizing these units improves the O&M characteristics of an installation and increases reliability and availability. Landfills of sufficient volume to cost justify multiple generator sets would likely benefit from a free standing building structure rather than the modular approach.

Interconnection

The generation produced must be put onto a local grid or added to the distribution system of a local user. As with gas cleanup, the interconnection scheme and cost will likely vary from site to site. The local utility or distribution system will dictate the voltage, relay, switching, protection, metering and monitoring system required by a prospective project. The impact to the cost of the project and to its viability could be significant.

Key Parameters

• Capital Cost: $ 1000 - 1600 kWe
• Collection System Cost: Varies with Site
• Gas Treatment Cost: $ 100 / kWh
• Power Island Equipment Cost: $ 650 - 700 / kWh
• Interconnection System: $ 250 - 350 / kWh
• O&M Cost: Variable

Factors that adversely impact the cost and scope of a project - in no particular order:

• Cleanup of gas
• Gas compression
• Cost of collection system
• Interconnection system
• Property leases
• O&M costs
• Civil construction costs and site improvements
• Operational and scope preferences by local authorities
• Pipeline (if any)

Note: These parameters are based on our current body of knowledge and will vary from site to site. They are subject to change based on the volume of gas available and local conditions.