Renewable Energy Technology Assessments - Kauai Island Utility ...

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Kaua’i Island Utility Cooperative Renewable Energy Technology Assessments 10.0 Landfill Gas 10.0 Landfill Gas There is only one viable landfill gas project on Kauai, located at the Kekaha landfill. (There is one smaller landfill, but it is not suitable for development.) Black & Veatch estimated the energy production of this project after landfill closure in 2009. A project based on reciprocating engine technology could produce about 800 kW. The results of this assessment are detailed here. 10.1 Basis for Assessment Black & Veatch reviewed the Landfill Gas (LFG) Utilization Feasibility Study for the Kekaha Landfill by SCS Engineers dated April 2004. This report provided information about the operating landfill at Kekaha with financial analysis results from the EPA LMOP E-PLUS program. Three scenarios were evaluated by SCS; the primary option utilized an internal combustion (IC) engine for power generation. 10.2 Assessment of Contributing Resource The source of the LFG is the Kekaha Landfill. It opened in 1953 and was originally scheduled to close in 2004. A closure extension until 2009 has recently been granted. SCS modeled landfill gas production assuming a 2004 closure. Black & Veatch extended the model to account for closure in 2009. The landfill is currently producing LFG, but it is not collected. A project could conceivably come on-line before 2009 to take advantage of gas being produced now. Additional capacity could be added later after the landfill is completely capped. However, such generation staging was not assumed for this study. It seems that few formal records were kept for waste deposits and waste-in-place (WIP) until recently. It is estimated by the landfill operators that the annual deposit rate was 14,600 tons per year until 1993. At that point, records show a dramatic increase up to the current rate of 79,000 tons per year. SCS used a program called E PLUS that was developed by the EPA LMOP to estimate landfill gas generation potential. The program uses a first order decay model based on the amount of WIP and empirical gas generation constants. Based on the SCS model, the year of the maximum WIP for the Kekaha Landfill will be 2004, the year of closure. Accordingly, the maximum gas generation will occur that year. SCS estimated the maximum gas flow will be 379 cubic feet per minute (cfm). Thereafter, the gas flow will decline, with the estimate for 2018 being 243 cfm. 21 March 2005 10-1 Black & Veatch
Kaua’i Island Utility Cooperative Renewable Energy Technology Assessments 10.0 Landfill Gas Black & Veatch has modified the analysis to determine the LFG generation potential assuming a closure date of 2009. The analysis was based on the first order decay equation: where: i = year, through the last projection year (n) QM = maximum expected LFG production flow rate (m 3 /yr) K = methane generation rate constant (1/yr) Lo = methane generation potential (m 3 /Mg) Mi = mass of solid waste disposed of in the i th year (Mg) = age of the waste disposed in the i th year (years) ti Black & Veatch’s gas estimates are shown in Figure 10-1. In this case, the maximum gas flow is approximately 465 cfm and occurs in 2009. Very little data has been provided regarding the quality of the gas. It is stated that the measured methane content is 40 percent. This is considered low for LFG and is borderline for use in IC engines. Methane typically constitutes 45 to 50 percent of the landfill gas. Other important qualities that have not been discussed are the oxygen, moisture, siloxane, halide, chloride and sulfur (H2S) contents. High oxygen content (more than 2 percent) can be an indicator of imbalanced gas collection flows. With adjustments, the oxygen level can be reduced and methane production increased. 21 March 2005 10-2 Black & Veatch
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Principal Investigators: Ryan Pletk
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Kaua’i Island Utility Cooperative
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