Apollo solar, electric models pump through Iowa winter: More methane, lower risks
Abstract
As the number of landfill gas-collection systems has grown, suboptimal methane production is a significant financial issue for many operators under contract to provide gas. Unrelated but noteworthy is the threat posed to nearby groundwater from fugitive leachate and subsurface gas migration. A third issue is the cost of providing electrical and/or pneumatic power to new or closed landfill cells, particularly at remote sites.
The Cedar Rapids/Linn County Solid Waste Agency (Agency), which serves Iowa’s second largest county, determined in 2011 that leachate was negatively impacting gas production. As an ameliorant, contracted engineers suggested reducing liquid levels in gas-collection wells using low-flow pumps and testing the viability of employing solar-powered pumping for efficiency and cost savings. The firm conducted a four-month test at a 30-acre cell at roughly 42º North latitude during the winter of 2011-2012.
The test compared pumping results from three power sources: 1) direct electrical power, 2) solar power with batteries and 3) solar power alone. Pressure transducers were installed to record levels every 15 minutes in each of three low-flow gas-collection wells, all exceeding depths of 50 feet. Methane and oxygen percentages were measured prior to and during operation.
The test showed that the low-flow pumps reduced average 24-hour liquid levels to satisfactorily address the migration issues, and the levels were consistently maintained by all power options, including solar-only.
Concomitantly, the lower liquid levels attained by all three options exposed an additional 15-18 feet of screen in each well, which resulted in an increased gas flows of at least 15% in all wells. The solar-only system demonstrated consistent recharge rates with a simple, low-maintenance linear-rod drive-motor design, at lower costs to purchase and operate.
Background
In 2010, the Solid Waste Agency installed a gas collection system in both active and closed landfill cells. A number of gas wells were consistently producing less gas then expected though modeling. The gas wells are located in a 30-acre closed landfill cell that received waste from 1972 to 2006.
The Agency engaged a regional engineering firm to present and implement potential solutions. The firm prepared a preliminary assessment and controlled-measures study in October, 2011, to gather data for planning and implementing corrective measures.
The study included the possible use of low-flow pumps to lower liquid levels in the gas-production wells, postulating that lower liquid levels in the collection wells would improve the efficiency of the gas-collection system and secondarily reduce potential groundwater impacts.
A four-month pilot test was performed at the Agency’s landfill Site 2, utilizing three wells exceeding 50 feet – GW-01, GW-02 and GW-05 – to examine the assessment that low-flow pumps could adequately lower system liquid levels. The test also evaluated three pump-power options: 1) electric, 2) solar with batteries, and 3) solar alone. In addition, the test assessed the long-term benefits of liquid reduction on gas collection.