Each day, the average person generates 4.6 pounds of trash per day in the United States. That's approximately 230 million tons of waste products being sent to be buried in landfills or incinerated. Less than one-quarter is recycled. In addition to taking up space, these landfills produce the third largest human-related amount of methane gas and account for more than 17 percent of all methane gas emissions for 2009, a number that is steadily growing. The question that has been asked since 1965 is 'how could these refuse landfills be used to produce gas for energy?'
The Energy Research and development Administration (ERDA), a creation of the federal Energy Reorganization Act of 1974, found that methane gas produced by waste-water treatment facilities could supply a city 10 to 15 times the amount of energy it used municipally. This discovery caused ERDA to turn it's microscope to landfills, and in 1975 the U.S.'s first commercial landfill gas-to-energy project in California. Today, higher energy prices and a demand for more 'greener' energy has caused the reemergence of using landfill gases to produce energy.
In terms of turning trash-to-gas the most common method is combustion, with non-combustion alternatives where landfill gas is converted to liquefied natural gas. The process of converting a stinky landfill into a Eco-friendly modernized gas producing facility is not without cost. Currently the price tag on any one of these plants starts at $600,000 and goes up from there. Annual operating costs average around $50,000.
To convert a landfill into a LFGTE facility (landfill gas-to-energy) a series of 'wells' are drilled into the ground within 15 feet of the bottom of the landfill. These holes are then fitted with perforated plastic pipe filled with gravel to prevent refuse from falling into the pipe and obstructing it, creating a block. The wells, which are strategically placed around the plant, are all connected by a series of pipes that converge into a 'header' pipe delivering the collected gas to the energy facility. A vacuum is created by blowers at the plant to cause the gas to flow from the wells.
After the gas is collected and delivered to the energy facility, internal combustion engines use the gas as fuel, similar to a locomotive, to spin generators which produce electricity. The electricity is then sent via a dedicated power line to the local municipal electrical grid. According to the EPA more than 520 of the roughly 2,400 currently operating landfills are utilizing landfill gas for energy purposes. The EPA also has estimated that as many as 510 additional landfills could cost-effectively be converted to a landfill gas-to-energy facility. The additional energy produced by these plants would provide electricity to power 700,000 to 1 million homes.
In the 1990's non-combustion methods were developed as an alternative to combustion. This process is not as efficient as combustion because the gas must undergo a pre-treatment to remove impurities such as water, Agency for Toxic Substance and Disease Registry, the only commercially available non-combustion energy recovery technology is the phosphoric acid fuel cell (PAFC). These PAFC systems consist of landfill gas collection and pre-treatment, a fuel cell processing system and fuel cell stacks, and a power conditioning system. Through chemical reactions many products are created such as water, electricity, heat, and some waste gases. The waste gases are destroyed in a flare.
In a direct gas-to-product conversion, the landfill gas is converted into commercial products such as compressed natural gas, purified carbon dioxide and methane, liquefied natural gas, and methanol. The process is the same as in energy recovery, with the gas undergoing collection, pre-treatment, and chemical reactions. Waste gases are burned in a flare as well.
While the EPA is a strong proponent of the landfill-to-gas energy program, that's not to say that it goes without some risks and concerns. There are numerous and stringent federal laws and regulations that govern the operation and maintenance of landfills to ensure optimum safety and a small carbon footprint. In an attempt to become less reliant on this green planet for our energy needs and to clean up after ourselves, much time, research, and money have been put into the perfection of these refuse landfill-to-energy facilities. Although far from a perpetual motion machine, these facilities can and will ensure sustainable, reusable energy for a long time to come.
Chapter 17 - Landfill Gas; Susan Combs, Texas Comptroller of Public Accounts; Window on State Government
Landfill Gas to Energy: A Growing Alternative Energy Resource; John Laumer; Treehugger.com