Technovations Sidebar: Converting Waste to Energy
Landfill Gas >> Electricity
1. Anaerobic decomposition In the landfill, bacteria feed on organic waste — items such as food, paper and cardboard — and produce methane and carbon dioxide. Liquid is sometimes added to the landfill to speed up the decomposition process.
2. Accessing the gas Wells are drilled into the landfill — the holes are about three feet in diameter — and perforated pipes are inserted. The pipes are then filled with gravel and sealed at the top, allowing gas to be collected from deep down in the waste.
After the gas is vacuumed out, it is piped to a nearby compression facility, where it is then dehydrated, filtered and pressurized.
3. Becoming electricity From the compression facility, the pressurized and processed methane gas is piped to an electricity-generating facility, either on the landfill site or away from it. There the gas works as fuel to spin turbines or engines that produce current.
4. Back to where it started Landfill gas in utility transmission lines ends up being delivered to the businesses and homes where the process of collecting garbage for the landfill began. In other cases, such as with the University of New Hampshire, the gas doesn’t get delivered to utility lines but is piped directly to where it may be needed as fuel.
Source: Waste Management
Garbage >> Steam
1. Sort it out Waste is delivered by truck to a processing facility, and all recyclable and noncombustible materials, such as dirt, glass and metal, are sorted out. This is done with shredders, magnetic separators and vibrators.
2. Creating steam The remaining waste is loaded by cranes into a boiler and burned at more than 2,500°F. The thermal energy created by the combustion of the garbage converts water into steam, which then creates electrical energy in a turbine generator.
3. Keep it clean State-of-the-art technology, including dry scrubbers and fabric filters, is used to collect and control emissions from the burn process.
Sources: Covanta, Wheelabrator
Waste >> Pellet fuel
1. Sort it out As with the garbage-to-steam process, the first step in making pellet- or fluff-type fuel is to sort out all noncombustible materials from a delivery of municipal waste.
2. Making the fuel product The pared-down waste then goes through an air separator and grinder and eventually through a two-way damper and PVC separator to create fluff-type refuse-derived fuel (RDF). Alternatively, once through the two-way damper, the waste could go through a feeder and a molder and be shaped into pellet-type RDF.
3. The burn The fuel product is delivered by truck to power plants, where it is burned — by itself or with other fuels — to create electricity.
Source: Veolia Environnement
