Environmental Engineering Reference
In-Depth Information
In plasma gasifi cation, an electric current is used to ionize an inert
gas—sometimes nitrogen, sometimes plain air. The ionized gas is called
a plasma, and it is raised to temperatures that can exceed 27,000°F,
hotter than the surface of the sun (10,000°F). Once the garbage has been
zapped, the gas produced is cleansed of harmful traces of hydrogen
chloride, which forms hydrochloric acid in the air. The decontaminated
syngas is burned like natural gas, producing enough electricity to power
the plant itself and offered for resale to the electrical grid. Mercury and
heavy metals must be removed from the glassy slag before it is sold, as
they must also from an incinerator.
The largest plasma gasifi cation plant in the world was scheduled for
completion in Saint Lucie, Florida, in 2009 but was not yet in service in
June 2010. It is expected to generate 160 megawatts of electricity,
enough to power 36,000 homes from a daily diet of trash.
23
The facility
is being built next to a landfi ll that contains 4.3 million tons of trash,
which the facility will excavate at a rate of 1,000 tons per day. Added
to this volume will be 2,000 tons of garbage trucked in from the sur-
rounding area. The plant cost $450 million to build, and the operating
company believes it will recoup its investment within twenty years
through the sale of electricity and slag.
Recycling
Approximately 33 percent of municipal solid waste (MSW) is recycled,
a percentage that has increased steadily since 1965 (fi gure 4.4). The
percentage did not exceed 15 percent until the early 1980s, and the
growth since then refl ects a rapid increase in infrastructure and increas-
ing market demand for products made using recycled materials. It is a
selling point for an increasing number of Americans. Recycling and reuse
businesses now employ about as many people as the auto industry does.
24
According to the editor of
Resource Recycling
magazine, “Without
recycling, given current virgin raw material supplies, we could not print
the daily newspaper, build a car, or ship a product in a cardboard box.
They are key ingredients to industrial growth and stability.”
25
Paper forms nearly one-third of our trash, and we recycle more than
half of it (table 4.2). The product most recycled is automobile batteries;
nearly everyone turns in their dead automobile batteries when they buy
a new one, and Americans recycle more than half their steel cans and
yard trimmings. The steel, aluminum, and mixed metals that were recy-
cled in 2007 eliminated the equivalent of 4.5 million cars from the road
