POWER April 2012 - 32

RENEWABLE ENERGY
MSW management provide analogous deployment
potential. China, for example, has indicated
that WTE technologies will be employed
to handle more than 30% of its MSW by 2030,
a huge increase over current practice.
Figure 2 illustrates how a global transformation
in MSW management-encompassing
increases in recycling, energy recovery,
and other practices to levels already being
achieved in many countries-could lead
to more than double current WTE capacity
while decreasing the amount of MSW being
landfilled by more than two-thirds (despite
the growing waste volume associated with a
growing population). If this transformation
were to include expanded energy recovery
from LFG, then a ninefold reduction in methane
emissions also could be realized. To grow
the role of WTE in meeting energy needs, advances
are required in resource management,
fuel processing, power generation systems,
O&M techniques, and environmental controls.
Supportive policies and incentives, and
greater public acceptance, also are needed.
Resource Management
Waste differs from other energy sources in
that MSW management practices, along
with producer and consumer behavior, determine
the volume and characteristics of
3. Greening up MSW management.
Incineration and advanced thermal
conversion of the residual waste remaining
after recycling and composting represent environmentally
sound municipal solid waste
(MSW) management options. Digestionbased
waste-to-energy technology also may
be deployed to extract useful energy from
compostable materials and from landfill gas
that is captured to reduce pollutant and greenhouse
gas emissions. Source: EPRI
Reduction
Reuse
Recycling
Composing & digestion
Energy recovery
Landfill & methane capture
Landfilling
Environmental hierarchy for
solid waste management
32
fuels suitable for conversion by individual
technologies. Figure 3 displays a solid waste
management hierarchy, with environmental
efficacy declining from top to bottom.
Traditionally, integrated MSW management
plans have focused on decreasing the
amount of material that must be disposed of
via incineration or landfilling. More recently,
" zero waste " strategies have come to the
fore, emphasizing prevention and materials
recovery but also sharpening the focus on
energy recovery as an approach for securing
additional environmental benefits, including
reductions in land use and emissions. In fact,
the small physical footprint of incinerators
and other WTE plants, relative to landfilling,
is an important driver behind their widespread
deployment for MSW disposal in heavily
populated European and Asian countries.
Furthermore, although modern landfills
are engineered and operated to avoid or
minimize environmental releases of methane,
volatile organic compounds, hazardous
air pollutants, and leachate, control systems
are nonexistent or inadequate at many locations,
while even new landfills may capture
as little as 60% of life-cycle methane emissions.
Globally and in the U.S., landfills thus
remain the second-largest anthropogenic
source of methane, which has a global warming
potential many times that of carbon dioxide
(CO2
). WTE plants avoid methane and
leachate production, and flue gases generally
are subject to stringent air quality controls.
On average, modern, electricity-only incinerators
also yield roughly an order of magnitude
more net energy per ton of MSW than
LFG plants. Energy recovery from MSW thus
is capable of displacing larger amounts of
fossil generation. Additional emission reductions
occur when materials removed from the
incoming fuel feed and/or metals recovered
from combustion byproducts are recycled.
This avoids emissions attributable to the extraction
and processing of virgin materials.
A frequently cited resource management
concern is that WTE facilities may undermine
recycling programs, but the European
experience shows that countries with high
energy recovery rates also exhibit higherthan-average
recycling rates. In 2006, 41%
of the MSW stream across Europe was recycled
or composted, 19% was delivered to
more than 400 WTE plants, and 40% was
landfilled. In 2008, the U.S. recycling rate
was 33%, 13% of MSW was delivered to a
total of 87 WTE incinerators and FBC units,
and 54% was landfilled, according to the
EPA. Similarly, the post-recycling energy
recovery rate is more than 30% across Europe,
less than 20% for the U.S., and even
lower in China and many other nations. By
contrast, this rate ranges from 70% to 80%
in Japan and exceeds 90% in Denmark and
the Netherlands, highlighting the potential
for increased WTE deployment.
Fuels and Processing Methods
As a fuel, MSW poses a number of challenges.
It is produced on a distributed basis, and
its composition is highly variable, including
a mix of organic and inorganic constituents.
Hazardous and toxic waste stream components
pose health and safety risks. Low energy
density and high moisture, chlorine, and
ash content lead to handling, combustion,
slagging and fouling, corrosion, and byproduct
management issues.
Lightly processed, post-recycling MSW
received at mass-burn WTE plants has a heating
value in the range of 4,500 to 5,500 Btu/
lb. High-intensity processing yields refuse-de4.
From refuse to electrons. When raw municipal solid waste (MSW) is transformed into
refuse-derived fuel (RDF) that can be used to generate electricity, large amounts of inorganic and
organic materials are recovered for recycling and composting. The end result is a higher-quality
fuel with more uniform content and significantly improved handling and combustion performance.
RDF also may be pelletized to improve transport. Sources: EPA and Scoullos et al., 2008
MSW composition
6.6%
wood
13.2%
yard waste
12.7%
food scraps
8.4%
metals
4.9% glass
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12%
plastic
5% textile
RDF composition
Composting
POWER | April 2012
31% paper
27.5%
plastic
59.2%
paper
11%
textile
Recycling
Waste to
energy

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POWER April 2012

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