Newsletter and Technical Publications
<Municipal Solid Waste Management>
1.5.5 Integration with other system components
Waste-to-energy facilities have a design capacity that
is based on a combination of two factors: first, the physical capacity of the
intake system and the grates which transport the waste through the flames, and
secondly, the heat generation capacity of the furnace. If the incinerator is
improperly designed for the specific waste stream, and the incoming waste is
either too wet or too dry, too rich in burnables or too high in non-burnables,
there can be difficulties with the incinerator's functioning.
Because of the traditions of materials recovery and extensive picking in
developing countries, the calorific values in the residual waste streams in
these countries tend to be low. High moisture levels can further lower energy
content. In such cases incineration can require auxiliary fuel. Taken together,
these factors are a further impediment to the use of incinerators in developing
countries, which will be very difficult to overcome until per-capita GNP rises.
The integration of MSW incinerators with materials recovery and composting
systems can be one of the more controversial aspects of waste management that
employs incineration. Most existing incinerators were planned a decade or more
ago, before materials recovery was viewed as a viable method for managing large
amounts of MSW. Plants built during this period were sized for maximum waste
flows to keep municipalities self-sufficient, so that waste would not have to be
transported out of the community for disposal.
Now, as some communities aim to recycle large portions of the waste stream,
there is a perception that the need to comply with incinerator plant contracts
for minimum tonnage and energy production will lessen incentives for materials
recovery. Both European and US incinerators have faced financial difficulties
when they were unable to actually attract the waste necessary for them to
operate at their design capacity. Although some communities with plants already
operating may experience conflicts because of these changing goals, proper
planning for new facilities can ensure that materials recovery and incineration
are better integrated, possibly enhancing each other's operations. In fact,
materials recovery facilities are now often part of new incinerator projects.
To ensure that an MSW incinerator allows for materials recovery, a community
can conservatively size the incineration facility (risking the need to add
another boiler later at greater expense, or sending more unprocessed waste to a
landfill). If extending landfill life is the most important goal, the
incineration facility can be sized for maximum waste flows and waste can be
imported from other communities if materials recovery programs are more
successful than anticipated. Although incineration facilities are commonly sized
to accommodate waste generated during peak times, introducing yard waste
composting programs can eliminate much of the seasonal fluctuation in generation
rates, and further reduce the need for excess capacity.
|Integration of incineration with other components of the MSWM system
- Siting should consider distance from points of MSW generation,
transfer, and disposal, as well as energy use.
- Sizing of facility should accommodate other MSW management options.
- Materials recovery and special waste separation should occur both
before and after incineration.
- The effect of materials recovery and composting on energy content
must be considered.
- Residual ash should be disposed of in properly designed landfills.
A successful materials recovery program can increase the energy content of
waste because many recyclables (e.g., glass bottles, metal cans, and yard waste)
are non-combustible or have low fuel value. The energy value of waste does not
begin declining until some of the more difficult-to- market materials (e.g.,
cereal boxes, junk mail, and mixed paper or plastic) are included in materials
Although materials recovery can increase energy content (per ton of waste),
total energy production usually declines slightly due to the reduction in the
amount of material combusted. For facilities that were not sized for this
possibility, energy contracts can be maintained by expanding service areas or
combusting supplementary fuel. By reducing the amount of waste to be combusted,
materials recovery programs also reduce the capital needed to build a new
facility. Although it has not been proven, materials recovery possibly also
lowers operating costs of incineration facilities if the removal of
non-combustibles reduces ash disposal costs. In addition, diverting glass and
aluminum, in some cases, reduces boiler maintenance costs. Melted glass can form
slag on boiler walls, and aluminum can clog air circulation holes in furnace
The integration of waste incineration and materials recovery can also give a
community more flexibility when dealing with fluctuations in secondary materials
markets. Although combusting waste collected for recycling is often a public
taboo, it can sometimes cost a community more to process and market recyclables
than to incinerate them with energy recovery. In these instances, incineration
of recyclables can help market prices rebound more quickly, by reducing the glut
of unwanted materials.