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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.

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 recovery estimates.

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 chambers.

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.

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