ENERGY CONSIDERATIONS

This subsection presents the results of a life-cycle analysis of energy inputs and outputs over the 20-year time frame used in this study. The basis is 1 ton of MSW at the curb.

Determining how much energy is used, saved, or avoided through recycling requires a complex analysis. Energy requirements for the entire recycling process include not only those for operations associated with the MSW management strategy, but also those for industries that remanufacture the products based on recycled materials. Energy is required for:

Curbside pickup of separated reusable materials (in addition to that required for the standard MSW collection program)
Processing the collected materials or separating and processing materials from mixed MSW
Transporting the products of the MRF to the point of remanufacture
Remanufacturing a new product(3)

Collection

The energy expended at the municipal level for collection is included in the data base, which shows the net difference between energy used to collect all MSW together in a packer truck and the energy used if separate collection of recyclables is added. In the comparison, the data base not only adds the energy for separate collection, but also somewhat reduces the energy for collecting all MSW to reflect the smaller quantity of refuse that is picked up in the packer truck at each stop.

The subsection called "Integrated Strategy Example" compares the energy and emissions for separate collection of reusable materials with those for consolidated collection of all MSW. In the community that was used as the basis for this comparison, the energy requirement per ton of collected material was found to be about 30% greater for separate curbside collection than the requirement for collecting a ton of mixed refuse in a single packer truck(4).

Processing

Table 7.1 shows estimated energy requirements for the operation of an MRF. These estimates are based on documentation submitted with bids for constructing an MRF, rather than on actual operating data. No data on energy consumption for an existing plant were found.




                                       Table 7.1

                 ENERGY REQUIREMENTS FOR OPERATING AN MRF
                   (Btu per Ton of Incoming Material)

     Processing Facility                         Energy        Reference
  
     Curbside-collected, separated, high tech            200,000          Tellus, 1990
     Mixed waste MRF, high tech                          150,000          wTe, 1992
     Mixed waste MRF, low tech                           110,000          wTe, 1992

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Energy Saved

Determining the energy saved by recycling is more complex than determining how much energy is recovered by MSW combustion and used to generate electricity. In the case of recycling, it is necessary to compare all the energy needed to manufacture an article from virgin material (including mining the ore, logging the trees, etc.) with all the energy needed to manufacture the same articles using some percentage of recycled material.

Net Energy Balance for Remanufacturing

To determine the amounts of energy used and saved for remanufactured materials made from the separated recyclables, the products had to be identified. For this analysis, the following assumptions were made:

Collected aluminum consists mainly of beverage containers used as aluminum sheet can stock. (Other collected aluminum is used to make other aluminum alloys.)
Collected steel is remanufactured in an electric furnace to sheet steel.
Glass containers are remanufactured to glass containers of the same or a darker color.
Paper separated at an MRF is used in a variety of products and exports:

About 21% of collected cardboard is exported; almost all of the remaining 79% is used to make paperboard (which includes cardboard).

Uses for old newsprint include exports (28%), remanufactured newsprint (34%), paperboard (29%), and tissue (10% ).

About 50% of mixed paper is used to make paperboard, 35% is exported, and 10% is used for tissue.

Extensive studies on energy use patterns, particularly for metals and scrap metals, have been completed (Kusik and Kenahan, 1978). The approach used in those studies, and adopted here, is a process analysis to determine energy requirements for each process step. Figures 7.3-7.5 illustrate representative energy requirements (inputs), amounts recovered (outputs), and savings (net energy balance) for MSW management, recycling, and preparing materials (such as high-density polyethylene and paper) for use, as well as the energy flows for recovery and reuse. Energy data for manufacturing paper products from virgin timber and used paper vary widely, as described in Exhibit VII.

Energy savings can be computed on several different bases, and a range of valid assumptions could be made. The assumptions for the estimates shown in Figures 7.3-7.5 are as follows:

Saved electrical energy is valued at 10,000 Btu/kWh, which is the amount of heat needed to generate a kilowatt-hour of electricity using an Illinois coal burned in a modern utility with a wet SO(2) scrubber. Coal was used because it accounts for about 55% of the U.S. electrical power mix, and it is reasonable to assume that savings in power demand from using recyclables would be used to reduce coal-fired electricity generation.

Figure 7.3
ENERGY FLOWS IN MSW MANAGEMENT

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Figure 7.4
COMPARISON OF RECYCLING AND VIRGIN MANUFACTURE ENERGY FLOWS FOR PAPER

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Figure 7.5
COMPARISON OF RECYCLING AND VIRGIN MANUFACTURE ENERGY FLOWS FOR HIGH-DENSITY POLYETHYLENE

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Energy accounting for plastic recycling can be very difficult. This study is based on the inherent Btu value of the plastic and the additional energy used to polymerize and process it; the energy used to wash and pelletize the plastic during recycling was subtracted. The pelletizing energy was used as a surrogate for molding of the thermoplastic into a new part. It is assumed that the plastic is displacing another legitimate plastic source, usually industrial scrap. Btu values are fuel Btu values; the washing and pelletizing are electrical Btus.
Btus for extracting and transporting oil to the point of conversion into plastic were included, but the Btu content in the virgin oil or gas that became the resin was excluded. These simplifying assumptions are valid only when the recycled plastic is legitimately substituting for the same virgin resin. The recycled material need not be applied to the same end use of the plastic; for example, refining used polyethylene terephthalate (PET) bottles into fiberfill displaces other PET.

Among the separated recyclable materials, the largest single saving in electrical generation is from reuse of aluminum, although the absolute quantity saved is small. The data were not adjusted to reflect the fact that hydropower is a major source of the energy used for producing aluminum, and that about 12% of the aluminum used in the United States is produced in Canada. Recycling would permit saved low-cost power to be transferred to locations that need it, and thus would reduce the need for total primary generation from other energy sources.

Analysis of energy savings for paper remanufacture is more complicated than determining the energy savings for aluminum or steel manufacture because:

The source of energy for papermaking varies with the kind of paper made; fossil fuels are used in some cases, but waste from papermaking is burned for fuel in others.
The amount of energy used to remanufacture a paper product varies with the particular product being produced.
The recycle content of remanufactured paper varies with the final product, and the percentage of waste paper used for each grade affects the energy savings for remanufacture.

These and similar factors are discussed in Exhibit VII.

Published estimates of the energy savings achieved by recycling vary from 10 million Btu per ton of paper product to zero. According to preliminary results of an ongoing study for recycling of newsprint alone, energy savings vary widely, depending on the assumptions made in the comparison (see Exhibit VII).

Special Issues

Two special issues related to energy analysis of recycling should be mentioned here:

Percentage of virgin resources displaced by recycled materials
Potential energy savings from repeated recycling.

Displacement of Virgin Resources. The analysis in this section assumes that the recycled material is displacing an equal amount of the same virgin resource; that is, that a pound of recycled aluminum displaces a pound of virgin aluminum used to produce cans or other products. In some cases, that assumption is invalid. For example, consider broken or green glass in the Northeast. Because the region has no green glass furnaces, the separated glass must be used in other applications, if it is to be recycled. If the glass displaces sand in asphalt slurry seal (glasphalt),-the potential energy savings will not be equivalent to the saving that would be achieved if it were displacing glass.

Energy Saving from Repeated Recycling. An uncertainty in conducting a life-cycle analysis that includes recycling is the effect of the 20-year period that is being considered for energy savings and releases in this report. The number of times the same material is recycled will affect the amount of energy that is saved over 20 years. The energy analysis used in the data base assumes that, for example, an aluminum can recycled displaces the energy needed to manufacture the aluminum needed for a new can from virgin resources (taking into account smelting losses). That assumption actually represents the maximum energy that could be saved; it thus overestimates the actual saving for all materials that already are recycled to a reasonable extent.

Nationwide about 62% of all aluminum beverage cans were recycled in 1990, and some can makers managed to buy more used cans than they made (Powell, 1992). When a can is recycled, about 13% of the metal is lost in shredding and resmelting (Kusik and Kenahan, 1979). If 62% of all cans are recycled, the recycled metal accounts for 54% of the new cans made from the mix of new metal and used cans.

Production of a can that consists entirely of recycled metal saves 80% of the energy need to produce the same can from virgin aluminum (Sellers and Sellers, 1989). For a can that is 54% recycled metal, the energy saving is 43%. A series sum for an infinite number of recycles shows that the maximum energy savings is 1.18 times the energy saved in the first recycle. If it is assumed that a can will be recycled "infinitely" over the 20-year period covered in this analysis, the total energy saving is 50% of the energy needed to make a new can from virgin metal.

Similar analyses can be made for paper, glass, and plastic. Because percentages of energy saved by recycling are lower for these materials than for aluminum, the total energy saving is smaller.

Transportation of Separated Materials for Remanufacture

Table 7.2 presents estimates developed for this report of energy consumed to transport materials from the point of separation (at the MRF) to the point of reuse or remanufacture, and compares those estimates with the energy required to transport the virgin raw materials to the point of original manufacture. (The assumptions on which the estimates in Table 7.2 were based are detailed in Exhibit II) The table shows that transportation energy to the point of remanufacture is a small percentage of the total energy of manufacture. Waste paper is excluded from the comparison. Despite an extensive search, no data on transportation distances for waste paper were found.

Clearly, variations between communities in the distances that separated products might travel to a remanufacturing site might be large. However, because the energy needs for transportation of the separated materials to remanufacture averaged to be a small percentage of energy of remanufacture, their contribution is not considered separately in the data base variables.


                                                 Table 7.2
             COMPARISON OF TRANSPORTATION ENERGY REQUIREMENTS FOR VIRGIN MATERIALS
                             AND SECONDARY MATERIALS SHIPPED FOR RECYCLING

                                  Transportation Energy             Share of Total
Material                          (Million Btu/Net Ton)        Manufacturing Energy (%)            Source

Glass containers                            0.386                                 2.2                           Kusik and Kenahan, 1979

Glass containers, recycled                  0.48(a)                               2.7                           SRI estimate

Steel slab, blast furnace,
and BOF                                     0.46                                  2.3                           Battelle,1975
 
Steel sheet electric furnace,
100% scrap                                  0.46                                  5.6                           Kusik and Kenahan, 1978

Aluminum ingot(b)                           2.7(t)                                1.1                           Battelle, 1975

Recycling aluminum cans to
can sheet                                   0.46                                  5.3                           Kusik and Kenahan, 1978


(a) New glass containers have a limited shipping distance before a new plant is built; a probable range of 200 miles
    at 0.0024 million Btu per ton-mile was assumed(Battelle, 1975).
(b) Ocean shipping of the bauxite accounts for 85% of the total transportation energy(Battelle, 1975).

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Cost Considerations

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