Cost Benefit Analysis And Energy Consumption Of

Cost Benefit Analysis and Energy Consumption of

Scrap Tire Management Options

Jorge Sousa, Ph.D.

Recipav, R. Luis de Camones, n 1.2070-101 Cartaxo, Portugal

George Way, P.E.

Arizona Department of Transportation, 1221 N. 21st Avenue, Phoenix, AZ 85009

Douglas D. Carlson*

Rubber Pavements Association, 1801 S. Jentilly Lane Suite A-2, Tempe, AZ 85281

ABSTRACT

Scrap tires have been recognized as one of the most difficult waste products to manage in

a modern society. They are not difficult individually, but are difficult collectively. Scrap

tires are generated in industrialized societies at an annual rate equal to the human

population which discards them, one scrap tire per person per year. The lack of adequate

disposal methods and management systems in years past had lead to wide spread,

cumbersome collection of scrap tires in unmanaged or poorly managed waste tire piles.

Problems associated with waste tire piles typically are: threat of fire and related

environmental damage from a tire pile fire and the potential increase in vectors

and pests. Secondary problems are that tire piles require substantial volume or space

prior to any type of processing and are an eyesore.

In this paper, a cost benefit analysis is considered for three streams (end uses). The end

uses analyzed are: shredding for use in landfills as Alternate Daily Cover (ADC),

shredding for use as tire derived fuel (TDF), and crumb rubber production with an end

use in asphalt-rubber (A-R) concrete pavements.

The major goal of this paper is to investigate the benefit to Society for each end use. The

overall approach will compare the energy costs in BTUs associated with each disposal

method and compare the benefits in energy recovery (if any) for each process.

INTRODUCTION

The disposal of scrap tires continues to be a major waste management issue. Scrap tires

must be managed and processed in some way to prevent the build up of scrap tire piles.

Many methods of disposal or end uses of scrap tires have evolved over the years. This

paper examines three common end uses of scrap tires, shredding for use as Alternate

Daily Cover (ADC) in landfills, shredding for use as a Tire Derived Fuel (TDF) in a

combustion process and crumb rubber production with an end use in asphalt-rubber (A-

R) concrete pavements. The purpose of the examination is to discuss the potential energy

use or recovery benefits of each method. It should be noted that all three methods are

currently in use and serve the intended purpose of removing scrap tires from the waste

stream. There are many methods of scrap tire disposal that can be used, these three were

chosen to represent the range options. Which method or a mix of methods used by a

governmental entity to dispose of scrap tires is a function of many factors not necessarily

just the potential energy recovery benefits. Nevertheless, using energy recovery benefits

is a first start in judging the overall value of each method to Society in general.

The technical approach taken in this paper is consistent with a study conducted by the

Argonne National Laboratory in 1979 for the United States Department of Energy

entitled “Discarded Tires: Energy Conservation Through Alternative Uses.” 1 At that time

there was an energy crisis and the usefulness of tires as a fuel source was carefully

examined. Also at that time waste disposal of tires was not an issue and air pollution

regulations were not as strict as they are today. In light of these changes, and others such

as potential global warming and the future of the Kyoto Treaty, which occurred over the

past 21 years it seemed appropriate to again review this always controversial topic in

some detail.

ANALYSIS

For each of the three disposal methods a BTU per pound of rubber scorecard was created.

Many of the BTU values were derived from the Argonne Laboratory study. Other values

were obtained from various industry sources for aggregate, steel, hauling (trucking) and

tire shredding and grinding. Table 1 is a list of typical heat combustion values for

common fuels.

Table 1. Combustion Heat BTU Per Pound of Fuel

Fuel BTU Per Unit

Coal (1 lb) 11,000

Tire (1 lb) 15,000

Asphalt (1 lb) 15,000

Natural Gas (ft3) 74,000

Propane (ft3) 92,000

Gasoline (US Gallon) 100,000

Diesel (US Gallon) 137,000

In this study scrap tires and asphalt have the same heat of combustion value of 15,000

BTU/Lb, which