Light C o . , and Otter Tail Power Co. They
discussed their operations at the workshop
and others reponed studies of the potential. A few furnace suppliers have completed test programs that also were covered in the conference.
Stockpiling to develop a consistent supply of tires for fuel is a real sleeper of an
opportunity. An enterprising utility conceivably could get all tires disposed of in
its own state and then seek out sources in
other areas. Hence, the conference also
addressed issues relating to Rgulatory
control, interstate transpon of waste, and
ownelship of “tipping fees.”
Thermal value makes
tires a decent fuel
for utilities
Higher gross B t d b of tires sets them apart from some coals,
RDF and wood chips as viable fuel for power plants.
Acquisition and costs remain a question
By John Marks, Science Writer
There is a use for old tires; and power
plants stand to gain operating, economic
and public relations benefits by convening
them to fuel. A major reason for their
value is that fuel derived from waste tires
P D F ) has a thermal value of 12.000 to
16.000 Btullb (Tables 1 and 2).
Although most fuel handling s y s t e m
and utility boilers can accommodate TDF.
a lew issues remain to be resolved. These
include a consistent and economic supply
of tires. safe bums, and agreement between regulators and utilities.
Figure 1. How TDF compares with crumb
rubber, one-Inch and two-inch rubber
c h i p s and coal. Photograph courtesy
Babcock & Wilcox Co.
Assuming that these issues can be resolved, utilities stand to cash in on a rich
fuel source and earn community recognition for helping to salve a nagging solid
w a s t e d i s p o s a l p r o b l e m . Roughly
240,oM).Mlo used tires accumulate each
year in the US.; this was discussed in
January 1991 during an Electric Power
Research Institute (EPRI) workshop titled
“Waste Tires as a Utility Fuel.”
More than 100 pankipants from utilities. boiler manufacturers, tire shredding
vendors, and universities discussed the
well-known problems of tire disposal (see
“The trouble with used tires”) and utility
experience with waste tires.
A number of utilities already are buming either whole or shredded tires on an
experimental basis, notably Ohio Edison.
Illinois Power Co., Wisconsin Power &
I
r
POWER ENGINEERINGIAUGUST 1991
* Circle 13 on Reader Request Card
The nature of tire-derived fuel
The cost of tire processing and recycling
depends on size reduction and steel removal. Various sizes for firing in a cyclone furnace are shown in Figure 1 .
Size reduction of rubber is very energyintensive. requiring exponentially increasing energy as panicle size is decreased.
Approximately 40 Btus are used to produce one pound of 6-inch tire shreds, but
it takes 750 Btu to produce a pound of
I-inch tire chips. Small rubber particles.
such as crumb rubber. would require
much more energy to produce.
The estimated cost of producing crumb
rubber, according to Scrap Tire News,
averages $IM)Iton from 20-30 mesh, nonsteel belted tires. Two-inch material may
cost as little as $2O/ron. Tire processing
machinery also varies i n price, according
to size and the output volume. Small
machines (io0 tiresihr) that produce
2-inch chips can cost $50,000, but the
progression to larger machines is linear:
I W - t p h machines cost $SM),oOO.
Four utilities reponed on their experiences using various types of boilers, various amounts 01 tires. and variations in
the quality of coal that is burned with
TDF.
Siicccssful burns at IPCo
Illinois Power Co. (IPCo) undertook a
three-phase program in which it would
assess the effects of burning increasing
amounts of TDF. The staff wanted to
know if tire-derived fuel could be delivered reliably, if it could be burned at all
in their cyclone boilers, and, if burned,
whether its combustion would pose hazards to the fuel-handling equipment. Finally, they wanted to be assured that no
added pollutants would be introduced as a
result of TDF combustion.
One concern was the possibility that
complete combustion would not occur in
the cyclone, and that unburned material
might be carried over into the dust collection system. Another concern was that the
TDF non-combustibles, mimarily steel
belting. would melt in ihe slag. If it
adversely affected slag flow or consistency, the belling could interfere with both
boiler operation and subsequent sale of
the slag.
35
1w
I
2w
1.50
Delmred coal cost, $/million Bfu
N
2.50
operating well within the 40% l i m i t .
Some easily removable soft deposits were
found on the precipitator plates and wires
during weekend shutdowns. The TDF had
no impact on the flyash and slag renioval
systems. but a magnetic separator had to
be used to remove heavy bead wire from
the slag before it could be sold.
Emission test data from Rock River
showed that, as at other power plants, the
use of TDF reduces emissions of many
trace metals and sulfur dioxide. Future
plans at WP&L call for continued testing
through 1991 and upgrades of the fuel
handling equipment Io provide more accurate blends.
Figure 2. Comparison between value of TDF and coal delivered,
Co-firing TDF and lignite
“Otter Tail Power Co. views the burning
with TDF discounted at 0%. 20% and 40%.
Because 1PCo’s entire coal system was
enclosed, the TDF had to be mixed with
the coal ahead of the coal crushers; this
meant that the hammermills must grind up
the coal and TDF without gumming up
the system. And funher, the engineers
had to guard against subsequent segregation of the TDF and coal. which could
cause erratic boiler operation.
Another serious problem would be an
increase of unburned carbon in the dust
collection equipment. This could lead to
fires that would pose hazards to employees. As for longer term problems, corrosion or dewsits developing in the boiler
could reduce its efficiency or life.
In IPCo’s first test, 750 Ib of I-inch
and 2-inch TDF was mixed with 50 tons
of coal and fed through a crusher in about
five minutes. The one-inch material was
handled by all the equipment with no
problems. However, the 2-inch material
caused initial coal crusher motor current
to jump to 300 A (nameplate rating:
200 A, normal operation a1 170 A). The
high current condition cleared within a
few minutes and subsequent inspection of
the crusher showed no evidence of TDF
deposits.
During the second Dhase. IPCo blended
38 tonsbf TDF witi 1910 tons of coal
and fed it to a boiler over a two-hour
period. The coal handling system was
inspected every four hours, as was the
stack opacity. Operation of the plant was
unchanged.
In Phase 3, completed in March, 1991,
engineers conducted a four-day test burn
of 30,000 tires at IPCo’s Baldwin Plant
(near St. Louis, Ma.) without mishap.
The TDF was fed to the boilers. the same
as in Phases I and 2. but the boiler was
operated at varying loads and heat rate
calculations and emission tests were performed. No data was available at this
writing.
Burning whole fires
In early 1990, Ohio Edison modified its
Toronto Plant so that whole tires could be
fed to a cyclone boiler. constituting 5%.
IO%. 15%. and 20% of its total Btu
36
of TDF as a benefit. T D F supplements
input. An independent contractor analyzed
lignite to maintain furnace flame stability,
the stack gas, flyash, bottom ash. and
thereby improving boiler performance,”
bottom ash transport water.
states StuaR Schreun, Results Supervisor
For all runs, the paniculate and sulfur
at Otter Tail’s Big Stone plant in South
dioxide emission rates were less than state
Dakota. The plant’s cyclone burners are
EPA compliance limits. When the perdesigned to burn 6200 Btullb lignite and
centage of tires was increased, emission
their design is especially favorable to
rates for sulfur dioxide, nitrogen oxides,
burning I-2-inch size TDF with a heating
particulate and lead decreased. When tires
value of 15,000 Btu/lb. In the right mixmade up 20% of the total Btu input to the
ture. TDF offers improved flame stabiliboiler, sulfur dioxide emission rates were
zation.
equivalent to non-tire emission rates. lead
During a IS-month test at Otter Tail.
emission rates were 5% lower, particulate
the only problems encountered involved
emission rates were 28% lower. and nitromaterial handling. TDF that contained
gen oxides were 36% lower. Each time
free or loose metal from tires constantly
that the injection of tires approached a
plugged the fuel conditioner pyrite boxes
uniform rate, boiler operating conditions
stabilized and emission rates declined.
Table 1. Comparison of average fuel
Finally. when flyash, bottom ash. and
constituents in TDF and coal, percent
bottom ash transport water were tested for
bv weioht.-dissolved heavy metals, all were Well
within drinking water standards. In fact.
Tirefuel
Coal
leachate tests of flyash were below
37
USEPA hazardous waste limits of 100
Volatile
65
matter
times the drinking water standards.
77
Carbon
78
Similar firing tests at Wisconsin Power
0.8
& Light’s (WP&L) Rock River generating
6.3
Moisture
station near Beloit revealed no major plant
10
8
Ash
impacts. Its cyclone-fired boilers were un1.4
2.7
affected by the use of up to 10% blend of
0.01
0.15
TDF with Illinois Basin medium-sulfur
0.2
1.5
coal. However, WP&L‘s principal interest
I
Heal.;
14,500
12,400
was the impact that TDF would have on
i value%tu/lb
the fuel handling systems, flyash and slag
handling systems, and boiler and precipitator opera- Table 2. Comparison of alternate fuel properties Of coal,
tions.
TDF, refuse, and wood chips.
Some problems were enTireRefuseW. Virginia
countered with plugging of
bituminous derived derived Wood
the gravimetric feeders, but
fuel
chips
coal
fuel
this was eliminated by limiting the size of TDF 10 Proximate analysis (% wt):
I in. x I in. No new slag Moisture
8.8
24.0
39.1
6.6
accumulations formed, but Ash
14.8
12.0
0.4
16.0
some deposits were detect- Volatile
49.7
54.0
54.3
30.6
ed in the convection pass
matter
area of the reheater and su- Fixed
10.8
10.0
22.4
46.8
perheater. These are being
carbon
investigated.
0.02
0.2
1.2
Sulfur
0.85
Opacity at the precipita- Lb ashIMEtu
0.7
11.5
20.3
13.7
tor outlet increased by Gross Btullb
5,140
12.570
11,680
5.900
1.5%, but the unit still is
~~
.
~
I
i
-
.
POWER ENGINEEAINGIAUGUST 1 9 9 1
.
;,
'rm
sco~s. A\
,csuit. <,,liy
that is rree of loose iiictid now will be
;icceptcd. and 'r1>t%gIIite ratios Up to
a,lt~
IO%>:Yfl% hnac hceli bwned with no apparent niii,ior Iosscs.
"The future of buming TDF at Big
Stone appear, bright fmni a technic;tl
standpaint:. says Schreurs. "hecause it i s
such an attractive fuel supplement to lignite coal. TDI; lias about 2.5 tinies thc
heating value of lignite. and altiiost 2.5
times less sulfurIBtii i s generated. Otter
Tail would uelcome the opportunity 10
burn TDF blends at Big Stone on a daily
basis, but additional plant equipment
would be needed to handle large quantities that could exceed 100.000 tons a
year."
With such encouraging test results. one
might wonder why iiiore utilities haven't
implemented waste tirc fucl management
programs. As with any other technical
option. there IS II cost.
Economic and regulatory issues
The problem of waste management falls
primarily to local. state and national governments. While many governmental bo
"The trouble with
used tires"
Used tire disposal i s a perennial and vexing problcm. For enaniple. tires just
won't stay put in landfills. They resurface
not long after being buried. Stacks of tires
in outside dumping areas act as breeding
grounds for niosquitoes; and those
mounds of tires occasionally catch fire, as
one did in Canada a feu' years ago. The
tire bumed for a month.
Retreading. a traditional alternative use
for used tirei. no longer i s econoniical.
The number of successful retreads by the
industry has declined from 30% o f all
tires sold in 1988 to 1611 today. Expens
believe that less than one tenth of all
passenger cw tires will he retreaded by
the year Zoo0
There are applications for discarded tire
casings. The! citn be used for process
heat. or shredded and added to asphalt for
paving. Shredded tires also can be used
for landfill or as a banier i n dams. And
tire nianufactursrs can reclaim the rubber,
but this too i s declining hecause of cost.
I n any case. there simply i s a limit to how
many tires can be consumed for process
heat or shredded for other uses.
of old tires. among other things. But tlie
final b i l l won't appear for several years.
However, both Illinois and Wisconsin
state environmental protection bodies presented innovative papers at tlie S a i l Jose
workshop.
In January. 1989. the Illitlois Depailnient of Energy and Natural Resources
(ENK) commissioned a f ~ r nti u study I l l i nois scrap tire matiageinent. This was
because state laws places a ban on disposal
o f whole tires in landfills. effective
J u l y I. 1994. "Funher." states the law,
"landfills may oiily accept whole tire< i f
ec to shred. chop, or
slit the tires and they liave implementcd
programs 10 actively scek alternative uses
of the tire material."
The study found that landfills are either
closing their doors to tires. or charging a
premium tipping fee: 12 out of 35 landfills would nul accept whole tires. and the
ones that did charged an average of
$2.32lpassenger tire.
The Illinois study took a pvagmatic approach. based on tlie assumption that an
effective tire disposal program would
have 10 be driven b y nmrket deimnd for
tlie tires. And the r i m s 1 witable niaiAet
for large volumes of wartr tires ( I I iiiillionlyear i n Illinois' case1 is converting
them to energy. which tnieaiis getting utilities to lire them i n boilcrc. But i k h i i l can
utilities be expectcd to pay Iw TIX. even
i f they are geared to handlc i t ?
Based on a total cost of $l.Z(Iltirc for
collecting. transporting. and shredding. a
tire processor would have to ohtain at
least a dollar from tipping fees. and
20gltil-e from the utility. That's $20lton of
TDF.
dies havc been vocal ahout the "need to
address thc problem of wiiste tire disposal," few h a t e enacted ztny legislation
I t appears that federal legislation inight
be on i t s wa!. .According to Tlw Kipiirzger
Washi,igmi Lcrrcr (March X. 1991). thc
Resource C o n w u t i a r & Recovery Act is
duo to he r C \ i c d . I O C U
mi\ recycling
~II~
POWER ENGlNEERINGiAUGUST 1991
to compute TDF value
I n calculating tlie cost per ton of T D F
dclivered. tlie breakeven \ d u e is equal to
thc utility's CUlTelit cost of coal l a 5 the
extra cost of handling ;and processing
TDF. Bc sure to factor in the incieaxd
ther~nalvalue o f T D F .
A'iuiiiiiig t h a l a utility is uiinp S4Sltun
How