THE RELATIVE VALUE OF ENERGY DERIVED
FROM MUNICIPAL REFUSE
ROGER S. HECKLINGER
Charles R Velzy Associates, Inc.
Elmsford, New York
or, in the case of the U.S. Environmental Protec­
tion Agency, the system sponsor.
ABSTRACT
Many systems for utilizing the heat energy in
municipal refuse are in various stages of develop­
ment. These systems either use unprocessed solid
waste as a fuel or derive a fuel through processing.
The fuels produced vary radically in heating value.
The energy expended in processing differs from
one process to another and the potential end use
is not the same for each system. Six representative
systems are compared to determine the relative
potential value of refuse as a source of energy.
SYSTEMS CONSIDERED
The six systems considered and the system de­
velopers whose data were used are tabulated in
Table 1.
TABLE
1
System
Raw Refuse
Incineration
Developer
City of Chicago - Metcalf &
Eddy
(1)
City of Harrisburg - Gannett
Fleming Corddry and Carpenter,
INTRODUCTION
Inc.
In recent years, a number of systems have been
developed to make use of the energy value of
municipal refuse. Many of these systems have been
reported in the literature and some have become
operational. Not surprisingly, conflicting state­
ments have been made regarding the relative value
of the fuel or energy produced by the various sys­
tems. Many of the conflicts arise because claims
and comparisons are made based on varying raw
refuse compositions and at different points along
the energy transition path from raw refuse to
ultimate use of the energy released.
The purpose of this paper is to compare the
relative value of refuse as a fuel for six processes
beginning with a common raw refuse composition
following a similar path through fuel processing,
to combustion, heat absorption in steam, and
finally to electrical power generation.
All data used, except as noted, is taken from
literature published by either the system developer
(2)
Town of Hempstead - Charles R
Velzy Associates, Inc.
(3)
RESCO - Wheelabrator-Frye,
Inc. (4)
Mechanical
Processing
City of St. Louis - Horner &
Shifrin-Union Electric Co.
(5) (6)
Thermochemical
Processing
Liquid
Garrett Research and Development
Co., Inc.
Gas
1
(7)
Union Carbide Corporation
(9)
City of etc.
Gas
2
Biochemical
Union Carbide Corporation
Dynatech RID Company
(9)
(10)
Processing
The energy transition path is traced through
four phases:
Processing
Combustion
Steam Generation
Electrical Generation
133
The first three phases are tabulated in Table 3.
The relative potential for recovery of energy as
process'or heating steam is tabulated in Table 4.
The relative potential for recovery of energy as
electrical energy is tabulated in Table 5.
Specific comments for the various systems are
included in a brief description of each system.
Certain general comments pertain to all of the
systems compared.
1) All systems receive the same raw refuse as
tabulated in Table 2. Note the higher heating
value is on a per ton basis as refuse processing
plants are normally rated by capacity in tons per
day. Both metric tons and short tons (2000 lb)
are tabulated.
TABLE
2
7) It is assumed that with the proper selection
of heat traps, steam generation efficiency is un­
affected by the pressure or temperature of the
steam generated.
8) The energy cost of transporting prepared
fuel has not been considered or included for any
system.
9) Carbon dioxide in the fuel gases is listed as
"noncombustible", in Table 3.
10) For fuel gases, combustion losses are based
on the components of the fuel gas listed in the
description of the system.
The six systems selected for comparison general­
ly cover the range of systems that have been pro­
posed in recent years. The specific systems were
selected because adequate information was avail­
able in the literature to permit a meaningful companson.
.
Raw Refuse
Proximate Analysis
Moisture
27.0%
Volatile
44.0%
7.0%
Fixed Carbon
22.0%
Noncombustibles
Ultimate Analysis
H20
27.0%
Carbon
25.5%
3.4%
Hydrogen
21.5%
Oxygen
0.6%
Nitrogen
22.0%
Noncombustibles
Higher Heating Value
-
10.50 gigajoules per metric ton
(9.00 million Btu's per ton)
2) Electrical power requirements for the
Processing Phase have been adjusted from that re­
ported, where applicable, to exclude power require­
ments for materials recovery equipment which
may be an integral part of the system.
3) Combustibles lost in the Processing Phase
are those combustibles. that leave the system in a
stream other than the fuel stream. For example, in
the Mechanical Processing system, a significant
amount of combustibles leave the system with
the "heavy fraction" from the air classifier.
4) No attempt is made in Table 3 to relate
energy from refuse with energy from auxiliary
fuel or electrical energy.
5) Electrical power requirements tabulated in
the Combustion Phase include energy required to
operate the steam generating system.
6) Miscellaneous losses in the Steam Genera­
tion Phase include radiation loss and boiler blow­
down loss.
RAW R EFUSE INCINE R ATION
Raw refuse, as received, is continuously fed
onto a grate system for combustion. The products
of combustion are used to generate steam in a
boiler integral with the grate and combustion sys­
tem. The steam may be used for heating, process,
or electrical power generation.
The combustible loss tabulated for the Com­
bustion Phase is somewhat higher than reported,
to be conservative [J ,2,3]
Excess air requirements and stack temperatures
are higher than for most other systems. Steam
conditions selected for electrical generation are
lower than for most other processes. [4]
MECHANICAL P R OCESSING
The system tabulated follows data developed
from the demonstration plant operated in
St. Louis, Mo., to produce solid fuel for combus­
tion in utility boilers operated by the Union Elec­
tric Co.
Electric power requirements in the Processing
Phase were adjusted from that reported to account
for two-stage shredding in a full scale plant and to
exclude power requirements for ferrous metal
processing. [5] The combustible lost in
processing is somewhat better than reported in
anticipation of improvements in a full scale
plant. [5]
Combustible loss in the Combustion Phase as
tabulated is a considerable improvement over the
losses of 5-40 percent that have been reported. [6]
An improvement can be antiCipated for a full scale
134
w
Vl
......
?roduced
ENERGY TO ST:::AM
Excess Air
Stack Te�perature
Stack Loss
Miscellaneous Loss
STEAlo1 GE�E:<.ATION
Heat Available
6.63GJ
26GC
1.81GJ
0.35GJ
7.53)113
20KWH
0.27MB
1. 20:-lB
0.99NB
6.11MB
1. lSGJ
7.16GJ
17SC
O.72GJ
O.21GJ
6.23GJ
5.67MB
5.4SMB
0.44GJ
6.37GJ
0.09MB
3.97MB
O.llGJ
4.73GJ
O.lSMS
57SF
1.4 S�:3
0.38:13
l7SC
0.38GJ
5.31MB
-
0.44!'1B
7.31MB
SO%
0.51GJ
8.53GJ
-
20KI-/H
300C
1.72GJ
0.36�IB
4.39HB
-
0.08GJ
350F
0.33:-\3
10%
0.42GJ
5.12GJ
-
0.04GJ
10J.a-IH
4.75MB
0.25
5.54GJ
1.0
0.5
O. 9
4.9
60.9
15.7
9.04GJ
7.75MB
2.58
7.6
33.4
•
1.02MB
1.19GJ
12.8%
60KWH
0.24GJ
4.8
-
-
130KWH
5%
per Ton
4.1
35.5
30.0%
-
-
-
135K:-IH
2
6.46�:B
0.54:-\3
6.83GJ
0.15GJ
17SC
0.5SGJ
-
- 15KViH
5.S6:-\3
O. 13:-\3
350F
O.47:�3
15%
0.63GJ
7.53GJ
-
0.06':;J
0.7
1.3
29.1
7.00:-\B
S.16GJ
-
0.54GJ
Gas
(2000 Ibs.)
Thermochemical Processing
Gas 1
(MB)
57.5%
-
0.52GJ
Liquid
3S0F
0.62:-\3
30%
0.64GJ
30KWH
O. 55�1B
0.12GJ
0.80
18.0
S.9SGJ
7.65MB
23.6
O. 7
500F
1.56MB
O. 3O�:B
1:) O\l'
1. 40GJ
8.79GJ
Vaporization
Loss
0.08GJ
0.31GJ
1.0
0.6
22.0
9.00MB
10.50GJ
3.4
21.5
28.0
3. 7
15%
-
30KWH
25.5
-
0.12GJ
Mechanical
Processing_
26.0%
-
-
10KWH
(GJ)
Based On Raw Refuse Containing
per Metric 70n or 9.00 �Iillion Btu's
27.0%
-
0.04GJ
Power Requirement
Corr.bustible Loss
CO�!BUSTION
Energy in Fuel
t Fuel/ t Refuse
Nitrogen
Noncombustible
H20
Carbon
Hydrogen
Oxygen
Fu�l
PROCESSII\G
Po��r Requirement
Auxiliary Fuel
Combustible Lost
Raw Refuse
Incineration
10.50 Gigajoules
3
ENERGY PER TON OF REFUSE
Table
3.53GJ
O.O S G J
l7SC
0.29GJ
5%
O.48GJ
3.20GJ
-
O.O<:GJ
.
•
...
. � .-'
..... ...... �
?
_ :).,.. .:l
3.03:-!5
o
o
.,- �'C'
... :J,J�
O.':l!'1S
3.351-13
-
'U
10'"
� �....
0.1
12.6
4.38GJ
3.76:-\3
-
-
21.9
65.5\
-
0.22GJ
5 SKIlH
0.66GJ
0.57:-1B
45%
Bioc�e:::ical
P!"ocessina
W
0\
Refuse
Based on Steam Generation at 80%
Efficiency
1.00 (Base)
4.83MB
0.89
5.67GJ
0.48MB
** Based on 42.5\ Turbine Eff. (8000 Btu/KwH Turbine Heat Rate)
*
Relative Value
5.43MB
0.56GJ
2.8SMB
1.12MB
0.53
3.41GJ
1. 32GJ
1
3.99MB
0.64MB
80KWH
0.82MB
5.4SMB
0.74
4.67GJ
0.75GJ
6.35GJ
6.37GJ
Net Refuse Energy
To Steam
0.24MB
140KWH
3.97:1B
Gas
0.28GJ
0.56GJ
4.73GJ
per Ton
4. 661-'.B
1.20MB
lSOKWH
5.86MB
0.85
5.42GJ
1.41GJ
0.60GJ
6.93GJ
2
Ibs.)
Gas
(2000
Ther�ocheffiical Processing
Less Steam Equivalent
Electrical Energy **
Of
60KWH
5.31MB
Liouid
(MB)
0.32GJ
0.24GJ
6.23GJ
Mec�anical
Processinq
Btu's
Containing
)Iillion
0.12GJ
30KWH·
Raw
Total Electrical
Energy Required
5.67MB
Based On
per Mecric Ton or 9.00
0.95GJ
6.63GJ
(GJ)
Less Auxiliary Fuel
@ 80\ Eft.*
Energy To Steam
I n c i n e ra c i on
Raw Refuse
10.50 Gigajoules
ENERGY PER TON OF REFUSE
Table 4
2.05MB
0.521-'.B
6SK:m
0.46:1B
3.03z.<.B
0.38
2.39GJ
0.61GJ
0.26GJ
0.S3GJ
3.53GJ
P:-c::essi:1o
Bioc�e:cical
W
-J
....
**
*
(1800 psi),
540/540C
470C(875F)
B
-
605KWH
60KWH
665KWH
5.31MB
1.09
2.41GJ
0.24GJ
2.65GJ
6.23GJ
Pro�essing
Mechanical
356KWH
l40KWH
496KWH
3.97MB
(9750 Btu/KWH)
0.65
1.45GJ
0.56GJ
2.01GJ
B
4.73GJ
Liauid
per Ton
378KWH
80X\<IH
l02KWH
560K\<IH
5.45MB
0.68
1.56GJ
0.32GJ
0.35GJ
2.23GJ
A
6.73GJ
Gas 1
B
5B4KWH
l50KWH
734KWH
5.86)013
1.06
2.30GJ
-
0.60GJ
-
2.90GJ
6.83GJ
Ga s 2
(2000 lbs.)
�hermochemic3l Processi�g
(MB)
(lOOO/lOOOF) Turbine Heat Rate 2.35 (8000 Btu/KWH)
Turbine Heat Rate 2.86
1.00 (Base)
553KIYH
30KWH
583KWH
5.67MB
(GJ)
Electrical Equivalent Based on Plant Heat Rate of 3.4 (10,000 Btu/KWH)
B-12.40 MPa
A- 4. 50 MFa ( 650 psi),
Relative Value
2.21GJ
-
Net Electrical Energy
From Refuse
2.33GJ
A
0.12GJ
*
6.63GJ
Less Electric"al Energy
Less Electrical
Equivalent of
Auxiliary Fuel **
Electrical Output
Steam Conditions
Energy to Steam
Raw Refuse
Incineration
10.50 Gigajoules
Based On Raw Refuse Containi�g
per Metric 70n or 9.00 Hillion Btu's
ENERGY PER TON OF REFUSE
Table 5
257hl.H
65h....'H
57KHH
379KHH
3.03MB
.46
1.04GJ
0.26GJ
0.20GJ
1.50GJ
B
3.53GJ
.
Bioc�e�ical
Processina
by volume:
plant due to two-stage shredding, a more effective
injection point, and, if necessary, installation of a
burn-out grate at the bottom of the furnace.
CO
H2
CO2
CO.
C2Hx
N2
THE R MOCHEMICAL P R OCESSING - LIQUID
Raw refuse is shredded in two stages to 0.4 mm
(0.015 in.) size and pyrolized under controlled
conditions to produce a liquid fuel.
Power requirements for the Processing Phase
have been adjusted to exclude power requirements
for materials reclamation features of the system.
[7]
The pyrolysis process also produces a com­
bustible gas and carbonaceous char. The gas is used
for drying purposes and to sustain the process. The
char is unsuitable for use as a fuel.
The liquid fuel could be burned in most con­
ventional steam generators.
Higher heating value at standard conditions is
11.2 MJ/m' (300 Btu/ft').
Pure oxygen is introduced into the bottom of
the vertical pyrolyzing chamber. The oxygen com­
bines with some of the carbon in the refuse to
produce the heat of pyrolyzation. There is no
residue char.
Electrical power requirements have been ad­
justed from that reported to account for the
power requirements of the shredder. [9]
The fuel produced can be burned in most con­
ventional steam generators. The gas clean-up system
is assumed to produce a dry gas.
,
•
THER MOCHEMICAL P R OCESSING - GAS I
Raw refuse is coarsely shredded and pyrolyzed
in an oxygen starved atmosphere to produce a fuel
gas composed of the following by volume:
H20
N2
CO2
CO
H2
CH.
C2 H.
O2
47%
33%
14%
4%
1%
1%
BIOCHEMICAL P R OCESSING
Raw refuse is shredded and introduced into a
liquid environment where microorganisms convert
the cellulose in the refuse into methane and carbon
dioxide. Most noncellulosic hydrocarbons are un­
affected by the microorganisms and thus are lost
to the process. In addition, cellulose is lost in the
continuous bleed of effluent from the digestor.
Auxiliary fuel is required to support the process.
[10]
Methane is separated from the bulk of the
carbon dioxide by absorption with mono­
ethanolamine to produce a fuel gas composed of
the following by volume:
CH.
95%
CO2
5%
The fuel gas can be burned in any boiler where
natural gas can be burned.
18.5%
56.8%
9.3%
5.4%
5.2%
2.1%
1.4%
1.3%
This wet analysis by volume and the individual
losses were derived from the dry analysis and
overall heat balance that have been reported.
Higher heating value calculates to roughly 1.1
MJ/m' at 650C (30 Btu/ft' @ 1200 F). Auxiliary
fuel is required to sustain the process. The losses
tabulated have been adjusted from those reported
to suit the Raw Refuse analysis. [8]
Because of the volume of fuel produced and the
sensible heat in the fuel, combustion must take
place in close proximity to the point of pyrolysis.
A specially designed combustion chamber and
boiler are required. The steam conditions used for
raw refuse incineration are also tabulated for this
system.
DISCUSSION
It should be emphasized that all data for the
Processing Phase of energy transition has been
taken from the published references and adjusted
only as noted. Combustible losses in the Combus­
tion Phase have also been based on published data
as noted. Power Requirements in the Combustion
Phase and Miscellaneous Losses in the Steam
Generation Phase are either taken from the refer­
ences or are assumed based on experience with
similar equipment. Vaporization Losses and Stack
THE R MOCHEMICAL P ROCESSING - GAS 2
Raw refuse is coarsely shredded and pyrolyzed
to produce a fuel gas composed of the following
138
Losses are either straightforward calculations
CONCLUSIONS
using established procedures or have been taken
from the references. See Appendix for sample
calculations of Vaporization -Loss and Stack Loss.
One should understand, however, that none of
the systems are presently operating as tabulated
to the end point of Electrical Generation.
Two general observations can be made. First, a
great deal of energy can be lost in the Processing
Phase. The fact that this happens is expressed as
the Second Law of Thermodynamics. Second, the
more complex (and thus less efficient) Processing
Phases tend to produce a fuel that can be com­
busted relatively more efficiently. Therefore, in
two of the systems tabulated, Mechanical Proces­
sing and Thermochemical Processing - Gas 2,
Electrical Generation is more efficient than for
Raw Refuse Incineration. ]n all other cases, Raw
1) None of the processing �stems tabulated is
inherently more efficient than Raw Refuse In­
cineration as a means of utilizing the energy in
refuse.
2) As a source of energy for process or heating
steam, Raw Refuse Incineration is more energy­
efficient than all other processing systems
tabulated.
3) Two of the processing systems tabulated,
Mechanical Processing and Thermochemical
Processing-Gas 2, can be more efficient for Elec­
trical Generation than Raw Refuse Incineration.
4) A careful study is required to determine if
there are other benefits derived from a process to
offset the inherent reduction in available energy
that results from processing.
Refuse Incineration is the most efficient system
REFERENCES
for utilizing the energy in refuse.
Based on the data tabulated, the Raw Refuse
Incineration system appears to have a potential
for improvement that is not available to the other
systems. For example, 10 percent more Steam
[1]
Stabenow, G., "Performance of the New Chicago
Northwest Incinerator," Proceedings of 1972 National
Incinerator Conference, ASME, New York, N.Y., 1972,
pp. 178-200.
[21
Pepperman, C. M., "The Harrisburg Incinerator:
Generation energy or Electrical Generation energy
A Systems Approach," Resource Recovery Thru Incinera­
could be realized if stack temperature could be
tion, ASME, New York, N. Y., 1974, pp. 247-266.
reduced from 260C (500F) to
I 75C (350F). This
is not an unreasonably low temperature to con­
sider. Or, 10 percent more Electrical Generation
ings of
(I 000 F) turbine. This has been done in
Duessel­
forf, Germany, for over ten years.
It may come as a surprise that combustible loss
in the Combustion Phase is less for Raw Refuse
Incineration than for Mechanical Processing. This
may not be so surprising, if one understands that in
Raw Refuse Incineration, unshredded refuse is ex­
posed to the combustion process for upwards of
one hour, whereas in the Mechanical Processing
[4]
course factors other than time bear on combustible
loss. The Tabulated loss for Raw Refuse Incinera­
tion is somewhat greater than reported [1,2,3], and
MacAdam, W. K., Design and Pollution Control
Features of the Saugus, Massachusetts, Stream Generating
and Refuse-Energy Plant, APCA, Pittsburgh, Pa., 1974,
Paper #74-95.
[5]
Shannon, L. J., Fiscus, D. E., and Gorman, P. G.,
St. Louis Refuse Processing Plant: Equipment, Facility,
and Environmental Evaluations, U. S. Environmental Pro­
tection Agency, Washington, D. C., 1975, EPA-650/275-044.
[6]
Shannon, L. J., et aI., St. Louis/Union Electric
Refuse Firing Demonstration Air Pol/ution Test Report,
U. S. Environmental Protection Agency, Washington,
D. C., 1974, EPA-650/2-74-073.
system, processed refuse is exposed to the com­
bustion process for approximately one second. Of
1968 National Incinerator Conference, ASME,
New York, N. Y., 1968, pp. 142-153.
energy could be realized if steam could be
generated for a 8.60 MPa (1250 psi), 540C
Kaiser, E. R., Zeit, C. D., and McCaffery, J. B.,
[3]
"Municipal Incinerator Refuse and Residue," Proceed­
[7]
Mallen, G. M., and Titlow, E. I., "Energy and
Resource Recovery From Solid Wastes," Garrett Research
and Development Company, I nc., La Verne, California,
1975.
[8]
Sussman, D. B., Baltimore Demonstrates Gas
Pyrolysis: The Energy Recovery Solid Waste Facility in
the tabulated loss for Mechanical Processing is
Baltimore, Maryland, U. S. Environmental Protection
somewhat less than reported [6] .
Agency, Washington, D. C., 1974, EPA/530, sw-75d.i.
It must be understood that the tabulated data
does not recognize such potentially significant
[9]
Anon, "Solid Waste Disposal Resource Recovery,"
Union Carbide, New York, N. Y., 1974, F-3698.
[10]
Kispert, R. G., et aI., "Fuel Gas Preparation from
factors as economics, size, capacity, or by-product
Solid Waste: Final Report," Dynatech R/D Company,
benefits of a particular system.
Cambridge, Mass., 1975, NSF/RANN/SE/C·827/PR/74/5.
139
APPENDIX
Sample calculations of Vaporization Loss and
Stack Loss for Mechanical Processing System.
Theoretical Air
® . @ + @ =3.23 + 0.24=3.47 tons air/ton
fuel
Analysis of Processed Fuel
ffi
CD
8)
0)
@
(j)
Moisture
0.260
Carbon
0.280
Hydrogen
Excess Air
@ ®
0.037
Oxygen
0.236
Nitrogen
0.007
Noncombustible
0.180
Tons fuel per ton of refuse
0.80
@ @+ @
Fuel to Stack Gas
@
H.O/ton fuel
1040 Btu/lb. x 2000 Ib./ton x
Stack Temperature
@ @.;- @ =0.592';-5.32=.112 tonsH.O/
350F
ton stack gas
Air Requirements for Combustion of Carbon
11.52 tons air/ton carbon x
CD =
SpecificHeat of Stack Gas
@
11.52 x 0.28= 3.23 tons air/ton fuel
dW g,n x
34.56 x (.037
;7
-
(0
-
0.24 x (1.0
-
@
) + 0.48 x
@
0.24 (I .0-.112) = 0.48 x .112=0.267 Btu/lb.-oF
Air Requirements for Combustion of Hydrogen
3
+ 0.81=5.32 tons stack
Moisture in Stack Gases
0.30
34.56 ton"i'/to
= 4.51
gas/ton fuel
refuse
@
-(
@ @+ @
® x (j) =
1040 x 2000 x 0.593 x 0.8= 990;000 Btu/ton
@
® + 0.05 x CD ) =
1.0 - (0.18 + 0.01)= 0.81 tons gas/ton fuel
1.0
Total Stack Gas Weight
Vaporization Loss per Ton of Refuse
Excess Air
= 3.47 + 1.04=4.51 tons air/ton
fuel
® CD+ ( CD x 9)=0.26 + (0.037x9)=0.593 tons
@
@
@ = 3.47 x 0.30=1.04 tOIlS air/ton
Total Air
H. O,per Ton of Fuel
®
x
fuel
<p)
=
Stack Loss per Ton of Refuse
@ @
x
® -x ( @
- 80F) x
(j) x 2000
Ib./ton= 5.32 x 0.267 x (350-80) x 0.8 x
8)=0.24 tons air/ton fuel.
2000=620,000 Btu/ton of refuse
140