Optimization of the final waste treatment system in the Netherlands
Transcript of Optimization of the final waste treatment system in the Netherlands
Resources, Conservation and Recycling 22 (1998) 47–82
Optimization of the final waste treatment systemin the Netherlands
A. Faaij *, M. Hekkert, E. Worrell, A. van Wijk
Department of Science Technology and Society, Utrecht Uni6ersity, Padualaan 14,3584 CH Utrecht, The Netherlands
Received 13 May 1997; accepted 2 November 1997
Abstract
The potential for optimizing, in both economic and energetic terms, the final wastetreatment system in the Netherlands is evaluated in the light of the performance of newtechnologies. Projections of the final waste supply and waste treatment technologies arecombined to construct several scenarios for waste treatment in the year 2010. Technologiesinclude processes currently in the demonstration or pilot phase. It is concluded that finalwaste treatment could be performed at lower cost and with substantially greater energyrecovery than at present. In a minimum cost scenario, the final waste treatment might cost300–600 MECU/year, compared to 1000–1600 MECU/year in a reference scenario, on theassumption that conventional, but improved waste treatment technologies are used. Amaximum energy recovery scenario might save 80–90 PJ primary energy per year comparedto 39–47 PJ/year for the reference case. Two major competing technologies are gasification,both for biomass waste and integral waste, and fluidized bed incineration. Further develop-ment of these technologies integrated with electricity production is recommended. © 1998Elsevier Science B.V. All rights reserved.
Keywords: Waste treatment; Energy from waste; Gasification; Combustion
* Corresponding author. Tel.: +31 30 2537643/00; fax: +31 30 2537601; e-mail:[email protected]
0921-3449/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved.
PII S0921 -3449 (97 )00043 -8
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8248
1. Introduction
Over the period of 10 years (1985–1995) the total amount of waste produced inthe Netherlands (excluding contaminated soil, sludge and manure) increased fromabout 46–50 million tons; in the same period the amount of waste that was re-usedincreased from 50 to more than 70%. Consequently the total volume of waste thathad to be treated by final waste treatment facilities (incineration, landfilling,discharge) decreased from 23 million tons in 1985 to 15 million tons in 1995. Theamount of waste that was discharged decreased from 3.5 to 1.5 million tons and theamount of waste that was landfilled decreased from 16 million tons to less than ninemillion tons. The amount of waste incinerated increased from nearly three milliontons in 1985 to more than four million tons in 1995 [1–3]. The figures show that atpresent the waste treatment system of the Netherlands depends heavily onlandfilling and incineration.
Major policy goals in the Netherlands are the prevention of waste productionand the re-use of waste produced such that less final waste treatment is required.Nevertheless, it might well be that in the year 2010 the capacity of the final wastetreatment system will be about 16 million tons [4]. Governmental policy is alsodirected towards putting a stop to the landfilling of organic waste and increasingthe waste incineration capacity.
At present the production and use of energy from the incineration of wasteresults in annual savings of about 17 PJ in fossil fuel consumption [5]. Sixty percentof this amount was generated in large scale facilities that produce heat andelectricity.
In the Netherlands the so-called Waste Consultative (Afval OverlegOrgaan;AOO) deals with the planning of the capacity for treating final waste. The planningis presented in a Ten Year Waste Programme (TYWP), which is updated every 3years. The current TYWP covers the time frame 1995–2005 and indicates that inthe year 2005 incineration plants should be able to process approximately 60% ofthe final waste; this will require a substantial expansion of the incineration capacity.In addition, incineration of waste is to be combined with the production of steamto generate heat and electricity using a steam turbine [6,7].
Biomass wastes and residues are not considered in the TYWP, since these streamsare not defined as waste. The main point of attention is the treatment of integralwaste from e.g. households and the service sector. This is waste that contains amixture of organic material, plastics, paper, etc. and inorganic materials. In theTYWP, the performance of different waste treatment systems, consisting of differ-ent mixtures of waste treatment technologies, are evaluated and compared. Also theeffects of different policies on the production and treatment of wastes are assessed.In all cases the existing waste treatment structure (and the lifetime of the existingwaste treatment capacity) is the starting point. Environmental effects, like emissionsto air and water and the handling of residues are analyzed by means of a Life CycleInventory (LCI) approach.
According to the TYWP, the recovery of energy from wastes will increasesubstantially. However, the question that arises is whether the incineration of waste
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 49
to produce electricity is an optimal route to utilize the energy potential of waste.The electrical conversion efficiency of these systems is at present approximately12–24%. New designs can increase this efficiency to some extent, [8,9] but othertechnologies, like gasification (integrated with electricity production using a com-bined cycle), may achieve higher conversion efficiencies at lower costs [8–10]. Inaddition, other options like increased separation, digestion of (wet) organic materi-als and various technologies to process specific waste streams (such as plastics),look promising, both from an economic and an energetic point of view.
Therefore, it is not yet known what the optimal configuration of the total finalwaste treatment system will look like when various new technologies graduallybecome commercially available. White et al. recommend that complete wastetreatment systems be studied instead of only the performance of separate technolo-gies, since changing the waste composition by waste separation technologies andreplacing waste treatment capacity by other options will effect the performance ofthe entire system [11]. Such an integral analysis will be the topic of this article.
In this paper we evaluate, from an energetic and economic point of view, thepotential for optimizing the treatment system for final waste1 in the Netherlands inthe year 2010. In this time frame a considerable part of the current capacity to treatwaste will have to be replaced.
In this study we will evaluate the potential performance and costs of differentwaste treatment systems without taking the current operational waste treatmentfacilities into account. This enables us to assess and compare the maximum possiblepotential effect on energy recovery and the waste treatment costs if specifictechnologies are introduced on a large scale. We will include all biomass wastestreams in our analysis, since they will probably play a substantial role in theproduction of energy from waste in the near future and thus, affect the optimumconfiguration of the waste treatment system as a whole.
Taking 2010 as a reference year means that some technologies at present underdevelopment will probably become commercially available within this time frame.A number of new technologies, like pyrolysis and gasification are currently beingtested and demonstrated. In this study, we will review the potential waste treatmentcosts and energy conversion efficiency of these new technologies in the year 2010.
Because our focus is on final waste treatment, waste collection and logistics areexcluded from the analysis. Although the costs of collection can be considerable, itcan be argued that in any structure waste has to be collected and transported,which—as a first approach—will result in relatively small differences in energy useand in the costs of transport in alternative waste treatment systems. Furtherprevention of waste and the recycling of waste materials will not be investigated.The rates at which these options might be applied in the year 2010 are merely usedas starting points. However, recycling waste after further separation will bediscussed. In these cases the (energetic) value of recyclable products (such as metalsand paper, etc.) that result from the final waste treatment will be taken intoaccount.
1 We define final waste as waste which is not re-used or recycled. Main features of a final wastetreatment are the total capacity and the applied mix of technologies for treating the final waste.
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8250
In this article, we will first discuss the projected characteristics and supply of finalwaste in the year 2010. Next an overview is presented of relevant current and futurewaste treatment technologies, the focus being on the expected performance in theyear 2010. In Section 4 the results will be integrated and compared. The perfor-mance of different final waste treatment systems consisting of different technologymixes is assessed. From the results, conclusions are drawn about the energyrecovery potential and waste treatment costs in the Netherlands in the year 2010.
2. Waste streams and supply
Table 1 presents projections for the year 2010 about the route and the supply ofrelevant waste streams in the Netherlands. The figures are taken mainly fromNagelhout et al. [4]. In these figures the effects of increased prevention of waste andthe re-use of materials and products, strongly promoted by the government, havealready been taken into account. Therefore, the indicated figures for 2010 can beconsidered as the amounts of waste that will have to be treated by the final wastetreatment system. For comparison Table 1 also shows figures for the year 1990.
In Table 1 three categories of waste are distinguished: integral waste, biomasswaste and specific waste. Each category is subdivided into flows defined by thesource of the waste (e.g. households, specific process or sector). In this article theseflows are called waste streams. The composition of a waste stream is often ratherheterogeneous.
In this study we will focus on waste streams that are at present subject to finalwaste treatment by public utilities. This excludes a number of specific industrialwastes, such as those from the food and beverage industry. Most of this waste istreated by facilities (often digestors) on site. Chemical and nuclear wastes are alsoexcluded from our analysis.
The inventory of Nagelhout et al. [4] ignores a number of biomass waste streams.Therefore, in Table 1 the figures on biomass waste have been derived from ananalysis of Faaij et al. for the year 1994 [12]. No projections of the potential supplyof biomass waste in the year 2010 are available. In this study we will assume thatthe size of the different biomass waste streams will remain roughly constant in thetime frame considered. In Table 1 biomass residues like straw and thinnings fromcommercial forestry are not included since their market value implies that theyshould not be considered as waste [12,14]. Until recently, sludges have been used asfertilizer in the agricultural sector, however, stricter standards and increasingcontamination of sludges have put a halt to this practice. Therefore, almost allsludge is now considered as waste and is processed accordingly [14,16].
A far more detailed split of waste streams can be made following a directive ofthe European Union [17]. However, in relation to this assessment of final wastetreatment systems and technologies considered here, the split made by Nagelhout etal. [4] (extended with a number of biomass wastes streams) is considered sufficient.
The composition and characteristics of a waste stream determine whether or notthe stream can be treated by a specific technology. Important parameters are
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 51
Tab
le1
Was
test
ream
ssu
bjec
tto
final
was
tetr
eatm
ent
aspr
ojec
ted
for
2010
inth
eN
ethe
rlan
ds(b
ased
larg
ely
onN
agel
hout
etal
.[4
])
Tre
atm
ent
byT
reat
men
tby
Tot
alfin
altr
eatm
ent
Tot
alfin
altr
eatm
ent
LH
Vof
the
was
teT
reat
men
tby
land
fill
(kto
n)(G
J/to
n)co
mpo
stin
gin
2010
(kto
n)in
cine
rati
on(k
ton)
in19
90(k
ton)
(kto
n)a
Inte
gral
was
teD
omes
tic
was
te54
9042
5015
5058
00—
870
800
700
70—
Coa
rse
dom
esti
cw
aste
1290
1310
9cSw
eepi
ngw
aste
s60
019
050
027
0023
0050
018
00—
Serv
ice
sect
orw
aste
100
130
10—
Hos
pita
lw
aste
110
110
140
Pub
licut
iliti
es10
—10
0B
iom
ass
was
te15
300
150
—D
emol
itio
nw
ood
—30
031
017
05
Auc
tion
was
te31
0—
—5
400
Ver
gegr
assb
230
8P
runi
ngsb
305
Agr
icul
ture
100
2G
reen
hous
ese
c-to
rb
526
0B
ulb
cult
ivat
ionb
200
8F
ruit
farm
ingb
Spec
ific
was
tes
280
13d
285
—28
5—
Slud
ge(d
rym
at-
ter)
200
200
120e
30—
—C
arw
reck
s(m
ainl
ypl
asti
cs)
2700
—27
0035
000
—C
onst
ruct
ion
and
dem
olit
ion
was
te50
0—
40—
40M
iner
alex
trac
tion
was
tes
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8252
Tab
le1
(Con
tinu
ed)
Tot
alfin
altr
eatm
ent
Tre
atm
ent
byT
otal
final
trea
tmen
tL
HV
ofth
ew
aste
Tre
atm
ent
byT
reat
men
tby
in20
10(k
ton)
(GJ/
ton)
com
post
ing
inci
nera
tion
(kto
n)in
1990
(kto
n)la
ndfil
l(k
ton)
(kto
n)a
No
proj
ecti
ons
avai
labl
eab
out
trea
tmen
tro
utes
in20
10fo
rth
ebi
omas
sw
aste
slis
ted
abov
ebe
twee
nve
rge
gras
san
dfr
uit
farm
ing
incl
usiv
e.a
Com
post
ing
refe
rsto
the
orga
nic
frac
tion
sof
vari
ous
inte
gral
was
test
ream
s.T
heav
erag
elo
wer
heat
ing
valu
eof
thes
est
ream
sis
esti
mat
edto
be5.
5G
J/to
n;lo
wer
valu
esar
efo
rex
ampl
efo
und
for
swill
-lik
est
ream
sw
ith
very
high
moi
stur
eco
nten
t;th
ehe
atin
gva
lue
can
beab
ove
aver
age
for
woo
dco
ntai
ning
gard
enw
aste
[10,
13,1
4].
bSt
ream
sno
tin
clud
edin
the
anal
ysis
ofN
agel
hout
etal
.[4
];qu
anti
ties
and
heat
ing
valu
esar
edi
scus
sed
and
sum
mar
ized
inF
aaij
etal
.[1
2].
The
volu
mes
pres
ente
dar
efo
r19
94;
nosu
bsta
ntia
lch
ange
sin
the
supp
lyar
eex
pect
edfo
r20
10.
cA
heat
ing
valu
eof
9G
J/to
nis
used
asan
aver
age
valu
efo
ral
lco
mbu
stib
lein
tegr
alw
aste
s[3
9,42
].T
heva
lue
appl
ies
toth
efr
acti
ons
that
are
give
nin
the
colu
mn
‘inci
nera
tion
’.T
heor
gani
cfr
acti
ongi
ven
inth
eco
lum
n‘c
ompo
stin
g’ha
slo
wer
heat
ing
valu
es.
dT
hehe
atin
gva
lue
can
vary
betw
een
10an
d15
GJ/
ton
dry
mat
ter
[15]
;he
re,
anav
erag
eva
lue
ispr
esen
ted.
eF
igur
efo
r19
90ex
clud
esty
res,
whi
char
eex
pect
edto
beto
tally
re-u
sed
in20
10[4
].
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 53
moisture and mineral fraction content, heating value and degree of contamination,e.g. with heavy metals. In Table 1 the lower heating value (LHV) of different wastestreams is given. For biomass waste this value depends largely on moisture and ashcontent. The LHV figures are taken from Van Doorn [13] and Faaij et al. [12]. Withrespect to the category integral waste, it is considered realistic to make no differencebetween the various sources of integral waste; no specific facility will be built toprocess domestic waste separately from waste from e.g. the service sector. There-fore, although differences can be found in the composition of the various streamsfalling under the heading integral waste, an average lower heating value of 9 GJ/tonis used for all waste in this category. The figure is based on analyses of thecompostion of integral waste [8,9].
3. Waste treatment technologies
Before making an integral assessment of final waste treatment systems that mightbe applied in the year 2010, one has to assess the future performance of present andupcoming final waste treatment technologies. In this study, we will focus onprocesses that are at present commercially available, those that have been demon-strated and those which are presently in the pilot stage. Improvement options interms of energy efficiency and costs of currently used technologies are included inthe assessment as well. Given the time between now and the year 2010, it would beunrealistic to take into account processes which are currently in the design phase.Some possible waste treatment technologies, such as Hydro Thermal Upgradingand some pyrolyis processes [18], are therefore excluded from the assessment. Ourassessment will be based on a critical analysis of the literature. In some cases, wheninsufficient data are available, a more detailed analysis will be made to assess thepotential performance of the technology involved in 2010.
The technologies are divided into two categories: The first category containstechnoloiges that are especially suited for processing the biomass waste and most ofthe specific waste streams such as plastics; they are described in Section 3.1. Thesecond category, described in Section 3.2, consists of technologies that are designedto process particularly the integral waste. In this overview only the main features ofthe technologies are distinguished. It should be noted that often a number ofmanufacturers are able to supply the equipment for each technology. This results inlarger or smaller deviations in the performance and the waste treatment costs ofthese technologies. We will not describe these differences in detail, but will expressthe performance in average figures or ranges.
Each technology will be described briefly, together with its field of application.Main characteristics are presented in terms of the waste treatment costs and the netenergy conversion efficiency that can be achieved or the input of energy required touse the technology. The waste treatment costs will be presented as costs per ton ofwaste treated. Those figures includes investment costs and operation and mainte-nance costs. The level of these costs is influenced by a number of factors: scale ofthe facility, cost of capital at the time of construction, depreciation period,
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8254
efficiency of the treatment, type of gas or water cleaning applied, etc. Consequently,in this study the costs are presented as ranges. A disadvantage of presenting rangesis that the differences in the cost of specific technologies become more difficult toestablish, but an advantage is that the differences in the waste treatment costsobserved for a given technology are taken into account. So that we have a commonapproach for establishing cost figures, our analysis will be based on tariff figures asfar as possible. Table 2 summarizes the main results of the evaluations.
3.1. Dedicated technologies to treat specific waste streams
In this section we will discuss dedicated technologies for the treatment of biomasswaste, plastic waste and sludge.
3.1.1. Composting of biomass wasteComposting is an aerobic conversion of biomass waste to organic matter by
means of biological degradation. In the process electricity is consumed for pre-treatment, ventilation, moving of material and sometimes forced aeration. Theenergy use varies between 40 and 70 kW/ton of waste, depending on the specificprocess used and the scale of the facility [19,20]. The costs of the process arestrongly influenced by the capacity of the facility. Net treatment costs vary between40 and 50 ECU/ton [19], on the assumption that the compost can be used at zerocost. These figures apply to the current situation. No substantial development isexpected in the technology and costs of composting [18]. Therefore we assumesimilar performance data for 2010.
3.1.2. Anaerobic digestion of biomass wasteBy anaerobic digestion, biomass waste is converted to biogas (by bacteria in the
absence of oxygen) and compost. The biogas is mainly a mixture of CO2 and CH4.The biogas is partly utilised to heat the digestion reactors. The rest can be used togenerate electricity and/or heat (e.g. with a gas engine) or, after treatment, be fedinto the natural gas grid.
Various digestion processes have been developed. In these processes the energyefficiency of the conversion of biomass waste to biogas can vary between 10 and45% [19,20]. This figure does not include further conversion to heat or electricity.
The costs of the process are strongly influenced by the capacity of the facility andmay vary between 50 and 70 ECU/ton of waste [19]. In this figure the savings onconventional energy consumption are taken into account. No substantial develop-ments are expected in the performance and costs of digestion [18]. Assuming thatthe value of the energy saved will not change substantially either, we assume similarperformance data for digestion in the year 2010.
3.1.3. Co-combustion of waste wood in (existing) coal-fired power plantsWaste wood can be co-combusted in coal-fired power plants. Emission standards
may limit the extent to which the wood can be added if it is contaminated with e.g.heavy metals. The type of coal plant (e.g. pulverized, fluidized bed) determines what
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 55
Tab
le2
Mai
npa
ram
eter
sof
exis
ting
and
new
was
tetr
eatm
ent
tech
nolo
gies
.Ran
ges
inco
sts,
effic
ienc
yan
den
ergy
use
expr
ess
the
obse
rved
orpr
ojec
ted
diff
eren
ces
inpe
rfor
man
ce
Ene
rgy
cons
umpt
ion
Ene
rgy
conv
ersi
onef
ficie
ncya
Tre
atm
ent
cost
s(E
CU
1995/t
on
Ele
ctri
city
effic
ienc
yP
rim
ary
ener
gy(M
J/E
ffici
ency
prim
ary
Ele
ctri
city
(kW
h/to
nof
was
te)
(%L
HV
)en
ergy
(%L
HV
)to
nof
was
te)
Max
Min
Min
Max
Min
Min
Max
Max
Min
Max
80Im
prov
edin
cine
rati
on(i
n-15
026
30cr
ease
dst
eam
cond
itio
nsan
dco
uplin
gto
CC
)27
1680
Inci
nera
tion
wit
hC
HP
;15
021
2727
%w
aste
heat
utili
sa-
tion
assu
med
3050
25F
luid
bed
inci
nera
tion
22P
yrol
ysis/g
asifi
cati
on90
1214
022
8019
016
Pyr
olys
is/i
ncin
erat
ion
2560
6023
023
0209
20%
fW
aste
sepa
rati
onb
Sepa
rati
on-d
iges
tion
-inc
in-
2410
012
028
erat
ion
1209
20%
fSe
para
tion
-com
post
ing-
in-
1111
cine
rati
on40
3060
43R
DF
gasi
ficat
ion
−10
Bio
mas
sga
sific
atio
n10
3543
4040
5070
Com
post
ing
5070
1045
Ana
erob
icdi
gest
ion
30C
o-co
mbu
stio
nw
ood
5035
456
1500
021
033
06
Co-
com
bust
ion
slud
gec
3747
400
400
280
330
Slud
gein
cine
rati
ond
2709
20%
fW
etox
idat
iond
00
00
280
330
Slud
gega
sific
atio
nd
013
083
g83
gP
last
ics
pyro
lysi
s
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8256
Tab
le2
(Con
tinu
ed)
Ene
rgy
conv
ersi
onef
ficie
ncya
Ene
rgy
cons
umpt
ion
Tre
atm
ent
cost
s(E
CU
1995/t
on
Ele
ctri
city
effic
ienc
yP
rim
ary
ener
gy(M
J/E
ffici
ency
prim
ary
Ele
ctri
city
(kW
h/to
nto
nof
was
te)
ofw
aste
)(%
LH
V)
ener
gy(%
LH
V)
Min
Max
Min
Min
Max
Max
Min
Max
Min
Max
aE
ffici
ency
isde
fined
asne
ten
ergy
effic
ienc
y,in
clud
ing
ener
gyre
quir
emen
tsof
the
proc
ess.
Pri
mar
yen
ergy
isde
fined
asei
ther
heat
orga
sw
ith
asu
bseq
uent
ener
gyco
nten
t.b
Per
form
ance
data
for
was
tese
para
tion
are
give
nfo
ra
wet
sepa
rati
onpr
oces
sth
atpr
oduc
esR
DF
,or
gani
cw
aste
,pl
asti
c,pa
per
and
met
alfr
acti
ons.
cC
o-co
mbu
stio
nof
slud
geis
prec
eded
bydr
ying
.It
isas
sum
edth
atsl
udge
wit
ha
moi
stur
eco
nten
tof
50%
(obt
aine
daf
ter
mec
hani
cal
dew
ater
ing)
isto
bedr
ied
to10
%m
oist
ure
cont
ent
orle
ss.
The
cost
sm
enti
oned
pres
ent
the
cost
incl
udin
gan
dex
clud
ing
natu
ral
gas
inpu
tpe
rto
nne
ofdr
ym
atte
r;th
ela
tter
are
obta
ined
whe
nw
aste
heat
isut
ilise
dfo
rsl
udge
dryi
ng.
dP
erfo
rman
ceda
tafo
rsl
udge
inci
nera
tion
,w
etox
idat
ion
and
slud
gega
sifc
iati
onar
egi
ven
per
dry
tonn
eof
slud
ge.
eT
heen
ergy
cons
umpt
ion
for
land
fillin
gin
clud
esen
ergy
reco
very
from
land
fill
gas.
fO
nly
one
cost
esti
mat
ew
asav
aila
ble.
To
refle
ctun
cert
aint
ies
inpe
rfor
man
ce,
scal
e,co
stof
capi
tal,
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A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 57
kind of pre-treatment of the waste wood is required. The pre-treatment consists ofsizing, sieving and drying, when necessary. Generally, a relatively low percentage ofthe coal input is replaced by wood; partly to prevent potential operationaldifficulties and limit the influence of co-combustion on the ash compostion.
In the Netherlands it is mainly pulverized coal-fired power plants that areoperational. In the EPON coal-fired plant in Nijmegen, the Netherlands, co-com-bustion of waste wood has recently been demonstrated. Wood is dried to 10%moisture content and pulverized. Treatment costs amount to 30–50 ECU/ton ofwaste wood, taking into account the savings on coal use. The required pre-treat-ment contributes substantially to these costs. The net energy conversion efficiencyis 35–38% taking into account the energy use of the pre-treatment [21]. Theseperformance data can be considered representative for the current state-of-the-artpulverized coal fired power plants. Several of these plants are likely to be inoperation in 2010. Higher conversion efficiencies can be expected if new coal plantsare built. We assume that for co-combustion of waste wood an overall energyconversion efficiency of 45% is obtainable in 2010 at a comparable cost level.
3.1.4. Gasification of biomass wasteGasification is a thermochemical conversion route that can be used to convert
biomass waste to fuel gas. The heating value of this fuel gas is relatively low(typically 4–8 MJ/Nm3). Various processes and reactor designs for gasifyingbiomass are at present available or under development. The main advantage ofgasification is that it can be integrated with electricity production using a gasturbine or a combined cycle: the so-called Biomass Integrated Gasification/Com-bined Cycle plant (BIG/CC) which is expected to result in relatively high conversionefficiency and low capital costs per kW installed. In this paper we focus on suchintegrated concepts, although BIG/CC systems have not yet been demonstratedcommercially. Here we will focus on the gasification of relatively clean biomasswaste streams. Gasification of integral waste (MSW or RDF), which is much moreheterogeneous, will be discussed later.
Most biomass gasification schemes are designed to convert clean biomass likecultivated wood [22–24]. Faaij et al. have analyzed the gasification of biomasswastes [25]. They selected a system based on Atmospheric Circulating Fluidized Bedgasification and low temperature gas cleaning. It was found that the highestconversion efficiency is obtained with woody materials (such as waste wood). Theuse of biomass wastes such as verge grass or organic domestic waste results in arelatively low conversion efficiency because of the higher energy use of drying andthe lower power output of the gas turbine. Sludge, even if dried beforehand, is adifficult fuel for a BIG/CC system because of its high ash content, which decreasesthe heating value of the fuel gas produced2.
2 Note that the net electrical efficiency is influenced by the fuel composition. Fuels need to be driedup to a moisture content of 10–15% before gasification. Waste heat can be used for this purpose. Forvery wet fuels (moisture content over 50–60%) the heating requirements may result in reducedavailability of steam for power generation. Furthermore, streams with higher inert fractions produce a
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8258
Pressurized gasification seems especially suited for the treatment of clean biomassbecause it involves dry and high temperature gas cleaning. At the current stage thistype of gas cleaning is less flexible in dealing with more contaminated fuels. In thisstudy we will use the performance data of an atmospheric BIG/CC as estimated byFaaij et al. [25]. According to this study, the treatment costs of biomass wastes mightrange from approximately −10 to +10 ECU/ton. Negative cost figures are achievedif high revenues are obtained from electricity production. The electric conversionefficiency has been estimated to vary between 35 and 41% [25]. Consonni et al. [22,23]expect that the efficiency of a similar 30 MWe system using woody biomass couldbe 43%. We consider a range of 35–43% for the electrical efficiency of a BIG/CCpower plant and the above-mentioned biomass treatment costs to be representativefor the year 2010. However, it should be noted that the expected performance appliesto a 30 MWe unit and thus scale effects have not been taken into account here. Largerscales will most probably result in higher efficiencies and lower capital costs per kWinstalled [25,24].
3.1.5. Combustion or pyrolysis of biomass wasteNumerous processes are available or under development for combusting or
purolysing especially relatively dry biomass materials. Most of those processes havebeen developed for clean wood. Their performance is uncertain when used for thetreatment of contaminated biomass materials, especially with respect to emissioncontrol and related costs. In general, dedicated biomass combustion facilities yieldlower energy conversion efficiencies and involve higher investment costs than projectedperformance data of BIG/CC systems on similar scales (see e.g. van den Broek etal. [26]). We will therefore not discuss biomass combustion further in this study.
Most pyrolysis processes under development for clean wood obtain energyefficiencies of about 60–70% for conversion of wood to oil [27]. When this oil is usedin engines or turbines, the net overall electrical efficiency is about 18% rising to 35%if efficient combined cycles were to be used. The costs of pyrolysis processes usingcontaminated biomass are uncertain, especially since the bio-oil may require furtherupgrading, such as by the removal of alkalis, before it is used in turbines [27]. Becausepyrolysis is expected to be less efficient than gasification if combined with electricityproduction and because the treatment costs are uncertain at the present stage, wedo not include pyrolysis as a treatment option for biomass waste in this study. Pyrolysisprocesses for the treatment of contaminated, integral wastes will be discussed later.
3.1.6. Pyrolysis of plasticsPyrolysis (thermochemical conversion of material by high temperature heating in
an oxygen-free environment) can be used to convert mixed plastic wastes to oilproducts, or so called syncrude, combustible gas and heavy residue. The heavy
leaner fuel gas due to the increased energy needed to heat the mineral fraction of the biomass to thegasification temperature. Combustion of leaner gas results in reduced temperatures in the combustor ofthe gas turbine and thus reduces the electrical output. For more details see Faaij et al. [12,25].
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 59
residue is combusted in order to provide process heat. Syncrude can replace mineraloil in e.g. refineries. A representative example of a pyrolysis process that is beingdeveloped for plastic waste treatment is the VEBA process. To calculate the energyefficiency of this process it is assumed that the oil produced replaces crude oil andthe gas produced replaces natural gas. Taking into account the avoided fossilenergy carriers and the energy consumption of the process, the overall energyefficiency is 83%. The projected treatment costs per ton of waste are expected tovary between 0 and 130 ECU/ton [28]. The lower side of the cost range is expectedto be reached as a result of the potentially high revenues obtainable for the oilproduced and the favourable future development of the process [28].
Smit et al. report another pyrolysis process for plastic waste similar to the VEBAprocess. Their process is being tested on a pilot scale. The manufacturer INETIexpects waste treatment costs of about 60 ECU/ton, revenues not included. INETIclaims the revenues could be up to 90 ECU/ton resulting in negative wastetreatment costs [18]. In this study we will use the performance data of the VEBAprocess since they are based on a demonstration unit.
3.1.7. Gasification of plasticsHigh temperature gasification of plastic waste can be used to produce a syngas.
An example is the TEXACO gasification process [28]. Before gasification the plasticwaste needs to be pre-treated by means of screening and sizing. The syngasproduced is first cleaned (for instance by the removal of HCl which stems fromPVC) and can subsequently be used for methanol or hydrogen production or forthe production of other chemicals, thus replacing the use of mineral oil or naturalgas. The gross efficiency of converting the plastic waste to syngas is about 70%. Ifthe energy consumption of the process and the avoided fossil energy carriers whichwould be used in conventional syngas production are taken into account the overallenergy efficiency of the TEXACO process is 98%. Costs are projected to varybetween 120 and 140 ECU/ton treated [28].
3.1.8. Incineration of sludgeSewage sludge can be incinerated until only an ash fraction remains. Before being
incinerated sludge is mechanically dewatered to a moisture content of 50–60%. Thisoperation is not counted in the waste treatment costs or energy input, because theseoperations are usually performed at waste water treatment facilities.
Incineration of sludge does not produce a net energy output, but requires anadditional energy-input (e.g. natural gas) of approximately 400 MJ/ton of drysludge because of the substantial volumes of water that have to be evaporated [15].The costs of incineration are 280–330 ECU/ton of dry sludge [15]. Furtheroptimization of this process seems unlikely and no substantial changes in theabove-mentioned performance are expected for the year 2010.
3.1.9. Co-combustion of sludgeSludge can be also be co-combusted, just like waste wood. In the Netherlands
co-combustion of sludge is planned [29]. At present special sludge driers are
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8260
operational; these reduce the moisture content of sludge from approximately50–60% to less than 10%. This requires a high natural gas input of 1500 MJ/ton ofdry sludge. Some electricity is required to drive the dryer and air vents: 6 kWh/tonof dry sludge [30]. Drying costs amount to approximately 140 ECU/ton [30]. It isassumed that additional costs in the coal plant (such as for modified burners) aremore or less compensated by avoided fuel costs.
Utilization of waste heat (from the coal power plant) in order to dry sludgewould result in considerable energy savings, but this concept has not yet beendemonstrated. We assume however that the use of waste heat for sludge drying willbe possible in 2010. Consequently the costs are expected to be lowered to about 60ECU/ton dry sludge [30]. The overall conversion efficiency is determined mainly bythe efficiency of the (coal) power plant. Coal fired power plants currently inoperation have an efficiency of 37–42% [13]. Coal plants with an efficiency of 48%might be in operation in 2010. For this study we will use a cost range of 60–140ECU/ton sludge for 2010 and an electrical efficiency range of 37% if sludge iscombusted in currently operational coal plants and up to 47% if new, more efficientcoal plants are constructed. Energy inputs for the drying process may vary between0 and 1500 MJ, plus electricity consumption per ton dry sludge.
3.1.10. Wet oxidation of sludgeWet oxidation is a treatment method in which sludge is processed under high
pressure and at high temperature. An example is the VERTECH process, demon-strated in the Netherlands [32]. The high pressure is created by leading the sludgeto the bottom of a cylinder dug into the ground. A column of water on top createsa high pressure at the bottom of the cylinder. By feeding air the sludge oxidizes anddecomposes at high temperatures. Inerts are pumped to the surface. The process isself-sufficient in energy; the costs of a commercial facility are expected to amountto about 270 ECU/ton dry sludge treated [32]. We assume similar performance datafor the year 2010, taking a cost range of 270 ECU/ton 920% into account. Sucha cost range is also observed for incineration.
3.1.11. Gasification of sludgeSmall scale gasification of sludge has been developed and demonstrated by Royal
Schelde [33]. In this process dried sludge is gasified using an Atmospheric Circulat-ing Fluidized Bed (ACFB) gasifier. The fuel gas produced is used to dry theincoming sludge. The process is almost self sufficient in energy consumption,depending somewhat on the sludge composition. Treatment costs for 2010 areprojected to be in the range of large scale incineration (approximately 280–330ECU/ton dry matter) [33].
3.2. Treatment technologies suited for integral waste streams
In this section incineration, gasification, pyrolysis and landfilling of integral wastewill be discussed. Furthermore separation as a method for handling integral wastewill be dealt with, despite the fact that this paper focuses on final waste treatment.
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 61
Mechanical separation of mixed waste can be considered as a pre-treatmenttechnology for final waste treatment, allowing for re-use of materials. Conse-quently, separation is part of the integrated concepts for treating integral waste.Examples are integrated separation-digestion/incineration and separation-compost-ing/incineration concepts. These final waste treatment technologies will be discussedas well.3.2.1. Incineration of integral waste
There a number of ways to incinerate waste. Various concepts are used, like fixedbed, moving grid, bubbling bed and circulating fluidized bed incineration. Varioussystems and processes are used to clean off gases from the incineration process,depending on the emission standards applied. All present MSW (Municipal SolidWaste) incineration facilities in the Netherlands produce steam, which is used tosupply heat or to generate electricity. The current electrical efficiency of these plantsranges from 12% for older plants to 24% for the latest plants [8]. The electricalefficiencies are generally low because of the high energy consumption of the plant,low steam temperature, a high excess air flow, a high moisture content of the wasteand large inert fractions of the waste [8,10]. At present the total costs of treatingwaste by incineration vary between about 80 and 150 ECU/ton of integral waste [6].
A specific issue related to incineration is the utilisation of waste heat. The extentto which chp is applied depends partly on the extent to which waste heat can beused in the proximity of the plant. Chp based incineration of integral waste isincluded in the overview of technologies presented in Table 2. In the case consid-ered, 27% of the energy from the waste is used as heat. As a result the electricalefficiency is decreased by 7%, i.e. 24–17% [8,10,34]. The figure of 27% for heatproduction represents the current average situation in the netherlands [6,7]. Thecost range of 80–150 ecu/ton of integral waste treated is also applicable to wasteincineration in a chp plant.
The performance of conventional incneration, such as incineration based on theuse of a moving grid, can be improved. Examples of improvement options are:higher steam pressure and steam temperature and a reduction of the excess air. Bymeans of these and other overall process improvements, the electrical conversionefficiency can increase to 26% [8,10].
The steam system of the incinerator can also be coupled to a (natural gas fired)gas turbine to create a combined cycle. This option allows the steam produced bythe waste incinerator to be superheated by the flue gases of the natural gas fired gasturbine. This can result in a net conversion efficiency of the energy content of thewaste to electricity of approximately 39% [8,10]. On the other hand there is also aloss in efficiency since the natural gas is not used in an optimal way to generateelectricity, as at present in a natural gas fired Combined Cycle plant conversionefficiencies of over 55% are obtained. When a correction is made for this loss, thenet efficiency of the waste incinerator is approximately 30% [8,35].
Waste treatment costs for improved incineration are assumed to be similar to thecosts of current incineration (80–150 ECU/ton). Additional investments to improvethe conversion efficiency and potentially higher operation and maintenance costsare assumed to be offset by higher revenues from electricity production.
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Circulating Fluidized Bed (CFB) incineration is a variation on the conventionalincinerators. In Europe a few commercial CFB installations incinerate waste. Theadvantage of this technology is the good boiler efficiency and the relatively highburnout of the fuel. Pre-treatment (mechanical) is required to remove metal partsand to obtain the required particle size for the fluidized bed. Furthermore, theelectricity consumption of a CFB boiler is generally higher because the bed has tobe forced to circulate by fans. Flue gas cleaning can consist of a dry or a wetsystem. The latter results in lower emissions, but is more extensive and results inhigher costs. It is assumed that the characteristics of the residues like ashes aresimilar to the characteristics of the residues from a conventional incinerator.Reported electrical efficiencies are 22–25% and treatment costs 30–50 ECU/ton(based on vendor quotes) depending on the type of gas cleaning [36]. An explana-tion for these low cost levels is the relatively high throughput capacity that can beachieved with a CFB furnace, which limits the investment costs per unit of capacity.When the indicated gas cleaning system is not sufficient to meet the Dutch emissionstandards for waste incineration more extensive gas cleaning is required, leading tohigher waste treatment costs. Whether this is the case at this stage is not unknown.Therefore, in this study we consider the mentioned conversion efficiency (22–25%)and cost (30–50 ECU/ton) as being representative figures for the year 2010,although it should be borne in mind that a more advanced gas cleaning systemmight increase these costs.
3.2.2. Gasification of integral waste (MSW/RDF)Integral waste is more difficult to gasify than (cleaner) biomass wastes because of
its heterogeneous composition. RDF (Refuse Derived Fuel) consists of organicwaste, plastics, wood, paper and board. Gasification of RDF has been demon-strated in Greve (Italy), where an Atmospheric Circulating Fluidized Bed gasifica-tion process is in use [36]. In this plant the syngas from the gasifier is used forgenerating steam by direct combustion and for firing a lime kiln. The plant usesRDF pellets. The pellets are produced in an extensive and costly pre-treatmentscheme [36].
It seems reasonable to assume that the demonstration of BIG/CC technology forgenerating electricity from clean biomass will also allow RDF gasifiers to beintegrated with gas turbines in the longer term. There are no fundamental differ-ences between RDF and biomass gasification except that the former requiresextensive pre-treatment. Niesen et al. and other authors report that so called fluff(loose waste) feeding of waste to an (atmospheric) gasifier is not expected to causefundamental technical problems [24,37,38]. Thorough screening to remove metaland larger inert parts and sizing however remains necessary. Fluff feeding however,has not yet been proven technically.
For a 30 MWe IG/CC system using MSW (Municipal Solid Waste) as fuel, theconversion efficiency is projected to be 41% [37]. MSW has a relatively high heatingvalue which causes the gasifier to produce a richer fuel gas and consequently leadsto a higher gas turbine output. Furthermore, the use of MSW may allow plantswith a larger capacity (and consequently more efficient) since MSW is often
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 63
available in large quantities in a small area. In this study we assume that theconversion efficiency of these plants ranges from 40 to 43%.
The treatment costs per ton of waste are less certain. They depend on the stageof development (number of plants realized) and the required pre-treatment (sieving,grinding, magnetic screening, drying). Niessen et al. report net waste treatmentcosts (including energy credits) of 35 US$/ton [37]. The costs may be higher whenmore extensive gas cleaning and especially more extensive pre-treatment of thewaste, like pelletizing, are required. Pelletizing may increase the treatment costsignificantly [25,38]. We assume that the treatment costs will vary between 30 and60 ECU/ton in 2010; the higher value representing the case where both pelletisingand extensive gas cleaning are required.
3.2.3. Combined pyrolysis/gasification to treat integral wasteA combined pyrolysis-gasification scheme for treating integral waste has been
demonstrated in Italy by Thermoselect [36]. The core of the process is pyrolysis ofthe waste followed by high temperature gasification using oxygen as oxidant. Theprocess is suitable for destroying coarse integral wastes and achieves low emissionlevels. The energy use of the process itself is relatively high. In the thermoselectapproach the remaining fuel gas is combusted in a gas engine to produce electricity[36]. The treatment costs are quoted to be 136 ECU/ton and the electrical efficiency12% [36]. However, those are performance data for a first demonstration unit. Itmight be possible to apply the process on a larger scale. Moreover it might becoupled to a combined cycle to obtain a higher energy conversion efficiency. Forsuch a concept Niessen et al. estimate the net operating costs at approximately 100US$/ton and the net electrical conversion efficiency at 22% [37]. For this study weconsider a performance range of 12–22% for the electrical conversion efficiency anda cost range of 90–140 ECU/ton of waste treated in the year 2010.
3.2.4. Combined pyrolysis/combustion schemes to treat integral wasteIn a inventorizing study covering innovative solid waste processing techniques
Smit et al. briefly summarize a number of other pyrolysis-based processes fortreating integral waste which are currently under development [18]. Almost allprocesses are either in the pilot or demonstration phase. Various manufacturersproject treatment costs of 40–190 ECU/ton integral waste. The low costs areobtained for biomass waste [18].
The so-called Schwellbrenn process is an example of a combined pyrolysis/com-bustion scheme [9]. In this process waste is first pyrolized at modest temperatures;thereafter the produced oils and chars are combusted. The energy produced is usedto generate electricity. The process has been demonstrated in Germany withtreatment costs of approximately 140 ECU/ton. The reported electrical efficiency isabout 17% [7,9]. No other performance data are known to us.
Smit et al. state that the costs of treating integral waste with pyrolysis processesare expected to be in the same range as the costs of current incineration (i.e. 80–150ECU/ton) [18]. The energy efficiency of the processes depends on the compositionof the waste treated and the utilisation of the syncrude produced. Most concepts
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8264
are described excluding power generation from syncrude. The conversion efficiencyof these processes is calculated typically at about 40–50%. If the products of thepyrolysis were to be used for power generation with an efficiency of 40–50%, thiswould result in an overall electrical efficiency of 16–25%. For this study we willassume a performance range in the year 2010 of 16–25%. This figure is based onthe conversion of waste to electricity and treatment costs ranging from 80 to 190ECU/ton.
3.2.5. Separation of integral wasteSeparation of integral waste into different components is possible as a prelimi-
nary step in the treatment of all integral waste incineration, gasification, orpyrolysis. There are several separation techniques available. The type of waste andthe desired composition of the separated fractions determine the process selection.Here we will describe the basics of a process which is applied to separate MunicipalSolid Waste (MSW). After receipt, the waste is loosened, crushed and sieved, bywhich separates the waste into a large and a small particle fraction. Next, metalsare removed (magnetic separation), and paper (35% efficiency) and foils and films(90% efficiency) with help of wind sifting. Paper is separated from plastic by addingwater which creates paper pulp. The remaining plastic fraction is sieved. The smallparticle fraction is led through a sieving drum to create again a small and a biggerparticle fraction. The small fraction contains approximately 30% inert materialwhich is largely removed by further sieving. The remaining waste of the process isseparated in Refuse Derived Fuel (RDF), and an organic fraction which can eitherbe composted, digested or thermochemically treated [7].
The volumes of the separated fractions depend on the waste composition. Typicalfigures for the separated fractions, based on the present average composition of1000 kg MSW in the Netherlands is: 22.5 kg plastic films (largely PE), 60 kg offerrous materials, 53 kg of waste paper and 4.4 kg of non-ferrous metals (largelyaluminium) [7]. The total costs of this separation are about 20 ECU/ton treated.The electricity input is 60 kWh/ton and the heat input 230 MJ/ton [7]. We do notexpect this performance to change substantially in the near future and we willconsider these performance data as being representative for the year 2010, taking acost range of 20 ECU/ton 920% into account. Such a cost range is also observedfor incineration.
3.2.6. Integrated separation-incineration and digestion and integratedseparation-incineration and composting
As already indicated, separation of integral waste could be a preliminary step inthe final treatment of the waste. Here we will focus on separation combined withincineration and digestion or composting of the waste. The main reason forintegrating these technologies in one facility is to obtain efficiency benefits andreduce costs.
The process scheme could read as follows: integral waste is separated, whichyields amongst others RDF and organic waste. The RDF is incinerated, the organicwaste is digested. Produced biogas is fed to a gas turbine which in turn feeds its flue
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 65
gas to a heat recovery steam generator (HRSG) to produce steam. The hot fluegases of the incinerator are also fed to the HRSG. Steam is superheated by therelatively high temperature of the gas turbine exhaust gases and used for driving asteam turbine to generate electricity.
The quality of the compost which is produced in the digestion step is not as goodas compost from separately collected streams and it is doubtful whether it will meetapplicable standards or can compete with clean compost. Therefore, in theseintegrated concepts it is usually proposed to incinerate the residue from thedigestion step in the incinerator.
Various integrated concepts have been evaluated by Hazewinkel et al. [35]; theseinclude retrofitting existing waste incinerators, concepts with and without gasturbines and options to co-fire additional natural gas. The use of a gas turbine/com-bined cycle to utilize biogas produced seems the most promising concept from anenergy efficiency point of view. The projected cost ranges from about 100 to 120ECU/ton and the projected overall electrical efficiency from 24 to approximately28% [35]. The concepts evaluated already include potential future improvements ofthe technology. Therefore we consider the mentioned performance data to berepresentative for the year 2010.
A variant on this concept is integrated separation-incineration and composting,which logically results in lower overall efficiency compared to digestion since noenergy recovery takes place during the composting process. According toHazewinkel et al. the net electrical efficiency of the energy content of the incomingwaste of this concept may be about 11% [35]. The projected costs may beapproximately 120 ECU/ton. We take a cost range of 120 ECU/ton 920% intoaccount. Such a cost range is also found for incineration.
3.2.7. LandfillingLandfilling requires energy input for groundwork and other activities on site.
Energy-use depends somewhat on the density of the waste. High density streams(with larger fractions of inert material) require more energy per ton of waste forlandfills. Expected total energy use for these landfilling activities is approximately140 MJ/ton, in the longer term when landfilled material is expected to consistlargely of inert and high density material [39,40].
On the other hand energy can be recovered by the utilization of landfill gas.Landfill gas can be converted to electricity (and heat) in gas engines, be combustedfor heat production or purified to obtain gas of natural gas quality which can be fedinto the natural gas grid. Landfilling of organic materials will in principle ceasecompletely in the Netherlands. Although existing landfills will produce landfill gasin longer term it is questionable whether landfill gas production can be accountedto inert streams like ashes. Here we will circumvent this problem by using a rangefor maximally possible and zero landfill gas utilisation: Average landfill gasproduction and utilisation was 47.5 MJ/ton of waste in 1990 [5]. We assume thatlandfilling in 2010 will require a net 90–140 MJ/ton of waste processed. Landfilltariffs amount currently to 60–140 ECU/ton of waste landfilled [6]. Such tariffs arehowever affected by levies and do not represent the true costs. According to
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Kuijper et al. the expected future costs of landfilling, which include a number ofmeasures to prevent leakages and smell, are about 20–30 ECU/ton [41].
4. Evaluation of final waste treatment systems
In Section 2 we outlined the expected supply of waste in the Netherlands in theyear 2010. Section 3 gave an overview of waste treatment technologies that mightbe applied in the year 2010 and their expected performance range in terms of wastetreatment costs and energy use or energy conversion efficiency. In this section threedifferent systems for handling all final waste of the Netherlands in the year 2010 arepresented and discussed. For each system a selection is made of the technologiesapplicable. In one system the selection is based on the criterion that the costsshould be as low as possible; another system is selected on the criterion that theenergy production should be as high as possible. For comparison, a third system isalso investigated in which conventional technologies that are currently in usedominate the total future waste treatment system.
In this section total waste treatment costs and total primary energy savings arecalculated for each mix of selected technologies. However, first we will discuss howthe savings on primary fossil fuel consumption-both through energy productionand by re-use of materials-and the cost of waste treatment are calculated. Next,details of the selected waste treatment systems are presented. Finally, the overalloutcomes for these systems are given.
4.1. Calculation of energy reco6ered and waste treatment costs
4.1.1. Energy reco6eryWaste treatment technologies are compared in Table 2; the focus is on the
efficiency of converting a ton of waste to useful energy carriers (electricity, gas,heat). In most cases the figure for the conversion efficiency (or energy consumption)is given as a range. On the basis of these figures for each waste stream theappropriate technology for handling the waste is established.
Given the total volume of waste that must be treated in the year 2010 pertechnology selected, the total amount of energy that could be produced or might berequired is calculated. A figure for the minimum energy recovery (using lowestefficiencies) and for the maximum energy recovery (using the highest values of theperformance ranges) is calculated, which results in the widest possible range forenergy recovery per technology used. The total energy recovery for an entire wastetreatment system then consists of a summation of the energy production of eachtechnology selected per waste stream.
From the energy carriers produced we have calculated the savings (or consump-tion) in fossil fuels that normally would have been required to produce the sameamount of electricity or heat. In these calculations we assume the average conver-sion efficiency for electricity and for heat production in the Netherlands to be 50and 95% respectively in the year 2010 [31]. The gas produced from various
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processes (e.g. digestion) is assumed to be upgraded to the quality of natural gas;then it could replace the same amount of natural gas.
4.1.2. Energy sa6ings through reco6ery of materialsRecycling materials saves primary energy in the production of new material. In
our final waste treatment systems, recyclable materials are produced by wasteseparation of integral waste and by the composting and digestion processes thatproduce compost. Here we will discuss both options in terms of their potentialimpact on energy savings:
4.1.3. Waste separationSeparation of integral waste is a pre-treatment option for incineration, gasifica-
tion or pyrolysis. The indirect savings on primary energy consumption throughrecycling of materials are substantial, as summarized in Table 3. The primaryenergy saved is calculated by means of the energy content of the recyclable
Table 3Potential net primary energy savings by recycling of separated materials from integral wastes
Total energy recovery (GJ/Net energy saved whenkg Material/tonwaste produced ton waste)recycled (MJ/kg)
59a22.5Plastic films 1.325 0.6Paper 25b
60 1.2Ferrous metal 20c
0.8188dNon-ferrous 4.4metal
3.9112Total
a Assuming that mostly low density polyethylene is produced. The GER of PE is 69 MJ/kg [43];mechanical recycling of PE including additional separation, washing and extruding requires approxi-mately 10 MJ/kg [43]. The net energy yield is 59 MJ/kg.b Assuming that the separated paper replaces pulp. Pulp production following the sulphite processwithout bleaching requires 31.6 MJ/kg (including energy content of the wood) and operations likescreening and de-inking require 0.27 MJ/kg [43]. Paper recycling is restricted by the loss of quality of thefibres. It is assumed that each recycling loop results in a 20% loss of fiber quality [42]. The resulting netenergy saved is therefore 25 MJ/kg.c The ferrous metal is expected to be relatively poor quality, which means that its use is most applicablein the blast oxygen furnace iron-making process. The pig iron replaced has a GER of 20 GJ/ton [42,43].d It is assumed that most non-ferrous metal is aluminium. Recycled aluminium can be used for moldedapplications. Primary aluminium production requires 198 MJ/kg; melting of (recycled) aluminiumrequires 10 MJ/kg. The net energy saved amounts to 188 MJ/kg [42,43].
3 GER (Gross Energy Requirement) values are determined by energy analysis of e.g. productionprocesses and by taking direct and indirect energy consumption into account. The direct energy inputsand outputs of a process are inventorized (e.g. steam, electricity), followed by an analysis of the primaryenergy carriers that are required (or saved) for those inputs (e.g. natural gas, coal). The energy use ofproducing and delivering primary energy carriers and for the equipment involved is included as well. Thetotal energy use (or production) that results from such analyses is the GER. For a detailed descriptionsee Worrell et al. [40].
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8268
Table 4Fertilising components in compost; content and energy saved
Total energy savedGER values (MJ/Component kg Fertiliser/tonContent (g/kg dry(ODW)matter)a [20] (MJ/ton ODW)kg) [16,44]
0.93 (KCl) 6Potassium 3.36 K14 (13–19)(6.42 kg KCl)
4515.1 (P2O5)Phosphor 1.86 P7 (6–10)(3 kg P2O5)
14112.1 (NH4NO3)Nitrogen 17 (13–26) 4.08 N(11.6 kgNH4NO3)
a One tonne of organic domestic waste (60% moisture content) produces 400 kg compost (40% moisturecontent).
materials. Quantities produced during the separation of integral waste were alreadygiven in Section 3.2. The net potential savings on primary energy consumption arecalculated by substracting the energy required to regenerate recycled materials fromthe energy content of the materials saved. In our calculation GER values from theliterature are used3. Some details are given in the footnotes of Table 3.
4.1.4. CompostingComposting is also an option to re-use material. Composting is currently the main
treatment route for organic waste. The energy savings due to compost use aretherefore of relevance. The application of compost determines what material isreplaced and therefore the savings on primary energy consumption. Compost can beused as a substitute for peat, as a fertilizer and use as a cover layer (e.g. in parksor on landfills). The applications are very different in purpose and replace differentmaterials. Compost is used as a fertilizer and soil improver in agriculture (59% ofall compost produced from organic domestic waste in 1994), in the private sector(20%), in the public sector such as public parks (20%) and others, e.g. export (1%)[40].
Heijningen et al. have indicated that the heating value of peat determines about98% of the GER value of peat [40]; transport and handling make only a smallcontribution. However, for our purpose it is doubtful whether peat should beconsidered as a fuel, since only a few countries use peat on a substantial scale forenergy purposes (Finland, Ireland). Moreover, the replacement of peat by compostis very modest in terms of quantities replaced. The dominant application of compostis in agriculture where compost can (partly) offset the use of fertilizer. We thereforecalculate the avoided energy use for the production of fertilizers. The content of themain fertilising substances (N, K and P) in compost is given in Table 4. The GERvalues of fertilizers are given as well. Table 4 shows that the energy content of compostrepresented by fertilising components is modest.
The use of compost as ground cover could replace soil or sand; the GER valueof the replaced materials is nearly 100 MJ/ton [40]. In these cases the net energy savedby producing and using compost as a substitute is negative. Note that for all
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 69
applications of compost the transport of the compost itself is excluded from theenergy required.
The lower heating value (LHV) of organic domestic waste is about 5 GJ/ton(depending on source and time of year) [12,13]. In terms of primary energy used,utilizing this type of waste with an efficiency of 35% (in case of gasification) istherefore favourable compared to composting. Digestion allows for both energyproduction as well as production of compost, but does not result in higher energysavings than e.g. gasification (see Section 3).
4.1.5. Waste treatment costsIn Table 2 the expected waste treatment costs per ton of waste for all technolo-
gies considered are summarized. Total waste treatment costs are calculated bymultiplying the volumes of waste treated by the waste treatment costs of theselected technology for that stream and adding together the costs for all streams.This is done for both minimum and maximum treatment costs per selectedtechnology and yields in the maximum possible range for the total waste treatmentcosts.
4.2. Definition of final waste treatment systems
A projection of the waste treatment costs and energy recovery in the year 2010is calculated for final waste treatment systems consisting of different mixes oftechnologies. The choice of the technologies is discussed below for each system (seealso Hekkert [44]):
‘Reference system 2010’: in this system the present mix of waste treatmenttechnologies is maintained, but improved versions of conventional technologies areimplemented. Efficient incineration of integral wastes and plastic waste, as well asco-combustion of waste wood are assumed. Other biomass waste is composted.Furthermore, sludge is incinerated in dedicated facilities. This scenario is a reflec-tion of the current policy to increase incineration of integral waste and to rely oncomposting for treatment of most organic wastes.
‘Minimum cost system’: the objective of this system is to obtain the lowestpossible overall waste treatment costs. The criterion for selecting technologies perwaste stream is therefore the lowest possible cost. Landfilling, however, is out of thequestion for all streams except inert materials. For some technologies the projectedcosts are low in the minimum cost case, but high in the maximum cost case. In suchcases the technology with the lowest minimum costs is selected for this system. Thisresults in the selection of fluidized bed incineration to treat integral wastes andgasification to handle biomass waste streams. In this system sludge is treated byco-combustion, whereas plastics are treated separately by pyrolysis (VEBA pro-cess).
‘Maximum energy recovery system’: the objective of this system is to obtainmaximum energy recovery from waste treatment. The selection of technologies isdetermined by the overall net efficiencies per waste stream. In this system gasifica-tion is selected for the treatment of integral wastes. Biomass waste streams are
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8270
gasified as well, assuming that streams with relatively high moisture and ashcontents are mixed with cleaner and drier streams. Co-combustion of wood may besomewhat more efficient if new and more efficient coal fired power plants come intouse, although this seems uncertain if power generation with natural gas remainscheaper than coal based power generation. It should be borne in mind that theefficiencies given here for biomass gasification apply to 30 MWe units. On a largerscale higher efficiencies are likely to be obtained. In this scenario we assume thatwaste wood can be converted with an electrical efficiency of 45%. Furthermore,sludge is co-combusted in coal fired power plants, whereas plastics are gasified in aseparate process.
For each system a summary of the selected waste treatment technologies and theprojected volumes of waste treated per technology is given in Table 5.
4.3. Results
For each system we calculated the potential energy recovery and waste treatmentcosts. The results are presented in Figs. 1–4. Fig. 1(a), Fig. 2(a) and Fig. 3(a) showthe breakdown of minimum and maximum energy recovery for each systemseparately. It is concluded that in all cases the treatment of integral waste remainsthe most important contributor to the total energy recovery from the final wastetreatment systems. However, the total amount of energy recovered differs stronglybetween the systems.
Fig. 1(b), Fig. 2(b) and Fig. 3(b) show the breakdown of waste treatment costsper major waste stream category for the three systems. The costs for treatingintegral waste and to a lesser extent for landfilling dominate the total costs. Thecosts for landfilling are the same for all systems. Large differences are howeverobserved between the costs for integral waste treatment.
Fig. 4(a,b) depicts the comparison of the overall energy recovery and wastetreatment costs of the three systems.
Table 5Technology choices for the three final waste treatment systems in 2010.
Minimum costs system Max energy recovery system Reference system 2010
Conventional (improved)Fluid bed incineration of Gasification of integral wastes(9400 kton)integral wastes (9400 kton) incineration of integral wastes
(9400 kton)Co-combustion of waste woodGasification of biomass wastes Gasification of biomass wastes(300 kton); Composting of other(1830 kton)(1830 kton)biomass wastes (1530 kton)
Co-combustion of sludges (285 Pyrolysis of plastics (200 kton) Drying and co-combustion ofsludge (285 kton)kton)
Sludge incineration (specificGasification of plastics (200 Conventional incineration offacility) (285 kton)kton) plastics (200 kton)
Landfilled waste (4290 kton) Landfilled waste (4290 kton)Landfilled waste (4290 kton)
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 71
Fig. 1. Minimum costs system. (a) Net primary energy saved, (b) waste treatment costs.
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8272
Fig. 2. aximum energy recovery system. (a) Net primary energy saved, (b) waste tratment costs.
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 73
Fig. 3. Reference system 2010. (a) Net primary energy saved, (b) waste treatment costs.
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8274
Fig. 4. Comparison of systems. (a) Net primary energy saved, (b) waste treatment costs.
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 75
Table 6Overall primary energy savings and waste treatment costs of the three final waste treatment systems
Total primary energy savings Total waste treatment costsSystems(MECU/year)(PJ/year)
MaxMinMaxMin
310Minimum cost 55 64 590310 730Maximum energy recovery 9080980Reference 2010 39 47 1590
Table 6 summarizes the main outcomes with respect to primary energy saved andwaste treatment costs. The increase in energy recovery for all systems compared tothe current energy production (situation 1990; 17 PJ/year [5]) is striking; between 39and 47 PJ in the reference case and between 80 and 90 PJ in the maximum energyrecovery case can be recovered from the projected waste supply. This excludes possiblesavings by means of the increased recovery of materials. A major reason for theincreased energy recovery is that all organic material is used for energy production.Efficiency improvements in various technologies are a second explanation. Withrespect to the total waste treatment costs the differences are less clear, although thereference system is clearly the most expensive one. The minimum cost case resultsin total waste treatment costs ranging from approximately 300 to 600 MECU/year.In the reference case these figures were as high as 1000–1600 MECU/year.
Some of the ranges between minimum and maximum energy recovery andminimum and maximum waste treatment costs are fairly wide. This is due touncertainties in the expected performance of potentially attractive technologies fromthe cost and efficiency point of view. The integral waste treatment technologies areimportant since they make a large contribution to both total costs and total energyrecovery. In our new systems two main technologies are deployed: Fluidized BedCombustion (FBC) and gasification. The performance of both of these technologiesin the Dutch context (with applicable emissions standards) is however still uncertain.Differences in costs for FBC are caused mainly by the type of gas cleaning required.For gasification, uncertainties in projected costs of biomass waste treatment resultfrom potentially required additional investments for pre-treatment and gas cleaningand the scale at which the technology is realized.
As discussed in Section 3.2, all technologies suited for treating integral waste canbe preceded by waste separation. In Table 5 the primary energy savings for thetreatment of 1 ton of integral waste are presented with and without separation. Inthe latter case energy savings through the re-use of materials have been taken intoaccount. In Table 5 also the treatment costs per ton of waste are presented with andwithout separation.
Re-use of materials is possible, if there is a steady demand for recycled material.Lower grade materials can be used as raw material in production processes. Thenthe separation of metals, plastics and paper is useful as a pre-treatment step for allintegral waste treatment technologies from the energy point of view (see Table 7).
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8276
Tab
le7
Com
pari
son
ofw
aste
trea
tmen
tte
chno
logi
esfo
rin
tegr
alw
aste
sin
term
sof
was
tetr
eatm
ent
cost
san
den
ergy
reco
very
,bo
thin
clud
ing
and
excl
udin
gin
dire
cten
ergy
savi
ngs
thro
ugh
recy
clin
gof
reco
vere
dm
ater
ials
IG/C
CSe
para
tion
-dig
esti
on-
Impr
oved
inci
nera
tion
Impr
oved
inci
nera
tion
+F
luid
ised
bed
inci
nera
tion
inci
nera
tion
CH
P
Max
Min
Max
Min
Max
Min
Max
Min
Max
Min
Wit
hout
sepa
rati
on48
3060
Was
tetr
eatm
ent
cost
s(E
CU
/ton
ne)
8314
583
145
33 4.0
4.5
6.3
7.6
4.3
6.2
5.0
5.4
5.5
Pri
mar
yen
ergy
save
d(G
J/to
nne
was
te4.
7tr
eate
d)In
clud
ing
sepa
rati
on60
4572
96W
aste
trea
tmen
tco
sts
(EC
U/t
onne
)12
091
115
9111
547 6.
87.
38.
910
.08.
38.
98.
97.
58.
28.
1P
rim
ary
ener
gysa
ved
(GJ/
tonn
ew
aste
trea
ted)
Dat
aon
was
tetr
eatm
ent
cost
san
den
ergy
effic
ienc
ies
are
take
nfr
omT
able
2.P
rim
ary
ener
gysa
ved
isca
lcul
ated
asde
scri
bed
inth
em
ain
text
.Was
tetr
eatm
ent
cost
sin
clud
ing
sepa
rati
onar
eca
lcul
ated
byco
rrec
ting
for
the
mas
sfr
acti
onof
sepa
rate
dm
ater
ials
.P
rim
ary
ener
gysa
ving
sar
eca
lcul
ated
byas
sum
ing
anav
erag
e50
%ef
ficie
ncy
ofel
ectr
icit
ypr
oduc
tion
and
95%
for
heat
prod
ucti
on.
Itis
assu
med
225
kgpl
asti
cs,
60kg
ferr
o,4.
4kg
non-
ferr
oan
d22
.5kg
pape
rar
epr
oduc
edpe
rto
nne
ofw
aste
sepa
rate
d[7
].In
ert
mat
eria
lca
nal
sobe
extr
acte
d.T
his
will
resu
ltin
asm
alle
rvo
lum
eof
com
bust
ible
was
tebu
tw
ith
ahi
gher
heat
ing
valu
e.W
eas
sum
eho
wev
erth
aton
lyre
cycl
able
sar
ese
para
ted
and
that
the
rem
aini
ngw
aste
has
ahe
atin
gva
lue
of9
GJ/
tonn
e[8
,9].
The
net
prim
ary
ener
gysa
ved
byus
ing
recy
cled
mat
eria
lw
asgi
ven
inT
able
3an
dis
incl
uded
inth
eto
tal
ener
gysa
ved
whe
nw
aste
sepa
rati
onis
perf
orm
ed.
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 77
Waste separation does however not result in a net difference in energy recovery ortreatment costs between the various systems, since waste separation can be implementedin all systems.
Table 7 also shows that waste heat utilisation (as taken up for incineration) wouldresult in somewhat higher total net primary energy savings. Note that waste heatutilization has not been taken into account in the set-up of the three systems. In practice,however, waste heat will be utilised, depending on location-specific circumstances.It is however reasonable to assume that in each system the degree of waste heatutilisation will be comparable. Therefore it will not fundamentally influence thecomparison between the systems.
Finally the results suggest that fluidised bed incineration is on average the treatmentroute with the lowest expected cost per ton of waste treated. IG/CC technology givesthe highest energy savings due to the expected high efficiency of conversion to electricity.
5. Discussion
Although substantial re-use and recycling rates are assumed in the waste supplydata for 2010, higher recycling rates might prove possible. This aspect has not beeninvestigated here. Nevertheless, the results presented remain relevant for the treatmentof any future waste supply that consists largely of integral and biomass waste streams.
The assessment of the projected performance of different waste treatment technolo-gies is based on data obtained from literature sources. In some cases cited data resultfrom limited studies. Moreover, the methods used to calculate waste treatment costsmay vary among different sources. Therefore, the figures presented in this article shouldbe considered as indications. An aspect for futher study is the performance oftechnologies in relation to emissions standards that have to be met. Although almostevery new waste treatment technology is developed with strict standards as startingpoint, the influence of more extensive gas cleaning techniques on costs and performancecan be considerable. This is especially true for combustion processes.
Future technological developments and applications will alter the performance rangeassessment. Processes based on pyrolysis are currently at an early stage of developmentand their performance (both in terms of costs and efficiency) is therefore especiallyuncertain. A more detailed study of such concepts as well as more practical experiencecan reduce such uncertainties and consequently influence the optimum configurationfor the final waste treatment system of the year 2010.
The final waste treatment systems considered have been composed in a relativelysimple manner. One main characteristic is that the diverse supply of waste was dividedinto a limited number of categories. This does not reflect the diversity of waste streamsand different qualities that occur in practice. An example is the biomass waste fractionwhich varies from very wet waste streams to dry wood. Very wet waste is less suitedor even not suited for gasification. In this case digestion may be a better alternative.In this study, however, we have assumed that wet materials are mixed with dry fuelsprior to drying and gasification. This may lead to higher energy recovery than digestion.In specific situations, however, digestion might still be a favourable option.
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8278
A further limitation of this study is the fact that logistics have been excludedfrom the analysis of waste treatment systems. The collection and transport of wastecan have a major impact on the total waste removal and treatment costs. On theother hand for all systems evaluated the total quantity of waste to be transportedis the same. However, no analysis has been made of treatment plant size in eachsystem, and therefore of the distances over which waste has to be transported. Astructure with a larger number of smaller facilities will show different logistic costsfrom a structure with a limited number of large facilities. Further analysis of thispoint is desired. Also the nature of the various waste collection systems willinfluence the results and should be investigated in further studies.
The analysis has been limited to primary energy savings and costs. Effectsattributable to differences in emissions of pollutants have not been investigated.The impact of emissions on the outcome of results can be included via a Life CycleAnalysis approach. This is not done here because of the large amount of datarequired and uncertainties in the environmental performance of technologies on thelonger term. Assuming that all waste treatment facilities will meet the very strict(emission) standards for waste treatment in the Netherlands, the differences be-tween various waste treatment systems with respect to the emissions of pollutantsmay not be too large.
6. Summary and conclusion
Projections for the Netherlands of the future waste supply (to be treated by thecurrent utility sector) indicate that, apart from biomass waste streams, 16 milliontons (of which 10 million tons are integral ‘mixed’ wastes and 1.8 million tons areorganic waste) might require final waste treatment in the year 2010. Despiteincreased prevention and recycling efforts, it is expected that final waste treatmentsystem requirements will be substantial. Between now and 2010 a significant part ofthe existing final waste treatment facilities in the Netherlands will have to bereplaced or will be replaced within a relatively short time after 2010. This situationenables opportunities for improvement of the final waste treatment system, bothfrom the energy recovery and economic point of view. In this paper the improve-ment potential of the final waste treatment system, assuming that the entire currentwaste treatment capacity in the Netherlands will be replaced between now and theyear 2010.
Three final waste treatment systems have been evaluated. First, a referencesystem was defined in which the waste is treated by conventional (but improved)technologies. This system leads to total waste treatment costs of about 1000–1600MECU/year and savings on primary energy consumption of 39–47 PJ/year. Ifmaximum energy recovery is the main objective of the treatment system, gasifica-tion technology may be preferred, both for biomass wastes, for integral wastes andfor plastics. In this system the total primary energy saved might be 80–90 PJ/yearand the costs between 300 and 700 MECU/year. Co-combustion of sludge andwaste wood appears to be a promising option, especially if new coal fired power
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–82 79
plants, with a high conversion efficiency (i.e. 48%), are put into use. If the objectiveof the system is minimum waste treatment costs, the primary energy saved couldamount to 55–64 PJ with total waste treatment costs of 300–600 MECU/year.
Compared to the reference system, the results suggest that substantially increasedenergy recovery and lower costs can be obtained simultaneously. The structureselected in the minimum cost case is rather similar to the maximum energy recoverycase. In the latter, fluidized bed combustion is used to treat integral waste insteadof RDF gasification, although the difference into projected waste treatment costsfor these two options is not large.
Mechanical separation of metal, plastic and paper streams from integral waste isfavourable from an energy point of view in all cases, provided there are markets forthe regenerated material. The electrical conversion efficiency of integral wastetreatment technologies remains the dominating parameter for total energy recoveryduring integral waste treatment and therefore was the main formed focus ofattention in this analysis.
Composting is generally not attractive in terms of primary energy savings, sincein most applications the energy content of the material replaced by compost is low.The results of this study suggest that separate collection and treatment of organicdomestic waste is not the best course from an energy and economic point of view.
Compared to the current situation and the defined reference system for the year2010, new waste treatment processes allow substantially increased energy recoveryfrom waste as well as lower waste treatment costs. Key technologies are expected tobe the gasification of various waste streams and fluidized bed incineration. Therelatively wide ranges in the characteristics of these technologies, especially thetreatment costs, illustrate current uncertainties about long term performance. Asignificant factor for cost and efficiency is the required level of environmentalperformance. Emission standards can substantially influence the cost and efficiencyof waste treatment technologies. In this respect gasification has the inherentadvantage of gas cleaning before combustion of the fuel gas. Further developmentof the gasification of integral waste integrated with combined cycle technology istherefore desirable. However, it should be noted that the future performance ofmany technologies is uncertain due to limited experience (e.g. pyrolysis basedprocesses) and their performance under specific Dutch emissions standards (e.g.fluid bed combustion). More detailed analyses and practical experience of thesetechnologies are therefore needed too.
Acknowledgements
The authors are grateful to Professor Wim Turkenburg (STS/UU) and Dr JoDaemen of the Waste Consultative (Afval OverlegOrgaan; AOO) for criticalcomments and suggestions. Eva Olsson (TPS) and Maggie Mann (NREL) arethanked for providing useful information. Sheila McNab is thanked for linguisticassistance.
A. Faaij et al. / Resources, Conser6ation and Recycling 22 (1998) 47–8280
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