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1 Copyright © 2010 by ASME
Proceedings of the 18th Annual North American Waste-to-Energy Conference NAWTEC18 May 11-13, 2010, Orlando, Florida, USA
NAWTEC18-3567
HIGH EFFICIENCY WASTE TO ENERGY POWER PLANTS COMBINING MUNICIPAL SOLID WASTE AND NATURAL GAS OR ETHANOL
Sergio Guerreiro Ribeiro
University of Brasil – COPPE-UFRJ Rio de Janeiro, RJ 21945-970, Brazil
Tyler Kimberlin Omega Energy Consulting Fort Collins, CO 80525, USA
ABSTRACT
A new WTE (Waste-to-Energy) power plant configuration combining municipal solid waste and gas turbines or landfill gas engines is proposed. The system has two objectives: increase the thermodynamic efficiency of the plant and avoid the corrosion in the MSW (Municipal Solid Waste) boiler caused by high tube metal temperatures. The difference between this concept and other existing configurations, such as the Zabalgarbi plant in Bilbao, Spain, is lower natural gas consumption, allowing an 80% waste contribution to the net energy exported or more. This high efficiency is achieved through four main steps: 1. introducing condensing heat exchangers to capture low temperature heat from the boiler flue gases; the stack temperature can drop to 70°C; 2. high steam temperatures in external superheaters using hot clean gases heated with duct burners; 3. mixing the exhaust gases of a small gas turbine with hot air preheated in a specially designed heat exchangers. The resulting temperature of this gas mixture is almost the same as a standard gas turbine but with the flow similar to that of a large machine with a higher O2 content; 4. After the duct burner and heat exchangers, the oxygen content of the clean gas mixture is still high, nearly 18%, and the temperature is approximately 200°C. The gas is then used as combustion air to the MSW boiler such that all the energy stays in the system. The efficiency can be as high as 33% for the MSW part of the plant and 49% for the natural gas system. Since the natural gas consumption is almost ten times less than the existing designs, it can be replaced by landfill gas or gasified ethanol or biodiesel. Currently an 850 ton/day plant is being designed in Brazil in partnership with a large power company. Other advantages include, self generation of internal power and lower steam superheating temperatures in the MSW boiler. This concept can be used with any grate design.
1. INTRODUCTION
Conventional WTE plants burn waste on specially designed grates and the hot flue gases generate steam in a boiler. Due to the very corrosive nature of these flue gases, [1], the steam temperature and pressure are limited to 400°C / 40 bar resulting in low thermodynamic efficiencies, around 22%, for power generation. One way to overcome this difficulty is to combine a natural gas turbine with a waste incinerator in such a way that the superheated steam produced in the MSW boiler is further heated using the “clean” exhaust from a gas turbine in an external superheater. Many WTE plants have been built using this concept, the most important one being the Zabalgarbi plant, Figure 1. This power plant generates 100 MWe gross and the thermodynamic efficiency for the MSW portion of the fuel is approximately 30%. For natural gas the efficiency is around 50%. The disadvantage of this scheme is that 75% or more of the electric energy produced comes from natural gas. Although in some cases, this can be a good solution from an energy point of view, it is not as environmentally desirable since natural gas is a fossil fuel and contributes to global warming, cancelling the benefits of landfill diversion. Also natural gas prices can vary unpredictably and it may not be economical to dispatch such plants. However, WTE plants have to run with a high availability which poses additional problems to the grid operator. 2. OPTIMIZED COMBINED CYCLE – OCC The proposed concept, named Optimized Combined Cycle - OCC, greatly reduces the amount of natural gas needed to increase the efficiency of MSW combustion. With OCC, 80% or more of the net energy comes from MSW allowing the natural gas to be replaced by fuels not commonly available in large amounts, including landfill gas or biogas from anaerobic digestion. Another possibility is to replace natural gas with gasified bio-fuels such as ethanol or biodiesel using the LPP Combustion,
LLCeffic33%gas witheven(Optadvamoisrefraemphere
Fig. 3. D smaturbThe a cotempLP sflue Aftetempprehturbamothe prehprehexchcom supecomat (9
C, a Marylaciency of the% and the na
turbine if it wout MSW. Thn for small timized Coantages sucsture MSW actory walls. ploy the scheein.
1 – Zabalga
DESCRIPTIO
Consider Fall gas turbiine (17) andHP steam is
orrosion safeperature in tsteam is rehgas then furr the externperature T2, heat the air, ine exhaust
ount of naturO2 content
heater (13), heat the bhanger (25)
mbustion air inCorrosion is
erheaters (2)ming from the
9) and (13).
and-based ce MSW canatural gas ewas used in he natural gagas turbines
ombined Cch as beinas well as Nevertheles
eme with ma
arbi Plant C
ON OF THE
Figure 2. Thene (10), a a LP (Low s superheatee temperaturthe external heated in (5rther reheatenal superheabove 400°
from (9), bef(Y). This ha
ral gas in theof the gas tthe flue gasoiler feedw) and then n the MSW bs avoided by) and (3) hea gas turbine This mixtur
company, p reach valu
efficiencies aa standaloneas efficiency s around 5 ycle) concg specially for small in
ss large wateany advantag
oncept in B
PROCESS
e power is gHP (High
Pressure) sted in the MSWre and, optiosuperheater) below 400
ed in the exteater, (3) theC, and can bfore being mas two effece duct burneturbine exhases from the water in the
be used boiler. y using one ated by the c(10) mixed w
re is heated
process [2].es of more
are higher the combined approachesMWe. The
cept has suited for
ncinerators erwall boilersges as discu
ilbao, Spain
generated byPressure) s
team turbine W boiler (6)
onally, to a hr (3). Similarl0°C first by Mernal reheatee flue gas be used in (1
mixed with thets: it reduce
ers and increaust. After th
gas turbinee optional as part of
or more extclean gas exhwith preheated to tempera
2
The than
han a cycle
s 50% OCC other high
using s can ussed
n [4]
y one steam
(18). up to
higher ly the MSW er (2). is at
13) to e gas
es the eases he air e may
heat f the
ternal haust ed air atures
b(inntteblo
F
PceteFteEtotecrincTpwfowfmpptectuli
2
between 60012) to adjusncrease the natural gas uhe steam cyemperature by lowering owering the
Fig. 2 – Opti
Since thPollution Concan recoveexchangers (eflon coatedFröhlich [3].emperatureExchangers)o preheat temperature. can be as lowrecovery but ncreasing combustion iT9 which ispartially reciwaste combformation in twithout the gflow Y, andmaintenanceproduced by plant parasitihe plant wiefficiency wilcycle efficienurbine wouldutilized, partimited quant
0°C and 700st the steamoverall effic
used in the dycle efficiency
and reheatithe waste bcombustion
mized Com
e flue gas tentrol) with drr this ene(CHX) maded steel tube. Combustio
Tair2 usinair heater (9
the feedwateIn a good de
w as 70°C alalso the lat
the heatn the boiler (cooler andrculated as
bustion temthe MSW furgas turbine natural gas
e periods. In the natural
ic load andll come froll be lower ncy, howeved be a goodicularly becatities. This is
Copyr
0°C, with dum superheatiency of the duct burnersy increased ng), the sta
boiler flue gaexcess air .
bined Cycle
emperature lry scrubbers ergy using e of glass tues, built by on air canng a CHX 9) and CHX er close to esign, the stalowing not otent heat frotransferred
(14) to the sthas a lowercombustion
perature anrnace. We ca(10) by incrduct firing (this case, thgas approxmost of the m the wastsince it is li
er, such a pd solution ifause it is ges also a go
right © 2010 b
uct burners (ting temperaplant, the am
s must be op(higher pressck losses mas temperat
e Scheme
leaving the Ais 140 to 17
condensinubes, teflon Swiss comp
n be prehe(Condensin
economizer the deaera
ack (16) temonly the sensm water con
from theteam. The flur O2 contentn air to connd to reducan also run treasing the (11) and (12he amount oximately matc
energy expte. The natimited by thlant without f landfill gasenerally ava
ood solution
by ASME
(11) and ature. To mount of ptimized, sure and
minimized ure, and
APC (Air 70°C, we ng heat tubes or pany Air eated to ng Heat (8) used
ator (23) mperature sible heat ndensing e waste ue gas at t can be ntrol the ce NOx the plant pure air
2) during of energy ches the
ported by ural gas e steam the gas
s can be ailable in
from an
enviprodpara oppoturbapplgas a sucoolfeedexchcoolwhicto coof 7hot O2 cturbgas usedchoohas MWturb MSWthe Oformthe for addi 4. N requparavarycharelectippiare the whiceconneedrene[2] o deveto qtherMSWsoftwGate
ronmental pduced will casitic load. In some caosed to a gines with relications in tturbines goe
ubstantial paing the cylin
dwater prehehanger (25),ing system
ch at the samool the engin
7-11%, compambient air content of thines exhauscombined c
d, we can osing the bespecial advae, where gaines. In the propo
W boiler is pO2 content is
mation and tocombustion high moistuitional fuel to
UMERICAL
The actual uires extensiameters govy for differacteristics. Fctricity sales ng fees are higher than internationalch the MSWnomic feasibded opens ewable, exceor landfill gasTo reach
eloped speciquickly run modynamic W propertiesware was veCycle comp
point of viecome from
ases it is begas turbine. espect to thtwo ways: ales to the exhart of the heders. Thus weater before, to captureto increase
me time redune. Gas engipared to a g
from heat ehe gas engi
st, usually higcycle plants, employ eith
est solution fantages for as engines
osed schempreheated bes close to 18o vaporize th
grate. This ure waste tho promote co
RESULTS
design of ive calculatio
verning the perent locatFor examplefor power plavery low, unin the USA price and m
W efficiency bility. The sthe door f
ept for plastics. the optimu
ific OCC planhundreds oquantities b
s, as well asvalidated (Anputer progra
ew, becausewaste, inc
etter to use Gas engineheir use in lmost all the
haust flue gaseat loss occwe can introde or after the the heat e the efficieuces the neene exhaust h
gas turbines exchanger (1ne exhaust gher. In conwhere only er gas engfor each parsmall machiare more e
e, the combetween 200°C8%. This helphe water in t
is particularhat otherwisntinuous com
a WTE pons in ordeproject. Desions as , in Brazil, thants up to 3
nder US$ 20. Natural ga
must be reduis optimized
small amounfor a WTE/cs, allowing t
m design nt software mof cases, v
but also plans economic nnexes A am showing a
e all the pcluding the
a gas engins differ fromcombined
e heat rejects. In gas engcurs in the wduce an addithe optional from the enncy of theed for a heathas an O2 co13-16%. M
13) increaseto that of a
ntrast with nagas turbine
ines or turbrticular case.nes, say be
efficient than
bustion air foC and 230°Cps to reducethe MSW early advantagse would rembustion.
lant using r to optimize
sign requiremwell as M
here is a tax 0 MWe. Alth
0/ton, power as is almost uced to a pod with respent of natura/gas plant 1the use of eth
point, we making it posvarying not nt configuraparameters.
and B) usingan almost pe
3
power plant
ne as m gas
cycle ted in gines, water tional heat
ngine plant t sink
ontent Mixing es the a gas atural s are
bines, This low 2
n gas
or the C and e NOx arly in geous equire
OCC e the ments MSW cut in
hough costs twice
oint in ect to l gas 100% hanol
have ssible
only tions, This g the erfect
ac 37(cgin4c4esc
Z
O
b1b
OO
Mmfomeclod3w
T
3
agreement bcase of OCC To emph
3 represents792 TPD (mLow Heating
combined wigas turbine, in Figure 1. T41% while thcycle, Gener43%, respecefficiencies insame amouncycle plant, a
Zabalgarbi
OCC
It can beby a factor o10% higher. be calculated
OCC MSW aOCC Nat Ga
A naturalMWth, is nomachine avafor this amomaximum efengines this consumption ower value fdesign requir30%, approxwaste. These
Table 1 – Or wit
between the configuratioasize the ad
s a case whmetric tons pg Value) wasith a 5.5 MWinstead of a The LM6000he GE5 valural Electric lictively. Conn the MSW/gnt of gas waas described
MSW appa Total Nat G
MSW appa Total Nat G
e seen that thof seven anThe actual e
d and are sho
actual efficiens efficiency
l gas efficienot achievab
ailable. Also,ount is not efficiency thasize is unde
can be defor the MSWrements. Forimately 80%
e results are
riginal Bilbath OCC.
Copyr
two calculaton. dvantages ofere the Zabper day) of ste corresponWe GeneraGE LM6000
0 has an opee is 30.7%. ists the efficnsidering thagas plant ar
as used in aby Korobitsy
arent efficiencGas consump
arent efficiencGas consump
he natural gad the MSW
efficiencies foown below:
ncy = 32.65% = 49
ncy of 49% ble in any a pure comeconomical at can be r 40%. Of coecreased w
W efficiency r an apparen
% of the net psummarized
o Plant x Sa
right © 2010 b
tions for a p
f the concepbalgarbi MSW
1,850 Kcal/nding to 71 Ml Electric (G(46 MWe) a
en cycle efficIn a pure c
ciencies as 5at the natue the same
a standard cyn [1], we ha
cy = 31.66%ption = 152 M
cy = 34.51%ption = 21.84
as needed deefficiency is
or the OCC c
% 9.06%
on this scalinternal com
mbined cycleand in pracobtained usourse the natith a corresas a functio
nt MSW efficpower will cod in Table 1.
ame MSW b
by ASME
particular
pt, Figure W boiler, /Kg LHV MWth, is
GE) GE5 as shown ciency of ombined 51% and ural gas as if the ombined
ave:
% MWth
% 4 MWth
ecreases s almost case can
le, 21.84 mbustion e system ctice, the sing gas tural gas sponding on of the ciency of ome from
oiler
landa smdepefuels Texamthe applthe Indu
For this casdfill gas, gasimaller gas tuending on ths. The Optimizmined by the
Patent Colication No. statements
ustrial applica
e, it is feasibfied ethanol,
urbine, gas ehe economics
zed Combinee Austrian Pooperation PCT/BR 200of Novelty
ability (IA).
ble to replace, or biodieseengine or juss and the av
ed Cycle coPatent Office
Treaty (PC08/000347. I(N), Inventiv
e natural gasel [2]. We canst the duct bvailability of t
oncept has e in Vienna uCT) Internatt has been ve step (IS)
4
s with n use urner these
been under tional given ) and
F
4
netfr gscinpC
C
cpisne
C
3t(to
4
Fig. 3 - OCC
4. CO2 EMI
The nexnatural gas emissions. Fhat the total fraction is 1renewable. T Consider
gas, burning same carboncapacity factnput of 71 Mpower produCO2 emission
O2 from MSW
Now co
consuming producing 33s equal to pnatural gas wemission from
CO2 from NG
Since th33.89 - 15.62he same pomaximum ao burn 18.27
Applied to
SSIONS
xt item to cowill affect
For Italian wacarbon cont
16.0%, i.e., This seems tor a conventi792 TPD o
n characteristor of 90%. MWth. With uced will be n from MSW
W (fossil) = 7
=
onsider the 21.84 MWt
3.89 MWe. Cpure methanwill produce m NG would
G in OCC=21
e 21.84 MW2 = 18.27 Mower using chievable fo7 / 0.4 =45.6
Copyr
Zabalgarbi
onsider is hot the globaaste, Consotent is 27.6% 58% of to be true for onal WTE pf a 1.850 Kc
stics as the This corres22% efficien15.62 MWe
W burning wou
792 x 365 x 0
= 110,660 TP
same MSWth of naturonsidering, fne (CH4), b0.2 ton of Cbe:
.84 x 0.2 x 7
Wth of NG sWe additionNG alone
or this amou8 MWth of N
right © 2010 b
Boiler.
ow the use al warming nni et al [6]
% and the rethe total caseveral loca
plant, withoucal/Kg LHV, Italian waste
sponds to a ncy, the totae. The annuuld be:
0.9 x 0.116 x
PY (Tons per
W boiler wiral gas (Nfor simplicity,
burning one CO2. The ann
7884 = 34,43
spent would al power, gewith 40% ent), one wou
NG. This wou
by ASME
of fossil related
showed enewable arbon is tions. t natural with the
e, and a thermal
l electric ual fossil
x (44/12)
r year)
th OCC NG) and , that NG MWh of
nual CO2
37 TPY
result in enerating efficiency uld need uld result
5 Copyright © 2010 by ASME
in 72,028 TPY of CO2. The difference of 37,591 TPY of avoided CO2 is due to the efficiency improvement of OCC. This corresponds to 34% of the CO2 emissions of the fossil fraction of the MSW. If we replace natural gas with landfill gas or ethanol, this will increase to 65%. Additionally, the avoided methane from landfill diversion will correspond to approximately 338,000 TPY of CO2 meaning that, even for the NG case, the annual net CO2 sequestration would be 265,000 TPY of CO2 for a 792 TPD WTE plant. 5. CONCLUSIONS This process allows WTE to be feasible at very modest tipping fees. Developing Countries that could not afford the costs of landfill diversion will be able to stop burying their organic wastes. Also Europe, North America and Japan could benefit from this concept and apply the surplus of resources from lower tipping fees in other ways to mitigate global warming. The OCC concept can be generalized to other types of thermal electric power plants such as sugarcane bagasse fuel for which the efficiency improvement can surpass 50% with very modest increase in the investment.
ACKNOWLEDGMENTS I would like to express my gratitude and deepest
admiration for Professor Nickolas J. Themelis, Chair of WTERT, who probably does not realize that the seeds he planted when he visited Rio de Janeiro in 2006 are about to germinate into large trees.
REFERENCES [1] Korobitsyn, M.A., “New and Advanced Energy
Conversion Technologies. Analysis of Cogeneration, Combined and Integrated Cycles” – Laboratory of Thermal Engineering of the University of Twente – 1998.
[2] LPP Combustion, “Dispatchable Renewable Energy: Gas Turbines Can Burn Liquid Biofuels as Cleanly as
Natural Gas”- Renewable Energy World March 10 - 12, 2009.
[3] Air Fröhlich - Flue Gas Heat Exchangers Catalog (http://www.airfrohlich.com/).
[4] Martin, J., “Global Use and Future Prospects of Waste-to-Energy Technologies” - Fall Meeting Columbia University, Oct.7-8, 2004.
[5] Alison Smith, Keith Brown, Steve Ogilvie, Kathryn Rushton, Judith Bates, “Waste Management Options and Climate Change” - Final report to the European Commission - DG Environment - July 2001
[6] S. Consonni, M. Giugliano, M. Grosso, “Alternative strategies for energy recovery from municipal solid waste Part A: Mass and energy balances” - Waste Management 25 (2005) 123 135.
[7] Reference Document on the Best Available Techniques for Waste Incineration, Integrated Pollution Prevention and Control - EUROPEAN COMMISSION – August 2006.
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