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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A

PLAN

6

ANNEX A

T SPECIFIC

6

C OCC MODE

EL

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GAT

7

ANNEX B

TECYCLE O

7

B

OCC MODELL

Copyrright © 2010 bby ASME